U.S. Department of the Interior

U.S. Geological Survey

Professional Paper 1763

Geology, Geochemistry, and Genesis of the Greens 

Creek Massive Sulfide Deposit, Admiralty Island, 

Southeastern Alaska

Prepared in cooperation with Kennecott Greens Creek Mining Company

Geology, Geochemistry, and Genesis of the 

Greens Creek Massive Sulfide Deposit, 

Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with Kennecott Greens Creek Mining Company
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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Suggested citation:

Taylor, C.D., and Johnson, C.A., editors, 2010, Geology, geochemistry, and genesis of the 

Greens Creek massive sulfide deposit, Admiralty Island, southeastern Alaska: U.S. Geological Survey 

Professional Paper 1763, 429 p., 7 plates on CD.

Library of Congress Cataloging-in-Publication Data

Geology, geochemistry, and genesis of the Greens Creek massive sulfide deposit, Admiralty Island, Southeastern 

Alaska / edited by Cliff D. Taylor and Craig A. Johnson ; prepared in cooperation with Kennecott Greens Creek Mining 

Company. 

 p. cm. -- (Professional paper ; 1763) 

 Includes bibliographical references. 

 ISBN 978-1-4113-2622-4 (pbk.) 

 1. Sulfide minerals--Alaska--Greens Creek. 2. Geochemistry--Alaska--Greens Creek. I. Taylor, Cliff D. II. Johnson, 

Craig A. III. Kennecott Greens Creek Mining Company. 

 QE389.2.G46 2010 

 549’.32097982--dc22

2010033687
Volume Contents

1. Introduction and Overview of the U.S. Geological Survey–Kennecott 

Greens Creek Mining Company Cooperative Applied Research Project 

at the Greens Creek Mine ...........................................................................................................3

By Cliff D. Taylor and Craig A. Johnson

2. The Late Triassic Metallogenic Setting of the Greens Creek Massive Sulfide 

Deposit in Southeastern Alaska ...............................................................................................13

By Cliff D. Taylor, John Philpotts, Wayne R. Premo, Alan L. Meier, and 

Joseph E. Taggart, Jr.

3. The History of Greens Creek Exploration ................................................................................65

By Andrew W. West

4. Geology of the Greens Creek Mining District .........................................................................93

By Norman A. Duke, Paul A. Lindberg, and Andrew W. West

5. The Airborne Geophysical Survey of the Greens Creek Area ...........................................109

By James Fueg

6. Geology and Metal Zoning of the Greens Creek Massive Sulfide Deposit, 

Southeastern Alaska ................................................................................................................125

By Cliff D. Taylor, Andrew W. West, Kerry G. Lear, Tim E. Hall, and 

John M. Proffett

7. Geologic Structure of the Greens Creek Mine Area, Southeastern Alaska ....................141

By John M. Proffett

8. Geochemistry of Metasedimentary Rocks in the Hanging Wall of the Greens 

Creek Massive Sulfide Deposit and of Shales Elsewhere on Admiralty Island .............163

By Craig A. Johnson, Cliff D. Taylor, Joel S. Leventhal, and Katja Freitag

9. Mineralogical, Textural, and Metal Residence Studies of Primary, Recrystallized, 

and Remobilized Ores of the Greens Creek Deposit ...........................................................187

By Cliff D. Taylor, Steven J. Sutley, and Frederick E. Lichte

10. Sulfur and Lead Isotope Characteristics of the Greens Creek Polymetallic 

Massive Sulfide Deposit, Admiralty Island, Southeastern Alaska ...................................241

By Cliff D. Taylor, Wayne R. Premo, and Craig A. Johnson

11. Microfossil and Radioisotopic Geochronological Studies of the Greens Creek 

Host Rocks .................................................................................................................................287

By Wayne R. Premo, Cliff D. Taylor, Lawrence W. Snee, and Anita G. Harris

12. Radiogenic Isotopic Characterization and Petrogenesis of Host Rocks to the 

Greens Creek Deposit ..............................................................................................................339

By Wayne R. Premo and Cliff D. Taylor

13. Structure of the Lower Southwest Orebody, Structural Comparison to Neighboring 

Orebodies, and Tectonic Model for the Greens Creek Deposit ........................................371

By Katja Freitag

14. Three-Dimensional Modeling and Visualization of Greens Creek Drill-hole Data .........405

By Gregory K. Lee and Cliff D. Taylor

15. A Genetic Model for the Greens Creek Polymetallic Massive Sulfide Deposit, 

Admiralty Island, Southeastern Alaska .................................................................................417

By Cliff D. Taylor, Kerry G. Lear, and Steven R. Newkirk

iii
Plates

4–1. Geology of the Greens Creek mine area.

7–1. Geologic map of the surface, Greens Creek mine, Alaska.

7–2A. Greens Creek mine, Alaska, Cross Section 3000.

7–2B. Greens Creek mine, Alaska, Long Section 4800.

7–3. Map of the surface, Greens Creek mine, Alaska; F2, S2, L2, and S2/bedding 

intersections.

7–4. Map of underground workings, Greens Creek mine, Alaska; F2, L2, and S2/bedding 

intersections.

7–5. Map of the surface, Greens Creek mine, Alaska; F3, S3, L3, F4, S4, L4.

iv
USGS Contributors to the Professional Paper

Harris, Anita G.

Johnson, Craig A.

Lee, Gregory K.

Leventhal, Joel S.

Lichte, Frederick E. 

Meier, Alan L.

Philpotts, John A.

Premo, Wayne R.

Snee, Lawrence W.

Sutley, Steven J.

Taggart, Joseph E., Jr.

Taylor, Cliff D.*

*Principal contact:

U.S. Geological Survey – Mineral Resources Program

Box 25046 Federal Center, MS-973 

Denver, CO 80225-0046 USA

303-236-2499

ctaylor@usgs.gov

Kennecott Greens Creek Mining Company Contributors to the Professional Paper

Hall, Tim E.

Lear, Kerry G.

Newkirk, Steven R. 

West, Andrew W.

Kennecott Greens Creek Mining Company

P.O. Box 32199

Juneau, AK 99803

(Newkirk now at Department of Earth Sciences, University of Memphis, Memphis, TN 38152)

Other Contributors to the Professional Paper

Duke, Norman A.

Department of Earth Sciences

University of Western Ontario

London, Ontario, Canada N6A 5B7

Fueg, James

Chugiak, AK 99567-0236

Lindberg, Paul A.

Sedona, AZ 86336

v
Proffett, John M.

Eagle River, AK 99577-7124

Freitag, Katja

Department of Geology and Geological Engineering

Colorado School of Mines

Golden, CO 80401

(now at McKinsey & Company, Johannesburg, South Africa)

vi
Introduction and Overview of the U.S. 

Geological Survey–Kennecott Greens 

Creek Mining Company Cooperative 

Applied Research Project at the Greens 

Creek Mine

By Cliff D. Taylor and Craig A. Johnson

Chapter 1 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Background.....................................................................................................................................................3

Geology and Geophysics..............................................................................................................................3

Geochemistry..................................................................................................................................................4

Models.............................................................................................................................................................6

Final Comment................................................................................................................................................7

Reference Cited..............................................................................................................................................7
Background

In 1996, a memorandum of understanding was signed 

by representatives of the U.S. Geological Survey and Kennecott Greens Creek Mining Company to initiate a cooperative applied research project focused on the Greens Creek 

massive sulfide deposit in southeastern Alaska. The goals 

of the project were consistent with the mandate of the U.S. 

Geological Survey Mineral Resources Program to maintain a 

leading role in national mineral deposits research and with the 

need of Kennecott Greens Creek Mining Company to further 

development of the Greens Creek deposit and similar deposits 

in Alaska and elsewhere. The memorandum enumerated four 

main research priorities: (1) characterization of protoliths for 

the wall rocks, and elucidation of their alteration histories, (2) 

determination of the ore mineralogy and paragenesis, including metal residences and metal zonation within the deposit, (3) 

determination of the ages of events important to ore formation 

using both geochronology and paleontology, and (4) development of computer models that would allow the deposit and its 

host rocks to be examined in detail in three dimensions.

The work was carried out by numerous scientists of 

diverse expertise over a period of several years. The written 

results, which are contained in this Professional Paper, are 

presented by 21 authors: 13 from the U.S. Geological Survey, 

4 from Kennecott Greens Creek Mining Company, 2 from 

academia, and 2 from consultants.

Geology and Geophysics

The first six papers in the Professional Paper summarize 

a large body of geologic and geophysical information starting at the regional scale and ending at the scale of the Greens 

Creek mine and immediate vicinity. The lead-off paper, by 

Taylor and others (chap. 2), describes the regional setting for 

Greens Creek on the eastern margin of the Alexander terrane 

in southeastern Alaska. The deposit lies in what Taylor and 

others (chap. 2) term the Alexander Triassic Metallogenic 

Belt (ATMB), a 200–800-m-thick sequence of conglomerates, 

limestones, marine clastic sediments, and tuffs with overlying 

and intercalated pyroclastic rocks and flows that can be traced 

some 600 km along strike. Fossil evidence suggests that the 

sequence spans Anisian to late Norian time (Middle Triassic 

to Late Triassic). In addition to Greens Creek, numerous 

other sulfide deposits are within the belt, most notably Windy 

Craggy, which is the largest volcanogenic massive sulfide 

deposit known in North America.

Within the ATMB, there are along-strike changes in the 

nature of the sulfide deposits and the depositional setting of 

the host rocks. From south to north, sulfide deposits change 

from structurally controlled Pb+Zn+Ag±Cu veins or pods or 

small stratiform lenses, to stratiform sulfosalt-bearing Zn-PbAg deposits (Greens Creek), to stratiform copper-rich deposits 

(Windy Craggy). The host rocks also change from felsic volcanics with overlying oolitic limestones to mafic and ultramafic 

phyllites with overlying argillites or mafic volcanics. Taylor 

and others (chap. 2) suggest that the change in host rocks 

reflects a change in depositional environment from shallower 

waters on the flanks of the Alexander volcanic arc to deeper 

waters in a back-arc or intra-arc basin. A modern analog for 

the ATMB may be the southern projection of the Lau Basin, 

from Valu Fa Ridge to the Taupo Volcanic Zone on the North 

Island of New Zealand.

West (chap. 3) documents the exploration programs 

that focused attention on northern Admiralty Island and 

then defined and expanded the Greens Creek ore reserve. In 

1973, Noranda Exploration, Marietta Resources, Exhalas 

Resources, and Texas Gas Exploration formed a partnership, 

Pan Sound Joint Venture, to explore for base and precious 

metals in the northern part of southeastern Alaska, in the 

Prince William Sound area, and on the Kenai Peninsula. That 

same year, extensive stream-sediment sampling across northern Admiralty Island revealed high concentrations of zinc and 

copper in the Cliff Creek drainage, just east of the present-day 

mine site, and near Hawk Inlet, northwest of the mine site. 

The following year, a large exposure of unvegetated ferricrete 

was discovered and dubbed the “Big Sore,” and geophysics 

and soil geochemistry surveys of the area were carried out. 

The first drill hole, which was completed in 1975, recovered 

an 89-foot interval of massive pyrite and base metal sulfides.

Introduction and Overview of the U.S. Geological Survey–

Kennecott Greens Creek Mining Company Cooperative 

Applied Research Project at the Greens Creek Mine

By Cliff D. Taylor and Craig A. Johnson
4 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

The first production from the Greens Creek mine was in 

1989, following a development stage that was greatly complicated by the Alaska National Interest Lands Conservation 

Act of 1980. Throughout the development of the mine, and 

in subsequent exploration programs, the understanding of the 

geology of the deposit and the preferred model for ore genesis have evolved considerably. The stratabound nature of the 

mineral deposits was recognized early on. Although the ores 

were first thought to be brine pool deposits and the host rocks 

to be volcanic tuffs and hydrothermal precipitates (exhalites) 

that had accumulated on the Devonian sea floor, subsequent 

interpretations favored sulfide precipitation in Triassic time in 

association with intense hydrothermal alteration of preexisting 

volcanic and plutonic rocks. It was suggested also that the heat 

source for the hydrothermal system was ultramafic magmas 

that were emplaced along faults, and that the ores formed epigenetically by replacement of Triassic sedimentary rocks. The 

understanding of post-ore deformation has also evolved. An 

accurate model of the structural geology is considered critical 

for mine planning and continuing exploration.

Duke and others (chap. 4) and Fueg (chap. 5) report on 

surface geologic mapping and results of an airborne geophysical survey, respectively, of the greater Greens Creek area. 

The geologic and geophysical coverages are nearly the same 

and can be conveniently compared. The data are displayed as 

maps that cover a 10–12-mile-long segment of the northwesttrending phyllite belt that hosts the Greens Creek deposit.

Greens Creek is in the low-grade metamorphic core of the 

Admiralty subterrane of Alexandria. The overall tectonostratigraphic setting is back-arc basement of late Paleozoic age overlain by flood basalts of Late Triassic age. The Admiralty backarc basin is represented by Devonian greenstones of the Retreat 

Group, overlying Mississippian to Permian siliciclastics and 

dolomite-chert facies of the Cannery Formation, and the Lower 

Permian Pybus Formation. Amalgamation of the Alexander and 

Wrangellia terranes resulted in subaerial exposure of the region, 

and the formation of an unconformity. Rifting commenced 

in Late Triassic time leading to the accumulation of the Hyd 

Group, which is dominated by black argillite and flood basalts. 

Compressional tectonism in mid-Cretaceous time caused fold 

and thrust imbrication. Dextral transpression on the Denali 

transform system in the Tertiary caused strike-slip faulting.

The Greens Creek sulfide bodies are located at the unconformity between the Retreat and Hyd Groups. At the mine site, 

the Retreat Group contains serpentinite and metagabbro in 

addition to greenstone; hydrothermal alteration of this assemblage has given rise to phyllitic rocks (termed mine phyllite following common usage by Kennecott Greens Creek geologists; 

see also Proffett, chap. 7). The Hyd Group consists of a basal 

breccia/conglomerate, a medial argillite (termed mine argillite 

by Kennecott Greens Creek geologists; see also Proffett, chap. 

7), and an upper basalt member.

The airborne geophysics has proven to be a valuable 

guide to stratigraphy and structure in the area. Ultramafic 

units appear as magnetic highs, and the argillite-phyllite contact, which is the mineralized horizon, is revealed as a sharp 

gradient in the electromagnetic data (contrast between low 

and high resistivities, respectively). The Greens Creek sulfide 

deposit is not apparent in the electromagnetic data mainly 

because the bulk of it is buried.

The geology of the mine site is described by Taylor and 

others (chap. 6), who focus on the ores and their immediate wall 

rocks, and Proffett (chap. 7), who focuses on the structural geology. The Greens Creek ore deposit is a series of massive sulfide 

bodies that lie along the contact between altered mafic-ultramafic 

phyllites and stratigraphically overlying Upper Triassic argillites. 

There are three main orebodies, East, West, and Southwest, that 

are themselves segmented by faults or attenuated zones. Within 

individual orebodies there is a common stratigraphic sequence in 

which white ores (less than 50 percent sulfides) give way upward 

to pyritic massive ores, and then to base-metal-rich massive ores 

(both greater than 50 percent sulfides). The global reserve, for a 

cutoff grade of zero percent metal, is estimated to be 21.9 million metric tonnes with grades of 13.9 weight percent zinc, 5.1 

weight percent lead, 19.2 troy ounce per metric tonne silver, and 

0.15 troy ounce per metric tonne gold.

Restoration of offsets along the Maki and Klaus faults, the 

two major ore-displacing faults, suggests that the mineral deposit 

was originally a single continuous horizon that was thickest in 

the Central West orebody and thinned to the north, east, and 

south. It appears that, in general, the ores change from Cu+Ferich against the footwall phyllites, to Zn-rich, to Zn+Pb-rich, 

to Ag-rich and polymetallic against the hanging-wall argillites. 

The absence of concentric metal zoning in plan view suggests 

that the sulfide-bearing mineral deposits may have formed above 

multiple centers of hydrothermal upwelling, or a broad zone of 

diffuse upwelling, rather than a single pipelike vent.

The host rocks show the effects of hydrothermal alteration, lower greenschist facies metamorphism, and multiple 

deformations. In the footwall, mafic rocks are higher in silica 

content and richer in sericite at the ore contact and become 

richer in chlorite and carbonate away from ore. Ultramafic 

rocks are either serpentinized or carbonate altered. In the 

hanging wall, the argillites are massive or slaty and can contain 

graphite, dolomite, or calcite. Carbonate rocks occur locally at 

or near the ore contact.

 The complex distribution of ore at Greens Creek results 

mainly from the complex deformation history of the area. 

The earliest structures are schistosities (S1 and S1.5) that are 

apparent only in Paleozoic rocks. Three cleavage-forming 

folding events (F2–S2, F3–S3, F4–S4) affected both ores and 

wall rocks. Ductile shear zones are present above and below 

the ore zone; these formed between F2 and F3. Brittle faulting 

postdated the youngest folding event (F4).

Geochemistry

Next in the Professional Paper are five papers on geochemical topics. Johnson and others (chap. 8) report on the organic 

geochemistry, major and trace element geochemistry, and stable 

isotope geochemistry of sedimentary rocks in the hanging wall 
Geochemistry 5

of the Greens Creek deposit and of shales elsewhere on Admiralty Island. The sedimentary section immediately overlying the 

ores ranges from carbonate-poor shale to nearly pure dolomite. 

Some samples resemble normal marine shales in their base and 

precious metal contents, sulfur-to-organic carbon ratios, and 

degree-of-pyritization values. These sediments were laid down 

during periods when the overlying water column was oxic; the 

only suggestion of hydrothermal venting is a slight enrichment 

in barium. More commonly the hanging-wall samples are high 

in sulfur, metals, and degree of pyritization. This could reflect 

metal accumulation beneath an anoxic metalliferous brine pool 

but could also be explained by epigenetic emplacement of sulfur 

and metals during massive sulfide formation or during Cretaceous regional metamorphism as a consequence of mobilization 

from the neighboring sulfide bodies.

The carbon and oxygen isotopic compositions of hanging-wall carbonates are indistinguishable from the compositions of dolomite in the sulfide ores. The compositional ranges 

suggest precipitation from a single fluid over a temperature 

range of 200° to 350°C, which overlaps the range that has 

been inferred independently for formation of the adjacent massive sulfides (see Taylor and others, chap. 10). However, the 

compositions may also be consistent with dolomite formation 

from mixtures of hydrothermal and marine fluids. Whatever 

the dolomite precipitation mechanism, the isotopic similarity 

of hanging-wall and ore dolomites is strong evidence that the 

Greens Creek hydrothermal system persisted until after the 

hanging-wall sediments had been laid down.

Carbonate carbon isotopes show a negative correlation with the sulfur content of the rocks, which suggests 

that the oxidation of organic matter, or of methane produced 

therefrom, was linked to sulfate reduction to form hydrogen 

sulfide. During growth of the framboidal pyrite forms, sulfate 

reduction was probably microbially mediated, whereas during 

formation of base-metal sulfides, sulfate reduction could have 

been microbial or abiotic. Thus, at least some sulfate reduction 

took place during early diagenesis beneath the sediment/seawater interface. Limited isotopic data from Hyd Group shales 

elsewhere on Admiralty Island suggest that the same hydrothermal fluid that formed the Greens Creek massive sulfide 

deposit may also have interacted with basin-floor sediments 

several kilometers distant from Greens Creek.

The mineralogy, mineral chemistry, and textures of 

Greens Creek ores are described by Taylor and others (chap. 

9). For mapping purposes, the ores have been divided into 

massive sulfide ores (greater than 50 percent sulfides), which 

can be either pyrite- or base-metal-rich, and white ores (less 

than 50 percent sulfides), which can contain carbonate, silica, 

or barite. Veining, brecciation, and faulting are also recognized 

giving rise to subdivisions of the main ore types. In the cores 

of individual orebodies, white ore gives way stratigraphically 

upward to massive pyritic ore, which gives way upward and 

laterally to massive base-metal-rich ore.

Ore with primary textures, which constitutes an estimated 

30 percent of the deposit, contains pyrite with framboidal, 

colloform, dendritic, or “spongy” forms intergrown with 

sphalerite, galena, tetrahedrite, chalcopyrite, free gold, and 

various Pb-Sb-As(-Hg-Tl) sulfosalts. The textures exhibited 

by pyrite are consistent with formation during diagenesis from 

bacterial hydrogen sulfide and support a similar inference 

based on sulfur isotopic analyses (see Taylor and others, chap. 

10). The remaining 70 percent of the ores show the effects of 

secondary processes including recrystallization and coarsening 

of sulfides, formation of atoll structures, and formation of secondary minerals in late fractures, veinlets, and matrix interstitial to euhedral pyrites. Common secondary minerals include 

chalcopyrite, low-iron sphalerite, galena, free gold, electrum, 

antimony-rich tetrahedrite, pyrargyrite, and numerous sulfosalts. Recrystallization also resulted in higher pyrite purity. A 

process akin to zone refining is inferred, causing recrystallization of large volumes of ore and the migration of lead, zinc, 

and precious metals outward toward the lower temperature 

margins of individual orebodies.

Sulfur and lead isotope analyses of Greens Creek sulfides 

and of hanging wall and footwall rocks provide information 

on the sources of these two ore constituents (Taylor and others, chap. 10). Ore pyrite ranged in δ34S from –38 to 2 permil, 

and chalcopyrite, sphalerite, and galena were mostly between 

–16 and –11 permil. The lower values are strong evidence 

for sulfur acquisition from bacterial hydrogen sulfide, which 

was produced from seawater sulfate within the pore waters of 

argillaceous sediments. The higher values suggest that sulfur 

may have been derived also from mafic and ultramafic rocks 

beneath the sulfide deposit. Analyses of barite gave δ34S values 

of 13 to 22 permil, which is consistent with sulfate derivation 

from Triassic seawater. The sulfur isotopic difference between 

coexisting sphalerite and galena suggests that the minerals 

equilibrated at temperatures of 276–313°C. It is uncertain 

whether this equilibration occurred during hydrothermal metal 

emplacement or during Cretaceous regional metamorphism.

Lead isotope analyses of Greens Creek samples and of 

sulfide minerals from elsewhere on Admiralty Island suggest 

that the lead represents mixtures from multiple sources. Ore 

sulfides display linear arrays on 208Pb/204Pb versus 206Pb/204Pb 

and 207Pb/204Pb versus 206Pb/204Pb plots that are consistent 

with mixing of less radiogenic lead from a source resembling 

enriched midocean-ridge-type basalt (EMORB) and more 

radiogenic lead from an older crustal source. Analyses of 

host rocks suggest that the less radiogenic source could have 

been Upper Triassic basalts and gabbros, select phyllites, or 

Cannery Formation argillites. The more radiogenic source 

may have been the hanging-wall argillites, although the lack 

of obvious depletions in lead and other metals immediately 

above the Greens Creek deposit (Johnson and others, chap. 8) 

suggests that the source argillites would have been distal to the 

site of massive sulfide formation. For other sulfide localities 

on Admiralty Island, there appear to have been contributions 

from different sources. These include an older or less radiogenic source for the Kennecott Rand, Pyrola, Killer Creek, and 

Mt. Robert Barron localities that may correspond to Retreat 

Group sedimentary rocks, and a more highly radiogenic source 

for the Mammoth Claims, Cascade Creek, Portage, and Cub 
6 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Creek localities, as well as to a minor extent at Greens Creek, 

that may correspond to metasomatic additions of lead during 

the Cretaceous metamorphic event.

The last two geochemical papers cover age determinations from radiogenic isotopes and biostratigraphy and 

radiogenic isotope geochemistry of the Greens Creek wall 

rocks. Premo and others (chap. 11) report on conodonts from 

calcareous argillites that were obtained from mine workings 

and outcrops. The most age-restrictive index species is Metapolygnathus primitius, which lived during a narrow time interval at the Carnian-Norian boundary for which the estimated 

age is 220.7±4.4 Ma (Gradstein and others, 1995). The CAI 

(color alteration index) of most Greens Creek conodonts is 5 

or 5–5.5, which implies that the samples experienced temperatures of 300° to 350°C. The general consistency of CAI values 

within individual samples, and from one sample to another, 

suggests that the values reflect a low-grade metamorphic 

event. Less common higher CAI values of 5.5–6 and 6.5–7 

reflect higher temperatures or more prolonged heating locally, 

most likely due to contact metamorphism near basaltic flows 

or intrusions, or interaction with hydrothermal fluids. The 

conodont-bearing argillites were hemipelagic basinal deposits 

with additions of storm- or wave-generated siliciclastic and 

carbonate muds from shallow-water platforms or other nearsurface submarine edifices that were transported and redeposited in deeper marine environments.

Measurements of whole-rock lead, neodymium, and 

strontium isotopic compositions gave scattered results for 

some sample suites implying post-depositional disturbance, 

but gave apparent isochrons for other suites. The U-Pb results 

for a suite of Hyd Group basalts gave an apparent isochron age 

of 218±16 Ma, which is consistent with their eruption after 

argillite sedimentation (220.7±4.4). A suite of altered gabbros 

that intruded both Hyd Group argillites and Hyd Group basalts 

gave ages of 206±35 Ma (U-Pb) and 200±27 Ma (Sm-Nd) 

consistent with the crosscutting relationships. Numerous sericite and fuchsite samples were dated by the 40Ar/39Ar technique, 

but most showed evidence for argon loss during Cretaceous 

time and thus were of limited value in dating hydrothermal 

mineral growth. However, fuchsite from an altered ultramafic 

rock at Gambier Bay yielded an undisturbed age of 210.3±0.3 

Ma. Taken together, the geochronological data suggest that 

the lifetime of the Greens Creek hydrothermal system was 

between 0.4 and 15.1 million years. For some sample suites 

the U-Pb, Sm-Nd, Rb-Sr, and 40Ar/39Ar systematics appear to 

have been perturbed in the time period 110–85 Ma, which corresponds to the Cretaceous metamorphic event.

Premo and Taylor (chap. 12) present whole-rock 

U-Th-Pb, Rb-Sr, and Sm-Nd isotope data for metabasalts, 

metagabbros, serpentinites, phyllites, argillites, and crosscutting diabases from the vicinity of the Greens Creek deposit. 

The metabasalts and metagabbros yield Pb-Pb, Sm-Nd, and 

Rb-Sr systematics that are consistent with Triassic emplacement ages and with magma production in a depleted mantle 

source region within a volcanic arc setting. Phyllites show 

more compositional scatter, suggesting U-Pb fractionation 

during hydrothermal alteration and interaction with seawater 

or marine carbonate rocks. The hanging-wall argillites give 

Pb-Pb apparent ages consistent with sedimentation during 

Triassic time of detritus derived in part from an older, more 

radiogenic source region. The Rb-Sr isotope systematics of the 

argillites show evidence of disruption in Cretaceous time. Serpentinites also show disrupted isotope systematics. Values of 

epsilon-Nd increase through the stratigraphy from metabasalts 

to mafic volcanics and gabbroic plutons to Hyd Group basalts 

at the top of the Triassic section. The increase implies progressive depletion of magma source regions, which is consistent 

with the opening of preexisting crust in a rift setting.

The Greens Creek wall rocks span wider lead isotopic 

ranges than the ores. A comparison of ore and wall-rock 

compositions suggests that the ore lead was derived mainly 

from basaltic and gabbroic lithologies with a lesser contribution from the hanging-wall argillites. The isotopic uniformity 

of the orebody implies that the lead was homogenized prior to 

being deposited in sulfide minerals.

Models

The final three chapters in the Professional Paper (chaps. 

13, 14, 15) describe models for the Greens Creek deposit. 

The first paper, by Freitag (chap. 13), presents a model for the 

geometry and structural development of the Lower Southwest 

orebody. The model is based on rib and plan maps that were 

prepared for the Lower Southwest orebody and for parts of the 

Upper Southwest, 244 West Bench, and 200 South orebodies. 

Similarities are apparent between the structures revealed in the 

deposit and the structures that have been observed regionally 

(see Proffett, chap. 7). Thus, the model may provide guidance 

for exploration away from the mine as well as for continued 

development within the mine.

Syndepositional normal faults were inferred from northsouth-trending accumulations of sulfide and mineralized dolomite that appeared on isopach maps created from palispastic 

reconstructions. The accumulations are believed to represent 

thicker sulfide sections that developed above fault-controlled 

fluid conduits. Next in the structural history were ladder veins 

that developed perpendicular to bedding in argillaceous rocks; 

these were later offset by pressure solution seams. Compressional tectonics associated with terrane accretion in Late 

Jurassic to Cretaceous time caused small thrust faults, and then 

resulted in south-southwest- to southeast-plunging, open-toisoclinal folds and southeast-plunging open folds. The effects 

of the folding events were more pronounced in less competent, 

thinner sulfide sections leading to greater fold frequencies and 

fold amplitudes, and more varied orientations of foliations and 

cleavages. The folding events were followed by a transition to 

a more brittle deformation style that produced gentle folds and 

thrust faults. Wrench tectonics in Eocene time led to highangle faulting, in some cases along reactivated thrust faults.

Next, Lee and Taylor (chap. 14) present three-dimensional 

depictions of the orebodies, major workings, faults, shear 
Reference Cited 7

zones, and assay values for zinc, silver, gold, and antimony. 

The basis of the depictions is lithologic, structure, and assay 

data for 1,895 core holes that were drilled in the vicinity of 

the mine. The results are displayed relative to the mine grid, 

which is rotated 26.5651 degrees counterclockwise from due 

north. Mine coordinate elevations are 60 ft higher than abovesea-level elevations. The depictions allow readers to visualize 

and quickly appreciate a number of important aspects of the 

deposit and the mine, including the topography of the area, the 

complexity of the ore distribution, the influence of faults on 

the ore distribution, and the spatial relationship between zinc 

mineralization and precious metal mineralization.

In synthesizing the results of the entire cooperative 

research project, Taylor and others (chap. 15) point out that 

the Greens Creek deposit is not easily classified because it 

displays features characteristic of volcanogenic massive sulfide 

(VMS) deposits, features characteristic of sedimentary exhalative (SEDEX) sulfide deposits, and features characteristic of 

Mississippi Valley-type (MVT) sulfide deposits. Among the 

VMS characteristics are an association with abundant volcanic 

rocks (footwall phyllites), the existence of an alteration profile 

beneath the mineralized horizons, a metal endowment (Zn-PbAg-Au-Cu) resembling Kuroko- or bimodal-felsic-type VMS 

deposits, and a mineral deposit type (white ores) that resembles 

the white smoker deposits found on the modern sea floor in 

areas of active volcanism. SEDEX characteristics include an 

association with carbonaceous sedimentary rocks (hanging-wall 

argillites), the presence of a broad chromium-barium-carbonate 

alteration halo, the lack of a hydrothermal root beneath the ores, 

and the diagenetic/bacterial origin of sulfide sulfur. The MVT 

characteristics are less compelling from a classification standpoint, but they include the local presence of epigenetic sulfide 

mineralization in carbonate rocks in the deposit footwall.

The tectonic setting for the Greens Creek deposit was a 

rift basin that developed in the Alexander terrane following 

a period of shale accumulation in open basins and carbonate 

platform development, and subsequent emergence and erosion of the Alexander landmass. Rifting commenced in Late 

Triassic time. Arc-contaminated tholeiites and minor alkaline 

basalts were extruded, probably subaqueously, in the Greens 

Creek area. Subsequently, a thin carbonate platform developed 

within the rift during a period of quiescence. Resumption of 

rifting caused the carbonate platform to founder, and it was at 

this time that the Greens Creek hydrothermal system was initiated. Shallowly emplaced mafic and ultramafic magmas supplied the requisite heat for the development of hydrothermal 

circulation. The first hydrothermal products to be formed were 

precious-metal-bearing silica-barite-carbonate deposits that 

formed at or just beneath the sea floor by mixing of metalliferous fluids with sulfate-bearing seawater. The accumulation of 

organic-rich sediments in the subsiding basin resulted in bacterial sulfate reduction within the sediment column, and possibly 

also within stagnant basin waters. Base-metal and iron sulfide 

minerals were formed where hydrothermal fluids encountered 

bacterial hydrogen sulfide, resulting in the replacement of 

both unlithified shale and preexisting silica-barite-carbonate 

deposits. The deposit underwent a process akin to zone 

refining during prograde hydrothermal heating, causing precious metals, antimony, mercury, and other metals to migrate 

upward and outward within the deposit. Hydrothermal activity 

and shale accumulation were followed by the eruption of 

voluminous basalts. Heating and deformation during Cretaceous greenschist facies metamorphism recrystallized sulfide 

minerals and thickened the ore horizon locally.

Greens Creek is a hybrid deposit intermediate between 

more typical VMS and SEDEX deposits. Deposit characteristics suggest formation in a transitional environment within 

a rift that was propagating from dominantly oceanic crust 

toward the core of the Alexander terrane where the crust was 

increasingly continental. The change in crustal character 

along the strike of the propagating rift is thought to explain 

the change in metal endowments from copper-dominant at 

Windy Craggy to zinc-lead-silver-dominant at Greens Creek. 

Whereas the Windy Craggy hydrothermal system scavenged 

metals predominantly from copper-rich, lead- and zinc-poor 

ocean ridge basaltic rocks, the Greens Creek hydrothermal 

system scavenged metals from mafic and ultramafic rocks that 

were richer in zinc and lead because they had assimilated the 

evolved basement of the Alexander terrane.

Final Comment

As the reader proceeds through this Professional Paper, 

it will become clear that some research priorities set out in the 

original memorandum of understanding proved to be quite 

fruitful, whereas others proved to be less so. This is perhaps 

inevitable for a complex project with an ambitious work plan 

and a wide diversity of participants. In particular, attempts to 

characterize the protoliths and alteration histories of the footwall 

rocks were only partially successful because, as the data of 

Premo and Taylor (chap. 12) demonstrate, it is difficult to see 

backward through the multiple thermal and metasomatic overprints to determine original chemical and isotopic properties. On 

the other hand, the discovery of disturbed isotope systematics 

provides strong support for the conclusion that the Greens Creek 

footwall was intensely altered by throughgoing hydrothermal 

fluids. Overall, there is no question that the U.S. Geological 

Survey–Kennecott Greens Creek Mining Company cooperative 

research project was highly worthwhile; the final product—this 

Professional Paper—far exceeds what the individual organizations could have accomplished working in isolation.

Reference Cited

Gradstein, F.M., Agterberg, F.P., Ogg, J.G., Hardenbol, Jan, 

Van Veen, Paul, Thierry, Jacques, and Huang, Zehui, 1995, 

A Triassic, Jurassic, and Cretaceous time scale, in Geochronology time scales and global stratigraphic correlation: 

SEPM Special Publication No. 54, p. 95–126.

The Late Triassic Metallogenic Setting of 

the Greens Creek Massive Sulfide Deposit 

in Southeastern Alaska

By Cliff D. Taylor, John Philpotts, Wayne R. Premo, Alan L. Meier, and 

Joseph E. Taggart, Jr.

Chapter 2 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract.........................................................................................................................................................13

Introduction...................................................................................................................................................13

Terrane Relationships .................................................................................................................................21

Stratigraphy of Host Rocks to Late Triassic Mineral Occurrences and Correlation

Throughout Southeastern Alaska................................................................................................22

Geochemistry of Upper Triassic Basalts and Rhyolites of Southeastern Alaska .............................31

The Geochemistry and Significance of Late Triassic Hypabyssal Mafic-Ultramafic

Intrusive Rocks ...............................................................................................................................38

Late Triassic Mineral Occurrences in Southeastern Alaska................................................................39

Mineral Occurrences in the Southern ATMB ................................................................................39

Mineral Occurrences in the Northern ATMB.................................................................................42

Mineral Occurrences in the Central ATMB....................................................................................43

Discussion.....................................................................................................................................................52

References Cited..........................................................................................................................................55

Figures

1. Generalized map of southeastern Alaska showing the locations of mines,

mineral deposits, and mineral occurrences and other features discussed

in the text, in relation to the Alexander Triassic Mineral Belt (ATMB) and

insets showing detailed maps ..................................................................................................14

2. Tectonostratigraphic terranes of southeastern Alaska.......................................................23

3. Stratigraphy and correlation of Upper Triassic host rocks in southeastern

Alaska and adjacent British Columbia ....................................................................................24

4. Composite stratigraphic column of the Upper Triassic section on

Annette Island .............................................................................................................................25

5. Composite stratigraphic column of the Upper Triassic section on

Gravina Island .............................................................................................................................25

6. Composite stratigraphic column of the Upper Triassic section in the

Keku Strait area ..........................................................................................................................26

7. Photograph of the basal Upper Triassic conglomerate in Nehenta Bay,

Gravina Island .............................................................................................................................27

8. Composite stratigraphic column of the Middle and Upper Triassic

section in the Duncan Canal area............................................................................................28

9. Composite stratigraphic column of the Upper Triassic section on the north

shore of Gambier Bay, southern Admiralty Island ................................................................28

10. Composite stratigraphic column of the Upper Triassic section at the

Greens Creek mine, northern Admiralty Island .....................................................................29

11. Composite stratigraphic column of the Upper Triassic section in the Mt. Henry

Clay area, northern southeastern Alaska and northwestern British Columbia ...............30

12. Photograph of pillowed basalt flow near the base of the Upper Triassic section

on the north shore of Gambier Bay, southern Admiralty Island..........................................31

13. Composite stratigraphic column of the Upper Triassic section at the Windy

Craggy deposit, northwestern British Columbia....................................................................33
14. Accuracy and precision of blind standards plotted on the diagrams used

in the text as compared to accepted values..........................................................................34

15. Volcanic rock classification diagram of Winchester and Floyd (1977)

based on immobile-element ratios, showing the composition of

southeastern Alaska Upper Triassic volcanic rocks analyzed for this study...................35

16. Discrimination diagrams showing compositions of southeastern

Alaska Upper Triassic basalts and rhyolites analyzed for this study.................................37

17. MORB-normalized abbreviated immobile-trace-element and REE plots of

data for samples from locations throughout the ATMB corresponding to the

samples and locations shown on the discriminant plots.....................................................40

18. Photographs of outcrops throughout the ATMB demonstrating the spatial

relationship between mineral occurrences and mafic-ultramafic hypabyssal

sills, dikes, and intrusions .........................................................................................................44

19–22. Photographs of outcrops and polished rock slabs from mineral occurrences

in the southern portion of the:

 19. Southern portion of the ATMB........................................................................................46

 20. Northern portion of the ATMB ........................................................................................47

 21. Central portion of the ATMB............................................................................................50

 22. Central and northern portion of the ATMB ...................................................................53

23. Schematic drawing showing a cross-sectional view of the Upper Triassic

metallogenic setting of mineral deposits and occurrences in southeastern

Alaska ...........................................................................................................................................54

Tables

1. Summary whole-rock geochemical data for Upper Triassic basaltic rocks at

key locations in southeastern Alaska .....................................................................................32

2. Whole-rock geochemical data for igneous rocks collected throughout the

ATMB in southeastern Alaska and British Columbia..........................................on CD–ROM

Abstract

The Alexander terrane of southeastern Alaska contains a belt of unusual volcanogenic massive sulfide (VMS) 

deposits along its eastern margin. The deposits occur within a 

lithologic sequence that is exposed discontinuously along its 

600-kilometer strike length and consists of a 200–800-meter 

thickness of conglomerate, limestone, marine clastic sediment, 

and tuff with intercalated and overlying mafic pyroclastic 

rocks and pillowed flows. The rocks range in age from Anisian 

(Middle Triassic) to late Norian (middle Late Triassic). Major 

deposits within the belt, which is referred to herein as the 

Alexander Triassic Metallogenic Belt (ATMB), are Greens 

Creek, the most economically significant VMS deposit in 

Alaska, and Windy Craggy, the largest VMS deposit known in 

North America.

The VMS deposits vary in structural appearance, chemistry, and stratigraphic setting along strike within the ATMB, 

which suggests spatial or temporal changes in the tectonic 

environment. In the southern portion of the belt, the deposit 

host rocks are felsic volcanics and overlying shallow-water 

limestones. In the central portion of the belt, a pebble conglomerate appears at the base of the section, suggesting higher 

energy deposition in a near-slope or basin-margin setting. In 

the north, the felsic volcanics, limestones, and conglomerates 

give way to deeper water sediments and mafic volcanic rocks. 

There is an accompanying change in the sulfide deposits from 

dominantly structurally controlled Pb-Zn-Ag-Ba±Cu deposits 

in the south (for example, west of Ketchikan), to sulfosaltbearing VMS deposits (for example, Greens Creek on Admiralty Island), to larger Cu-Zn±Co±Au VMS deposits in the 

north (for example, Windy Craggy in northeastern British 

Columbia).

Igneous activity in the ATMB was characterized by 

bimodal volcanism and hypabyssal emplacement of maficultramafic magmas. Analyses of immobile trace elements and 

rare earth elements suggest that the felsic rocks change from 

calc-alkaline rhyolites in the southern ATMB to peralkaline 

rhyolites in the middle part of the belt. The capping basaltic 

rocks have compositions consistent with variable assimilation of mature island arc crust by more primitive, midocean 

ridge-type or intraplate-type basaltic melts. Radiogenic isotope 

data for the capping basalts and associated gabbros support the 

variable assimilation hypothesis (epsilon-Nd=+4–+9, initial 

206Pb/204Pb=18.42–18.92, initial 87Sr/86Sr=0.7037–0.7074).

Overall, the regional geology and geochemistry are 

consistent with sulfide deposition in the south having occurred 

in shallow, subaqueous environments on the flanks of the 

Alexander terrane, and sulfide deposition farther north having 

occurred in progressively deeper environments in an evolving 

back-arc or intra-arc rift. In their ore and host-rock geochemistry and sulfide mineralogy, the ATMB deposits resemble 

deposits that have been found at active sea-floor hydrothermal 

vents (white smokers) associated with back arcs of the southwest Pacific Ocean. A modern analog for the ATMB may be 

the southward projection of the Lau basin, from the active seafloor hydrothermal vents of the Valu Fa Ridge to the Taupo 

Volcanic Zone of the North Island, New Zealand.

Introduction

Numerous papers (compilations by Cobb, 1972, 1978; 

Berg and Grybeck, 1980; Goldfarb and others, 1987; Taylor 

and others, 1992; Newberry and Brew, 1997, 1999; Newberry and others, 1997; Taylor and others, 2008) over the last 

few decades have identified a series of unusual polymetallic 

volcanogenic massive sulfide (VMS; see reviews by Franklin and others, 1981, and Large, 1992) deposits hosted in an 

Upper Triassic sequence of volcano-sedimentary rocks that 

stretch the length of southeastern Alaska (fig. 1). Assuming 

that correlations among host rocks are correct, these deposits 

constitute a metallogenically important belt that comprises the 

easternmost and youngest portion of the Alexander terrane 

(fig. 2). With the notable exception of the world-class Greens 

Creek mine having estimated reserves of 21.9 million metric 

tonnes of ore at 13.9 percent zinc, 5.1 percent lead, 4.8 grams 

per metric tonne gold, and 599 grams per metric tonne silver 

at zero cutoff, these are generally small deposits (less than 1 

million metric tonnes) dominated by Ba-Zn-Pb-Ag ± Cu-Au, 

or Cu-Zn ± Au. From south to north, they occur on Annette 

and Gravina Islands near Ketchikan (fig. 1, inset a), through 

Keku Strait (fig. 1, inset c) and Duncan Canal–Zarembo Island 

area west of Petersburg (fig. 1, inset b), through Admiralty 

Island south of Juneau (fig. 1, inset d), and on and near Mt. 

Henry Clay west of Haines (fig. 1, inset f). If correlation to 

The Late Triassic Metallogenic Setting of the Greens 

Creek Massive Sulfide Deposit in Southeastern Alaska

By Cliff D. Taylor, John Philpotts, Wayne R. Premo, Alan L. Meier, and Joseph E. Taggart, Jr.
14 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Triassic Rocks

Mt. Henry

Clay

Windy Craggy 

Greens

Creek

Gambier

Bay

Keku

Strait

Duncan Canal

Zarembo

 Island

Gravina Island Annette Island

Juneau

Sitka

Petersburg

Ketchikan

Duke Island

Screen Islands

Haines

BRITISH COLUMBIA

ALASKA

inset f.

inset d.

inset c.

inset b.

inset a.

inset e.

EXPLANATION

0 40 80 KILOMETERS

N

Area of

figure 1

ALASKA

59° 59°

137°

58°

136°

56°

135°

55°

133° 132° 131°

55°

130°

130°

56°

131°

57°

133°

58°

Figure 1. Generalized map of southeastern Alaska (modified from Gehrels and Berg, 1992) showing the locations of mines, mineral 

deposits, and mineral occurrences (all shown as solid circles) and other features discussed in the text, in relation to the Alexander 

Triassic Mineral Belt (ATMB). (Inset a) Detailed map of the southern ATMB showing the locations of mines, mineral deposits, and 

mineral occurrences and other features discussed in the text on Annette and Gravina Islands. (Inset b) Detailed map of the central 

ATMB showing the locations of mines, mineral deposits, and mineral occurrences and other features discussed in the text in the 

Duncan Canal area and on Woewodski and Zarembo Islands. (Inset c) Detailed map of the central ATMB showing showing the 

locations of mines, mineral deposits, and mineral occurrences and other features discussed in the text in the Keku Strait area. (Inset 

d) Detailed map of the central ATMB showing the locations of mines, mineral deposits, and mineral occurrences and other features 

discussed in the text on Admiralty Island. (Inset e) Detailed map of the Greens Creek mine area on northern Admiralty Island showing 

the locations of mines, mineral deposits, and mineral occurrences and other features discussed in the text. (Inset f) Detailed map of 

the northern ATMB showing the locations of mines, mineral deposits, and mineral occurrences and other features discussed in the 

text between the Mt. Henry Clay area and Windy Craggy.
Abstract 15

Nehenta Bay

Sylburn

Peninsula

Annette

Island

Gravina

Island

Japan Bay

Crab 

Bay

Bostwick Inlet

0 50 10 KILOMETERS

55°05'

55°10'

55°25'

55°20'

55°15'

131°50' 131°40' 131°30' 131°20'

Figure 1, inset a. Detailed map of the southern ATMB showing the locations of mines, mineral deposits, and mineral 

occurrences and other features discussed in the text on Annette and Gravina Islands.
16 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Round Point

Frenchie

(St. John Harbor)

Brushy Creek

Lost Show

Helen S

Butterworth Island

Taylor Creek

Castle River Mouth

Castle Island Barite

Junior Creek

Wetboot

(Towers Creek)

Towers Peninsula

0 5 10 KILOMETERS

56°15'

56°30'

56°45'

133°30' 133°15' 133°00' 132°45'

Figure 1, inset b. Detailed map of the central ATMB showing the locations of mines, mineral deposits, and mineral occurrences 

and other features discussed in the text in the Duncan Canal area and on Woewodski and Zarembo Islands.
Introduction 17

the Windy Craggy deposit (reserves estimated at 297.4 million 

metric tonnes at 1.38 percent copper, 0.07 percent cobalt, 0.2 

gram per metric tonne gold, and 3.8 grams per metric tonne 

silver; Peter and Scott, 1999) to the north is correct, then a 

belt approximately 600 kilometers in length is defined that 

contains the largest Besshi-type VMS deposit (see review by 

Slack, 1993) in the world and the leading producer of silver in 

the United States. This metallogenic belt is herein referred to 

as the Alexander Triassic Metallogenic Belt (ATMB).

Host lithologies identify a distinctive geologic setting. 

The VMS deposits are nearly uniformly hosted within a thin 

package of structurally dismembered Upper Triassic (Norian) 

rocks characterized by bimodal volcanics and abundant 

flysch-type sediments. Mafic volcanic rocks predominate and 

commonly are volcaniclastics or flow breccias with lesser pillowed and massive flows. At larger, more obviously stratiform 

occurrences, sediments tend to be basinal in appearance, 

with high proportions of graphitic argillite and thin lenses of 

pyrite. Metamorphic grade varies from prehnite-pumpellyite to 

mid-greenschist. The base of the package is typically marked 

by the presence of angular to rounded polymictic conglomerate with clasts composed of the immediately underlying unit. 

In places, discrete packages of conglomerate occupy flow 

channels that migrate laterally and vertically within a short 

distance. High-angle faults of probable normal displacement 

are common and tend to mark changes in lithology, such as 

from sedimentary to volcanic rocks. Thin carbonate units are 

common as well and are generally dolomitic. Small outcrops 

of serpentinized mafic/ultramafic rock also tend to be spatially 

associated with deposits throughout the ATMB.

From south to north, a distinct variation in both the nature 

of the deposits and the host rocks is evident. At the southern 

end of the ATMB, the felsic component of the bimodal volcanic rocks is significant and becomes more rare or even absent 

northwards. The volcanic stratigraphy on both Annette and 

Gravina Islands is characterized by a thick sequence of rhyolitic volcaniclastics and tuffs low in the Upper Triassic section, 

which give way to voluminous mafic volcaniclastics and 

flows in the upper portion of the section. On the Cornwallis 

Peninsula in the Keku Strait area, minor mafic volcanic rocks 

constitute the base of the package and are overlain by a thick 

sequence of rhyolitic volcaniclastics and flows. Felsic volcanic 

rocks are rare north of Keku Strait. The northernmost occurrence of felsic volcanic rocks is on Mt. Henry Clay where 

thin flows of trachyandesite and quartz-sericite-pyrite altered 

rhyolite and rhyolitic tuffs are associated with the occurrences 

(Green and others, 2003). Additional but perhaps less obvious regional changes in the host rocks are an increase in the 

percentage of volcanic to sedimentary rocks to the north, and 

possibly an increase in metamorphic grade.

A noticeable change in the nature of the deposits parallels the change in host rock lithology. The deposits in the 

south are predominantly zinc-lead-silver bearing with large 

amounts of barite. In fact, some of the deposits such as on the 

Sylburn Peninsula on Annette Island and the Castle Island 

barite deposit in the Duncan Canal area are composed primarily of barite with minor sphalerite, galena, and tetrahedrite. 

These deposits share many similarities with Kuroko-type 

ores (for example, Franklin, 1986, 1993). From the latitude 

of about Petersburg to the north, deposits appear that contain 

Cornwallis Peninsula

Hungerford Creek

Kuiu Zinc

Ladder Vein

56°52'

56°54'

56°56'

0 5 KILOMETERS

134°10' 134°00'

Figure 1, inset c. Detailed map of the central ATMB showing showing the locations of mines, mineral deposits, and mineral 

occurrences and other features discussed in the text in the Keku Strait area.
18 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

North Gambier North Shore

Gambier Bay

Cave Mountain Point

Yellow Bear Mountain

Etta

Windfall Harbor

Pyrola

Mansfield

Peninsula

57°30'

57°45'

58°00'

58°15'

134°45' 134°30' 134°15' 134°00'

0 10 KILOMETERS

inset e.

Greens Creek Mine
Introduction 19

Gallagher Ridge

Cliff Creek

Cirque

Mariposite Ridge

Lil Sore

Greens Creek mine

"A" Road

0 2 KILOMETERS

58°10'

58°05'

134°40' 134°30'

Zinc Creek

Figure 1, inset d (facing page). Detailed map of the central ATMB showing the locations of mines, mineral deposits, and 

mineral occurrences and other features discussed in the text on Admiralty Island.

Figure 1, inset e. Detailed map of the Greens Creek mine area on northern Admiralty Island showing the locations of mines, 

mineral deposits, and mineral occurrences and other features discussed in the text. (Inset f) Detailed map of the northern ATMB 

showing the locations of mines, mineral deposits, and mineral occurrences and other features discussed in the text between 

the Mt. Henry Clay area and Windy Craggy.
Windy Craggy Tats Rainy Monday Low Herbert Mt. Henry Clay (Boulderad

Little J

Herbert Mouth West Buckwell Moraine Grizzly Heights X 0 10 KILOMETERS 59°40' 59°30' 59°20' 137°30' 137°00' 

Figure 1, inset f. Detailed map of the northern ATMB showing the locations of mines, mineral deposits, and mineral occurrences and other feattext between the Mt. Henry Clay area and Windy Craggy.
Terrane Relationships 21

Cu-Zn ± Au-Co-Ni and are similar to many Besshi-type ores 

(for example, Slack, 1993). The Frenchie VMS occurrence 

(St. John’s Harbor ) may be the southernmost of this type, and 

deposits of both descriptions occur on either side of the international border in the Mt. Henry Clay area. By the latitude of 

about the Tatshenshini River, the majority of the deposits are 

Besshi-like with Windy Craggy being the notable example. 

The Greens Creek deposit itself is unusual in that it exhibits 

a range of syngenetic, diagenetic, and epigenetic features 

that are transitional between VMS, sedimentary exhalative 

(SEDEX; see review by Goodfellow and others, 1993), and 

Mississippi Valley-type (MVT; see review by Leach and 

Sangster, 1993) genetic models (Taylor and others, 1999).

In the several locations where the host rocks of the 

ATMB have been studied, data uniformly suggest that the 

environment of deposition was some type of intra-arc or backarc setting. Trace and REE chemistry of the mafic volcanics 

is transitional between midocean ridge basalt (MORB) and 

island-arc basalt (IAB), with discriminant plots based on 

immobile elements showing tectonic environments from 

MORB to within-plate basalts. Radiogenic isotopic data are 

indicative of a juvenile (mantle ?) source for the basalts. The 

several tectonic settings suggested to have produced these host 

rocks are variably: a brief episode of Late Triassic rifting prior 

to final docking of outboard terranes to the continental margin, 

small pull-apart basins in response to transpressive motion 

along the margin, or a failed rift.

Under close examination, however, the correlation of host 

rocks throughout the 600-km-long ATMB is problematic. Traditionally, the central strip of Upper Triassic volcanics, from 

Annette Island to at least the latitude of mid-Admiralty Island, 

was placed in the Alexander terrane. The Upper Triassic rocks 

on the mainland to the east were assigned to the Taku terrane, 

and the strip of Upper Triassic greenstones at Goondip to the 

west were placed in the Wrangellia terrane (for example, Berg 

and others, 1972, 1978; Churkin and Eberlein, 1977; Gehrels 

and Berg, 1994). Tentative correlation of the Hyd Group rocks 

on Admiralty Island with the informally named Jarvis basalts 

at Mt. Henry Clay, and with the informally named Tatshenshini basalts on the Canadian side of the border, would extend 

the central strip of rocks at least as far north as Windy Craggy 

within the Alexander terrane. However, correlation of the 

basalts at Chilkat in the central strip with the basalts at Taku 

of the eastern strip near Juneau (Ford and Brew, 1993; Gehrels 

and Barker, 1993) and with possible Hyd Group-equivalent 

rocks on the north end of Admiralty Island (Ford and Brew, 

1993), raises the possibility that all of the Upper Triassic rocks 

of the composite Alexander-Wrangellia terrane are genetically 

related and formed during the same igneous event.

As originally defined, the distinguishing difference 

between the Alexander and Wrangellia terranes is the age 

and character of the Upper Triassic volcanic rocks. Wrangellia terrane basalts, as exemplified by the Nikolai Greenstone, 

basalts at Chilkat, greenstones at Goondip, and Karmutsen 

Formation, are voluminous, subaerial to shallow subaqueous, 

flood basalts of Carnian (230 Ma) age that were extruded over 

a period of about 5 million years (Panuska, 1990; Richards 

and others, 1991). In contrast, the basalts of the Alexander 

terrane, as exemplified by the Hyd Group, the Hound Island 

Volcanics of the Hyd, and possibly the Jarvis basalts of the 

Mt. Henry Clay area and the Tatshenshini basalts of northern 

British Columbia, are much thinner flows of Norian (210 Ma) 

age that are intercalated with graywacke and graphitic/pyritic 

mudstone. Several competing models for the production of 

the basalts of the Wrangellia terrane include an episode of 

volcanism related to intra-arc or back-arc rifting (Barker and 

others, 1989; Sampson and others, 1991; Barker, 1994), or 

to production of an oceanic plateau flood-basalt province in 

response to initiation of a mantle plume beneath the Paleozoic 

arc (Richards and others, 1991). The Alexander terrane basalts 

have generally been ascribed to formation during a period of 

intra-arc or back-arc rifting.

Since the recognition that Pennsylvanian plutons stitch 

the two terranes into one Wrangellia supercontinent (Gardner 

and others, 1988), distinctions between the Alexander and 

Wrangellian Upper Triassic rocks have been glossed over, 

and they are generally regarded as probable lateral facies of 

the same extensive unit. The extreme structural dismemberment and juxtaposition of parallel strips of rocks in southeastern Alaska, and thus the rapid variation in thickness of 

the Upper Triassic section and the associated variation in the 

percentage of volcanic to sedimentary rock, are explained as 

having occurred primarily in the Tertiary as a result of lateral 

transport of terranes northward along the continental margin. 

Alternatively, the volcanism could have occurred at multiple 

sites of rifting during discrete intervals from Carnian to 

Norian time.

Whereas the lumping of all of the Triassic volcanic rocks 

into one related package of rift- or plume-related rocks is convenient, it leaves unanswered the important question of why 

the belt of VMS deposits is only associated with basalts of the 

Alexander terrane. In this chapter we document the geology, 

stratigraphic setting, and mineral and host-rock geochemistry 

at a number of mineral occurrences within the ATMB. Our 

goal is to assemble a coherent metallogenic framework for the 

ATMB that will serve as a foundation for the more detailed 

chapters that follow on the Greens Creek deposit. This chapter 

treats a topic that was covered in a previous publication (Taylor and others, 2008), but it reports a greatly expanded chemical and isotopic database, many new figures, and extended 

descriptions and discussions.

Terrane Relationships

Host rocks to the ATMB are within the Admiralty and 

Craig subterranes of the Alexander terrane (Berg and others, 

1972, 1978; Churkin and Eberlein, 1977). Terrane relation Terrane re -

ships in southeastern Alaska are shown in figure 2. The 

general evolution of the Alexander terrane has been discussed 

by Sampson and others (1989), who suggested that it has the 

characteristics of a wholly oceanic island arc. The terrane is 
22 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

an allochthonous, continent-sized fragment of island arc crust 

that began forming in latest Precambrian time in low latitudes. It consists of as much as 35,000 feet of predominantly 

marine sedimentary and volcanic strata and plutonic rocks of 

latest Precambrian(?) to Middle(?) Jurassic age (Gehrels and 

Saleeby, 1987; Gehrels and Berg, 1994). By Devonian time 

the terrane had gone through two orogenies and a protracted 

period of quiescence marked by erosion and formation of 

extensive carbonate platforms. Paleomagnetic, paleontologic, 

and detrital zircon studies (Hillhouse, 1987; Hillhouse and 

Gromme, 1984; Haeussler and others, 1992; Bazard and 

others, 1994; Gehrels and others, 1994; Savage, 1994) suggest 

that by middle Permian time the terrane was outboard of a 

continental landmass and that depositional environments were 

characterized by shallow, tropical marine, possibly evaporitic, 

conditions.

Rift-fill stratigraphic sequences and bimodal volcanism 

along the eastern edge of the terrane (MacIntyre, 1986; Gehrels and others, 1986, 1987; Taylor and others, 2008) mark the 

beginning of an extensional tectonic event in the Late Triassic 

that either split the terrane or separated it from its low-latitude, 

offshore position and transported it to its present location on 

the western North American continental margin (Gehrels and 

Berg, 1994). The allochthonous Wrangellia terrane of Pennsylvanian to Late Triassic age (Jones and others, 1977), which 

is also of oceanic arc derivation (Sampson and others, 1990), 

adjoins the Alexander terrane on its western, northern, and 

northeastern sides. These terranes were stitched together by 

Middle Pennsylvanian plutons in southern Alaska (Gardner 

and others, 1988) to form the Wrangellia superterrane. Accretion of the Wrangellia superterrane may have commenced by 

the Early or Middle Jurassic (McClelland and Gehrels, 1990) 

or the Late Jurassic (Saleeby, 1994) and was complete by 

about middle Cretaceous time, as indicated by the intrusion of 

subduction-related, magmatic-epidote-bearing plutons and the 

development of the Jurassic-Cretaceous Chugach accretionary 

prism outboard of the superterrane.

Collision resulted in regional metamorphism and 

deformation related to underthrusting of the continental 

margin. This event produced relatively flat-lying, northwestvergent thrust faults identified underground and in surface 

outcrops on Admiralty Island and throughout southeastern 

Alaska. Mapping of regional metamorphic facies by DuselBacon (1994) places Triassic and older rocks in southeastern 

Alaska within the lower to middle greenschist facies. In early 

Tertiary time (Goldfarb and others, 1991; Miller and others, 

1994), oblique subduction changed to right-lateral transcurrent motion along the margin, imparting the present structural grain to the country rocks and causing the formation 

of numerous, subparallel, high-angle, strike-slip faults that 

dismember the outboard terranes.

Stratigraphy of Host Rocks to Late 

Triassic Mineral Occurrences and 

Correlation Throughout Southeastern 

Alaska

The host rocks to the mines, deposits, and mineral occurrences examined during the course of this study are discontinuously exposed for approximately 600 kilometers along the 

eastern margin of the Alexander terrane, from Annette Island 

in the south, northward to Windy Craggy. In general, the 

stratigraphy within the ATMB consists of a 200–800-m-thick 

sequence of conglomerate, limestone, marine clastic sediment, 

volcanic rock, and tuff that are intercalated with and overlain 

by a distinctive unit of mafic pyroclastic rocks and pillowed 

flows (fig. 3). Faunal data bracket the age of the host rocks 

between Anisian (Middle Triassic) and late Norian (middle 

Late Triassic) time.

On Annette (fig. 4) and Gravina Islands (fig. 5) at the 

southern end, and in Keku Strait (fig. 6) in the middle portion 

of the ATMB, the base of the section is marked by a distinctive pebble conglomerate indicative of high-energy deposition 

in a near-slope or basin-margin setting. Clasts are polymictic, 

extremely immature, and are locally derived from the immediately underlying rocks. Features of the conglomerates indicate 

changing proximity to the source area. The median size and 

sorting of the clasts as well as the thickness and continuity 

of the units substantially change to the north. On Annette 

and Gravina Islands the dominant clast lithology is Silurian 

trondhjemite derived from the extensive pluton that underlies 

most of Annette Island and the south end of Gravina Island 

(Berg, 1972, 1973; Karl, 1992). Clast sizes range from pebbles 

to boulders 3 meters in diameter in continuous conglomerate 

sheets 30–45 meters thick (fig. 7). In Keku Strait clasts are 

dominantly composed of dolomite and chert from the underlying Pybus and Cannery Formations. Clasts are pebble- to 

boulder-sized (maximum of 0.3 m in long dimension) and 

occur in thin (0–6 m) discontinuous outcrops. In places, most 

notably on the northern shore of Hamilton Island, conglomerates occupy discrete scour channels that migrate laterally and 

vertically in a graywacke host.

A profound change in the character of the Upper Triassic 

stratigraphy occurs between Keku Strait and Duncan Canal. 

Both the sedimentary and volcanic units that comprise the 

section transition into rock types indicative of a position more 

distal to the Late Triassic rift margin. Whether this simply 

reflects a more seaward Late Triassic relative position of the 

Duncan Canal area to the east of Keku Strait or whether juxtaposition by faulting or folding of the two areas has occurred 

is not resolvable, given the current state of mapping and the 
Terrane Relationships 23

130

133

58

BRITISH COLUMBIA

ALASKA

59°

Yukon-Tanana terrane

EXPLANATION

Taku terrane

Gravina overlap assemblage

Alexander terrane

Triassic rocks

Wrangellia terrane

Chugach terrane

Sitka

Juneau

Haines

Petersburg

Ketchikan

Gravina Island Nehenta Bay Annette Island Duke Island

Woewodski

Island

Gambier

Bay

Admiralty

Island

Greens

Creek

Mansfield

Peninsula

Keku Strait

Duncan Canal

Screen Islands

Windfall Harbor

Swan Island

Young Bay

Kupreanof

Island

Zarembo

Island

0 40 80 KILOMETERS

58°

57°

56°

55°

57°

56°

55°

59°

137°

136°

135°

133° 132° 133°

131°

130°

Figure 2. Tectonostratigraphic terranes of southeastern Alaska.
Annette Island Gravina Island Keku Inlet Duncan Canal Gambier Bay Mt. He

Cla

Norian Carnian Pre- Triassic Silurian Permian 

Greens Creek ??? 

? ? ? Dolomitic limestone Rhyolite Polymictic conglomerate Pre-Triassic intrusive rocks Basalt Coarse-grained arkose and calcareous graywacke Pyritic-graphitic shales and impure carbonates Pre-Triassic carbonate rocks Permian 

EXPLANATION

Figure 3. Stratigraphy and correlation of Upper Triassic host rocks in southeastern Alaska and adjacent British Columbia.
Stratigraphy of Host Rocks to Late Triassic Mineral Occurrences and Correlation Throughout Southeastern Alaska 25

Basalt pillow/massive

Limy siltstone

Dolomitic limestone

Mineralization Mafic/ultramafic hypabyssal

 intrusive rocks

Rhyolite/tuff

Polymictic conglomerate

Trondhjemite

Fossil age (macrofossils)

EXPLANATION

F

Annette Island

F

F

F

F

Carnian

Norian

Upper

Triassic

Silurian

Figure 4. Composite stratigraphic column of the Upper Triassic 

section on Annette Island. Interpretation is based on Berg 

(1972), Gehrels and others (1987), Karl (1992), and this study.

generally poor exposure on most of Kupreanof Island. Tectonic shortening of a former basin is consistent with the synclinal structure proposed for the Keku Strait (Muffler, 1967) 

and is also compatible with the pattern of open folding and 

northwest-vergent thrusting documented by recent mapping 

in the Duncan Canal area (Karl and others, 1999a). Alternatively, juxtaposition of seaward (Duncan Canal) and landward 

(Keku Strait) areas of a northward-deepening rift basin may 

have resulted due to northward transport of the southern portion of the ATMB during Tertiary margin-parallel faulting.

When present, the basal polymictic conglomerate in 

Duncan Canal (fig. 8) reflects the character of a debris flow 

225 Ma

(U-Pb)

Basalt pillow/massive

Limy siltstone

Dolomitic limestone Mineralization

Trondhjemite/

diorite/volcanics

Rhyolite/tuff

Polymictic conglomerate

EXPLANATION

Gravina Island

F

F

F

F

F

F

F

F

Carnian

Norian

Upper

Triassic

Ordovician

through

Devonian

F Fossil age (macrofossils)

Figure 5. Composite stratigraphic column of the Upper 

Triassic section on Gravina Island. Interpretation is based on 

Berg (1973), Gehrels and others (1987), and this study.

that is distal to its source. Clasts are millimeters to several 

centimeters in size and occur in thin (0–10 meters) discontinuous outcrops. However, clasts appear to be subrounded 

and somewhat more sorted than conglomerates to the south. 

Clasts are dominantly composed of white quartz pebbles and 

chert with a lesser but important component of black shale 

chips that are probably derived from the underlying Cannery 

Formation. In two outcrops examined, one on the northwestern shore of Woewodski Island and a second on the west 

side of Duncan Canal north of the Castle River, the clasts are 

stretched considerably and the sericitic matrix appears drawn 

out by shearing. This deformation, related to movement in the 
26 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Duncan Canal shear zone (McClelland and Gehrels, 1990; 

Haeussler and others, 1999), has imparted a platy, fissile 

character to the conglomerates not observed at the previously 

described locations.

By the latitude of Gambier Bay and Windfall Harbor on 

Admiralty Island the basal polymictic conglomerate is only 

locally present (fig. 9). Clasts are mostly pebble to cobble 

sized and are dominantly composed of chert and dolomite, 

derived from the underlying Permian units. Individual 

conglomerate horizons are no thicker than about 3 meters. 

Although thin and discontinuous conglomerate horizons 

occur in the northern half of Admiralty Island, their stratigraphic positions within the Triassic section are uncertain. 

In most cases, they are thought to be above the base of the 

section within the shales that constitute the middle sedimentary portion of the Triassic stratigraphy. Additionally, these 

midsection conglomerates are similar in clast composition 

and maturity to the more distal-looking conglomerates in 

the Duncan Canal area. Notable examples are the thin quartz 

pebble-rich horizons in the 720 access ramp underground at 

the Greens Creek mine (fig. 10), and the 2-m-thick horizon 

immediately west of the drill pad at the Little Sore prospect 

several kilometers north of the mine. The stretched quartzpebble-rich conglomerate near Young Bay along the A-road 

may be an additional example.

The northernmost occurrences of a conglomerate “marker 

horizon” at the base of the Triassic section are on the eastern 

shore of Windfall Harbor immediately overlying the siliceous 

black shales of the Cannery Formation, and the debriite in 

Zinc Creek, described by Duke and others (chap. 4, the term 

debriite is used here to connote debris-flow deposits, following Warme and Kuehner, 1998). Our examination of this 

unit shows it to be a very poorly sorted, proximally derived 

polymictic conglomerate, composed of angular fragments of 

the immediately underlying lithologies. Abundant pyrite and 

iron carbonate in the matrix suggest the unit has been mineralized. Similarity to angular conglomerates in the footwall 

stratigraphy at the North Gambier pyritic copper-zinc-silverbarite occurrence (Taylor and others, 1992) suggests local fault 

control on the distribution of the basal conglomerates and on 

hydrothermal fluid flow. North of Admiralty Island, the basal 

conglomerate is absent, and no midstratigraphy conglomerate 

lenses are reported in the Triassic section.

In the southern end of the ATMB, dominantly felsic volcanic rocks immediately overlie the basal conglomerate. Thin 

basaltic flows are variably present as well near the bottom of 

the section and tend toward alkali basalt compositions. Massive 

and pillowed basalt flows occur within the sedimentary portion 

of the section on Gravina Island overlying the Puppets Formation. In the Keku Strait area we place thin basaltic flows within 

an interval of arkosic sediments immediately below the Keku 

Volcanics. Muffler (1967) also described mafic flows intercalated with the Keku Volcanics. On Annette and Gravina Islands 

the rhyolites are continuous, massive, flow-banded units; the 

cliff exposure of the Puppets Formation in Nehenta Bay is on 

the order of 150 meters thick. Berg (1973) estimated the unit 

to be 165 meters thick. On the Cornwallis Peninsula the Keku 

Volcanics is of uncertain thickness due to structural complexities but occupies an eastward-dipping belt 1.5 to 5 kilometers 

wide (Muffler, 1967). Drilling on the peninsula in 1995 by 

Sealaska Corporation was collared in the Keku Volcanics and 

penetrated over 366 meters of massive, flow-banded, volcaniclastic, and tuffaceous rhyolite without encountering a bottom 

contact. The position low in the section beneath the sedimentary and overlying mafic volcanic rocks, as well as the distinctive chemistry of the Keku Volcanics (discussed in succeeding 

F

F

F

oolitic

F

oolitic F

F

cherty

F

Basalt pillow/massive

Siltstone/arkose

Limestone/dolomite

Mineralization

Rhyolite/tuff

Polymictic conglomerate

Mafic dikes/intrusives

Fossil age (macrofossils)

EXPLANATION

F

Keku Strait area

Carnian

Norian

Upper

Triassic

Permian

Figure 6. Composite stratigraphic column of the Upper 

Triassic section in the Keku Strait area. Interpretation is based 

on Muffler (1967), and this study.
Stratigraphy of Host Rocks to Late Triassic Mineral Occurrences and Correlation Throughout Southeastern Alaska 27

Figure 7. Photograph of the basal Upper Triassic conglomerate in Nehenta Bay, Gravina Island. Note 

abundance of light-colored clasts of Silurian trondhjemite derived from the pluton that underlies much 

of Annette and southern Gravina Islands.
28 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

paragraphs), strongly suggest origins as bimodal volcanic rocks 

that were produced during the initiation of rifting.

In the Duncan Canal area, the stratigraphy is poorly 

constrained due to poor exposure. Rhyolites are largely 

absent north of Keku Strait, and their place low in the section is occupied instead by minor basalt flows interbedded 

with black shale. At the mouth of Castle River on the west 

side of Duncan Canal, thin (~4-m-thick) columnar-jointed 

basalt flows occupy a stratigraphic position just above the 

F

F

F

Mineralization Limestone

Polymictic conglomerate Pyritic-graphitic argillite

Basalt pillow/massive Mafic/ultramafic hypabyssal

 intrusive rocks

Fossil age (macrofossils)

EXPLANATION

F

Duncan Canal

Carnian

Ladinian

Norian

Upper

Triassic

Middle

Triassic

Permian

Figure 8. Composite stratigraphic column of the Middle and 

Upper Triassic section in the Duncan Canal area. Present 

interpretation is based on McClelland and Gehrels (1990), Karl 

and others (1999b), and this study.

F

F

F

F

F

F

F

Pillow/massive basalt

Pyritic-graphitic argillite

Limestone/dolomite

Mineralization

Serpentinite

Stratabound

 qtz-carb-talc-mariposite

Polymictic conglomerate

Mafic dikes/sills

EXPLANATION

F Fossil age (macrofossils)

North Shore Gambier Bay

Carnian

Norian

Upper

Triassic

Permian

Figure 9. Composite stratigraphic column of the Upper Triassic 

section on the north shore of Gambier Bay, southern Admiralty 

Island. Interpretation is based on Loney (1964), Taylor and others 

(1992), and this study.

conglomerates. Similarly, pillowed basalt flows are present on the north tip of Little Castle Island immediately west 

of (underlying ?) the Castle Island barite deposit. On the 

northwest shore of Woewodski Island, a thin basalt flow lies 

immediately beneath a stretched pebble conglomerate lens 

that we interpret to be the Upper Triassic basal conglomerate. Black shales immediately overlying the conglomerate 

contain several 15-cm-thick horizons of pyritic felsic tuff. To 

the south on Woewodski Island, several crudely stratiform 
Stratigraphy of Host Rocks to Late Triassic Mineral Occurrences and Correlation Throughout Southeastern Alaska 29

mineral occurrences of probable Late Triassic age (for 

example, Lost Show and Brushy Creek) are hosted in highly 

altered volcanic rocks. Although protoliths are obscured, it is 

unlikely that the altered volcanics were rhyolites. Their chemistry (for example, 98DC–33, table 2) and mineralogy is most 

consistent with altered mafic volcanic rocks. Less altered 

country rocks consist of mafic volcanic, volcaniclastic, and 

tuffaceous rocks. Highly altered tuffaceous rocks at Brushy 

Creek and sericite schist in creek exposures several hundred 

meters south of the occurrence could represent felsic tuffs. 

Poor exposure precludes assignment of these volcanic rocks 

to a specific position within the Upper Triassic stratigraphy.

On Zarembo Island, Upper Triassic rocks occur in 

a northwest-trending swath of flat topography that limits 

exposures to creek banks and borrow pits along logging roads. 

Absence of a recognizable stratigraphic marker horizon at the 

Frenchie pyritic massive sulfide deposit prevents distinguishing the stratigraphic position. However, the host rock immediately overlying the Frenchie deposit is a 6- to 10-meter-thick 

unit of pyritic quartz-sericite schist; the immediate footwall 

contains a thin lens of muscovite schist overlying graphitic 

pyritic argillite. Relationships at the Round Point mineral 

occurrence to the southeast are similarly obscure. Like the 

volcanic-hosted deposits on Woewodski Island, Round Point is 

hosted in altered volcanic rocks of probable mafic parentage.

Felsic volcanic rocks in the ATMB north of the felsic 

tuffs on the northwest shore of Woewodski Island and the 

Keku Volcanics in Keku Strait are rare. Recent mapping (S.M. 

Karl, oral commun., 2004) has identified outcrops of rhyolite 

of probable Triassic age on central Admiralty Island along the 

shoreline of Seymour Canal west of Swan Island, and vicinity. Thin units of quartz-sericite-pyrite altered trachyandesite, 

rhyolite, and felsic tuffaceous rocks associated with the RW 

zone (also called the Little Jarvis occurrence) of the Glacier 

Creek (Main) deposit (fig. 11) (Green and others, 2003) constitute the northernmost occurrence of Upper Triassic felsic 

volcanic rocks.

North of the Duncan Canal area, the position low in the 

Triassic section occupied by the rhyolites is filled by mafic lava 

flows. On the north shore of Gambier Bay, at least two separate 

pillowed flows are present in graphitic sediments above the 

basal conglomerate (fig. 12). Similarly, an outcrop of pillow 

basalt is present between the conglomerates and sediments 

in the footwall section of the North Gambier occurrence, 2.5 

kilometers to the north (Taylor and others, 1992). At Greens 

Creek, the age of the footwall phyllites remains the major 

unanswered question of the current research effort. The position 

of the phyllites immediately below and in apparent conformable contact with the argillites suggest that they represent a 

locally thickened accumulation of mafic volcanics low in the 

section, as observed in Gambier Bay and elsewhere. The presence of the conglomerate horizons, both in the footwall and in 

the immediate hanging wall as previously described, does little 

to clarify the problem, as they are not clearly identifiable as 

the locally derived, polymictic conglomerate marker horizon 

commonly present at the base of the section. The highly altered 

and foliated nature of the footwall phyllite also distinguishes 

it from other mafic volcanics low in the section and invites 

comparison to other, older mafic units that display similar styles 

of deformation. Current mapping by Duke and others (chap. 4) 

assigns the footwall phyllites to the Middle(?) Devonian Retreat 

Group. Karl and others (S.M. Karl, oral commun., 2004) map a 

metamorphic unit of mixed lithologies including black phyllite, 

greenschist, and Devonian metalimestone on the north side of 

Greens Creek, stratigraphically beneath the Cannery Formation 

C

F

F

Unconformity

Unconformity

C

Limestone/dolomite

Pyritic-graphitic argillite Siliceous/cherty argillite

Pillow/massive basalt

Stratiform massive sulfide

Greenstone

Serpentinite

Polymictic conglomerate

Gabbroic dikes/sills

EXPLANATION

F Macrofossils

C Conodonts

Greens Creek Mine

Carnian

Norian

Upper

Triassic

Age uncertain

Permian

Figure 10. Composite stratigraphic column of the Upper 

Triassic section at the Greens Creek mine, northern Admiralty 

Island. Interpretation is based on this study.
30 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

and Hyd Group. We note the evidence to suggest a Late Triassic 

age for the footwall; however, in the absence of direct evidence 

of a Late Triassic age we assign the footwall to an uncertain 

Late Triassic, Permian, or older lithologic association (fig. 10). 

At both Mt. Henry Clay and Windy Craggy (fig. 13), felsic 

volcanic rocks are absent, and their position low in the section 

is occupied by mafic volcanic rocks (MacIntyre and Schroeter, 

1985; Forbes and others, 1989; Peter and Scott, 1999).

In the southern portion of the ATMB the rhyolites are 

overlain by dolomitic limestones that in places contain ooids 

(Muffler, 1967) and abundant fossils (Muffler, 1967; Berg, 

1973), indicative of a shallow marine depositional environment (Muffler, 1967). The carbonate portion of the section 

also contains carbonate turbidites and carbonate breccias 

with fining-upwards sequences (for example, Nehenta Bay of 

Gravina Island, Screen Islands) indicative of the destruction 

of a shallow carbonate ramp during the onset of rifting. The 

limestones are present as 15-meter-high cliffs on the Cornwallis Peninsula, but thin substantially northward. They occur 

discontinuously in the Duncan Canal area and across Admiralty Island. In Gambier Bay the limestones are present as a 

locally exposed carbonate/dolomite breccia near the base of 

the section. In the Cliff Creek Cirque and in several locations 

along Gallagher Ridge immediately south of the Greens Creek 

mine, thin carbonate beds lie just below and are intercalated 

with the capping Hyd basalts. Underground at Greens Creek, 

thin discontinuous beds of fossiliferous limestone with Halobia fragments establish a Late Triassic age for carbonates in 

the footwall of the orebody and represent additional evidence 

for a Triassic age of the underlying phyllites. Unfortunately, 

the highly altered nature of the footwall carbonate rocks and 

their commonly brecciated texture yields uncertainty regarding the nature of the phyllite-carbonate contact. The footwall 

carbonate rocks may well be carbonate debris flows and thus 

could be stratigraphically equivalent to the basal conglomerate. North of Admiralty Island, discrete limestone units appear 

to be missing from the section.

The disappearance of the limestones from the section is 

accompanied by a corresponding increase in carbonaceous 

shales, indicative of deeper water settings. As far north as 

Keku Strait, the middle portion of the section is composed 

of very limy, arkosic sediments characteristic of a proximal, 

carbonate-rich source on the flanks of the Alexander terrane. 

From Zarembo Island northward the sediments contain more 

graphitic, pyritic black shale, indicative of an anoxic to euxinic, 

sediment-starved depositional environment distal to the flanks 

of the rift. At Greens Creek the shales (argillites) are intercalated with dolomitic limestone, and at Windy Craggy the black 

shales are markedly calcareous (Peter and Scott, 1999).

Most everywhere throughout southeastern Alaska and 

adjacent British Columbia the Triassic stratigraphy is capped 

by a thick (200–600 m) sequence of basalts. These basalts 

are massive to pillowed and commonly show spectacular 

volcaniclastic textures. In hand specimen and thin section, the 

basalts are vesicular and mostly aphanitic; minor porphyriticaphanitic varieties contain relict phenocrysts of clinopyroxene, 

plagioclase, hornblende, and rare olivine. Compared to the 

generally foliated Paleozoic greenstones of the Alexander 

terrane, these Norian-age basalts are relatively undeformed. In 

the absence of the basal conglomerates, the thick sequence of 

greenstones overlying the sedimentary portion of the section is 

the most distinguishing feature of the Upper Triassic stratigraphy. Although the basalts have a variety of names throughout the ATMB—Chapin Peak Formation of Hyd Group on 

?

Massive/pillow basalt

Qtz-ser-talc schist/carbonate

 phyllite

Massive/fragmental basalt

Limy argillite

Argillaceous limestone

Dioritic sill or dike

Massive barite/sulfide

Fossil age (conodonts)

EXPLANATION

F

Mt. Henry Clay area

F

Upper

Triassic

(Norian)

Devonian

(?)

Figure 11. Composite stratigraphic column of the Upper Triassic 

section in the Mt. Henry Clay area, northern southeastern Alaska 

and northwestern British Columbia. Modified from MacIntyre and 

Schroeter (1985).
Geochemistry of Upper Triassic Basalts and Rhyolites of Southeastern Alaska 31

Gravina Island (Berg, 1973); Hound Island Volcanics in the 

Keku Strait (Muffler, 1967); Hyd Group basalts on Admiralty 

Island (Lathram and others, 1965); Jarvis basalts (informal) 

in the Mt. Henry Clay area (Forbes and others, 1989); Tatshenshini basalts (informal) of northwestern British Columbia 

(MacIntyre and Schroeter, 1985)—they are all related by 

similar age, chemistry, and stratigraphic position.

Geochemistry of Upper Triassic Basalts 

and Rhyolites of Southeastern Alaska

Whole-rock geochemical data for Upper Triassic igneous rocks at mineral occurrences and unmineralized outcrops 

throughout southeastern Alaska were obtained in order to 

evaluate the petrogenetic setting of the ATMB. Major, minor, 

and trace-element abundances were determined by XRF, lithium metaborate fusion ICP–MS, and ICP–AES in the USGS 

laboratories in Denver. Summary data for a number of key 

locations are given in table 1; all the data are presented in 

table 2. General analytical methods and information on accuracy and precision of each method are described in Taggart 

(2002). Specific information on the lithium metaborate 

fusion ICP–MS analytical method used to obtain rare-earth 

and high field-strength elemental data critical to the tectonic 

discriminant analysis presented herein is available in Meier 

and Slowik (2002). Lower limits of detection (LOD) are 

represented in table 2 as less-thans and are 3 sigma values 

that are calculated for each instrument run based on multiple 

analyses of reagent blanks. Multiple analyses of internal 

laboratory standards are used to calibrate the instrument 

response, and then accuracy and precision of the analyses are 

verified to be within published limits by analysis of several 

USGS standard reference materials that are included in each 

run. Due to the nature of the ICP–MS technique, lower limits 

of detection vary between analytical runs. Also, there was 

an instrumentation change during the course of this study, 

with a resulting order-of-magnitude increase in instrument 

sensitivity for analyses performed after 1994. Variation in 

LOD for most of the elements reported in table 2 are due to 

these factors and are a normal feature of ICP–MS analyses 

(P.J. Lamothe, oral commun., 2004). Additional discussion 

of the use of ICP–MS analysis for the determination of trace 

elements in igneous rocks is available in Longerich and others (1990), Jenner and others (1990), and Jenner (1996).

Figure 12. Pillowed basalt flow near the base of the Upper Triassic section on the north shore of Gambier Bay, southern Admiralty Island.
Table 1. Summary whole-rock geochemical data for Upper Triassic basaltic rocks at key locations in southeastern Alaska. Location Annette Island Gravina Island Gravina Island Keku Strait Duncan Canal Gambier Bay Central Admiralty Island Greens Creek south Greens Creek north Mansfield Peninsu

Lithology basalt basalt gabbro basalt basalt basalt basalt basalt basalt basalt 

Number (n) 7 2 2 7 21 6 7 13 4 5 

SiO2 50.1 44.3 44.4 45.8 48.4 45.7 52.1 51.9 46.6 47.3 

Al2O3 17.6 14.3 17.4 14.8 13.6 15.4 15.0 15.8 16.4 14.6 

FeTO3 10.2 10.8 11.1 13.4 13.1 10.4 10.9 10.1 11.4 11.4 

MgO 3.6 4.3 8.7 6.1 6.1 5.1 6.9 6.4 6.6 6.7 

CaO 6.5 12.3 10.1 7.5 9.1 11.8 5.3 4.4 6.6 11.0 Na2O 3.7 3.0 2.4 3.3 3.1 2.9 3.1 4.3 2.8 2.3 

K2O 2.2 1.1 0.3 0.8 0.7 0.6 1.0 1.3 1.9 0.9 

TiO2 0.9 2.0 1.3 2.4 1.9 1.2 1.1 0.8 1.4 1.6 

P2O5 0.3 0.6 0.2 0.4 0.2 0.2 0.2 0.2 0.3 0.2 

MnO 0.2 0.2 0.2 0.2 0.2 0.2 0.1 0.2 0.2 0.2 

CO2 1.7 1.6 0.9 2.7 Total H2O 3.3 4.9 3.1 LOI 4.1 6.5 3.9 4.8 2.7 5.7 3.8 4.1 5.6 3.4 

Sum 100.2 99.4 99.9 101.1 100.4 101.9 99.5 99.4 99.8 99.4 

 La 11.4 17.4 5.4 13.4 9.3 9.4 10.6 11.9 8.6 7.1 

 Ce 25.6 43.0 15.0 31.0 22.2 21.5 22.4 22.8 22.0 18.4 

 Pr 3.4 6.4 2.4 4.5 3.2 3.1 3.0 2.7 3.4 2.7 

 Nd 15.1 31.0 11.5 20.0 15.3 14.2 13.0 11.4 16.0 13.0 

 Sm 3.5 7.8 3.4 5.2 4.2 3.7 3.3 2.6 4.4 3.6 

 Eu 1.0 2.6 1.3 1.8 1.4 1.1 1.0 0.8 1.5 1.3 

 Gd 3.5 8.9 3.9 6.5 5.0 4.2 3.8 3.1 4.6 4.4 

 Tb 0.6 1.4 0.6 1.1 0.9 0.7 0.7 0.5 0.8 0.7 

 Dy 3.8 8.3 3.8 6.5 5.0 4.1 3.9 3.4 4.5 4.4 

 Ho 0.8 1.8 0.8 1.2 1.0 0.9 0.8 0.8 0.9 0.9 

 Er 2.4 4.9 2.1 3.7 2.8 2.5 2.4 2.3 2.6 2.6 

 Tm 0.4 0.7 0.3 0.6 0.4 0.4 0.4 0.3 0.4 0.4 

 Yb 2.4 4.5 1.8 3.6 2.8 2.4 2.4 2.5 2.4 2.3 

 Hf 2.3 4.3 1.9 4.7 3.6 2.3 3.2 2.3 2.8 3.2 

 Ta 0.4 0.6 0.4 0.7 0.8 0.5 1.3 0.4 0.6 0.6 Rb 43.6 19.5 4.3 14.5 14.5 16.0 20.5 19.6 53.1 14.4 

 Y 21.0 42.0 17.5 34.0 28.5 22.5 23.4 19.4 22.5 22.6 

 Zr 54.0 205.0 90.0 140.3 124.1 78.8 134.0 85.3 109.8 105.0 

 Nb 3.4 5.3 2.2 11.8 7.2 4.8 7.1 5.7 4.8 5.6 

 Ba 562.9 270.0 140.0 1017.1 956.4 791.8 378.6 633.8 467.8 174.0 

 Th 2.7 3.2 1.1 1.1 0.9 1.8 2.6 1.1 0.8 

 Sc 28.3 27.0 27.0 37.6 41.5 29.2 31.0 28.4 30.5 33.8 

 V 268.6 219.5 255.0 358.6 434.5 333.3 295.7 222.3 307.5 382.0 

 Cr 53.7 120.0 97.0 121.3 185.6 578.0 200.7 314.6 875.0 770.0 

 Ni 19.4 51.0 142.5 43.3 71.9 46.5 47.3 44.2 67.3 70.6 

 Co 29.6 52.0 68.0 44.4 50.1 45.0 39.0 38.7 44.5 47.6 

 Cu 123.4 48.5 62.5 59.7 167.3 219.5 45.8 83.5 80.3 107.4 

 Zn 174.6 135.0 90.0 115.6 112.0 84.3 130.9 111.1 92.0 92.2 

 Ga 20.7 24.0 21.0 17.0 

 Sr 727.1 425.0 365.0 468.6 307.2 773.3 152.9 146.6 330.0 362.0  Cs 0.5 0.4 0.3 0.9 0.5 1.4 1.2 0.8 2.0 0.4

 Pb 12.3 3.2 27.0 3.8 6.5 5.3 8.0 4.7 5.2 

 Sn 2.5 0.9 2.0 2.4 0.9 3.5 3.7 0.7 1.4

 W 0.1 0.4 0.3 2.3 1.4 0.9 0.8 0.3 0.4

 U 0.3 0.7 0.1 0.6 0.4 0.2 0.7 0.7 0.4 0.4
Geochemistry of Upper Triassic Basalts and Rhyolites of Southeastern Alaska 33

petrogenetic modeling but rather to make a first-order assessment of tectonic settings suggested by the immobile-element 

geochemistry of igneous rocks of the ATMB, and to look for 

consistency with the volcanosedimentary, metallogenic, and 

radiogenic isotopic characteristics that we describe here and in 

later chapters of this volume.

In acknowledgment of the difficulty of obtaining reliable 

data at the low abundance levels of the immobile elements 

commonly used in discriminant diagrams, we have made every 

effort to be conservative in the representation of our geochemical data. After removing all obviously veined, mineralized, 

altered, and nonigneous rocks, the data set was stripped of all 

potential sediments and cumulate rocks using the geochemical 

criteria of Pearce (1996). The primary geochemical compositions of the volcanic host rocks have been modified by sea-floor 

alteration as well as by middle-greenschist-facies regional 

metamorphism during collision and underthrusting of the 

Alexander terrane with the North American continental margin. 

The resulting moderate to extreme alteration (loss on ignitionLOI, commonly 4–10 weight percent and as high as 30 weight 

percent) precludes the use of major element data for identification and tectonic discrimination of the volcanic rocks. Therefore, in order to maximize the utility of the immobile-element 

chemistry, all extremely altered samples with LOI greater than 

10 weight percent also were removed from the database. An 

additional conservative control was placed on our use of the 

data by selecting a plotting routine that assigns a null value to 

all data at the LOD; thus, only data at abundances above the 

LOD are considered during the discriminant analysis. As a final 

check on the utility of our data, we have plotted the analyses of 

the USGS basalt standards BIR–1, BCR–2, and BHVO–2 and 

of two replicate standards that were inserted as blind standards 

throughout the duration of the study (fig. 14) onto the suite of 

discriminant diagrams used in this analysis. We note the acceptable size of the error elipses relative to the various discriminant 

fields (Dudas, 1992) and suggest that these plots demonstrate 

the sufficiency of our data for discriminant analysis.

For plotting purposes, the data in table 2 have been organized by rock type, by known or inferred age (for example, 

Triassic vs. Triassic(?)), and by principal location. Figure 15 

shows the known Upper Triassic igneous whole-rock data 

plotted on the immobile-element classification diagram of 

Winchester and Floyd (1977). The most important feature of 

the data is that a bimodal suite of rocks is clearly distinguishable. Further, basalt-rhyolite suites are evident on Annette 

Island and on the Cornwallis Peninsula, the latter constituting 

the western shore of Keku Strait. North of Keku Strait, rhyolites are absent and the volcanic rocks are entirely basaltic. 

Such bimodal suites of volcanic rocks are a common feature of 

rift-related tectonic environments worldwide (Wilson, 1989) 

and are commonly associated with VMS mineral districts 

(Lentz, 1998; Barrett and MacLean, 1999). These compositions provide first-order evidence of the rift-related origin of 

the Upper Triassic volcanic rocks of the ATMB. The basaltic 

rocks (fig. 15) mainly plot in the subalkaline basalt and basaltic andesite fields, with a few examples of alkaline basalts.

F

F

F

F

F

?

Massive/pillow basalt

Massive/fragmental basalt

Limy argillite

Argillaceous limestone

Dioritic sill or dike

Massive sulfide/stockwork

Fossil age (conodonts)

EXPLANATION

F

Windy Craggy area

Upper

Triassic

(Norian)

Devonian

(?)

Figure 13. Composite stratigraphic column of the Upper 

Triassic section at the Windy Craggy deposit, northwestern 

British Columbia. Modified from MacIntyre and Schroeter (1985).

In the presentation that follows we attempt to shed 

additional information on the nature of the tectonic setting 

of the ATMB through the use of immobile-element-based 

tectonic discriminant diagrams. In general, we have followed 

the recommendations and cautions regarding the use of such 

diagrams as explained by Pearce (1996). The literature is full 

of examples of the use and misuse of discriminant diagrams 

(for example, Wood, 1980; Arculus, 1987; Dudas, 1992; Rollison, 1993) in developing petrogenetic models for the origin of 

suites of igneous rocks. Our purpose is not to attempt rigorous 
34 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

AI=WP Alkali basalt

AII=WP Alkali basalt and WP tholeiite

B=E-MORB

C=WP tholeiite and VAB

D=N-MORB and VAB

A=Island arc tholeiites (IAT)

C=Calc-alkaline basalts (CAB)

D=Within-plate basalts (WPB)

B=Midocean ridge basalts (MORB),

 IAT, and CAB 

A=N-MORB

B=E-MORB and WP tholeiite

C=alkaline WPB

D=VAB 

blind standard BCR-2

Th Nb Ce Zr Ti Y

rock/MORB

0.1

1

10

100

BCR-2 values

after Pearce (1996)

blind standard BCR-2

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

REE Sample/REE Chondrite

1

10

100

BCR-2 published values 

BCR-1 published values

+ BHVO-1 published values

X BIR-1 published values

blind standard 93KK-37 altered Keku rhyolite

blind standard 93KK-66 Hound Island basalt

blind standard BCR-2

BHVO-2 published values

blind standard BHVO-2

blind standard BIR-1

after Winchester and Floyd (1977)

Comendite/pantellerite

Phonolite

Trachyte

Trachyandesite

Basanite

nephelinite

Alkaline basalt

Rhyolite

Rhyodacite/dacite

Andesite

Andesite/basalt

Subalkaline basalt

Nb/Y

0.01 0.1 1 01

Zr/TiO2

0.001

0.01

0.1

1

+

X

Y*3

Ti/100

Zr

+

X

after Pearce and Cann (1973)

A

B

C

D

Y

Nb*2

Zr/4

+

X

AI

AlI

B

C

D

after Meschede (1986)

Nb/16

(Zr/39)/3

Th

+

D

A

B

C

CAB

IAT

after Wood (1980)

EXPLANATION
Geochemistry of Upper Triassic Basalts and Rhyolites of Southeastern Alaska 35

The felsic volcanic rocks on Annette and Gravina Islands 

are typical calc-alkaline rhyolites with bulk compositions 

similar to those of island arc rocks. However, data for the rhyolitic rocks at Keku Strait (Cornwallis Peninsula–Keku Strait 

area, fig. 15) consistently fall into the comendite/pantellerite 

to trachyte fields of Winchester and Floyd (1977). Whereas 

the peralkaline composition of the Keku Volcanics rhyolites 

is difficult to confirm due to a high degree of brecciation and 

alteration, at least some of the samples approach the excess of 

Na2O + K2O over Al2O3 that characterizes such rocks (Cole, 

1978). This is an important observation due to the relatively 

distinctive tectonic setting of such rocks, which commonly 

occur in rift-related environments and are often the indicators 

of incipient rifting (for example, Mayor Island in the Bay of 

Plenty, New Zealand, and the D’Entrecasteaux Islands west of 

the Woodlark Basin, Papua, New Guinea, Smith and others, 

1977; Smith and Johnson, 1981; also Civetta and others, 1984; 

Mahood and Baker, 1986; Pin and Paquette, 1997). The occurrence of felsic volcanism prior to basaltic volcanism throughout 

the southern portion of the ATMB and the peralkaline composition of the rhyolites of Keku Strait are typical features of intraand back-arc rifts. The transition from calc-alkaline rhyolites to 

Figure 14 (facing page). Accuracy and precision of blind 

standards plotted on the diagrams used in the text as compared to 

accepted values. Multiple analyses of the USGS standards BIR-1, 

BHVO-2, and BCR-2 inserted as blinds into analytical batches 

throughout the duration of the study are shown on the immobileelement-based rock type diagram of Winchester and Floyd (1977) 

and on the tectonic discriminant diagrams of Pearce and Cann 

(1973), Meschede (1986), and Wood (1980). Multiple analyses of 

BCR-2 are also shown on the MORB-normalized, abbreviated 

trace-element plot of Pearce (1996) and on a standard chondritenormalized REE diagram (using the chondrite values of Boynton, 

1984). Note the acceptably small size of the data clusters for a 

given standard relative to the discriminant fields of the diagrams. 

Acceptable accuracy and precision are also demonstrated by 

multiple analyses of BCR-2 on the trace and REE plots.

Nb/Y

0.01 0.1 10

Zr/TiO2 0.001

0.01

0.1

1

X X

X

X

X

+

+

+

+

+

+

+

Comendite/pantellerite

Phonolite

Trachyte

Trachyandesite

Basanite

nephelinite

Alkaline basalt

Rhyolite

Rhyodacite/dacite

Andesite

Andesite/basalt

Subalkaline basalt

after Winchester and Floyd (1977)

1

Greens Creek area south-basalt

Greens Creek area north-basalt

Annette Island-rhyolite

Annette Island-basalt

Gravina Island-rhyolite

Gravina Island-basalt

Keku Strait area-rhyolite

Keku Strait area-basalt

Duncan Canal area-basalt

X Gambier Bay-basalt

+ Central Admiralty Island-basalt

Mansfield Peninsula-basalt

Mt. Henry Clay area-basalt

Windy Craggy-basalt

EXPLANATION

Figure 15. Volcanic rock classification diagram of Winchester and Floyd (1977) based on immobile-element ratios, 

showing the composition of southeastern Alaska Upper Triassic volcanic rocks analyzed for this study. Note the 

distinctly bimodal basalt-rhyolite distribution of data, and the comendite-pantellerite to trachytic compositions of the 

Keku Volcanics rhyolites (Cornwallis Peninsula suite).
36 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

peralkaline rhyolites northward along the ATMB is also consistent with a shift from a proximal-arc to an arc-slope or basinmargin setting. The peralkaline Keku rhyolites are indicative 

of small degrees of partial melting of a deep, garnet-bearing 

source during the earliest stages of rifting, followed by extreme 

fractionation and eruption from a shallow magma chamber (for 

example, Smith and Johnson, 1981; Mahood and Baker, 1986).

Application of discriminant analysis to the basaltic rocks 

of the ATMB provides additional information regarding their 

petrotectonic origins. We use a progression of three ternary 

plots based upon the immobile elements Ti, Zr, Th, Nb, and Y 

(fig. 16 a–f), and follow with the MORB-normalized traceelement plot recommended by Pearce (1996) and chondritenormalized REE plots (fig. 17 a–v). The diagram of Pearce 

and Cann (1973), which is shown in figures 16a and d, is most 

effective for separating within-plate basalts (WPB) from those 

showing either destructive plate margin (volcanic arc basalt—

VAB, including both calc-alkaline and tholeiitic trends; CAB 

and IAT, respectively) or MORB compositions. This discriminant is based largely on the effect of melting and residual 

enrichment of yttrium in a mantle garnet lherzolite source. 

Thus, WPB compositions on this diagram are suggestive of 

small degrees of melting from a deep source. In contrast, compositions in the MORB–VAB fields are largely controlled by 

partial melting at shallower levels of a spinel lherzolite source. 

Transitional processes such as attenuation of continental lithosphere cause trends from the WPB to the MORB field (due 

to progressively shallower and increased degrees of partial 

melting), and assimilation of upper crust results in trends from 

these compositions toward the CAB field (Pearce, 1996). The 

Meschede plot (1986), which is shown in figures 16b and e, 

is similar to the first plot but has the advantage of providing 

a discriminant between normal and enriched (or transitional) 

MORB compositions.

The discriminant diagram of Wood (1980), which is 

shown in figures 16c and f, is most efficient at separating VAB 

from MORB–WPB compositions and at separating calcalkaline and tholeiitic VAB trends. As with the previous two 

diagrams, complex tectonic settings result in transitional data 

arrays between fields. Lavas erupted on attenuated continental 

lithosphere are perhaps the most problematic as they occupy 

overlapping fields in the center of the diagram. Syn- and 

postcollision zone magmas define a field that stretches from the 

center of the diagram toward the CAB end of the VAB field, 

reflecting the assimilation of upper crust by enriched MORB or 

intraplate magmas. Petrogenetic vectors toward or away from 

the zirconium apex from the within plate fields of the diagram 

are controlled by variations in the degree of partial melting and 

enrichment or depletion of the mantle source. Mantle enrichment and(or) low degrees of partial melting shift basalt compositions toward lower zirconium abundances. VAB compositions 

are controlled by the characteristic depletion in niobium with 

increasing input of a subduction component reflected by vectors moving toward the thorium apex (Pearce, 1996).

Data for volcanic rocks from the ATMB fall most readily 

into two basic groups based on how they plot on this series 

of discriminants. Lavas from locations predominantly in the 

central portion of the ATMB (Keku Strait to the Mansfield 

Peninsula) show a transitional nature with compositions 

characteristic of WPB that exhibit a spread between variably 

enriched or depleted MORB and CAB. The second group is 

composed of rocks from the southern and northern ends of 

the ATMB and the area immediately surrounding the Greens 

Creek mine (Annette Island, Greens Creek area south, and 

Mt. Henry Clay area). This group plots in arrays suggestive of 

compositions transitional between CAB and variably enriched 

MORB. Several areas along the ATMB (Gravina Island, Gambier Bay, Greens Creek area north, and the Mansfield Peninsula) exhibit examples of both groups. Notable exceptions 

are the rocks from Keku Strait which exhibit a shift toward 

alkaline intraplate compositions on the Wood (1980) diagram, 

and the consistent display of NMORB to EMORB or alkaline 

intraplate compositions of the Windy Craggy rocks.

Trace and REE plots of the basaltic rocks of the ATMB 

(fig. 17 a–v) generally support the division of rocks into two 

groups. The first group of rocks that plot in the transitional 

WPB/EMORB to CAB array exhibit the gently sloping profile 

from enriched thorium, niobium, and zirconium, to depleted 

yttrium that is characteristic of intraplate rocks and of complex 

tectonic settings. Similarly, the REE patterns show uniformly 

smooth slopes without negative europium anomalies. The 

second group of rocks that exhibit an array transitional between 

CAB and NMORB on the discriminant plots are all characterized by depletions in niobium, zirconium, titanium, and yttrium 

that are the hallmark of destructive margin basalts. The REE 

profiles of these rocks generally have steeper LREE profiles 

and a slight negative europium anomaly, which probably 

indicates separation of plagioclase and input of a subduction 

component to the melt.

We note that there is some consistency in the tectonic 

environments suggested by the discriminant diagrams and trace 

and REE plots. On both the Pearce and Cann (1973) and the 

Wood (1980) plots, the first group of rocks occupy fields that 

are characteristic of attenuated continental lithosphere, whereas 

the second group occupy fields defined by rocks produced in 

syn- and postcollisional environments (Pearce, 1996). In both 

cases, the data form arrays that are best described as transitional and are indicative of tectonic settings that are more 

complex than the midocean ridge, intraplate, or destructive 

margin settings that compose the fields of most of discriminant 

diagrams. We know that the pre-Jurassic history of the Alexander terrane involved the formation and transport of a continentsized fragment of island-arc crust to a position just outboard of 

a subduction zone prior to the Late Triassic. Whether collision 

and partial subduction (or obduction) of the Alexander terrane 

occurred is uncertain; however, by Late Triassic the production 

of ATMB volcanic rocks indicate that a period of crustal relaxation outboard of the destructive margin had occurred, resulting 

in lithospheric extension and incipient rifting in the Alexander terrane. We suggest that the Alexander terrane must have 

been thick enough that initial rifting resulted in deep melting 

of a relatively enriched mantle and that the first melt products 
C

X

X

X

X

X

X

+

+

+

+

+

+

X

X

X X

X

X

+

+

+

++

+

+

C

X

+

+

+

+

+

+

+

X

+

(Zr/39)/3

Th 

CAB

IAT

A

D B

C

f.

(Zr/39)/3

Th 

Nb*2

Zr/4 Y

Nb*2

Zr/4 Y

Tl/100

Zr Y*3

Tl/100

Zr Y*3

D

A

C

B

after Pearce and Cann (1973)

D

C

B

A

after Pearce and Cann (1973)

AI

AII

B

D

after Meschede (1986)

AI

AII

B

D

after Meschede (1986)

IAT

A

D B

C

CAB

AI=WP alkali basaltAII=WP alkali basalt and WP tholeiiteB=E-MORBC=WP tholeiite and VABD=N-MORB and VAB

A=Island arc tholeiites (IAT)B=Midocean ridge basalts (MORB), IAT, and CABC= Calc-alkaline basalts (CAB)D=Within-plate basalts (WPB)

Keku Strait area-rhyoliteKeku Strait area-basaltDuncan Canal area-basaltGambier Bay-basaltCentral Admiralty IslandGreens Creek area north-basaltMansfield Peninsula-basalt

Annette Island-rhyoliteAnnette Island-basaltGravina Island-rhyoliteGravina Island-basaltGreens Creek area south-basaltMt. Henry Clay area-basaltWindy Craggy-basalt

d. e.

a. b. c.

EXPLANATION

EXPLANATION

Figure 16 a–f. Discrimination diagrams showing compositions of southeastern Alaska Upper Triassic basalts and rhyolites (on the Wood, 1980, difor this study. Diagrams a–c show data from locations within the central ATMB and are characterized by transitional chemistry that reflects a strothan samples from the north and south end of the ATMB and from the ridge south of the Greens Creek mine as shown in diagrams d–f. The second indicate chemistries transitional between that of WPB and/or EMORB and CAB.
38 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

thus have chemistry similar to WPB and EMORB depending 

upon how much assimilation of the overlying island-arc crust 

occurred. In places where attenuation or rifting of the crust 

was more pronounced, shallower melting of variably enriched 

mantle at variable degrees of partial melting produced the data 

array between arclike CAB and NMORB of the second group. 

Thus the transitional chemistry of the ATMB volcanic rocks 

are a product of a combination of variable depths and degrees 

of partial melting beneath the rifting Alexander landmass and 

of variable amounts of crustal assimilation (to achieve the CAB 

signature).

As with previous radiogenic isotopic studies (Sampson 

and others, 1989, 1990, 1991), Sr-Nd-Pb isotope analyses of 

pre-Triassic rocks of the Alexander terrane (Premo and Taylor, 

unpub. data, 2004) and of footwall host rocks at Greens Creek 

(chap. 11) suggest derivation from a depleted mantle source 

and are consistent with isotopic signatures of oceanic island 

arcs. Initial niodymium compositions at 215 Ma (average age 

of host rocks) of metabasalts and gabbros vary between eNd = 

+4 to +9, and initial 206Pb/204Pb and 87Sr/86Sr = 18.45 to 18.92 

and 0.7037 to 0.7074, respectively, and are enriched compared 

to MORB or oceanic island basalt (OIB) sources. Isotopic data 

for Permian and Triassic argillites are similarly enriched and 

indicate derivation from an island-arc terrane with input of 

older, more radiogenic source material. Interestingly, radiogenic isotopic data on footwall phyllites at Greens Creek are 

bimodal (eNd ~ +8 and +2), which we interpret to indicate 

the intrusion of Late Triassic gabbroic sills into the footwall 

basaltic pile. Hyd Group basalts exhibit a relatively primitive 

isotopic signature (eNd = +8 to +9) consistent with derivation 

from a mantle source (chap. 12).

Results of the tectonic discriminant analysis, in combination with the fairly primitive and transitional trace, REE, and 

radiogenic isotopic geochemical signatures, are consistent with 

rift-related basalt produced in an incipient intra-arc or back-arc 

setting. We note that basalts at several locations, especially in 

the southern end of the ATMB, the Greens Creek area, and at 

Mt. Henry Clay, have compositions that are similar to those 

of relatively unfractionated calc-alkaline basalts formed in an 

oceanic volcanic arc, whereas those in others, most notably in 

the central portion of the ATMB, display transitional chemistry 

consistent with derivation from EMORB or OIB sources and 

variable assimilation of preexisting arc crust. Similar to the 

trends for the mafic volcanic rocks, the felsic volcanic rocks 

show a transition from more arclike compositions in the southern end of the ATMB to intraplate compositions in the center 

of the ATMB. The most MORB-like rock compositions in the 

ATMB are displayed by Tats Group basalts at Windy Craggy. 

Consistent with the extensive geochemical data of Peter and 

Scott (1999) we note elevated LREE compositions and lower 

eNd compositions for the Tats Group as compared to Triassic 

basalts to the south. Peter and Scott (1999) interpret the tectonic setting at Windy Craggy at the time of ore formation as a 

mature back-arc basin.

The Geochemistry and Significance 

of Late Triassic Hypabyssal MaficUltramafic Intrusive Rocks

 An important and largely unrecognized feature of many 

of the mineral occurrences that has important genetic implications is their spatial and temporal relationship to a mafic-ultramafic suite of hypabyssal (probably rift-related) intrusions. 

Throughout the ATMB there are numerous mapped outcrops 

of gabbros, microgabbros, and less commonly, ultramafic 

intrusive rocks of either Triassic or uncertain age. Notable 

examples are the Duke Island ultramafic complex lying 

immediately south of Annette Island, and the microgabbros on 

the southwestern shore of Bostwick Inlet on Gravina Island. 

Microgabbros on Hare Island, just west of Hound Island in 

Keku Strait, are mapped as Cenozoic igneous rocks; however, we note the similar geochemical compositions of these 

rocks to those of the Upper Triassic basalts of Hound Island 

Volcanics. More strikingly perhaps is the growing realization 

that a significant portion of the capping Triassic basaltic unit 

throughout the ATMB is composed of gabbroic sills and that 

immediately underlying serpentinite bodies are probably the 

residual cumulate sources of these voluminous flows. Both 

serpentinite and gabbro bodies are commonly intersected by 

underground mine workings and are seen to crop out at Greens 

Creek (chaps. 6, 7). Similarly, the stratigraphic sequence at 

Windy Craggy is composed of interbedded gabbro sills, sediments, and basalts (MacIntyre and Schroeter, 1985).

Even more compelling is the observation that many of 

the mineral occurrences are within, or are in close proximity 

to, barite-sulfide-mineralized mafic sills and dikes that have 

strikingly similar chemistry to the overlying basalts. Figure 

18A is a photograph of a heavily carbonate altered gabbroic sill hosted in late Upper Triassic sedimentary rocks at 

a mineral occurrence (Berg #17, Berg, 1972) on the Sylburn 

Peninsula of Annette Island. The altered sill sits immediately 

beneath a large, discontinuous pod of barite accompanied 

by minor sphalerite, and galena. Similarly, the Ladder vein 

occurrence (Muffler, 1967) in the Keku Strait and at least two 

other similar occurrences represent instances of mineralized 

basaltic intrusions that are spatially associated with Late Triassic mineral occurrences. The Ladder vein (fig. 18B) consists 

of a basaltic dike cutting Permian and Triassic(?) conglomerates and sedimentary rocks that have distinctive, associated, 

2.5-cm-thick, massive sphalerite veins crosscutting the dike 

and occurring along its margins. A similar sill several hundred 

meters to the south exhibits peperitic margins with the host 

(upper Upper Triassic?) sedimentary strata, indicating that the 

sediments were unlithified and water saturated at the time of 

intrusion (fig. 18C).

Some of the best examples of both mineralized basaltic 

dikes and mineralized and altered ultramafic intrusions are in 

Gambier Bay (fig. 1, inset d). In the southwest arm of the bay 

at Cave Mountain Point, several 1–2-meter-wide basaltic dikes 

(fig. 18D) intrude Devonian limestone and Upper Triassic 
Late Triassic Mineral Occurrences in Southeastern Alaska 39

Figure 17 a–v (following pages). MORB-normalized abbreviated 

immobile-trace-element (after Pearce, 1996) and REE plots of data 

for samples from locations throughout the ATMB corresponding 

to the samples and locations shown on the discriminant plots. 

Chondrite values from Boynton (1984). Note that arc-type traceelement patterns and steeper LREE patterns with slight to 

moderate negative europium anomalies characterize the samples 

from the northern and southern ATMB and the ridge south of 

the Greens Creek mine, consistent with data shown on the 

discriminant diagrams. Trace-element patterns consistent with 

transitional mixtures of intraplate rocks and CAB, as are often seen 

in areas of attenuated lithosphere and in syn- and postcollision 

settings, are exhibited by samples from locations in the central 

ATMB. Corresponding REE patterns are generally flatter and do not 

exhibit europium anomalies.

sedimentary rocks. Veins up to 15 centimeters wide consisting of barite, quartz, iron carbonate, chalcopyrite, sphalerite, 

and galena are present along the dike margins, locally forming replacement bodies in the limestone. Outcrops of altered 

serpentinite sills are a striking feature of the Upper Triassic section on the north shore of Gambier Bay and occur as 

distinctive, orange-weathered outcrops consisting of green and 

white quartz, magnesite, iron carbonate, sericite, and bright 

green fuchsite (fig. 18E). Often misidentified as exhalite beds 

or altered dolomite bodies, the presence of relict chromian 

spinel and olivine in the altered rocks, the compositionally 

distinct mafic-ultramafic element suite, and the preservation 

of serpentinite enclaves and breccia clasts within the altered 

bodies identify them as heavily carbon dioxide-metasomatized 

serpentinites. Although attempts to directly date relict serpentinite enclaves (fig. 18F) within these altered ultramafic 

bodies were unsuccessful, they are thought to be part of the 

mafic-ultramafic hypabyssal intrusive event related to Triassic rifting (chap. 11). An 40Ar/39Ar isotopic age for fuchsite 

separated from a quartz-iron carbonate-fuchsite altered body 

in Gambier Bay yielded an apparent plateau age of 210.3 ± 

0.3 Ma (chap. 11), thus demonstrating that emplacement had 

occurred by the Late Triassic, and suggesting that alteration 

and mineralization of the intrusives were nearly synchronous. 

This relationship and the presence of skarn minerals in the 

aureoles of serpentinites in the Greens Creek area (N.A. Duke, 

oral commun., 1997), suggest that the precursor ultramafic 

rocks were emplaced hot in the shallow subsurface during 

Late Triassic time. Associated mineralization includes barite, 

pyrite, chalcopyrite, sphalerite, galena, tetrahedrite, siegenite, 

nickel bloom, and anomalous gold values, further suggesting 

that the ultramafic precursor intrusives drove hydrothermal 

circulation and in the process were themselves altered. Similar 

examples of mineralized and altered mafic-ultramafic hypabyssal intrusions occur on Zarembo and Woewodski Islands, 

and in Duncan Canal (Taylor, 2003), and at numerous locations across Admiralty Island, notably at the North Gambier 

occurrence, Yellow Bear Mountain, Etta prospect, Mariposite 

Ridge just north of Greens Creek (fig. 18G), and at several 

localities on the Mansfield Peninsula.

Late Triassic Mineral Occurrences in 

Southeastern Alaska

The northward change in depositional environment 

and volcanic host-rock chemistry in Upper Triassic strata is 

accompanied by a northward transition from epithermal-type 

base-metal occurrences having a relatively simple mineralogy, 

to sulfosalt-enriched polymetallic VMS occurrences, and 

finally to larger copper-cobalt-bearing deposits with more 

clearly stratiform morphologies. In the following sections we 

describe some of the more important mineral occurrences that 

demonstrate the evolving nature of the Late Triassic metallogeny from south to north in the ATMB.

Mineral Occurrences in the Southern ATMB

Occurrences on Annette and Gravina Islands are typified 

by structurally controlled, discontinuous veins, breccias, and 

pod-shaped bodies, and less commonly, by small stratiform 

lenses. The occurrences are Pb-Zn-Ag-Ba-(Cu)-enriched with 

a relatively simple sulfide mineralogy, at or near the contact 

between felsic volcanic rocks and overlying fossiliferous and 

locally oolitic limestone. In places, the limestone is dolomitized and brecciated. A pervasive orange to black, iron- and 

manganese-rich hydrothermal alteration locally colors the 

otherwise medium gray dolomite (for example, Nehenta Bay 

on Gravina Island; fig. 19A). Where this alteration is most 

intense, the matrix of the dolomite breccia consists of quartz 

and iron-rich dolomite cement with sparsely disseminated 

sulfides. Solution cavities are present and commonly have 

inward-projecting euhedral crystals of quartz, late dolomite, 

and sulfides. Texturally, the hydrothermal features exhibited 

in such outcrops of shallow platform carbonates are similar to 

those in Mississippi Valley-type deposits of the U.S. midcontinent region (Leach and Sangster, 1993).

Examples of the pod-shaped and veinlike occurrences 

are numerous, especially on Annette Island, and include the 

previously described barite-chalcopyrite-sphalerite-galena pods 

(fig. 18A) associated with the altered gabbroic dike at Berg #17 

(Berg, 1972). Another weakly mineralized, pod-shaped barite 

occurrence at Japan Bay on the Sylburn Peninsula (Berg #18) 

has a similar mineralogy, and botryoidal textures suggestive of 

growth in open space or in unlithified sediments during early 

diagenesis (fig. 19C). Interestingly, in 1976, 181.4 meters of 

diamond core was drilled in five holes at three different locations on the Sylburn Peninsula to test for the presence of minable quantities of barite and Pb-Zn-Ag. Of these, four holes at 

two locations intersected low-grade stratabound barite-sulfide 

intervals dipping west under the peninsula at 25 degrees. At 
40 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Annette Island basalts 93AN-15B 

93AN-35 

93AN-29 

93AN-13 

96AN-05 

93AN-22 

93AN-37 

rock/MORB 0. 1

1

10

100

Gravina Island basalts and gabbros

Th Nb Ce Zr Ti Y

rock/MORB 0.1

1

10

100

Keku Strait area basalts 93KK-24 

92KK-21 

93KK-23 

92KK-19 

93KK-67 

93KK-66 

98KK-31 

Th Nb Ce Zr Ti Y

rock/MORB 0.1

1

10

100

Duncan Canal area-basalts

Th Nb Ce Zr Ti Y

rock/MORB 0.1

1

10

100

Gambier Bay basalts 92GB-42 

96AD-58 

92GB-22 

97ADM-80 

92GB-37 

92GB-47 

Th Nb Ce Zr Ti Y

rock/MORB 0.1

1

10

100

central Admiralty Island-basalts 97ADM-95 

97JCW-01 

97ADM-54 

97JCW-04 

97ADM-88 

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

REE Sample/REE Chondrite 1

10

100

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

REE Sample/REE Chondrite

1

10

100

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

REE Sample/REE Chondrite 1

10

100

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

REE Sample/REE Chondrite 1

10

100

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

REE Sample/REE Chondrite 1

10

100

Th Nb Ce Zr Ti Y

Th Nb Ce Zr Ti Y

rock/MORB 0.1

1

10

100

96GR-20 basalt

96GR-18 basalt

96GR-22 gabbro 

96GR-21 gabbro 

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

REE Sample/REE Chondrite 1

10

100

a. b.

c. d.

e. f.

g. h.

i. j.

k. l.

93DC-23A 

93DC-22 

98SK091A 

93DC-21 

93DC-30 

98SK082A 

93DC-24B 

98DC-067 

98DC-077 

98DC-066 

98SK139A 

93DC-44 

98SK084A 

98DC-062 

98DC-063 

98DC-078 

98DC-055 

98SK076A 
Late Triassic Mineral Occurrences in Southeastern Alaska 41

Greens Creek area south-basalts

Th Nb Ce Zr Ti Y

rock/MORB

0. 1

1

10

100

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

REE Sample/REE Chondrite

1

10

100

Greens Creek area north-basalts 96AD-60 

96AD-61 

97ADM-03 

96AD-59 

Th Nb Ce Zr Ti Y

rock/MORB

0.1

1

10

100

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

REE Sample/REE Chondrite

1

10

100

Mansfield Peninsula-basalts 96ADM-08 

97ADM-28 

97ADM-72 

96ADM-01 

96ADM-05 

Th Nb Ce Zr Ti Y

rock/MORB

0.1

1

10

100

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

REE Sample/REE Chondrite

1

10

100

Mt. Henry Clay area-basalts

94LH-06 

94LH-07 

MZ-1-05 

94LJ-12 

94MZ-09 

P94-1-19 

 P94-1-22 

94LH-09 

P94-1-24 

Th Nb Ce Zr Ti Y

rock/MORB

0.1

1

10

100

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

REE Sample/REE Chondrite

1

10

100

Windy Craggy-basalts 94WC-RG03 

94WC-WP06 

94WC-WP10 

Th Nb Ce Zr Ti Y

rock/MORB

0.1

1

10

100

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

REE Sample/REE Chondrite

1

10

100

m. n.

o. p.

q. r.

s. t.

u. v.

96ADM-23 

NAD T4-5-8 

96ADM-24 

97ADM-43A 

NAD T4-5-9 

NAD T4-5-10 

97LG-06 

97LG-08 

97LG-02 

97LG-10 

97LG-07 
42 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

the first location (Berg #18, previously described), geochemical analyses indicate the presence of a 14.6- to 15.5-meterthick interval grading 25.8- to 38.3-percent barite with minor 

lead, zinc, and silver. At the second location 120 meters to the 

south, drilling revealed a structurally complicated, lower grade 

mineralized section that may also dip 25 degrees to the west. 

Geochemical analyses indicate a 21.3-meter-thick interval 

having an average grade of 16 percent barite and minor lead, 

zinc, and silver. Within this interval is a 5.8-meter-thick section 

grading 45.2 percent barite, 3.4 percent lead, and 34 parts per 

million silver (D.C. McCrillis, written commun., 1976; Berg 

and Clautice, written commun., 1982). Estimation of size and 

grade based on the drilling results and the persistence of soil 

geochemical anomalies indicate a 1–2 million metric tonne 

deposit averaging 32 percent barite, 2–3 percent combined lead 

and zinc, and 28 grams per metric tonne silver could be present 

(A.L. Eng, written commun., 1983; Taylor, 1993). A second, 

very small stratabound occurrence was noted during this study 

at the mouth of Nehenta Bay, Gravina Island, enclosed within 

the gritty limestone sequence overlying the basal conglomerate. Several stacked horizons of bladed barite up to 7 cm thick 

and 10 m long are present and provide additional evidence for 

stratabound, early diagenetic if not exhalative mineralization 

(fig. 19C).

Clearly epigenetic, veinlike mineral occurrences are also 

common on Annette and Gravina Islands and are typified by 

occurrences in the Crab Bay area on the east side of Annette 

Island. As on the Sylburn Peninsula, mineralization occurs 

predominantly at and near the contact of rhyolitic volcaniclastic 

rocks and locally dolomitized limestone. Discontinuous and 

generally small ribbon and ladder quartz veins occurring as en 

echelon sets tens to 100 meters long are best developed within 

the limestone (Hawley and Associates, written commun., 

1975). They contain sphalerite, galena, and rare chalcopyrite, 

malachite, tetrahedrite, barite, and possibly stibnite. Most of 

the veins in the Crab Bay area are too discontinuous and poorly 

mineralized to be of economic interest (Hawley and Associates, 

written commun., 1975; A.L. Eng, written commun., 1983; 

Taylor, 1993). The largest vein is 0.45 meter thick and contains 

30 to 50 percent sulfides over an exposed length of 6 meters. 

A minor amount of galena and sphalerite also is disseminated 

locally within the limestone. In general, mineral occurrences in 

the southern end of the ATMB, regardless of morphology, are 

characterized by an anomalous geochemical signature of Pb, 

Zn, Cu, Au, Ag, Ba, and minor Sb, As, Cd, Bi, and Ni (Taylor, 

1993). Comparison of this geochemical suite to that which 

characterizes the Greens Creek deposit (chap. 6) demonstrates 

their similarity and possible genetic relationship.

Mineral Occurrences in the Northern ATMB

Relative to the southern end, the northern end of the 

ATMB is characterized by larger and more clearly stratiform 

occurrences of pyrite-pyrrhotite-(chalcopyrite-sphalerite) with 

Cu-Zn-(Co-Au)-enrichments. They are hosted by thick sections of argillite intercalated with basaltic flows and sills, or 

by the uppermost Triassic sequence of mafic volcanic rocks. 

The best example is the giant Windy Craggy massive sulfide 

deposit in northwestern British Columbia, approximately 

100 km north of the international border. Published data for 

Windy Craggy indicate a minable resource of 297 million 

metric tonnes at 1.38 percent copper, 0.07 percent cobalt, 0.2 

gram per metric tonne gold, and 3.8 grams per metric tonne 

silver (Peter and Scott, 1999). The total resource estimate is 

thought to be in excess of 500 million metric tonnes (Gerald 

Harper, oral commun., 1995). Currently regarded as the largest 

Besshi-type VMS deposit in the world (Peter and Scott, 1999), 

Windy Craggy is hosted in a rift-succession (Mihalynuk and 

others, 1993) of mafic flows, sills, and argillites (fig. 20A) 

which, based on the presence of Norian conodonts both below 

and immediately above the massive sulfide lenses, can be 

confidently correlated with the ATMB in southeastern Alaska. 

Windy Craggy consists of three stratiform massive sulfide 

lenses composed predominantly of pyrite and pyrrhotite with 

lesser and variably distributed chalcopyrite, sphalerite, marcasite, galena, digenite, arsenopyrite, an unidentified bismuth telluride, cobaltite, cubanite, electrum, and native gold and silver. 

Each sulfide lens is associated with a well-developed sulfide 

stringer zone (Peter and Scott, 1999). Typical massive ore 

consists of fine- to medium-grained (about 50–500 micrometers) primary-textured to variably recrystallized pyrite and 

pyrrhotite in a volumetrically minor gangue of quartz, calcite, 

and siderite gangue (fig. 20B). In striking contrast to many of 

the Late Triassic occurrences to the south, tetrahedrite-bearing, 

gangue-rich white ores are absent at Windy Craggy, and barite 

only occurs in trace amounts. Interestingly, hydrothermal 

sediments (exhalites) are present at the base of the massive 

sulfide lenses and suggest that hydrothermal fluids breached 

the sediment/water interface early in the ore-forming process 

(Peter and Scott, 1999). Early fluid exhalation may also have 

occurred at Greens Creek (chap. 15).

Numerous other deposits in the northern end of the 

ATMB consist of similar stratiform accumulations of pyritepyrrhotite massive sulfide characterized by Cu-Zn (-Au-CoAg) enrichments. The Tats, X, and Rainy Monday occurrences 

(Peter and Scott, 1999; Mihalynuk and others, 1993) in the 

vicinity of Windy Craggy, and several others on the Canadian side of the border in the Mt. Henry Clay area such as the 

Herbert Mouth West, Grizzly Heights, and Buckwell Moraine 

(MacIntyre and Schroeter, 1985), all display features similar to 

Windy Craggy. Notably, they are all hosted in Upper Triassic 

strata dominated by distal turbiditic sediments, and by mafic 

sills and flows with transitional chemistry indicative of rifting. 

At Mt. Henry Clay on the U.S. side of the border, the stratigraphic setting is similar to that in the Windy Craggy area; 

however, occurrences mostly consist of stratiform lead-zincsilver-barite deposits such as Glacier Creek (Main) and upper 

Cap. The Little Jarvis occurrence on the opposite side of the 

ridge from the Glacier Creek deposit contains pyrite-pyrrhotite-chalcopyrite-sphalerite-bearing semimassive sulfides that 

may be more similar to the northern group of occurrences. 

Massive sulfide boulders at the Mt. Henry Clay (Boulderado) 
Late Triassic Mineral Occurrences in Southeastern Alaska 43

Figure 18 A–G (pages 44–45). Photographs of outcrops 

throughout the ATMB demonstrating the spatial relationship 

between mineral occurrences and mafic-ultramafic hypabyssal 

sills, dikes, and intrusions. (A) Altered gabbroic sill beneath 

barite-sulfide pod. Berg # 17 occurrence, Sylburn Peninsula, 

Annette Island. (B) The Keku Islet Ladder vein occurrence. 

Altered basaltic dike intrudes Permian-Triassic conglomerates 

and sedimentary rocks and is cut by dark reddish-brown 

sphalerite veins. (C) Peperitic margin of altered dike intruding 

Permian-Triassic sedimentary rocks on Keku Islet, south of the 

Ladder vein occurrence. (D) Basaltic dike cutting Devonian 

limestone and Upper Triassic sedimentary rocks and basalts 

in the south arm of Gambier Bay, southern Admiralty Island. 

Barite-quartz-carbonate-sulfide veins occupy the selvages 

of the dike and also cut the dike. (E) Quartz-iron carbonatemagnesite-fuchsite-altered ultramafic sills intruding the Upper 

Triassic sedimentary sections on the north shore of Gambier 

Bay, southern Admiralty Island. (F) Relatively unaltered enclave 

of serpentinite within a large body of altered ultramafic rock on 

the north shore of Gambier Bay, southern Admiralty Island. (G) 

Quartz-iron carbonate-magnesite-fuchsite-altered ultramafic 

intrusion on Mariposite Ridge 1 kilometer north of the Greens 

Creek mine.

occurrence are difficult to place in stratigraphic context due to 

their occurrence as float on a moraine. However they are mineralogically and texturally (fig. 20C) more like Windy Craggy 

than the stratiform lead-zinc-silver-barite occurrences in the 

Mt. Henry Clay area and to the south.

The southernmost occurrences of the northern type 

may be the numerous small stratiform pyritic bodies in the 

Duncan Canal and Woewodski and Zarembo Islands area in 

the central portion of the ATMB. The Junior Creek occurrence on the eastern shore of Duncan Canal consists entirely 

of semimassive pyrite lenses hosted in Upper Triassic graphitic argillites. On the west side of Woewodski Island, a 

0.5- to 1-m-thick pod of pyritic massive sulfide is sandwiched 

between apparently conformable footwall and hanging-wall 

rocks composed of highly altered greenschist at the Helen-S 

occurrence (Taylor, 2003). As described herein, the Frenchie 

deposit on Zarembo Island is difficult to place in stratigraphic 

context. It is one of the larger and more clearly stratiform 

deposits within the ATMB, however, and has mineralogical 

and textural features most closely associated with the pyritic 

deposits in the Mt. Henry Clay and Windy Craggy areas. The 

Frenchie deposit consists of a 2–3-m-thick, ~250-m-long 

massive sulfide lens (fig. 20D) composed primarily of pyrite 

with lesser and variable chalcopyrite, sphalerite, and barite 

(fig. 20E; Taylor, 2003), much like the Windy Craggy and Mt. 

Henry Clay (Boulderado) deposits. At the adit the massive 

sulfide lens is approximately 3 meters thick and consists predominantly of coarsely recrystallized pyrite with minor chalcopyrite and sphalerite in a siliceous quartz-carbonate gangue. 

Along strike 50 to 100 meters upstream, the lens becomes 

semimassive and then dies out into the hanging-wall quartzsericite schist. Along strike in the down-creek (westerly) direction for approximately 75 meters the lens maintains its thickness. However, over this interval the massive sulfide becomes 

finely crystalline, more sphalerite rich, and exhibits a footwall 

to hanging-wall zonation. Minor barite was observed in the 

footwall margin of the lens 45 meters west of the adit. Massive 

sulfide overlying the barite is sphalerite rich compared to the 

massive pyrite at the adit. The center of the lens becomes more 

pyritic and then grades into more galena-rich pyritic massive 

sulfide toward the hanging wall. Remobilization of ductile sulfides into fractures in the immediately overlying, more brittle 

quartz-sericite schist has caused local chalcopyrite and galena 

accumulations in the hanging wall. The massive sulfide lens 

is truncated by a fault oriented N. 65° E., 60° N. (Buddington, 

1923) 75 meters downstream from the adit, and then reappears 

in the north creek bank approximately 150 meters downstream 

from the adit. The lens is continuous downstream for approximately another 100 meters and is approximately 2 meters 

thick. Samples collected from the downstream end of the lens 

in the south bank and from the downstream end of the portion 

of the lens in the north bank become increasingly sphalerite 

rich, indicating that a proximal-distal zonation exists as well. 

From the adit (proximal) to the distal downstream end, the 

massive lens is zoned from copper-gold to zinc. From footwall 

to hanging wall the lens is zoned from Zn-Mn-Ba, to Fe-CuAu, to Pb. In addition to the zonation described, the Frenchie 

occurrence has a geochemical signature containing Fe, Zn, Cu, 

Au, Fe, (Hg, Ag, As, Cd, Mo, Pb, and Sb; Taylor, 2003).

Mineral Occurrences in the Central ATMB

Mineral occurrences in the middle of the ATMB are 

transitional and define an overlap area between structurally 

controlled types that we believe formed in a shallow water, 

near-arc setting, to those having a more stratiform appearance, 

reflecting a deeper water, rifted basin-margin setting. Examples 

of structurally controlled mineral occurrences, similar to those 

described as characteristic of the southern end of the ATMB, 

extend northward to about the latitude of Keku Strait, Woewodski Island, and southern Admiralty Island. They include 

galena-sphalerite breccias in limestone at the contact with 

felsic volcanics, and galena-sphalerite-bearing mafic dikes 

on the Cornwallis Peninsula, weakly stockwork-mineralized 

tuffaceous mafic volcanics at the Lost Show and Brushy Creek 

on Woewodski Island, and similarly mineralized mafic dikes 

and chalcopyrite-bornite-tetrahedrite-barite-bearing, quartzcarbonate stockwork veins in mafic volcanics in the Gambier 

Bay area. Stratiform deposits in this transition region tend to 

be Pb-Zn-Ag-Ba (-Cu-Au)-rich and are typified by Greens 

Creek, described in detail in this volume. Other examples of 

these increasingly larger, polymetallic, silica-barite-carbonate 

gangue-rich, more obviously stratiform occurrences include 

silica-barite-sulfide-sulfosalt-rich occurrences on Zarembo 

Island (Frenchie occurrence described previously) and Woewodski Island, Duncan Canal, Pyrola, Greens Creek, as well 
44 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska
Late Triassic Mineral Occurrences in Southeastern Alaska 45
46 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Figure 19 A–C. Photographs of outcrops and 

polished rock slabs from mineral occurrences in 

the southern portion of the ATMB. (A) Pervasive 

orange-black, hydrothermal iron and manganese 

alteration of the Nehenta Formation limestone and 

carbonate debris flows in Nehenta Bay, southern 

Gravina Island. Note pod-shaped occurrence of 

bladed white barite and minor sulfides to the right 

of the hammer. (B) Stratiform horizons of bladed 

barite in iron- and manganese-altered calcareous 

sedimentary rocks of the Nehenta Formation 

near the mouth of Nehenta Bay, southern Gravina 

Island. (C) Massive botryoidal barite and galena 

from the Berg # 18 occurrence in Japan Bay of the 

Sylburn Peninsula, Annette Island. Texture of the 

barite and the fine-scale galena bands suggest 

growth in open space or into unconsolidated 

sediments during diagenesis.
Late Triassic Mineral Occurrences in Southeastern Alaska 47

Figure 20 A–E. Photographs of outcrops and polished rock slabs 

from mineral deposits in the northern portion of the ATMB. (A) South 

side of Windy Peak at the Windy Craggy deposit in northwestern 

British Columbia. Light and dark subhorizontal layering composes 

intercalated mafic sills and flows with calcareous black argillites. (B) 

Typical pyritic massive sulfide with minor pyrrhotite and chalcopyrite 

in a quartz-carbonate gangue, from the north crosscut of the Windy 

Craggy deposit in northwestern British Columbia. The black elongate 

inclusion in the lower right part of the sample is an argillite clast. 

(C) Pyrite- and sphalerite-rich massive sulfide from a boulder 

found at the Mt. Henry Clay (Boulderado) occurrence in northern 

southeastern Alaska. (D) Massive sulfide lens at the Frenchie 

deposit on Zarembo Island, central southeastern Alaska. Timbers 

in the adit are about 2 meters high and are holding up a hanging 

wall of graphitic quartz-sericite schist. (E) Massive sulfide 

from the Frenchie deposit. Top sample is dominantly pyritic and 

characterizes the majority of the sulfide lens. The center sample 

is more sphalerite- and galena-rich; the bottom sample has 

significant barite. As shown, the three samples mimic the ore 

stratigraphy in the distal downstream portion of the lens.
48 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

as the Glacier Creek (Main), upper Cap, and other deposits on 

either side of the border in the Mt. Henry Clay area described.

Numerous small, clearly epigenetic barite-sphaleritegalena (-chalcopyrite) occurrences dot the islets and shoreline of the Cornwallis Peninsula in the Keku Strait area. The 

majority of the occurrences consist of weakly mineralized, 

irregular pods and veins composed of massive to bladed, pink 

to white barite with minor sulfides. Less commonly, colloform 

banded textures suggestive of mineral growth in open space 

or in unlithified sediments are observed (fig. 21A), similar to 

the textures in the barite-rich occurrences on Annette Island. 

The colloform banded vein shown in figure 21A also exhibits 

a close spatial relationship with a 1-m-wide mafic dike that 

contains 1-cm-thick galena veins along its margins.

With few exceptions these occurrences are localized at 

the contact between the Keku Volcanics and the overlying Cornwallis Limestone. Two of the more highly mineralized occurrences are at the rhyolite/limestone contact 

along creeks roughly 300 meters from the shoreline. One 

is generally referred to as the Kuiu zinc deposit, the second 

is an undescribed occurrence located about half way up the 

second tributary entering Hungerford Creek south from its 

mouth. Both occurrences are characterized by stockwork- and 

breccia-textured Cornwallis Limestone cemented and replaced 

by sphalerite, galena, and pyrite (fig. 21B). A similar breccia 

composed of greenstone clasts in a matrix of pink barite, dolomite, and fine bands of galena occurs in the creek bed at the 

mouth of Hungerford Creek. Whereas all of the occurrences in 

the Keku Strait area are clearly epigenetic in style, it is worth 

noting that iron- and manganese-rich hydrothermal alteration 

is widespread at the rhyolite/limestone contact, which in many 

places is marked by clastic sediments and thin chert horizons 

(Muffler, 1967; this study).

A nearly identical style of mineralized limestone 

breccia associated with mafic dikes is present at the Taylor 

Creek occurrence on the west side of Duncan Canal. The 

occurrences are hosted entirely in a massive to thin-bedded, 

fractured, buff-colored to light gray dolomitic limestone. 

The limestone is in depositional contact with and overlies a 

penetratively foliated greenstone composed predominantly of 

a chlorite-calcite- (muscovite-quartz) phyllite. The units strike 

northwest to west-northwest and dip shallowly to moderately 

steeply to the northeast. Numerous north- to north-northeaststriking dikes of probable Tertiary-Quaternary age intrude the 

country rock.

A Carnian (early Late Triassic) age is firmly established 

for the limestone at Taylor Creek by a series of conodont 

samples collected by Kennecott Exploration and identified 

by Anita Harris (chap. 11). Sampling sites are identified 

on the recent geologic map of the Duncan Canal–Zarembo 

Island area (Karl and others, 1999a). Carnian conodonts were 

recovered from a sample of limestone located on strike about 

2.5 kilometers northwest of the creek occurrences; collections 

from the immediate vicinity of the open cut were barren. Two 

samples containing latest Early Permian conodonts, located on 

the ridge a mile to the southwest, and south of the mouth of 

Taylor Creek along strike a mile to the southeast, respectively, 

support the younging-to-the-northeast stratigraphic interpretation of early workers (Kerns, 1950). These conodont samples 

also bracket the permissive age of the pillowed basaltic volcanics and phyllitic greenstone located on the ridge southwest of 

the occurrence and in the footwall of the Taylor Creek occurrence, respectively, between late Early Permian and early Late 

Triassic time.

Mineralized rock in the creek bank exposures of Taylor 

Creek has two distinct styles. The first and most prevalent 

consists of irregularly distributed veins, patches, and pods 

of disseminated to locally abundant pyrite, sphalerite, and 

galena in a matrix of opaque, light gray to white dolomite 

gangue (fig. 21C). Marcasite has been reported at Taylor 

Creek (Kerns, 1950); however, X-ray diffraction analysis of 

suspected marcasite identified only pyrite in a dolomite and 

ankerite gangue (S.J. Sutley, U.S. Geological Survey, written 

commun., 1999). Pyrite forms millimeter- to centimeter-sized 

clots and rounded aggregates in white dolomite or in a fine 

crystalline groundmass of a dark gray sulfide and yelloworange sphalerite. Galena occurs as fine crystalline blebs and 

streaks, and less commonly as coarse crystalline remobilized 

clots. Although not visually identified, the strong silverantimony enrichment of this assemblage described below 

suggests the presence of antimonian tetrahedrite, a common 

mineral in Late Triassic mineral deposits throughout the 

ATMB. This style appears to be a replacement of the host 

limestone. However, the presence of rounded grains of pyrite 

is not a typical texture of epigenetic replacement deposits 

in carbonate strata and raises the possibility that the present 

textural form is a result of remobilization. The best example 

of this style of mineralization is in the south bank of Taylor 

Creek in a 1.6-meter-thick subhorizontal band over the top of 

the discovery trench (Taylor, 2003).

The second style of mineralization has only recently 

been recognized (Taylor, 2003) and may provide critical evidence of genetic process at Taylor Creek. This style consists 

of matrix- to grain-supported, rounded nodules of pyrite 

up to several centimeters in diameter in a dolomite matrix, 

and irregular botryoidal crusts of pyrite growing in and on 

dolomitic limestone. Locally, orange sphalerite and galena 

are present as a fine-grained crystalline matrix and as sparse, 

coarse crystalline clots. The best example of this textural 

style is in the north creek bank about 200 meters upstream 

from the open cut. A stratiform(?) horizon about 12 meters 

long and roughly parallel to the creek consists predominantly 

of this nodular pyrite “pudding stone” (fig. 21D). Conspicuously absent are common indicators of epigenetic styles of 

mineralization such as discrete quartz-dolomite-sulfide veins 

or mineralized breccias. The nodular and botryoidal pyrite 

textures are likely a result of early diagenetic replacement 

of limestone during carbonate sedimentation. The nodular 

pyrite textures and intercalations of dolomitic limestone with 

sulfidic limy phyllite are similar to those observed at the Wetboot occurrence in Towers Creek (Taylor, 2003) except the 

former are on a larger scale. Significantly, identical nodular 
Late Triassic Mineral Occurrences in Southeastern Alaska 49

Figure 21 A–E. Photographs of outcrops and polished rock 

slabs from mineral occurrences in the central portion of 

the ATMB. (A) Massive vein of pink and white barite cutting 

clastic sedimentary rocks and limestone at the top of the 

Keku Volcanics rhyolite. Note botryoidal banding defined by 

fine-scale galena. Northeastern shoreline of the Cornwallis 

Peninsula on Kuiu Island, Keku Strait area, central 

southeastern Alaska. (B) Mineralized Cornwallis Limestone 

breccia from the Kuiu zinc deposit on the Cornwallis 

Peninsula. Matrix to the clast is composed of sphalerite, 

galena, and carbonate. (C) Mineralized limestone from top 

of the open cut at the Taylor Creek occurrence, Duncan 

Canal, central southeastern Alaska. Sample contains pyrite, 

sphalerite, galena, and tetrahedrite in irregular veins and as 

replacements of limestone, with a white dolomite gangue. 

(D) Nodular pyrite in limestone from outcrop in creek bank, 

upstream from the Taylor Creek open cut. This texture is 

interpreted to be the result of early diagenetic replacement 

of carbonate mud. (E) Semimassive sulfide in a quartzcarbonate-chlorite-altered greenstone at the Lost Show 

occurrence, near the northwest shore of Woewodski Island 

in Duncan Canal, central southeastern Alaska. Dark reddishbrown streaks of sphalerite are prevalent, and sulfides fill 

vuggy open cavities.
50 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

pyrite textures are present in footwall carbonate units and in 

massive pyritic ore at the Greens Creek mine (chap. 9; see 

also figs. 4C and D in chap. 11). The Taylor Creek occurrences have a geochemical signature consisting of Fe, Zn, Pb, 

Ag, Sb, Hg, Cd, Mn (Au, As, Cu, and Mo) (Taylor, 2003).

An additional style of structurally hosted, discontinuous, 

and vein or stockwork-like occurrences are also present in the 

central portion of the ATMB. These are typified by Lost Show 

and Brushy Creek on Woewodski Island and by the North 

Gambier occurrence in Gambier Bay of Admiralty Island. 

The Lost Show occurrence is located in the northeast quadrant 

of Section 22 of the Petersburg C–4 15-minute quadrangle, 

less than a kilometer from the northwest point of Woewodski 

Island. The occurrence consists of an east-west-trending low 

ridge of rock on the north side of a small lake. Two trenches 

have been cleared over the occurrence, exposing its width at 

the center and at the west end of the low ridge.

The Lost Show occurrence consists of a single, near vertically dipping, 3–4-m-wide stratiform lens of silicified greenstone. The silicified horizon contains as many as six bands 

(1–30 cm in thickness) of pyrite- and sphalerite-rich, semimassive to massive sulfide in the center trench, which coalesce 

into thicker bands in the west trench. The lens is continuous 

along strike for at least 40 meters between the two trenches. 

Continuity of the lens to the east and west is unknown but 

likely, based on its consistent thickness over 40 meters. The 

thickest and best-mineralized massive sulfide is in the western 

trench and appears to be zoned somewhat across the width of 

the lens. Massive sulfide against the north side of the lens is 

sphalerite rich and grades into more silica-pyrite-rich massive 

sulfide toward the southern edge of the lens. Where massive, 

the sulfides comprise a fine-grained mixture of pyrite, dark red 

sphalerite, and minor amounts of a dark gray mineral, possibly galena or tetrahedrite. Semimassive sulfides are texturally similar, with a gangue of gray to white silica. Breccia 

fragments of quartz, minor vug-fillings of euhedral pyrite, 

and pyrite veinlets cutting silicified breccia fragments suggest 

tectonic disruption of the lens and redistribution of sulfides 

(fig. 21E). The occurrence is characterized by a geochemical 

signature containing Zn, Fe, Cd, Hg, Ag, Sb (Pb, Au, Cu, and 

Mn) (Taylor, 2003).

The Brushy Creek occurrence is in the southwestern quadrant of section 1 of the Petersburg C–4 15-minute 

quadrangle, on the southern end of Woewodski Island. Two 

mineralized open cuts in the southeast bank of the creek 

are located approximately 50 meters apart, and evidence of 

weak mineralization is present intermittently for at least 250 

meters downstream. Country rock exposed in the creek bank 

is entirely composed of a brecciated, heavily altered, and 

weakly foliated mafic metavolcanic or volcaniclastic rock. 

A small side drainage flowing into Brushy Creek from the 

southeast contains exposures of thin-bedded, calcareous, 

quartz-sericite schist with bands of semimassive sulfide. Precursor of the schist is uncertain but could have been a felsic 

tuff (Taylor, 2003).

The mineral occurrences at Brushy Creek consist of 

irregularly distributed stockwork calcite-quartz-sulfide veins 

within brecciated mafic volcanic rock. Two shallow pits in the 

creek bank each expose 2–3-meter-wide areas crisscrossed by 

veins. Similar areas of stockwork veining are intermittently 

exposed in the creek bank downstream for approximately 

200 meters. Texturally, all of the sulfides are fine to medium 

crystalline aggregates of pyrite, dark-reddish sphalerite, and 

lesser galena. Gangue consists of white quartz and calcite. 

In slightly more foliated rocks, the clasts are stretched and 

flattened and the sulfides appear as irregular bands and wisps 

millimeters to one centimeter in width. In more competent 

volcaniclastic rocks, sulfides are clearly paragenetically earlier 

than brecciation of the host rock as the clasts are mineralized 

and are rotated within the unmineralized matrix and are cut by 

late quartz-calcite veinlets. In addition to rotation of mineralized clasts, individual bands or stockwork veins are folded. 

The geochemical signature of the Brushy Creek occurrence 

consists of Fe, Zn, Ag, Hg, Pb, Sb, Cd, Mn (Au, As, Cu, Co, 

Ni, and V) (Taylor, 2003).

The barite-quartz-carbonate polymetallic veins and 

semimassive sulfides at the North Gambier occurrence 

described in detail by Taylor and others (1992) compose perhaps the northernmost structurally controlled, clearly epigenetic mineral occurrence within the ATMB. The occurrence 

predominantly consists of sulfide-rich quartz-carbonatebarite veins at the transition between sedimentary rocks and 

spilitized mafic volcanics. Mineralization occurs primarily 

within sheared and brecciated zones. Chalcopyrite and barite 

are the major constituents with lesser bornite, pyrite, sphalerite, galena, covellite, and silver-rich tetrahedrite. Chalcopyrite occurs as clots up to several centimeters in diameter 

with associated coarsely crystalline bladed, white barite, as 

millimeter-sized grains disseminated in the greenstone, and 

as massive, flow-banded material that is intimately intergrown with bornite, covellite, tetrahedrite, and fine-grained 

pyrite and quartz. Covellite occurs as fine, hairlike needles 

and laths within the bornite. Tetrahedrite forms small blebs 

and fracture fillings within the chalcopyrite-bornite assemblage. The dominance of chalcopyrite at the North Gambier 

occurrence is unusual for the ATMB as is the relatively 

major proportion of bornite. However, mineralized samples 

contain 0.1–1 percent copper, 0.1 percent zinc, several parts 

per million silver, and highly anomalous concentrations of 

Mn, As, Cd, Mo, Pb, Sb, and Hg, similar to the Greens Creek 

geochemical signature that occurs consistently throughout 

the ATMB.

Mineral occurrences that typify the progression to 

larger, more stratiform morphologies with mineralogical and 

geochemical features like Greens Creek are also present in the 

central area of the ATMB and persist northward to the latitude 

of Mt. Henry Clay. The Butterworth Island occurrence is 

located just south of the southeastern corner of section 34, in 

the Petersburg C–4 15-minute quadrangle, just west of Woewodski Island. The occurrence is located below the high tide 

line in the small spit of land that separates the southeastern 
Late Triassic Mineral Occurrences in Southeastern Alaska 51

end of Butterworth Island from the small islet to the south. 

Rocks exposed at low tide between the islands consist of foliated, reddish, highly altered siliceous schist. Immediately to 

the north, and forming the southern shoreline of Butterworth 

Island, the siliceous schist is in sharp contact with massive, 

fractured, unfoliated Cretaceous(?) diorite. Southward the 

schist grades into a sequence of rocks mapped as Mesozoic 

volcanics (Brew, 1997). The altered schist hosting the mineral 

occurrence grades southward into greenschist and moderately 

foliated mafic metavolcanic rocks that have been intruded by 

sills of Cretaceous(?) diorite. The diorite contains xenoliths 

of gabbro probably incorporated from the Mesozoic gabbroic 

intrusive body that crops out on the northern one-third of Butterworth Island (Brew, 1997).

The Butterworth Island occurrence consists of several 

subparallel 1–10-cm-thick, semimassive to massive sulfide 

bands that are conformable with foliation and occur over 

a width of approximately 4 meters. The mineralized bands 

are traceable along foliation across the entire width of the 

low-tide land bridge. The better, more massive sulfide bands 

are located at low tide on the east side. The best single band 

is a 10-cm-thick layer of massive pyrite, dark red sphalerite, 

galena, and probable tetrahedrite. Texturally, the sulfides are 

fine crystalline and equigranular and appear to form a matrix 

to clasts of white quartz or chert pebbles and very elongate 

fragments of thoroughly altered rock. The geochemical 

signature of the massive sulfide is characterized by very high 

values of Zn, Fe, Pb, Ag, Hg, Cd, Sb, Co, Mn, (Cu, Au, Mo, 

and V).

The Castle Island barite deposit is, or was, located in a 

group of small islands in the middle of Duncan Canal, several 

kilometers east of the mouth of Castle River. The deposit 

consisted of a small island almost entirely composed of barite 

just east of, and connected by a small spit of land to, “Little” 

Castle Island, the small islet immediately south of Big Castle 

Island. Little Castle Island is composed from west to east of 

massive, volcaniclastic, and pillowed mafic volcanic rocks 

that grade into phyllitic greenstone, which in turn grade into 

a thin layer of phyllitic pebble conglomerate. Orange-weathering iron-carbonate-altered rock marks a distinctive sheared 

fault zone running the length of the island that is exposed 

along the east shoreline. The eastern shore south of the former 

ore-loading pad consists of a sequence of phyllitic calcareous 

mudstone, silty limestone, and possibly interbedded graywacke; this sequence is approximately 100 meters southeast 

of the loading pad along strike and likely represents the 

footwall rocks to the deposit that are now covered. A small 

knob in the tide zone south of the loading pad and east of the 

Little Castle Island shoreline is composed of the calcareous 

phyllite and is cut by poddy and discontinuous, sulfide-bearing, quartz-carbonate veins, centimeters to 0.7 meter thick. 

Sulfides are disseminated euhedral grains of coarse crystalline 

pyrite, green (low iron) sphalerite, and minor galena. Geochemical analyses of the veins indicate that the carbonate is 

iron and manganese rich, as are carbonate alteration minerals 

associated with mineral occurrences throughout the ATMB 

(C.D. Taylor, this study and unpublished data). These veins 

are probably the metamorphosed feeders to the Castle Island 

barite deposit.

Previously published records indicate that the Castle 

Island barite deposit was approximately 95 meters long, 63 

meters wide, and extended below sea level to a depth of 47 

meters (Grybeck and others, 1984). Maximum elevation of 

the barite outcrop was between 11 and 18.5 meters above 

sea level. Enclosing rocks strike northwesterly and dip 50 to 

60 degrees to the northeast. A premining estimate based on 

drilling of the size of the deposit down to 12.5 meters below 

sea level was 218,000 metric tonnes with a true thickness 

of the main barite body of 25 to 31 meters (Burchard, 1914; 

Williams and Decker, 1932). These reports also suggest 

that the footwall to the deposit consisted of 3–6 meters of 

“baritic grayschist and limestone” above black slaty argillite, all of which rested on “dark volcanic rocks” that are 

probably equivalent to the basalt exposed on the islet to the 

west. Such a stratigraphy is consistent with exposures of 

presumed footwall sediments to the southeast of the deposit, 

as previously described. Cross sections based on drilling 

data suggest that the deposit was essentially a single massive lens dipping eastward, conformably with the enclosing 

sediments, into Duncan Canal. A horse composed of impure 

barite, calcite, and schist is indicated at depth near the hanging wall. Sparse exposures of hanging-wall lithologies suggest phyllitic schist and volcanic tuff. The northern limit of 

the deposit was defined by drilling; the southern boundary 

was not determined. The barite body was thought to “rake 

somewhat to the southeast and extend southerly beyond the 

southern tip of the island” (Williams and Decker, 1932, p. 

3), consistent with the general southeast plunge direction of 

fold axes in Triassic rocks of the area (P.J. Haeussler, written commun., 2000).

Grybeck and others (1984) reported a total production 

for the Castle Island barite deposit of approximately 0.68 

million metric tonnes of barite based upon undocumented 

sources. Their reinterpretation of unpublished drilling data 

and cross sections led them to suggest that the deposit 

“occurred along the trough of a symmetrical open syncline 

trending about N. 70o

 W. and centered on the now minedout island, with limbs dipping 30 to 45 degrees.” Grybeck 

and others (1984) also reported that drilling “indicated a 

considerable tonnage of lower grade barite interbedded with 

‘gray schist’ (metafelsite?), ‘chert,’ and ‘graphitic schist,’ 

and indications of at least one more high-grade barite lens 

offshore.” Texturally, samples of the barite are massive, 

sugary, and white to light gray, with millimeter-scale bands 

and discontinuous wisps of fine crystalline sulfides (fig. 

22A). Examination of thin sections indicates the presence of 

disseminated sphalerite, galena, pyrite, pyrrhotite, bornite, 

tetrahedrite-tennantite, and chalcopyrite occurring as equant 

grains 5–300 micrometers in size (Berg and Grybeck, 1980; 

Grybeck and others, 1984).

Numerous assays of composite drill-core samples and 

surface chip samples established an average grade of 89 
52 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

percent barite and 4.5 percent silica, with 0.5–2.5 percent zinc, 

0.5–1 percent lead, 1–2 percent iron, 0.5–2.0 troy ounces per 

ton silver, and traces of gold (Williams and Decker, 1932; 

Race, 1963; Grybeck and others, 1984). The geochemical signature of the massive barite consists of Ba, Zn, Pb, Ag, Fe, Cd, 

Sb, Sr (Cu, Au, and Mo). Quartz-carbonate-sulfide veins in 

the footwall have a similar signature with the notable addition 

of manganese, arsenic, mercury, and a mafic-ultramafic suite 

consisting of cobalt, chromium, nickel, and vanadium (Taylor, 

2003).

The Pyrola deposit is located in the north-central part 

of Admiralty Island within a sequence of greenschist-facies 

rocks correlated with the Retreat Group schists and unconformably overlying limestone, argillite, and mafic volcanic 

rocks. This sequence of lithologies bears a strong resemblance to the sequence that characterizes the Hyd Group and, 

although the age of the Pyrola host rocks are not known with 

certainty, Van Nieuwenhuyse (1984) suggested that they are 

either Permian or Triassic. The deposit consists of stratiform 

layers of interbedded barite and massive sulfide hosted in 

graphitic sediments. A siliceous disseminated pyritic stockwork zone is also present and contains precious metals. The 

deposit is underlain by a large, semiconformable chloritecarbonate alteration halo, which is overprinted in the immediate footwall by intense sericite-quartz-pyrite altered rock. The 

ore mineralogy consists of pyrite, sphalerite, galena, minor 

chalcopyrite, jamesonite, and boulangerite (Van Nieuwenhuyse, 1984). In addition to the many geological similarities 

to Greens Creek and other barite-rich polymetallic deposits 

in the central portion of the ATMB, at Pyrola both sulfur and 

lead isotopic values of galena are very similar to values at 

Greens Creek (chap.10).

The Glacier Creek (Main) deposit and the nearby Upper 

Cap occurrence are on the U.S. side of the border in the 

Mt. Henry Clay area. They are both stratiform, barite-rich, 

polymetallic deposits of Late Triassic age that represent the 

northernmost examples characteristic of the central, transitional portion of the ATMB. The Glacier Creek deposit consists of a 20–30-m-thick, 600-m-long layer of highly altered 

quartz-sericite schist that contains lenses of massive barite 

accompanied by bands of sphalerite, galena, and chalcopyrite 

(MacIntyre and Schroeter, 1985). The deposit is underlain 

by mafic flows and sedimentary rocks and is overlain by 

massive pillow lavas (fig. 22B). The Upper Cap occurrence, 

located several kilometers up Glacier Creek, displays similar 

features to the Glacier Creek deposit. The occurrence consists 

predominantly of a 3-m-thick, silica-barite lens with minor 

amounts of pyrite, sphalerite, galena, and tetrahedrite (fig. 

22C; MacIntyre and Schroeter, 1985). The footwall is largely 

covered by ice; the hanging wall consists of massive basalt 

flows. Reports of ruby silver (Ag-sulfosalt) at Upper Cap 

(Merrill Palmer, oral commun., 1994) suggest mineralogical 

similarities to Greens Creek. X-ray diffraction analysis of 

reddish-black crystals in silica-barite identified the leadantimony sulfide mineral geocronite, which also occurs at 

Greens Creek (chap. 9).

Discussion

We propose, based on the transitional features of the 

ATMB just described, that the Late Triassic rift in southeastern 

Alaska formed by oblique propagation into the Alexander terrane resulting in a metallogenic environment setting common 

both to VMS and to SEDEX environments. Recent work relating the specific nature of both ancient (Barrett and MacLean, 

1999) and modern (Hannington and others, 1986; Halbach and 

others, 1993; Binns and others, 1993; Fouquet and others, 1993; 

Stoffers and others, 1999) VMS deposits to the location (continental margin, oceanic) and maturity level of the hosting rift 

basins helps to explain the variations in the mineral occurrences 

of the ATMB in southeastern Alaska. For example, deposits 

that form at the tip of rifts propagating into mature arcs (the 

western Woodlark basin propagating into Papua New Guinea 

[Binns and others, 1993]; the southern Lau Basin propagating 

into the North Island of New Zealand from the Valu Fa Ridge 

to the Taupo volcanic zone [Fouquet and others, 1993]) or 

where nascent intracontinental rifts split arcs (Japan [Barrett 

and MacLean, 1999]) are generally of the Kuroko type and are 

associated with arc-type or heavily calc-alkaline contaminated 

transitional lavas such as E-MORB (Barrett and MacLean, 

1999; cf. the bimodal-mafic division of Barrie and Hannington, 

1999). Deposits landward of the propagating rift, or deposits that form on land in the early stages of rifting, display an 

epithermal or hot-springs style of mineralization (for example, 

Stoffers and others, 1999; cf. deposits of the Taupo volcanic 

zone, White, 1981; Hedenquist and Henley, 1985). Deposits 

that form in the deeper, seaward portion of propagating rifts or 

in mature rifts are more likely to have a dominantly copper-zinc 

rich metal assemblage and may be associated with distal clastic 

sediments (for example, Windy Craggy [Peter and Scott, 1999]; 

and the Besshi deposits [Slack, 1993]). The deposits occurring 

in the mature rift settings are usually generally associated with 

primitive mafic melts that are forming segments of new oceanic 

crust and may or may not show contamination by melting and 

incorporation of the rifted crust (Barrett and MacLean, 1999; cf. 

the mafic-siliciclastic division of Barrie and Hannington, 1999). 

That such a variation of deposit styles, associated with predictably varying suites of igneous rocks, can be found in a single 

rift propagating into a mature arc or continental margin provides 

confirmation for the lithogeochemical and deposit variability 

of the mineral occurrences in southeastern Alaska. Figure 23 

depicts a cross-sectional view through such a tectonic setting 

showing the various subaerial to deepwater settings of the southeastern Alaska Late Triassic mineral occurrences in the ATMB.

The segment of a propagating oceanic rift that we believe 

is analogous to the Greens Creek tectonic setting is that portion 

seaward of the propagating tip of a rift basin and landward of 

the point at which new oceanic crust begins to form. Within 

this segment, bimodal volcanism is characterized by peralkaline 

rhyolites and variably enriched basalts that exhibit chemistry similar to intraplate rocks and varying degrees of crustal 

contamination (for example, Smith and others, 1977; Smith 

and Johnson, 1981). Moving seaward, rhyolites disappear from 
Late Triassic Mineral Occurrences in Southeastern Alaska 53

Figure 22 A–C. Photographs of outcrops and 

polished rock slabs from mineral occurrences 

in the central and northern portion of the ATMB. 

(A) Barite-galena-rich float collected on the 

loading pad at the Castle Island barite mine in the 

Duncan Canal area, central southeastern Alaska. 

(B) Glacier Creek (Main) deposit in the Mt. Henry 

Clay area, northern southeastern Alaska. The 

central, orange-white stripe consists of quartzsericite-carbonate schist with lenses of massive 

barite and lesser sulfides. Outcrop above and 

below consists of massive and pillowed basalt 

flows. (C) Barite-sulfide lens at the Upper Cap 

occurrence in the Mt. Henry Clay area, northern 

southeastern Alaska. Rocks overlying the lens 

are massive basalt flows.
54 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

the section and mafic melts become less arc-contaminated and 

compositionally more similar to ocean ridge basalts, commonly 

E-MORB or “transitional” basalts (for example, modern examples include Gill and Whelan, 1989, and Stern and others, 1990; 

and ancient examples include Aitchison and Flood, 1995, and 

Dadd, 1998). The seaward transition may or may not evolve into 

a sediment-covered ridge; however, the transition is nevertheless 

significant in representing the change from a bimodal-mafic to 

a mafic-siliciclastic metallogenic environment. This transition 

is exactly like the observed changes in the tectonostratigraphic 

settings between the Keku Strait, where mineral occurrences of 

the ATMB are hosted in dolomitic limestone overlying peralkaline rhyolites, and the Greens Creek deposit, where rhyolites 

are absent. The rift has become sediment-covered, and coeval 

mafic-ultramafic melts are still heavily contaminated by the 

Alexander terrane basement that they rise through.

We suggest that the portion of an evolving rift where host 

lithologies include footwall mafic-ultramafic rocks contaminated by a mature arc and distal clastic sedimentation is strikingly similar to the failed epicontinental rift tectonic setting 

common to most SEDEX deposits. At the time of Late Triassic 

rifting, the Alexander terrane was an inactive, continent-sized 

PALEOZOIC ISLAND ARC

SHALLOW SHELF

DEEP INTRA/BACK-ARC RIFT

CONTINENTAL MARGIN(?)

ISLAND ARC(?)

EXPLANATION

Mantle

Oceanic crust

Paleozoic arc terrane

Conglomerate

Rhyolite

Limestone/dolomite

Arkose

Basalt/gabbro

Shale

Mineral deposit

southern 

central

northern ATMB

AN/GR KK/DC/GB GC/MHC WC

Rift-related rocks

Figure 23. Schematic drawing showing a cross-sectional view of the Upper Triassic metallogenic setting of mineral deposits and 

occurrences in southeastern Alaska. Diagram shows a series of mineral deposits at progressively deeper water positions within 

an evolving intra- or back-arc rift. AN/GR, Annette and Gravina Islands; KK/DC/GB, Keku Strait, Duncan Canal, and Gambier Bay on 

southern Admiralty Island; GC/MHC, Greens Creek on northern Admiralty Island and Mt. Henry Clay; WC, Windy Craggy.
References Cited 55

landmass of wholly oceanic affinities, cored by sialic Proterozoic and lower Paleozoic crust. At the latitude of Greens Creek, 

rifting resulted in the formation of a small (second order?), 

restricted, anoxic, and very organic-rich sedimentary basin, 

which was intruded by rift-related mafic-ultramafic intrusive 

rocks. This SEDEX-like metallogenic setting occurred within a 

propagating rift, which on a larger scale is more similar to the 

metallogenic setting common to many VMS deposits.

References Cited

Aitchison, J.C., and Flood, P.G., 1995, Gamilaroi Terrane—A 

Devonian rifted intra-oceanic island-arc assemblage, NSW, 

Australia, in Smellie, J.L., ed., Volcanism associated with 

extension at consuming plate margins: Geological Society 

Special Publication no. 81, p. 155–168.

Arculus, R.J., 1987, The significance of source versus process in the tectonic controls of magma genesis: Journal of 

Volcanology and Geothermal Research, v. 32, p. 1–12.

Barker, Fred, 1994, Some accreted volcanic rocks of Alaska 

and their elemental abundances, in Plafker, G., and Berg, 

H.C., eds., The geology of Alaska: Boulder, Colorado, 

Geological Society of America, Decade of North American 

Geology, v. G–1, p. 555–587.

Barker, Fred, Sutherland-Brown, A., Budahn, J.R., and 

Plafker, G., 1989, Back-arc with frontal-arc component origin of Triassic Karmutsen basalt, British Columbia, Canada: 

Chemical Geology, v. 75, p. 81–102.

Barrett, T.J., and MacLean, W.H., 1999, Volcanic sequences, 

lithogeochemistry, and hydrothermal alteration in some 

bimodal volcanic-associated massive sulfide systems, 

in Barrie, C.T., and Hannington, M.D., eds., Volcanicassociated massive sulfide deposits—Processes and 

examples in modern and ancient settings: Society of 

Economic Geologists Reviews in Economic Geology, v. 8, 

p. 101–127.

Barrie, C.T., and Hannington, M.D., 1999, Classification 

of volcanic-associated massive sulfide deposits based on 

host-rock composition, in Barrie, C.T., and Hannington, 

M.D., eds., Volcanic-associated massive sulfide deposits—

Processes and examples in modern and ancient settings: 

Society of Economic Geologists Reviews in Economic 

Geology, v. 8, p. 1–11.

Bazard, D.R., Butler, R., Gehrels, G., and Soja, C.M., 1994, 

New constraints for Late Silurian-Devonian paleogeography 

of the Alexander terrane, southeastern Alaska: Geological 

Society of America Abstracts with Programs, v. 26, p. A384.

Berg, H.C., 1972, Geologic map of Annette Island, Alaska: 

U.S. Geological Survey Miscellaneous Investigations Series 

Map I–684, scale 1:63,360.

Berg, H.C., 1973, The geology of Gravina Island, Alaska: U.S. 

Geological Survey Bulletin 1373, 41 p.

Berg, H.C., and Grybeck, D., 1980, Upper Triassic volcanogenic Zn-Pb-Ag-(Cu-Au)-barite mineral deposits near 

Petersburg, Alaska: U.S. Geological Survey Open-File 

Report 80–527, 9 p.

Berg, H.C., Jones, D.L., and Coney, P.J., 1978, Map showing 

pre-Cenozoic tectono-stratigraphic terranes of southeastern 

Alaska and adjacent areas: U.S. Geological Survey OpenFile Report 78–1085, 2 sheets, scale 1:1,000,000.

Berg, H.C., Jones, D.L., and Richter, D.H., 1972, GravinaNutzotin belt—Tectonic significance of an upper Mesozoic 

sedimentary and volcanic sequence in southern and southeastern Alaska: U.S. Geological Survey Professional Paper 

800–D, p. D1–D24.

Binns, R.A., Scott, S.D., Bogdanov, Y.A., Lisitzin, A.P., Gordeev, V.V., Gurvich, E.G., Finlayson, E.J., Boyd, T., Dotter, 

L.E., Wheller, G.E., and Muravyev, K.G., 1993, Hydrothermal oxide and gold-rich sulfate deposits of Franklin 

Seamount, western Woodlark basin, Papua New Guinea: 

Economic Geology, v. 88, p. 2122–2153.

Boynton, W.V., 1984, Cosmochemistry of the rare earth 

elements—Meteorite studies, in Henderson, P., ed., Rare 

earth element geochemistry: Amsterdam, Elsevier, 

p. 63–114.

Brew, D.A., 1997, Reconnaissance geologic map of the 

Petersburg C–4 quadrangle, southeastern Alaska: U.S. Geological Survey Open-File Report 97–156–J, 21 p., 1 sheet, 

scale 1:63,360.

Buddington, A.F., 1923, Mineral deposits of the Wrangell 

district: U.S. Geological Survey Bulletin 739, p. 51–75.

Burchard, E.F., 1914, A barite deposit near Wrangell: U.S. 

Geological Survey Bulletin 592, p. 109–117.

Churkin, Michael, Jr., and Eberlein, G.D., 1977, Ancient 

borderland terranes of the North American Cordillera—

Correlation and microplate tectonics: Geological Society of 

America Bulletin, v. 88, p. 769–786.

Civetta, Lucia, Cornette, Y., Crisci, G., Gillot, P.Y., Orsi, G., 

and Requejos, C.S., 1984, Geology, geochronology and 

chemical evolution of the island of Pantelleria: Geological 

Magazine, v. 121, no. 6, p. 541–562.

Cobb, E.H., 1972, Metallic mineral resources map of the 

Petersburg quadrangle, Alaska: U.S. Geological Survey 

Miscellaneous Field Studies Map MF–415, 1 sheet, scale 

1:250,000.

Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Petersburg quadrangle, Alaska: U.S. Geological 

Survey Open-File Report 78–870, 52 p.
56 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Cole, J.W., 1978, Tectonic setting of Mayor Island volcano: 

New Zealand Journal of Geology and Geophysics, v. 21, 

p. 645–647.

Dadd, K.A., 1998, Incipient backarc magmatism in the Silurian Tumut Trough, new South Wales—An ancient analogue 

of the early Lau Basin: Australian Journal of Earth Science, 

v. 45, p. 109–121.

Dudas, F.O., 1992, Petrogenetic evaluation of trace element 

discrimination diagrams, in Bartholomew, M.J., Hyndman, 

D.W., Mogk, D.W., and Mason, R., Basement tectonics 8—

Characterization and comparison of ancient and Mesozoic 

continental margins—Proceedings of the 8th International 

Conference on Basement Tectonics (Butte, Montana, 1988): 

Dordrecht, The Netherlands, Kluwer Academic Publishers, 

p. 93–127.

Dusel-Bacon, Cynthia, 1994, Metamorphic history of Alaska, 

in Plafker, G., and Berg, H.C., eds., The geology of Alaska: 

Boulder, Colorado, Geological Society of America, Decade 

of North American Geology, v. G1, p. 495–533.

Forbes, R.B., Gilbert, W., and Redman, E., 1989, Geologic setting and petrology of the metavolcanic rocks in 

the northwestern part of the Skagway B-4 quadrangle, 

southeastern Alaska: Alaska Division of Geological and 

Geophysical Surveys, Public-Data File 89–14, 43 p.

Ford, A.B., and Brew, D.A., 1993, Geochemical character 

of upper Paleozoic and Triassic greenstone and related 

metavolcanic rocks of the Wrangellia terrane in northern 

southeastern Alaska, in Dusel-Bacon, Cynthia, and Till, 

A.B., eds., Geologic studies in Alaska by the U.S. Geological Survey, 1992: U.S. Geological Survey Bulletin 2068, 

p. 197–217.

Fouquet, Yves, Von Stackelberg, U., Charlou, J.L., Erzinger, 

J., Herzig, P.M., Muhe, R., and Wiedicke, M., 1993, 

Metallogenesis in back-arc environments—The Lau basin 

example: Economic Geology, v. 88, p. 2154–2181.

Franklin, J.M., 1986, Volcanic-associated massive sulphide 

deposits—An update, in Andrew, C.J., Crowe, R.W.A., 

Finlay, S., Pennel, W.M., and Pyne, J.F., eds., Geology and 

genesis of mineral deposits in Ireland: Irish Association for 

Economic Geology, p. 49–69.

Franklin, J.M., 1993, Volcanic-associated massive sulphide 

deposits, in Kirkham, R.V., Sinclair, W.D., Thorpe, R.I., 

and Duke, J.M., eds., Mineral deposit modeling: Geological Association of Canada, Special Paper 40, 

p. 315–334.

Franklin, J.M., Lydon, J.W., and Sangster, D.F., 1981, Volcanic-associated massive sulfide deposits, in Skinner, B.J., 

ed., Economic geology—Seventy-fifth anniversary volume, 

1905–1980: El Paso, Texas, The Economic Geology Publishing Company, p. 485–627.

Gardner, M.C., Bergman, S.C., Cushing, G.W., MacKevett, 

E.M., Jr., Plafker, G., Campbell, R.B., Dodds, C.J., McClelland, W.C., and Mueller, P.A., 1988, Pennsylvanian pluton 

stitching of Wrangellia and the Alexander terrane, Wrangell 

Mountains, Alaska: Geology, v. 16, p. 967–971.

Gehrels, G.E., and Barker, G., 1993, Reconnaissance geochemistry of Permian and Triassic basalts of the Taku and 

Wrangellia terranes, southeastern Alaska, in Dusel-Bacon, 

Cynthia, and Till, A.B., eds., Geologic studies in Alaska by 

the U.S. Geological Survey, 1992: U.S. Geological Survey 

Bulletin 2068, p. 218–227.

Gehrels, G.E., and Berg, H.C., 1992, Geologic map of southeastern Alaska: U.S. Geological Survey Miscellaneous 

Investigations Series Map I–1867, scale 1:600,000.

Gehrels, G.E., and Berg, H.C., 1994, Geology of southeastern Alaska, in Plafker, George, and Berg, H.C., eds., The 

geology of Alaska: Boulder, Colorado, Geological Society 

of America, Decade of North American Geology, v. G1, 

p. 451–468.

Gehrels, G.E., Dickinson, W.R., Ross, G.M., Stewart, J.H., 

and Howell, D.G., 1994, Provenance of detrital zircons in 

strata of the Cordilleran miogeocline and selected outboard 

terranes: Geological Society of America Abstracts with 

Programs, v. 26, p. A384.

Gehrels, G.E., Dodds, C.J., and Campbell, R.B., 1986, 

Upper Triassic rocks of the Alexander terrane, SE Alaska, 

and the Saint Elias Mountains of B.C. and Yukon: Geological Society of America Abstracts with Programs, v. 

18, p. 109.

Gehrels, G.E., and Saleeby, J.B., 1987, Geologic framework, 

tectonic evolution, and displacement history of the Alexander terrane: Tectonics, v. 6, p. 151–173.

Gehrels, G.E., Saleeby, J.B., and Berg, H.C., 1987, Geology of 

Annette, Gravina, and Duke Islands, southeastern Alaska: 

Canadian Journal of Earth Sciences, v. 24, p. 866–881.

Gill, James, and Whelan, P., 1989, Early rifting of an oceanic 

island arc (Fiji) produced shoshonitic to tholeiitic basalts: 

Journal of Geophysical Research, v. 94, no. B4, p. 4561–

4578.

Goldfarb, R.J., Nelson, S.W., Berg, H.C., and Light, T.D., 

1987, Distribution of mineral deposits in the Pacific 

Border Ranges and Coast Mountains of the Alaska 

Cordillera, in Elliot, I.L., and Smee, B.W., eds., Geoexpo/86—Exploration in the North American Cordillera: 

Vancouver, B.C., Association of Exploration Geochemists, p. 19–41.

Goldfarb, R.J., Snee, L.W., Miller, L.D., and Newberry, R.J., 

1991, Rapid dewatering of the crust deduced from ages of 

mesothermal gold deposits: Nature, v. 354, p. 296–298.
References Cited 57

Goodfellow, W.D., Lydon, J.W., and Turner, R.J.W., 1993, 

Geology and genesis of stratiform sediment-hosted 

(SEDEX) zinc-lead-silver sulphide deposits, in Kirkham, 

R.V., Sinclair, W.D., Thorpe, R.I., and Duke, J.M., eds., 

Mineral deposit modelling: Geological Association of 

Canada, Special Paper 40, p. 201–251.

Green, Darwin, MacVeigh, J.G., Palmer, M., Watkinson, D.H., 

and Orchard, M.J., 2003, Stratigraphy and geochemistry of 

the RW Zone, a new discovery at the Glacier Creek VMS 

prospect, Palmer Property, Porcupine mining district, southeastern Alaska, in Clautice, K.H., and Davis, P.K., eds., 

Short notes on Alaska geology 2003: Alaska Division of 

Geological and Geophysical Surveys, Professional Report 

120, p. 35–51.

Grybeck, D.J., Berg, H.C., and Karl, S.M., 1984, Map and 

description of the mineral deposits in the Petersburg and 

eastern Port Alexander quadrangles, southeastern Alaska: 

U.S. Geological Survey Open-File Report 84–837, 87 p., 1 

sheet, scale 1:250,000.

Haeussler, P.J., Coe, R.S., and Onstott, T.C., 1992, Paleomagnetism of the Late Triassic Hound Island Volcanics—Revisited: 

Journal of Geophysical Research, v. 97, p. 19617–19639.

Haeussler, P.J., Karl, S.M., Mortensen, J.K., Layer, P., and Himmelberg, G.R., 1999, Permian and mid-Cretaceous deformation of the Alexander terrane on Admiralty and Kupreanof 

Islands, southeastern Alaska: Geological Society of America 

Abstracts with Programs, v. 31, no. 6, p. A–60.

Halbach, Peter, Pracejus, B., and Marten, A., 1993, Geology and 

mineralogy of massive sulfide ores from the central Okinawa 

trough, Japan: Economic Geology, v. 88, p. 2210–2225.

Hannington, M.D., Peter, J.M., and Scott, S.D., 1986, Gold in 

sea-floor polymetallic sulfide deposits: Economic Geology, 

v. 81, p. 1867–1883.

Hedenquist, J.W., and Henley, R.W., 1985, Hydrothermal eruptions in the Waiotapu geothermal system, New Zealand—

Their origin, associated breccias, and relation to precious 

metal mineralization: Economic Geology, v. 80, p.1640–1668.

Hillhouse, J.W., 1987, Accretion of southern Alaska, in Kent, 

D.V., and Krs, M., eds., Laurasian paleomagnetism and 

tectonics: Tectonophysics, v. 139, p. 107–122.

Hillhouse, J.W., and Gromme, C.S., 1984, Northward displacement and accretion of Wrangellia—New paleomagnetic evidence from Alaska: Journal of Geophysical 

Research, v. 89, p. 4461–4477.

Jenner, G.A., 1996, Trace element geochemistry of igneous 

rocks—Geochemical nomenclature and analytical geochemistry, in Wyman, D.A., ed., Trace element geochemistry of 

volcanic rocks—Applications for massive sulfide exploration: Geological Association of Canada, Short Course 

Notes, v. 12, p. 51–77.

Jenner, G.A., Longerich, H.P., Jackson, S.E., and Fryer, B.J., 

1990, ICP–MS—A powerful tool for high-precision traceelement analysis in earth sciences—Evidence from analysis 

of selected U.S.G.S. reference samples: Chemical Geology, 

v. 83, p. 133–148.

Jones, D.L., Silberling, N.J., and Hillhouse, J., 1977, Wrangellia—A displaced terrane in northwestern North America: 

Canadian Journal of Earth Sciences, v. 14, p. 2565–2577.

Karl, S.M., 1992, Map and table of mineral deposits on 

Annette Island, Alaska: U.S. Geological Survey Open-File 

Report 92–690, scale 1:63,360, 57 p.

Karl, S.M., Haeussler, P.J., and McCafferty, A., 1999a, Reconnaissance geologic map of the Duncan Canal/Zarembo 

Island area, southeastern Alaska: U.S. Geological Survey 

Open-File Report 99–168, 23 p.

Karl, S.M., Haeussler, P.J., Mortenson, J.K., Layer, P., Savage, 

N., Wardlaw, B., Harris, A., Murchey, B., and Blome, C., 

1999b, New stratigraphic and isotopic constraints on the 

depositional and deformational history of the Alexander terrane, southeastern Alaska: Geological Society of America 

Abstracts with Programs v. 31, no. 6, p. A–68.

Kerns, W.H., 1950, Investigation of Taylor Creek lead-zinc 

deposit, Kupreanof Island, Petersburg, Alaska: U.S. Bureau 

of Mines Report of Investigations 4669, 13 p.

Large, R.R., 1992, Australian VHMS deposits—Features, 

styles, models: Economic Geology, v. 87, p. 471–510.

Lathram, E.H., Pomeroy, J.S., Berg, H.C., and Loney, R.A., 

1965, Reconnaissance geology of Admiralty Island, Alaska: 

U.S. Geological Survey Bulletin 1181–R, 48 p.

Leach, D.L., and Sangster, D.F., 1993, Mississippi Valley-type 

lead-zinc deposits, in Kirkham, R.V., Sinclair, W.D., Thorpe, 

R.I., and Duke, J.M., eds., Mineral deposit modeling: Geological Association of Canada, Special Paper 40, p. 289–314.

Lentz, D.R., 1998, Petrogenetic evolution of felsic volcanic 

sequences associated with Phanerozoic volcanic-hosted 

massive sulphide systems—The role of extensional geodynamics: Ore Geology Reviews, v. 12, p. 289–327.

Loney, R.A., 1964, Stratigraphy and petrography of the PybusGambier area, Admiralty Island, Alaska: U.S. Geological 

Survey Bulletin 1178, 103 p.

Longerich, H.P., Jenner, G.A., Fryer, B.J., and Jackson, S.E., 

1990, Inductively coupled plasma-mass spectrometric 

analysis of geological samples—A critical evaluation based 

on case studies: Chemical Geology, v. 83, p. 105–118.

MacIntyre, D.G., 1986, The geochemistry of basalts hosting 

massive sulfide deposits, Alexander terrane northwest British Columbia: British Columbia Ministry of Energy, Mines, 

and Petroleum Resources, Geological Fieldwork, 1985, 

Paper 1986–1, p. 197–210.
58 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

MacIntyre, D.G., and Schroeter, T.G., 1985, Mineral occurrences in the Mt. Henry Clay area: British Columbia Ministry of Energy, Mines and Petroleum Resources, Geological 

Fieldwork, 1984, Paper 1985–1, p. 365–379.

Mahood, G.A., and Baker, D.R., 1986, Experimental 

constraints on depths of fractionation of mildly alkalic 

basalts and associated felsic rocks—Pantelleria, Strait of 

Sicily: Contributions to Mineralogy and Petrology, v. 93, 

p. 251–264.

McClelland, W.C., and Gehrels, G.E., 1990, Geology of the 

Duncan Canal shear zone—Evidence for Early to Middle 

Jurassic deformation of the Alexander terrane, southeastern 

Alaska: Geological Society of America Bulletin, v. 102, 

p. 1378–1392.

Meier, A.L., and Slowik, T., 2002, Chapter K, Rare earth elements by inductively coupled plasma-mass spectrometry, 

in Taggart, J.E., Jr., ed., Analytical methods for chemical 

analysis of geologic and other materials: U.S. Geological 

Survey Open-File Report 2002–223, 10 p.

Meschede, Martin, 1986, A method of discriminating 

between different types of mid-ocean ridge basalts and 

continental tholeiites with the Nb-Zr-Y diagram: Chemical 

Geology, v. 56, p. 207–218.

Mihalynuk, M.G., Smith, M.T., MacIntyre, D.G., and 

Deschenes, M., 1993, Tatshenshini project, northwestern 

British Columbia—Part B, Stratigraphic and magmatic 

setting of mineral occurrences: British Columbia Ministry 

of Energy, Mines and Petroleum Resources, Geological 

Fieldwork 1992, Paper 1993–1, p. 189–202.

Miller, L.D., Goldfarb, R.J., Gehrels, G.E., and Snee, L.W., 

1994, Genetic links among fluid cycling, vein formation, 

regional deformation, and plutonism in the Juneau gold belt, 

southeastern Alaska: Geology, v. 22, p. 203–206.

Muffler, L.J.P., 1967, Stratigraphy of the Keku Islets and 

neighbouring parts of Kuiu and Kupreanof Islands, southeastern Alaska: U.S. Geological Survey Bulletin 1241–C, 

52 p.

Newberry, R.J., and Brew, D.A., 1997, The Upper Triassic Greens Creek VMS (volcanogenic massive sulfide) 

deposit and Woewodski Island VMS prospects, southeastern 

Alaska—Chemical and isotopic data for rocks and ores 

demonstrate similarity of these deposits and their host rocks: 

U.S. Geological Survey Open-File Report 97–539, 49 p.

Newberry, R.J., and Brew, D.A., 1999, Chemical and isotopic 

data for rocks and ores from the Upper Triassic Greens 

Creek and Woewodski Island volcanogenic massive sulfide deposits, southeastern Alaska, in Kelley, K.D., ed., 

Geologic studies in Alaska by the U.S. Geological Survey, 

1997: U.S. Geological Survey Professional Paper 1614, 

p. 35–55.

Newberry, R.J., Crafford, T.C., Newkirk, S.R., Young, L.E., 

Nelson, S.W., and Duke, N.A., 1997, Volcanogenic massive 

sulfide deposits of Alaska, in Goldfarb, R.J., and Miller, 

L.E., eds., Mineral deposits of Alaska: Economic Geology 

Monograph 9, p. 120–150.

Panuska, B.C., 1990, An overlooked world class Triassic flood 

basalt event: Geological Society of America Abstracts with 

Programs, v. 22, p. A168.

Pearce, J.A., 1996, A user’s guide to basalt discrimination 

diagrams, in Wyman, D.A., ed., Trace element geochemistry of volcanic rocks—Applications for massive sulfide 

exploration: Geological Association of Canada, Short 

Course Notes, v. 12, p. 79–113.

Pearce, J.A., and Cann, J.R., 1973, Tectonic setting of 

basic volcanic rocks determined using trace element 

analyses: Earth and Planetary Science Letters, v. 19, 

p. 290–300.

Peter, J.M., and Scott, S.D., 1999, Windy Craggy, northwestern British Columbia—The world’s largest Besshitype deposit, in Barrie, C.T., and Hannington, M.D., eds., 

Volcanic-associated massive sulfide deposits—Processes 

and examples in modern and ancient settings: Society of 

Economic Geologists Reviews in Economic Geology, v. 8, 

p. 261–295.

Pin, Christian, and Paquette, J.-L., 1997, A mantle-derived 

bimodal suite in the Hercynian Belt—Nd isotope and trace 

element evidence for a subduction-related rift origin of the 

Late Devonian Brevenne metavolcanics, Massif Central 

(France): Contributions to Mineralogy and Petrology, v. 129, 

p. 222–238.

Race, W.H., 1963, Property examination report, Castle 

Island barite deposit, Duncan Canal, Alaska, Petersburg 

quadrangle: State of Alaska Division of Mines and Minerals, 13 p.

Richards, M.A., Jones, D.L., Duncan, R.A., and DePaolo, D.J., 

1991, A mantle plume initiation model for the Wrangellia 

flood basalt and other oceanic plateaus: Science, v. 254, 

p. 263–267.

Rollison, Hugh, 1993, Using geochemical data—Evaluation, 

presentation, interpretation: New York, Longman Scientific 

and Technical, 352 p.

Saleeby, J.B., 1994, Tectonic history of the Insular Suture 

Zone, southeastern Alaska: Geological Society of America 

Abstracts with Programs, v. 26, p. A384.

Sampson, S.D., McClelland, W.C., Patchett, P.J., Gehrels, 

G.E., and Anderson, R.G., 1989, Evidence from neodymium isotopes for mantle contributions to Phanerozoic crustal 

genesis in the Canadian Cordillera: Nature, v. 337, 

p. 705–709.
References Cited 59

Sampson, S.D., Patchett, P.J., Gehrels, G.E., and Anderson, 

R.G., 1990, Nd and Sr isotopic characterization of the 

Wrangellia terrane and implications for crustal growth of 

the Canadian Cordillera: Journal of Geology, v. 98, 

p. 749–762.

Sampson, S.D., Patchett, P.J., McClelland, W.C., and Gehrels, 

G.E., 1991, Nd and Sr isotopic constraints on the petrogenesis of the west side of the northern Coast Mountains batholith, Alaska and Canadian Cordillera: Canadian Journal of 

Earth Science, v. 28, p. 939–946.

Savage, N.M., 1994, Terrane affinities of Middle and Late 

Devonian conodonts from the Wadleigh limestone, southeastern Alaska: Geological Society of America Abstracts 

with Programs, v. 26, p. A158.

Slack, J.F., 1993, Descriptive and grade-tonnage models for 

Besshi-type massive sulphide deposits, in Kirkham, R.V., 

Sinclair, W.D., Thorpe, R.I., and Duke, J.M., eds., Mineral 

deposit modeling: Geological Association of Canada, Special Paper 40, p. 343–371.

Smith, I.E.M., Chappell, B.W., Ward, G.K., and Freeman, 

R.S., 1977, Peralkaline rhyolites associated with andesitic 

arcs of the southwest Pacific: Earth and Planetary Science 

Letters, v. 37, p. 230–236.

Smith, I.E.M., and Johnson, R.W., 1981, Contrasting rhyolite 

suites in the Late Cenozoic of Papua New Guinea: Journal 

of Geophysical Research, v. 86, no. B11, p. 10257–10272.

Stern, R.J., Lin, P.-N., Morris, J.D., Jackson, M.C., Fryer, P., 

Bloomer, S.H., and Ito, E., 1990, Enriched back-arc basin 

basalts from the northern Mariana Trough—Implications 

for the magmatic evolution of back-arc basins: Earth and 

Planetary Science Letters, v. 100, p. 210–225.

Stoffers, Peter, Hannington, M., Wright, I., Herzig, P., de 

Ronde, C., and Shipboard Scientific Party, 1999, Elemental 

mercury at submarine hydrothermal vents in the Bay of 

Plenty, Taupo volcanic zone, New Zealand: Geology, v. 27, 

p. 931–934.

Taggart, J.E., Jr., ed., 2002, Analytical methods for chemical 

analysis of geologic and other materials, U.S. Geological 

Survey Open-File Report 2002–223, variously paginated.

Taylor, C.D., 1993, Summary of geochemical data—Annette 

Islands Reserve, southeast Alaska, in Godwin, L.H., and 

Smith, B.D., eds.: Northwest Mining Association special 

symposium 1993 on economic mineral resources of the 

Annette Islands Reserve, Alaska, p. 77–82.

Taylor, C.D., 2003, Descriptions of mineral occurrences and 

interpretation of mineralized rock geochemical data in the 

Stikine geophysical survey area, southeastern Alaska: U.S. 

Geological Survey Open-File Report 2003–154, 51 p.

Taylor, C.D., Cieutat, B.A., and Miller, L.D., 1992, A followup geochemical survey of base metal anomalies in the Ward 

Creek/Windfall Harbor and Gambier Bay areas, Admiralty 

Island, S.E. Alaska, in Bradley, D.C., and Dusel-Bacon, 

C., eds., 1991 Geologic Studies in Alaska: U.S. Geological 

Survey Bulletin 2041, p. 70–85.

Taylor, C.D., Newkirk, S.R., Hall, T.E., Lear, K.G., Premo, 

W.R., Leventhal, J.S., Meier, A.L., Johnson, C.A., and 

Harris, A.G., 1999, The Greens Creek deposit, southeastern Alaska—A VMS-SEDEX hybrid, in Stanley, C.J., and 

others, eds., Mineral deposits—Processes to processing: 

Rotterdam, Balkema, p. 597–600.

Taylor, C.D., Premo, W.R., Meier, A.L., and Taggart, J.E., 

Jr., 2008, The metallogeny of Late Triassic rifting of the 

Alexander Terrane in southeastern Alaska and northwestern British Columbia: Economic Geology, v. 103, 

p. 89–115.

Van Nieuwenhuyse, R.E., 1984, Geology and geochemistry 

of the Pyrola massive sulfide deposit, Admiralty Island, 

Alaska: Tucson, University of Arizona, unpublished Master’s thesis, 170 p.

Warme, J.E., and Kuehner, H-C., 1998, Anatomy of an anomaly—The Devonian catastrophic Alamo impact breccia of 

southern Nevada, in Ernst, W.G., and Nelson, C.A., eds., 

Integrated earth and environmental evolution of the southwestern United States: Boulder, Colo., Geological Society 

of America, p. 80–110.

White, D.E., 1981, Active geothermal systems and hydrothermal ore deposits, in Skinner, B.J., ed., Economic geology—Seventy-fifth anniversary volume, 1905–1980: El 

Paso, The Economic Geology Publishing Company, 

p. 392–423.

Williams, J.A., and Decker, P.A., 1932, Exploring Castle 

Island barite deposit by diamond drilling, a compilation—

Unpublished report available from the Juneau office of the 

U.S. Bureau of Land Management, listing # MR 117–1, 

46 p.

Wilson, Marjorie, 1989, Igneous petrogenesis—A global 

tectonic approach: London, Unwin Hyman, 466 p.

Winchester, J.A., and Floyd, P.A., 1977, Geochemical discrimination of different magma series and their differentiation products using immobile elements: Chemical Geology, 

v. 20, p. 325–343.

Wood, D.A., 1980, The application of a Th-Hf-Ta diagram 

to problems of tectonomagmatic classification and to 

establishing the nature of crustal contamination of basaltic 

lavas of the British Tertiary Volcanic Province: Earth and 

Planetary Science Letters, v. 50, p. 11–30.

The History of Greens Creek Exploration

By Andrew W. West

Chapter 3 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract.........................................................................................................................................................65

Introduction...................................................................................................................................................65

Pan Sound Joint Venture, 1973–78............................................................................................................65

1975 Program..............................................................................................................................67

1976 Program..............................................................................................................................69

1977 Program..............................................................................................................................70

Initial Underground Development and Land Battles, 1978–80 .............................................................71

Driving of 1350 Drift....................................................................................................................72

Federal Proclamations..............................................................................................................72

1980 Exploration Program.........................................................................................................73

Race to “Perfect” Claims and Predevelopment, 1981–85.....................................................................73

1981 Exploration Program.........................................................................................................73

1982 Drill Program......................................................................................................................74

1983 Feasibility Study ................................................................................................................75

1983 Exploration Program.........................................................................................................75

1984 Exploration Program.........................................................................................................76

1985 Surface Exploration Program .........................................................................................77

Land Strategies and Negotiations, 1983–85 ............................................................................................78

Ownership Changes and Consolidation, Development, 1986–89.........................................................80

1986 Surface Exploration Program .........................................................................................80

1987 Surface Exploration Program .........................................................................................81

1988 and 1989 Surface Exploration Projects .........................................................................82

Continuing Underground Exploration, Production to Shutdown to Reopening, 1990–95.................82

1991 Exploration Program.........................................................................................................83

1992 Exploration Program.........................................................................................................83

1993 Closure..................................................................................................................................................84

1994 Exploration .........................................................................................................................84

Land Exchange Act and Continuing Production and Exploration, 1995–Present..............................85

1996 Exploration and Reopening .............................................................................................85

1997 Exploration .........................................................................................................................86

Discovery of the 200 South Ore Zone .....................................................................................86

1998 Exploration .........................................................................................................................87

1999 Exploration Program.........................................................................................................87

2000 Surface Exploration..........................................................................................................88

Conclusion.....................................................................................................................................................88

Reference Cited............................................................................................................................................88
Figures

1. Map of northern Admiralty Island showing the Greens Creek mine and other

localities discussed in the text.................................................................................................66

2. Ownership and exploration timeline........................................................................................68

3. Chart showing proven and probable reserves compared to total (cumulative)

production....................................................................................................................................79

Abstract

The exploration history of the Greens Creek mine and 

district includes not only battles fought on the steep and 

intimidating terrain of Admiralty Island, but also in Washington, D.C., and the Oval Office of the White House. The Greens 

Creek mine is unique in that it is completely enclosed within a 

national monument. The time period that began with the initial 

discovery, in 1974, of the “Big Sore” ore suboutcropping and 

ended with the underground definition drilling of the orebody, 

overlapped with the largest national conservation movement 

of this century that ultimately led to congressional approval of 

Alaska National Interest Land Claims Act (ANILCA) in 1980. 

Not only did this legislative act have a profound effect on the 

subsequent exploration of the district and eventual production 

of Greens Creek, ANILCA shaped the economic life of Alaska 

as a whole.

Introduction

The Greens Creek mine (fig. 1) went from initial discovery to predevelopment and production in a fairly orderly, 

yet untimely manner. The Pan-Sound Joint Venture (JV), 

charged with mineral exploration in southeast Alaska in 

1973, intersected ore in the very first “discovery” drill hole in 

1975. The timeline for the project, which is shown in figure 

2, demonstrates that despite nearly continuous exploration 

and(or) predevelopment work, production did not begin until 

February 1989. During this 16-year period, many changes 

occurred both within and between the joint venture partners. 

The conservation movement in the late 1970s also had a 

huge effect on the Greens Creek project, culminating in the 

passage of the Alaska National Interest Lands Conservation 

Act (ANILCA) in 1980. Exploration during the first years of 

production was successful in increasing reserves; however 

declining metal prices precipitated a shutdown of production in April 1993. Exploration and definition drilling of the 

higher grade Southwest Ore Zone from 1993 to 1994 resulted 

in a new feasibility study that was accepted by the joint 

venture partners, Kennecott Minerals and Hecla Mining. The 

mine reopened in 1996. National legislation reentered the 

picture when President Clinton signed the Land Exchange 

Bill in August of 1996. This unique piece of legislation 

allows for exploration and grants subsurface mineral rights 

to much of what was the original unpatented claim block that 

existed prior to ANILCA. The 7,301 acres of prospective 

ground allows Greens Creek to continue exploration activities aimed at increasing the life of the mine.

Pan Sound Joint Venture, 1973–78

The Pan Sound Joint Venture was formed in 1973 as a 

grass-roots exploration program to find base and(or) precious 

metal deposits in the northern part of southeast Alaska, the 

Prince William Sound area, and the Kenai Peninsula. The 

original partners were Noranda Exploration (29.73 percent), 

Marietta Resources (29.73 percent), Exhalas Resources 

(29.73 percent), and Texas Gas Exploration (10.81 percent). 

The rationale behind the exploration program in Alaska was 

fourfold: (1) exploration was risky in other parts of the world 

due to unfavorable politics; (2) exploration opportunities in 

the rest of North America were dwindling; (3) the geology 

of Alaska was seen as being highly favorable for economic 

deposits; and (4) the ongoing national energy crisis was 

underscoring the importance of a healthy domestic natural 

resource industry (L.M. Klingmueller and G.G. Bigelow, 

Watts, Griffis and McQuat, Inc., written commun., 1973). 

Watts, Griffis and McQuat (WGM) of Anchorage was contracted by the Pan Sound JV to carry out an extensive stream 

silt-sampling project in southeast Alaska. Their 1973 survey 

yielded anomalous zinc and copper stream silt samples collected from Cliff Creek (east of Big Sore Creek) and just 

southeast of Hawk Inlet (fig. 1). The sample from Cliff Creek 

contained 0.13 percent zinc and appeared to be associated 

with mineralized (disseminated pyrite and chalcopyrite) float 

from the Triassic Hyd basalt that forms the major cliff above 

Cliff Creek. Inclement weather prevented any followup work, 

but an intensive followup survey was recommended for the 

Cliff Creek drainage as well as first-pass coverage of the 

areas north and south of Greens Creek. WGM did not stake 

any claims in the Greens Creek area.

The History of Greens Creek Exploration1

By Andrew W. West

1

 Much of the information conveyed in this chapter was first documented in

memoranda or reports to Kennecott Greens Creek Mining Company or its antecedents. Because they are unavailable to the public, these documents are cited

in text only.
66 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

SOUTHEASTERN ALASKA

Mansfield Peninsula

Admiralty Island

Juneau

f .

Cascade

 Creek

- .

.

Killer Creek

Bruin Creek

Cub Creek

Gallagher Creek

Big Sore Creek

Cliff Creek

Greens Creek

CREW

FERRY

TERMINAL

HAWK

INLET

FACILITY

"A" Road

"B" Road

Tributary Creek

Mammoth

 Claim

EXPERIMENTAL

FOREST

Big

Sore

Big

Boil

NORTHERN

ADMIRALTY

ISLAND AND 

THE GREENS

CREEK MINE

YOUNG BAY

HAWK INLET

Mariposite Ridge

GREENS CREEK

MINE PORTAL

TONGASS

 NATIONAL

 FOREST

Gallagher Ridge

Lil Sore

East Lil

Sore

National Monument Boundary

Zinc

Creek

roadcut

Antenna

Mountain

High

Sore

Zinc

Creek

Pass

0 4,000 8,000 FEET

0 1,000 2,000 METERS

N

Area of

figure 1

ALASKA

National Monument

Wilderness Boundary

Lakes

District

Zinc Creek
Pan Sound Joint Venture, 1973–78 67

WGM geologists Bill “Boomer” Block and Joe Dreschler 

discovered the Greens Creek orebody in 1974 when they 

observed a large ferricrete kill zone from the air during the 

followup program (T.E. Andrews and others, Watts, Griffis and 

McQuat, Inc., written commun., 1975). Dubbed the “Big Sore,” 

this area (fig. 1) quickly became the focal point of exploration. 

A soil geochemistry grid laid out over the Big Sore delineated 

numerous silver-zinc anomalies on the order of 100 parts per 

million (ppm) silver and up to 1.7 percent zinc. WGM completed a Crone shootback electromagnetic (CEM) geophysical 

survey over 19,800 feet of gridline and a surface magnetometer 

survey totaling 12,500 feet. The CEM survey detected a partial 

conductor roughly coincident with soil anomalies. Two magnetic highs were identified in the lower reaches of Killer Creek. 

The WGM geologists postulated that the source of the CEM 

conductor was a mapped graphitic quartz-mica schist (T.E. 

Andrews and others, Watts, Griffis and McQuat, Inc., written 

commun., 1975). The magnetic anomalies were due to magnetite-bearing sulfide layers discovered in Killer Creek. A float 

sample believed to be from the same unit assayed for more than 

10 percent copper. These two items generated additional interest in Killer Creek. Most of the exposed mineralization found 

by WGM, other than the Big Sore itself, was from the Killer 

Creek area.

WGM staked 134 lode claims, named the Big Sore claims, 

to establish the land position. The claims stretched from the 

southeast corner of Cliff Creek across the Greens Creek valley 

to the northeast corner of Upper Zinc Creek. WGM suggested 

that the land on the north, east, and south sides also be staked. 

There was concern that the large claim block would attract 

attention from various competitors (T.E. Andrews and others, 

Watts, Griffis and McQuat, Inc., written commun., 1975). Until 

1974, very little competitor activity was noted for Admiralty Island except for a small backpack-supported survey of 

Northern Chicagof and Admiralty Islands by Placid Oil. Also, 

Resource Associates of Alaska (RAA) and Urangellschaft were 

exploring parts of Northern Admiralty Island.

The 1974 exploration results led WGM and the Pan 

Sound JV to believe that the “strongest reconnaissance 

potential for the discovery of a stratabound massive sulfide is 

considered to be within the Paleozoic schists located north and 

south of the Greens Creek discoveries on Admiralty Island” 

(T.E. Andrews and others, Watts, Griffis and McQuat, Inc., 

written commun., 1975). WGM recommended additional soil 

sampling, extension of the CEM survey, detailed geologic 

mapping, and diamond drill testing of the main Big Sore 

anomaly. They believed that the Big Sore and Killer Creek 

areas had the potential to host one or more copper-lead-zinc 

sulfide body(s) of unknown grade with greater than 1,000 feet 

of strike length.

1975 Program

The Big Sore project and a detailed reconnaissance of 

Admiralty Island were two of three projects that the 1975 Pan 

Sound JV undertook. The third project was followup work on 

a copper prospect of Latouche Island in Prince William Sound. 

The 1975 Big Sore project was the most ambitious thus far 

with more than 1,000 soil, rock, and stream silt samples taken; 

80,000 feet of CEM and magnetometer surveys; initial detailed 

geologic mapping; and trenching and blasting to outline drill 

targets. Diamond drilling also commenced with three holes 

completed before the end of the field season. The Big Sore 

project began on June 4 with a camp at Big Sore Creek. The 

project demobilized on September 20 when the drilling program finished.

Results from expanding the Big Sore soil grid led the 

WGM geologists to believe that the stratabound mineralization occurred along three to five stratigraphic horizons within 

Devonian units (T.E. Andrews and others, Watts, Griffis and 

McQuat, Inc., written commun., 1976). They believed that soil 

sampling was the best tool to establish drill targets because of 

the thick glacier till, the vegetation cover, and the difficulty in 

defining the stratigraphy. However, WGM did not associate 

the geochemical and electromagnetic (EM) signatures with a 

chlorite-carbonate-schist and graphitic schist contact (determined later to be the mineralized horizon).

The three completed diamond drill holes totaled 997 feet. 

The first drillhole, DDH–1 (later renamed PS–1), was drilled 

about 150 feet above the Big Sore to test the high-order soil 

anomaly and the coincident CEM anomaly. The “discovery” 

hole intersected 89 feet of continuous pyrite and base-metal 

massive sulfide beginning at 138 feet downhole. This hole 

remains the longest continuous intersection of massive sulfide mineralization drilled from the surface at Greens Creek. 

The interval averaged 0.123 troy ounce per ton gold, 5.77 troy 

ounces per ton silver, 2.04 percent lead, 8.03 percent zinc, and 

0.43 percent copper. A marked increase in pyrite and decrease in 

chlorite-muscovite near the massive sulfide interval was noted. 

The hole terminated at 296 feet in dolomitic graphite-quartzmica schist, with local bands of massive sulfide. Holes DDH–1 

and DDH–2 were both lost due to caving ground, a harbinger 

for drilling problems to come. Hole DDH–1 was not able to test 

the two lower targets identified from the soil sampling.

Hole DDH–2 (PS–2) was collared about 500 feet to the 

south-southeast of hole DDH–1, downhill from the graphite 

schist contact. The hole intersected graphitic schist with two 

massive sulfide bands containing 4.86 percent zinc and 4.3 

troy ounces per ton silver over 12 feet, and 6.32 percent zinc, 

7.2 troy ounces per ton silver, and 0.275 troy ounce per ton 

gold over 29.5 feet. The hole was lost due to poor ground conditions before it reached its target horizon. DDH–3 (PS–3) was 

collared 200 feet downhill from DDH–2 to test the previously 

untested lower soil anomaly. No visible base-metal sulfides 

were intersected to the termination depth of 635 feet, despite 

the presence of “fresh” massive sulfide float and high multielement soil values directly below the hole.

Figure 1 (facing page). Map of northern Admiralty Island 

showing the Greens Creek mine and other localities discussed in 

the text.
Pan Sound JV formed with Noranda, Marietta, Exhalas, and Texas Gas Expl. Greens Creek JV Noranda Exploration Co. Becomes operator Bristol Bay Native Corp. added Noranda Mining Co. becomes operator Anaconda buys out Marietta interests Big Sore discovered PS-1 intersects 80 ft of massive sulfide 1350 Adit driven and undergrou

and definition drilling begins Admiralty Island withdrawn and declared a national monument A

1973 1974 1975 1976 1977 1978 1979 1980 

Regional recon stream - sediment geochem sampling Surface drilling program and grid geochem sampling and geophysics

1991 1992 1993 1994 1995 1996 1997 

Aggressive surface drilling resumes to validateas many claims as possible

Bristol Bay bought out

Amselco (BP) buys out Anaconda and Noranda

Amselco sells portion to Hecla,

CSX aquires Texas Gas

Mine and mill construction begins

1990

(Cont.) Kennecott Minerals Companyis designated operator of the mineProduction continues with 

underground exploration and definition drilling

 Accelerated exploration and defintion drilling of Southwest and West orebodies during shut-down 

 Mine reopens at 1 district exploratio

West Ore discovered

Southwest Ore

discovered President Clinton signs

Land Exchange Act

20

Mine shuts down due d

to low metal prices

Exhalas bought out

CSX bought out

Current ownership: Kennecott 70.27%, Hecla (29.73%)

1982 1983 1984 1985 1986 1987 1988 

Exploration deadline is

extended one year

First feasibility study

is completed

Exploration deadlines passes

17 claims patented, rest become national monument
Pan Sound Joint Venture, 1973–78 69

Correlation of the above drill holes and soil anomalies 

led the WGM geologists to believe there were at least four, 

and maybe more, separate mineralized horizons to target (T.E. 

Andrews and others, Watts, Griffis and McQuat, Inc., written 

commun., 1976). DDH–3 displayed wildly fluctuating foliation orientations, but folding of the mineralized horizon was not 

considered. Using the drill-hole results and a tonnage factor of 

12, WGM estimated an inferred metal “inventory” of 2 to 20 

million tons of greater than 1.5 percent lead, 6.0 percent zinc, 

0.1 troy ounce per ton gold, and 6.0 troy ounces per ton silver 

(T.E. Andrews and others, Watts, Griffis and McQuat, Inc., 

written commun., 1976). WGM recommended an aggressive 

(>10,00-foot) drilling program to rapidly bring the Big Sore 

Prospect to a development decision. They believed that the 1976 

drilling program would place the inventory into “exploration” or 

“possible” reserves category, “barring unusual structural, facies 

complexity, or external factors” (T.E. Andrews and C. Bigelow, 

Watts, Griffis and McQuat, Inc., written commun., 1975).

Exploration work was also carried out in the Gallagher 

Creek, Killer Creek, and North Ridge (Mariposite Ridge) areas 

(fig. 1). Highlights include the discovery of massive sulfide 

float and outcrops in Gallagher Creek containing up to 31 

percent zinc and 2.1 troy ounces per ton silver (T.E. Andrews 

and C. Bigelow, Watts, Griffis and McQuat, Inc., written commun., 1976). The outcrops contain sulfide veins up to 2 inches 

wide over a mineralized interval approximately 100 feet thick. 

Various mineralization styles were described, sampled, and 

mapped from the North Ridge, mostly in the vicinity of the 

Mammoth claims (see next paragraph). “Impressive” values 

were returned for gold, silver, lead, and zinc. Preliminary sampling and mapping did not provide sufficient data to determine 

the structural or stratigraphic setting of the mineralization.

The land status was further enhanced surrounding the 

Big Sore prospect during 1975. An additional 150 claims 

were added to the Big Sore claim group in all directions. The 

claim block was extended to the north, overlapping the four 

patented Mammoth claims that were originally staked in 1889 

and patented in 1915. The overlapping claims were not to 

“jump” the existing claims but to ensure no area was left open 

between the two claim groups (fig. 1) (T.E. Andrews and C. 

Bigelow, Watts, Griffis and McQuat, Inc., written commun., 

1975). An abandoned adit exists on the Mammoth claim that 

was excavated about 1904 along a massive galena-sphalerite 

band. WGM suggested that the owner, Herman Meiners of 

Juneau, be approached to see if the property could be leased or 

bought outright before the increased activity at Greens Creek 

increased the asking price.

The separate reconnaissance program of Admiralty Island 

completed much of its work near Greens Creek. The Tom 

claims were staked (a total of 52) to the east of Hawk Inlet 

within the lower Greens Creek and Zinc Creek drainages (T.E. 

Andrews and C. Bigelow, Watts, Griffis and McQuat, Inc., 

written commun., 1976). WGM sampled Big Sore-type mineralization in graphitic quartz-mica schist, greenstones, and 

quartz-chlorite-carbonate schists with mariposite. In addition, 

work was done near ferricrete “sores” in a prospect named Kit 

Creek (now Lil Sore, fig. 1). The north-northwest-trending 

sores that contain up to 9,500 ppm zinc were postulated as 

representing a stratabound zinc sulfide body at moderate depth 

cut by permeable faults or fractures. No claims were staked 

during the field season because the land was nominated for 

Native Selection but was later withdrawn. Other prospects or 

claims explored included the Scull, Eagle Peak, and Jimbo to 

the northeast of Greens Creek, the Wheeler and Pyrola to the 

south and southwest of Greens Creek, and the JS and Barron 

on Mansfield Peninsula. As a result of the reconnaissance 

program, 472 new claims were staked on these new prospects. 

The Big Sore prospect was the standard with which the other 

prospects were compared, based on type of mineralization 

present and similar stratigraphy.

1976 Program

Noranda became the operator of the Big Sore program 

in 1976 for the Pan Sound JV. The program was composed 

of two projects again, one project concentrating on continued reconnaissance of Northern Admiralty Island, looking 

for other Greens Creek-type targets, while the other project 

continued exploration on the Big Sore and Tom claims. The 

principal objectives at Big Sore were to define the extent of 

the mineralized horizon intersected in DDH–1 and determine 

the geologic and geochemical nature of the mineralized zone 

(John Dunbier, Noranda Exploration, Inc., written commun., 

1976). A geochemical grid with CEM and magnetic surveys 

was oriented north to south along Gallagher and Killer Creeks. 

The existing grid system was reoriented to trend N. 30° W. 

and center the baseline on the discovery hole. Two drill rigs 

were used for the program. A Longyear-34 hydraulic drill rig 

operated by Diamond Drill Contractors completed the deeper 

holes. A much smaller Winkie drill, owned and operated by 

Noranda, drilled 1.197-inch-diameter (AQ) core to penetrate 

the overburden and determine the lithology of the bedrock in 

areas of no outcrop. An additional 400+ claims were staked to 

fill in the gap between the Tom and Big Sore claims.

The diamond drilling program was successful in extending the known mineralized zone to the south-southeast, 

north-northwest, and slightly downdip (John Dunbier, Noranda 

Exploration, Inc., written commun., 1976). Three of the five 

holes drilled with the Longyear-34 intersected low- to highgrade ore along the contact between sericite-quartz phyllite 

(identified as “tuffites”) and the graphitic schist unit. The other 

two holes intersected minor mineralization in the tuffites (the 

hanging wall). Hole PS–3–76 intersected 11 feet of 0.042 troy 

ounce per ton gold, 22.7 troy ounces per ton silver, 5.9 percent 

lead, and 14.6 percent zinc to extend the known mineralized 

zone about 300 feet to the south-southeast of the discovery 

hole. PS–4–76 intersected a lower grade, yet thicker 12-foot 

Figure 2 (facing page). Ownership (blue) and exploration (red) 

timeline.
70 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

interval grading 9.9 troy ounces per ton silver and 3.45 percent 

zinc about 320 feet to the north-northwest. PS–7–76 extended 

the envelope even farther to the north-northwest (600 feet) 

with a 6-foot intercept of 29.3 troy ounces per ton silver and 

only 1.7 percent zinc.

The Winkie drill program consisted of eight holes. 

Only two of the holes intersected mineralization within the 

hanging-wall rocks while testing soil anomalies to the northwest of PS–1. One hole, PSW–4, was later followed up by 

hole PS–7–76 (mentioned previously). Two of the holes were 

unable to penetrate the overburden. Two large-diameter holes 

and one Winkie drill hole were drilled in Gallagher Creek. 

PS–1–76 and PS–2–76 intersected only minor mineralization 

of up to 4.4 percent zinc over 5 feet.

Noranda Exploration initiated a geologic mapping project 

carried out by one of their geologists, M.D. Bingham. Noranda 

anticipated taking a more active role in the Big Sore prospect 

and wanted to gain firsthand familiarity of the project (M.D. 

Bingham, Noranda Exploration, Inc., written commun., 1977). 

His mapping outlined three units favorable for massive sulfide 

mineralization: the chlorite-carbonate schist, a quartz carbonate (sericitic phyllite), and a quartz graphite schist (differentiated from the graphitic schist unit intersected immediately 

below the ore horizon in DDH–1).

Noranda attempted to better define and describe the 

lithologic units, geological and structural setting, and mineralization style of the Big Sore deposit in the 1976 year-end 

report. The hanging wall was described as chlorite and sericitic tuffites representing volcaniclastics of a mafic to felsic 

cycle. The footwall rocks were described as epiclastic perigenic conglomerates and carbonaceous argillites (formerly the 

graphitic schist unit). The pyritic and high-sphalerite ore zones 

and carbonaceous cherts were classified as exhalative rocks. 

Essentially, Noranda was trying to pigeonhole Greens Creek 

into a Kuroko-type deposit. All of the lithologic units were 

interpreted as grading into one another. Noranda estimated that 

the mineralized zone contained ±0.5 million tons of ore (John 

Dunbier, Noranda Exploration, Inc., written commun., 1976).

An effort was made to determine the age of the described 

units. Despite the lack of any fossil control or unambiguous 

small-scale sedimentary structure (that is, graded bedding), 

Noranda correctly believed that the section was inverted 

(Noranda Exploration, Inc., written commun., 1977). The 

circumstantial evidence cited was the observed mafic to felsic 

volcanic cycle (incorrect), volcanic to sedimentary cycle, 

paleorelief features, and lithological and geochemical zonation 

within the exhalites similar to Kuroko-type deposits.

Structurally they observed that minor folds were very 

common, but no tight or isoclinal folds were found except 

within the carbonaceous argillites. The rare appearance of fault 

gouge, tectonic breccias, and slickensides did not allow for 

any major faults to be identified in the drill sections. However, 

evidence for intense deformation was described between the 

mineralized zone and footwall argillites, thought to be the 

result of adjustments induced by flexuring of units due to a 

major recumbent fold.

Noranda envisioned the Big Sore deposit as occurring in 

a predominantly sedimentary basin associated with a nearby 

mafic to felsic volcanic system. The quiescent submarine 

environment received ash but no intrusive or extrusive rocks 

from the volcanic system. The volcanic system did, however, 

give rise to hydrothermal systems and possible explosive 

exhalations (as evidenced by the conglomerates near the ore 

interface). Brines from the hydrothermal system settled into 

depressions and precipitated chemical sediments (sulfides, 

cherts, and carbonates). Noranda compared Greens Creek to 

“artesian” exhalative deposits similar to Iron King in Arizona, 

Faro in the Yukon, and Sullivan and Rosebury in Tasmania 

(Noranda Exploration, Inc., written commun., 1977). These 

geologic observations and deductions formed the working 

geologic framework for exploration work at Greens Creek and 

Northern Admiralty Island for the next 10 years.

1977 Program

The 1977 exploration program in the Greens Creek area 

included two projects; the Big Sore drilling program was the 

primary project, and detailed exploration of Mariposite Ridge, 

Gallagher, Killer, and Zinc Creeks was the other project. 

Noranda continued as the operator of both programs. Surface 

drilling included 22 holes totaling 8,810 feet, primarily along 

the Big Sore mineralization trend, but also in Gallagher and 

Killer Creeks. Soil grids were extended or established for 

all the prospects/areas mentioned herein. The second project 

was the most ambitious for the area surrounding the Big Sore 

prospect to date, and remained so until the passage of the Land 

Exchange Act spurred the exploration programs of 1996 to 

1999.

Surface geologic mapping to the south and southwest 

outlined the carbonaceous argillite unit as wrapping around 

the tuffite units. The argillite unit was believed to be the upper 

limb of an overturned fold (John Dunbier, Noranda Exploration, Inc., written commun., 1977). A new soil grid of five 

lines oriented at N. 60° E.–S. 60° W. was emplaced over the 

upper limb contact zone. The soil anomalies generated were 

more erratic than those of the overturned limb, but local silver 

and zinc anomalous zones along the contact were delineated. 

A CEM geophysical survey delineated the argillite unit but did 

not generate any drill targets.

The 1977 drill program at Big Sore was a success in 

extending the known mineralized zone along strike and downdip. Eight diamond drill holes were drilled, totaling 4,446 feet, 

plus 1,415 feet of Hydra-Wink drilling. PS–4–77 (PS–23) 

intersected a 75-foot section that averaged 12.6 troy ounces 

per ton silver with a 3-foot high-grade section of 92.2 troy 

ounces per ton silver. This hole was located 900 feet to the 

southeast of PS–1. In addition, PS–5–77 (PS–28) intersected 

6.5 feet of mineralized material about 300 feet downdip from 

PS–4–77. The mineralized zone was extended another 800 to 

1,000 feet northwest of PS–6–76 by holes PS–6–77 (8.1 feet 

of 17 percent zinc and 12.25 troy ounces per ton silver) and 

PS–W1–77 (28 feet of 18.2 percent lead, 32.75 percent zinc, 
Initial Underground Development and Land Battles, 1978–80 71

and 10.2 troy ounces per ton silver). PS–8–77 (PS–27) intersected 20 feet of ore 300 feet downdip from PS–3–76.

The total strike length of mineralized rock along the 

overturned limb now totaled 3,500 feet and was open on both 

ends (Noranda Exploration, Inc., written commun., 1977). 

However, future surface drilling did not extend the mineralized 

zone farther along strike in either direction. The mineralized 

interval also extended at least 500 feet downdip on many of 

the sections tested. The Noranda geologist (Dunbier) realized 

that the main mineralized zone was at the lithologic contact 

between the argillites and tuffites. The calculated, geologically indicated resource was 2.1 million tons with an NSR (net 

smelter return) value of about $90/ton (John Dunbier, Noranda 

Exploration, Inc., written commun., 1977).

Dunbier’s recommendation for 1978 was to verify the 

geologically indicated resource with an underground drill program augmented with Hydra-Wink drilling from the surface. 

Drill hole PS–W1–77 showed that the Winkie drill was capable 

of piercing the overburden and the mineralized zone. The current 300-foot drill spacing was considered inadequate for ore 

reserve calculations, and it was recommended that the underground holes be drilled at regular spacings between the surface 

holes. Additional reserves could be added by downdip testing 

of the mineralized zone, drilling along strike to the south-southeast, and surface exploration of the upper limb contact (John 

Dunbier, Noranda Exploration, Inc., written commun., 1977).

Exploration continued within the Gallagher Creek prospect to follow up on the previous CEM and geochemical soil 

surveys and to test the massive sulfide outcrops and float. The 

Noranda geologists thought the rocks in Gallagher Creek were 

part of the upper (upright) limb of the Big Sore fold (Noranda 

Exploration, Inc., written commun., 1977). One Hydra-Wink 

hole was drilled on the west side of the creek and intersected 

weakly mineralized tuffites with one 5-foot zone of 10.2 

percent zinc. The contrasting sections intersected by this hole 

and the two 1976 drill holes led them to believe that a fold or 

shear (later to be mapped as the Gallagher fault, a significant 

right-lateral fault) ran along Gallagher Creek.

Killer Creek was also extensively explored in 1977. The 

1976 Gallagher–Killer Creek soil grid was extended, and a 

new grid with a baseline oriented southeast-northwest was 

surveyed in middle Killer Creek. The new Killer Creek grid 

generated 16 primary soil anomalies. Noranda identified three 

types of mineralization associated with the anomalies, which 

were tested by drilling. PS–77–1 (PS–20) tested below surface 

exposures of stringers, veins, and clots of coarse sphalerite 

with pyrite, magnetite, galena, and chalcopyrite within a talcserpentine-chlorite-carbonate rock. No significant mineralized rock was intersected. A stratiform massive chalcopyrite, 

pyrite, and pyrrhotite band within greenstone in Upper Killer 

Creek was tested by two Hydra-Winkie holes, PS–W4 and 

PS–W5–77 (PS 32 and PS–33). Both holes intersected copperbearing mineralized rock with grades up to 2.3 percent. Two 

other holes were attempted in lower Killer Creek to test stratiform sphalerite-galena sulfide bands, but the attempts failed to 

drill through the thick glacier till overburden.

Noranda recognized the Killer Creek sequence of rocks 

as distinct lithologies from Big Sore, consisting mostly of 

andesites, andesitic tuffs, and three types of serpentinites 

(one described as being a magnesium-rich exhalite)(Noranda 

Exploration, Inc., written commun., 1977). Noranda envisioned Killer Creek as a tectonic hinge zone, next to a subsiding sedimentary basin (Big Sore and Gallagher prospects), 

with active faulting, mafic volcanism, and associated exhalative activity. Noranda looked favorably upon the results and 

estimated that Killer Creek had the potential for 1–3 highgrade (greater than 10 percent zinc) deposits of more than 

50,000 tons, at least one deposit of 2–5 percent zinc greater 

than one million tons, and one to three 1.5 percent copper 

deposits of greater than 100,000 tons.

Soil surveys, CEM and magnetic geophysical surveys, 

and geologic mapping were also carried out on the Zinc Creek 

and Mariposite Ridge prospects. The results from Zinc Creek 

were not encouraging: only weakly anomalous soil samples 

(as compared to Big Sore and Killer Creek grids) and no finite 

geophysical anomalies. On the other hand, the Mariposite grid 

generated nine soil anomalies associated with vein, disseminated stratiform, and massive stratiform lead-zinc mineralization within, or along the contacts of, the mariposite-carbonate 

unit. The Noranda geologists believed this unit was a metacarbonate (Noranda Exploration, Inc., written commun., 1977). 

Noranda suggested that the joint venture attempt to purchase 

the Mammoth claims not only for its mineral potential, but 

because its “main value would be as bargaining chips during 

land negotiations with federal bureaucrats” (Noranda Exploration, Inc., written commun., 1977).

The 1977 exploration program identified many targets 

and prospective areas outside the immediate Big Sore prospect and recommended continued work, including drilling at 

Gallagher and Killer Creeks and Mariposite Ridge. However, 

the urgency of proving-up the Big Sore deposit and events 

in Washington, D.C., worked against any further work until 

1982.

Initial Underground Development and 

Land Battles, 1978–80

The Pan Sound Joint Venture was dissolved in 1978 and 

the Greens Creek Joint Venture formed in its place. The Pan 

Sound Joint Venture was redrafted in part due to the addition of Bristol Bay Native Corporation. The members of the 

Greens Creek Joint Venture decided in January of 1978 to 

begin underground diamond drilling and initiate an environmental baseline study after carefully analyzing the political, 

environmental, geological, and economic aspects of the project 

(Ernest Simmons, memorandum to W.W. Holmes, 1978). The 

Greens Creek Joint Venture agreed to a plan to drive a 4,200-

foot drift from which to drill about 30,000 feet of core. The 

environmental baseline study began April 1 and was carried 

out by VTN Consulting.
72 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

The project’s first legal battle came on May 2, 1978. 

The Southeast Alaska Conservation Council (SEACC), with 

the legal aid of the Sierra Club, appealed the Regional Forest Supervisor’s decision to approve the exploration operation plan. They believed that public involvement was not 

adequately sought in the process. They cited the overwhelming opposition to the planned ferry dock on the north side of 

Douglas Island and the public’s overall negative sentiment 

toward Noranda (Ernest Simmons, memorandum to W.W. Holmes, 1978). SEACC was also concerned with recent turbidity 

measurements in Greens Creek that violated USDA Forest 

Service regulations. Their appeal was denied by the Regional 

Forest Supervisor on grounds that public involvement is not 

necessary for an exploration plan and that Noranda was taking 

the proper steps to mitigate the turbidity exceedances caused 

by heavy rains.

Driving of 1350 Drift

Noranda contracted the Mining Company of Denver, 

Colorado, to drive an exploration drift (1350 Drift) at the 

1,350-foot elevation mark. Glacial overburden was removed 

from the portal site by July 13, 1978, and the initial bench 

round was drilled out on July 14 (Ernest Simmons, memorandum to W.W. Holmes, 1978). By the end of the year, 1,667 

feet of drift had been driven, including drill station cutouts 

at 150-foot spacings. Work continued through the winter and 

spring months (with a 45-day weather shutdown in February 

and March) in an effort to complete the 1350 Drift (T.A. Butler, memorandum to S. Nakata, 1979). The drift was finished 

in November 1979. A total of 4,190 feet of drifting with a 

219-foot rise was completed along with 24 diamond drill stations, assorted sumps, and an underground shop. All work was 

completed using helicopter support and a camp located just 

below the portal. The total cost for the 1978–79 drifting and 

drill program was $5.05 million (Noranda Exploration, Inc., 

written commun., 1980).

The initial underground drilling program began in October 1978 and finished in December 1979. Drilling took place 

on an intermittent basis as new drill stations were cut, and 

water and power became available from the drifting program. 

Fifty holes (GC–1 to GC–50) were drilled during this period, 

totaling 20,240 feet (Noranda Exploration, Inc., written commun., 1980). Most of the drill stations (14 out of 24) were 

drilled out to help confirm the 2,750 feet of strike length of 

mineralized rock. The fifty drill holes encountered 59 ore 

intercepts. Noranda estimated the drill indicated reserves to be 

about 3 million tons with an approximate grade of 10–16 troy 

ounces per ton silver, 0.1 troy ounce per ton gold, 7–10 percent zinc, 2–2.5 percent lead, and 0.5 percent copper. The ore 

zone was still believed to be open downdip and along strike to 

the southeast (Noranda Exploration, Inc., written commun., 

1980).

Noranda performed a base cash-flow model for Greens 

Creek to estimate the economics of the project. The order of 

magnitude estimates indicated that the project had a DCF–ROR 

(discounted cash flow – rate of return) of 39.3 percent, NPV 

(net profit value) of $22.6 million, with payback in 1.8 years 

(Noranda Exploration, Inc., written commun., 1980). Assumptions and criteria used for the estimate included metal prices 

at $300 per troy ounce gold and $10 per troy ounce silver, a 

production rate of 800 tons per day (TPD), $18.4 million in 

preproduction costs, $65 per ton operating costs, and 15.75-

year mine life. However, Noranda concluded that “Political 

imponderables far exceed the technical unknowns insofar as the 

Greens Creek project is concerned” (Noranda Exploration, Inc., 

written commun., 1980).

The land status of the Greens Creek property changed 

greatly during the underground drifting and drilling program. 

Nineteen Big Sore claims were surveyed for patent in July and 

submitted to the Cadastral Survey Office in April 1979 (T.A. 

Butler, memorandum to S. Nakata, 1979). The Greens Creek 

Joint Venture employed the law firm of Pruitt and Gushee of 

Salt Lake City to aid in the intricate patenting process. An 

additional 27 lode claims were staked during 1978: 23 to the 

south of the Big Sore group to cover the downdip projection 

of the current orebody, three on the southwest to cover an area 

dubbed the “football field” that was a potential tailings site, 

and one to cover an open area that developed as a result of 

the patent survey. A total of 136 mill-site claims were staked 

to the south and east of the Hawk Inlet Cannery site between 

November 27 and December 1. The latter date, December 1, 

proved to be a very fateful day that would change the whole 

scope of the project and have repercussions throughout the 

entire State of Alaska.

Federal Proclamations

Federal land-management policy in Alaska was one 

of the hotly debated topics during the 95th Session of the 

United States Congress. The Alaska Native Claims Settlement Act (ANCSA) of 1971 provided an 8-year time limit 

for Federal action on protecting or otherwise designating 

use of “special national interest lands” that up to 1978 were 

termed “d-2” lands. The largest conservation lobby ever 

assembled along with politicians like Congressman Morris Udall and Secretary of the Interior Cecil Andrus were 

concerned with the fast-approaching 8-year deadline of 

December 18, 1978 (Nash, 1982). They were worried that if 

no protective action were taken, there would be a huge “land 

grab” by mining companies and other developers within 

pristine parts of Alaska. They felt once the deadline was 

passed, State, Native, and private parties would be able to 

stake claims on Federal land, which constituted 99 percent of 

Alaska. If this happened, they reasoned it would be hopelessly complicated to establish any new national parks or 

wilderness areas. Bill HR–39, which would have protected 

92 million acres of Federal land in Alaska, passed through 

the House of Representatives by a wide margin. However, 

Alaska Senator Mike Gravel’s threatened filibuster of any 

bill that withdrew or placed restrictions on Federal land in 

Alaska stalled the bill in the Senate (Nash, 1982).
Race to “Perfect” Claims and Predevelopment, 1981–85 73

The Carter administration took action once it was evident 

that Congress was not going to pass any Alaska land bill by 

the end of the congressional session. Interior Secretary Andrus 

withdrew 110 million acres of Federal lands in Alaska from 

all forms of development for 3 years on November 16. He 

used the 1976 Federal Land Policy and Management Act to 

authorize this action. This act was controversial, and many 

thought it to be unfair since it was made before the close of the 

comment period (November 20) on the draft Environmental 

Supplement (T.E. Butler, written commun., 1978). The Environmental Supplement was to document, in part, the impact 

on Alaska citizens of the closing to development of land in 

Alaska. The lands withdrawn included most of Admiralty 

Island, including Greens Creek.

The big move came on December 1, 1978, when President Jimmy Carter declared 56 million acres of Federal land, 

including most of Admiralty Island, as national monuments 

under the authority of the 1906 Antiquities Act, which was 

designed to protect places of historical interest. Never before 

had the act been used on such a colossal scale (Nash, 1982). 

This move was applauded by the numerous conservation and 

environmental organizations and by the American public in 

general. Most Alaskans reacted with shock and outrage. The 

national monument status still had to be approved by Congress, giving the Greens Creek Joint Venture time to formulate 

a strategy to lobby Congress.

Immediately the land position of the Greens Creek Joint 

Venture was in jeopardy. The Greens Creek Joint Venture 

felt that their prior existing rights to the claims would be 

honored (T.E. Butler, memorandum to S. Nakata, 1979). 

However, there was a question as to whether a mine could be 

established within a designated monument, since there was 

no legal precedent. The 1979 Minerals Availability System 

Deposit Summary Report by the Bureau of Mines listed the 

land environmental factor as “prohibitive” until the status is 

legislatively determined in court (T.E. Butler, memorandum to 

S. Nakata, 1979). Claims could no longer be staked, nor could 

any surface construction activities not already approved under 

the 1978 Exploration Work Plan take place until the USDA 

Forest Service validated those claims. Considerable energy 

and resources were expended during the next 2 years to gain 

legislative relief from the Carter administration decision.

The next 2 years saw extensive lobbying by both sides. 

Noranda and the Joint Venture partners were actively lobbying Congress for a less restrictive designation for the Greens 

Creek drainage. One such group that the JV helped fund was 

the Citizens for Management of Alaska Lands (T.E. Butler, 

memorandum to S. Nakata, 1979). On the other side of the 

fence was the Alaska Coalition made up of the Nation’s five 

leading conservation groups (Sierra Club, Wilderness Society, 

the National Audubon Society, Friends of the Earth, and the 

National Parks and Conservation Association), the largest and 

most powerful conservation group ever assembled in American history (Nash, 1982). The House passed Bill HR–39 in 

May of 1980, which would have recognized the Greens Creek 

deposit but would have surrounded it with land designated 

as wilderness. The Senate passed a much less restrictive bill 

(S–9) sponsored by Alaska Senator Ted Stevens that excluded 

Greens Creek from the national monument. House leaders initially did not wish to compromise on their bill, but on November 4 Ronald Reagan was elected president and they realized 

they had only a small window of opportunity left to pass a bill 

that would not be vetoed (Nash, 1982). The compromised bill 

was named the Alaska National Interest Land Conservation 

Act (ANILCA).

President Carter signed ANILCA into law on December 

2, 1980. The act set aside 104 million acres of Federal land in 

Alaska for permanent protection. The Greens Creek deposit 

was included in the newly created Admiralty Island National 

Monument but was excluded from wilderness classification. 

It was decided legislatively that the Greens Creek project 

should proceed. Section 504 of ANILCA allowed for exploration on previously located, unpatented claims that fell within 

three-quarters of a mile of a valid mineral discovery. However, 

exploration would have to cease in 5 years and any claims not 

“perfected” would revert to national monument status. Thus 

the Joint Venture had until December 2, 1985, to perfect any 

of the 127 claims that fell within the 0.75-mile radius.

1980 Exploration Program

Exploration work was limited while the above political 

and legislative battles took place. Restrictions were placed 

on surface activities, and the previously approved plan of 

operation was only valid until May 31, 1980. Resources were 

directed toward finishing the environmental impact statement 

(EIS), which was taken over by International Environmental 

Consultants. Thirty-three drill holes (GC–51 to GC–83) were 

completed by the end of March (Noranda Mining, Inc., written 

commun., 1981). Another 35 feet of drifting intersected the 

footwall argillite at the south end of the 1350 exploration drift. 

An important milestone in 1980 was the USDA Forest Service 

Mineral Examiner’s report that recognized valid discoveries 

on seven Big Sore claims (Noranda Exploration, Inc., and 

Noranda Mining, Inc., written commun., 1981). These seven 

claims formed the core claims with surface and subsurface 

rights.

Race to “Perfect” Claims and 

Predevelopment, 1981–85

1981 Exploration Program

With the political situation clarified by the passage of 

ANILCA, the Greens Creek Joint Venture members approved 

the appointment of Noranda Mining, Inc., as the operator, 

replacing Noranda Exploration. This change emphasized the 

point that Greens Creek was passing from the exploration 
74 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

stage to development. Much of the activity in 1981 reflected 

this change in status. The primary emphasis was on environmental and engineering studies of various components of the 

project. The various projects completed included road alignment surveys from Young Bay to the Hawk Inlet Cannery, 

drilling and geophysical investigations of the tailings site 

near the cannery, and boat transportation study. The draft EIS 

was completed by December (Noranda Exploration, Inc., and 

Noranda Mining, Inc., written commun., 1981).

No surface exploration work was documented for the 

1981 summer season. Despite the fact that the clock was 

already ticking on the 5-year exploration limit, Noranda chose 

to work on development issues. The USDA Forest Service 

approved the exploration permit in April; thus, the permit was 

not the limiting factor for exploration. Noranda lost one valuable season for perfecting claims as they pursued other studies 

of the project.

Underground development continued in 1981. A 424-

foot crosscut was driven from the 1350 adit to expose the ore 

zone. The drifting continued along the ore to the north and 

south for a distance of 176 feet (Noranda Mining, Inc., written 

commun., 1981). This provided material for a 4,200-pound 

bulk sample for metallurgical bench flotation tests in Salt Lake 

City. The first exposure of the ore zone in three dimensions 

provided a “quantum leap” in the knowledge of the deposit 

(Noranda Mining, Inc., written commun., 1981). The exposure 

helped to confirm that three types of ore (Massive, White, 

and Black) were present and relatively lithologically discrete 

from each other. Vein mineralization, especially with regard 

to precious metal upgrading, was found to be more prevalent 

than thought from data obtained from the diamond drill core. 

Coarse visible gold was intersected in several areas. Overall, 

the Noranda geologists believed that the original reserve and 

grade estimates were too conservative based on the precious 

metals intersected and the inability of the LHDs (load, haul, 

dump equipment) to carry a full bucket of ore (Noranda 

Exploration, Inc., and Noranda Mining, Inc., written commun., 

1981). A tonnage factor of 9 cubic feet per ton was more 

realistic than the original estimate of 11 cubic feet per ton. 

The crosscut also exposed ubiquitous intermediate scale folds 

(25–75-foot wavelengths) oriented normal to the interpolated 

large-scale folds that would have great implications for mining 

methods and grade, tonnage, and dilution estimates.

More legal difficulties arose in 1981. The Southeast 

Alaska Conservation Council (SEACC) and the Sierra Club 

challenged the USDA Forest Service’s granting of the exploration permit for a second time. They appealed the granting of 

the exploration permit to the Chief Forester on the basis that 

the original claims were not valid as of December 1, 1978 

(Noranda Exploration, Inc., and Noranda Mining, Inc., written 

commun., 1981). They argued that the Greens Creek deposit 

did not pass the marketability test, and no reclamation costs 

were included in the study. The Regional and Chief Foresters sustained the previous decisions, stating that the mineral 

inspector used the correct criteria for determining that the 

seven core claims contained valid mineral discoveries.

1982 Drill Program

Noranda shifted emphasis back to surface exploration and 

drilling in 1982. The goal was to validate unperfected claims 

and add to the total mineral inventory. Noranda Exploration, 

Inc., led by Joe Drechsler, was contracted by Noranda Mining, 

Inc., to manage the program (J.S. Drechsler, Jr., and others, 

Noranda Mining, Inc., written commun., 1982). Noranda 

drilled 12 holes totaling 11,210 feet during the summer field 

season. Nine of those holes were in the Big Sore area, two in 

Gallagher Creek, and one in Bruin Creek, on the north side of 

Greens Creek.

The Big Sore drilling program successfully intersected 

discoveries on unperfected claims. Three holes were drilled 

to test the northwest strike extension of the orebody on claims 

1107 and 1108. All three intersected only minor mineralization, and the lack of chert buildup (siliceous alteration) along 

the argillite/phyllite contact suggested that the ore pinches out 

to the north (J.S. Drechsler, Jr., and others, Noranda Mining, 

Inc., written commun., 1982). On the south side of the orebody, 

only argillite was contacted in hole GC–82–9 (PS–50) targeting claim block 901. Holes GC–82–2 (PS–43) and GC–82–7 

(PS–48) tested the downdip extent of the argillite/phyllite 

contact. Both holes intersected thin (4-foot) ore intercepts 

with high-grade silver up to 26.7 troy ounces per ton. The 

ore intercepts in these two holes were at a higher level (about 

500 feet) than expected from projections from previous holes, 

indicating flattening of the ore horizon due to folding or faulting. Holes GC–82–8 and GC–82–10 (PS–49 and PS–51) were 

drilled from claim 1106. GC–82–8 intersected 12 feet of 26.7 

troy ounces per ton silver and 11.93 percent zinc. The other 

hole intersected a barren contact. The final hole of the season, 

GC–82–12 drilled from claim 1107, intersected a 6-foot 

interval of argillite running 6.22 troy ounces per ton silver, 3.75 

percent lead, and 4.10 percent zinc. Noranda did not make clear 

in the yearly report which of these intersections would qualify 

for discovery and claim validation.

The two holes in Gallagher Creek attempted to better 

outline the mineralization present there from intercepts from 

the 1976–77 drilling program and test for Greens Creek-type 

stratigraphy. Drill hole GC–82–5 ( PS–46) was successful in 

intersecting 15 feet of high-grade zinc mineralization (10.22 

percent). The hole was located on claim 1304 at the western edge of the 0.75-mile limit. The other hole, GC–82–11 

(PS–52) located farther south, intersected minor zinc enrichment. The Bruin Creek hole GC–82–6 (PS–47) was drilled 

on claim 1213 and intersected several 3–5 foot sections of 

chert-carbonate rock containing up to 1 percent zinc. However, Noranda did not view the results as being favorable for 

discovering any significant sulfide occurrences in the area (J.S. 

Drechsler, Jr., and others, Noranda Mining, Inc., written commun., 1982).

Noranda still saw Greens Creek as being open along 

strike to the northwest and downdip, with the potential of 

another 2–5 million tons of ore (J.S. Drechsler, Jr., and others, 

Noranda Mining, Inc., written commun., 1982). Noranda felt 
Race to “Perfect” Claims and Predevelopment, 1981–85 75

that five of the holes drilled on unperfected claims intersected 

mineralization of sufficient quality and quantity to be considered “discoveries.” However, section 504(e)(1) of ANILCA 

left some doubt as to what constituted a valid discovery; 

whether the standards applied would be those of the USDA 

Forest Service Mineral Examiners or the stricter Bureau of 

Land Management (BLM) requirements for issuance of a patent (which appeared to be how the section was worded) was 

unclear. An unofficial draft of the Mineral Examiner’s report 

stated that claims 1304 and 1305 in Gallagher Creek contained 

valid mineral discoveries, but claim 1605 in Killer Creek did 

not. Noranda maintained that drillcore of 2.3 percent copper 

is a valid discovery, but their legal counsel suggested that this 

interpretation would not hold up in court (J.S. Drechsler, Jr., 

and others, Noranda Mining, Inc., written commun., 1982).

Noranda and the JV partners reviewed other options and 

strategies to protect the exploration potential of Greens Creek. 

The alternatives to the current aggressive discovery-oriented 

drill program included a minor boundary change putting Greens 

Creek outside the national monument, a land swap, or extension of the 5-year period to prove the claims (J.S. Drechsler, Jr., 

and others, Noranda Mining, Inc., written commun., 1982). The 

first choice was to lobby the USDA Forest Service for a minor 

boundary adjustment, a power the USDA Forest Service had 

under one of the provisions of ANILCA. The other two choices 

were less attractive because a land swap would be costly and an 

extension would only delay resolution of the problem.

The cost of the drill program was becoming a concern 

for Noranda. More definition drilling was necessary to bring 

the “new” 1982 geologically inferred reserves into indicated 

reserves (J.S. Drechsler, Jr., and others, Noranda Mining, 

Inc., written commun., 1982). Even at 400-foot spacings, it 

would require about 11,000 feet of surface drilling to validate 

indicated reserve status, leaving very little funds for perfecting claims. Drilling on 150-foot centers, which was preferred, 

would be extremely expensive. Underground drilling would 

be less expensive, but the platforms did not exist and would 

be best established simultaneously with mine development 

and mining, still years away. Underground and surface drilling both would require helicopter support, adding to the cost. 

Drilling would be much less expensive after road construction, but road construction might not be possible until after 

the expiration of the permit period due to political and budget 

constraints. Noranda was faced with either continuing drilling 

at a higher expense or pursuing the above-land options and 

risk losing potential mineral assets.

Noranda Exploration geologist Daryl Scherkenbach 

completed a geologic mapping project at a scale of 1 inch=500 

feet for the Greens Creek area. This work was the basis for his 

geologic model of the Greens Creek deposit. He suggests that 

the Big Sore orebody formed within a second- or third-order 

extensional basin (D.A. Scherkenbach, written commun., 

1983). In his model, tectonic extension was accompanied 

by mafic and ultramafic volcanics and shallow intrusives. 

The serpentinization of these rocks is a strong indicator of 

hydrothermal activity that caused the metal transportation. 

The effusive vents for the hydrothermal fluids manifested 

themselves as slump breccias, as mapped within the footwall 

tuffites. These vents formed fault scarp basins, in which the 

metallifereous brines could settle and deposit metals. The massive ores accumulated near the vents while black ores accumulated distally, hundreds of meters from the vent. The white 

ores represented remobilized sulfides as the solutions migrated 

around sulfide-clogged vent areas. Scherkenbach thought the 

difference between the sericitic and chloritic tuffites/sediments 

was due to different source areas or modes of deposition. The 

highly negative d S isotope values for the argillite and black 

ore indicate biogenic reduction of seawater sulfate. The less 

negative values for the remaining ore types and tuffites suggest 

a mixing with magmatic sulfur.

1983 Feasibility Study

Noranda completed a feasibility study in 1983 that 

outlined the economic viability of the project. The study was 

based on probable and possible reserves (including dilution 

due to mining method) of 2.84 million tons at 0.093 troy 

ounce per ton gold, 14.42 troy ounces per ton silver, 2.93 

percent lead, and 8.56 percent zinc located above the 950-foot 

level. An additional geologic reserve of 1.45 million tons was 

estimated to be below that level (Noranda Mining, Inc., written 

commun., 1983). Noranda envisioned using conventional cut 

and fill mining methods utilizing jacklegs within “captured” 

stopes. Five to six separate levels/portals on 200-foot spacings 

would be connected by a winze and raises. Rail haulage would 

take place on all levels. Noranda preferred this method to 

mechanized cut and fill to reduce the amount of ramp development and allow for more selective mining where the ore is too 

narrow for rubber tire equipment. Mining rates were estimated 

at 1,200 tons per day (TPD) with dilution at 17 percent and 

mining recovery at 90 percent. Carbon, lead, and zinc concentrates would be produced over the estimated 20-year mine 

life (including development time). The mine would have a 

workforce of 344 people. The economic/cash-flow model 

given these parameters required a 1987 silver price of $22.95 

for a 15 percent DCF–ROR. The estimated capital investment 

was $254.3 million with an operating cost of $151.85 per ton 

(Noranda Mining, Inc., written commun., 1983). This was a 

huge contrast from the 1980 estimate of 39.3 percent DCF–

ROR and $65 per ton operating costs.

1983 Exploration Program

The objectives of the 1983 program were much the same 

as before, to validate peripheral claims and continue detailed 

definition drilling of the southern end of the orebody. The 

management of the program fell back to Noranda Mining, Inc., 

with Edwin Harrison supervising. The decision to proceed 

with the drill program did not come until July 7, and the four 

crews required for the work were not completely mobilized 

until August 1 (E.D. Harrison, Noranda Mining, Inc., written 

commun., 1983).
76 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

A total of 17 holes were drilled during the season. Most 

of the holes (15) were drilled from the southern core claims 

(902, 903, and 904). The aim was to upgrade the southernmost 

part of the resource to measured reserves status. Noranda 

viewed the south end as being critical to the initial mine design 

and development, and they needed a better understanding of 

the fold closure (E.D. Harrison, Noranda Mining, Inc., written 

commun., 1983). Three holes drilled updip from the 1982 ore 

crosscut intersected white, massive, and black ore of economic 

length and grade. One hole drilled at the southernmost known 

limits of the orebody intersected 12 feet of high-grade precious metals (0.644 troy ounce per ton gold and 55 troy ounces 

per ton silver). This hole also tested the upper limb argillite 

but intersected no mineralization. The remaining nine holes 

were in-fill drillholes of which five intersected significant ore 

intervals. The in-fill holes helped “prove” the continuity of ore 

in the south end of the designed mine plan and helped define 

the major fold closure controlling the ore to the south (E.D. 

Harrison, Noranda Mining, Inc., written commun., 1983).

Many high-grade intercepts were assayed during the drill 

program. A 2-foot interval from PS–62 assayed greater than 

11 troy ounces per ton gold, which was confirmed by numerous re-assays. Noranda considered the question of cutting high 

gold/silver assays for reserve calculations. They felt this idea 

should be studied closely and put into practice (E.D. Harrison, 

Noranda Mining, Inc., written commun., 1983).

Little effort was made in proving unperfected claims 

in 1983. Only two holes were drilled and an older hole was 

reentered and wedged in a different direction. PS–70 was 

drilled on claim 1107. Perfecting this claim was a high priority 

because the 1350 portal, mine camp, and waste dump were 

all located there. The hole intersected a short (1-foot) but 

high-grade (109 troy ounces per ton silver) mineralized zone 

deemed sufficient to prove the claim. The attempt to prove 

claim 1003 was an expensive ordeal (E.D. Harrison, Noranda 

Mining, Inc., written commun., 1983). The target was a 

recumbent drag fold intersected just outside of the claim by 

PS–48 (1982). An attempt was made to reenter that hole and 

place a directional wedge to deflect the hole onto claim 1003. 

The wedge failed to deflect the hole. A new hole, PS–54, 

was collared at the same site. Despite orienting the hole to 

compensate for the expected deviation, downhole surveys 

showed the hole was going to miss the projected contact to the 

northeast. Poor weather forced the postponement of the drill 

program before another mechanical wedge could be used to 

correct the hole. Thus, a valid discovery was made on only one 

unperfected claim in 1983, with only 2 years remaining on the 

exploration permit.

The first change within the Greens Creek Joint Venture partners occurred in 1983. Anaconda purchased all of 

Martin-Marietta’s interest in the Greens Creek Joint Venture 

in March of 1983 after first approaching them in December 

of 1982 (Anaconda Minerals Company, written commun., 

1984). Anaconda already had exploration experience in 

southeast Alaska, including the Pyrola claims to the south 

of Greens Creek. Anaconda’s Project Evaluation Report 

in January of 1984 justified their purchase on the basis of 

Noranda’s prefeasibility study. They believed that Noranda’s 

approach was too conservative and estimated the minable 

reserve greater by 0.5 million tons with higher silver (16 

rather than 14.4 troy ounces per ton) and gold (0.11 rather 

than 0.093 troy ounce per ton) grades. In addition, they 

thought that utilizing the mechanized cut and fill mining 

method would reduce capital costs for full production by 20 

percent from Noranda’s conventional cut and fill proposal.

Anaconda saw many potential problems with the project. They were concerned with the marketability of the 

concentrates produced due to the high level of contaminants 

(cadmium, arsenic, antimony, and mercury). Other concerns 

were the limited size and accessibility of Juneau, making it 

difficult to obtain and keep experienced personnel. They felt 

the lower levels of the deposit lacked the necessary drilling 

for production to be justified. Anaconda foresaw future delays 

in the project due to political and environmental factors. 

However, they did not see the pending exploration deadline 

and land issues as having an adverse effect on the base case 

economics. Anaconda’s preferred solution to the land situation 

was a land exchange with the Federal Government (Anaconda 

Minerals Company, written commun., 1984).

1984 Exploration Program

The 1984 drill program budget was $3.3 million, a fivefold increase from the $0.655 million budget of the previous 

year (E.D. Harrison and others, Noranda Mining, Inc., written 

commun., 1984). The increased budget, and the primary objective of the 1984 drill program to extend the proven claim block 

to the north and south, underscored the increasing pressure of 

the exploration deadline. The northern claims were tested to 

the 0.75-mile limit by surface holes while the southern claims 

could only be tested practically by underground drilling. 

Surface holes would be too long as a result of the increase in 

topography and southeast-plunging ore zone. An 847-footlong drift (1984 crosscut) was driven to the edge of the unperfected claims, with drill-cuts along the way for detailed ore 

reserve drilling.

The secondary objective of the 1984 program was to 

increase the downdip potential of the previously defined ore 

zones. The deposit was now divided into three ore zones, the 

North, South, and Central zones. The drilling took place from 

the 1350 drift and the new 1984 crosscut. Much rehabilitation 

work had to be completed on the 1350 drift due to numerous 

ground falls since 1981 before drilling took place.

The farthest north and northwest drilling in Gallagher 

Creek (PS–83), Killer Creek (PS–82, PS–86), and Bruin Creek 

(PS–76 to PS–81 and PS–84) failed to intersect mineralization sufficient to perfect claims. Likewise, hole PS–75 located 

near the camp on claim 1108 did not intersect mineralization 

along the argillite/phyllite contact. Drillholes closer to the 

core claims were more successful. PS–72 and PS–73 extended 

the now-named North Ore zone downdip another 250 and 

350 feet, respectively, although the intersections occurred on 
Race to “Perfect” Claims and Predevelopment, 1981–85 77

already perfected claims. PS–74 intersected the North Ore 

zone at the 400-foot level with a 7-foot interval of 17 troy 

ounces per ton silver and 5 percent zinc. This was the deepest ore intersection to date and perfected claim 1105. Another 

hole, PS–85, tested claim 1106 and intersected the North Ore 

zone and 9.4 feet of “black” ore mineralization. This hole 

perfected claim 1106.

Most of the barren surface holes intersected chloritic sediments or mudstones instead of cherty sericitic tuffites above 

the argillite contact. Noranda believed that the chloritic rocks 

were not very conducive to Greens Creek-type ore mineralization, though they did not state any geologic reasoning for their 

conclusion (E.D. Harrison and others, Noranda Mining, Inc., 

written commun., 1984).

No claims were perfected on the south end of the ore 

trend. Three holes were attempted from the southern end of 

the 1984 crosscut, and all three terminated within 220 feet of 

the collar due to poor drilling conditions caused by a major 

northwest-trending fault (later defined as the Maki fault). 

Another attempt was made to perfect claim 901 to the south 

by drilling from a station farther back in the crosscut. However that hole, GC–91, intersected a barren contact within that 

claim. The in-fill drilling was very successful in increasing the 

reserves. Two stations were drilled from the new 1984 crosscut 

to test the downdip potential of the South Ore zone while 

one station was drilled from the 1350 exploration drift to test 

the downdip potential of the Central Ore zone. Hole GC–86 

intersected numerous fold-repeated ore intervals, the lowest 

of which was located within the southeast corner of unperfected claim 1003. Noranda thought that the 5.9 feet of 16 troy 

ounces per ton silver would be sufficient to perfect this claim 

(E.D. Harrison and others, Noranda Mining, Inc., written commun., 1984). Two holes drilled in the South Ore zone, GC–88 

and GC–94, intersected ore of higher precious metal grade, 

coarser grain size, and silica-baritic groundmass that had not 

been identified previously. Noranda thought that they might be 

approaching the primary vent to the south and that the grades 

might continue to increase downdip and to the south (E.D. 

Harrison and others, Noranda Mining, Inc., written commun., 

1984).

The underground drilling program was successful in 

delineating more reserves below the 950-foot level and provided more insight to fold and fault structures, especially in 

the southern part of the deposit. Noranda did not add these 

new reserves to the “probable” category because they were not 

drilled on 150-foot centers (E.D. Harrison and others, Noranda 

Mining, Inc., written commun., 1984). However, they believed 

that the number of good ore intercepts supported the assignment of these areas into the geologic resource category. Thus, 

they classified the preliminary estimate of 670,000 tons to the 

“possible” category, with the majority of the tons in the North 

and South Ore zones. The increase in possible reserves, especially for the North Ore zone, was expected to have a large 

effect on the mine plan.

Other work included mining of ore underground for 

two bulk samples, one to be tested by Noranda and the other 

by Anaconda. Noranda geologist Floyd Branson initiated a 

trenching program in an attempt to expose the productive 

contact and patent claims 1007 and 1107. “Discovering” 

mineralization on the surface would allow the Greens Creek 

Joint Venture to exert extralateral rights under the Apex Rule 

(E.D. Harrison and others, Noranda Mining, Inc., written commun., 1984). The work was very difficult and expensive due 

to the difficulty in locating the contact under the thick glacier 

overburden.

Tom Crafford of Anaconda began his active role in the 

project by completing an extensive geologic mapping project 

to the north and east of the Greens Creek core claims. Crafford’s surface mapping included defining two northwesttrending faults, one on Mariposite Ridge just west of the 

Mammoth claims, and the other at the head of Big Sore Creek. 

He believed that these faults were the same structure (T.C. 

Crafford, written commun., 1984). Sampling of mineralization 

on the Mammoth claims showed ore-grade material within 

mariposite-carbonate rocks, which Crafford thought might 

represent a link between that alteration style and the mineralizing event. Several rock samples were taken for conodont 

analysis for age determinations, as there was a debate whether 

the age of the Greens Creek orebody was Paleozoic or Triassic. However, these samples were barren. He also mapped 

to the northeast of the mine to determine whether or not the 

overturned limb of the Big Sore anticline reappeared on the 

surface, but he found no evidence of a fold repeat.

Some of Crafford’s ideas expressed in his report were 

contrary to Noranda’s view of the geology. He did not agree 

with the tuffite designation for the footwall rocks. He viewed 

these rocks as hydrothermally altered mafic rocks that were 

proximal to vents (T.C. Crafford, written commun., 1984). He 

was also doubtful of the large-scale anticline hypothesis.

The end of the year saw a change in the ownership of the 

Greens Creek Joint Venture. Anaconda and Noranda equally 

bought out Bristol Bay Native Corporation’s properties at 

Hawk Inlet for a cash payment and a 0.28-percent net smelter 

royalty. The land would revert back to Bristol Bay upon termination of the Greens Creek Joint Venture.

1985 Surface Exploration Program

The objectives remained much the same as previous 

years for the 1985 drill program, the final year of the exploration permit granted under ANILCA. The surface drilling of 

10 holes totaling 12,266 feet was designed to perfect as many 

claims as possible. The underground drill program involved 

definition drilling on 150-foot centers to place 1984’s “possible” tons into the probable reserve category. This was the 

largest underground drill program to date, totaling 47 holes 

and 34,749 feet of drilling.

PS–87 was the only surface hole successful in perfecting a claim. The hole was drilled vertically from the northwest corner of claim 1206 to test the area between Gallagher 

Creek to the west and the North Ore zone to the east. The 

hole intersected 11.3 feet of “black ore” averaging 0.114 troy 
78 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

ounce per ton gold, 16.88 troy ounces per ton silver, and 4.9 

percent zinc (E.D. Harrison and M. Severson, Noranda Mining, Inc., written commun., 1985). The intercept was 40 feet 

inside claim 1207 due to hole deviation. A wedged hole off 

of PS–87 also intersected 5.6 feet of ore-grade material, but it 

too missed claim 1206. Ed Harrison recognized this intersection as a separate orebody that to this day is still isolated 

from the nearest defined orebody by about 1,000 feet. PS–88 

through PS–92 were drilled from already perfected claims 

1106 and 1107 to define the eastern edge (or upper shelf) 

of the North Ore zone. PS–92 was the first and only hole 

drilled on the east side of Big Sore Creek, above the High 

Sore, another ferricrete kill zone (fig. 1). Highly fractured 

and deformed argillite was the only lithology encountered in 

PS–92. The remaining four holes were drilled on claims 1207, 

1208, and 1209 to follow up the ore intercept in PS–87. None 

of these holes intersected significant mineralization.

The underground drill program was successful in delineating more reserves in all three ore zones. Noranda nearly 

doubled the probable reserves, adding another 1.33 million 

tons to the already identified 1.333 million tons (fig. 3). The 

total tonnage of 2.663 million at 0.13 troy ounce per ton gold, 

22.24 troy ounces per ton silver, 3.49 percent lead, and 9.00 

percent zinc exceeded their original goal of 2.1 million tons 

(Noranda Mining, Inc., written commun., 1985). Noranda was 

very optimistic due to the fact that the grades were increasing 

with depth and all three ore zones were still open at depth. 

Hole GC–139, drilled from the southern end of the 1984 crosscut, succeeded in perfecting claim 1002 with numerous 8- to 

13-foot ore-grade intercepts. Four holes were attempted from 

the same station to perfect claims 901 and 1001 to the south. 

They were all abandoned or lost, however, due to poor drilling 

conditions in the fault zone where three drill holes were lost in 

1984.

The Greens Creek Joint Venture’s land position was 

augmented in 1985 with the signing of an exploration/development agreement with the owners of the Mammoth claims. The 

agreement was a 10-year lease with a drill commitment and 

royalty payment due to the owners on any production (E.D. 

Harrison and M. Severson, Noranda Mining, Inc., written 

commun., 1985). The old “Mammoth Tunnel #2” was cleared 

and mapped. Other old pits and trenches were sampled. A 

grab sample of a tetrahedrite-bearing outcrop just above the 

portal assayed at 0.778 troy ounce per ton gold, and 17.91 troy 

ounces per ton silver. An additional 85 claims were staked to 

the north of the Mammoth claims, just outside the monument 

boundary, to cover ground not claimed by the Lil Sore claim 

group controlled by the Norbritex Venture. The crew spent 

more than 3 weeks staking claims, enduring snow depths up 

to 12 feet (E.D. Harrison and M. Severson, Noranda Mining, 

Inc., written commun., 1985).

The south face of the 1981 ore crosscut was advanced to 

test the ability of the miners and grade-control geologists to 

stay on the ore and to test the lateral variability of the ore types. 

This experience left Noranda feeling that it would be a faceto-face requirement of the production geologist to follow the 

highly deformed ore (E.D. Harrison and M. Severson, Noranda 

Mining, Inc., written commun., 1985). A United Nuclear’s 

silver probe was successfully tested as a grade control tool in 

estimating silver content of drill-core and face chip samples.

Land Strategies and Negotiations, 

1983–85

While the exploration projects tried to perfect as many 

claims as possible before the December 2, 1985, deadline, 

efforts were underway to find a legal solution or compromise 

to the dilemma. Just prior to the deadline, the Greens Creek 

Joint Venture filed proof of discovery of nine additional claims 

(1002, 1003, 1004, 1005, 1105, 1106, 1107, 1207, and 1304) 

to add to the original eight core claims (E.D. Harrison and M. 

Severson, Noranda Mining, Inc., written commun., 1985). The 

Greens Creek Joint Venture was concerned that the accelerated 

exploration was too costly and risky, and other avenues needed 

to be explored to remedy the land situation. The three separate 

avenues that were explored are discussed in the following 

paragraphs.

The first option was a boundary change regarding the 

Admiralty Island National Monument (AINM) and wilderness 

areas. ANILCA (section 103b) allowed for the Forest Service to make minor boundary adjustments to the various land 

selections. This idea was being pursued as early as 1983. The 

Greens Creek Joint Venture was hoping to exchange 18,174 

acres of private land in the Young Bay/Young Lakes area for 

17,225 acres within the Greens Creek area. However, the Sierra 

Club was against the boundary change even if it meant no net 

loss to the AINM because it would set a precedent for boundaries based on economics. Attorneys for Noranda thought any 

changes in boundaries were unlikely because the USDA Forest 

Service would be named as the defendant in any litigation, 

threatening their power to grant minor boundary changes (J.P. 

Tangen, esq., memorandum to P. Richardson, 1983). In addition, Noranda would not be involved directly in the litigation, 

thus losing control of the nature and timing of any solution.

The second option that was pursued was legislative relief 

through extension of the exploration permit (J.P. Tangen, 

esq., memorandum to P. Richardson, 1983). Representative 

Don Young, Alaska’s sole representative, introduced bill H.R. 

2651 on June 3, 1985, to amend section 504 of ANILCA. 

The amendment would allow the Greens Creek Joint Venture to renew the 5-year exploration permit up to six times so 

exploration could continue until December 2, 2020. Senator 

Murkowski of Alaska introduced an identical bill as S. 1330. 

These bills would only provide for exploration within the 0.75-

mile limit. However, neither bill made it out of committee.

The third option was a proposed land exchange involving 

Sealaska, the southeast Alaska Native corporation. The first 

iteration of the land-exchange proposal called for Sealaska 

to exchange subsurface mineral rights in the Cube Cove area 

for subsurface rights in the Greens Creek area. This land was 
0 2,000,000 4,000,000

6,000,0008,000,000

10,000,00012,000,00014,000,00016,000,000

TONS (SHORT)

1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 

YEAR

Total production

Mine reserves (proven and probable)

EXPLANATION

Figure 3. Chart showing proven and probable reserves compared to total (cumulative) production (Kennecott Greens Creek Mining Comcommun., 2001).
80 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

selected by Sealaska under ANCSA. The tentative agreement 

reached in November of 1985 called for Sealaska to lease 

these rights to the Greens Creek Joint Venture in return for a 

yearly lease fee to be negotiated and a 3.5-percent net smelter 

return royalty on any ore mined outside the existing core and 

perfected claims and extralateral rights from those claims. 

The lease would have a life of 25 years with mandatory work 

commitments made by the Greens Creek Joint Venture for 

each year. Sealaska saw themselves as a “passive” landowner 

(Birch, Horton, Bittner, Pestinger, and Anderson, written 

commun., 1985). This agreement hinged on at least a one-year 

extension of the exploration permit deadline to allow Sealaska 

adequate time to complete the land exchange.

The exchange with Sealaska Corporation was seen as 

the best option. The attorneys employed by Sealaska believed 

that the various environmental groups would support only this 

option. Litigation was unlikely since Sealaska, a Native corporation, was involved. Sealaska and the Sierra Club were trying 

to link the Greens Creek land exchange with another landmanagement dispute on Admiralty Island. The Shee Atika 

Native corporation was planning to harvest trees on the land 

at Cube Cove for which Sealaska owned the mineral rights. 

This clearcutting plan had the Sierra Club up in arms. Sealaska 

thought that the Sierra Club and the Forest Service would support a plan that halted the imminent harvesting (Birch, Horton, 

Bittner, Pestinger, and Anderson, written commun., 1985). 

However, Greens Creek wanted the issues resolved separately 

so that no additional complications would arise. Many groups, 

including the Shee Atika, the Alaskan congressional delegation, and the Greens Creek Joint Venture, were becoming 

increasingly dubious about Sealaska and their actions (Steven 

Silver, memorandum to P. Richardson, 1985).

The exploration permit was extended by one year in 1985. 

This allowed for continuing negotiations with Sealaska and 

further exploration to prove additional claims. By 1988 the 

USDA Forest Service rendered a decision denying the landexchange proposal. The land exchange still could be completed 

if the agreement involved the surface rights to the Cube Cove 

land. This would require a direct agreement with the Shee Atika 

owners. Despite these problems, the Greens Creek Joint Venture 

felt that a land exchange opening the remainder of the Greens 

Creek area to subsurface mineral development was just a matter 

of time (T.C. Crafford, memorandum to H. Griffith, 1988).

Ownership Changes and Consolidation, 

Development, 1986–89

A major ownership change occurred at the beginning of 

1986. Amselco (parent company, BP) purchased Noranda’s 

and Anaconda’s (which had just been liquidated by its parent 

company, ARCO) interest in the Greens Creek Joint Venture. 

That gave Amselco 70 percent of the total interest in Greens 

Creek, and they became the operators of the property. The 

geology staff did not change.

1986 Surface Exploration Program

The 1986 surface exploration program drilled surface 

and subsurface drill holes in an attempt to perfect four claims. 

Two of the claims (1001 and 1208) would be considered 

strike extension claims that Amselco believed, if allowed to 

patent, would extend their extralateral rights to the north and 

south (E.D. Harrison, Greens Creek Mining Company, written 

commun., 1986). The other two claims, 1104 and 1206, were 

believed to be covered under existing extralateral rights but 

were drilled anyway to test for downdip mineralization. Three 

surface holes were completed, totaling 4,694 feet, and one 

underground exploration hole was drilled to 1,271 feet.

The first hole drilled, PS–97, was the only one of major 

success. Two ore intervals were intersected consisting of mineralized gray chert and massive to semimassive sulfides. The 

lower intercept was at an elevation of 760 feet and was 25.9 

feet long, averaging 0.08 troy ounce per ton gold, 16.68 troy 

ounces per ton silver, and 6.2 percent zinc. The rocks were 

unusual in that the mineralized chert was complexly folded 

and(or) interfingered with argillite, and the contact was 500 

feet above the projection of the ore horizon in holes from the 

North and lower Central Ore zones. Ed Harrison believed the 

mineralization was continuous (E.D. Harrison, Greens Creek 

Mining Company, written commun., 1986); however, later 

drilling would define this as a separate ore zone, the Upper 

Southwest. The claim line between 1103 and 1104 had not 

been accurately surveyed and the ore horizon was right along 

the apparent boundary, thus making it difficult to prove the 

claim. The other two surface holes, PS–98 and PS–99, did not 

intersect mineralization on claims 1208 or 1206, respectively.

An underground hole was yet another attempt to prove 

claims to the south (1001) by drilling through the major fault 

at the end of the exploration drift. For the first 250 feet of hole 

GC–143, which corresponded to the faulted zone, 3.25-inchdiameter (PHR) core was taken, and then 2.5-inch diameter 

(HHR) core was taken to 411.3 feet. The core diameter was 

reduced to 1.875 inches (NQ) to 1,271 feet. The hole intersected ore grade intervals (up to 16.4 troy ounces per ton silver 

and 23.7 percent zinc), 3 to 100 feet wide, of mostly faulted 

white baritic ore (WBA) within argillite. This hole extended 

the known mineralization of the South Ore zone another 300 

feet to the south into an unperfected claim.

Surface mapping and exploration were mostly limited to 

the Mammoth and Mariposite claim groups. The first occurrence of silver sulfides on Greens Creek Joint Venture lands 

was sampled in a 10-foot zone just to the north outside of the 

Mammoth claims. The sample assayed at 53.75 troy ounces 

per ton silver. Four diamond drill targets were outlined for 

drilling in 1987 on the Mammoth claims, as specified in the 

work commitment spelled out in the lease agreement (E.D. 

Harrison, Greens Creek Mining Company, written commun., 

1986).

Tom Crafford’s 1986 map and report outlined his ideas 

and conclusions concerning Greens Creek geology. He verified through field evidence that the linear aerial photography 
Ownership Changes and Consolidation, Development, 1986–89 81

features do represent major faults of probable right-lateral 

movement with possible oblique or reverse slip components 

(T.C. Crafford, written commun., 1987). The youngest cleavage identified (now defined as S3

) within the Greens Creek 

rock package is a fracture cleavage related to the above major 

faults. He believed the first structural event is manifested by 

the recumbent isoclinal folds (later described as the D2 event). 

He further refined the Mammoth claim geology and thought 

that the previously exhalative explanation for the QCM 

(quartz-carbonate-mariposite) unit was incorrect. Field evidence supports the idea of the altered mafic tuffs grading into 

the QCM unit, thus being serpentinized mafics (T.C. Crafford, 

written commun., 1987).

Four EM and magnetic survey lines were flown over 

the Greens Creek area piggybacked on Amselco’s Mansfield 

aerial geophysical survey. No magnetic anomalies were identified from the survey. However, 6 of the 11 EM anomalies 

coincided with soil geochemical anomalies in the Big Sore 

area (E.D. Harrison, Greens Creek Mining Company, written 

commun., 1986).

Underground work continued to define the orebody in 

greater detail and to test different drifting and grade-control 

practices. A footwall drift was extended 94 feet from the east 

rib of the 1981 ore crosscut. The 9-foot-wide by 8-foot-high 

drift driven by jacklegs tested for mining problems within 

argillite. Four 1.432-inch diameter (BX) core holes were 

drilled using a CP–65 pneumatic drill rig from the new footwall drift. Two holes were drilled from the 1981 ore crosscut. 

These holes were drilled at tight 10- to 15-foot spacings along 

the contact to obtain more detailed structural data than from 

the drilling at 150-foot spacings. Detailed sampling of this 

core was carried out to determine the actual ore-waste boundary. The contact between the ore and hanging-wall argillite 

was the most important contact to define because most of the 

high-grade precious metals were found within 6 to 18 inches 

of that contact (E.D. Harrison, Greens Creek Mining Company, written commun., 1986).

1987 Surface Exploration Program

The exploration permit for the Big Sore and Tom claim 

groups was not extended another year by legislative means. 

The Greens Creek Joint Venture lost all rights to the Big Sore 

claims except for the eight core claims and the nine additional perfected claims. Negotiations were continuing with 

the USDA Forest Service and Sealaska to work out a landexchange agreement.

The 1987 program concentrated on prospects away from 

the Greens Creek mine area. The Mammoth claims received 

the bulk of the attention and funds. Four diamond drill holes 

were completed, totaling 1,441 feet (W.C. Meyers, written 

commun., 1988). Three of the holes tested the mineralization 

seen on the ridgetop exposure of the QCM unit, and one hole 

targeted the lower QCM band. All holes intersected minor 

mineralization over short (less than 3-foot) intervals, assaying up to 0.236 troy ounce per ton gold, 1.72 troy ounces per 

ton silver, and 3.8 percent zinc. The mineralization occurred 

within the QCM units for the ridge trend holes, while the mineralization occurred with the graphitic schist unit in the lower 

band. Six additional holes were outlined for drilling in 1988, 

mostly along strike of the graphitic schist/QCM contact.

Exploration work also was completed within the Fowler, 

Lil Sore, and Mariposite claim blocks. The first two claim 

groups were part of the original Norbritex Joint Venture. This 

joint venture was formed by Noranda, Bristol Bay, and Texas 

Gas in 1980 to explore lands outside of the Big Sore and Tom 

claim groups in which the other members of the Greens Creek 

Joint Venture did not wish to participate. Norbritex drilled one 

hole in Lil Sore that intersected a quartz-sericite unit overlying 

a graphitic unit, both thought to be part of the mine stratigraphy (W.C. Meyers, written commun., 1988). Soil sampling 

and CEM geophysics were carried out on soil grids to outline 

possible Greens Creek-type volcanogenic massive sulfide 

(VMS) targets or epithermal gold targets. Six anomalous soil 

geochemical zones were outlined, two of which occurred 

proximal to, or over, a sericitized pyrite breccia unit. Some of 

the soil anomalies had coincident CEM conductors. Additional 

soil sampling (in-fill), mapping, and trenching were recommended for these three claim groups.

The Greens Creek Joint Venture recognized the need 

for a better understanding of the structural geology of the 

mine, especially for mine planning. Three structural geology 

consultants (John Proffett, Ken McClay of the University of 

London, and Brian Marten of BP Minerals International) were 

contracted to perform separate structural studies. Marten’s 

study was the first undertaken in early April of 1987. Marten 

deemed his results to be very preliminary by himself after 

he discovered that the 2 weeks he allotted for the study were 

“totally inadequate due to the unexpected structural complexity that was found” (B.E. Marten, BP Minerals International, 

written commun., 1987). He concluded that at least two 

intense penetrative shear deformational events were present 

that have been refolded by a third fold phase (D1

 through D3). 

Marten believed that the first deformation had the greatest 

effect on the massive sulfides and result in milling, brecciation, and plastic flow. The hanging-wall breccia was also a 

result of this intense shearing (not phreatoclastic). He stated 

that the ore zone was likely a major shear zone. He expressed 

concern that the previous quantity and quality of structural 

observations underground, in drill core, and on surface were 

woefully inadequate for ore reserve calculations and mine 

planning (B.E. Marten, BP Minerals International, written 

commun., 1987).

John Proffett largely agreed with Marten’s observations, 

though he did not see direct evidence for the first deformation 

event and he added a fourth, open-fold event (J.M. Proffett, 

written commun., 1987). He saw the second event to be the 

most intense, giving rise to S2

 axial planar to steeply plunging 

isoclinal F2

 folds. Gently south-southeast-plunging F3 folds 

in turn fold F2. He thought that the S2 was nearly parallel to 

bedding. The S2

 foliation is the dominant foliation seen in all 

rock types (compositional banding within the phyllites and ore, 
82 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

and the slaty cleavage in argillite). He found no evidence for 

major thrust faulting along the ore/argillite contact. In addition, 

he mapped local F4

 folds that plunge nearly parallel to F3. The 

structural nomenclature suggested by Marten and refined by 

Proffett is still accepted and used by mine geologists at Greens 

Creek. McClay also largely agreed with Marten and Proffett. He 

adds a later D5

 event to describe the later brittle faulting (K.R. 

McClay, University of London, written commun., 1987). His 

conclusion mirrored Marten’s that the current structural database was inadequate, and more detailed work was necessary for 

ore reserve calculations and mine planning (K.R. McClay, University of London, written commun., 1987). Despite the inherent structural complexities at Greens Creek, all three geologists 

agreed on a structural framework that still stood in 2001.

1988 and 1989 Surface Exploration Projects

Development and preproduction projects took priority 

over the next 2 years. Greens Creek management was waiting for the finalization of a land-exchange agreement with 

Sealaska (Greens Creek Mining Company, written commun., 

1988). The minimum assessment work was completed on the 

various claim blocks in 1988, mostly consisting of mapping 

and trenching. Work on the Mammoth claims included the 

completion of one diamond drill hole. MRD–5 was drilled 

600 feet southeast of hole MRD–4, testing for sulfides along 

the quartz-carbonate/graphitic schist contact. The hole did 

intersect minor disseminated galena and sphalerite, though no 

assay numbers are reported.

The Greens Creek Life of Mine Plan was released on 

March 25, 1988. The plan called for the startup of production 

operations in early 1989 with concentrate being produced by 

that February. Full-production rate was expected to be 1,000 

tons per day (TPD) operating 355 days a year. The mine life 

was expected to be 11 years. Total capital expenditures necessary for development and startup were reported as $105.8 million, with another $12.1 million expected over the life of mine.

This plan proved workable. The Greens Creek mill processed the first ore from the mine on February 5, 1989. This 

was achieved despite the ferry dock being severely damaged 

by a winter storm on January 30 (Greens Creek Mining Company, written commun., 1989). Crews were transported to and 

from the mine by way of helicopters and float planes until a 

temporary dock was installed on February 7. The mill processed 8,150 tons of ore during the first month of operations.

Surface exploration activities consisted of two holes 

drilled from Big Sore claim 1105, targeting downdip of the 

North Ore zone. PS–100 was abandoned after 456 feet due to 

poor drilling conditions. PS–101, drilled from the northwest 

corner of the claim, reached 2,106 feet and intersected three 

barren contacts. No record exists of any assessment work done 

on the outlying claims. One significant underground drilling 

discovery was made. Hole GC–265, drilled along section 33, 

intersected 235 feet of ore-grade massive sulfide at a lower 

elevation than that of the North Ore zone. This was an apparent new ore trend in a previously untested area (Greens Creek 

Joint Venture, written commun., 1994). This zone was later 

defined as the (Central) West zone.

Continuing Underground Exploration, 

Production to Shutdown to Reopening, 

1990–95

The 1990 surface exploration campaign was very active 

after two summers of mostly minimum assessment work 

during startup. Diamond drilling took place on validated and 

unvalidated claims to the west of the established orebody. 

Drilling was allowed off the validated claims and within the 

national monument nonwilderness after the USDA Forest 

Service determined the Greens Creek Joint Venture had sufficient claim of extralateral rights (William Edwards, written 

commun.,1990). This final effort to validate claims to the west 

of the core claim group was the largest surface drilling project 

to date (10 holes totaling 23,287 feet).

The first hole, PS–102, was drilled at the same site as 

PS–100, which was abandoned the previous year. This hole 

did not intersect any economic mineralization. However, the 

next three holes all intersected ore from widely scattered 

drillpads. PS–103 was collared along the very southern edge 

of claim 1105 to test the possible southwest extension of the 

North Orebody. The hole intersected three ore-grade intervals 

along a contact between a siliceous breccia and argillite. The 

bottommost 5.5-foot intercept included visible electrum that 

ran 0.524 troy ounce per ton gold and 86.4 troy ounces per ton 

silver (J.G. Baughman, memorandum to T. Crawford, 1990). 

PS–104 was drilled 1,200 feet to the southeast of PS–103 

and intersected two ore intervals, including 24 feet of 0.102 

troy ounce per ton gold, 35.99 troy ounces per ton silver, and 

9.1 percent zinc at the 860-foot level. PS–105, 500 feet from 

PS–103, tested the northwest extension of this mineralized 

interval. This hole intersected ore-grade massive sulfide at 

the 950- and 500-foot levels. The drill program geologists 

believed that the mineralization was continuous for over 1,600 

feet, but they could not confidently correlate it with other 

recognized orebodies (J.G. Baughman, memorandum to T. 

Crawford, 1990). PS–103 and PS–105 were the first holes 

to intersect the Northwest West Ore zone on the west side of 

the Maki fault. The underground drilling program intersected 

significant base-metal intervals in hole GC–502, drilled from 

the 33 Exploration drift. This hole helped to define the Central 

West Ore zone as a separate orebody (Greens Creek Joint 

Venture, written commun., 1994). PS–104 intersected the top 

of what was later defined as the Southwest Ore zone.

Three more surface holes tested the extent of the mineralization intersected by GC–502: PS–108 and PS–110 to the 

south, and PS–109 to the west. Only hole PS–110 and a wedge 

drilled off the hole (PS–110a) intersected significant mineralization. A 16.1-foot-long ore-grade interval (2.11 troy ounces 

per ton silver, 16.69 percent zinc) was intersected deep (2,050 

feet) in the hole. This pierced the 5250 orebody (a somewhat 
Continuing Underground Exploration, Production to Shutdown to Reopening, 1990–95 83

continuous satellite of the West Orebody). The other two holes 

of the 1990 summer program, PS–106 and PS–107, tested 

downdip (to the southwest) of the intersections in PS–103 and 

PS–105, respectively. Both holes intersected only stratigraphic 

footwall (phyllite) rocks.

The 1990 surface drilling program intersected three new 

orebodies: the Central West, the Northwest West, and the 

Southwest. Much more drilling from underground was needed 

before most of the structural complications could be solved 

and the three new orebodies roughly defined. The following 2 

years involved a very aggressive underground drill program to 

define the Central West Ore zone on 100-foot centers. By the 

end of 1990, underground drilling had increased the indicated 

reserves from 3.6 million tons to 6.9 million tons (Greens 

Creek Joint Venture, written commun., 1990) of which 2.8 

million tons were in the probable category (Kennecott Greens 

Creek Mining Company, written commun., 2001). No additional surface drilling took place until the passage of the Land 

Exchange Act in 1996.

Assessment work continued on the claim groups to the 

north, and minor geologic mapping and geochemical sampling 

took place within the AINM boundary. Two soil geochemistry grids were completed in Fowler Creek and the “L” zone 

along the Maki fault (Upper Zinc Creek), south of the Lil Sore 

grid. Only the “L” zone showed any geochemical anomalies 

(D.L. Lorge and others, written commun., 1990). Previously 

unidentified mineralization was sampled on Antenna Mountain, Zinc Creek Pass, and the Zinc Creek roadcut south of the 

Zinc Creek bridge (fig. 1). The latter was the most significant 

at 8.07 percent lead and 22.86 percent zinc.

A different geologic model for the Greens Creek deposit 

emerged from the geologic mapping and sampling completed 

during the summer. The surface crew consisting of David 

Lorge, Eric Lalechuer, and William McClelland felt that all 

the anomalous soils and surface mineralization occurred along 

major faults (D.L. Lorge and others, written commun., 1990). 

Their new deposit model envisioned these faults (presumably 

the northwest-trending Maki-type faults) as being the main ore 

control and horizons. They interpreted the faults as forming 

during metamorphism and formation of the S2

 foliation. These 

faults were structural channels for the intrusion of ultramafic 

plutons and replacement mineralization. In a separate report, 

McClelland (W.C. McClelland, written commun., 1990) 

suggests that the Greens Creek deposit is a replacement of 

Upper Triassic sediments associated with a hydrothermal 

system driven by Upper Triassic volcanic rocks and(or) Late 

Triassic hypabyssal mafic to ultramafic intrusions. He cited 

the presence of an Upper Triassic Halobia fossil within an 

ore-enclosed concretion as evidence of replacement of the surrounding sediments. He described that much of the mineralization observed in core and on surface was controlled by veins 

that crosscut the S2

 foliation. All of the workers felt confident 

that additional massive sulfide deposits could be discovered 

within the Upper Triassic units with exploration concentrated 

along suspected northwest-trending faults (D.L. Lorge and 

others, written commun., 1990).

1991 Exploration Program

Underground exploration and continued production were 

emphasized in 1991. Only the minimum amount of assessment 

work necessary for claim maintenance was completed on the 

surface. Underground drilling to define the West Orebody 

was successful and resulted in subdividing it into three 

distinct zones (Greens Creek Joint Venture, written commun., 1994). Drilling to the south and west of the projected 

trend of the West Orebody intercepted high-grade intervals 

in holes GC–738, GC–739, and GC–753 that further defined 

the Southwest Ore zone. Continued definition and exploration drilling underground to the south was given an additional 

boost when the Forest Service’s mineral examiner and council 

gave positive comments during a preliminary meeting discussing extralateral rights to the south of the Big Sore claim block 

(Greens Creek Joint Venture, written commun., 1991). The 

1991 definition drilling campaign increased the ore resource 

to 13.0 million tons, an increase of 6.1 million tons (Kennecott 

Greens Creek Mining Company, written commun., 1991). The 

proven and probable reserves, however, dropped to 1.2 million 

tons (Kennecott Greens Creek Mining Company, written commun., 2001).

On-Line Exploration from Anchorage was contracted to 

complete the assessment work required for claim maintenance. 

Their work concentrated on the leased Mammoth claims and 

unpatented Mariposite claim block. A soil geochemistry grid 

just north of the Mammoth claims yielded two minor discoveries. The first was a barite-bearing outcrop with visible gold 

(J.E. Adler and others, On-Line Exploration Services, Inc., 

written commun., 1991). However, assays did not confirm 

anomalous gold. The other discovery was disseminated 

sphalerite, galena, and chalcopyrite within a quartz vein. Both 

mineralized occurrences had slight soil geochemical expressions. On-Line Exploration recommended drill testing on the 

“L” zone pyrite, previously mapped and sampled within the 

Mammoth claims (J.E. Adler and others, On-Line Exploration 

Services, Inc., written commun., 1991).

1992 Exploration Program

The 1992 surface exploration program consisted of 

diamond drilling to fulfill the annual assessment work requirements. Wink Drilling of Juneau was contracted to drill 2,000 

feet on unpatented claims north of the AINM boundary 

(Greens Creek Joint Venture, written commun., 1992). Two 

drill holes, MC–1 and MC–2, tested a weak silver-zinc soil 

anomaly on the Mariposite claim group defined by the 1991 

program. Both holes were abandoned before reaching the 

target depth and did not intersect any mineralized intervals. 

Drilling was completed on the HI East and HI West claims 

leased from NERCO on the Mansfield Peninsula with no success. The underground drilling program completed drilling of 

most of the West Ore zone on 100-foot centers.

Ed Harrison recommended dropping the Mansfield claim 

groups in order to focus resources on the Fowler, Lil Sore, 
84 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Mariposite, and Big Sore claim groups. Harrison also advocated continued drilling on the Mariposite block and forming a Greens Creek joint venture exploration company with 

a separate budget from the mine because Kennecott Greens 

Creek Mining Company finances lacked the necessary funds 

to mount an effective exploration campaign (E.D. Harrison, 

memorandum to C. Davis, 1992).

Negotiations began on a new land-exchange proposal that 

only involved Greens Creek and the Forest Service. Greens 

Creek submitted a “bare-bones” proposal to the Forest Service 

in September of 1992. The proposal called for Kennecott 

Greens Creek Mining Company to purchase $1,375,000 worth 

of private land in-holdings on Admiralty Island and other areas 

of the Tongass National Forest and convey the land to the 

Forest Service in exchange for the subsurface mineral rights to 

6,875 acres surrounding the core claims (Steven Silver, memorandum to R. Pierce and C. Davis, 1992). The agreement also 

called for a net smelter interest paid to the Forest Service for 

any minerals produced from the area. This item proved to 

be the most contentious in the negotiations. Congressional 

approval was necessary for any land exchange involving a 

national monument. Greens Creek finally received title to the 

17 core claims and one millsite claim after the USDA Forest Service and Bureau of Land Management approved the 

final validity test in December, 14 years after the process had 

been initiated (Greens Creek Joint Venture, written commun., 

1992).

1993 Closure

Kennecott announced in February 1993 that production 

mining and milling operations would cease by mid-April. The 

primary cause of the closure was low metal prices (Greens 

Creek Joint Venture, written commun., 1993). Greens Creek 

lost $2.2 million during the month of February alone. Milling ceased on April 10 and all but 24 employees were laid off 

by April 30 (Greens Creek Joint Venture, written commun., 

1993). The remaining personnel were involved in the maintenance of permits and in development of the West Ore zone 

to satisfy the Forest Service’s requirement of “use” of the 

property.

Underground diamond drilling began on July 17 to 

explore and define the Southwest Ore zone. The drilling 

occurred mostly from the 36 Exploration drift, which was 

being driven to the west of the 920 Main Haulage at the same 

time. Tim Hall was hired as the new Chief Geologist, and 

Deborah Apel returned to supervise the drilling program in 

November. A total of 30,261 feet was drilled along 200-foot 

spacings from section 3200 to 2400.

1994 Exploration

The Greens Creek Joint Venture agreed on November 

17, 1993, that the Southwest Ore zone would require drilling 

at tighter (50-foot) spacings to adequately define the resource 

(Greens Creek Joint Venture, unpub. data, 1993). They 

approved a 120,000-foot drill program and initiated a feasibility program to explore and develop the Southwest Ore zone. 

Development continued in the 36 Exploration Drift to provide 

platforms for drilling. The drift passed through the southern 

boundary of the claim block in February. It was not until April 

that the Forest Service confirmed the assertion of extralateral 

rights that included the Southwest Ore zone (Greens Creek 

Joint Venture, written commun., 1994).

By the end of 1994, 130,803 feet of diamond drilling 

had been completed, mostly within the Southwest Ore zone 

(Greens Creek Joint Venture, written commun., 1994). Most of 

the drilling was accomplished on 50-foot spacings and centers. 

At the end of 1994 the recoverable ore reserve for the Southwest Ore stood at 2.4 million tons at 0.244 troy ounce per 

ton gold, 32.86 troy ounces per ton silver, 5.91 percent lead 

and 12.35 percent zinc (Greens Creek Joint Venture, written 

commun., 1994). The feasibility report called for startup of 

the mill by January 1, 1997, at a rate of 1,320 TPD using the 

higher grade Southwest ore. The plan also called for expansion to 2,000 TPD by 1999, with additional lower grade ore 

sourced from the West Ore zone.

The land-exchange agreement with the USDA Forest 

Service was signed in Washington, D.C., on December 17, 

1994, after much bargaining over a sliding royalty scale based 

on net smelter return (NSR). A compromise was reached in 

September when Greens Creek accepted the Forest Service’s 

sliding royalty of 3.0 percent for ore greater than $120/ton in 

exchange for reducing the $1.5 million in-holding purchase 

amount to $1.0 million (Greens Creek Joint Venture, written 

commun., 1994). A royalty of 0.5 percent was imposed on 

ore between $80/ton and $120/ton. The next step was to gain 

congressional approval through legislation.

Very little surface activity took place in 1994. Geologists from Kennecott Exploration completed a reconnaissance 

sampling program in the mine area and on Mariposite Ridge. 

Paul Lindberg began a 4-year stint as a consulting geologist 

to work on various projects, including geologic investigation 

of the Southwest Ore zone and interpretations and reconstructions along the Maki fault and other shears. Lindberg’s interpretation of drillcore from the Southwest Ore zone led him to 

believe that much of the ore horizon was rooted in the argillite 

section and not at the argillite/phyllite contact (P.A. Lindberg, 

written commun., 1994). He also (re)identified the Klaus 

fault, which he believed decapitated the Southwest Orebody, 

displacing the top 700 feet to the northwest (P.A. Lindberg, 

written commun., 1994). The imminent completion of the land 

exchange led Lindberg to comment on future exploration. He 

proposed allowing a great deal of lead time to compile and 

digitize historical exploration data and maps that had been 

essentially archived for the past 4-plus years (P.A. Lindberg, 

written commun., 1994). Other ideas for initiating the exploration program were airborne geophysical and photometric 

surveys and liaising of the new exploration personnel with 

current geology staff.
Land Exchange Act and Continuing Production and Exploration, 1995–Present 85

The leased claims in HI East and HI West with NERCO 

were dropped as the area of Joint Venture was reduced to the 

lands south of Young Bay and east of Hawk Inlet (Greens 

Creek Joint Venture, written commun., 1994). The Joint 

Venture changed when Kennecott bought out CSX (Exhalas 

was bought out by the three remaining partners in 1993). 

The ownership split was 70.27 percent Kennecott and 29.73 

percent Hecla.

Land Exchange Act and Continuing 

Production and Exploration, 1995–

Present

The Greens Creek Land Exchange bill was introduced to 

the Resource Committee of the U.S. House of Representatives 

on March 16, 1995. The bill was cosponsored by Don Young 

(R-Alaska) and George Miller (D-California), who were 

usually on the opposite side of an issue from each other. The 

bill did not make it out of committee in 1995. Greens Creek 

employees received good news when the Kennecott Board of 

Directors, on April 5, 1995, approved the allocation of $87.3 

million to reopen Greens Creek with production at 1,320 TPD 

(Greens Creek Joint Venture, written commun., 1995).

Paul Lindberg and Norm Duke of the University of 

Western Ontario completed a preliminary geologic mapping 

and sampling project in and around the Greens Creek mine in 

the summer of 1995 while the Greens Creek Land Exchange 

bill was in legislative limbo. They spent 2 weeks traversing 

various parts of the property, including the Mammoth claims, 

Cliff Creek (the area of the original geochemical anomaly 

leading to the discovery of Greens Creek), Gallagher Creek, 

Killer Creek, and along the road corridor. Duke concluded that 

the Greens Creek orebody was upgraded by remobilization of 

syngenetic lead-zinc-silver from the argillites (SEDEX model) 

and gold sourced from the strongly carbonitized mafic and 

ultramafic rocks (N.A. Duke, written commun., 1996). Duke 

subsequently refined and redefined his model based on his 

regional geologic mapping.

1996 Exploration and Reopening

The 12-year battle for gaining exploration rights to 

the original claim group finally ended on April 1, 1996, 

when President Bill Clinton signed the Greens Creek Land 

Exchange Act. Work began immediately on purchasing $1.0 

million of private in-holdings, primarily from a list of preferred properties compiled by the USDA Forest Service. This 

process took nearly 2 years to complete.

Steve Newkirk was hired during the winter of 1995 

to resurrect an active surface exploration program after a 

7-year hiatus. Staking and filing 213 Federal lode claims in 

unclaimed holes south of Young Bay further refined the land 

picture. In addition, 15 State tideland claims were staked along 

upper Hawk Inlet. However, the State of Alaska also selected 

the land for potential community development and thus its 

status remains in limbo. The 10-year lease of the Mammoth 

claims expired at the end of 1995. Negotiations took place 

over several months with the owner, Herman Meiners, to 

renew the lease or to purchase the claims outright. However, 

Meiners did not budge from his high asking price and evidently shopped the property around to other potential buyers 

with no results (S.R. Newkirk, written commun., 1996). No 

further negotiations took place.

Surface diamond drilling was limited to the patented 

claim block until the land-exchange lands were fully conveyed. The Forest Service would allow only nonimpact activities such as helicopter landings, soil and rock sampling, airborne and ground geophysical surveys, and geologic mapping. 

The 1996 program initially involved one drill rig operated by 

Connors Drilling. However, poor advance rates due to poor 

ground conditions, frequent mechanical failures, and driller 

inexperience with Greens Creek-type conditions necessitated 

mobilizing a second drill rig.

Nine holes totaling 7,755.5 feet were completed. The 

first three holes, PS–111, PS–112a (abandoned after 487 

feet), and PS–112, were collared from the 1350 adit access 

road and targeted the possible northwest extension of the 

North Ore zone. Neither completed hole intersected significant mineralization. PS–113 through PS–117 were drilled 

from three drillpads targeting the Upper Plate Extension of 

the Northwest West Ore zone (the Maki offset on the west 

side of the West Ore zone). This thin, flat-lying mineralized 

horizon had been intersected in a few holes from underground 

but was not systemically explored. PS–115 had the only significant intercept, a 1.5-foot interval of ore running 0.16 troy 

ounce per ton gold, 19.44 troy ounces per ton silver, 3.4 percent lead and 6.8 percent zinc. PS–118 targeted the possible 

north extension of the West Ore, first intersected by PS–87 in 

1984. The hole was located 600 feet north-northeast of PS–87 

and did not intersect mineralization.

Numerous geophysics methods were tested at Greens 

Creek to determine which might be more effective in surface 

exploration. Airborne EM, radiometric, and magnetometer 

surveys were completed in conjunction with Kennecott 

Exploration’s Mansfield project. The surveys, carried out by 

Aerodat, flew more than 1,200 kilometers of line that covered 

the entire Greens Creek area, including the land exchange. 

Distinct magnetic anomalies corresponded with already 

mapped ultramafic bodies (for example, Killer Creek serpentinite). The EM survey proved useful in identifying graphitic 

rocks, such as the Hyd argillite. Underground and surface 

gravity surveys were completed. The underground survey, 

extending from the portal to the end of the 36 Exploration 

drift, detected a subtle ~1.5-Mgal anomaly over the West Ore 

zone. The surface survey over the Northwest West Ore zone 

failed to detect any coincident anomaly. Two test lines over 

the West and Northwest West Ore zones were surveyed by the 

CSAMT (controlled source audio-magnetotelluric) method. A 

resistivity low associated with the Northwest West Ore zone 
86 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

and Maki fault was detected, but the West Ore zone was not. A 

time-domain electromagnetic (TEM) survey was also completed over eight lines in the same area and measured a strong 

response from the West Ore. Downhole TEM surveys were 

completed on surface and underground holes. GC–1530, an 

underground exploration hole, produced a strong EM anomaly 

within the West Ore. This geophysical test work was done to 

develop the tools for a multiyear exploration program (S.R. 

Newkirk and others, written commun., 1996).

Norm Duke and Paul Lindberg completed reconnaissance and detailed geologic mapping and sampling within 

the land-exchange boundary. Their work culminated in a 

completely revised 1 inch=1,000 foot scale district map and 

numerous 1 inch=200-foot scale mine geologic maps. The 

prospective mine stratigraphy was traced to the south and 

north (S.R. Newkirk and others, written commun., 1996). 

The land-exchange boundary survey was finalized in November. Kennecott Greens Creek Mining Company developed a 

cooperative research agreement with Cliff Taylor of the USGS 

for a program to focus on many of the outstanding geologic 

problems of the Greens Creek mine (reported in this volume).

The work completed in 1996 was designed to lay the 

groundwork for a multiyear exploration program. The geologic mapping and research agreement was to refine the 

geologic model for the deposit. A GIS system, using ArcView 

software, was set up to aid in organizing the 20+ years of data. 

Historical geologic maps and geochemistry were digitized for 

the GIS project during the summer and fall.

Underground exploration was limited to definition drilling in the Northwest West and 5250 Ore zones. Preproduction drilling, consisting of horizontal fans of short (100- to 

400-foot) holes, was carried out from various ore accesses 

in the Southwest Ore zone. These holes drilled on 10- to 

25-foot centers aided in stope planning. The recommissioned 

mill began running ore from the Southwest orebody in July 

1996. Kennecott Greens Creek Mining Company produced 

about 143,000 tons of ore averaging 0.108 troy ounce per ton 

gold, 23.80 troy ounces per ton silver, 4.84 percent lead, and 

10.3 percent zinc. Almost all of the ore was sourced from the 

Southwest Ore zone.

1997 Exploration

Surface exploration activities were accelerated on the 

land-exchange property. Seven new grids totaling 230,000 linear feet, were cut and sampled within the Greens Creek Joint 

Venture lands. The grids within the land exchange included 

High Sore, Bruin, Lower Zinc, Upper Zinc, and Gallagher. 

The “A” Road and East Lil Sore (fig. 1) were cut within the 

unpatented claim groups north of the land exchange. Detailed 

work along each grid included soil sampling, gravity, magnetic and TEM geophysical surveying, and geologic mapping. 

No high-priority, near-surface coincident gravity and TEM 

anomalies (possible shallow massive-sulfide bodies) were 

identified (S.R. Newkirk and others, written commun., 1997). 

Soil sampling and geologic mapping outlined drill targets 

or areas for detailed followup work in Bruin, Gallagher, and 

Lower Zinc Creeks. The “A” Road prospect was discovered 

in 1995 during the road traverse of Paul Lindberg and was 

thought to be a possible distal “mine” horizon with exhalative 

quartz, barite, and pyrite (P.A. Lindberg, written commun., 

1997). Work in 1997 defined soil anomalies coincident with 

the exhalative horizon, but convincing evidence was not found 

to determine whether or not it was the mine horizon. Norm 

Duke and Paul Lindberg completed reconnaissance scale and 

detailed geologic mapping. John Proffett returned for the first 

time since 1987 and carried out structural mapping. Lindberg 

completed detailed mapping of the road corridor and borrow 

pits, all of which was compiled in a 15-sheet map folio (P.A. 

Lindberg, written commun., 1997).

Four diamond drill holes totaling 6,316 feet were 

completed in 1997. All were drilled from pads constructed 

on patented Big Sore claims because the land exchange had 

not been conveyed. Hole PS–119 targeted the lower phylliteover-argillite contact 800 feet to the northwest of hole PS–87. 

Only scattered zinc mineralization was intersected in the 

phyllite, and two argillite intervals intersected were clearly 

fault-bounded and nonmineralized. PS–120 targeted the same 

contact, except to the north-northeast (200 feet due east of 

PS–118). The hole did not intersect the contact, but a downhole TEM survey mapped a steeply dipping conductor to the 

southwest of the hole and a subhorizontal conductor 200 feet 

below the hole. This hole was reentered in 1998 to test the 

deeper conductor but did not intersect an interval corresponding to the conductor. PS–121 and PS–122 were collared in 

Big Sore claims 1305 and 1304, respectively, in the Gallagher 

Creek grid/prospect. Both holes intersected semimassive to 

massive pyrite and sphalerite zones with up to 9 percent zinc 

over 2-foot intervals. Mineralization in PS–122 occurred at 

and below a contact between graphitic phyllite and chloritic 

phyllite, which was thought to represent a new mineralized 

horizon at a different stratigraphic horizon (S.R. Newkirk and 

others, written commun., 1997). The surface drill program was 

cut short by a new discovery underground.

Discovery of the 200 South Ore Zone

Preproduction drilling continued to be a major portion 

of the underground drilling program. During December1996, 

a preproduction fan was drilled from the 200 Ore Access, 

targeting the 164-foot level. The southernmost hole, PP0204, 

intersected ore widths showing that the orebody was still open 

to the south of cross section 18, previously modeled as the 

end of the Southwest Ore zone. No additional preproduction 

holes were drilled to the south to find the terminus of the ore 

because of the oblique drilling angle. The 200 South stope 

(at the 164-foot level) began mining from the ore crosscut 

shortly afterwards. The 200 South stope reached section 18, 

the end of the ore reserve for that level, but still showed a full 

face of ore. Expecting the ore to terminate at any time, mining 

continued on a round-by-round basis for another 300 feet. At 

the same time, exploration drilling to the south commenced 
Land Exchange Act and Continuing Production and Exploration, 1995–Present 87

from the 480 Exploration drift. Hole GC–1632, drilled along 

section 16, intersected a 42-foot interval of zinc-rich massive ore about 200 feet below the 200 South stope. Kennecott 

Greens Creek Mining Company geologists quickly realized 

that the 200 South stope was the proverbial tip of the iceberg. 

Four drill rigs (including a diesel-powered surface drill rig) 

were mobilized to quickly define this new ore zone, named the 

200 South orebody. Two drill rigs were positioned in the 480 

Exploration drift and the other two in the 200 South stope, to 

drill the zone from the inside out. Long-section drilling from 

the face of the stope indicated that the ore zone continued to at 

least section 11. Drilling from the south extension of the 480 

Exploration (4711 Drift) continued from 1998 through 2000 

and defined a reserve of 2.08 million tons at 0.189 troy ounce 

per ton gold, 21.29 troy ounces per ton silver, 5.15 percent 

lead, and 12.50 percent zinc. Discovery and definition of the 

200 South orebody drastically changed the mining schedule 

of the various ore zones. Due to the higher grade of the 200 

South ore, it was mined ahead of the more accessible West Ore 

zone(s). The 200 South orebody accounted for 42 percent of 

the total mine production from 1998 to 2000.

1998 Exploration

The 1998 exploration program was boosted with the completion of the land exchange on August 5, 1998. The combined 

holdings of the Greens Creek Joint Venture now included 445 

unpatented lode mining claims, 58 unpatented millsite claims, 

17 patented lode claims, 1 patented millsite claim, and landexchange lands totaling 17,617 acres. Drilling was completed 

on lands off of the validated claim block or extralateral rights 

assertions for the first time since 1985. Four holes (PS–124 

through PS–127) were drilled in Bruin Creek, targeting the 

downdip potential of the north-striking phyllite-over-argillite 

contact. PS–124 and PS–125 were drilled from the same site 

as PS–47 and tested downdip and updip, respectively, from 

the semimassive sulfides intersected near an argillite/phyllite 

contact in that hole. Both holes intersected only minor mineralization in the upper phyllite unit. Both holes terminated 

in altered ultramafic rocks below a carbonate-rich contact 

zone with argillite. PS–126 was drilled near treeline in upper 

Bruin Creek to test coincident soil and TEM anomalies. The 

hole intersected a barren phyllite/argillite contact at 1,275 feet 

and terminated in a gabbro at 1,724 feet. PS–127 was drilled 

from the site of PS–81, drilled in 1984 by Noranda. This hole 

intersected two fault-controlled blocks of argillite with no 

sulfides. The only other hole drilled (besides the reentry of 

PS–120) was PS–123 in Gallagher Creek, testing the phyllite 

stratabound zinc-rich zone intersected in PS–46 and PS–122. 

Minor sphalerite and chalcopyrite were intersected, but to a 

lesser degree than in holes PS–46 and PS–122, indicating that 

the mineralization decreases to the southwest (A.W. West and 

others, written commun., 1999).

One new grid (Upper Big Sore) and extensions of three 

1997 grids (Lower Zinc, Bruin, and “A” Road) were geochemically sampled and geophysically surveyed in 1998. 

The work outlined numerous multielement anomalies with 

coincident TEM anomalies, but none were significant enough 

to warrant immediate drilling (A.W. West and others, written 

commun., 1999).

John Proffett extended his 1997 mapping in the Big Sore 

area toward the 920 portal and west of the Maki fault. He also 

reviewed surface drill core from both sides of the Maki fault. 

He found evidence for a major shear zone (Upper Shear Zone) 

that juxtaposes nonmine-type slates, silts, and phyllites of 

uncertain age over mine-type argillites, phyllites, and ultramafic rocks (J.M. Proffett, written commun., 1998). Subsequent work in 1999 defined a deeper shear zone (Lower Shear 

Zone). These two shear zones bracket the mine stratigraphy 

(J.M. Proffett, written commun., 1999). The amount and direction of offset along the two shear zones and the stratigraphic 

position of the upper-plate rocks remain outstanding and 

important questions for surface exploration.

1999 Exploration Program

1999 was the first exploration season entirely focused 

in the land exchange. However, the season began poorly 

when the contracted Bell-206 helicopter crashed into the 

mill during takeoff on the first day of service. Fortunately, 

no one was seriously hurt. Two new geochemical grids were 

completed and one extended. A large grid was surveyed 

in Killer Creek, spanning 8,000 feet from the “B” Road to 

the Mammoth claims. Numerous high-rank, multielement 

soil anomalies were defined, and numerous sulfide-bearing 

outcrops and gossan zones were sampled and mapped. A new 

grid was cut in Cub Grid, just east of Bruin Creek. Two sets 

of major right-slip faults repeat the argillite/phyllite contact 

several times in Cub Creek. Anomalous geochemistry was 

coincident with an inferred contact zone in upper Cub Creek, 

near the land-exchange boundary (A.W. West and others, 

written commun., 2000). The Upper Zinc grid of 1997 was 

extended to the west. No significant discoveries were made 

in Upper Zinc Creek. However, two significant base-metal 

mineralized outcrops were sampled and mapped by Norm 

Duke to the southwest in the Lakes District prospect (N.A. 

Duke, written commun., 1999). One of the occurrences is 

near the contact between chlorite phyllite and possible Triassic carbonate rocks.

Ten diamond drill holes were completed totaling 

12,715 feet. Seven of the holes were drilled in Bruin Creek. 

PS–128, PS–129, and PS–130 were drilled from the backslope directly behind (north of) the 920 administrative 

building. A shallow southwest-dipping barren phyllite-overargillite contact was intersected in all three holes. PS–128 

drilled through Proffett’s Lower Shear Zone and into more 

than 1,000 feet of ultramafic rocks. PS–131, PS–133, 

PS–137, and PS–138 were collared from two different pads 

on the west side of the mapped contact in middle Bruin 

Creek, about 1,000 feet east of the 1998 drill holes. Only 

PS–137 intersected conformable argillite/phyllite contacts. 

PS–136 was collared on the east side of the contact and also 
88 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

intersected the contact. In both holes, the contact was intersected multiple times, but no indication of mineralization 

was found. Three holes were drilled in Killer Creek. The 

first two holes, PS–132 and PS–134, were collared from the 

site of PS–20, drilled in 1977. Both holes intersected long 

intervals of semimassive to massive pyrite bands with minor 

sphalerite up to 15 feet wide within greenstones and serpentinites. PS–132 also intersected a deep (800 feet below the 

surface), fault-bounded, 3.6-foot band of massive chalcopyrite that ran 4.2 percent copper. PS–135 was drilled from a 

pad constructed above Pit 405, at mile 7.6 of the “B” Road. 

This hole intersected long intervals (up to 15 feet) of patchy 

zinc mineralization in chloritic phyllites.

2000 Surface Exploration

Two new prospects were drilled in 2000. Two pads were 

constructed in Cub Creek to test soil anomalies coincident 

with the phyllite/argillite contact. The targets were further 

refined by a CSAMT geophysical survey along three lines 

in Bruin and Cub Creek (three lines were also surveyed in 

Killer Creek). Results from the survey were of better quality 

than the 1996 survey due to better location of the transmitter 

line. The four holes drilled in Cub Creek (PS–144, PS–145, 

PS–147, and PS–151) did not intersect any significant metal 

enrichment along the contacts intersected. Data collected from 

these holes and two others (PS–147 and PS–148) in East Bruin 

Creek aided in the interpretation of the Bruin and Cub Creek 

regions. A large-scale recumbent syncline (cored by argillite) 

that closes to the west-southwest was found to be the dominant 

structure (A.W. West and others, written commun., 2001). The 

nearly isoclinal fold has mineral potential along both upper 

and lower limbs.

The Lower Zinc Creek prospect was drill tested for the 

first time from a pad constructed at the 2.8-mile mark of the 

“B” Road. Holes PS–152 and PS–153 were drilled to the 

northeast, targeting the mine contact. The contact intersected in 

both holes was strongly silicified and sulfidized (massive bands 

of pyrite). The geochemical results were highly anomalous in 

Ag, As, Hg, Ba, and Tl. Due to the mine lithologies intersected, 

abundant pyrite, silica alteration, and a distal geochemical 

signature, the potential of the Lower Zinc Creek prospect was 

upgraded (A.W. West and others, written commun., 2001).

Five holes were drilled in Killer Creek. The first two 

holes, PS–139 and PS–142, targeted a northwest-striking zone 

of zinc-rich, poorly exposed gossan. Both holes were abandoned in a wide fault zone (middle Gallagher fault) before 

reaching their target depth. Three holes drilled from two 

platforms in middle Killer Creek targeted a deep phyllite-overargillite contact inferred from the CSAMT survey. None of 

the holes intersected argillite. However, all three did intersect 

fault-controlled secondary mineralization within 400 feet of 

their collars. Four moderately southwest-dipping zones with 

silver and zinc enrichment were defined with assays as high 

as 22.4 troy ounces per ton silver and 9.62 percent zinc (A.W. 

West and others, written commun., 2001). The intervals did 

not have sufficiently consistent grades or widths to be of economic significance.

Conclusion

For more than three decades, exploration, development, 

and production at the Greens Creek mine has been challenging. Fourteen years passed between the discovery drill 

hole intersecting over 80 feet of massive sulfide and the mill 

processing the first ore. During that time Greens Creek nearly 

became a casualty of a large conservation movement that 

included the White House and Congress. This movement culminated in the passage of ANILCA, which at first threatened 

to kill the project and then severely limited the land position 

at Greens Creek. Greens Creek emerged from this situation 

as an apparent incongruity: a mine within a national monument bordering a wilderness area. However, exploration for 

new orebodies from the surface effectively ceased. After 12 

years of negotiations on local, State, and Federal levels, the 

land position was remedied in 1996 with signing of the Land 

Exchange Act. This unique act supported by conservation/

environmental groups and industry alike increased Greens 

Creek’s land position to what it was previous to ANILCA and 

added to the federally protected lands in the Admiralty Island 

National Monument and elsewhere in Alaska.

Exploration from the surface and underground has been 

successful in adding to Greens Creek’s known reserves during 

the life of the mine. The nearly constant changes in ownership, personnel, and geologic models did not prevent new 

orebodies or extensions from being discovered. When low 

metal prices temporarily closed the mine in 1993, the highgrade Southwest Ore zone was discovered and drilled out. 

This new orebody allowed Greens Creek to reopen profitably 

in 1996. Since reopening, new reserves have kept pace with 

production, adding nearly 4 million tons of ore. The mine’s 

proven and probable reserves, as of the end of 2001, are 7.6 

million tons grading 0.133 troy ounce per ton gold, 16.67 troy 

ounces per ton silver, 4.57 percent lead, and 11.63 percent zinc 

(Kennecott Greens Creek Mining Company, written commun., 

2001). The newly (re)acquired land-exchange lands provide 

abundant opportunities for future discoveries.

Reference Cited

Nash, Roderick, 1982, Wilderness and the American mind,

3d ed.: New Haven, Conn., Yale University Press, 425 p.
Geology of the Greens Creek Mining 

District

By Norman A. Duke, Paul A. Lindberg, and Andrew W. West

Chapter 4 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract.........................................................................................................................................................93

Introduction...................................................................................................................................................93

Regional Geotectonic Framework ............................................................................................................94

Structural Framework within the Greens Creek Domain .............................................................95

Tectonostratigraphic Assemblages..........................................................................................................96

Retreat Group ......................................................................................................................................96

Cannery Formation..............................................................................................................................97

Serpentinite..........................................................................................................................................97

Black Phyllite.......................................................................................................................................98

Hyd Group.............................................................................................................................................98

Basal Hyd Group Breccia/Debriite/Conglomerate Deposits .......................................................98

Restricted Mine Argillite Troughs ....................................................................................................99

Upper Hyd Group Gabbro Sills/Flood Basalts .......................................................................99

Mine Site and Prospect Geology ............................................................................................................100

Prospects in the Greens Creek District.........................................................................................100

Upper Cliff Creek......................................................................................................................101

Gallagher Creek........................................................................................................................101

West End ...................................................................................................................................101

Cub Creek/Lower Bruin Creek ...............................................................................................101

Upper Bruin Creek/Mammoth Ridge ....................................................................................101

Mammoth Pyritic Massive Sulfide Deposit .........................................................................102

Killer Creek................................................................................................................................102

Cascade Creek .........................................................................................................................102

Lakes District............................................................................................................................102

Zinc Creek .................................................................................................................................103

Lil Sore Creek............................................................................................................................103

A-Road Barite...........................................................................................................................103

Metallogeny................................................................................................................................................104

Conclusion...................................................................................................................................................105

Acknowledgment.......................................................................................................................................105

References Cited........................................................................................................................................105

Figures

1. Lodging facilities at Hawk Inlet................................................................................................94

2. Big Sore, the discovery site of the Greens Creek deposit...................................................94

3. Mine argillite exposed at mile 2.2 on the B-access road.....................................................95

4. Convolute-folded black dolomite beds in massive sulfide, M120-S200 Ext ......................96

5. Hyd Group basalt capping the South Ridge at the headwall of Gallagher Creek..........101

6. Surface drill site in upper Cub Creek.....................................................................................101

7. P. Lindberg examining green carbonate on Mammoth Ridge ...........................................102
8. The trace of the Maki fault system north of Gunsight Pass ..............................................102

9. Silicified rock developed below the Killer Creek serpentinite..........................................102

10. Basal Hyd Group phyllite breccia exposed in upper Zinc Creek......................................103

11. Basal Hyd Group heterolithic debriite exposed in lower Zinc Creek...............................103

12. A. West examining mine argillite exposed in Lil Sore Creek.............................................103

Plate

[on CD–ROM]

4–1. Geology of the Greens Creek mine area.

Abstract

The Greens Creek polymetallic sulfide deposit occurs 

within the low-grade metamorphic core of the Admiralty 

subterrane of Alexandria. Local tectonostratigraphic assemblages constitute late Paleozoic back-arc basement and its 

Upper Triassic flood basalt cover sequence. The Admiralty 

back-arc basin was volcanically active into the Devonian, 

giving rise to Retreat Group greenstones. The Upper Devonian through Lower Permian Cannery Formation includes 

older deep marine siliciclastics and a younger shallow marine 

dolomite-chert facies. The uppermost Pybus Formation signals 

the termination of back-arc sedimentation through shoaling 

accompanying the amalgamation of Alexandria and Wrangellia by the mid-Permian. The post-amalgamation unconformity 

ended with Late Triassic rifting driven by the Nikolai plume: 

the Carnian Nikolai Greenstone and Norian Hyd Group flood 

basalt provinces, occurring respectively in Wrangellia and 

Alexandria, overlap in time. The Greens Creek deposit is 

hosted within Carnian/Norian-age black argillite occurring 

below the Hyd basalts.

Protracted compressional tectonism attended the suturing 

of the Wrangellian superterrane to continental North America. 

Mid-Cretaceous collision resulted in fold and thrust-style 

imbrication, while dextral transpression on the Tertiary Denali 

transform system caused severe strike-slip dislocation of the 

imbricated stratigraphic package. The back-arc assemblage and 

its flood basalt cover were decoupled, resulting in a stacked 

series of inversely metamorphosed thrusts south of the mine. 

The Greens Creek deposit occurs in low-grade phyllites, which 

make up the lowest exposed thrust plate. This mineralized 

domain is bound by major ductile faults bordering on Hawk 

Inlet and Young Bay. Brittle northwest-southeast fault fracture 

systems are common; the Maki fault through the immediate 

mine site dextrally offsets the mineralization about 1,800 feet.

The Hyd Group is subdivided informally into basal 

growth-fault-related breccia/conglomerate, medial mine 

argillite, and upper basalt members. At the mine, the Retreat 

Group greenstone substrate to mine argillite is interleaved 

with sheets of serpentinite and lesser metagabbro. Intense 

hydrothermal alteration of this rock association forms 

the informal mine phyllite in the stratigraphic footwall of 

the ore. Widespread occurrence of barian mariposite ties 

hydrothermal alteration of serpentinite to massive baritic 

ores capping mine phyllite. High-grade laminated ores at the 

base of mine argillite are capped by bedded pyrite, and thin, 

cherty, black manganoan dolomite beds persist into overlying 

slaty argillite.

Greens Creek is unique in that it comprises high-grade 

zinc-lead-silver-gold ores at a major unconformity in a 

juvenile arc setting. The deposit is linked to an active rift 

segment plumbed by serpentinite/gabbro and filled with 

euxenic pyritic-graphitic argillite. Gabbro sills intruding 

mine argillite have the same geochemistry as the upper 

Hyd Group basalt, thus tying rifting to the Nikolai plume. 

Although somewhat of a volcanogenic massive sulfide/sedimentary exhalative hybrid, the Greens Creek setting lacks 

the felsic volcanics that characterize polymetallic Kurokotype volcanogenic massive sulfide districts. The link to a 

growth-fault-controlled, starved sedimentary trough makes it 

more appropriate to classify Greens Creek as a sedimentary 

exhalative deposit.

Introduction

The Greens Creek polymetallic (Zn-Pb-Ag-Sb-As-CuAu-Ba) sulfide deposit, the location of which is shown on 

plate 1 (plate 1 in digital form only), occurs in complexly 

deformed, low-grade phyllites exposed between Hawk Inlet 

and Young Bay on northern Admiralty Island. The mine is 

situated in the upper reaches of Greens Creek, outcropping 

as a gossanous kill zone on the west wall of the Big Sore 

tributary. This chapter describes the district geology of the 

Greens Creek mining area, extending from the cirque headwall of Cliff Creek, approximately 3 miles southeast of the 

mine, through the Zinc Creek drainage northeastward to the 

isthmus separating Hawk Inlet and Young Bay. The geological overview covers an approximate 10-mile-long segment of 

the northwest-trending phyllite belt on strike with the mine. 

The road connecting the mine to accommodation facilities on 

Hawk Inlet and docking facilities on Young Bay provides the 

most accessible transect through the complex tectonostratigraphy of the area (fig. 1). Because the mine is within the 

Admiralty Island National Monument, surface exploration is 

restricted to lands specified by a Federal land-exchange agreement dating from 1995, together with the area immediately to 

the north through the Lil Sore Creek drainage that is covered 

by Federal Mining Lode Claims. A total of 119 square miles is 

open to mineral exploration.

Geology of the Greens Creek Mining District

By Norman A. Duke, Paul A. Lindberg, and Andrew W. West
94 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Geological mapping in this area is severely hampered by 

rugged mountainous topography, a near-complete veneer of 

glacial till, and dense vegetation below ridge crests. Ridges 

provide the best exposures, with common rocky knobs outcropping through thin, clayey basal till. The steep U-shaped 

valley walls and heavy foliage, including patches of devils club 

wherever sunshine penetrates the canopy formed by old-growth 

stands of hemlock and spruce, restrict helicopter access largely 

to ridge crests. Muskegs that develop over the larger serpentinite bodies offer a few additional landing sites. The thickness 

of till cover increases downslope, with almost no bedrock exposure except on truncated spurs forming cliff faces and along 

deeply incised stream courses. Although creek traverses from 

ridge crests to valley floors are physically taxing, these provide 

the most effective means of attaining bedrock information.

The district geological map (plate 1) is based on 1-inch 

to 500-foot scale mapping carried out over most of the area 

shown and documented in unpublished Greens Creek Mining 

Company reports. The compilation incorporates data collected 

since the discovery of the Greens Creek deposit in the mid1970s (fig. 2). This information has been reinterpreted in the 

light of airborne geophysical surveys carried out in 1995–96. 

The core of the area, including upper Cliff Creek, the Greens 

Creek mine site, Mammoth Ridge to Killer Creek, and the 

Zinc Creek and Lil Sore Creek drainages, has been mapped in 

greatest detail. The geology shown for outlying areas is less 

detailed but is included to provide a broader context for situating the mine stratigraphy.

This chapter describes the district geological setting of 

the Greens Creek ore deposit. Results from limited supporting 

microscopy and geochemistry are reported; however, lithological subdivision is based essentially on field observations. We 

refine the Retreat-Cannery-Hyd tectonostratigraphic grouping 

based on earlier reconnaissance mapping by the U.S. Geological Survey (Lathram and others, 1965). The main objective 

is to define the structural/stratigraphic controls of the Greens 

Creek ores. The second section of this chapter presents a 

regional geotectonic framework for the district. The third section provides brief lithological descriptions and an overview 

of the local structural/stratigraphic relationships of the various 

rock units. The fourth section describes the mine-site geology and places several prospects within their geological 

framework. The fifth section offers a number of hypotheses 

concerning the genesis of the Greens Creek deposit, based on 

observed ore/host-rock relationships.

Regional Geotectonic Framework

Admiralty Island occupies a central position in the Alexander Archipelago and is the type locale for the Admiralty 

subterrane of the Alexander terrane (Alexandria). Alexandria 

formed as a Late Proterozoic-Paleozoic oceanic island arc 

system somewhat older than the late Paleozoic Wrangellian 

oceanic island arc system with which it had amalgamated by 

the Permian (Berg and others, 1978; Gehrels and Saleeby, 

1987a; Gardner and others, 1988; Karl and others, 1999a). On 

Admiralty Island, 265-Ma (mega-annum) metamorphic dates 

(Karl and others, 1999b; Haeussler and others, 1999) and a 

regional mid-Permian to Late Triassic unconformity record 

the time of amalgamation. The 50-Ma period of nondeposition following this event ended in the Middle to Late Triassic 

with rift-related flood basalt volcanism caused by the Nikolai 

Greenstone plume (Richards and Jones, 1991).

Recent geochronology (S.M. Karl, oral commun., 2002) 

identifies substrate on Admiralty Island dating back to the Late 

Proterozoic, thus linking the Admiralty subterrane to the Craig 

subterrane, which includes similar-aged Late Proterozoic and 

Paleozoic arc volcanics on Prince of Wales Island (Gehrels 

and Saleeby, 1987b). The deep-water, black argillite-chertpillow basalt assemblage forming the Middle Ordovician Hood 

Bay Formation on southern Admiralty Island (Carter, 1977) 

indicates that the Admiralty subterrane developed back arc 

to the frontal Craig volcanic chain. The Admiralty back-arc 

setting was still volcanically active in the late Paleozoic, with 

regional deposition of the Retreat Group greenstones, locally 

incorporating Devonian/Mississippian-age reefal carbonates. 

The Middle(?) Devonian through Lower Permian stratigraphic 

Figure 1. Lodging facilities at Hawk Inlet. Figure 2. Big Sore, the discovery site of the Greens Creek deposit.
Regional Geotectonic Framework 95

succession, constituting the Retreat Group and overlying 

Cannery Formation, appears to be more or less continuous on 

Admiralty Island. The Upper Devonian through Lower Permian 

Cannery Formation includes both an older, deep-water siliciclastic assemblage and a younger, shallow-marine chemical/

clastic dolomite-chert facies (Loney, 1964). The Lower Permian Pybus Formation chert member signifies termination of 

back-arc sedimentation under shoaling conditions accompanying the amalgamation of Alexandria and Wrangellia. The welding together of these two juvenile oceanic settings may have 

imparted the penetrative S1

 metamorphic segregation foliation 

that characterizes the Retreat Group.

The post-amalgamation unconformity ended with Middle 

to Late Triassic rifting related to the Nikolai plume. The 

Wrangellian Nikolai Greenstone and Admiralty Hyd Group 

flood basalt provinces overlap in time, although the Nikolai 

basalts are dominantly Carnian and the Hyd basalts Norian in 

age (fig. 3). As discussed in this paper, the Greens Creek ore 

deposit is hosted within Hyd Group rocks, specifically occurring at the base of the informal mine argillite member immediately underlying upper Hyd basalts. Conodont studies demonstrate that the mine argillite was deposited at the Carnian/

Norian transition between 225 and 221 Ma (chap. 11). Following the Nikolai rifting event, a Jurassic-Cretaceous arc/trench 

system developed between the Wrangellian superterrane and 

the North American craton, accounting for the flysche of the 

Seymour Canal Formation and the Douglas Island Volcanics 

occurring on the eastern side of Admiralty Island. Arc/craton 

collision driven by eastward subduction along the leading 

Wrangellian foredeep culminated in mid-Cretaceous through 

early Tertiary Coast Range plutonism.

The prolonged period of late Mesozoic compressional 

tectonism, an expression of the Laramide in the northern 

Cordillera, led to polyphase deformation in the Greens Creek 

mining area. The dominant regional tectonic grain relates to 

D2

 thrusting. That the Retreat Group and Cannery Formation lithologies are penetratively foliated by S2

, that mine 

argillite is isoclinally folded by F2

, but that upper Hyd Group 

flood basalts only show strong S2

 development along their 

basal contact, indicates that the Upper Triassic deposits were 

ramped at relatively shallow crustal levels. Following the D2

overprint, the accreted complex was subjected to protracted 

transpression, giving rise to upright chevron-style F3

 folding 

and related steeply dipping shear zones that strongly disrupt 

the regional D2

 structural/stratigraphic framework. Reactivation of D2

 thrusts post-D3 produced shallow-dipping D4

shears that locally overprint S3

. Mid- to late-Tertiary dextral 

transform faulting along the Denali transform system, with 

major strands following Chatham Strait and Gastineau Channel, occurring respectively west and east of Admiralty Island, 

caused brittle D5

 faults, such as the Maki system cutting 

through the immediate Greens Creek mine site. The similar 

orientations of D3

-ductile and D5-brittle structures indicate 

that the D3

 structural grain was reactivated in D5. The late 

dextral fault strands locally develop complementary interior 

sinistral fault/fracture sets of minimal displacement.

Structural Framework within the Greens Creek 

Domain

The Greens Creek domain is defined as comprising the 

low-grade metamorphic assemblages which occur between 

major north- to northwest-striking shear zones bordering 

Hawk Inlet and Young Bay. Hyd Group rocks east of the 

Young Bay shear zone are at epidote-amphibolite hornfels 

facies, suggesting proximity to a Coast Range pluton such as 

the one mapped on the northeast corner of Admiralty Island. 

The mafic metavolcanic rocks occurring southwest of the 

Greens Creek thrust are overprinted by regional epidoteamphibolite facies metamorphism. These amphibolites may 

include amygdaloidal Retreat greenstones as well as Hyd-age 

metagabbro sills. The uppermost thrust forming the Cliff 

Creek headwall at the southeast corner of the map is a garnetamphibolite facies. Recent U/Pb dates demonstrate the presence of Hyd-age metadiorite intrusions (S.M. Karl, oral commun., 2002). These garnet amphibolite gneisses are strongly 

injected by mid-Cretaceous(?) ferrodiorite and pegmatite 

dikes. The stacking of higher grade amphibolites structurally 

above the low-grade Greens Creek domain suggests that the 

area was strongly telescoped in a subductionlike setting typified by hot over cold metamorphic plates. The low greenschist 

facies domain hosting mineralization forms the structurally 

lowest plate, and the ambient metamorphic overprint within 

the Greens Creek domain is below biotite stability. Limited 

Ar/Ar work on white mica identifies a mid-Cretaceous age for 

the low greenschist facies metamorphic conditions (Brew and 

others, 1992; Haeussler and others, 1999).

The gross distribution of lithological units in the Greens 

Creek domain reflects dome-and-basin structural egg-crating. 

The prominent bluff of Retreat Group marble surrounded by 

Retreat Group greenstone that is shown in the central-northwest portion of the map area is identified as an F2

 isocline preserved on the nose of an F3

 anticline. The serpentinite-cored 

area of Retreat greenstone, extending westerly from the mine 

site through the Killer Creek drainage, is another basement 

high interrupting the Zinc Creek/Lil Sore Creek and Gallagher 

Figure 3. Mine argillite exposed at mile 2.2 on the B-access road.
96 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Ridge tracts of mine argillite. The undifferentiated Cannery 

Formation sedimentary rocks on the eastern side of the map 

area and transected by the Young Bay shear zone form a subtly 

developed structural high. These domal elements are bordered 

by peripheral black phyllite. The more restricted tracts of mine 

argillite are tectonically imbricated with Retreat greenstone. 

In its regional context the Greens Creek domain comprises a 

window of complexly deformed low-grade phyllites exposed 

beneath Hyd flood basalts, forming nearly complete cover 

along the southern margin and a continuous belt along the 

northeastern boundary of the mapped area.

Tectonic imbrication, dome-and-basin interference patterns, and major northwest-trending faults collectively indicate 

that the area of the Greens Creek deposit has been subjected 

to polyphase deformation. There is evidence of five deformational events. The dominant penetrative S2

 schistosity trends 

approximately east-west and dips moderately 20–40° south. 

An earlier S1

 segregation foliation within Retreat greenstone 

forms isoclinal microfold closures in S2

. The thin-bedded 

mine argillite exhibits isoclinal F2

 folding: spaced S2 cleavage 

in these rocks is axial planar to exceptionally appressed F2

folds, which are particularly well exposed at mile 2.2 on the 

B-access road and in the underground workings. S2

 is more or 

less penetrative in all lithologies in the Greens Creek domain 

except for massive serpentinite, metagabbro, and the black 

dolomite beds, which occur within mine argillite. The ultramafic/mafic intrusions escaped this deformation through strain 

partitioning into marginal shears, while the black dolomite 

beds deformed brittlely, giving rise to ubiquitous ladder quartz 

veining (fig. 4). D2

 accounts for the structural imbrication of 

the serpentinite-cored panels of Retreat greenstone north of 

the Killer Creek serpentinite body as the shallow to moderate, 

south-dipping lithological contacts paralleling S2

 are clearly 

overprinted by high-angle D3

 fabrics.

D3

 gave rise to northwest-southeast-trending shears and 

variably tight, upright, chevron-style folding of S2

. This fabric 

is only penetrative within the bounding Young Bay shear zone 

and the north-trending Hawk Inlet high strain zone. S3

 intensifies along the numerous northwest-trending brittle/ductile fault 

zones. Most of the deformation along these topographic linears 

appears ductile, stress being accommodated largely by ductile 

stratal thinning rather than through brittle fault failure. D4

 relates 

to late (post-S3

) low-angle shearing and intensifies southward 

toward the base of the thrust plates of amphibolite. S4

 is rather 

common in the immediate mine area (for example, the Klaus 

fault), causing low-angle transposition of the steeply dipping 

S3

 cleavage sets. It is notable that D2 thrusts and D4 shears both 

show broadly coincident orientation and vergence, suggesting 

reactivation of D2

 thrusts late in the history of transpressional 

D3

 shearing. All rocks have been displaced by late northwestsoutheast-trending brittle faults showing dextral displacement—

the Gallagher and Maki fault/fracture systems through the area 

of the mine show on the order of 1,000 and 1,800 feet of dextral 

west-side-up displacement, respectively. Complementary 

sinistral fault splays have only minor displacements; but where 

present, these make tracing geological units very difficult.

Tectonostratigraphic Assemblages

Retreat Group

Three lithotypes are differentiated in the Retreat Group: 

greenstone, black phyllite, and marble. The only map-scale 

unit of Retreat marble is restricted to Limestone Bluff. Fossils 

collected by the USGS suggest that the marble is Silurian or 

Devonian (D.A. Brew, oral commun., 2002), which is consistent 

with the Middle(?) Devonian age assignment for this unit proposed by Lathram and others (1965). Limestone units occurring 

on strike to the north on the west shore of Hawk Inlet have been 

identified as Middle Devonian on the basis of recent conodont 

determinations (A.G. Harris, oral commun., 2001). The marble 

at Limestone Bluff is gray- to buff-weathering and composed 

essentially of coarsely crystalline calcite. Primary bedding 

is only weakly discernible, with buff dolomitic and siliceous 

layers slightly more resistant to weathering. Transecting shears 

weather brown and have limited quartz vein development. Lustrous gray to black phyllite forms thick units interlayered with 

the Retreat greenstones. That these monotonous “black shale” 

units have intimately interstratified greenstone panels suggests 

that they represent background sedimentation coincident with 

Retreat mafic volcanism. Also, like the Retreat greenstone units, 

these tracts of lustrous black phyllite retain no primary bedding 

features due to an intense S1 schistosity that developed prior to 

overprint by the regionally penetrative S2-crenulation cleavage.

Units of Retreat Group greenstone are dominated by 

monotonous green chloritic phyllite with variable interlayering 

of lustrous gray phyllite after graphitic shale and rare thin gray 

to white marble bands. Retreat Group greenstone is without 

doubt the most enigmatic lithology in the district. This greenstone is everywhere characterized by streaky light/dark green 

layering of tectonic origin. The S1

 overprint was so severe that 

neither flow nor intrusive contacts were observed. Rare relict 

amygdules in samples collected north of Limestone Bluff, 

in the Lakes District, and at the west end of Gallagher Ridge 

Figure 4. Convolute-folded black dolomite beds in massive sulfide, 

M120-S200 Ext. Photograph by N.A. Duke, University of Western 

Ontario.
Tectonostratigraphic Assemblages 97

indicate a flow origin. Contacts with bordering units appear 

entirely tectonic; the streaky-foliated greenstone panels are 

structurally interleaved with gray phyllite and massive serpentinite. Greenstone contacts against graphitic units are strongly 

carbonatized. Contacts with interleaved serpentinites are 

extremely slivered, with greenstone/serpentinite sheeting on 

the meter scale. At the mine site, variably intense hydrothermal alteration of greenstone/serpentinite protoliths gives rise 

to voluminous mine phyllite in the stratigraphic footwall of 

the Greens Creek ore horizon (discussed herein and in Chap. 

6). Limited geochemical work on Retreat greenstone broadly 

indicates that the protolith was compositionally similar to 

midocean-ridge basalt. Based on the present level of mapping, 

Retreat Group greenstone forms the primary flooring for the 

Hyd Group at the site of the Greens Creek mineralization. The 

S1 foliations indicate that this substrate was extremely tectonically attenuated prior to S2

 deformation. The mine phyllite 

enveloping serpentinite may have been radically thinned at the 

time of serpentinite emplacement.

Cannery Formation

Although the map shows the Cannery Formation as 

essentially undivided, the separate areas mapped as Cannery 

show marked lithological differences. The main domical exposure transected by the Young Bay shear zone is dominated 

by low-grade phyllites after core dolomitic arenite, medial 

dolomitic siltstone, and peripheral phyllitic chert. The outer 

phyllitic chert likely accounts for the on-strike cherty white 

phyllite units interleaved with black phyllite east of the mine. 

This same siliceous white phyllite accounts for the slaty siliceous sediments capping northerly trending spurs off the eastwest-trending Gallagher Ridge of Hyd Group basalt south of 

the mine. These isolated white phyllite domains form klippen 

overlying the immediate mine stratigraphy at the Gallagher 

Creek headwall. This cherty white phyllite unit in the Greens 

Creek area is tentatively correlated to the Pybus Formation 

that caps the Cannery Formation regionally. Weathering of 

Pybus Formation accounts for common chert pebbles in basal 

Hyd Group conglomerate over Admiralty Island.

The metasedimentary rocks bordering on Retreat Group 

greenstone at Limestone Bluff are dominantly lustrous black 

and white siliceous schist. The more siliceous (cherty) units in 

this package form the prominent ridge crests paralleling Hawk 

Inlet. The Cannery Formation exposed along the shore of 

Hawk Inlet at the Cannery and along the A-road to Young Bay 

comprises varicolored gray-green-white-black banded schists, 

in part graphitic (black), in part marly (green) and in part dolomitic (white). The graphitic units are locally rich in nodular 

pyrite. The thin-banded character of these siliceous units is in 

part attributed to high D3

-strain overprinting a compositionally 

varied deep marine siliciclastic facies. This assemblage is interpreted as an older (Carboniferous?) component of the Cannery 

Formation. It is possible that some black phyllite now identified as Retreat Group sediment may include infolds of Carboniferous(?) siliceous rock. The Retreat “black schists” mapped 

below the serpentinite of Killer Creek and the Mammoth Ridge 

green carbonate are strongly silicified, thus showing lithological similarity to the siliceous schists mapped as Cannery. The 

masking of lithotype by silicification is even more extreme 

in the Lakes District where considerable thicknesses of silica 

rock could be protolithed in either Retreat black phyllite or 

the Cannery siliceous sedimentary rocks. The lower Cascade 

Creek section is somewhat transitional in lithology between 

Retreat phyllite and Cannery siliceous-graphitic-pyritic schist. 

This particular section is classed as Cannery on the basis that 

it is somewhat more lithologically varied than is typical for the 

units mapped as black phyllite of the Retreat Group.

Serpentinite

The largest single serpentinite mass in the map area is 

the Killer Creek body, located 1.5 miles west-northwest of 

the mine site. This unit is strongly sheared on its upper and 

lower contacts against variably altered Retreat greenstone. 

Serpentinite-injected greenstone forming substrate to mine 

argillite is strongly carbonatized. The panel of Retreat greenstone in the immediate footwall of mine argillite is variably 

sulfidized, with pyrite-pyrrhotite-chalcopyrite forming patchy 

disseminations and locally massive replacement pods of meter 

scale. The northern contact of the serpentinite of Killer Creek 

has occasional talc-sericite-carbonate shears with associated 

zinc-lead-silver disseminations. The faulted southeast nose, 

exposed in Killer Creek at the B-road bridge, has associated 

massive magnetite-pyrite skarn mineralization.

Although the margins of the Killer Creek serpentinite 

are strongly deformed and mineralized, the interior is massive 

nonfoliated serpentinite. Limited microscopic study shows 

coarse honeycomb-textured serpentine outlined by the distribution of fine magnetite (up to about 10 modal percent). Ubiquitous disseminated magnetite in massive serpentinite accounts 

for coincident magnetic anomalies. The massive serpentinite 

of Killer Creek is a striking airborne magnetic anomaly, as are 

structural repeats at the mine site and in the upper reaches of 

Zinc Creek. However, serpentinite replaced by green carbonate 

(listwanite) is not magnetic, indicating magnetite breakdown 

during pervasive carbonatization. Extreme carbonatization of 

serpentinite is accompanied by formation of spaced waxy green 

foliations defined by barian mariposite. Limited microprobe 

work on green carbonate collected from Mammoth Ridge 

identifies paragenetically early magnesite and later species 

within the ankerite-kutnahorite solid solution series. Barite, barian mica, and barian feldspar species are also present. In some 

panels, like the one in upper Zinc Creek, green carbonate locally 

retains relict metagabbroic textures. Green micas in these 

domains are chromium-poor and barium-rich (oellacherite), 

indicating similar carbonate-barite replacement of the gabbroic 

injections into serpentinite. The best locale for demonstrating that sheeted gabbro dikes locally inject serpentinite is at 

Serpentine Gulch, the most northeasterly green carbonate body 

exposed on the Bruin Creek/Cub Creek ridge crest. Here, massive serpentine appears rather fresh, while numerous phases of 
98 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

gabbro with preserved multiple chill margins are pervasively 

retrograded to green-brown mica, complex magnesium-ironmanganese carbonates, and pumpellyite (Reich, 1996). The 

mixed serpentinite/green carbonate sheet exposed in the uppermost tributaries of Lil Sore Creek shows considerable lithological affinity to the serpentine/gabbro complex at Serpentine 

Gulch.

In the more highly sheared and altered serpentinite/green 

carbonate sheets north of the main Killer Creek body there 

is ample evidence for structurally controlled talc-carbonate 

replacement of massive serpentinite. Toward sheared margins 

the massive serpentine becomes increasingly transected by 

brown carbonate fracture sets. Tectonic milling of serpentine 

blocks results in talc-carbonate schist enveloping “knockers” 

of massive serpentine. Within green-yellow talc schist, slips 

of green barian mariposite progressively replace serpentine 

smears. Talc-mariposite-barite veins crosscutting carbonated 

serpentinite and associated green carbonate are themselves 

deformed in S2

, clearly indicating that serpentinite emplacement/replacement predated regional D2

 metamorphism. Common occurrence of green carbonate clasts in basal Hyd debriite 

(debriite is used here to connote debris-flow deposits, following Warme and Kuehner, 1998) conclusively ties serpentinite 

emplacement, alteration, and exposure to basal Hyd times. 

On the basis of detailed structural/stratigraphic evidence, the 

emplacement of serpentinite, with limited associated sheeted 

gabbro, can thus be linked to the initial stages of Hyd rifting. It 

is hypothesized that the serpentinite sheets were injected into 

growth faults that controlled the deposition of the mine argillite member of the Hyd Group.

Black Phyllite

The extensive tracts of black phyllite that occupy the 

structural lows between the domains of Retreat greenstone 

and the Cannery metasedimentary rocks present a critical 

stratigraphic problem within the Greens Creek mining area. It 

is somewhat unclear to which unit they should be assigned; as 

mapped, they may include similar lithology of differing ages. 

The fact that the panels of Retreat Group greenstone are interlayered with panels of lustrous black phyllite indicates that 

black phyllite is a major member of the Retreat Group. However, that black phyllite also occurs peripheral to siliceous 

schist domains tentatively correlated with Pybus Formation 

suggests a black phyllite member that is younger than the 

uppermost member of the Cannery Formation. This problem 

is exacerbated by the difficulty of differentiating slaty to phyllitic facies of mine argillite from the more regionally extensive tracts of younger black phyllite. As currently shown on 

the map, the contact between black phyllite and mine argillite 

is a rather arbitrary boundary placed between (a) euxenic 

argillite with easily discernible black dolomite beds and (b) 

monotonous gray to black phyllite lacking recognizable bedding. At the current level of mapping, the tracts of undifferentiated black phyllite are considered primarily to postdate the 

Cannery Formation and, at least in part, to show stratigraphic 

continuity with the mine argillite—the youngest black phyllite may occur on the weak sides and restricted mine argillite 

buttressing against fault blocks of Retreat greenstone on the 

strong downthrown sides of half grabens.

Hyd Group

Unlike the Retreat Group and Cannery Formation in 

which detailed stratigraphy remains but poorly resolved due 

to complex regional metamorphic overprinting, the Upper 

Triassic Hyd Group, postdating the mid-Permian amalgamation of Wrangellia, can be clearly subdivided into basal growth 

fault-related breccia/debriite/conglomerate deposits, medial 

argillite, and upper basalt members. Other units include local 

argillaceous limestones at the base of the upper basalt and 

gabbro sills within medial mine argillite. Gabbro sill-argillite 

complexes occur below the upper Hyd basalts capping the 

Gallagher Ridge south of the mine, in the Lakes District, and 

in lower Lil Sore Valley south of Young Bay.

Basal Hyd Group Breccia/Debriite/

Conglomerate Deposits

The primary significance of the occurrence of extensive 

basal Hyd fragmental units is that these stratigraphically tie 

the Hyd Group to Retreat substrate. Most importantly, the 

lithological diversity of basal Hyd growth-fault-related rocks 

identifies the specific nature of the Hyd rift just prior to the 

deposition of mine argillite, host to the high-grade Greens 

Creek ores. The deepest seated manifestation of growth-fault 

lithotypes comprises 10–100-meter-thick zones of silicified 

mylonite (mapped as Trhsr—siliceous rock) closely affiliated 

with carbonate-altered serpentinite. There is a semicontinuous 

siliceous band striking from the immediate mine site along the 

length of Mammoth Ridge. The silicified rock delineating this 

structural unit is derived primarily through intense silicification of greenstone protolith, accounting for finely disseminated leucoxene. Not shown are associated alteration zones 

grading outward from siliceous rocks into tan sericite-leucoxene phyllite, sericite-chlorite-ankerite phyllite, and chloritecalcite phyllite into greenstone. These various hydrothermal 

alteration zones overprinting Retreat greenstone collectively 

make up the mine phyllite occurring in the stratigraphic footwall of the Greens Creek ore deposit. As this zoning is best 

developed at the mine site, it is described in more detail in the 

section below on mine geology. The silica rock that forms a 

series of benches in the Lakes District is thought to represent a 

major sheet of silicification related to the emplacement of the 

Killer Creek serpentinite.

By far the best exposures of basal fault-breccia and 

debriite are found in outcrops following Zinc Creek and forming a near-continuous unit extending northeast along the Lil 

Sore drainage. The best development of nonbedded fault breccia is in the lower and middle reaches of Zinc Creek. These 
Tectonostratigraphic Assemblages 99

areas are dominated by massive heterolithic phyllite breccia 

protolithed wholly in mine phyllite and green carbonatealtered serpentinite. The fact that no fresh greenstone and 

only rare serpentinite clasts are observed in these breccias, 

despite their provenance in greenstone/serpentinite-altered 

equivalents, unequivocally links the formation of basal Hyd 

fault breccia to hydrothermal alteration of active fault structures controlling the deposition of mine argillite.

The first appearance of mine argillite clasts in fault breccia 

approximates the transit from poorly layered breccia to bedded 

debriite. Significantly, the most readily identifiable mine phyllite clasts in bedded debriite tend to be the most highly altered 

sericite-mariposite phyllite and green carbonate clasts. The 

matrix of debriite adjacent to basal mine argillite is typically 

crystalline quartz-carbonate, signifying a hydrothermal silicadolomite cementing agent. Nodular pyrite, with or without 

barite, is relatively common. The contact between basal Hyd 

debriite and medial Hyd mine argillite is placed at the transition 

from dolomite-clast debriite, which comprises cryptocrystalline black dolomite clasts in a crystalline carbonate matrix, 

to coherently bedded black dolomite interlayered within slaty 

black pyritic argillite. North of the Zinc Creek/Lil Sore Creek 

divide, resedimented argillaceous grit overlies non- to poorly 

layered mine phyllite pebble debriite. The unit of Hyd Group 

conglomerate (Trhc) traced from exposures on the A-road 

southeasterly to the mouth of Lil Sore Creek on Young Bay is 

also poorly layered but contains a greater variety of clasts—the 

red jasper clasts are weathered from Pybus Formation while the 

green carbonate clasts indicate a source in mine phyllite. The 

Hyd conglomerate unit shown at the headwall of Greens Creek 

separates black phyllite and Hyd flows; that is, no mine argillite 

is recognized at this locale. This particular conglomeratic unit 

includes upper Hyd Group basalt clasts, indicating that deposition postdated the initiation of the flood basalt volcanism.

Restricted Mine Argillite Troughs

The occurrence of well-bedded black argillite/black 

dolomite overlying debriite deposits of the same lithological makeup conclusively ties mine argillite stratigraphically 

to the basal Hyd Group fault-controlled breccia/debriite/

conglomerate deposits. Using dolomite beds as a defining 

characteristic of mine argillite restricts its distribution to (1) 

the faulted margins against altered Retreat greenstone (mine 

phyllite) and (2) the immediate base of upper Hyd flood 

basalt. At the mine, the high-grade laminated zinc-leadsilver ores form a basal mine argillite facies that immediately 

overlies massive white carbonate-barite ores capping mine 

phyllite. Here, the well-bedded mine argillite overlies only 

minor basal Hyd fault breccia/chert conglomerate, indicating the juxtaposition of a coherent panel of intensely hydrothermally altered Retreat greenstone almost directly against 

slump-folded mine argillite.

In the Zinc Creek trough, the Greens Creek ore horizon 

occurs well below the base of coherently bedded black dolomite interlayered with pyritic slaty argillite. Given the setting 

at the mine site, ore should occur below the first appearance 

of black dolomite clasts within debriite stratigraphy. Thin 

(decimeter scale) black dolomite interbeds persist vertically 

through mine argillite even where this unit is apparently thickest, as in the Lil Sore Valley and on Gallagher Ridge. That 

no significant mineralization is known to occur much above 

the basal contact suggests that hydrothermal activity and ore 

deposition coincided with the collapse that initiated restricted 

trough-controlled mine argillite sedimentation.

The upper termination of mine argillite is represented by 

a thin, discontinuous argillaceous limestone member deposited 

immediately below the upper Hyd flood basalts. Conodont 

specimens from basal ores to the capping limestone identify 

a relatively short time span for mine argillite deposition 

(220.7±4.4 Ma, chap. 11). The variable yet considerable thickness of mine argillite (locally up to a few hundred meters) may 

be attributed to chemical precipitation within hydrothermally 

active troughs keeping pace with tectonic subsidence; that is, 

the host mine argillite to the Greens Creek ore may represent a 

highly reduced hydrothermal brine pool lithofacies.

Upper Hyd Group Gabbro Sills/Flood Basalts

The Greens Creek District includes only the basal members of the upper Hyd Group: the gabbro sills intruding into 

the medial Hyd mine argillite and the immediately overlying, 

similarly metagabbroic-textured massive flows, flow breccias, 

and minor pillow basalt. Intense swarms of gabbro sills intrude 

white phyllites (a Pybus equivalent?) in upper Cliff Creek and 

mine argillite south of the mine, in the Lakes District, and 

in Lil Sore Valley. These gabbros are medium grained and 

nonfoliated and exhibit relict gabbroic to diabasic textures. 

They are completely hydrated, being composed essentially of 

uralitized pyroxene and saussuritized plagioclase. The limited 

petrographic work carried out to date has not identified any 

relict primary pyroxene or plagioclase. Observed fining of 

grain size toward sill margins indicates that the secondary 

mineralogy faithfully pseudomorphs the primary igneous textures. The massive metagabbroic units overlying mine argillite 

in the Lakes District are fine to medium grained and could 

include massive flows capping the medial Hyd argillite. Upper 

Hyd flows capping Gallagher Ridge and traced to the headwall 

of Cliff Creek immediately overlie a discontinuous limestone 

unit occurring at the top of the mine argillite. These may show 

the same metagabbroic textures as the sills into underlying 

mine argillite but are retrograded to greenschist facies chloritealbite-calcite mineral assemblages. The Hyd Group basalts of 

upper Cliff Creek are dominantly flow breccias. Rare pillowed flows in the lowermost volcanic units indicate initial 

eruption into locally submarine conditions. Hydrothermal 

breccias crosscutting the basal flows have associated minor 

chalcopyrite-pyrite mineralization.

Little information is presently available for the superjacent garnet amphibolite facies mafic gneisses in upper Cliff 

Creek. The boundary between the greenschist and amphibolite facies rocks is a sharp, moderately south-dipping thrust 
100 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

surface along which amphibolitic gneisses are juxtaposed 

over greenschist facies metavolcanics. The amphibolitic 

gneisses are characterized by metamorphic layering and 

common ferrodiorite and pegmatite diking. Only one dike of 

ferrodiorite was observed on the Gallagher Creek headwall 

below the Cliff Creek thrust. Notably, similar ferrodiorite 

dikes have also been intersected locally in the underground 

mine workings where they clearly crosscut S2, but both inject 

and are overprinted by D3 cleavages. The relation of the 

garnet amphibolite facies gneisses at the base of the Cliff 

Creek thrust to epidote-actinolite amphibolite occurring at 

the base of the central Greens Creek thrust is unknown. The 

strong airborne magnetic anomaly associated with this latter 

boundary may relate to basal serpentinite and(or) a pyrite to 

pyrrhotite metamorphic conversion.

Mine Site and Prospect Geology

Bedrock exposures at the Greens Creek mine site are limited, and the specific geological setting of the ores is best deciphered on the basis of underground mapping and drill sections. 

Only features that place the mineralization within the regional 

structural/stratigraphic framework and bearing most directly 

on the origin of the high-grade ores are considered here. Following a brief review of the mine-site geology, selected known 

mineral prospects are described to illustrate the metal endowment of the district as a whole.

The Greens Creek ore horizon outcrops near the eastern 

nose of Retreat greenstone cored by the Killer Creek serpentinite. This nose of greenstone is intensely altered, forming 

mine phyllite proximal to the mineralization. The host structure has the geometry of an F2

 anticline. Given the subtle 

but significant change from structurally lower mine argillite 

to structurally overlying black phyllite on the limbs, it is 

possible that the core of greenstone may have originated as 

a basement horst, sidewall to a mine argillite trough. Crossfolding causes marked structural egg-crating and accounts 

for symmetrical hour-glass pinchouts of the immediate mine 

stratigraphy on the opposing limbs. The Greens Creek ores 

are specifically sited on the overturned eastern limb. Offsets postdating F3

 folding caused by the Klaus and Maki 

fault systems severely hamper stratigraphic reconstructions. 

Nevertheless, the detailed exploratory work clearly demonstrates that ore is confined to the immediate mine argillite/

mine phyllite contact. The Greens Creek ore horizon is 

sandwiched between structural-hanging-wall mine phyllite, 

derived from hydrothermal alteration of Retreat greenstone, 

and structural-footwall mine argillite, on the lower overturned F2

 fold limb. The original host-rock stratigraphy had 

mine argillite deposited against pervasively hydrothermally 

altered Retreat greenstone (the mine phyllite). Mine phyllite 

comprises chlorite-calcite phyllite, chlorite-sericite-ankerite 

phyllite, tan sericite-leucoxene phyllite, and silica rock 

developed through increasingly intense hydrothermal alteration of an already S1

-foliated greenstone protolith, as well as 

green barian mariposite-talc-carbonate-barite phyllite developed through alteration of serpentinite and lesser gabbro.

At the mine portal, mine argillite is separated from the 

mine phyllite by a thin interval of dolomitic phyllite/cherty 

dolomite. This assemblage has lithological kinship to the white 

phyllite occurring south and west of the mine and is tentatively 

correlated with the Cannery Formation (PDcpw on plate 1). 

Both undergound and surface drilling have commonly intersected impure dolomitic to phyllitic cherts below a persistent 

black and white banded chert marker. Where this impure chert/

dolomite sequence stratigraphically underlies the high-grade 

ores, it carries appreciable pyrite and may contain up to 2 

percent zinc. Massive bodies of white dolomite-barite, capping 

mine phyllite and at least partly derived through hydrothermal 

replacement of greenstone protolith, can locally constitute 

high-grade zinc (20 percent), lead (8 percent), silver (20 troy 

ounces per ton), and gold (0.5 troy ounce per ton) “White Ore.” 

The very high-grade zinc (30 percent), lead (10 percent), and 

silver (>50 troy ounces per ton) laminated “Black Ore” occurs 

at the base of anoxic graphitic argillite peripheral to massive, 

non- to poorly bedded “mounds” of framboidal textured pyrite. 

The highest grade ores are essentially restricted to the base of 

the mine argillite. Immediately above ore, the mine argillite is 

characterized by dense, cherty, black dolomite interbeds that 

are moderately manganiferous (2 percent MnO2

). Away from 

mineralization, the host mine argillite tends to be limy rather 

than graphitic and dolomitic, suggesting waning of hydrothermal input away from zones of discharge.

The stratigraphic position of the Greens Creek ores at 

the Retreat Group/Hyd Group contact places the site of the 

mineralization at the regional mid-Permian to Upper Triassic 

unconformity. Where preserved, the footwall cherts are commonly hydrothermally silicified and brecciated and are locally 

conglomeratic. These sometimes-graded chert pebble beds 

represent erosional lags of the Pybus Formation and therefore 

identify the basal Hyd unconformity. The affiliation of silicified conglomerates with limited, growth-fault-controlled mine 

phyllite breccia indicates that Greens Creek mineralization 

accompanied the initial collapse of the Hyd rift, the deposition of the overlying high-grade black ores coinciding with 

restricted marine incursion.

Prospects in the Greens Creek District

A number of prospects have been discovered during 

ongoing surface exploration efforts in the Greens Creek 

district. The following brief descriptions of selected targets 

illustrate the character of mineralization away from the 

immediate mine site. Prospects are listed from the south 

extension of the land exchange northward; the primary aim is 

to situate various mineralized sites within their local geological environment.
Mine Site and Prospect Geology 101

Upper Cliff Creek

Mine argillite underlies the upper Hyd basalt in the 

headwall of Cliff Creek. Numerous Hyd gabbro sills are 

injected into white cherty phyllite immediately below argillite. 

Geochemically anomalous but weak sulfide mineralization is 

associated with the sill margins. The absence of footwall mine 

phyllite after altered Retreat greenstone suggests that this is 

a distal, non-fault-controlled contact where the mine argillite 

onlapped Pybus Formation.

Gallagher Creek

The Gallagher Creek area overlies the downdip extension of the mine (fig. 5). Just as the Maki fault cuts through 

the underground workings, the Gallagher fault system 

cuts through the Gallagher Creek area. The mineralization 

exposed in lower Gallagher Creek consists of pyrite-pyrrhotite-sphalerite-impregnated mine phyllite. This is interpreted 

as footwall alteration to the Greens Creek ore horizon. 

Polymetallic sulfide mineralization occurs within the isoclinal F2

 infold of mine argillite overlying a substantial thickness of basal Hyd debriite. This is identified as a structural 

repeat of the Greens Creek ore horizon. The Gallagher infold 

occurs immediately below a shallow, south-dipping, late D2

thrust in central Gallagher Creek. The upper-plate rocks consist of black phyllite and sericitic siliceous sediment, which 

is in turn overlain by gabbro-silled mine argillite and the 

upper Hyd basalt flows, forming the ridge crest. Lithologies 

making up the upper plate are broadly correlative to the Cliff 

Creek section.

West End

The West End prospect is at the western termination of 

the prominent Gallagher Ridge southwest of the mine. At 

West End, mine argillite overlies a thin interval of debriite 

developed on a serpentinite-plumbed panel of mine phyllite. Though structurally thin, the upright mine argillite/mine 

phyllite section at West End is basically lithologically similar 

to the overturned section hosting the Greens Creek ore.

Cub Creek/Lower Bruin Creek

Mine phyllite structurally overlies mine argillite between 

Cub and Bruin Creeks, the same overturned structural/stratigraphic setting as the mine (fig. 6). Anomalous geochemistry 

and evidence of growth-fault breccia at the phyllite/argillite 

contact are positive indicators for occurrence of Greens Creek 

type ores.

Upper Bruin Creek/Mammoth Ridge

The Mammoth Ridge green carbonate and related 

mariposite phyllite association represents the most highly 

altered ultramafic/mafic rocks in the district. This rock 

package has considerable lithological similarity to California Mother Lode-type gold systems. Despite the intensity 

and magnitude of alteration, the adjacent mine argillite is 

less “sooty” and more “phyllitic” than the host argillite 

at the mine site. A possible explanation is that Mammoth 

Ridge was a topographic high at the time of fluid expulsion 

and is juxtaposed against argillite deposited stratigraphically above or lateral to the restricted sooty facies of argillite hosting the ore.

Figure 5. Hyd Group basalt capping the South Ridge at the 

headwall of Gallagher Creek.

Figure 6. Surface drill site in upper Cub Creek.
102 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Mammoth Pyritic Massive Sulfide Deposit

The Mammoth pyritic massive sulfide deposit is hosted 

in lustrous black schist immediately below the green carbonate 

altered serpentinite that extends the length of Mammoth Ridge 

(fig. 7). Bands of massive pyrite interleaved with schist are 

exposed over about 200 feet of elevation, with the central 50 

feet of the interval dominated by massive pyrite bands of meter 

scale. These central bands are the most massive and have the 

finest grained textures. Grab samples reveal chalcopyrite-rich 

breccia clasts in pyrite-quartz-barite gangue. Like the Greens 

Creek deposit, the Mammoth deposit is intersected by the Maki 

fault system (fig. 8). Although more highly recrystallized, the 

Mammoth pyrite deposit may be akin to the barren pyrite centers developed within the Greens Creek deposit.

Killer Creek

The Killer Creek serpentinite is a south-dipping sheet 

overlying strongly sulfidized chlorite phyllite developed from 

Retreat greenstone (fig. 9). Local zones of sericite-talc phyllite 

with patchy sub-ore grade silver values lie along this basal 

contact at surface. However, mapping has yet to identify host 

mine argillite in the section. Exploratory work suggests a footwall feeder system with the serpentine mass occurring where 

the Greens Creek ore zone would be expected.

Cascade Creek

Several zinc prospects are in the Cascade Creek 

drainage. These take the form of patchy disseminations of 

sphalerite along phyllite/greenstone contacts. The sphalerite 

mineralization has been overprinted by S2 foliations, 

suggesting zinc remobilization into the strongly S1-sheared 

margins of greenstone units bordering on graphitic-pyritic 

phyllite. These contacts tend to be strongly carbonatized, 

silicified and, more locally, sulfidized. The occurrence of 

stringery sphalerite in this environment suggests that the 

Retreat black phyllite/greenstone association is a preferred 

reservoir for the Greens Creek pay metals.

Lakes District

Extensive stockwork mineralization occurs in strongly 

brecciated quartz-graphite schist below gabbro-silled mine 

argillite at the northwest termination of the Killer Creek 

serpentinite in the Lakes District. Mineralization includes 

veinlets of pyrite-sphalerite-chalcopyrite and patchy, semimassive, coarsely granular aggregates cemented by galenasphalerite-tetrahedrite. Well-mineralized samples have also 

been collected from the immediate contact of the mine argillite 

overlying mine phyllite. Anomalous zinc-lead-silver is associated with overlying gabbro sill/argillite contacts. The Lakes 

District is a prime target for the preservation of a satellite 

Greens Creek-type deposit.

Figure 8. The trace of the Maki fault system north of Gunsight 

Pass.

Figure 7. Examining green carbonate on Mammoth Ridge.

Figure 9. Silicified rock developed below the Killer Creek 

serpentinite.
Mine Site and Prospect Geology 103

Zinc Creek

As the name indicates, the Zinc Creek drainage is 

characterized by anomalously high zinc in stream geochemical surveys. The creek cuts across the southern culmination 

of the Zinc Creek/Lil Sore Creek trough of mine argillite. In 

lower Zinc Creek, thick phyllite breccia capped by heterolithic 

debriite underlies strongly sulfidic mine argillite (figs. 10, 

11), with meter-scale intervals containing 30 to 40 percent 

laminated pyrite with associated barite. This facies of argillite 

is lithologically identical to mineralized slaty argillite in the 

mine stratigraphy. Underlying crystalline-carbonate cemented 

debriite is also sulphidic with trace to minor disseminated 

chalcopyrite. In places, the debriite is wholly replaced by 

crystalline carbonate-barite lithologically similar to dolomitic 

massive argillite hosting white ores in the mine series.

Lil Sore Creek

The mine argillite/phyllite breccia contact in lower Zinc 

Creek extends northward into argillite/phyllite debriite following the Lil Sore drainage (fig. 12). Like Zinc Creek, Lil Sore 

Creek is geochemically anomalous, attributed to the fact that 

this stream course runs along the basal argillite/debriite contact. 

Geochemical sampling surveys carried out over the Lil Sore 

mine argillite trough also identify weak sulfide mineralization 

related to gabbro sills in argillite well above the basal contact.

A-Road Barite

This roadside outcrop exposes a baritic chert horizon 

occurring near or at the contact between quartz schist and very 

highly sheared black phyllite. A strongly carbonatized gabbro sill intrudes the immediate contact. This prospect may be 

a baritic member of the Pybus Formation or demark the distal 

tail-end of the Greens Creek ore horizon. 

Figure 11. Basal Hyd Group heterolithic debriite exposed in 

lower Zinc Creek.

Figure 10. Basal Hyd Group phyllite breccia exposed in upper 

Zinc Creek.

Figure 12. Examining mine argillite exposed in Lil Sore Creek.
104 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Metallogeny

Although the high-grade Zn-Pb-Ag-Au-Ba ores at Greens 

Creek are similar to Kuroko-type volcanogenic massive sulfide 

(VMS) deposits, and the mine is located in an island arc system, 

the absence of associated felsic volcanics argues against any 

direct application of a Kuroko-VMS model. Similarly, although 

the metal signatures at Greens Creek are also consistent with 

shale-hosted sedimentary-exhalative (SEDEX) mineralization 

of the Mount Isa type, application of the model is made problematic by the juvenile arc setting at Greens Creek—SEDEX 

mineralization is generally held to relate to intercontinental to 

continental-margin rift settings. Based on the foregoing overview 

of the regional geological setting and of the deposit itself, it is 

here proposed that Greens Creek is a unique type of polymetallic 

sulfide mineralization, with the ores being essentially SEDEX in 

origin but linked to rifting within a juvenile arc system.

The most unusual feature of the immediate host-rock 

stratigraphy at Greens Creek is the evidence it presents for a 

150-Ma time gap between the origin of the Retreat greenstone, 

protolith to mine phyllite, and the deposition of polymetallic 

ores at the base of the mine argillite. This time gap may be 

attributed to uplift of the Retreat Group after deposition of the 

Lower Permian Pybus Formation, accounting for the occurrence of chert pebble conglomerates below the Upper Triassic 

zinc-lead-silver-gold ores. These lag deposits represent the 

weathering of the Pybus Formation cover sequence. The absence 

of the full Cannery Formation at the mine suggests that the site 

of mineralization may have been a mid-Permian high, with 

uparched Retreat greenstone being onlapped only by impure 

dolomitic cherts capping the Cannery Formation regionally.

The ongoing conodont dating program of mine argillite has confirmed that the Greens Creek ore was deposited 

at 220.7±4.4 Ma at the Carnian/Norian transition (chap. 11). 

This age, falling between the Carnian-age Nikolai flood 

basalts in Wrangellia and the Norian-age Hyd flood basalts in 

Alexandria, is key for linking arc rifting to the effects of the 

Nikolai plume. The thinness of juvenile back-arc crust may 

account for the association of Greens Creek ore with massive 

serpentinite. Serpentine emplacement is intimately associated 

with dewatering along growth-fault structures that controlled 

deposition of the mine argillite. There is a strong spatial relationship between the serpentinite sheeting and the wholesale 

hydrothermal alteration of Retreat greenstone to mine phyllite. Occurrence of footwall mine phyllite breccia and debris 

deposits irrefutably ties the host mine argillite stratigraphically to altered Retreat Group greenstone substrate. The green 

carbonate clasts developed from altered serpentinite, which are 

common in basal Hyd phyllite breccia/debriite units, indicate 

that the serpentinite must have (a) been present in the controlling growth-fault structures, (b) participated in fault-focused 

hydrothermal alteration, and (c) been exposed on fault scarps 

prior to ore deposition. More study is needed to address the 

origin of the associated serpentinite and its function in fluid 

evolution. Certainly the widespread occurrence of barian 

mariposite in green carbonate altered serpentinite ties this 

alteration to the baritic replacement ores hosted in footwall 

mine phyllite. The similarity of this green carbonate to that 

occurring in the California Mother Lode mesothermal gold 

district is striking—so much so, in fact, that one wonders if the 

Greens Creek ores could in some fashion be a surface manifestation of a mesothermal gold system at depth, perhaps in some 

way accounting for its richness in precious metals.

At Greens Creek, the host mine argillite overlies massive crystalline barite-carbonate bodies developed in part 

by hydrothermal replacement of mine phyllite; these bodies 

locally comprise white ores. The occurrence of such ores 

low in a mineralized system capped by stratiform high-grade 

black ores with the same metal signature strongly suggests 

that the ores formed proximally within an environment of 

active hydrothermal venting. The fact that the stratiform 

ores were deposited at the base of a considerable thickness 

of anoxic black argillite interlayered with thin dolomite 

beds indicates that they represent initial deposits related to 

marine inundation of restricted, hydrothermally active trough 

environments at the time of rift collapse. The widespread 

occurrence of growth-fault breccia and debriite signifies 

considerable mass wasting from hydrothermally altered fault 

scarps prior to mine argillite deposition. The evidence thus 

points to hydrothermal fluid expulsion in a dynamic growthfault-controlled depositional regimen. Fault control is clearly 

indicated by the fact that the Greens Creek ore horizon 

coincides with a “silica rock” structural marker that extends 

from the mine site for several kilometers and runs the length 

of Mammoth Ridge. Farther north, in the Zinc Creek/Lil Sore 

Creek trough of mine argillite, this same structural/stratigraphic position is occupied by considerable thicknesses of 

phyllite breccia and debriite, indicating preservation of the 

surficial “depositional” growth-fault environment.

Both mine phyllite and the related phyllite breccia/debriite 

deposits are locally replaced by siliceous dolomite variably rich 

in pyrite and barite. This “hydrothermal dolomite” may have 

kinship to footwall copper orebodies that accompany several 

large SEDEX deposits, suggesting that yet undiscovered copper ores may well occur deeper in the Greens Creek system. 

The debriite deposits themselves are cemented by crystalline 

carbonate and zones of quartz-pyrite-ankerite-barite, indicating dynamic hydrothermal plumbing. Primary hydrothermal 

textures are common in the overlying stratiform ores as well. 

Porous-textured framboidal pyrite forming massive centers of 

mineralization is variably recrystallized into compact euhedral 

forms. Analytical work reveals that the most primitive porous 

pyrite species coexisting with colloform sphalerite and galena 

are enriched in arsenic-antimony-silver-gold (Bennett, 1999). 

Perhaps some form of zone refining of both precious and 

semiprecious metals toward the margins of growing framboidal 

pyrite mounds was instrumental in concentrating the unusually 

high grade zinc-lead-silver ores. To what extent recrystallization 

was induced by heat buildup due to capping of the hydrothermal 

system and to what extent it is related to the Late Cretaceous 

metamorphic overprint has yet to be determined. The Greens 

Creek ores have certainly not undergone complete metamorphic 
References Cited 105

recrystallization since they retain many original depositional 

textural features. Nevertheless, some features of the deposit 

are best accounted for by secondary remobilization during 

metamorphic and later structural overprinting. In particular, the 

erratic distribution of the ruby silvers and of silver-rich electrum 

signifies marked precious metal mobility.

Conclusion

Geological mapping in the Greens Creek district broadly 

supports a dynamic growth-fault-controlled depositional environment for the Greens Creek ores. The specific contact relationships within the immediate mine stratigraphy are subject to 

dynamic change. Adjacent Retreat greenstones may show no 

hydrothermal alteration, altered contacts have been subjected 

to variable mass wasting, and the basal “sooty” facies of mine 

argillite is commonly missing. It seems probable that the 

high-grade stratiform ores represent the front of an anoxic 

marine transgression into dynamic restricted trough settings. 

The ores ponded against hydrothermally active fault scarps 

plumbed by serpentinite accompanied by limited sheeted 

gabbro diking. The serpentinite and gabbro dike association 

suggests development of active igneous fissure segments at the 

inception of Late Triassic rifting. The Killer Creek serpentinite body may have provided a sustained heat source within 

uparched Retreat Group greenstone essentially denuded of its 

Permian-Carboniferous cover. In contrast to classic SEDEX 

systems, the Greens Creek setting is therefore one in which 

“igneous” heat may have had a more formative function in 

driving a dynamic hydrothermal fluid cell, perhaps initiating a 

component of fluid recharge from surface, above and beyond 

discharge of formational brine. That the Greens Creek ores 

occupy the profound regional mid-Permian to Late Triassic unconformity that characterizes the geological record on 

Admiralty Island suggests that the Greens Creek fluid reservoir may well have tapped evaporitic brines from the surface.

Acknowledgment

This chapter benefited from constructive reviews by Sue 

Karl and David Brew.

References Cited

Bennett, Cora, 1999, A SIMS study of framboidal pyrite at 

the Greens Creek mine, southeast Alaska: Unpublished 

Bachelor of Science thesis, University of Western Ontario, 

London, Canada, 87 p.

Berg, H.C., Jones, D.L., and Coney, P.J., 1978, Pre-Cenozoic 

tectonostratigraphic terranes of southeastern Alaska and 

adjacent areas: U.S. Geological Survey Open-File Report 

78–1085, 2 sheets, scale 1:1,000,000.

Brew, D.A., Himmelberg, G.R., Loney, R.A., and 

Ford, A.B., 1992, Distribution and characteristics of 

metamorphic belts in the southeastern Alaska part of 

the North American Cordillera: Journal of Metamorphic 

Geology, v. 10, p. 465–482.

Carter, Claire, 1977, Age of the Hood Bay Formation, Alaska, 

in Sohl, N.F., and Wright, W.B., eds., Changes in stratigraphic nomenclature by the U.S. Geological Survey, 1976: 

U.S. Geological Survey Bulletin 1435–A, p. A117–A118.

Gardner, M.C., Bergman, S.C., Cushing, G.W., Mackevett, 

E.M., Plafker, G., Cambell, R.B., McClelland, W.C., and 

Mueller, P.A., 1988, Pennsylvanian pluton stitching of 

Wrangellia and the Alexander terrane, Wrangell Mountains, 

Alaska: Geology, v. 16, p. 967–971.

Gehrels, G.E., and Saleeby, J.B., 1987a, Geological framework, tectonic evolution and displacement history of the 

Alexander terrane: Tectonics, v. 6, p. 151–173.

Gehrels, G.E., and Saleeby, J.B., 1987b, Geology of southern 

Prince of Wales Island, southeastern Alaska: Geological 

Society of America Bulletin, v. 98, p. 123–137.

Haeussler, P.J., Karl, S.M., Mortensen, J.K., Layer, Paul, and 

Himmelberg, G.R., 1999, Permian and mid-Cretaceous 

deformation of the Alexander terrane on Admiralty and 

Kupreanof Islands, southeastern Alaska: Geological 

Society of America Abstracts with Programs v. 31, no. 6, 

p. A–60.

Karl, S.M., Haeussler, P.J., Layer, P., Soja, C., and Himmelberg, G.R., 1999a, Incremental Paleozoic amalgamation of 

the composite Alexander/Wrangellia/Taku terrane, southeast Alaska, in Evenchick, C.A., Woodsworth, G.C., and 

Jorgens, R., eds., Terrane Paths 99—Circum-Pacific Terrane 

Conference, Vernon, British Columbia, 1999, Abstracts with 

Program: Vancouver, Geological Survey of Canada, p. 44.

Karl, S.M., Haeussler, P.J., Mortenson, J.K., Layer, P., Savage, N., Wardlaw, B., Harris, A., Murchey, B., and Blome, 

C., 1999b, New stratigraphic and isotopic constraints on 

the depositional and deformational history of the Alexander Terrane, southeastern Alaska: Geological Society of 

America Abstracts with Programs, v. 31, no. 6, p. A–68.

Lathram, E.H., Pomeroy, J.S., Berg, H.C., and Loney, R.A., 

1965, Reconnaissance geology of Admiralty Island Alaska: 

U.S. Geological Survey Bulletin 1181–R, 48 p.

Loney, R.A., 1964, Stratigraphy and petrography of the PybusGambier Bay area, Admiralty Island, Alaska: U.S. Geological Survey Bulletin 1178, 100 p.

Reich, Michael, 1996, Ultramafic/mafic protoliths to massive 

carbonate replacement bodies at the Greens Creek Zn-PbAg-Au deposit, Southeast Alaska: Unpublished Bachelor 

of Science thesis, University of Western Ontario, London, 

Canada, 120 p.
106 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Richards, M.A., and Jones, D.L., 1991, A mantle plume initiation model for the formation of Wrangellia (and other flood 

basalt plateaus): Geological Society of America Abstracts 

with Programs, v. 23, no. 2, p. 92.

Warme, J.E., and Kuehner, H-C., 1998, Anatomy of an anomaly—The Devonian catastrophic Alamo impact breccia of 

southern Nevada, in Ernst, W.G., and Nelson, C.A., eds., 

Integrated earth and environmental evolution of the southwestern United States: Boulder, Colo., Geological Society 

of America, p. 80–110.
The Airborne Geophysical Survey of the 

Greens Creek Area

By James Fueg

Chapter 5 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract.......................................................................................................................................................109

Introduction.................................................................................................................................................109

Geology........................................................................................................................................................109

Physical Properties....................................................................................................................................109

Airborne Survey Parameters ...................................................................................................................110

Results .........................................................................................................................................................111

Conclusions.................................................................................................................................................121

Reference Cited..........................................................................................................................................121

Figures

1. Total magnetic field ..................................................................................................................112

2. Magnetics—calculated vertical gradient............................................................................113

3. 800-hertz apparent resistivity .................................................................................................114

4. 4,000-hertz apparent resistivity ..............................................................................................115

5. Topography ................................................................................................................................116

6. Radiometrics—Potassium ......................................................................................................117

7. Radiometrics—Thorium ..........................................................................................................118

8. Radiometrics—Uranium..........................................................................................................119

9. Radiometrics—Potassium over thorium...............................................................................120

Tables

1. Resistivity and chargeability of Greens Creek area rocks.................................................110

2. Airborne geophysical survey parameters............................................................................110
Abstract

An airborne geophysical survey of the Greens Creek 

massive sulfide deposit was flown in 1996 to collect magnetic, 

radiometric, and five frequencies of electromagnetic (EM) 

data. Results of a physical properties study conducted prior to 

the survey showed the mineralization to be strongly conductive, and with the lithologies showing a wide range in both 

conductivity and susceptibility.

The magnetic response of the area was dominated by the 

highs associated with the ultramafic units, while the EM data 

were useful in mapping out the argillite/phyllite (low/high 

resistivity) contact. Large numbers of EM anomalies were 

picked from the data, but none of those checked corresponded 

to mineralization. The count rates of the radiometric data were 

extremely low, and the effects of topography dominated the 

response. The survey provided valuable structural and stratigraphic data, but selection of valid exploration targets in this 

environment cannot be done using geophysics alone.

Introduction

A combined helicopter-borne electromagnetic (EM), 

magnetic, and radiometric survey was flown over the Greens 

Creek area in September 1996. The objective of the survey 

was twofold:

1. To attempt direct detection of additional Greens 

Creek-style mineralization.

2. To assist in the mapping of stratigraphy and structure 

throughout the area.

Results have shown that the magnetic and apparent resistivity 

maps produced from the survey were probably the most useful 

products produced. A large number of conductors were identified in the survey, mostly formational conductors associated 

with the more graphitic argillite units.

Geology

Greens Creek is a high-grade massive sulfide deposit 

with a global resource that is estimated to be 21.9 million 

metric tonnes of ore at 13.9 percent zinc, 5.1 percent lead, 

4.8 grams per metric tonne gold, and 599 grams per metric 

tonne silver at zero cutoff (chap. 2). The deposit can be 

regarded as a hybrid volcanogenic massive sulfide/sedimentary exhalative (VMS/SEDEX) deposit, as it exhibits characteristics of both categories of deposit (Taylor and others, 

1999; chap. 15).

Host rocks to the Greens Creek deposit lie within a 

600-km-long belt of Triassic-aged conglomerates, limestones, 

marine clastic sediments, tuffs and intercalated mafic pyroclastics, and pillowed flows that form the eastern margin 

of the Alexander terrane. Deposits within this belt include 

Greens Creek and Windy Craggy (chap. 2). The deposit is 

located at the contact between a footwall sequence consisting 

predominantly of various categories of phyllite and a hangingwall sequence of massive and slaty black argillites (chap. 6). 

Deformation in the area is extremely complex and involves at 

least four periods of folding, one of semiductile shearing, and 

two of faulting (chap. 7).

Ore lithologies at Greens Creek are broken into two main 

groups of massive sulfide ores and semimassive or gangue-rich 

“white” ores. The massive ores contain greater than 50 percent 

sulfides and consist of massive fine- to very fine grained ore 

in which base-metal sulfides are greater than pyrite and massive medium- to very fine grained pyrite-rich ore in which 

pyrite predominates. The white ores are a group of mineralized lithologies that contain less than 50 percent sulfides and 

are defined by their principal gangue mineral. There are three 

types: white carbonate ore, white siliceous ore, and white 

baritic ore (chap. 6).

Physical Properties

During 1996, 18 rock samples from the Greens Creek 

area, including both drill-core and hand samples, were sent to 

Zonge Engineering and Research Organization for physical 

properties testing. Samples were tested for the induced polarization response (time-domain) and resistivity. The samples 

were vacuum impregnated with distilled water and the induced 

polarization measurements were made using an 8-second cycle 

time. The data are listed in table 1.

The Airborne Geophysical Survey of the Greens Creek 

Area

By James Fueg
110 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Table 1. Resistivity and chargeability of Greens Creek area rocks.

[ohm-m, ohm-meters; msec, millisecond]

Description Source Resistivity

(ohm-m)

Chargeability

(msec)

Massive very fine grained base-metal sulfides Drill core 4.7 289.5

Massive fine-grained base-metal sulfides Drill core 2.1 202.0

Massive fine-grained base-metal sulfides Drill core 2.7 291.6

Massive fine-grained base-metal sulfides Drill core 4.7 174.3

Pyritic semimassive sulfide Hand specimen 20.1 44.0

Sericitic phyllite Drill core 134 74.2

Siliceous sericitic phyllite Drill core 191 83.0

Chloritic phyllite Drill core 200 110.0

Mineralized sericitic phyllite Drill core 1,446 121.8

Sericitic phyllite Drill core 1,470 10.9

Laminated black argillite Hand specimen 272 110.8

Slaty argillite Drill core 9.9 117.5

Slaty argillite Drill core 458 14.6

Slaty argillite Drill core 572 28.0

Contorted black argillite Hand specimen 862 65.5

Baritic sericitic schist Hand specimen 610 23.4

Chloritic serpentinite Drill core 1,604 6.3

Chloritic serpentinite Drill core 1,187 2.9

Analysis of the results shows that the massive sulfide samples are strongly conductive (less than 5 ohm-m), the argillites 

vary from conductive to resistive (9 to 860 ohm-m) depending on 

the amount of shearing and carbon, and the phyllites range from 

resistive to highly resistive (130 to 1,600 ohm-m). See table 1.

These results initially suggested to us that not only should 

it be possible to directly detect Greens Creek-style zones of 

massive sulfide mineralization using airborne EM (provided the 

zones are large enough, not too deep, and not masked by other 

conductive material such as graphitic argillite), but there should 

also be sufficient resistivity contrast between many of the 

Greens Creek-area lithologies to allow them to be discriminated 

in the apparent resistivity maps produced from the EM data.

Susceptibility measurements on core and hand samples 

were also done at Greens Creek using a hand-held Exploranium 

KT–9 susceptibility meter. As expected, results showed that the 

more mafic rocks (serpentinite, gabbro, chloritic phyllite) have 

susceptibilities at least one or two orders of magnitude greater 

than the more silicic units (silicic phyllite, chert), the dolomitic 

units, the argillites, and also the massive sulfides. Clearly, 

the Greens Creek ore would not be directly detectable using 

aeromagnetic data, and the contrast between some of the more 

important lithologies in the area is not as well defined as in the 

resistivities. The results nevertheless suggested that aeromagnetic data would be of use in mapping lithologies in the area.

The possibility of elevated potassium levels in some of the 

altered volcanics around Greens Creek suggested that radiometric data might be of use in mapping these units. Obvious 

concerns existed with the high rainfall, the dense nature of the 

vegetation cover, and the amount of swamp-covered areas that 

could potentially mask the radiometric response of the various 

lithologies. However, it was relatively inexpensive to add this 

technique to the planned survey.

Airborne Survey Parameters

Based on the previous analysis, it was decided that a 

combined airborne electromagnetic, magnetic, and radiometric 

survey should be flown over the property. The contract to fly 

the survey was awarded to Aerodat, and it was completed over 

a 5-day period in late September 1996. A total of 1,227 line 

kilometers of data were collected. Some of the data over the 

northern part of the Mansfield Peninsula remain proprietary 

and have not been included in this report. The survey parameters and instrumentation are shown in table 2.

Table 2. Airborne geophysical survey parameters.

[m, meter; EM, electromagnetic; Hz, hertz; GPS, global positioning system]

Survey elements Parameter or instrumentation

Line direction 070°

Line spacing 200 m (100 m over immediate GC area)

Survey altitude 60-m crystal, 45-m magnetometer, 

30-m EM

Survey aircraft Aerospatiale SA 315B Lama

EM system

Aerodat 5 frequency; coplanar 865, 

4175, 32k Hz; coaxial 935, 4,600 Hz 

@ 10 Hz

Magnetometer Scintrex H8 Cs sensor @ 10 Hz

Spectrometer Exploranium GR-820 (16.81) recording 

4 channels @ 1 Hz (TC, K, U, Th)

Navigation Differential GPS
Results 111

Results

Figures 1 through 9 are images of the various data sets 

collected, including total magnetic field, calculated vertical 

gradient of the magnetic field, 4,000-Hz and 800-Hz apparent 

resistivity, topography, the potassium, thorium, and uranium 

spectrometer channels, and a ratio of the potassium and 

thorium spectrometer channels. All images were gridded at a 

50-m cell size and sunshaded at an inclination of 45° from the 

northeast.

The magnetic response of the Greens Creek area is dominated by a series of circular and irregularly shaped magnetic 

highs (with amplitudes up to 500 nanoteslas) immersed within 

a relatively quiet background. Most of the highs correspond 

with mapped mafic and ultramafic rock units. A predominantly northwest trending structural grain is visible in the 

magnetic data, and several structures offsetting magnetic 

features can be identified in the data. North of Hawk Inlet 

the character of the data changes substantially and consists 

primarily of northwest-trending linear magnetic features.

Comparison of the apparent resistivity data with mapped 

geology (chap. 4) reveals a distinct correlation between areas 

of low resistivity and mapped argillite and more resistive 

areas and mapped phyllite. In the mine area the main phyllite/argillite contact can clearly be tracked in the resistivity 

data. The Greens Creek mineralization itself is not visible in 

the data, primarily due to the depth of burial of the bulk of 

the ore. Analysis of the EM profile data by Aerodat processing staff resulted in the picking of about 3,100 “EM anomalies.” The bulk of these occur within the low-resistivity zones 

associated with the argillites and probably represent more 

graphitic zones within the metasediments. The large number 

of anomalies made impractical the ground followups of all 

the identified bedrock conductors, but field visits to some 

of the best-ranked conductors did not result in any obvious 

targets being identified.

The average count rate for all four channels of the 

radiometric data is extremely low. The radiometric response is 

dominated by the effects of topography, with most anomalous 

areas correlating to topographic highs. These are zones of 

little or no vegetation, in strong contrast to the heavily forested 

slopes and muskeg-covered lowlands. Count rates are generally so low that even ratio maps such as potassium/thorium 

show little consistency outside the topographic highs.
112 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

57087

57026

56998

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orebody

515000 520000 525000

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Hawk

Inlet

6435000 6440000 6445000

6445000 6440000 6435000

nT

NAD27/UTM zone 8N

0

0 1 2 3 KILOMETERS

1 2 MILES

Total magnetic field

N

Figure 1. Total magnetic field.
Physical Properties 113

Magnetics—calculated vertical gradient

515000 520000 525000

515000 520000 525000

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6450000

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nT/m

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N

0

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Figure 2. Magnetics—calculated vertical gradient.
114 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

515000 520000 525000

515000 520000 525000

6445000 6440000 6435000

6450000

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6435000 6440000 6445000

800-hertz apparent resistivity

3.1

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N

Figure 3. 800-hertz apparent resistivity.
Physical Properties 115

515000 520000 525000

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6445000 6440000 6435000

6450000

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6435000 6440000 6445000

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N

Figure 4. 4,000-hertz apparent resistivity.
116 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

515000 520000 525000

515000 520000 525000

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6450000

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6435000 6440000 6445000

Topography

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Figure 5. Topography.
Physical Properties 117

515000 520000 525000

515000 520000 525000

6445000 6440000 6435000

6450000

6450000

NAD27/UTM zone 8N

6435000 6440000 6445000

Radiometrics—Potassium

3444

3201

3047

2918

2786

2651

2506

2389

2263

2146

2052

1963

1857

1763

1674

1591

1503

1428

1345

1260

1176

1095

1004

909

834

753

663

581

490

384

298

235

184

143

113

84

58

19

8

6

3444

3201

3047

2918

2786

2651

2506

2389

2263

2146

2052

1963

1857

1763

1674

1591

1503

1428

1345

1260

1176

1095

1004

909

834

753

663

581

490

384

298

235

184

143

113

84

58

19

8

6

cps

0

0 1 2 3 KILOMETERS

1 2 MILES

N

Figure 6. Radiometrics—Potassium.
118 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

515000 520000 525000

515000 520000 525000

6445000 6440000 6435000

6450000

6450000

NAD27/UTM zone 8N

6435000 6440000 6445000

Radiometrics—Thorium

12.3

11.3

10.6

10.1

9.7

9.4

9.0

8.7

8.4

8.2

7.9

7.7

7.5

7.3

7.2

7.0

6.9

6.8

6.6

6.5

6.4

6.3

6.2

6.1

6.0

5.9

5.8

5.7

5.6

5.5

5.4

5.3

5.2

5.1

5.0

4.8

4.7

4.5

4.2

3.8

cps

0

0 1 2 3 KILOMETERS

1 2 MILES

N

Figure 7. Radiometrics—Thorium.
Physical Properties 119

515000 520000 525000

515000 520000 525000

6445000 6440000 6435000

6450000

6450000

NAD27/UTM zone 8N

6435000 6440000 6445000

Radiometrics—Uranium

12.3

11.3

10.6

10.1

9.7

9.4

9.0

8.7

8.4

8.2

7.9

7.7

7.5

7.3

7.2

7.0

6.9

6.8

6.6

6.5

6.4

6.3

6.2

6.1

6.0

5.9

5.8

5.7

5.6

5.5

5.4

5.3

5.2

5.1

5.0

4.8

4.7

4.5

4.2

3.8

14.7

13.6

12.9

12.3

11.9

11.5

11.2

10.9

10.7

10.5

10.3

10.1

9.9

9.8

9.6

9.5

9.4

9.2

9.1

9.0

8.8

8.7

8.6

8.4

8.3

8.2

8.1

7.9

7.8

7.6

7.4

7.3

7.1

6.9

6.6

6.4

6.1

5.8

5.5

5.0

cps

0

0 1 2 3 KILOMETERS

1 2 MILES

N

Figure 8. Radiometrics—Uranium.
120 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

515000 520000 525000

515000 520000 525000

6445000 6440000 6435000

6450000

6450000

NAD27/UTM zone 8N

6435000 6440000 6445000

Radiometrics—Potassium/Thorium

6.59

5.88

5.45

5.04

4.70

4.44

4.15

3.92

3.71

3.46

3.30

3.14

2.99

2.89

2.78

2.68

2.60

2.54

2.48

2.43

2.38

2.32

2.27

2.21

2.16

2.10

2.05

2.00

1.95

1.89

1.83

1.77

1.71

1.64

1.58

1.47

1.37

1.25

1.08

0.82

K/Th

0

0 1 2 3 KILOMETERS

1 2 MILES

N

Figure 9. Radiometrics—Potassium over thorium.
Reference Cited 121

Conclusions

The Greens Creek airborne geophysical survey was 

successful in providing valuable stratigraphic and structural 

information about the area. The most useful products of 

the survey were the apparent resistivity and magnetic maps 

produced, as may be expected given the range of physical 

properties in table 1. The radiometric data did not provide 

much useful information, primarily due to the effects on the 

data of ground cover, which dominated the response. The 

EM data produced a large number of anomalies, most of 

which are associated with graphitic metasediments. Identification of valid exploration targets within these conductive 

zones cannot be done using geophysics alone.

Reference Cited

Taylor, C.D., Newkirk, S.R., Hall, T.E., Lear, K.G., Premo, 

W.R., Leventhal, J.S., Meier, A.L., Johnson, C.A., and 

Harris, A.G., 1999, The Greens Creek deposit, southeastern Alaska—A VMS-SEDEX hybrid, in Stanley, C.J., and 

others, eds., Mineral deposits—Processes to processing: 

Rotterdam, Balkema, v. 1, p. 597–600.

Geology and Metal Zoning of the 

Greens Creek Massive Sulfide Deposit, 

Southeastern Alaska

By Cliff D. Taylor, Andrew W. West, Kerry G. Lear, Tim E. Hall, and 

John M. Proffett

Chapter 6 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract.......................................................................................................................................................125

Introduction.................................................................................................................................................125

Description of the Wall Rocks .................................................................................................................127

Stratigraphic Footwall......................................................................................................................127

Breccia and Conglomeratic Rocks of the Footwall and Hanging Wall....................................129

Stratigraphic Hanging Wall.............................................................................................................129

Description of the Ores.............................................................................................................................130

Geometry of the Ore Zones ......................................................................................................................132

East Orebody......................................................................................................................................132

West Orebody....................................................................................................................................132

Central West.............................................................................................................................132

9A................................................................................................................................................132

Northwest West................................................................................................................................133

5250.............................................................................................................................................133

Southwest Orebody..........................................................................................................................134

200 South...................................................................................................................................134

Metal Zoning...............................................................................................................................................135

References Cited........................................................................................................................................136

Figures

1. Map of southeastern Alaska showing the location of the Greens Creek mine .............127

2. Geologic cross section through the Lower Southwest ore zone, which lies

at the contact between phyllites of the stratigraphic footwall and argillites

of the stratigraphic hanging wall ...........................................................................................127

3. Schematic distribution of ore types within an individual Greens Creek orebody

prior to deformation..................................................................................................................130

4. Photographs of representative samples of Greens Creek ore .........................................131

5. Surface projections of the Greens Creek ore zones ..........................................................133

6. North-looking cross section showing, in black, the East, 9A, 5250,

Lower Southwest, and 224 West Bench ore zones ............................................................134

7. Metal zoning observed in the core of the Central West ore zone....................................135
Abstract

The Greens Creek deposit is a series of massive sulfide 

bodies that lie along the contact between altered mafic-ultramafic rocks and stratigraphically overlying Upper Triassic 

argillites. Both the deposit and its enclosing rocks show the 

effects of lower greenschist facies metamorphism and multiple episodes of deformation. In the footwall, mafic rocks are 

enriched in silica and have abundant sericite at the ore contact; they become richer in chlorite and carbonate away from 

ore. Ultramafic rocks in the footwall are either serpentinized 

or carbonate altered. The hanging-wall argillite is massive 

or slaty and contains graphite, dolomite, or calcite. Locally, 

nongraphitic carbonate rocks are present at or near the ore 

contact. Geologic mapping in the underground workings and 

examination of drill core have revealed a common stratigraphic 

sequence in which white ores (less than 50 percent sulfides) 

give way upward to pyritic massive ores and then base-metalrich massive ores (both greater than 50 percent sulfides).

The deposit consists of three main orebodies, East, West, 

and Southwest, that are themselves segmented by faults or 

attenuated zones that are too thin to mine. The global reserve, 

for a cutoff grade of zero percent metal, is estimated to be 

24.2 million tons with grades of 13.9 weight percent zinc, 5.1 

weight percent lead, 19.2 troy ounces per ton silver, and 0.15 

troy ounce per ton gold. It is likely that continuing exploration 

will lead to additional discoveries that will increase the size 

estimate for the deposit.

Restoration of offsets along the Maki and Klaus faults, the 

two major ore-displacing faults, suggests that the mineralization 

was originally a single continuous horizon that was thickest in 

the Central West ore zone and thinned to the north, east, and 

south. The Central West zone shows a progression from a copper-iron zone against the footwall phyllites, to a zinc zone, to 

a zinc-lead zone, and finally a silver-polymetallic zone against 

the hanging-wall argillites. Similar footwall-to-hanging-wall 

progressions are apparent in the East and Southwest orebodies, although these orebodies are not yet completely characterized, and in some locations the metal progression appears to be 

different. The absence of mine-scale concentric metal zoning 

suggests that the Greens Creek deposit may have formed above 

multiple centers of hydrothermal upwelling, or a broad zone of 

diffuse upwelling, rather than above a single vent.

Introduction

The Greens Creek mine, which is located on Admiralty 

Island 29 km south of Juneau, Alaska (fig. 1), is surrounded 

by the Admiralty Island National Monument, an entity created in 1980 by the Alaska National Interest Land Conservation Act. The mine site is accessed by a 14-km road that 

leads southeast from a permanent port and camp facility 

at Hawk Inlet. A second road joins Hawk Inlet and Young 

Bay, 4 km to the north, where miners are ferried to and from 

Juneau.

For two decades mining activity was a joint venture 

between Kennecott Minerals Co. (70.27 percent), a whollyowned subsidiary of Rio Tinto, and Hecla Mining Co. (29.73 

percent), but in early 2008 Hecla acquired Kennecott Minerals’ share of the operation and became sole owner. At the 

present time a work force numbering about 300 people mines 

and mills about 2,000 tons of ore per day. Mining has been 

by selective overhand cut and fill, drift and fill, and, most 

recently, long-hole stoping with ore transport to the surface 

by rubber-tired vehicles using ramps. Separate zinc, lead, and 

bulk concentrates are prepared using conventional flotation 

techniques, and gold is recovered using a gravitational circuit. 

The concentrates are loaded onto ocean-going vessels at Hawk 

Inlet for transportation to smelters around the world. About 

half the mill tailings are mixed with cement and used as backfill in the underground workings, and the remainder is placed 

in a dry tailings pile near Hawk Inlet.

The Greens Creek deposit lies in a narrow belt of riftrelated volcanic and sedimentary rocks that stretches the 

length of Admiralty Island and continues both north and 

south (chaps. 2, 4). The mineral deposit is stratiform and 

lies along the contact between Triassic argillites of the Hyd 

Group and stratigraphically underlying greenschist phyllites 

of uncertain age. Ore crops out at a locality referred to as the 

Big Sore kill zone. This 20-m by 40-m iron-oxide gossan 

was first seen from the air in 1974 by geologists investigating 

stream-sediment zinc anomalies. The first drill hole at the 

property, which was collared in 1975, contacted more than 

25 m of massive sulfide material. Exploration and development activities involved numerous changes in property 

ownership and in the interpretation of the geology (chap. 3). 

The first ore was milled in 1989.

Geology and Metal Zoning of the Greens Creek Massive 

Sulfide Deposit, Southeastern Alaska

By Cliff D. Taylor, Andrew W. West, Kerry G. Lear, Tim E. Hall, and John M. Proffett
126 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

SOUTHEASTERN ALASKA

Mansfield Peninsula

Admiralty Island

Juneau

f .

- .

.

Killer Creek

Creek

Bruin

Cub Creek

Gallagher Creek

Big Sore Creek

Cliff Creek

Greens Creek

CREW

FERRY

TERMINAL

HAWK

INLET

FACILITY

"A" Road

"B" Road

Tributary Creek

Mammoth

 Claim

EXPERIMENTAL

FOREST

Big

Boil

NORTHERN

ADMIRALTY

ISLAND AND 

THE GREENS

CREEK MINE

YOUNG BAY

HAWK INLET

Mariposite Ridge

TONGASS

 NATIONAL

 FOREST

Gallagher Ridge

Lil Sore

East Lil

Sore

National Monument Boundary

Lakes

District

High

Sore

0 4,000 8,000 FEET

0 1,000 2,000 METERS

N

Area of

figure 1

ALASKA

GREENS

 CREEK

 MINE

National Monument

Wilderness Boundary

Zinc Creek

Cascade

Creek
Description of the Wall Rocks 127

The purpose of this chapter is to describe the ores and 

their immediate wall rocks. The lithologic descriptions are 

based on core logging, underground and surface mapping, and 

limited petrographic studies that were carried out by a number 

of different geologists over a number of years. Information is 

also given on the geometry of the ore zones and on the metal 

zoning within them. Much of the information was first documented in reports to the Kennecott Greens Creek Mining Company or its antecedents. The structural geology referred to in 

this paper is described in detail in chapter 7. For more complete 

descriptions of the mineralogy and mineral chemistry of the 

ores, the reader is referred to chapter 9.

Description of the Wall Rocks

The Greens Creek ores occur at the contact between 

altered and metamorphosed mafic/ultramafic rocks and stratigraphically overlying argillites. Figure 2 is a geologic cross 

section through the Southwest orebody that serves to illustrate 

the stratigraphy and structure of the wall rocks.

Stratigraphic Footwall

The stratigraphic footwall to the Greens Creek mineral 

deposit consists of variably altered mafic to ultramafic volcanics, minor clastic sediments, and hypabyssal sills and intrusions. For the purpose of underground and surface mapping in 

the mine area, these rocks are classified by their metamorphic 

Figure 1 (facing page). Map of southeastern Alaska showing the 

location of the Greens Creek mine.

LS4300

LS4600

A A‘ 0 150 300 FEET

Greens Creek Lower Southwest

orebody, cross section 2600

view looking north

HOST ROCK LITHOLOGIES

Graphitic, pyritic argillite

Massive sulfide orebody

Siliceous phyllite (qtz-ser±carb)

Sericite phyllite (ser-carb±qtz-chl)

Chlorite hyllite (chl-ser-carb±qtz)

Mariposite phyllite

 (qtz-carb-ser-fuchsite)

Serpentinite

Fault

600 elev.

0 elev. 

300 elev.

Figure 2. Geologic cross section through the Lower Southwest ore zone, which lies at the contact between phyllites of the stratigraphic 

footwall and argillites of the stratigraphic hanging wall. Line of section (A–A’) is shown in figure 5. Elevations are in feet relative to sea 

level; long sections are labeled in feet according to the mine grid. Abbreviations are: qtz, quartz; ser, sericite; carb, carbonate; chl, chlorite.
128 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

or alteration mineralogy. The mafic lithologies are subdivided 

into siliceous phyllite, which typically occurs adjacent to ore, 

sericite phyllite, which is more distal, and chlorite phyllite, which is found farthest from ore. Mariposite (chromian 

phengite) phyllite, which is also believed to have a mafic 

protolith, is less abundant and less regular in its distribution. 

The ultramafic lithologies are subdivided into serpentinite and 

quartz-carbonate-mariposite phyllite, which is believed to be 

an alteration of serpentinite. Diabase dikes and highly altered 

gabbros have also been identified, but they are less common.

Siliceous phyllite is white to dark gray and dense and 

displays a broadly spaced foliation (S2). The rock is composed 

of cryptocrystalline quartz with minor sericite and mediumgrained euhedral pyrite. By definition, siliceous phyllite 

contains 80 weight percent or more silica. Clasts of angular to 

rounded quartz or chert are common; these are believed to be 

tectonic breccias in some locations and sedimentary conglomerates in others.

The protolith for siliceous phyllite is thought to be a 

mafic volcanic rock that had been enriched in silica and 

potassium by metasomatism related to ore formation (see also 

Newberry and Brew, 1999). However, it is also possible that 

the protolith was a sediment that had formed prior to ore formation from hydrothermal fluids exhaled onto the sea floor.

Sericite phyllite, which is the most abundant footwall 

lithology, is tan to greenish gray. It is strongly foliated (S2) 

and commonly displays a crenulation cleavage (S3). Quartz, 

sericite, and carbonate are the main constituents. The rock can 

also contain minor chlorite, leucoxene, chromian phengite, 

serpentine, or graphite. Pyrite is present as disseminations 

and massive bands, generally increasing in abundance toward 

ore where it can attain 40 volume percent or more. Sphalerite, 

galena, and chalcopyrite disseminations are also common 

(1–3 volume percent). Bands of sphalerite, pyrite, galena, and 

chalcopyrite occur sporadically, most commonly in the 200 

South ore zone where they are interpreted to be feeders for 

the mineralizing fluids. Remobilized sulfides and remobilized 

tetrahedrite are present in quartz-carbonate veins adjacent to 

ore zones.

The original fabrics of the sericite phyllite protolith are 

no longer evident because they were obliterated by hydrothermal alteration and metamorphism. Consequently, the 

unit is subdivided on the basis of alteration mineralogy and 

is mapped using the modifiers siliceous, graphitic, chloritic, 

carbonate-rich, and tan (leucoxene). Siliceous sericite phyllite 

contains quartz-graphite segregations that are believed to represent original quartz-rich sedimentary layers. Where graphite 

exceeds quartz, the rock is referred to as graphitic. Chloritic 

sericite phyllite contains 15 volume percent or more chlorite 

along foliation segregations and grades into chlorite phyllite, a 

separate unit that is described in a subsequent paragraph. Carbonate-rich sericite phyllite is composed of massive dolomite 

or ankerite with minor quartz and sericite. The carbonate-rich 

lithology was formed by alteration of footwall mafic or ultramafic rocks, and it commonly grades into quartz-carbonatemariposite phyllite or highly sheared rocks of the Upper Shear 

Zone (chap. 7). Carbonate-rich sericite phyllite can also occur 

against the hanging-wall argillites where it is believed to be 

a replacement of an original debris-flow carbonate rock. Tan 

sericite phyllite contains 0.5- to 10-cm-thick bands of leucoxene wisps that, by definition, make up 15 volume percent or 

more of the rock.

The age of the sericite phyllite is not known. Radiometric 

methods have yielded Cretaceous dates indicative of metamorphic resetting (chap. 11). The carbonate-rich and graphitic 

sericite phyllites, which are thought to have sedimentary 

protoliths, are not fossiliferous. Duke and others (chap. 4) and 

Proffett (chap. 7) have proposed a Devonian age based on the 

identification within both sericite phyllite and siliceous phyllite of an early foliation that may correlate with a late Paleozoic metamorphic event that has been documented elsewhere 

on Admiralty Island and on Kupreanof Island (Hauessler and 

others, 1999).

Chlorite phyllite is medium to dark green and thinly 

to broadly foliated. The rock contains 60 volume percent or 

more chlorite in addition to quartz veins and segregations, 

sericite, carbonate, leucoxene, and magnetite. Far from ore, 

chlorite phyllite can be massive granular chlorite and calcite. 

Bull quartz and quartz-carbonate veins are common with 

thicknesses up to 20 cm. Locally, these veins contain sphalerite, galena, pyrite, chalcopyrite, and rare silver sulfides and 

sulfosalts. A subdivision of chlorite phyllite, termed diorite 

gabbro, is composed of chlorite, relict pyroxene phenocrysts 

(2–3 mm), and disseminated pyrite (up to 15 volume percent). 

The presence of phenocrysts indicates that the protolith was a 

cumulate or intrusive rock.

Mariposite phyllite is a banded to foliated, gray-green to 

brilliant green rock. It is named for its distinctive green mica, 

which has been referred to by the varietal names mariposite 

and fuchsite (for example, Newberry and Brew, 1999; Anderson and Taylor, 2000) but is most appropriately classified as 

chromian phengite according to the scheme of Bailey (1984). 

A survey of representative examples has shown chromium to 

be characteristically high, reaching 3 weight percent Cr2

O3, 

and barium to be occasionally high, reaching 11 weight percent BaO (C.D. Taylor, U.S. Geological Survey, unpub. data, 

2008). Other minerals are quartz, sericite, carbonate, leucoxene, and locally chlorite. Mariposite phyllite is found near 

most of the Greens Creek ore zones (for example, fig. 2), and 

also where the footwall/hanging-wall contact is unmineralized. 

Mariposite phyllite is concordant with the mafic stratigraphy 

and is believed to have had a mafic or ultramafic protolith (see 

also Newberry and Brew, 1999).

The most abundant ultramafic lithology is serpentinite, which is a light to dark green and is typically sheared 

or crudely foliated. Locally, the rock can be massive. The 

mineralogy is serpentine, chlorite, carbonate (normally ankerite), and talc, with minor leucoxene and chromian phengite. 

Serpentinite is not consistently associated with ore but rather 

occurs as large masses or irregularly shaped bodies within 

shear zones, fault zones, or fold noses (for example, fig. 2). It 
Description of the Wall Rocks 129

is clear from field observations that considerable strain was 

localized within this ductile lithology.

Quartz-carbonate-mariposite phyllite, which has not been 

identified in the cross section shown in figure 2, is massive to 

crudely foliated and can be white, orange, green, or lavender. 

The rock is composed of quartz, ankerite, and chromian phengite with local occurrences of a lavender phyllosilicate that is 

believed to be chromian chlorite. In underground exposures 

this lithology forms massive irregular pods adjacent to serpentinite or dolomitic massive argillite. The same lithology outcrops north of the mine on Mammoth Ridge where it has been 

mapped as green carbonate by Duke and others (chap. 4). The 

protolith is believed to have been an altered ultramafic rock.

Diabase dikes crosscut both the footwall and the hanging wall. They are most common in the southern portion of 

the mine near the 200 South ore zone. The dikes are medium 

to dark gray, aphanitic to fine-grained granular, and range 

from less than 1 centimeter to 1 m in thickness. Plagioclase, 

pyroxene, and hornblende are phenocrysts. Thicker dikes 

have well-developed, chilled margins. The dikes are less 

altered than the surrounding country rock and have not been 

affected by the D2 deformation that was defined by Proffett 

(chap. 7). Whether they have been affected by the D3/S3 

deformation of Proffett (chap. 7) is uncertain. The dikes are 

not mineralized themselves, but near ore their emplacement 

remobilized sulfides, sulfosalts, and rare electrum and native 

silver along selvages.

Breccia and Conglomeratic Rocks of the 

Footwall and Hanging Wall

The Greens Creek footwall contains 30-m-thick lenses 

of dense, white to gray, silicified, quartz+carbonate or chert 

clasts in a siliceous matrix. The clasts are generally 1–10 cm 

in diameter, and their mineralogy suggests that they were 

derived from the underlying phyllites and, less commonly, 

footwall carbonates. In some locations the clasts are subrounded and the rock appears to be a polymict breccia. These 

occurrences are believed to be debris flows that formed during 

rifting in Late Triassic time. More commonly, the clasts are 

subangular and the rock appears to be a monomict breccia. 

These occurrences, which are typically near silica-altered 

rocks, are believed to be tectonic breccias that formed by postore fracturing of brittle siliceous lithologies. Some tectonic 

breccias display prominent S2 and S3 foliations; these are 

mapped separately as foliation breccias.

A third breccia type has been observed underground in 

the stratigraphic hanging wall. This breccia is polymict and 

consists of 1–5-cm rounded white quartz and argillite clasts in 

a matrix of fine-to-coarse subhedral pyrite. Good exposures 

are found within argillite 20–30 m from ore on the 720 access 

ramp to the Upper Southwest ore zone (for location see plate 

4 in chap. 7). These breccias are thought to be mineralized 

debris-flow conglomerates.

Beyond indicating depositional environments, the sedimentary breccias and conglomerates serve as a marker horizon 

for regional stratigraphic correlation. South of Greens Creek, 

a polymict conglomerate underlies the lower volcanic member 

of the Hyd Group (chap. 4). This conglomerate is believed to 

be correlative to the sedimentary breccias and conglomerates 

at Greens Creek, and to record rifting in the area.

Stratigraphic Hanging Wall

Hanging-wall rocks at Greens Creek are broadly categorized as either massive argillite or slaty argillite. Locally, rocks 

of both categories can approach dolostone. Massive argillite is 

light gray to black with 1–50-cm-thick beds separated by slaty 

intervals. Where it is graphite-rich, the rock tends to be finer 

grained than where it is carbonate-rich. Fractures are commonly filled with quartz±calcite or quartz±dolomite.

Slaty argillite is light gray to black. This rock exhibits a 

prominent slaty cleavage (S2) as well as a crenulation cleavage 

(S3) near fold hinges (F3). Quartz±calcite or quartz±dolomite 

lightning veins follow and also crosscut foliation planes. Thinsection study reveals that slaty argillite is composed of fine 

quartz, feldspar, muscovite, and lesser dolomite in a carbonaceous matrix. The predominance of silicates over dolomite 

distinguishes this rock unit from massive argillite in which 

dolomite is more abundant.

Dolomitic massive argillite is characterized by light 

to medium gray, 1- to 2-m-thick beds of medium to coarse 

dolomite separated by thin micaceous bands. Graphite is 

absent. Peloidal textures are common, as are poorly preserved fossil fragments that include crinoid stems and rare 

occurrences of the Triassic indicator fossil Halobia. Premo 

and others (chap. 11) used conodonts from this unit to establish a minimum age for the Greens Creek deposit of latest 

Carnian/earliest Norian.

Dolomitic massive argillite can grade into carbonatebearing ore, particularly in the Lower Southwest ore zone. 

Here, dolomitic massive argillite directly overlies phyllite and 

forms the footwall to ore. Weakly dolomitized areas are cut by 

stockwork and gash veins containing pyrite, sphalerite, galena, 

tetrahedrite, chalcopyrite, white quartz, and white dolomite, 

suggesting that dolomitization preceded sulfide emplacement. 

In other ore zones, dolomitic massive argillite can be absent 

in favor of greater thicknesses of silica rock, which may be a 

replacement of original carbonate rock.

Dolomitic slaty argillite contains dolomite, quartz, sericite, graphite, and coarse pyrite (15 volume percent or more). 

Discontinuous siliceous lenses, 1 to 25 cm in length, are 

common. Pyrite can be massive adjacent to the stratigraphic 

footwall. The occurrence of this lithology adjacent to ore, and 

its high content of pyrite, both suggest that dolomitization of 

slaty argillite occurred during sulfide emplacement.

A systematic stratigraphy has not been recognized in the 

argillites. However, some spatial variations are evident. Sericite can be abundant near major faults, and there are indications 

that sericite increases in abundance upsection. Massive argillite is more abundant nearer to the ores, where this lithology 

can also be enriched in silica. The silica-enriched massive 
130 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

argillite grades locally into gray-green or olive-brown chert. 

The occurrence of precious metals in this chert suggests that 

the silica enrichment was caused by ore-associated hydrothermal alteration, but petrographic study has also revealed 

primary depositional cryptocrystalline quartz chert, which 

suggests a sedimentary origin for the silica.

Sulfide mineralization in the hanging-wall argillite 

includes ubiquitous pyrite as fine disseminations, stringers, 

bands, and framboidal clots. Base-metal sulfides are rare 

except near ore. Precious metals can be abundant locally (>1 

troy ounce per ton gold, >500 troy ounces per ton silver) 

within meters of ore as microfracture-hosted acanthite, electrum, or native silver. This mineralization can be difficult to 

recognize in hand specimen.

Description of the Ores

For mapping purposes, the Greens Creek sulfide 

deposits have been divided by mine geologists into massive 

ore in which sulfides exceed 50 volume percent and white 

ore in which sulfides are below 50 volume percent. Massive 

ores are subdivided depending on the relative abundance 

of base-metal sulfides (sphalerite plus galena) and pyrite, 

whether the grain size is fine or very fine, and whether there 

is intercalated graphitic argillite. This gives rise to six map 

units: massive fine-grained base-metal ore; massive very fine 

grained base-metal ore; massive fine-grained base-metal ore 

with graphite, massive fine-grained pyrite ore, massive very 

fine-grained pyrite ore, and massive fine-grained pyrite ore 

with graphite. White ore is subdivided into three map units 

according to whether the dominant gangue mineral is carbonate, barite, or quartz (silica).

Ore types tend to have a consistent distribution within 

individual orebodies. This is illustrated in figure 3, which shows 

a schematic cross section generalized from detailed maps of 

several individual Greens Creek orebodies. In general, siliceous 

phyllite is stratigraphically overlain by white ore, followed by 

massive pyritic ore, and then massive base-metal ore. In the core 

of the orebody, the white ore tends to be siliceous, giving way 

laterally to carbonate-rich and then baritic equivalents.

An example of massive fine-grained base-metal ore is 

shown in figure 4A. The rock is metallic gray, blue gray, or 

dull tannish yellow depending on the relative abundance of 

sphalerite, galena, and pyrite. Layering is often apparent in 

which 1–5-mm-thick bands are distinguished by different relative abundances of the sulfides. Gangue minerals are quartz, 

sericite, barite, and chromian phengite. Silver contents vary 

widely, particularly in the Lower Southwest ore zone where 

assays range from 5 to more than 200 troy ounces per ton.

Massive fine-grained pyrite ore (fig. 4B) is yellowbronze to metallic brown, is coarser than massive fine-grained 

base-metal ore, and lacks visible banding. Quartz is the dominant gangue mineral in veins or in the matrix. Base-metal sulfides range from a few disseminated grains to segregations that 

collectively approach the abundance of pyrite. Precious metals 

can exceed 50 troy ounces per ton silver and 0.5 troy ounce per 

ton gold. Massive fine-grained pyrite ore is not generally mined 

because the ore metal content is insufficient.

Very fine grained massive ores (fig. 4C) lack megascopic 

sulfides and have a polished appearance in drill core. Graphitic 

varieties contain 15 percent or more argillite as massive bands, 

slaty intervals, or deformed rip-up clasts. In some locations 

argillite and massive sulfide appear to have been codeposited, 

and in other locations the lithologies appear to have been 

mixed tectonically. Graphitic massive ore is characteristically 

high in precious metals.

Argillite

WCA WSI WCA

MFP

MFB

MFB

WBA WBA

Silicified footwall

Footwall phyllite

ORE LITHOLOGIES

MFB Massive fine-grained base metal

MFP Massive fine-grained pyritic

WSI White siliceous

WCA White carbonate-rich

WBA White baritic

Figure 3. Schematic distribution of ore types within an individual Greens Creek orebody prior to deformation. 

Generalized from detailed maps of several individual Greens Creek orebodies. Ore types that do not appear in this 

section (very fine grained, graphitic) are less abundant and have less regular distributions.
Description of the Ores 131

Figure 4. Photographs of representative samples of Greens Creek 

ore. A, Massive, fine-grained base-metal ore; B, Massive, finegrained pyritic ore; C, Massive, very fine grained base-metal ore; D, 

White carbonate-rich ore; E, White siliceous ore; F, White baritic ore.
132 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Among the white ores the carbonate-rich variety is most 

abundant. White carbonate ore is massive and white to light 

gray (fig. 4D). It is composed of granular dolomite with disseminated and banded sulfides. Quartz- and carbonate-filled 

fractures are ubiquitous. White carbonate ore can grade into 

massive ore, particularly in the West orebody where nearly pure 

sulfide bands 1 to 50 cm thick are interlayered with carbonate. 

The sulfide assemblage in these rocks includes pyrite, sphalerite, galena, bornite, and, locally, chalcopyrite. Argentiferous 

tetrahedrite is present within quartz-carbonate veins as subcentimeter blebs. Acanthite, electrum, native silver, and native 

gold are rare, as are gangue minerals other than carbonate.

White siliceous ore (fig. 4E) is found in all of the known 

orebodies, although it is usually minor. The silica is dominantly cryptocrystalline hydrothermal quartz with lesser vein 

quartz and chert, but there can also be appreciable carbonate, 

sericite, chromian phengite, or graphite. The rock is highly 

variable in texture, sulfide content, and gangue content and 

can show precious metal grades exceeding 1,000 troy ounces 

per ton silver and 4 troy ounces per ton gold.

White baritic ore (fig. 4F) is thinly laminated to massive and contains fine sulfides as disseminations or stringers. 

This lithology is easily identified by its sugary texture and 

high specific gravity. White baritic ore tends to be base metal 

sulfide-poor (typically less than 5 volume percent), but silverrich. Higher grade examples contain disseminated bright red 

pyrargyrite/proustite. In many locations white baritic ore is too 

low in metal content to be mined.

Locally, all of the ore types can be veined, brecciated, or 

crosscut by gouge or rubble zones as a consequence of postore faulting or folding. Veining is most common in the white 

ores. Vein-associated remobilization and recrystallization have 

resulted in spectacular concentrations of native gold and silver 

sulfosalts. Good examples are found in the Upper Southwest ore 

zone where quartz veins contain coarse remobilized sulfides, 

native gold, electrum, native silver, and argentite/acanthite. 

Brecciated ores in some cases formed by slumping of massive 

sulfide, often into weakly mineralized surrounding sediments. In 

other cases brecciated ores formed by postdepositional faulting 

and shearing. Solution-collapse breccias have also been identified, particularly in the white carbonate ores.

Geometry of the Ore Zones

At the Greens Creek mine site, sulfide mineralization 

is nearly continuous along the phyllite/argillite contact. The 

major sulfide accumulations, which are shown projected to 

the surface in figure 5, are the East orebody, the West orebody 

(including the Central West, 9A, Northwest West, and 5250 

zones), and the Southwest orebody (including the Upper and 

Lower Southwest, 224 West Bench, 200 West Bench, and 

200 South zones). The boundaries between orebodies and ore 

zones are defined by faults, shear zones, or changes in the 

thickness of the mineralized horizon.

East Orebody

The East orebody crops out at the Big Sore kill zone (fig. 

6) where the stratigraphy is inverted by folding with phyllite 

overlying argillite. The deposit forms a sheet 3 to 12 m thick 

that strikes N. 15° E. for 920 m. At the surface the mineralization dips 60–80° to the west, but the dip shallows with depth 

to near horizontal as a result of F3 folding. The deeper portion 

of the orebody consists of two parallel flat-lying panels that 

were affected by the shallowly dipping Klaus shear. North of 

the Big Sore kill zone, the updip boundary of the East orebody 

is the Upper Shear Zone, which displaced massive sulfide an 

unknown distance to the west (chap. 7). To the south, the mineralized horizon rotates to an east-west strike before truncation 

by the Maki fault.

Folding produced three lobes within the East orebody 

that are thick enough to mine: the North, Central, and South 

zones. The Greens Creek mine was capitalized on an East 

orebody reserve of 2.7 million tons at 9.7 weight percent zinc, 

3.9 weight percent lead, 14.7 troy ounces per ton silver, and 

0.111 troy ounce per ton gold, with an additional resource of 

522,000 tons at the same grades.

West Orebody

The West orebody, which was originally the downdip 

extension of the East orebody, is subdivided into the Central West, 9A, Northwest West, and 5250 zones (figs. 5, 6). 

Through the year 2000, the West orebody had produced 

379,000 tons of ore grading 14.2 weight percent zinc, 4.1 

weight percent lead, 0.180 troy ounce per ton gold, and 17.2 

troy ounces per ton silver. At that time reserves were 6.62 million tons grading 12.0 weight percent zinc, 4.3 weight percent 

lead, 13.7 troy ounces per ton silver, and 0.119 troy ounce per 

ton gold, with an additional resource of 2.6 million tons at 

slightly lower grades.

Central West

The Central West zone lies beneath the Klaus fault and 

between the East orebody and the Maki fault (figs. 5, 6). At its 

eastern boundary the mineralized horizon is near vertical and 

3–6 m thick. The horizon shallows to the west due to F3 folding becoming horizontal and then east-dipping (10–20°). Here 

the east-dipping ore band forms the upper limb of a recumbent 

F2 fold, the lower limb of which contains a 100-m thickness of 

ore. The unusual thickness of the sulfide accumulation is interpreted to reflect a greater primary buildup as well as structural 

thickening due to F2 folding.

9A

The Maki fault marks the transition from the Central 

West to the 9A ore zone (fig. 5). The 9A zone extends for 

600 m along strike and measures 150 m perpendicular to 
Geometry of the Ore Zones 133

strike. It is composed of numerous fault blocks, all of which 

display the characteristic stratabound nature of Greens Creek 

ore. Restoration of the movement along the Maki fault reveals 

that the 9A zone represents the southwesterly, down-plunge 

extension of the East orebody and Central West ore zone. 

Throughout the 9A zone, grain-size reduction during faulting 

has yielded gouge with millimeter- to centimeter-sized clots of 

electrum that are rich in gold, silver, and base metals.

Northwest West

The Northwest West zone is an extension of the Central 

West that was offset along the Maki fault. The structure is 

dominated by a pair of recumbent F2 folds that form an acute 

S-shape in cross section, the upper fold an argillite-cored 

syncline, and the lower fold a phyllite-cored anticline. The 

axial planes of these folds were affected by south-southeastplunging F3 folds (J.M. Proffett, written commun., 1998). The 

main part of the ore zone lies on the lower limb of the syncline.

5250

The 5250 ore zone is a portion of the East orebody that 

was offset by the Maki fault (figs. 5, 6). The mineralization 

continues for 550 m along a north-northwest strike and extends 

100 m perpendicular to strike. The intensity of F2 folding 

increases to the north where the Klaus shear may affect the mineralization. In the southern portion of the zone, the ore horizon 

dips more regularly at 60° to 70° to the west and plunges 20° 

south. The 5250 zone is atypical among the Greens Creek ore 

zones in containing a high proportion of white baritic ore. This 

zone is base-metal poor and has not yet been mined.

200

South

200 West

Bench

South-

 west

224 W

Bench

5250

Central

West

Northwest

West

9A East

Maki

fault

zone

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

A A’

A‘

0 1,000 FEET

Figure 5. Surface projections of the Greens Creek ore zones. A–A’ is the line of 

section for figure 2; A–A’ is the line of section for figure 6.
134 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Southwest Orebody

The Southwest orebody is an extension of the Northwest 

West ore zone along the lower F2 fold. An upper zone extends 

260 m along a N. 20° W. strike with a plan width of 210 m. 

A lower zone extends 360 m along a northerly strike and has 

a plan width of 240 m. The transition between the upper and 

lower zones, which lies at an elevation of about 120 m above 

sea level, is marked by conspicuous changes in structure and 

style of mineralization.

The Upper Southwest zone is characterized by vertical, 

tight, south-closing F2 folds that are phyllite cored. The overall 

geometry of the ore is that of a “ripple-fall.” The “falls” are the 

near-vertical F2 fold limbs, some of which extend to 50 m in 

height. The “ripple” areas, which show undulations on scales of 

a few meters or less, dip shallowly to the west as a consequence 

of F3 folding. The intense folding produced remobilizations 

with high precious-metal grades.

The Lower Southwest zone lies mainly along the limb of a 

major F2 fold. The overall geometry is a phyllite-cored upright 

anticline with a steeply dipping eastern limb and a flat, undulating western limb (fig. 6). The ore is up to 25 m thick in the core 

of the anticline. Along the eastern limb, mineralization thins to 

less than 3 m before it is truncated by a series of moderately to 

steeply dipping faults that are thought to be a western strand of 

the Maki fault with right-lateral displacement of several hundred feet. The ore zone is cut by other steeply dipping rightlateral faults as well as by low-angle shears.

The Southwest orebody is smaller than the West 

orebody, but its higher precious-metal grades offer a premium that was important in the 1996 reopening of the mine. 

Through the year 2000, total production from the Upper and 

Lower Southwest zones was 1.3 million tons at 11.3 weight 

percent zinc, 5.2 weight percent lead, 25.8 troy ounces per 

ton silver, and 0.189 troy ounce per ton gold. At that time the 

remaining reserve was 554,000 tons at 10.1 weight percent 

zinc, 4.8 weight percent lead, 24.1 troy ounces per ton silver, 

and 0.190 troy ounce per ton gold. Continued exploration 

downdip and along strike has resulted in the discovery of 

the 224 West Bench, 200 West Bench, and 200 South zones 

(figs. 5, 6). At the time of writing of this chapter, sufficient 

development work has been carried out in the 200 South 

zone such that a general description can be given.

200 South

The 200 South zone displays the same general anticlinal 

geometry as the Lower Southwest zone with a steeply dipping eastern limb and a flat-lying western limb. Mineralization continues for 340 m along a strike of N. 15° W. The plan 

Klaus

shear

?

?

Surface

5250

Lower

Southwest

East

Maki

fault

zone Argillite

Phyllite

9A

0 (sea level)

Big Sore

kill zone

500

1,000

1,500

2,000

4,000

5,000

7,000

224 West

Bench

A A’

0 500 FEET

Figure 6. North-looking cross section showing, in black, the East, 9A, 5250, Lower Southwest, and 224 West Bench 

ore zones. Line of section is shown in figure 5. The East orebody crops out at the Big Sore kill zone.
Metal Zoning 135

width is 60 m with an additional 140 m westward extension 

of bench-style mineralization. The mineralized horizon is 45 

m thick in the crest of the anticline and tapers downdip and 

to the south, although the Greens Creek reserve is currently 

open to the south.

The 200 South zone extends from 160 m below sea level 

to 65 m above. There appears to be at least one major F2 

anticline in the core of the deposit that has been affected by 

an F3 fold with east-dipping axial plane. Mineralization is 

bounded on the east by a steep, brittle fault zone (a strand of 

the Maki fault) that offsets the ore horizon several hundred 

feet in a dextral sense.

The 200 South extension is atypical in showing the highest silver grades adjacent to the footwall phyllite. Production 

through 2000 was 352,000 tons at 14.6 weight percent zinc, 

6.0 weight percent lead, 22.2 troy ounces per ton silver, and 

0.237 troy ounce per ton gold. At that time the remaining 

reserve was 1.15 million tons at 12.9 weight percent zinc, 5.2 

weight percent lead, 21.0 troy ounces per ton silver, and 0.184 

troy ounce per ton gold.

Metal Zoning

As they are presently known, the distributions of ore 

types and the shapes and thicknesses of the major mineralized zones suggest that the Central West zone was a 

major center of sulfide precipitation. Drilling in this area 

has outlined a large, coherent block of massive sulfide and 

barite-poor white ore with a systematic metal zoning from 

the footwall phyllites to the hanging-wall argillites. The zoning is illustrated in figure 7. Adjacent to the phyllite lies a 

copper/iron zone that is composed of pyrite-rich massive to 

semimassive ores with silica as the dominant gangue. More 

copper-rich areas are 0.7–4 weight percent copper whereas 

more iron-rich areas are 0.2–0.7 weight percent copper. 

Ratios of iron to zinc (weight basis) are 5–10. Relative to 

average Greens Creek ore, silver, lead, and mercury concentrations are low and arsenic/antimony is high. (Note that 

As/Sb is high only on a relative basis; in Greens Creek ores 

generally antimony dominates arsenic.) The copper/iron zone 

is presently uneconomic.

Fe zone

Ag-polymetallic zone

Zn-Pb zone

Zn zone

Cu-Fe zone

Argillite

Phyllite

present locally, resembles Fe-rich areas in basal Cu-Fe zone

Fe/(Zn+Pb)<3 Zn/Pb=2 lowest As/Sb

Pb>3 wt% Zn/Pb=2 low As/Sb

Fe/Zn<2 Zn/Pb>10 high As/Sb

Fe/Zn=5-10 Cu=0.2-4 wt% high As/Sb

Orehorizon

Figure 7. Metal zoning observed in the core of the Central West ore zone. Broadly similar patterns have been identified in 

the Northwest West, East, 200 South, and 5250 ore zones. Note that high arsenic:antimony in the zinc and copper/iron zones 

is relative to other zones. Most everywhere in the Greens Creek deposit, antimony exceeds arsenic.
136 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Stratigraphically overlying the copper/iron zone is a zinc 

zone where iron to zinc ratios are less than 2 and zinc to lead 

ratios are greater than 10. Mercury concentrations are 2–10 

times the concentration in the copper/iron zone, and arsenic/

antimony is relatively high.

Above the zinc zone is a zinc/lead zone. Here, lead is 3 

weight percent or higher, zinc to lead ratios are about 2, and 

mercury concentrations are 10–15 times the concentrations in 

the copper/iron zone.

A silver/polymetallic zone typically occurs adjacent to 

argillite or within the cores of synclines. This zone is characterized by Fe/(Zn+Pb) of 3 or less, zinc/lead of 2, relatively 

high concentrations of arsenic and antimony, and the lowest 

arsenic/antimony ratios of all the zones. Gold concentrations 

are slightly elevated.

In some locations, an iron-rich, zinc- and lead-poor zone 

can be found between the silver/polymetallic zone and the 

hanging-wall argillite. Metal concentrations resemble those in 

iron-rich portions of the basal copper/iron zone.

Restoration of the displacement along the Maki fault 

places the high-copper pyritic ores of the Central West ore 

zone adjacent to copper/iron-rich mineralization of the 

Northwest West ore zone. Detailed metal zoning studies of the 

Northwest West have not been carried out, but a cursory investigation indicates a pattern similar to that in the Central West 

zone, but overlying a thicker sequence of siliceous phyllite in 

the footwall.

The East orebody (particularly the steeply dipping portion of the South zone), the 200 South zone, and the 5250 zone 

show metal zoning patterns similar to the Central West and 

Northwest West zones. However, the understanding of metal 

distributions in these locations is incomplete, and locally the 

zoning can differ from the Central West. As it is presently 

understood, the overall Greens Creek metal distributions do 

not show the concentric zoning pattern that would be expected 

if the sulfide mineralization formed above a single hydrothermal center. Thus, despite the fact that the ore horizon 

thins away from the Central West ore zone as if this were the 

principal vent for the metalliferous fluids, the metal zoning 

patterns suggest instead that hydrothermal upwelling was from 

multiple centers or was diffuse across a broad area.

References Cited

Anderson, V.M., and Taylor, C.D., 2000, Alteration mineralogy and zonation in host rocks to the Greens Creek deposit, 

southeastern Alaska [abs.]: Geological Society of America 

Abstracts with Programs, v. 32, p. A–2.

Bailey, S.W., 1984, Classification and structure of the micas: 

Reviews in Mineralogy, v. 13, p. 1–12.

Haeussler, P.J., Karl, S.M., Mortensen, J.K., Layer, Paul, and 

Himmelberg, G.R., 1999, Permian and mid-Cretaceous 

deformation of the Alexander terrane on Admiralty and 

Kupreanof Islands, southeastern Alaska [abs.]: Geological 

Society of America Abstracts with Programs v. 31,

p. A–60.

Newberry, R.J., and Brew, D.A., 1999, Chemical and isotopic 

data for rocks and ores from the Upper Triassic Greens 

Creek and Woewodski Island volcanogenic massive sulfide deposits, southeastern Alaska, in Kelley, K.D., ed., 

Geologic studies in Alaska by the U.S. Geological Survey, 

1997: U.S. Geological Survey Professional Paper 1614, 

p. 35–55.
Geologic Structure of the Greens Creek 

Mine Area, Southeastern Alaska

By John M. Proffett

Chapter 7 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Introduction.................................................................................................................................................141

Rock Units and Their Distribution ...........................................................................................................141

Regional Rock Units..........................................................................................................................141

Paleozoic Rocks.......................................................................................................................141

Triassic Rocks...........................................................................................................................142

Jurassic and Cretaceous .......................................................................................................143

Intrusive Rocks.........................................................................................................................143

Rock Units of the Greens Creek Mine Area .................................................................................143

Graphitic Quartz Mica Schist (Retreat? Group)..................................................................143

Ultramafic Rocks......................................................................................................................143

Mafic Rocks..............................................................................................................................143

Conglomerate/Breccia............................................................................................................143

Argillites and Mafic Rocks .....................................................................................................144

Graphitic Slates and Sericitic Slaty Sediments..................................................................145

Geologic Structure.....................................................................................................................................145

Pre-Hyd Group Deformation (S1 and S1.5) ..........................................................................147

F2 Folding and S2 Foliation..............................................................................................................147

Ductile Shear Zones (S2.5)..............................................................................................................149

Upper Shear Zone....................................................................................................................149

Klaus Shear...............................................................................................................................152

Lower Shear Zone ...................................................................................................................152

Possible F2.5 Folds (?) .............................................................................................................152

F3 Folding and S3 Foliation..............................................................................................................154

S3 Shear Zones .................................................................................................................................154

F4 Folding............................................................................................................................................154

Brittle Faults.......................................................................................................................................154

Low-Angle Faults .....................................................................................................................154

Northwest-Striking Right-Slip Faults....................................................................................156

North-Northeast-Trending Left-Slip Faults..........................................................................156

Relationship Between Ore and Structure..............................................................................................156

References Cited........................................................................................................................................157

Figures

1. Diagrammatic 3-dimensional sketch showing relationships between the

different stages of ductile deformation at the Greens Creek mine..................................142

2. Photographs of Greens Creek rocks .....................................................................................144

3. Photographs of F2 related structures in the Greens Creek mine .....................................147

4. Map of 344 stope and 350 ore access crosscut (344–354-foot mine elevation) ............148

5. Map of 524 stope and 530 ore access crosscut (524–532-foot mine elevation) ............150

6. Fence section, looking north and down at 60°, showing variation in orientation

of F2 axes in West orebody between 28XS to 32XS............................................................151
7. Three-dimensional sketch of northern part of Central West orebody,

diagrammatically showing interpretation of F2 folds refolded by F3,

east of Maki fault......................................................................................................................152

8. Diagrammatic plan view, showing relationships between bedding, F2/S2,

and F3/S3 in the main part of the Mine Plate .......................................................................152

9. A, Photograph of shear foliated quartz-sericite-(carbonate) phyllite

(a mylonite), showing asymmetric tails on quartz pods that suggest

top-to-the-west sense of shear. B, Thin section of A, crossed polarizers,

showing preferred orientations of flattened quartz grains oblique to shear

foliation, also indicating top-to-the-west sense of shear..................................................153

10. Photographs. A, Steeply west-dipping beds of argillite, with massive sulfide

layers, on the east limb of a large-scale F3 synform. B, Cherty argillite with

massive base-metal sulfide layers and pyritic beds, folded in an F3 antiform.

C, S2, and quartz veins parallel to S2, in tan phyllite, folded by F3 and refolded

by F4 ............................................................................................................................................155

Plates

[on CD–ROM]

7–1. Geologic map of the surface, Greens Creek mine, Alaska.

7–2A. Greens Creek mine, Alaska, Cross Section 3000.

7–2B. Greens Creek mine, Alaska, Long Section 4800.

7–3. Map of the surface, Greens Creek mine, Alaska; F2, S2, L2, and S2/bedding 

intersections.

7–4. Map of underground workings, Greens Creek mine, Alaska; F2, L2, and S2/bedding 

intersections.

7–5. Map of the surface, Greens Creek mine, Alaska; F3, S3, L3, F4, S4, L4.

Introduction

This chapter discusses the surface and subsurface structural 

geology of the Greens Creek mine and surrounding area. It is 

based on detailed geologic mapping of selected mine workings 

at a scale of 1 inch = 20 feet and 1 inch = 40 feet, and of surface 

outcrops at 1 inch = 200 feet and 1 inch = 40 feet (J.M. Proffett, 

written commun., 1987, 1997, 1998, 1999, 2000, 2001, 2002). 

The mapping was supplemented with detailed logging of drill 

core at various scales. In addition to field work by the writer, drill 

logs and underground maps by numerous Greens Creek geologists have been essential to developing the present understanding 

of the geologic structure. Work by others on various aspects of 

the structural and regional geology at Greens Creek, including 

Brian Martin, Thomas Crafford, Klaus Triebel, Paul Lindberg, 

Norman Duke, Kerry Lear, Andrew West, Brian Erikson, Peter 

Powers, and Christian Schrader, have also been helpful.

Greens Creek geology is extremely complicated due 

to complex structure and a wide variety of metaigneous and 

metasedimentary rock units, many of which have undergone 

hydrothermal alteration. Regionally, the rock units can be 

divided into a Late Triassic (and younger?) age group and a 

Paleozoic (and older?) age group. The ore at the Greens Creek 

mine lies mostly near the base of the Triassic rocks. The earliest structures (S1 and S1.5) are known only from the older 

rocks and do not affect the ores. Three major folding-cleavageforming events (F2–S2, F3–S3, and F4–S4) overprint the Upper 

Triassic rocks and ore, as well as older rocks (fig. 1). Major 

ductile shear zones, between F2 and F3 in age, occur above and 

below the ore zone, and one or more periods of brittle faulting, 

involving at least three sets of faults, postdate the youngest (F4) 

folding event. Understanding this complex geology is essential 

not only for directing exploration and interpreting results for 

resource estimates and mine planning, but also for planning and 

interpreting work directed toward understanding the genesis of 

the Greens Creek ore deposit. This paper will begin with a brief 

review of rock units, which is essential to understanding the 

discussion of structures that follows.

Rock Units and Their Distribution

Rock units, as defined regionally (Loney, 1964; Lathram 

and others, 1965; Muffler, 1967), have been used somewhat 

differently from those used for more detailed geologic work 

in the mine and vicinity. Regional units are discussed first, 

followed by a discussion of mine units and how they may correlate with regional units. More detailed discussions of rock 

units are provided in chapters 2, 4, and 6 of this volume.

Regional Rock Units

The Greens Creek region is underlain by several Paleozoic 

and Upper Triassic metasedimentary and metavolcanic rock 

units. Upper Jurassic to Lower Cretaceous metasedimentary 

and metavolcanic rock units are known to the north and east 

(Lathram and others, 1965). Paleozoic rocks are separated from 

Upper Triassic rocks by what appears to be a major unconformity (Lathram and others, 1965; Brew and Karl, 1988). Mafic 

and ultramafic intrusive rocks also are present in the mine area.

Paleozoic Rocks

A sequence of dark gray, graphitic, quartz-mica schists 

(fig. 2A) and interlayered white, pale yellow to pale green 

quartz-muscovite schists (fig. 2B) is exposed along Hawk Inlet 

and for a variable distance inland. Rare marble units interlayered with these rocks in the north part of Hawk Inlet have 

yielded conodonts of Late Devonian age (collected by Russ 

Franklin and Duane Olsen; identified by Anita Harris, chap. 

11). Calcite marble on the ridge east of Hawk Inlet has yielded 

a Devonian or Silurian megafossil (Brew and Ford, 1985) and 

is probably part of this sequence. These rocks were called the 

Retreat Group by Lathram and others (1965).

Metacherts and siliceous metasedimentary rocks of Late 

Devonian to Early Permian age, assigned to the Cannery 

Formation, occur on southern Admiralty Island and adjacent 

areas (Muffler, 1967; Jones and others, 1981). Early Permian 

megafossils southwest of Eagle Peak (3 miles northeast of the 

Greens Creek mine) indicate the presence of Cannery Formation partial equivalents there (Lathram and others, 1965).

Stratigraphy and structure in these older rocks are not 

well understood in the Greens Creek area, and it is not known 

whether or not the “Retreat Group” and the Cannery Formation in the Greens Creek area belong to the same sequence. 

Clasts of the deformed and metamorphosed Paleozoic rocks 

occur in Triassic conglomerates at Greens Creek (fig. 2C) 

Geologic Structure of the Greens Creek Mine Area, 

Southeastern Alaska

By John M. Proffett
142 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

and near Young Bay. 40Ar/39Ar cooling ages of about 265 m.y. 

on metamorphic white mica and hornblende from the Paleozoic rocks of Admiralty Island (Haeussler and others, 1999) 

indicate a deformational and metamorphic event prior to late 

middle Permian time.

Triassic Rocks

The Upper Triassic Hyd Group of Admiralty Island and 

vicinity consists of locally derived conglomerate and sedimentary breccia, black slaty, calcareous, and dolomitic argillite, 

limestone, dolomite, and metabasalt. The conglomerate and 

sedimentary breccia (fig. 2C) are near or at the base of the section in most areas near Greens Creek. The overlying argillite 

section, which contains the Greens Creek orebodies near its 

base, has yielded conodonts of late Carnian to earliest Norian 

age (chap. 11). Metabasalts on Gallagher Ridge, just south of 

the Greens Creek mine, conformably overlie argillite, contain 

late Carnian to earliest Norian conodonts (chap. 11), and 

have a U/Pb isochron age of 218 ±16 Ma and a Sm/Nd age of 

215±95 Ma (chap. 11). Argillite with Monotis subcircularis, a 

late Norian pelecypod, reported from farther south on Admiralty 

Island (Loney, 1964; Lathram and others, 1965), indicates that 

the Hyd Group includes rocks younger than those dated in the 

mine area.

F2 axes vary

from SSE to

NW in trend,

and steep to

gentle in

plunge

Cutaway

view of F2

fold where

it is recumbent

in the hinge

area of F3

F2 folds

F3 F2

F2

F2 axial planes (=S2)

F3 axial planes

F4 axial

plane

Lensy shear foliation (S2.5)

cuts and displaces S2; is

folded by F3

Folded bed

F4 fold

F3 folds

F4

UPPER PLATE

DOWN

WEST

F3

Figure 1. Diagrammatic 3-dimensional sketch showing relationships between the 

different stages of ductile deformation at the Greens Creek mine.
Rock Units and Their Distribution 143

Jurassic and Cretaceous

Sedimentary rocks with Late Jurassic and Early Cretaceous fossils and interbedded volcanic rocks (the Seymour 

Canal Formation) occur in a belt along the east side of Admiralty Island, 4 miles northeast of Greens Creek (Loney, 1964; 

Lathram and others, 1965; Cohen and Lundberg, 1993). Rocks 

along the southwestern side of this belt, nearest to Greens 

Creek, consist mainly of dark gray slate and slaty graywacke. 

Contacts between the Seymour Canal Formation and the 

Triassic rocks were not observed during this study. However, 

Barker (1957) indicates that observed contacts between these 

units appear conformable (Barker’s Barlow Cove Formation is 

apparently partly equivalent to the Triassic Hyd Group and his 

Symonds Formation (abandoned by Lathram and others, 1965) 

is equivalent to the Seymour Canal Formation). Fossils suggest 

a significant nondepositional hiatus between the Hyd Group and 

the Seymour Canal Formation. Structures observed during this 

study in the Hyd Group and in the lower part of the Seymour 

Canal Formation are similar, which is interpreted to suggest 

that a major metamorphic or deformational event did not occur 

during this hiatus.

Intrusive Rocks

Intrusive rocks include middle Cretaceous quartz diorite 

plutons 11 to 15 miles east of Greens Creek (Haeussler, 1992) 

and ultramafic and mafic rocks near the Greens Creek mine 

and to the northwest. The ultramafic and mafic rocks are of 

uncertain age, but fragments of some of them in basal Hyd 

Group conglomerates at Greens Creek indicate that they are at 

least in part older than Upper Triassic Hyd Group and therefore are at least in part older than ore.

Rock Units of the Greens Creek Mine Area

Rock units in the mine area are briefly summarized here 

for use in the following discussion. More detailed descriptions can be found in chapter 6 of this volume. The units are 

grouped according to whether they are stratigraphically below 

or above the ore horizon. Those stratigraphically below the ore 

horizon include deformed and metamorphosed ultramafic and 

mafic rocks and their intensely altered, deformed, and metamorphosed equivalents, which comprise a group collectively 

referred to as “phyllites.” Conglomerate and sedimentary 

breccia, with clasts of the mafic and ultramafic rocks and of 

phyllites, lie above these rocks and below the ore horizon. 

Rocks stratigraphically above the ore horizon are argillites, 

metabasalts, and minor metagabbros of the Upper Triassic 

Hyd Group and slaty siltstones and lithic sandstones that are 

either part of the Hyd Group or part of a younger unit.

Graphitic Quartz Mica Schist (Retreat? Group)

Outcrops of graphitic quartz mica schist and phyllite are 

in the northern part of the Bruin Creek area, near the 1350 

portal, just east of the mouth of Gallagher Creek, and in a 

few other localities (pl. 7–1). These are highly deformed, 

commonly graphitic, quartz-rich metasedimentary rocks that 

resemble the Paleozoic rocks referred to as “Retreat Group” 

(Lathram and others, 1965) along Hawk Inlet. In the mine 

area, these rocks lie structurally below the altered mafic rocks 

discussed herein, but in the Bruin Creek area they locally lie 

structurally above these rocks, though below the conglomerate 

and sedimentary breccia (pl. 7–1).

Ultramafic Rocks

Ultramafic rocks include serpentinite (±chlorite) (SC), 

and its hydrothermally altered, deformed equivalent, carbonate (magnesite, ankerite or dolomite)-±mariposite-±chlorite-

±talc(?)-±quartz-±leucoxene phyllite.

Mafic Rocks

Most mafic rocks are strongly altered and deformed, 

but where alteration and deformation are least intense, relict 

textures generally indicate the rock is gabbro (DG). Relict textures indicative of basalt are generally rare to absent within the 

phyllites of the mine area. However, if basalts had been present, 

their textures may have been destroyed because of the finer 

grain size. Altered, deformed equivalents of the mafic rocks, 

in order of increasing alteration intensity, are chloritic rock 

or phyllite (CR), chlorite-sericite-±quartz-pyrite-±carbonateleucoxene phyllite (SPc), sericite-quartz-±carbonate-pyrite-

±leucoxene phyllite (SP), and siliceous rock (SR, essentially 

alteration silica with pyrite, ±minor sericite). Phyllites representing the most intense alteration are most commonly 

found stratigraphically directly below the ore. These rocks are 

discussed in more detail in chapter 6 of this volume.

Conglomerate/Breccia

A unit of strongly deformed conglomerate and sedimentary breccia is commonly present at the top of the phyllites. 

Coarse sandstone is present locally and may be bedded (fig. 

2C). West of Gallagher Creek (16675N, 17150E, pl. 7–1) 

conglomerate and coarse sandstone are interbedded with the 

lower part of the argillite unit. Throughout the mine area 

clasts mostly consist of various metamorphic rocks of types 

found in the Paleozoic section and of altered, deformed, and 

metamorphosed mafic and ultramafic rocks, like those they 

overlie. Due to the intense deformation, it is not always certain 

whether the altered mafic/ultramafic clasts were altered before 

or after becoming clasts. In a few exposures, however, such 

as west of Gallagher Creek (16788N, 17193E, pl. 7–1), the 

presence of carbonate-mariposite-quartz (probable altered 

ultramafic) clasts adjacent to serpentine clasts in a serpentinerich clastic matrix suggests at least some alteration took place 

before deposition of the conglomerate. Except for the presence 

of clasts, the conglomerates closely resemble sericitic phyllites and siliceous rock of the underlying “phyllites” and when 

clasts are difficult to see, these rocks are usually mapped as 
144 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

part of the phyllite package. However, the presence of Paleozoic metamorphic clasts indicates that they are probably part 

of the conglomerate unit near the base of the Upper Triassic 

Hyd Group.

Clasts of mafic and ultramafic metaintrusive rocks and of 

their phyllitic altered equivalents in the conglomerate indicate 

that at least some mafic and ultramafic rocks are of pre-Hyd 

age, older than Greens Creek ore, and may not be related to 

the Hyd basalts. Alternatively, they may, at least in part, have 

been emplaced early in a protracted igneous episode that 

included later ore deposition and still later Hyd basalts.

Argillites and Mafic Rocks

Most ore occurs in the basal part of the argillite unit of the 

Upper Triassic Hyd Group. The main lithologies in this unit are 

black to dark gray, slaty argillite (SA) and gray to brown, dolomitic and calcareous, massive argillite (MA). Massive argillite 

occurs in beds that vary from about 2 cm to 20 cm (rarely up to 

a meter) thick. They are characterized by abundant white ladder 

veins or “lightning veins” (fig. 3A). Some massive argillite beds 

mainly consist of fine dark silica, but it is not known if this is 

primary chert or the result of silicification of carbonate beds. 

Figure 2 (above and facing page). Photographs of Greens Creek rocks. A, Graphitic quartz-mica phyllite or schist of Paleozoic Retreat(?) 

Group, 3.4 mile “B” road, 3.6 miles (5.9 km) west-northwest of Greens Creek mine. White to pale gray lenses are mainly highly deformed 

vein quartz of predeformation origin. B, White to pale greenish quartz-muscovite schist of Retreat(?) Group, Pit 7, “A” road, 6.5 miles 

(10.5 km) northwest of Greens Creek mine. White layers are mainly quartz; gray (actually greenish) is muscovite. C, Angular pebble 

conglomerate with faintly bedded sandstone in upper right. White dashes show contact between conglomerate and sandstone and 

are parallel to bedding; black dashes show orientation of S2. Some fragments contain a preconglomerate foliation and metamorphic 

segregation at various angles to each other and to S2, and some fragments contain preconglomerate quartz veins. Matrix and sandstone 

largely pyritized. From 720 ore access (17250N, 20300E, 718-foot elevation), looking N. 27 W., with up indicated by white arrow in upper left.
Geologic Structure 145

Massive argillite beds are generally separated by interbeds of 

slaty argillite and occur in sequences up to tens of meters thick 

(for example, fig. 4). Sequences of slaty argillite with few or 

no massive argillite beds are also common and seem to become 

more abundant in the upper part of the section. Locally minor, 

thinly laminated, pale gray to pinkish chert is associated with 

the ore horizon (for example, fig. 5).

Conodonts from two localities near the base of the argillite 

in the mine have yielded Late Triassic ages with possible ranges 

from late Carnian through about middle Norian (chap. 11). Two 

samples, one from the mine and one from Big Sore Creek, from 

argillite farther from the phyllite contact (presumably higher in 

the section?) have yielded possible age ranges of late Carnian 

through earliest Norian (chap. 11). Conodonts from a limestone 

bed at the phyllite/argillite contact west of Gallagher Creek are 

also latest Carnian through earliest Norian (chap. 11).

On Gallagher Ridge south of the Greens Creek mine, 

a sequence of Hyd metabasalts overlies typical argillite in 

conformable depositional contact. Conodonts from limestone 

interbedded with the lowermost two or three flows also are of 

late Carnian through earliest Norian age. Gabbro sills in the 

underlying argillite may be related to feeders for the flows and 

are discussed further in chapter 12.

Graphitic Slates and Sericitic Slaty Sediments

Above the Greens Creek mine, a sequence of metasedimentary rocks of uncertain correlation with other rock units 

in the area overlies a major low-angle ductile shear zone (see 

pl. 7–1; shear zone described in “Geologic Structure” section). 

Although these rocks are strongly deformed, a few graded 

beds suggest they are mostly right-side-up. The lowermost 

part of the sequence consists of black to pale gray, graphitic, 

slaty sedimentary rocks with rare beds of calcareous or dolomitic argillite a few centimeters thick. Some of the calcareous or dolomitic beds have lightning veins, and the sequence 

somewhat resembles parts of the argillite sequence above the 

orebodies. However, sequences with abundant massive argillite beds, such as are common above the ore, have never been 

observed in this upper sequence. Upwards in the section, the 

few beds of massive argillite are absent, and the rocks resemble argillite above the orebodies even less. The graphitic slaty 

sedimentary rocks are overlain by greenish to pale gray, sericitic, slaty rocks. These consist of siltstones and lithic sandstones that are commonly well bedded and which may locally 

be interbedded with rocks similar to those of the underlying 

graphitic unit. A few beds are very fine grained and siliceous, 

but it has not been determined if these are primary cherts or 

silicified siltstones. Rare dolomitic beds are also present.

More than 20 samples of calcareous and dolomitic beds 

from the graphitic slaty sedimentary unit and the sericitic slaty 

sedimentary unit were sampled for conodonts, but all were 

barren (chap. 11). Possibilities for correlation of these two units 

are: (1) They represent an upper part of the Upper Triassic Hyd 

Group well above the ore horizon; (2) they may correlate with 

parts of the Upper Jurassic and Lower Cretaceous Seymour 

Canal Formation, which they somewhat resemble, except for the 

slightly stronger deformation, alteration, and metamorphism; or 

(3) they may be part of an unrecognized post-Hyd unit.

Geologic Structure

Structural features are described in the following subsections from oldest to youngest; the younger structures have had 

important effects on the distribution and orientation of older 

structures. Northwest-trending strike-slip faults are the youngest 

features and divide the area into several major blocks. The best 

known blocks are those on each side of the Maki fault; structure 

and stratigraphy are readily correlated across the fault (pl. 7–1). 

Other blocks occur within and southwest from the Gallagher 

fault system, southwest of the mine (pl. 7–1). In addition, all 

blocks are further subdivided by major low-angle ductile shear 

zones of post-F2, pre-F3 age. The best known is the “Upper 

Shear Zone” above the mine workings, which separates the geology within the mine (“Mine Plate” or footwall of Upper Shear 

Zone) from the geology exposed on the surface along Big Sore 

Ridge (“Upper Plate” or hanging wall of Upper Shear Zone) 

above the mine (pl. 7–2A, B). Also, a less well known “Lower 

Shear Zone” lies below the mine workings; the footwall rocks 

(“Lower Plate”) are poorly known (pl. 7–2A, B).
146 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska
Geologic Structure 147

Figure 3 (facing page). Photographs of F2 related structures in 

the Greens Creek mine. A, Tight F2 fold in massive argillite beds, 

looking down plunge (N. 58 W., 67°). F2 axial plane (white dashed 

lines) and axial planar S2 foliation in slaty interbeds are slightly 

refolded by F3. Ladder veins are at a high angle to S2 and are not 

folded by F2, even in the tight F2 hinge zone, but are folded by the 

small F3 fold. 580 ore access, 17450N, 20355E, 584-foot elevation. 

B, S2 foliation plane, showing L2 (half-barbed arrow) and small 

F4 folds (full arrow). 1350 tunnel, 73 feet from portal, northeast 

rib, looking N. 60 E. (20085N, 19995E, 1,365-foot elevation). C, 

Layers of massive sulfides (lighter colored bands in upper half 

of photograph) in slaty argillite, tightly folded by F2 (open arrows 

point to hinges). Strong, penetrative S2 is subparallel to the tightly 

folded layers, and many S2 planes appear to have accommodated 

shearing. Lower part of photograph is massive argillite. 344S stope, 

view of back, looking up (16905N, 20392E, 360-foot elevation).

Pre-Hyd Group Deformation (S1 and S1.5)

Pre-Hyd Group deformation is represented by foliation in 

metamorphic clasts in the conglomerate/sedimentary breccia unit (fig. 2C), and by foliations observed in outcrops of 

the graphitic quartz mica schists and phyllites correlated with 

the Retreat(?) Group (see section “Rock Units of the Greens 

Creek Mine Area”). The most common type of early foliation, in outcrops and in clasts, is a prominent metamorphic, 

segregation-type layering, in which quartz-rich layers, 1–10 

mm thick, alternate with thinner, gray to black, sericitic layers. 

This layering is here referred to as S1.5. Although S2 foliation 

(described in the following subsection) overprints this layering and is commonly parallel to the layering, outcrops can be 

found in which S2 is at an angle to the layering, and the layers 

are folded by F2. Rare outcrops can also be found (pl. 7–1, 

23880N, 18820E) in which the layering is truncated at the 

basal contact of the conglomerate/sedimentary breccia unit. In 

conglomerate, the metamorphic layering is restricted to clasts, 

is of different orientations in different clasts, and is truncated 

by the conglomerate matrix (fig. 2C). Clasts, metamorphic 

layering within clasts, and conglomerate matrix are all overprinted by S2 foliation (fig. 2C).

Within the quartz-rich layers of the graphitic sericitic 

schists and phyllites, a relict foliation at an angle to the layering can be observed locally (pl. 7–1, just east of the mouth 

of Gallagher Creek, and in the Bruin Creek area). This relict 

foliation, here referred to as S1, is defined by grain size, grain 

shape, and by white to dark gray colored layers, in quartz and 

associated carbonate. Rarely, micas are parallel to this relict 

foliation, but in most rocks mica has been reoriented parallel 

to S2 or S1.5.

Muscovite that defines S1 or S1.5 is commonly coarser 

grained than that which defines S2 or younger foliations 

(fig. 2B). Layers rich in leucoxene, carbonate, chlorite, or 

other silicates may define S1.5 or S1 in mafic and ultramafic 

rocks.

It is likely that S1.5 and possibly S1 were formed as part 

of the Permian metamorphic event documented by the 265-

m.y. cooling ages reported by Haeussler and others (1999). 

This event likely involved structural features other than these 

foliations but has not yet been studied in detail in the Greens 

Creek area.

F2 Folding and S2 Foliation

F2 folding at Greens Creek and related S2 foliation 

represent the oldest deformation known to have affected 

rocks of the Upper Triassic Hyd Group and overprint all 

older rocks. Folding and foliation that appear to be similar to 

F2 and S2 at Greens Creek, with regard to its characteristics 

and age relationships, are well developed in the surrounding 

region, extending at least from Hawk Inlet to Young Bay. At 

Young Bay the folding and related foliation overprint Hyd 

Group rocks as well as rocks of at least the lower part of the 

Upper Jurassic to Lower Cretaceous Seymour Canal Formation. Therefore, this deformation is tentatively considered to 

be an early phase of the middle Cretaceous deformation that 

occurred in a belt along the east margin of the Alexander terrane in southeastern Alaska (Haeussler and others, 1999).

F2 folds in the Greens Creek mine area are extremely 

tight and are isoclinal in many places (figs. 3A, 3C, 4, 5). S2, 

which is axial planar to these folds, is very strongly developed 

and is usually penetrative. In most of the phyllites, S2 is the 

dominant structural fabric (for example, see fig. 10C) and 

S2 is also well developed in most argillites. A lineation, L2, 

is common on S2 planes. In metasedimentary rocks, L2 is 

commonly a color streaking due to S2-bedding intersections 

and, in these cases, is essentially parallel to F2 fold axes. In 

phyllites, L2 is commonly a color streaking or, in some cases, 

is defined by small, hard ridges and grooves (fig. 3B). L2 in 

phyllites is commonly, but not always, subparallel to fold axes. 

L2 may be the result of the intersection of S2 with various 

features in the phyllite, such as altered relict primary mineral 

grains, fragments, or small veinlets, that have been elongated 

subparallel to fold axes or flattened subparallel to axial planes 

during deformation.

F2 folds have highly variable orientations, at least partly 

because they have been strongly refolded by F3 folds. F2 

axial planes and S2 planes generally strike north-northwest 

and dip steeply on the east limbs of F3 synforms, dip gently 

in most F3 hinge zones, and dip gently to moderately easterly on west limbs of F3 synforms (fig. 1). With the effects 

of F3 folding removed, it appears that the average S2 orientation would have dipped moderately to the southwest. F2 

axes also vary greatly in orientation within the refolded F2 

axial planes (fig. 6). In most of the Mine Plate, F2 axes, L2, 

and bedding-S2 intersections (pl. 7–3, 7–4) plunge mostly 

steeply where S2 is steep, and have a northeast-southwest 

to west-northwest–east-southeast orientation where S2 dips 

gently. There are many exceptions, however, and many F2, 

L2, and bedding-S2 intersections also plunge gently northerly or southerly. In the Upper Plate, F2 orientation is also 
6

17000N

20200E

17100N

20400E

16900N

2500 XS

2600 XS

2700 XS

4500 LS

4600 LS

4400 LS

4700 LS

2800 XS

low

dip

?

55

80

steep

52

57

53

70

78

77

75

69

46

steep 68

75

50

40 ±35

86

89

70

76

56

58 5

70

68

46

27

10

8

47

22 37

11

24

61

59

87

steep

0

73

35

72

63

63

±50

83

50

77

45 45

63 70

87

85

69

87

63

41

36

47

78 50

27

32

85

75

63

21 84 58

87 87

59

75

80 66

87

25

lowdip

63

84

63

65

37?

45-60

61

50

32

A74

42

A78

14

16

26 25

42

26

A72

49

A64

A42

A16

5

18

A39

19

A63

39

23

A43

F3 folds are foldedby F4, whichcauses flatteningof F3 axial planes.

Ore "flames out"to south into argillite.Small dismemberedisoclinal folds, withaxial planar S2,observed in argillitearound ends of ore"flames". The ore"flame out" isapparently dueto F2 folding. Bedsare locally shearedalong S2 foliation.(See photo, Fig. 3c).

Ore dips steeply overall;local flat dip due to F3folding

Where the phyllite pinches out,it has thick massive sulfides onthe east side, but only a fewinches of massive sulfides onthe west side. The pinchoutappears to be a near-isoclinalfold hinge, with axial planar S2;the S2 is also folded, possiblydue to drag along the flat fault.This is interpreted to be a tightF2 anticline that coincides withan abrupt thinning of the orelens along the phyllite-argillitecontact. There is also shearingalong S2.

N. 30° E slickensides on lowangle fault; if displacementis parallel to this, it wouldbe ~ 45 feet, hanging wallto N. 30° E

Ruby Ag

Fault flattens upward to13°W dip and continuesat this dip up ramp for 30feet to east, where itsteepens to a 40° W dip.

Tight F2 folding of

thin pyritic beds

well bedded dolomiticand slaty argillite withthin pyritic beds

Conformable contactslocally flattened by F3folding

(contactsteeperin back)

Thin massive sulfidelayers in silica-rich andcarbonate-rich rock

massive silica-rich and carbonaterich rock with pyritic layers andirregular sericitic and chloriticphyllite layers and wisps(±leucoxene and mariposite)

Band of foldedmassive sulfidesnear sill w/phyllite aboveand below. Thisappears to be atight F2 synclinein the phyllite-orecontact that isrefolded bygently N-plungingF3 folds. Argillitesouth of this wasnot seen; it isonly projectedhere.

Tight F2 fold closure of massivesulfides surrounded by phylliteexposed ~ 3 feet above sill. S2 isaxial planar to fold, but is itself foldedinto an F3 synform 2-3 feet to west

Mainly massive carbonatewith silica, pyrite, minorleucoxene & mariposite

Sericite-quartz and chlorite-quartzpyritic phyllite with irregularmassive carbonate and silica-richlayers. ±mariposite andleucoxene.

Thin bedswith 5-20 %pyrite alongcontact

Chloriticphyllite;dissem.pyriteincreasestowardargillitecontact

Probable phyllite,but not examinedclosely (badground)

well bedded dolomiticand slaty argillite withthin pyritic beds

Ore not actually seen here (stope partlyfilled and bad ground); sketched basedon mine geologist's description and drillhole intercepts.

?

??

?

? ?

? ? ?

?

Thin chert lenses

Bedded "DMA"

Mapping 

GR

MI

3

Low

BedArgMaMFsulfPhyMaassmar

FaFF

26 A67

57 S

62 F

63 L

S

87

Bs

72

C

33 i

72

5

SM

A46 24

Laysulf

Figure 4. Map of 344 stope and 350 ore access crosscut (344–354-foot mine elevation).
Geologic Structure 149

highly variable (pl. 7–3), but here F2 has a tendency to trend 

south-southeast at gentle to moderate plunges, especially in 

the southern part of the area.

The variability of measured axial orientations is also 

reflected in direct observations of F2 folds in outcrops and 

mine workings. Axes are observed to bend more than 60 

degrees across a few feet of mine workings.

Although much of the variability of F2 axis orientations 

is due to refolding by F3, observations suggest that some variability may be due to causes other than later folding. Possible 

causes are F2 folding of previously deformed rocks, possibly 

the result of pre-F2 folding or faulting that is not yet understood, or nonhomogeneous deformation, resulting in amplitude 

variations along fold axes. Nonhomogeneity is not uncommon 

in strong deformation, such as F2.

In phyllites, S2 is defined by oriented sheet silicates 

and, in some cases, by layers or lenses rich in quartz and(or) 

carbonates that alternate with layers rich in sheet silicates. 

Generally, minerals that define S2 are finer grained than those 

that define S1.

Most massive argillite beds have white ladder veins of 

quartz and calcite (“lightning veins”). Generally these are 

oriented at a high angle to S2 but are parallel to, or within a 

few tens of degrees of, F2. They have not been observed to 

be folded by F2, but are folded by F3 (fig. 3A). The veins are 

interpreted to have formed as tension fractures more or less 

perpendicular to the lengthening direction that was perpendicular to F2 shortening.

In mine workings many F2 folds have been mapped that 

have amplitudes of up to several tens of feet, and in some 

cases up to 200 feet (fig. 5). Based on correlation between 

various workings and drill holes, larger F2 folds with up to 

several hundred feet amplitude are interpreted. In the eastern and northern parts of the mine, most F2 anticlines (that 

is, folds with phyllite cores and argillite outer parts) close 

southward and have long eastern limbs and short western 

limbs (when viewed looking downward where the F2 folds 

are exposed on steep east limbs of F3 synforms; see figs. 7, 

8). Overall, with F3 unfolded, it appears this zone would have 

been the overturned lower limb of a major, inclined, south- or 

southeast-closing F2 anticline, with older rocks above and 

to the west (fig. 8). The hinge and west (right-side-up) limb 

of this anticline is mostly truncated upward by the Upper 

Shear Zone, but parts of the west limb are exposed just below 

the Upper Shear Zone east of the mouth of Gallagher Creek 

(pl. 7–1, ~18800N., 17300E.).

Several F2 folds, with geometries consistent with location 

on the overturned lower limb of a major F2 anticline, cross 

through the West orebody (see pl. 7–4 for orebody locations). 

Their axes can be traced southwestward through the north 

part of the Central West orebody (fig. 7) to where they are 

displaced 1,750 feet northwestward across the Maki fault to 

the Northwest West orebody. They trend southward through 

the Northwest West orebody, where they bend to the southeast and, at the south end of this orebody, are again cut by the 

Maki fault and displaced southeast back to the south part of 

the Central West orebody (fig. 6). Here they trend southeast, 

and as they are followed southeastward, they again bend to the 

south (fig. 6).

The Upper Southwest and Lower Southwest orebodies 

appear to be situated on a large F2 anticline (pl. 7–2A). The 

eastern part of the Lower Southwest orebody is mostly on the 

steep east limb of the anticline (fig. 4) and flat-lying ore is 

on the west limb. The Upper Southwest orebody consists of 

several tight anticlines within the hinge zone of the main anticline (fig. 5) that have been refolded by F3. These anticlines 

appear to define an overall axial zone that plunges moderately 

to the south.

In surface exposures above the Upper Shear Zone, 

most F2 anticlines also appear to close to the south, but with 

long west limbs and short east limbs, and with older rocks 

apparently exposed below and to the east. Overall, this area 

appears to be on the upright lower limb of a major, inclined, 

F2 syncline, with older rocks below. The hinge zone of this 

major F2 syncline is exposed west of Gallagher Creek (pl. 

7–1, 7–3, ~ 17650N, 15000E).

Where examined in detail, beds are sometimes found to 

end abruptly at S2 planes, especially in areas of strongest F2 

deformation. Apparently, cleavage plane shearing has taken 

place, but it is not certain if this was part of the F2 deformation process or related to the S2.5 ductile shearing event that 

followed (described below).

Ductile Shear Zones (S2.5)

Upper Shear Zone

The Upper Shear Zone is a major ductile shear zone 

exposed above the uppermost mine workings, on the surface, 

and in several drill holes (pl. 7–1, 7–2A,7–2B). This zone dips 

gently and separates the geology of the mine (Mine Plate) 

from the somewhat different geology exposed on the surface 

above (Upper Plate).

The shear zone is tens to several hundred feet thick, 

and rocks within this zone are overprinted by a strong shear 

foliation (fig. 9). Immediately below the zone in the mine area 

are mafic and ultramafic rocks and their altered equivalents, 

mostly phyllites consisting of carbonates and sheet silicate. 

Rocks immediately above the zone are black graphitic slates 

and slaty argillites with rare carbonate or siliceous massive 

argillite interbeds. In parts of the shear zone, shear-foliated 

equivalents of rocks above and below can be recognized, but 

intensely shear-foliated rocks of uncertain origin also are present within the shear zone. These latter rocks consist of quartz 

and(or) carbonate with minor sericite and other sheet silicates 

(qsc unit—see pl. 7–1, 7–2A,7–2B; fig. 9). The protoliths for 

the quartz-rich rocks probably were siliceous metasedimentary 

rocks and(or) phyllites, and the protoliths for the carbonate-rich 

rocks probably were altered ultramafic and mafic rocks.

The shear foliation consists of slightly undulating, bifurcating, thin, discrete layers rich in sheet silicates, that separate thin, lens-shaped layers relatively rich in quartz and(or) 
150 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

17600N

17500N

17400N

17300N

17200N

17600N

17500N

17400N

17300N

17200N

20100E

20200E

20300E

20400E

20100E

20300E

20400E

20100E20200E

20300E

20400E

3100XS

3000XS

2800XS

4500LS

4600LS

4700LS

4800LS

3100XS

3000XS

2800XS

4700LS

4600LS

4500LS

3200XS

2900XS

2900XS

524 W2

524 N6

524 N5

530 O/A 88

52

77

67

88 78 73

60

85

78

84

63

77

68

79

45

80 52

56

70

78 68

61

66

85

75

87

89

71

81

69

78

77

73

90

78

80

80°above

85°below

90

73

75

77 38

54 90

85

50

75

67

75

84

75

80

54

50

80

22

80 60

80

45

45

72

86

88 74

75

66

72

85

80 81

82

84

82

ave78

83

87

88

85

73

73

88 52

45 ave56

85

52

82

87

78

85 85

86 88

90

90

88

52

30

87

76

52

30-50

90

90

87

70

70

80

40

45

60

90

90

80

54

61

87 7272

7722

67

65

64

660

18

51

85 25 50

45

34

53

44

35

AP45

32

AP66

40

AP85

AP77

AP90

47

AP60

AP80

AP85

AP77

"D" fault

SA

?

?

? ?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

GREENS CREEK

MINE, ALASKA

530 / 524 UC LEVEL

S C A L E

5 0 F E E T

Mapping by J. M. Proffett, 1997, except

524 N5 and 524 N6 by Greens Creek staff.

Drill holes logged by Greens Creek staff.

EXPLANATION

Argillite (SA, MA,

DMA)

Massive sulfides

(MFB and MFP)

Fault, showing

dip

Survey point

Selected drill

holes

Bedding 56

S2 foliation 63

42 Contact, showing

dip 

F3 fold showing

dip of axial plane

27

AP83

28 F2 fold

L2 lineation 4

Bedding form

surface

Layers or veins of

sulfide mineralization

Healed shear, 64 showing dip

68

Trace of F2 axial

plane

Phyllite

(SP, MP, SR)

Chert

Semimassive sulfides

(WCA, WSI, WBA)

Figure 5. Map of 524 stope and 530 ore access crosscut (524–532-foot mine elevation).
Geologic Structure 151

56LS

100 FEET

100 FEET

N

Figure 6. Fence section, looking north and down at 60°, showing variation in orientation of F2 axes in West orebody between 

28XS to 32XS. The axial trace of the uppermost F2 fold is shown as a dot-dash line on each section. F2 fold axes for this fold 

are shown in three dimensions as they would have projected across both sides of the Maki fault, as double-dot-dash lines 

connecting the sections, one showing the hinge for the argillite/ore contact, and one showing the hinge for the ore/phyllite 

contact. The ore horizon is interpreted as thickest on the east limb of this F2 fold south of 31XS, resulting in the 700 orebody, and 

as thicker on the west limb of the fold north of 31XS, resulting in the main Central West orebody. The shape of orebodies on the 

sections appears flattened because of the perspective resulting from the view looking down at a 60° angle (compare the center 

section, 30XS, with the same area on pl. 7–2A (in CD), which shows a slightly more detailed interpretation).
152 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

carbonates (fig. 9). A stretching or mineral lineation (L2.5) 

is usually present on shear foliation surfaces, and the quartz/

carbonate-rich lenses between shear-foliation planes are elongate parallel to the lineation. The lenses are thus ribbonlike, 

with length to width to thickness ratios of as much as 50:10:1.

Shear foliation (S2.5) postdates F2 and predates F3; it 

displaces and deforms S2 foliation but is folded by F3.

Zones of breccia, or partly brecciated wall rock, are present 

along the shear zone (pl. 7–2A,7–2B) and are overprinted by the 

shear foliation. Therefore, it appears that the shear zone began 

as a brittle fault zone, which became ductile with time.

Direction and amount of displacement across the Upper 

Shear Zone are uncertain. Although some generalized stratigraphic units can be matched across the shear zone, complex 

F2 structure and limited exposures have precluded establishment of a satisfactory match. Displacement direction is likely 

in the direction of the shear lineation previously described, 

which in most outcrops measured trends E–W to WNW–ESE. 

Rare megascopic shear-sense indicators suggest top-to-thewest (fig. 9A) as does limited petrographic work (fig. 9B), but 

more work is needed. Effects on shear sense indicators of F3 

and of other postshearing deformations are still being evaluated. Top-to-the-west displacement would be consistent with 

the apparent younging directions in the Mine Plate and Upper 

Plate (pl. 7–2A).

Klaus Shear

The Klaus shear, first noted by Klaus Triebel (written 

commun., 1992), is a low-angle healed fault that displaces the 

argillite/phyllite contact in the east part of the mine (pl. 7–2A). 

A displacement of a few hundred feet of hanging wall northwest has been estimated by Lindberg (P.A. Lindberg, written 

commun., 1994). This shear zone appears to correlate with one 

mapped in the 1350 tunnel (J.M. Proffett, written commun., 

1987), which is associated with ductile shear foliation and is 

folded by F3. The Klaus shear could, therefore, be part of the 

same deformational event as the Upper Shear Zone.

Lower Shear Zone

Evidence for another shear zone has been found in a few 

deep drill holes below the mine (pl. 7–2A, 7–2B). In most 

holes, argillite is juxtaposed against underlying phyllites. 

Ductile shearing fabrics similar to those in the Upper Shear 

Zone occur in the Lower Shear Zone, as do zones of breccia 

and partly brecciated wall rock that are overprinted by shear 

foliation.

Possible F2.5 Folds (?)

A few folds have been found that appear to fold S2 but 

are overprinted and transected by S3. These are not common, 

but their age relationships suggest they could be related to the 

ductile shearing event.

contact

S2

S2

S2

S2

Approximate scale

Projection

of F2 axial

planes and S2

onto cross

section

F2 folds of

phyllite-argillite

contact

Figure 7. Three-dimensional sketch of northern part of Central 

West orebody, diagrammatically showing interpretation of F2 folds 

refolded by F3, east of Maki fault. 

S3

S2

S2

S2

Group of F3 folds

with steep axial planes 

steep

steep

Bedding

low

dip

low

F2 fold

axis

steep Bedding

DIRECTION

YOUNGING

N

Figure 8. Diagrammatic plan view, showing relationships 

between bedding, F2/S2, and F3/S3 in the main part of the 

Mine Plate. South-closing F2 folds (which are anticlines here) 

have short west limbs and long east limbs. Bedding and S2 are 

locally folded by groups of F3 folds with axial planar S3.
Geologic Structure 153

Figure 9. A, Photograph of shear foliated quartz-sericite-(carbonate) phyllite (a mylonite), 

showing asymmetric tails on quartz pods that suggest top-to-the-west sense of shear. B, 

Thin section of A, crossed polarizers, showing preferred orientations of flattened quartz 

grains (white arrows) oblique to shear foliation (which is parallel to bottom and top edges 

of photograph), also indicating top-to-the-west sense of shear (Simpson and Schmid, 1983; 

Lister and Snoke, 1984). Quartz-rich lenses indicated by “q,” sericite-rich areas by “sr.” Top 

of both photographs is top in the field; both photographs looking south; view is of a plane 

cut perpendicular to foliation (S2.5) and parallel to lineation (L2.5); location: 18681N, 21137E, 

surface, 1,952-foot elevation.
154 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

F3 Folding and S3 Foliation

F3 folds are generally tight to open upright folds and are 

the most common and obvious folds in the mine (fig. 10A, B). 

They clearly fold S2 as well as bedding and shear foliation and 

are refolded by F4 (fig. 10C). Where not affected by post-F3 

structural events, F3 axial surfaces generally strike northnorthwest in the northern and eastern part of the area, gradually bend to an approximate north-south strike farther south, 

and to a south-southwest to southwest strike in the southwest 

part of the area (pl. 7–5). Most axial surfaces dip moderately 

to steeply eastward throughout the area. There are many local 

exceptions to these general trends. Where refolded by F4, the 

F3 axial surfaces commonly dip gently eastward overall (fig. 

1). Locally, axial surfaces dip near vertically, or steeply west, 

which could also be due to F4 refolding.

F3 fold axes generally plunge gently to the south in 

the plane of the axial surface, but locally they plunge gently 

northward (pl. 7–5). In rare cases, they plunge quite steeply 

north or south. In the 530 Ore Access in the Upper Southwest orebody, F3 changes from a 50°N plunge to a 45°S 

plunge across a 15-foot-wide crosscut (fig. 5). This could be 

due to bedding that was previously deformed rather than to 

refolding of F3.

F3 synforms generally have steeply dipping east limbs 

(fig. 10A) and moderately east dipping west limbs. The mine 

area includes several large-scale F3 folds with wavelengths 

of several hundred feet. Hinge zones of these larger scale 

folds are characterized by numerous smaller scale F3 folds 

(fig. 10B) with wavelengths and amplitudes of a few inches 

to a few feet. These smaller scale folds are less common on 

the limbs of the larger scale folds. Most of the upper east part 

of the mine is on the east limb of a large synform (see pl. 

7–2A), with an antiform and another synform west of this. 

Much of the Upper Southwest orebody is in an F3 antiformal 

hinge zone with abundant smaller scale folds, and the eastern 

part of the Lower Southwest orebody is on the west limb of 

this same anticline (pl. 7–2A).

S3 foliation is axial planar to F3 folds, is usually spaced, 

and usually crenulates S2 (fig. 10B). In some areas it is not 

developed, especially in massive rocks such as massive argillite. It is most strongly developed in rocks that have abundant 

fine sheet silicates, such as many of the phyllites and some 

of the slaty argillites. In a few areas, S3 can be very strongly 

developed, especially where F3 hinge zones occur in rocks 

with abundant fine sheet silicates, locally causing complete 

reorientation of S2. In such areas, it is possible to distinguish 

S3 from S2 only by mapping the structures into an area where 

the S3 overprinting is less strong. L3 is a crenulation lineation, 

generally consisting of small-scale (millimeter scale) folding 

of S2 foliation planes (fig. 3B).

In general, F2 folds tend to change in orientation irregularly through the mine and on the surface from a roughly 

southwest trend in the north to a more or less south-southeast 

trend in the south, whereas F3 folds appear to do the opposite 

(pl. 7–3, 7–4, 7–5).

S3 Shear Zones

Apparent displacement of older structures or rock units 

is commonly observed across certain S3 foliation planes. In 

most cases apparent displacements are only a few centimeters, 

and many of these could be the result of rock dissolution along 

cleavage planes. Others are on the scale of mine workings and 

can locally displace ore and other rock units several feet. At the 

northern end of the map (pl. 7–1 and 7–5, 24300N, 17900E) the 

Upper Shear Zone and rock units above and below are displaced 

by a north-northwest-trending shear zone that is parallel to 

strongly developed S3. Where exposed, this shear zone forms 

the contact between graphitic sericitic phyllite to the southwest 

and carbonate-altered ultramafic rock to the northeast. The 

contact zone consists of several centimeters of sericitic phyllite, strongly foliated parallel to S3, but no late fault gouge. The 

vertical component of displacement of the Upper Shear Zone 

by this S3 shear zone (which is the minimum possible displacement) is 300–400 feet, northeast-side-down. The net direction 

and total amount of displacement are not known.

F4 Folding

F4 folds and axial planar S4 cleavage are locally developed throughout the mine and surface (fig. 10C). They are 

abundant in certain areas near the 1350 portal and in the upper 

part of Big Sore Ridge (pl. 7–5).

F4 folds, which are usually open, have axial planes that 

generally dip gently southerly and axes that plunge southwest to south (pl. 7–5). They are commonly nearly coaxial 

with F3, but F4 axial planes generally are at high angles to 

F3 axial planes (fig. 1). Where F4 and F3 occur together, F3 

axial planes are folded by F4 folds (fig. 10C), and the folded 

F3 axial planes commonly are flattened to an overall gentle 

east dip. S4 cleavage is only locally developed and is either a 

spaced fracture cleavage or a crenulation cleavage.

The nearly coaxial orientation of F3 and F4 folds suggests they may be related to the same period of deformation. 

However, the age relationships and differing orientations of 

these two fold sets is consistent throughout the mine area, as 

well as in other areas, such as along the access road (2.5 mi 

“B” road) just east of Hawk Inlet. In the 1350 tunnel (450 feet 

southeast of portal), where F4 refolds F3, a quartz vein cuts 

an F3 axial plane without being folded by F3, but is folded by 

F4 (fig. 10C). Therefore, these two periods of folding were 

separated by a fracturing and veining event.

Brittle Faults

Low-Angle Faults

Small, gently dipping faults occur in several parts of the 

mine. Many of these are healed by white quartz and calcite 

vein material, and some have been refractured and have dark 

clay gouge. Other faults consist mainly of clay gouge. These 
Geologic Structure 155

Figure 10. Photographs. A, Steeply 

west-dipping beds of argillite, with 

massive sulfide layers, on the east limb 

of a large-scale F3 synform. Note that 

bedding is flattened only where crossed 

by rare F3 folds, such as along hammer 

handle and 1 foot left of hammer. 580E 

stope, looking north-northwest (17520N, 

20395E, 580-foot elevation). B, Cherty 

argillite with massive base-metal sulfide 

layers and pyritic beds, folded in an 

F3 antiform. Note spaced S3 cleavage 

parallel to axial plane. 580E stope looking 

north-northwest (17502N, 20385E, 580-

foot elevation). C, S2, and quartz veins 

parallel to S2, in tan phyllite, folded by F3 

and refolded by F4. Note later quartz vein 

that cuts across F3 axial plane without 

being folded, but which is folded by F4. 

1350 tunnel at 423 feet from portal, NE 

rib, looking N. 20 W., up plunge (19912N, 

20275E, 1,407-foot elevation).
156 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

low-angle faults truncate F3 folds, but their relationship to 

F4 folds has not been established. Many seem to be closely 

related to strike-slip faults (described below) and may represent bends in strike-slip fault planes or connecting faults 

between different strike-slip faults. None of these faults are 

known to have large displacement. For example, the fault 

shown in figure 4 appears to have about 45 feet of north-northeast displacement of the hanging wall.

Northwest-Striking Right-Slip Faults

The most important brittle faults in the mine area are 

northwest-striking right-slip faults. These dip steeply, generally to the southwest. The best known is the Maki fault, which 

separates the east and west parts of the mine (pl. 7–1, 7–4). 

This fault was defined by T.C. Crafford (written commun., 

1986), and an estimate of about 1,800 feet of right slip was 

made by P.A. Lindberg (written commun., 1994). Correlation 

of axes of large F2 folds and thickened ore in the Central West 

ore zone east of the fault with similar structures and thickening 

in the Northwest West ore zone on the west indicates 1,755 

feet (535 meters) of right slip, with 110 feet (34 meters) of 

west-side-up slip, closely confirming Lindberg’s estimate.

The Maki fault consists of several strands within a zone 

nearly 200 m wide in the southern part of the mine. Northward, the strands merge to a zone about 10 m wide in the 

north part of the mine. The fault strands consist mainly of 

soft, sheared, clay-rich gouge and breccia. The Maki fault is 

also exposed on the surface above and southeast of the mine 

and can be traced across the district as a prominent topographic lineament.

 The Gallagher fault in the Gallagher Creek area west of 

the mine (see pl. 7–1) is similar to the Maki fault. It consists 

of at least two main branches, referred to as the East Gallagher fault and the Middle Gallagher fault (P.A. Lindberg, 

written commun., 1998). Each branch may have up to a few 

hundred feet of displacement. Topographic lineaments and 

mapping to the north (for example, T.C. Crafford, written 

commun., 1987) suggest that another northwest-trending 

right-slip fault may occur to the northeast of the mine, northeast of Big Sore Creek.

North-Northeast-Trending Left-Slip Faults

Steep, north- to northeast-trending faults with left slip 

occur in a few areas of the mine. Like the northwest-trending 

strike-slip faults, these also have brittle clay gouges and breccias. An example is the “D” fault in the Southwest orebody area 

(fig. 5), which has tens of feet of displacement. Several such 

faults occur on the surface near the headwaters of Gallagher 

Creek (pl. 7–1). These have from a few feet to about 250 feet 

of left slip, with a possible north-side-down component. Some 

strands displace branches of the Middle Gallagher fault, but it 

is possible that the left-slip faults are displaced by the East Gallagher fault. Another set of northeast-trending faults, possibly 

with left slip and north-side-down displacement, are interpreted 

to cut the rocks west of the Maki fault about 1,700 feet south of 

the 1350 portal (see pl. 7–1) based on drill-hole intercepts and 

surface outcrop patterns.

The similarity of gouges on northwest-trending right-slip 

faults and northeast-trending left-slip faults, and the apparent 

mutual crosscutting relationship between the two sets, suggest 

that they are related. They may be a complementary set, and 

would indicate regional north-south shortening. Haeussler 

(1992) found similar relationships and came to similar conclusions in the Seymour Canal Formation rocks to the east.

Relationship Between Ore and 

Structure

Ore minerals replace matrix and clasts in conglomerate, which contains clasts in which S1.5 is truncated by the 

conglomerate matrix, and base-metal-bearing veins cut the 

conglomerate. Mineralization is therefore younger than 

S1.5. Orebodies are clearly folded by F2 and overprinted by 

S2 foliation. The S2 foliation near F2 hinges is sometimes 

refracted where it passes from slaty host rocks into ore, but S2 

is not well developed in ore except where ore contains patches 

of sheet silicates. Many sulfide-bearing veinlets in sericitic 

phyllite and siliceous rock adjacent to ore are also folded by 

F2 and overprinted by S2. Sericite and chlorite of the phyllite, 

which are part of the alteration halo of the ore, are strongly 

recrystallized and reoriented along S2, and these minerals 

along with the quartz, carbonate, and sulfides of the phyllite 

are in many cases segregated along S2 foliation planes. Thus, 

the mineralization predated F2 events.

Small tension fractures related to F2 folding, or in some 

cases F3 folding, commonly cut the ore. These may be filled 

with various ore minerals, such as chalcopyrite, bornite, 

galena, silver-sulfosalts, or electrum, which apparently formed 

by remobilization of certain ore elements during deformation 

(see also chap. 9).

Essentially all alteration minerals, especially sheet 

silicates, have been strongly affected by S2 deformation 

and probably recrystallized during related greenschist facies 

metamorphism. In F2 hinge zones, such as most of the Upper 

Southwest orebody, most ore appears to have been largely 

recrystallized. Even in the least-deformed, least-recrystallized 

ore on the limbs of F2 folds, such as in much of the Lower 

Southwest orebody, most primary ore components have been 

modified, though up to 30 percent of the ore components 

appear to retain primary textures, mineralogy, and traceelement distributions (chap. 9). The age of gangue and ore 

mineral recrystallization and other modification is tentatively 

considered to be middle Cretaceous, based on the tentative age 

assignment of F2 (previously discussed).

In addition to effects on the ore itself, the intense nature 

of F2 deformation makes the original overall geometry of 

the Greens Creek deposit extremely difficult to decipher. To 
References Cited 157

arrive at even a rudimentary understanding of the distribution of such features as possible syndepositional faults or 

feeders, location of intrusive or volcanic units, sedimentary 

facies distribution, original mineral or alteration zoning, or 

other features that might be of interest would require detailed 

understanding of all F2 and younger structure, as well 

as stratigraphic younging directions. Such a study would 

require very careful lithologic and structural mapping and 

analysis of essentially all workings in the mine and of most 

available drill core.

References Cited

Barker, Fred, 1957, Geology of the Juneau B-3 quadrangle, 

Alaska: U.S. Geological Survey map GQ–100, scale 

1:63,360.

Brew, D.A., and Ford, A.B., 1985, Preliminary reconnaissance geologic map of the Juneau, Taku River, Atlin, and 

part of the Skagway 1:250,000 quadrangles, southeastern 

Alaska: U.S. Geological Survey Open-File Report 85–395, 

23 p.

Brew, D.A., and Karl, S.M., 1988, A reexamination of the 

contacts and other features of the Gravina belt, southeastern Alaska: U.S. Geological Survey Circular 1016, 

p. 143–146.

Cohen, H.A., and Lundberg, N., 1993, Detrital record of the 

Gravina arc, southeastern Alaska—Petrology and provenance of Seymour Canal Formation sandstones: Geological 

Society of America Bulletin, v. 105, p. 1400–1414.

Haeussler, P.J., 1992, Structural evolution of an arc-basin—

The Gravina belt in central southeastern Alaska: Tectonics, 

v. 11, no. 6, p. 1245–1265.

Haeussler, P.J., Karl, S.M., Mortensen, J.K., Layer, P., and 

Himmelberg, G.R., 1999, Permian and mid-Cretaceous 

deformation of the Alexander terrane on Admiralty and 

Kupreanof Islands, southeastern Alaska: Geological Society 

of America Abstracts with Programs, v. 31, no. 6, p. A–60.

Jones, D.L., Berg, H.C., Coney, P., and Harris, A., 1981, Structural and stratigraphic significance of Upper Devonian and 

Mississippian fossils from the Cannery Formation, Kupreanof Island, southeastern Alaska: U.S. Geological Survey 

Circular 823–B, p. B109–B112.

Lathram, E.H., Pomeroy, J.S., Berg, H.C., and Loney, R.A., 

1965, Reconnaissance geology of Admiralty Island, Alaska: 

U.S. Geological Survey Bulletin 1181–R, 48 p.

Lister, G.S., and Snoke, A.W., 1984, S-C mylonites: Journal of 

Structural Geology, v. 6, p. 617–638.

Loney, R.A., 1964, Stratigraphy and petrography of the PybusGambier area, Admiralty Island, Alaska: U.S. Geological 

Survey Bulletin 1178, 103 p.

Muffler, L.J.P., 1967, Stratigraphy of the Keku Islets and 

neighboring parts of Kuiu and Kupreanof Islands, southeastern Alaska: U.S. Geological Survey Bulletin 1241–C, 52 p.

Simpson, Carol, and Schmid, S.M., 1983, An evaluation 

of criteria to deduce the sense of movement in sheared 

rocks: Geological Society of America Bulletin, v. 94, 

p. 1281–1288.

Geochemistry of Metasedimentary Rocks 

in the Hanging Wall of the Greens Creek 

Massive Sulfide Deposit and of Shales 

Elsewhere on Admiralty Island

By Craig A. Johnson, Cliff D. Taylor, Joel S. Leventhal, and Katja Freitag

Chapter 8 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract.......................................................................................................................................................163

Introduction.................................................................................................................................................163

Sampling and Analytical Methods..........................................................................................................164

Samples..............................................................................................................................................164

Chemical Analysis.............................................................................................................................164

Degree of Pyritization.......................................................................................................................165

Rock-Eval............................................................................................................................................165

Stable Isotope Analysis ...................................................................................................................165

Results .........................................................................................................................................................165

Major-Element Chemical Compositions........................................................................................165

Rock-Eval............................................................................................................................................166

Carbon-Sulfur-Iron Relationships ..................................................................................................166

Metals.................................................................................................................................................167

Stable Carbon and Oxygen Isotopes .............................................................................................169

Effects of Cretaceous Regional Metamorphism...................................................................................172

Implications of Whole-Rock Chemical Compositions..........................................................................177

Implications of Carbonate Isotopic Compositions ...............................................................................177

Conclusions.................................................................................................................................................180

References Cited........................................................................................................................................181

Figures

1. Plot of aluminum compared to carbonate carbon illustrating that the

metasediments in the Greens Creek hanging wall span a broad lithologic

range from carbonate-poor shale to nearly pure carbonate, and exhibit

variable contents of quartz or chert......................................................................................166

2. Comparison of the calcium and magnesium contents of hanging-wall

samples with the ratio characteristic of dolomite ..............................................................167

3. Plot of organic carbon (C) (determined by Rock-Eval) compared to sulfur

(S) for hanging-wall samples..................................................................................................169

4. Plot of organic carbon (C) (total carbon minus carbonate carbon) compared

to sulfur (S) for Hyd Group, Cannery Formation, Gambier Bay Formation, and

Retreat Group samples ............................................................................................................170

5. Plot of degree-of-pyritization compared to organic carbon (C) for Hyd Group,

Cannery Formation, and Retreat Group samples ................................................................170

6. Concentrations of several metals in hanging-wall shales (only those samples

that contain less than 15 percent carbonate) compared with the concentrations

in (A) average black shale and (B) average Hyd Group shale (table 1)...........................171

7. Correlations in hanging-wall samples of various elements with organic carbon

(Corg) compared to the correlations of the same elements with sulfur (S),

expressed as correlation coefficients (R-values)...............................................................172

8. Plots of degree-of-pyritization (DOP) compared to (A) lead and (B) zinc (Zn) for 

hanging-wall samples..............................................................................................................173
9. (A) The carbon isotopic compositions of coexisting carbonate (filled symbols)

and organic matter (open symbols) in hanging-wall samples, (B) The carbon 

isotopic compositions of Hyd Group, Cannery Formation, and Retreat Group 

(squares) samples ......................................................................................................................174

10. Carbon isotopic compositions of organic matter................................................................175

11. The carbon and oxygen isotopic compositions of carbonate minerals in

hanging-wall rocks, white carbonate-rich ore, Hyd Group, and Cannery

Formation samples ...................................................................................................................175

12. Comparison of the isotopic compositions of carbonate in the hanging-wall

rocks (filled circles) with dolomite in white carbonate-rich ore ......................................178

13. Plot of the carbon isotopic composition of coexisting carbonate and organic

matter in hanging-wall rocks..................................................................................................179

14. Plot of the carbon (C) isotopic composition of carbonate relative to the sulfur

(S) content of hanging-wall rocks..........................................................................................180

Tables

1. Chemical analyses....................................................................................................on CD–ROM

2. Average chemical compositions of Admiralty Island shales compared

with average shale and average black shale ......................................................................168

3. Rock-Eval analyses of hanging-wall samples .....................................................................176

4. Stable isotopic compositions of carbonate minerals and organic matter......................176

5. Chemical analyses of hanging-wall samples with low sulfur: organic

carbon and low degree-of-pyritization (DOP) values .........................................................177

Abstract

Metasedimentary rocks in the hanging wall of the 

Greens Creek massive sulfide deposit span a lithologic range 

from carbonate-poor shale to nearly pure dolomite, and have 

organic carbon contents higher than average shale, but lower 

than average black shale. Rock-Eval analyses of the organic 

matter reveal that the rocks have undergone heating beyond 

the oil and gas generation stages, and that carbon-oxygenhydrogen volatiles have been released. Some hanging-wall 

samples have sulfur-to-organic carbon ratios and degree-ofpyritization values similar to normal marine shales. These 

same samples also have base- and precious-metal contents 

like normal shales but are somewhat enriched in barium. 

The data are evidence that the depositional history of the 

hanging-wall sediments included periods where the overlying 

water column was oxic, with only a slight barium enrichment as possible evidence for venting of hydrothermal fluids 

to the basin waters. More commonly, hanging-wall samples 

are high in sulfur, high in metals, and high in degree-ofpyritization, consistent either with (1) sediment accumulation beneath an anoxic water column strongly affected by 

hydrothermal venting, (2) epigenetic hydrothermal sulfur 

and metal emplacement, or (3) sulfur and metal release from 

the underlying massive sulfide body during the Cretaceous 

regional metamorphism.

The carbon and oxygen isotopic compositions of 

hanging-wall carbonates appear to have been unaffected by 

the Cretaceous regional metamorphism, and they are indistinguishable from the isotopic compositions of dolomite in the 

underlying massive sulfide ores. This observation provides 

strong evidence that the Greens Creek hydrothermal system 

continued operating until after the hanging-wall sequence was 

laid down. The isotopic variations in both the hanging-wall 

rocks and the ores are consistent with dolomite precipitation 

from a single carbonate-bearing fluid over the temperature 

range 200–350°C, or dolomite precipitation from mixed 

marine and hydrothermal fluids. Carbonate δ13C correlates 

positively with organic matter δ13C, which suggests that 

carbonate precipitation was accompanied by oxidation of the 

ambient organic matter or organic-matter-derived methane. 

Carbonate δ13C correlates negatively with the sulfur content 

of the rocks, which suggests that organic-matter or methane 

oxidation was accompanied by reduction of dissolved sulfate 

to produce hydrogen sulfide. Some sulfate reduction, but not 

necessarily all, was microbially mediated and took place during early diagenesis beneath the sediment/seawater interface. 

Limited isotopic data from Hyd Group shales elsewhere on 

Admiralty Island, which are thought to be distal equivalents 

of the hanging-wall section, suggest that the same hydrothermal fluid that formed the Greens Creek massive sulfide may 

also have interacted with basin-floor sediments at distances of 

several kilometers from the Greens Creek deposit.

Introduction

The metasedimentary rocks in the hanging wall of 

the Greens Creek massive sulfide deposit have been variously referred to as argillites, calc-argillites, metasiltstones, 

metashales, and argillaceous limestones (for example, Newberry and others, 1997; Taylor and others, 1999, 2000; Freitag, 

2000). Common to all descriptions of these rocks has been 

the observation that they contain abundant reduced carbon, 

presumably sedimentary organic matter that has been depleted 

in hydrogen and oxygen by postdepositional heating. Carbonaceous sediments can be critical to the development of sulfide 

ores because they can supply metals to ore-forming fluids, or 

they can supply the reduced sulfur necessary to form sulfide 

minerals (Tourtelot, 1979; Leventhal, 1993). Simple massbalance calculations demonstrate that it is not unreasonable to 

hypothesize that these shales and their distal equivalents were 

the primary metal source for the Greens Creek hydrothermal 

system. For example, the zinc content of the presently defined 

Greens Creek reserve could have been obtained by hydrothermal scavenging from a geologically reasonable volume of 

shale measuring 5 km3

 if the metal concentration was the same 

as in average black shale. Carbonaceous sediments can also 

act to preserve sulfide ores because the anoxic conditions that 

led to their formation can protect underlying sulfide minerals from destruction by seawater oxidation (Goodfellow and 

others, 1993; Eastoe and Gustin, 1996).

Geochemistry of Metasedimentary Rocks in the Hanging 

Wall of the Greens Creek Massive Sulfide Deposit and of 

Shales Elsewhere on Admiralty Island

By Craig A. Johnson, Cliff D. Taylor, Joel S. Leventhal, and Katja Freitag
164 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

The purpose of this paper is to report on the organic 

geochemistry, major and trace-element geochemistry, and 

stable isotope geochemistry of the hanging-wall rocks at 

Greens Creek in order to examine their function in the genesis 

of the underlying ore deposit. Also reported are data from 

Hyd Group shales collected elsewhere on Admiralty Island, 

which are presumed to be stratigraphic equivalents of the 

hanging-wall section (chap. 4), and data from shales that occur 

lower in the Admiralty Island section, in the Retreat Group 

(Devonian?), the Gambier Bay Formation (Devonian), and the 

Cannery Formation (Permian). For descriptions of the Admiralty Island stratigraphy, the reader is referred to chapters 4, 7, 

and 11. Chapter 7 also gives photographs and descriptions of 

typical exposures of the rocks.

Sampling and Analytical Methods

Samples

In the immediate mine area hanging-wall rocks were 

obtained from drill core and from underground workings. An 

effort was made to obtain a variety of samples from the two 

main lithologic groups that have been recognized in the mine 

area: massive argillite and slaty argillite (chap. 6). Petrographic observations have indicated that the massive argillites are characteristically richer in dolomite with abundant 

included organic matter (the field term that is used for this 

material is graphite), whereas the slaty argillites are richer 

in quartz and feldspar (up to 50 volume percent) commonly 

with rhombic dolomite overgrowths. Samples were taken 

from (1) core GC1136, which intersected a 275-foot section 

of wall rock overlying the Lower Southwest orebody; (2) core 

GC1530, which intersected a 675-foot section of wall rock 

overlying the Northwest orebody; (3) core GCPP173, which 

was collared on the 350 level and intersected a 150-foot section of wall rock above the Lower Southwest orebody; (4) 

core GCPP177, which was also collared on the 350 level and 

intersected a 280-foot section of wall rock above the Lower 

Southwest orebody; (5) cores PP–198 and PP–204, which 

were collared on the 170 level above the Lower Southwest 

orebody; and (6) core PS–50, which was collared at the surface due south of the South zone of the East orebody. Hand 

specimens were collected on the 350 level in the 2650 crosscut 

from rocks overlying the Lower Southwest orebody (96GC 

prefixes in table 1, on CD–ROM), and from the exposure at 

the 920 portal (GCPF–1).

The hanging-wall samples included specimens with varying degrees of veining, shearing, and fracturing and also specimens showing none of these features. In all cases, the entire 

sample was crushed and ground for geochemical analysis. 

The reasons for this are threefold. First, in most cases it is not 

clear from the textures whether chemical transport to or from 

veins occurred on length scales exceeding the size of a typical hand specimen (none of the analyzed samples approached 

100 percent of what was clearly vein material). Thus, analysis 

of entire samples may be a more appropriate measure of 

original whole-rock compositions than analysis of material 

between veins. Second, any longer range remobilizations that 

did occur during either a protracted hydrothermal history or 

later metamorphism/deformation event were thought to be best 

characterized by comparing whole-rock analyses of veined 

or fractured samples with those of unveined samples. Third, 

analysis of entire samples has been the common practice in 

geochemical studies of sediment-hosted mineralization at other 

similar deposits (Williams, 1978, and references therein); thus, 

comparisons to other occurrences are best made using data that 

include samples with textural evidence of remobilization.

Shales and related sedimentary rocks also were sampled 

elsewhere on Admiralty Island from surface exposures of the 

Retreat Group (Devonian?), Gambier Bay Formation (Devonian), Cannery Formation (Permian), and Hyd Group (Triassic). Sample locations are given in table 1. In all cases efforts 

were made to obtain fresh rock minimally affected by weathering, but some samples probably experienced pyrite oxidation 

and sulfur loss, as noted below.

Chemical Analysis

For whole-rock chemical analysis, samples were analyzed 

either by a protocol referred to as U or by a protocol referred to 

as A, depending on the analytical services that were available 

at the time of sample collection. In the U protocol, 50–100 mg 

of rock was passed through a jaw crusher and then through a 

pulverizer equipped with ceramic plates. Splits of the resulting powders were decomposed in a mixture of hydrochloric, 

nitric, perchloric, and hydrofluoric acids, and the solutions 

were analyzed for Ag, Al, As, Au, Ba, Be, Ca, Cd, Ce, Co, Cr, 

Cu, Eu, Fe, Ga, Hg, K, La, Li, Mg, Mn, Mo, Na, Nb, Nd, Ni, 

P, Pb, Sc, Sn, Sr, Ta, Th, Ti, U, V, Y, Yb, and Zn by inductively 

coupled plasma atomic emission spectrometry using procedures described by Arbogast (1996). Some minerals are known 

to resist dissolution in the acid mixture, including barite and 

chromite. Because the shales studied here may contain these 

two minerals, the results reported for barium and chromium 

may be too low. Apart from this potential difficulty, the analytical results are considered on the basis of data reported in Arbogast (1996) to be accurate to within ±10 percent of the amount 

of the element present, except for beryllium, molybdenum, 

and phosphorus, which are considered to be accurate to within 

±20 percent. As part of this same protocol, gold was analyzed 

by fire assay, mercury was analyzed by vapor extraction using 

a Leeman PS200 analyzer, carbonate carbon was analyzed by 

coulometric titration after digestion in perchloric acid, and 

total carbon and total sulfur were analyzed by high temperature 

(LECO) combustion. Analyses of standard materials indicate 

that these methods give results that are generally accurate to 

within ±10 percent (Arbogast, 1996).

In the A protocol, rock samples were crushed and 

passed through a pulverizer equipped with steel plates. Splits 

of the resulting powders were analyzed by instrumental 

neutron activation (INAA) for Au, As, Ba, Ce, Co, Cr, Eu, 

Fe, Hg, La, Na, Nd, Sc, Sn, Ta, Th, U, W, and Yb. Splits also 
Results 165

were dissolved in a mixture of hydrochloric, nitric, perchloric, and hydrofluoric acids, and the resulting solutions were 

analyzed by inductively coupled plasma mass spectrometry 

(ICP–MS) for Al, Ag, Be, Bi, Ca, Cd, Cu, K, Mg, Mn, Mo, 

Ni, Pb, Sr, Ti, V, Y, and Zn. Incomplete dissolution of the 

acid-resistant minerals barite and chromite would have no 

effect on the barium and chromium values reported for these 

samples because only the INAA results were used. However, 

the ICP–MS results for strontium might be low for samples 

containing barite. As part of this same protocol, carbonate 

carbon was analyzed by acid digestion, and total carbon and 

total sulfur were analyzed by high temperature (LECO) combustion. Analyses of standard materials indicated that these 

methods give results that are generally within ±10 percent 

of the accepted concentrations, except for silver, cadmium, 

nickel, and vanadium, which have greater uncertainties. 

Results for these latter elements are not tabulated in this 

paper, but correlations among them are noted assuming that 

the relative concentrations were determined more accurately 

than the absolute concentrations.

For some hanging-wall samples there is evidence that the 

carbonate carbon values were erroneously low, probably due 

to the presence of dolomite which is known to be more resistant to acid digestion than calcite. Thus, the carbonate carbon 

results given for hanging-wall rocks in table 1 should be considered minima. For the Hyd Group, Cannery Formation, and 

Gambier Bay Formation samples, carbonate is present at lower 

concentrations, and the carbonate mineral is probably calcite. 

The carbonate carbon results for these rocks are believed to be 

accurate due to the greater reliability of the coulometric titration method for calcite. For these samples, organic carbon was 

determined by taking the difference between total carbon and 

carbonate carbon (table 1).

Degree of Pyritization

Degree of pyritization (DOP), which is defined as

DOP = Fepyrite / (Fepyrite + Fereactive),

was determined using methods that have been described 

by Leventhal and Taylor (1990). The parameter Fepyrite was 

calculated from the measured sulfur contents of the samples 

after correcting for sulfur contained in sphalerite, galena, and 

chalcopyrite using the equations

Spyrite = Stotal – 0.490 (Zn) – 0.155 (Pb) – 1.009 (Cu),

and

Fepyrite = 0.871 (Spyrite).

In some rocks, sulfur is also contained in barite. However, the barium contents of the samples analyzed in this study 

are low enough that the correction to Spyrite for barite sulfur is 

insignificant (table 1). The parameter Fereactive was determined 

by measuring the amount of iron leached from the samples by 

a 1N HCl solution at room temperature in a 24-hour period 

(Leventhal and Taylor, 1990).

Rock-Eval

Rock-Eval analyses were carried out using the standard 

pyrolysis procedure (Tissot and Welte, 1984), and the results 

were used to calculate total organic carbon content (TOC), the 

parameter Tmax, the hydrogen index (HI), and the oxygen index 

(OI). Because the organic matter in the rocks is mature and possibly graphitic (see Rock-Eval results, and the conodont color 

alteration indices reported in chapter 11), the pyrolysis reactions 

may have been incomplete, resulting in erroneously low values 

for total organic carbon content. However, prior experience with 

similar types of samples (J.S. Leventhal, unpub. data, 2001) 

suggests that the underreporting is no more than 5–10 percent. 

Conclusions that will be drawn herein from the total organic 

carbon data are insensitive to errors of this magnitude.

Stable Isotope Analysis

Carbonate minerals were converted to carbon dioxide for 

isotopic analysis by treating whole-rock powders with phosphoric acid as described by McCrea (1950). All samples were 

reacted for 2 days at 25°C to ensure that yields were complete 

whether the carbonate mineral was dolomite or calcite. Isotopic 

compositions of the gases were determined using a Finnigan 

MAT 252 isotope ratio mass spectrometer equipped with a dual 

viscous inlet system. The acid fractionation factor for dolomite 

was used to calculate the oxygen isotopic compositions (Friedman and O’Neil, 1977). For samples containing calcite, which 

probably include the Hyd, Cannery, Retreat, and Gambier Bay 

samples, this has resulted in δ18O values that are 0.8 permil too 

low. This potential error is small enough to have no effect on our 

conclusions. Carbon isotopic compositions determined by the 

phosphoric acid method do not depend on carbonate mineralogy.

For isotopic analysis of organic matter, powders were 

treated with 6N HCl to remove all carbonate carbon and then 

rinsed in deionized water. The solid residues were combusted 

in an elemental analyzer to convert the remaining carbon to 

carbon dioxide gas, which was admitted directly to a Micromass Optima mass spectrometer for determination of isotopic 

compositions by the continuous flow method.

Isotopic data are reported in δ-notation relative to Vienna 

Standard Mean Ocean Water (VSMOW) for oxygen and 

Vienna Pee Dee belemnite (VPDB) for carbon. Reproducibility 

was typically ±0.1 permil or better for δ13C, and ±0.2 permil or 

better for δ18O.

Results

Major-Element Chemical Compositions

The hanging-wall samples span a wide range of chemical compositions corresponding to lithologic variation from 

carbonate-free shale to nearly pure carbonate rock (table 1). 

Elements normally found in detrital silicates or clays, such 

as aluminum, potassium, and sodium, generally show inverse 
166 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

relationships with elements normally found in carbonate minerals, such as calcium, magnesium, and carbon. An example 

is shown in figure 1 where aluminum and carbonate carbon 

are shown to span the entire range from typical shale or black 

shale to silicate-poor carbonate. Also evident in figure 1 are 

samples low in both aluminum and carbonate carbon, presumably due to an abundance of quartz or chert (silicon was 

not analyzed in this study). The calcium:magnesium ratios 

for many samples are within analytical error of the dolomite 

ratio (fig. 2), which is strong evidence that dolomite is the 

predominant host mineral for these two elements. Organic 

carbon in samples analyzed by Rock-Eval ranges from 0.5 to 

5.0 percent, averaging 1.9 percent (table 2). This is higher than 

the values that have been proposed for average shale (Blatt and 

others, 1972; Krauskopf, 1979) but lower than the 2–10 percent range characteristic of black shales (Tourtelot, 1979). The 

dark appearance of the Greens Creek rocks probably reflects 

the graphitization of the organic matter due to heating rather 

than a particularly high organic content (Leventhal, 1993).

Chemical compositions are more restricted for other shale 

units on Admiralty Island, and the data are summarized as 

averages in table 2. The Cannery and Gambier Bay samples 

have major element compositions within the ranges characteristic of shales (Blatt and others, 1972), but the Hyd Group and 

Retreat Group samples are lower in aluminum. The carbonate 

carbon values are no higher for these units, so we infer that 

they contain a greater proportion of quartz or chert relative 

to feldspars and clay minerals. This inference conflicts with 

observations made during field mapping (chap. 4) that the Hyd 

Group is less siliceous than the Cannery Formation. However, 

other observations from field mapping are borne out by the 

chemical data. The observation that the Hyd Group is more 

pyritic than the Cannery Formation is confirmed by higher 

sulfur contents (1.7 versus 0.7 wt%), and the observation that 

the Hyd Group is more graphitic than the Cannery Formation 

is borne out by higher organic carbon (1.9 versus 0.7 wt%).

Rock-Eval

Rock-Eval results for hanging-wall samples are given 

in table 3. The HI and OI values are generally low, and the 

Tmax values generally are greater than 500, indicating that the 

samples are overmature with respect to oil and gas generation, 

having been heated to temperatures exceeding 150°C. For 

comparison, black shales from unmetamorphosed localities 

elsewhere typically display HI values of 300–500, OI values of 

50–100, and Tmax below 460 (Leventhal, 1998).

Carbon-Sulfur-Iron Relationships

Most hanging-wall samples have sulfur:organic carbon 

ratios well above the value of ~0.36 that is characteristic of 

normal marine shale (for example, Berner and Raiswell, 1983) 

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12 14

Al (wt%)

Carbonate-C (wt%)

C content of pure calcite

C content of pure dolomite

Al content of 

average shale

Al content of average

black shale

Mixtures of shale

and carbonate

Higher

silica?

Figure 1. Plot of aluminum compared to carbonate carbon illustrating that the metasediments in the Greens 

Creek hanging wall span a broad lithologic range from carbonate-poor shale to nearly pure carbonate, and 

exhibit variable contents of quartz or chert. Aluminum (Al) contents of average shale and average black 

shale are from Krauskopf (1979) and Quinby-Hunt and others (1989), respectively. wt%, weight percent.
Results 167

in which diagenetic sulfide has been formed in anoxic sediment 

overlain by an oxic water column (fig. 3). The high ratios could 

be a consequence of organic matter loss during postdepositional 

heating, but the sulfur contents of many samples would require 

organic contents far higher than ordinary marine shales. Sulfide 

precipitation within an anoxic, hydrogen sulfide-bearing water 

column could also explain the high sulfur content of the rocks, 

but this typically preserves a positive- or zero-slope correlation between organic carbon and sulfur (Leventhal, 1983; 

Raiswell and Berner, 1985), a feature that is not apparent in the 

hanging-wall data. Epigenetic introduction of sulfur is a third 

mechanism that can lead to high sulfur:organic carbon ratios 

(Leventhal, 1995). The very high degree-of-pyritization values 

determined for many hanging-wall samples (table 1) is consistent with this process.

The Hyd Group and Cannery Formation samples also 

span wide ranges of sulfur:organic carbon (fig. 4). However, 

the very low sulfur contents and very low DOP values (less 

than 0.2, see Leventhal, 1993) displayed by many samples 

(fig. 5) are strong evidence that the chemical compositions 

of Admiralty Island surface outcrops have been affected by 

weathering. The fact that a few Hyd Group and Cannery Formation samples extend to high sulfur contents and high DOP 

values (figs. 4 and 5) suggests that at least some experienced 

substantial sulfur addition. Whether epigenetic sulfur addition is widespread in these units cannot be determined from 

the limited number of fresh samples that were available for 

this study.

Metals

For most of the listed metals, the agreement between Hyd 

Group samples analyzed by the A protocol and Hyd Group 

samples analyzed by the U protocol is reasonably good (table 2). 

However, for chromium and barium the results obtained using the 

A protocol are higher, possibly reflecting incomplete dissolution of 

chromite and barite in the U protocol, or chromium contamination 

from steel pulverizer plates in the A protocol.

The hanging-wall rocks show extremely broad ranges of 

metal contents (table 1). For samples that are true shales, which 

is defined here as samples containing less than 15 percent 

carbonate, the concentrations of iron and cobalt are the same 

as average black shale, copper and zinc are the same or slightly 

higher than in average black shale, and lead, gold, barium, and 

arsenic are higher than in average black shale (fig. 6A).

A comparison of metal concentrations in the hanging-wall 

shales with concentrations in their stratigraphic equivalents, the 

Hyd Group shales, is shown in figure 6B. The concentrations of 

cobalt, iron, and molybdenum are similar in the two units, and 

for each of the other elements the hanging-wall analyses overlap 

the Hyd average and extend to higher concentrations. No strong 

evidence exists in the data for metal depletions in the exposed 

Hyd Group rocks, as might be expected if this unit were the 

main metal source for the Greens Creek massive sulfide deposit.

With regard to chemical variations within the entire 

hanging-wall shale + carbonate package, cobalt, chromium, 

nickel, and vanadium were found to correlate with organic 

0

2

4

6

8

10

12

14

0 5 10 15 20 25

Ca (wt%)

Mg (wt%)

Stoichiometric

dolomite

Figure 2. Comparison of the calcium and magnesium contents of hanging-wall samples with the ratio 

characteristic of dolomite. The close correspondence suggests that dolomite is the dominant host mineral 

for these elements. Ca, calcium; Mg, magnesium; wt%, weight percent.
168 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Table 2. Average chemical compositions of Admiralty Island shales compared with average shale and average black shale.#

[<, less than; - , no data; Gp., Group; Fm.; Formation; Ave., average] 

Element Hyd (A) Gp. Hyd (U) Gp. Cannery Fm. Gambier Bay 

Fm. Retreat Gp. Ave. shale@@ Ave. black shale^

Al2O3 7.6 - 11.4 16.8 8.3 17 15.5

CaO 0.8 - 1.0 0.1 0.01 3.5 2.4

FeO* 3.6 - 4.8 4.4 2.0 6.0 4.7

K2

O 1.6 - 2.0 3.4 2.2 3.0 3.6

MgO 1.5 - 2.2 1.5 2.0 2.3 1.7

Na2

O 1.0 - 1.6 0.9 0.03 1.2 0.7

TiO2 0.3 - 0.5 0.6 0.4 0.8 0.7

S 1.7 1.1 0.7 0.9 0.01 0.25 1

Corg

** 1.9 - 0.7 2.3 0.5 0.8 3.2

U 4 - - - - 3.5 15.2

Mo 6 14 7 <2 <2 2 65

V - 196 206 181 82 130 500

Ni - 35 36 38 13 80 50

Cu 20 31 37 25 17 50 70

Cr 130@ 43*** 36 68 16 100 111

Co 5 8 9 5 <2 20 17

As 23 - - 18 <10 10 29

Pb 32 16 18 29 9 20 20

Ba 2,078 1,539*** 2,327 810 4,083 600 1,120

Zn 81 85 119 81 49 90 310

Ag - <2 <2 <2 <2 0.1 0.1

Cd - <2 <2 <2 <2 0.3 -

P - 570 717 500 233 750 -

Mn - 191 479 97 189 850 383

no. samples 9 33 17 1 3 - -

#

Oxides in percent, elements in parts per million.

*

Total iron as iron (II) oxide.

**

Organic carbon from Rock-Eval for mine argillite, from difference between total carbon and carbonate carbon for all others.

@May be high by this method (see text).

***May be low by this method (see text).

@@Krauskopf (1979), except for organic carbon which is from Leventhal (unpub. data, 2001).

^

Quinby-Hunt and others (1989), except for lead, organic carbon, nickel, copper, which are from Vine and Tourtelot (1970), and sulfur and silver, which are 

from Leventhal (unpub. data, 2001).
Results 169

0

5

10

15

20

25

30

0 1 2 3 4 5 6

Organic C (wt%)

S (wt%)

Euxinic

Normal

marine

Hanging wall above

massive ore

Figure 3. Plot of organic carbon (C) (determined by Rock-Eval) compared to sulfur (S) for hanging-wall 

samples. The lines marking normal marine sediments and sediments deposited in euxinic environments 

were taken from Leventhal (1995). wt%, weight percent.

carbon with R-values of around 0.7 (fig. 7). Silver, As, Au, Cd, 

Cu, Fe, Mo, Pb, and Zn were found to correlate only weakly 

with organic carbon (R-values less than 0.4), but more strongly 

with sulfur (R-values of 0.4–0.5 for cadmium, silver; 0.5–0.6 

for copper, molybdenum, lead; about 0.7 for gold, arsenic, 

zinc; 0.9 for iron) (fig. 7). Figure 8 illustrates that samples with 

intermediate degree-of-pyritization values have lead and zinc 

contents that are typical of shale or black shale, but samples 

with higher degree-of-pyritization values have substantially 

higher metal contents. Barium falls in neither of the two suites 

of metals shown in figure 8, displaying a fair correlation with 

organic carbon, but no correlation with sulfur. This may imply 

that barium was added during sedimentation or diagenesis.

Stable Carbon and Oxygen Isotopes

The stable isotopic compositions of carbonates and total 

organic carbon are given in table 4. Hanging-wall carbonates have an average δ18O of 18 permil and an average δ13C 

of –6 permil. Both values are significantly lower than marine 

limestones and dolomites of Triassic age (Veizer and others, 

1999). Organic carbon isotopic compositions are –25.9±0.9 

(1–σ) permil, which is intermediate between the compositions 

characteristic of the two kerogen types found in Phanerozoic 

sedimentary rocks (Lewan, 1986). Thermal maturation can 

cause an upward shift in organic matter δ13C values of as 

much as 3 permil (Schidlowski, 1987). Thus the hanging-wall 

organic matter may originally have had isotopic compositions 

resembling l (italic “el”)-amorphous kerogen (Lewan, 1986). 

The isotopic fractionations between carbonate carbon and 

organic carbon are 19.9±0.8 (1–σ) permil across a wide range 

of organic carbon:carbonate carbon ratios (fig. 9A).

Fewer analyses were made of the Cannery Formation and 

Hyd Group shales (fig. 9B). The isotopic compositions of Hyd 

carbonates resemble those of the hanging-wall carbonates, 

whereas three Cannery samples have compositions spanning a 

wide δ13C range of –13 to –2 permil. Organic carbon δ13C values for the Hyd Group and Cannery Formation are very similar to the hanging-wall samples, although two Hyd samples 

extend to significantly higher δ13C (fig. 10). Of note is the low 

carbonate δ13C value and the small carbonate-organic carbon 

fractionation in Cannery sample Ard–02, which suggest that 

there may have been isotope exchange between carbonate 

minerals and organic matter during a postdepositional heating 

event. The fact that isotopic exchange is apparent in this Permian unit, but neither in the mine argillite nor in the Hyd Group, 

both of which are Triassic, may mean that the exchange was 

a consequence of the Early Permian low-grade metamorphic 

event that affected some areas on Admiralty Island (Haeussler 

and others, 1999; Karl and others, 1999).

On a plot of δ18O and δ13C (fig. 11) the hanging-wall 

carbonates display a broad linear trend with a regression slope 

of 0.6. The Hyd samples conform closely to this trend, but two 

Cannery samples do not. This observation may imply a genetic 
170 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

0

1

2

3

4

5

6

0 1 2 3 4 5 6

Hyd

Cannery

Gambier

Retreat

Organic C (wt%)

S (wt%)

Normal

marine

Euxinic

(Hyd, 10.3)

(Hyd, 32.2)

0

1

2

3

4

5

6

0 0.2 0.4 0.6 0.8 1

Hyd

Cannery 

Retreat

Degree of pyritization

Organic C (wt%)

Figure 5. Plot of degree-of-pyritization compared to organic carbon (C) for Hyd Group, Cannery 

Formation, and Retreat Group samples. wt%, weight percent.

Figure 4. Plot of organic carbon (C) (total carbon minus carbonate carbon) compared to sulfur (S) for 

Hyd Group, Cannery Formation, Gambier Bay Formation, and Retreat Group samples. wt%, weight percent.
Results 171

0.001

0.1

10

1,000

100,000

0.001 0.1 10 1,000 100,000

Concentration in average black shale (ppm)

Concentration in hanging-wall shales (ppm)

Fe

Ba

Zn

Cu

Pb

Co

As

Mo

Au

A

0.001

0.1

10

1,000

100,000

0.001 0.1 10 1,000 100,000

Average concentration in Hyd Group (ppm)

Concentration in hanging-wall rocks (ppm)

Fe

Ba

Zn

Pb

As

Cu

Mo

Co

Au

B

Figure 6. Concentrations of several metals in hanging-wall shales (only those samples that contain less than 15 

percent carbonate) compared with the concentrations in (A) average black shale (Quinby-Hunt and others, 1989) and 

(B) average Hyd Group shale (table 1). The Hyd average includes only those samples analyzed by the same protocol 

used for the hanging-wall samples (see text). ppm, parts per million.
172 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

link between the carbonate minerals in the hanging-wall rocks 

and those in Hyd Group rocks found several kilometers to the 

northwest near Hawk Inlet (see succeeding discussion).

Effects of Cretaceous Regional 

Metamorphism

The regional metamorphic-deformation event that affected 

Admiralty Island in Cretaceous time could have caused 

significant changes in the hanging-wall rocks, and it is important 

that any such changes be considered so that primary features can 

be discriminated from any secondary metamorphic features. In 

underground exposures and in drill core, there is clear textural 

evidence for remobilization of metals and sulfur, including 

crosscutting sulfide veinlets, and fractures and shears with sulfide minerals dispersed along them. Whether these remobilizations were caused by a protracted hydrothermal event or by the 

Cretaceous metamorphism-deformation is uncertain, in much 

the same way that remobilization textures within the underlying 

massive sulfide bodies are of uncertain origin (chap. 9).

Volatile species would very likely have been released 

from the hanging-wall section during regional metamorphism. 

Kerogen is known to lose methane starting at around 120°C 

(Tissot and others, 1974), and clays begin to dehydrate at 

100–200°C (Fyfe and others, 1978). The Rock-Eval results 

(table 3) are consistent with these types of prograde reactions 

because they indicate carbon-oxygen-hydrogen volatile loss 

at temperatures greater than 150°C. On the other hand, any 

pre-Cretaceous heating event, including the metal-depositing 

event itself, could also explain the Rock-Eval data. The production and movement of fluids during low-grade metamorphism 

could have led to redistribution of volatile species within the 

rocks and may be partly responsible for the wide variation 

in sulfur:organic carbon ratios observed in the hanging-wall 

samples (fig. 3). Because the metamorphic event was regional, 

the same phenomenon might also explain the wide variation 

in sulfur:organic carbon ratios observed in the Hyd Group and 

Cannery Formation rocks. The fact that the hanging-wall rocks 

have systematically high degree-of-pyritization values indicates 

that aqueous sulfide or hydrogen sulfide was abundantly available at some time during the history of these rocks, possibly 

during the Cretaceous metamorphism when hydrogen sulfidebearing fluids may have been released from the nearby massive 

sulfide bodies. For the Hyd Group and Cannery Formation, 

the wide range in degree-of-pyritization values indicates that 

reduced sulfur was abundantly available at some locations but 

was never available at others, presumably due to heterogeneity 

of flow paths and bulk permeability.

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

Correlation with Corg (R-value)

Correlation with S (R-value)

Fe

Cd

Mo

Ag

As

Au Zn

Pb

Mn

Ni Co

Cr

V

Ba

Cu

Figure 7. Correlations in hanging-wall samples of various elements with organic carbon (Corg) compared 

to the correlations of the same elements with sulfur (S), expressed as correlation coefficients (R-values). 

Base metals, precious metals, iron, molybdenum, and arsenic show a higher correlation with sulfur than with 

organic carbon, and the reverse is true for cobalt, chromium, nickel, and vanadium, suggesting that different 

processes were responsible for the emplacement of these two groups of elements.
Effects of Cretaceous Regional Metamorphism 173

1

10

100

1,000

10,000

100,000

1,000,000

0 0.2 0.4 0.6 0.8 1

DOP

Pb (ppm)

Pb content of

average black shale Pb content of

average shale

A

Figure 8. Plots of degree-of-pyritization (DOP) compared to (A) lead and (B) zinc (Zn) for hanging-wall samples. 

ppm, parts per million.

1

10

100

1,000

10,000

100,000

1,000,000

0 0.2 0.4 0.6 0.8 1

Zn (ppm)

DOP

Zn (ppm)

Zn content of

average black shale

Zn content of

average shale

B
174 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

–30

–25

–20

–15

–10

–5

0

0 0.2 0.4 0.6 0.8 1

Corg/Ctotal

δ13C (‰, relative to PDB)

Hanging-wall carbonate

Hanging-wall

organic matter

A

–30

–25

–20

–15

–10

–5

0

0 0.2 0.4 0.6 0.8 1

Corg/Ctotal

δ13C (‰, relative to PDB)

B

Figure 9. (A) The carbon isotopic compositions of coexisting carbonate (filled symbols) and organic matter 

(open symbols) in hanging-wall samples. Diamonds indicate samples for which organic carbon was calculated 

by difference and could be erroneously low. (B) The carbon isotopic compositions of Hyd Group (circles), 

Cannery Formation (triangles), and Retreat Group (squares) samples. PDB, Pee Dee Belemnite.
Effects of Cretaceous Regional Metamorphism 175

–30 –28 –26 –24 –22 –20 –18 –16

δ13C of organic matter

Retreat

Cannery

Hyd

Hanging wall

–14

–12

–10

–8

–6

–4

–2

0

12 14 16 18 20 22 24

Mine argillite

WCA type I

WCA type II

WCA type III

Hyd

Cannery

δ18O (‰, relative to VSMOW)

δ13C (‰, relative to VSMOW)

Figure 10. Carbon isotopic compositions of organic matter.

Figure 11. The carbon and oxygen isotopic compositions of carbonate minerals in hanging-wall rocks, white 

carbonate-rich ore, Hyd Group, and Cannery Formation samples. VSMOW, Vienna Standard Mean Ocean Water.
176 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Table 3. Rock-Eval analyses of hanging-wall samples.

Sample Tmax

* TOC** HI OI

1136–4 519 3.01 6 3

1136–5A 501 1.62 3 12

1136–8 533 5.04 2 0

1136–12 494 4.48 2 1

1136–26 564 1.02 2 12

1136–27 502 0.75 4 36

1136–13 566 0.7 7 20

1136–16 583 1.26 4 10

96GC–5 527 1.41 2 14

96GC–7 521 2.4 4 6

96GC–9 571 2.48 12 2

96GC–14 514 1.53 9 8

96GC–28 546 0.8 41 36

96GC–37 496 0.56 62 30

*

Tmax is an instrumental, not geologic, temperature. Tmax<420 is immature 

relative to petroleum generation (geologic less than about 70°C), Tmax=420–

440 is oil generation (geologic 80–100°C), Tmax=440–460 is gas generation 

(geologic 100–150°C), Tmax>460 is anthracite rank coal equivalent proceeding 

to amorphous graphite with higher temperature.

**

Total organic carbon.

Metamorphic heating also could cause exchange of carbon isotopes between organic matter and carbonate minerals, 

and this phenomenon could be argued to explain the low carbonate δ13C values in the hanging-wall rocks compared with 

typical marine carbonates of Triassic age. However, low-grade 

metamorphism does not always cause significant exchange 

(Kitchen and Valley, 1995) due to differences in the duration 

of heating or to variable exchange kinetics from one locality 

to another. The work of Himmelberg and others (1995) in the 

Juneau area on the same metamorphic event that affected the 

Greens Creek area (their M1

 metamorphism) suggests that the 

event was characterized by rapid burial, limited duration of 

heating, and rapid uplift, all of which would have minimized 

isotope exchange among coexisting minerals.

Two observations suggest that isotope exchange was not 

important for the Greens Creek rocks and that the carbonates 

have retained their premetamorphic compositions. First, the 

carbonate carbon–organic carbon isotopic fractionations are 

very uniform, quite different from the wide variability observed 

in other low-grade metamorphic localities reflecting different degrees of isotopic reequilibration from one hand specimen to another (for example, Arneth and others, 1985). The 

second observation is that the carbonate carbon–organic carbon 

fractionation does not vary with the relative proportions of the 

two carbon reservoirs, as would be required by isotope mass 

balance in systems approaching isotopic equilibrium (Gregory 

and others, 1989).

Table 4. Stable isotopic compositions of carbonate minerals 

and organic matter.

Sample Unit δ18Ocarb δ18Ccarb δ18Corg

96GC–5 hanging wall 18.7 –5.7 –26.1

96GC–7 hanging wall 17.6 –6.0 –26.5

96GC–14 hanging wall 16.2 –6.4 –26.4

96GC–28 hanging wall 15.6 –6.7 –24.7

96GC–37 hanging wall 16.3 –6.7 –26.0

GC1136–4 hanging wall 18.2 –6.4 –25.0

GC1136–5 hanging wall 18.1 –5.0 –25.7

GC1136–8 hanging wall 16.2 –7.4 –26.6

GC1136–12 hanging wall 17.1 –6.5 –26.8

GC1136–13 hanging wall 18.3 –6.5 –25.6

GC1136–16 hanging wall 18.8 –6.1 –26.0

GC1136–26 hanging wall 17.9 –5.5 –26.0

GC1136–27 hanging wall 16.8 –6.1 –26.7

PP204–01 hanging wall 18.3 –5.4 –25.5

PS50–01 hanging wall* 19.0 –7.6 –27.8

PS50–02 hanging wall 21.1 –4.3 –24.9

PS50–03 hanging wall 20.9 –3.8 –24.2

GCPF–1 hanging wall 19.4 –2.5 –24.5

96ADM7 Hyd –26.9

96ADM19 Hyd –28.3

97ADM27 Hyd 16.6 –6.4 –27.3

Brd–01 Hyd 18.6 –6.0 –24.8

Brd–02 Hyd –24.6

Brd–03 Hyd –19.6

Brd–04 Hyd 16.5 –5.9 –22.4

NAD T9–1 Hyd –27.8

NAD T9–6B Hyd –28.4

NAD T16–7 Hyd –26.6

NAD T17–3 Hyd –24.8

97LG11 Hyd –25.3

97LG14 Hyd –26.1

97LG57 Hyd –25.6

97LG60 Hyd –25.6

97LG65 Hyd –24.9

97LG66 Hyd –24.8

97LG75 Hyd –27.1

97ADM6 Cannery 14.1 –1.7 –24.7

Ard–02 Cannery 20.1 –13.0 –25.8

Ard–03 Cannery 20.0 –6.0 –24.7

Ard–01 Cannery –24.9

Ard–04 Cannery –28.9

96ADM13 Cannery –25.9

97LG25 Cannery –24.7

97ADM22 Retreat –28.4

97LG76 Retreat –25.4

*

This sample is from what may be a separate lithologic unit overlying the 

hanging-wall unit.
Implications of Carbonate Isotopic Compositions 177

That premetamorphic isotopic compositions might be 

preserved is somewhat surprising given the ladder veins of quartz 

and carbonate evident in many hanging-wall rocks (chap. 7) that 

formed by mobilization of chemical constituents into tension 

fractures during Cretaceous time (the F2 folding event described 

in chap. 7). The preservation of isotopic compositions may 

be due to the sample-selection protocol that was used for the 

carbonate isotopic work in which rocks with abundant carbonate 

veining were generally avoided. However, the isotopic results 

for sample 96GC–37, which did contain megascopic carbonate 

veins, were indistinguishable from those for other hanging-wall 

samples (table 4), which suggests that the ladder veins may have 

been local redistributions (compare Ramsay, 1980; Hobbs, 1986) 

that did not significantly alter the δ13C value of the carbonate.

It is noteworthy that the smallest observed carbonate 

carbon–organic carbon isotopic fractionations are in a Hyd Group 

sample collected 6 km west-northwest of the mine site (Brd–04) 

and a Cannery Formation sample collected 10 km northwest of 

the mine site (Ard–02) (table 4). If these fractionations reflect 

exchange between organic matter and carbonate minerals on 

heating, then the highest temperatures (whether hydrothermal 

or metamorphic), or the longest duration of heating, or the most 

favorable exchange kinetics were not in the vicinity of the mine 

but rather to the west and northwest nearer Hawk Inlet.

Implications of Whole-Rock Chemical 

Compositions

The overall high sulfur:organic carbon ratios and high 

degree-of-pyritization values found for many hanging-wall samples are strong evidence for epigenetic sulfur addition in much 

of the section, and the close correlation of lead, zinc, and other 

metals with sulfur is evidence for epigenetic metal addition as 

well. However, there are hanging-wall samples that were collected in close proximity to ore that have sulfur:organic carbon 

ratios and degree-of-pyritization values characteristic of normal 

marine sediments. In these samples (table 5), the concentrations 

of zinc, gold, and silver are no greater than in average black 

shale or average shale, and lead is higher than in average black 

shale or shale in only one of five samples. Barium is systematically high at about twice the average black shale value. Thus, 

for at least part of the depositional history of the hanging-wall 

section, the accumulating sediment appears to have been overlain by an oxic water column with dissolved metal contents that 

were for the most part like normal seawater. The twofold enrichment in barium suggests enhanced barite precipitation in the 

water column, which could have been a consequence of elevated 

barium. This might reflect a hydrothermal fluid flux to the basin 

producing a geochemical fingerprint in the sediment similar to 

that observed in the barite-rich, precious metal-rich, base metalpoor, earliest stages of massive sulfide mineralization (chap. 6). 

Thus, there is some evidence, albeit weak, for hydrothermal 

venting to the basin waters during the most normal marinelike 

periods of sediment accumulation. A substantial hydrothermal 

flux, or a standing brine pool, at the Greens Creek vent site is 

ruled out during sedimentation of these samples (table 5).

On the other hand, during deposition of the more common metal- and sulfur-rich samples, a hydrothermal brine 

could have been a significant component of the overlying water 

column. Many hanging-wall samples show very strong enrichments in sulfur, lead, arsenic, and gold with respect to normal 

black shales, but these same samples are not enriched in cobalt, 

nor, for the most part, in copper and zinc (fig. 6A). Thus, even 

if the accumulating sediments were overlain by a brine pool or 

a hydrothermally impacted water column, evidence is lacking 

for the basaltic or ultramafic metal source that influenced the 

metal abundances of the underlying massive sulfide deposit and 

its alteration envelope in the footwall phyllites.

Implications of Carbonate Isotopic 

Compositions

Isotopic data from hanging-wall carbonates are compared 

with data from dolomite in white ore (Freitag, 2000) in figure 

11. The hanging-wall compositions are indistinguishable from 

the compositions of Freitag’s (2000) dolomite types I, II, and 

III. Textural evidence indicates that dolomite types II and III 

Table 5. Chemical analyses of hanging-wall samples with low sulfur:organic carbon (Corg) and low degree-of-pyritization (DOP) values.#

[<, less than; -, no data; S, sulfur; Ba, barium; Pb, lead; Zn, zinc; Au, gold; As, arsenic]

Sample DOP Corg S S:Corg carbonate C Ba Pb Zn Au As

96GC1136–3 - 3.00 1.19 0.39 2.31 3,500 142 222 31 15

5 0.68 1.60 0.48 0.30 1.74 1,200 12 68 13 11

16 0.82 1.30 0.69 0.53 2.59 2,200 12 37 40 17

PS–50–01 0.28 - 0.36 - 1.29 1,900 14 93 <2 3.9

PS–50–03 0.47 - 1.14 - 6.42 1,700 25 78 19 11

Average black shale 0.6 3.2 1 0.3 - 1,120 20 310 23 28.8

Average shale 0.5 0.8 0.25 0.3 - 600 20 90 3 10

#

Corg, S, and carbonate C in percent; Ba, Pb, Zn, and As in parts per million; Au in parts per billion.
178 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

filled open spaces and that type III coprecipitated with sphalerite, galena, and silver sulfosalts (Freitag, 2000). The isotopic 

similarity is strong evidence that the carbonate contained in the 

hanging-wall rocks precipitated from the same fluid that deposited metals in the underlying massive sulfide deposit. Thus, 

hydrothermal activity at Greens Creek must have persisted until 

after the hanging-wall sediments had been laid down, a finding 

which is consistent with the sulfur isotopic evidence that the 

main sulfur source for the massive ores was bacterial reduction 

of pore-water sulfate in overlying anoxic sediments (chap. 10).

There are two possible explanations for the carbonate 

isotopic data shown in figure 11. The first is that the trend 

reflects variable mixtures of two different carbonate types. 

One possible end-member is any marine carbonate that may 

have been present during hydrothermal activity. Evidence for 

the existence of such an end-member is the platform carbonate rocks that occur discontinuously on Admiralty Island at 

the same stratigraphic position as the Greens Creek massive 

sulfide deposit (chap. 2). Triassic marine carbonates would be 

expected to have δ18O values of about 30 permil and δ13C values of about 2 permil (Veizer and others, 1999), compositions 

which lie along the upper extension of the hanging-wall array 

shown in figure 11. The low-δ18O, low-δ13C end-member might 

reasonably be hypothesized to be a hydrothermal precipitate.

The second possible explanation for the isotopic trend is 

that it reflects carbonates precipitated from a single hydrothermal fluid over a range of temperatures. Shown in figure 12 are 

two curves that define the isotopic compositions of dolomite 

precipitated from two different hypothetical fluids at temperatures ranging from 150 to 350°C, a range that includes the 

temperatures inferred for sulfide precipitation in the massive 

sulfide body (chap. 15). Both fluids were assigned a δ18OH2O

value of 10.4 permil on the basis of visual best-fit. The upper 

curve corresponds to a fluid in which the carbon species is 

carbonic acid (H2CO3) with a δ13C value of –4.2 permil, and the 

lower curve corresponds to a fluid in which the carbon species 

is also H2CO3, but with a δ13C value of –6.2 permil. These δ13C 

values were chosen so that the curves would enclose the majority of the hanging-wall and ore data. The development of the 

dolomite curves follows Rye and Williams (1981), to which the 

reader is referred for the underlying details and assumptions.

The slope of the model curves corresponds quite well 

to the trend of the data (fig. 12). Variation of the fluid δ13C 

value from –4.2 permil to –6.2 permil could be explained by 

–10

–8

–6

–4

–2

0

12 14 16 18 20 22 24

δ

18O (‰, relative to VSMOW)

δ13O (‰, relative to VSMOW)

350°C

250°C

150°C

350°C

250°C

150°C

Dolomite in equilibrium with a fluid

 with δ

18OH2O=10.4 and δ13CH2CO3

=–4.2

Dolomite in equilibrium with a fluid

 with δ

18OH2O=10.4 and δ13CH2CO3

=–6.2

Figure 12. Comparison of the isotopic compositions of carbonate in the hanging-wall rocks (filled circles) 

with dolomite in white carbonate-rich ore (open circles, Freitag, 2000). Freitag’s (2000) tabulated δ18O values 

have been reduced by 0.8 permil to correct for the difference between the acid fractionation factors for calcite 

and dolomite (Friedman and O’Neil, 1977; Rosebaum and Sheppard, 1986; Swart and others, 1991). Also plotted 

are curves showing the dolomite compositions that would be predicted for precipitation from a hydrothermal 

fluid with δ18OH2O value of 10.4 permil and δ13CH2CO3

 value of either –4.2 or –6.2 permil over a temperature range 

of 150–350°C, the same range that has been inferred for formation of the underlying massive sulfide deposit. 

VSMOW, Vienna Standard Mean Ocean Water; ‰, permil.
Implications of Carbonate Isotopic Compositions 179

progressive precipitation of dolomite, which would have the 

effect of depleting the fluid in the heavy isotope and driving 

the δ13C value of dissolved H2

CO3 downward over time, or by 

oxidation of organic matter or methane, which would contribute isotopically light carbon also driving the δ13C value of 

H2

CO3 downward (Rye and Williams, 1981).

Two observations suggest that oxidation of organic matter 

or methane was an important process during deposition of 

the hanging-wall section. The first is that the δ13C values of 

carbonate and organic matter are correlated (fig. 13), consistent with carbonate production by oxidation of ambient 

organic carbon or of methane produced by thermal maturation 

of organic matter. The fact that the carbonate δ13C values are 

much higher than the organic carbon δ13C values implies that 

organic matter or methane oxidation was a minor carbonate 

source compared with higher δ13C marine carbonate rocks or 

marine fluids. The second observation suggesting that organic 

matter or methane oxidation was important is that carbonate 

δ13C values and sulfur contents of the hanging-wall rocks are 

correlated (fig. 14). This relationship suggests that hydrogen 

sulfide was produced from sulfate by reaction with low-δ13C 

reduced carbon compounds by chemical pathways such as:

2CH2

O + SO4

2- —-> H2

S + 2CO3

2- + 2H+

, or

CH4

 + SO4

2- —-> H2

S + CO3

2- + H2

O.

The subsequent reaction of hydrogen sulfide with iron or other 

metals then caused the reduced sulfur to become fixed in the 

sediments.

The links illustrated in figures 13 and 14 between sulfide 

sulfur and carbonate carbon, and between carbonate carbon and 

organic carbon are strong evidence that sulfide minerals formed, 

at least in part, during early diagenesis beneath the sediment/

seawater interface. Whether any of the hanging-wall sulfides 

represent true syngenetic accumulations on the ancient sea floor 

cannot be determined from the observations made in this study.

Also uncertain is the relative importance of microbially 

mediated and inorganic reactions during formation of the hanging-wall section. The abundance of framboidal pyrite in many 

of the rocks (chap. 9) and the low and variable δ34S values of 

the hanging-wall pyrite (ave. δ34S is –17 permil, range is –29 to 

1 permil ([n=12], chap. 10) are evidence that microbial sulfate 

reduction was important during this paragenetic stage, but the 

~300°C mineralization temperatures that have been inferred 

for the formation of the base-metal sulfides within the orebody 

(chap. 10) is high enough that inorganic sulfate reduction could 

also have been important (compare Orr, 1974; Kiyosu, 1980; 

Powell and Macqueen, 1984).

The fluid isotopic compositions implied by the model 

curves (fig. 12), δ18O=10.4 permil and δ13C=–5.2±1 permil, 

should be viewed as approximate. They are within the isotopic 

ranges expected for fluids that had undergone isotopic exchange 

with the shale + carbonate + basalt stratigraphic package in 

which the Greens Creek deposit sits, but they do not rule out 

magmatic fluids associated with the Triassic mafic/ultramafic 

magmatism in the region.

The isotopic data for Hyd Group and Cannery Formation carbonates are compared with the hanging-wall data in 

–8

–7

–6

–5

–4

–3

–2

–28 –27 –26 –25 –24 –23 –22

δ

13C of organic matter

δ13C of carbonate

Figure 13. Plot of the carbon isotopic composition of coexisting carbonate and organic matter in hanging-wall 

rocks. The two parameters show a weak but significant positive correlation (R=0.64).
180 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

figure 11. The Hyd samples conform quite well to the hangingwall array, but the Cannery Formation samples do not. The 

implication of the hanging wall–Hyd Group correspondence 

is that both units were exposed to the same fluid over approximately the same temperature range. This finding is consistent 

with hydrothermal metal scavenging from the Hyd Group sediments but could also be explained by flushing of Hyd sediments 

by spent hydrothermal fluids after metals had been precipitated. 

The absence of obvious metal depletions in the Hyd Group 

occurrences analyzed for this work would seem to favor the 

spent hydrothermal fluid alternative. The poor correspondence 

between the hanging-wall and Cannery data suggests that the 

hydrothermal fluid did not encounter the Cannery section. The 

Cannery results also support our conclusion that the carbonate isotopic compositions of Admiralty Island shales were not 

significantly affected by the Cretaceous metamorphism because 

the three analyzed samples show neither similar isotopic compositions nor a consistent isotopic trend as they might if isotopic 

exchange had occurred among minerals or between minerals 

and fluids during regional prograde heating.

Conclusions

Several conclusions arising from this study have implications for the genesis of the Greens Creek ores. First, large 

volumes of the hanging-wall sediments experienced epigenetic 

sulfur addition with associated addition of Ag, As, Au, Cd, 

Cu, Fe, Mo, Pb, and Zn. However, Co, Cr, Ni, and V show no 

evidence for similar addition; their abundances appear to be 

related to the syngenetic accumulation of organic matter.

Second, for at least part of the time that the hanging-wall 

sediments were accumulating, the overlying water column was 

oxic, with evidence for possible water column hydrothermal 

enrichment only in barium. For the remainder of the accumulation 

history, a hydrothermal component in the overlying water column 

is neither proved nor disproved. Whatever the exact nature of the 

overlying water column, there is no clear evidence in the hangingwall sediments for the basaltic or ultramafic metal source that 

appears to have been important for the underlying massive sulfide 

deposit and its alteration envelope in the footwall phyllites.

Third, the isotopic variations of carbonate minerals in both 

the hanging wall and the white ores are consistent with precipitation from a single hydrothermal fluid over a temperature 

range of 200 to 350°C, essentially the same temperature range 

that has been inferred from other observations for formation of 

the underlying massive ores, or with precipitation from mixed 

marine and hydrothermal fluids. Whatever the exact dolomite 

formation mechanism, the close similarity of the compositions 

in the hanging-wall metasediments and in the white carbonaterich ores implies deposition from the same fluid by the same 

mechanism and thus provides strong evidence that hydrothermal 

–8

–7

–6

–5

–4

–3

–2

0 5 10 15 20

S (wt %)

δ13C of carbonate

Figure 14. Plot of the carbon (C) isotopic composition of carbonate relative to the sulfur (S) content of 

hanging-wall rocks. The negative correlation is evidence that the reduction of sulfate to form hydrogen 

sulfide, which subsequently combined with metals to form sulfide minerals, was accompanied by oxidation 

of low δ13 C organic matter or methane. wt%, weight percent.
References Cited 181

fluid flow at Greens Creek persisted until after the hanging-wall 

sediments were laid down. The carbonaceous sediment cap may 

have been an important feature that protected the underlying 

massive sulfide body from destruction by seawater oxidation.

Fourth, carbonate precipitation was accompanied by, 

and perhaps driven by, oxidation of organic matter or organicderived methane. These same reactions resulted in reduction 

of sulfate to hydrogen sulfide which then reacted with iron 

and other metals to form sulfide minerals. During growth of 

framboidal pyrite, sulfate reduction was probably microbially 

mediated. During formation of base-metal sulfides, sulfate 

reduction could have proceeded inorganically. Thus, some 

sulfide minerals, but not necessarily all, formed during early 

diagenesis beneath the sediment/seawater interface.

Fifth, Hyd Group sediments several kilometers west and 

northwest of the Greens Creek deposit may have been exposed 

to hydrothermal fluids either before sulfide mineral precipitation, in which case the fluids may have scavenged metals from 

Hyd sediments, or after sulfide precipitation from hydrothermal fluids that were spent. The absence of obvious metal 

depletions in these Hyd rocks suggests that the fluids were 

spent. Older Cannery Formation shales do not appear to have 

been exposed to these fluids, although the number of Cannery 

samples that were studied is too small to exclude this possibility on a regional basis.

References Cited

Arbogast, B.F., ed., 1996, Analytical methods manual for the 

Mineral Resource Surveys program: U.S. Geological Survey 

Open-File Report 96–525, 149 p.

Arneth, J.D., Schidlowski, M., Sarbas, B., Goerg, U., and 

Amstutz, G.C., 1985, Graphite content and isotopic fractionation between calcite-graphite pairs in metasediments 

from the Mgama Hill, southern Kenya: Geochimica et 

Cosmochimica Acta, v. 49, p. 1553–1560.

Berner, R.A., and Raiswell, R., 1983, Burial of organic 

carbon and pyrite sulfur in sediments over Phanerozoic 

time—A new theory: Geochimica et Cosmochimica Acta, 

v. 47, p. 855–862.

Blatt, Harvey, Middleton, G., and Murray, R., 1972, Origin of 

sedimentary rocks: Englewood Cliffs, New Jersey, PrenticeHall, 634 p.

Eastoe, C.J., and Gustin, M.M., 1996, Volcanogenic massive 

sulfide deposits and anoxia in the Phanerozoic oceans: Ore 

Geology Reviews, v. 10, p. 179–197.

Freitag, Katje, 2000, Geology and structure of the lower 

southwest orebody, Greens Creek mine, Alaska: Golden, 

Colorado School of Mines, Ph.D. dissertation, 248 p.

Friedman, Irving, and O’Neil, J.R., 1977, Compilation of 

stable isotope fractionation factors of geochemical interest: 

U.S. Geological Survey Professional Paper 440–KK, 12 p.

Fyfe, W.S., Price, N.J., and Thompson, A.B., 1978, Fluids in 

the Earth’s crust: Amsterdam, Elsevier, 383 p.

Goodfellow, W.D., Lydon, J.W., and Turner, R.J.W., 1993, 

Geology and genesis of stratiform sediment-hosted 

(SEDEX) zinc-lead-silver deposits: Geological Association 

of Canada Special Paper 40, p. 201–252.

Gregory, R.T., Criss, R.E., and Taylor, H.P., Jr., 1989, Oxygen 

isotope exchange kinetics of mineral pairs in closed and 

open systems—Applications to problems of hydrothermal 

alteration of igneous rocks and Precambrian iron formations: Chemical Geology, v. 75, p. 1–42.

Haeussler, P.J., Karl, S.M., Mortensen, J.K., Layer, P., and 

Himmelberg, G.R., 1999, Permian and mid-Cretaceous 

deformation of the Alexander terrane on Admiralty and 

Kupreanof Islands, southeastern Alaska: Geological Society 

of America Abstracts with Programs, v. 31, no. 6, p. A–60.

Himmelberg, G.R., Brew, D.A., and Ford, A.B., 1995, Lowgrade, M1

 metamorphism of the Douglas Island volcanics, 

western metamorphic belt near Juneau, Alaska, in Schiffman, P., and Day, H.W., eds., Low-grade metamorphism 

of mafic rocks: Boulder, Colorado, Geological Society of 

America Special Paper 296, p. 51–66.

Hobbs, B.E., 1986, Principles involved in mobilization and 

remobilization: Ore Geology Reviews, v. 3, p. 37–45.

Karl, S.M., Haeussler, P.J., Mortensen, J.K., Layer, P., Savage, N., Wardlaw, B., Harris, A., Murchey, B., and Blane, 

C., 1999, New stratigraphic and isotopic constraints on the 

depositional and deformational history of the Alexander terrane, southeastern Alaska: Geological Society of America 

Abstracts with Programs, v. 31, no. 6, p. A–68.

Kitchen, N.E., and Valley, J.W., 1995, Carbon isotope thermometry in marbles of the Adirondack Mountains, New 

York: Journal of Metamorphic Geology, v. 13, p. 577–594.

Kiyosu, Yasuhiro, 1980, Chemical reduction and sulfur-isotope effects of sulfate by organic matter under hydrothermal 

conditions: Chemical Geology, v. 30, p. 47–56.

Krauskopf, K.B., 1979, Introduction to geochemistry (2d ed.): 

New York, McGraw-Hill, 617 p.

Leventhal, J.S., 1983, An interpretation of carbon and sulfur 

relationships in Black Sea sediments as indicators of environments of deposition: Geochimica et Cosmochimica Acta, 

v. 47, p. 133–137.

Leventhal, Joel, 1993, Metals in black shales, in Engel, M.H., 

and Macko, S.A., eds., Organic geochemistry: New York, 

Plenum Press, p. 581–592.

Leventhal, J.S., 1995, Carbon-sulfur plots to show diagenetic 

and epigenetic sulfidation in sediments: Geochimica et 

Cosmochimica Acta, v. 59, p. 1207–1211.
182 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Leventhal, J.S., 1998, Metal-rich black shales—Formation, 

economic geology and environmental considerations, in

Schieber, J., Zimmerle, W., and Sethi, P., eds., Shales and 

mudstones II: Stuttgart, E. Schweizerbart’sche Verlagsbuchhandlung (Nägele u. Obermiller), p. 255–282.

Leventhal, Joel, and Taylor, C., 1990, Comparison of methods 

to determine degree of pyritization: Geochimica et Cosmochimica Acta, v. 54, p. 2621–2625.

Lewan, M.D., 1986, Stable carbon isotopes of amorphous 

kerogens from Phanerozoic sedimentary rocks: Geochimica 

et Cosmochimica Acta, v. 50, p. 1583–1591.

McCrea, J.M., 1950, On the isotope chemistry of carbonates 

and a paleotemperature scale: Journal of Chemical Physics, 

v. 18, p. 849–857.

Newberry, R.F., Crafford, T.C., Newkirk, S.R., Young, L.E., 

Nelson, S.W., and Duke, N.A., 1997, Volcanogenic massive 

sulfide deposits of Alaska, in Goldfarb, R.J., and Miller, 

L.D., eds., Economic geology monograph 9—Mineral 

deposits of Alaska: Littleton, Colorado, Economic Geology 

Publishing Company, p. 120–150.

Orr, W.L., 1974, Changes in sulfur content and isotopic ratios 

of sulfur during petroleum maturation—Study of Big Horn 

basin Paleozoic oils: American Association of Petroleum 

Geologists Bulletin, v. 58, p. 2295–2318.

Powell, T.G., and Macqueen, R.W., 1984, Precipitation of 

sulfide ores and organic matter—Sulfate reactions at Pine 

Point, Canada: Science, v. 224, p. 63–66.

Quinby-Hunt, M.S., Wilde, P., Orth, C.J., and Berry W.B.N., 

1989, Elemental geochemistry of black shales—Statistical comparison of low-calcic shales with other shales: U.S. 

Geological Survey Circular 1037, p. 8–15.

Raiswell, R., and Berner, R.A., 1985, Pyrite formation in 

euxinic and semi-euxinic sediments: American Journal of 

Science, v. 285, p. 710–724.

Ramsay, J.G., 1980, The crack-seal mechanism of rock deformation: Nature, v. 284, p. 135–139.

Rosebaum, Joseph, and Sheppard, S.M.F., 1986, An isotopic 

study of siderites, dolomites and ankerites at hightemperatures: 

Geochimica et Cosmochimica Acta, v. 50, p. 1147–1150.

Rye, D.M., and Williams, N., 1981, Studies of the base metal 

sulfide deposits at McArthur River, Northern Territory, Australia, III. The stable isotope geochemistry of the H.Y.C., Ridge 

and Cooley deposits: Economic Geology, v. 76, p. 1–26.

Schidlowski, Manfred, 1987, Application of stable carbon 

isotopes to early biochemical evolution on Earth: Annual 

Review of Earth and Planetary Sciences, v. 15, p. 47–72.

Swart, P.K., Burns, S.J., and Leder, J.J., 1991, Fractionation of 

the stable isotopes of oxygen and carbon in carbon dioxide 

during the reaction of calcite with phosphoric acid as a 

function of temperature and technique: Isotope Geoscience, 

v. 12, p. 89–96.

Taylor, C.D., Leventhal, J.S., Johnson, C.A., and Lear, K.G., 

2000, The Greens Creek massive sulfide deposit, southeastern Alaska—Stable isotopic evidence for the involvement of biogenic sulfate reduction in the formation of ores 

and carbonates, in Gemmell, J.B., and Pongratz, J., eds., 

Volcanic environments and massive sulfide deposits: Program and Abstracts, Special Publication 3, Centre for Ore 

Deposits Research, Hobart, University of Tasmania, 

p. 209–210.

Taylor, C.D., Newkirk, S.R., Hall, T.E., Lear, K.G., Premo, 

W.R., Leventhal, J.S., Meier, A.L., Johnson, C.A., and 

Harris, A.G., 1999, The Greens Creek deposit, southeastern Alaska—A VMS-SEDEX hybrid, in Stanley, C.J., and 

others, eds., Mineral deposits, processes to processing: Rotterdam, Balkema, p. 597–600.

Tissot, B.P., and Welte, D.H., 1984, Petroleum formation and 

occurrence (2d ed.): Berlin, Springer-Verlag, 699 p.

Tissot, B., Durand, B., Espitalie, J., and Combaz, A., 1974, 

Influence of the nature and diagenesis of organic matter on 

the formation of petroleum: American Association of Petroleum Geologists Bulletin, v. 58, p. 499–506.

Tourtelot, H.A., 1979, Black shale—Its deposition and diagenesis: Clays and Clay Minerals, v. 27, p. 313–321.

Veizer, Jan, Ala, D., Azmy, K., Bruckschen, P., Buhl, D., 

Bruhn, F., Carden, G.A.F., Diener, A., Ebneth, S., Godderis, Y., Jasper, T., Korte, C., Pawellek, F., Podlaha, O.G., 

and Strauss, H., 1999, 87Sr/86Sr, δ13C and δ18O evolution of 

Phanerozoic seawater: Chemical Geology, v. 161, p. 59–88.

Vine, J.D., and Tourtelot, E.B., 1970, Geochemistry of 

black shale deposits—A summary report: Economic 

Geology, v. 65, p. 253–272.

Williams, Neil, 1978, Studies of the base metal sulfide deposits at McArthur River, Northern Territory, Australia—II. 

The sulfide-S and organic-C relationships of the concordant 

deposits and their significance: Economic Geology, v. 73, 

p. 1036–1056.
Mineralogical, Textural, and Metal 

Residence Studies of Primary, 

Recrystallized, and Remobilized Ores of the 

Greens Creek Deposit

By Cliff D. Taylor, Steven J. Sutley, and Frederick E. Lichte

Chapter 9 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract.......................................................................................................................................................187

Introduction.................................................................................................................................................187

Mine Location, General Host Rocks, Metamorphic History, Deposit Morphology,

and Structural History .................................................................................................................189

Previous Mineralogical and Mineral Geochemical Studies...............................................................191

Ore Types.....................................................................................................................................................194

Primary Ore Mineralogy and Textures ...................................................................................................196

Recrystallized and Remobilized Ore Mineralogy and Textures..........................................................196

Free Gold—Mineralogy and Textures ....................................................................................................199

Paragenetic Relationships—Physical and Chemical Modification of Ores ....................................200

LA–ICP–MS Mineral Chemistry Studies ................................................................................................204

Methods..............................................................................................................................................204

Results ................................................................................................................................................209

Discussion...................................................................................................................................................230

Conclusions.................................................................................................................................................234

References Cited........................................................................................................................................234

Figures

1. Maps of northern Admiralty Island showing the location of the Greens Creek

mine and other features mentioned in the text....................................................................191

2. Plan and cross-sectional views of the Greens Creek deposit showing features 

described in the text.................................................................................................................192

3. Photographs of hand samples illustrating the various massive sulfide and white

ore types.....................................................................................................................................194

4. Photographs of hand samples illustrating textures present in various ore types.........197

5. Photomicrographs of polished thin sections showing primary mineral textures..........198

6. Photomicrographs of polished thin sections showing recrystallized ore textures.......201

7. Photomicrographs of arsenian pyrite and arsenopyrite in polished thin sections .......205

8. Photographs and photomicrographs of free gold (Au) in hand samples and

polished sections......................................................................................................................207

9. LA–ICP–MS traverses across heavy concentrate grains recovered from the

Greens Creek mill......................................................................................................................208

10. Photographs and photomicrographs showing textural relationships in Greens

Creek ores..................................................................................................................................210

11. Summary LA–ICP–MS data on sulfide ore minerals in the Greens Creek deposit.

Box plots of percentiles shows the log10 concentration range for primary,

recrystallized, and remobilized ore textures for each of 19 elements.............................212

12. Single element plots of LA–ICP–MS data showing the range of elemental

abundances of metals in primary and recrystallized pyrite and sphalerite,

and in primary, recrystallized, and remobilized galena......................................................221
Tables

1. Greens Creek ore mineralogy—minerals identified...........................................................188

2. Trace-element composition of primary pyrite as determined by Laser

Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses.........................213

3. Trace-element composition of recrystallized pyrite as determined by Laser

Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses.........................214

4. Trace-element composition of arsenian pyrite as determined by Laser

Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses.........................215

5. Trace-element composition of galena as determined by Laser

Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses.........................215

6. Trace-element composition of sphalerite as determined by Laser

Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses.........................216

7. Trace-element composition of tetrahedrite as determined by Laser

Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses.........................217

8. Trace-element composition of mixed primary-textured mineral aggregates

as determined by Laser Ablation–Inductively Coupled Plasma—Mass

Spectroscopy analyses ...........................................................................................................218

9. Trace-element composition of recrystallized mixed mineral aggregates as

determined by Laser Ablation–Inductively Coupled Plasma––Mass

Spectroscopy analyses ...........................................................................................................219

10. Trace-element composition of remobilized mixed mineral aggregates as

determined by Laser Ablation–Inductively Coupled Plasma––Mass

Spectroscopy analyses ...........................................................................................................220

Abstract

The Greens Creek deposit is a 24.2-million-ton polymetallic massive sulfide with a diverse base- and preciousmetal-rich mineralogy, which has been subjected to regional 

lower greenschist facies metamorphism. Roughly 30 percent 

of the ores retain primary mineralogy and mineral textures 

as well as gross original ore stratigraphy. Ore lithologies fall 

into two groups: massive sulfide ores (greater than 50 percent 

sulfides) and semimassive or disseminated sulfide gangue-rich 

“white” ores (less than 50 percent sulfides). There are two 

types of massive ore: massive pyritic and massive base-metalrich ore. The white ores are of three types: white carbonate 

and white siliceous ores (common), and white baritic ore. All 

the ore types can be further subdivided on the basis of modification by veins, breccias, and gouge or rubble zones produced during faulting or folding. Veining due to metamorphic 

remobilization and recrystallization can result in enrichment 

of free gold and a variety of silver-sulfosalt minerals. The ore 

stratigraphy at Greens Creek is characterized by proximal 

copper-arsenic-gold-enriched massive pyritic ores centered 

over white siliceous ores and silicified footwall. Laterally, the 

white siliceous ores grade outward into white carbonate and 

barite ores. White ores are overlain by massive pyritic ores that 

change upward and outward toward lower copper-gold grades. 

Proximal ores transition to increasingly higher grade zinclead-silver-(gold)-rich, massive, fine-grained, base-metal-rich 

ores toward the argillite hanging wall and the margins of the 

deposit. Distal ore commonly is characterized by carbonateand barite-rich white ores against footwall phyllites, which 

grade into massive, fine-grained, base-metal-rich ores toward 

the hanging wall. This progression of ore types is the most 

common throughout the mine.

Primary mineral textures are characterized by framboidal, 

colloform, dendritic, and “spongy” pyrite intergrown with 

base-metal sulfides and sulfosalts. Primary assemblages also 

include sphalerite, galena, tetrahedrite, chalcopyrite, free gold, 

and a variety of lead-antimony-arsenic (-mercury-thallium) 

sulfosalts. The abundance of polyframboidal, colloform, 

and nodular pyrite textures coupled with their δ34S-depleted 

isotopic signature provides strong evidence that the main stage 

of massive sulfide mineralization at Greens Creek occurred 

primarily during early diagenesis, synchronous with accumulation of the hanging-wall sediments. The early development 

of framboid-derived, atoll-shaped textures in the ores may 

indicate that a zone-refinement process occurred in the presence of colloidal base-metal-sulfide gels. Metamorphic recrystallization produced advanced atoll-shaped structures in the 

ores and resulted in much coarser textures and the formation 

and(or) remobilization of secondary, precious-metal-enriched 

minerals. Secondary minerals are present as matrix to pyrite 

euhedra and in late fractures and veinlets. Secondary mineralogy includes chalcopyrite, sphalerite (low iron), galena, free 

gold, electrum, tetrahedrite (antimony-rich), pyrargyrite, and 

many other sulfosalt minerals. Metamorphism resulted in visible cleaning and coarsening of the ore mineralogy and caused 

local trace-element redistribution and upgrading of the ores.

Introduction

The Greens Creek deposit is a mineralogically diverse, 

polymetallic (zinc-lead-silver-gold-copper) massive sulfide of 

Late Triassic age and unusually high silver content. The global 

resource is currently 24.2 million tons at an average grade of 

13.9 percent zinc, 5.1 percent lead, 0.15 troy ounces per ton 

gold, and 19.2 troy ounces per ton silver. Twenty-nine ore sulfide minerals have been reported, 18 of which are silver bearing (table 1). In addition to the metals of economic interest, 

the ores are enriched in trace elements such as As, Sb, Hg, Tl, 

Ni, Co, Cr, and Mo. These metals and minerals are contained 

in a suite of five ore types, which define an ore stratigraphy 

that progressed from early white ores to main-stage massive 

sulfide ores during the growth of the system. This progression 

(see chap. 15 for a more thorough description) is thought to 

have started at low temperature, at or very near the sediment/

water interface in a basin containing oxygenated seawater, and 

then evolved to higher temperature within a growing sulfide 

blanket that formed in and beneath a progressively thickening 

layer of black shales. As deposition progressed, pore fluids in 

the shales and probably the overlying water column gradually became anoxic. These early and main-stage ore-forming 

Mineralogical, Textural, and Metal Residence Studies 

of Primary, Recrystallized, and Remobilized Ores of the 

Greens Creek Deposit

By Cliff D. Taylor, Steven J. Sutley, and Frederick E. Lichte
Table 1. Greens Creek ore mineralogyóminerals identified. Mineral name Mineral formula How identified Reference silver Ag XRD, LA--ICP--MS this study acanthite Ag2S electron microprobe, XRD C.J. Carter (written commun., 1994) proustite Ag3AsS3 optical microscope, XRD, electron microprobe this study jalpaite Ag3CuS2 electron microprobe C.J. Carter (written commun., 1994); T.K. Bundtzen (wri

pyrargyrite Ag3SbS3 optical microscope, electron microprobe T.C. Crafford (written commun., 1989) stephanite Ag5SbS4 electron microprobe T.C. Crafford (written commun., 1989) argyrodite Ag8GeS6 electron microprobe K.G. Lear (oral commun., 2000) stromeyerite AgCuS electron microprobe E.U. Peterson (written commun., 1991) realgar AsS optical microscope, XRD this study pearceite (Ag,Cu)16As2S11 electron microprobe E.U. Peterson (written commun., 1991) antimonpearceite (Ag,Cu)16Sb2S11 optical microscope, XRD, electron microprobe K.G. Lear (oral commun., 2000) polybasite (Ag,Cu)16Sb2S11 electron microprobe T.C. Crafford (written commun., 1989) mckinstryite (Ag,Cu)2S electron microprobe E.U. Peterson and D. Chirban (written commun., 1994) freibergite (Ag,Cu,Fe)12(Sb,As)4S13 optical microscope, electron microprobe T.C. Crafford (written commun., 1989) gold Au,(Ag) optical microscope, LA–ICP–MS T.C. Crafford (written commun., 1989); this study electrum Au,Ag,(Hg) optical microscope, LA–ICP–MS T.C. Crafford (written commun., 1989); E.U. Peterson (w

chalcocite - Ag-bearing Cu2S +Ag electron microprobe E.U. Peterson (written commun., 1991) bornite Cu5FeS4 optical microscope E.U. Peterson (written commun., 1991) bornite - Ag-bearing Cu5FeS4 +Ag electron microprobe E.U. Peterson (written commun., 1991) chalcopyrite CuFeS2 optical microscope T.C. Crafford (written commun., 1989); E.U. Peterson (w

tennantite (Cu,Fe)12As4S13 optical microscope, XRD, electron microprobe this study tetrahedrite (Cu,Fe)12Sb4S13 optical microscope, electron microprobe, XRD T.C. Crafford (written commun., 1989); E.U. Peterson (wcovellite CuS optical microscope E.U. Peterson (written commun., 1991) covellite-acanthite mineral CuS-Ag2S electron microprobe E.U. Peterson (written commun., 1991) unknown (possibly thalcusite) CuTlS (Tl2(Cu,Fe)4S4) electron microprobe K.G. Lear (oral commun., 2000) arsenopyrite FeAsS electron microprobe, XRD C.J. Carter (written commun., 1994) marcasite FeS2 optical microscope C.J. Carter (written commun., 1994) pyrite FeS2 optical microscope T.C. Crafford (written commun., 1989); E.U. Peterson (wgeocronite Pb14(As,Sb)6S23 electron microprobe K.G. Lear (oral commun., 2000) jordanite Pb14(As,Sb)6S23 optical microscope, XRD, electron microprobe this study boulangerite Pb5Sb4S11 electron microprobe K.G. Lear (oral commun., 2000) galena PbS optical microscope T.C. Crafford (written commun., 1989); E.U. Peterson (w

cassiterite SnO2 electron microprobe K.G. Lear (oral commun., 2000)

sphalerite ZnS optical microscope T.C. Crafford (written commun., 1989); E.U. Peterson (w

Spelling of mineral names and mineral formulas follows the usage of Blackburn and Dennen, 1997.KGCMC, Kennecott Greens Creek Mining Company; XRD, X-ray diffraction; LA–ICP–MS, laser ablation–inductively coupled plasma–mass spectrometry.
Mine Location, General Host Rocks, Metamorphic History, Deposit Morphology, and Structural History 189

processes produced a trace-element-rich orebody with a 

diverse silver- and base-metal-rich mineralogy, primarily by 

replacement of shale, early sulfides, and silica-barite gangue. 

Remnants of primary mineral textures are represented by 

fine- to very fine grained aggregates of framboidal, dendritic, 

and colloform or botryoidal pyrite intimately intergrown and 

banded with base-metal sulfides and the diverse suite of traceelement and silver-bearing sulfides.

Following the cessation of mineral deposition in latest Triassic time, the deposit was buried by continued shale 

sedimentation, which effectively prevented sea-floor oxidation of the newly formed sulfides. During the next 215 

million years the deposit went through at least three phases 

of deformation (see chap. 7) and a regional subgreenschist 

to lower greenschist facies metamorphic event (see chap. 2) 

that reached temperatures of 275–350o

C (see chap. 12) and 

buried host rocks in the Greens Creek area to a depth of about 

17–18 kilometers (Himmelberg and others, 1995). Although 

the metamorphism and multiple deformation of the orebody 

resulted in pronounced structural dismemberment, folding, 

recrystallization, and remobilization of the ores, large areas 

of the deposit preserve primary mineralogy, textures, and 

chemistry. A range of preservation states exists, from pristine 

to completely modified. This fortuitous situation presents an 

opportunity to study the effects of deformation and metamorphism upon massive sulfide mineral textures and to understand 

the details of mineral residence of specific trace elements and 

their redistribution as a result of textural modification.

Most of the initial mineral identifications, descriptions of 

ore textures, and preliminary determinations of mineral chemistry are contained in unpublished mining company reports (see 

“Previous Mineralogical and Mineral Geochemical Studies” 

section). In particular, electron microprobe mineral-chemistry 

studies were conducted to improve the beneficiation of various 

mill products, and metal zonation studies of tetrahedrites were 

conducted in an attempt to obtain geochemical vectors within 

ore assemblages. We summarize these unpublished reports, 

compile their mineral identifications and textural observations, 

and significantly extend the petrographic descriptions and geochemistry of the various ores at Greens Creek.

Here we describe the five principal ore types in detail and 

the mineralogy and mineral textures present in these ores. We 

then discuss the paragenesis of the ores and the progressive 

modification of the mineralogy and mineral textures as a result 

of deformation and metamorphism. We follow the descriptive 

portion of the chapter with the presentation of preliminary Laser 

Ablation–Inductively Coupled Plasma–Mass Spectroscopy 

(LA–ICP–MS) mineral geochemical studies of the ores. The 

LA–ICP–MS studies provide mineral-specific geochemical data 

in support of the petrographic observations. These data demonstrate that the specific mineral residence and concentrations of 

trace elements in the ores change as a result of recrystallization 

and remobilization, in addition to the resulting mineralogical 

and textural modifications. Based on the petrographic observations and mineral chemistry presented, we propose a sequence 

of events that explain the formation and modification of the 

mineralogy, textures, metal endowments, and zonation of the 

ores throughout the deposit. The chapter concludes with a 

discussion of the mobility of metals in deformed massive sulfide 

deposits and a comparison of Greens Creek mineralogy and 

chemistry to modern and ancient analogs.

Mine Location, General Host Rocks, 

Metamorphic History, Deposit 

Morphology, and Structural History

The Greens Creek mine is 29 km south of Juneau, 

Alaska, near the northern end of Admiralty Island and within 

Admiralty Island National Monument (fig. 1). The deposit is 

located at the contact between a footwall sequence of predominantly phyllitic mafic volcanic rocks and mafic-ultramafic 

hypabyssal sills and intrusions, and a hanging wall of black 

argillites. Geochronologic studies (chap. 11) have established 

that the hanging-wall argillites have an age of 220 Ma and are 

thus part of the sedimentary portion of the regionally extensive 

Hyd Group of latest Triassic (Norian) age. Less precise age 

controls suggest strongly that the mafic-ultramafic intrusive 

suite in the footwall is also of Late Triassic age and are the 

parent rocks to the Hyd Group basalts that cap the argillites. 

Uncertainty remains as to the age and identity of the footwall 

phyllites. They are most likely either of middle Permian or of 

Late Triassic age.

Constraints on the metamorphic history of the host rocks 

and ore at Greens Creek are few. The Late Triassic and older 

rocks of most of Admiralty Island are within the Admiralty 

Island Metamorphic Belt of Brew and others (1992), which 

refers to most of the island west of the Glass Peninsula. Within 

this region, mineral assemblage data are limited, no isograds 

have been mapped, and no thermobarometric data are available. No clear trends in the metamorphic pattern are discernible, and rocks from subgreenschist through amphibolite facies 

are present, produced during post-Triassic metamorphism and 

deformation (Brew and others, 1992). Loney (1964) suggested 

there is a westward decrease in metamorphic grade present in 

correlative rocks on the southern portion of Admiralty Island. 

Regional mapping of metamorphic units (Dusel-Bacon, 1994) 

places the Admiralty Island Metamorphic Belt in the greenschist facies; descriptions of Late Triassic and younger rock 

units within this belt in the area around the mine (Lathram 

and others, 1965; S.M. Karl, written commun., 2003) suggest 

subgreenschist to lower greenschist facies metamorphic grade. 

Limited petrographic and electron microprobe work conducted 

during this study on Hyd Group basalt samples from the 

immediate vicinity of the mine suggest a dominantly chloritealbite-epidote-quartz-sericite-calcite assemblage with occasional relict clinopyroxene and(or) hornblende phenocrysts. 

Tentative petrographic and electron microprobe identification 

of minor pumpellyite may indicate that the Late Triassic and 

younger rocks of the mine area are near the prehnite-pumpellyite to lower greenschist facies transition.
190 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

SOUTHEASTERN ALASKA

Mansfield Peninsula

Admiralty Island

Juneau

f .

Cascade

 Creek

- .

.

Killer Creek

Bruin Creek

Cub Creek

Gallagher Creek

Big Sore Creek

Cliff Creek

Greens Creek

CREW

FERRY

TERMINAL

HAWK

INLET

FACILITY

"A" Road

"B" Road

Tributary Creek

Zinc Creek

Mammoth

 Claim

EXPERIMENTAL

FOREST

Big

Sore

Big

Boil

NORTHERN

ADMIRALTY

ISLAND AND 

THE GREENS

CREEK MINE

YOUNG BAY

HAWK INLET

Mariposite Ridge

GREENS CREEK

MINE PORTAL

TONGASS

 NATIONAL

 FOREST

Gallagher Ridge

Lil Sore

East Lil

Sore

National Monument Boundary

Zinc

Creek

roadcut

Antenna

Mountain

High

Sore

Zinc

Creek

Pass

0 4,000 8,000 FEET

0 1,000 2,000 METERS

N

Area of

figure 1

ALASKA

National Monument

Wilderness Boundary

Lakes

District
Previous Mineralogical and Mineral Geochemical Studies 191

In general, the metamorphic history of Permian and 

younger rocks in the mine area is thought to be similar to the 

better-studied western metamorphic belt, the western edge of 

which is located several kilometers northeast of the mine. The 

western metamorphic belt is part of the Coast plutonic-metamorphic complex (Brew and others, 1989) of western Canada 

and southeastern Alaska that developed during the collision of 

the Alexander terrane and Gravina overlap assemblage with 

the Stikine terrane (Brew and others, 1989, 1992; Himmelberg and others, 1994, 1995). The western metamorphic belt 

is about 30 kilometers wide in the vicinity of Juneau and is 

characterized by Barrovian metamorphism. Multiple periods 

of deformation, metamorphism, and plutonism occurred from 

about 120 to 50 Ma, with the earliest, a regional dynamothermal event termed M1

, constrained by fabrics that predate 

intrusion of 110-Ma mafic-ultramafic rocks (Brew and others, 

1989, 1992; Himmelberg and others, 1994, 1995). Himmelberg and others (1995) conducted a mineral chemistry 

and phase equilibria study of the M1 event in subgreenschist 

to lower greenschist facies Douglas Island volcanics along 

the western edge of the western metamorphic belt. They 

concluded that thermal peak metamorphism of pumpellyitebearing assemblages occurred at about 325°C and 2 to 4.8 

kbar, equal to a maximum burial depth, assuming a normal 

geothermal gradient, of about 17–18 kilometers (Himmelberg 

and others, 1995). They also argued that in order to preserve 

the M1 mineral assemblage observed at the western edge of 

the belt given a structurally and metamorphically continuous 120- to 50-Ma event, that rapid burial, a limited extent of 

thermal pulse (from the 70-Ma intrusive event along the Coast 

batholith), and rapid uplift must have occurred. They suggest 

that uplift rates of 6 km/106 years are required, which implies 

exhumation of the western edge of the belt in as little as several hundred thousand years.

A variety of indirect constraints on temperature (40Ar/39Ar 

closure temperature of 2M1 muscovite, conodont color 

alteration indices of 5 to 5.5, lack of carbonate and organic 

carbon isotopic reequilibration, sphalerite-galena sulfur 

isotope pairs; chaps. 8, 10, 11) at Greens Creek suggest that 

maximum temperature during either the mineralizing event 

or Cretaceous regional metamorphism was no greater than 

about 275–350oC. These various lines of evidence coupled 

with the limited petrographic and microprobe data previously 

described are consistent with metamorphic conditions near 

the prehnite-pumpellyite to lower greenschist transition in the 

Greens Creek area. The preservation of primary isotopic and 

geochemical features of the deposit as well as the primary 

textural features of the ores described in this chapter further 

suggest that the M1

 metamorphic event was neither pervasive 

nor long lived.

Ore is nearly continuous along the phyllite/argillite contact and consists of three main orebodies—the East, West, and 

Southwest—and three extensions (fig. 2). The East orebody 

outcrops near the northeastern edge of the property, plunges 

shallowly to the southwest, and dips steeply west, flattening 

out gradually into the West orebody. The Klaus thrust fault 

separates the East and West orebodies approximately halfway 

through the flat. West of the flat, the West orebody continues 

beneath the Klaus fault as a thin horizontal layer, which dips 

to near vertical and then swells into a multiply folded and 

thickened mass that occupies a trough-shaped depression in 

the phyllite/argillite contact. A southward extension of the 

West orebody is hosted entirely within the hanging-wall argillites. The Northwest extension is a dextral fault translation of 

the western portion of the West orebody along the Maki fault, 

a major, near-vertical, strike-slip fault that cuts the property 

in two.

The Southwest orebody extends from the West/Northwest 

orebody in a complex helical fold that plunges shallowly to the 

southwest. Like the southward extension of the West orebody, 

the upper portion of the Southwest orebody transgresses the 

phyllite/argillite contact into the argillites. Maximum separation is about 35 m. The 200 South orebody is a southward 

extension of the Southwest orebody.

Deformation at Greens Creek is extremely complex 

and involves at least four periods of folding, one period of 

semiductile shearing, and two periods of faulting (see chap. 

7). Continuity of the orebodies is interrupted by numerous 

thrusts and strike-slip faults on and parallel to the Klaus and 

Maki faults. The four phases of folding have further modified the deposit morphology. However, with few exceptions 

the ore horizon is traceable along the phyllite/argillite contact 

throughout the mine. Restoration of 600 m of movement along 

the Maki fault and 200 m of movement along the Klaus fault 

(P.A. Lindberg, written commun., 1994) results in a single 

orebody with a thickened central core in the West/Northwest 

orebody, which thins to the north, east, and south. The only 

indication that stacked orebodies may be present is the separate occurrence of ore above and south of the main ore concentration in the 5250 orebody (fig. 2).

Previous Mineralogical and Mineral 

Geochemical Studies

The earliest report on the mineralogy of Greens Creek 

ores of which we are aware consists of a brief summary 

and petrographic descriptions of six samples from the East 

orebody (George Alorno, written commun., 1987). Two 

samples of phyllite, one argillite, one white ore that probably 

would be currently classified as a white carbonate ore type, 

and two massive sulfide ores are described in detail. The major 

conclusions were that (1) variable deformation and degree of 

recrystallization between the phyllites and argillites indicate 

that the ore horizon is a tectonic contact, (2) massive sulfides 

Figure 1 (facing page). Maps of northern Admiralty Island 

showing the location of the Greens Creek mine and other features 

mentioned in the text.
192 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

LS4000

LS5000

LS6000

LS7000

XS5000XS4000

XS3000

XS2000XS1000XS0000

Southwest orebody

5250 orebody

9A

orebody

West orebody

Northwest

orebody

Shop

orebodies 224

West

Bench

200

West

Bench

200 South

orebody

Upper

Northwest

orebody

MAKI FAULT ZONE

MAKI FAULT ZONE

N

LS4500

LS5500LS6500

224 West Bench

Southwest

orebody

West

orebody

East

orebody

9A orebody

Cross section 2400

view looking grid North

1,000 feet elevation

0 feet elevation

(sea level)

–1,000 feet elevation

CROSS-SECTIONAL VIEW OF THE GREENS CREEK DEPOSIT.

PLAN VIEW OF THE GREENS CREEK DEPOSIT.

A

A

A‘

East orebody

South zone Central zone

A‘

MAKI

FAULT

KLAUS

FAULT

5250

orebody

North zone

Figure 2. Plan and cross-sectional views of the Greens Creek deposit showing features described in the text.
Previous Mineralogical and Mineral Geochemical Studies 193

show a mix of primary and intensely granulated textures but 

no evidence for ductile deformation, and (3) the white ore 

sample contains abundant cymrite (hydrous barium aluminosilicate) and probably barian muscovite. Importantly, Alorno 

(written commun., 1987) also noted that the ore sulfides, 

particularly tetrahedrite, were confined to veinlets in the white 

ore and were not part of the “early assemblage.” Both polycrystalline quartz and rotated dolomite porphyroblasts were 

observed in the phyllites, establishing a predeformation age 

of silica-carbonate alteration, similar to the findings of this 

study (V.M. Anderson and C.D. Taylor, unpub. data, 2000), 

and compositional layering in the phyllite occasionally was 

truncated against pyrite bands. If so, this observation suggests 

the presence of a premineralization fabric in the phyllites that 

is probably equivalent to the S1

 foliation of current usage (see 

chap. 7). Alorno’s report documents the occurrence of all of 

the currently known major sulfide minerals as well as gangue 

graphite, rutile, ilmenite, “green mica,” and the postulated 

barian muscovite. Although cymrite may be present, it has 

not been documented in any of the later studies. He notes the 

presence of delicate botryoidal features in pyrite-tetrahedritesphalerite bands, describes either cataclasis or the lack of 

deformation features in pyrite, and “granoblastic,” “annealed,” 

and “flame” textures in galena and sphalerite. Paragenetically, Alorno (George Alorno, written commun., 1987) notes 

the remobilization of tetrahedrite and galena into fractures 

in, and as matrix to, pyrite and refers to “pseudoframboidal” 

pyrite features produced by replacement of base-metal sulfides 

by pyrite. Additionally, he makes the important observation 

that early primary textured pyrite is commonly overgrown by 

euhedral pyrite.

The next and most significant effort at understanding the 

mineralogy and mineral chemistry of the ores at Greens Creek 

is contained in a series of internal mining company reports. 

These reports detail the results of three major phases of work. 

The first phase consists of three reports that describe the 

mineralogy and mineral chemistry, as determined by electron 

microprobe analysis, on a variety of mill products drawn 

from East orebody ore: mill head; lead (Pb), zinc (Zn), and 

bulk concentrates; tails; and final tails (E.U. Petersen, written 

commun., 1991, 1992a, b). These early studies recognized 

the complexity of the silver (Ag) mineralogy at Greens Creek 

(see table 1) and placed some preliminary constraints on the 

mineral chemistry of a few of the major phases. East orebody 

sphalerite was shown to have fairly homogeneous low iron 

(Fe) content (less than 1.0 percent) and measurable cadmium 

(Cd), mercury (Hg), copper (Cu), and manganese (Mn) (less 

than 1.0 percent combined). Analyses of tetrahedrite showed 

them to be the zinc-antimony-rich, iron-arsenic-poor end 

member, with measurable cadmium. Silver in tetrahedrite 

ranged from about 0.5 to 6.5 percent with several exceptionally silver-rich analyses up to 15.9 percent. E.U. Petersen 

(written commun., 1992) also noted the common occurrence 

of an unknown silver-rich mineral (up to 44 percent silver), 

previously identified as covellite, which plots along the covellite (CuS) – acanthite (Ag2

S) join.

Results of the second phase of mineralogical research at 

Greens Creek are contained in a series of memorandums from 

Chris J. Carter to the Greens Creek mine staff (C.J. Carter, written commun., 1994a, b, c, d). In these memorandums, Carter 

presents a reevaluation of Petersen’s concentrate microprobe 

data and a preliminary evaluation of microprobe data from a set 

of 12 samples collected from the Southwest orebody. A report 

containing detailed descriptions and assay data provides context for the 12 hand samples (Debora Apel, written commun., 

1993). Carter’s evaluation of Petersen’s data focuses on the 

variation of silver content in tetrahedrite and the possible utility 

of using silver as a vector for exploration. He suggests that the 

broad range of silver/copper values determined for tetrahedrites 

from East orebody concentrates indicates that original metal 

zoning features have probably been preserved and thus might 

provide a useful exploration criterion.

Petrographic and geochemical studies of mineralogy in 

the Southwest orebody samples noted a broad range of sulfide 

textures and grain sizes. Four distinct textural varieties of pyrite 

were observed: euhedral, spongy, colloform, and framboidal. Minor to moderate amounts of arsenopyrite also were 

observed, and microprobe data on pyrite, arsenian pyrite, and 

arsenopyrite indicated measurable gold and nickel (Ni). Galena 

was noted to be weakly argentiferous and thus not a significant contributor to the silver budget. The antimony content of 

tetrahedrite was shown to vary greatly from about 13 percent 

(expressed as the molar ratio Sb/[Sb+As]) to about 81 percent, 

demonstrating that a series of tetrahedrite-tennantite minerals are present in the Southwest orebody. These tetrahedrites 

also have three times the average silver content (expressed as 

the molar ratio Ag/[Ag+Cu]) than those in the East orebody 

(17.6 versus 5.2 percent), lower zinc content, and higher iron 

and cadmium content. They also report silver-rich minerals 

belonging to the proustite-pyrargyrite series, jalpaite, and an 

unidentified mineral with 86 weight percent silver (C.J. Carter, 

written commun., 1994). Ag/Ag+Cu versus Sb/Sb+As plots of 

tetrahedrite analyses were interpreted as having three distinct 

trends, indicating three distinct starting fluid compositions may 

have contributed to the ore-forming process (C.J. Carter, written commun., 1994). Sphalerite iron content was observed to 

be as homogeneous as in East orebody sphalerites with perhaps 

a slightly higher average value (0.9 weight percent).

The potential use of iron in sphalerite and Ag-Cu versus 

Sb-As trends in tetrahedrites as exploration tools led to a third 

phase of mineralogical research. E.U. Petersen and D. Chirban 

(written commun., 1994) conducted a study aimed at characterizing the mineralogical and chemical zoning of the Greens 

Creek deposit based on tetrahedrite chemistry. Tetrahedrites in 

44 samples primarily from drill holes on the 2400 cross section of the Lower Southwest orebody, representing four major 

ore types, were analyzed by electron microprobe (Denise 

Chirban, written commun., 1995; Denise Chirban and E.U. 

Petersen, written commun., 1996).

The concentration of silver in tetrahedrite was found to 

vary from 2.45 to 20.95 weight percent and was accompanied 

by large variations in all three solid solutions as expressed by 
194 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

XAg (Ag atoms/[Ag+Cu]), XSb (100 × Sb atoms/[Sb+As+Bi]), 

and XZn (100 × Zn atoms/[Zn+Fe]). The silver index, XAg, 

ranged from 0 to 0.4, the antimony index, XSb, ranged from 

0.1 to 1, and the zinc index, XZn, ranged from 0.1 to 1. They 

determined that the chemical variation within a sample was 

much less than the variation between samples, indicating that 

the average of several spot analyses of a sample is a good 

representation of the tetrahedrite composition for that location. 

This also implies that zoning patterns, if present, should be 

discernible between samples. They applied this to cross-stratigraphic variations in ore types on the 2400 cross section and 

concluded that each ore type has its own “mini-stratigraphy” 

with all of the above index ratios increasing stratigraphically 

upward. Each ore type was found to have characteristic tetrahedrite compositions, which define a trend. However, these 

trends were not sufficient to identify an ore type based on 

inspection of single spot analyses (Denise Chirban and E.U. 

Petersen, written commun., 1996). Their work on the highsilver sulfosalt minerals demonstrated that tetrahedrite could 

coexist with, or occur independently of, the covellite-acanthite 

solid solution, mckinstryite, or jalpaite. Data from one pulp 

sample also indicates that these silver-rich minerals may occur 

independently from tetrahedrite.

Finally, electron microprobe results were reported for 

a single sample of native-silver-bearing, high-grade white 

siliceous ore from the 764N1 stope of the Upper Southwest 

orebody (T.K. Bundtzen, written commun., 1996). The data 

indicate the presence of coarse grains of jalpaite occurring as 

bluish rims around native silver and that the silver contains 

less than 0.1 percent gold. The sample also contained euhedral 

crystals of gangue celsian or harmotome.

Ore Types

Ore lithologies at Greens Creek are broken into two main 

groups of massive sulfide ores and semimassive or disseminated sulfide gangue-rich “white” ores. The group of massive 

ores contain greater than 50 percent sulfides and consist of 

two types: (1) massive fine- to very fine grained ore in which 

base-metal sulfides are greater than pyrite (hereinafter referred 

to by the ore lithology code MFB, for Massive, Fine-grained, 

Base-metal-rich, and MVB, for Massive, Very fine grained, 

Base-metal-rich ores, respectively), and (2) massive mediumto very fine grained pyrite-rich ore in which pyrite predominates (hereinafter referred to as MFP and MVP, respectively). 

The distinction between the fine- and very fine grained ore 

types is subjective and based on the visual appearance of 

grain sizes in drill core. In general, the very fine grained ore 

types are so designated when individual sulfide grains cannot 

be seen with the naked eye. The MFBs are a medium to dark 

metallic gray to blue-gray (fig. 3A); the MFPs are bronze to 

metallic brown (fig. 3B). The MVBs and MVPs are similar in 

color to the coarser grained ore types with two notable variations. MVBs occasionally take on a distinct yellow-orange hue 

due to high concentrations of low-iron sphalerite (fig. 3C), and 

MVPs take on a light creamy bronze color due to increased 

content of arsenian pyrite. All the massive ores have variable 

subordinate gangue of quartz, dolomite, sericite, barite, and 

fuchsite. Graphite is a less ubiquitous but locally abundant 

gangue mineral. The massive sulfide ores constitute the main 

stage of ore formation.

The white ores are a group of mineralized lithologies 

that contain less than 50 percent sulfides and are defined 

by their principal gangue mineral. They commonly contain 

base- and precious-metal enrichments and are usually, but for 

core logging purposes are not required to be, of ore grade. 

The three types are (1) white carbonate ore (WCA) and (2) 

white siliceous ore (WSI), which are most common, and (3) 

white baritic ore (WBA). The WCAs are characterized by 

granular textured, medium- to coarse-grained dolomite (fig. 

3D). Accessory gangue minerals are present but less abundant 

than in WSIs. WSIs are dominated by massive cryptocrystalline aggregates of hydrothermal quartz or chert and regularly 

contain significant dolomite, sericite, fuchsite, and barite (fig. 

3E). WBAs are characterized by coarse, sugary, massive barite 

and other gangue (as above) (fig. 3F). They commanly are not 

ore grade despite their inclusion as an ore lithology. The white 

ores constitute the early stage of ore formation and precede the 

main stage of massive sulfide ores.

All the ore types previously mentioned include subtypes 

that are modifications resulting from veins, breccias, and 

gouge or rubble zones produced during faulting or folding. 

Veining due to secondary metamorphic remobilization and 

accompanying recrystallization can result in spectacular 

enrichments of free gold and a variety of silver-sulfosalt minerals, which are described herein. Ore breccias appear to be 

both primary sedimentary breccias produced by slumping of 

the massive sulfides and inclusion of clasts of the underlying 

as well as overlying host rocks, and tectonic breccias produced 

during deformation. Solution brecciation may also be present, 

particularly in the WCAs.

Figure 3 (facing page). Photographs of hand samples illustrating 

the various massive sulfide and white ore types: (A) typical MFB 

with primary-textured pyrite (py) in a matrix of sphalerite (sph) and 

galena (gn) (drill-core sample GC127-18, 1007’, ST–2 84 crosscut 

East orebody; (B) typical MFP (drill-core sample GC1136–05, 602’, 

Lower Southwest orebody), note the breccia texture caused by 

the brittle failure of massive pyrite; (C) typical MVB (drill-core 

sample GC1643–10, 272’, 200 South orebody), the orange color is 

due to the very high proportion of sphalerite in the sample and 

the low iron content of the sphalerite; (D) typical WCA (rib sample 

164 crosscut, 82’, Lower Southwest orebody); (E) typical WSI (rib 

sample from East orebody); (F) typical WBA (rib sample from the 

164 crosscut, 164N1 stope, Lower Southwest orebody.
Ore Types 195
196 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Primary Ore Mineralogy and Textures

Roughly 30 percent of the Greens Creek ores retain primary 

mineralogy and textures. With one notable exception, primary 

features are present in massive, homogeneous, fine-grained 

MFPs that usually contain a high percentage of silica gangue. 

Apparently, large, cohesive blocks of pyritic ore have acted as 

undeformed nuclei around which the more ductile MFBs have 

flowed during deformation. Brecciation of the MFPs is a common feature within these cohesive blocks, resulting in angular to 

subangular, tectonically milled clasts of primary-textured MFP 

in a sheared sulfide matrix consisting mostly of more ductile and 

recrystallized base-metal sulfides (fig. 4A). Clear evidence for 

primary depositional layering of sulfides is lacking. However, 

mineralogically banded massive ores are common and are composed of entirely recrystallized sulfides (fig. 4B).

Within primary-textured MFPs, framboidal, colloform, and 

dendritic-textured pyrite is common and is intimately intergrown 

with a variety of base-metal sulfides and sulfosalts. Framboids 

are commonly in the 1–5 micrometer (mm) size range and are 

as large as 30 mm (figs. 5A–C). Colloform-textured areas can 

be millimeters in size (fig. 5D), with individual mineral bands 

ranging from less than 1 to 10 mm in width (fig. 5E). Mineral 

bands are most commonly composed of pyrite interbanded with 

sphalerite, galena, tetrahedrite, and a lead-antimony sulfosalt 

mineral (fig. 5F). Rarely, chalcopyrite replaces pyrite or infills 

bands between pyrite layers in the more copper-rich orebodies 

(fig. 5G). Dendritic-textured areas of pyrite are less common, 

only occur in MFP, and can have individual dendrites in the 

100–200 mm size range (fig. 5H). Common accessory mineralogy in the primary textured ores includes sphalerite, galena, 

tetrahedrite, chalcopyrite, free gold, and a variety of Pb-Sb-As 

(-Hg-Tl) sulfosalts.

Primary-textured sulfides are also present in WCAs. 

Rounded grains of pyrite up to a centimeter in diameter with 

radial growth textures occur in a matrix of massive, coarse 

crystalline dolostone. These features produce a “pudding stone” 

texture and are reminiscent of diagenetic pyrite nodules (fig. 

4C). Similar nodular pyrite textures, fragments of nodules, 

pyrite rinds, and concentrations of framboidal and colloform 

pyrite intergrown with base-metal sulfides also occur in association with concentrations of white, hydrothermal dolomite that 

typically cuts more massive, coarse crystalline dolostone. These 

textures are clearly linked to hydrothermal veining and in some 

cases may be produced by solution brecciation of footwall 

dolostones and WCAs followed by precipitation of dolomite 

and quartz cements in the resulting cavities (fig. 4D).

Recrystallized and Remobilized Ore 

Mineralogy and Textures

Recrystallization of the primary textures in individual 

hand samples ranges from 20 percent to 100 percent and results 

in a range of textures. Incipient recrystallization results in the 

formation of polyframboidal aggregates (rogenpyrite; fig. 6A), 

“spongy” textured pyrite, and atoll-shaped pyrite. Spongy 

texture is most common in the massive ores in millimeter- to 

centimeter-scale areas of massive and aggregated pyrite. These 

areas often show relict framboidal and colloform textures. The 

pyrite itself commonly appears quite “clean” or monomineralic. 

However, the spongy areas are full of micrometer-scale inclusions of other sulfides, sulfosalts, and gangue minerals (fig. 6B). 

The centers of euhedral pyrite crystals larger than about 100 

mm also tend to have spongy texture. As recrystallization progresses, atoll-shaped pyrite forms at the expense of framboids 

and colloform pyrite (fig. 6C). The larger aggregates of polyframboids and spongy textures coalesce further into large areas 

of inclusion-rich anhedral to subhedral pyrite (fig. 6D).

The major effects of more advanced recrystallization is 

much coarser grain sizes and the formation and(or) remobilization of secondary, precious-metal-enriched minerals (fig. 

6E). Pyrite recrystallization is characterized by development 

of euhedral crystals and polygonal textured masses that appear 

to be unzoned and free of mineral inclusions (fig. 6F). Recrystallization of pyrite tends to roughly double the grain size; for 

example, pyrite euhedra in areas of 1–5-μm framboids are 

5–10 μm in size. In recrystallized aggregates or massive areas 

of pyrite with development of polygonal texture, individual 

grains are commonly in the 50–100-μm range. In MFPs that 

have been entirely recrystallized, pyrite euhedra are commonly 

in the 0.1- to 1-mm size range or larger (fig. 6G). Secondary 

minerals occur as discrete rounded inclusions within pyrite 

grains (figs. 6H and I), as growth zones within, and as margins to, pyrite (figs. 6J and K), and as matrix to pyrite euhedra. Subhedral to euhedral sphalerite occurs in recrystallized 

MFB, usually in a matrix of anhedral galena (figs. 6L and M). 

Secondary mineralogy includes chalcopyrite, sphalerite (low 

iron), galena, free gold, electrum, tetrahedrite (antimony-rich), 

bornite, covellite, pyrargyrite, and a host of other sulfosalt 

minerals. Rare realgar has been identified (by X-ray diffraction) in the WBAs of the 200 South orebody. Base-metal 

sulfides in recrystallized ores most commonly occur as anhedral intercrystalline masses of secondary sphalerite, galena, 

chalcopyrite, tetrahedrite, and pyrargyrite. Individual anhedral 

crystals are commonly 50–200 mm in size (fig. 6N). Secondary sulfides also commonly occur in late fractures and veinlets 

millimeters wide and centimeters long (figs. 6O and P).

An interesting and potentially genetically important 

modification that affects MFPs in proximal, copper-arsenicgold-rich areas of the deposit is the occurrence of subhedral 

to euhedral, light creamy yellow to white, arsenian pyrite 

(FeS2

 with variable substitution of arsenic for iron) and arsenopyrite (FeAsS, 46 percent arsenic). These phases appear to 

replace primary pyrite (figs. 7A–C) or form as overgrowths 

on primary-textured pyrite masses (figs. 7D and E). They 

are present in trace amounts to as much as 50 percent of a 

sample. Powder X-ray diffraction analyses of two MFP ores, 

each with approximately 50 percent of this sulfide visible in 

polished thin section, confirmed the presence of arsenopyrite, 

but only in trace to minor amounts. In both cases the major 
Recrystallized and Remobilized Ore Mineralogy and Textures 197

Figure 4. Photographs of hand samples illustrating textures present in various ore types: (A) brecciated MFP consisting of angular to 

subangular, tectonically milled clasts of siliceous, primary-textured, fine-grained, pyritic massive ore in a sheared sulfide matrix consisting 

mostly of more ductile and recrystallized base-metal sulfides (drill-core sample GC1136-04, 594.5’, Lower Southwest orebody); (B) 

tectonically banded MFB (rib sample from the 764 crosscut, 764N1 stope, Upper Southwest orebody); (C) nodular diagenetic pyrite texture 

in MFP (rib sample from the 2250 crosscut, 215 stope, Lower Southwest orebody); and (D) closeup photograph of WCA showing nodular 

pyrite textures, fragments of nodules, pyrite rinds, and concentrations of framboidal and colloform pyrite intergrown with base-metal 

sulfides in association with concentrations of white, hydrothermal dolomite usually cutting more massive, coarse crystalline dolostone 

(drill-core sample GC1092-02, 711’, Lower Southwest orebody). py, pyrite; sph, sphalerite; gn, galena; dol, dolomite; tetr, tetrahedrite.

phase identified was pyrite, indicating that the majority of 

the creamy white mineral observed must be arsenian pyrite. 

Rarely, euhedral arsenopyrite has been observed in a silicadolomite matrix (fig. 7F).

Physical remobilization of the more ductile base-metal 

sulfides is indicated by fractured masses of pyrite filled with 

flow-textured anhedral chalcopyrite, galena, and tetrahedrite (fig. 6E). Flow-textured galena is characterized by the 

near total absence of the triangular pits usually observed 

in unstrained galena (fig. 6L). Physical remobilization and 

recrystallization in tectonized ores is probably responsible for 

creating the mineralogically segregated layers in banded ores. 

Creation of base-metal-rich veinlets and infilling of fractures 

by physical remobilization is an important process of metals 

redistribution in ores on a hand-sample scale and is ubiquitous 

in the more thoroughly recrystallized and tectonized ores. It is 

distinguished from the process of chemical remobilization by 

the lack of associated gangue minerals in the base-metal-rich 

fractures, veinlets, and piercement structures.

Chemical remobilization and reprecipitation of basemetal sulfides is also a locally important process and is 

characterized by the formation of paragenetically late veinlets 

and veins of chalcopyrite, sphalerite, galena, tetrahedrite, and 

pyrargyrite usually in association with quartz and dolomite 

(figs. 6Q and R). Occasionally, sericite and fuchsite gangue 

are present as well. Yellow and silvery-white gold is present 
198 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Figure 5 (above and facing page). Photomicrographs of polished thin sections showing primary mineral textures: (A) framboidal pyrite 

(rib sample 96GC–14, 31’, 344 crosscut, Lower Southwest orebody); (B) pyrite (py) framboids and galena (gn) spheres in spongy-textured 

to massive pyrite (drill-core sample GC1643–04, 75’ 200 South orebody); (C) aggregated pyrite framboids in a matrix of sphalerite (sph) 

(drill-core sample GC1643–03, 54’, 200 South orebody); (D) colloform-textured aggregate of pyrite with a spongy-textured interior and 

growth zones composed of sphalerite, galena, and tetrahedrite (rib sample 96GC–12, 21.5’, 344 crosscut, Lower Southwest orebody); 
Free Gold—Mineralogy and Textures 199

in chemically remobilized veins and is particularly abundant 

in association with late quartz-carbonate-pyrargyrite veins. 

Concentrations of these precious metal enriched veins usually 

occur in or within close proximity to areas of primary-textured 

ore and account for the highest grade ores in the mine, with 

total metal values reaching $10,000/ton.

Free Gold—Mineralogy and Textures

Free gold is a relatively common feature at Greens 

Creek and has been found in a wide variety of both ore and 

host-rock lithologies. Two types are visually distinguishable, and a third was identified during LA–ICP–MS analysis. 

Bright yellow gold of high fineness occurs in thin section 

as rounded blebs and inclusions from 5 to 100 μm in size, 

although the most common size is about 5 to 20 μm (fig. 8A). 

Most of the grains are in cracks in pyrite and in the matrix 

to pyrite grains in association with secondary chalcopyrite, 

sphalerite, galena, tetrahedrite, and pyrargyrite (figs. 8B and 

C). Most gold grains are in contact with either pyrite or arsenian pyrite (fig. 8D); however, a few grains were observed 

included within coarse-grained subhedral to euhedral pyrite 

(fig. 8E). Yellow gold is most commonly seen in the large 

blocks of MFP ore but also has been observed in all of the 

ore types at the mine and in both hanging-wall and footwall 

rocks, usually in association with quartz-carbonate veins.

The second type of free gold is silvery white and occurs 

predominantly as a thin foil coating late fractures and shear 

planes in underground exposures and hand samples (figs. 8F

and G). In thin section, white gold appears as thin veinlets 

and spaced sheets that occupy fractures up to 0.5 millimeter 

wide. These fractures are paragenetically late and appear 

to be tension gashes and piercement structures that occur at 

high angles to S2

 foliation (fig. 8H). Geochemical data suggest this is a gold-silver electrum.

Free gold occurs in ores that exhibit a high degree of 

recrystallization and remobilization of the more ductile 

sulfides and are usually in close proximity to areas of primarytextured ores. Exceptions include yellow gold that occurs in 

quartz-carbonate veins in the host rock and rare instances of 

white gold foil in highly sheared and fractured argillites in the 

immediate hanging wall. These electrum-bearing quartz-carbonate veins typically are within 1–2 m of high-grade primary 

ores. Yellow gold has also been observed in association with 

chalcopyrite and tetrahedrite in hairline fractures cutting late 

diabase dikes in the 200 South portion of the Lower Southwest 

orebody. This relationship thus requires remobilization of gold 

at some time after emplacement of the dikes.

The two types of gold, as well as native silver, are easily 

distinguished based upon LA–ICP–MS geochemical studies 

of free gold separates recovered from the mill (figs. 9A–I). 

Laser traverses across 0.5- to 1.0-mm-sized grains recovered 

from heavy concentrates, represented as time versus elemental 

intensity plots, clearly indicate the presence of nearly pure 

gold grains with a high ratio of gold to silver (figs. 9A, D–F). 

Other grains that appear silvery-white on polished surfaces 

show lower gold-to-silver ratios and consistently elevated 

mercury, demonstrating that the silvery white gold is actually a 

(E) colloform banded spheres in pyrite with growth bands filled with galena or perhaps lead-antimony sulfosalt minerals (rib sample 

96GC-13, 25.5’, 344 crosscut, Lower Southwest orebody); (F) aggregate of colloform shapes in pyrite (rib sample 96GC–13, 25.5’, 344 

crosscut, Lower Southwest orebody); (G) chalcopyrite (cpy) infilling or replacing bands between pyrite layers in colloform-textured MFP 

(drill-core sample GC1527–09, 402.5’, Northwest orebody); and (H) dendritic-textured pyrite fronds in massive pyrite (rib sample 96GC–16, 

43.5’, 344 crosscut, Lower Southwest orebody).
200 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

gold-silver-mercury amalgam (figs. 9B and C). A few traverses 

suggest that some of the gold grains may also incorporate significant copper (fig. 9G). Silver grains either contain irregular 

inclusions of gold or are relatively pure (figs. 9H and I). The 

silver quickly tarnishes to a dirty, bluish-gray color, enabling 

visual identification in slides of the mill separates.

Paragenetic Relationships—Physical 

and Chemical Modification of Ores

Two major processes govern paragenetic relationships 

in Greens Creek ores. Primary ores are dominated by textures 

indicative of rapid crystallization, very early infilling of void 

spaces, and replacement of one sulfide by another during 

growth of the massive sulfide body, whereas the secondary 

ores are the product of recrystallization and remobilization of 

primary ores during zone refinement and metamorphism. In 

primary ores, framboidal and colloform pyrite are the earliest 

formed sulfides. Sphalerite, galena, tetrahedrite, and leadantimony sulfosalts appear to be coeval and form the matrix of 

framboidal aggregates (figs. 10A; 3A; 5C; 6A) as well as the 

intervening bands in colloform-textured pyrite (figs. 5D–F). 

Bands of pyrite are nearly always present in colloform-textured 

ores; in the few cases where successive bands of base-metal 

sulfides without intervening pyrite bands occur, they are present 

as colloform growths within predominantly pyritic primary-textured masses (figs. 10B; 5G). These primary-textured, pyriteand base-metal-sulfide-rich masses appear to undergo modification early in the growth of the massive sulfide bodies by a 

process of zone refinement. Early, porous masses, composed 

of framboidal and colloform pyrite with a high percentage of 

sphalerite, galena, and lead-antimony sulfides (figs. 5A, D–F; 

6A), progress into more densely packed pyrite-chalcopyritearsenopyrite-rich masses through a combined process of pyrite 

coalescence and replacement of the base-metal sulfides. The 

resulting ores exhibit a progression of textures characterized by 

the destruction of discrete framboids (figs. 5B; 6B) and the formation of polyframboidal (figs. 6A; 10A) and spongy-textured 

(figs. 5D; 6C, I) pyrite aggregates, atoll-shaped and subhedral 

pyrite grains (figs. 6J, K), and subhedral to euhedral arsenian 

pyrite and arsenopyrite (figs. 7A–F). Chalcopyrite generally 

occurs as matrix in the resulting pyritic masses along with a 

much lower percentage of sphalerite, galena, and tetrahedrite 

(figs. 6E, G). Replacement of the base-metal sulfides presumably results in expulsion of lead, zinc, and other trace elements 

upward and outward to form the MFBs. Rarely, in copper-rich 

primary-textured MFPs, chalcopyrite has been observed, partially replacing bands of other base-metal sulfides in colloform ores (fig. 5G). Several examples of framboids composed 

of chalcopyrite crystallites in a matrix of pyrite have been 

observed; however, it is questionable whether such examples 

indicate a paragenetically early position of chalcopyrite relative to pyrite (fig. 10C). Framboids composed of sphalerite or 

other base-metal sulfides have not been observed in this study. 

Graphite is a ubiquitous feature of primary ores and occurs 

as fine disseminations in the matrix between framboids and 

colloform-textured masses (fig. 5C) and in association with 

dendritic and spongy-textured pyrite (fig. 5H).

The formation of light creamy yellow to white, arsenian pyrite and arsenopyrite (figs. 7A–F) is a paragenetically important feature of the primary-textured ores and is of 

uncertain origin. It is most commonly observed in association 

with primary ores that have undergone incipient to moderate 

recrystallization. As the “dirty” trace-element-rich primarytextured pyrites undergo recrystallization, the stoichiometric 

reorganization of the pyrite mineral structure expels excess 

trace elements from its structure, including arsenic. Liberated 

arsenic is then available to form new arsenian pyrite or arsenopyrite. However, both arsenian pyrite and arsenopyrite are 

concentrated in areas of primary-textured ores where permeability is greater, either due to presence of abundant spongytextured pyrite, loose packing of framboidal aggregates, or the 

presence of veining. This relationship suggests that arsenian 

pyrite and arsenopyrite may have formed early in the paragenesis, after the formation of primary-textured sulfides but prior 

to advanced recrystallization of the ores. A possible explanation is that these minerals represent a hotter, more reducing 

period of fluid circulation and mineral formation by replacement of earlier formed minerals during a zone-refining stage 

of sulfide mound growth.

Nonprimary-textured ores exhibit a range of features that 

suggest a progression from incipient through complete recrystallization and physical as well as chemical remobilization as 

a result of metamorphism. Incipient recrystallization causes 

individual framboids to coalesce into atoll-shaped grains, with 

centers filled with base-metal sulfides and rims of clean, bright 

pyrite (figs. 10D; 5E–G; 6C, J). Aggregates of framboids 

develop into large spongy-textured masses with numerous 

discrete inclusions of base-metal sulfides and graphite (figs. 

10E; 6D, H, I). Graphite tends to recrystallize into felty concentrations of needle- or lath-shaped crystals that are aligned 

subparallel to S2 foliation (fig. 10F). As recrystallization 

progresses, large areas of inclusion-free pyrite form with relict 

framboidal shapes preserved in the interiors of the masses. 

Euhedral-shaped growth zones are defined by thin bands of 

sphalerite or galena (figs. 10G; 6J). Fully recrystallized pyritic 

ores are characterized by very large areas of inclusion-free, 

monomineralic pyrite with polygonal grain boundaries (figs. 

10H; 6F). Matrix between the large areas of pyrite is filled with 

anhedral masses of sphalerite, galena, and tetrahedrite, which 

are generally also inclusion free (fig. 6G). Bright yellow free 

gold is most commonly seen in partially to fully recrystallized 

MFPs as inclusions within recrystallized pyrite grains (fig. 8E) 

and in matrix with base-metal sulfides (figs. 8A–D). In recrystallized MFBs, clean, euhedral pyrite and euhedral to subhedral 

sphalerite are contained in a matrix of anhedral galena and 

tetrahedrite (figs. 6L–N). Areas of macroscopically banded ore 

in thin section alternate between pyrite-rich and base-metalsulfide-rich layers that are texturally as previously described 

(fig. 4B). Recrystallization of chalcopyrite-rich MFPs generally 
Paragenetic Relationships—Physical and Chemical Modification of Ores 201

Figure 6 (pages 15–17). Photomicrographs of polished thin sections showing recrystallized ore textures: (A) growth of polyframboidal 

clusters in a matrix of sphalerite (sph) (rib sample 96GC–12, 21.5’, 344 crosscut, Lower Southwest orebody); (B) spongy-textured pyrite 

(py) with relict framboidal and colloform shapes, and numerous inclusions of sulfides, sulfosalts, and gangue (rib sample 96GC–18, 

51’, 344 crosscut, Lower Southwest orebody); (C) atoll structure of clean recrystallized pyrite forming around a grain of spongytextured pyrite (rib sample 96GC–13, 25.5’, 344 crosscut, Lower Southwest orebody); (D) clean anhedral pyrite with numerous rounded 

inclusions of tetrahedrite (tetr) and galena (gn) (drill-core sample GC1643–06, 119.5’, 200 South orebody); (E) veinlets of chalcopyrite 

(cpy), tetrahedrite (tetr), galena (gn), and yellow gold (Au) cutting recrystallized pyrite (drill-core sample GC1643–05, 100.5’, 200 South 

orebody); (F) clean, completely recrystallized, polygonal-textured pyrite (rib sample 96GC–14, 31’, 344 crosscut, Lower Southwest 
202 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

orebody); (G) recrystallized pyrite euhedra in a matrix of chalcopyrite, galena, tetrahedrite, and sphalerite (drill-core sample GC1643–08, 

147.5’, 200 South orebody); (H) clean, recrystallized anhedral pyrite with rounded inclusions of sphalerite (drill-core sample GC1643–08, 

147.5’, 200 South orebody); (I) partially recrystallized spongy pyrite with rounded inclusions of chalcopyrite and galena (drill-core 

sample GC1643–07, 143.5’, 200 South orebody); (J) clean, recrystallized pyrite with discrete, atoll-shaped growth zones of chalcopyrite 

and galena GC1527–08, 397.5’, Northwest orebody); (K) recrystallized pyrite with rims of galena (drill-core sample GC1643–11, 438’, 

200 South orebody); (L) recrystallized euhedral pyrite and sphalerite in a matrix of anhedral tetrahedrite and galena (drill-core sample 
Paragenetic Relationships—Physical and Chemical Modification of Ores 203

GC1643–01, 11.7’, 200 South orebody); (M) recrystallized euhedral sphalerite in galena matrix (drill-core sample GC1643–10, 272’, 200 

South orebody); (N) inclusion-free, euhedral pyrite with anhedral sphalerite, galena, and tetrahedrite as matrix (rib sample 96GC–10, 

18.5’, 344 crosscut, Lower Southwest orebody); (O) late galena and tetrahedrite veinlet cutting spongy-textured pyrite (rib sample 

96GC–15, 39’, 344 crosscut, Lower Southwest orebody); (P) late chalcopyrite, galena, and tetrahedrite veinlet cutting framboidal pyrite 

(drill-core sample GC1643–03, 54’, 200 South orebody); (Q) remobilized veinlet of tetrahedrite, galena, and yellow gold in dolomite (drillcore sample GC1643–06, 119.5’, 200 South orebody); and (R) veinlet of anhedral sphalerite, galena, chalcopyrite, and tetrahedrite, and 

pyrargyrite cutting recrystallized pyrite (rib sample 96GC–17, 49’, 344 crosscut, Lower Southwest orebody).
204 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

progresses from spongy-textured masses of pyrite with chalcopyrite in the matrix and numerous small chalcopyrite inclusions 

to clean, monomineralic, polygonal-textured masses of pyrite 

with grain boundaries and intercrystal spaces filled with anhedral, monomineralic chalcopyrite (fig. 10I).

Physical remobilization of the ductile sulfides and 

electrum is a feature of the ores that is clearly related to 

Cretaceous deformation (figs. 6E, O, P; 8B, C). Evidence for 

flow-textured sulfides is most pronounced in areas of welldeveloped fabric where F2 and F3 folding can be discerned, as 

described by Proffett (chap. 7). Chemical remobilization and 

reprecipitation of sulfides is also a paragenetically late feature 

as indicated by the formation of veinlets and veins that crosscut the metamorphic fabric (figs. 6Q, R).

LA–ICP–MS Mineral Chemistry Studies

Methods

The LA–ICP–MS analytical technique is a relatively new 

and rapidly evolving method of solid sample microanalysis 

that holds great promise for the study of ore mineral chemistry. A focused laser beam directed onto the surface of a 

mineral grain is used to excavate, or “ablate,” a small volume 

of sample. The ablated material, in the form of micrometersize fragments and condensed droplets, is transported by 

a carrier gas into the induction port of an ICP where the 

solids are melted, dissociated, and ionized. The ions are then 

focused into a quadrupole mass spectrometer where detection 

of a broad range of elemental masses occurs. The technique 

offers a wide dynamic range with trace and ultratrace detection limits coupled with simultaneous major-element determinations. However, the introduction of solid sample material 

to the instrument as opposed to the usual solution creates 

a new set of complexities. The mechanical, chemical, and 

physical factors involved in laser ablation and transport of the 

sample to the instrument result in a variety of fractionation 

effects (Ludden and others, 1995). Elemental fractionation 

occurs primarily because of secondary heating of the sample 

crater following the laser shot and thus, consequently, is of 

particular concern in infrared laser determinations. Elements 

more volatile than the host material can be volatilized from 

the area surrounding the crater and carried to the plasma, 

resulting in erroneously high element concentrations. For an 

element such as mercury this can be as much as 30-percent 

error in a poorly designed experiment. For this study, we used 

the Q-switched mode of an Nd/YAG laser with a shot duration of approximately 4 nanoseconds. Most sulfide minerals 

measured for this study have similar melting and boiling 

points, which should also minimize the fractionation effects 

reported in the literature. A second constraint on the accuracy 

of LA–ICP–MS analyses is the paucity of well-characterized 

reference materials for use in calibration and as secondary 

standards (Ridley, 2000). To date, only a handful of studies 

report quantitative analyses of solid mineral species (Norman and others, 1996). The only previous study of traceelement content in sulfides, using the LA–ICP–MS system 

in the Denver laboratory under operating conditions using a 

free-running laser with a 100-msec pulse duration, reported 

semiquantitative elemental concentrations (Viets and others, 

1996). For the purposes of this study, a brief description of 

the Denver LA–ICP–MS system is given below and followed 

by a rough estimation of the accuracy and precision of the 

resulting analyses. For an in-depth review of the method, the 

instrumentation involved, and a detailed evaluation of the 

various fractionation factors, development of solid standards, 

and sources of analytical error, see Ridley and Lichte (1998), 

Ridley (2000), and references therein.

At the time the analyses of the Greens Creek ores were 

made, instrumentation in the Denver laboratory consisted of 

a CETAC laser, controlled by CETAC computer software, 

coupled to an ELAN 5000 ICP–MS. The Nd/YAG laser was 

operated in the Q-switched mode at a quadrupled frequency 

resulting in an ultraviolet wavelength of 266 nanometers, with a 

maximum energy output of about 3 millijoules. Analyses were 

performed on minerals previously identified by optical methods 

in standard (30 mm) polished thin sections. Thin sections were 

placed in a cylindrical Plexiglas sample cell driven by computer-controlled x-y-z stepper motors capable of movement in 

0.05-mm steps. Laser spot selection was provided by a zoomable color video camera with 15–1500X magnification. After 

some experimentation to optimize the instrument response to 

the amount of sample ablated and the delivery to the ICP–MS, 

a beam diameter of 50 mm was selected. Individual mineral 

grains were sampled with two laser pulses per spot spaced by 

one second to allow the crater to cool and to offer a wider window for the analysis of the vapor cloud by the ICP–MS.

Calibration was performed using a combination of external 

standards. The ICP–MS was initially calibrated using in-house 

solution standards that use lutetium as an internal standard. The 

LA–ICP–MS system was then calibrated against an external 

glass standard (either NIST612 or GSE, an in-house standard) 

and checked against an experimental natural sulfide before, 

during, and after sample analyses. The natural sulfide standard 

used was a centimeter-sized crystal of pyrite from the Groundhog mine in southwest New Mexico (Hawksworth and Meinert, 1990). This pyrite was selected due to its large range of 

measurable trace elements and its relative homogeneity based 

on rastered laser analysis as compared to the solution ICP–MS 

method. By conducting routine analysis of the Groundhog 

pyrite during a session, instrument performance and major 

variations in transport efficiency were monitored.

All reduction of raw ICP–MS data was performed in a 

spreadsheet using linear relationships. The instrument mass 

counts for a given element were converted to an absolute concentration by normalization to an “ablation efficiency factor.” 

The ablation efficiency factor was calculated for each analysis 

by ratio of the measured sum of all concentrations to 100 percent or in some cases by ratio of the measured concentration of 

a single major element (such as iron) based on the assumption 
LA–ICP–MS Mineral Chemistry Studies 205

Figure 7. Photomicrographs of arsenian pyrite and arsenopyrite in polished thin sections: (A–C) euhedral arsenian pyrite and 

arsenopyrite (aspy) replacing framboidal and spongy-textured pyrite (A and B: drill-core sample GC1643–03, 119.5’, 200 South orebody, C: 

rib sample 96GC–17, 49’, 344 crosscut, Lower Southwest orebody); (D) subhedral to euhedral crystals of arsenian pyrite and arsenopyrite 

overgrowing colloform pyrite (rib sample 96GC–17, 49’, 344 crosscut, Lower Southwest orebody); (E) euhedral arsenian pyrite and 

arsenopyrite overgrowing and replacing framboidal and atoll-shaped pyrite (rib sample 96GC–17, 49’, 344 crosscut, Lower Southwest 

orebody); and (F) euhedral arsenopyrite in silica and dolomite matrix (rib sample 96GC–18, 51’, 344 crosscut, Lower Southwest orebody).
206 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska
LA–ICP–MS Mineral Chemistry Studies 207

that all iron in the analysis came from a pure mineral (such as 

pyrite). In such a case, the concentration of iron is used as an 

internal standard. Use of a major element of known concentration as an internal standard was not possible due to the lack of 

sulfide electron microprobe data for the samples analyzed.

Constraints on the accuracy and precision of sulfide LA–

ICP–MS data have been difficult to assess. So far, all studies 

on natural sulfides report data as semiquantitative (Watling 

and others, 1995; Viets and others, 1996; Butler and Nesbitt, 

1999; J.L. Houghton, W.C. Shanks, and W.E. Seyfried, written 

commun., 2003). Major reasons for this include poorly quantified differences in ablation efficiency of different sulfides, a 

near universal lack of appropriate natural or synthetic sulfide 

calibration standards, and poorly characterized matrix effects 

that arise as a result of using glass or pressed powder standards. Careful work on glass standards using microprobe data 

to provide internal standard elemental concentrations has demonstrated that current LA–ICP–MS instrumentation is capable 

of 2–5 percent accuracy and precision (Norman and others, 

1996). Similar careful studies of trace elements in NiS beads, a 

matrix similar to natural sulfides, document much wider error 

limits; Shibuya and others (1998) report better than 17 percent 

accuracy for platinum-group elements and gold, and Guo and 

Lichte (1995) report between 2 and 12 percent accuracy for 

chalcophile elements. For an excellent discussion of error 

analysis of LA–ICP–MS data, see Norman and others (1996).

The data in this study are preliminary and, although absolute concentrations are presented, the results should be evaluated semiquantitatively. Major sources of uncertainty in these 

data include the lack of independently determined internal 

element concentrations, thus requiring the assumption of pure 

mineral species, the reliance on glass standards for calibration, 

the unknown volume of ablated material, the various differences in elemental fractionations and mineral ablation efficiencies, and finally, the uncertainty of target mineral purity due 

to the relatively large size of the ablation crater compared 

with the size of many of the mineral grains. This last feature is 

perhaps the largest of all the uncertainty factors.

Figure 8 (above and facing page). Photographs and 

photomicrographs of free gold (Au) in hand samples and polished 

sections: (A) rounded grains of yellow gold in matrix of sphalerite 

(sph), galena (gn), and tetrahedrite (tetr) (rib sample 96GC–13, 

25.5’, 344 crosscut, Lower Southwest orebody); (B) large grain of 

yellow gold, and galena and tetrahedrite filling crack in massive 

recrystallized pyrite (rib sample 96GC–16, 43.5’, 344 crosscut, 

Lower Southwest orebody); (C) bright yellow gold, chalcopyrite, 

sphalerite, and galena in a veinlet cutting recrystallized pyrite 

(drill-core sample GC1643–06, 119.5’, 200 South orebody); (D) 

grains of yellow gold in contact with pyrite and arsenopyrite 

(aspy) (rib sample 96GC–19, 53’, 344 crosscut, Lower Southwest 

orebody); (E) yellow gold included within clean, recrystallized 

pyrite (rib sample 96GC–13, 25.5’, 344 crosscut, Lower Southwest 

orebody); (F and G) silver-white electrum filling fractures and 

coating fracture surfaces in drill core (GC1155, 319.5’, Lower 

Southwest orebody); and (H) hand sample showing electrum 

in thin veinlets and spaced sheets that occupy fractures up to 

0.5 millimeter wide (rib sample, 30 East decline, 650’ level, East 

orebody). These fractures are paragenetically late and appear to 

be tension gashes and piercement structures that occur at high 

angles to S2 foliation.
208 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Au

Ag

Hg

S

Cu

GC-CONC-5 GRAIN #6 LA-ICP-MS TRAVERSE GC-CONC-5 GRAIN #8 LA-ICP-MS TRAVERSE

Au

Ag

Hg

Pb

Sb

GC-CONC-5 GRAIN #9 LA-ICP-MS TRAVERSE

Au

Ag

Cu

Hg

Pb

GC-CONC-5 GRAIN #4 LA-ICP-MS TRAVERSE

Au

Ag

Cu

S

Hg

GC-CONC-5 GRAIN #7 LA-ICP-MS TRAVERSE

Ag

Au

Hg

Cd

Sb

GC-CONC-5 GRAIN #10 LA-ICP-MS TRAVERSE

Ag

Cu

AuHg

Pb

0 10 20 30 40

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60 70 80 90

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ANALOGUE INTENSITY

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GC-CONC-5 GRAIN #2 LA-ICP-MS TRAVERSE

Au

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HgS

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A

GC-CONC-5 GRAIN #3 LA-ICP-MS TRAVERSE

Au

Ag

Hg

Sb S

103

0 10 20 30 40 50 60 70 80 90

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B

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Ag

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GC-CONC-5 GRAIN #5 LA-ICP-MS TRAVERSE

C

D E F

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50

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103 103 103 ANALOGUE INTENSITY

H I

Figure 9. LA–ICP–MS traverses across heavy concentrate grains recovered from the Greens Creek mill. All grains analyzed are from 

the coarsest fraction of sample GC–CONC–5. Each profile was obtained by operating the laser in continuous mode across a traverse of 

approximately 100 micrometers with the ICP–MS detectors set to record the relative abundances, measured as the log10 of analogue 

intensity, of five selected elements. Each plot exhibits the relative abundances of the elements selected and shows the variation in 

relative concentration with time (distance along the traverse). Note that plots A and B have a greater y-axis range than plots C–I. Plots 

a and b exhibit the two types of gold identified at Greens Creek: yellow gold of high fineness and silver-white electrum composed of an 

amalgam of gold, silver, and mercury. Plot C is an example of electrum, plots D–F are analyses of yellow gold grains, plot g represents 

a possible copper-rich variant of yellow gold, and plots h and i are examples of nearly pure native silver grains. (A) grain #2, Au and Ag 

only, high Au/Ag; (B) grain #3, Au, Ag, and Hg, lower Au/Ag; (C) grain #5, Au, Ag, and Hg, lower Au/Ag; (D) grain #6, Au and Ag, high Au/

Ag; (E) grain #8, Au and Ag, high Au/Ag; (F ) grain #9, Au and Ag, high Au/Ag; (G) grain #4, Au, Ag, and Cu, high Au/Ag; (H) grain #7, nearly 

pure Ag; and (I) grain #10, nearly pure Ag.
LA–ICP–MS Mineral Chemistry Studies 209

Results

Progressive recrystallization of the primary-textured 

ores and the remobilization of base-metal sulfides have had a 

profound effect on the siting of trace elements in the ores. LA–

ICP–MS studies indicate that a wide range of trace elements 

is present in the major primary-textured sulfide minerals at 

relatively high concentrations (fig. 11). As the recrystallization 

process progresses, trace-element abundances decrease in later 

formed pyrites and increase predictably in recrystallized and 

remobilized base-metal sulfides. A second result of the metamorphic refining process is a decrease in the variety of intermediate solid solution sulfosalt minerals and the formation of 

a less diverse mineral assemblage with a greater proportion of 

the trace elements contained in discrete end-member mineral 

phases such as sphalerite and tetrahedrite.

The data from the LA–ICP–MS analyses are presented in 

tables 2–7. These tables contain data on selected trace-element 

abundances in primary-textured pyrite, recrystallized pyrite, 

arsenian pyrite, galena, sphalerite, and tetrahedrite. Plots 

showing the changes in major- and trace-element concentrations in pyrite, sphalerite, and galena with modification from 

primary to recrystallized and remobilized textures are shown 

in figures 12a–ay. Tables 8–10 contain data on primarytextured, recrystallized, and remobilized mixed mineral aggregates. Even though these data are considered semiquantitative 

for the reasons discussed, the order of magnitude differences 

in trace-element concentrations within these data reflects 

usable information on the relative abundances and siting of 

trace elements in minerals and on the range of trace-element 

abundances in the various major types of ores present at 

Greens Creek. These data are discussed below.

Typical trace-element abundances in primary-textured ores 

as determined by LA–ICP–MS are difficult to interpret due to 

the fine-scale banding and grain sizes present in the framboidal 

aggregates and colloform textures. In most cases, the 50-mm 

beam size of the instrument is incapable of acquiring data from 

single phases within these ores. Smaller beam size would result 

in higher limits of detection because the amount of material 

sampled varies with the square of the crater diameter. Thus, 

there is a tradeoff between detectability and sampling integrity 

for these fine-grained minerals. However, data from a limited 

number of analyses of primary-textured pyrite (mostly spongy 

pyrite; table 2) and primary-textured ores of mixed mineralogy 

(table 8) provide a baseline against which to compare analyses of discrete recrystallized or remobilized grains. Typical 

trace-element abundances in primary-textured pyrite and mixed 

primary-textured ores are: gold at <240 parts per billion (ppb), 

silver commonly in the hundreds of parts per million (ppm) and 

as high as 19,400 ppm, and arsenic at 0.1–4.8 percent. Antimony is clearly the dominant trace element present ubiquitously 

in the primary-textured pyritic ores near the 1 percent level, and 

rises to the 9 percent level. Thallium is present in primary ores 

in the hundreds of parts per million and rises as high as 2,300 

ppm. Molybdenum is present from the hundreds to several 

thousand parts per million and rises as high as 11,930 ppm.

LA–ICP–MS analyses of recrystallized and remobilized 

phases demonstrate that trace elements are predictably concentrated in fewer, more stoichiometrically ordered minerals. 

After free gold, the next consistently high concentrations of 

gold, up to 2,613 ppb, occur in arsenian pyrite (table 4). Gold 

is inhomogeneously distributed, tends to be concentrated 

near the edges of euhedral grains, and is probably present 

as discrete, submicrometer inclusions within the recrystallized pyrite/arsenopyrite. The next most obvious residence 

of gold, at the 0–700-ppb range with a high of 5,401 ppb, is 

in the secondary masses of sphalerite and tetrahedrite (table 

9). The relatively uniform distribution of gold in these phases 

suggests that it forms a solid solution rather than occurring 

as inclusions (fig. 12y). Silver is present in pyrargyrite and in 

secondary tetrahedrite at 2.9 to 6.7 percent (table 7). Grains 

of other secondary silver-bearing minerals known to be present at Greens Creek of a size large enough to analyze were 

not found. Other silver-bearing minerals are recrystallized 

and remobilized “clean” crystals of pyrite, arsenian pyrite/

arsenopyrite, and galena that typically contain hundreds 

of parts per million and as high as 3,740 ppm (table 5; fig. 

12ao). The silver content of sphalerite is extremely variable 

but generally low. Copper is present in chalcopyrite and in tetrahedrite up to 47 percent, and zinc is present in tetrahedrite 

at 2.4–7.7 percent (table 7). Arsenic is present in arsenian 

pyrite/arsenopyrite at the 19–24 percent level (table 4), and 

in late tetrahedrite in the 2.4–10.2 percent range. Recrystallized pyrite and large secondary anhedral grains of sphalerite and galena typically have less than 0.5 percent arsenic, 

with maximum values of 1.9 percent. Antimony is a major 

component of tetrahedrite, is present at 7.6–28 percent and 

is clearly the dominant and ubiquitous trace element present 

in Greens Creek ores. It is present at more than 1,000 ppm 

in every mineral examined with the exceptions of recrystallized pyrite and secondary sphalerite (figs. 12f, w, and aj). 

Mercury is present at the 58–2,390-ppm level in secondary 

sphalerite and tetrahedrite and is lowest in secondary galena 

and arsenian pyrite (figs. 12i, z, and aq). Thallium is present in secondary galena to just less than 1.2 percent (table 5, 

fig. 12ar). Cadmium is present in sphalerite up to 2,731 ppm. 

Chromium, cobalt, and nickel are ubiquitous and appear to be 

associated. These elements occur routinely at levels of tens 

to hundreds of parts per million in all minerals and ore types. 

Note that their concentrations are very similar in primary and 

recrystallized phases but tend to drop to low abundances in 

the remobilized phases (figs. 12n, o, p, ae, af, ag, av, aw, and 

ax; tables 8–10). Bismuth, a trace element that is commonly 

enriched in sulfosalt-bearing massive sulfide deposits, occurs 

in notably low concentrations in Greens Creek ores. Selenium 

occurs in all ore types up to 6,000 ppm and is present at 1.1 

percent and 1.8 percent in recrystallized pyrite and sphalerite, respectively. Interestingly, the distribution of selenium 

is generally antithetic to that of antimony, which is notably 

low in recrystallized pyrite and sphalerite. Selenium shares a 

distribution similar to chromium, cobalt, and nickel.
210 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Figure 10 (above and facing page). Photographs and photomicrographs showing textural relationships in Greens Creek ores: (A) 

polyframboidal pyrite aggregate in galena or lead-antimony sulfosalt matrix (rib sample 96GC–12, 21.5’, 344 crosscut, Lower Southwest 

orebody); (B) successive bands of colloform-textured base-metal sulfides without intervening pyrite bands, within predominantly pyritic 

primary textured masses (rib sample 96GC–16, 43.5’, 344 crosscut, Lower Southwest orebody); (C) framboids composed of chalcopyrite 

crystallites in a matrix of pyrite, quartz, and dolomite (drill-core sample GC1527–15, 454.2’, Northwest orebody); (D) incipient recrystallization 

of individual framboids resulting in atoll-shaped grains, with centers filled with base-metal sulfides and rims of clean, bright pyrite (drill-core 

sample GC1527–09, 402.5’, Northwest orebody); (E) an aggregate of framboids developed into a large, spongy-textured mass with numerous 

discrete inclusions of base-metal sulfides and graphite (drill-core sample GC1643–05, 100.5’, 200 South orebody); (F ) a felty concentration of 
LA–ICP–MS Mineral Chemistry Studies 211

needle- or lath-shaped crystals of recrystallized graphite that are aligned subparallel to S2 foliation (rib sample 96GC–16, 43.5’, 344 crosscut, 

Lower Southwest orebody); (G) progressive recrystallization showing a large area of inclusion-free pyrite with relict framboidal shapes 

preserved in the interior of the mass and euhedral-shaped growth zones defined by thin bands of galena (drill-core sample GC1643–07, 

143.5’, 200 South orebody); (H) fully recrystallized pyritic ore showing very large areas of inclusion-free, monomineralic pyrite with 

polygonal grain boundaries cut by chalcopyrite-galena-tetrahedrite veinlets (drill-core sample GC1643–04, 75’, 200 South orebody); and (I) 

chalcopyrite-rich MFP showing the progression from spongy-textured masses with chalcopyrite matrix and numerous small chalcopyrite 

inclusions on the right, to clean, monomineralic, polygonal-textured masses of pyrite with grain boundaries and intercrystal spaces filled 

with anhedral, monomineralic chalcopyrite on the left (drill-core sample GC1527–14, 447.2’, Northwest orebody).
LA–ICP–MS 

Fe Pb Zn Cu As Sb Ag Au Hg Tl Mo Cd Bi Cr Co Ni 

ELEMENTS IN ORE ELEMENTS

LOG PARTS PER MILLION 1,000

10,000

100,000

1,000,000

100

10

1

90th75th

50th (median)

25th

10th

OutlierOutlier

Figure 11. Summary LA–ICP–MS data on sulfide ore minerals in the Greens Creek deposit. Box plots of percentiles shows the log10 concentration ra

recrystallized, and remobilized ore textures for each of 19 elements. All elements measured in parts per million, except gold, which is in parts per billeach box show the geometric mean (median value). Each box extends from the 25th to the 75th percentile, whiskers extend out to the 5th and 95th peclosed circles show individual outlier values. Data plotted from data in tables 2–10.
Table 2. Trace-element composition of primary pyrite as determined by Laser Ablation Inductively Coupled Plasma – –Mass Spectroscopy 

Sample #

Fe

%

Pb

%

As

%

Sb

%

Zn

ppm

Cu

ppm

Ag

ppm

Au

ppb

Hg

ppm

Tl

ppm

Mo

ppm

Cd

ppm

Bi

ppm

Cr

ppm

p

96GC-25

96GC-2596GC-25

96GC-25

96GC-25

96GC-25

96GC-2596GC-25

96GC-25

96GC-25

meanstd. deviation

maximum

minimum

34.8

44.135.4

30.9

32.3

44.8

24.836.6

35.7

42.936.2

6.3

44.8

24.8

16.9

1.1

19.9

17.8

16.3

1.3

35.010.6

17.4

4.1

14.110.3

35.0

1.1

0.60.7

0.3

0.8

1.1

0.1

0.61.3

0.6

1.5

0.80.4

1.5

0.1

0.20.6

0.1

1.1

0.4

0.1

0.50.8

0.3

0.3

0.40.3

1.1

0.1

25,166

1,484

538

46,813

56,832

12,694

15,71117,645

3,201

862

18,09519,758

56,832

538

4,400

13,826

683

23,025

7,009

1,193

12,12222,264

6,242

223

9,0998,469

23,025

223

765

1,929

2,4003,217

1,302

338

2,1014,027

1,310

291

1,7681,220

4,027

291

49

45

3974

47

240

5582

124

317963

240

31

66

85

65

123

129

71

45

123

37

307736

129

30

591

107

2,3041,067

1,072

37

535

1,433

1,270

690911675

2,304

37

2,585

48

524

2,703

2,284

235

2,5621,747

2,396

115

1,5201,1452,703

48

77

31

26

167

196

4980

136

146

118103

59

196

26

6

3

1

9

2

1215

8

20

386

20

1

81

146

181

96

199

137411848

566

598326264848

81
Table 3. Trace-element composition of recrystallized pyrite as determined by Laser Ablation–Inductively Coupled Plasma Mass Spectrosc

– Sample # Fe% As% Pb ppm Zn ppm Cu ppm Sb ppm Ag ppm Au ppb Hg ppm Tl ppm Mo ppm Cd ppm Bi ppm C

ppm 

96GC-18 96GC-18 96GC-18 96GC-18 96GC-18 96GC-18 96GC-18 96GC-19 96GC-19 96GC-19 96GC-19 96GC-19 96GC-19meanstd. deviationmaximumminimum

45.845.743.446.145.344.845.744.046.345.546.346.343.9

45.3

1.0

46.3

43.4

0.40.11.50.20.30.30.51.70.10.60.10.30.4

0.5

0.5

1.7

0.1

1,076

53

2,230

708

2,292

744

95

11,570

786

7,5631,430

584

4,704

2,603

3,423

11,570

53

2,031

1,513

6,211

1,239

521

2,790

0

9,8121,474

1,141

0

1,121

28,550

4,339

7,778

28,550

0

541

2,003

553

902399700

224

55

446

349

721

153

2,578

740

737

2,578

55

948

228

9,743

435

8,9456,995

229

330

0

49

94

60

156

2,170

3,697

9,743

0

307

518

850

76

126687

360

100

80

110

123

7866

268

263

850

66

33

0

222

5020

103

66

54

20

45

0

1656

53

58

222

0

4225

190

24

212

146

0

23

32

31

23

3247

64

70

212

0

109

30

1,109

37

1,080

912

36

123

50

91

68

26

0

282

432

1,109

0

78

235

194

155

120

253

41

62

170

84

38

40

0

113

82

253

0

78

52

228

49

70

223

119

51

114

44

45

487

270

141

130

487

44

14

15

0

14

5

29

39

9

5

12

2

18

12

13

11

39

0

476

610

990

340484

912

326

195

255

392

416

466

549

493

233

990

195
Table 5. Trace-element composition of galena as determined by Laser Ablation–Inductively Coupled Plasma Mass Spectroscopy analyses. –

Sample # Mineral texture

Pb

%

Sb

%

Fe

ppm

Zn

ppm

Cu

ppm

As

ppm

Ag

ppm

Au

ppb

Hg

ppm

Tl

ppm

Mo

ppm

Cd

ppm

Bi

ppm

p

96GC-26b

96GC-26b

96GC-19

96GC-19

96GC-19

96GC-19

96GC-19

96GC-19

96GC-19

96GC-26b96GC-26b

96GC-26b

96GC-26b

mean

std. deviation

maximum

minimum

primary

primary

recrystallized

recrystallized

recrystallized

recrystallized

recrystallized

recrystallized

recrystallized

remobilizedremobilized

remobilized

remobilized

75.7

78.3

84.1

84.8

85.5

85.5

85.4

85.4

85.2

86.579.4

79.9

82.9

83.0

3.5

86.5

75.7

3.2

3.0

0.3

0.3

0.2

0.3

0.3

0.3

0.3

0.24.1

3.6

0.7

1.3

1.5

4.1

0.2

3,513

2,767

4,557

687

153

0

97

418

903

196270

3,102

2,151

1,447

1,565

4,557

0

36,069

619

845

888

420

271

512

271

480

8475

1,252

3,012

3,446

9,832

36,069

75

176

4,810

79

117

76

122

137

114

62

154

83

95

10,970

1,307

3,181

10,970

62

14,015

6,435

114

135

331

232

266

498

556

728

18,801

14,793

5,118

4,771

6,719

18,801

114

234

37

891

773

518

749

761

640

791

222

97

85

3,740

734

955

3,740

37

12

11

19

10

5

8

3

22

2

19

3

6

9

6

22

1

56

22

16

16

11

11

14

15

14

6049

23

88

30

25

88

11

124

327

11,724

11,558

8,515

8,275

8,654

8,597

8,655

11

237

152

11

5,142

4,935

11,724

11

27

35

30

19

28

31

46

18

36

35

27

1725

12

46

3

47

24

12

31

29

24

26

0

35

1352

14

5528

16

55

0

3

3

4

2

3

4

4

2

2

21

1

12

1

41

Table 4. Trace-element composition of arsenian pyrite as determined by Laser Ablation Inductively Coupled Plasma – –Mass Spectrosco

Fe Zn As Sb Pb Cu Ag Au Hg Tl Mo Cd 

Sample # Mineral texture % % % % ppm ppm ppm ppb ppm ppm ppm ppm pp

96GC-18 recrystallized 25.0 3.3 24.1 0.5 4,285 1,258 361 95 59 24 4,061 233 

96GC-19 recrystallized 30.9 0.8 18.9 0.2 647 349 2,478 2,613 9 32 158 71 

96GC-19 recrystallized 26.8 2.3 23.0 0.3 620 577 225 1,172 14 48 1,566 256 

mean 27.6 2.1 22.0 0.4 1,851 728 1,021 1,294 27 35 1,928 187 

std. deviation 3.0 1.3 2.7 0.2 2,109 473 1,264 1,263 28 12 1,977 101 

maximum 30.9 3.3 24.1 0.5 4,285 1,258 2,478 2,613 59 48 4,061 256 

minimum 25.0 0.8 18.9 0.2 620 349 225 95 9 24 158 71 
Table 6. Trace-element composition of sphalerite as determined by Laser Ablation–Inductively Coupled Plasma Mass Spectroscopy analyses. – Sample # Mineral texture Zn% Fe ppm Pb ppm Cu ppm As ppm Sb ppm Ag ppm Au ppb Hg ppm Tl ppm Mo ppm Cd ppm Bi ppm 

96GC-25 96GC-25 96GC-19 96GC-19 96GC-19 96GC-19 96GC-19 96GC-19 96GC-19 96GC-19 96GC-25 96GC-26b

meanstd. deviation

maximum

minimum

primaryprimaryrecrystallizedrecrystallizedrecrystallizedrecrystallized

recrystallized

recrystallizedrecrystallizedrecrystallized

recrystallized

recrystallized

35.435.1

62.662.765.862.0

63.4

65.365.557.1

62.4

64.6

58.5

11.1

65.8

35.1

159,769155,144

7,0647,6734,7809,138

2,702

5,5465,420

19,407

12,227

1,589

32,538

58,545

159,769

1,589

98,16668,913

18,78812,170

152

16,250

5,517

169

78

128

15,494

17,558

21,115

30,718

98,166

78

3,170

30,489

100454822589

4,100

556

0

646

4,968

962

3,905

8,534

30,489

0

4,939

5,855

843404219779

5,199

272

0

504

1,320

685

1,752

2,194

5,855

0

1,8138,637

314474270392

9,766

179

99

176

7,562

558

2,520

3,756

9,766

99

650

2,637

588645

98

821

1,256

262

187

78,422

1,734

86

7,282

22,416

78,422

86

41

50

375365

601

448

644

697

717

772

55

94

405

285

772

41

58

742

371401

1,115

521

1,142

1,301

1,184

1,351

1,581

2,3901,013

639

2,390

58

161

42

314245

277

342

361

347

350

304

36

58

236

128

361

36

1,899

368

247154

119

346

133

224

175

117

57

87

327

504

1,899

57

376396

2,7292,570

2,707

2,731

2,438

2,227

2,292

1,301

625

1,045

1,786

962

2,731

376

56

41

9

27

23

20

24

15

4

10

22

17

11

41

4

2

2
Table 7. Trace-element composition of tetrahedrite as determined by Laser Ablation–Inductively Coupled Plasma Mass Spectroscopy 

–

Sample # Mineral texture

Fe

%

Zn

%

Cu

%

As

%

Sb

%

Ag

%

Pb

ppm

Au

ppb

Hg

ppm

Tl

ppm

Mo

ppm

Cd

ppm

Bi

ppm

Cr

ppm

96GC-1896GC-1996GC-1996GC-1996GC-1996GC-1996GC-19

96GC-1996GC-2596GC-2596GC-2596GC-2596GC-25

recrystallizedrecrystallizedrecrystallizedrecrystallizedrecrystallizedrecrystallizedrecrystallized

recrystallizedrecrystallizedrecrystallized

recrystallized

recrystallized

remobilized

3.9

1.55.31.81.41.6

2.01.9

3.13.1

3.6

1.7

2.8

2.4

4.03.73.34.93.7

3.63.8

4.14.2

4.6

7.7

4.0

37.5

33.432.934.333.934.0

36.535.8

38.340.5

38.5

47.1

38.1

2.9

2.74.12.92.42.5

4.14.2

7.79.7

10.2

6.5

7.0

21.1

27.521.227.127.227.8

22.923.4

13.010.7

8.9

7.6

12.9

6.2

5.94.65.55.35.5

5.05.1

6.74.4

4.2

2.9

5.7

270

226145892183162

98

146

6,741

3,542

28,714

10,519

34,783

429

311474291243301

409

472

58

16

32

97

20

804

485566513416545

506

600

879

775

781

1,273

894

141

92

152132123

95

163

223

67

51

47

93

24

35

48

671680

22

111

127

71

391

164

66

40

805

990

931981954

984

730

838

808

980

903

210

1,144

2

5

11

34

8

11

5

3

4

2

5

0

71

167

546

344282

286

606

811

32

0

119

79

370

meanstd. deviationmaximum

minimum

2.6

1.2

5.3

1.4

4.2

1.2

7.7

2.4

37.0

3.8

47.1

32.9

5.2

2.8

10.2

2.4

19.3

7.6

27.8

7.6

5.2

1.0

6.7

2.9

6,648

11,653

34,783

98

242

178

474

16

695

237

1,273

416

108

55

223

24

95

99

391

16

866

224

1,144

210

5

3

11

0

286

247

81

0
Table 8. Trace-element composition of mixed primary- textured mineral aggregates as determined by Laser Ablation–Inductively Coupled Plasma–Ma

Sample # Mineralogy Fe% Pb% Zn% Cu% As% Sb% Ag ppm Au ppb Hg ppm Tl ppm Mo ppm Cd ppm Bi ppm C

pp

96GC-25 96GC-25 96GC-25 96GC-25 96GC-26b 96GC-25 96GC-25 96GC-25 96GC-25 96GC-25 96GC-25 96GC-26b 96GC-26b 96GC-26b 96GC-26b 96GC-25 96GC-25 96GC-25 96GC-26b 96GC-26b 96GC-26b 96GC-26b 96GC-26b 96GC-26b 96GC-26b 96GC-26b 96GC-26b 96GC-25 96GC-25 96GC-18 96GC-18 96GC-18 96GC-25 96GC-25 96GC-25 96GC-25

meanstd. deviationmaximum

minimum

???

gn-gcrgn-py-tetr-sphgn-tetrgn-tetrpy-gn

py-gn

py-gn

py-gn-qtzpy-gn-sph

py-gn-sph

py-gn-tetr-sph

py-gn-tetr-sph

py-qtzpy-sph

py-sph-gn

py-sph-gn

py-sph-gn

py-sph-gn

py-sph-gn

py-sph-gn

py-sph-gn

py-sph-gn

py-sph-gn

py-sph-gn

py-tetrpy-tetr

py-tetr-gnpy-tetr-gnpy-tetr-gn

py-tetr-gnpy-tetr-gn-sph

py-tetr-qtztetr-gn

31.622.629.1

22.0

14.6

2.3

27.0

34.3

31.3

26.0

27.2

20.3

16.5

19.4

22.131.8

31.1

28.2

14.8

34.9

27.3

22.8

26.4

22.5

26.4

24.9

18.1

38.741.245.143.745.1

13.624.3

43.9

6.9

26.6

10.2

45.1

2.3

20.133.828.2

42.0

41.0

58.020.1

17.5

16.2

36.6

35.0

36.2

30.3

28.0

13.618.2

7.9

14.1

44.6

5.9

11.3

7.1

12.0

7.6

5.1

6.2

11.3

4.91.10.92.90.5

27.114.2

2.2

25.9

19.1

14.7

58.0

0.5

0.42.50.4

1.2

6.4

0.91.7

0.5

3.6

0.1

0.0

7.7

17.5

12.4

20.0

0.4

14.514.4

8.8

11.4

17.8

26.7

18.5

27.6

24.0

25.4

30.3

4.93.50.10.20.0

1.46.6

0.1

1.3

8.7

9.6

30.3

0.0

1.13.01.2

0.7

6.2

12.011.0

1.9

0.9

0.5

0.1

0.2

1.2

2.2

2.54.3

0.60.5

0.3

0.2

0.2

0.3

0.1

0.2

0.1

0.1

0.2

1.42.20.20.20.1

22.2

5.1

1.1

29.0

3.1

6.2

29.0

0.1

1.01.30.9

0.5

1.4

3.00.6

0.8

0.7

0.5

0.6

0.6

0.5

1.1

0.81.3

0.50.4

0.5

0.3

0.4

0.7

0.3

0.4

0.6

0.3

0.7

0.80.70.71.21.1

2.41.4

0.7

4.8

1.0

0.9

4.8

0.3

4.01.60.4

0.3

0.9

3.70.8

0.8

4.8

0.2

0.1

1.4

0.7

1.7

1.11.3

0.30.2

1.8

0.3

0.5

0.6

0.4

0.5

0.4

0.3

0.7

0.40.60.30.20.1

3.29.2

0.3

4.9

1.4

1.9

9.2

0.1

1,2035,8712,097

1,425

3,125

15,427

3,605

5,224

1,764

936

644

670

2,371

2,663

2,9995,271

998846

690

487

578

834

518

723

501

457

368

1,3222,639

224221242

11,825

5,350

1,438

19,399

2,915

4,274

19,399

221

604755

91

5

1178

32

70

64

81

28

41

2

16

156

4943

15

32

39

32

48

8

30

77

22

6362

132

9696

96

31

66

207

58

43

207

2

3886

105

23

88

314

66

56

86

19

53

81

189

250

215

85

121164

165

113

206

381

163

263

216

265

278

7266846751

309

158

53

237

144

95

381

19

399768979

633

157

77

324

1,059

693

174

839

240

612

232

270

2,155

312429

312

134

301

995

364

159

169

1,106

153

1,461

43

913729268

719

636

891

59

549

451

2,155

43

4,973

11,930

7,026

3,533

169

16

3,704

898

2,092

210

618

1,248

492

458

990804

4,2931,736

435

606

1,037

2,562

1,530

1,003

674

821

221

7,427

88

3,5531,914

756

1,230

1,831

332

481

1,991

2,510

11,930

16

43

223143

54

417

218163

62

158

61

75

250

731

617

834135

387347

370

392

817

980

746

754

589

740

1,295

820215128

24

177

270

417

106

418

394

319

1,295

24

16

19

10

8

08

3

8

3

7

2

7

12

10

6

10

6

8

11

4

13

1

15

16

16

25

064

1816

1

6

11

10

9

6

25

0

131976

24

38

2

41

5

10

28

15

23

53

59

1,25

28

1,20

16

36

38

48

64

46

44

55

17

59

1538282050

7

21

59

3

37

28

1,25

2
Table 9. Trace-element composition of recrystallized mixed mineral aggregates as determined by Laser Ablation–Inductively Coupled Plasma– Mass Spec

Sample # Mineralogy

Fe

%

Pb

%

Zn

%

Cu

%

As

%

Sb

%

Ag

ppm

Au

ppb

Hg

ppm

Tl

ppm

Mo

ppm

Cd

ppm

Bi

ppm

Cr

ppm

96GC-1896GC-2596GC-2596GC-1996GC-1996GC-26b96GC-26b

96GC-26b96GC-2596GC-1896GC-1996GC-1996GC-1996GC-26b96GC-26b96GC-26b96GC-26b96GC-26b96GC-26b96GC-1896GC-25

96GC-26b

96GC-26b96GC-1896GC-1996GC-1996GC-1996GC-1996GC-1996GC-2596GC-2596GC-26b

meanstd. deviation

maximum

minimum

aspy-gngn-sph-dologn-tetrpy-gnpy-gn

py-gn-sphpy-gn-sph

py-gn-sph

py-qtzpy-sphpy-sphpy-sph-gnpy-sph-gn

py-sph-gnpy-sph-gnpy-sph-gnpy-sph-gnpy-sph-gnpy-sph-gn

py-sph-gn-tetrpy-tetrsph-dolo

sph-py-gn

sph-tetrsph-tetrsph-tetrtetr-gntetr-gntetr-gntetr-sphtetr-sph

tetr-sph-gn

21.0

29.9

1.3

33.037.5

13.431.2

27.3

24.4

32.138.039.738.1

29.113.723.623.340.234.3

29.5

31.0

2.8

20.1

1.90.80.4

1.81.51.7

3.6

8.19.4

20.1

14.2

40.2

0.4

25.8

2.3

44.3

12.611.4

31.618.8

14.8

37.5

0.33.62.92.1

20.524.8

7.4

14.2

4.2

6.8

7.3

6.3

1.0

9.0

0.00.01.4

0.2

13.7

0.1

1.7

6.0

24.4

11.2

11.8

44.3

0.0

0.7

10.6

1.4

1.02.8

19.9

5.3

14.0

0.2

19.8

9.53.46.1

8.5

26.5

26.4

20.9

4.6

11.6

8.1

4.9

60.8

30.4

43.041.858.5

3.6

3.2

4.6

27.7

16.520.5

16.1

16.3

60.8

0.2

1.5

0.3

21.5

0.10.0

0.9

0.1

0.3

1.4

0.2

0.00.60.1

0.1

0.3

0.1

0.40.2

0.1

5.1

7.0

0.2

0.1

8.1

12.7

2.2

32.1

27.1

32.6

16.2

18.1

9.1

6.2

9.9

32.6

0.0

12.3

0.6

4.3

7.71.1

0.8

0.9

0.9

0.7

0.2

0.13.23.9

0.2

0.6

0.3

0.50.5

0.2

0.6

3.9

0.3

0.3

0.7

1.0

0.8

2.8

2.5

2.8

4.2

6.7

1.0

2.1

2.7

12.3

0.1

0.5

0.2

5.3

0.30.1

1.6

1.3

1.0

0.5

0.1

0.00.20.1

0.4

0.6

0.5

0.50.2

0.4

5.0

1.0

0.2

0.4

14.0

11.6

3.4

28.5

23.3

26.7

7.2

9.5

4.4

4.6

7.9

28.5

0.0

494

23952

23107

861

64

1749

532

887

2013

374

0

505263

3,126

4,075

487

1,1662,781

161

10,149

17,964

557

636

1,422

21,153

4,566

55,492

51,249

61,569

96,112

34,892

13,988

13,636

22,893

96,112

0

196

164

10

76

32

13

88

136

86

411

34

6510

10

43

87

72

176

118

70

119

89

60

579

353

745

428

307

346

169

318

5,401

338

941

5,401

10

79

109

306

26

51

247

76

209

60

173

50

5366

86

133

241

248

264

655

158

284

1,667

357

1,359

549

1,283

698

566

618

1,573

942

128

416

466

1,667

26

2158

651

8

743

756

290

122

360

1960

68

230

160165

895

316

305

158

203

164

764

970

116

401260

117

396

140

1,431

144

124

303

193

471

525

2,158

8

1601

2680

7

538

194

574

168

1695

231

341

135

253285

516

597

3,316

1,334

382

217

3,989

2,688

180870147

25

0

60

56

5

117

889

178

758

1,041

3,989

0

1191

546

321

41

182

464

225

709

110

657

515

437450

179

623

874

968112

127

531

239

1,843

491

4,6311,283

2,022

947

864

1,060

501

1,133

710

781

849

4,631

41

37

33

1

3

14

1113

170

10

9

21

2018

4

7

15

7

16

37

23

5

9

10

48

28

10

5

3

6

13

2

18

30

170

1

420

722

31

259312

178275

365

233

218

419

671630

46

350

277

228995

942

289

427

223

403438648

757

380

289

551

294

4,826

22

535

819

4,826

22
Table 10. Trace-element composition of remobilized mixed mineral aggregates as determined by Laser Ablation–Inductively Coupled Plasma Mass Spectro

– Sample # Mineralogy Fe% Pb% Zn% Cu% As% Sb% Ag ppm Au ppb Hg ppm Tl ppm Mo ppm Cd ppm Bi ppm 

p

96GC-26b 96GC-26b 96GC-26b 96GC-26b 96GC-26b 96GC-26b 96GC-26b 96GC-26b

meanstd. deviation

maximum

minimum

gn-tetrgn-tetrgn-tetrgn-tetrpy-gn-sphsph-py-gntetr-gntetr-py-sph-gn

0.2

0.0

0.70.9

16.6

13.7

1.6

18.0

6.5

8.1

18.0

0.0

81.2

81.1

74.458.8

32.0

10.2

36.1

4.6

47.3

31.0

81.2

4.6

0.3

0.0

0.61.3

16.3

37.4

2.2

6.1

8.0

13.1

37.4

0.0

2.2

0.0

4.7

11.5

0.6

0.1

22.129.4

8.8

11.2

29.4

0.0

0.7

1.3

1.4

2.90.6

0.1

4.43.4

1.9

1.5

4.4

0.1

0.8

3.4

2.1

4.90.6

1.7

8.91.5

3.0

2.8

8.9

0.6

4,483

77

7,903

20,229

3,307

2,497

37,43919,174

11,889

12,804

37,439

77

1

1

10

7

46

21

4

79

21

28

79

1

111

21

209

310

50

920

360

259

280

286

920

21

10

157

10

48

597

71

95

110

137

192

597

10

6

5

7

21

206

365

53

123

98

129

365

5

104

7

208

468

301

606

680

2,095

558

664

2,095

7

4

2

4

4

1

10

4

8

5

3

10

1

1

7

2

3

2

2

7
LA–ICP–MS Mineral Chemistry Studies 221

IRON IN PYRITE

250,000

300,000

350,000

400,000

450,000

500,000

primary

recrystallized

LEAD IN PYRITE

0

100,000

200,000

300,000

400,000

ZINC IN PYRITE

TEXTURE TEXTURE

PARTS PER MILLION

PARTS PER MILLION

0

10,000

20,000

30,000

40,000

50,000

60,000

COPPER IN PYRITE

0

5,000

10,000

15,000

20,000

25,000

a b

c d

Figure 12. Single element plots of LA–ICP–MS data showing the range of elemental abundances of metals in primary and 

recrystallized pyrite (a–q) and sphalerite (r–ah), and in primary, recrystallized, and remobilized galena (ai–ay). (a) Fe in pyrite, 

(b) Pb in pyrite, (c) Zn in pyrite, (d) Cu in pyrite, (e) As in pyrite, (f) Sb in pyrite, (g) Ag in pyrite, (h) Au in pyrite, (i) Hg in pyrite, 

(j) Tl in pyrite, (k) Mo in pyrite, (l) Cd in pyrite, (m) Bi in pyrite, (n) Cr in pyrite, (o) Co in pyrite, (p) Ni in pyrite, (q) Se in pyrite, 

(r) Fe in sphalerite, (s) Pb in sphalerite, (t) Zn in sphalerite, (u) Cu in sphalerite, (v) As in sphalerite, (w) Sb in sphalerite, (x) Ag 

in sphalerite, (y) Au in sphalerite, (z) Hg in sphalerite, (aa) Tl in sphalerite, (ab) Mo in sphalerite, (ac) Cd in sphalerite, (ad) Bi 

in sphalerite, (ae) Cr in sphalerite, (af) Co in sphalerite, (ag) Ni in sphalerite, (ah) Se in sphalerite, (ai) Pb in galena, (aj) Sb in 

galena, (ak) Fe in galena, (al) Zn in galena, (am) Cu in galena, (an) As in galena, (ao) Ag in galena, (ap) Au in galena, (aq) Hg 

in galena, (ar) Tl in galena, (as) Mo in galena, (at) Cd in galena, (au) Bi in galena, (av) Cr in galena, (aw) Co in galena, (ax) Ni 

in galena, (ay) Se in galena. Pyrite data plotted from tables 2 and 3. Galena data plotted from table 5. Sphalerite data plotted 

from table 6.
222 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

primary

recrystallized

PARTS PER MILLION

PARTS PER MILLION

SILVER IN PYRITE

0

1,000

2,000

3,000

4,000

5,000

GOLD IN PYRITE

0

50

100

150

200

250

300

MERCURY IN PYRITE

0

50

100

150

200

250

THALLIUM IN PYRITE

0

500

1,000

1,500

2,000

2,500

j

g h

i

ARSENIC IN PYRITE

0

5,000

10,000

15,000

20,000

ANTIMONY IN PYRITE

0

3,000

6,000

9,000

12,000

TEXTURE TEXTURE

e f
LA–ICP–MS Mineral Chemistry Studies 223

BISMUTH IN PYRITE

0

10

20

30

40

50

CHROMIUM IN PYRITE

0

200

400

600

800

1,000

1,200

COBALT IN PYRITE

0

100

200

300

400

500

NICKEL IN PYRITE

100

150

200

250

300

350

400

450

p

primary

recrystallized

TEXTURE TEXTURE

PARTS PER MILLIONPARTS PER MILLION

m n

o

MOLYBDENUM IN PYRITE

0

500

1,000

1,500

2,000

2,500

3,000

CADMIUM IN PYRITE

0

100

200

300

400

500

600

k l
224 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

IRON IN SPHALERITE

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

180,000

LEAD IN SPHALERITE

0

20,000

40,000

60,000

80,000

100,000

120,000

ZINC IN SPHALERITE

300,000

350,000

400,000

450,000

500,000

550,000

600,000

650,000

700,000

COPPER IN SPHALERITE

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

ARSENIC IN SPHALERITE

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

u

s

primary

recrystallized

TEXTURE

PARTS PER MILLION

PARTS PER MILLION

r

t

v

SELENIUM IN PYRITE

0

2,000

4,000

6,000

8,000

10,000

12,000

TEXTURE

q
LA–ICP–MS Mineral Chemistry Studies 225

SILVER IN SPHALERITE

0

20,000

40,000

60,000

80,000

100,000

GOLD IN SPHALERITE

0

200

400

600

800

1,000

MERCURY IN SPHALERITE

0

500

1,000

1,500

2,000

2,500

3,000

THALLIUM IN SPHALERITE

0

50

100

150

200

250

300

350

400

MOLYBDENUM IN SPHALERITE

0

500

1,000

1,500

2,000

aa

primary

recrystallized

TEXTURE

PARTS PER MILLION

PARTS PER MILLION

y

x

z

ab

ANTIMONY IN SPHALERITE

0

2,000

4,000

6,000

8,000

10,000

12,000

TEXTURE

w
226 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

0

10

20

30

40

50

0

100

200

300

400

500

600

700

800

20

40

60

80

100

120

140

0

5,000

10,000

15,000

20,000

NICKEL IN SPHALERITE SELENIUM IN SPHALERITE

COBALT IN SPHALERITE

0

500

1,000

1,500

2,000

2,500

CHROMIUM IN SPHALERITE

BISMUTH IN SPHALERITE

primary

recrystallized

TEXTURE TEXTURE PARTS PER MILLION

PARTS PER MILLION

af

ag ah

ad

ae

CADMIUM IN SPHALERITE

0

500

1,000

1,500

2,000

2,500

3,000

ac
LA–ICP–MS Mineral Chemistry Studies 227

TEXTURE TEXTURE

PARTS PER MILLION

PARTS PER MILLION

ai aj

al

am

LEAD IN GALENA

760,000

780,000

800,000

820,000

840,000

860,000

ANTIMONY IN GALENA

0

10,000

20,000

30,000

40,000

50,000

IRON IN GALENA

0

1,000

2,000

3,000

4,000

5,000

ZINC IN GALENA

0

500

1,000

1,500

2,000

2,500

3,000

3,500

COPPER IN GALENA

0

2,000

4,000

6,000

8,000

10,000

12,000

ARSENIC IN GALENA

0

5,000

10,000

15,000

20,000

ak

an

primary

recrystallized

remobilized
228 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

TEXTURE TEXTURE

PARTS PER MILLION

PARTS PER MILLION

ar

at

SILVER IN GALENA

0

1,000

2,000

3,000

4,000

GOLD IN GALENA

0

5

10

15

20

25

MERCURY IN GALENA

0

20

40

60

80

100

THALLIUM IN GALENA

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

MOLYBDENUM IN GALENA

0

2,000

4,000

6,000

8,000

10,000

12,000

CADMIUM IN GALENA

0

10

20

30

40

50

60

ao ap

aq

as

primary

recrystallized

remobilized
LA–ICP–MS Mineral Chemistry Studies 229

BISMUTH IN GALENA

1

1

2

2

3

3

4

4

5

CHROMIUM IN GALENA

0

50

100

150

200

250

300

COBALT IN GALENA

0

20

40

60

80

100

NICKEL IN GALENA

0

50

100

150

200

SELENIUM IN GALENA

0

500

1,000

1,500

2,000

2,500

au av

aw ax

ay

primary

recrystallized

remobilized

TEXTURE

TEXTURE

PARTS PER MILLION

PARTS PER MILLION
230 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Discussion

There are a number of mineralogical, textural, and 

geochemical features of the ores as described herein that bear 

directly on elucidating the genetic processes of formation 

leading to the Greens Creek deposit and its subsequent modification during regional deformation. We will concentrate 

first on characteristics of the primary ores and whether their 

textures and geochemistry yield useful information regarding 

their origin. We will then discuss the subsequent deformation of the ores and whether specific textures are indicative of 

the timing or physical parameters of the deformation event. 

Finally, we will look at the nature and the extent of both 

solid- and liquid-state remobilization of minerals and metals 

in the ores and the effect of remobilization on the distribution 

and grade of the ores.

Pyrite provides the most complete textural record of mineral formation and subsequent modification due to its ubiquity 

in all ores and host rocks throughout the deposit and as the 

hardest ore mineral, as indicated by its resistance to textureobliterating plastic deformation. The paragenetically earliest 

pyrites have framboidal and colloform banded textures with 

layers of sphalerite, galena, tetrahedrite, and probably other 

complex lead-antimony sulfides, and dendritic textures. These 

textures are preserved in relatively undeformed blocks of massive pyritic ore or in clasts within blocks of MFP that display 

abundant evidence of brittle failure and cataclasis. Similar 

textures are commonly preserved in ancient massive sulfide 

deposits and are usually referred to as primary depositional 

textures that are taken as evidence of ore deposition on or 

near the sea floor as a result of rapid cooling and mixing of a 

hydrothermal fluid with cold seawater (Leitch, 1981; Eldridge 

and others, 1983; Yui, 1983; McClay, 1991; Craig and Vokes, 

1992; Gaspar and Pinto, 1993; Larocque and Hodgson, 1995; 

Hannington and others, 1999). Numerous observations of 

identical textures forming in active sea-floor systems worldwide (Graham and others, 1988; Koski and others, 1988, 1994; 

Paradis and others, 1988; Binns and others, 1993; Halbach and 

others, 1993; Duckworth and others, 1995; Knott and others, 

1995; Krasnov and others, 1995) would seem to confirm the 

sea-floor origin of such textures.

Detailed studies of active systems, however, indicate that 

a substrate is necessary upon which such primary textures 

form by replacement of amorphous silica and cementation of 

porosity. Two likely substrates include a biotic framework of 

tubeworms and filamentous bacteria (Knott and others, 1995; 

Juniper and others, 1992) or a porous boxwork of silicaanhydrite-barite formed by early low-temperature venting 

of fluids (Haymon, 1983). Once a substrate is established, 

sulfide mound growth occurs within this substrate initially by 

constructional growth of spheroidal, colloform, and dendritic 

pyrite with lesser sphalerite and galena, and then by replacement of the early colloform textures by euhedral forms. 

Growth of the sulfide body proceeds by high-temperature 

replacement of previously formed lower temperature phases 

and outward metal displacement or “zone refinement.” Even 

the earliest formed sulfides in most active sea-floor massive 

sulfides form by replacement processes and rapidly evolve 

to exhibit euhedral mineral textures. Therefore, the earliest 

mineral textures at Greens Creek likely represent formation 

beneath the sediment/water interface.

An additional feature of the primary mineral textures 

at Greens Creek indicates that the hanging-wall shales were 

being deposited early in the ore-forming process. We note that 

the majority of the primary-textured pyrite that has survived 

metamorphism exhibits polyframboidal and spongy pyrite textures. These textures suggest that large masses of MFP were 

formed by coalescence of framboids and infilling of porosity 

by precipitation of additional pyrite. Because true framboids 

are generally thought of as products of early iron sulfide 

diagenesis in sediments, their presence as the major precursor 

to spongy-textured massive pyrite indicates the shales were in 

place and undergoing early diagenesis during the main-stage 

ore-forming event. True framboids are distinguished from the 

colloform- and spheroidal-textured sulfide grains commonly 

seen in both modern and ancient massive sulfides by their 

characteristic raspberrylike appearance. They typically consist 

of spherical aggregates, 5–40 mm in size, of 0.2–5-mm pyrite 

crystallites. Crystallites exhibit ordered or disordered packing 

with intercrystallite spaces left void or infilled with later sulfides, quartz, and(or) carbonate (England and Ostwald, 1993). 

The presence of abundant framboids in all Greens Creek ores 

with relict primary texture is consistent with the sulfur, carbon, 

and oxygen isotope data that support the origin of the main 

stage ores by biogenic sulfate reduction in and beneath an 

accumulating shale cap (chaps. 8, 10).

Direct evidence of widespread replacement of shales by 

sulfide minerals is generally lacking. This may indicate that 

growth of main stage ore happened primarily at the phyllite/

argillite contact or by inflation of a previously formed silicabarite-sulfide framework, as is often indicated for actively 

forming systems today (Haymon, 1983; Paradis and others, 

1988; Binns and others, 1993; Petersen and others, 2000). 

Another possibility is that we do not have the undisturbed 

mesoscale exposures necessary to observe sulfide replacement 

fronts in the hanging-wall shales at the margins of the orebodies. In general the ore/hanging-wall contact is sharp, but in 

many places the sulfide content of the argillite is gradational 

over several meters. The ore/hanging-wall contact is commonly a zone of strong deformation due to the tendency for 

the shales to accommodate strain and the usual superposition 

of the shales against the ductile massive base-metal-rich ores. 

The MFBs at this contact are generally tectonically banded 

with near-complete destruction of primary textures, and the 

ore/argillite contact can be a slip surface exhibiting graphiterich, polished gouge. Thus, direct observational evidence for 

sulfide replacement of argillites is inconclusive.

We suggest, based largely on ore stratigraphic and geochemical considerations, that the earliest mineral precipitation 

at Greens Creek was exhalative, silica-barite-carbonate-rich 

material that acted as the substrate within which the later, 
Discussion 231

main-stage massive sulfide grew. Discontinuous massive and 

debris-flow carbonate units in the immediate footwall exhibit 

both nodular-colloform pyrite and late dolomite cement textures that are indicative of diagenetic and epigenetic formation 

in fractures and dissolution cavities. These features, reminiscent of mineral textures common in Mississippi Valley-type 

(MVT) deposits (Leach and Sangster, 1993), demonstrate 

that hydrothermal fluids traversed through the carbonates on 

route to the site of ore formation. Primary textures similar 

to those observed in the MFPs are occasionally preserved in 

the more competent WSIs and support the idea that growth 

of main-stage mineralization occurred primarily by sulfide 

replacement of the white ores. Additionally, the association 

of occasional grains of free gold and electrum and elevated 

precious metal grades within these WSIs supports the suggestion that the early fluids were hydrogen sulfide and precious 

metal rich and base metal poor. The absence of well-developed 

WCAs and WBAs directly beneath proximal accumulations 

of WSI and MFP and the presence of these barite-carbonaterich white ores beneath and lateral to massive sulfide ores in 

distal portions of the mine further indicates that main-stage ore 

transgressed and obliterated much of the early white ores. The 

less competent WCAs and especially the WBAs usually do not 

preserve evidence of primary mineral textures.

Several features suggest that as main-stage massive sulfide 

mineralization progressed, the Greens Creek system went 

through a process of zone refinement as described in many 

ancient and modern VMS systems (Eldridge and others, 1983; 

Goldfarb and others, 1983; Huston and Large, 1989; Large and 

others, 1989; Hannington and others, 1986; Petersen and others, 

2000). Most compelling is the typical pattern of metal zonation 

observed at Greens Creek. Where the complete ore stratigraphy 

is present, metal zonation progresses from proximal coppergold-arsenic rich, to zinc-lead-silver rich, to more lead, silver, 

and gold-enriched zinc-lead-silver ores at the margins. Such 

a pattern is identical to that expected due to selective remobilization of metals by a hydrothermal fluid from the interior 

of a growing sulfide accumulation, transport of metals toward 

the margins of the accumulation, and reprecipitation along a 

temperature-solubility gradient (Huston and Large, 1989). Thus, 

despite considerable subsequent remobilization of metals and 

deformation of the ores as a result of the Cretaceous metamorphism, we believe Greens Creek preserves an original mineral 

and metal zonation that is attributable to early sulfide replacement and zone refining within a growing sulfide accumulation.

A more circumstantial feature indicative of zone refinement is indicated by early replacement textures within proximal, primary-textured ores. In the proximal copper-rich ores 

of the Northwest West orebody, chalcopyrite has been found 

replacing pyrite within concentrically banded spheroids and 

colloform pyrite-sphalerite-galena-rich structures (fig. 5G). 

Close examination shows that chalcopyrite cuts across banding 

and engulfs remnants of other sulfide minerals, demonstrating that the paragenetic order of chalcopyrite succeeds the 

primary-textured sulfides. Similar observations have been used 

to establish the paragenetic position of chalcopyrite in the 

undeformed ores of the Kuroko deposits (Eldridge and others, 

1983). Also, in one instance, framboidal-textured crystallites 

of chalcopyrite occur within a pyrite matrix that is surrounded 

by dolomite (fig. 10C). This sample may represent a rare case 

of primary chalcopyrite framboids. However, if all modern 

framboids are composed of pyrite (England and Ostwald, 

1993), then this occurrence demonstrates replacement of pyrite 

by chalcopyrite. Replacement must have occurred prior to 

metamorphism and probably during the zone-refining stage.

Euhedral arsenian pyrite and arsenopyrite crystals in proximal MFPs (figs. 7A–F) appear to be another textural feature 

that occurs as a secondary modification of primary ores prior 

to metamorphism. When present, arsenian pyrite is always in 

spatial association with primary-textured pyritic ores and tends 

to be concentrated along the margins of, or in passageways 

through, areas of massive sulfide where original porosity would 

have been greatest. It always exhibits unstrained subhedral to 

euhedral shapes, does not show a preferred orientation, and 

is generally clean and free of inclusions of other minerals. 

Elevated nickel, arsenic, and gold contents of the arsenian pyrite 

suggest a high-temperature metal association (for example, note 

similarity to the high-temperature metal assemblage at Kidd 

Creek in Hannington and others, 1999) as does the generally 

proximal position of these arsenic-rich pyritic ores and their 

close association to chalcopyrite-rich MFPs with elevated 

copper-gold contents. Thus, arsenian pyrite appears to have 

formed in the high-temperature proximal areas of the deposit 

by replacement of trace-element-rich, primary-textured pyrite. 

Though we cannot demonstrate conclusively that arsenian pyrite 

is not a product of metamorphic remobilization of constituents 

out of the primary ores, the lack of (1) strained crystals, (2) 

location in pressure shadows, or (3) evidence of solution creep, 

suggests formation after the primary ores in areas unaffected 

by metamorphism. Additionally, the observation that some of 

the most 34S-depleted sulfur isotope values are from arsenian 

pyrite-rich ores (see chap. 10) is consistent with formation when 

supply of isotopically light sulfur from the hanging wall was at 

a maximum, presumably during main-stage ore formation. The 

extreme d34S depletion of the arsenic-rich ores also demonstrates the lack of a homogenized sulfur isotope signature that 

might be expected of a sulfide produced as a result of metamorphic remobilization and further demonstrates the association 

of light sulfur with the main-stage massive sulfides (chap. 10). 

Koski and others (1994) document the formation of arsenopyrite-lollingite “fronts” during zone refining of black smoker 

chimneys in the Escanaba Trough.

One of the most interesting textural features of the 

primary-textured ores is the abundance of pyrite framboids, polyframboids (rogenpyrite), nodules, and a variety 

of spheroidal and atoll-shaped structures that appear to be 

modifications of originally framboidal grains. Collectively, 

these features provide strong evidence for the concurrence of 

main-stage ore formation at Greens Creek with the accumulation and early diagenetic history of the hanging-wall 

sediments. Examination of polished thin sections provides 

evidence for a complete textural evolution from early 
232 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

framboidal and colloform features, through intermediate 

stages where coalescence of atoll-shaped and spheroidal 

aggregates occurs, to a final spongy-textured pyrite stage 

with abundant inclusions of other ore and gangue minerals. 

Such an origin and evolutionary process has been described 

by England and Ostwald (1993) for syngenetic and vein-type 

massive sulfides of the Lachlan Fold Belt of Eastern Australia. Several points emphasized in their work have significance for the origin of such textures at Greens Creek. First, 

they conclude that the presence of framboids and subsequently derived atoll structures is indicative of early diagenetic processes in anoxic sediments. Second, they suggest 

that the recrystallization and crystal growth of polyframboid 

aggregates and the subsequent development of atoll structures requires the presence of a gel-like substance such as 

colloidal silica, chalcopyrite gel, or other base-metal-sulfide 

gels through which iron and sulfur can diffuse to the framboidal growth centers. If England and Ostwald (1993) are 

correct, the presence of framboid-derived textures at Greens 

Creek constitutes additional compelling evidence for our 

suggestion that the main-stage ores formed predominantly 

during and after deposition of the hanging wall, that is, during early diagenesis. If a gel-like medium is required for the 

diffusion of iron and sulfur into polyframboid aggregates to 

create atolls and spongy-textured massive pyrite, this implies 

that diffusion of other metals also may occur at this time and 

has important implications for the zone refinement process. 

Simply based on mineralogical and textural observations, the 

process of framboid agglomeration, coalescence, and recrystallization described herein appears to result in a migration 

of base metals out of the predominantly pyritic masses. This 

results in spongy pyritic masses with elevated copper, arsenic, and gold and a spatial association with euhedral arsenian 

pyrite, which we previously suggested is a product of zone 

refinement. It seems reasonable that the zone-refinement 

process would be facilitated if the process occurred within 

a growing sulfide accumulation that was partially colloidal 

gel and partially a crystalline silica-sulfide framework, and 

by the presence of unlithified sediments. Perhaps the presence and coalescence of framboid-derived textures at Greens 

Creek and other massive sulfide deposits represent textural 

evidence of a zone-refinement process and link the timing of 

ore formation to early diagenesis of the enclosing sediments.

In the massive sulfide ores studied by England and 

Ostwald (1993), chalcopyrite was the major phase associated with the more evolved framboid-derived pyrite textures, 

leading these workers to suggest chalcopyrite gel was the 

primary diffusion media. We note that at Greens Creek 

chalcopyrite only rarely occurs in association with framboidderived structures and then only as a clearly replacive and(or) 

infilling phase. However, in all cases where atoll-shaped 

grains occur, they are associated with other base-metal 

sulfides such as sphalerite, galena, tetrahedrite, and probably 

other more complex lead-antimony sulfides. The association 

of atolls with base-metal-sulfide matrix is consistent with the 

suggestion of England and Ostwald (1993) that the presence 

of a gel-like diffusion media is required for the growth of 

more texturally evolved pyrite structures.

We also note the abundant documentation of the zonerefinement process in chimney structures on the modern sea 

floor (Graham and others, 1988; Paradis and others, 1988; 

Krasnov and others, 1995; Duckworth and others, 1995; 

Knott and others, 1995; Petersen and others, 2000). Many of 

these chimneys occur in nonsedimented settings or project well above any sediment cover. Clearly these examples 

demonstrate that early diagenetic processes in enclosing 

sediments are not a requirement for zone refinement to occur. 

However, these do not invalidate the notion that zone refinement may be enhanced by the presence of gel sulfides in the 

porous framework of the chimneys.

Also, we note that although spherical, framboidlike textures are described in the modern sea-floor sulfide literature and 

that true framboids have been documented from a wide variety 

of massive sulfide deposit types, including veins, and VMS 

deposits not associated with sediments (Leitch, 1981; Eldridge 

and others, 1983; England and Ostwald, 1993; Hannington and 

others, 1999), they are far more ubiquitous in deposits associated with sediments such as MVT, SEDEX lead-zinc, and 

sedimentary copper deposits (Schouten, 1946; Croxford and 

Jephcott, 1972; Chen, 1978; Leach and Sangster, 1993; Large 

and Walcher, 1999). A literature search also indicates that, while 

spheroidal and colloform textures are common in modern massive sulfides, true framboids are described only from sedimentcovered sites (Koski and others, 1988, 1994; Peter and Scott, 

1988). We suggest that true framboids are relatively uncommon 

in nonsediment-associated modern and ancient massive sulfide 

deposits and that when present, they indicate early diagenetic 

mineral formation. The presence of framboid-derived textures at 

Greens Creek and in numerous other, more typical VMS deposits suggests that early diagenetic ore formation may be more 

common than has been previously recognized. The presence 

of true framboid-derived textures is not common in most VMS 

and is ubiquitous in SEDEX (sedimentary exhalative) deposits, 

reflecting the diagenetic origin of most of the latter.

While the textures described above are striking and 

provide us with information regarding the earliest events at 

Greens Creek through possibly late diagenetic modifications 

to the ores, they represent only about 30 percent of the deposit 

and are skewed heavily toward features in pyritic ores. Most 

of the deposit shows the effects of Cretaceous metamorphism 

and polyphase deformation that was destructive to primary ore 

textures. In general, sulfide textures in the metamorphosed ores 

are characterized by cataclasis, annealing recrystallization, pressure solution, and solution creep that are consistent with lower 

greenschist facies dynamic metamorphism (Cox, 1987; Gilligan 

and Marshall, 1987; Marshall and Gilligan, 1987). Intramineral 

translocation and diffusional features such as dislocation glide, 

kinking, twinning, nabbarro-herring creep, and coble creep, 

indicative of deformation at higher metamorphic grades, are 

absent or have not been observed. None of the various etching 

techniques useful for elucidating such textures were used during 

the course of this study.
Discussion 233

As previously mentioned, pyrite, due to its hardness, exhibits 

the greatest range of mineral textures. The most obvious and 

widespread pyrite texture that can be attributed to deformation 

of the deposit is the abundant instances of cataclasis exhibited 

by the more competent MFP ores. Especially where gangue 

silica content is high, large blocks of MFP have acted as 

deformation-resistant buttresses around which the softer ores 

and host rocks have flowed. When deformation does occur, it 

is usually manifested by brittle failure, resulting in a cataclastic breccia composed of angular, primary-textured pyrite clasts 

in a matrix of smaller pyrite fragments and ductile sulfides. 

In cases where deformation has shattered and transposed 

the MFP enough to impose a fabric, pyrite clasts of widely 

varying size become strung out in cataclastic trails. Clasts in 

these strings commonly exhibit pressure shadows filled with 

galena, tetrahedrite, chalcopyrite, and gangue minerals. In 

cases where the primary-textured fragments are precious metal 

enriched, pressure shadows can be occupied by native gold, 

electrum, pyrargyrite, and other exotic secondary silver minerals. Another brittle failure texture commonly seen in association with cataclastically deformed pyritic ores is intragranular 

extension microfractures in pyrite crystals that also become 

filled by secondary remobilized phases.

The other dominant texture present in pyrite as well as 

in base-metal sulfides is annealing recrystallization. As with 

the gradational development described above for the production of spongy pyrite, the annealing recrystallization produced 

a spectrum of textures. In incipient stages, the texture is 

characterized by inclusion-free areas in otherwise spongytextured pyrite masses. Intermediate stages are characterized by masses of relatively clean, inclusion-free pyrite with 

subhedral grain boundaries. When other minerals are present, they occur within the clean pyrite as rounded, irregular 

inclusions or as fillings within extensional microfractures. 

We also have observed more advanced stages of framboidderived atoll-shaped structures as described by England and 

Ostwald (1993). Relict rounded shapes within otherwise clean, 

monomineralic pyrite (figs. 6B, 10E) are common, as are 

euhedral-crystal-shaped sphalerite-, galena-, or tetrahedritefilled growth zones (atolls) within subhedral to euhedral pyrite 

grains (figs. 6J, K; 10D, G). The presence of such textures in 

ores that show evidence of progressive metamorphism seems 

to confirm the suggestion of England and Ostwald (1993) that 

additional heat energy beyond that supplied during diagenesis is required to develop advanced atoll-shaped textures in 

sulfides. In their most advanced textural state, fully annealed 

pyritic ores exhibit the typical close-packed polygonal grainboundary shapes (foam texture) commonly seen in higher 

grade metamorphosed massive sulfides. At this stage of deformation the pyritic ores are monomineralic with the exception 

of remobilized minerals that occupy late veinlets and extension microfractures (figs. 6F, 10H).

With the exception of the minor amounts of sphalerite, galena, tetrahedrite, and chalcopyrite that appear as 

bands, infillings, and matrix in the primary-textured ores, 

95 percent of these minerals exhibit either recrystallization 

or remobilization textures. Of the base-metal sulfides, only 

sphalerite displays subhedral to euhedral crystal development, 

probably as a result of annealing recrystallization. When present, subhedral to euhedral crystals of sphalerite (fig. 6L, M) 

occur usually in a galena matrix or in a mixed base-metal-rich 

assemblage of annealed (?) sphalerite-galena-tetrahedrite-

(pyrite). In extremely high grade zinc-rich MFBs (fig. 3C), 

nearly monomineralic aggregates of sphalerite have formed 

that exhibit rounded and bulging grain boundaries with anhedral galena. The prominence of recrystallization, as opposed to 

ductile flow, as a major process in Greens Creek ores is difficult to assess. The near universal absence of the characteristic 

triangular cleavage pits common to unstrained galena may be 

indicative of widespread recrystallization.

The complete absence of euhedral or even subhedral 

crystal shapes of tetrahedrite, chalcopyrite, and in most cases 

galena suggests that their occurrence in Greens Creek ores 

is largely the result of either physical (solid state) or chemical (fluid state) remobilization. The ubiquitous occurrence 

of these three minerals in extension microfractures and in 

pressure shadows of harder grains supports this contention. In 

well-banded MFBs it appears as though the primary means of 

mineral layer segregation is by ductile flow of the softer sulfides. Similarly, some fractures appear to have ductile sulfides 

injected into the open space. In such cases, quartz, dolomite, 

or other gangue minerals do not accompany the physically 

remobilized phases.

Instances of fluid-state remobilization over distances of 

millimeters to several meters are much more prevalent and 

easier to document. In such cases, grains of tetrahedrite, galena, 

chalcopyrite, and especially pyrargyrite and other exotic silver 

minerals clearly occupy veinlets (figs. 6Q, R; 5A) and veins that 

cut the massive ores. Fluid-state remobilization also appears 

to cause remobilization and concentration of free gold and electrum into late quartz veins and silica-flooded WSIs.

Overall, the process of metamorphic recrystallization 

and micro- to mesoscale remobilization of primary-textured 

ores has a visible (fig. 10I) as well as geochemical cleaning 

effect. As determined by LA–ICP–MS analyses, the relatively uniform low-level concentrations of trace elements in 

the primary-textured ores is consistent with redistribution of 

trace elements into predictable mineral phases based on free 

energy considerations. Specific trace elements are selectively 

partitioned into specific secondary mineral phases based on 

the size of the trace-element cations that are expelled from the 

trace-element-rich and poorly ordered primary ores into the 

appropriate-sized lattices of new phases. Thus, recrystallized 

sphalerite has high cadmium and mercury content but very low 

antimony and silver content, whereas remobilized tetrahedrite 

displays the opposite relationship. This metamorphic cleaning of primary ore and remobilization of metals into new 

mineral assemblages is a feature that has been documented at 

other massive sulfide deposits in metamorphic terranes (for 

example, the Sulitjelma deposit, Norway, Cook, 1996; nickel 

deposits of the Yilgarn craton, Australia, McQueen, 1987; 

Marshall and others, 2000).
234 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Conclusions

The mineralogy, mineral textures, and mineral geochemical relationships at Greens Creek present the relatively 

unusual case of a trace-element-rich polymetallic massive 

sulfide deposit that has been subjected to partial metamorphic modification at low to moderate grade. The resulting 

array of textures spans the range from pristine primary 

features that provide insight into the genetic origins of the 

deposit through completely recrystallized and remobilized 

metamorphic features that provide an excellent opportunity to document the textural and chemical evolution of the 

deposit during its subsequent diagenetic and metamorphic 

history.

We believe that textures preserved in the primary ores 

exhibit an overwhelming preponderance of features attributable to formation of main-stage sulfide mineralization during 

early diagenesis of the accumulating hanging-wall sediments. 

These framboidal, colloform, and nodular pyrite textures also 

appear to preserve an early phase of coalescence and replacement, possibly enhanced by colloidal base-metal-sulfide gels, 

that marks the textural development of zone refinement in 

the growing sulfide accumulation. Subsequently, these same 

textures were modified to varying degrees by at least two 

periods of deformation related to the Cretaceous dynamic 

metamorphism that affected the region. This resulted in the 

continued development of more advanced atoll-shaped textures at the expense of polyframboid aggregates and spongytextured pyrite. Progressive metamorphism of most of the 

ores resulted in recrystallization and remobilization of minerals and trace elements. The major effect of metamorphism 

was mineralogical cleaning of the ores resulting in redistribution and local upgrading of specific metals into predictable 

and more stoichiometrically ordered minerals.

References Cited

Binns, R.A., Scott, S.D., Bogdanov, Y.A., Lisitzin, A.P., 

Gordeev, V.V., Gurvich, E.G., Finlayson, E.J., Boyd, T., 

Dotter, L.E., Wheller, G.E., and Muravyev, K.G., 1993, 

Hydrothermal oxide and gold-rich sulfate deposits of 

Franklin Seamount, western Woodlark basin, Papua New 

Guinea: Economic Geology, v. 88, p. 2122–2153.

Blackburn, W.H., and Dennen, W.H., 1997, Encyclopedia of 

mineral names: The Canadian Mineralogist, Special Publication 1, 360 p.

Brew, D.A., Ford, A.B., and Himmelberg, G.R., 1989, Evolution of the western part of the Coast plutonic-metamorphic 

complex, southeastern Alaska, U.S.A.—A summary, in

Daly, S.R., Cliff, R.A., and Yardley, B.W., eds., Evolution of 

metamorphic belts: London, Blackwell, Geological Society 

Special Publication 43, p. 447–451.

Brew, D.A., Himmelberg, G.R., Loney, R.A., and Ford, 

A.B., 1992, Distribution and characteristics of metamorphic belts in the southeastern Alaska part of the North 

American Cordillera: Journal of Metamorphic Geology, 

v. 10, p. 465–482.

Butler, I.B., and Nesbitt, R.W., 1999, Trace element distributions in the chalcopyrite wall of a black smoker chimney—

Insights from laser ablation inductively coupled plasma 

mass spectrometry (LA–ICP–MS): Earth and Planetary 

Science Letters, v. 167, p. 335–345.

Chen, T.T., 1978, Colloform and framboidal pyrite from the 

Caribou deposit, New Brunswick: Canadian Mineralogist, 

v. 16, p. 9–15.

Cook, N.J., 1996, Mineralogy of the sulphide deposits at 

Sulitjelma, northern Norway: Ore Geology Reviews, v. 11, 

p. 303–338.

Cox, S.F., 1987, Flow mechanisms in sulphide minerals: Ore 

Geology Reviews, v. 2, p. 133–171.

Craig, J.R., and Vokes, F.M., 1992, Ore mineralogy of the 

Appalachian-Caledonian stratabound sulfide deposits: Ore 

Geology Reviews, v. 7, p. 77–123.

Croxford, N.J.W., and Jephcott, S., 1972, The McArthur River 

lead-zinc-silver deposit, NT, in Newcastle Conference 1972, 

Proceedings: Parkville, Victoria, Australasian Institute of 

Mining and Metallurgy, p. 1–27.

Duckworth, R.C., Knott, R., Fallick, A.E., Rickard, D., Murton, B.J., and Van Dover, C., 1995, Mineralogy and sulphur 

isotope geochemistry of the Broken Spur sulphides, 29o

N, 

Mid-Atlantic Ridge, in Parson, L.M., Walker, C.L., and 

Dixon, D.R., eds., Hydrothermal vents and processes: Geological Society Special Publication no. 87, p. 175–189.

Dusel-Bacon, Cynthia, 1994, Metamorphic history of Alaska, 

in Plafker, G., and Berg, H.C., eds., The geology of Alaska: 

Boulder, Colorado, Geological Society of America, v. G1, 

p. 495–533.

Eldridge, S.E., Barton, P.B., Jr., and Ohmoto, H., 1983, Mineral textures and their bearing on formation of the Kuroko 

orebodies: Economic Geology Monograph 5, p. 241–281.

England, B.M., and Ostwald, J., 1993, Framboid-derived 

structures in some Tasman fold belt base-metal sulphide 

deposits, New South Wales, Australia: Ore Geology 

Reviews, v. 7, p. 381–412.

Gaspar, O.C., and Pinto, A., 1993, Neves-Corvo, a Kuroko 

type deposit in the Iberian Pyrite Belt: Resource Geology 

Special Issue, no. 17, p. 249–262.

Gilligan, L.B., and Marshall, B., 1987, Textural evidence for 

remobilization in metamorphic environments: Ore Geology 

Reviews, v. 2, p. 205–229.
References Cited 235

Goldfarb, M.S., Converse, D.R., Holland, H.D., and 

Edmond, J.M., 1983, The genesis of hot springs deposits 

on the East Pacific Rise, 21oN: Economic Geology Monograph 5, p. 184–197.

Graham, U.M., Bluth, G.J., and Ohmoto, H., 1988, Sulfidesulfate chimneys on the East Pacific Rise, 11o and 13oN 

latitudes, part I—Mineralogy and paragenesis: Canadian 

Mineralogist, v. 26, p. 487–504.

Guo, Xun, and Lichte, F.E., 1995, Analysis of rocks, soils, 

and sediments for the chalcophile elements by laser 

ablation–inductively coupled plasma mass spectrometry: 

Analyst, v. 120, p. 2707–2711.

Halbach, Peter, Pracejus, B., and Marten, A., 1993, Geology and 

mineralogy of massive sulfide ores from the central Okinawa 

trough, Japan: Economic Geology, v. 88, p. 2210–2225.

Hannington, M.D., Bleeker, W., and Kjarsgaard, I., 1999, Sulfide mineralogy, geochemistry, and ore genesis of the Kidd 

Creek deposit—Part I. North, Central, and South orebodies: 

Economic Geology Monograph 10, p. 163–224.

Hannington, M.D., Peter, J.M., and Scott, S.D., 1986, Gold in 

sea-floor polymetallic sulfide deposits: Economic Geology, 

v. 81, p. 1867–1883.

Hawksworth, M.A., and Meinert, L.D., 1990, Alteration and 

fluid inclusion study of the Groundhog mine vein system, 

Central mining district, New Mexico: Economic Geology, 

v. 85, p. 1825–1839.

Haymon, R.M., 1983, Growth history of hydrothermal black 

smoker chimneys: Nature, v. 301, p. 695–698.

Himmelberg, G.R., Brew, D.A., and Ford, A.B., 1994, Petrologic characterization of pelitic schists in the western 

metamorphic belt, Coast plutonic-metamorphic complex, 

near Juneau, southeastern Alaska: U.S. Geological Survey 

Bulletin 2074, 18 p.

Himmelberg, G.R., Brew, D.A., and Ford, A.B., 1995, Lowgrade, M1

 metamorphism of the Douglas Island Volcanics, 

western metamorphic belt near Juneau, Alaska, in Schiffman, P., and Day, H.W., eds., Low-grade metamorphism 

of mafic rocks: Boulder, Colorado, Geological Society of 

America Special Paper 296, p. 51–66.

Huston, D.L., and Large, R.R., 1989, A chemical model for 

the concentration of gold in volcanogenic massive sulphide 

deposits: Ore Geology Reviews, v. 4, p. 171–200.

Juniper, S.K., Jonasson, I.R., Tunnicliffe, V., and Southward, 

A.J., 1992, Influence of a tube-building polychaete on hydrothermal chimney mineralization: Geology, v. 20, p. 895–898.

Knott, Richard, Fallick, A.E., Rickard, D., and Backer, H., 

1995, Mineralogy and sulfur isotope characteristics of a 

massive sulfide boulder, Galapagos Rift, 58°55'W, in

Parson, L.M., Walker, C.L., and Dixon, D.R., eds., Hydrothermal vents and processes: Geological Society Special 

Publication no. 87, p. 207–222.

Koski, R.A., Benninger, L.M., Zierenberg, R.A., and Jonasson, 

I.R., 1994, Chapter 16, Composition and growth history 

of hydrothermal deposits in Escanaba Trough, southern 

Gorda Ridge, in Morton, J.L., Zierenberg, R.A., and Reiss, 

C.A., eds., Geologic hydrothermal and biologic studies at 

Escanaba Trough, Gorda Ridge, offshore northern California: U.S. Geological Survey Bulletin 2022, p. 293–324.

Koski, R.A., Shanks, W.C. III, Bohrson, W.A., and Oscarson, 

R.L., 1988, The composition of massive sulfide deposits 

from the sediment-covered floor of Escanaba Trough, Gorda 

Ridge—Implications for depositional processes: Canadian 

Mineralogist, v. 26, p. 655–673.

Krasnov, S.G., Cherkashev, G.A., Stepanova, T.V., Batuyev, 

B.N., Krotov, A.G., Malin, B.V., Maslov, M.N., Markov, 

V.F., Poroshina, I.M., Samovarov, M.S., Ashadze, A.M., 

Lazareva, L.I., and Ermolayev, I.K., 1995, Detailed geological studies of hydrothermal fields in the North Atlantic, in

Parson, L.M., Walker, C.L., and Dixon, D.R., eds., Hydrothermal vents and processes: Geological Society Special 

Publication no. 87, p. 43–64.

Large, Duncan, and Walcher, E., 1999, The Rammelsberg 

Cu-Zn-Pb-Ba deposit, Germany—An example of sedimenthosted, massive sulfide mineralization: Mineralium Deposita, v. 34, p. 522–538.

Large, R.R., Huston, D.L., McGoldrick, P.J., and Ruxton, P.A., 

1989, Gold distribution and genesis in Australian volcanogenic massive sulfide deposits and their significance for 

gold transport models: Economic Geology Monograph 6, 

p. 520–536.

Larocque, A.C.L., and Hodgson, C.J., 1995, Effects of 

greenschist-facies metamorphism and related deformation 

on the Mobrun massive sulfide deposit, Quebec, Canada: 

Mineralium Deposita, v. 30, p. 439–448.

Lathram, E.H., Pomeroy, J.S., Berg, H.C., and Loney, R.A., 

1965, Reconnaissance geology of Admiralty Island, Alaska: 

U.S. Geological Survey Bulletin 1181–R, 48 p.

Leach, D.L., and Sangster, D.F., 1993, Mississippi Valley-type 

lead-zinc deposits, in Kirkham, R.V., Sinclair, W.D., Thorpe, 

R.I., and Duke, J.M., eds., Mineral deposit modeling: Geological Association of Canada, Special Paper 40, p. 289–314.

Leitch, C.H.B., 1981, Mineralogy and textures of the Lahanos and Kizilkaya massive sulfide deposits, northeastern 

Turkey, and their similarity to Kuroko ores: Mineralium 

Deposita, v. 16, p. 241–257.

Loney, R.A., 1964, Stratigraphy and petrography of the PybusGambier area, Admiralty Island, Alaska: U.S. Geological 

Survey Bulletin 1178, 103 p.
236 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Ludden, J.N., Feng, R., Gauthier, G., Stix, J., Shi, L., Francis, 

D., Machado, N., and Wu, G., 1995, Applications of LAM–

ICP–MS analysis to minerals: Canadian Mineralogist, v. 33, 

p. 419–434.

Marshall, Brian, and Gilligan, L.B., 1987, An introduction to 

remobilization—Information from ore-body geometry and 

experimental considerations: Ore Geology Reviews, v. 2, 

p. 87–131.

Marshall, Brian, Vokes, F.M., and Larocque, A.C.L., 2000, 

Chapter 2, Regional metamorphic remobilization—

Upgrading and formation of ore deposits, in Spry, P.G., 

Marshall, B., and Vokes, F.M., eds., Metamorphosed and 

metamorphogenic ore deposits: Reviews in Economic 

Geology, v. 11, p. 19–38.

McClay, K.R., 1991, Deformation of stratiform Zn-Pb (-barite) 

deposits in the northern Canadian cordillera: Ore Geology 

Reviews, v. 6, p. 435–462.

McQueen, K.G., 1987, Deformation and remobilization in 

some western Australian nickel ores: Ore Geology Reviews, 

v. 2, p. 269–286.

Norman, M.D., Pearson, N.J., Sharma, A., and Griffin, W.L., 

1996, Quantitative analysis of trace elements in geological 

materials by laser ablation ICPMS—Instrument operating 

conditions and calibration values of NIST glasses: Geostandards Newsletter, v. 20, p. 247–261.

Paradis, Suzanne, Jonasson, I.R., Le Cheminant, G.M., and 

Watkinson, D.H., 1988, Two zinc-rich chimneys from the 

Plume site, southern Juan de Fuca Ridge: Canadian Mineralogist, v. 26, p. 637–654.

Peter, J.M., and Scott, S.D., 1988, Mineralogy, composition, and fluid-inclusion microthermometry of seafloor 

hydrothermal deposits in the Southern Trough of Guaymas 

Basin, Gulf of California: Canadian Mineralogist, v. 26, 

p. 567–587.

Petersen, Sven, Herzig, P.M., and Hannington, M.D., 2000, 

Third dimension of a presently forming VMS deposit, TAG 

hydrothermal mound, mid-Atlantic ridge, 26°N: Mineralium 

Deposita, v. 35, p. 233–259.

Ridley, W.I., 2000, The ICP–MS laser microprobe—A new 

geochemical tool: Trends in Geochemistry, v. 1, p. 1–14.

Ridley, W.I., and Lichte, F.E., 1998, Chapter 11, Major, trace, 

and ultratrace element analysis by laser ablation ICP–MS, 

in McKibben, M.A., Shanks III, W.C., and Ridley, W.I., 

eds., Application of microanalytical techniques to understanding mineralizing processes: Reviews in Economic 

Geology, v. 7, p. 199–215.

Schouten, Cornelius, 1946, The role of sulphur bacteria in 

the formation of the so-called sedimentary copper ores 

and pyritic orebodies: Economic Geology, v. 41, 

p. 517–538.

Shibuya, E.K., Sarkis, J.E.S., Enzweiler, J., Jorge, A.P.S., and 

Figueiredo, A.G., 1998, Determination of platinum group 

elements and gold in geologic materials using an ultraviolet 

laser ablation high-resolution inductively coupled plasma 

mass spectrometric technique: Journal of Analytical Atomic 

Spectrometry, v. 13, p. 941–944.

Viets, J.G., Leach, D.L., Lichte, F.E., Hopkins, R.T., Gent, 

C.A., and Powell, J.W., 1996, Paragenetic and minor- and 

trace-element studies of Mississippi Valley-type ore deposits of the Cracow-Silesia district, southern Poland: Prace 

Panstwowego Instytutu Geologicznego, v. 154, p. 51–71.

Watling, R.J., Herbert, H.K., and Abell, I.D., 1995, The application of laser ablation–inductively coupled plasma–mass 

spectrometry (LA–ICP–MS) to the analysis of selected 

sulphide minerals: Chemical Geology, v. 124, p. 67–81.

Yui, Shunzo, 1983, Textures of some Japanese Besshi-type 

ores and their implications for Kuroko deposits: Economic 

Geology Monograph 5, p. 231–240.
Sulfur and Lead Isotope Characteristics 

of the Greens Creek Polymetallic Massive 

Sulfide Deposit, Admiralty Island, 

Southeastern Alaska

By Cliff D. Taylor, Wayne R. Premo, and Craig A. Johnson

Chapter 10 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract.......................................................................................................................................................241

Introduction.................................................................................................................................................241

Regional and District Setting ...................................................................................................................242

Terrane Relationships ......................................................................................................................242

District Geology..........................................................................................................................................242

Deposit Geology.........................................................................................................................................243

Mine Sequence Nomenclature and Stratigraphy .......................................................................243

Ore Types and Ore Mineralogy................................................................................................................244

Ore Distribution: Ore-Type Zonation and Metal Zoning.......................................................................245

Previous Sulfur and Lead Isotope Studies ............................................................................................246

Methods.......................................................................................................................................................247

Lead Isotope Analyses.....................................................................................................................247

Sulfur Isotope Analyses...................................................................................................................247

Isotopic Data...............................................................................................................................................247

Sulfur Isotopes ..................................................................................................................................247

Lead Isotopes ....................................................................................................................................261

Interpretation of Sulfur Isotopes....................................................................................................271

Interpretation of Lead Isotope Data .......................................................................................................276

Conclusions.................................................................................................................................................280

Acknowledgments.....................................................................................................................................280

References Cited........................................................................................................................................280

Figures

1. Composite stratigraphic column of the Upper Triassic section at the

Greens Creek mine, northern Admiralty Island ...................................................................243

2. Plan view map of the Greens Creek mine showing the spatial distribution

of major orebodies and major structures .............................................................................245

3. Histogram showing the distribution of all sulfide and sulfate d34S values

obtained from the Greens Creek deposit..............................................................................248

4. Greens Creek sulfide sulfur isotope data sorted by: (A) mineral texture,

(B) mine location, and (C) type of host rock .........................................................................249

5. Comparison of sulfide sulfur isotope data in footwall versus hanging-wall

lithologies...................................................................................................................................260

6. Sulfide sulfur isotope data sorted by mineralogy and ore type........................................263

7. Sulfide and barite sulfur isotope data from host rocks and occurrences

elsewhere on Admiralty Island...............................................................................................263

8. Plot showing the range of galena lead isotopic compositions from Greens

Creek ore and several occurrences on Admiralty Island..................................................268

9. Plot showing the range of lead isotopic compositions of pyrargyrite and

tetrahedrite from Greens Creek ore, and compared to galena from Greens

Creek (shaded field) and from several occurrences on Admiralty Island ......................269
10. Plot showing the range of lead isotopic compositions of sphalerite and

pyrite from Greens Creek ore, and compared to galena from Greens Creek

(shaded field) and from several occurrences on Admiralty Island..................................270

11. Plot showing the range of lead isotopic compositions of pyrrhotite, chalcopyrite,

and several ore bands from Greens Creek, and compared to galena from

Greens Creek and from several occurrences on Admiralty Island..................................272

12. Plots showing d34S versus 207Pb/204Pb and 206Pb/204Pb isotopic data for ores and

sulfides in the Greens Creek deposit and for sulfides from Late Triassic and

other mineral occurrences on Admiralty Island..................................................................273

13. Figure showing calculated ranges of various major processes of sulfate

reduction compared to the histogram showing the range of all sulfide and

sulfate d34S analyses from the Greens Creek deposit ........................................................275

14. Plot comparing Greens Creek sulfide lead data with initial lead values at

215 Ma for argillites as well as many of the metabasalts and metagabbros

of the area, including other Admiralty Island host rock samples, presumably

of the same age.........................................................................................................................277

15. Plot (206Pb/204Pb versus 207Pb/204Pb) showing a comparison of the range of Greens

Creek lead isotope values to those from other Alaskan VMS deposits of various ages......279

Tables

1. Greens Creek sulfur isotope data, sample locations, and descriptions for

samples from drill core and underground exposures ........................................................252

2. Sulfur isotope data, sample locations, and descriptions for samples from

Admiralty Island host rocks and mineral occurrences ......................................................258

3. Uranium-thorium-lead (U-Th-Pb) isotope data, sample locations, and

descriptions of ores and sulfide minerals from the Greens Creek mine,

and mineral occurrences and host rocks on Admiralty Island.........................................264

Abstract

Sulfur isotopic analyses were obtained for 221 sulfide 

mineral separates and bulk ore samples and 14 barite separates 

taken from the mine workings and underground drill core. Also, 

55 sulfide mineral separates and 4 barites from mineral occurrences and country rock elsewhere on Admiralty Island were 

analyzed. Pyrite d34S values span the range –38 to 2 per mil, 

and chalcopyrite, sphalerite, and galena values cluster tightly 

between –11 and –16 per mil. Sphalerite-galena mineral pairs 

display consistent isotopic fractionations corresponding to an 

equilibrium temperature of about 300 degrees Celsius. Primarytextured sulfides are generally more 34S-depleted than recrystallized or remobilized sulfides, and the most 34S-enriched values 

occur in the smaller and more distally located orebodies. On a 

deposit scale the most 34S-enriched sulfides are near the footwall 

igneous rocks and white siliceous ores. The progression toward 

34S-depleted sulfides roughly follows the ore paragenesis from 

white ores against the footwall, to massive pyritic, to massive 

base-metal-rich ores against the hanging wall. Pyrite d34S values 

in the overlying shales exhibit a wide range of values from 

–29.0 to 1.1 per mil. Sulfate d34S values fall between 13 and 22 

per mil, consistent with global values for Triassic evaporites. 

The unimodal distribution of both ore-stage pyrite and basemetal sulfide sulfur isotope values suggests a single fluid supply 

of sulfur from two main sources. The data suggest input of 

heavy sulfur from the mafic-ultramafic footwall igneous rocks 

and a dominant source of light sulfur from biogenically reduced 

seawater sulfate present in pore water and (or) in diagenetic 

pyrite in the hanging-wall shales.

Seventy-six lead isotopic analyses have been made on 

34 sulfides and 9 ores from underground and 15 sulfides from 

11 different sites on Admiralty Island. Sulfides analyzed are 

chalcopyrite, pyrite, sphalerite, galena, tetrahedrite, pyrargyrite, 

and pyrrhotite. Ore and host-rock lead isotope values indicate 

derivation of metal from two major sources. Sulfide lead isotopic values define a mixing line on an uranogenic plot between 

a relatively nonradiogenic component similar to slightly 

enriched E-MOR basalt and a 207Pb-enriched component from 

an older crustal source. The nonradiogenic end of the mixing 

line overlaps the field of Late Triassic age basalts and gabbros. 

The 207Pb-enriched end is poorly constrained but permissive of 

lead extraction from the hanging-wall argillites.

Introduction

In this chapter we describe the results of a comprehensive study of the sulfur and lead isotopic characteristics of the 

Greens Creek ores. We have attempted to sample in such a 

manner as to allow evaluation of the isotopic variations within 

the deposit in a spatial as well as temporal/textural context. 

Thus, we have analyzed all of the major sulfide minerals 

present in the deposit and have obtained a series of footwall 

to hanging-wall profiles, primarily in drill core and several 

underground crosscuts, in each of the six major orebodies of 

the mine. For each analysis the type of ore or host rock has 

been noted, as has the primary, recrystallized, or remobilized 

texture of the sulfide sampled. In a handful of ore samples, 

two or three coexisting sulfides have been analyzed in an 

attempt to utilize sulfur isotopes for geothermometry.

Sulfur and lead (Pb) isotopic data on ores can be powerful indicators of the sources of sulfur and metals to the deposit 

and can help to constrain the possible sulfide precipitation 

mechanisms that lead to economic ore accumulation. Additionally, if the spatial sampling is sufficient, identification of 

sulfur isotopic gradients may provide vectors toward thermal centers of fluid upwelling or provide information on the 

oxidation state and activity of sulfur in the source fluids. Lead 

isotopic gradients may help identify the proportions of metals 

contributed to the system from various host rocks. Isotopic 

variations with respect to ore paragenesis and textural state of 

the sulfides provide information on how the source fluids and 

the input of metal to them may have evolved over the lifespan 

of the system. In the case of the Greens Creek deposit, where 

lower greenschist facies metamorphism has caused recrystallization and local remobilization of the ores, comparison of isotopic values with respect to sulfide mineral textures provides 

the opportunity to evaluate the degree to which the isotopic 

systems may have been reset or modified.

Sulfur and Lead Isotope Characteristics of the Greens 

Creek Polymetallic Massive Sulfide Deposit, Admiralty 

Island, Southeastern Alaska

Cliff D. Taylor, Wayne R. Premo, and Craig A. Johnson
242 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

In the following sections we provide brief reviews of the 

regional and local geology, Greens Creek ore types, mineralogy, and metal zonation in order to provide background 

for the sulfur and lead isotope discussion that follows. We 

also review the recent literature for previous sulfur and lead 

isotope data. We then present the sulfur and lead isotope data 

obtained from the Greens Creek system as well as a number 

of other mineralized occurrences elsewhere on Admiralty 

Island. The regional values are used for comparison of the 

Greens Creek system to other Triassic-age occurrences on the 

Island and to contrast the Triassic mineralization against older 

and younger mineral occurrences. The initial lead-isotope 

compositions of probable source rocks to the Greens Creek 

ores are shown in this chapter in the context of the ore leadisotope systematics. The radiogenic isotopic data on the host 

rocks and a full discussion of their isotopic character as they 

relate to petrogenesis and age relationships are presented by 

Premo, Taylor, and others (chap. 11). Finally, we discuss the 

data presented in terms of a genetic model for Greens Creek 

and how it compares with similar data from other major ore 

districts and deposit types.

Regional and District Setting

Terrane Relationships

Host rocks to the Greens Creek deposit on Admiralty 

Island are within the Admiralty subterrane of the Alexander terrane (Berg and others, 1972, 1978; Churkin and 

Eberlein, 1977; see fig. 2 and a more complete presentation 

of southeastern Alaska terrane relationships in chap. 2). 

The general evolution of the terrane has been discussed by 

Samson and others (1989) who suggested, based primarily 

on whole-rock neodymium-strontium radiogenic isotopic 

studies, that it has the characteristics of a wholly oceanic 

island arc (also see chap. 11). The terrane is an allochthonous, 

continent-sized piece of intraoceanic island-arc crust that 

began forming in latest Precambrian time in low latitudes. It 

consists of as much as 35,000 feet of predominantly marine 

sedimentary and volcanic strata, and plutonic rocks, of latest Precambrian(?) to Middle(?) Jurassic age (Gehrels and 

Saleeby, 1987; Gehrels and Berg, 1994). Rift-fill stratigraphic 

sequences and bimodal volcanism along the eastern edge of 

the terrane (Taylor, 1997; Taylor and others, 1995a and b, 

1999a, 2000a) mark the beginning of an extensional tectonic 

event in latest Triassic time that either split the terrane or 

separated it from its low-latitude offshore position and transported it to its present position on the western North American continental margin (Gehrels and Berg, 1994). Accretion 

may have commenced by Early or Middle Jurassic (McClelland and Gehrels, 1990) or Late Jurassic (Saleeby, 1994) and 

was complete by about middle Cretaceous. Collision resulted 

in regional metamorphism and deformation related to underthrusting of the margin. This produced relatively flat-lying, 

northwest-vergent thrust faults identified underground and in 

surface outcrops on Admiralty Island (see chaps. 7 and 13). 

Compilation of regional metamorphic facies by Dusel-Bacon 

(1994) places Triassic and older rocks on northern Admiralty 

Island within lower to middle greenschist facies isograds. In 

early Tertiary time (Goldfarb and others, 1991; Miller and 

others, 1994), oblique subduction changed to right-lateral 

transcurrent motion along the margin, imparting the present 

structural grain to the country rock, and caused the formation 

of numerous, subparallel, high-angle, strike-slip faults that 

have dismembered the outboard terranes.

District Geology

The eastern margin of the terrane is marked by a discontinuously exposed, 600-km-long belt of rocks that host 

numerous polymetallic volcanogenic massive sulfide (VMS) 

occurrences (see figure 1, inset a in chap. 2), including Greens 

Creek and Windy Craggy, the most significant VMS deposit in 

Alaska and the largest in North America, respectively. Stratigraphy within the belt consists of a 200–800-m-thick sequence 

of conglomerates, limestones, marine clastic sediments, and 

tuffs that are intercalated with and overlain by a distinctive 

unit of mafic pyroclastics and pillowed flows (see figure 3 in 

chap. 2). Faunal data bracket the age of the host rocks between 

early Carnian (early Late Triassic) and late Norian (middle 

Late Triassic) time (see chap. 12). Changes in the stratigraphic 

setting and chemistry of the volcanic rocks from south to 

north along the belt are accompanied by crude yet systematic 

changes in the structural appearance, chemistry, and mineralogy of the occurrences. Together, these systematic variations 

suggest important spatial or temporal changes in the Late Triassic tectonic/metallogenic environment. The geologic setting in 

the south is consistent with shallow subaqueous emplacement 

on the flanks of the Alexander edifice. Northward, the setting 

changes to increasingly deeper subaqueous deposition in an 

evolving back-arc or intra-arc rift basin (Taylor, 1997; Taylor 

and others, 1995a and b, 1999a, 2000a, chap. 2).

In the southern end of the belt, felsic volcanic rocks fill 

the position in the sequence immediately overlying a basal 

conglomerate. On Annette and Gravina Islands the rhyolites 

are continuous, massive, flow-banded units with arclike geochemistry. On the Cornwallis Peninsula the Keku Volcanics 

are approximately 300 meters thick. The position low in the 

section beneath the overlying mafic volcanics as well as the 

distinctive peralkaline chemistry of the Keku Volcanics suggest 

their origins as bimodal volcanics produced during the initiation of rifting. Rhyolites are largely absent north of Keku Inlet, 

and their place low in the section is occupied by minor basalt 

flows interbedded with black shales. The occurrence of felsic 

volcanism prior to basaltic volcanism throughout the southern 

portion of the belt and the peralkaline composition of the Keku 

Volcanics are typical features of intra- and back-arc rifts. The 

transition from calc-alkaline rhyolites to peralkaline rhyolites 

and finally to basalt northward along the belt is also consistent with a shift from a proximal-arc to an arc-slope or basin 
Deposit Geology 243

margin setting. The peralkaline Keku rhyolites formed by small 

degrees of partial melting of a deep source during the earliest 

stages of rifting of a thick overlying oceanic island arc crust.

In the southern portion of the belt the rhyolites are overlain 

by shallow water, dolomitic limestones that in places contain 

ooids (Muffler, 1967; Berg, 1973), indicative of formation at 

wave base. They also contain carbonate turbidites and carbonate breccias with fining upwards sequences suggesting the 

destruction of a shallow carbonate ramp by onset of rifting. The 

limestones are present as 15-meter-high cliffs on the Cornwallis 

Peninsula but thin markedly northward. They occur discontinuously in the Duncan Canal area and across Admiralty Island. In 

Gambier Bay they are present as a discontinuously exposed carbonate/dolomite breccia near the base of the section. In the Cliff 

Creek Cirque, and in several locations along Gallagher Ridge 

immediately south of the Greens Creek mine, thin carbonate 

beds occur just below, and intercalated with, the capping basalts 

of the Hyd Group. North of Admiralty Island, limestones appear 

to be absent from the section.

The disappearance of the limestones from the stratigraphy is accompanied by a corresponding evolution in 

the sedimentary portion of the stratigraphy. As far north as 

Keku Inlet, the middle portion of the section is composed 

of very limy, arkosic sediments characteristic of proximal, 

carbonate-rich sources on the flanks of the Alexander edifice. 

From Zarembo Island northward the sediments become 

highly graphitic, pyritic black shales, indicative of an anoxic 

to euxinic, sediment-starved depositional environment distal 

to the flanks of the rift. At Greens Creek the shales (argillites) are intercalated with dolomitic limestone, and at Windy 

Craggy the black shales are markedly calcareous (Peter and 

Scott, 1999).

Everywhere throughout southeastern Alaska and neighboring British Columbia the Triassic stratigraphy is capped by 

a thick (200–600 m) sequence of basalts. They are massive to 

pillowed and often show spectacular volcaniclastic textures. 

In hand specimen and thin section the basalts are vesicular 

and mostly aphanitic with minor porphyritic-aphanitic varieties containing relict phenocrysts of rare olivine, clinopyroxene, plagioclase, and hornblende. Compared to the highly 

foliated Paleozoic greenstones of the Alexander terrane, these 

Norian-age basalts are relatively undeformed. The geochemistry of the volcanic host rocks has been modified by sea-floor 

alteration as well as mid-greenschist facies regional metamorphism during collision and underthrusting of the Alexander 

terrane with the North American continental margin. However, a heavily arc-contaminated, primitive basaltic suite of 

rocks is distinguishable based upon immobile-element ratios 

(see chap. 2), radiogenic isotopes (see chap. 11), and relict 

mineralogy in the least-altered samples.

Deposit Geology

Mine Sequence Nomenclature and Stratigraphy

The Greens Creek deposit is located at the contact 

between a footwall sequence of predominantly mafic-ultramafic volcanic rocks, minor clastic sediments, hypabyssal 

sills and intrusions, and a hanging wall of black argillites 

(fig. 1). Five main rock types are recognized in the stratigraphic footwall to the Greens Creek deposit. In proximal 

to distal order they are: (1) a white to gray, dense, hard, 

siliceous sericite-phyllite (SR for siliceous rock); (2) variably 

C

F

F

Unconformity

Unconformity

C

?

?

Pillow/massive basalt

Pyritic-graphitic argillite

Limestone/dolomite

Greenstone

Siliceous/cherty argillite

Stratiform massive sulfide

Serpentinite

Polymictic conglomerate

Gabbroic dikes/sills

EXPLANATION

Greens Creek Mine

Upper

Triassic

(part)

Permian

Carnian

Norian

F Macrofossils

C Conodonts

Figure 1. Composite stratigraphic column of the Upper Triassic 

section at the Greens Creek mine, northern Admiralty Island.
244 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

quartz-carbonate-pyrite veined, dark gray to greenish sericite 

phyllite (SP); and (3) carbonate-pyrite-quartz veined, light to 

dark green, chlorite phyllite (CR for chloritic rock). Footwall 

lithologies that have less consistent spatial distribution are: 

(4) serpentine-chlorite phyllites (SC) and (5) maripositephyllites (MP). Rarely, poorly preserved gabbros and postore diabase dikes are recognized (Taylor and others, 1999b, 

2000a, 2000b; chap. 6).

Hanging-wall rocks are dominated by massive and slaty 

black argillites (MAs and SAs, respectively). In underground 

exposures and in hand samples, the MAs are generally dull, 

very dark gray to black, blocky, and thick bedded. They are 

composed of very fine silt to mud-sized grains of fine crystalline, organic-rich dolomite, and lesser quartz and feldspar in 

a matrix of dark organic residue and carbonate (dolomite). 

The SAs are also dark gray to black but are platy and thin 

bedded and often have a shine on parting surfaces. In contrast 

to the MAs, the SAs have fine-grained quartz, feldspar, and 

muscovite as their major component with lesser fine crystalline organic-rich dolomite in a matrix of dark organic residue. 

More carbonate-rich variants of these two basic rock types, 

dolomitic massive and slaty argillites (DMAs and DSAs, 

respectively), occupy variable stratigraphic positions. These 

beds represent quiescent periods of carbonate deposition interspersed with dolosiltstone and organic-rich siliciclastic layers 

characteristic of the distal turbidite sedimentation that formed 

the MAs and SAs.

A subset of DMAs have the genetically important 

distinction of being located in the footwall between the 

phyllites and ore (Taylor and others, 2000a). When present, 

they occur as a single, discontinuous massive lens of medium 

to coarse crystalline dolomite, which can contain peloidal 

textures or even poorly preserved fossil fragments (typically 

crinoid stems). In a few cases, such footwall DMAs have 

been observed to contain fragments of the Triassic indicator 

fossil Halobia (J.M. Proffett, oral commun., 1999). Where 

footwall carbonate bodies grade into white carbonate ore 

(WCA), the massive dolostone becomes indistinguishable 

from the hydrothermal quartz-dolomite veins that constitute 

the majority of the WCAs. Thus, in proximal areas of intense 

alteration the distinction between a primary, fossil-bearing, 

depositional carbonate unit and a hydrothermal carbonate 

body produced during mineralization becomes blurred.

The existence of a thin, discontinuous carbonate platform on the footwall phyllites is an important point both in 

terms of determining the tectonic setting at Greens Creek 

just prior to mineralization and providing a time-stratigraphic 

marker horizon useful for regional correlation. The presence 

of platform carbonates in the immediate footwall suggests 

that the depositional environment at Greens Creek just prior 

to the onset of mineralization was a relatively quiescent, 

shallow water, marine setting on the flanks of the Alexander 

edifice. The presence of Halobia fragments establishes the age 

of the carbonate bodies as Norian (Late Triassic) (see chap. 

11), consistent with the age of the conodont-bearing layers 

in the immediate hanging-wall argillites. Additionally, the 

stratigraphic position of the carbonate unit low in the sedimentary portion of the Upper Triassic section at Greens Creek 

is consistent with the stratigraphic position of other similar 

carbonate units at other Late Triassic occurrences in southeastern Alaska south of Greens Creek (Taylor, 1997; Taylor and 

others, 1999a, 2000a).

A problematic feature of the footwall at Greens Creek 

is the discontinuous presence of silicified conglomerates and 

breccias. When present, they occur as 0–30-meter-thick lenses 

of dense, white to gray, nonporous accumulations of silicified clasts in a siliceous matrix. The appearance of the clasts 

suggests that their protoliths were derived primarily from the 

underlying phyllites and, less prevalently, from the footwall 

carbonates. Clasts are generally 1–10 cm in size and are 

distinctly subrounded or subangular, indicating that there may 

be at least two types of breccias. The first type are polymictic, 

with subrounded clasts, and are likely conglomeratic breccias 

that formed as locally derived debris flows in response to the 

onset of Late Triassic rifting. The second type, subangular 

breccias that constitute the majority of these footwall accumulations, are monomictic and are spatially associated with the 

proximal footwall SR lithology. They are probably tectonic 

breccias produced by fracturing of the SRs after ore formation. A third, less common type of breccia has been observed 

in a few locations underground. This is a polymictic breccia 

in the immediate hanging wall that consists of slightly smaller 

(1–5 cm) clasts of predominantly white quartz pebbles, minor 

phyllite, and argillite in a matrix of fine to coarse crystalline, 

subhedral pyrite (also see chap. 7). This breccia, here interpreted as a conglomeratic lens that formed as a debris flow 

during deposition of the hanging wall, is distinctly different in 

terms of its stratigraphic position, size and composition of the 

constituent clasts, and composition of its matrix.

Similar to the footwall carbonates, the breccias have 

significance both as indicators of the tectonic environment at 

Greens Creek and as a possible stratigraphic marker horizon. 

Elsewhere in southeastern Alaska south of Greens Creek the 

base of the Upper Triassic section is marked by a polymictic 

conglomerate of local derivation that is thought to mark the 

onset of Late Triassic rifting. In other locations, this conglomerate is consistently located beneath the lower volcanic 

member of the Hyd Group, which is in turn overlain by a thin 

platform carbonate unit. It therefore serves as a correlatable 

marker horizon at the base of the Upper Triassic section as 

well as a tectonic indicator of the onset of rifting (Taylor, 

1997; Taylor and others, 1999a).

Ore Types and Ore Mineralogy

Ore lithologies at Greens Creek are broken into two main 

groups: (1) massive sulfide ores and (2) semimassive or disseminated sulfide gangue-rich “white” ores. The massive ores 

contain greater than 50 percent sulfides and consist of massive, 

fine- to very fine grained ore in which base-metal sulfides are 

greater than pyrite (MFB, MVB) and massive, medium- to very 
Ore Distribution: Ore-Type Zonation and Metal Zoning 245

fine grained pyrite-rich ore in which pyrite predominates (MFP, 

MVP). All the massive ores have variable amounts and proportions of quartz, dolomite, sericite, barite, and fuchsite gangue. 

Graphite is a less ubiquitous but locally abundant gangue 

mineral (Taylor and others, 1999b, 2000b).

The white ores are a group of mineralized lithologies 

that contain less than 50 percent sulfides and are defined 

by their principal gangue mineral. They commonly contain 

base metal and spectacular precious-metal enrichments. 

There are three types: (1) white carbonate ore (WCA) and (2) 

white siliceous ore (WSI) are most common; and (3) white 

baritic ore (WBA). The WCAs are characterized by granulartextured, medium- to coarse-grained dolomite. Accessory 

gangue minerals, as previously mentioned, are present but 

less abundant than in WSIs. The WSIs are dominated by 

massive cryptocrystalline aggregates of hydrothermal quartz 

or chert and regularly contain significant dolomite, sericite, 

fuchsite, and barite. WBAs are characterized by coarse, sugary, massive barite and other gangue as above. Commonly, 

they are not ore grade.

All the above ore types include subtypes that are modified 

by the presence of veins, breccias, and gouge or rubble zones 

produced during faulting or folding. Veining due to secondary remobilization and accompanying recrystallization during 

metamorphism can result in spectacular enrichments of free 

gold and a variety of silver sulfosalt minerals. Breccias appear 

to be both primary sedimentary breccias produced by slumping 

of the massive sulfides and inclusion of clasts of the underlying 

as well as overlying host rocks, and tectonic breccias produced 

during deformation. Solution brecciation may also be present, 

particularly in the WCAs. For a more complete presentation of 

ore types, mineralogy, and ore textures, see chapter 9.

Ore Distribution: Ore-Type Zonation 

and Metal Zoning

The mineral deposit at Greens Creek (fig. 2) is nearly 

continuous along the phyllite/argillite contact and consists of 

three main orebodies—the East, West, and Southwest—and 

three extensions—the Northwest, 200 South, and 5250. This 

section is excerpted from chapter 6. See chapter 6 for a more 

complete presentation. The East orebody outcrops at the Big 

Sore and is continuous along a north 10o

–20o east strike for 

920 m to the south. The orebody plunges to the southwest at 

20o and dips initially at 60° to 80° to the west and flattens out 

to near horizontal due to F3 folding. The main Klaus fault 

bisects the flat, lower portion of the East ore zone so that it 

appears to form two parallel flat panels. The demarcation line 

between the East and West orebodies occurs where the ore 

transitions from the lower flat-lying panel back to near vertical. The width of the East orebody in plan is approximately 

460 m with a true thickness of ore of 3 to 12 m.

The West orebody continues to the west beneath the 

Klaus fault and is subdivided into two subzones and two 

extensions: the Central West, and 9A subzones, and the 

Northwest West and 5250 extensions (fig. 2). The Central 

West ore zone lies between the East orebody and the Maki 

fault. The near-vertical portion is referred to as the Wall, 

which has an average thickness of 3 to 6 m, strikes northwest 

for 620 m and dips steeply (80° to 90°) to the west for over 

90 m of vertical extent. The ore horizon then begins to flatten 

due to F3 folding. The northern half of the flattened part forms 

a 3- to 5-meter-thick ore horizon, dipping at 45° to the west, 

that pinches out to less than 1 m to the north. In the southern half, the intensity of F3 folding is greater and the 2- to 

4-m-thick ore becomes flat and then recumbent with 10° to 

20° E dips. This band of east-dipping ore forms the upper limb 

to a nearly isoclinal, recumbent F2 fold. The lower limb is 

characterized by a marked increase in thickness up to 100 m. 

The thickened lower limb runs for a strike length of 250 m and 

varies in thickness from 10 m up to a maximum of 120 m.

The Maki fault marks the transition from the Central 

West ore zone into the 9A ore zone. The 9A zone is composed 

of numerous fault blocks of ore, which, when the right-lateral 

200S

200S

Bench

SW

SW

Bench

5250

Central

West

NWW

9A

EAST

Maki

fault

zone

0 1,000 FEET

Figure 2. Plan view map of the Greens Creek mine showing 

the spatial distribution of major orebodies and major 

structures.
246 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

strike-slip motion of the Maki fault zone is removed, represent 

the continued southwest, down-plunge continuations of the 

East and Central West ore zone. Individual fault blocks maintain the typical stratabound nature of Greens Creek ores, but 

detailed structure interpretations are difficult due to complexity of faulting within this zone. The overall strike length of 9A 

is 600 m with a plan width of 150 m.

The two extensions to the West orebody, the Northwest 

West and 5250, represent the fault-offset portions of the 

Central West ore zone and East orebody, respectively. Both 

zones show the effect of increasing intensity of F2 folding, 

and the northern 100-m portion of 5250 may be transected by 

the Klaus fault. The 5250 orebody strikes north-northwest for 

550 m and has a plan width of 100 m. To the south, the ore 

trend becomes more regular with the ore dipping to the west 

at 60° to 70° and plunging near 20° south. The 5250 zone 

is atypical of most ore zones at Greens Creek, as the zone 

contains a high proportion of white baritic ore as compared 

to the others. The Northwest extension is the dextral fault 

translation of the Central West. The Northwest shows the 

continuing development of the F2 folding noted in the Central West. The ore decreases in thickness downdip and to the 

south from 50 m to less than a few meters. A pair of recumbent F2 folds that form an acute “S” when viewed in cross 

section dominates the large-scale structure. The upper fold 

is a west- to northwest-closing syncline (cored by argillite) 

that lies above an east- to southeast-closing anticline (cored 

by phyllite) below. The main part of the orebody lies on the 

lower limb of the syncline.

The Southwest orebody extends from the West/Northwest orebody as a continuation of the trend along the lower F2 

fold. The Southwest orebody is subdivided into two zones, the 

Upper and Lower ore zones, and has one extension, the 200 

South. The Upper Southwest ore zone strikes north 20° west 

for 260 m and has a plan width of 210 m. The Lower Southwest ore zone strikes approximately due north for over 360 m 

and the main portion of the ore zone has a plan width of 240 

m. The vertical extent for the entire Southwest orebody runs 

from 35 m below sea level to 275 m above with the demarcation line between lower Southwest and upper Southwest being 

placed at approximately 120 m above sea level.

Exploration downdip and along strike of the Lower 

Southwest resulted in the discovery of the 200 South extension along strike to the south. The 200 South extension displays the same gross-scale geometry of the Lower Southwest 

with a steeply dipping eastern limb and a nearly flat-lying 

western limb. The 200 South extension strikes north 10°–20° 

west for 340 m. The plan width is 60 m with an additional 

140-m width, the 200 South Bench, to the west of the main 

mass of ore, which is similar to the Lower Southwest thin, 

flat-lying, SW Bench mineralized trend. The central and 

upper half of the eastern limb have ore thickness of 45 m. 

The thickness tapers downdip and along strike to the south 

until the mineralization becomes too narrow to economically 

recover. Vertically, the 200 South extension extends from 

160 m below sea level to 65 m above.

Due to the polyphase deformation and faulting at Greens 

Creek, the ore stratigraphy and metal zonation from footwall 

to hanging wall and from center to margin of an orebody is 

quite variable and difficult to reconstruct. However, there is a 

sequence of ores present in most of the orebodies such that an 

original configuration is suggested (Taylor and others, 1999b, 

2000b). Individual orebodies are generally centered over a particularly thick footwall sequence of highly siliceous SRs (see 

figure 3 in chap. 6). Laterally away from this area of intense 

alteration the first ore types encountered above the footwall are 

WSIs followed upward and outward by WCAs and rare WBAs 

at the extreme lateral edges. These white ores are overlain by 

MFPs that are copper-rich in proximal core areas and change 

upward and outward toward lower copper-gold grades and 

increasing zinc. Ores change gradationally into increasingly 

higher grade zinc-lead-silver-(gold)-rich MFBs as the argillite hanging wall and the thinned distal edges of the deposit 

are reached. Distal ore progressions often are characterized 

by carbonate- and barite-rich white ores against phyllites that 

transition into MFBs toward the hanging wall. This progression of ore types from white ores against the phyllites grading 

into massive pyritic ores and then into the massive base-metalrich ores against the argillites is the pattern most commonly 

seen throughout the mine (Taylor and others, 1999b, 2000b; 

see chap. 6, fig. 3). Although this pattern of ore types is highly 

simplified, and numerous examples can be found to contradict 

this model, it is broadly consistent at the orebody but not at a 

deposit scale. There are distinct differences between orebodies such that trying to explain the orebodies as proximal-distal 

portions of a single deposit is not possible. The implications of 

this observation is that multiple centers of upwelling may have 

been active along a paleo-Maki fault but with variable and different fluid chemistry and temperatures (for example, Freitag, 

2000). For details of metal zonation in individual orebodies 

see chapter 6.

Previous Sulfur and Lead Isotope 

Studies

Very little previous isotopic data are available for the 

Greens Creek deposit or for other mineral occurrences on 

Admiralty Island. Newberry and others (1997) display isotopic 

ranges of both sulfur and lead for Late Triassic-hosted VMS 

deposits of southeastern Alaska. Sulfide sulfur spans a range 

of 0 to about –15 per mil d34S, and the isotopically light values 

are attributed to the light isotopic composition of Late Triassic seawater. Ore lead isotope values form an irregular field 

with 206Pb/204Pb values of 18.65 to18.85 and 207Pb/204Pb values 

of 15.52 to 15.60 (Newberry and others, 1997). Van Nieuwenhuyse (1984) reported lead isotope values for “composite 

samples of galena-bearing mineralization” from Pyrola and 

Glacier Creek and a galena from Greens Creek (exploration 

core PS-27, 660’). The Greens Creek sample has ratios of 

206Pb/204Pb = 18.670, 207Pb/204Pb = 15.610, and 208Pb/204Pb = 
Isotopic Data 247

38.449. The Pyrola sample has ratios of 206Pb/204Pb = 18.520, 207Pb/204Pb = 15.570, and 208Pb/204Pb = 38.224. On the basis of 

these analyses, Van Nieuwenhuyse (1984) concluded that the 

deposits formed in either a primitive arc or oceanic volcanic environment and that the data also support a back-arc or 

marginal basin environment in which the crust was ensimatic 

in nature. Newberry and Brew (1999) reported an additional 

galena lead isotope analysis from Greens Creek with ratios of 

206Pb/204Pb = 18.635, 207Pb/204Pb = 15.583, and 208Pb/204Pb = 

38.239. They note that this analysis falls within the range of 

ore-lead previously determined (Newberry and others, 1997) 

for Triassic-Jurassic VMS deposit of southeastern Alaska and 

nearby Canada. No sulfur isotopic data for Greens Creek or 

any other mineral occurrences on Admiralty Island have been 

reported in the literature.

Methods

Lead Isotope Analyses

Lead isotope samples were obtained either by microdrilling or handpicking slabbed hand samples and core. Mineral 

separates were checked for purity under a binocular microscope. Each was then hand-ground in an agate mortar to 

homogenize the sample. Analyses were performed at the U.S. 

Geological Survey in Denver, Colorado. Galena separates were 

roughly measured out (about 0.5 to 1 mg) in order to provide a 

dilute enough concentration of lead by dissolution with ultrapure 7N nitric acid in a precleaned 7-mL-volume, PFA-Teflon 

vial to produce a 1 to 9V signal during the thermal ionization 

mass spectrometry. Dissolution of the sulfide fractions were 

aided by heating on a hot plate overnight. Samples were then 

evaporated and redissolved in dilute nitric acid. Other sulfide 

separates (excluding galena) were washed once with ethanol 

and ultrapure distilled water and then leached once with 1N 

hydrochloric acid for 10 minutes in an ultrasonic bath and 

finally rinsed with ultrapure water. The separates were dissolved in 7-mL PFA Teflon vials with ultrapure 2N–6N nitric 

acid and then spiked with a dilute mixed tracer of 205Pb-233U- 236U-230Th. Extraction of lead was achieved using Dowex AG 

1-X8 anion-exchange resin in a 0.5–1N hydrobromic acid 

medium. Uranium and thorium were separated using the same 

kind of anion resin in a 6N nitric acid medium.

For all samples, lead was loaded onto a single rhenium 

filament with very dilute phosphoric acid and ionized in the 

mass spectrometer at currents between 1.7 and 2.3 amps, corresponding to a temperature range of about 1,150 to 1,300°C 

for which mass fractionation factors were calculated. Uranium 

and thorium were loaded together onto rhenium side filaments 

and run in the triple rhenium filament mode at temperatures 

of about 2,100°C. Lead, uranium, and thorium isotopic ratios 

were measured using a fully automated, multisample, singlecollector, VG Isomass 54R thermal-ionization mass spectrometer. Instrumental bias was monitored using the NBS Common 

Lead Standard 981 and was found to be negligible.

Lead isotopic ratios were corrected for mass fractionation 

of 0.08 ± 0.03 percent per atomic mass unit and a laboratory blank of 6 ± 4 picograms total lead (negligible) with 

an assumed composition of 206Pb/204Pb = 18.458 ± 0.093, 207Pb/204Pb = 15.287 ± 0.03, and 208Pb/204Pb = 37.54 ± 0.11. 

Raw data were reduced using the programming of Ludwig 

(1980, 1985) and plotted using Isoplot software of Ludwig 

(1991).

Sulfur Isotope Analyses

Sulfur isotope samples were obtained by handpicking 

or microdrilling slabbed hand samples and core, checked for 

purity under a binocular microscope, and hand-ground in an 

agate mortar to homogenize the sample. Analyses were made 

in the stable isotope laboratories of the U.S. Geological Survey 

in Denver, Colorado. Quantities of a few hundred micrograms 

of mineral powder were weighed into tin capsules along with 

1–2 milligrams of vanadium pentoxide oxidant. The samples 

were converted to sulfur dioxide gas using a Carlo Erba NA 

2500 elemental analyzer, and the gases were admitted directly 

to a Micromass Optima mass spectrometer. Isotope ratios were 

measured by isotope ratio monitoring using a method similar 

to that described by Giesmann and others (1994). Sulfur isotope compositions are reported in d-notation in units of per mil 

relative to Cañon Diablo troilite (CDT). Reproducibility was 

generally within ± 0.2 per mil.

Isotopic Data

Sulfur Isotopes

A comprehensive sulfur isotopic study was conducted on 

221 sulfide mineral separates and bulk ore samples and 14 barite separates from samples collected from the mine workings 

and underground drill core. Fifty-five sulfide mineral separates 

and four barites from various mineral occurrences and from 

country rock on Admiralty Island were also analyzed. Figure 3 

shows all the sulfide and sulfate d34S results obtained for the 

Greens Creek deposit. Data for samples from drill core and 

underground exposures in the mine are contained in table 1. 

Data for samples from Admiralty Island host rocks and 

mineral occurrences are presented in table 2. Greens Creek 

sulfides are strongly 34S-depleted showing a d34S range of –38 

to 2 per mil and a distinctly unimodal distribution with the bulk 

of the analyses between about –9 and –16 per mil. Greens Creek 

sulfates fall between 13.4 and 21.9 per mil, which is within the 

range exhibited by seawater sulfate in Triassic time (Strauss, 

1997; Claypool and others, 1980). Figures 4 A–C show the sulfur isotope data sorted according to the texture of the sulfide 

analyzed, the mine location, and the type of host rock or ore 

lithology, respectively. Primary-textured sulfides are generally 

more 34S-depleted than recrystallized or remobilized sulfides 

(see chap. 9 for descriptions and photomicrographs of sulfide 
248 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Greens Creek sulfur isotopes n=235

δ34S(CDT)

–50 –40 –30 –20 –10 0 10 20 30

FREQUENCY

0

2

4

6

8

10

12

14

16

chalcopyrite

galena

pyrite

pyrargyrite

sphalerite

tetrahedrite

barite

EXPLANATION

Figure 3. Histogram showing the distribution of all sulfide and sulfate d34S values obtained from the Greens Creek 

deposit. CDT, Cañon Diablo troilite.

textures); the isotopically heaviest primary-textured sulfide has 

a value of –10 per mil. Recrystallized sulfides span the isotopic range and have an almost bell-shaped distribution centered 

between –18 and –4 per mil. The range of remobilized sulfides 

is more restricted than that of the recrystallized sulfides, with a 

more restricted distribution as well, clustered between –10 and 

–16 per mil (fig. 4A).

Spatially, the two largest orebodies (West and Southwest) exhibit sulfur isotope values that span the range. The 

34S-enriched values are most likely to occur in the smaller and 

more distally located orebodies such as the East or 5250 (fig. 

4B). On a deposit scale the most 34S-enriched sulfides are in 

and near the footwall igneous rocks and white siliceous ores. 

The progression upward and outward toward 34S-depleted 

sulfides roughly follows the ore paragenesis from white ores 

against the footwall, to massive pyritic, to massive base-metalrich ores against the hanging wall. Pyrite d34S values in the 

overlying shales exhibit a wide range of values (fig. 4C).This 

comparative 34S enrichment of footwall sulfur isotope values 

over those in the hanging wall is further demonstrated by the 

histograms shown in figure 5. Minewide, the average value 

of sulfide sulfur in the footwall phyllites and white siliceous 

ore type is –9.9±5.0 per mil d34S. The average value of sulfide 

sulfur in massive fine grained base-metal-rich ores and in the 

hanging-wall argillites is –15.5±6.6 per mil d34S. Thus, on 

average, ore stratigraphic profiles at Greens Creek exhibit a 

5.6 per mil d34S depletion from footwall to hanging wall.

Figure 6 shows the sulfide sulfur isotope data sorted 

by mineralogy. Pyrite values span the entire isotopic range, 

a feature that has been noted at other sediment-hosted massive sulfide deposits (Ohmoto, 1986). Tetrahedrite values also 

are broadly distributed. In contrast, chalcopyrite, sphalerite, 

galena, and pyrargyrite cluster tightly between –11 and –18 

per mil. Whole rock analyses of MFP and MFB ore types 

show that they are isotopically indistinguishable, with compositions typically in the range –9 to –18 per mil (fig. 6). Examination of the histogram in figure 6 shows that the average d34S 

values increase in the order galena-sphalerite-pyrite, consistent 

with the order expected for equilibrium fractionation (Ohmoto 

and Rye, 1979). This same ordering was also observed for 

sulfide separates from individual hand samples. Pyritechalcopyrite, pyrite-sphalerite, and pyrite-galena mineral pair 

geothermometers generally gave extremely high or impossible 

temperatures. The sphalerite-galena mineral pair geothermometer yielded three relatively consistent and low temperature 

values with a range of 276–313°C.
Isotopic Data 249

Remobilized sulfides (n=61)

avg. δ34S value = –14.1 ± 4.5

δ34SCDT

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

2

4

6

8

10

12

14

Primary textured sulfides (n=28)

avg. δ34S value = –18.7 ± 7.0

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

2

4

6

8

Recrystallized sulfides (n=110)

avg. δ34S value = –13.6 ± 6.8

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

5

10

15

20

A

Figure 4. Greens Creek sulfide sulfur isotope data sorted by: (A) mineral texture, (B) mine location, and (C) type of 

host rock. n, number of samples. CDT, Cañon Diablo troilite.

It is important to note that wherever sulfur isotope determinations were made on multiple base-metal sulfides from 

the same sample, the minerals displayed textures indicative of 

recrystallization or remobilization. In most samples where only 

pyrite was analyzed, the pyrite displayed primary textures or 

had relict primary features. The base-metal sulfides that coexist 

with such pyrite were too fine grained and intimately intergrown to separate by conventional techniques. The base-metal 

sulfides that were of sufficient grain size to sample were always 

texturally recrystallized or remobilized. In the one sample (GC164-08) where recrystallized pyrite and coexisting sphalerite 

were analyzed, the pyrite-sphalerite geothermometer gave an 

isotopic equilibration temperature of 275°C. These relationships imply that the isotopic fractionations displayed by the ore 

sulfides may reflect isotopic exchange during the same event 

that modified the textures of the Greens Creek ores. The critical 

question is, therefore, whether the recrystallization/remobilization was the result of zone refining (for example, Hannington 

and others, 1998) during the mineralization process, or of metamorphism during the Cretaceous deformation.

Isotope analyses of sulfide minerals in host rocks and 

mineralized occurrences elsewhere on Admiralty Island 

show trends similar to Greens Creek (fig. 7). The 34S-values 

of sulfides from known or suspected Triassic-hosted mineral 

occurrences tend to be very low, whereas those of unknown 

or non-Triassic-hosted occurrences are generally in a more 

restricted range near 0 per mil. Analyses of barites from two 

Triassic mineralized occurrences on and north of the north 

shore of Gambier Bay (Taylor and others, 1992) range from 

12.8 to 14.6 per mil. Analyses of pyrites in Devonian(?)-

Triassic greenstones, phyllites, and other metaigneous rocks 

on Admiralty commonly are 0 to –12 per mil. Pyrite in 

country-rock argillite of Triassic age, like the hanging-wall 

argillite, is strongly 34S-depleted, with a range of –30 to –1 

per mil. The d34S values of sulfides from older host rocks are 

noticeably higher than the Greens Creek values.
250 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

200 South (n=26)

5250 orebody (n=11)

East (n=20)

Southwest (n=93)

West (n=81)

–40 –35 –30 –25 –20 –15 –10 –5 0 5

δ34SCDT

–40 –35 –30 –25 –20 –15 –10 –5 0 5

–40 –35 –30 –25 –20 –15 –10 –5 0 5

–40 –35 –30 –25 –20 –15 –10 –5 0 5

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

1

2

3

0

1

2

3

0

10

20

30

0

10

20

30

0

2

4

6

8

B

Figure 4. Greens Creek sulfide sulfur isotope data sorted by: (A) mineral texture, (B) mine location, and (C) type of 

host rock. n, number of samples. CDT, Cañon Diablo troilite.—Continued
Isotopic Data 251

MFB (n=60)

Hanging wall (n=26)

MFP (n=52)

WCA (n=37)

WSI (n=11)

Footwall (n=34)

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

2

1

3

4

C

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

4

8

12

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

4

8

12

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

4

8

12

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

2

4

6

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

1

2

3

δ34SCDT

Figure 4. Greens Creek sulfide sulfur isotope data sorted by: (A) mineral texture, (B) mine location, and (C) type of 

host rock. n, number of samples. CDT, Cañon Diablo troilite.—Continued
Table 1. Greens Creek sulfur isotope data, sample locations, and descriptions for samples from drill core and underground exposures. Sample id Mineralogy δ34S value DH depth Location Host rock Mineral texture Comments 350-2650 py -33.3 79 lower SW MFP primary primary textured clasts, very fine grained 350-2650 pyrar -16.8 79 lower SW MFP remobilized qtz-pyrar veinlets crosscutting MFP 350-2650 dup py -33.9 79 lower SW MFP primary primary textured clasts, very fine grained 764N1A tetr -5.6 upper SW WCA remobilized qtz-tetr-electrum veined dolomite 764N1B cpy -4.2 upper SW MCHT remobilized coarse tetr-cpy 764N1B tetr -5.0 upper SW MCHT remobilized coarse tetr-cpy 88-RN-80D py -9.9 103 East SPgr recrystallized clots of qtz-carb-py 88-RN-80H py -0.1 200 East SPgr recrystallized coarse pyrite 88-RN-80K py -11.9 310 East SP recrystallized coarse pyrite 88-RN-80N py -9.7 370 East SP recrystallized coarse py to 1 mm in carb 91-GC-01 gn -14.7 East MFB remobilized 91-GC-02A MFP -14.6 East MFP primary? 91-GC-02B bt 21.3 East WBA coarse xlline 91-GC-04B bt 13.4 East WBA coarse xlline 91-GC-04C acan -8.1 East WBA remobilized 91-GC-07 MFB -10.7 East MFB primary? orange, fine crystalline 91-GC-08A tetr -12.7 East WSI remobilized 91-GC-13 tetr -27.6 East MA remobilized graphite-tetr-qtz vein near hw contact 91-GC-14A bt 13.9 East WBA coarse xlline 91-GC-15 py -8.0 East WSI recrystallized ground up pyrite separate from Ar/Ar sample 91-GC-16 bt 14.8 East WBA coarse xlline dark gray, bedded 91-GC-17 bt 16.5 East WBA coarse xlline medium gray, sugary, ser-fuch rich 96-GC-01 pyrar -18.2 79 lower SW MFP remobilized 96-GC-02 sph -20.4 62.5 lower SW MFP recrystallized 96-GC-03 pyrar -15.3 79 lower SW MCHT remobilized 96-GC-08 py -23.3 16 lower SW MSA recrystallized spongy, subhedral grains, 50-100μm 96-GC-11 MFP -18.5 20 lower SW MFP recrystallized bright, euhedral-subhedral, 10-100μm 96-GC-12 MVB -11.5 21.5 lower SW MVB recrystallized orange, fine crystalline, euhedral to subhedral 96-GC-13 MFP -16.7 25.5 lower SW MFP clastic pyrite consists of massive to spongy aggregate

96-GC-14 py -28.3 31 lower SW FMSAS recrystallized cm-sized broken grains of py 96-GC-15 py -29.2 39 lower SW XMFBgr recrystallized 0.5 – -1.0 cm pyrites in framboid-rich graphitic 

96-GC-17 py-aspy -37.3 49 lower SW MFP recrystallized slightly spongy py with aspy replacement 96-GC-19 py-aspy -33.7 53 lower SW MFP recrystallized equal proportions of euhedal py-aspy 96-GC-19 sph -15.8 53 lower SW WCA remobilized 96-GC-21A tetr -16.2 62.5 lower SW WCA remobilized 96-GC-21B sph -15.9 62.5 lower SW WCA remobilized 96-GC-23 py-aspy -38.8 67 lower SW MFP recrystallized bright, massive euhedral with minor primary te

96-GC-24 MFP -16.8 72 lower SW MFP primary 50% recrystallized, 50% framboidal 96-GC-24 tetr -21.5 72 lower SW MFB remobilized Clot of tetr in qtz vein

96-GC-24 dup tetr -21.2 72 lower SW MFB remobilized Clot of tetr in qtz vein

96-GC-26 MFP -15.9 79 lower SW MFP primary framboidal pyrite in sph matrix

96-GC-29 MFP -14.4 89 lower SW MFP recrystallized clean, euhedral, 0.1-1.0 mm

96-GC-34 py -7.5 104 lower SW MDMA recrystallized bright, subhedral 50-200 μm

96-GC-38 py -6.3 148 lower SW MP recrystallized bright, euhedral-subhedral
Table 1. Greens Creek sulfur isotope data, sample locations, and descriptions for samples from drill core and underground exposures.—Continued 

Sample id Mineralogy δ34S value DH depth Location Host rock Mineral texture Comments

GC-1093-03 gn -15.3 lower SW WCA remobilized very coarse grained, monomineralic 

GC-1093-05 cpy -15.0 lower SW WCA remobilized gn-cpy clots in qtz-dol veins adj to MFP

GC-1093-05 gn -16.9 lower SW WCA remobilized gn-cpy clots in qtz-dol veins adj to MFP

GC-1136-08 py -14 443 lower SW MA recrystallized highly sheared/foliated

GC-1136-12 py -24.8 491 lower SW SA recrystallized finely laminated, minor py

GC-1136-21 py -17.2 541 lower SW MFP recrystallized (sph-rich) MFP bands

GC-1136-29 py -23.8 583 lower SW MFP recrystallized coarse pyritic

GC-1136-33 py -14.6 607 lower SW MFB recrystallized Pb-Zn rich

GC-1136-35 py -13.4 617 lower SW MFB recrystallized graphitic MFB lens in MA

GC-1136-36 py -25.1 626 lower SW MA recrystallized pyrite stringer (mean of two analyses)

GC-1136-39 py -7.8 652.5 lower SW MP recrystallized sericitic (mean of two analyses)

GC-1136-40 py -6.4 lower SW MP recrystallized

GC-1136-42A py -13.8 667 lower SW SCcb recrystallized breccia frags of SC in carb-py matrix. Clean py 

GC-1136-42B py -11.2 667 lower SW SCcb recrystallized breccia frags of SC in carb-py matrix. Clean py 

GC-1136-44 py -10 680 lower SW SC recrystallized SC phyllite (two identical analyses)

GC-1136-55 py -4.6 818.5 lower SW SC recrystallized serpentinite (chl-leuc?)

GC-1136-61 py -14.1 898 lower SW SC recrystallized euhedral to massive, spongy aggregates

yp60-721C-G PStsaE5.4170.01- yp fo stolc dna spsiw esraps

GC-127-17 MFB -5.3 1,001 East MFB remobilized

yp81-721C-G ISWtsaE700,11.7- ISW ni tolc BFM citiryp

GC-127-19 tetr -3.9 1,010 East WSI remobilized

GC-1514 -03 MFB -16.8 22 Northwest MFB recrystallized fine crystalline py-sph-gn, euhedral

GC-1514-14 py -8.6 381 Northwest SP recrytallized 1 cm sized clots in dolo-ser

GC-1514-25A py -27.2 489.8 Northwest MFB primary/recrystallized 1- -

- -

5 mm clastic grains in gn-rich MFB, spongy

GC-1514-25B gn-rich MFB -22.5 489.8 Northwest MFB remobilized gn-rich MFBGC-1514-34 py -2.4 636 Northwest WCA recrytallized wispy, in silicified dolo

GC-1514-36 py -11.7 648 Northwest MFP recrystallized qtz-carb matrix

GC-1514-38 py -11.5 654 Northwest MFP recrystallized bright, in qtz-carb matrix

GC-1514-40 py -12.4 676.5 Northwest MFP recrystallized bright, cpy-rich(?)

GC-1514-41 py -12.4 682 Northwest MFP recrystallized bright, cpy-rich(?)

GC-1514-42 cpy-rich MFP -12.2 686.5 Northwest MFP recrystallized non-remobilized cpy-rich portion

GC-1514-44 cpy -13.1 696 Northwest MFP remobilized cpy on fracture

GC-1514-44 cpy-rich MFP -12.1 696 Northwest MFP recrystallized cpy-rich MFP

GC-1514-45 cpy-rich MFP -12.6 703 Northwest MFP recrystallized cpy-rich MFP

GC-1514-46 cpy -12.8 707 Northwest MFP remobilized euhedral cpy and sph on fracture

GC-1514-46 cpy-rich MFP -12.2 707 Northwest MFP recrystallized cpy-rich MFP

GC-1514-46 sph -14.1 707 Northwest MFP remobilized euhedral cpy and sph on fracture

GC-1514-46 dup cpy -12.7 707 Northwest MFP remobilized euhedral cpy and sph on fracture

GC-1514-49 py -12.5 718 Northwest SR recrystallized wispy, semimassive band, euhedral py, anhedra

GC-1514-52 py -11.1 735 Northwest SRcx recrystallized cpy-rich clastic py to 1 cm, subhedral-euhedral 

GC-1514-53 py -9.8 737 Northwest SRcx recrystallized cpy-rich clastic py to 1 cm, subhedral-euhedral 

GC-1514-57 py -10.5 779 Northwest SR recrystallized in siliceous chl-carb schist

GC-1527-01 py -6.8 96 Northwest SP recrystallized subhedral, <1mm disseminated

GC-1527-05 py -9.5 357.4 Northwest MSR recrystallized
Table 1. Greens Creek sulfur isotope data, sample locations, and descriptions for samples from drill core and underground exposures.—Continued Sample id Mineralogy δ34S value DH depth Location Host rock Mineral texture Comments GC-1527-07A py -17.6 390.5 Northwest MDMA recrystallized subhedral, dull, bronze colored, fine grained GC-1527-07B cpy -12.3 390.5 Northwest MMA remobilized remobilized cpy in qtz GC-1527-07C py -11.4 390.5 Northwest MDMA recrystallized bright, coarse crystalline GC-1527-08 cpy -12.7 397.5 Northwest WCA remobilized 2 mm x 1 cm clots, silicified matrix GC-1527-09 MFB -13.4 402.5 Northwest MFB primary spectacular framboidal and colloform banded GC-1527-12 cpy-rich MFP -3.8 429.7 Northwest MFP recrystallized GC-1527-13 cpy-rich MFP -9.7 438.5 Northwest MFP recrystallized spongy to clean massive aggregates GC-1527-14 cpy -15.3 447.2 Northwest WCA remobilized cpy remobilized, siliceous, wisps of dull, brassy 

GC-1527-15 py -11.7 454.2 Northwest WCA recrystallized dull, brassy, fine grained GC-1527-16 cpy-rich MFP -11.0 459.8 Northwest MFP recrystallized GC-1527-18 MFP -11.5 472.2 Northwest MFP recrystallized euhedral-subhedral, dull, brassy, sph-rich matri

GC-1527-19 MFP -9.1 482.5 Northwest MFP recrystallized euhedral-subhedral, bright, bronze colored, mod

GC-1527-20 MFB -11.1 491.5 Northwest MFB recrystallized gn-tetr rich, banded with pyritic DMA GC-1527-21 tetr -12.1 498 Northwest MFBgr remobilized tetr-acn-cpy veinlets GC-1527-22 py -10.9 498 Northwest MFPgr recrystallized fine grained, wispy, euhedral, clean GC-1527-28 MFB -11.3 570.4 Northwest MSAS or MSR recrystallized siliceous, secondary cpy GC-1527-36 py -8.6 665 Northwest SP recrystallized discrete 2–3 mm subhedral grains in dolo GC-1527-40 py -8.5 722 Northwest SP recrystallized subhedral, 1– - - 3 mm py GC-1530-03 py -6.2 50.5 Northwest SP recrystallized euhedral, , clean fine-grained py in dolo-rich ba

GC-1530-08 cpy-rich MFB -12.5 141 Northwest MFP/MFB remobilized streaks of remobilized cpy in silicified matrix GC-1530-09 gn-rich MFB -14.1 142.6 Northwest MFB remobilized graphitic MFB/MFP with remobilized galena m

GC-1530-11 py -31.7 148.5 Northwest MFB primary >1-mm pyrite clasts, colloform internal texture GC-1530-12A py -21.0 154.4 Northwest MFB primary >1-mm pyrite clasts GC-1530-12B gn-rich MFB -18.4 154.4 Northwest MFB primary galena-rich bands GC-1530-13 py -29.0 164 Northwest SA recrystallized clasts to 1cm in carbonate GC-1530-19 py -16.5 222.5 Northwest MFP recrystallized/primary large areas of fractured clasts, spongy GC-1530-21 py -27.6 260 Northwest MA recrystallized 1-cm clots of py in qtz-carb veins GC-1530-22 py -17.5 276.5 Northwest MFPgr recrystallized 1-cm clasts in graphitic MFB GC-1530-28 gn-rich MFB -15.3 420.2 Northwest MFB primary fine grained, galena-rich GC-1530-30 MFB -13.8 440.5 Northwest MFB recrystallized dolo-rich py-sph-gn GC-1530-30 dup MFB -13.8 440.5 Northwest MFB recrystallized dolo-rich py-sph-gn GC-1530-31 py +cpy -12.5 449.8 Northwest WCA recrystallized dull, brassy, minor to moderate cpy GC-1530-34 py -11.1 476.7 Northwest MFP recrystallized dull, brassy, minor cpy GC-1530-36 py -11.5 507.2 Northwest WCA recrystallized wispy, dull, brassy pyrite GC-1530-39 py -12.3 541.5 Northwest WCA recrystallized wispy, bright, brassy pyrite GC-1530-41A py -15.6 558.5 Northwest WCA primary/recrystallized dull, brassy, in 3- cm bands with cpy GC-1530-41B cpy -13.2 558.5 Northwest WCA remobilized late veinlets with dolo-tetr GC-1530-42 py -9.0 569.7 Northwest MFP recrystallized lemon-yellow colored, in dolo (cpy-rich?) GC-1530-44 py -9.1 582.2 Northwest SR recrystallized nonclastic looking, sulfide bands

GC-1530-46 py -11.1 595 Northwest SRcx recrystallized bright, shiny, clastic, to 1cm

GC-1530-52 py -4.9 692 Northwest SRcx recrystallized 1–2- cm in qtz-carb matrix

GC-1530-59B MFP -10.4 781.2 Northwest MFP recrystallized dull, brassy, fine grained

GC-1530-60 bt 15.0 787.4 Northwest WBA coarse xlline sugary white barite with py wisps

GC-1530-62A bt 19.3 802.3 Northwest WBA coarse xlline foliated barite minor pyrite
Table 1. Greens Creek sulfur isotope data, sample locations, and descriptions for samples from drill core and underground exposures.—Continued 

Sample id Mineralogy δ34S value DH depth Location Host rock Mineral texture Comments

GC-1530-64 MFB -8.0 825.5 Northwest MFB recrystallized very fine crystalline, euhedral

yp66-0351C-G AMtsewhtroN2.9281.91- tcatnoc citilolyts gnola hps-yp

yppud 66-0351C-G AMtsewhtroN2.9280.91- tcatnoc citilolyts gnola hps-yp

GC-1530-67 py -24.6 838.2 Northwest MA remobilized crosscutting pyrite vein

yp20-6351C-G PStseW6.3326.2- sniev yp-brac-ztq

GC-1536-06 py -18.5 372 West SPgr recrystallized 1–2- mm euhedral py

ypB80-6351C-G PStseW9842.6- niev yp deniarg- enif gnittucssorc

yp90-6351C-G ACWtseW4.9255.52- rt dica ,yp llud fo stolc detae

BFMtseW6.4350.21-BFM hcir-hps01-6351C-G hcir-hps ,dednab ,deniarg enif

BFMtseW6.4352.21-BFM hcir-hpspud 01-6351C-G hcir-hps ,dednab ,deniarg enif

yp31-6351C-G ASMtseW8456.6- yp thgirb fo dnab

GC-1536-15 tetr -11.6 576.2 West WSI remobilized qtz-tetr vein crosscutting DMA

hps61-6351C-G ISWtseW4.6755.11- AMD ni hps thgil fo stolc egral

C-G BFM81-6351 BFMtseW4063.41- AS ni dnab kciht m-c- 5.2

yp30-3061C-G AMDderF3327.31- deniev yp-pm-brac-ztq

BFM50-3061C-G BFMderF6.6325.5- deniarg enif

GC-1603-06 tetr -5.4 237.5 Fred WCA remobilized coarse clots

BFM80-3061C-G BFMderF3422.6- dednab ,deniarg enif

yp90-3061C-G ASderF5.6424.3- ypsiw ,llud

GC-1605-02 py 1.1 115.7 Fred SA recrystallized 1-mm-sized, clean

BFM30-5061C-G ACWderF7.8116.1- dnab BFM

GC-1605-06 tetr -6.4 166.1 Fred SA remobilized 1- cm clot in qtz vein

GC-1605-08A MFB -1.5 171 Fred MFB

GC-1605-08B bt 21.9 171 Fred WBA coarse xlline coarse white barite

BFMA90-5061C-G BFMderF8.3718.3- dnab deniarg enif yrev

GC-1605-09B bt 19.8 173.8 Fred WBA coarse xlline coarse white barite

GC-1605-10 bt 18.7 176.5 Fred WBA coarse xlline white, banded, massive, sugary

GC-1605-11 bt 15.8 185.1 Fred WBA coarse xlline gray, massive, sugary

yp41-5061C-G PSderF2123.51- etiryp ypsiw

GC-164-02 MVP -15.1 -3 lower SW MVP primary fine-grained pyrite band

GC-164-02 dup MVP -15.5 -3 lower SW MVP primary fine-grained pyrite band

GC-164-03 MVP -28.0 0.5 lower SW MVB primary very fine grained banded

GC-164-03 dup MVP -27.9 0.5 lower SW MVB primary very fine grained banded

GC-164-04 gn-rich MVB -15.5 4.5 lower SW MVB remobilized silver-gray with gn in center of band

GC-164-04 MVB -15.9 4.5 lower SW MVB remobilized dark gray to shiny black

GC-164-04A MVP -14.2 4.5 lower SW MVB primary very fine grained, in dolostone

GC-164-04A dup MVP -14.6 4.5 lower SW MVB primary very fine grained, in dolostone

GC-164-04B tetr -16.1 4.5 lower SW MVB remobilized dark gray to shiny black

GC-164-04B dup tetr -16.3 4.5 lower SW MVB remobilized

GC-164-04B dup tetr -15.7 4.5 lower SW MVB remobilized dark gray to shiny black

GC-164-06 gn -16.2 10.5 lower SW MVB remobilized dull, brassy, fine grained, with large areas of g

GC-164-06A MVP -15.3 10.5 lower SW MVB primary dull, brassy, fine grained

GC-164-06A dup MVP -15.1 10.5 lower SW MVB primary dull, brassy, fine grainedGC-164-06B gn -16.7 10.5 lower SW MVB remobilized dull, brassy, fine grained, with large areas of g
Table 1. Greens Creek sulfur isotope data, sample locations, and descriptions for samples from drill core and underground exposures.—Continued Sample id Mineralogy δ34S value DH depth Location Host rock Mineral texture Comments GC-164-06B dup gn -16.7 10.5 lower SW MVB remobilized dull, brassy, fine grained, with large areas of g

GC-164-06B dup gn -16.5 10.5 lower SW MVB remobilized dull, brassy, fine grained, with large areas of g

GC-164-08 tetr -13.3 30 lower SW WCA remobilized in pyritic gray dolostone GC-164-08B py -12.6 30 lower SW WCA primary/recrystallized bands in gray dolostone, minor aspy GC-164-08B dup py -12.1 30 lower SW WCA primary/recrystallized bands in gray dolostone, minor aspy GC-164-08C sph -13.7 30 lower SW WCA remobilized in pyritic gray dolostone GC-164-08C dup sph -13.9 30 lower SW WCA remobilized in pyritic gray dolostone GC-164-08C dup sph -13.7 30 lower SW WCA remobilized in pyritic gray dolostone GC-164-09 py -14.2 40 lower SW WCA primary dull, fine grained, wispy GC-164-10A py -13.7 50 lower SW WCA primary/recrystallized dull, fine grained in gray dolostone GC-164-10B tetr -14.0 50 lower SW WCA remobilized in gray dolostone GC-164-11 gn -15.9 60 lower SW WCA remobilized GC-164-11 sph -13.8 60 lower SW WCA remobilized GC-164-11 MFP -18.3 60 lower SW WCA recrystallized GC-164-11 tetr -13.8 60 lower SW WCA remobilized GC-164-11dup sph -13.5 60 lower SW WCA remobilized GC-164-13 py -32.6 67 lower SW WSI recrystallized 0.5–1-cm grains in banded py-sph-gn-tetr rich 

GC-164-14 gn-rich MFB -14.5 80 lower SW MFBgr recrystallized graphitic, carb-rich GC-164-15 cpy-rich MFB -12.8 85 lower SW MFB remobilized py with abundant remobilized cpy GC-164-16 MFP -12.7 88 lower SW MFP recrystallized 1–2- mm aggregates in base-metal-rich MFP GC-164-17A py -10.5 90 lower SW SP recrystallized <1 mm grains in wispy veinlets GC-164-17B gn-rich MFB -14.2 90 lower SW SP recrystallized GC-164-17B cpy-rich MFP -11.3 90 lower SW SP recrystallized GC-164-18 py -11.8 94 lower SW MSP recrystallized 5-mm clots in heavily altered SP GC-164-19 py -13.7 100 lower SW SP recrystallized 0.5–1- mm clots GC-1643-02 MFB -15.4 29 200 South MFB recrystallized fine-grained typical MFB GC-1643-06 tetr -15.1 119.5 200 South WCA remobilized clot in white dolomite vein, minor cpy GC-1643-07 MFP -14.2 143.5 200 South MFP recrystallized growth banded crystals with gn-cpy GC-1643-10 sph-rich MFB -13.8 272 200 South MFB recrystallized orange sph-rich band GC-1643-10 gn-rich MFB -14.3 272 200 South MFB recrystallized banded MFB GC-1643-10 dup sph-rich MFB -13.7 272 200 South MFB recrystallized orange sph-rich band GC-164N1 bt 17.0 lower SW WBA coarse xlline white barite GC-1656-02 py -21.4 606.5 200 South SA primary GC-1656-06 MFP -10.0 911 200 South MFP recrystallized banded MFP/WCA, drilled out MFP band GC-1656-06 mixed -16.8 911 200 South MFP recrystallized GC-1656-11 py -15.4 987.7 200 South MFB recrystallized MFB with 1–2- mm rounded clots GC-1656-12 bt 19.0 1,004 200 South WCA/WBA coarse xlline white barite GC-1656-13 gn -14.7 1,008 200 South MFB recrystallized galena-rich banded MFB/MFP GC-1656-13 MFP -13.9 1,008 200 South MFB recrystallized galena-rich banded MFB/MFP

GC-1656-13 dup MFP -14.5 1,008 200 South MFP recrystallized galena-rich banded MFB/MFP

GC-1656-15 MFB -12.0 1,017 200 South MFB recrystallized massive fine grained MFB with areas of WCA

GC-1656-18 MFB -13.7 1,037 200 South MFB recrystallizedGC-1656-18A gn-rich MFB -14.4 1,037 200 South MFB recrystallized fine- grained gn-rich MFB in bands

GC-1656-19A py -10.4 1,052 200 South WCA primary light brassy pyrite in carb
Table 1. Greens Creek sulfur isotope data, sample locations, and descriptions for samples from drill core and underground exposures.—Continued 

Sample id Mineralogy δ34S value DH depth Location Host rock Mineral texture Comments

GC-1656-19B tetr -10.1 1,052 200 South WCA remobilized Clots on white dolomite

GC-1656-20 py -24.4 1,062 200 South MFP primary dull, brassy, pyritic MFP

GC-1656-20 pyrar -15.9 1,062 200 South MFP remobilized

GC-1656-20 tetr -14.0 1,062 200 South MFP remobilized

GC-1656-20 dup tetr -13.6 1,062 200 South MFP remobilized

GC-1656-20 dup tetr -13.8 1,062 200 South MFP remobilized

GC-1656-21 gn -15.5 1,071 200 South MFB recrystallized very fine grained, banded, gn-rich

GC-1656-21 sph-rich MFB -13.2 1,071 200 South MFB recrystallized area of yellow sph-rich MFB

GC-764N3-03 MFB -11.0 upper SW MSA recrystallized 2–3- cm-thick band of carb-MFB

GC-764N3-06 MFB -15.2 upper SW SA recrystallized 1–2- mm thick bands

GC-764N3-07 MFP -11.0 upper SW MSA recrystallized py-gn-dol-qtz bands to 2 cm

GC-764N3-09 py -9.2 upper SW MMA recrystallized graphite-py-rich clots to 2 cm

GC-764N3-10 py -6.6 upper SW MCHT recrystallized banded py-dol in chert

GC-764N3-11 bt 18.0 upper SW WBA coarse xlline light gray barite

PP173-06 gn -15.2 63.5 lower SW MFB remobilized galena-rich MFB
Table 2. Sulfur isotope data, sample locations, and descriptions for samples from Admiralty Island host rocks and mineral occurrences. dielpmaS noitacoL ygolareniM δ34S value kcortsoH stnemmoC H06-DA1-9 ecnerruccoreibmaGhtroN tb tlasab8.21 

isgniraebrtet-ng-hps-ypc-tb 12-BG2-9 yaBreibmaG,erohshtroN tb etinawtsil6.41 

nitnepresderetla-pm-brac-ztq 06-BG2-9 ecnerruccoreibmaGhtroN tb 

etirabdedalbevissamfonievekidcitlasabhtiwtcatnoctaenotsemil1.41 76-BG2-9 ecnerruccoreibmaGhtroN tb tlasab8.31 tlasabdenievhps-tb 64-BG2-9 ecnerruccoreibmaGhtroN ypc tlasab5- 

-brac-ztqdedarg-hgih;'5011 36-BG2-9 ecnerruccoreibmaGhtroN ypc enotsemil3.4- 

otsemildenievcc-ztq-nb-ypc 33-GL7-9 mialchtommaM ng etanobrac-ztqdezilarenimng-hps-yp5.5- 53-GL7-9 mialchtommaM ng )hpsneergthgil(hcir-brac-tb-yp-hps-ng6.5- KENNECOTT RAND Mansfield Peninsula, Kennecott-Rand occurrence gn 0.4 B7-71TD-AN ecnerruccokeerCrelliK ng PFM3.8- ps-yp brac-ztq-ypc-ng-h D7-71TD-AN ecnerruccokeerCrelliK ng ISW4.9- ecnerruccokeerCrelliKpudD7-71TD-AN ng ISW3.9- tisopedaloryP'262,31-7Y-P ng etilligraevissam6.61- 

-ng-hps-tbdednabfosnel"2 tisopedaloryPpud'262,31-7Y-P ng etilligraevissam6.61- 

-ng-hps-tbdednabfosnel"2 tisopedaloryP'492,02-7Y-P ng graevissam8.61- etilli 

irohediflus-etirabkciht"5.1 tisopedaloryPpud'492,02-7Y-P ng etilligraevissam8.61- 

irohediflus-etirabkciht"5.1 81-B daoR-B PFM 2.41- 97-ADM-67 Mt. Robert Barron profile sta RA-K po -5.2 po-rich vein quartz 51-BG2-9 yaBreibmaG,erohshtroN yp etinawtsil32- 

lushtiwetanobrac-ztqneerg 71-BG2-9 yaBreibmaG,erohshtroN yp tsihcscitihparg2.51- rg aphitic schist with bands o

52-BG2-9 yaBreibmaG,erohshtroN yp stnemides9.91- kciht"2 nozirohetiryp 60-MDA7-9 selim9.3,daoR-A yp etilligracitiryp0.6- 97-ADM-09A A-Road occurrence, 3.6 miles py -7.1 4' thick bedded bt-py-qtz 97-ADM-09Adup A-Road occurrence, 3.6 miles py -7.0 4' thick bedded bt-py-qtz 97-ADM-09C A-Road occurrence, 3.6 miles py -1.4 mineralized graphitic black argillite 97-ADM-13 B-Road, 1.1 miles, "wide corner" py -2.2 pyritic graphitic sericite phyllite 97-ADM-17 North Gambier occurrence discovery bend py -11.7 qtz-flooded volcanic w sph-gn-tetr 97-ADM-20 North Gambier occurrence VLFsta 200' N py -15.9 qtz-sulfide stockwork in hematized basalt 64-MDA7-9 kaePelgaE,70-DAkeerC yp brac-pm-yphtiwetillyhpdednabnat-neerg8.2- 97-ADM-52 W. of Swan Island occurrence py 1.3 vein of py-qtz-carb in altered basalt 97-ADM-66 Mt. Robert Barron profile sta RA-J py 3.8 metadiorite 97-ADM-70 Mt. Robert Barron profile sta RA-P py 3.8 metadiorite with disseminated pyrite 97-ADM-79 North shore, Gambier Bay, VLF station 5800' py -30.1 pyritic bands in mixed argillite/tuff 19-MDA7-9 tcepsorpattE yp ztrauqdelttomdenievediflus9.2- 97-LG-11 Gallagher Ridge, east end, south side py -31.1 pyritic argillite 53-GL7-9 mialchtommaM yp )hpsneergthgil(hcir-brac-tb-yp-hps-ng7.0 65-GL7-9 keerCcniZreppu yp etillyhpeticireshcir-ypdeniats-eF,rgPS3.02- 20-dR-A im1.3,daoR-A yp etillyhpsuoecalligracitihpargderaehs6.2 40-dR-A 7tiP,selim9.1,daoR-A yp cssuoecalligra4.53- etirypcitsyrcatem,tsih 81-B daoR-B yp 3.31- 20-dR-B selim24.2,daoR-B yp etilligrakcalbnietirypevissamimes0.31- B-Rd-04 B-Road, 3.3 mi, just up from pit py -15.5 sericitic carbonated argillite B-Rd-04 dup B-Road, 3.3 mi, just up from pit py -15.5 sericitic carbonated argillite 11-61TD-AN keerCcniZreppu yp etilligra4.8- 

aztqhtiwetilligradetaiccerb

01-71TD-AN ecnerruccokeerCrelliKA yp etirypevissam0.11-

B1-71TD-AN ecnerruccokeerCrelliK yp brac-ztq-ypcitihpargevissamimes3.21-
Table 2. Sulfur isotope data, sample locations, and descriptions for samples from Admiralty Island host rocks and mineral occurrences.—Continued

di elpmaS noitacoL ygolareniM δ34S value kcor tsoH stnemmoC

B4-71T D-AN ecnerrucco keerC relliK yp etilligra2.8- 

flus latem-esab evissamimes

B8-71T D-AN ecnerrucco keerC relliK yp enotsneerg7.11- 

cifam deretla brac-ztq citiryp

A9-71T D-AN ecnerrucco keerC relliK yp etiryp evissam0.01-

 '127 221S-P aera enim yp etillyhp3.01-

76-BG2-9 ecnerrucco reibmaG htroN hps tlasab4.7- tlasab deniev hps-tb

97 -ADM-17 North Gambier occurrence discovery bend sph -4.8 qtz-flooded volcanic w sph-gn-tetr

97-ADM-67 Mt. Robert Barron profile sta RA-K sph -4.5 po-rich vein quartz

33-GL7-9 mialc htommaM hps etanobrac-ztq dezilarenim ng-hps-yp7.2-

selim 4.3 ,daoR-B.RC EDACSAC hps 3.31-

D7-71T D-AN ecnerrucco keerC relliK hps ISW6.8-

ecnerrucco keerC relliKpud D7-71T D-AN hps ISW5.8-

PORTAGE Mansfield Peninsula, Portage occurrence sph -2.1

PORTAGE dup Mansfield Peninsula, Portage occurrence sph -2.1
260 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Hanging wall (n=26) and Massive black ore (n=60)

FREQUENCY FREQUENCY

0

2

4

6

8

10

12

MFB 

Hanging wall

Footwall (n=34) and White Siliceous ore (n=11)

–35 –30 –25 –15 –10 –5 0 5

0

1

2

3

4

5

6

7

8

Footwall

WSI 

Greens Creek 34S data sorted by host lithology 

avg. δ34S value

= –15.5 ± 6.6

avg. δ34S value

= –9.9 ± 5.0

–20

δ34S(CDT)

–35 –30 –25 –20 –15 –10 –5 0 5

δ34S(CDT)

Figure 5. Comparison of sulfide sulfur isotope data in footwall versus hanging-wall lithologies. The upper plot shows 

all data from the hanging-wall argillites and MFB ore type, with an average value of –15.5 ± 6.6 per mil d34S. The lower 

plot shows all data from the footwall phyllites and WSI ore type, with an average value of –9.9 ± 5.0 per mil d34S. 

Together, the plots demonstrate the minewide 34S-depletion with stratigraphic height through the ore stratigraphy. CDT, 

Cañon Diablo troilite.
Isotopic Data 261

Lead Isotopes

Fifty-five lead isotopic determinations were performed 

on 46 sulfides and 9 ores from underground, and 15 sulfides 

from 11 surface sites on Admiralty Island. Sulfides analyzed 

are chalcopyrite, pyrite, sphalerite, galena, tetrahedrite, 

pyrargyrite, and pyrrhotite. Data are presented in table 3. 

Whole-rock uranium-thorium-lead (as well as rubidiumstrontium and samarium-neodymium) isotopic analyses were 

performed on a suite of mafic-ultramafic igneous rocks, 

argillites, and phyllites from Admiralty Island, and these data 

are used to characterize host rocks and possible source rocks 

in the mine area as well as compare host-rock and sulfide 

lead isotope compositions (see chap. 11).

Figure 8 shows the distribution of galena lead isotopic 

compositions from Greens Creek ore and several occurrences 

on Admiralty Island (Mammoth claim, Kennecott Rand, and 

Pyrola). Data from the Greens Creek galenas define a trend 

that is very similar to that produced by fractionation of the 

lead isotopes during ionization in the mass spectrometer. The 

majority of lead isotopic values for the Greens Creek galena 

vary between 206Pb/204Pb = 18.645 to 18.708 and 207Pb/204Pb = 

15.594 to 15.669 (fig. 8A) and 208Pb/204Pb = 38.34 to 38.625 

(fig. 8B). Some of the trend is undoubtedly produced by 

mass discrimination effects during spectrometry; however, 

the full isotopic range shown by the galena data appears to 

be too large (see below). Although none of the Greens Creek 

galena separates were measured more than once, two analyses 

for the same Kennecott-Rand sample yielded nearly identical results at 206Pb/204Pb = 18.535, 207Pb/204Pb = 15.60, and 208Pb/204Pb = 38.29, a composition that deviates from the orelead trend. Two galenas from the Pyrola occurrence plot on 

top of each other and also fall off the Greens Creek ore-lead 

trend, similar to, but slightly more 207Pb and 208Pb depleted 

than, the Kennecott-Rand galenas. Galena from an occurrence 

on the Mammoth claim (LG-33) just north of Greens Creek 

plots slightly off of the Greens Creek ore-lead trend. These 

data are then compared to average model lead values of the 

orogene curve of Zartman (1984). A similar average model 

lead curve for the mantle is out of the scope of this diagram 

to the lower left corner. Comparisons of the 206Pb/204Pb and 208Pb/204Pb data produce very similar relationships (fig. 8B).

Pyrargyrite and tetrahedrite are compared to the galena 

ore-lead trend and were found to conform to it (fig. 9), 

although on average at slightly less radiogenic values. The 

least radiogenic compositions for these sulfides are 206Pb/204Pb 

= 18.642 and 18.637, respectively, 207Pb/204Pb = 15.584 and 

15.578, respectively (fig. 9A), and 208Pb/204Pb = 38.343 and 

38.330, respectively (fig. 9B). One notable exception is the 

pyrargyrite from diabase dike GC-1701-01 that plots on the 

Greens Creek ore-lead trend to the high 207Pb and 208Pb side. 

Although this analysis deviates from the main cluster, it is 

presumed to be accurate as multiple runs at differing currents 

and temperatures of the same tetrahedrite sample, GC-24, vary 

less than the deviation shown by sample GC-1701-01 from 

the main cluster (fig. 9). Maximum deviations due to mass 

discrimination effects in the lead isotopic ratios for the five 

GC-24 analyses are d206Pb/204Pb = 0.013, d207Pb/204Pb = 0.018, 

and d208Pb/204Pb = 0.052 (table 3), corresponding to slopes of 

7/6 = 1.4 and 8/6 = 4.

Sphalerite and pyrite data are compared with the galena 

ore-lead trend and are found to deviate in some cases (fig. 

10). In both 207Pb-206Pb and 208Pb-206Pb correlation diagrams, two sphalerites (Cascade Creek and Portage) and 

four pyrites (NAD-T13-3c and three samples from drill hole 

GC-1656) plot with a higher 206Pb/204Pb value than Greens 

Creek galena. One obvious explanation is that several of 

these separates contain measurable uranium that has since 

produced enough radiogenic lead to evolve the lead isotopic 

composition to higher 206Pb/204Pb values. For example, the 

Portage sphalerite contained significant amounts of uranium 

such that a correction for radiogenic lead due to in-situ decay 

of uranium since 215 Ma in the Portage sphalerite results in 

a composition slightly less radiogenic than Kennecott-Rand 

galena (fig. 10A).

In contrast, an analysis of sphalerite from Cascade Creek 

also exhibits a more radiogenic value, 206Pb/204Pb = 19.017, 207Pb/204Pb = 15.646, and 208Pb/204Pb = 39.204 (fig. 10), clearly 

more enriched and quite different than either the Greens Creek 

ore-lead trend or the Portage sphalerite, but did not contain 

enough uranium to produce a significant change in this lead 

isotopic composition (table 3). Initial lead isotopic compositions for all mineral separates for which uranium was measured are given in table 3.

Another exception is sphalerite lead (97-ADM-17) from 

the North Gambier occurrence (Taylor and others, 1992) that 

is less 206Pb-rich, but more 207Pb-rich than the Greens Creek 

ore-lead trend (fig. 10). Sphalerites from underground are 

also variable. GC-1514-46 (Northwest West orebody) sphalerite is slightly off the Greens Creek ore-lead trend, whereas 

sphalerite from GC-19 and GC-164-11 (both lower Southwest 

orebody) are both on the trend. Sphalerite sample GC-19 was 

measured five times (fig. 10), again to evaluate deviations due 

to mass discrimination effects. Maximum deviations in the 

lead isotopic ratios for the five GC-19 analyses are d206Pb/204Pb 

= 0.035, d207Pb/204Pb = 0.034, and d208Pb/204Pb = 0.102 (table 

3), corresponding to slopes of 7/6 = 1.0 and 8/6 = 2.9.

Similar relationships are found in some of the 206Pb-208Pb 

data (fig. 10B). However, slight differences can be observed 

in the pyrite and sphalerite data, indicating slightly different 

thorium/uranium values for these mineral separates as can be 

noted from the data in table 3. In particular, Cascade Creek 

exhibits the highest 208Pb/204Pb value (39.35), indicating that 

the lead for this sphalerite was derived from a source with 

higher thorium/uranium values than other sphalerites.

Pyrite lead data can be found both on and off the Greens 

Creek galena ore-lead trend. Thirteen of 20 pyrite analyses 

lie on or very near the ore-lead trend. Exceptions include 

massive pyrite (NAD-T17-9a) from the Killer Creek occurrence with a composition very similar to the Kennecott-Rand 

galena (fig. 10). Several other pyrites from Killer Creek and 

the upper Zinc Creek area plot off the Greens Creek ore-lead 
262 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

MFB ore type (n=38)

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

4

2

6

8

MFP ore type (n=32)

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

4

2

6

8

pyrite (n=92)

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

4

8

12

sphalerite (n=10)

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

4

2

6

chalcopyrite (n=9)

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

4

3

2

1

5

galena (n=11)

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

4

2

6

pyrargyrite (n=4)

–40 –35 –30 –25 –20 –15 –10 –5 0 5

0

3

2

1

tetrahedrite (n=23)

–40 –35 –30 –25 –20 –15 –10 –5 0 5

δ34SCDT

0

4

2

6
Isotopic Data 263

Figure 6 (facing page). Sulfide sulfur isotope data sorted by mineralogy and ore type. MFB, massive fine-grained 

black ore; WSI, white siliceous ore. CDT, Cañon Diablo troilite.

Admiralty Island Late Triassic age host rocks and occurrences

sulfide sulfur, n = 45, barite, n = 4 

0

2

4

6

8

Triassic argillite

Triassic occurrence

Triassic phyllite

Triassic barite

Admiralty Island non-Triassic host rocks and occurrences

sulfide sulfur, n = 10 

2

3

4

5

Devonian(?) argillite

Devonian(?) occurrence

Devonian(?) phyllite

Permian(?) phyllite

–40 –35 –30 –25 –20 –15 –10 –5 0 5 10 15 20 25 30

0

1

δ34SCDT

–40 –35 –30 –25 –20 –15 –10 –5 0 5 10 15 20 25 30

δ34SCDT

FREQUENCY FREQUENCY

Figure 7. Sulfide and barite sulfur isotope data from host rocks and occurrences elsewhere on Admiralty Island. 

The upper histogram shows the d34S distribution of sulfide and barite sulfur in Late Triassic age argillites, phyllites, 

and mineral occurrences on Admiralty Island. The lower histogram shows the d34S distribution of Devonian(?) 

argillites, phyllites, and mineral occurrences, and Permian(?) phyllites. The histograms demonstrate the strongly 

34S-depleted signature of Late Triassic age host rocks and occurrences as compared to the near-zero values of 

non-Triassic host rocks and occurrences. CDT, Cañon Diablo troilite.
Table 3. Uranium-thorium-lead (U-Th-Pb) isotope data, sample locations, and descriptions of ores and sulfide minerals from the Greens Creek mine, and mineral occurrences and host rocks on Adm

Sample Mineralogy Sample U Th Pb 206/204Pb † 206/204Pb 207/204Pb † 207/204Pb 208/204Pb † 208/204Pb 238U/204Pb † 238

eman )mpp()mpp()mpp()gm( .tw rorre % rorre % rorre % 

% 

GC-1093-05 cpy 4.39 0.013 0.052 1,998 18.6580 0.063 15.6090 0.093 38.4200 0.124 0.00042 

GC-1514-44 cpy 2.37 0.093 0.010 130 18.6850 0.079 15.6050 0.114 38.4070 0.152 0.04590 GC-1514-46 cpy 3.43 0.294 0.134 66 18.7830 0.067 15.6090 0.096 38.4040 0.124 0.28571 

61CG7-9 ng60-4 88.2 690.05785.83070.09756.51340.00996.81 ng80-461CG7-9 82.1 490.03714.83850.05706.51340.08956.81 33-GL7-9 ng 56.0 570.08524.83150.05416.51730.08086.81 30-3901C-G ng 89.5 291.00526.83431.08866.51885.09707.81 50-3901C-G ng 61.2 870.00605.83850.00436.51840.04976.81 11-461C-G ng 80.2 930.03725.83830.04836.51720.05486.81 60-3461C-G ng 33.0 240.00244.83620.06116.51610.06266.81 31-6561C-G ng 12.1 721.04015.83090.00436.51460.08086.81 12-6561C-G ng 3 57. 721.03625.83121.04046.51460.08586.81 ngdnaR t-tocenneK 60.1 740.09682.83830.02595.51220.08335.81 ng2# dnaR- ttocenneK 60.1 170.00492.83540.03895.51830.06735.81 60-371P-P ng 560.00043.83460.06395.51950.07546.81 '066 72S-P ng 651.00944.83291.00016.51161.00076.81 31-7Y-P ng 3.0 530.07051.83820.09765.51120.00145.81 02-7Y-P ng 6.0 030.08051.83220.02765.51510.07935.81 97-ADM-67 po 11.52 0.024 0.010 948 18.4350 0.180 15.5950 0.232 38.2130 0.235 0.00161 

 0562-053 yp 19.4 840,8 460.04266.81 .83090.00216.51 4 221.0503 96-GC-38 py 1.64 0.202 0.122 10,494 18.6710 0.062 15.6180 0.092 38.4530 0.122 0.00122 

97 -ADM-06 py 4.45 0.265 1.240 177 18.6440 0.062 15.5830 0.092 38.3000 0.122 0.09520 

97-ADM-06 #2 py 4.45 0.265 1.240 177 18.6450 0.064 15.5850 0.093 38.3070 0.122 0.09535 97-LG-64 py 7.61 0.094 0.275 1.233 18.7970 0.079 15.4730 0.111 38.0510 0.135 4.81320 

B-18 py 1.86 0.024 0.134 53 18.6730 0.063 15.6030 0.093 38.3810 0.122 0.02860 B-18 py 1.8 0.012 0.043 96 18.6730 0.065 15.6180 0.094 38.4360 0.123 0.00830 

GC- 1656-02 py 0.54 1.026 0.958 427 18.7520 0.061 15.6040 0.091 38.3620 0.122 0.15291 

GC- 1656-02 py 0.94 3.499 0.501 352 18.7170 0.061 15.5920 0.091 38.3360 0.121 0.63329 GC- 1701-01 py 4.75 0.040 0.084 5,859 18.6550 0.063 15.6070 0.094 38.4100 0.123 0.00044 

GC-1136-40 py 2.1 0.893 0.130 4,151 18.6758 0.193 15.6102 0.211 38.4384 0.221 0.01370 GC-1656-05 py 0.48 23.630 2.098 874 18.7330 0.063 15.6310 0.093 38.4760 0.122 1.72500 

02-6561C-G yp 98.0 221.09834.83090.02516.51950.02666.81 NAD- T16-11 py 1.5 0.029 0.023 582 18.6650 0.065 15.6020 0.095 38.3960 0.124 0.00318 

NAD- T17-1b py 1.56 0.039 0.033 353 18.6530 0.064 15.5900 0.093 38.3520 0.124 0.00703 NAD- T17-1b #2 py 1.56 0.039 0.033 353 18.6610 0.061 15.5990 0.091 38.3820 0.121 0.00702 

NAD- T17-8b py 1.74 0.062 0.416 146 18.6910 0.061 15.6150 0.091 38.4300 0.121 0.02702 NAD- T17-9a py 2.52 0.026 0.023 1,708 18.5420 0.089 15.5930 0.111 38.2800 0.143 0.00096 

NAD- T17-9a #2 py 2.52 0.026 0.023 1,708 18.5400 0.061 15.5920 0.091 38.2760 0.121 0.00096 NAD-T13-3c py 1.28 0.132 0.255 65 18.8000 0.078 15.6050 0.105 38.4300 0.136 0.12918 

 0562-053 ryp 88.0 060.06983.83540.02895.51040.09946.81 10-CG6-9 ryp 67.6 143.05844.83093.04226.51492.08876.81 30-CG6-9 ryp 72.51 831.04973.83141.02295.51321.08146.81 02-6561C-G ryp 30.0 060.01343.83540.06385.51040.08146.81 10-1071C-G ryp 41.1 831.00096.83701.00296.51080.00727.81 20-CG6-9 hps 30.5 031.01034.83980.03016.51460.09956.81 1-CG6-9 9 hps 7.0 863.02514.83653.06595.51543.03346.81 2# 91-CG6-9 hps 7.0 60.02166.81 221.06924.83090.01216.514

3# 91-CG6-9 hps 7.0 021.00893.83190.00106.51060.00356.81

4# 91-CG6-9 hps 7.0 121.00564.83190.00026.51160.00966.81

5# 91-CG6-9 hps 7.0 121.00005.83190.00036.51160.00876.81

71-MDA7-9 hps 66.3 221.03179.83090.02377.51060.06955.81
Table 3. Uranium-thorium-lead (U-Th-Pb) isotope data, sample locations, and descriptions of ores and sulfide minerals from the Greens Creek mine, and mineral occurrences and host rocks on Adm

Sample Mineralogyname

GC-1093-05 cpyGC-1514-44 cpyGC-1514-46 cpy

97-GC164-06 gn

97-GC164-08 gn97-LG-33 gn

GC-1093-03 gnGC-1093-05 gnGC-164-11 gnGC-1643-06 gnGC-1656-13 gnGC-1656-21 gn

Kennecott-Rand gn

Kennecott-Rand #2 gn

PP-173-06 gn

PS-27 660' gn

PY-7-13 gn

PY-7-20 gn97-ADM-67 po

350-2650 py

96-GC-38 py97-ADM-06 py

97-ADM-06 #2 py

97-LG-64 py

B-18 pyB-18 py

GC- 1656-02 pyGC- 1656-02 pyGC- 1701-01 pyGC-1136-40 pyGC-1656-05 pyGC-1656-20 py

NAD- T16-11 pyNAD- T17-1b py

NAD- T17-1b #2 pyNAD- T17-8b py

NAD- T17-9a pyNAD- T17-9a #2 pyNAD-T13-3c py

350-2650 pyr

96-GC-01 pyr

96-GC-03 pyrGC-1656-20 pyrGC-1701-01 pyr

96-GC-02 sph

96-GC-19 sph

96-GC-19 #2 sph

96-GC-19 #3 sph

96-GC-19 #4 sph

96-GC-19 #5 sph97-ADM-17 sph

206/204Pb †† 207/204Pb †† 208/204 noitacoLhtped HD†† bP stnemmoCerutxet lareniMkcor tsoH

WS rewol ACW 

q ni stolc ypc-ngdezilibomer

tsewhtroN696 PFM erutcarf no ypcdezilibomer

tsewhtroN707304.83906.51377.81 PFM 

dna ypc lardehuedezilibomer

WS rewol5.01 BVM 

enif ,yssarb ,lluddezilibomer

WS rewol03 ACW primary/recrystalbands in gray do

mialc htommaM 

renim ng-hps-yp

WS rewol ACW 

iarg esraoc yrevdezilibomer

WS rewol ACW 

q ni stolc ypc-ngdezilibomer

WS rewol06 ACW dezilibomer

htuoS 0025.911 ACW bomer ilized clot in white dol

htuoS 002800,1 BFM atsyrcer llized galena-rich band

htuoS 002170,1 BFM atsyrcer llized very fine grained

Mansfield Peninsula, Kennecott- Rand occurrence

Mansfield Peninsula, Kennecott- Rand occurrence

WS rewol5.36 BFM BFM hcir-anelagdezilibomer

660 mine area

K-AR ats eliforp norraB treboR .tM 

auq niev hcir-op

WS rewol97 PFM 

derutxet-yramirpyramirp

WS rewol841 PM 

-lardehue ,thgirbdezillatsyrcer

592.83385.51146.81 selim 9.3 ,daoR-A etilligra etilligra citiryp

1246.81 203.83585.5 selim 9.3 ,daoR-A etilligra etilligra citiryp

18.599 15.463 37.862 Gallagher Ridge

B-RoadB-Road

htuoS 0025.606063.83406.51747.81 AS yramirp

htuoS 0025.606533.83195.51696.81 AS yramirp

200 South

WS rewol PM dezillatsyrcer

18.674 15.628 38.474 200 South

htuoS 002260,1 PFM 

ryp ,yssarb ,lludyramirp

keerC cniZ reppu etilligra rb ecciated argill

ecnerrucco keerC relliK 

arg evissamimes

ecnerrucco keerC relliK 

arg evissamimes

ecnerrucco keerC relliK enotsneerg 

 brac-ztq citiryp 

ecnerrucco keerC relliK etiryp evissam

ecnerrucco keerC relliK etiryp evissam

18.796 15.605 38.427

WS rewol97 PFM 

 stelniev ryp-ztqdezilibomer 

WS rewol97 PFM dezilibomer

WS rewol97 THCM dezilibomer

htuoS 002260,1 PFM bomer ilized

WS rewol5.26 PFM dezillatsyrcer

WS rewol35 ACW dezilibomer

WS rewol35 ACW dezilibomer

WS rewol35 ACW dezilibomer

WS rewol35 ACW er dezilibom

WS rewol35 ACW dezilibomer

dneb yrevocsid ecnerrucco reibmaG htroN tlasab 

clov dedoolf-ztq
Table 3. Uranium-thorium-lead (U-Th-Pb) isotope data, sample locations, and descriptions of ores and sulfide minerals from the Greens Creek mine, and mineral occurrences and host rocks on Admi

Sample Mineralogy Sample U Th Pb 206/204Pb † 206/204Pb 207/204Pb † 207/204Pb 208/204Pb † 208/204Pb 238U/204Pb † 238U

eman )mpp()mpp()mpp()gm( .tw rorre % rorre % rorre % 

 % 

Cascade Ck sph 20.32 0.928 0.140 2,182 19.0170 0.065 15.6460 0.094 39.2040 0.123 0.02752 2.

GC-1514-46 sph 3.79 0.024 0.014 77 18.6860 0.063 15.6000 0.093 38.3850 0.122 0.02023 1GC-164-11 sph 3.85 0.020 0.009 1,109 18.6410 0.062 15.5850 0.092 38.3470 0.122 0.00117 2

Portage sph 24.53 2.476 1.495 17.4 18.7900 0.061 15.6090 0.091 38.3500 0.121 9.06880 0

42-CG6-9 rtet 16.1 521.04453.83690.04985.51460.01446.81 2# 42-CG6-9 rtet 16.1 521.06604.83690.01706.51460.05656.81 3# 42-CG6-9 tet r 16.1 021.00653.83090.00095.51060.00446.81 4# 42-CG6-9 rtet 16.1 121.00173.83190.00495.51160.00746.81 5# 42-CG6-9 rtet 16.1 321.00483.83290.00895.51260.00156.81 97-GC164-11 tetr 0.23 0.064 0.322 30,660 18.6636 0.064 15.6133 0.093 38.4420 0.122 0.00013 8

40-461C-G rtet 25.3 521.02033.83690.02875.51460.01736.81 GC-1643-06 tetr 1.52 0.060 0.018 2,112 18.6680 0.065 15.6180 0.094 38.4570 0.126 0.00182 1

02-6561C-G rtet 11.6 498,9 031.08683.83301.07795.51070.04056.81 96-GC-24 MFB 25.27 0.491 703 18.6860 0.134 15.6640 0.242 38.5340 0.435 0.04460 5

46-0351C-G BFM 1 .83540.06806.51230.09366.81 4 560.0071 BFM2# 46-0351C-G 1 560.09614.83540.09806.51230.07466.81 01-3461C-G 11.2 hcir-ng BFM 651.00373.83511.08195.51201.08146.81 01-3461C-G 8.2 hcir-hps BFM 432.03694.83112.02826.51891.08286.81 8.2 hcir-hps BFM2# 01-3461C-G 221.00374.83390.00326.51260.00076.81 8.2 hcir-hps BFM3# 01-3461C-G 321.00094.83390.00036.51360.00876.81 r-hps BFM 4# 01-3461C-G 8.2 hci 321.00274.83890.00526.51560.00276.81 8.2 hcir-hps BFM5# 01-3461C-G 921.00784.83501.00236.51470.00776.81 40-461C-G 25.1 hcir-ng BVM 880.07944.83150.02416.51230.04466.81 42-CG6-9 PFM 32.81 626.05115.83566.02926.51616.08966.81 2# 42-CG6-9 PFM 32.81 062.05615.83962.00336.51051.09686.81 3# 42-CG6-9 PFM 32.81 920.09084.83230.08726.51610.06576.81 60-6561C-G PFM 18.82 131.07378.83201.03547.51570.09077.81 31-6561C-G M PF 78.9 860.00194.83850.01036.51730.06576.81 PFM2# 31-6561C-G 78.9 860.05305.83850.07236.51730.00476.81 44-4151C-G 23.81 hcir-ypc PFM 021.05653.83090.07195.51950.07166.81 † - corrected ratios; corrected for Pb mass fractionation (0.08 ± 0.03 % per atomic mass unit) and blank Pb (variable amounts between 5 and 20 pg total Pb; blank composition: 206Pb/204Pb = 18.8 ± 0.6; 207Pb/204Pb = 15.65 ± 0.2; and 208Pb/204Pb = 38.65 ± 0.75); U mass fractionation using a double U spike (233/236) = 1.018 ; and assumed Th fractionation of ~0.2 ± 0.5 % per atomic mass unit

using the programming of Ludwig (1985). U and Th blanks ranged between 2 - 15 and 7 - 50 pg, respectively.

†† - initial ratio values; corrected for mass fractionation, blank Pb, radiogenic Pb accumulated from the in-situ decay of U and Th over the age 

of the sample taken to be 215 Ma.

gn = galena, pyr = pyrargyrite, sph = sphalerite, py = pyrite, tetr = tetrahedrite, cpy = chalcopyrite, po = pyrrhotite, aspy = arsenopyrite, 

MFP = massive fine-grained pyritic ore, MFB = massive fine-grained base-metal-rich ore, MVB = massive very fine

grained base-metal-rich ore, qtz = quartz, carb = carbonate, mp = mariposite. 
Table 3. Uranium-thorium-lead (U-Th-Pb) isotope data, sample locations, and descriptions of ores and sulfide minerals from the Greens Creek mine, and mineral occurrences and host rocks on Adm

Sample Mineralogy

name

Cascade Ck sph

GC-1514-46 sphGC-164-11 sph

Portage sph

96-GC-24 tetr

96-GC-24 #2 tetr

96-GC-24 #3 tetr96-GC-24 #4 tetr96-GC-24 #5 tetr97-GC164-11 tetr

GC-164-04 tetr

GC-1643-06 tetrGC-1656-20 tetr96-GC-24 MFB

GC-1530-64 MFB

GC-1530-64 #2 MFBGC-1643-10 MFB gn-richGC-1643-10 MFB sph-richGC-1643-10 #2 MFB sph-rich

GC-1643-10 #3 MFB sph-richGC-1643-10 #4 MFB sph-rich

GC-1643-10 #5 MFB sph-richGC-164-04 MVB gn-rich

96-GC-24 MFP

96-GC-24 #2 MFP

96-GC-24 #3 MFP

GC-1656-06 MFPGC-1656-13 MFP

GC-1656-13 #2 MFP

GC-1514-44 MFP cpy-rich

206/204Pb †† 207/204Pb †† 208/204 noitacoLhtpedHD††bP stnemmoCerutxetlareniMkcortsoH

B-Road, 3.4 miles

tsewhtroN707 PFM 

dnaypclardehuedezilibomer

WSrewol06 ACW dezilibomer

18.482 15.593 38.290 Mansfield Peninsula, Portage occurrence

WSrewol27 BFM 

ztqnirtetfotolCdezilibomer

WSrewol27 BFM 

ztqnirtetfotolCdezilibomer

WSrewol27 BFM 

ztqnirtetfotolCdezilibomer

WSrewol27 BFM 

ztqnirtetfotolCdezilibomer

WSrewol27 BFM 

ztqnirtetfotolCdezilibomer

ol06 WSrew ACW dezilibomer

WSrewol5.4 BVM 

ynihsotyargkraddezilibomer

htuoS0025.911 ACW bomer ilized clot in white dolom

htuoS002260,1 PFM bomer ilized

WSrewol27 BFM 

ztqfosegdegnoladezillatsyrcer 

tsewhtroN5.528 BFM atsyrcer llized very fine crystallin

tsewhtroN5.528 BFM atsyrcer llized very fine crystallin

htuoS002272 BFM atsyrcer llized gn-rich banded M

htuoS002272 BFM atsyrcer llized orange sph-rich b

htuoS002272 BFM atsyrcer llized orange sph-rich b

htuoS002272 BFM atsyrcer llized orange sph-rich b

htuoS002272 BFM atsyrcer llized orange sph-rich b

htuoS002272 BFM atsyrcer llized orange sph-rich b

WSrewol5.4 BVM libomer 

ghtiwyarg-revlisdezi

WSrewol27 PFM 

dezillatsyrcer%05yramirp

WSrewol27 PFM 

dezillatsyrcer%05yramirp

WSrewol27 PFM 

dezillatsyrcer%05yramirp

htuoS002119 PFM syrcer at llized banded MFP/WC

htuoS002800,1 BFM atsyrcer llized galena-rich bande

htuoS002800,1 BFM atsyrcer llized galena-rich bande

tsewhtroN696 PFM PFMhcir-ypcdezillatsyrcer

† - corrected ratios; corrected for Pb mass fractionation (0.08 ± 0.03 % per atomic mass unit) and blank Pb (variable amounts between 5 and 20 pg total Pb; 

blank composition: 206Pb/204Pb = 18.8 ± 0.6; 207Pb/204Pb = 15.65 ± 0.2; and 208Pb/204Pb = 38.65 ± 0.75); U mass

fractionation using a double U spike (233/236) = 1.018; and assumed Th fractionation of ~0.2 ± 0.5 % per atomic mass unit

using the programming of Ludwig (1985). U and Th blanks ranged between 2 –15 and 7 –50 pg, respectively.

††- initial ratio values; corrected for mass fractionation, blank Pb, radiogenic Pb accumulated from the in-situ decay of U and Th over the age

of the sample taken to be 215 Ma.

gn = galena, pyr = pyrargyrite, sph = sphalerite, py = pyrite, tetr = tetrahedrite, cpy = chalcopyrite, po = pyrrhotite, aspy = arsenopyrite,

MFP = massive fine-grained pyritic ore, MFB = massive fine-grained base-metal-rich ore, MVB = massive very fine

grained base-metal-rich ore, qtz = quartz, carb = carbonate, mp = mariposite.
268 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

15.5

15.6

15.7

15.8

18.3 18.5 18.7 18.9 19.1

206Pb/204Pb

Greens Creek - Admiralty Island

Galena only

Kennecott-Rand

Pyrola

0 Ma

38.0

18.3 18.5 18.7 18.9 19.1

38.2

38.4

38.6

38.8

39.0

data-point error ellipses are 2σ

Greens Creek - Admiralty Island

Galena only

Pyrola

0 Ma

data-point error ellipses are 2σ

Mammoth

claim; LG-33

Greens Creek

ore trend

Kennecott-Rand

Mammoth

claim; LG-33

Greens Creek

ore trend

B

A

orogene curve

orogene curve

206Pb/204Pb

208Pb/204Pb 207Pb/204Pb

Figure 8. Plot showing the range of galena lead isotopic compositions from Greens Creek ore 

and several occurrences on Admiralty Island (Mammoth claim, Kennecott-Rand, and Pyrola). 

(A) 206Pb/204Pb versus 207Pb/204Pb; (B) 206Pb/204Pb versus 208Pb/204Pb. Error ellipses are 2s. Orogene 

curve is that of Zartman (1984).
Isotopic Data 269

Pyrargyrite

Tetrahedrite

Galena

Pyrargyrite

Tetrahedrite

Galena

Pyrola

0 Ma

GC-1701-01

Pyrola

0 Ma

GC-1701-01

GC-24

GC-24

orogene curve

orogene curve

Greens Creek

galena ore trend

38.0

18.3 18.5 18.7 18.9 19.1

38.2

38.4

38.6

38.8

39.0

data-point error ellipses are 2σ

Greens Creek - Admiralty Island

Pyrargyrite and Tetrahedrite

Kennecott-Rand

Greens Creek

galena ore trend

B

206Pb/204Pb

208Pb/204Pb

15.5

15.6

15.7

15.8

18.3 18.5 18.7 18.9 19.1

206Pb/204Pb

Greens Creek - Admiralty Island

Pyrargyrite and Tetrahedrite

Kennecott-Rand

data-point error ellipses are 2σ

A

207Pb/204Pb

Figure 9. Plot showing the range of lead isotopic compositions of pyrargyrite (crosses) and 

tetrahedrite (open diamonds) from Greens Creek ore, and compared to galena from Greens Creek 

(shaded field) and from several occurrences on Admiralty Island (open squares; Kennecott-Rand 

and Pyrola). (A) 206Pb/204Pb versus 207Pb/204Pb; (B) 206Pb/204Pb versus 208Pb/204Pb. Error ellipses are 

2s. Orogene curve is that of Zartman (1984).
270 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Galena

Pyrite

Sphalerite

Pyrola

0 Ma

orogene curve

ADM-17

Cascade

Creek Portage

(measured)

Portage

(U-corrected)

NAD-T17-9a

38.0

Pyrola

Galena

Pyrite

Sphalerite

orogene curve

NADT17-9a

GC-19

Cascade

Creek

ADM-17

Portage

(measured)

NAD-T13-3c

GC-1656

NAD-T13-3c

GC-1656

GC-19

0 Ma

Kennecott-Rand

Kennecott-Rand

Greens Creek

galena ore trend

Greens Creek

galena ore trend

18.3 18.5 18.7 18.9 19.1

B

206Pb/204Pb

38.8

39.0

39.2

39.4

38.6

38.4

38.2

208Pb/204Pb

18.3 18.5 18.7 18.9 19.1

206Pb/204Pb

Greens Creek - Admiralty Island

Sphalerite and Pyrite

Greens Creek - Admiralty Island

Sphalerite and Pyrite

data-point error ellipses are 2σ

data-point error ellipses are 2σ

A

15.5

15.6

15.7

15.8

207Pb/204Pb

Figure 10. Plot showing the range of lead isotopic compositions of sphalerite (inverted open 

triangles) and pyrite (solid triangles) from Greens Creek ore, and compared to galena from 

Greens Creek (shaded field) and from several occurrences on Admiralty Island (open squares; 

Kennecott-Rand and Pyrola). (A) 206Pb/204Pb versus 207Pb/204Pb; (B) 206Pb/204Pb versus 208Pb/204Pb. 

Error ellipses are 2s. Orogene curve is that of Zartman (1984).
Isotopic Data 271

trend in the high 206Pb-direction. Pyrite in argillite (NAD 

T13-3c) from the sediments at the head of Cub Creek on 

Mariposite Ridge has a measured lead isotopic composition 

similar to that reported for Portage sphalerite. Three pyrites 

from drill hole GC-1656 in the hanging-wall argillite (2) and 

from massive ore in the 200 South orebody scatter off the 

Greens Creek ore-lead trend in the high 206Pb direction. Two 

of these pyrites had measurable uranium such that a correction for radiogenic lead resulted in slightly less radiogenic 

values (table 3; fig. 10). One pyrite analysis is corrected to 

the Greens Creek ore lead trend.

Figure 11 compares analyses of chalcopyrite, pyrrhotite, 

and ore bands (MFB and MFP) with the galena ore-lead trend. 

The chalcopyrite generally conforms to the Greens Creek 

galena ore-lead trend with two exceptions: one chalcopyrite 

(GC-1514-46) plots on the high-206Pb trend, very near the Portage sphalerite composition. This chalcopyrite sample is notable 

because texturally the chalcopyrite occurs as euhedral crystals 

on a fracture through chalcopyrite-rich, massive pyritic ore. The 

late chalcopyrite is therefore a remobilized phase, probably as 

a result of metamorphism or deformation at a time when the 

massive Greens Creek ore was behaving in a brittle fashion. 

The other exception, chalcopyrite GC-1514-44, plots slightly 

higher in 206Pb/204Pb than the Greens Creek ore-lead trend and 

coincident with the composition of sphalerite GC-1514-46. The 

pyrrhotite analysis does not conform to the other lead analyses 

but is a potentially informative sample as it is from a vein occurrence near Mt. Robert Barron on the Mansfield Peninsula where 

rocks in the vicinity of this occurrence are mapped as the older, 

highly metamorphosed Retreat Group sedimentary rocks.

The massive ores conform to the Greens Creek ore-lead 

trend, and one sample (GC-1656-06), an MFP, extends the 

trends toward higher 207Pb and 208Pb values of 206Pb/204Pb = 

18.771, 207Pb/204Pb = 15.745, and 208Pb/204Pb = 38.874 (fig. 11). 

Sphalerite-rich MFB sample GC-1643-10 was measured five 

times, once again to evaluate deviations due to mass discrimination effects. Maximum deviations in the lead isotopic ratios 

for the five analyses are d206Pb/204Pb = 0.013, d207Pb/204Pb = 

0.009, and d208Pb/204Pb = 0.024 (table 3), corresponding to 

slopes of 7/6 = 1.4 and 8/6 = 1.8. In general, like galena and 

tetrahedrite, the massive ores tend to be enriched in 207Pb and 208Pb relative to chalcopyrite and pyrite.

Finally, figure 12 displays plots of d34S versus 206Pb/204Pb 

and 207Pb/204Pb for sulfides and ores at Greens Creek as well 

as sulfides in host rocks and other mineral occurrences on 

Admiralty Island. In general, for Greens Creek sulfide minerals, both plots exhibit a lack of systematic variation of sulfur 

with lead. In detail there is a rough vertical separation on each 

plot of mineral species by d34S value, as observed in figure 6. 

The lack of variation in lead isotope values may indicate that 

the metal supply to the Greens Creek ore-lead trend was fairly 

homogeneous. Analyses of sulfides from other occurrences 

on Admiralty Island tend to group in the upper left quadrant 

of each diagram. Analyses from Pyrola and Cascade Creek 

have similarly 34S-depleted sulfur isotope values as Greens 

Creek sulfides and are less radiogenic. Analyses from the 

Kennecott-Rand, Portage, and Mt. Robert Barron occurrences 

fall within and at the less radiogenic end of the Greens Creek 

ore-lead trend but have noticeably 34S-enriched sulfur isotope 

values. This is potentially significant, as all three of these 

occurrences are on the Mansfield Peninsula and are hosted by 

the older Retreat Group rocks.

Interpretation of Sulfur Isotopes

The seawater sulfate d34S curve (Strauss, 1997; Claypool 

and others, 1980) increases rapidly from a low of 10.5 per mil 

at the end of the Permian to a high of about 19 per mil in the 

Middle Jurassic. The isotopic similarity to Greens Creek barite, 

which probably formed in latest Triassic time, suggests that the 

barite sulfate was derived from early Mesozoic seawater.

The Greens Creek sulfide data are intriguing because 

they are lower than the d34S values commonly found in either 

VMS or clastic-hosted SEDEX deposits. Studies of numerous Phanerozoic VMS indicate that sulfide d34S values are 

15–25 per mil less than those of coeval seawater sulfate. The 

total range for over 200 deposits worldwide is between –20 and 

27 per mil (fig. 13) with means for individual deposits falling 

between –5 and 20 per mil (Huston, 1999). These data suggest 

that for most deposits, inorganic reduction of seawater sulfate by 

ferrous iron in country rocks is the dominant source of reduced 

sulfur and thus the dominant mechanism for its fixation in the 

rocks (Shanks and others, 1981). Another common sulfur source 

is igneous sulfide from leaching of volcanic host rocks and input 

of sulfur from degassing magmas.

In clastic-hosted SEDEX deposits, sulfide d34S values 

show a slightly broader range of values although fewer data are 

available than for VMS deposits. If the sedimentary pyrite that is 

commonly associated with SEDEX ores is considered, the total 

range is between –22 and 43 per mil with values for massive 

ores between –10 and 28 (fig. 13). In general, these wide ranges 

of values and typical fractionations of –45±20 per mil from 

coeval seawater sulfate (Ohmoto and others, 1990) are cited as 

evidence for biogenically reduced seawater sulfate (Goodfellow 

and others, 1993; Solomon and Groves, 1994; Lydon, 1996). 

Strongly 34S-depleted sulfides are thought to form directly 

from bacterially produced hydrogen sulfide in anoxic stratified bottom waters, from hydrogen sulfide-rich pore fluids in 

saturated sediments, or from partial dissolution of diagenetic 

pyrite. The tighter ranges and generally more 34S-enriched values of the base-metal sulfides than for pyrite in most SEDEX 

deposits can be explained by the addition of a hydrothermal 

component carrying isotopically heavier sulfur formed by 

inorganic sulfate reduction (Large, 1980; Ohmoto and others, 

1990; many of the northern Australia examples such as HYC 

and Lady Loretta, the so-called dual-sulfur source model). 

Clastic-hosted SEDEX deposits also commonly exhibit an 

increase in sulfide 34S stratigraphically upward through the ore 

section. This feature is interpreted as evidence of bacterial sulfate reduction in a basin with restricted communication with 

the open ocean (Large, 1980; Goodfellow and others, 1993). 

Pyrite profiles that do not become 34S-enriched with increasing 
272 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Pyrrhotite

Galena

Chalcopyrite

MFP ore

MFB ore

GC-24

ADM-67

GC-1514-46

GC-1656-06

Pyrrhotite

Galena

Chalcopyrite

MFP ore

MFB ore

ADM-67

GC-1514-46

GC-1656-06

Pyrola

0 Ma

orogene

curve

Greens Creek

galena ore trend

15.5

15.6

15.7

15.8

18.3 18.5 18.7 18.9 19.1

206Pb/204Pb

Greens Creek - Admiralty Island

Pyrrhotite, Chalcopyrite,

MFP and MFB ore

Kennecott-Rand

data-point error ellipses are 2σ

A

207Pb/204Pb

Pyrola

0 Ma

orogene curve

38.0

18.3 18.5 18.7 18.9 19.1

38.2

38.4

38.6

38.8

39.0

data-point error ellipses are 2σ

Greens Creek - Admiralty Island

Pyrrhotite, Chalcopyrite,

MFP and MFB ore

Kennecott-Rand

Greens Creek

galena ore trend

B

206Pb/204Pb

208Pb/204Pb

Figure 11. Plot showing the range of lead isotopic compositions of pyrrhotite (X), chalcopyrite 

(open circles), and several ore bands (MFB, solid circles; MFP, solid squares) from Greens 

Creek, and compared to galena from Greens Creek (shaded field) and from several occurrences 

on Admiralty Island (open squares; Kennecott-Rand and Pyrola). (A) 206Pb/204Pb versus 207Pb/204Pb; 

(B) 206Pb/204Pb versus 208Pb/204Pb. Error ellipses are 2s. Orogene curve is that of Zartman (1984).
Isotopic Data 273

Greens Creek and Admiralty Island sulfide sulfur and lead isotope data

δ34S versus207Pb/204Pb and 206Pb/204Pb

15.55 15.60 15.65 15.70 15.75

–40

–35

–30

–25

–20

–15

–10

–5

0

5

10

KR

PY

RB M

Z

K K K

K

A

B B

NG

C

P

18.40 18.45 18.50 18.55 18.60 18.65 18.70 18.75 18.80 18.85 18.90 18.95 19.00

–40

–35

–30

–25

–20

–15

–10

–5

0

5

10

KR

PY

RB M

Z

K K

K

A

B

NG

C

P

207Pb/204Pb

206Pb/204Pb

δ34SCDT (‰) δ34SCDT (‰)

chalcopyrite

galena (gn)

Kennecott-Rand gn

Pyrola gn

Mammoth Claim gn

Mt. Robert Barron po

pyrite (py)

Zinc Creek py

Killer Creek py

3.9 mile A-Rd py

B-Rd py

pyrargyrite

sphalerite (sph)

N. Gambier sph

Cascade Creek sph

Portage sph

tetrahedrite

MFB

MFP

KR

PY

M

RB

Z

K

A

B

NG

C

P

Figure 12. Plots showing d34S versus 207Pb/204Pb and 206Pb/204Pb isotopic data for ores and sulfides in the Greens Creek 

deposit and for sulfides from Late Triassic and other mineral occurrences on Admiralty Island.
274 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Sulfides

Sulfates

δ34SCDT

–45 –40 –30–35 –25 –20 –15 –10 –5 0 5 10 15 20 25 30

0

5

10

15

20

25

30

FREQUENCY

Sulfides

Sulfates

closed to SO4

Thermochemical SO4 reduction,

T~100° – 200°C

open to SO4

sulfates

T>250°C

sulfides

Greens Creek δ34S data. All samples (n=235) 

Irish Midlands orefield

Permian-Jurassic marine sulfate

MVT Pb-Zn Viburnum Trend 

Bacterial sulfate reduction, T~30° – 110°C

Inorganic SO4

 reduction

Global VHMS deposits 

Global SEDEX deposits
Isotopic Data 275

stratigraphic height suggest open basin settings. The dual 

source model is invoked when diagenetic pyrite exhibits the 

upward-increasing 34S profile, but base-metal sulfides show 

tight and nonsystematic patterns.

One of the important differences between the sulfide 

sulfur isotopic characteristics of Greens Creek ores and those 

of typical clastic-hosted SEDEX deposits is the similarity of 

sulfur in the massive pyritic ores to sulfur in the base-metal 

sulfide minerals. Recrystallized pyrite in the massive, ironrich orebodies demonstrates the proper equilibrium relationship to the coexisting base-metal sulfides. While the most 

34S-depleted pyrites analyzed formed from hydrogen sulfide 

dominantly produced by bacterial sulfate reduction, the bulk 

of the pyrite and associated base-metal sulfides were produced 

by fluids carrying heavier sulfur derived from the footwall 

mafic rocks. As the hydrothermal system grew, it incorporated 

steadily increasing proportions of biogenic sulfur derived from 

dissolution of diagenetic pyrite or from biogenically reduced 

hydrogen sulfide in pore fluids of the accumulating shale cap. 

This mixing of isotopically heavier fluids with a progressively 

greater biogenic component from the hanging-wall argillites 

explains the unusual upward progression toward lower sulfur 

isotope values.

Arsenopyrite at Greens Creek accounts for some of the 

very lightest values. Texturally, these minerals are not primary 

framboidal aggregates forming in sediments but are incipient 

replacements of colloform pyrite (see chap. 9, fig. 4C) in the 

most proximal, massive pyritic portions of the Greens Creek 

deposit. The extremely light arsenopyrite sulfur implies that 

by the time the hydrothermal system had evolved to a zonerefining stage, not only was the fluid probably hotter and 

more reducing than early in the ore-forming process, but the 

shale cap was developed and was supplying an abundance 

of isotopically light sulfur to the hydrothermal system. This 

sulfur was of biogenic origin, either as hydrogen sulfide from 

pore fluids or from hydrolysis of diagenetic pyrite forming in 

the shale cap. The observation that both pyrite and base-metal 

sulfides follow this footwall-to-hanging-wall progression 

demonstrates that the bulk of the iron was introduced with the 

base metals in a single evolving mineralization episode.

This is a markedly different process than the “dualsulfur source” model (Large, 1980; Ohmoto and others, 1990) 

invoked in the genesis of many of the classic clastic-hosted 

SEDEX deposits. The common interpretation for these deposits is early formation of isotopically light diagenetic pyrite, 

which becomes isotopically heavier with stratigraphic height 

as sulfate is progressively consumed in a restricted basin. This 

is followed by the introduction of base-metal sulfides with 

a heavier and more restricted range of sulfide d34S values. 

Formation of the later, main-stage base-metal mineralization 

occurs as a result of hydrothermal fluid circulation, which 

carries a component of sulfur derived from magma or from 

volcanic rocks that is abiotically reduced at the site of mineral 

deposition. In contrast, Greens Creek sulfur isotope relationships indicate mixing of sulfur from a hanging-wall sedimentary source and from a mafic-ultramafic igneous footwall 

source in differing proportions during a single, evolving 

hydrothermal episode. As in VMS systems, a component 

of the sulfur at Greens Creek may have been produced by 

inorganic reduction of sulfate by interaction with the footwall, 

especially early in the history of the hydrothermal system. 

However, the data require that the bulk of the sulfide involved 

in the formation of both massive pyritic and base-metal 

sulfides had a dominantly biogenic origin. This conclusion is 

one of the strongest pieces of evidence available to support 

the suggestion that the shale cap was present for most of the 

Greens Creek hydrothermal episode.

The deposits of the Irish Midlands orefield display sulfide isotopic ranges similar to those at Greens Creek. These 

deposits, which are commonly included in the SEDEX class 

(Large, 1980; Goodfellow and others, 1993; Solomon and 

Groves, 1994), are predominantly carbonate hosted and have 

sulfide d34S values that are more negative than in the clastichosted deposits described above. As a whole, the Irish deposits 

range from –45 to 30 per mil with base-metal sulfides ranging 

from –36 to 30 per mil (fig. 13). Notably, there is a distinction 

between deposits with the isotopically lightest sulfides and 

those with d34S values in the range more commonly seen in the 

SEDEX literature. The isotopically lightest sulfides are observed 

from deposits that are hosted by the argillaceous Waulsortian 

Group sediments. The deposits hosted in carbonates of the 

Navan Group are uniformly heavier (Hitzman and Beaty, 1996).

The paragenetic order of barite and sulfides at Greens 

Creek, combined with the consistent values of both sulfates 

and sulfides, provides additional information about how the 

hydrothermal system evolved. Early barite with d34S values 

the same as coeval seawater sulfate were followed by sulfides 

with d34S values that do not vary or become progressively 

lighter with stratigraphic height, which suggests that the Greens 

Creek depositional setting had a plentiful supply of marine 

sulfate throughout its history. Also, the paragenetic progression 

from early barite precious-metal-rich ores to later barite-free, 

base-metal-rich and proximal pyrite-arsenopyrite ores suggests 

a progression from oxic to anoxic conditions through time. 

Early in the mineralizing sequence, reduced low-temperature 

hydrothermal fluids carrying barium, minor amounts of gold, 

Figure 13 (facing page). Figure showing calculated ranges 

of various major processes of sulfate reduction compared to 

the histogram showing the range of all sulfide and sulfate d34S 

analyses from the Greens Creek deposit. Calculations based on 

15–18 per mil d34S seawater sulfate. Also shown is the range 

of Permian through Jurassic seawater sulfate (Claypool and 

others, 1980) and summary d34S ranges of four major types of 

massive sulfide deposits: VMHS deposits, showing the total 

and most common ranges of values (Huston, 1999); SEDEX 

pyrite- and base-metal sulfide-sulfur isotope ranges (Large, 

1980; Solomon and Groves, 1994); MVT deposits of the Viburnum 

Trend (Leach and Sangster, 1993) and the Irish-type base-metal 

deposits, showing range of sulfides and sulfates (Hitzman and 

Beaty, 1996). CDT, Cañon Diablo troilite.
276 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

abiogenic hydrogen sulfide, silver, and base metals from the 

underlying volcanic rocks mixed with oxygenated, sulfate-rich 

seawater. As downfaulting and shale sedimentation progressed, 

the seawater source gradually became anoxic, resulting in 

cessation of barite precipitation. As the insulating shale cap 

accumulated, the hydrothermal fluid gradually increased in 

temperature. Thus, the hydrothermal fluid evolved to carry a 

greater metal load as a chloride complex to the site of fluid 

mixing and ore deposition in the accumulating and probably 

unlithified shales.

Interpretation of Lead Isotope Data

The lead isotopic data from Greens Creek sulfide 

samples, regardless of mineral species, form a very definite 

ore-lead trend. Most ore sulfides fall on this tightly constrained, remarkably linear, 207Pb- and 208Pb-enriched trend 

that unfortunately is coincident with the slope produced by 

natural mass discrimination of the lead isotopes during mass 

spectrometry. Three different samples were run five times 

each through a range of currents and temperatures to evaluate the range or deviation of isotopic values expected during 

mass spectrometry using our procedures and techniques. 

206Pb/204Pb and 207Pb/204Pb values were found not to vary more 

than 0.035 (about 0.19 percent), and 208Pb/204Pb not more than 

0.102 (about 0.26 percent). These deviations are considerably 

less— approximately 4 to 5 times less— than the maximum 

range of isotopic values exhibited by the 207Pb – 208Pb trends of 

the Greens Creek ore: 206Pb/204Pb about 0.134 (0.72 percent); 207Pb/204Pb = about 0.167 (1.07 percent); and 208Pb/204Pb about 

0.544 (1.41 percent). Although these maximum deviations 

are controlled by one datum, that of the massive ore sample 

GC-1656-06 that extends the mine-ore trend toward highly 

207Pb- and 208Pb-enriched values, four other analyses help 

define the high end of this trend. Barring those analyses, 61 

others fall within a smaller range of values: 206Pb/204Pb about 

0.049; 207Pb/204Pb = about 0.062; and 208Pb/204Pb about 0.196, 

still greater than the maximum deviations shown by multiple 

mass spectrometer runs on the same sample.

These observations lead us to believe that the 207Pb – 208Pb 

trend of the Greens Creek ore is not an analytical artifact but 

involves the mixing of at least two sources of different lead 

isotopic compositions, one at approximately 206Pb/204Pb = 

18.645, 207Pb/204Pb = 15.594, and 208Pb/204Pb = 38.34, and a 

second, undetermined, but a more enriched lead isotopic composition. The massive ore sample GC-1656-06 with 207Pb- and 208Pb-enriched values implies the probability of mixing with an 

older “crustal” source of lead.

A second, less well defined trend within the 206Pb–207Pb 

correlation is delineated by the Cascade Creek sphalerite, 

chalcopyrite GC-1514-46, and several pyrites—three GC-1656 

separates from the mine and NAD-T13-3c, a surface sample—a 

small number compared to the 61 analyses of the Greens Creek 

ore-lead trend. These results may indicate a second mixing line 

of lead isotopic compositions that are strongly influenced by 

206Pb. Mixing in this direction implies that the sphalerite lead 

compositions more radiogenic than the Greens Creek ore-lead 

trend are derived from younger or more radiogenic (or both) 

sources and apparently are not related to the main Greens 

Creek mineralization event. However, this trend is not completely supported within the 206Pb-208Pb correlation (fig. 10B), 

indicating that thorium/uranium values for some sources for 

these mineral separates are not similar. In particular, Cascade 

Creek exhibits the highest 208Pb/204Pb value (39.35), indicating 

that the lead for this sphalerite was derived from a source with 

higher thorium/uranium than the other sphalerites.

Some of these samples have enough, though small, 

uranium and thorium contents that lead growth has occurred 

since the sulfides formed. Correction of these analyses for 

their radiogenic lead (given in table 3) replots some of them to 

the galena ore-lead trend, but others do not. For example, the 

Portage sphalerite, when corrected for radiogenic lead, has a 

composition similar to that of the Kennecott-Rand galena (fig. 

10), suggesting a genetic link between the two or the uraniumlead systematics in this sphalerite sample have been disturbed, 

and therefore possibly overcorrected. The less radiogenic end 

of the 206Pb trend is defined by Kennecott-Rand galena and the 

massive pyrite sample from the Killer Creek occurrence. Other 

deviates in the lower-206Pb field are analyses of sphalerite 

(ADM-17 from the North Gambier occurrence) and pyrrhotite 

(ADM-67 from an occurrence on the Mansfield Peninsula), 

both involving different geologic environments than that found 

at Greens Creek. Again, this is a small number of deviates 

compared to the bulk of the Greens Creek ore. The deviation 

of these samples to less radiogenic values than the ore-lead 

trend implies that the lead in these samples is either older or 

from a more depleted source, or both, and not related to the 

main Greens Creek mineralization event.

We evaluate possible sources of lead for the Greens Creek 

ore deposit by comparing the Greens Creek ore-lead trend to 

initial lead values of the surrounding host rocks (see chap. 11) at 

215 Ma (fig. 14), including samples of the Hyd Group argillites, 

many of the metabasalts and metagabbros in the mine area, and 

samples, presumably of the same age, from other occurrences 

on Admiralty Island (for example, Gambier Bay, Pyrola). If the 

ore lead was derived from any of these rocks or from a similar 

source at 215 Ma, then the ore-lead compositions should match 

the initial lead values of the source rock(s). In order for this 

comparison to be valid, several assumptions must be met with 

respect to the data: (1) The lead isotopic compositions of the 

sulfides/ore have not changed since their formation at about 215 

Ma. This assumption applies both to closed system behavior 

(leads of different composition have not been added) and that 

ore minerals are nonradiogenic (that is, they do not contain significant amounts of uranium or thorium); and (2) The uraniumlead isotopic systematics of the host whole rocks have not been 

disturbed since their formation. This assumption is the least 

likely to be true. States of alteration within these host-source 

rocks have been evaluated, and some samples were found to be 

altered enough to expect disturbed whole-rock isotopic behavior 

(see chap. 11, figs. 6 through 9).
Interpretation of Lead Isotope Data 277

All initials at 215 Ma

All initials at 215 Ma

GC-1656-06

(MF ore)

Footwall

phyllites

Hyd Group

argillites

Hyd Group

argillites

Cannery Fm.

argillites

metabasalts

metagabbros

Pyrola

Galena

Pyrargyrite

Sphalerite

Pyrite

Tetrahedrite

Chalcopyrite

Pyrrhotite

MFB ore

MFP ore

92-GB-24

(metabasalt)

metabasalts

92-GB-24

(metabasalt)

Galena

Pyrargyrite

Sphalerite

Pyrite

Tetrahedrite

Chalcopyrite

Pyrrhotite

MFB ore

MFP ore

serpentinites

metagabbros

Footwall

phyllites

Cascade

Creek

Hyd Group

argillites

Hyd Group

argillites

Cannery Fm.

argillites

Pyrola

Footwall

phyllites

Footwall

phyllites

ADM-17

37.4

18.2 18.4 18.6 18.8 19.0

37.8

38.2

38.6

39.0

39.4

Greens Creek

Pb Isotopic Data

Kennecott-Rand

galena

B

206Pb/204Pb

208Pb/204Pb

15.4

15.6

15.8

16.0

18.2 18.4 18.6 18.8 19.0

206Pb/204Pb

Greens Creek

Pb Isotopic Data

Kennecott-Rand

galena

A

207Pb/204Pb

Figure 14. Plot comparing Greens Creek sulfide lead data with initial lead values at 215 Ma for argillites as well 

as many of the metabasalts and metagabbros of the area, including other Admiralty Island host rock samples, 

presumably of the same age (for example, Gambier Bay, Pyrola). (A) 206Pb/204Pb versus 207Pb/204Pb; (B) 206Pb/204Pb 

versus 208Pb/204Pb.
278 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Several observations can be made with respect to the orelead data and the sources of Greens Creek ore-lead. Greens 

Creek lead isotopic systematics involve four components, 

two major and two minor. The first major source is a slightly 

enriched mantle component (E-MORB), very similar to those 

values indicative of arc-type environments (Plumbotectonics 

“orogene” curve; Doe and Zartman, 1979; Zartman, 1984; see 

chap. 11, fig. 10). The E-MORB component is represented by 

the vast majority of the metabasaltic and metagabbroic samples, some footwall phyllites, and the three Cannery Formation 

argillites (see chap. 11, fig. 15). At 215 Ma, the least radiogenic end of the Greens Creek ore-lead trend falls within these 

fields, indicating their direct connection. The Greens Creek 

ore-lead trend suggests mixing between the mafic-ultramafic 

source and a 207Pb-enriched source more radiogenic than the 

most radiogenic sulfide.

The second major component is a poorly defined high- 207Pb component that controls the position of the radiogenic 

end of the Greens Creek ore-lead trend. The enrichment of 

207Pb relative to 206Pb implies the addition of “older” more 

radiogenic lead into the system. The high-207Pb trend suggests 

that this component incorporated “crustal” lead similar to 

Ordovician to Devonian model lead compositions (Plumbotectonics “upper crust” curve; for example see chap. 11, fig. 15). 

An obvious candidate for the source of this 207Pb-enrichment is 

the hanging-wall argillite. As discussed previously, the sulfur 

isotope data provide evidence that sedimentation of the shales 

was occurring during the growth of the Greens Creek system, 

and the shales were a source of sulfur, if not metals. However, 

the argillites measured define a broad field of argillite lead 

that encompasses all of the Greens Creek sulfide lead at and 

above the line of 206Pb variation. In detail, the argillites are 

grouped in three distinct clusters: two that plot on either end of 

the 206Pb trend line and a third, consisting of the three Cannery 

Formation argillites that plot within the E-MORB field at the 

depleted end of the Greens Creek ore-lead trend.

Although we believe the actual source for the Greens 

Creek high-207Pb component is poorly defined, these results 

indicate a probable source within the Hyd Group argillites. 

The ore-lead trend could be produced by homogenization of 

all lead sources, and the high 207Pb portion actually represents 

an average of 206Pb/204Pb compositions for high 207Pb compositions of some Hyd Group argillites.

The third and fourth components are relatively minor 

compared to the bulk of the data, which lies on the ore-lead 

trend. These minor components lie at either end of the 206Pb 

trend. The third component is less radiogenic than the bulk 

of the data and is found in the Kennecott Rand and Pyrola 

galenas, a Killer Creek pyrite (NAD-T17-9a), and the Mt. 

Robert Barron pyrrhotite. These samples plot within the field of 

least radiogenic argillites and perhaps within the field defined 

by the Greens Creek footwall phyllites (fig. 14). These least 

radiogenic samples require that their lead be derived from 

older or less radiogenic source rocks (or both) than the bulk of 

the Greens Creek ore lead. We find it compelling that sulfides 

from the Kennecott-Rand and Mt. Robert Barron occurrences, 

both of which are hosted in (Devonian?) Retreat Group rocks, 

define this third component. Similarly, the Pyrola galenas are 

hosted in rocks of uncertain age and of possibly older origins 

than those at Greens Creek. Current mapping (Karl and others, 

unpub. data, 2000) suggests a possible Devonian age for the 

Pyrola schist. The composition of the Killer Creek massive 

pyrite sample is problematic, especially with regard to the other 

samples from the Killer Creek occurrence, which all plot on the 

Greens Creek ore-lead trend. However, we note that Duke and 

others (see chap. 4) map the greenstones associated with Killer 

Creek as belonging to the (Devonian?) Retreat Group.

Considered as a group, the sulfide analyses that define the 

less radiogenic end of the 206Pb-trend have derived their lead 

from source rocks that are older than and distinctly separate 

from the rocks that supplied the bulk of the lead to the Greens 

Creek system. Further, we suggest that available age constraints 

indicate that this older source rock is probably Devonian in age 

and represents a Paleozoic unit of what is commonly referred 

to as the medium- to high-grade metamorphosed Retreat 

Group. Whereas the age of mineralization at these occurrences 

may have been Late Triassic, as indicated by numerous other 

similarities of most of these occurrences to Greens Creek, it 

is clear that the lead in these occurrences was derived from 

older rocks that are of minor importance to the metal budget at 

Greens Creek. It is significant that none of the Greens Creek 

ore sulfides analyzed exhibit lead isotopic compositions coincident with these older, less radiogenic compositions.

The fourth component is the radiogenic end of the 206Pb 

trend, defined by the Mammoth claim galena, Cascade Creek 

and Portage sphalerites, a Cub Creek pyrite, a subset of Greens 

Creek pyrites, and two chalcopyrites. As previously discussed, 

some of these analyses can be corrected (and possibly overcorrected) for accumulation of radiogenic lead that may or 

may not result in an initial lead composition on or near the 

Greens Creek ore-lead trend. Therefore, the high 206Pb component must have a distinctly different source than the Greens 

Creek ore lead. The only field of host-rock initial lead-isotopic 

compositions that could be involved in generating the radiogenic 206Pb trend is a group of the most radiogenic Hyd Group 

argillites (fig. 14). Whereas it is a possibility these 206Pb-rich 

signatures were generated from these argillites, we believe 

this component is more likely a younger, perhaps Cretaceous, 

lead-isotopic signature. The trajectory of the 206Pb trend is 

consistent with the uranium-thorium-lead isotopic evolution 

of Greens Creek host rocks and parallel to Doe and Zartman’s 

(1979) “orogene” growth curve. Additional data on host-rock 

radiogenic isotopic characteristics presented in chapter 11 

demonstrate that Cretaceous lead-isotope compositions are 

mainly more radiogenic than these radiogenic data for some 

Greens Creek and Admiralty Island mineral occurrences.

Both pyrite and chalcopyrite from Greens Creek that plot 

on the 206Pb trend are paragenetically late minerals that were 

probably remobilized from the main ore mass during Cretaceous metamorphism (see chap. 11) and therefore probably 

represent mixtures of Greens Creek ore lead with radiogenic 

lead from surrounding host rock. While the majority of data 
Interpretation of Lead Isotope Data 279

presented here and elsewhere suggests that the effects of Cretaceous metamorphism on the geochemistry and isotopic systematics of the Greens Creek orebody were minor, the deviation 

of these few ore sulfides along a high 206Pb trend may provide 

evidence for minor incorporation of Cretaceous lead signatures.

Finally, figure 15 compares Greens Creek lead values and 

other Alaskan ore deposits of various ages with model lead 

compositions from several major lead reservoirs (for example, 

mantle, orogene, upper crust; Zartman and Doe, 1981; Zartman, 1984). Readers should bear in mind that these curves 

are averages and not absolute values for these grand, planetscale reservoirs. Also, the “upper crust” curve is defined from 

mostly Phanerozoic data, such that lead from much older (for 

example, Archean to Proterozoic) crustal sources could yield 

considerably different lead compositions.

Lead isotopic values from Greens Creek more or less fall 

within a region defined by analyses from other Late Triassic 

occurrences within the belt (Newberry and others, 1997; this 

study). As is typical of volcanogenic massive sulfide deposits, 

the range of values from Greens Creek is restricted despite the 

fact that there are over 43 sulfide lead determinations from 

Greens Creek compared to less than 10 for any other late 

Triassic Alaskan ore deposit. There is more isotopic variation 

between deposits of a given age or district than within a single 

deposit. Our analyses extend the field of common lead isotope 

values for Greens Creek and for other late Triassic deposits of 

southeastern Alaska. However, as suggested by Newberry and 

others (1997), fields of lead-isotope values for massive sulfide 

deposits of Alaska fall in discrete positions on lead-isotope 

plots and can be distinguished generally by age.

The similarity of Greens Creek ore lead to that of the orogene curve, and not the mantle curve, indicates its origin within 

a primitive arc environment, a conclusion also reached by Van 

Nieuwenhuyse (1984) and supported by the whole-rock neodymium-strontium-lead isotopic data of Greens Creek host rock (see 

chap. 11) and adjacent regions (Samson and others, 1989, 1990).

Kennecott-Rand

Greens

Creek ore

Annette

Island

Duncan Canal

and Keku Island

typical

analytical

error

Mount Henry

Clay

AJ – PerseveranceSweetheart Ground Hog – Ascension

Ridge

Treadwell

Pyrola

Savage

Glacier Basin and

Trokna Silver

Alaskan

Treasure

Orogene

Upper Crust

0 Ma

400 Ma

Data from Cretaceous-Tertiary

VMS ore deposits of Alaska

Data from Triassic

VMS ore deposits of Alaska

15.65

15.75

15.55

15.45

206Pb/204Pb

207Pb/204Pb

18.2 18.4 18.6 18.8 19.0 19.2 19.4 19.6

Figure 15. Plot (206Pb/204Pb versus 207Pb/204Pb) showing a comparison of the range of Greens Creek lead isotope 

values to those from other Alaskan VMS deposits of various ages (modified from Newberry and others, 1997). 

Model lead isotopic evolution curves are from Zartman (1984).
280 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Conclusions

The Greens Creek sulfur isotope data are indicative of a 

single evolving hydrothermal system that derived sulfur from 

two major sources. Early in the hydrothermal history, reduced 

low-temperature fluids leached metals, barium, and sulfur from 

the footwall mafic igneous rocks and mixed with oxygenated 

seawater to produce the early white ores. As rifting and downfaulting progressed, leading to isolation of the basin and onset 

of shale sedimentation, the water column became progressively 

less oxic, resulting in bacterial sulfate reduction, formation 

of diagenetic pyrite in the shales, and resulting in hydrogen 

sulfide-rich pore fluids in the unconsolidated sediments. As the 

shale cap formed, the temperature of the hydrothermal system 

increased and resulted in greater base-metal solubility as chloride 

complexes. The hydrothermal fluid also leached a progressively 

greater component of isotopically light biogenic sulfur from 

the shales. Ultimately, the lightest sulfides formed late in the 

hydrothermal history during its peak temperature and most 

reducing phase. At this point, zone refining occurred, resulting in 

proximal footwall silicification and replacement/removal of early 

carbonate-barite assemblages, movement of silver-lead-zinc 

upward and outward, proximal enrichment of copper-gold, and 

incipient replacement of colloform sulfides with arsenopyrite. 

Main-stage ores formed by mixing, cooling, and dilution of a 

reduced metal-rich hydrothermal fluid with an anoxic seawater 

column and hydrogen sulfide-rich pore fluids that nevertheless 

remained in contact with isotopically normal seawater.

Ore and host-rock lead isotope studies indicate derivation 

of metal from two major sources. Sulfide lead isotopic values 

define a mixing line on an uranogenic lead plot between a nonradiogenic component similar to slightly enriched MORB and 

a 207Pb-enriched component from an older or more radiogenic 

source. The nonradiogenic end of the mixing line overlaps the 

field defined by Late Triassic age basalts and related gabbros, 

some phyllites, and the Cannery Formation argillites. The 

207Pb-enriched end is permissive of lead extraction from the 

hanging-wall argillites. A second minor 206Pb-trend is present that suggests that an older, less radiogenic lead source is 

present on Admiralty Island and contributed lead to some of 

the Late Triassic occurrences but not significantly to Greens 

Creek. More radiogenic lead compositions were found in some 

of the Greens Creek ore sulfides, indicating the likelihood of 

addition of Cretaceous lead to the Greens Creek system during 

regional metamorphism.

Acknowledgments

The authors would like to thank the Kennecott Greens 

Creek Mining Company for their cooperation, hospitality, and 

special equipment during sample collection on Admiralty Island. 

Also, thanks to all the workers at the USGS that were responsible for the majority of sample preparation and chemical analysis. 

Special thanks to manuscript reviewers Pat Shanks, Dan Unruh, 

and Robert Ayuso for their helpful comments and criticisms.

References Cited

Berg, H.C., 1973, The geology of Gravina Island, Alaska: U.S. 

Geological Survey Bulletin 1373, 41 p.

Berg, H.C., Jones, D.L., and Richter, D.H., 1972, GravinaNutzotin belt—Tectonic significance of an upper Mesozoic 

sedimentary and volcanic sequence in southern and southeastern Alaska: U.S. Geological Survey Professional Paper 

800–D, p. D1–D24.

Berg, H.C., Jones, D.L., and Coney, P.J., 1978, Map showing 

pre-Cenozoic tectono-stratigraphic terranes of southeastern 

Alaska and adjacent areas: U.S. Geological Survey OpenFile Report 78–1085, 2 sheets, scale 1:1,000,000.

Churkin, Michael, Jr., and Eberlein, G.D., 1977, Ancient 

borderland terranes of the North American Cordillera—

Correlation and microplate tectonics: Geological Society of 

America Bulletin, v. 88, p. 769–786.

Claypool, G.E., Holster, W.T., Kaplan, I.R., Sakai, H., and 

Zak, I., 1980, The age curves of sulfur and oxygen isotopes 

in marine sulfate and their mutual interpretation: Chemical 

Geology, v. 28, 199–260.

Doe, B.R., and Zartman, R.E., 1979, Plumbotectonics, the Phanerozoic, in Barnes, H.L., ed., Geochemistry of hydrothermal 

ore deposits: New York, John Wiley and Sons, p. 22–70.

Dusel-Bacon, C., 1994, Metamorphic history of Alaska, in

Plafker, G., and Berg, H.C., eds., The geology of Alaska: 

Boulder, Colorado, Geological Society of America, v. G1, 

p. 495–533.

Freitag, Katja, 2000, Geology and structure of the Lower 

Southwest orebody, Greens Creek mine, Alaska: Golden, 

Colorado School of Mines, Ph.D. dissertation, 248 p.

Gehrels, G.E., and Berg, H.C., 1994, Geology of southeastern 

Alaska, in Plafker, George, and Berg, H.C., eds., The geology of Alaska: Boulder, Colorado, Geological Society of 

America, v. G1, p. 451–468.

Gehrels, G.E., and Saleeby, J.B., 1987, Geologic framework, 

tectonic evolution, and displacement history of the Alexander terrane: Tectonics, v. 6, p. 151–173.

Giesmann, A., Jasper, H.J., Norman, A.L., Krouse, H.R., and 

Brand, W.A., 1994, On-line sulfur isotope determination 

using an elemental analyzer coupled to a mass spectrometer: 

Analytical Chemistry, v. 66, p. 2816–2819.

Goldfarb, R.J., Snee, L.W., Miller, L.D., and Newberry, R.J., 

1991, Rapid dewatering of the crust deduced from ages of 

mesothermal gold deposits: Nature, v. 354, p. 296–298.

Goodfellow, W.D., Lydon, J.W., and Turner, R.J.W., 1993, Geology and genesis of stratiform sediment-hosted (SEDEX) 
References Cited 281

zinc-lead-silver sulphide deposits, in Kirkham, R.V., Sinclair,

W.D., Thorpe, R.I., and Duke, J.M., eds., Mineral deposit 

modeling: Geological Association of Canada, Special Paper 

40, p. 201–251.

Hannington, M.D., Galley, A.G., Herzig, P.M., and Petersen, 

S., 1998, Comparison of the TAG mound and stockwork 

complex with Cyprus-type massive sulfide deposits, in

Herzig, P.M., Humphris, S.E., Miller, D.J., and Zierenberg, 

R.A., eds., Proceedings of the ocean drilling program: Scientific Results, v. 158, p. 389–415.

Hitzman, M.W., and Beaty, D.W., 1996, The Irish Zn-Pb-(Ba) 

orefield, in Sangster, D.F., ed., Carbonate-hosted lead-zinc 

deposits, 75th Anniversary Volume: Society of Economic 

Geologists Special Publication Number 4, p. 112–143.

Huston, D.L., 1999, Stable isotopes and their significance 

for understanding the genesis of volcanic-hosted massive 

sulfide deposits—A review, in Barrie, C.T., and Hannington, 

M.D., eds., Volcanic-associated massive sulfide deposits—

Processes and examples in modern and ancient settings: 

Society of Economic Geologists Reviews in Economic 

Geology, v. 8, p. 261–295.

Large, D.E., 1980, Geological parameters associated with 

sediment-hosted, submarine exhalative Pb-Zn deposits—An 

empirical model for mineral exploration: Geologisches Jahrbuch, v. D40, p. 59–129.

Leach, D.L., and Sangster, D.F., 1993, Mississippi Valleytype lead-zinc deposits, in Kirkham, R.V., Sinclair, W.D., 

Thorpe, R.I., and Duke, J.M., eds., Mineral deposit modeling: Geological Association of Canada, Special Paper 40, 

p. 289–314.

Ludwig, K.R., 1980, Calculation of uncertainties of U-Pb data: 

Earth and Planetary Science Letters, v. 46, p. 212–220.

Ludwig, K.R., 1985, PBDAT200—A Computer Program for 

processing raw Pb-U-Th isotope data: U.S. Geological Survey Open-File Report 85–547, 54 p.

Ludwig, K.R., 1991, ISOPLOT —A plotting and regression 

program for radiogenic-isotope data; version 2.53: U.S. 

Geological Survey Open-File Report 91–0445, 39 p.

Lydon, J.W., 1996, Sedimentary exhalative sulphides (Sedex), 

in Eckstrand, O.R., Sinclair, W.D., and Thorpe, R.I., eds., 

Geology of Canadian mineral deposit types: Geological 

Society of America, The geology of North America, v. P–1, 

p. 130–152.

McClelland, W.C., and Gehrels, G.E., 1990, Geology of the Duncan Canal shear zone—Evidence for Early to Middle Jurassic 

deformation of the Alexander terrane, southeastern Alaska: 

Geological Society of America Bulletin, v. 102, p. 1378–1392.

Miller, L.D., Goldfarb, R.J., Gehrels, G.E., and Snee, L.W., 

1994, Genetic links among fluid cycling, vein formation, 

regional deformation, and plutonism in the Juneau gold belt, 

southeastern Alaska: Geology, v. 22, p. 203–206.

Muffler, L.J.P., 1967, Stratigraphy of the Keku Islets and 

neighboring parts of Kuiu and Kupreanof Islands southeastern Alaska: U.S. Geological Survey Bulletin 1241–C, 52 p.

Newberry, R.J., and Brew, D.A., 1999, Chemical and isotopic 

data for rocks and ores from the Upper Triassic Greens 

Creek and Woewodski Island volcanogenic massive sulfide 

deposits, southeastern Alaska, in Kelley, K.D., ed., Geologic 

studies in Alaska by the U.S. Geological Survey, 1997: U.S. 

Geological Survey Professional Paper 1614, p. 35–55.

Newberry, R.J., Crafford, T.C., Newkirk, S.R., Young, L.E., 

Nelson, S.W., and Duke, N.A., 1997, Volcanogenic massive 

sulfide deposits of Alaska, in Goldfarb, R.J., and Miller, 

L.E., eds., Mineral deposits of Alaska: Economic Geology 

Monograph 9, p. 120–150.

Ohmoto, Hiroshi, 1986, Stable isotope geochemistry of ore 

deposits, in Valley, J.W., Taylor, H.P., Jr., and O’Neil, J.R., 

eds., chapter 14, Stable isotopes in high temperature geological processes: Reviews in Mineralogy, v. 16, p. 491–559.

Ohmoto, Hiroshi, Kaiser, C.J., and Geer, K.A., 1990, Systematics of sulfur isotopes in recent marine sediments and ancient 

sediment-hosted base metal deposits, in Herbert, H.K., and 

Ho, S.E., eds., Stable isotopes and fluid processes in mineralization: Nedlands, Western Australia, The University of 

Western Australia, Publication 23, p. 70–120.

Ohmoto, Hiroshi, and Rye, R.O., 1979, Isotopes of sulfur 

and carbon, in Barnes, H.L., ed., Geochemistry of hydrothermal ore deposits: John Wiley and Sons, New York,

p. 509–567.

Peter, J.M., and Scott, S.D., 1999, Windy Craggy, northwestern British Columbia—The world’s largest Besshitype deposit, in Barrie, C.T., and Hannington, M.D., eds., 

Vocanic-associated massive sulfide deposits—Processes 

and examples in modern and ancient settings: Society of 

Economic Geologists Reviews in Economic Geology, v. 8, 

p. 261–295.

Saleeby, J.B., 1994, Tectonic history of the Insular Suture 

Zone, southeastern Alaska: Geological Society of America 

Abstracts v. 26, p. A384.

Samson, S.D., McClelland, W.C., Patchett, P.J., Gehrels, G.E., 

and Anderson, R.G., 1989, Evidence from neodymium 

isotopes for mantle contributions to Phanerozoic crustal 

genesis in the Canadian Cordillera: Nature, v. 337, no. 23, 

p. 705–709.

Samson S.D., Patchett P.J., Gehrels G.E., and Anderson R.G., 

1990, Nd and Sr Isotopic characterization of the Wrangellia 

Terrane and implications for crustal growth of the Canadian 

Cordillera: Journal of Geology, v. 98, p. 749–762.
282 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Shanks, W.C. III, Bischoff, J.L., and Rosenbauer, R.J., 1981, 

Seawater sulfate reduction and sulfur isotope fractionation 

in basaltic systems—Interaction of seawater with fayalite 

and magnetite at 200–300o C: Geochimica et Cosmochimica 

Acta, v. 48, p. 557–569.

Solomon, Michael, and Groves, D.I., 1994, The geology and origin of Australia’s mineral deposits: Oxford, Oxford Science 

Publications, 951 p.

Stacey, J.S., and Kramers, J.D., 1975, Approximation of 

terrestrial lead evolution by a two-stage model: Earth and 

Planetary Science Letters, v. 26, p. 207–221.

Strauss, Harald, 1997, The isotopic composition of sedimentary sulfur through time: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 132, p. 97–118.

Taylor, C.D., 1997, An arc-flank to back-arc transect—

Metallogeny of Late Triassic volcanogenic massive sulfide 

occurrences of the Alexander terrane, southeastern Alaska 

and British Columbia: [extended abs.] in Society of Economic Geologists Neves Corvo Field Conference, May 

7–17, 1997, Lisbon, Portugal, Abstracts and Programs 

volume, p. 68.

Taylor, C.D., Cieutat, B.A., and Miller, L.D., 1992, A followup geochemical survey of base metal anomalies in the Ward 

Creek/Windfall Harbor and Gambier Bay areas, Admiralty 

Island, S.E. Alaska, in Bradley, D., and Dusel-Bacon, C., 

eds., 1991 Geologic studies in Alaska: U.S. Geological 

Survey Bulletin 2041, p. 70–85.

Taylor, C.D., Leventhal, J.S., Johnson, C.A., and Lear, K.G., 

2000b, The Greens Creek massive sulfide deposit southeastern Alaska—Stable isotopic evidence for the involvement 

of biogenic sulfate reduction in the formation of ores and 

carbonates, in Gemmell, J.B., and Pongratz, J., eds., Volcanic environments and massive sulfide deposits: Program and 

abstracts, CODES special publication #3, p. 209–210.

Taylor, C.D., Newkirk, S.R., Hall, T.E., Lear, K.G., Premo, 

W.R., Leventhal, J.S., Meier, A.L., Johnson, C.A. and Harris, 

A.G., 1999b, The Greens Creek deposit, southeastern 

Alaska—A VMS-SEDEX hybrid, in Stanley, C.J., and 

others, eds., Mineral deposits—Processes to processing: 

Balkema, Rotterdam, v. 1, p. 597–600.

Taylor, C.D., Philpotts, J.A., Hall, T.E., and Wakeman, B.W., 

1995b, New information on the geochemistry, age, and tectonic history of Late Triassic volcanic host rocks and associated massive sulfide occurrences of the Alexander terrane, 

southeast Alaska: Alaska Miners Association Conference 

Juneau, Program with Abstracts, p. 31–32.

Taylor, C.D., Philpotts, J., Sutley, S., Gent, C., Harlan, S., 

Premo, W., Tatsumoto, M., Emsbo, P., and Meier, A., 

1995a, Geochemistry of Late Triassic volcanic rocks and 

age of alteration associated with volcanogenic massive 

sulfide occurrences, Alexander terrane, southeast Alaska: 

Geological Society of Nevada, Geology and ore deposits of 

the American cordillera abstracts volume, p. A74.

Taylor, C.D., Premo, W.R., and Meier, A.L., 1999a, The Late 

Triassic metallogeny of the Alexander terrane, southeastern Alaska and British Columbia: Geological Society of 

America Abstracts with Programs, v. 31, no. 6, p. A–101.

Taylor, C.D., Premo, W.R., and Lear, K.G., 2000b, The Greens 

Creek massive sulfide deposit—Premier example of the 

Late Triassic metallogeny of the Alexander terrane, southeastern Alaska and British Columbia: Geological Society of 

America Abstracts with Programs, v. 32, no. 6, p. A–71.

Van Nieuwenhuyse, R.E., 1984, Geology and geochemistry 

of the Pyrola massive sulfide deposit, Admiralty Island, 

Alaska: Tucson, Arizona, unpublished Master’s thesis, University of Arizona, 170 p.

Zartman R.E., 1984, Lead, strontium, and neodymium isotopic 

characterization of mineral deposits relative to their geologic environments, in Proceedings of the 27th International 

Geological Congress, Moscow, v. 12, p. 83–106, Metallogenesis and Mineral Ore Deposits: Utrecht, The Netherlands, VNU Science Press.

Zartman, R.E., and Doe, B.R., 1981, Plumbotectonics—The 

model: Tectonophysics, v. 75, p. 135–162.
Microfossil and Radioisotopic 

Geochronological Studies of the Greens 

Creek Host Rocks

By Wayne R. Premo, Cliff D. Taylor, Lawrence W. Snee, and Anita G. Harris

Chapter 11 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract.......................................................................................................................................................287

Introduction.................................................................................................................................................287

Geology........................................................................................................................................................291

Geochronology...........................................................................................................................................293

Paleontology—Conodont Studies..................................................................................................293

Conodonts from the Greens Creek Mine Area....................................................................294

Underground Collections...............................................................................................294

Outcrop Collections........................................................................................................295

Color Alteration Index (CAI) ...................................................................................................299

Paleoenvironmental and Depositional Controls for Conodont Distribution ...................299

Conodonts from the Mansfield Peninsula and Northern Kupreanof Island...................299

Radiogenic Isotopic Age Determinations.....................................................................................300

40Ar-39Ar Age Determinations .................................................................................................300

U-Th-Pb, Rb-Sr, and Sm-Nd Ages on Host-Rock Lithologies ...........................................307

Whole-Rock Compared to Mineral (Internal) Isochron Ages .................................307

Analytical Methods ........................................................................................................307

Results .........................................................................................................................................................310

Metabasalts and Phyllites...............................................................................................................310

Metagabbros ...................................................................................................................311

Argillites............................................................................................................................320

Serpentinites ...................................................................................................................321

Discussion...................................................................................................................................................324

Late Triassic Igneous Activity.........................................................................................................324

Age of Greens Creek Mineralization .............................................................................................324

Isotopic Resetting of the Older Stratigraphy................................................................................324

Age of Cretaceous Overprinting on Greens Creek Mineralization...........................................326

Acknowledgments.....................................................................................................................................327

References Cited........................................................................................................................................327

Appendix......................................................................................................................................................331

Figures

1. Generalized map of terrane boundaries and major volcanogenic massive

sulfide prospects, southeast Alaska, showing the locations of the Late

Triassic age volcanogenic massive sulfide (VMS) deposits, including

Greens Creek, Pyrola, and Gambier Bay on Admiralty Island...........................................288

2. Simplified geologic map of Admiralty Island, showing locations for Greens Creek

and Pyrola deposits, Gambier Bay, Windfall Harbor, the Mansfield Peninsula, and 

Staunch Point (locations of some whole-rock samples) ...................................................289

3. Map of surface sampling sites at and near Greens Creek mine, Admiralty Island.......290

4. Photograph of Halobia in clast of siliceous argillite milled into massive sulfide ore....292
5. Stratigraphy of the Greens Creek section, Admiralty Island, showing the orebody

at the contact between footwall phyllites and hanging-wall argillites ...........................293

6. Lower and Upper primitius Zone conodonts (latest Carnian-earliest Norian)

from the Hyd Group, northern Admiralty Island, Alaska ....................................................295

6. A-I, Pa elements from outcrop in cirque at head of upper Cliff Creek ............................295

6. A, B, Metapolygnathus primitius (Mosher), Upper views of two incomplete adult

specimens with quadrate platform with five nodes on lateral margins and posterior

margin without nodes ................................................................................................................295

6. C, D, Metapolygnathus primitius Upper and lower views of small adult with three 

lateral nodes on inner margin and four on outer margin...................................................295

6. H, A Metapolygnathus primitius Pa element bent out of shape .......................................295

6. I, Metapolygnathus primitius Juvenile with three nodes on lateral margins and

midplatform constriction .........................................................................................................295

6. E-G, Metapolygnathus primitius transitional to Epigondolella, well-preserved

subadult, lateral, upper, and lower views.............................................................................295

6. J-O, Metapolygnathus primitius specimens from mine workings at 37 Ramp drift,

no. 1 passing bay and within 20 meters of the orebody .....................................................295

6. J-M, Juvenile and subadult Pa elements of Metapolygnathus primitius (Mosher)......295

6. N, O, Neogonodolella sp., Pa element, upper and lower views .......................................295

6. P-R, Specimens from mine workings in 620-2955 drift and within 15 meters of the 

orebody.......................................................................................................................................295

7. Carnian-Middle Norian conodont zonation showing age range of

biostratigraphically useful and (or) geologically significant conodont

collections from Hyd Group host rocks, Greens Creek mine and vicinity, and

four collections from the Hyd in the vicinity of the Taylor Creek deposit, northern 

Kupreanof Island.......................................................................................................................298

8. Conodont zonation for the Lower and part of the Upper Permian showing age

range of conodont collections from the uppermost exposed beds of the Cannery

Formation in the vicinity of the Taylor Creek deposit and the Pybus Formation

about 15 kilometers farther northwest, northern Kupreanof Island.................................301

9. 40Ar/39Ar step-release spectra for four samples: one from the Greens Creek mine,

two from other locations on Admiralty Island, and one fuchsite, 92–GB–05, from

altered ultramafic rocks on the north shore of Gambier Bay showing a two-step 

40Ar/39Ar plateau date of 210.3 ± 0.3 Ma (1σ) ........................................................................306

10. 40Ar/39Ar spectra for Greens Creek fuchsite and sericite — Spectra that

indicate complete resetting of argon in the alteration assemblage prior

to 105 – 95 Ma............................................................................................................................308

11. Uranium-lead isotopic correlation diagram of data from metabasalt rocks

(Hyd Group and Gambier Bay Formation) and footwall phyllites of the Green

Creek area..................................................................................................................................311

12. Samarium-neodymium isotopic correlation diagram of data from metabasalt

rocks and footwall phyllites — Greens Creek area............................................................318

13. Rubidium-strontium isotopic correlation diagram of data from metabasalt

rocks and footwall phyllites of the Greens Creek area......................................................319

14. Uranium-lead isotopic correlation diagram of data from some of the Greens

Creek metagabbros, yielding a whole-rock isochron age of 206 ± 35 Ma and

initial 206Pb/204Pb value of 18.61 ± 0.19, similar to that of the Greens Creek ore..............320

15. Samarium-neodymium isotopic correlation diagram of data from Greens Creek 

metagabbros..............................................................................................................................321
 16. Rubidium-strontium isotopic correlation diagram of whole-rock data from 
Microfossil and Radioisotopic Geochronological Studies 

of the Greens Creek Host Rocks

Wayne R. Premo,1 Cliff D. Taylor,1 and Lawrence W. Snee,1 and Anita G. Harris2

1

U.S. Geological Survey, Denver, Colorado.

2

U.S. Geological Survey, Reston, Virginia.

Abstract

Paleontologic and radiometric ages were determined for 

samples from the Greens Creek strata in order to more precisely date the timing and duration of ore deposition as well 

as provide an overall chronology at Greens Creek. Conodonts 

were the biostratigraphic index of choice because of the Triassic age, marine depositional setting, and low-grade metamorphism. Four conodont samples tightly constrain the age 

of the host rock within the Late Triassic. Two samples from 

the hanging wall in underground workings yielded an index 

species that restricts these samples to an interval that includes 

the Carnian-Norian boundary, which was previously dated at 

220.7 ± 4.4 Ma (mega-annum). 40Ar/39Ar geochronologic studies of sericite and fuchsite 

in the mine and of ultramafic bodies in the mine area generated 

argon age spectra that indicate Cretaceous-Tertiary metamorphic 

resetting of older minerals. However, one fuchsite separate from 

the thickest of the alteration zones yielded a two-step 40Ar/39Ar 

plateau age of 210.3 ± 0.3 Ma (1σ). If this age approximates the 

age of alteration of the ultramafic bodies, then it also estimates 

intrusion of Greens Creek mafic-ultramafic heat sources at 

between 215 and 211 Ma, allowing a few million years for 

emplacement, crystallization, and cooling. If the ultramafic bodies across the island are coeval and they were altered by hydrothermal fluids related to the Greens Creek ore-forming event, 

then the age of 210.3 ± 0.3 Ma represents the best constraint 

available on the age of the Greens Creek orebody.

Minimum and maximum estimates for the lifespan of 

the Greens Creek hydrothermal system can be calculated by 

assuming the initiation of mineralization occurred either during emplacement of mafic-ultramafic heat sources at between 

215 and 211 Ma, or at the time of shale sedimentation at 220.7 

± 4.4 Ma, and that the 40Ar-39Ar age on fuchsite dates the oreforming event. If either of these scenarios is correct, then the 

age data indicate that the Greens Creek hydrothermal system 

had minimum and maximum lifespans of 2.7 ± 2.3 million 

years and 10.4 ± 4.7 million years, respectively.

Whole-rock uranium-lead (U-Pb), rubidium-strontium 

(Rb-Sr), and samarium-neodymium (Sm-Nd) isotopic data 

were used to evaluate apparent isochron ages for several 

sample suites. U-Pb and Sm-Nd isotopic data for most of 

the Hyd Group metabasalt samples collected from Gambier 

Bay yielded apparent isochron ages of about 215 Ma. Several 

apparent Rb-Sr isochron ages agree with partially disturbed 

40Ar-39Ar ages from fuchsite and sericite that yield total gas 

ages between 80 and 100 Ma, ages that are consistent with the 

timing for terrane accretion during the Cretaceous.

Introduction

The Greens Creek ore deposit, one of many suspected 

volcanogenic massive sulfide (VMS) deposits in southeastern 

Alaska (fig. 1), is located at the north end of Admiralty Island 

(figs. 1 and 2). Age constraints on the host sedimentary rocks 

and for ore formation at Greens Creek have been conspicuously lacking throughout the existence of the mine and have 

been a source of uncertainty regarding the tectonic history 

and style of mineralization. Reconnaissance geologic mapping in the 1960s (Lathram and others, 1965) identified the 

lithologic units in the vicinity of Greens Creek as the Retreat 

Group, which at the time was thought to be Devonian in age, 

and those at the mine portal as belonging to the Permian 

Cannery Formation (chap. 4). Unaltered ultramafic bodies on 

Mariposite Ridge north of the mine (fig. 3) were mapped as 

middle Cretaceous in age, and the quartz-carbonate-fuchsite 

altered serpentinite body at Bruin Knob was considered to be 

a Middle Devonian serpentinized dolomite. As late as 1985, 

company geologists were uncertain regarding the age of the 

host rocks within a range of Permian to Late Triassic because 

Permian macrofossils recovered from a limestone body about 

6.5 km from the deposit and its probable association to Greens 

Creek, assigned by D. Grybeck and H.C. Berg (U.S. Geological Survey), conflicted with Late Triassic Halobia faunas 

found at other southeastern Alaska massive sulfide deposits 

(Crafford, 1984). Preliminary mapping by the U.S. Geological 

Survey (Brew and Ford, 1985) showed the mine hosted in the 

Cannery Formation and revised the age of the Retreat Group 

to indeterminate Mesozoic lithologies. It was also noted that 

the ultramafic bodies on the ridge north of the mine are variably altered dunites and peridotites; their age was revised to 

Mesozoic.
288 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

N

Ch

Ch

W

Cr

Cr

A

G

G

G

Cr

Cr

134°

56°

130°

Terrane Key

Ch

W

G

A

Cr

Y

&

T

C

Y

&

T

Y

&

T

C

Chugach

Wrangellia

Gravina

Admiralty

10

11

Admiralty

Island

6 7

8

22

21

Alexander

Craig

Y & T

C

Yukon-Tanana/

 Taku

Coastal

12 13

14

15

1

2

3

5

4

Prince of Wales

Island

16

17

18

19

Late Proterozoic -

lower Paleozoic

1. Niblack

2. Khayyam-Stumble-On

3. Big Harbor

4. Corbin

5. Copper City

Devonian(?)

6. Sweetheart Ridge

7. Tracy Arm

8. Sumdum

9. Moth Bay

Upper Triassic

10. Greens Creek

11. Pyrola

12. Palmer Prospect

13. Mt. Henry Clay

14. Woewodki Island

15. Frenchie (Zarembo Is.)

16. Keku Strait (Kuiu Is.)

17. Duncan Canal

18. Annette Island

19. Gambier Bay

20. Windy Craggy

Cretaceous

21. Fremming

22. Alaska Treasure

Deposits

9

Figure 3

20

Map

area Alaska

Terrane boundary

58°

0 50 100 KILOMETERS

Skagway

Haines

BRITISH COLUMBIA

ALASKA

Sitka

Juneau

Ketchikan

Petersburg

Wrangell

Figure 1. Generalized map of terrane boundaries (bold lines) and major volcanogenic massive sulfide prospects 

(numbered circles), southeast Alaska, showing the locations of the Late Triassic age volcanogenic massive sulfide (VMS) 

deposits, including Greens Creek (#10), Pyrola (#11), and Gambier Bay (#9) on Admiralty Island (after Newberry and others, 

1997).
Introduction 289

Greens Creek

Windfall Harbor

Pyrola

deposit

Juneau

Thane

Douglas

Auke Bay

Tee Harbor

Baranof

Chatham Angoon

Kake

Chicagof 

Island

Baranof

Island

Kupreanof

Island

Hawk

 Inlet

Passage

Seymour Canal

Stephens

Chatham Strait fault

G

A

G

N

Staunch Point

Quaternary surficial sediments

EXPLANATION

Tertiary volcanic rocks 

Tertiary sedimentary rocks 

Cretaceous granitoids 

Cretaceous ultramafic rocks 

Cretaceous-Jurassic sedimentary

 rocks

Cretaceous-Jurassic volcanic and

 sedimentary rocks

Cretaceous-Jurassic volcanic rocks

Triassic-Permian sedimentary and

 volcanic rocks, und. 

Triassic-Ordovician sedimentary and

 volcanic rocks, und. 

Triassic-Ordovician carbonate rocks,

 und.

Permian sedimentary rocks

Permian carbonate rocks

Devonian-Silurian carbonate rocks

Silurian sedimentary rocks

Silurian-Ordovician sedimentary rocks

Other rocks

Major fault

Inferred fault trace

Terrane boundary

0 25 KILOMETERS

Qs

KJs

KJsv

KJv

TrPsv

TrOsv

TrOc

Ps

DSc

Ss

SOs

Pc

Kum

Tv

Ts

Kg

Gambier

Bay

TrOc

Area of

figure 5

Funter

DSc

Glass Peninsula

Kum?

Mansfield Peninsula

Figure 2. Simplified geologic map of 

Admiralty Island, showing locations for 

Greens Creek and Pyrola deposits, Gambier 

Bay, Windfall Harbor, the Mansfield 

Peninsula, and Staunch Point (locations 

of some whole-rock samples). Bold dotted 

line is approximate boundary between the 

Alexander (A) and Gravina (G) terranes 

(after mapping by Gehrels and Berg, 1992).
82 79 80 5253 54 57 18 28 2219 2325 East Lil Sore Lil Sore Upper Zinc Ck Mammoth Bruin Knob Gallagher Ridge GREENS CREEK MINE Big Sore High Sore 39 48 46 51 293036 32 59 5860 6467 1 2 9 69 71 72 76 78 10 11 17 Mariposite Ridg

A-rd-03 B-rd-04 GST 97ADM-29 97ADM

PF-09 & PF-18 

Lakes District

1 .5 0 1 2 3 4 5 6 7 KILOMETERS

SCALE 1:63 360

1 1/2 0 1 2 3 4 5 MILES

3000 0 3000 6000 9000 12000 15000 18000 21000 24000 27000 FEET

Figure 3. Map of surface sampling sites at and near Greens Creek mine, Admiralty Island. Single-numbered locations are from the 97–LG-series (for example, “82” is the locations of 97–LG–82, and so forth). PF-series (–09 and –18) are from the Portal Face. Topographic map compiled from USGS Juneau A3 and A2 1:63,360 scale, 1997.
Geology 291

The first important age constraint based on data collected at the mine came in 1988 when, in a rib of the first 

stope at Greens Creek, Andrew Hawthorne and T.C. Crafford 

found two fossils in a clast of siliceous argillite interpreted 

to have been tectonically milled into the massive sulfide ore 

(Crafford, 1989, oral commun., 2002). One is the shell of the 

cosmopolitan Middle and Late Triassic flat clam Halobia

(N.J. Silberling, written commun., 1988; fig. 4); the other is a 

poorly preserved patelliform gastropod that merely indicates 

a Silurian to Holocene age (R.B. Blodgett, written commun., 

1988). According to T.R. Waller (written commun., 2002), 

Halobia first appears in the Ladinian (late Middle Triassic) of 

the Tethys sea but has its main occurrence in younger Triassic rocks, so that a Carnian or Norian age would be likely for 

the Alaskan specimen. Prior to our study, the Halobia was the 

only paleontologic evidence that could be tied to either the 

mine host rocks or the age of mineralization, and the deposit 

was assigned a Late Triassic age (Crafford, 1989; Newberry 

and others, 1990, 1997). Other assignments of a Triassic age 

for the deposit have been based on the similarity of the geochemical signature, basalt geochemistry, stratigraphic position 

of the metals, and correlation to other paleontologically dated 

Late Triassic massive sulfide occurrences in southeastern 

Alaska and British Columbia (MacIntyre, 1986; Taylor and 

others, 1995a, b, and 1999; Newberry and Brew, 1997, 1999). 

Because of uncertainty about the precise age of the Halobia

from the mine area and the absence of other direct age data for 

the immediate host rocks or absolute age of mineralization, 

a concerted effort was made during our study to develop age 

constraints for the host rocks and to determine the age of ore 

formation. Accordingly, conodont samples were taken from 

the immediate hanging wall, 40Ar/39Ar analyses of sericite and 

fuchsite alteration from ore and altered footwall phyllites, 

and construction of U-Pb and Sm-Nd mineral and whole-rock 

isochrons on specific host lithologies have all been performed 

to provide usable constraints on the age of ore formation in 

relationship to the age of the host rocks.

Geology

The detailed geology of Greens Creek is presented elsewhere in this volume so that only a brief summary of the rocks 

sampled for geochronology is included here.

The stratigraphy at Greens Creek can be summarized 

in three distinct sections, separated by unconformities. The 

first section is composed of siliceous to cherty argillite of 

the Cannery Formation of at least very late Early Permian 

age (Appendix, localities 8–10), the oldest stratigraphic unit 

at Greens Creek. These argillites are then unconformably 

overlain by the second section composed of metabasalts 

of unknown age (fig. 5). These metabasalts were variably 

metamorphosed at greenschist to amphibolite grade and 

subsequently hydrothermally altered (for example, Newberry 

and others, 1990), producing several types of phyllitic rocks. 

It is likely that this phyllitic sequence originally consisted of 

a composite mafic-ultramafic collection of massive flows and 

volcaniclastic deposits. Geochemical signatures of many of 

these phyllites are inconclusive but are consistent with basaltic 

protoliths, either as a rift-related basalt produced in an intraarc setting or as a fairly unfractionated calc-alkaline basalt 

formed in an oceanic volcanic arc. The arc-related signatures 

could be indicative of variable amounts of assimilation of 

preexisting island arc crust.

The metabasalts are unconformably overlain by the third 

section — the Upper Triassic Hyd Group — that consists of 

a basal conglomerate, overlain by a thick sequence of argillites, and finally capped by a thick sequence of basalts (fig. 5). 

Such conglomerates are found throughout the southern and 

middle portions of the Upper Triassic volcano-sedimentary belt 

throughout southeastern Alaska. Although thin, discontinuous, 

polymictic, conglomerate horizons occur in the northern half of 

Admiralty Island, their stratigraphic positions within the Triassic stratigraphy are uncertain. Mostly they are interpreted to be 

above the base of the section and within the shales that comprise the middle sedimentary part of the Triassic stratigraphy.

A thin, discontinuous, carbonate bed occurs between the 

conglomerate and the main ore body, and other carbonate beds 

are found just underlying and intercalated with the capping 

basalts and related argillites.

Within the Hyd Group, thick sequences of massive to 

slaty, graphitic, pyritic, black argillite and massive to slaty, 

carbonate-rich, dolomitic argillite overlie the main orebody 

and are of Carnian to Norian age based on fossil assemblages 

within underlying and overlying carbonate beds (fig. 5). Thick 

sequences of massive to pillowed basalts cap the section at 

Greens Creek and, like the basal conglomerate, they are a distinctive marker horizon throughout the Upper Triassic stratigraphy of southeastern Alaska.

Serpentinites of uncertain age crosscut the lower 

sequences of the Permian-Triassic sections at Greens Creek 

(fig. 5) and may represent the shallow ultramafic source of the 

metabasaltic protoliths or the overlying mafic volcanic flows 

of the Hyd Group, perhaps highly altered cumulates left after 

extraction of mafic melts. Gabbro-clinopyroxenite, both as 

relatively fresh rock and as highly quartz-carbonate-fuchsitealtered serpentinite, is common in outcrops in the mine area.

Continued emplacement of basaltic magmas at shallow 

levels accounts for the common occurrence of large gabbroic 

sills and stocks, particularly well exposed along Gallagher 

Ridge, south of the mine. These intrusions are thought either 

to just precede or to be coeval with extrusion of the overlying 

Hyd Group mafic flows (fig. 5). Continued production of 

heat in the immediate footwall of the deposit would similarly 

result in the extreme alteration of the gabbro-basalt pile during 

hydrothermal convection.

Diabase dikes are observed to crosscut massive ore and 

are not well understood. Obviously younger and much less 

deformed and altered, they are thought to be products of 

Jurassic-Cretaceous resumption of island-arc volcanism.
292 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Figure 4. Photograph of Halobia in clast of siliceous argillite milled into massive sulfide ore 

(courtesy of T.C. Crafford). Fingertip is shown for scale.
Geochronology 293

Geochronology

Paleontology—Conodont Studies

In 1997, the U.S. Geological Survey and Kennecott 

Greens Creek Mining Company joined in an effort to better understand the geologic setting and metallogenesis of 

the Greens Creek area. To that end, conodont samples were 

collected to provide higher biostratigraphic resolution for the 

age of the host rock and timing of mineralization. Conodonts 

were the fossil of choice because: (1) they are the major 

micropaleontologic index fossils in marine rocks of Triassic 

age; (2) they are apatitic and remain identifiable in low- to 

lower medium-grade metamorphic and hydrothermal regimes 

(Epstein and others, 1977; Rejebian and others, 1987); and (3) 

they are most easily recovered from carbonate rocks and had 

been recovered from Triassic carbonate and metacarbonate 

rocks throughout Alaska, including Admiralty and Kupreanof 

Islands (fig. 2 and Appendix).

By the end of 2001, thirty-nine conodont samples from 

host rocks in the Greens Creek mine and from outcrops of 

carbonate-bearing strata in the vicinity of the mine had been 

processed, searched for conodonts, and analyzed in order to 

refine the age of the host rock and timing of mineralization 

(table 1; Appendix, localities 23–31). In addition, carbonate 

samples from exploration areas on the Mansfield Peninsula 

(fig. 2 and Appendix, localities 1–4) and from the vicinity of 

the Taylor Creek deposit in the Duncan Canal area, northern 

Kupreanof Island (Appendix, localities 6–21), were also processed and analyzed.

All of the conodont samples from the immediate vicinity of the Greens Creek mine are from the Hyd Group of 

Late Triassic age. The group extends the length of Admiralty 

Island in a relatively narrow belt that parallels the island’s 

eastern margin and also crops out on northern Kupreanof 

Island (see chap. 2). The Hyd Group is part of the Admiralty subterrane of the Alexander terrane (Gehrels and Berg, 

1994). It unconformably overlies the Cannery or Pybus 

Formations on Admiralty and northern Kupreanof Islands. 

Conodont collections from northern Kupreanof Island 

indicate both formations are at least as young as very late 

Early Permian (Appendix, localities 8–10, and 22). The Hyd 

Group is mostly low-grade metamorphosed greenstone and 

phyllites that are hydrothermally altered locally. Crucial for 

the extraction of conodonts are the carbonate-rich intervals 

within calcareous and (or) dolomitic, carbonaceous, pyritic 

black phyllites and argillites and thin carbonate beds intercalated with these rocks (fig. 5).

The taxonomy and biochronology used for species and 

age determination, particularly for conodonts of late Carnian and earliest Norian age, are based on data from systematic and integrated conodont and ammonoid collections 

from many Upper Triassic successions in northeast British 

Columbia and, closer to Greens Creek both geographically 

and paleogeographically, from the lower part of the Kunga 

Group (Wrangellia terrane) in the Queen Charlotte Islands 

Unconformity

Unconformity

Conodonts

Conodonts

Macrofossils

Macrofossils

Limestone/dolomite

Polymictic conglomerate

Greenstones/phyllites

Pillow/massive basalt

Gabbroic dikes/sills

Siliceous/cherty argillite

 (Cannery Fm.)

Serpentinite Stratiform massive sulfide

Serpentinite

Pyritic-graphitic argillite

EXPLANATION

Greens Creek Stratigraphic Section

Upper

Triassic

Hyd Group

Lower Permian

Cannery Fm.

Carnian

Norian

Figure 5. Stratigraphy of the Greens Creek section, Admiralty 

Island, showing the orebody at the contact between footwall 

phyllites and hanging-wall argillites (from Taylor and others, 2000).
294 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

(Orchard, 1991a, b), about 400 km southeast. The CarnianNorian boundary and the interval of the Lower and Upper 

primitius Zones lie within the lower member of the Peril 

Formation; the formation ranges in age from late Carnian to 

late Norian. Both the type section of the Peril and reference 

sections for the Lower and Upper primitius Zones are in 

northwesternmost Queen Charlotte Islands (Desrochers and 

Orchard, 1991; Orchard, 1991a).

Conodonts from the Greens Creek Mine Area

Underground Collections

Twenty-seven samples were collected from various 

levels above the ore zone; some are from the underground 

workings, within about 50 m of the hanging-wall/ore 

contact, and others are from drill core taken in the hanging wall. Only four samples yielded conodonts (figs. 6 

and 7; table 1, samples 1–4; Appendix, localities 27–31). 

The results are not as disappointing as the low number 

of productive samples might imply. Two samples from 

the underground workings (table 1, samples 1–2) yielded 

conodonts diagnostic of the Lower and Upper primitius

Zones (figs. 6 and 7). Medium-gray, medium-grained 

dolomite from sample 1 collected about 20 m above the 

orebody (table 1) yielded the index species Metapolygnathus primitius (Mosher) and other less biostratigraphically 

diagnostic forms including Neogondolella sp. (fig. 6, A–D, 

and I). M. primitius restricts the collection to the Lower or 

Upper primitius Zone — a narrow interval that straddles 

the Carnian-Norian boundary. M. primitius is also the only 

conodont recovered from very dark gray, slightly silty dolomitic lime mudstone and fine-grained dolomite of sample 

2 that is only 15 m above the orebody (fig. 6, P and R; 

table 1). Sample 3, from medium-gray, slightly dolomitic, 

calcareous phyllitic mudstone, was selected from a drill 

core that penetrated the stratigraphic package on Big Sore 

Ridge (fig. 3) immediately above the mine workings. This 

sample yielded deformed fragments of neogondolellids and 

Metapolygnathus? sp. that indicate a Late Triassic, likely 

Carnian to very earliest Norian age (the age range of Metapolygnathus). The fourth sample from the workings, produced one ramiform conodont element that merely indicates 

a Triassic age. These four samples confine rocks in the 

hanging wall close to the ore to the Lower and (or) Upper 

primitius Zone (latest Carnian and (or) earliest Norian).
Geochronology 295

Figure 6 (facing page). Lower and Upper primitius Zone conodonts (latest Carnian-earliest Norian) from the Hyd Group, northern 

Admiralty Island, Alaska. Collections are from underground workings and outcrop, Greens Creek mine (scanning electron micrographs 

of carbon-coated specimens, x70; illustrated specimens deposited in the U.S. National Museum, USNM, Washington, D.C. See table 1 

for locality data, sample description, and analysis of faunules).

Figure 6. A-I, Pa elements from outcrop in cirque at head of upper Cliff Creek (table 1, sample 5); USGS colln. Mes. 35007.

Figure 6. A, B, Metapolygnathus primitius (Mosher), Upper views of two incomplete adult specimens with quadrate platform with five 

nodes on lateral margins and posterior margin without nodes (B); USNM 519818, 19.

Figure 6. C, D, Metapolygnathus primitius Upper and lower views of small adult with three lateral nodes on inner margin and four on 

outer margin. Even though the lower surface is corroded, there is still evidence of a bifurcate scar and the pit close to the center of the 

platform; USNM 519820.

Figure 6. H, A Metapolygnathus primitius Pa element bent out of shape. Preservation like this is more typical of specimens in this 

collection rather than other specimens shown here; USNM 519827.

Figure 6. I, Metapolygnathus primitius Juvenile with three nodes on lateral margins and midplatform constriction; USNM 519821.

Figure 6. E-G, Metapolygnathus primitius transitional to Epigondolella, well-preserved subadult, lateral, upper, and lower views. This 

specimen already has five nodes on one lateral margin; lateral view shows microreticulation on nodes confirming assignment to M. 

primitius but, like Epigondolella (its likely descendant), the pit is centrally located on the platform; USNM 519826.

Figure 6. J-O, Metapolygnathus primitius Specimens from mine workings at 37 Ramp drift, no. 1 passing bay and within 20 meters of 

the orebody (table 1, sample 1); USGS colln. Mes. 35004.

Figure 6. J-M, Juvenile (L, M) and subadult (J, K) Pa elements of Metapolygnathus primitius (Mosher), upper and lower views; K 

shows squared-off scar that is incipiently bifurcate and pit slightly posterior of platform center. J has lateral margins with three nodes 

whereas L, even though a juvenile, has four nodes on one margin; USNM 519822, 23.

Figure 6. N, O, Neogonodolella sp., Pa element, upper and lower views; specimen poorly preserved but clearly shows this is a 

neogondolellid and not a metapolygnathid homeomorph of Neogondolella, such as M. communisti; USNM 519828.

Figure 6. P-R, Specimens from mine workings in 620-2955 drift and within 15 meters of the orebody (table 1, sample 2); USGS colln. 

Mes. 35003. Subadult and juvenile complete Pa elements, though poorly preserved, Metapolygnathus primitius (Mosher), upper and 

lower views, USNM 519824, 25.

Outcrop Collections

Conodont samples from outcrops in the mine area were 

more productive than those from underground as the choices of 

sampling sites in the Triassic stratigraphy are much greater. Conodonts were found in 7 of the 16 outcrop samples (table 1, samples 5–11; Appendix, localities 24–26). Like the underground 

samples, the most tightly constrained collections are diagnostic 

of the Lower and (or) Upper primitius Zones; all other productive 

samples contain conodonts whose range, though not restricted to 

these zones, includes all or part of the Upper and Lower primitius Zones (fig. 7). Sample 5, from an outcrop of medium-gray 

lime mudstone in the cirque at the head of Cliff Creek yielded 

at least 100 deformed and (or) fractured conodont fragments, 

several incomplete though generically identifiable platform elements, and several others identifiable to species (table 1, sample 

5); some of the best and one of the worst are shown in figure 6, 

A–I. Four specimens can be confidently assigned to Metapolygnathus primitius (fig. 6, A–D, and I) and two others are transitional between M. primitius and Epigondolella (fig. 6, E–G). 

A sample of calcareous argillite (table 1, sample 6) at Big Sore 

Creek (fig. 3), produced the most biostratigraphically constrained 

conodont collection. M. primitius and abundant Neogondolella

spp., including many N. navicula, likely restrict this collection 

to the Upper primitius Zone of the earliest Norian. Even though 

the assignment of one definitive Metapolygnathus to a species (M. primitius) is uncertain, the occurrence of a definitive 

ornate Metapolygnathus with N. navicula restricts the age of the 

collection to the Upper primitius Zone as the first appearance 

of N. navicula marks the base of the Upper primitius Zone and 

Metapolygnathus should not extend above that zone. At Lil Sore 

(fig. 3), another calcareous argillite yielded a juvenile fragment 

of a metapolygnathid or epigondolellid and a deformed subadult 

of M. primitius or M. nodosus. The age range for this sample is 

no older than the Lower nodosus Zone and no younger than the 

Upper primitius Zone. Sample localities 8–11 yielded poorly 

preserved conodonts that could only be assigned a rather broad 

age range from or within the early or late Carnian to the earliest or middle Norian, even though one collection, from sample 

locality 10, has abundant conodonts.
Table 1. Data for geologically and biostratigraphically significant conodont collections from the Greens Creek mine and immediate vicinity, Alaska.—[Conodont zonation and age range of collections shown in figure 7; samples from Juneau A–2 quadrangle; all conodonts analyzed by A.G. Harris. CAI, conodont color alteratio1977, and Rejebian and others, 1987; Pa, platform element; m, meter; mm, millimeter] Sample no. and location Stratigraphic unit, lithology, and collector(s) Conodont fauna and remarks Zone/Age CAI 

Sample 1 37 Ramp drift, no. 1 passing bay; collection is ~20 meters above orebody, but intervening rocks are structurally complex 58°04'57"N., 134°37'50"W. Hyd Group Medium-gray, medium-grained do- lomite containing abundant pyrite and crosscutting dolomite vein fillings as much as 3 millimeters thick. Collectors: C.D. Taylor and K.G. Lear, 1996 USGS colln. Mes. 35004 Conodonts are poorly preserved. 1 subadult and 1 juvenile Pa elements Metapolygnathus primitius (Mosher) [fig. 6, J–M] 1 anterior half of Pa element Metapolygnathus sp. indet. 1 Pa element Neogon- dolella sp. indet. [fig. 6, N and O]. Sample also contains phosphatized steinkerns of gastropods and pelecypods. Lower and Upper primitius Zones (lat- est Carnian to earliest Norian) 5-5.5 In

Sample 2 620-2955 drift; 15 meters above orebody 58°04'57"N., 134°37'50"W. Hyd Group Very dark gray, dolomitic, slightly silty, fine-grained lime mudstone and fine-grained dolomite. Col- lectors: C.D. Taylor and K.G. Lear, 1996 USGS colln. Mes. 35003 2 (a juvenile and an adult) Pa elements Metapolygna- thus primitius (Mosher) [fig. 6, P–R]. The keel and pit on the lower side of the adult specimen is poorly preserved (eroded and (or) corroded). Lower and Upper primitius Zones (lat- est Carnian to earliest Norian) 5 In

Sample 3 480 South drift; 58°04'57"N., 134°37'50"W. Hyd Group Medium-gray, slightly dolomitic, calcareous, phyllitic mudstone. Collectors: C.D. Taylor and K.G. Lear, 1996 USGS colln. Mes. 35006 6 deformed Pa element fragments of neogondolellids 2 Pa element fragments Metapolygnathus? sp. indet. 1 indet. bar fragment. Conodonts are deformed and fractured. Late Triassic, likely Carnian to very earliest Norian 5 In

Sample 4 PS-112, 1347 ft.Core drilled on Big Sore Ridge, immediately above mine workings 58°04.8'N., 134°38.1'W. Hyd Group Medium-gray, fossiliferous (cri- noid ossicles and other indet. bioclasts), calcareous dolomite containing quartz-filled gashes. Collector: S. Newkirk, 1996 USGS colln. Mes. 35005 1 incomplete M element of Triassic morphotype. Triassic 5 or 5.5 In

Sample 5 Cliff-2; Outcrop in cirque at up- per Cliff Creek 58°03'35"N., 134°34'03"W. Hyd Group Medium-gray lime mudstone containing <10% calcite veins. Collectors: N.A. Duke and P.A. Lindberg, 1996 USGS colln. Mes. 35007 83 deformed, fragmented, fractured, and (or) corroded Pa elements. Metapolygnathus nodosus or M. primitius (Mosher) [fig. 6, H]. 4 Pa elements Metapolygnathus primitius (Mosher) [fig. 6, A–D, I]. 2 Pa elements M. primitius (Mosher) transitional to Epigondolella [fig. 6, E–G). 12 indet. blade fragments 1 ichthyolith. Minor phosphatic and phosphatized bioclasts. Lower-Upper primitius Zones (latest Carnian to earliest Norian 5 Po

Sample 6 JMP-131 Outcrop at Big Sore Creek 58°04 '47"N.134°36'53"W. Hyd Group Calcareous argillite. Collector: J.M. Proffett, 1999 USGS colln. Mes. 35018. Most of the conodonts in this collection are covered with or invaded by organic matter. 1 incomplete Pa element Metapolygnathus primitius (Mosher)? 4 juvenile Pa elements Metapolygnathus sp. indet. and (or) Epigondolella sp. indet. 2 incomplete, fractured and deformed Pa elements Metapolygnathus sp. in- det. and (or) Epigondolella sp. indet. 21 Pa elements 

Neogondolella navicula (Huckriede). 43 Pa element fragments or juveniles of chiefly Neogondolella spp. indet. Neogondolella spp. indet. vicarious elements. 2 Pb, 1 M, 2 Sa, and 2 Sc 14 indet. bar, blade, and juvenile platform fragments. 

Lower-Upper primitius Zone, probably Upper primitius Zone (latest 

Carnian to earliest Norian; probably earliest Norian). This is the most tightly dated conodont collection from the Hyd Group in the Greens Creek mine area (fig. 7).

Most 5; 

rare 4

N
Table 1. Data for geologically and biostratigraphically significant conodont collections from the Greens Creek mine and immediate vicinity, Alaska.—[Conodont zonation and age range of collections shown in figure 7; samples from Juneau A–2 quadrangle; all conodonts analyzed by A.G. Harris. CAI, conodont color alteratio1977, and Rejebian and others, 1987; Pa, platform element; m, meter; mm, millimeter]

Sample no. and location Stratigraphic unit, lithology, 

and collector(s)

Conodont fauna and remarks Zone/Age CAI 

Sample 7NAD-170 Outcrop at Lil’ Sore 

58°07'56"N. 134°41'26.5"W. 

Hyd GroupCalcareous argillite. Collector: N.A. 

Duke, 1999

USGS colln. Mes. 35051.1 juvenile Pa element fragment (free blade and small 

part of anterior end of platform) of a metapolygnathid or epigondolellid. 1 deformed subadult Pa element of Metapolygnathus nodosus (Hayashi) or M. primitius(Mosher).

nodosus Zone through Upper primitius

Zone (late Carnian to earliest Norian)

5 In

Sample 8NAD-2B Outcrop in Lakes District 

58°05'23"N. 134°42'04"W. 

Hyd GroupBlack calcareous argillite. Collector: 

N.A. Duke, 1999

USGS colln. Mes. 35050.Conodonts are deformed, fractured, corroded and 

mostly incomplete. 6 Pa elements Metapolygnathussp. 3 poorly preserved neogondolellid Pa element fragments.

Carnian to very earliest Norian 5 Po

Sample 9NAD-99A Outcrop in Lakes District 

58°05'27"N. 134°42'09.6"W.

Argillitic limestone. Collector: N.A. 

Duke, 1999

USGS colln. Mes. 35022.Conodonts are extremely poorly preserved; the chemical 

composition of a few was determined using EDAX (energy dispersive X-ray system); results are consistent with conodont composition. 5 Pa elements of Metapolygnathus? sp. indet. or Epigondolella? sp. indet. of Late Triassic age or even Polygnathus? sp. indet. of Middle Devonian-Early Mississippian age. These specimens most resemble Late Triassic metapolygnathids and epigondolellids; the geologic framework favors a Late Triassic age.

Carnian to middle Norian 5 In

Sample 1097-LG-05 Outcrop on Gallagher 

Ridge, 200 m west of top of Big Sore Ridge and above mine workings. 58°03'38"N. 134°37'29"W.

Hyd Group Metalimestone. Collector: C.D. 

Taylor, 1997 

USGS colln. Mes. 35023.All specimens are incomplete, variably deformed, and 

recrystallized so that species determination is not possible. These specimens are, however, confidently assigned to Metapolygnathus because the lateral marginal nodes are relatively few, the free blade is low, the keel bifurcates posteriorly, and there are no posterior margin nodes. 47 Pa element fragments Metapolygnathus sp. indet. (better preserved specimens have 3–5 marginal nodes). 76 Pa (small fragments) elements Metapolygnathus sp. indet. Minor phosphatic and phosphatized bioclasts.

late Carnian to very earliest Norian (no 

older than nodosus Zone)

6.5-7 Po

Sample 1197-LG-09 Outcrop on Gallagher 

Ridge, 11 m west of interbedded basalt and limestone exposure. 58°03'39"N. 134°37'22"W. 

Hyd GroupMetalimestone. Collector: C.D. 

Taylor, 1997

USGS colln. Mes. 35024 1 incomplete, deformed, and 

fractured Pa element Metapolygnathus? sp. indet.

Probably latest early Carnian to very 

earliest Norian

5.5-6 In
298 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

M.

polygnathiformis

M.

nodosus

E. quadrata

M. communisti

M.

primitius

Lower

Middle

Upper

Lower

Upper

E.

triangularis

UPPER TRIASSIC (part)

UPPER LOWER NORIAN

Lower

Middle

Upper

SERIES

STAGE /

SUBSTAGE

CONODONT ZONATION

(from Orchard, 1991b,

and

Kozur, 1989)

AGE

220.7

( ) +_ 4.4

Ma

Upper

Lower

E.

multidentata

E. spiulata

E. elongata

E. postera

E. serrulata

MIDDLE NORIAN

AGE RANGE OF SELECTED TRIASSIC

CONODONT COLLECTIONS

OUTCROPNAD-170

97LG-09

97LG-05

NAD-99A

JMP-131

Cliff 2

LOWER

CARNIAN

G. tethydis A.Z.

S. diebeli

Appendix, sample 3

NAD-2B

37 Ramp

PS-112 core

620 drift

480S drift

UNDERGROUND

GREENS CREEK MINE AND VICINITY AREA

TAYLOR

CREEK Appendix, samples 7, 19, 20

Appendix, sample 16

OUTCROP

Figure 7. Carnian-Middle Norian conodont zonation showing age range of biostratigraphically useful 

and (or) geologically significant conodont collections from Hyd Group host rocks, Greens Creek mine and 

vicinity, and four collections from the Hyd in the vicinity of the Taylor Creek deposit, northern Kupreanof 

Island. Plain solid bar indicates age range of collection; arrow at either end of bar indicates range extends 

beyond the Carnian and (or) middle Norian; dashed part of range indicates probable restricted age. The 

combined light and dark shaded areas indicate the common age of all biostratigraphically useful samples 

in the Greens Creek area; the narrow dark band marks the range of the four most biostratigraphically 

diagnostic collections, which is coincident with the boundaries of the Lower and Upper primitius Zones. 

Note that the age range of all collections overlap in the lower part of the Upper primitius Zone and that 

collection JMP–131 is most likely restricted to the Upper primitius Zone (see table 1). Radiometric age from 

Gradstein and others (1995). Abbreviations: A.Z., assemblage Zone; E., Epigondolella; G., Gladigondolella; 

M., Metapolygnathus; S, Sephardiella;
Geochronology 299

Color Alteration Index (CAI)

The CAI of most Greens Creek area samples is 5 or 

5–5.5, indicating the immediate host rock of each conodont 

sample reached at least 300° (CAI 5) or 350°C (CAI 5–5.5) 

using the experimental data of Epstein and others (1977) and 

Rejebian and others (1987). The fracturing and flowage of 

the conodonts, the consistency of CAI values within a sample 

and from sample to sample within the area, and the general 

absence of recrystallization suggest a low-grade metamorphic 

event. Conodonts from samples 10 and 11, however, have 

higher CAI values of 5.5–6 and 6.5–7 and, unlike conodonts 

from other Greens Creek area samples, they are partly 

recrystallized. Recrystallization of conodont carbonate apatite 

(approximating francolite) first begins at CAI 5.5 (Königshof, 

1992); recrystallization generally increases with increasing 

CAI as a function of time, temperature, and mineralogy of the 

host rock as well as the porosity of the host during metamorphism and (or) hydrothermal alteration (Rejebian and others, 

1987, their figs. 1 and 2; Königshof, 1992). Sample 11 is from 

an outcrop on Gallagher Ridge (fig. 3), just 11 m west of exposures of interbedded basalt and limestone. The CAI values of 

conodonts from sample 11 are higher than CAIs of conodonts 

from most Hyd samples and were either elevated soon after 

their deposition as a consequence of contact metamorphism 

(by basalt flows or intrusions) and (or) hydrothermal alteration associated with the nearby interbedded basalts or at a later 

time during larger scale metamorphism and contemporaneous 

or subsequent hydrothermal alteration. Nonetheless, conodonts 

from sample 11, and the more thermally altered conodonts 

from nearby sample 10 experienced higher temperatures and 

(or) contact with low- or high-temperature fluids that produced 

higher color and textural alteration of these conodonts than of 

conodonts from other collections in the Greens Creek mine 

area. Several collections of Permian and Triassic age from 

northern Kupreanof Island also contain conodonts having a 

range of high CAI values within a single sample. These are 

discussed later in this chapter.

Paleoenvironmental and Depositional Controls 

for Conodont Distribution

The conodonts in the Greens Creek area collections 

are metapolygnathids and neogondolellids. The former are 

predominantly tropical to subtropical, cosmopolitan, relatively 

warm shallow-water open-marine forms (ornate metapolygnathids) that were widespread in the western Cordillera of 

North America and elsewhere. If well enough preserved to permit species determination, the conodont found from the Greens 

Creek area includes only one or two species. Six collections 

contain only metapolygnathids, and of these, only samples 

5 and 10 produced relatively abundant conodonts, whereas 

the other four samples yielded only a few metapolygnathid 

platform (Pa) elements (table 1). The carbonaceous, calcareous and (or) dolomitic phyllitic mudstones and argillites that 

preserve these conodonts likely represent mainly hemipelagic 

basinal deposits with additions of storm- or wave-generated 

siliciclastic and carbonate muds from shallow-water platforms 

or other near-surface submarine edifices that were transported 

and redeposited in deeper marine environments. In the same 

way, the metapolygnathid conodont platform elements are also 

post-mortem hydraulic additions to these basinal deposits. 

Most conodont animals contained an array of morphologically distinct and functionally specialized conodonts in their 

feeding apparatus, like the variety of tooth shapes in humans. 

The conodont apparatus includes fanglike grasping and piercing elements, sawbladelike (ramiform) shredding elements, 

and more massive, nodose, ribbed, and (or) crenulate platelike 

(platform) grinding elements (for example, Purnell and Donoghue, 1997, 1998; Sweet, 1989). All conodonts shown in figure 

6 are the more massive platform elements, which were the 

more rapidly evolving and therefore more biostratigraphically 

useful conodonts in the feeding apparatus. The Hyd Group collections lack the more abundant and lighter ramiform elements 

of the conodont feeding apparatus; these, being lighter, were 

probably carried farther basinward from their shallow-water 

area of origin. The conodont animal was, for the most part, 

an active predator but was also preyed upon. Well-preserved 

fossils exist of Late Devonian sharks with their innards filled 

with the recognizable remains of conodont animals, that is, 

with indigestible conodont elements (Williams, 1990). Thus, 

some of the conodonts in the Greens Creek collections may 

have come from fecal pellets of other marine animals, probably other fish, that fed on conodonts. Conodonts have been 

reported in phosphatized fecal pellets in acid residues (Lange, 

1968) and are commonly observed in associated fecal-pelletrich areas that litter bedding planes of some black shales. Limestone samples containing abundant metapolygnathids probably 

originated as calciturbidites from sites closer to a shallow-water 

carbonate platform (table 1, samples 5 and 10). Sample 6, the 

most precisely dated collection, contains conodonts that lived 

in a basinal setting. The conodonts are predominantly deep and 

(or) cool-water neogondolellids. In this collection, most of the 

lighter conodont elements of the feeding apparatus have been 

winnowed away, but more ramiform elements are present here 

than in any of our other collections. Metapolygnathids make up 

only a small percentage of this collection and are undoubtedly 

post-mortem additions.

Conodonts from the Mansfield Peninsula and 

Northern Kupreanof Island

Conodont samples were also collected from exploration 

areas on the Mansfield Peninsula, northwestern Admiralty 

Island (fig. 2), at least 7 km northwest of the mine (Appendix, 

localities 1–4) and on northern Kupreanof Island, mostly in 

the vicinity of the Taylor Creek deposit in the Duncan Canal 

area (Appendix, localities 6–21). Only one collection from 

the Mansfield Peninsula produced conodonts of Triassic age 

(Appendix, sample 3). The collection includes nine platform 

elements of an ornate Metapolygnathus, likely M. primitius

and (or) M. nodosus, and six platform elements of either 
300 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Neogondolella sp. or Metapolygnathus communisti. Most 

of the conodonts are deformed and (or) incomplete; all are 

partly corroded and heavily coated with carbonaceous matter. 

Nonetheless, based on the broadest age interpretation for these 

conodont species, the collection could range from the nodosus

Zone through the primitius Zone (upper Carnian–lowermost 

Norian). This range includes the interval of the mostly tightly 

constrained conodont collections from the immediate vicinity 

of the Greens Creek mine (table 1, samples 1, 2, and 6; fig. 7).

On northern Kupreanof Island, conodont samples from 

the Hyd Group and stratigraphically older Cannery and 

Pybus Formations were collected in the course of this study 

or collected previously by U.S. Geological Survey personnel 

involved in geologic mapping or topical studies. Data for all 

these samples are given in the Appendix.

More than 60 percent of the samples from the vicinity 

of the Taylor Creek deposit were productive. Samples were 

taken from the Cannery Formation and Hyd Group and from 

carbonate-bearing rocks of uncertain stratigraphic assignment. 

Three samples, from the highest exposed beds of the Cannery, all produced the same conodont species association. The 

presence of Mesogondolella idahoensis in all three collections 

restricts their age to the Kungurian (late Leonardian; fig. 8). 

In addition, a sample collected from the Pybus Formation in 

1980, about 15 km northwest of the Taylor Creek deposit, 

produced conodonts of the same age but of greater diversity 

(Appendix, locality 22). These collections confirm the opinion 

of Karl and others (1999) that the Pybus is a facies equivalent 

of the Cannery. Most of the conodonts from the Cannery and 

Pybus have a range of CAI values within a sample (some from 

5 to 6.5). Moreover, a few other collections that contain less 

biostratigraphically diagnostic conodonts and therefore have 

longer age ranges also have a range of CAI values within 

a single sample; these might also be Permian collections 

(Appendix, localities 13 and 15).

The conodont collections from the Taylor Creek area 

assigned to the Hyd Group are of latest early to earliest late Carnian age (Appendix, localities 7, 19, and 20). The predominant 

conodont in these collections is Metapolygnathus polygnathiformis, the nominate species of the polygnathiformis Zone (fig. 

7). These Hyd conodonts from the vicinity of the Taylor Creek 

deposit are of older Carnian age than any of the well-dated 

samples from the Greens Creek area. A fourth sample, probably from the Hyd, produced conodonts that can confidently be 

assigned a late Early to early Late Triassic age. However, some 

specimens that are less deformed than others could be representatives of M. polygnathiformis, so this collection may be the 

same age as the other collections from the Hyd at Taylor Creek 

(Appendix, locality 16). The CAI of conodonts from the Hyd is 

mostly 5 (Appendix, localities 7, 19, and 20); conodonts from 

locality 16, however, have a range of CAI values from 5.5 to 7. 

Although stratigraphic levels apparently high in the Cannery 

and Pybus Formations and locally within the Hyd show effects 

of hydrothermal activity, and at least three conodont collections 

from the Hyd are older than the host rock or any Triassic rock 

thus far biostratigraphically well constrained in the vicinity of 

Greens Creek, the paleontologic data available at this time do 

not necessarily restrict the age of mineralization at Taylor Creek 

to the latest early or earliest late Carnian. The CAI of conodonts 

from the Hyd in the Taylor Creek area is mostly the same as that 

exhibited by conodonts from the Hyd in the vicinity of Greens 

Creek — 5 or 5–5.5. Higher CAI values occur locally in the 

Hyd in both areas (table 1, samples 10 and 11; Appendix, locality 16). The Hyd Group likely hosts the mineralization at Greens 

and Taylor Creeks, but the mineralization may not occur at the 

same stratigraphic level in both areas. At Greens Creek, the ore 

lies at or very close to the Carnian-Norian boundary interval 

(within rocks that are dated as Lower and(or) Upper primitius

Zone). In the vicinity of the Taylor Creek deposits, probably no 

closer than 3 km, the Hyd strata are of older Late Triassic age. 

As yet, no conodont samples have been taken in the immediate 

vicinity of the Taylor Creek deposit.

Radiogenic Isotopic Age Determinations

Radiogenic isotopic systems (for example, U-Pb, Th-Pb, 

Sm-Nd, Rb-Sr, K-Ca, 40Ar-39Ar, and Re-Os) are mainly used for 

age determinations of igneous and metamorphic rocks and for 

tracing the source(s) of fluids and magmas (for example, Dickin, 

1995, and references within). However, these isotopic methods 

can also be used to determine ages for mineralization or remobilization of ore fluids, interpreted as disturbances to radioisotopic 

systems (for example, Snee and others, 1988; Hart and Kinloch, 

1989; Lambert and others, 1989; Walker and others, 1991; Kerrich, 1991; Brannon and others, 1992, 1996; Chesley and others, 

1993, 1994; Kerrich and King, 1993; Christensen and others, 

1995a, 1995b; Snee, 2002). To this end, we used (1) the 40Ar/39Ar 

dating method to determine either the age of mineralization if 

it were preserved or the age of a disturbance to this isotopic 

system, and (2) the U-Pb, Th-Pb, Sm-Nd, and Rb-Sr systems to 

date mineralization, host rocks, or disturbances.

40Ar-39Ar Age Determinations

40Ar/39Ar geochronologic studies of sericite and fuchsite 

alteration in the Greens Creek mine and of fuchsitic alteration of ultramafic bodies near the mine area were conducted 

in an attempt to constrain the timing of ore formation. Eight 

samples yielded data: six samples of sericite, mixed sericite/

fuchsite, and fuchsite from ore and altered footwall phyllites, 

one sample of fuchsite from the Bruin Knob altered ultramafic body in the Mammoth claim area of Mariposite Ridge, 

and one sample of fuchsite from a similar altered ultramafic 

body on the Mansfield Peninsula (chap. 4). Unfortunately, 

all eight samples generated step-release-argon spectra that 

indicate Cretaceous metamorphic resetting of older minerals. The 40Ar/39Ar data are presented in table 2 and in figures 

9 and 10 that show the age spectra for each sample analyzed. 

In the simplest case, each of the spectra is the product of gas 

released from minerals that define the minimum age of the 

oldest mineral domains and the maximum age of the youngest 
Geochronology 301

PERMIAN (part)

LOWER (CISURALIAN) MIDDLE (pt.)

ASSELIAN SAKMARIAN ARTINSKIAN KUNGURIAN

WOLFCAMPIAN LEONARDIAN

WORDIAN

M. idahoensis

Neostr. prayi

Neostr. sulcoplicatus

Neostr. newelli -

M. serrata

M. phosphorensis

M. bitteri

J. aserrata

Me. phosphoriensisMe. prolongata

SYSTEM/

SERIES

SERIES/

STAGE GUADALUPIAN (pt.) UFIMIAN

M. bisselli-Sw. merrilliSt. simplex A.Z.

St. artin.-Sw. adent. A.Z.

Sw. whitei -St. artinski. A.Z.

St. elongatus-St. simplexSt. wabaunensis A.Z.

St. baskovi-St. constrictus

M. striata-St. simplex

M. bisselli-Sw. whitei A.Z.

Neostr. pequopensisNeostr. ruzencevi A.Z.

Neostr. pnevi

CONODONT ZONES

(modified from Mei and

Henderson, 2002)

Pybus Fm.sample 22

Cannery Fm.

samples 8-10

Figure 8. Conodont zonation for 

the Lower and part of the Upper 

Permian showing age range of 

conodont collections from the 

uppermost exposed beds of the 

Cannery Formation in the vicinity 

of the Taylor Creek deposit and 

the Pybus Formation about 15 

kilometers farther northwest, 

northern Kupreanof Island 

(Appendix, localities 8–10 and 22). 

Abbreviations: A.Z., assemblage 

Zone; M., Mesogondolella; 

Neostr., Neostreptognathodus; 

St., Streptognathodus; Sw., 

Sweetognathus.
302 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Table 2. 40Ar/39Ar data for samples* from Greens Creek VMS deposit, Admiralty Island, Alaska.

[T, temperature; °C, degrees Celsius; %, percent; Ma, mega-annum; mg, milligram]

T

(°C)

Radiogenic 40Ar+K-derived 39Ar+

40ArR

/

39ArK

# 39ArK

/

37ArCa

** Radiogenic yield 

(%)

39ArK

(%)

Apparent age and 

error@ (Ma)

96AD–06, Mammoth claim, fuchsite

Total-gas date: 97.5+0.2 Ma; No plateau; J=0.007599, +0.1%; wt. 49.4 mg

600 0.0374 0.0194 1.930 -- 24.3 0.3 26.2 + 0.6

700 0.7494 0.1621 4.623 19 92.1 2.4 62.3 + 0.2

750 1.9497 0.3238 6.022 4.0 98.7 4.8 80.7 + 0.2

800 4.3911 0.6496 6.759 4.2 93.7 9.7 90.4 + 0.1

850 4.9855 0.6976 7.146 28 98.6 10.4 95.4 + 0.2

900 9.7913 1.3262 7.383 237 99.5 19.8 98.5 + 0.2

950 10.4570 1.3874 7.537 404 99.6 20.7 100.5 + 0.2

1,000 7.2248 0.9411 7.677 1045 99.4 14.1 102.3 + 0.2

1,050 3.8559 0.4917 7.843 265 98.9 7.4 104.4 + 0.2

1,100 1.8586 0.2359 7.878 217 97.2 3.5 104.9 + 0.2

1,150 1.4989 0.1901 7.885 235 95.9 2.8 105.0 + 0.4

1,300 2.0917 0.2634 7.940 124 97.0 3.9 105.7 + 0.2

96AD–02, Mansfield Peninsula, fuchsite

Total-gas date: 60.8+0.2 Ma; No plateau; J=0.007579, +0.1%; wt. 15.5 mg

600 0.0116 0.0057 2.025 9 15.8 0.3 27.0 + 4.0

700 0.1991 0.0532 3.743 23 79.2 2.4 50.5 + 0.7

800 1.0028 0.2278 4.402 4.2 75.9 10.2 59.2 + 0.1

850 1.4919 0.3199 4.663 26 95.3 14.4 62.7 + 0.1

950 4.2774 0.9069 4.717 1161 98.6 40.8 63.4 + 0.1

1,050 1.9078 0.4363 4.372 950 97.0 19.6 58.8 + 0.2

1,150 0.5167 0.1180 4.378 133 82.3 5.3 58.9 + 0.1

1,300 0.6486 0.1567 4.140 -- 88.1 7.0 55.7 + 0.2

Greens Creek East orebody, fuchsite

Total-gas date: 89.0+0.2 Ma; No plateau; J=0.007566, +0.1; wt. 52.4 mg

600 0.2318 0.0791 2.929 161 62.6 1.2 39.5 + 0.3

700 1.6182 0.3235 5.002 129 96.6 4.9 67.0 + 0.1

750 2.5339 0.4350 5.002 48 97.4 6.6 77.8 + 0.2

800 5.5079 0.8689 6.339 37 94.5 13.3 84.5 + 0.1

850 9.3754 1.4021 6.687 169 98.6 21.4 89.0 + 0.2

900 7.1184 1.0289 6.918 393 98.6 15.7 92.0 + 0.1

950 5.3942 0.7659 7.043 737 98.5 11.7 93.7 + 0.1

1,000 4.8071 0.6708 7.166 847 98.6 10.2 95.2 + 0.1

1,050 2.6971 0.3716 7.258 1331 97.5 5.8 96.4 + 0.2

1,100 1.7354 0.2369 7.326 342 97.7 3.6 97.3 + 0.2

1,150 1.8212 0.2451 7.432 609 97.9 3.7 98.7 + 0.2

1,350 0.9466 0.1255 7.541 230 93.6 1.9 100.1 + 0.3
Geochronology 303

Greens Creek east orebody, sericite

Total-gas date: 77.5+0.1 Ma; No plateau; J=0.007558, +0.1%; wt. 62.3 mg

500 0.2166 0.0710 3.049 136 40.8 1.0 41.1 + 0.6

600 0.1743 0.0535 3.258 184 81.5 0.8 43.9 + 0.6

650 0.3973 0.1043 3.808 261 97.7 1.5 51.2 + 0.2

700 1.1167 0.2793 3.998 33 95.8 3.9 53.7 + 0.2

750 1.9110 0.4414 4.330 13 89.2 6.2 58.1 + 0.1

800 3.2430 0.6784 4.781 79 92.7 9.5 64.0 + 0.1

850 4.9680 0.9466 5.248 424 98.1 13.3 70.2 + 0.1

900 4.4801 0.7855 5.703 557 98.2 11.0 76.1 + 0.1

950 4.8884 0.7948 6.150 658 98.3 11.2 82.0 + 0.1

1,000 5.4835 0.8411 6.520 584 98.8 11.8 86.8 + 0.1

1,050 3.6438 0.5462 6.672 584 98.6 7.7 88.8 + 0.1

1,100 4.3078 0.6418 6.712 392 98.5 9.0 89.3 + 0.1

1,150 3.6127 0.5298 6.819 261 96.4 7.4 90.7 + 0.1

1,200 2.2907 0.3282 6.980 154 97.5 4.6 92.7 + 0.1

1,250 0.5304 0.0691 7.673 32 93.5 1.0 101.7 + 0.3

1,350 0.1032 0.0103 10.010 2 76.2 0.1 132.0 + 6.0

96GC–38, Greens Creek lower southwest orebody, fuchsite

Total-gas date: 83.4+0.2 Ma; No plateau; J=0.007581, +0.1%; wt. 36.8 mg

600 0.0744 0.0297 2.501 35 33.1 0.7 34.0 + 1.0

700 0.8166 0.2333 3.501 48 89.7 5.3 47.2 + 0.1

800 2.0386 0.4062 5.019 21 87.9 9.3 67.4 + 0.2

850 4.7641 0.7882 6.045 407 98.3 18.0 80.8 + 0.1

900 4.5305 0.7021 6.452 283 98.9 16.1 86.2 + 0.2

950 3.6134 0.5406 6.684 513 99.2 12.4 89.2 + 0.1

1,000 3.7288 0.5501 6.778 232 98.9 12.6 90.4 + 0.1

1,050 2.3592 0.3451 6.837 463 98.3 7.9 91.2 + 0.2

1,100 2.5145 0.3674 6.844 292 97.8 8.4 96.2 + 0.1

1,150 1.6150 0.2332 6.925 152 97.2 5.3 92.3 + 0.1

1,200 0.8956 0.1287 6.960 183 95.6 2.9 92.8 + 0.4

1,350 0.3332 0.0491 6.793 2 88.3 1.1 90.6 + 0.8

Table 2. 40Ar/39Ar data for samples* from Greens Creek VMS deposit, Admiralty Island, Alaska.—Continued

[T, temperature; °C, degrees Celsius; %, percent; Ma, mega-annum; mg, milligram]

T

(°C)

Radiogenic 40Ar+K-derived 39Ar+

40ArR

/

39ArK

# 39ArK

/

37ArCa

** Radiogenic yield 

(%)

39ArK

(%)

Apparent age and 

error@ (Ma)
304 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

29F-heading, north zone, east orebody, fuchsite

Total-gas date: 85.4+0.2 Ma; No plateau; J=0.007588, +0.2%; wt. 28.7 mg

550 0.0136 0.0070 1.959 26 19.4 0.2 27.0 + 3.0

650 0.2641 0.0639 4.135 123 87.7 1.8 55.7 + 0.9

750 1.1341 0.2377 4.771 72 96.7 6.7 64.2 + 0.1

800 0.9370 0.1769 5.297 94 69.7 5.0 71.1 + 0.2

850 2.3265 0.4040 5.758 202 96.9 11.4 77.2 + 0.2

900 4.9914 0.7810 6.391 203 98.7 22.0 85.4 + 0.1

950 3.2131 0.4716 6.814 162 98.1 13.3 90.9 + 0.1

1,000 3.7706 0.5420 6.957 95 98.6 15.2 92.8 + 0.2

1,050 1.2301 0.1772 6.943 146 97.5 5.0 92.6 + 0.4

1,100 1.0498 0.1512 6.945 74 97.0 4.2 92.6 + 0.2

1,150 1.3104 0.1910 6.861 37 97.2 5.4 91.6 + 0.1

1,300 2.4946 0.3548 7.031 12 97.1 10.0 93.8 + 0.1

PS115, Greens Creek exploration drill hole, mica; Total-gas date: 98.6+1.0 Ma; J=0.007597, +0.2%; wt. 45.5 mg

600 0.0440 0.0034 12.93 2.70 22.5 1.3 169.0 + 8.0

700 0.1375 0.0279 4.94 1.50 53.7 11.0 66.4 + 0.8

800 0.3475 0.0536 6.48 0.16 55.7 21.1 86.7 + 0.5

850 0.4348 0.0399 10.91 0.05 68.9 15.7 143.6 + 0.8

900 0.3841 0.0539 7.13 0.96 86.0 21.2 95.1 + 0.6

950 0.1651 0.0245 6.73 14.00 82.4 9.7 90.0 + 0.6

1,000 0.0946 0.0137 6.91 43.00 73.8 5.4 92.0 + 3.0

1,100 0.1834 0.0257 7.14 20.00 71.4 10.1 95.0 + 1.0

1,300 0.0871 0.0116 7.52 0.75 36.8 4.6 100.0 + 3.0

PS111, Greens Creek exploration drill hole, fuchsite; No plateau; J=0.007608, +0.2%; wt. 29.4 mg

600 0.1460 0.0477 3.065 7050 37.9 1.1 42.0 + 2.0

700 0.2302 0.0535 4.304 17 84.1 1.2 58.1 + 0.4

750 0.7133 0.1460 4.887 14 91.5 3.4 65.8 + 0.4

800 1.1261 0.2019 5.577 3 71.5 4.7 75.0 + 0.2

850 2.3371 0.3827 6.106 32 95.1 8.8 81.9 + 0.1

900 5.6769 0.8508 6.672 233 98.9 19.6 89.3 + 0.1

950 3.2973 0.4688 7.034 nd 99.2 10.8 94.0 + 0.1

1,000 4.0846 0.5684 7.186 339 99.1 13.1 96.0 + 0.2

1,050 5.1016 0.6932 7.360 408 99.4 16.0 98.3 + 0.2

1,100 3.8179 0.5078 7.518 284 99.0 11.7 100.4 + 0.2

1,150 2.1332 0.2815 7.579 160 98.7 6.5 101.1 + 0.3

1,200 0.8787 0.1141 7.701 37 98.2 2.6 102.7 + 0.7

1,350 0.1821 0.0231 7.875 2 77.5 0.5 105.0 + 1.0

Table 2. 40Ar/39Ar data for samples* from Greens Creek VMS deposit, Admiralty Island, Alaska.—Continued

[T, temperature; °C, degrees Celsius; %, percent; Ma, mega-annum; mg, milligram]

T

(°C)

Radiogenic 40Ar+K-derived 39Ar+

40ArR

/

39ArK

# 39ArK

/

37ArCa

** Radiogenic yield 

(%)

39ArK

(%)

Apparent age and 

error@ (Ma)
Geochronology 305

92GB–05, north shore, Gambier Bay, fuchsite

Total-gas date: 204.6+0.4 Ma; Plateau age: 210.3+0.3 Ma; J=0.007830, +0.2%; wt. 22.1 mg

500 9.2430 0.6296 14.68 205 96.7 36.1 196.3 + 0.3

600 P 13.2510 0.8376 15.82 238 97.0 48.0 210.7 + 0.3

650 P 3.9534 0.2517 15.71 202 96.6 14.4 209.2 + 0.5

700 0.1033 0.0080 12.97 1246 86.2 0.5 174.0 + 2.0

750 0.0476 0.0034 14.15 23 89.1 0.2 190.0 + 13.0

800 0.0401 0.0033 12.02 329 66.3 0.2 162.0 + 11.0

1,050 0.1170 0.0105 11.13 18 60.7 0.6 151.0 + 4.0

*

Mineral concentrates were derived from rock samples that were crushed, ground, and sieved to 60–120 mesh size (250–125 micrometers). Concentrates were 

passed through magnetic separator and heavy liquids and then handpicked to greater than 99 percent purity. All samples then were cleaned with reagent-grade 

acetone, alcohol, and deionized water and air-dried in an oven at 75°C. Fifteen to 65 mg of mineral were wrapped in aluminum foil packages and encapsulated 

in silica vials along with neutron-fluence standards prior to irradiation. The standard for this experiment was hornblende MMhb-1 with percent K = 1.555, 40ArR 

= 1.624 x 10-9 mole/gm, and K-Ar age = 520.4 Ma (Samson and Alexander, 1987). For irradiation, an aluminum canister was loaded with six silica vials, each 

containing samples and standards. Standards were placed between every two samples as well as at the top and bottom of each silica vial. Samples were irradiated 

in one of three different irradiation packages in the TRIGA reactor at the U.S. Geological Survey in Denver, Colorado. Length of each irradiation was 30 hours. 

Each irradiation package was rotated at 1rpm during irradiation. All samples and standards were analyzed in the Denver Argon Laboratory of the U.S. Geological Survey using a Mass Analyser Products 215 rare-gas mass spectrometer on a Faraday-cup collector. Each sample was heated in a double-vacuum low-blank 

resistance furnace for 20 minutes, in a series of 7 to 16 steps, to a maximum of 1,350°C, and analyzed using the standard stepwise heating technique described 

by Snee (2002). MMhb-1 standards were degassed to release argon in a single step at 1,250°C. For every argon measurement, five isotopes of argon (40Ar, 39Ar, 38Ar, 37Ar, and 36Ar) are measured. Detection limit at the time of these experiments was 2x10-17 moles of argon.

+

Abundance of “radiogenic 40Ar” and “K-derived 39Ar” is measured in volts and calculated to five decimal places. Voltage may be converted to moles using 

1.160 x 10-12 moles argon per volt signal. “40ArR/

39ArK” is calculated to three decimal places. All three are rounded to significant figures using analytical precision.

#

 “40ArR/

39ArK” has been corrected for mass discrimination. Mass discrimination was determined by calculating the 40Ar/36Ar ratio of aliquots of atmospheric 

argon pipetted from a fixed pipette on the extraction line; the ratio during these experiment was between 296.6 and 299.1, which was corrected to 295.5 to account 

for mass discrimination. “40ArR/

39ArK” was corrected for all interfering isotopes of argon including atmospheric argon. 37Ar and 39Ar, which are produced during 

irradiation, are radioactive and their abundances were corrected for radioactive decay. Abundances of interfering isotopes from potassium and calcuim were calculated from reactor production ratios determined by irradiating and analyzing pure CaF2

 and K2SO4; the K2SO4 was degassed in a vacuum furnace prior to irradiation to release extraneous argon. Correction for chlorine-derived 36Ar was determined using the method of Roddick (1983). Production ratios for this experiment 

were determined for (40Ar/39Ar)K , (38Ar/39Ar)K , (37Ar/39Ar)K , (36Ar/37Ar)Ca , (39Ar/37Ar)Ca , and (38Ar/37Ar)Ca ; measured values are available upon request.

@ Apparent ages and associated errors were calculated from raw analytical data then rounded using associated analytical errors. Apparent ages of each fraction include the error in J value (0.11 percent), which was calculated from the reproducibility of splits of the argon from several standards. Apparent ages were 

calculated using decay constants of Steiger and Jäger (1977). All apparent age errors are cited at 1 sigma. Uncertainties in the calculations for apparent age of 

individual fractions were calculated using equations of Dalrymple and others (1981).

** To calculate apparent K/Ca ratios, divide the “39ArK/37ArCa” by 2. The accuracy of apparent K/Ca ratios is dependent upon fast to thermal neutron ratios in 

the particular reactor. In the U.S. Geological Survey TRIGA reactor the correction factor has not been determined since Dalrymple and others (1981). Because 

reactor fuel in the USGS TRIGA has been changed since 1981, this ratio must be viewed as approximate but is internally consistent for each sample and reveals 

within-sample variability.

p

 Fraction included in plateau date. Plateaus determined according to the method of Fleck and others (1977).

Table 2. 40Ar/39Ar data for samples* from Greens Creek VMS deposit, Admiralty Island, Alaska.—Continued

[T, temperature; °C, degrees Celsius; %, percent; Ma, mega-annum; mg, milligram]

T

(°C)

Radiogenic 40Ar+K-derived 39Ar+

40ArR

/

39ArK

# 39ArK

/

37ArCa

** Radiogenic yield 

(%)

39ArK

(%)

Apparent age and 

error@ (Ma)
Ar/ Ar Age Spectrum for Greens Ck fuchsite

40 39

105 90 75 60 45

0 10 20 30 40 50 60 70 80 90 100

Percent Ar Released

Apparent Age (Ma)

39

K

Greens Creek, 29F heading, core

Ar/ Ar Age Spectrum for G

40 39

230210190170150130

0 10 20 30 40 50 

Percent Ar Relea

Apparent Age (Ma)

39

K

t = 

p 

92GB-0 Ga

Ar/ Ar Age Spectrum for Mansfield fuchsite 40 39

100 80 60 40 20 0

0 10 20 30 40 50 60 70 80 90 100

Apparent Age (Ma)

96AD-02; Mansfield Peninsula 

Ar/ Ar Age Spectrum for 

40 39

120100 80 60 40 20

0 10 20 30 40 50 

Apparent Age (Ma)

96AD-06; Mam

Percent Ar Released 39 K Percent Ar Relea

39 K

Figure 9. 40Ar/39Ar step-release spectra for four samples: one from the Greens Creek mine, two from other locations on Admi

fuchsite, 92–GB–05, from altered ultramafic rocks on the north shore of Gambier Bay showing a two-step 40Ar/39Ar plateau dat
Geochronology 307

mineral domains represented in the sample analyzed. They 

thus provide information on the minimum time period within 

which the minerals were reset. The actual age of the alteration 

mineral is therefore older than the oldest step indicated by 

each spectra. The five samples from the mine and the sample 

from Bruin Knob (chap. 4) indicate that complete resetting of 

argon in the alteration assemblage had occurred prior to about 

105–95 Ma. The Mansfield Peninsula sample is interesting 

in that it appears to indicate a plateau age of 60.8 Ma (fig. 9), 

consistent with alteration of the ultramafic body during the 

transition from oblique convergence to margin-parallel motion 

of the Alexander terrane during the Paleocene.

A ninth sample, reported in Taylor and others (1995a), 

provides an important age constraint on the Greens Creek 

hydrothermal system. On the southeastern side of Admiralty 

Island, on the north shore of Gambier Bay, several mineral 

occurrences are hosted in Upper Triassic rocks that bear a 

strong resemblance to those at Greens Creek (Taylor and 

others, 1992). These occurrences are associated with bodies 

of altered ultramafic rocks identical to the rocks at Greens 

Creek. On the north shore they consist of several horizons of 

graphitic/pyritic sediments, tuffs, and mafic volcanics of the 

Hyd Group that are 3 to 60 meters wide, conformable, and 

contain pervasively altered quartz-carbonate-fuchsite. Characteristics that link them to the altered ultramafic rocks near the 

mine include a similar mineralogy of serpentine, talc, barite, 

traces of magnesium-chromite, siegenite, pyrite, chalcopyrite, 

sphalerite, and tetrahedrite and a trace-element geochemical 

signature that is dominated by As, Cr, Co, Hg, Ni, and Sb. We 

interpret these altered ultramafics as part of a series of similar 

occurrences that occur in a linear belt from Gambier Bay to 

the Mansfield Peninsula that are associated with the Greens 

Creek ore-forming event.

Geochronologic data from a fuchsite separate from the 

thickest of these alteration zones yields a two-step 40Ar/39Ar 

plateau date of 210.3 ± 0.3 Ma (1σ; fig. 10) and a total gas 

age of 204.6 ± 0.4 Ma. The lack of evidence of thermal resetting of this relatively disordered mica (2M1

 structure) implies 

that this portion of the belt, in contrast to the seven analyses 

from the northern end of the island, has not undergone subsequent thermal events hotter than lower greenschist facies 

metamorphism since the Late Triassic.

U-Th-Pb, Rb-Sr, and Sm-Nd Ages on Host-Rock 

Lithologies

Whole-Rock Compared to Mineral (Internal) Isochron Ages

Because all attempts to separate uranium-bearing 

geochronometers (for example, zircon, baddeleyite, sphene, 

monazite) from several variably altered gabbros, diorites, 

and serpentinites in the immediate footwall were unsuccessful, the following age information was extracted from the 

U-Th-Pb, Sm-Nd, and Rb-Sr isotopic data from host-rock 

samples used for tracer studies (chap. 12). Although some 

of these ages can be considered accurate as well as precise, 

none are “internal” isochrons; that is, isochrons defined by 

the isotopic systematics of individual mineral separates (for 

example, plagioclase, pyroxene, ilmenite) from the same 

sample (for example, gabbro), as it is highly probable that 

all were formed from exactly the same melt with exactly the 

same initial isotopic composition, a criterion necessary to 

yield a valid isochron age. However, several studies showed 

that the isotopic systematics in minerals are sometimes disturbed during subsequent alteration and (or) metamorphism, 

whereas whole-rock systematics often are preserved even 

under adverse conditions (for example, Fairbairn and others, 

1961; Lanphere and others, 1964; Wetherill and others, 1968; 

Taylor and others, 1980; Moorbath and Taylor, 1981; Whitehouse, 1988; Barovich and Patchett, 1988).

Specific examples of both successful and unsuccessful whole-rock isochron ages from the literature should 

be a warning that this method of determining ages is not 

always reliable. Most whole-rock isochron ages that fail, 

do so because the isotopic composition of the source of the 

magma(s) is changing slightly over the geologically short 

duration of magma ascent and emplacement (less than 1 Ma), 

such that the data yield a mixing line of at least two initial 

isotopic compositions for the sample suite. In addition, problems in the isotopic systematics can occur during alteration 

and (or) metamorphism, as this sample suite has undergone 

(table 3), because of the instability of the elements of either 

the parent or daughter isotope.

Nonetheless, this is an important exercise because isochrons, if they exist, can help us to evaluate the stability of the 

isotopic systems and the reliability of their calculated initial 

values that have important implications on petro-tectonic origins for these rocks (chap. 12).

Analytical Methods

The analytical techniques used for the simultaneous, 

single dissolution of U-Th-Pb, Rb-Sr, and Sm-Nd analysis 

on whole-rock and mineral separates were similar to those 

reported by Tatsumoto and Unruh (1976) and Premo and 

Tatsumoto (1991, 1992), except that the mineral separates 

analyzed in this study were washed once with ethanol and 

ultrapure distilled water and then leached once with 1N 

hydrochloric acid for 10 minutes in an ultrasonic bath and 

finally rinsed with ultrapure water.

The whole rocks and separates were dissolved in 7-mL 

PFA Teflon vials with ultrapure concentrated hydrofluoric 

and nitric acids and then spiked with a dilute mixed tracer of 

205Pb-233U-236U-230Th as well as dilute mixed tracers of 84Sr- 87Rb and 150Nd-149Sm. Reheating was conducted to achieve 

isotopic equilibration. Lead was extracted from the dissolved 

powders using AG 1–X8 anion exchange resin in a dilute 

hydrobromic acid medium, then loaded in phosphoric acid 

onto single rhenium filaments, and isotopic ratios measured 

using a multisample, single-collector, VG Isomass 54R mass 

spectrometer. Lead isotopic ratios were corrected for a mass 

fractionation of 0.08 ± 0.03 percent per atomic mass unit 
308 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

40Ar/39Ar Age Spectrum for Greens Ck fuchsite

40Ar/39Ar Age Spectrum for Greens Ck fuchsite

40Ar/39Ar Age Spectrum for Greens Ck fuchsite 40Ar/39Ar Age Spectrum for Greens Ck fuchsite

40Ar/39Ar Age Spectrum for Greens Ck sericite

105

 90

 75

 60

 45

0 10 20 30 40 50 60 70 80 90 100

Percent 39ArK Released

Percent 39ArK Released Percent 39ArK Released

Percent 39ArK Released Percent 39ArK Released Apparent Age (Ma)

Greens Creek, 350 x-cut, 148 feet 

105

 90

 75

 60

 45

0 10 20 30 40 50 60 70 80 90 100

Apparent Age (Ma)

Greens Creek east orebody 

105

 90

 75

 60

 45

0 10 20 30 40 50 60 70 80 90 100

Apparent Age (Ma)

Greens Creek east orebody 

150

125

100

 75

 55

0 10 20 30 40 50 60 70 80 90 100

Apparent Age (Ma)

Greens Creek, PS111 core, 275' 

105

 90

 75

 60

 45

0 10 20 30 40 50 60 70 80 90 100

Apparent Age (Ma)

Greens Creek, PS115 core, 666' 

Figure 10. 40Ar/39Ar spectra for Greens Creek fuchsite and sericite — spectra that indicate complete resetting of argon in the alteration 

assemblage prior to 105 – 95 Ma.
Table 3. Descriptions and locations for host rock and adjacent samples of the Greens Creek VMS deposit.

Sample/ Rock Sample Sample Degree of alteration/ 

fraction type mode location grade of metamorphism 

Mafic rocksGambier Bay basalts92-GB-22 massive basalt WR powder Gambier Bay, Admiralty Island relatively unaltered Upper T

92-GB-24 metabasalt WR powder Gambier Bay, Admiralty Island greenschist facies, chloritized Gambie

92-GB-42 massive basalt WR WR powder Gambier Bay, Admiralty Island relatively unaltered Upper T

92-GB-55 metabasalt WR powder Gambier Bay, Admiralty Island greenschist facies, chloritized Gambie

92-GB-59 massive basalt WR WR powder Gambier Bay, Admiralty Island relatively unaltered Upper T

92-GB-80 massive basalt WR WR powder Gambier Bay, Admiralty Island relatively unaltered Upper T

basalt97-LG-17 chlorite-epidote basalt WR powder Gallagher Ridge, middle of east GR highly altered, chlorite- epidote- promin

biotite-carbonate-quartz-feldspar

serpentinite97-LG-19 serpentinite WR powder Gallagher Ridge, middle of east GR highly altered, serpentinized

97-LG-20 serpentinite WR powder Gallagher Ridge, middle of east GR highly altered, serpentinized

97-LG-32 serpentinite WR powder Mariposite Ridge-Mammoth Claim area altered, relict plag & olivine

96-GC1136-53 serpentinite WR powder Footwall, from southwest orebody altered, relict plag & oliv + carb

96-GC1136-59 serpentinite WR powder Footwall, from southwest orebody altered, relict plag & oliv + carb spatiall

97-ADM-59 serpentinite WR powder Gambier Bay, Admiralty Island highly altered, serpentinized known 

biotite-carbonate-quartz-feldspar

gabbro97-LG-45 altered gabbro or basalt? WR powder Zinc Creek area, north side of hill, west of saddle massive, highly-altered + carbonate relict ga

97-LG-69 gabbro WR powder Gallagher Ridge, immediately to the east side of the lake altered, hornblde, sericite, albite hornble

97-LG-70 microgabbro WR powder Gallagher Cirque, at base of cliff altered, hornblde, sericite, albite pyroxen

97-LG-71 PL gabbro, plagioclase mineral sep Gallagher Cirque, under the face of the cliff highly altered - sericitic to albitic gabbr

97-LG-71 gabbro WR powder Gallagher Cirque, under the face of the cliff altered, hornblde, sericite, albite coarse-

97-LG-82 hornblende gabbro WR powder East Little Sore grid, gabbro cliff altered, hornblde, sericite, albite

Gst, NW1/4, Sec 6 altered gabbro or basalt? WR powder Mariposite Ridge altered, hornblde, sericite, albite from N

other mafic rocks

96-ADM-01 massive basalt WR powder Mansfield Peninsula, Admiralty Island altered basalt grdmass + carb + qtz

96-ADM-12 porph. microgabbro WR powder Staunch Point, Admiralty Island highly-altered, ser-chlor-qtz-serpent

96-AD-58 cemented mafic volcanic WR powder North Gambier Bay, Admiralty Island altered basalt grdmass + carb + qtz

+ hornblende

PhyllitesGC-PF-09 sericitic phyllite WR powder Portal Face, footwall sericite + chlorite + qtz + carb

GC-PF-18 chlorite-carbonate phyl WR powder Portal Face, footwall sericite + chlorite + qtz + carb

GC-462-02 sericitic phyllite WR powder Footwall, from east ore sericitic greensc

GC-462-07 sericitic, chloritic WR powder Footwall, from east ore chloritic

GC-1103-16 sericitic phyllite WR powder Footwall, from southwest orebody sericitic

GC-1637-44 sericitic phyllite WR powder Footwall, from deepest hole sampled to date unaltered (?)

ArgillitesA-Rd-03 argillite WR powder from 3.66 mi on the A-road low grade alteration thought B-Rd-04 argillite WR powder from 3.3 mi on the B-road low grade alteration thought 97-LG-78 siliceous argillite WR powder from the top of Big Sore Ridge deformed laminae, siliceous thought 

97-LG-75 graphitic argillite WR powder from north-facing slope of Gallagher Ridge, s. of Big Sore deformed laminae, siliceous (?) thought 

96-GC1136-05 massive WR powder Hanging wall, from lower southwest orebody sericite + feldspar + qtz + carb known 

PP-204-01 argillite WR powder Hanging wall, from level 170, lower southwest orebody undetermined known 97-LG-66 slaty argillite WR powder from west side of Gallagher cirque deformed, siliceous-micaceous clay thought 

97-ADM-29 massive WR powder from east Mariposite Ridge undeformed, siliceous clay + carb thought NAD-T4-2 argillite WR powder from Cliff Creek cirque finely laminated, undeformed, siliceous known 97-ADM-34 massive WR powder from eastern end of east Mariposite Ridge undeformed, siliceous clay + carb thought 

Crosscutting dikes97-LG-64 diorite? dike WR powder Gallagher Ridge, moving ~100 m east of LG-63 hornblde-plag (altered), relic pyrox one of tGC-1701-01 diabase dike WR powder Greens Creek mine, at 645 ft sericite-fldspar + chlorite + qtz + carbGC-1704-01 diabase dike WR powder Greens Creek mine, at 1,335 ft amphibole-altered plag + carb + pyrox with LG

 samp

Pyrola minePY-5-09 qtz-sericite-schist WR powder Pyrola mine site, southern Admiralty Island highly-altered, chloritic, 
310 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

(amu) and a laboratory blank varying between 107 and 242 

picograms (pg) (average = 165 pg) total lead with an average measured composition of 206Pb/204Pb = 18.681 ± 0.064, 207Pb/204Pb = 15.432 ± 0.033, and 208Pb/204Pb = 37.72 ± 0.12 

(table 4 footnotes). Uranium and thorium were extracted 

using AG 1–X8 anion exchange resin in a 7N nitric acid 

medium and residues were loaded onto rhenium filaments 

using dilute nitric acid. Uranium and thorium ratios were 

measured in the triple filament mode using the tandem mass 

spectrometer and were corrected for a mass fractionation 

of about 0.20 ± 0.03 percent per amu and laboratory blanks 

ranging between 2 and 15 (average 9) and 7 and 50 (average 25) pg, respectively. Uranium-thorium-lead (U-Th-Pb) 

isotopic ratios were measured using a fully automated (Ludwig, 1993), multisample, single-collector, VG Isomass 54R 

mass spectrometer, and corrected using the algorithms and 

programming of Ludwig (1980, 1985).

The effluent from the U-Th-Pb chemistry was then 

passed through a large (30 mL resin-volume) column with 

AG 50W–X8 cation exchange resin, separating Rb, Sr, and 

rare-earth elements (REE). Samarium was separated from 

neodymiun using AG50W–X8 cation exchange resin and the 

a-isobutyric method of Lugmair and others (1975), and then 

both were loaded with very dilute phosphoric acid onto tantalum filaments in either the single or triple filament mode and 

run on the fully automated, multisample, VG Isomass 54R 

mass spectrometer. Total strontium blanks ranged between 

0.03 and 0.3 nanogram (ng), and total neodymium blanks 

ranged between 0.03 and 0.1 ng. Uncertainties on isotopic 

ratios are given in tables 4 through 6 and are reported at the 

2σ level. See footnotes of the analytical tables for other correction information.

Results

Attempts at producing internal isochron ages using the 

U-Pb, Rb-Sr, and Sm-Nd isotopic data from whole-rock and 

mineral separates from several of the least-altered basalts, 

serpentinites, and metagabbros were unsuccessful, probably due 

to the advanced state of alteration in nearly every sample (table 

3). Therefore, mostly whole-rock U-Pb, Rb-Sr, and Sm-Nd 

isotopic data are used here to evaluate possible isochron ages for 

specific groups of host-rock lithologies. Age determinations and 

diagrams were made using the programming of Ludwig (1998). 

Surface sampling sites are shown in figure 3.

Metabasalts and Phyllites

Uranium-lead isotopic data for whole-rock samples of 

metabasalts from Gambier Bay and Greens Creek and phyllites from in and around the mine are relatively scattered and 

do not form well-defined arrays. These metabasaltic rocks are 

not the same age and therefore not cogenetic. The phyllites 

are highly altered metabasalts from the second section of the 

Greens Creek stratigraphy known to be older than Carnian 

(fig. 5), whereas several of the metabasalts at Gambier Bay are 

samples from the upper horizons of the Hyd Group that caps 

the stratigraphy and are younger than Norian.

An apparent U-Pb isochron age can be calculated for the 

best-preserved or least-altered metabasaltic samples from the 

Hyd Group (97–GB-22, 42, 59, and 80; table 3), and data from 

three out of four of these whole-rock samples form an array 

with an isochron age of 218 ± 16 Ma and an initial lead value 

of 18.515 ± 0.04 (dashed line; fig. 11). This age is interpreted 

to approximate the timing for extrusion of the Hyd Group 

basalts at Gambier Bay.

Hyd Group metabasalt 92–GB-59 does not conform to 

the Hyd Group isochron and appears to contain excess radiogenic lead as is exhibited by both of the chloritized metabasalts 

92–GB–24 and 92–GB–55 of the Gambier Bay Formation. 

Highly altered metabasalt from Gallagher Ridge (97–LG–17) 

and several mine phyllites (GC–PF–18, GC–1103–16, and 

GC–1637–44) plot in a cluster near the initial 206Pb/204Pb 

value of 18.640 ± 0.032, which is very similar to the Greens 

Creek ore lead composition of about 18.64 (chap. 10). The 

cluster also contains data from a sample of sericitic phyllite 

(PY–5–09) from Pyrola (fig. 2), another orebody to the south 

of Greens Creek (chap. 2). These data suggest that the wholerock, U-Pb isotopic systematics of the highly altered, chloritized metabasalts and phyllites were disturbed and reset, and 

plot coincident with a 215-Ma reference line (fig. 11).

The Sm-Nd isotopic data (table 6) for metabasalts and 

associated phyllites are mostly scattered and do not form obvious linear arrays or yield any precise isochron ages. However, 

several of the Hyd Group metabasalts — the same group used to 

form a U-Pb isochron above (92–GB–22, 42, and 80) — yielded 

a poorly defined, apparent Sm-Nd isochron age of 215 ± 95 Ma 

(dashed line, fig. 12) with an initial eNd value of +7.4 at 215 Ma. 

One of the chloritized metabasalts from the Gambier Bay Formation (92–GB–24) and two analyses from phyllite GC–PF–18 

yielded data that appear to be coincident with this apparent 

isochron. The other Hyd Group metabasalt 92–GB–59 yielded a 

more enriched (lower) Nd isotopic signature (fig. 12), indicating 

either derivation from a more enriched source, contamination by 

older crust during ascent and extrusion, or open-system behavior due to exchange of REE with more enriched rocks during 

subsequent metamorphism and(or) alteration. The other chloritized metabasalt from the Gambier Bay Formation, 92–GB–55, 

plots very near 97–LG–17, the highly altered metabasalt from 

Gallagher Ridge, and both data plot near a 215-Ma reference 

line (dashed, fig. 12) that includes Hyd Group metabasalt 92–

GB–59 and Pyrola phyllite PY–5–09. This same association of 

samples was observed in the U-Pb isotopic data (fig. 11).

Samarium-neodymium analyses from footwall phyllites do not form an array but a field of enriched (lower) Nd 

isotopic signatures (fig. 12), again indicating either derivation 

from more enriched sources, contamination by older crust 

during ascent and extrusion, or open-system behavior due to 

exchange of REE with more enriched rocks during subsequent 

metamorphism and(or) alteration.
Results 311

18.0

18.4

18.8

19.2

19.6

20.0

20.4

238U/204Pb

206Pb/204Pb

Hyd Group basalts

Gambier Bay Fm

Footwall phyllites

maximum

analytical

error 92-GB-42

92-GB-59

97-LG-17

U-Pb isotopic ages for

basalts, metabasalts

and phyllites

92-GB-55

92-GB-22

92-GB-80

92-GB-24

PY-5-09

GC-PF-09 &

GC-462-02

GC-462-07

218 ± 16 Ma; I = 18.515

GC-PF-18

215-Ma reference line

0 10 20 30 40 50

Figure 11. Uranium-lead isotopic correlation diagram of data from metabasalt rocks (Hyd Group and Gambier Bay Formation) and 

footwall phyllites (altered mafic volcanic rock?) of the Green Creek area. Three whole-rock samples of the Hyd Group metabasalts 

define a U-Pb isochron age of 218 ± 16 Ma (dashed line). Several other metabasalts that are highly altered and some of the 

phyllites form a possible isochron (215-My reference line) yielding an initial 206Pb/204Pb value of 18.640 ± 0.032, exactly that of the 

Greens Creek ore.

The same samples were analyzed for their Rb-Sr wholerock isotopic systematics, and these results appear to be even 

less stable and more varied than results from the other two 

isotopic systems. The least-altered Hyd Group metabasalts 

(92–GB–22 and –80; and 92–GB–42 and –59) appear to form 

arrays that suggest apparent Rb-Sr ages of about 180 Ma that 

might be interpreted as disturbed or reset. One Gambier Bay 

Formation metabasalt, 92–GB–24, has a slightly higher initial 

87Sr/86Sr value of about 0.7052, whereas the other, 92–GB–55, 

has a lower value and plots along with Hyd Group metabasalts 92–GB–59 and GB–42 that indicate an initial Sr value of 

about 0.70409 (fig. 13), the lowest observed from this suite of 

rocks.

Rubidium-strontium isotopic data from footwall phyllites vary widely; some exhibiting elevated initial Sr values 

between about 0.706 and 0.707 at 215 Ma, perhaps indicating partial resetting of the Rb-Sr isotopic systematics during 

Cretaceous metamorphism (for example, Rubin and others, 

1990; chap. 12). However, an apparent Rb-Sr isochron age 

of 182 ± 29 Ma (dashed line, fig. 13) can be calculated using 

all the data from the phyllites and highly altered metabasalts, 

implying that the Rb-Sr isotopic systematics were reset in 

these rocks at about that time.

Metagabbros

Most of the metagabbro data of Greens Creek form an 

imprecise, apparent U-Pb whole-rock isochron indicating 

an age of 206 ± 35 Ma with initial 206Pb/204Pb value of about 

18.61 (fig. 14), which excludes analyses from three samples. 
Table 4. Uranium-thorium-lead analytical data for host-rock samples from the Greens Creek VMS deposit.—Continued [wgt, weight; g, gram; ppm, parts per million; U, uranium; Th, thorium; Pb, lead] Sample/fraction Sample wgt (g) U (ppm) Th (ppm) Pb (ppm) 206Pb/204Pba % err 206/204 207Pb/204Pba % err 207/204 208Pb/ 204Pba % err 208/204 238U/ 204Pba % 

238

Mafic rocks Gambier Bay basalts 92-GB-22 0.063 0.693 0.401 1.79 19.369 0.076 15.574 0.103 38.339 0.131 24.903 0.

92-GB-22-2 0.176 0.676 0.384 1.69 19.397 0.171 15.592 0.191 38.407 0.202 25.764 0.

92-GB-24 0.052 0.051 0.111 0.19 19.499 0.098 15.622 0.121 38.821 0.150 17.485 0.

92-GB-24-2 0.147 0.042 0.101 0.17 19.464 0.172 15.547 0.251 38.633 0.209 15.783 0.

92-GB-42 0.058 1.030 2.450 8.90 18.772 0.066 15.530 0.095 38.119 0.132 7.348 0.92-GB-42-2 0.110 1.000 2.330 8.03 18.769 0.064 15.531 0.093 38.121 0.123 7.924 0.

92-GB-55 0.090 0.545 1.560 2.31 19.150 0.066 15.566 0.094 38.500 0.123 15.128 0.

92-GB-55-2 0.149 0.515 failed 2.23 19.114 0.062 15.547 0.092 14.765 0.

92-GB-59 0.067 0.231 0.608 2.60 18.856 0.107 15.547 0.130 38.262 0.157 5.659 0.

92-GB-59-2 0.226 0.221 0.557 2.12 18.859 0.065 15.543 0.094 38.253 0.123 6.619 0.

92-GB-80 0.072 0.334 1.090 1.87 18.919 0.074 15.527 0.101 38.401 0.128 11.410 0.

92-GB-80-2 0.131 0.322 1.040 1.74 18.976 0.415 15.581 0.421 38.571 0.429 11.839 0.

basalt 97-LG-17 0.079 0.067 0.292 5.64 18.598 0.095 15.545 0.116 38.109 0.141 0.746 1.

97-LG-17-2 0.123 0.064 0.244 9.46 18.644 0.152 15.602 0.167 38.285 0.185 0.431 0.

serpentinite 97-LG-19-2 0.140 0.011 0.032 0.51 18.450 0.695 15.376 0.738 37.829 0.749 1.361 0.

97-LG-20-2 0.155 0.011 0.031 0.54 18.610 1.610 15.568 1.630 38.324 1.620 1.298 2.

97-LG-32 0.080 0.034 0.190 0.65 18.626 0.479 15.596 0.542 38.643 0.535 3.336 1.

96-GC 1136-53 0.104 0.038 0.045 75.48 18.656 0.061 15.603 0.091 38.402 0.121 0.032 1.

96-GC 1136-59 0.176 0.061 0.069 26.48 18.646 0.061 15.589 0.090 38.354 0.120 0.147 0.

97-ADM-59 0.153 0.110 0.949 4.74 18.929 1.200 15.888 1.230 39.057 1.270 1.497 4.

gabbro 97-LG-45 0.099 0.517 0.602 2.53 18.962 0.062 15.584 0.092 38.332 0.121 13.029 2.

97-LG-45-2 0.186 0.484 0.579 3.03 18.983 0.134 15.638 0.154 38.561 0.171 10.249 0.

97-LG-69-2 0.232 0.288 0.854 0.42 20.127 0.366 15.596 0.384 39.478 0.393 45.468 0.

97-LG-70 0.083 0.081 0.246 0.24 19.312 0.183 15.613 0.196 38.808 0.214 21.580 0.

97-LG-71 0.337 0.308 0.917 0.50 19.634 0.153 15.629 0.168 39.117 0.186 39.900 0.

97-LG-82 0.090 0.424 1.430 0.68 20.021 0.068 15.640 0.096 39.644 0.125 41.048 0.

97-LG-82-2 0.163 0.467 1.430 0.62 20.119 0.070 15.658 0.099 39.731 0.127 49.460 0.

Gst, NW1/4, Sec 6 0.100 0.256 failed 1.03 19.911 0.326 15.705 0.336 38.686 0.343 16.236 0.

Admiralty Island 96-ADM-01 0.104 0.603 0.519 2.14 18.872 0.069 15.611 0.097 38.410 0.125 17.980 0.

96-ADM-01-2 0.156 0.675 0.501 5.30 18.847 0.062 15.610 0.091 38.436 0.121 8.124 0.

96-ADM-12 0.061 0.830 1.990 9.47 18.901 0.089 15.588 0.113 37.773 0.137 5.551 0.

96-ADM-12-2 0.200 0.840 2.010 11.80 18.795 0.238 15.528 0.253 38.301 0.262 4.526 0.96-AD-58 0.166 0.240 0.737 2.18 18.872 0.073 15.558 0.099 38.377 0.127 7.011 0.
Table 4. Uranium-thorium-lead analytical data for host-rock samples from the Greens Creek VMS deposit.—Continued[wgt, weight; g, gram; ppm, parts per million; U, uranium; Th, thorium; Pb, lead]

PhyllitesGC-PF-09 0.124 0.632 1.280 4.37 18.851 0.078 15.597 0.143 38.502 0.247 9.249 0.

GC-PF-18 0.108 0.097 0.402 5.81 18.698 0.062 15.580 0.092 38.088 0.125 1.054 0.

GC-PF-18-2 0.108 0.150 0.485 5.91 18.742 0.069 15.631 0.097 38.513 0.125 1.626 0.

GC-PF-18-3 0.184 0.191 0.550 6.96 18.688 0.062 15.568 0.091 38.285 0.121 1.741 0.

GC-462-02 0.156 1.270 1.580 8.60 18.808 0.117 15.599 0.141 38.309 0.161 9.609 0.

GC-462-02-2 0.156 1.080 9.290 11.90 18.633 0.090 15.464 0.119 37.890 0.139 5.744 3.

GC-462-07 0.165 1.870 2.360 9.42 18.830 0.060 15.579 0.090 38.342 0.120 12.651 0.

GC-1103-16 0.142 0.881 2.370 59.80 18.677 0.061 15.604 0.091 38.420 0.122 0.943 0.

GC-1637-44 0.189 1.350 2.060 97.82 18.657 0.073 15.587 0.101 38.361 0.130 0.881 1.

ArgillitesA-Rd-03 0.073 1.770 4.290 7.93 19.559 0.061 15.677 0.093 38.895 0.124 14.483 0.

B-Rd-04 0.076 2.880 4.110 7.34 19.731 0.077 15.656 0.103 38.678 0.131 25.406 0.

97-LG-78 0.057 1.430 3.010 3.21 19.489 0.071 15.598 0.098 38.667 0.126 28.776 0.

97-LG-75 0.095 1.800 1.000 5.62 19.219 0.062 15.616 0.092 38.371 0.122 20.510 1.

96-GC 1136-05 0.074 1.480 0.244 9.82 18.865 0.062 15.645 0.094 38.487 0.127 9.609 0.

PP-204-01-1 0.147 7.400 1.220 14.50 19.962 0.190 15.668 0.202 38.486 0.221 33.093 1.

97-LG-66 0.191 1.590 0.684 11.60 19.215 0.076 15.672 0.103 38.570 0.131 8.763 0.

97-ADM-29 0.059 2.900 2.080 5.52 19.824 0.092 15.633 0.117 38.443 0.141 33.949 0.

NAD-T4-2 0.236 0.720 1.980 1.70 19.396 0.152 15.627 0.168 38.816 0.185 27.464 0.

97ADM-34 0.201 2.220 4.130 18.85 18.973 0.060 15.563 0.090 38.282 0.120 7.501 0.

Crosscutting dikes97-LG-64-2 0.16818 1.220 2.270 4.22 18.923 0.084 15.608 0.110 38.478 0.139 18.479 0.

GC-1701-01 0.084 0.873 2.010 312.80 18.659 0.072 15.612 0.100 38.432 0.133 0.178 7.

GC-1701-01-2 0.136 0.901 2.080 640.40 18.759 0.083 15.745 0.113 38.897 0.154 0.091 3.

GC-1704-01 0.256 0.840 1.650 6.55 18.721 0.072 15.563 0.100 38.274 0.130 8.153 0.

GC-1704-01-2 0.210 0.835 1.620 5.09 18.591 0.134 15.450 0.155 37.991 0.186 10.353 1.

Pyrola minePY-5-09 0.193 2.170 2.525 130.70 18.673 0.061 15.567 0.091 38.183 0.121 1.053 0.

a a – corrected for Pb mass fractionation (0.08 ± 0.03 % per a.m.u.) and blank Pb (variable amounts between 107 and 242 pg total Pb) with average composition: 

206Pb/204Pb = 18.681± 0.064; 207Pb/204Pb = 15.432 ± 0.033; and 208Pb/204Pb = 37.72 ± 0.12).

f failed – Some mass spectrometric runs failed and were not reattempted.
Table 5. Initial lead compositions for host-rock samples from the Greens Creek VMS deposit.—Continued [ Ma, mega-annum; Pb, lead; U, uranium; Th, thorium; pg, picograms; a.m.u., atomic mass unit] Sample/fraction Initial Pb values at 215 Ma Initial Pb values at 185 Ma Initial Pb values at 260 Ma Initial Pb values at 90 Ma 

206Pb/ 204Pba 207Pb/ 204Pba 206Pb/ 204Pba 207Pb/ 204Pba 206Pb/ 204Pba 207Pb/ 204Pba 206Pb/ 204Pba 207Pb/ 204Pba 

Mafic rocks Gambier Bay basalts 92-GB-22 18.524 15.531 18.644 15.538 18.344 15.521 N/A 

92-GB-22-2 18.523 15.548 18.647 15.555 18.337 15.537 92-GB-24 18.906 15.592 18.990 15.597 18.779 15.585 92-GB-24-2 18.929 15.520 19.004 15.524 18.814 15.514 92-GB-42 18.523 15.517 18.558 15.519 18.470 15.514 92-GB-42-2 18.500 15.517 18.538 15.520 18.443 15.514 92-GB-55 18.637 15.540 18.710 15.544 18.527 15.534 92-GB-55-2 18.613 15.522 18.684 15.526 18.506 15.516 92-GB-59 18.664 15.537 18.691 15.539 18.623 15.535 92-GB-59-2 18.635 15.532 18.666 15.533 18.587 15.529 92-GB-80 18.532 15.507 18.587 15.510 18.449 15.503 92-GB-80-2 18.574 15.561 18.631 15.564 18.489 15.556 basalt 97-LG-17 18.573 15.544 18.576 15.544 18.567 15.543 18.588 15.544 

97-LG-17-2 18.629 15.601 18.631 15.601 18.626 15.601 18.638 15.602 

serpentinite 97-LG-19-2 18.404 15.374 18.410 15.374 18.394 15.373 18.431 15.375 

97-LG-20-2 18.566 15.566 18.572 15.566 18.557 15.565 18.592 15.567 

97-LG-32 18.513 15.590 18.529 15.591 18.489 15.589 18.579 15.594 

96-GC 1136-53 18.655 15.603 18.655 15.603 18.655 15.603 18.656 15.603 

96-GC 1136-59 18.641 15.589 18.642 15.589 18.640 15.589 18.644 15.589 

97-ADM-59 18.878 15.885 18.885 15.886 18.867 15.885 18.908 15.887 

gabbro 97-LG-45 18.520 15.562 18.583 15.565 18.426 15.556 18.779 15.575 

97-LG-45-2 18.635 15.620 18.685 15.623 18.561 15.616 18.839 15.631 

97-LG-69-2 18.585 15.518 18.803 15.530 18.256 15.500 19.488 15.565 

97-LG-70 18.580 15.576 18.684 15.582 18.424 15.567 19.009 15.598 

97-LG-71-1 18.281 15.561 18.472 15.571 17.992 15.545 19.073 15.602 

97-LG-82 18.662 15.572 18.826 15.581 18.332 15.553 19.444 15.612 

97-LG-82-2 18.481 15.576 18.679 15.586 18.083 15.553 19.424 15.625 

Gst, NW1/4, Sec 6 19.373 15.678 19.438 15.681 19.243 15.671 19.683 15.694 

Admiralty Island96-ADM-01 18.262 15.580 18.349 15.585 18.132 15.573 18.619 15.599 

96-ADM-01-2 18.571 15.596 18.610 15.598 18.513 15.593 18.733 15.605 

96-ADM-12 18.713 15.579 18.739 15.580 18.672 15.576 18.823 15.584 

96ADM-12-2 18.642 15.520 18.663 15.521 18.609 15.518 18.731 15.525 

96-AD-58 18.634 15.546 18.668 15.548 18.583 15.543 18.773 15.553 
Table 5. Initial lead compositions for host-rock samples from the Greens Creek VMS deposit.—Continued[ Ma, mega-annum; Pb, lead; U, uranium; Th, thorium; pg, picograms; a.m.u., atomic mass unit]

PhyllitesGC-PF-09 18.537 15.581 18.582 15.584 18.470 15.577 18.721 15.591 

GC-PF-18 18.662 15.578 18.667 15.578 18.655 15.578 18.683 15.579 

GC-PF-18-2 18.687 15.628 18.695 15.629 18.675 15.628 18.719 15.630 

GC-PF-18-3 18.629 15.565 18.637 15.565 18.616 15.564 18.664 15.567 

GC-462-02 18.489 15.583 18.534 15.585 18.421 15.579 18.676 15.593 

GC-462-02-2 18.438 15.454 18.466 15.456 18.397 15.452 18.552 15.460 

GC-462-07 18.401 15.557 18.462 15.561 18.309 15.552 18.652 15.570 

GC-1103-16 18.645 15.602 18.650 15.603 18.638 15.602 18.664 15.603 

GC-1637-44 18.627 15.585 18.631 15.586 18.621 15.585 18.645 15.586 

ArgillitesA-Rd-03 19.068 15.652 19.137 15.656 18.963 15.646 19.355 15.667 

B-Rd-04 18.869 15.613 18.991 15.619 18.685 15.602 19.374 15.639 

97-LG-78 18.533 15.573 18.671 15.580 18.324 15.561 19.104 15.603 

97-LG-75 18.523 15.581 18.622 15.586 18.375 15.573 18.931 15.602 

96-GC 1136-05 18.539 15.629 18.585 15.631 18.470 15.625 18.730 15.639 

PP-204-01-1 18.840 15.611 18.999 15.620 18.600 15.598 19.497 15.646 

97-LG-66 18.918 15.657 18.960 15.659 18.854 15.653 19.092 15.666 

97-ADM-29 18.673 15.575 18.836 15.584 18.427 15.561 19.347 15.610 

NAD-T4-2 18.465 15.580 18.596 15.587 18.266 15.569 19.010 15.609 

97-ADM-34 18.719 15.550 18.755 15.552 18.664 15.547 18.868 15.558 

Crosscutting dikes97-LG-64-2 18.296 15.576 18.385 15.581 18.162 15.569 18.663 15.596 

GC-1701-01 18.653 15.612 18.654 15.612 18.652 15.612 18.657 15.612 

GC-1701-01-2 18.756 15.745 18.756 15.745 18.755 15.745 18.758 15.745 

GC-1701-04 18.444 15.549 18.484 15.551 18.385 15.546 18.606 15.558 

GC-1701-04-2 18.240 15.432 18.290 15.435 18.165 15.428 18.445 15.443 

Pyrola minePY-5-09 18.637 15.565 18.642 15.565 18.630 15.565 18.658 15.566 

a – corrected ratios; corrected for Pb mass fractionation (0.08 ± 0.03 % per a.m.u.) and blank Pb (variable amounts between 5 and 20 pg total Pb; blank composition: 206Pb/204P

15.65 ± 0.2; and 208Pb/204Pb = 38.65 ± 0.75); U mass fractionation using a double U spike (233/236) = 1.02 ???; and assumed Th fractionation of ~0.2 ± 0.5 % per a.m.u

Ludwig (1985). Uranium and thorium blanks ranged between 2-15 and 7-50 pg, respectively.
Table 6. Rb-Sr and Sm-Nd analytical data for host-rock and adjacent samples of the Greens Creek VMS deposit.—Continued [wgt, weight; g, gram; ppm, parts per million; Rb, rubidium; Sr, strontium; Sm, samarium; Nd, neodymium] Sample name Sample wgt (g) Rb * (ppm) Sr * (ppm) Sm * (ppm) Nd * (ppm) 87Rb/ 86Sr † Rb/Sr abs err 87Sr/ 86Sr † 87/86 abs err 147Sm/ 144Nd † 147/144 abs err 143Nd/ 144Nd † 143/

abs 

Mafic rocks Gambier Bay basalts 92-GB-22-2 0.176 92-GB-24-2 0.147 92-GB-42 0.058 92-GB-55 0.090 92-GB-55-2 0.149 92-GB-59-2 0.226 92-GB-80 0.072 92-GB-80-2 0.131 basalt 97-LG-17 0.079 97-LG-17-2 0.123 serpentinite 97-LG-19-2 0.140 97-LG-20-2 0.155 97-LG-32-2 0.162 96-GC-1136-53 0.104 96-GC-1136-59 0.176 97ADM-59 0.153 gabbro 97-LG-45 0.099 97-LG-45-2 0.186 97-LG-69 0.109 97-LG-69-2 0.232 97-LG-70 0.083 97-LG-70-2 0.147 97-LG-71 PL-2 0.105 97-LG-71-1 0.337 97-LG-82 0.090 97-LG-82-2 0.163 Gst, NW1/4, 0.100 Sec 6 Gst-2, NW1/4, 0.10587 Sec 6 Admiralty Island mafic rocks 96-ADM-01 0.104

96-ADM-01-2 0.156

96-ADM-12 0.061

96-ADM-12-2 0.200

96AD-58 0.166

4.1

0.8

3.6

25.8

25.0

7.3

40.9

41.3

41.7

41.4

0.140.150.25

32.844.5

0.32

15.1

15.9

3.53

3.35

3.46

3.72

23.2

4.00

4.00

0.75

19.9

20.6

17.1

14.4

8.5

233

17.5

708

568

539

122

199

198

158

189

15.9

8.38.0

153

68.0

6.8

219

260

318

331

151

165

160

238

241

144

148

171

173

146

125

2.7

1.9

4.6

4.8

4.3

2.0

4.6

4.5

0.71

0.75

0.020.020.020.200.100.0174.4

4.1

1.8

1.8

1.3

1.2

0.51.9

2.8

2.7

3.03.4

4.5

3.2

4.0

3.7

4.4

7.3

4.6

19.2

20.6

18.7

7.2

17.0

16.9

3.0

3.1

0.120.090.130.702.66

15.5

14.5

6.0

6.2

3.3

3.2

2.36.8

10.3

10.1

10.211.6

12.8

10.9

15.8

14.9

15.4

0.050

0.136

0.015

0.131

0.134

0.174

0.593

0.603

0.763

0.632

0.0250.0520.0900.619611.896240.1370.200

0.177

0.032

0.029

0.066

0.065

0.419

0.049

0.048

0.015

0.387

0.348

0.286

0.284

0.196

0.000

0.000

0.000

0.000

0.000

0.001

0.002

0.003

0.001

0.002

0.0000.0000.0000.0010.0040.0030.000

0.001

0.000

0.000

0.000

0.000

failed

0.053

0.000

0.000

failed

0.000

0.003

0.001

0.001

0.001

0.000

0.705

0.706

0.704

0.705

0.705

0.705

0.707

0.707

0.707

0.707

0.7050.7050.7060.7080.7100660.708

0.705

0.705

0.704

0.704

0.705

0.705

0.705

0.704

0.704

0.705

0.705

0.705

0.706

0.706

0.705

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.0000.0000.0000.0000.0000.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.001

0.000

0.000

0.000

0.000

0.223

0.252

0.146

0.140

0.139

0.171

0.162

0.163

0.145

0.145

0.1250.1150.1050.1950.173

0.174

0.172

0.179

0.178

0.226

0.2340.136

0.171

0.163

0.1750.176

0.175

0.212

0.176

0.153

0.148

0.172

0.001

0.001

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.0000.0000.0000.001

failed

0.001

0.000

0.000

0.000

0.000

0.000

0.0000.000

0.000

0.000

0.0000.000

0.000

0.114

0.000

0.003

0.000

0.000

0.513

0.513

0.513

0.513

0.513

0.513

0.513

0.513

0.513

0.513

0.5130.5120.5120.5130.513

0.513

0.513

0.513

0.513

0.513

0.5130.513

0.513

0.513

0.5130.513

0.513

0.513

0.513

0.513

0.513

0.513

0

0

0

0

0

0

0

0

0

0

0000

0

0

0

0

0

0

00

0

0

00

0

0

0

0

0

0
Table 6. Rb-Sr and Sm-Nd analytical data for host-rock and adjacent samples of the Greens Creek VMS deposit.—Continued[wgt, weight; g, gram; ppm, parts per million; Rb, rubidium; Sr, strontium; Sm, samarium; Nd, neodymium]

PhyllitesGC-PF-09 0.124 47.6 39.7 3.1 12.6 3.472 0.006 0.712 0.000 0.150 0.000 0.513 0.

GC-PF-18-2 0.108 13.3 112 2.9 9.4 0.344 0.001 0.707 0.000019 0.185 0.000 0.513 0.

GC-PF-18-3 0.184 13.3 106 2.7 8.3 0.364 0.000 0.707 0.000 0.193 0.000 0.513 0.

GC-462-02 0.156 1.0 107 0.6 3.1 0.026 0.000 0.705 0.000 0.126 0.000 0.513 0.

GC-462-02-2 0.156 n.d. 108 0.6 3.1 n.d. 0.705 0.000021 0.126 0.000 0.513 0.

GC-462-07 0.165 4.0 18.4 failed 0.131 0.000 0.513 0

GC-1103-16 0.142 44.5 65.6 2.3 9.8 1.96433 .00223 0.712 0.000024 0.14357 0.000 0.512666 0

GC-1637-44 0.189 55.3 25.6 3.7 15.7 6.26289 .01838 0.722 0.000025 0.14143 0.000 0.512774 0

ArgillitesA-Rd-03 0.073 n.d. 3.8 18.2 n.d. 0.712 0.000 0.126 0.000 0.512 0.

B-Rd-04 0.076 n.d. 3.4 17.4 n.d. 0.715 0.000 0.118 0.000 0.512 0.

97-LG-78 0.057 n.d. 2.6 13.6 n.d. 0.737 0.000 0.118 0.000 0.513 0.97-LG-75 0.095 1.0 1.8 3.1 18.1 1.607 0.002 0.710 0.000 0.103 0.000 0.512 0.

96-GC 1136-05 0.074 7.1 134 0.7 3.2 0.153 0.000 0.708 0.000 0.129 0.000 0.513 0.PP-204-01-1 0.147 27.3 130 2.5 11.5 0.606 0.001 0.708 0.000 0.132 0.000 0.513 0.

97-LG-66 0.191 26.1 1.3 2.2 12.4 59.091 0.058 0.784 0.000 0.108 0.000 0.512 0.97-ADM-29 0.059 31.7 105 2.7 11.1 0.877 0.001 0.707 0.000 0.148 0.000 0.513 0.

NAD-T4-2 0.236 34.0 13.9 2.1 9.2 7.087 0.011 0.716 0.000 0.138 0.000 0.513 0.

97-ADM-34 0.201 47.1 63.7 1.9 8.1 2.138 0.004 0.709 0.000 0.142 0.000 0.513 0.

Crosscutting dikes97-LG-64-2 0.16818 16.1 678 4.5 21.2 0.06850 0.000 0.703466 0.000022 0.129 0.000 0.513 0.

GC-1701-01 0.084 7.4 1578 10.3 55.8 0.014 0.000 0.705 0.000 0.112 0.000 0.513 0.

GC-1701-01-2 0.136 10.6 60.3 failed 0.107 0.000 0.513 0.GC-1704-01 0.256 9.9 326 3.9 17.1 0.088 0.000 0.706 0.000 0.139 0.000 0.513 0.

GC-1704-01-2 0.210 10.0 560 3.8 16.4 0.052 0.000 0.704 0.000 0.138 0.000 0.513 0.

Pyrola minePY-5-09 0.193 109.0 676 4.5 24.1 0.467 0.001 0.709 0.000 0.114 0.000 0.513 0

† Isotopic ratios corrected for blank and mass fractionation, 87Sr/86Sr data are normalized to 86Sr/88Sr = 0.1194 and adjusted for instrumental bias to 87Sr/86Sr = 0.710265 for N

mean value of 87Sr/86Sr for 30 analyses the Sr standard was 0.710265 ±10. Isotopic ratios corrected for blank and mass fractionation, 143Nd/144Nd data are normalized to 

adjusted for instrumental bias to 143Nd/144Nd = 0.511860 for the La Jolla Nd standard. The mean value of 143Nd/144Nd for 30 analyses of the La Jolla Nd standard was 0.5

§ Initial 87Sr/86Sr ratios and initial εNd values are calculated using an age of 215 Ma; λ = 1.42 x 10-11/yr, λ = 6.54 x 10-12/yr (Steiger and Jäger, 1977). where present day (143N

and (147Sm/144Nd)CHUR = 0.1967; CHUR = chondritic uniform reservoir.

n n.d. – Not determined.f failed – Some mass spectrometric runs failed and were not reattempted.
318 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

0.5126

0.5127

0.5128

0.5129

0.5130

0.5131

0.5132

92-GB-42

92-GB-59-2

92-GB-55

92-GB-22-2

92-GB-80

92-GB-24-2

215 ± 95 Ma

GC-PF-09

97-LG-17

PY-5-09

GC-PF-18

GC-1637-44

footwall

phyllites

Sm-Nd isotopic ages for

basalts, metabasalts,

and phyllites

GC-1103-16

GC-462-07

GC-462-02

215-Ma reference line

147Sm/144Nd

143Nd/144Nd

0.11 0.13 0.15 0.17 0.19 0.21 0.23 0.25

Hyd Group basalts

Gambier Bay Fm

Footwall phyllites

Figure 12. Samarium-neodymium isotopic correlation diagram of data from metabasalts rocks (Hyd Group and 

Gambier Bay Formation) and footwall phyllites (altered mafic volcanic rock?) — Greens Creek area. The same three 

Hyd Group metabasalts that yield a U-Pb age of 218 ± 16 Ma, yield a Sm-Nd isochron age of 215 ± 95 Ma (N = 4; solid 

line). Data from a phyllite sample, PF–18, and Gambier Bay metabasalt, 92–GB–24, are coincident with this isochron. 

Other metabasaltic samples and footwall phyllites did not form linear arrays or yield Sm-Nd age results, but define 

a field indicating more enriched (lower) Nd signatures, either through differences in their sources or by alteration 

and (or) metamorphism as many as of these samples are highly altered. Gambier Bay metabasalts 92–GB–55 and 59, 

Gallagher Ridge metabasalt 97–LG–17, and Pyrola phyllite, PY–5–09, appear to form an array approximating an age 

near 215 Ma. This same association of samples was observed in the U-Pb isotopic data (fig. 8, chap. 12, this volume).
Results 319

The three exclusions are GST– NW1/4-Sec 6 from Mariposite 

Ridge, which is clearly different with respect to its U-Pb 

systematics; 97–LG–71 from Gallagher Ridge, which appears 

to have been isotopically disturbed (also see figs. 7, 10, and 11 

in chap. 12); and 96–ADM–12, which is from Gambier Bay. 

This latter sample, although from Gambier Bay, yielded U-Pb 

data consistent with the Greens Creek metagabbro array. The 

corresponding initial lead composition defined by the regression of Greens Creek metagabbro data is similar to the Greens 

Creek ore lead composition as well as that for metabasalt at 

Gallagher Ridge 97–LG–17 (fig. 14). An age of 216 ± 20 

Ma is indicated by two of the three metagabbros at Gallagher 

Ridge (97–LG–69 and 70), which does not include the isotopically disturbed sample 97–LG–71 (fig. 14). Gallagher Ridge 

metabasalt 97–LG–17 also lies upon this array.

The Sm-Nd isotopic systematics are equally varied 

and none of the rock suites form a well-constrained linear 

array. Whole rocks and a plagioclase separate from adjacent 

samples 97–LG–70 and LG–71 from the Gallagher Ridge 

metagabbro suite yield a Sm-Nd isochron age of 200 ± 27 Ma 

with εNd = +5.6 (fig. 15), consistent with the U-Pb age of 216 

± 20 Ma. These particular analyses are more enriched (lower 

Nd value) than other Gallagher Ridge metagabbros (fig. 15) 

that plot between the Hyd Group metabasalt array at εNd = 

+7.4 and the 97LG–70, 71 metagabbro array. For example, 

sample GST–2–NW1/4-Sec 6 (GST) yielded a depleted εNd

value (+6.7 at 215 Ma) and actually plots closer to the Hyd 

Group metabasalt array. Two apparent Hyd Group metabasalts, 92–GB–59 and 97–LG–17, plot below but within 

error limits of the Gallagher Ridge array.

Greens Creek metagabbros and metabasalts span initial 

εNd values from +5 to +7, indicating either progressive 

changes in the Nd isotopic composition of their parental 

magmas due to contamination by older crustal material or 

mixing between different isotopic compositions of mantle 

sources.

0.702

0.706

0.710

0.714

0.718

0.722

92-GB-42 92-GB-59

and GB-55

92-GB-22-2

92-GB-80

92-GB-24-2

GC-PF-09

97-LG-17

PY-5-09

GC-PF-18

GC-1637-44

GC-462-02

GC-1103-16

182 ± 29 Ma

87Rb/86Sr

87Sr/86Sr

0 2 4 6

Hyd Group basalts

Gambier Bay Fm

Footwall phyllites

Rb-Sr isotopic ages for

basalts, metabasalts,

and phyllites

Figure 13. Rubidium-strontium isotopic correlation diagram of data from metabasalts rocks (Hyd Group and Gambier Bay 

Formation) and footwall phyllites (altered mafic volcanic rock?) of the Greens Creek area. An overall Rb-Sr isochron age for 

these rocks yielded an age of 182 ± 29 Ma, interpreted as an age for resetting of the Rb-Sr isotopic system.
320 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Rubidium-strontium whole-rock isotopic systematics for 

the Gallagher Ridge metagabbros are equally complex, yielding no definitive arrays. Whole-rock data for these metagabbros indicate that initial 87Sr/86Sr values can vary between 

0.7039 and about 0.7048 at 215 Ma, noticably lower than the 

metabasalt–phyllite suite (chap. 12).

Argillites

Argillitic rocks from the Greens Creek area probably 

represent the erosional products of basalt flow sequences that 

underlie and host the ore horizon (chap. 8). In the Greens 

Creek area, argillites have been divided into two formations; 

the Lower Permian Cannery Formation (97LG–78, ADM–29 

and ADM–34) and the Upper Triassic Hyd Group (all other 

argillite samples — table 3).

The U-Pb isotopic data for the argillites do not yield 

a well-defined linear array, but rather an elongate field that 

indicates an age of about 185 Ma. None of the Sm-Nd isotopic 

data for the argillites yielded any age information.

Rubidium-Sr isotopic age data for the argillite samples 

suggest a single resetting age of 91.4 ± 2.6 Ma that includes 

Hyd Group and Cannery Formation alike. It is essentially 

a three-point isochron controlled by two Hyd Group argillites, 97LG–66 and NAD T4–2, neither of which is carbonaceous. Omission of the Cannery Formation data alters the 

Rb-Sr isochron age to 90.8 ± 2.2 Ma with initial 87Sr/86Sr 

at 0.70733 for the Hyd Group argillites (fig. 16A), a value 

that approaches the strontium composition of Late Cretaceous seawater (fig. 8 in chap.12). However, the Hyd Group 

argillite data are quasi-linear (MSWD = 1104) and basically 

18.0

18.4

19.2

19.6

20.0

20.4

20.8

gabbros of Gallagher Ridge

other gabbros, Admiralty Island

LG-17

LG-82-2;

E. Lil Sore

LG-69

LG-70

LG-71

LG-82;

E. Lil Sore

GST; Mariposite Ridge

Age = 216 ± 20 Ma

Initial 206Pb/204Pb = 18.576 ± 0.088

MSWD = 0.000

96-ADM-12;

Gambier Bay

LG-45-2;

Lakes Dist.

LG-45;

Lakes Dist.

All gabbros (minus GST; LG-71; ADM-12)

18.8

Age = 206 ± 35 Ma

Initial 206Pb/204Pb = 18.61 ± 0.19

MSWD = 104

GREENS CREEK

U-Pb isotopic ages

for gabbroic samples

238U/204Pb

206Pb/204Pb

0 10 20 30 40 50

maximum

analytical

error

LG-69 and 70: Gallagher Ridge

Figure 14. Uranium-lead isotopic correlation diagram of data from some of the Greens Creek metagabbros, yielding 

a whole-rock isochron age of 206 ± 35 Ma and initial 206Pb/204Pb value of 18.61 ± 0.19, similar to that of the Greens 

Creek ore.
Results 321

LG-82;

E. Lil Sore

LG-45-2

LG-45

LG-69

LG-71-1

LG-17-2

LG-71

plag-2

LG-70

GB-22-2

GB-80

GB-42

GB-59-2

GST; Mariposite Ridge

0.5128

0.5129

0.5131

200 ± 27 Ma; ε = + 5.6

Hyd Group metabasalts:

210 ± 95 Ma; ε = + 7.4

0.5130

147Sm/144Nd

143Nd/144Nd

0.12 0.14 0.16 0.18 0.20 0.22 0.24

Sm-Nd isochron ages for

gabbros of Gallagher Ridge

Hyd Group basalts

gabbros of Gallagher Ridge

other gabbros, Admiralty Island

Figure 15. Samarium-neodymium isotopic correlation diagram of data from Greens Creek metagabbros. One array of adjacent 

Gallagher Ridge samples yielded a whole-rock and plagioclase separate “internal” isochron age of 200 ± 27 Ma and initial εNd

value of +5.6; other metagabbros do not lie on this isochron but plot toward Hyd Group metabasalt data at εNd = +7.4 at 215 Ma.

controlled by the radiogenic strontium from 97–LG–66. An 

alternate apparent isochron age excluding 97–LG–66 is 81 

± 14 Ma for the other Hyd Group argillites that include two 

mine argillites with slightly different strontium initial values 

(fig. 16B). Another alternative isochron age excluding the two 

mine argillites but including 97–LG–66 (that is, surface argillite samples) is 91 ± 15 Ma (fig. 16B).

Rubidium-Sr data from the two Cannery Formation samples indicate a lower initial strontium value of about 0.7066 

and perhaps a younger age, but more analyses are needed in 

order to verify these indications.

Serpentinites

Neither the U-Pb or Sm-Nd isotopic systematics for 

serpentinites yield any age data. However, the initial lead 

signature for two mine serpentinites GC–1136–53 and 

GC–1136–59 is about 18.65, a value very similar to the 

Greens Creek ore lead signature (chap. 10). The other serpentinites initial lead signatures vary widely from about 18.4 

(97–LG–19) to almost 18.8 (97–ADM–59) consistent with 

their strong differences in neodymium initial values (fig. 13 

in chap. 12).
322 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

0.70

0.72

0.74

0.78

0.80

Greens Creek argillites

NAD-T4-2

LG-66

90.8 ± 2.2 Ma

0.703

0.705

0.707

0.709

0.711

0.713

0.715

0.717

NAD-T4-2

97-ADM-29

97-ADM-34

mine argillites LG-75

PP-204-01 &

 GC-1136-05

B

0.76

Cannery Fm.

Hyd Group

Hyd Group argillites

Age = 90.8 ± 2.2 Ma

Initial 87Sr/86Sr = 0.70733 ± 0.00082

MSWD = 1104

Hyd Group argillites (minus mine samples)

Age = 91 ± 15 Ma

Initial 87Sr/86Sr = 0.7071 ± 0.0072

MSWD = 57

Hyd Group argillites (minus LG-66)

Age = 81 ± 14 Ma

Initial 87Sr/86Sr = 0.70763 ± 0.00076

MSWD = 158

Cannery Fm. argillites

Age = 66.7 ± 1.5 Ma

Initial 87Sr/86Sr = 0.706585 ± 0.000032

MSWD = 0.000

87Sr/86Sr 87Sr/86Sr

0 20 40 60

87Rb/86Sr

A

87Rb/86Sr

0 2 4 6 8

Greens Creek argillites
Results 323

Figure 16. Rubidium-strontium isotopic correlation diagram of whole-rock data from argillites. All data (including Cannery Formation 

units) yield an isochron age of 91.4 ± 2.6 Ma and initial 87Sr/86Sr value of 0.70689, indicating that these isotopic systematics have been 

reset during Late Cretaceous deformation and metamorphism. Omission of the Cannery Formation data alters the Rb-Sr isochron age 

to 90.8 ± 2.2 Ma and initial 87Sr/86Sr at 0.70733 for the Hyd Group argillites (table 14.3), a value that approaches Cretaceous seawater 

strontium composition (see chap. 12). MSWD, mean square of weighted deviates.

Figure 17. Rubidium-strontium isotopic correlation diagram of whole-rock data from serpentinites. At least two weak 

isochrons can be constructed through the data. Two samples from the Lakes District (97–LG–19–2 and 97–LG–20–2) 

plot near the initial 87Sr/86Sr composition of 0.70461, a value similar to that defined by disturbed isochrons from the 

metabasalts and suggest an age of about 195 Ma. In contrast, the Rb-Sr data for the two mine serpentinites, GC–1136–53 

and GC–1136–59, yield a reset age of 89 ± 15 Ma and initial 87Sr/86Sr value of 0.70767, very close to the value defined by 

reset isochron data (87Sr/86Sr = 0.70733) at 91 Ma for the Hyd Group argillites.

0.703

0.705

0.707

0.709

0.711

ADM-59

LG-19-2

LG-20-2

GC-1136-53

LG-32-2

GC-1136-59

89 ± 15 Ma; I ~0.70767

~195 Ma; I = 0.7046

87Sr/86Sr

87Rb/86Sr

0.0 0.4 0.8 1.2 1.6 2.0

Greens Creek serpentinites
324 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Although the Rb-Sr isotopic data from serpentinite 

samples are scattered and do not form well-defined isochrons, 

a very imprecise apparent age of 195 ± 100 Ma is calculated 

for serpentinites 97–LG–19 and LG–20 from the Upper Zinc 

Creek area. An initial strontium value of 0.70462 ± 6 is calculated from this age, a value very similar to both metabasalts 

and some metagabbros.

Another apparent Rb-Sr age of 89 ± 15 Ma (fig. 17) 

is defined by the two mine serpentinites, GC–1136–53 

and GC–1136–59, indicating an initial strontium value of 

0.70767, a value very similar to that from the Hyd Group 

argillites (0.70733) with a Rb-Sr age of resetting at 91 Ma 

(fig. 16; table 7). Serpentinite 97–ADM–59 from Gambier 

Bay plots near this possible “reset” isochron.

Discussion

A comparison of the ages obtained both from conodonts 

and radiogenic isotopes works to constrain the timing of several geologic events at Greens Creek (fig. 18). The conodont 

age of 220.7 ± 4.4 Ma (Gradstein and others, 1995) provides 

a sedimentation age for the Hyd Group argillite that contains 

them and serves as a marker to help interpret other ages.

Late Triassic Igneous Activity

The U-Pb isochron age of 218 ± 16 Ma for several Hyd 

Group metabasalts is consistent with the stratigraphy and suggests that the capping basalts are only slightly younger than 

the underlying argillites (fig. 18 and table 7). Samples of massive, yet altered gabbro collected in the vicinity of the mine 

form whole-rock isochrons with apparent ages of 206 ± 35 Ma 

(U-Pb) and 200 ± 27 Ma (Sm-Nd) with initial values of 18.61 

and +5.6, respectively (table 7). If these ages for the gabbros 

are accurate, then they are also consistent with crosscutting 

relationships (fig. 5) as these gabbros (about 206 to 200 Ma) 

intrude the Hyd Group basalts (about 218 Ma) and the Hyd 

Group argillites (about 221 Ma).

The 40Ar-39Ar age of 210.3 ± 0.3 Ma for fuchsite from an 

altered ultramafic body in Gambier Bay apparently records 

the timing for argon isotopic closure at less than about 300°C 

in this particular ultramafic body, and at average cooling rates 

for upper crustal intrusions, suggests emplacement of this 

ultramafic body at about 216 to 212 Ma. Obtaining age constraints on the protolith age of altered serpentinites is difficult 

due to their low trace- and rare-earth-element abundances 

and their susceptibility to resetting of the U-Pb and Rb-Sr 

systems. Two mine serpentinites yield a Rb-Sr age suggesting resetting at about 90 Ma (fig. 17). Geological constraints 

on the probable age of the serpentinites are sparse due to 

the plasticity and tendency of the original ultramafic magma 

(protoserpentinite) to move into zones of structural activity. 

However, the available field data are consistent with a probable Late Triassic age between 221 and 199 Ma for at least 

some of these serpentinites (fig. 5). The serpentinite bodies 

on the north shore of Gambier Bay exhibit baked contacts 

with the Hyd Group argillites, implying that the ultramafic 

protoliths were intruded into the sediments while still hot, and 

contain xenoliths of gabbro. One of the serpentinite bodies on 

Mariposite Ridge is in contact with, but does not crosscut, the 

overlying Hyd Group basalt.

Together, the evidence suggests that the gabbros, ultramafic rocks (serpentinites), and Hyd Group basalts in the 

mine area are contemporaneous and are of Late Triassic age, 

although some of the gabbros appear to have been emplaced 

last and therefore could be significantly younger.

Age of Greens Creek Mineralization

The available age constraints suggest that intrusion 

of mafic-ultramafic heat sources at Greens Creek occurred 

between 215 and 211 Ma and were then altered and cooled 

below about 300°C (closure temperature for argon diffusion 

in fuchsite is assumed to be below about 300°C) by 210.3 ± 

0.3 Ma. If intrusion of these mafic-ultramafic heat sources 

at Greens Creek initiated the ore-forming process and this 

process ceased when temperatures cooled below the fuchsite 

argon closure temperature, then the hydrothermal system may 

have had a lifespan as short as 2.7 ± 2.3 m.y. (that is, a maximum span from 215 to 210 Ma, or 5 m.y., and a minimum 

span from 211 to 210.6 Ma, or 0.4 m.y.).

Another estimate for the duration of the Greens Creek 

hydrothermal system, based on the assumption that the initiation of mineralization occurred at or about the time of Hyd 

Group shale sedimentation, is provided by the conodont age 

data (220.7 ± 4.4 Ma) and the age of alteration of the serpentinite body in Gambier Bay (210.3 ± 0.3 Ma), again interpreted 

as the age of cessation of the ore-forming event. If we are 

correct in the assumption that the altered ultramafic bodies across the island are coeval and that they were altered by 

hydrothermal fluids related to the Greens Creek ore-forming 

event, then the age of 210.3 ± 0.3 Ma represents the best 

constraint available for the formation of the Greens Creek 

orebody. If we are also correct in our assumption that the onset 

of mineralization coincided with the onset of sedimentation 

of the hanging-wall argillites, then these data suggest that the 

Greens Creek hydrothermal system had a maximum lifespan 

of 10.4 ± 4.7 m.y. (that is, a maximum span from 225.1 to 210 

Ma, or 15.1 m.y., and a minimum span from 216.3 to 210.6 

Ma, or 5.7 m.y.). Following these arguments, intrusion of the 

gabbroic bodies (about 206 to 200 Ma) occurred after cessation of the ore-forming event (aout 210 Ma), implying that the 

heat source for mineralization was supplied by the ultramafic 

intrusions and not by the gabbroic bodies.

Isotopic Resetting of the Older Stratigraphy

Whole-rock U-Pb and Rb-Sr data from the phyllites and 

argillites suggest an isotopic disturbance or partial resetting 
Discussion 325

40

80

120

160

200

240

280

Age determinations

Age (Ma)

Hyd Group argillite

conodont age

Hyd Group

metabasalts

Ar-Ar

Sm-Nd

U-Pb

Rb-Sr

Metagabbros

Serpentinite

Phyllites

Fuchsite

Argillites

Argon closure 

in fuchsite and 

sericite

Age of

Greens

Creek

ore

event

alteration of

host rock

Carnian-Norian

boundary

Figure 18. Diagram summarizing the various ages for Greens Creek samples. The isotopic age accompanying 

the conodont symbol is from Gradstein and others (1995) and dates the Carnian-Norian boundary. The most 

biochronologically constrained conodont collections from mine workings and outcrops in the Greens Creek mine 

area are diagnostic of the Lower and (or) Upper primitius Zone(s). The boundary between these zones coincides 

with the Carnian-Norian boundary (fig. 5). The best ages suggest that the Hyd Group argillites and metabasalts are 

coeval at 220.7 ± 4.4 Ma and that subsequent intrusion(s) of gabbroic magmas at 206 to 200 Ma, disturbed many of 

the U-Pb and Rb-Sr isotopic systematics of older rock suites (metabasalt, serpentinite, argillite). The main phase of 

polymetallic mineralization is constrained to have occurred between these two ages and is confirmed by the 40Ar/39Ar 

plateau age of 210.3 ± 0.3 Ma for fuchsite from Gambier Bay. Other U-Pb, Rb-Sr, and 40Ar/39Ar total gas ages from 

argillites, sulfides, fuchsite, and sericite define much younger, “reset” ages between 90 and 105 Ma, and also about 

61 Ma, consistent with known ages for Late Cretaceous deformation and metamorphism, and Early Tertiary gold 

mineralization, respectively.
326 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Table 7. Age results for various Greens Creek rocks and minerals.

[Fmn., Formation; Gp., Group; GC, Greens Creek; Pen., Peninsula; OB, orebody]

Location/

stratigraphic unit

Rock/

mineral

Dating

technique

Age

(Ma)

Error

(Ma)

Initial

value*

Confidence 

(Precision)

Interpretation

Cliff Creek argillite conodont 220.7 4.4 High

(Great)

Age of Hyd Group 

argillite

Gambier Bay fuchsite Ar-Ar 210.3 0.3 High

(Great)

Age of argon closure 

in fuchsite

Hyd Group metabasalts Sm-Nd 215 95 7.4 High

(Poor)

Age of Hyd Group 

basalts

Hyd Group metabasalts U-Pb 218 16 18.515 High Age of Hyd Group

Hyd Gp. - Gambier Bay metabasalts

+ phyllites U-Pb 211 27 18.64 High(Poor)

Age of disturbance of 

metabasalts

Hyd Gp. - Gambier Bay metabasalts Rb-Sr 182 29 0.70494 Fair

(Poor)

Age of disturbance of 

metabasalts

Greens Creek area metabasalts U-Pb 206 35 18.61 Good

(Poor)

Age of gabbros on 

Gallagher Ridge U-Pb 216 20 18.576 Gallagher Ridge

Gallagher Ridge metabasalts Sm-Nd 200 27 5.6 Good

(Poor)

Age of gabbros on 

Gallagher Ridge

Hyd Group and

Cannery Fm. argillites U-Pb 186 100 18.81 Good(Poor)

Age of disturbance of 

argillites

Hyd Group argillites Rb-Sr 90.8 2.2 0.70733 Good

(Good)

Age of disturbance of 

argillites

Greens Creek serpentinites Rb-Sr 89 15 0.70767 Fair

(Poor)

Age of disturbance of 

mine serpentinites

GC DC ovr West OB mica Ar-Ar 98.6 1

Total

gas ages

Argon closure is 

interpreted to have 

occurred between 

105 and 95 Ma for 

these samples

Mammoth claim fushsite Ar-Ar 97.5 0.2

GC - east OB fushsite Ar-Ar 89 0.2

GC - east OB sericite Ar-Ar 77.5 0.1

GC - SW OB fuchsite Ar-Ar 83.4 0.2

GC 29F N heading fuchsite Ar-Ar 85.4 0.2

Mansfield Pen. fuchsite Ar-Ar 60.8 0.2

*

 - Initial values for U-Pb ages are 206Pb/204Pb; for Rb-Sr ages, 87 Sr/86Sr: and for Sm-Nd ages, epsilon Nd (εNd) define as the initial 134Nd/144Nd value in 

parts per 104 deviation from the CHUR evolution line.

that occurred between 211 and 190 Ma (figs. 11, 13, and 16; 

table 7), an age range that is coincident with intrusion of the 

gabbroic suite. Initial 206Pb/204Pb values near 18.64 for some 

of these suites of altered rock are very similar to both the 

initial lead value defined by U-Pb data from Gallagher Ridge 

metagabbros (figs. 11 and 14) and the Greens Creek ore lead 

composition, suggesting that alteration and isotopic resetting 

of the older stratigraphy may be related to intrusion of the Gallagher Ridge gabbroic suite.

Age of Cretaceous Overprinting on Greens 

Creek Mineralization

Several lines of evidence indicate that the Greens Creek 

region was isotopically affected by Cretaceous metamorphism 

at 110 to 85 Ma (Rubin and others, 1990). An apparent Rb-Sr 

isochron age from argillites indicates a disturbance of this isotopic system at about 90 Ma (table 7 and fig. 16). An imprecise, apparent Rb-Sr age was also found in mine serpentinite, 
References Cited 327

suggesting ages around 90 Ma. These ages are likewise similar 

to age results that infer complete resetting of argon in fuchsite 

and sericite just prior to around 105 to 95 Ma and are consistent with Cretaceous ages for the accretion of the Alexander, 

Wrangellia, and Gravina terranes with the North American 

craton (Rubin and others, 1990).

The Mansfield Peninsula sample is interesting in that it 

appears to indicate a plateau age of 60.8 Ma, consisent with 

alteration of the ultramafic body during the transition from 

oblique convergence to margin-parallel motion of the Alexander terrane during the Eocene. The age is also very close 

to that accepted for mineralization of the Alaskan-Juneau 

district (about 55 Ma; Goldfarb and others, 1991), only 40 km 

to the east.

Acknowledgments

The authors would like to thank the Kennecott Greens 

Creek Mining Company for their cooperation, hospitality, 

and special equipment during sample collection on Admiralty 

Island. Also, thanks to all the workers at the USGS that were 

responsible for the majority of sample preparation and chemical analysis, especially Ross Yeoman and Elaine Gilman. 

Special thanks to manuscript reviewers J.N. Aleinikoff, M.L. 

Kunk, and Daniel M. Unruh for their helpful comments and 

criticisms. And special thanks to Cliff D. Taylor and Craig 

Johnson, our editors, for having the patience to see this manuscript into review and eventual fruition.

A.G. Harris thanks N.A. Duke, P.A. Lindberg, J.M. Proffett, and A.W. West, associates and personnel of Greens Creek 

Kennecott Mining Company, and C.D. Taylor, U.S. Geological 

Survey, for collecting the conodont samples, the productive 

and, less enthusiastically, nonproductive, that made this study 

possible and successful. Thanks are also due the Greens Creek 

explorationists who went farther afield to sample on Admiralty 

and northern Kupreanof Islands to provide broader coverage 

regionally and stratigraphically.

References Cited

Barovich, K.M., and Patchett, P.J., 1988, Behavior of isotopic 

systematics during deformation and metamorphism— A Hf, 

Nd and Sr isotopic study of mylonitized granite: Contributions to Mineralogy and Petrology, v. 109, p. 386–393.

Brannon, J.C., Podosek, F.A., and McLimans, R.K.,1992, 

Alleghenian age of the Upper Mississippi Valley zinc-lead 

deposit determined by Rb-Sr dating of sphalerite: Nature, 

v. 356, p. 509–511.

Brannon, J.C., Cole, S.C., Podosek, F.A., Ragan, V.M., 

Coveney, R.M., Jr., Wallace, M.W., and Bradley, A.J.,1996, 

Th-Pb and U-Pb dating of ore-stage calcite and Paleozoic 

fluid flow: Science, v. 271, p. 491–493.

Brew, D.A., and Ford, A.B., 1985, Preliminary reconnaissance 

geologic map of the Juneau, Taku River, Atlin, and part of 

the Skagway 1:250,000 quadrangles, southeastern Alaska: 

U.S. Geological Survey Open-File Report 85–395, 23 p.

Chesley, J.T., Halliday, A.N., Snee, L.W., Mezger, K., Shepherd, T.J., and Scrivener, R.C., 1993, Thermochronology of 

the Cornubian batholith in southwest England — Implications for pluton emplacement and protracted hydrothermal 

mineralization: Geochimica et Coscochimica Acta, v. 57, 

p. 1817–1835.

Chesley, J.T., Halliday, A.N., Kyser, T.K., and Spry, P.G., 

1994, Direct dating of Mississippi Valley-type mineralization — Use of Sm-Nd in fluorite: Economic Geology, v. 89, 

p. 1192–1199.

Christensen, J.N., Halliday, A.N., Leigh, K.E., Randell, 

R.N., and Kesler, S.E., 1995a, Direct dating of sulfides 

by Rb-Sr — A critical test using the Polaris Mississippi 

Valley-type Zn-Pb deposit: Geochimica et Coscochimica 

Acta, v. 59, p. 5191–5197.

Christensen, J.N., Halliday, A.N., Vearncombe, J.R., and Kesler, S.E., 1995b, Testing models of large-scale crustal fluid 

flow using direct dating of sulfides — Rb-Sr evidence for 

early dewatering and formation of Mississippi Valley-type 

deposits, Canning Basin, Australia: Economic Geology, 

v. 90, p. 877–884.

Crafford, T.C., 1984, Greens Creek-type massive sulfide 

exploration criteria — Anaconda Minerals Company memorandum to D.A. Heatwole, Anaconda Geological Document 

Collection: Laramie, American Heritage Center, University 

of Wyoming, 6 p.

Crafford, T.C., 1989, The Greens Creek Ag-Au-Pb-Zn massive 

sulfide deposit, Admiralty Island, southeast Alaska [abs.]: 

Alaska Miners Association Conference Juneau, Program 

with Abstracts, p. 27–29.

Dalrymple, G.B., Alexander, E.C., Lanphere, M.A., and 

Kraker, G.P., 1981, Irradiation of samples for 40Ar/39Ar 

dating using the Geological Survey TRIGA reactor: U.S. 

Geological Survey Professional Paper 1176, 55 p.

Desrochers, A., and Orchard, M.J., 1991, Stratigraphic revisions 

and carbonate sedimentology of the Kunga Group (Upper 

Triassic-Lower Jurassic), Queen Charlotte Islands, British 

Columbia, in Woodsworth, G.J., ed., Evolution and hydrocarbon potential of the Queen Charlotte Basin, British Columbia: Geological Survey of Canada Paper 90–10, p. 163–172.

Dickin, Alan, 1995, Radiogenic isotope geology: Oxford, 

Cambridge Press, 490 p.

Epstein, A.G., Epstein, J.B., and Harris, L.D., 1977, Conodont 

color alteration — An index to organic metamorphism: U.S. 

Geological Survey Professional Paper 995, 27 p.
328 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Fairbairn, H.W., Hurley, P.M., and Pinson, W.H., 1961, The 

relation of discordant Rb-Sr mineral and rock ages in an 

igneous rock to its time of subsequent Sr87/Sr86 metamorphism: Geochimica et Coscochimica Acta, v. 23, p. 135–144.

Fleck, R.J., Sutter, J.F., and Elliot, D.H., 1977, Interpretation 

of discordant 40Ar/39Ar age spectra of Mesozoic tholeiites 

from Antarctica: Geochimica et Cosmochimica Acta, v. 41, 

p. 15–32.

Gehrels, G.E., and Berg, H.D., 1994, Geology of southeastern 

Alaska, in Plafker, George, and Berg, H.C., eds., The geology of Alaska: Boulder, Colo., Geological Society of America, The Geology of North America, v. G–1, p. 451–467.

Goldfarb, R.J., Newberry, R.J., Pickthorn, W.J., and Gent, 

C.A., 1991, Oxygen, hydrogen, and sulfur isotope studies in 

the Juneau gold belt, southeastern Alaska — Constraints on 

the origin of the hydrothermal fluids: Economic Geology, 

v. 86, p. 66–80.

Gradstein, F.M., Agterberg, F.P., Ogg, J.G., Hardenbol, Jan, 

Van Veen, Paul, Thierry, Jacques, and Huang, Zehui, 1995, 

A Triassic, Jurassic, and Cretaceous time scale, in Geochronology time scales and global stratigraphic correlation: 

SEPM Special Publication no. 54, p. 95–126.

Hart, S.R., and Kinloch, E.D., 1989, Osmium isotope systematics in Witwatersrand and Bushveld ore deposits: Economic Geology, v. 84, p. 1651–1655.

Karl, S.M., Haeussler, P.J., and McCafferty, Anne, 1999, 

Reconnaissance geologic map of the Duncan Canal-Zarembo 

Island area, southeastern Alaska: U.S. Geological Survey 

Open-file Report 99–168, 29 p., map scale 1:150,000.

Kerrich, Robert, 1991, Radiogenic isotope systems applied to 

ore deposits, in Heaman, L., and Ludden, J.N., eds., Applications of radiogenic isotopes systems to problems in geology: Mineralogical Association of Canada, Short Course 19, 

p. 365–421.

Kerrich, Robert, and King, R., 1993, Hydrothermal zircon 

and baddeleyite in Val-d’Or Archean mesothermal gold 

deposits — Characteristics, compositions, and fluid-inclusion 

properties, with implications for timing of primary gold mineralization: Canadian Journal of Earth Sciences, v. 30, p. 2334–2351.

Königshof, Peter, 1992, Conodont colour alteration index 

(CAI) in Paleozoic rocks (Middle Devonian to Lower 

Carboniferous) of the Rhenish Massif — A comparison to 

vitrinite reflectance: Courier Forschungsinstitut Senckenberg, no. 149, 118 p. [in German].

Kozur, Heinz, 1989, Significance of events in conodont evolution for the Permian and Triassic stratigraphy, in Ziegler, 

Willi, ed., 1st International Senckenberg conference and 5th 

European Conodont Symposium (ECOS V), Contributions 

III — Papers on Ordovician to Triassic conodonts: Courier 

Forschungsinstitut Senckenberg, no. 117, p. 385–408.

Lambert, D.D., Morgan, J.W., Walker, R.J., Shirey, S.B., Carlson, R.W., Zientek, M.L., and Koski, M.S., 1989, Rheniumosmium and samarium-neodymium isotopic systematics of 

the Stillwater Complex: Science, v. 244, p. 1169–1174.

Lange, F.-G., 1968, Conodonten-Gruppenfunde aus Kalken 

des tieferen Oberdevon: Geological et Palaeontologica, v. 2, 

p. 37–57.

Lanphere, M.A., Wasserburg, G.J., Albee, A.L., and Tilton, 

G.R., 1964, Redistribution of strontium and rubidium 

isotopes during metamorphism, World Beater Complex, 

Panamint Range, California, in Craig, H., Miller, S.L., and 

Wasserburg, G.J., eds., Isotopic and cosmic chemistry: 

Amsterdam, North Holland Publications, p. 269–320.

Lathram, E.H., Pomeroy, J.S., Berg, H.C., and Loney, R.A., 

1965, Reconnaissance geology of Admiralty Island, Alaska: 

U.S. Geological Survey Bulletin 1181–R, 48 p.

Ludwig, K.R., 1980, Calculation of uncertainties of U-Pb data: 

Earth and Planetary Science Letters, v. 46, p. 212–220.

Ludwig, K.R., 1985, PBDAT200 — A computer program 

for processing raw Pb-U-Th isotope data: U.S. Geological 

Survey Open-File Report 85–547, 54 p.

Ludwig, K.R., 1993, ANALYST: VER. 2.20 — A computer 

program for control of a thermal-ionization, single-collector 

mass spectrometer, user’s manual: U.S. Geological Survey 

Open-File Report 92–543, rev. Dec. 7, 1993, 94 p.

Ludwig, K.R., 1998, ISOPLOT/Ex, version 1.00, A geochronological toolkit for Microsoft Excel: Berkeley Geochronology Center, Special Publication no.1, 43 p.

Lugmair, G.W., Scheinin, N.B., and Marti, K., 1975, Sm-Nd 

age and history of Apollo 17 basalt 75075 — Evidence for 

early differentiation of the lunar exterior: Proceedings of the 

6th Lunar Science Conference, p. 1419–1429.

MacIntyre, D.G., 1986, The geochemistry of basalts hosting 

massive sulfide deposits, Alexander terrane northwest British Columbia: British Columbia Ministry of Energy, Mines, 

and Petroleum Resources, Geological Fieldwork, 1985, 

Paper 1986–1, pp. 197–210.

Mei, S., and Henderson, C.M., 2002, Comments on some 

Permian conodont faunas reported from southeast Asia and 

adjacent areas and their global correlation: Journal of Asian 

Earth Sciences, v. 20, p. 599–608.

Moorbath, Stephen, and Taylor, P.N., 1981, Isotopic evidence 

for continental growth in the Precambrian, in Kroner, A., 

ed., Precambrian plate tectonics: Elsevier, p. 491–525.

Newberry, R.J., and Brew, D.A., 1997, The Upper Triassic 

Greens Creek VMS (volcanogenic massive sulfide) deposit 

and Woewodski Island VMS prospects, southeastern 

Alaska — Chemical and isotopic data for rocks and 
References Cited 329

ores demonstrate similarity of these deposits and their host 

rocks: U.S. Geological Survey Open-File Report 97–539, 

49 p.

Newberry, R.J., and Brew, D.A., 1999, Chemical and 

isotopic data for rocks and ores from the Upper Triassic Greens Creek and Woewodski Island volcanogenic 

massive sulfide deposits, southeastern Alaska, in Kelley, 

K.D., ed., Geologic studies in Alaska by the U.S. Geological Survey, 1997: U.S. Geological Survey Professional 

Paper 1614, p. 35–55.

Newberry, R.J., Brew, D.A., and Crafford, T.C., 1990, Genesis 

of the Greens Creek volcanogenic massive sulfide deposit, 

S.E. Alaska — A geochemical study [abs.]: Geological Association of Canada Program with Abstracts, v. 15, p. A96.

Newberry, R.J., Crafford, T.C., Newkirk, S.R., Young, L.E., 

Nelson, S.W., and Duke, N.A., 1997, Volcanogenic massive 

sulfide deposits of Alaska: Economic Geology Monograph 

9, p. 120–150.

Orchard, M.J., 1991a, Upper Triassic conodont biochronology 

and biostratigraphy of the Kunga Group, Queen Charlotte 

Islands, British Columbia, in Woodsworth, G.J., ed., Evolution and hydrocarbon potential of the Queen Charlotte 

Basin, British Columbia: Geological Survey of Canada 

Paper 90–10, p. 173–193.

Orchard, M.J., 1991b, Upper Triassic conodont biochronology and new index species from the Canadian Cordillera, 

in Orchard, M.J., and McCracken, A.D., eds., Ordovician 

and Triassic conodont paleontology of the Canadian Cordillera: Geological Survey of Canada Bulletin 417, 

p. 299–335.

Premo, W.R., and Tatsumoto, M., 1991, U-Th-Pb isotopic systematics of lunar norite 78235, in Proceedings of the 21st 

Lunar and Planetary Science Conference: Houston, The 

Lunar and Planetary Institute, p. 89–100.

Premo, W.R., and Tatsumoto, M., 1992, U-Th-Pb, Rb-Sr, and 

Sm-Nd isotopic systematics of lunar troctolitic cumulate 

76535—Implications on the age and origin of this early 

lunar, deep-seated cumulate, in Proceedings of the 22d 

Lunar and Planetary Science Conference, p. 381–397: 

Houston, Texas, The Lunar and Planetary Institute.

Purnell, M.A., and Donoghue, P.C.J., 1997, Architecture and 

functional morphology of the skeletal apparatus of ozarkodinid conodonts: Philosophical Transactions of the Royal 

Society of London, Series B, v. 352, no. 1361, p. 1545–1655.

Purnell, M.A., and Donoghue, P.C.J., 1998, Skeletal architecture, homologies and taphonomy of ozarkodinid conodonts: 

Palaeontology, v. 41, part l, p. 57–102.

Rejebian, V.A., Harris, A.G., and Huebner, J.S., 1987, Conodont 

color and textural alteration—An index to regional 

metamorphism, contact metamorphism, and hydrothermal 

alteration: Geological Society of America Bulletin, v. 99, 

p. 471–479.

Roddick, J.C., 1983, High-precision intercalibration of 40Ar/39Ar standards: Geochimica et Cosmochimica Acta, 

v. 47, p. 887–898.

Rubin, C.M., Saleeby, J.B., Cowan, D.S., Brandon, M.T., 

and McGroder, M.F., 1990, Regionally extensive midCretaceous west-vergent thrust system in the northwestern 

Cordillera — Implications for continent-margin tectonism: 

Geology, v. 18, p. 276–280.

Samson, S.D., and Alexander, E.C., 1987, Calibration of 

interlaboratory 40Ar/39Ar dating standard, MMhb-1: Isotope 

Science, v. 66, p. 27–34.

Snee, L.W., 2002, Argon thermochronology of mineral deposits—A review: U.S. Geological Survey E-Bulletin 2194, 39 p.

Snee, L.W., Sutter, J.F., and Kelly, W.C., 1988, Thermochronology of economic mineral deposits — Dating the 

stages of mineralization at Panasqueira, Portugal, by highprecision 40Ar/39Ar age spectrum techniques on muscovite: 

Economic Geology, v. 83, p. 335–354.

Steiger, R.H., and Jäger, E., 1977, Subcommission on geochronology — Convention on the use of decay constants in 

geo- and cosmochronology: Earth and Planetary Science 

Letters, v. 36, p. 359–362.

Sweet, W.C., 1989, The Conodonta: Oxford Monographs on 

Geology and Geophysics no. 10, 212 p.

Tatsumoto, Mitsunobu, and Unruh, D.M., 1976, KREEP basalt 

age — Grain by grain U-Th-Pb systematics study of the 

quartz monzodiorite clast 15405, 88: Proceedings of the 

7th Lunar and Planetary Science Conference, Houston, The 

Lunar and Planetary Institute, p. 2107–2129.

Taylor, C.D., 1997, An arc-flank to back-arc transect—Metallogeny of Upper Triassic volcanogenic massive sulfide occurrences of the Alexander terrane, southeastern Alaska and 

British Columbia: [extended abs.] in Society of Economic 

Geologists Neves Corvo Field Conference, May 7–17, 1997, 

Lisbon, Portugal, Abstracts and Programs volume, p. 68.

Taylor, C.D., Cieutat, B.A., and Miller, L.D., 1992, A followup geochemical survey of base metal anomalies in the Ward 

Creek/Windfall Harbor and Gambier Bay areas, Admiralty 

Island, S.E. Alaska, in Bradley, D., and Dusel-Bacon, C., 

eds., 1991 Geologic studies in Alaska: U.S. Geological 

Survey Bulletin 2041, p. 70–85.

Taylor, C.D., Philpotts, J., Sutley, S., Gent, C., Harlan, S., 

Premo, W.R., Tatsumoto, M., Emsbo, P., and Meier, A., 

1995a, Geochemistry of Late Triassic volcanic rocks and 

age of alteration associated with volcanogenic massive sulfide occurrences, Alexander terrane, southeast Alaska, in
330 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Geology and ore deposits of the American cordillera — A 

symposium: Geological Society of Nevada, p. A74.

Taylor, C.D., Philpotts, J.A., Hall, T.E., and Wakeman, B.W., 

1995b, New information on the geochemistry, age, and tectonic history of Late Triassic volcanic host rocks and associated massive sulfide occurrences of the Alexander terrane, 

southeast Alaska: Alaska Miners Association Conference, 

Juneau, Program with Abstracts, p. 31–32.

Taylor, C.D., Premo, W. R., and Meier, A. L., 1999, The 

Late Triassic metallogeny of the Alexander terrane, 

southeastern Alaska and British Columbia: Geological 

Society of America Abstracts with Programs, v. 31, no. 

6, p. A–101.

Taylor, C.D., Premo, W.R., and Lear, K.G., 2000, The Greens 

Creek massive sulfide deposit — Premier example of the 

Late Triassic metallogeny of the Alexander terrane, southeastern Alaska and British Columbia: Geological Society 

of America Abstracts with Programs, v. 32, no. 6, p. A–71.

Taylor, P.N., Moorbath, S., Goodwin, R., and Petrykowski, 

A.C., 1980, Crustal contamination as an indicator of the 

extent of early Archaean continental crust—Pb isotopic evidence from the late Archaean gneisses of West Greenland: 

Geochimica et Cosmochimica Acta, v. 44, p. 1437–1453.

Walker, R.J., Morgan, J.W., Naldrett, A.J., and Li C., 1991, 

Re-Os isotopic systematics of Ni-Cu sulfide ores, Sudbury 

Igneous Complex, Ontario — Evidence for a major crustal 

component: Earth and Planetary Science Letters, v. 105, 

p. 416–429.

Wetherill, G.W., Davis, G.L., and Lee-Hu C., 1968, Rb-Sr 

measurements on whole rocks and separated minerals from 

the Baltimore Gneiss, Maryland: Geological Society of 

America Bulletin, v. 79, p. 757–762.

Whitehouse, M.J., 1988, Granulite facies Nd-isotopic homogenization in the Lewisian complex of northwest Scotland: 

Nature, v. 331, p. 705–707.

Williams, M.E., 1990, Feeding behavior in Cleveland 

Shale sharks, in Boucot, A.J., ed., Evolutionary paleobiology of behavior and coevolution: Elsevier, Amsterdam, p. 273–287.
References Cited 331

Appendix. Data for Permian and Triassic conodont samples from Admiralty and northern Kupreanof Islands, Alaska (exclusive of 

samples listed in table 1).

[CAI, color alteration index; samples collected by Greens Creek and U.S. Geological Survey personnel. See figures 7 and 8 for Permian and 

Triassic conodont zonation and range of biostratigraphically useful collections; colln., collection]

Locality no., field no., 

and USGS Colln. no. 

Location Lithology and stratigraphic unit CAI Age

1 AK14701 Juneau A-3 quadrangle 

58°09.97'N., 134°46.37'W.

Dark-gray coarsely crystalline 

dolomite. Barren.

2 AK14718 Juneau A-3 quadrangle 

58°14.05'N., 134°49.7'W.

Not designated. Barren.

3 AK14747

(Mes. 35016)

Juneau A-3 quadrangle 

58°12.60'N., 134°45.36'W. 

Not designated; age indicates 

Hyd Group.

5 late Carnian-very earliest 

Norian

4 SP-32373 Juneau A-3 quadrangle 

58°11.67'N., 134°44.38'W.

Shaly dark-gray limestone, near 

contact with overlying(?) 

Hyd Group greenstone; lies 

structurally above a thick 

chert-clast conglomerate. 

Barren.

5 SP-32356 Sitka D-2 quadrangle 

57°57.39'N., 134°32.4'W.

Gray limestone structurally 

above graphitic argillite that 

hosts a stratiform, barite-rich 

massive sulfide. Hyd Group 

sequence? Barren.

6 AK14920 Petersburg D-5 quadrangle 

56°48.52'N., 133°24.28'W. 

Not designated. Barren.

7 AK14973 (Mes. 35013) Petersburg D-5 quadrangle 

56°48.52'N., 133°24.28'W. 

Gray limestone; Hyd Group. 5 polygnathiformis Zone

(latest early-earliest late 

Carnian)

8 AK15066 (33405-PC) Petersburg D-5 quadrangle 

56°46.26'N., 133°23.09'W.

Cherty limestone; Cannery 

Formation.

5 very late Early Permian 

(late Leonardian; Kungurian)

9 AK15553 (33486-PC) Petersburg D-5 quadrangle 

56°47.71'N., 133°21.26'W.

Cannery Formation. 5–6.5 very late Early Permian 

(late Leonardian; Kungurian)

10 AK15554 (33487-PC) Petersburg D-5 quadrangle 

56°47.97'N., 133°21.33'W.

Cannery Formation. 5.5 and 

minor 5 

and 6

very late Early Permian 

(late Leonardian; Kungurian)

11 AK15601 Petersburg D-5 quadrangle 

56°47.65'N., 133°21.66'W.

Not designated. about 5 Mississippian-Early Triassic
332 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Appendix. Data for Permian and Triassic conodont samples from Admiralty and northern Kupreanof Islands, Alaska.—Continued

[CAI, color alteration index; samples collected by Greens Creek and U.S. Geological Survey personnel. See figs.7 and 8 for Permian and 

Triassic conodont zonation and range of biostratigraphically useful collections; colln., collection]

Locality no., field no., 

and USGS Colln. no. 

Location Lithology and stratigraphic unit CAI Age

12 AK15614 Petersburg D-5 quadrangle 

56°46.42'N., 133°21.73'W.

Not designated. Barren.

13 AK15615 Petersburg D-5 quadrangle 

56°47.64'N., 133°21.57'W.

Not designated. 6, 6.5, minor 5.5, 7Permian-Triassic

14 AK15616 Petersburg D-5 quadrangle 

56°47.57'N., 133°21.48'W.

Not designated. Barren.

15 AK15617 Petersburg D-5 quadrangle 

56°47.55'N., 133°21.35'W.

Not designated. 5.5-6.5 Early Permian-early 

Late Triassic

16 AK15618 (Mes. 35017) Petersburg D-5 quadrangle 

56°47.53'N., 133°21.24'W.

Likely Hyd Group. 5.5-6.5 and 

rare 7

late Early Triassic to 

early Late Triassic 

(late Carnian)

17 AK15970 Petersburg D-5 quadrangle 

56°47.52'N., 133°20.59'W.

Not designated. Barren.

18 AK19903 Petersburg D-5 quadrangle 

56°47.8'N., 133°23.3'W.

Graphitic phyllite and argillite 

with limy beds. Barren.

19 AK19904 (Mes. 35025) Petersburg D-5 quadrangle 

56°47.8'N., 133°23.1'W.

Dark-gray to black silty limestone; Hyd Group.5 polygnathiformis Zone

(latest early-earliest 

late Carnian)

20 AK19912 (Mes. 35026) Petersburg D-5 quadrangle 

56°47.8'N., 133°23.0'W.

Graphitic, phyllitic carbonate; 

Hyd Group.

5 polygnathiformis Zone

(latest early-earliest 

late Carnian)

21 AK19918 Petersburg D-5 quadrangle 56° 

48.0'N., 133°21.8'W.

Light-gray massive dolomite. 

Barren.

22 80EK107

(27118-PC)

Petersburg D-6 quadrangle

56°54'46"N., 133°48'30"

Partly dolomitic, chert-bearing 

limestone; Pybus Formation.

6-6.5 very late Early Permian

(late Leonardian; Kungurian)

23 600-Wis

underground

Juneau A-2 quadrangle 

58°04'07"N., 134°37'50"W.

3 samples

White, massive dolomite. Barren.

24 Cliff 1 Juneau A-2 quadrangle 

58°03’35”N., 134°34'03"W.

Light-gray, medium-grained dolomite; Hyd Group. Barren.

25 JMP-115A, 115B, and 115C Juneau A-2 quadrangle 

58°03.98’N., 134°37.12'W.

3 samples

Dark-gray slate with carbonate. 

Barren.

26 JMP-126 Juneau A-2 quadrangle 

58°04.58'N., 134°36.77'W.

Argillite; Hyd Group. Barren.
References Cited 333

Appendix. Data for Permian and Triassic conodont samples from Admiralty and northern Kupreanof Islands, Alaska.—Continued

[CAI, color alteration index; samples collected by Greens Creek and U.S. Geological Survey personnel. See figs.7 and 8 for Permian and 

Triassic conodont zonation and range of biostratigraphically useful collections; colln., collection]

Locality no., field no., 

and USGS Colln. no. 

Location Lithology and stratigraphic 

unit

CAI Age

27 Drill core PP-365 (260-67 ft) Juneau A-2 quadrangle 

58°04.06'N., 134°37.55'W.

Massive dolomitic argillite; 

Hyd Group. Barren.

28 Drill core PP-365 (287-303 ft) Juneau A-2 quadrangle 

58°04.06'N., 134°37.55'W.

2 samples

Massive dolomitic argillite; 

Hyd Group. Barren.

29 Drill core PS-97 (335-53; 360-

66; 371-376 ft) 

Juneau A-2 quadrangle 

58°04.39'N., 134°37.68'W.

3 samples

Likely Hyd Group. Barren.

30 Drill core PS-108 (from 173-

1161 ft)

Juneau A-2 quadrangle 

58°04.23'N., 134°37.58'W.

14 samples

Hyd Group. Barren.

31 Drill core PS116 (763 ft) Juneau A-2 quadrangle 

58°04'57"N., 134°37'50"W.

Medium-gray, fossiliferous 

(pelmatozoan ossicles and 

other indeterminate bioclasts), calcareous dolomite. 

Barren.

Radiogenic Isotopic Characterization and 

Petrogenesis of Host Rocks to the Greens 

Creek Deposit

By Wayne R. Premo and Cliff D. Taylor

Chapter 12 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract.......................................................................................................................................................339

Introduction.................................................................................................................................................339

Geology........................................................................................................................................................341

Sampling......................................................................................................................................................346

Results .........................................................................................................................................................347

Degree of Stability of the Isotopic Systematics ..........................................................................347

Initial Lead, Strontium, and Neodymium Isotopic Systematics of Greens Creek

Host-Rock Lithologies.........................................................................................................352

Metabasalts..............................................................................................................................354

Metagabbros ............................................................................................................................355

Phyllites .....................................................................................................................................356

Argillites.....................................................................................................................................358

Serpentinites.............................................................................................................................358

Crosscutting Diabases — Diorites .......................................................................................359

Discussion...................................................................................................................................................359

Geologic Framework at Greens Creek ..........................................................................................359

Petrotectonic Environment of the Greens Creek VMS Deposit ................................................360

Initial Lead Isotopes of Greens Creek Host Rocks Compared to Ore Lead

Compositions........................................................................................................................360

Summary......................................................................................................................................................363

Acknowledgments.....................................................................................................................................363

References..................................................................................................................................................363

Figures

1. Generalized map of terranes boundaries (bold lines) and major volcanogenic

massive sulfide prospects southeast Alaska, showing the locations of the Late 

Triassic-age VMS deposits, including Greens Creek (#10), Pyrola (#11), and

Gambier Bay (#19) on Admiralty Island.................................................................................340

2. 206Pb/204Pb – 207Pb/204Pb correlation diagram showing the distribution of lead

isotopic compositions (fields) for Alaskan volcanogenic massive sulfide (VMS)

occurrences compared to model lead evolution curves (“upper crust,”

“orogene,” and “depleted mantle”) ......................................................................................342

3. Simplified geologic map of Admiralty Island, showing locations for Greens

Creek and Pyrola deposits, Gambier Bay, Windfall Harbor, the Mansfield

Peninsula, and Staunch Point.................................................................................................343

4. Stratigraphy of the Greens Creek section, Admiralty Island, showing the orebody

at the contact between footwall phyllites and hanging-wall argillites ...................................344

5. Map of surface sampling sites at and near Greens Creek mine, Admiralty Island.......345

6. (A) Geologic cross section, Greens Creek mine..................................................................346

6. (B) Predeformation, cross-sectional model, Greens Creek deposit, based on

drill-core logging and underground and surface mapping................................................347
7. (A) Plot of uranium (U) concentration versus calculated initial 206Pb/204Pb at

215 Ma for whole-rock analyses of major Greens Creek host rocks, illustrating

the possible isotopic disturbance of some whole-rock samples, probably

during alteration........................................................................................................................348

8. A comparison of calculated initial 206Pb/204Pb versus initial εNd for whole-rock

analyses from Greens Creek host rocks at 90 Ma ..............................................................350

9. A comparision of the samarium-neodymium isotopic systematics of Greens

Creek host rocks to Hyd Group metabasalt and Gallagher Ridge metagabbro

isochrons, showing the extent of isotopic stability or variation within the

different lithologic units...........................................................................................................352

10. Pb-Pb correlation diagram (206Pb/204Pb versus 207Pb/204Pb) showing the

distribution of initial lead compositions of Greens Creek host rocks relative

to model lead evolution curves and fields for modern petrotectonic

environments.............................................................................................................................353

11. Pb-Pb correlation diagram (206Pb/204Pb versus 208Pb/204Pb) showing the

distribution of initial lead compositions of Greens Creek host rocks relative

to model lead evolution curves and fields for modern petrotectonic

environments.............................................................................................................................354

12. Initial strontium versus initial neodymium correlation diagram showing the 

distribution of initial Sr-Nd values for Greens Creek host rocks relative to 

model Sr-Nd fields for modern petro-tectonic environments...........................................356

13. Initial lead versus initial neodymium correlation diagram showing the distribution

of initial Pb-Nd values for Greens Creek host rocks relative to model leadneodymium fields for modern petrotectonic environments ..............................................357

14. Initial strontium versus initial neodymium correlation diagram showing the

distribution of initial Sr-Nd values for Greens Creek host rocks relative to

Sr-Nd fields for previously published Alexander and Gravina terrane rocks ................361

15. Pb-Pb correlation diagram (206Pb/204Pb versus 207Pb/204Pb) showing the

distribution of initial lead compositions of Greens Creek host rocks relative

to lead isotopic compositions for Greens Creek sulfides (ore).........................................362

Radiogenic Isotopic Characterization and Petrogenesis of 

Host Rocks to the Greens Creek Deposit

Wayne R. Premo1 and Cliff D. Taylor1

1

U.S. Geological Survey, Denver, Colorado.

Abstract

Samples representing the major host and adjacent lithologies at the Greens Creek deposit, Admiralty Island, were analyzed 

for their uranium-thorium-lead (U-Th-Pb), rubidium-strontium 

(Rb-Sr), and samarium-neodymium (Sm-Nd) isotopic systematics 

in order to provide petrogenetic information. A multisystematic 

procedure from a single-aliquot dissolution of whole-rock powders provided direct correlation of the isotopic systems in order to 

(1) characterize the tectonic environment(s) in which these rocks 

formed and provide a setting for the production of the Greens 

Creek style mineralization; (2) compare to other radiogenic 

isotopic results from various Upper Triassic rock suites throughout southeastern Alaska; and (3) compare with lead isotope data 

from Greens Creek ore (chap. 10) to determine the relationship of 

ore to host rock. The same set of isotopic data was evaluated for 

geochronologic purposes in chapter 11.

Initial Nd compositions at 215 Ma (average age for host 

rocks) of metabasalts and metagabbros varied between εNd = +4 

to +9; whereas, initial 206Pb/204Pb and 87Sr/86Sr isotopic compositions at 215 Ma for the same suite of samples ranged from 

18.45 to 18.92, and from 0.7037 to 0.7074, respectively, and 

are more enriched than mid-ocean ridge basalt values. These 

isotopic results are indicative of oceanic magmatic arcs environments and consistent with their derivation from a mostly 

depleted source(s) at about 215 Ma. Although initial Pb values 

from phyllite samples mimic those of the metabasaltic rocks, 

initial Sr and Nd values of phyllites are bimodal, some with εNd

= +8, others with values at +2. Argillites have lower initial Nd 

(εNd about –2 to +2), higher initial 206Pb/204Pb (18.4 to 19.0), 

and higher 87Sr/86Sr (0.705 to 0.707) than other host rocks, 

values that are typical for shales. These values suggest that the 

argillites contain some proportion of older, slightly more radiogenic crust. In general, initial Nd-Sr isotopic values for Greens 

Creek host rocks are comparable to previously published data 

from samples of the Alexander and Gravina terranes.

These radiogenic isotopic systematics indicate a progressively depleting source for the Upper Triassic Greens Creek 

rocks, suggesting a rift setting. The oldest argillites have 

slightly depleted signatures (εNd about +1.5), that are unconformably overlain by a sequence of metabasalts that exhibit 

depleted, island-arc-type isotopic signatures (εNd = +4 to +5 

with elevated 87Sr/86Sr and 206Pb/204Pb). The metabasalts are 

then unconformably overlain by conglomerate, dolomite, 

and more argillites of the Hyd Group. The Hyd Group argillites have slightly depleted to slightly enriched εNd between 

–5 and +2, indicating the incorporation of some older, more 

enriched crustal material. The lower metabasaltic sequences 

are intruded by ultramafic sills and stocks, represented now 

as highly altered serpentinites that exhibit a wide range of 

isotopic signatures (εNd between –12 and +8). Subsequent 

mafic volcanism and gabbroic plutonism are characterized by 

more depleted source signatures (εNd = +5 to +9). Hyd Group 

basalts that cap the Triassic section have even more depleted 

signatures (εNd = +8 to +9). This progressive sequence of least 

to most depletion implies opening of preexisting crust in a rift 

setting, probably within an oceanic arc environment.

Initial Pb isotopic compositions of Greens Creek host 

rocks for the most part are not the same as Pb isotopic compositions for Greens Creek galena and other sulfides. However, 

it is evident that the relatively uniform ore Pb signature may 

represent a homogenization of Pb derived mainly from host 

basalt and gabbro, but also including some Pb from hangingwall argillites, a Pb isotopic trend similar to those documented 

for volcanogenic massive sulfides (VMS) from modern rift 

zones and island-arc sequences.

Introduction

Volcanogenic massive sulfide (VMS) deposits are found 

in many locations and occurrences around the Pacific rim and 

particularly in Alaska. Their ages and styles vary somewhat, 

but most in Alaska are thought to originate in or near oceanic island-arc or rift-related settings (Newberry and others, 

1997; Newberry and Brew, 1997). The ages for most of the 

VMS deposits of southeastern Alaska (fig. 1), and particularly 

within the Alexander terrane, are thought to be the same as 

their host rock sequences, such that the ore is syngenetic. In 

general, however, precise ages of mineralization are scarce. In 

approaching an age and origin for VMS deposits, particularly 

Greens Creek, radiogenic isotopic systems can be invaluable.

Radiogenic isotopic systems (U-Pb, Th-Pb, Sm-Nd, 

Rb-Sr, K-Ca, 40Ar-39Ar, and Re-Os) can be and have been used 
340 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

N

Ch

Ch

W

Cr

Cr

A

G

G

G

Cr

Cr

Juneau

134°

Skagway

British Columbia

Alaska

58°

56°

130°

0 kilometers 100

Terrane Key

Ch

W

G

A

Cr

Y

&

T

C

Y

&

T

Y

&

T

C

Chugach

Wrangellia

Gravina

Admiralty

10

11

Admiralty

Island

6 7

8

22

21

Alexander

Craig

Y & T

C

Yukon-Tanana/

 Taku

Coastal

12 13

Sitka

Haines

14

15

1

2

3

5

4

Prince of Wales

Island

16

17

18

19

Late Proterozoic -

Lower Paleozoic

1. Niblack

2. Khayyam-Stumble-On

3. Big Harbor

4. Corbin

5. Copper City

Devonian(?)

6. Sweetheart Ridge

7. Tracy Arm

8. Sumdum

9. Moth Bay

Upper Triassic

10. Greens Creek

11. Pyrola

12. Palmer Prospect

13. Mt. Henry Clay

14. Woewodski Island

15. Frenchie (Zarembo Is.)

16. Keku Strait (Kuiu Is.)

17. Duncan Canal

18. Annette Island

19. Gambier Bay

20. Windy Craggy

Cretaceous

21. Fremming

22. Alaska Treasure

Deposits

Petersburg

Wrangell

Ketchikan

9

Figure 13.3

20

Map

Area Alaska

Terrane boundary

Figure 1. Generalized map of terranes boundaries (bold lines) and major volcanogenic massive sulfide prospects 

(numbered circles), southeast Alaska, showing the locations of the Late Triassic age VMS deposits, including Greens 

Creek (#10), Pyrola (#11), and Gambier Bay (#19) on Admiralty Island (after Newberry and others, 1997).
Geology 341

for shedding light on the source(s) of mineralizing fluids (for 

example, Allegre and Luck, 1980; DePaolo, 1981; Zartman 

and Doe, 1981; Burke and others, 1982; Fehn and others, 

1983; Zartman, 1984; Hart and Kinloch, 1989; Lambert and 

others, 1989; Walker and others, 1991; Kerrick, 1991; Martin, 

1991; Ayuso and others, 2004). Previous radiogenic isotopic work on Greens Creek and other Late Triassic age VMS 

deposits of Alaska include lead (Pb) isotopic data of various 

sulfides, including galena, pyrite, and chalcopyrite (compiled 

in Gaccetta and Church, 1989, and references within; Newberry and Brew, 1997), and Rb-Sr and(or) Sm-Nd isotopic data 

from a variety of lithologic units from the Alexander, Stikine, 

Wrangellia, Gravina, and Taku terranes as well as samples 

from the Coast Mountains batholith (Samson and others, 1989, 

1990, 1991a, 1991b).

An accurate yet simplistic interpretation of the Pb isotopic data for Alaskan VMS ore deposits including Greens 

Creek is discussed in Newberry and others (1997). These 

authors suggested that Pb isotopic compositions on sulfides 

from Alaskan VMS deposits are mixtures of mantle and 

crustal endmembers that exhibit apparent young model lead 

ages for ore deposition (fig. 2). Because crustal Pb compositions are typically more radiogenic (enriched 206Pb) than 

mantle Pb compositions, the sulfide Pb isotopic compositions 

from various VMS deposits plot beyond the model-Pb evolution isochron at their actual ages. For example, Greens Creek 

and Pyrola ore Pb plots along the 0-Ma model lead isochron, 

although these deposits are constrained to have occurred in 

the Late Triassic (chap. 11). Other deposits exhibit Pb isotopic 

fields corresponding to futuristic model lead ages (for example, Mt. Henry Clay and Kuiu; figs. 1 and 2). This effect is 

thought to be the result of mixing between radiogenic crustal 

Pb and depleted mantle Pb in the source(s) prior to ore deposition. Mixing of these components might occur as continental 

crustal detritus is subducted beneath ore-producing oceanic 

island arcs. Whereas it is obvious that Pb isotopic data should 

not be used for model age determinations, they do hold promise in helping to identify possible source(s) for ore metals.

This explanation for radiogenic Pb signatures is testable 

using correlated Pb-Sr-Nd isotopic systematics from syngenetic, host-rock lithologies, isotopic signatures that should 

indicate to what degree crustal source(s) were involved in 

ore-forming processes as well as help delineate petrotectonic 

origins of various Phanerozoic allochthonous terranes of 

southeastern Alaska.

Greens Creek is located at the edge of the Alexander and 

Gravina Belt terranes (#10 in fig. 1), both of early Paleozoic 

to Jurassic-Cretaceous age. Positive initial εNd (0 to +9) and 

low initial 87Sr/86Sr (0.7028 to 0.7071) isotopic values from 

volcanic, plutonic, and metasedimentary samples from these 

two terranes indicate that they were derived mainly from 

depleted mantle sources (Samson and others, 1989, 1991a) 

and were interpreted to represent Paleozoic island-arc terranes. 

Likewise, Sr-Nd isotopic data from samples of the adjacent 

Wrangellia terrane indicated a largely juvenile, mantle-derived 

arc terrane with less than 6 percent Proterozoic crustal input 

(Samson and others, 1990).

In this chapter, we use several different radioactive 

decay schemes (U-Pb, Th-Pb, Rb-Sr, and Sm-Nd) to isotopically characterize in detail the host/source rocks of the 

Greens Creek ore deposit in order to better understand their 

petrotectonic derivation and provide a geologic framework and 

tectonic setting that produced sulfide deposition. Radiogenic 

isotopic signatures can further provide clues toward source(s) 

of ore-forming metals and fluids, helping to develop genetic 

ore deposit models and aid in the classification and prediction 

of known and potential deposits.

Geology

The geology at Greens Creek has been covered in detail 

in other chapters of this volume. Only a brief outline of the 

geology of the major host/source rocks that have been sampled 

is included here.

Greens Creek mine is 29 km south of Juneau, in the 

southeastern coastal region of Alaska, near the northern end 

of Admiralty Island (figs. 1 and 3). The deposit is located in 

an 800-km-long belt of volcano-sedimentary rocks interpreted 

to represent a rift-fill sequence formed during a brief period 

of intra-arc or back-arc rifting in latest Triassic time (Berg 

and others, 1972; Taylor, 1997; Taylor and others, 1995a, 

1995b, 1999, 2000). Stratigraphy within the belt consists of a 

200- to 800-m-thick sequence of conglomerates, limestones, 

marine clastic sediments, and tuffs that are intercalated with 

and overlain by a distinctive unit of mafic pyroclastics and pillowed flows (figs. 3 and 4). Faunal data bracket the age of the 

host rocks between early Carnian (early Late Triassic) and late 

Norian (late Late Triassic) time (fig. 4 and fig. 5, chap. 11).

At Greens Creek, the stratigraphy includes a Permianage, siliceous to cherty argillite in the upper part of the Cannery Formation that is unconformably overlain by a sequence 

of metabasalts of unknown age (fig. 4). These metabasalts are 

variably metamorphosed at greenschist to amphibolite grade 

and subsequently altered during hydrothermal metasomatism 

(for example, Newberry and others, 1990), resulting in several 

types of phyllitic rocks. Geochemical signatures of many 

of these phyllites are not conclusive but are consistent with 

basaltic protoliths, either as a rift-related basalt produced in 

an intra-arc setting or as a fairly unfractionated calc-alkaline 

basalt formed in an oceanic volcanic arc. The arc-related 

signatures probably could be indicative of variable amounts of 

assimilation of preexisting island-arc crust.

These metabasalts are unconformably overlain by a 

thin, discontinuous polymictic conglomerate (fig. 4). Such 

conglomerates are found throughout the southern and middle 

portions of the Upper Triassic volcano-sedimentary belt at 

the base of most sections, indicative of high-energy deposition in a near slope or basin margin setting. Although thin and 

discontinuous conglomerate horizons occur in the northern 

half of Admiralty Island, their stratigraphic positions within 
342 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

17.5 18.0 18.5 19.0 19.5

15.3

15.4

15.5

15.6

15.7

15.8

15.9

Mt. Henry

Clay

Depleted mantle

Greens

Creek

Orogene

Upper crust

D-M

D-M 0 Ma

400 Ma

pre-D

pre-D

800 Ma

SE Alaska

Late Proterozoic

K

K

Tertiary

Y&T

SSE Alaska

Devonian

Kuiu

Tertiary

SE Alaska-LateTriassic

modern oceanic

hydrothermal

systems

206Pb/204Pb

207Pb/204Pb

ALASKAN VMS OCCURRENCES

d

d

d

h Pyrola

Figure 2. 206Pb/204Pb – 207Pb/204Pb correlation diagram showing the distribution of lead isotopic compositions (fields) for Alaskan 

volcanogenic massive sulfide (VMS) occurrences compared to model lead evolution curves (“upper crust,” “orogene,” and 

“depleted mantle”) of Zartman and Doe (1981). Greens Creek ore compositions lie near other Late Triassic deposits such as Pyrola, 

Kuiu, and Mt. Henry Clay (modified from Newberry and others, 1997), at model lead ages (isochrons shown as bold dashed lines) 

younger than the actual age of mineralization (separated by lighter dashed lines and labeled; D = Devonian, D-M = Devonian to 

Mississippian, h = Pennsylvanian, d = Triassic, K = Cretaceous). Y & T indicates the location of lead isotopic results from ores of the 

Yukon-Tanana/Taku terrane.
Geology 343

Greens Creek

Windfall Harbor

Pyrola

deposit

Juneau

Thane

Douglas

Auke Bay

Tee Harbor

Baranof

Chatham Angoon

Kake

Chicagof 

Island

Baranof

Island

Kupreanof

Island

Hawk

 Inlet

Passage

Seymour Canal

Stephens

Chatham Strait fault

G

A

G

N

Staunch Point

Quaternary surficial sediments

EXPLANATION

Tertiary volcanic rocks 

Tertiary sedimentary rocks 

Cretaceous granitoids 

Cretaceous ultramafic rocks 

Cretaceous-Jurassic sedimentary

 rocks

Cretaceous-Jurassic volcanic and

 sedimentary rocks

Cretaceous-Jurassic volcanic rocks

Triassic-Permian sedimentary and

 volcanic rocks, undifferentiated 

Triassic-Ordovician sedimentary and

 volcanic rocks, undifferentiated 

Triassic-Ordovician carbonate rocks,

 undifferentiated.

Permian sedimentary rocks

Permian carbonate rocks

Devonian-Silurian carbonate rocks

Silurian sedimentary rocks

Silurian-Ordovician sedimentary rocks

Other rocks

Major fault

Inferred fault trace

Terrane boundary

0 25 KILOMETERS

Qs

KJs

KJsv

KJv

TrPsv

TrOsv

TrOc

Ps

DSc

Ss

SOs

Pc

Kum

Tv

Ts

Kg

Gambier

Bay

TrOc

Area of

figure 5

Funter

DSc

Glass Peninsula

Kum?

Mansfield Peninsula

Figure 3. Simplified geologic map of 

Admiralty Island, showing locations for 

Greens Creek and Pyrola deposits, Gambier 

Bay, Windfall Harbor, the Mansfield 

Peninsula, and Staunch Point (locations 

of some whole-rock samples. Bold dotted 

line is approximate boundary between the 

Alexander (A) and Gravina (G) terranes 

(after mapping by Gehrels and Berg, 1992).
344 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

the Triassic stratigraphy are uncertain and in most cases are 

thought to be above the base of the section within the shales 

that compose the middle sedimentary portion of the Triassic 

stratigraphy. The northernmost occurrence of a conglomerate 

“marker horizon” at the base of the section is on the eastern 

shore of Windfall Harbor (fig. 3) immediately overlying the 

siliceous black shales of the Cannery Formation.

Thin carbonate beds lie just below and intercalated with 

the capping Hyd Group basalts and are intercalated with the 

shales (argillites). North of Admiralty Island, limestones 

appear to be absent from the section.

Serpentinites are clearly produced by alteration of an 

ultramafic protolith and probably represent the shallow intrusive sources to the primitive basalt protoliths or to the overlying 

Hyd Group mafic volcanic flows. Many of these serpentinite 

bodies were probably cumulates left after extraction of mafic 

melts. These serpentinites crosscut the older metabasalt and 

phyllite sequences as well as the basal conglomerate horizon 

(figs. 3 and 4). Gabbro-clinopyroxenite, both relatively fresh 

and highly quartz-carbonate-fuchsite-altered serpentinite, is 

a common outcrop occurrence in the mine area. It is likely 

that the footwall phyllite pile originally consisted of a composite mafic-ultramafic collection of massive to volcaniclastic 

textured volcanics.

These mafic/ultramafic rocks are in turn overlain by 

massive and slaty graphitic, pyritic, black argillites and by 

carbonate-rich dolomitic massive and slaty argillites of the 

Hyd Group.

Continued emplacement of basaltic magmas at shallow 

levels account for the common occurrence of large gabbroic 

sills and stocks, particularly exposed along Gallagher Ridge, 

south of the mine (fig. 5), and followed by mafic flows of the 

overlying Hyd Group (fig. 4). Continued production of heat in 

the immediate footwall of the deposit would similarly account 

for the extreme alteration of the gabbro-basalt pile by driving a 

hydrothermal convection system.

Diabase dikes are observed to crosscut massive ore and 

are, at this point, not well understood. It is likely that these 

dikes are the product of Jurassic-Cretaceous resumption of 

island-arc volcanism. The fact that they crosscut ore and the 

overlying argillites and themselves are mineralized with a late, 

precious-metal-enriched mineral assemblage brackets their age 

between 220 Ma and the 105- to 90-Ma mid-greenschist facies 

regional metamorphism.

The Greens Creek massive sulfides are located at the 

contact between a footwall sequence of predominantly mafic 

volcanic rocks and mafic-ultramafic hypabyssal sills and intrusions, and a hanging wall of black argillites (figs. 4 and 6A). 

With increasing proximity to ore, footwall lithologies are dominated by chlorite-phyllites, sericite-phyllites, and silicified 

sericite-phyllites (fig. 6B). Footwall lithologies which have 

less consistent spatial distribution are serpentine-chlorite phyllites, mariposite-phyllites, and rarely, recognizable gabbros 

and post-ore diabase dikes. Hanging-wall rocks are dominated 

by massive and slaty graphitic, pyritic, black argillites and by 

carbonate-rich dolomitic massive and slaty argillites. Three 

Unconformity

Unconformity

Conodonts

Conodonts

Macrofossils

Macrofossils

Greenstones/phyllites

Polymictic conglomerate Gabbroic dikes/sills

Limestone/dolomite

Siliceous/cherty argillite

 (Cannery Fm.)

Pillow/massive basalt

 (Hyd Group)

Stratiform massive sulfide

Serpentinite

Pyritic-graphitic argillite

 (Hyd Group)

EXPLANATION

Greens Creek Stratigraphic Section

Carnian

Norian

Upper

Triassic

Hyd Group

Permian

Cannery(?) Fm.

Figure 4. Stratigraphy of the Greens Creek section, Admiralty 

Island, showing the orebody at the contact between footwall 

phyllites and hanging-wall argillites (after Taylor and others, 

2000).
82

79

80

52

53

54

57

18

28

22

19

23

25

East Lil Sore

Lil Sore

Upper

Zinc Ck

Mammoth

BruinKnob

Gallagher Ridge

GREENS

CREEK

MINE

Big

Sore High

Sore

39

48 46

51

29

30

36

32

59

5860 64

67

1 2

9

69

71

72

76

78

10

11 17

Mariposite Ridge

Ard-03

Brd-04

GST

97-ADM-29 97-ADM-34

PF-09

and PF-18

NADT4-2

Lakes

 District

1 .5 0 1 2 3 4 5 6 7 KILOMETERS

SCALE 1:63 360

1 1/2 0 1 2 3 4 5 MILES

3000 0 3000 6000 9000 12000 15000 18000 21000 24000 27000 FEET

ALASKA

QUADRANGLE LOCATION
346 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

major contiguous orebodies lie along a single horizon marked 

by a footwall greenschist and a hanging wall composed of 

graphitic, pyritic, black argillite. Ores are zoned from silica-, 

carbonate-, and barite-rich white ores against the footwall, to 

massive pyritic, and then to base-metal-rich massive sulfiderich ores against the hanging wall (fig. 6).

Sampling

Ore deposits form from mineralizing fluids that have 

passed through a sequence of rocks and therefore have had 

some contact with various lithologies of differing geochemical 

signatures and isotopic compositions. The result is very likely 

a mixture of several components. Geochemical and isotopic 

data for the host/source rocks are therefore critical toward a 

clear interpretation of the isotopic signature of the ore. In addition, identification of multiple fluids and ore-forming stages 

can be crucial to evaluating the isotopic information.

Certain geologic conditions can unequally disrupt the 

stability and therefore the reliability of isotopic results. For 

example, elemental mobility through alteration and(or) metamorphism, can fractionate parent-daughter ratios and disturb the 

isotopic systematics. In general, a hierarchy of stability during 

metamorphism is recognized: Sm-Nd > U-Pb > Rb-Sr; however, 

extreme alteration can greatly affect any of the systematics.

Consequently, radiogenic isotopic systematics of altered 

rocks are often disturbed, yielding results that are not easily 

interpretable — interpretations that are necessary for distinguishing between syndepositional, tectonic, magmatic, or 

hydrothermal processes. Therefore, careful sampling of both 

ore and host/source rock is a critical aspect for the successful 

use of radiogenic isotopic systems on ore deposits.

With these possible difficulties in mind, only the best preserved and most representative samples (listed in table 3, chap. 

11) were carefully selected from several hundred other samples 

for this multisystematic isotopic analysis. U-Th-Pb, Rb-Sr, and 

Sm-Nd isotopic data from whole-rock powders and mineral 

separates were collected from Greens Creek host rocks and 

related units that include (1) a variety of argillites, both from 

the Cannery Formation and the Hyd Group, collected from 

inside and outside the mine; (2) various metabasalts including 

some from the Gambier Bay Formation and the Hyd Group; (3) 

various metagabbroic to ultramafic intrusives (serpentinites) of 

Late Triassic age, some perhaps slightly older or younger; (4) 

associated chloritic to sericitic phyllites that probably represent 

altered mafic volcanic rocks (Newberry and others, 1990), collected from inside and outside the mine proper; and (5) several 

crosscutting diabasic to dioritic intrusives of unknown age.

Figure 6. (A) Geologic cross section, Greens Creek mine. Courtesy of T. Hall, senior mine geologist, 

Kennecott Greens Creek Mining Co., 1995. VMS = volcanogenic massive sulfide (after Newberry 

and others, 1997), showing the orebody at the contact between footwall phyllites and hanging-wall 

argillites. Locations are shown for East, West, and the Southwest orebodies where samples of 

sulfides, host rocks, and alteration minerals for Ar–Ar work were collected.

A
Results 347

Figure 6. (B) Predeformation, cross-sectional model, Greens Creek deposit, based on drill-core 

logging and underground and surface mapping (Rainer Newberry, unpub. mapping, 1985–1994; 

after Newberry and others, 1997), again showing the orebody (mainly MB and MP) at the contact 

between footwall phyllites and hanging-wall argillites, but also the distribution and relationship 

of several types of footwall phyllites within the alteration zone of the mine area (see table 3 in 

chapter 11 for whole-rock sample designations).

B

Surface sampling sites around the Greens Creek mine are 

shown in figure 5; mine sample locations are more problematic and are simply stated in table 3 in chapter 11. Locations 

of samples from other parts of Admiralty Island are not shown 

but generally given in table 3, chapter 11, by their geographic 

location (for example, Gambier Bay, Pyrola, Staunch Point). 

Also, for the full names of samples used for whole-rock isotopic work, the reader is directed to tables 3 through 6, chapter 

11, as many of the sample names have been shortened in this 

text and in the figures by removing the front numbers corresponding to their year of collection (for example, LG-71 in the 

text is actually 97–LG-71 in the tables).

Results

The data were produced in order to calculate initial 

Pb-Sr-Nd isotopic compositions that can be compared with 

known, time-integrated, isotopic fields from different petrotectonic environments. This exercise is intended to delineate 

the geologic framework and tectonic setting in which Greens 

Creek and possibly other VMS deposits of southeastern 

Alaska were formed as well as to contribute to the growing 

isotopic database for such rocks for use in the scientific community at large. The U-Pb, Rb-Sr, and Sm-Nd isotopic data are 

given in tables 4 through 6 in chapter 11, where the same data 

were evaluated for geochronologic purposes.

The analytical techniques used for the simultaneous, 

single-dissolution of U-Th-Pb, Rb-Sr, and Sm-Nd analysis 

on whole-rock and mineral separates were similar to those 

reported by Tatsumoto and Unruh (1976) and Premo and Tatsumoto (1991, 1992) and are given in detail in chapter 11.

Degree of Stability of the Isotopic Systematics

There is some concern as to whether the isotopic systematics of these whole rocks, which have certainly been altered 

to some degree (table 3 in chap. 11), have remained stable or 

undisturbed. The processes of alteration involve mobilization 

of certain elements, and it is probable that elemental concentrations as well as their corresponding Pb-Sr-Nd isotopic 

compositions are to some degree disturbed in some samples. 

However, we expect that the Sm-Nd systematics are less 

affected than the more mobile and volatile Rb-Sr and U-Pb 

systematics (for example, Whitehouse, 1988; Barovich and 

Patchett, 1992).

There is no way to absolutely ascertain to what degree 

any particular isotopic system is undisturbed or overprinted 

without fresh, unaltered samples to compare. However, we 

expect that varying degrees of alteration should reflect the 
348 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

relative stability of their isotopic systematics. For example, 

the least-altered samples are the Hyd Group metabasalts from 

Gambier Bay (fig. 3) and their isotopic systematics are arguably the best preserved and are used to construct several isochron ages (chap. 11). In contrast, the isotopic systematics of 

highly altered serpentinites vary widely, and little confidence 

can be held for these results.

In an attempt to evaluate the degree of isotopic disturbance, uranium concentration in parts per million (ppm) is 

plotted against calculated initial 206Pb/204Pb values at 215 Ma 

(taken to be an average estimate of the age of the host-rock 

strata at Greens Creek; chap. 11) and Rb (ppm) against calculated initial 87Sr/86Sr values (fig. 7). Because we have defined 

an isochron age of 218 ± 16 Ma and initial 206Pb/204Pb value of 

18.515 for the Hyd Group metabasalts (chap. 11), this value is 

taken to represent the Greens Creek host-rock initial lead signature to which all other initial values can be compared (fig. 

7A). In addition, the majority of sulfide lead (mainly galena) 

from the Greens Creek deposit defines a 206Pb/204Pb isotopic 

composition of 18.64 ± 0.01 that we interpret to represent that 

of the mineralizing fluid that probably altered many of the 

host rocks. Therefore, samples that yielded initial 206Pb/204Pb 

values outside of the 18.515 to 18.640 range are suspected of 

either having some subsequent open-system isotopic disturbance or derivation from a distinctly different isotopic source. 

In some cases, the calculated initial 206Pb/204Pb values are 

unreasonably low such that the addition of uranium or loss of 

lead during subsequent alteration is suspected (for example, 

LG-71 and ADM-01; fig. 7A). In some other cases where the 

calculated initial 206Pb/204Pb values are significantly higher 

than 18.64, the addition of lead with a more radiogenic composition is suspected. This situation is reasonable as nearby 

Cretaceous-Tertiary ore 206Pb/204Pb signatures are between 

19.1 and 19.5 (discussed herein and also in chapter 10) and 

certainly could have been involved in a partial resetting of the 

lead isotopic composition of some lithologies (for example, 

some Hyd Group argillites and sample GST; fig. 7A).

A similar situation can be made in the case of rubidium 

concentration (ppm) versus calculated initial 87Sr/86Sr values 

(fig. 7B). The majority of least-altered mafic samples (for 

example, Hyd Group metabasalts and metagabbros at Gallagher Ridge) define a range of initial 87Sr/86Sr values between 

0.7038 to 0.7048 that we tentatively regard as the range of the 

original Greens Creek host-rock initial strontium composition. And all other samples that yielded initial strontium values 

outside that range, we suspect either have had some subsequent 

open-system isotopic disturbance or derivation from a distinctly 

different isotopic source. For example, samples PF-09 and 

ADM-34 yielded unreasonably low calculated initial 87Sr/86Sr 

values (less than 0.7023) and are therefore suspected of having 

secondary rubidium added during alteration (fig. 7B). This suspicion is reasonable as sericitization would involve alteration 

to micaceous minerals with the addition of potassium (K) and 

Rb. Other samples with “low” calculated initial 87Sr/86Sr values 

(less than 0.7038) may have had secondary rubidium added 

to lesser degrees. In cases where the calculated initial 87Sr/86Sr 

values are significantly higher than about 0.7048, the addition 

of secondary radiogenic strontium is suspected. A likely source 

for this secondary radiogenic strontium would be seawater 

alteration at just about any time after formation as all seawater 

strontium isotopic compositions from the Triassic to the present have been more radiogenic than 0.7065 (Burke and others, 

1982; Hess and others, 1986).

In another evaluation of possible alteration or contamination of some of these samples by subsequent elemental and 

isotopic exchange, calculated initial 206Pb/204Pb and 87Sr/86Sr 

values are plotted against calculated initial εNd values at 90 

Ma (fig. 8). This age corresponds to average ages defined by 

isochrons from the same isotopic data and similar to Ar-Ar 

isotopic data from sericite and fuchsite (chap. 11), and the 

age therefore represents a very likely time that some of the 

isotopic systems were disturbed. In figure 8A, nearly 6 of 

10 argillitic and 3 of 8 metagabbroic samples yielded initial 

206Pb/204Pb values at 90 Ma between 19.1 and 19.55, values 

that are very similar to lead isotopic compositions of Cretaceous to early Tertiary age, southeastern Alaskan ore deposits (for example, Alaska-Juneau, Ascension, Ground Hog, 

Perseverance, Trokna Silver, and Glacier Basin; Gaccetta and 

Church, 1989). These values are also very similar to those 

measured on the Cretaceous-Tertiary, arc-related, Valdez 

and Orca Group argillites and phyllites of southern Alaska 

(Farmer and others, 1993).

The suggestion here is that a Cretaceous-Tertiary lead 

signature may have overprinted several samples of argillite 

(ADM-29, Ard-03, PP–204-01, and Brd-04) and(or) gabbro 

(GST, LG-69, LG-82) during the already established Cretaceous 

accretionary event at ca. 115 to 90 Ma (for example, Rubin and 

Figure 7 (facing page). (A) Plot of uranium (U) concentration 

versus calculated initial 206Pb/204Pb at 215 Ma for whole-rock 

analyses of major Greens Creek host rocks, illustrating the 

possible isotopic disturbance of some whole-rock samples, 

probably during alteration. The expected range of initial 

206Pb/204Pb values is between 18.515 (Hyd Group metabasalt 

initial lead (Pb) and 18.64 (Greens Creek ore lead signature). All 

samples outside of this range are either isotopically disturbed or 

derived from distinctly different source(s). (B) Plot of rubidium 

(Rb) concentration versus calculated initial 87Sr/86Sr at 215 Ma for 

whole-rock analyses of major Greens Creek host rocks. Similar to 

the lead results, these strontium results possibly indicate isotopic 

disturbance within some whole-rock samples. The expected 

range of initial 87Sr/86Sr values is indicated by the least altered 

or best preserved Hyd Group metabasalts that indicate values 

between 0.7041 and 0.7049, and all samples with initial 87Sr/86Sr 

values outside this range are either isotopically disturbed or 

derived from distinctly different source(s). Ma, mega-annum. See 

text for further discussion.
Results 349

.

18.2

0 1 2 3

18.4

18.6

18.8

19.0

19.2

19.4

Hyd Gp

Argillites

 ADM-59

Cretaceous-Tertiary ore Pb signature

Hyd Group metabasalt

initial Pb signature (chap. 11)

GST

Cannery Fm

Argillites

LG-32

Greens Creek ore Pb

signature (chap. 10)

U gain or Pb loss

Pb gain or U loss

0.701

0 10 20 30 40 50 60

0.703

0.705

0.707

"Real" initial Sr

at 215 Ma?

Rb gain or Sr loss

Sr gain or Rb loss

GB-55

ADM-01

LG-17

GB-80

ADM-29

ADM-59

GC-1136-05 PP-204-01

GC-1136-53

GC-1103-16

LG-32

GB-24

PF-18

LG-19

LG-20

GC-1136-59

PF-09

GC-1637-44

ADM-34

LG-71

ADM-01

GC-462-02-2

GC-462-02 LG-82-2

LG-19

LG-20

Ard-03

PP-204-01-1

LG-66

Brd-04

GB-24

LG-82-2

Hyd Group basalts

Gambier Bay metabasalts

other mafic rocks

phyllites

gabbros

Hyd Group argillite

Cannery Fm argillite

serpentinite

EXPLANATION

Calculated initial Sr

values at 215 Ma

B

Rb (ppm)

U (ppm)

Calculated initial Pb

values at 215 Ma

Apparent Initial 206Pb/204Pb

A

Apparent Initial 87Sr/86Sr

Cretaceous Sr signature

at 90 Ma
350 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

others, 1990; Rubin and Saleeby, 1992), although alteration 

at any time after emplacement of these rock sequences may 

contribute to a disturbance of the U-Pb isotopic systematics. All 

of these samples yielded calculated 206Pb/204Pb values at 215 Ma 

outside the expected range of values (fig. 7A).

Another point of interest, six of nine phyllites and 

several other mafic samples exhibit calculated 206Pb/204Pb 

values at 90 Ma that are similar to the Greens Creek ore lead 

signature (fig. 8A), suggesting that the lead isotopic compositions of these samples had been overprinted during the 

Cretaceous. However, many of the better-preserved samples 

(for example, Hyd Group metabasalts and some metagabbros) 

yielded expected initial 206Pb/204Pb values at 215 Ma and keep 

a tight cluster through time (fig. 8), lending confidence to 

these whole-rock isotopic data.

Similar to initial 206Pb/204Pb values suggestive of Cretaceous resetting, initial 87Sr/86Sr isotopic compositions for 

several argillites, phyllites, and serpentinites at 90 Ma (fig. 8B) 

are similar to the range of Late Cretaceous seawater strontium 

isotopic compositions (about 0.7074; Burke and others, 1982; 

Hess and others, 1986). Metagabbros, metabasalts, and other 

mafic samples appear relatively stable with initial 87Sr/86Sr 

values between 0.703 and 0.706, but initial strontium values 

for serpentinites, phyllites, and argillites vary widely, some 

remaining similar to those of the igneous suite, and others 

enriched with values near or at the Cretaceous-Tertiary seawater signature at about 90 Ma (fig. 8B). It may be coincidence 

that several are similar to this seawater value, but the variation 

would suggest some disturbance to the strontium isotopic systematics, perhaps due to Rb/Sr fractionations during alteration.

Sm-Nd isotopic systematics can be compared between 

lithologies and their differences evaluated — caused largely 

due to source differences and not because of alteration or age 

effects. Stability of the Sm-Nd isotopic system for some of 

the better-preserved samples appears to be good (fig. 9, chap. 

11), and due to a fortunate spread in parent-daughter ratios, 

isochrons can be fitted to some of the analyses of two suites 

of samples. Four out of five Hyd Group metabasalt analyses 

define an apparent isochron age of 215 ± 95 Ma and four 

analyses from metagabbro samples LG-70 and LG-71 yielded 

an isochron age of 200 ± 27 Ma (chap. 11). Metagabbros and 

metabasalts have elevated 143Nd/144Nd (corresponding to initial 

εNd values of + 5.5 to 8) compared to coeval argillitic metasediments and most phyllites (less than 0.5128; initial εNd

= –2.5 to +4). Cannery Formation argillites yield uniform 

143Nd/144Nd values at about 0.51266 (initial εNd about +2.3) that 

contrast with Hyd Group argillites signatures (initial εNd about 

–5 to + 2.2). Serpentinites vary from very low 143Nd/144Nd (εNd

= –12.5; LG-32) to very high 143Nd/144Nd (εNd = +8.4; ADM59), indicating highly variable crustal to mantle source(s) 

for the ultramafic equivalents (fig. 9). However, because of 

very low Sm-Nd abundances in these samples, most of these 

isotopic analyses were obtained during low ion-beam intensity 

measurements that could produce results of questionable quality (see table 6, chap. 11). Therefore, the Sm-Nd isotopic differences in the serpentinites are regarded with skepticism and 

are included here for the sake of completeness and discussion 

in the event they may be accurate, though imprecise.

Because the Sm-Nd systematics were obtained from 

whole rocks, some associations can be made: (1) metabasalts 

GB-22, GB-42, and GB-80, and phyllite PF-18; (2) ADM01, AD-58, perhaps GB-59, and most of the metagabbros; 

(3) metabasalts GB-55, ADM-12, perhaps LG-17, phyllite 

GC-1637-44, and the serpentinite GC-1136-53; (4) phyllites 

GC-462-02, GC 462-07, and PF-09 with argillites PP-204-

01, LG-78, ADM-29, ADM-34, NAD T4-2, and serpentinite 

LG-19; and (5) argillites Ard-03, LG-75, and serpentinite 

LG-20. As will be discussed later, these Sm-Nd isotopic differences are largely indicative of source material such that low 

143Nd/144Nd compositions (and correspondingly low or negative εNd values) indicate contamination from an older, more 

enriched, crustal source, and that the progression of negative 

to positive εNd values may well indicate the evolution of a rifting event within the Alexander terrane.

Figure 8 (facing page). (A) A comparison of calculated initial 206Pb/204Pb versus initial εNd for whole rocks analyses from Greens 

Creek host rocks at 90 Ma. Because the Greens Creek section 

is known to have undergone at least greenschist metamorphism 

during the Cretaceous (ca. 115 to 90 Ma; Rubin and others, 1990; 

Rubin and Saleeby, 1992), initial Pb-Nd values were calculated 

back to 90 Ma for a comparison with known Late CretaceousTertiary ore lead compositions (for example, Gaccetta and Church, 

1989) and contemporaneous arc-related sediments (Farmer and 

others, 1993). Some whole-rock samples, particularly argillites 

and three metagabbros, have similar lead isotopic composition 

to Cretaceous-Tertiary ore deposits at 90 Ma, suggesting the 

possibility that these samples were overprinted by this lead 

isotopic composition. It could also be coincidence, although all 

other whole-rock samples do not plot near this composition at 90 

Ma with the possible exception of metabasalt, GB-24. Pb, lead; 

Nd, neodymium; Ma, mega-annum; CHUR, chondritic uniform 

reservoir. (B) A comparison of initial 87Sr/86Sr versus initial εNd

for whole rocks analyses from Greens Creek host rocks at 90 

Ma. Again, because the Greens Creek section is known to 

have undergone at least greenschist metamorphism during the 

Cretaceous (ca. 115 to 90 Ma; Rubin and others, 1990; Rubin and 

Saleeby, 1992), initial Sr-Nd values were calculated back to 90 Ma 

for a comparison with known Late Cretaceous-Tertiary seawater 

strontium compositions (for example, Burke and others, 1982; 

Hess and others, 1986). Again, some argillites (but not the same 

argillites), two phyllites, and two serpentinites appear to have 

possibly been affected or overprinted by Cretaceous-Tertiary 

seawater strontium. This observation may only be coincidence. 

However, in general, only relatively high Rb/Sr rocks show any 

appreciable variation between 215 and 90 Ma, and these rocks 

are mostly argillites and phyllites that contain a greater proportion 

of micaceous minerals. Sr, strontium; Nd, neodymium; Ma, megaannum; CHUR, chondritic uniform reservoir.
Results 351

–14

–10

–6

–2

6

10

2

CretaceousTertiary

ore Pb

CHUR

LG-32

GST, LG-69 and 82

Hyd Gp

argillites

ADM-59 GB-24 Diorites

LG-19

LG-20

Footwall

phyllites

Metagabbros

Hyd Group

metabasalts

Greens Creek

ore Pb signature

(chap. 12)

Cannery Fm

argillites

 PP-204-01

 Ard-03

 Brd-04

 ADM-29

Cretaceous

seawater

Nd signature

PP-204

LG-75 LG-66

–14

0.700 0.702 0.704 0.706 0.708 0.710

–10

–6

–2

2

6

10

Late Cretaceous

seawater

Sr signature

CHUR

ADM-59

GC 1136-53

Hyd Gp

argillites

LG-20

LG-19

Metagabbros

Hyd Group

metabasalts

Cannery Fm

argillites

Cretaceous

seawater

Nd signature

LG-32

LG-66

18.2 18.4 18.6 18.8 19.0 19.2 19.4 19.6

Hyd Group basalts

Gambier Bay metabasalts

other mafic rocks

phyllites

gabbros

Hyd Group argillite

Cannery Fm argillite

serpentinite

EXPLANATION

B

Initial 87Sr/86Sr

Initial 206Pb/204Pb

Initial values

at 90 Ma

Initial 

εNd Initial 

εNd

A

Initial values

at 90 Ma
352 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Initial Lead, Strontium, and Neodymium Isotopic 

Systematics of Greens Creek Host-Rock 

Lithologies

In figures 10 and 11, initial lead isotopic values (calculated at 215 Ma, Hyd Group metabasalt age) for Greens 

Creek host rocks are compared to model lead compositions 

from several major, planet-scale, lead reservoirs (Zartman 

and Doe, 1981). The lead isotopic evolution of these lead 

reservoirs is illustrated by separate curves emanating from a 

much older reservoir (ca. 4,000 Ma) that underwent planetscale U/Pb fractionations. Average isotopic compositions 

of these separate lead reservoirs over the Phanerozoic are 

labeled “depleted mantle,” “orogene,” “lower crust,” and 

“upper crust.” Readers should bear in mind that these curves 

represent the path of average values and do not convey the 

ranges of values that are possible for these reservoirs. Also, 

the “upper crust” curve is defined from mostly Phanerozoic 

data, such that lead from much older (for example, Archean 

to Proterozoic) crustal sources could be considerably more 

radiogenic with much higher 207Pb/204Pb values at equal 206Pb/204Pb compositions. Readers are referred to Dickin 

(1995) for a more detailed discussion of the U-Pb evolution 

of the Earth and its major reservoirs.

Important advantages can be found in the correlation of the 

two U-Pb decay schemes; one, they are geochemically similar, 

eliminating any effects due to natural fractionation processes; and 

two, their decay constants are different enough to cause a pronounced nonlinear correlation between them, and greater separation and distinction of their lead evolution curves (fig. 10). The 

0.5117

0.5119

0.5121

0.5123

0.5125

0.5127

0.5129

0.5131

LG-32

GB-22-2 ADM-59

LG-19

LG-20

 Ard-03

 Brd-04

GC-1136-53

LG-66

LG-70

LG-75

GC-1136-05

PF-09

GB-80

GB-42

Hyd Group metabasalts

Metagabbros

Argillites and

most phyllites

Serpentinites

GB-55

GB-59

PF-18

LG-82-2 ADM-01

and AD-58

GC-462-07

PF-18

0.08 0.12 0.16 0.20 0.24

Hyd Group basalts

Gambier Bay metabasalts

other mafic rocks

phyllites

gabbros

Hyd Group argillite

Cannery Fm argillite

serpentinite

EXPLANATION

147Sm/144Nd

143Nd/144Nd

Age = 215 ± 95 Ma

Initial 143Nd/144Nd = 0.51274 ± 0.00010

MSWD = 0.18

Hyd Group metabasalts

Age = 200 ± 27 Ma

Initial 143Nd/144Nd = 0.512664 ± 0.000034

MSWD = 1.11

Gallagher Ridge

metagabbros LG-70 and 71

Figure 9. A comparision of the samarium-neodymium isotopic systematics of Greens Creek host rocks to Hyd Group metabasalt 

and Gallagher Ridge metagabbro isochrons, showing the extent of isotopic stability or variation within the different lithologic units. 

Argillites and phyllites are significantly more enriched than the metabasalt and metagabbro suites, indicating older crustal input 

or subsequent alteration. Serpentinites are conspicuously different, initial εNd ranging from +8 (ADM-29) to –12 (LG-32), indicating 

distinctly different sources, probably at significantly different ages. MSWD, mean square of weighted deviates.
Results 353

15.3

15.4

15.5

15.6

15.7

15.9

15.8

Orogene

Upper Crust

Depleted mantle

Hyd Group

argillites

0 Ma

Hyd Group

metabasalts

ADM-59

GST

GB-24

800 Ma

400 Ma

15.6

Cannery Fm

argillites

LG-19

GC-462-02

GC 462-07

LG-71

Metagabbros

ADM-01

Initial 206Pb/204Pb

Greens Creek host rock

initial Pb values

All initials

at 215 Ma

17.4 17.8 18.2 18.6 19.0 19.4

Initial 207Pb/204Pb

Hyd Group basalts

Gambier Bay metabasalts

other mafic rocks

phyllites

gabbros

Hyd Group argillite

Cannery Fm argillite

serpentinite

EXPLANATION

Typical

analytical

uncertainty

Figure 10. Pb-Pb correlation diagram (206Pb/204Pb versus 207Pb/204Pb) showing the distribution of initial Pb compositions of Greens 

Creek host rocks relative to model lead evolution curves and fields for modern petrotectonic environments (Zartman, 1984). Most

mafic lithologies have initial lead values (at 215 Ma) between the “orogene” and “depleted mantle” curves, however, plotting at 

younger model lead ages (dashed isochrons). Scatter in the isotopic data may be due to postemplacement U-Pb fractionations 

caused by either low-grade metamorphism or subsequent alteration, particularly within the metagabbros. The field defined 

by metabasalts, largely those of the Hyd Group, is more discrete (less variation), plotting midway between the “orogene” and 

“depleted mantle” curves. Their altered equivalents, the phyllites plot just to the left, implying slight U-Pb fractionations during 

alteration. Argillites also define a wide field (see text for discussion) but basically plot at or near the “orogene” and trending 

toward the “upper crust” curve, suggesting some older, more radiogenic crustal input.

advantage is that evaluation of lead isotopic data in comparison 

to them is more definitive. Henceforth, lead isotopic data from 

Greens Creek will be displayed and discussed mainly using the 

206Pb/204Pb – 207Pb/204Pb correlation diagram.

Notably, all fields of initial 206Pb/204Pb – 207Pb/204Pb values 

at 215 Ma for Greens Creek host rocks do not plot on model 

lead compositions at the 200-Ma isochron (fig. 10). Nearly all of 

these initial lead values plot beyond — to younger model ages, 

indicating derivation from sources more enriched than average 

model reservoirs — and cluster nearer to the orogene curve than 

to either of the other two curves. This lead isotopic behavior 

is not unusual for arc-related VMS deposits, as pointed out by 

Newberry and others (1997), and discussed further by Kerrick 

(1991) and Dickin (1995).

Also, there are profound differences between the 206Pb/204Pb – 207Pb/204Pb correlation (U-derived only) and the 206Pb/204Pb – 208Pb/204Pb correlation (or lack thereof). In figure 

11, model lead evolution curves for “mantle,” “orogene,” and 

“upper crust” are subparallel and adjacent such that initial 

206Pb/204Pb – 208Pb/204Pb signatures from Greens Creek host 
354 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

rocks overlap both the upper crust and the orogene model lead 

evolution curves. However, the data do mainly cluster about 

the upper-crust model lead curve, and are unlike lead signatures for either the lower crust or a depleted mantle.

Metabasalts

Although the lead contents in the metabasalts are more 

variable (2 to 12 ppm), the uranium contents are between 0.2 

and 1 ppm, and thorium between 0.5 and 3 ppm (table 4, chap. 

11) typical of modern-day basalts. Two exceptions, LG-17 

and GB-24, are much more depleted and exhibit uranium and 

thorium concentrations similar to ultramafic rocks and Greens 

Creek serpentinite.

The U-Pb isotopic data for the Hyd Group metabasalts 

define an apparent isochron age of 218 ± 16 Ma with initial leads value of 18.515 (fig. 11; chap. 11) that, while not 

very precise, lends confidence to their calculated initial lead 

signatures at 215 Ma. These metabasalts (and related phyllites 

– altered mafic volcanics) plot between average lead compositions for “orogene” and “mantle,” consistent with their derivation from mainly mantle sources (fig. 10) but probably in a 

volcanic arc setting (Zartman and Doe, 1981; Zartman, 1984). 

Initial lead values for the Hyd Group metabasalts (mainly from 

Gambier Bay; fig. 3) plot within the metagabbroic/ultramafic 

field, but in a much more discrete area, perhaps indicative of 

their higher degree of preservation and isotopic stability. A 

notable exception, two analyses of metabasalt GB-24 plot to 

37.0

37.4

37.8

38.2

38.6

39.0

39.4

39.8

Upper crust

Lower crust

200

0

400

400

Orogene

0

200

GB-24

ADM-59

GST

Argillites

Metagabbros, and

most phyllites and

serpentinites

200

0

Hyd Group

metabasalts

ADM-01

LG-71

GC-462-07

GC-462-02-2

LG-19-2

ADM-12

Depleted mantle

Hyd Group basalts

Gambier Bay metabasalts

other mafic rocks

phyllites

gabbros

Hyd Group argillite

Cannery Fm argillite

serpentinite

EXPLANATION

Initial 206Pb/204Pb

Greens Creek host rocks

All initials

at 215 Ma

17.4 17.8 18.2 18.6 19.0 19.4

Initial 208Pb/204Pb

Typical

analytical

uncertainty

Figure 11. Pb-Pb correlation diagram (206Pb/204Pb versus 208Pb/204Pb) showing the distribution of initial lead compositions of Greens 

Creek host rocks relative to model lead evolution curves and fields for modern petrotectonic environments (Zartman, 1984). Model 

lead evolution curves for “mantle,” “orogene,” and “upper crust” are subparallel and adjacent such that modern-day isotopic fields 

for petrotectonic environments (for example, OIB, MORB, IAB) overlap grossly. Initial lead signatures from Greens Creek host rocks 

unfortunately overlap two of the model lead evolution curves and therefore are not uniquely interpretable using these model lead 

discriminators.
Results 355

the right with a higher 206Pb/204Pb relative to the other Gambier 

Bay Formation metabasalt (figs. 10 and 11).

Rubidium and strontium concentrations in metabasalts 

vary widely and apparently are not correlated with degree of 

alteration or metamorphism (tables 3 and 6). Typical unaltered 

basalts have Rb contents around 30 ppm and relatively high 

Sr contents (about 450 ppm) due to their more calcic mineral 

assemblages. Greens Creek metabasalts have variable Rb (3 

– 41 ppm) and low average Sr (125 – 250 ppm) contents, indicating either derivation from a less mafic source or mobility 

during subsequent metamorphism and/or alteration. A metabasalt, GB-24, from the Gambier Bay Formation is altered and 

exhibits extremely depleted Rb-Sr contents, similar to serpentinites. Two other metabasalts, GB-42 and GB-55, have high 

Sr contents (540 – 700 ppm). High Sr contents (>600 ppm) are 

indicative of carbonates.

Samarium and neodymium contents from the metabasalts 

are much less scattered (2–5 ppm and 5–21 ppm, respectively; 

table 6 in chap. 11) and are typical of tholeiites, although 

slightly more enriched than MORB and less enriched than 

continental tholeiites (for example, Faure, 1986). Metabasalt, LG-17, from Gallagher Ridge (fig. 5) is highly altered 

and exhibits more depleted Sm-Nd contents (0.7 and 3 ppm, 

respectively).

Sm-Nd isotopic data for the Hyd Group metabasalts 

define an apparent isochron age of 215 ± 95 Ma (fig. 12, chap. 

11) and, while not very precise, they do indicate that calculated initial neodymium signatures at 215 Ma are accurate. 

The Rb-Sr isotopic data for the same suite of Hyd Group 

metabasalts are not as well defined, but two separate arrays 

indicate ages at about 190 to 170 Ma but with slightly different initial strontium values of 0.7041 and 0.7049 (fig. 13; 

chap. 11). Therefore, their calculated intial strontium values 

are probably slightly lower than they should be. However, 

this small difference does not alter any of our interpretations 

regarding the Rb-Sr isotopic systematics for these metabasalts.

With respect to their Nd-Sr isotopic systematics, the 

metabasalts can be subdivided into at least two groups: a 

high-Nd (εNd = +7 to 9) group that includes most Hyd Group 

metabasalts from Gambier Bay, southeastern Admiralty Island 

(fig. 3), and a lower-Nd (εNd = +4 to 5) group (fig. 12). Some 

of the high-Nd metabasalts exhibit low-Sr values (for example, 

GB-42; 87Sr/86Sri

 about 0.704), whereas, others have more 

elevated Sr values (87Sr/86Sri

 = 0.7049 to 0.7056), possibly due 

to alteration. Samples GB-24 and GB-80 are in this category. 

Lower Nd and lower Sr values (εNd = +4 to 5, and 87Sr/86Sri

 = 

0.07038, respectively) are exemplified by sample GB-55, a 

chloritized greenstone from the Gambier Bay Formation at 

Gambier Bay, and a similarly lower-Nd metabasalt, GB-59, 

has an elevated Sr value (87Sr/86Sri

 about 0.7043). Other lowerNd metabasalts include LG-17 from Gallagher Ridge (εNd = 

+5) and ADM-12 (εNd = +4.3) from Staunch Point (fig. 3). 

Although this last sample is described as a microgabbro (table 

3), it is highly altered and could have a basaltic protolith.

All of the metabasalt data lie well within the modern 

“island arc” field with elevated 87Sr/86Sr relative to OIB or 

MORB (fig. 12). Time-corrected values (at 215 Ma) for the 

OIB and MORB fields plot slightly farther to the left in the 

diagram, enhancing the difference between initial Nd-Sr 

values for Greens Creek samples and those for different petrotectonic environments at 215 Ma.

A comparison of initial neodymium and lead (fig. 13) for 

Greens Creek metabasalts is even more discrete than that for 

Nd-Sr initial signatures. Lower-Nd metabasalts are also characterized by slightly higher average initial 206Pb/204Pb values 

than the more depleted, high-Nd metabasalts. Elevated initial 

206Pb/204Pb values relative to MORB and OIB like 87Sr/86Sr 

are indicative of some modern oceanic island arc settings (for 

example, Ellam and Hawkesworth, 1988; Ben Othman and 

others, 1989). Again, metabasalt GB-24 is notably an outlier 

with a significantly higher initial 206Pb/204Pb value similar to 

serpentinite, ADM-59 (fig. 13).

Metagabbros

Metagabbro lead contents are depleted (less than 1 

ppm) relative to metabasalt values, as are uranium contents 

(0.08–0.5 ppm) and thorium (0.25–2.5 ppm). All of these 

concentrations are at least half as depleted relative to typical, 

modern-day values for gabbro (for example, Faure, 1986). 

Th/U ratios are relatively uniform at about 3.3; a highly 

altered, massive microgabbro, LG-45, is the only exception.

The U-Pb isotopic data for the metagabbro data define 

an apparent isochron age of 206 ± 35 Ma indicating an initial 

206Pb/204Pb value of 18.61 (fig. 14; chap. 11) and again, while 

not very precise, these results do lend confidence in the calculated initial lead signatures at 215 Ma for these metagabbros.

The wide array of initial Pb values for metagabbros and 

serpentinites more than likely represents slight, yet significant 

U/Pb fractionations since their emplacement and crystallization. It should be noted, however, that average composition(s) 

for metagabbroic-serpentinitic magmatic source(s) are very 

similar to those for metabasalts and phyllites and lie between 

the “mantle” and “orogene” averages (fig. 10), again indicative 

of their partial derivation from a depleted mantle source.

Rb-Sr contents for the metagabbros (0.5–23 and 120–330 

ppm, respectively) are lower and less scattered than those for 

the metabasalts, and most lie along a Rb/Sr trend of about 

0.01; the highly altered metagabbros, LG-45 and LG-71, are 

the only exceptions. Samarium and neodymium concentrations 

(1–4.5 and 3–16 ppm, respectively), like Rb-Sr, are on average 

lower than those for metabasalts and more similar to typical 

average modern-day MORB concentrations.

Sm-Nd isotopic data for the Greens Creek metagabbros 

define an apparent isochron age of 200 ± 27 Ma (fig. 15; chap. 

11) and, while not very precise, they do indicate that calculated initial neodymium signatures at 215 Ma are accurate.

Metagabbros plot between the two groups of metabasalt 

(figs. 12 and 13) with initial εNd = +5 to 7, initial 87Sr/86Sr = 

0.07037 to 0.7048, and initial 206Pb/204Pb = 18.45 to 18.66, 

slightly more depleted than the lower-Nd metabasalts and 

slightly more enriched than the high-Nd metabasalts.
356 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Initial Sr and Nd values (at 215 Ma) for mafic igneous 

rocks from Greens Creek have higher εNd (+4 to +9) and 

lower 87Sr/86Sr (0.7035 to 0.7058) than phyllites and argillites, values indicating mainly mantle derivation (fig. 12). 

All samples are enriched in 87Sr/86Sr and 206Pb/204Pb compared to MORB (mid-ocean ridge basalt) or OIB (oceanic 

island basalt), a characteristic indicative of island arc rocks 

(Hawkesworth and others, 1977, 1979; Zartman, 1984; 

Ellam and Hawkesworth, 1988; Ben Othman and others, 

1989). Metagabbro LG-71 and metabasalt ADM-01 plot to 

the left with unusually low 206Pb/204Pb values of about 18.27 

(fig. 13). We suspect that the U-Th-Pb isotopic systematics 

from these whole-rock samples may be disturbed (fig. 7A), 

and caution is advised to the reader regarding some of these 

data.

Phyllites

Uranium, thorium, and lead concentrations for phyllites 

(0.1–2 ppm, 0.4–9.3 ppm, and 4–100 ppm, respectively) have 

a much broader range than the metabasalts, their less altered 

equivalents. On average, however, the phyllite concentrations are 

not significantly different. One sample, GC-462-02-2, produced 

an unusually high thorium concentration of 9.3 ppm; otherwise, 

thorium contents range between 0.4 and 2.4 ppm. Lead contents 

from two mine phyllites, GC-1103-16 and GC-1637-44, were 

uncharacteristically high (60 and 98 ppm, respectively); otherwise, the lead contents ranged between 4 and 13 ppm, almost 

exactly that of the metabasalts. Th/U ratios for phyllites are variable and typically have lower values than the main mafic trend of 

about 3.3 (with the exception of PF-18).

Hyd Grp

argillites

high-Nd

metabasalts

OIB trend

ADM-59

LG-32

modern

“island arc” field

LG-19-2

LG-20-2

GC-1136-53

–14

0.703 0.704 0.705 0.706 0.707 0.708

–10

–6

–2

6

10

2

PF-18

CHUR

MORB

Metagabbros

GB-55

GB-24

lower-Nd

mafic rocks

Hyd Group basalts

Gambier Bay metabasalts

other mafic rocks

phyllites

gabbros

Hyd Group argillite

Cannery Fm argillite

serpentinite

EXPLANATION

Initial 87Sr/86Sr

All WR initials

at 215 Ma

Typical

analytical

uncertainty

Initial 

εNd

Figure 12. Initial strontium versus initial neodymium correlation diagram showing the distribution of initial Sr-Nd 

values for Greens Creek host rocks relative to model Sr-Nd fields for modern petro-tectonic environments (for example, 

Zartman, 1984). Again, most initial Sr-Nd data for these host rocks plot between mid-ocean ridge basalt (MORB) and 

more enriched values, and mostly displaced to the right in the “island-arc” field relative to the oceanic-island basalt 

(OIB) trend. Serpentinite data vary widely. See text for more discussion. CHUR, chondritic uniform reservoir.
Results 357

The phyllites, interpreted as altered mafic volcanic rocks, 

exhibit initial Pb isotopic compositions similar to the meta-basalt 

and metagabbro initial Pb compositions (figs. 10 and 11), although 

more scatter is evident — an indication of U-Pb fractionations 

during subsequent alteration (fig. 11, chap. 11). Although the 

phyllites plot mostly within the metagabbro field, this field significantly overlaps fields for both the metabasalts and the argillites.

Rubidium and strontium concentrations vary somewhat 

(1–55 ppm and 26–112 ppm, respectively), notably lower 

in strontium and slightly higher in rubidium contents than 

associated metabasalts, perhaps due to alteration. Samarium 

and neodymium contents are less variable (0.6–4.4 ppm and 

3–18.4 ppm, respectively) and very similar to their less-altered 

equivalents, the metabasalts.

Although the calculated initial lead values for phyllite 

samples mimic those of the metabasalts and metagabbros, 

calculated initial Sr-Nd and Pb-Nd values of phyllites are more 

scattered (figs. 12 and 13). The difference in initial strontium in 

phyllites can be explained by alteration due to seawater interaction or incorporation of carbonate (87Sr/86Sr = 0.707 to 0.708), 

as is probably the case with some of the argillites, metabasalts, 

and serpentinites. Two phyllites (PF-09 and GC-1637-44) plot 

with very low initial strontium values (less than 0.703) are not 

within the scale of the diagram (fig. 12), and are suspected of 

containing secondary rubidium (see fig. 7B). Two analyses of 

phyllite PF-18 from the Portal Face are similar to the high-Nd 

metabasalt signature (εNd = +8), but with slightly more enriched 

strontium (0.7056) and lead (18.67) signatures. Other phyllites 

–14

18.2 18.4 18.6 18.8 19.0 19.2 19.4

–10

–6

6

10

Hyd Group

argillites

high-Nd,Hyd Group

metabasalts

OIB trend

ADM-59

LG-32

LG-20-2

GC-1136-53

PF-18

CHUR

Metagabbros

GB-24

GST

2

LG-71

MORB

Footwall

phyllites

lower-Nd,

ADM-01 mafic rocks

–2

Hyd Group basalts

Gambier Bay metabasalts

other mafic rocks

phyllites

gabbros

Hyd Group argillite

Cannery Fm argillite

serpentinite

EXPLANATION

Initial 206Pb/204Pb

All initials

at 215 Ma

Typical

analytical

uncertainty

Initial 

εNd

Figure 13. Initial lead versus initial neodymium correlation diagram showing the distribution of initial Pb-Nd values for 

Greens Creek host rocks relative to model Pb-Nd fields for modern petrotectonic environments (for example, Zartman, 

1984). Fields representing different lithologic units of Greens Creek host rocks are more discrete than those shown 

in figure 12, and a field for most of the phyllites is somewhat discernible from values for argillites. Although a field for 

modern “island arcs” is not shown, elevated 206Pb/204Pb values for most Greens Creek mafic rocks relative to the oceanarc basalt (OIB) trend is indicative of some modern island-arc rock suites (Ellam and Hawkesworth, 1988; Ben Othman 

and others, 1989). Again, serpentinite data vary widely (although ADM-59 is joined by metabasalt GB-24). MORB, midocean ridge basalt; OIB, oceanic-island basalt; CHUR, chondritic uniform reservoir.
358 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

plot toward initial signatures for argillites with εNd about +2, 

higher initial strontium and lower initial lead, consistent with 

their lower Th/U, increased uraniam content (leading to overcorrected initial lead values).

Differences in initial neodymium are not easily explained 

or well understood. Because the initial neodymium values of 

some phyllites tend toward values for argillites, one might 

suggest that hydrothermal fluids circulating through both the 

argillitic and older mafic volcanic packages (phyllites) mobilized rare-earth elements (REE) and therefore altered neodymium compositions. Nevertheless, lower εNd and higher 87Sr/86Sr 

values in some Greens Creek samples probably indicate the 

addition of older, more enriched crustal components either 

during sedimentation or subsequent alteration (figs. 7 and 8).

Argillites

Argillite samples are of two known ages: an older Permian suite from the Cannery Formation (LG-78, ADM-29, and 

ADM-34), and a younger, Late Triassic, Greens Creek-contemporary suite from the Hyd Group sequence (table 3, chap. 

11). A comparison of uranium, thorium, and lead concentrations from the two suites reveals no differences (0.7–4, 0.2–

4.5, and 1.7–20 ppm, respectively), nor do Th/U ratios show 

any distinction. As mentioned previously, the variations in 

Th/U would suggest variable fractionation either during shale 

deposition or subsequent alteration. Unusually high uranium 

contents were found in mine argillite PP-204-01 (7.4 ppm).

The argillites yielded an apparent U-Pb isochron age of 

186 ± 100 Ma (chap. 11), and whereas this age is very imprecise, if accurate, it is interestingly similar to U-Pb and Rb-Sr 

apparent isochron ages for some of the metabasalts and phyllites 

(about 205 and 182 Ma, respectively) and ages of either intrusion or alteration of the metagabbros (about 206 Ma). Despite 

slight alteration, these isochron ages lend confidence to calculated initial Pb signatures at 215 Ma for the argillite samples.

On average, a higher 207Pb component can be found in 

initial lead compositions from some of the argillites (fig. 10). 

These values range from average “orogene” to “upper crust” 

compositions, indicating that lead in some of the argillites is 

derived from an older, slightly more radiogenic source. The 

same indication is observed in 206Pb–208Pb space (fig. 11) — 

argillites plot approximately on the model “upper crust” Pb 

evolution curve at 200 Ma.

Argillite Pb signatures can be subdivided into two fields 

(see fig. 15, chap. 10). The least radiogenic argillite field 

is compatible with some phyllites, but also galena Pb from 

Kennecott-Rand. And the most radiogenic argillite field 

appears as a possible endmember composition consistent with 

some Greens Creek pyrite and sphalerite Pb compositions. In 

general, the older Cannery Formation argillites plot under the 

Hyd Group argillites (lower 206Pb /204Pb and 207Pb /204Pb) and 

within the upper section for the metabasalts and phyllites. The 

Hyd Group argillites, on the other hand, plot either to the low 

206Pb /204Pb side, similar to values for galena Pb from Kennecott-Rand, some phyllites and some metagabbros, or to the 

high 206Pb /204Pb side, similar to some Greens Creek pyrite and 

sphalerite Pb compositions that may contain more evolved, 

younger lead (Cretaceous pyrite formation?).

Rb-Sr concentrations from argillites vary widely (1–60 

ppm and 1–135 ppm, respectively), although in general Rb/

Sr ratios are quite high (0.2 – 20). These concentrations are 

considerably below the typical average shale concentations for 

Rb and Sr (about 140 and 300 ppm, respectively). Sm-Nd contents in typical modern shales are 10 and 50 ppm, respectively 

(for example, Faure, 1986), far greater than those exhibited by 

Greens Creek argillites (0.7–4 ppm and 3.2–18.2 ppm, respectively); however, Greens Creek argillites have Sm-Nd contents 

near exactly the same as associated phyllites and metabasalts 

from which they were supposedly derived.

Rb-Sr isotopic age data for the argillite samples suggest 

a single resetting age of 91.4 ± 2.6 Ma (fig. 16, chap. 11) that 

includes Hyd Group and Cannery Formation alike. It is essentially a three-point isochron controlled by two Hyd Group 

argillites, LG-66 and NAD-T4-2, neither of which is carbonaceous. Omission of the Cannery Formation data alters the Rb-Sr 

apparent isochron age to 90.8 ± 2.2 Ma with initial 87Sr/86Sr at 

0.70733 for the Hyd Group argillites, a value that approaches 

Cretaceous seawater strontium composition (figs. 7 and 8).

Correctable initial Nd-Sr-Pb isotopic data for argillites (only four analyses) lie in fields with lower initial Nd 

(εNd about –2 to +2), higher initial 206Pb/204Pb (18.45–19.08), 

and higher initial 87Sr/86Sr (0.7048 to 0.7070) than other host 

rocks (figs. 12 and 13), but typical of values for modern 

shales (between modern OIB and “orogene”). High 207Pb, low 

εNd, and higher Sr values all suggest that the argillites contain older, slightly more radiogenic source material, perhaps 

indicative of some Paleozoic provenance (Alexander terrane). 

However, because these Sr-Pb isotopic data may have been 

altered, even slightly (figs. 7 and 8), an emphasis on the initial 

Nd values is recommended. Nonetheless, the initial Pb-Sr-Nd 

isotopic signatures for argillites do plot on average where one 

might expect from the interpreted tectonic setting — an oceanic arc environment (for example, Zartman, 1984).

Serpentinites

Uranium, thorium, and lead contents in ultramafic rocks 

average 0.015, 0.05, and 0.3 ppm, respectively, and Greens 

Creek serpentinites exhibit comparable concentrations of 0.01–

0.06, 0.03–0.2, and 0.2–0.75 ppm, respectively. Several outliers 

are observed; ADM-59 is exceptional with uranium (0.11 ppm), 

thorium (0.95 ppm), and lead (4.7 ppm); and mine serpentinites 

GC-1136-53 and GC-1136-59 are enhanced with uranium and 

lead (0.04–0.07 and 75–26 ppm, respectively). The high lead 

contents in the latter two are indicative of alteration due to mineralization, and these lead results should therefore be ignored 

when evaluating the isotopic systematics of the serpentinites.

The initial lead compositions for most serpentinites lie 

within the mafic igneous field (fig. 10). However, two exceptions exist: an extremely low 207Pb/204Pb analysis of LG-19-2 

and an extremely high 207Pb/204Pb analysis of ADM-59. 
Discussion 359

Because of large errors (table 4, chap. 11) and the possibility of 

difficulties in maintaining stable 207Pb/204Pb measurements relative to 206Pb/204Pb (see chap. 10), these two serpentinite analyses are highly tentative. Nonetheless, if these results are even 

somewhat accurate, they do present interesting speculation.

Typical ultramafic rubidium and strontium concentrations 

are 0.2 and 1 ppm, respectively, and Greens Creek serpentinites range between 0.15 and 0.32, and 6.8 and 16 ppm, 

respectively (table 6, chap. 11). Exceptions are noted with 

mine serpentinites GC-1136-53 and GC-1136-59 that exhibit 

extreme Rb and Sr contents of 33 to 45 and 68 to 153 ppm, 

respectively, and these analyses again should be excluded 

when considering the Rb-Sr isotopic characteristics of the 

serpentinite protolith(s). Samarium and neodymium concentrations for typical modern ultramafic rocks vary, but generally 

are below 0.6 and 2.5 ppm, respectively. Greens Creek serpentinites range between 0.017–0.03 and 0.09–2.7 ppm, respectively, excluding the mine serpentinites (table 6, chap. 11).

Although the Rb-Sr isotopic data from serpentinite 

samples are scattered and do not form well-defined isochrons, 

an age of about 195 Ma is suggested for serpentinites LG-19 

and LG-20 from the Lakes District area (fig. 5), probably an 

age close to that of alteration. An initial Sr value of 0.70462 

± 6 is calculated from this regression, a value very similar to 

both metabasalts and some metagabbros (fig. 17, chap. 11).

Another Rb-Sr age of 89 ± 15 Ma (fig. 17, chap. 11) 

is defined by the two mine serpentinites, GC-1136-53 and 

GC-1136-59, with an initial Sr value of 0.70767 — a value 

very similar to that indicated by the data from the Hyd Group 

argillites (0.70733) with a Rb-Sr age of resetting at 91 Ma (fig. 

16, chap. 11). Serpentinite ADM-59 from Gambier Bay plots 

near this “reset” isochron.

Initial Pb-Sr-Nd isotopic values for serpentinite vary 

widely (figs. 10 through 13) due in part to the poor quality of 

the analyses (very low abundances and correspondingly low 

ion beam intensities). If one can believe the data, however, 

they suggest highly variable source(s) during emplacement 

(perhaps over a substantial time period) or isotopic resetting 

during alteration probably due to Cretaceous deformation. An 

attempt to date serpentinite sample LG-19 was largely unsuccessful in all isotopic systems, indicating that internal isotopic 

systematics had been disturbed (chap. 11).

With the hope that any of these serpentinite analyses are 

accurate, if not precise, their isotopic behavior imply several interesting points. One of the serpentinites (ADM-59) is 

much different than the rest, with high initial Nd (+8.4), high 

207Pb/204Pb (15.885), and high 87Sr/86Sr (0.7072), whereas the 

remainder of the serpentinites exhibit decreasing initial Nd 

values (GC-1136-53, +4.15; LG-19-2, +1.8; LG-20-2, -1.6; 

and so forth), indicating increasing crustal involvement in their 

production (figs. 9, 12, and 13). If these results are accurate, it 

would suggest that serpentinite LG-32, the most negative (εNd

about –12), was derived from a source enriched with much 

older crust (Nd model age, TDM, = 1,350 Ma). Unfortunately, 

age data for any of these serpentinites do not exist; they may 

range anywhere in age from Late Triassic to Cretaceous.

Crosscutting Diabases — Diorites

Uranium, thorium, and lead contents for these samples 

are given in table 4 (chap. 11), initial Pb values are given in 

table 5 (chap. 11), and they indicate that these sills/intrusions 

are of two types. Samples LG-64 (diorite) and GC-1704-01 are 

remarkably similar, especially with respect to their Nd-Sr and 

Nd-Pb isotopic systematics (not shown), and GC-1701-01 is 

notably different. All of these samples have uranium contents 

between 0.84 and 1.35 ppm and thorium contents between 1.6 

and 2.6 ppm, but variable lead contents of about 4 ppm to 640 

ppm, the latter indicative of contamination by mineralization 

— sample GC-1701-01. Otherwise, the diabasic intrusions are 

similar to the metabasalts, metagabbros, and phyllites with 

respect to their U, Th, and Pb contents.

Without an actual age for these intrusions, accurate initial 

Pb compositions are not possible. All of these bodies are 

known to be younger than the Greens Creek ore-forming event, 

but how much younger has not been established. Assuming 

reasonably contemporaneous ages for these crosscutting intrusions (from 185 to 90 Ma), initial lead and strontium values 

do not match Cretaceous lead and strontium model isotopic 

compositions (for example, Burke and others, 1982; Zartman, 

1984), suggesting that the isotopic systematics of these samples 

are not controlled by Cretaceous deformation and(or) seawater 

alteration. Initial Nd-Sr and Nd-Pb correlation diagrams (from 

215 Ma to 50 Ma) show that these samples, and especially 

LG-64 and GC-1704-01, are quite similar and depleted; in fact, 

the most depleted whole-rock samples at Greens Creek had 

initial εNd = +7 to 8, 87Sr/86Sr = 0.7033, and 206Pb/204Pb = 18.2 to 

18.45, values slightly less than MORB at 185 to 90 Ma.

Discussion

Geologic Framework at Greens Creek

We know from previous geologic studies that the Greens 

Creek ore deposit is located in a belt of volcano-sedimentary 

rocks interpreted to represent a rift-fill sequence formed 

during a brief period of intra-arc or back-arc rifting in latest 

Triassic time (Berg and others, 1972; Taylor, 1997; Taylor and 

others, 1995a, 1995b, 1999, 2000). The stratigraphy within the 

belt consists of conglomerates, limestones, marine clastic sediments, and tuffs that are intercalated with and overlain by a 

distinctive unit of mafic pyroclastics and pillowed flows (figs. 

3 and 4). Faunal data bracket the age of the host rocks between 

early Carnian (early Late Triassic) and late Norian (late Late 

Triassic) time (chap. 11).

The radiogenic isotopic systematics indicate a progressively depleting source for the Upper Triassic Greens Creek 

rocks, suggesting a rift setting. The oldest argillites have 

slightly depleted signatures (εNd about +1.5), consistent with 

their derivation from mainly oceanic-arc volcanic rocks of 

the Alexander terrane. These rocks in turn are unconformably overlain by a sequence of mainly altered metabasalts 
360 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

and related rocks, perhaps similar to metabasalts of either the 

Halleck Formation or the Gambier Bay Formation that exhibit 

depleted, island-arc-type isotopic signatures (εNd about +4 

to 5 and elevated 87Sr/86Sr and 206Pb/204Pb). The metabasalts 

are then unconformably overlain by conglomerate, dolomite, 

and more argillites of the Hyd Group. The Hyd Group argillites have slightly depleted to slightly enriched εNd about –5 

to +2, indicating partial incorporation of some older, more 

enriched source material. The lower metabasaltic sequences 

are intruded by ultramafic sills and stocks, represented now 

as highly altered serpentinites that exhibit a wide range of 

isotopic signatures (εNd about –12 to +8), suggesting that 

they may have been early to late rift-forming intrusions, and 

enriched relative to other igneous rocks. Subsequent mafic 

volcanism and gabbroic plutonism are characterized by more 

depleted source signatures (εNd = +5 to +9). Hyd Group basalts 

that cap the Triassic section have yet more depleted signatures 

(εNd = +8 to +9), and lastly, post-Greens Creek crosscutting 

diabase dikes are the most depleted (εNd = +9). This progressive sequence of least to most depleted isotopic signatures 

implies opening of preexisting crust in a rift setting, most 

likely within an oceanic arc environment.

Petrotectonic Environment of the Greens Creek 

VMS Deposit

Scatter in the isotopic data for phyllites, metagabbros, 

serpentinites, and argillites indicate the likelihood of opensystem behavior due to mobilization of either or both elements 

probably during Cretaceous deformation and metamorphism. 

However, despite this probable isotopic behavior, average 

initial Pb-Sr-Nd isotopic data from the mafic rock units 

(metabasalts, metagabbros, and associated phyllites) plot 

where one might expect them and indicate derivation from 

sources similar to those of oceanic-arc environments. Initial 

Pb signatures for the basaltic-gabbroic-ultramafic magmatic 

source(s) and related phyllites (altered mafic volcanics?) plot 

between average Pb compositions for “orogene” and “mantle,” 

consistent with their derivation from mainly mantle sources 

(fig. 10), but in a volcanic arc setting (Zartman and Doe, 1981; 

Zartman, 1984). Likewise, initial Sr and Nd (at 215 Ma) values for mafic igneous rocks from Greens Creek are depleted 

(higher εNd and lower 87Sr/86Sr), indicating mainly mantle 

derivation (fig. 12). All samples are enriched in 87Sr/86Sr and 206Pb/204Pb compared to MORB (mid-ocean ridge basalt) or the 

OIB (oceanic island basalt) trend, a characteristic indicative of 

island-arc rocks (Hawkesworth and others, 1977, 1979; Ellam 

and Hawkesworth, 1988; Ben Othman and others, 1989). 

Explanations for the elevated Sr values include the addition 

of subducted 87Sr from seawater and(or) oceanic sediments 

(Hawkesworth and others, 1977), or metasomatic contamination of the mantle wedge with high 87Sr/86Sr derived from 

subducted ocean crust (Pearce, 1983). Although some of these 

enriched values may be the result of alteration during Cretaceous deformation, even the most depleted values are slightly 

more enriched than MORB values.

Initial Nd values for phyllites are bimodal; some have a 

mafic igneous signature (+8), others trend toward initial signatures for the argillites (+2). Argillites tend to have lower Nd 

(εNd about –5 to +2) and higher 87Sr/86Sr (0.705 to 0.707) than 

other host rocks and serpentinite data scatter widely, partly due 

to the questionable quality of the analyses, but also because of 

post-emplacement alteration. High 207Pb, low εNd, and higher Sr 

values all suggest that the argillites contain older, slightly more 

radiogenic, crustal material, perhaps indicative of a partial 

Paleozoic provenance. Crosscutting diabase dikes have variable 

Pb and Sr, but high εNd values indicate that these dikes are from 

a depleted source — one sample exhibiting the most depleted 

isotopic signature of any of the Greens Creek host rocks.

Initial Nd-Sr isotopic signatures for Greens Creek host 

rocks are compared with other Nd-Sr isotopic results from 

Alexander and Gravina terranes (fig. 14) that have been 

interpreted to represent depleted, mantle-derived, oceanic 

island-arc environments (Samson and others, 1989, 1991a). 

Initial Nd isotopic compositions for Greens Creek metabasalt 

and metagabbro are similar to both Alexander and Gravina 

mafic rock data but vary more widely in Sr isotopic composition. This deviation could be the result of alteration and(or) 

mobilization of Rb and Sr during Cretaceous deformation. 

Greens Creek argillite and serpentinite signatures vary widely, 

not unlike values from Alexander and Gravina metasedimentary samples. Sr values for other Alexander terrane samples 

(Samson and others, 1989) also approach Cretaceous seawater 

values (about 0.7078).

Interestingly, Alexander terrane felsic igneous rocks are 

more depleted (higher initial Nd and lower initial Sr) than their 

relatively coeval mafic counterparts. Two crosscutting bodies 

in the Greens Creek area, GC-1704-01 and LG-64, plot with 

the Alexander terrane felsic igneous rocks (fig. 14). A third 

dike, GC-1701-01, however, does not, but instead plots with 

the mafic igneous rocks. There were no other samples analyzed that come close to isotopic signatures exhibited by the 

serpentinites ADM-59 or LG-32, throwing further doubt on 

their validity.

Initial Lead Isotopes of Greens Creek Host 

Rocks Compared to Ore Lead Compositions

Lead isotopic data were obtained from many samples of 

galena, pyrargyrite, sphalerite, pyrite, chalcopyrite, and tetrahedrite from inside the Greens Creek mine as well as several 

samples from outside the mine. Their lead isotopic compositions varied only slightly along a 207Pb trend (fig. 11, chap. 

10) and were compared to model lead evolutions for different 

large-scale, global sources or reservoirs (for example, mantle, 

orogene, upper crust; Zartman and Doe, 1981). The Greens 

Creek ore lead compositions (206Pb/204Pb = 18.6–18.8 and 207Pb/204Pb = 15.55–15.68) plotted along the “orogene” evolution curve at a model lead age between 0 and 100 Ma. Some 

lead compositions lie along a high-207Pb trend, suggesting mixing with older, more radiogenic material, not unlike lead that 

could be derived from the Paleozoic Alexander terrane.
Discussion 361

Hyd Group

metabasalts ADM-59

LG-32

LG-19-2

LG-20-2

GC-1136-53

–14

0.703 0.704 0.705 0.706 0.707 0.708

–10

–6

10

PF-18

CHUR

MORB

Metagabbros

GB-55

GB-24

Alexander terrane

metasedimentary rocks

(Samson and others, 1989)

Alexander terrane

felsic igneous rocks

(Samson and 

others, 1989)

Gravina terrane

mafic igneous rocks

(Samson and others, 1991a)

Alexander terrane

mafic igneous rocks

(Samson and others, 1989)

Gravina terrane

metasedimentary rocks

(Samson and others, 1991a)

Gravina terrane

felsic igneous rocks

(Samson and others, 1991a)

Greens Creek

metasedimentary rocks

(this study)

2

6

–2

Hyd Group basalts

Gambier Bay metabasalts

other mafic rocks

phyllites

gabbros

Hyd Group argillite

Cannery Fm argillite

serpentinite

EXPLANATION

Initial 87Sr/86Sr

All initials

at 215 Ma

Initial εNd

Typical

analytical

uncertainty

Figure 14. Initial strontium versus initial neodymium correlation diagram showing the distribution of initial Sr-Nd 

values for Greens Creek host rocks relative to Sr-Nd fields for previously published Alexander and Gravina terrane 

rocks (Samson and others, 1989, 1991a). Initial isotopic values for Greens Creek host rocks are more scattered than 

data shown for comparable lithologies of Alexander and Gravina terrane rocks; however, in general, the fields are 

not too dissimilar with relatively equal initial εNd values for mafic lithologies and on average equal 87Sr/86Sr values. 

There are no felsic igneous rock data from Greens Creek to compare with the other terranes (except perhaps LG-64), 

but metasedimentary rock data from Greens Creek are very similar to that reported for other Alexander terrane 

metasedimentary samples. Again, data from serpentinites do not match any other results from either terrane, 

supporting the idea that these analyses are not reliable. MORB, mid-ocean ridge basalt; CHUR, chondritic uniform 

reservoir.
362 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

15.3

17.4 17.8 18.6 19.0 19.4

15.4

15.5

15.7

15.8

15.9

Orogene

Upper crust

Hyd Group

argillites

0 Ma

Hyd Group

metabasalts

ADM-59

GST

GB-24

800 Ma

400 Ma

Cannery Fm

argillites

LG-19

GC-462-02

GC-462-07

LG-71

15.7 Metagabbros

Greens Creek

ore Pb

18.2

Hyd Group basalts

Gambier Bay metabasalts

other mafic rocks

phyllites

gabbros

Hyd Group argillite

Cannery Fm argillite

serpentinite

EXPLANATION

Initial 206Pb/204Pb

Depleted mantle

15.6

Greens Creek host rock

initial Pb values

All initials

at 215 Ma

Initial 207Pb/204Pb

Typical

analytical

uncertainty

Figure 15. Pb-Pb correlation diagram (206Pb/204Pb versus 207Pb/204Pb) showing the distribution of initial lead compositions of Greens 

Creek host rocks relative to lead isotopic compositions for Greens Creek sulfides (ore). The Greens Creek ore lead compositions 

(

206Pb/204Pb = 18.6 – 18.8 and 207Pb/204Pb = 15.55 – 15.68) plotted along the “orogene” evolution curve at a model lead age between 0 

and 100 Ma. The field for the ore lies within that for the argillites, however, none of the argillite initial lead compositions actually lie 

on the ore trend, but surround it. Lead isotopic data for Greens Creek ore suggest that it was formed through mixing beween two 

main components: mafic magmatic source(s) represented by compositions of the metabasalts, metagabbros, and serpentinites, 

and compositions given by the hanging-wall, pyritic, black argillites. See text and chapter 10 for more discussion.

Likewise, initial lead isotopic compositions for host 

rocks have been compared to model lead compositions to 

help delineate their petrotectonic derivation (figs. 10 and 11). 

More important, initial lead compositions can be calculated 

to match the assumed age of mineralization (215 Ma), such 

that ore lead compositions can be directly compared to host/

source-rock initial lead compositions to evaluate their genetic 

link, if any (fig. 15). A direct comparison such as this is a 

powerful tool in determining whether ore is syngenetic or 

epigenetic.

Lead isotopic data for Greens Creek ore suggest that it 

was formed through mixing beween two main components: 

mafic magmatic source(s) represented by compositions of the 

metabasalts, metagabbros, and serpentinites, and compositions 

given by the hanging-wall, pyritic, black argillites (fig. 15). 

The ore Pb field plots at the top of the mafic igneous fields, 

but not within it. Initial lead values for the various black argillites appear to embody the range of Pb values for the Greens 

Creek ore, suggesting that the ore Pb may be a homogenization of argillite Pb alone. On closer inspection, Pb values for 

unmineralized phyllites and argillites do not actually lie within 

the ore Pb field, but surround it (figs. 10 and 15). Therefore, 

it would appear that the Pb isotopic composition for Greens 

Creek ore is unique, and no particular host rock consistently 

shares that same composition. It is evident that the relatively 

uniform ore Pb signature may represent a homogenization of 

Pb derived from host metabasalt, metagabbro, some footwall 

phyllites, and the hanging-wall argillite(s).
References 363

The isotopic data imply that magmatic fluids, emanating 

from ascending volcanic-arc magmas, mix with overlying 

marine shales and volcanic sediment. Driven by the heat of 

the intrusion, hydrothermal circulation of these fluids with 

high salinity and moderate temperatures through the sediment 

package, metasomatize the sediment and deposit metals onto 

the sea floor and into adjacent sediments. The sulfides in this 

scenario would incorporate the lead isotopic compositions of 

the magmatic fluid and the marine sediment. This same lead 

isotopic behavior — ore compositions between basalts and 

pelagic sediment signatures — has been documented from 

several modern VMS ore deposits around the world: East 

Pacific Rise (Dasch and others, 1971; O’Nions and others, 

1978; Brevart and others, 1981), Nazca plate MORB (Unruh 

and Tatsumoto, 1976), Japanese Kuroko deposits (Fehn and 

others, 1983).

Summary

Initial Pb-Sr-Nd isotopic data indicate a depleted mantle 

source for Greens Creek host rocks and their associated ore, 

with very little to no input of any older crustal material. The 

initial isotopic data scatter somewhat, indicating the likelihood 

of post-emplacement isotopic disturbances during subsequent 

metamorphism and(or) alteration by fluid/rock interaction 

processes. Nonetheless, the isotopic data exhibit elevated 

206Pb/204Pb and 87Sr/86Sr relative to OIB or MORB trends at 

215 Ma and are consistent with isotopic signatures typical of 

oceanic-arc environments. The Greens Creek host-rock data are 

similar to other isotopic data from the Alexander and Gravina 

terranes that support these interpretations.

A sequence of progressively more positive or depleted εNd

and lower 87Sr/86Sr values throughout the Greens Creek hostrock stratigraphy implies rifting of the preexisting arc crust and 

emplacement of magmas with progressively higher mantlederived components. These isotopic data support a genetic 

model of ore deposition in a rifted oceanic-arc environment.

Lead isotopic values for Greens Creek ore indicate the 

probability that metals were derived from magmatic fluids 

emanating from mafic/ultramafic sources and circulating 

through or mixing with marine shales (argillites).

Acknowledgments

The authors thank the Kennecott Greens Creek Mining 

Company for their cooperation, hospitality, and special equipment during sample collection on Admiralty Island. Also, 

thanks to all the workers at the USGS that were responsible 

for the majority of sample preparation and chemical analysis, especially Elaine Gilman. Special thanks to manuscript 

reviewers Brian Marshall and Gary Landis for their helpful 

comments and criticisms. And special thanks to C.D. Taylor 

and C.A. Johnson, our editors, for having the patience to see 

this manuscript into review and eventual fruition.

References

Allegre, C.J., and Luck, J.M., 1980, Osmium isotopes as 

petrogenetic and geological tracers: Earth and Planetary 

Science Letters, v. 48, p. 148–54.

Ayuso, R.A., Wooden, J.L., Foley, N.K., Seal, R.R., Sinha, 

A.K., and Persing, H., 2004, U-Pb zircon ages and Pb isotope geochemistry of gold deposits in the Carolina Slate Belt 

of South Carolina: Economic Geology, v. 100, p. 225–252.

Barovich, K.M., and Patchett, P.J., 1992, Behavior of isotopic 

systematics during deformation and metamorphism—A Hf, 

Nd and Sr isotopic study of mylonitized granite: Contributions to Mineralogy Petrology, v. 109, p. 386–393.

Ben Othman, Dalila, White, W.M., and Patchett, J., 1989, 

The geochemistry of marine sediments, island arc magma 

genesis, and crust-mantle recycling: Earth and Planetary 

Science Letters, v. 94, p. 1–21.

Berg, H.C., Jones, D.L., and Richter, D.H., 1972, GravinaNutzotin Belt — Tectonic significance of an opper Mesozoic sedimentary and volcanic sequence in southern and 

southeastern Alaska: U.S. Geological Survey Professional 

Paper 800–D, p. D1–D24.

Brevart, Olivier, Dupre, B., and Allegre, C.J., 1981, Metallogenesis at spreading centers — Lead isotope systematics for 

sulfides, manganese-rich crusts, basalts, and sediments from 

the Cyamex and Alvin areas (East Pacific Rise): Economic 

Geology, v. 76, p. 1205–1210.

Burke, W.H., Denison, R.E., Hetherington, E.A., Koepnick, 

R.B., Nelson, H.F., and Otto, J.B., 1982, Variations of seawater 87Sr/86Sr throughout Phanerozoic time: Geology, v. 10, 

p. 516–519.

Dasch, E.J., Dymond, J.R., and Heath, G.R., 1971, Isotopic 

analysis of metalliferous sediment from the East Pacific 

Rise: Earth and Planetary Science Letters, v. 13, p. 175–

180.

DePaolo, D.J., 1981, Neodymium isotopes in the Colorado 

Front Range and crust-mantle evolution in the Proterozoic: 

Nature, v. 291, p. 193–196.

Dickin, Alan, 1995, Radiogenic isotope geology: Cambridge, 

England, Cambridge University Press, 490 p.

Ellam, R.M., and Hawkesworth, C.J., 1988, Elemental and 

isotopic variations in subduction related basalts — Evidence 

for a three component model: Contributions to Mineralogy 

and Petrology, v. 98, pp. 72–80.

Farmer, G. Lang, Ayuso, R., and Plafker, G., 1993, A Coast 

Mountains provenance for the Valdez and Orca Groups, 

southern Alaska, based on Nd, Sr, and Pb isotopic evidence: 

Earth and Planetary Science Letters, v. 116, pp. 9–21.
364 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Faure, Gunther, 1986, Principles of isotope geology: New 

York, John Wiley and Sons, 589 p.

Fehn, Udo, Doe, B.R., and Delevaux, M.H., 1983, The 

distribution of lead isotopes and the origin of Kuroko ore 

deposits in the Hokuroku district, Japan: Economic Geology 

Monograph no. 5, p. 488–506.

Gaccetta, J.D., and Church, S.E., 1989, Lead isotope data base 

for sulfide occurrences from Alaska, December, 1989: U.S. 

Geological Survey Open-File Report 89–688, 60 p.

Gehrels, G.E., and Berg, H.C., 1992, Geologic map of southeastern Alaska: U.S. Geological Survey Investigation Series 

Map I–1867, scale 1:600,000.

Hart, S.R., and Kinloch, E.D., 1989, Osmium isotope systematics in Witwatersrand and Bushveld ore deposits: Economic Geology, v. 84, p. 1651–1655.

Hawkesworth, C.J., O’Nions, R.K., Pankhurst, R.J., Hamilton, 

P.J., and Evensen, N.M., 1977, A geochemical study of 

island-arc and back-arc tholeiites from the Scotia Sea: Earth 

and Planetary Science Letters, v. 36, pp. 253–262.

Hawkesworth, C.J., O’Nions, R.K., and Arculus, R.J., 1979, 

Nd and Sr isotope geochemistry of island arc volcanics, 

Grenada, Lesser Antilles: Earth and Planetary Science Letters, v. 45, p. 237–248.

Hess, Jennifer, Bender, M.L., and Schilling, J.G., 1986, Evolution of the ratio of strontium–87 to strontium–86 in seawater from Cretaceous to present: Science, v. 231, p. 979–984.

Kerrick, Robert, 1991, Radiogenic isotope systems applied 

to ore deposits, in Heaman, L., and Ludden, J.N., eds., 

Applications of radiogenic isotopes systems to problems 

in geology, Mineralogical Association of Canada, Short 

Course 19, p. 365–421.

Lambert, D.D., Morgan, J.W., Walker, R.J., Shirey, S.B., Carlson, R.W., Zientek, M.L., and Koski, M.S., 1989, Rhenium–

osmium and samarium-neodymium isotopic systematics of 

the Stillwater Complex: Science, v. 244, p. 1169–1174.

Martin, C.E., 1991, Osmium isotopic characteristics of 

mantle-derived rocks: Geochimica et Cosmoochimica Acta, 

v. 55, p. 1421–1434.

Newberry, R.J., and Brew, D.A., 1997, Chemical and isotopic 

data for rocks and ores from the Upper Triassic Greens 

Creek and Woewodski Island volcanogenic massive sulfide 

deposits, southeastern Alaska, in Geologic studies in Alaska 

by the U.S. Geological Survey: U.S. Geological Survey 

Professional Paper 1614, p. 35–55.

Newberry, R.J., Brew, D.A., and Crafford, T.C., 1990, Genesis 

of the Greens Creek volcanogenic massive sulfide deposit, 

S.E. Alaska — A geochemical study, [abs.]: Geological 

Association of Canada Program with Abstracts, v. 15, p. A96.

Newberry, R.J., Crafford, T.C., Newkirk, S.R., Young, L.E., 

Nelson, S.W., and Duke, N.A., 1997, Volcanogenic massive 

sulfide deposits of Alaska: Economic Geology Monograph 

no. 9, p. 120–150.

O’Nions, R.K., Carter, S.R., Cohen, R.S., Evensen, N.M., 

and Hamilton, P.J., 1978, Pb, Nd and Sr isotopes in oceanic 

ferromanganese deposits and ocean floor basalts: Nature, 

v. 273, p. 435–438.

Pearce, J.A., 1983, The role of sub-continental lithosphere in 

magma genesis at destructive plate margins, in Hawkesworth, C.J., and Norry, M.J., eds., Continental basalts and 

mantle xenoliths, p. 230–249: Nantwich, United Kingdom, 

Shiva Publications, Ltd.

Premo, W.R., and Tatsumoto, M., 1991, U-Th-Pb isotopic systematics of lunar norite 78235, in Proceedings of Lunar and 

Planetary Science Conference, v. 21, p. 89–100: Houston, 

Texas, The Lunar and Planetary Institute.

Premo, W.R., and Tatsumoto, M., 1992, U-Th-Pb, Rb-Sr, and 

Sm-Nd isotopic systematics of lunar troctolitic cumulate 

76535: Implications on the age and origin of this early 

lunar, deep-seated cumulate, in Proceedings of Lunar and 

Planetary Science Conference, v. 22, p. 381–397: Houston, 

Texas, The Lunar and Planetary Institute.

Rubin, C.M., and Saleeby, J.B., 1992, Tectonic history of the 

eastern edge of the Alexander Terrane, southeast Alaska: 

Tectonics, v. 11, p. 586–602.

Rubin, C.M., Saleeby, J.B., Cowan, D.S., Brandon, M.T., 

and McGroder, M.F., 1990, Regionally extensive midCretaceous west-vergent thrust system in the northwestern 

Cordillera — Implications for continent-margin tectonism: 

Geology, v. 18, p. 276–280.

Samson, S.D., McClelland, W.C., Patchett, P.J., Gehrels, G.E., 

and Anderson, R.G., 1989, Evidence from neodymium isotopes for mantle contributions to Phanerozoic crustal genesis in the Canadian Cordillera: Nature, v. 337, p. 705–709.

Samson, S.D., Patchett, P.J., Gehrels, G.E., and Anderson, 

R.G., 1990, Nd and Sr isotopic characterization of the 

Wrangellia Terrane and implications for crustal growth 

of the Canadian Cordillera: Journal of Geology, v. 98, p. 

749–762.

Samson, S.D., Patchett, P.J., McClelland, W.C., and Gehrels, 

G.E., 1991a, Nd isotopic characterization of metamorphic rocks in the Coast Mountains, Alaskan and Canadian 

Cordillera — Ancient crust bounded by juvenile terranes: 

Tectonics, v. 10, p. 770–780.

Samson, S.D., Patchett, P.J., McClelland, W.C., and Gehrels, 

G.E., 1991b, Nd and Sr isotoic constraints on the petrogenesis of the west side of the northern Coast Mountains batholith, Alaskan and Canadian Cordillera: Canadian Journal of 

Earth Science, v. 28, p. 939–946.
References 365

Stacey, J.S., and Kramers, J.D., 1975, Approximation of terrestrial lead isotope evolution by a two stage model: Earth 

and Planetary Science Letters, v. 26, p. 207–221.

Tatsumoto, Mitsunobu, and Unruh, D.M., 1976, KREEP 

basalt age — Grain by grain U-Th-Pb systematics study of 

the quartz monzodiorite clast 15405, 88, in Proceedings of 

the 7th Lunar Science Conference, p. 2107–2129: Houston, Texas, The Lunar Planetary Institute.

Taylor, C.D., 1997, An arc-flank to back-arc transect — 

Metallogeny of Late Triassic volcanogenic massive 

sulfide occurrences of the Alexander terrane, southeastern 

Alaska and British Columbia: [extended abs.], in Society 

of Economic Geologists Neves Corvo Field Conference, 

May 7–17, 1997, Lisbon, Portugal, Abstracts and Programs, p. 68.

Taylor, C.D., Philpotts, J.A., Hall, T.E., and Wakeman, B.W., 

1995b, New information on the geochemistry, age, and 

tectonic history of Late Triassic volcanic host rocks and 

associated massive sulfide occurrences of the Alexander 

terrane, southeast Alaska: Alaska Miners Association 

Conference Juneau, Program with Abstracts, p. 31–32.

Taylor, C.D., Philpotts, J., Sutley, S., Gent, C., Harlan, S., 

Premo, W., Tatsumoto, M., Emsbo, P., and Meier, A., 

1995a, Geochemistry of late Triassic volcanic rocks and 

age of alteration associated with volcanogenic massive 

sulfide occurrences, Alexander terrane, southeast Alaska, 

in Geology and Ore Deposits of the American Cordillera, 

A Symposium, Reno, Nev., 1995: Reno, Nev., Geological 

Society of Nevada, p. A74.

Taylor, C.D., Premo, W.R., and Meier, A.L., 1999, The Late 

Triassic metallogeny of the Alexander terrane, southeastern Alaska and British Columbia: Geological Society of 

America Abstracts with Programs, v. 31, no. 6, p. A–101.

Taylor, C.D., Premo, W.R., and Lear, K.G., 2000, The Greens 

Creek massive sulfide deposit — Premier example of the 

Late Triassic metallogeny of the Alexander terrane, southeastern Alaska and British Columbia: Geological Society of 

America Abstracts with Programs, v. 32, no. 6, p. A–71.

Unruh, Daniel M., and Tatsumoto, M., 1976, Lead isotopic 

composition and uranium, thorium and lead concentrations 

in sediments and basalts from the Nazca plate: Initial Report 

of Deep Sea Drilling Project, v. 34, p. 341–347.

Walker, R.J., Morgan, J.W., Naldrett, A.J., and Li C., 1991, Re-Os 

isotopic systematics of Ni-Cu sulfide ores, Sudbury Igneous 

Complex, Ontario — Evidence for a major crustal component: 

Earth and Planetary Science Letters, v. 105, p. 416–429.

Whitehouse, M.J., 1988, Granulite facies Nd-isotopic homogenization in the Lewisian complex of northwest Scotland: 

Nature, v. 331, p. 705–707.

Zartman, R.E., 1984, Lead, strontium, and neodymium isotopic characterization of mineral deposits relative to their geologic environments, in Proceedings of the 27th International 

Geological Congress, Moscow, v. 12, p. 83–106, Metallogenesis and mineral ore deposits: Utrecht, The Netherlands, 

VNU Science Press.

Zartman, R.E., and Doe, B.R., 1981, Plumbotectonics — The 

model: Tectonophysics, v. 75, p. 135–162.

Structure of the Lower Southwest Orebody, 

Structural Comparison to Neighboring 

Orebodies, and Tectonic Model for the 

Greens Creek Deposit

By Katja Freitag

Chapter 13 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract.......................................................................................................................................................371

Introduction.................................................................................................................................................371

Structural Background..............................................................................................................................374

Methodology...............................................................................................................................................375

Structure of the Lower Southwest Orebody .........................................................................................375

Dmineral Deformation............................................................................................................................375

D0 Deformation..................................................................................................................................375

D1 Deformation..................................................................................................................................375

D2 Deformation..................................................................................................................................375

D3 Deformation..................................................................................................................................378

D4 Deformation..................................................................................................................................386

D5 Deformation..................................................................................................................................388

Structural Transition and Comparison to Neighboring Orebodies ....................................................389

Model of the Structural and Tectonic Evolution of the Greens Creek Deposit................................399

Summary and Conclusions.......................................................................................................................401

Acknowledgments.....................................................................................................................................401

References Cited........................................................................................................................................401

Figures

1. Location map of the Greens Creek deposit..........................................................................372

2. Cross section 2400 of the Greens Creek deposit looking north ........................................373

3. Plan of Greens Creek orebodies (A) and Lower Southwest orebody located

on the mine grid (B)..................................................................................................................376

4. Drawing and photograph of typical structures in massive argillite beds in the

stratigraphic hanging wall of the Lower Southwest orebody...........................................377

5. Rib map of siliceous rock showing well-developed S2 and S3 foliation.........................377

6. Cross section 2500 of the Lower Southwest orebody ........................................................378

7. Plan map of the 224 level, Lower Southwest orebody........................................................379

8. Photomicrograph of a quartz-carbonate “ladder” vein offset along a stylolite ............380

9. Cross section illustrating early east-directed thrust faults in massive argillite

beds after removing effects of F2 and F3 folding ................................................................380

10. Rib map showing argillite forming the core of a major isoclinal F2 syncline,

Lower Southwest orebody ......................................................................................................380

11. Plan map of level 224 onto which the locations of F2 fold axes are projected

to show the axis trends............................................................................................................381

12. Cross section 2400 onto which the locations of F2 fold axes are projected to

show the axis plunges .............................................................................................................383

13. Photomicrograph of S2 stylolitic foliation in stratigraphic footwall siliceous rocks.....383

14. Photomicrograph of white mica forming penetrative S2 foliation. S2 foliation is

folded S3 crenulation cleavage..............................................................................................383

15. Cross-sectional model showing the development of shears along F2 anticlines

during progressive D2 deformation .......................................................................................384
16. Rib map of F3 folds....................................................................................................................385

17. Schematic cross section illustrating the “ripple and fall” model of F3 fold

distributions at the Greens Creek deposit............................................................................386

18. Ramsay and Huber’s (1987) principal type-3 three-dimensional fold...............................387

19. Photomicrograph of S3 stylolites in siliceous rock.............................................................388

20. Photomicrograph and sketch of spaced S3 crenulation cleavage in sericitic

phyllite, defined by S3 cleavage domains and microlithons .............................................389

21. Rib map depicting intermediate to steeper sections along the upper thrust of

the Lower Southwest thrust system......................................................................................390

22. Rose diagram comparing strikes of left-slip faults (n=8) with right-slip

high-angle faults .......................................................................................................................390

23. Map of the various terranes and their bounding regional strike-slip faults,

southeast Alaska and the structural setting of the Greens Creek deposit.....................391

24. Schematic cross section illustrating the sequence of brittle deformation events .......392

25. Block diagram representing two fault blocks of massive sulfide of the

Lower Southwest orebody offset across right-slip faults, with an intensely

fractured fault zone ..................................................................................................................393

26. Schematic model for the transition from the Lower Southwest to the Upper

Southwest and 224 West Bench orebodies based on F2 fold geometry.........................394

27. Lower hemisphere equal area projections of F3 fold axes of the (a) Lower

Southwest and (b) Upper Southwest and 200 South orebodies .......................................396

28. Lower hemisphere equal area projections of L3 crenulation lineations of the

(a) Lower Southwest (n=22) and (b) Upper Southwest (triangles; n=16), 224

West Bench (square; n=1), and 200 South (star; n=1) orebodies .....................................396

29. Lower hemisphere equal-area projections of poles to S2 foliation planes

measured in footwall rocks of the (a) Lower Southwest (b) Upper Southwest,

and (c) 224 West Bench orebodies........................................................................................397

30. Lower hemisphere equal area projections of poles to S3 cleavage in the

(a) Lower Southwest, 200 South, (b) Upper Southwest, and (c) 224 West Bench

orebodies ...................................................................................................................................398

31. Schematic representation of polyharmonic folds developed in competent layers

of varying thickness and incompetent host materials showing the effect of the

thickness of the mineralized horizon during folding...........................................................399

32. Model of the structural and tectonic evolution of the Greens Creek deposit................400

Tables

1. Deformation nomenclature (taken from chap. 7) ................................................................374

2. Deformation nomenclature used in this study.............................................................................374

3. Comparison of orientations of structural features in the Lower Southwest,

Upper Southwest, 224 West Bench and 200 South orebodies..........................................395

4. Comparison of orebody thickness and orientations of structural features....................395

Abstract

Greens Creek is a Zn-Pb-Ag-(Cu-Au) volcanogenic massive sulfide deposit that formed in a back-arc basin in the Alexander terrane, southeastern Alaska. Numerous sulfide orebodies 

are located discontinuously along the contact between highly 

altered mafic volcanic/volcaniclastic stratigraphic footwall rocks 

and stratigraphically overlying graphitic metasiltstones and 

metashales. The orebodies were deformed several times during accretionary and subsequent wrench tectonic activity. The 

structurally complex deposit includes open to isoclinal folds that 

are refolded by open to closed folds, low-angle faults, and highangle strike-slip faults.

Detailed rib maps, plan maps, cross sections, and long 

sections were used to define the structural geometry and style 

of the Lower Southwest orebody. The earliest deformational 

features are inferred Late Triassic, syndepositional normal (?) 

faults (Dmineral deformation). Hydrothermal fluids are interpreted 

to have flowed along these inferred faults and resulted in spatially distinct distributions of mineralized dolomite and massive 

sulfide. During diagenesis (D0 deformation), early “ladder” 

veins formed perpendicular to metasiltstone beds and, during 

partial subduction of the Alexander terrane in the Jurassic, these 

beds were offset along small thrust faults (D1 deformation). 

Late Jurassic to early Tertiary accretion of the Alexander terrane 

resulted in south-southwest- to southeast-plunging, open to 

isoclinal folds (D2 deformation), and southeast-plunging open 

folds (D3 deformation), with orebody thickness and footwall 

and ore lithologies controlling fold geometry. Thicker sulfide 

horizons are not as complexly folded as thinner sulfide horizons, resulting in a polyharmonic style of fold geometry for the 

orebody. The D4 deformation event signified a change from 

ductile to brittle deformation and formed gentle folds and thrust 

faults. Starting in the Eocene, wrench tectonics resulted in highangle faults (D5), which locally reactivated the thrust faults.

Introduction

The Greens Creek zinc-lead-silver (copper-gold) volcanogenic massive sulfide deposit, in the Alexander terrane, 

southeastern Alaska (fig. 1), formed by structurally controlled hydrothermal activity in a back-arc basin environment. 

Numerous sulfide orebodies are located discontinuously along 

the contact between highly altered mafic volcanic/volcaniclastic stratigraphic footwall rocks (“phyllite”) and stratigraphically overlying graphitic metasiltstones and metashales (“argillite” unit) (chap. 6). The orebodies were multiply deformed 

during accretionary and subsequent wrench fault tectonic 

activity (fig. 2).

Stratigraphic footwall phyllites are quartz-carbonatemica-rich rocks, with variable contents of carbonate (dolomite, ankerite, magnesite, calcite), white mica, chlorite, 

mariposite, pyrite, titanium oxides, and graphite (Newberry 

and others, 1997). Footwall phyllites are more varied than 

hanging-wall argillites but are typically yellowish grey and 

contain abundant, very fine grained quartz, white mica, 

pyrite, and minor mariposite. Pyrite can occur as 0.5- to 

10-cm-wide bands oriented subparallel to the mineralized 

horizon contact.

The stratigraphic hanging-wall argillites are metasedimentary rocks that consist of dark brown to black, graphitic 

and calcareous metasiltstones and metashales, which probably 

represent distal turbidite sequences rather than true argillites, 

as well as occasional nonfossiliferous, argillaceous limestone 

beds. The limestone beds consist of calcite and dark brown 

to black, soft, opaque, organic material. The metasiltstones 

and metashales, hereinafter referred to as massive and slaty 

argillite (mine nomenclature), also have a simple mineralogy, 

consisting of varying amounts of very fine grained quartz, 

calcite, white mica, and organic material. Disseminated, 

frequently framboidal pyrite is ubiquitous. Slaty argillite beds 

(metashales) are thinly laminated, whereas massive argillites 

(metasiltstone) are slightly coarser grained than slaty argillites 

and form 10-cm- to 0.5-m-thick beds. The massive argillite 

beds are usually characterized by abundant quartz-calcite 

veins (“ladder” veins in mine terminology), which typically 

have a core of ribbon quartz oriented perpendicular to the 

vein walls.

The high degree of structural complexity of the Greens 

Creek deposit was recognized when mining of the Southwest 

orebody began. The Southwest orebody, which contains high 

Structure of the Lower Southwest Orebody, Structural 

Comparison to Neighboring Orebodies, and Tectonic 

Model for the Greens Creek Deposit

By Katja Freitag
ALASKAFairbanks Anchorage Ketchikan Prince Rupert YUKON TERRITORY BRITISH COLUMB

Victoria, B.C. Seattle Whitehorse

CANADA

Long.141 W

USA

Admiralty Island Young Bay

HawkInlet

Greens Creekmine portal

HawkPoint

Juneau

Hoonah

Sitka

Angoon

Juneau

0

20 MILES

40 KILOMETERS

0

0

5 MILES

10 KILOMETERS

0

A

A'

0

400 MILES

800 KILOMETERS

0

Figure 1. Location map of the Greens Creek deposit (modified after Freitag, 2000). A–A’ is line of cross section shown in figure 2.
Introduction 373

Phyllite

(altered footwall

mafic volcanic/

volcaniclastic

rocks)

Argillite

Big Sore Creek

0 meters

Maki fault

zone

Klaus thrust fault

Klaus 

thrust

fault

Lower

Southwest

orebody

Little Maki

West East

A A'

305 meters

0

500 FEET

200 METERS

0

Stratigraphic hanging-wall argillite

Mineralized rocks

Siliceous rock

Stratigraphic footwall phyllite

Serpentinite 

Fault

Klaus shear

Displacement to north (into plane of figure)

Displacement to south (out of plane of figure)

EXPLANATION

795 meters

Figure 2. Cross section 2400 of the Greens Creek deposit looking north (modified after P.A. Lindberg, written 

commun., 1996).

precious-metal grades, is divided into an upper part, the Upper 

Southwest orebody, and a lower part, the Lower Southwest 

orebody. The Upper Southwest orebody comprises massive 

sulfide bands that are generally less than 5 m thick. The Lower 

Southwest orebody, the focus of this study, is characterized 

by up to 25-m-thick massive sulfide and mineralized dolomite sections, which thin toward the periphery of the orebody 

(Freitag, 2000).

This detailed structural study of the Lower Southwest 

orebody is the first complete study of a Greens Creek deposit 

orebody. The objective was to understand the structure of the 

orebody through detailed stope mapping and to develop a 

model of the geometry and structural development of the Lower 

Southwest orebody. The results of this study may be used to 

understand the structure of other orebodies at the deposit and to 

understand local details of the regional structural development. 

A structural comparison and model for the transition between 

adjoining orebodies enabled the prediction of structural style to 

be encountered at other Greens Creek orebodies. The project 

built on existing structural studies and models developed by 

Proffett (chap. 7) and P.A. Lindberg (written commun., 1996). 

The tectonic history derived from the study of the Lower 

Southwest orebody was put in a regional context by comparing 

Lower Southwest structures to regional structures in this portion 

of southeastern Alaska. There are strong similarities between 

deposit-scale and regional structures.
374 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Structural Background

At least three folding and two faulting events deformed 

the Greens Creek deposit (chap. 7; P.A. Lindberg, oral commun., 1997). The postmineralization deformation nomenclature that is currently used at the mine, which is based on the 

work of Proffett (chap. 7), is summarized in table 1. For this 

study, the same basic nomenclature was used, but in a slightly 

modified form (table 2).

D1 deformation is poorly documented. Evidence for D1 

deformation is a bedding-cleavage intersection lineation (L1) 

recognized in the vicinity of the mine area (K.G. Lear, oral 

commun., 1999). This lineation is found in rocks similar to 

stratigraphic footwall rocks at the deposit, although it is not 

known whether these rocks are the same age as footwall rocks 

of the Greens Creek deposit.

The deposit was ductilely deformed into tight to isoclinal 

F2 folds that are recognized throughout the mine. Structurally thickened sulfide sections occur in hinge zones of major 

F2 synclines. Thin (less than 3 m) sulfide sections commonly 

were attenuated in hinges of F2 anticlines (chap. 7). Locally, 

F2 folds were refolded by open to tight F3 and open F4 folds 

(chap. 7; P.A. Lindberg, written communs., 1996, 1997).

Two major fault systems are recognized at the Greens 

Creek deposit. A thrust fault, known as the Klaus “shear” (P.A. 

Lindberg, written commun., 1996) at the mine, separates the 

East and the West orebodies and has approximately 213 m of 

reverse offset across the fault, with the hanging wall displaced 

in a N. 60° W. direction (P.A. Lindberg, oral commun., 1998). 

The Maki fault zone (fig. 2) is a wide (about 150 m) zone 

of anastomozing, high-angle, right-slip faults that offset the 

deposit approximately 600 m (P.A. Lindberg, written commun., 1996). Two minor low-angle thrust faults are interpreted 

to have developed subparallel to the Klaus thrust fault (chap. 

7; Freitag, 2000), and numerous high-angle faults formed 

subparallel to the Maki fault zone.

The only attempt at dating deformation episodes is the 

study reported by Premo and others (chap. 11), who determined 40Ar/39Ar spectra from white micas in the mine area. 

These spectra record the uplift and cooling of the area during 

mid-Cretaceous time. The uplift and cooling are interpreted to 

have followed accretion of the South Alaska superterrane to 

the North American margin (chap. 11).

Table 1. Deformation nomenclature (taken from chap. 7).

Deformation 

event

First Second Third Fourth Fifth

Symbol D1 D2 D3 D4 D5

Folds F2 F3 F4

Cleavage S2 S3 S4

Lineation L1 (?) L2 L3 L4

Faults Low-angle and cleavage 

plane shear

Cleavage plane shear Low-angle faults Brittle, high-angle strike-slip 

faults

Table 2. Deformation nomenclature used in this study.

Deformation 

event

Syndepositional 

faulting

Diagenesis First Second Third Fourth Fifth

Symbol Dmineral D0 D1 D2 D3 D4 D5

Folds F2 (open to isoclinal) F3 (open to closed) F4 (gentle)

Cleavage S0 stylolites S2 stylolitic foliation S3 crenulation 

cleavage and 

stylolites

Lineation L2 L3

Shears, faults 

and fractures

Syndepositional 

normal (?) 

faults

Diagenetic 

veins along 

extensional 

fractures

Low-angle 

thrust 

F2 axial plane shear Low- angle 

faults

High-angle 

strike-slip 

faults
Structure of the Lower Southwest Orebody 375

Methodology

This study is based on detailed underground mapping 

of the Lower Southwest orebody, and parts of the Upper 

Southwest, 224 West Bench, and 200 South orebodies (fig. 

3). Detailed maps were prepared by setting up a 33-cm (1-ft) 

grid along sidewalls (“ribs”) in ore accesses and stopes, and 

recording geological and structural data at a scale of 1 cm 

= 98 cm (1 inch = 8 feet). Structural analysis of the Lower 

Southwest, Upper Southwest, 224 West Bench, and 200 

South orebodies included orientations of bedding measured 

in the stratigraphic hanging-wall units, contacts between the 

mineralized horizon and footwall and hanging-wall units, 

F2 fold hinges, S2 stylolitic foliation, L2 bedding-cleavage 

intersection lineation, F3 fold hinges, S3 stylolitic spaced 

crenulation cleavage, L3 crenulation lineation, and low- and 

high-angle fault surfaces (table 2). Pre-D2 structural elements include inferred synmineralization faults, which were 

interpreted after reconstruction of the Lower Southwest 

orebody (Freitag, 2000), and diagenetic stylolites and veins, 

which were examined in petrographic studies. Early L1 

lineations were not recognized, and F4 folds were identified using plan and rib map patterns. Most measurements 

were taken in the stratigraphic hanging-wall argillite (fig. 4) 

and highly strained stratigraphic footwall phyllites (fig. 5) 

because they best reveal well-developed microfabrics. Petrographic studies of the host rocks were used to characterize 

structural elements.

Structure of the Lower Southwest 

Orebody

Structural analysis of the complexly deformed Lower 

Southwest orebody revealed structural elements similar to 

those described in studies by Lindberg (P.A. Lindberg, written commun., 1996) and Proffett (chap. 7) in other parts of 

the Greens Creek deposit, including F2 folds, S2 foliation, 

L2 lineation, F3 folds, S3 cleavage, L3 lineation, low-angle 

thrust faults, and high-angle faults. Detailed underground 

mapping of stopes and construction of plan view maps, cross 

sections, and long sections show that three major folds can 

be traced through the Lower Southwest orebody. These are 

an open F2 anticline, a tight to isoclinal F2 syncline, and 

a tight to isoclinal F2 anticline (figs. 6 and 7). The Lower 

Southwest orebody is refolded by stope-scale, open to closed 

F3 and gentle F4 folds, which locally complicate the structure. Displacement of the Lower Southwest orebody along 

low-angle thrust faults and high-angle strike-slip faults is 

minor. The thrust faults are interpreted as minor slip planes 

that formed below the Klaus thrust fault, and the high-angle 

faults are interpreted to have developed subparallel to and 

east of the Maki fault zone. Domain analysis indicates that 

the Lower Southwest orebody falls into a single structural 

domain.

Dmineral Deformation

Although pre- to synmineralization faults have not been 

mapped, Freitag (2000) interprets early faults on the basis of 

the original distributions of ore lithologies revealed by unfolding the Lower Southwest orebody to its predeformed state. 

Palinspastic reconstruction of the Lower Southwest orebody 

revealed very distinct ore lithology distributions on an orebody 

scale. Isopach maps of these ore lithologies, constructed 

on a restored base, showed spatially separate, north-southelongated accumulations of massive sulfide and mineralized 

dolomite (Freitag, 2000). Freitag interpreted the linear morphologies of the accumulations to reflect primary depositional 

thicknesses and interpreted that the thickest accumulations 

formed above, or adjacent to, inferred, normal faults. The 

interpreted synmineralizing faults would trend north, although 

no further evidence for these faults was found, and may have 

formed in a back-arc basin environment.

D0 Deformation

Quartz-carbonate veins (“ladder veins”) are in massive 

argillite beds in the hanging wall of the Lower Southwest 

orebody. The veins are oriented perpendicular to massive argillite beds and are interpreted to have formed during burial and 

diagenesis (D0). The veins are commonly offset along early 

(S0) stylolites (fig. 8).

D1 Deformation

Evidence for D1 deformation is recorded by small thrust 

faults that offset hanging-wall massive argillite beds in the 

Lower Southwest orebody (fig. 4). Beds offset by these small 

(less than 1 m) displacement thrust faults have subsequently 

been folded by ductile D2 and D3 events. In the studied areas, 

unfolding of later structures indicates offset is unidirectional, 

with the hanging wall offset to the east (fig. 9). Evidence of 

early thrust faulting at an orebody scale (greater than 100 m) 

was not recognized.

D2 Deformation

The earliest postmineralization ductile event (D2) to 

deform the Lower Southwest orebody led to the development of tight to isoclinal (interlimb angle 0–30o; Ramsay and 

Huber, 1987) F2 folds (fig. 6). These F2 folds are important 

features of the Lower Southwest orebody, as they structurally 

thickened parts of the orebody. Rarely, open F2 folds were 

recognized.

Small-scale F2 folds with amplitudes of up to 2 m are 

easily recognized in folded massive argillite beds (fig. 4). On 

a stope scale, major F2 folds with amplitudes greater than 9 

m can be traced on rib and plan maps (fig. 10); on an orebody 

scale, these major F2 folds are more easily recognized on 

cross sections (fig. 6).
376 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

?

200 West 

Bench

Upper

Northwest

North

Zone

5250 ore 

(Fred)

Maki fault zone

Central 

zone

South 

zone

N

0

1,000 FEET

300 METERS

0

“Shop

 ore”

West

ore

East ore

XS 2400

LS 5500

Northwest 

ore

Big Sore

Lower 9A

ore

Upper

XS 1500

Level 1000

Level 0

Portal

Level 500

XS 2500

XS 3000

XS 3500

XS 4000

XS 4500

XS 5000

XS 5500

XS 6000

XS 6500

XS 7000

LS 3500 LS 5500 LS 6500

XS 2000

LS 4500

500 Level

LS 4500

XS 2500

0 Level

XS 2800

XS 2200

Detail of study area

224 West

Bench

Southwest ore 200 South

A

B

EXPLANATION

XS cross section

LS long section

Figure 3. Plan of Greens Creek 

orebodies (A) and Lower Southwest 

orebody located on the mine grid (B).
Structure of the Lower Southwest Orebody 377

F3 axial traces

D1 thrust

fault

F2 axial trace

Folded massive

argillite beds

D1 thrust

fault

0

3 FEET

1 METER

0

Figure 4. Drawing and photograph of typical structures in massive argillite beds in the stratigraphic 

hanging wall of the Lower Southwest orebody (284 ore access, looking south).

S2

F

S2

F

F

S2

S3

Argillite

Siliceous rock

Massive pyrite band F

F

S2

F

F

S3

S3

F

F F S2

Quartz

F

0

9 FEET

3 METERS

0

 EXPLANATION

S3 - S3 crenulation cleavage

S2 - S2 foliation

 F Fault

Figure 5. Rib map of siliceous rock showing well-developed S2 and S3 foliation (224 West 1 access, looking north).
378 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

A plan projection of major F2 folds of the Lower Southwest orebody (fig. 11) shows that the general trend of these 

is to the south-southwest. The plunge of F2 axes varies along 

trend due to later F4 folding but generally ranges from 0o to 

22° (fig. 12).

S2 foliation of footwall siliceous rocks is formed by 

closely spaced, thin (less than 25–50 μm) stylolitic foliation 

planes composed of dark brown to black, soft, opaque, organic 

material (fig. 13). Some stylolites truncate small quartz veinlets. In mica-rich sericitic phyllites, white micas are aligned 

and form a penetrative S2 foliation (fig. 14).

The orientations of S2 foliation planes were measured in 

footwall rocks (sericitic phyllite, siliceous rock, chert). These 

S2 foliation planes strike north to northwest in the Lower 

Southwest orebody, with a subordinate strike to the northeast, 

and vary in dip from almost vertical to almost horizontal.

The author interprets cross-section patterns, such as 

mapped in the rib map of level 315 (fig. 15), to indicate that 

D2 shears formed during later stages of D2 deformation. The 

combination of mica-rich, incompetent footwall rocks and a 

thin, thus relatively incompetent, massive sulfide layer probably enabled a slip plane to form along axial planes of F2 

isoclines, which developed into D2 shears.

D3 Deformation

The ductile D3 deformation event led to the development of open to closed (120–30o; Ramsay and Huber, 1987) 

F3 folds throughout the argillite unit. The wavelength of F3 

folds in argillite varies but is generally about 5 m, and the F3 

axial planes are inclined 45o to 60o to the east (fig. 16). Proffett 

(chap. 7) describes the distribution of F3 folds in a “ripple and 

fall” model, which suggests that F3 folds are locally developed 

(fig. 17).

Hinges of F3 folds plunge 5o to 55° (average about 35o) 

to the southeast, although a few F3 fold hinges plunge to 

the northwest. The author interprets the northwest plunge to 

be due to later folding perpendicular to the trend of F3 fold 

hinges.

?

?

?

? ?

?

?

?

?

?

?

?

?

EXPLANATION

0

90 FEET

30 METERS

0

Level 224

Lower Southwest

thrust fault system

Lower Southwest fault

High-angle

fault

F3

F3

F3

F3

West East

F2

F2

F2 F2

F2

F2 anticline

F2 anticline

F2 syncline

F2

Argillite

Sulfide horizon (massive sulfide and

 mineralized dolomite)

Silicified slaty argillite

Chert

Mineralized chert

Siliceous rock

Silicified sericitic phyllite

Sericitic phyllite

Mariposite-bearing phyllite

Serpentine chlorite phyllite

Right-slip fault (cross moving away from

 plane and dot moving toward plane)

?

?

?

?

?

?

?

?

F2

?

?

Figure 6. Cross section 2500 of the Lower Southwest orebody. Section line is shown in figure 7.
Structure of the Lower Southwest Orebody 379

 F2

anticline

F2 syncline

F2 anticline

F4?

F2

LSW

Fault

XS 2500

0-30° dip of contact

30-60° dip of contact

60-90° dip of contact

F2 axial trace, arrow indicates 

direction of plunge of F2 fold

F4 axial trace

Lower Southwest fault, with dip 89 LSW

Fault

89

65

40

23

0

90 FEET

30 METERS

0

EXPLANATION

Argillite

Sulfide horizon (massive sulfide

 and mineralized dolomite)

Silicified slaty argillite

Chert

Siliceous rock

Silicified sericitic phyllite

Sericitic phyllite

Mariposite phyllite

Serpentine chlorite phyllite

N

Figure 7. Plan map of the 224 level, Lower Southwest orebody. Level is shown in figure 6.
380 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

The L3 intersection lineations, which formed at the intersection between S2 foliation and S3 cleavage, are fine, tightly 

spaced to almost penetrative, linear features on S2 foliation 

surfaces. The L3 lineations primarily plunge 10–50° to the 

southeast, though a few plunge to the northeast, similar to F3 

fold hinge orientations.

Although F2 fold hinges plunge steeper to the southsouthwest and southeast than F3 fold hinges, both F2 and 

F3 fold hinges in the Lower Southwest orebody are approximately coaxial. Ramsay and Huber (1987) developed patterns arising from superposition of different fold generations, 

and their principal type 3 fold pattern describes the observed 

geometry of the superposition of F2 and F3 folds in the Lower 

Southwest orebody (fig. 18).

A strongly developed S3 cleavage deforms footwall 

rocks, especially sericitic phyllites and siliceous rocks. In 

siliceous rocks, S3 forms a spaced dissolution and crenulation 

cleavage, which offsets or crenulates the S2 foliation. In thin 

section, this spaced cleavage is recognizable as thick (greater 

than 0.1 mm) stylolites composed of dark brown to black, soft, 

nontranslucent, and nonreflecting organic material (fig. 19). In 

phyllitic rocks, S3 crenulation cleavage is defined by spaced 

cleavage domains composed of both stylolites of opaque, 

organic material, and white mica, that have gradational transitions with microlithons (Passchier and Trouw, 1996) (fig. 20). 

The S3 cleavage strikes north-northwest and dips moderately 

to steeply to the east.

Structural analyses incorporated measurements from 

the entire Lower Southwest orebody. This was done because 

the Lower Southwest orebody belongs to a single structural 

domain, which was determined by Freitag (2000), who 

undertook a π-analysis of orientations of massive argillite beds 

for individual mapped levels and compared combined F2/F3 

π-axes. Because the beds are assumed to have been subparallel prior to deformation, F2/F3 π-axes of the same structural 

domain should show similar orientations, which is generally 

true for F2/F3 π-axes of massive argillite beds of each mapped 

level in the Lower Southwest orebody.

Figure 8. Photomicrograph of a quartz-carbonate “ladder” vein 

offset along a (S0) stylolite. Both “ladder” vein and stylolite were 

probably formed during burial and diagenesis (D0). mm, millimeters.

W E

0 1 METER

Quartz-carbonate

vein

0.1 mm

S0 stylolite

Quartz-carbonate

vein

Figure 9. Cross section illustrating early east-directed thrust 

faults (D1) in massive argillite beds after removing effects of F2 

and F3 folding (reconstructed from figure 4).

Start of 7.5-meterwide rubbly zone

F2

F2

F3

?

F2 fold closure

Mineralized

dolomite

Argillite

Massive sulfide

?

F3

?

High-angle 

fault

Fractured zone High-angle 

fault

High-angle 

faults

0 3 METERS

Figure 10. Rib map showing argillite forming the core of a major isoclinal F2 syncline, Lower Southwest 

orebody (level 224, looking north).
Structure of the Lower Southwest Orebody 381

85 meters

High-angle

fault

Lower Southwest

 thrust system

F2 

F2 

F3

F3

F2 

F2 

F2 

F2 

F2 F2 

F2 

F3 

F3 

ARGILLITE

ARGILLITE

F3 F3 

100 meters

67 meters

?

? ?

?

?

F2 

1

?

Lower Southwest

fault

Median line

PHYLLITE

2

F2 fold axis #1 

F2 fold axis #2

F2 fold axis #3

F2 fold axis #5

Long section

Cross section

LS

XS 0

15 METERS

50 FEET

0

0

30 METERS

100 FEET

0

N

EXPLANATION

XS 2250

XS 2300

XS 2350

XS 2400

XS 2450

XS 2500

LS 4400LS 4500

LS 4600

3 4

6 8 5

7

9

10

Figure 11. Plan map of level 224 onto which the locations of F2 fold axes are projected to show the axis trends. Inset map, which is a 

simplification of figure 6, gives the numbering of the fold hinges.
XS 2425 XS 2450 XS 2500 XS 2250 XS 2350XS 2400 XS 2300 XS 2450 XS 2600 XS 2425 XS 2400 XS 2500 XS 2350 XS 2300 XS 2250 XS 2600 1 2 XS 2600 XS 2600 XS 2500 XS 2450 XS 2500 XS 2450 XS 2425 XS 2425XS 2400 XS 2400 XS 2350 XS 2350 XS 2300 XS 2300 XS 2200 53 0

0

F2 F2 F2 F2 LoCro

LS

XS

EXPLA

LS 4400

LS 4450

LS 4500

LS 4550

LS 4600

85 meters

High-angle

fault Lower Southwest

 thrust system

F2 

F2 

F3

F3

F2 

F2 

F2 

F2 

F2 F2 

F2 

F3 

F3 

ARGILLITE

ARGILLITE

F3 F3 

100 meters

67 meters

?

? ?

?

?

F2 

1

?

Lower Southwest

fault

Median line

PHYLLITE

2

3 4

6 8 5

7

9

10

0

30 METERS

100 FEET

0

Level 300

Level 250

Level 200
Structure of the Lower Southwest Orebody 383

Figure 12 (facing page). Cross section 2400 (looking north) onto 

which the locations of F2 fold axes are projected to show the axis 

plunges. Inset map, which is a simplification of figure 6, gives the 

numbering of the fold hinges.

0.1 mm

Quartz-carbonate

vein

S2

S2

S2 S2

S2

S2

0.1 mm S3 crenulation

S3 crenulation

S2

S2

Figure 13. Photomicrograph of S2 

stylolitic foliation in stratigraphic 

footwall siliceous rocks. mm, 

millimeters.

Figure 14. Photomicrograph of 

white mica forming penetrative 

S2 foliation. S2 foliation is folded 

S3 crenulation cleavage. mm, 

millimeters.
384 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

I : tight to isoclinal

F2 folding event

II : D2 shearing 

along F2 anticline

III : F3 open folding

F3

F2

D2 shear

D2 shear

IV : Schematic diagram of the post-thrust structure—a detailed rib map of 

Level 315 is incorporated into the diagram.

?

Thrust system

Rib map of

 Level 315

D2 shear

?

F2

F3

F3 F3

F3

F3

0

11 METERS

30 FEET

0

F2

D2 shear F2 F2

F2 F2 F2 F2

F2

West East

EXPLANATION

Argillite (hanging-wall rocks)

Sulfide horizon

Phyllite (footwall rocks)

Figure 15. Cross-sectional model showing the development of shears along F2 anticlines during progressive 

D2 deformation. Subsequent D3 deformation and late faulting resulted in the geometry of the Lower Southwest 

orebody mapped on level 315.
F3

F3

F3

F3

F3

F3

F3

F2

F2

F2 

Mats for underground

rock support

0

0

West 

EXPLANATION

Massive argillite bedSlaty argilliteMassive sulfide

Figure 16. Rib map of F3 folds; F3 axial traces dip to the east (level 359, looking north).
386 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

D4 Deformation

Two low-angle fault systems, the Klaus thrust fault (fig. 

2), which has a northeasterly strike and dips 30o to 50o toward 

the southeast, and the Lower Southwest thrust faults, (fig. 6) 

deform the Greens Creek deposit. These low-angle faults postdate F3 folds as they truncate F3 folds. High-angle faults offset these low-angle thrust faults, which are therefore assigned 

to a D4 deformation event (P.A. Lindberg, written commun., 

1997; oral commun., 1998; Freitag, 2000; Freitag, unpub. data, 

1997). The low-angle faults mark the change from ductile to 

brittle deformation.

The Lower Southwest thrust fault system is a feature in 

the Lower Southwest orebody, which has brecciated a zone 

and weakened rocks, thus causing rock failure during mining. The thrust faults are of minor importance geologically 

because the offset along the faults is small (approximately 24 

m). The Lower Southwest thrust fault system consists of two 

subparallel thrust faults (upper and lower) that are less than 

3 m apart in the southern part and about 10 m apart in the 

northern part of the Lower Southwest orebody. Characteristically, a brecciated zone of about 15 cm, containing quartz and 

dolomite matrix, is present on both sides of the fault planes, 

and carbonate is locally abundant. The fault surfaces commonly contain a thin (less than 14 mm) layer of gouge.

These thrust fault systems generally dip gently (5–20o) 

southeast, southwest, or northwest; however, locally, they dip 

moderately to steeply (up to 85o). Steeper segments have the 

appearance of having been folded by F3 folds (fig. 21). But 

because the thrust faults generally cut F3 folds, the flexures 

are not considered the result of F3 folding, and the author suggests they formed after the F3 folding event. Furthermore, the 

frequency of F3 folds in argillite (three folds per 15 m) differs 

from the frequency of steeper sections of the thrust faults in 

argillite (1 steeper section per 15 m) (Katja Freitag, written 

commun., 1998). The author therefore interprets steeper thrust 

fault sections as transfer faults between thrust and high-angle 

faults (see subsequent sections).

“Ripple”

“Fall”

WSW ENE “Fall”

F3 axial planes

Sulfide horizon dips 

steeply where not

folded by F3

Average dip of

sulfide horizon

is lower where

folded by F3

Figure 17. Schematic cross section illustrating the “ripple and fall” model of F3 fold 

distributions at the Greens Creek deposit (modified after Proffett, written commun., 1997).
Structure of the Lower Southwest Orebody 387

2 - Superposition of open F3 folds

3 - Resulting convergent-divergent pattern

1 - Isoclinal F2 folding event

Frequently observed fold

pattern in folded massive 

argillite beds of the 

Lower Southwest orebody

F2 axial plane

F3 axial plane

Massive

argillite

bed

Figure 18. Ramsay and Huber’s (1987) principal type-3 three-dimensional fold. The form arises by the superposition of 

shear folds on preexisting fold forms. This leads to a convergent-divergent pattern. Although the first fold axial surfaces 

become curved, the first fold hinges are not markedly deflected, and all fold axial directions, both first and second 

phase, tend to be subparallel (modified after Ramsay and Huber, 1987).
388 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

S3 stylolite 0.1 mm

S3 stylolite

S2 stylolitic

cleavage

S2 stylolitic

cleavage

Figure 19. Photomicrograph of S3 stylolites in siliceous rock. mm, millimeters.

Offset along the thrust faults was determined using F2 

and F3 fold hinges as piercing points. To do this, the geology 

above and below the thrust faults was projected downward and 

upward, respectively, onto plan view maps (Freitag, 2000). In 

general, the geology on the hanging wall and footwall of the 

fault system could be correlated, with a maximum offset of 

22 m determined across the faults. There was little deformation of hanging wall and footwall during or after faulting.

Small-scale D4 fabrics, such as F4 hinges and S4 foliation, were not recognized in the Lower Southwest orebody. 

However, gentle (interlimb angle 180–120o; Ramsay and 

Huber, 1987) F4 folds were recognized on a stope scale as 

undulations of the orebody about east-west-oriented axes. The 

F4 folds resulted in local north-plunging F2 and F3 fold axes 

and are recognized on plan maps where stratigraphic footwall 

rocks are exposed along the southern part of the generally 

south- to southeast-plunging Lower Southwest orebody (fig. 7).

D5 Deformation

The final stage of deformation in the Lower Southwest 

orebody resulted in high-angle strike-slip faults referred to as 

Maki-type faults. The faults mostly show right-slip, although a 

few faults with left-slip were recognized. High-angle, right-slip 

faults strike northwest to north-northwest and dip 80–90°. 

Faults are commonly narrow (less than 10 cm) but widen 

locally to 2 m. In phyllitic rocks, faults are characterized by 

zones of soft, gougy, bleached phyllite. Massive sulfide and 

argillite in fault zones are brecciated, and discrete fault surfaces 

bounding the zone contain thin gouge (less than 14 mm).

The Lower Southwest orebody is offset along the Lower 

Southwest fault (Katja Freitag, written commun., 1998), which 

has a map separation of less than 30 m (fig. 7). An obliqueslip component is documented by slickenlines in calcite that 

plunge as much as 20°; however, this is of minor importance 

in the Lower Southwest orebody, as the map separation along 

the fault is less than 30 m.

Right-slip faults generally strike northwest, and left-lateral 

faults strike north (fig. 22). These two fault sets intersect at an 

angle of about 35o, suggesting they may be conjugate faults 

(Ramsay and Huber, 1987). The strike of both sets of highangle faults is similar to that of regional high-angle faults in 

southeast Alaska (fig. 23).

Faults with intermediate dips are not well understood. 

They are distinguished from the high-angle faults and lowangle thrust faults by having dips of approximately 40–50° 
Structural Transition and Comparison to Neighboring Orebodies 389

Stylolite

S3 cleavage

domain

Crenulated

S2 foliation

Microlithon

0.1 mm

0.1 mm

Figure 20. Photomicrograph and sketch of spaced S3 

crenulation cleavage in sericitic phyllite, defined by S3 

cleavage domains and microlithons. mm, millimeter.

and apparent normal offset of approximately 1 m. In addition, the faults may offset high-angle faults, which suggests 

they developed later than the high-angle faults. The author 

postulates that relaxation of the stress regime under which the 

high-angle faults developed resulted in small normal faults 

with minor (less than 1 m) offset.

Although the thrust faults of the Lower Southwest 

orebody are truncated by high-angle faults, they also splay into 

the high-angle faults. In such cases, propagation of the highangle faults across the thrust fault resulted in fractured, but not 

offset, rock units. Lear (K.G. Lear, oral commun., 1997) and 

Proffett (chap. 7) have suggested that the Lower Southwest 

thrust faults are kinematically related to high-angle faults. The 

author interprets the thrust faults to predate the high-angle 

faults, however, because quartz-calcite only precipitated along 

the thrust faults but not in the high-angle faults, and the thrust 

faults commonly are truncated by the high-angle faults.

In addition, the author suggests that the lower thrust fault 

of the Lower Southwest thrust fault system was locally reactivated during high-angle faulting. The author proposes a model 

where high-angle, right-slip faults transferred strain to the thrust 

fault along splaying faults and locally reactivated sections of 

the thrust fault (fig. 24). A three-dimensional block model (fig. 

25) shows the geometry of fault blocks and indicates that an 

intensely fractured zone developed between fault blocks.

Structural Transition and Comparison 

to Neighboring Orebodies

Understanding the transition between adjacent orebodies 

at Greens Creek is complicated by the complex structure of 

the deposit. A geometry of the transition between the Lower 

Southwest orebody and the Upper Southwest and 224 West 

Bench orebodies was developed by the author (fig. 26) based 

on plan map and cross-section patterns.

The orientations of bedding and ductile deformation 

structures of the Lower Southwest, Upper Southwest, 224 

West Bench, and 200 South orebodies were compared by 

the author (table 3) and used to develop the following model 

explaining the difference in deformation style between thick 

orebodies (Lower Southwest and 200 South orebodies; greater 

than 10 m) and thin orebodies (Upper Southwest and 224 West 

Bench orebodies; less than 3 m).

The Upper Southwest orebody is folded by isoclinal 

F2 folds, which have steeply plunging axes that are located 

approximately at cross section 2700 (fig. 3) and are less 

apparent farther to the south. The orebody is located along 

the eastern limbs of two F2 anticlines. Toward the south, the 

Lower Southwest orebody is also deformed by F2 folds. The 

hinge lines of the F2 anticlines and synclines of both orebodies 

can be interpolated to form continuous hinge lines between the 

orebodies. The model suggested for the change in plunge of 

F2 fold axes between the Upper and Lower Southwest orebodies is that an F4 fold axis is located in the area of cross section 

2700 (fig. 3), trending perpendicular to the F2 fold axes.

The 224 West Bench orebody is located to the west of the 

Lower Southwest and Upper Southwest orebodies. The Lower 

Southwest orebody is characterized thin (less than 1 m), usually 

discontinuous layers of stratigraphic footwall phyllite close to 

the western limb of a D2 shear that developed from an isoclinal F2 anticline. The author interprets phyllite as the core of 

this sheared anticline. The 224 West Bench orebody forms the 

continuation of the mineralized horizon toward the west and lies 

along the upper western limb of the sheared anticline. The mineralized horizon thins to form a barren contact between phyllite 

and argillite. The barren contact is interpreted by the author 

to be folded into a syncline. Proximal to the Upper Southwest 

orebody, which lies toward the northeast of the 224 West Bench 

orebody, the contact becomes mineralized, with the Upper 

Southwest orebody located on the eastern limb of the sheared 

anticline recognized in the Lower Southwest orebody.
390 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

F3

F2

F2 fold

closure

F3

F3

F2

Thrust - flat

Thrust - steep

0 3 METERS

EXPLANATION

Massive argillite bed

Slaty argillite

Sulfide horizon (massive sulfide

 and mineralized dolomite)

Figure 21. Rib map depicting intermediate to steeper sections along the upper thrust of the Lower Southwest thrust system (284 

level, looking north).

Right-slip faults Left-slip D fault

~35°

Figure 22. Rose diagram comparing strikes of left-slip faults (n=8) with right-slip high-angle faults (n=57). The difference in strike is 

about 40°, suggesting these are conjugate faults.
Structural Transition and Comparison to Neighboring Orebodies 391

Ch

Ch

W

Cr

Cr

A

G

G

G

Cr

134°

56°

130°

Terrane Key

Ch

W

G

A

Cr

Y

&

T

C

Y

&

T

Y

&

T

C

Chugach

Wrangellia

Gravina

Admiralty

Admiralty

Island

Alexander

Craig

Y & T

C

Yukon-Tanana/

 Taku

Coastal

Prince of Wales Island

58°

0

50 MILES

100 KILOMETERS

Skagway

Haines

BRITISH COLUMBIA

ALASKA

Sitka

Juneau

Ketchikan

Wrangell

FAIRWEATHER FAULT

CHATHA

M STRA

TI FA

U

T

CLARENCE

STRAIT

FAULT

PERIL

STRAIT FAULT

Petersburg

GREENS

CREEK

DEPOSIT

N

Figure 23. Map of the various terranes and their bounding regional strike-slip faults, southeast Alaska (modified from 

Sutley and others, 1990, and Newberry and others, 1997), and the structural setting of the Greens Creek deposit.
392 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

1 - thrusting event

2 - right-slip faulting event

(relatively smaller offset indicated by smaller displacement symbol)

Summary diagram combining the two stages of faulting

(localized reactivation of the lower thrust is marked)

Upper thrust

Lower thrust

Propagation of

high-angle

fault (no offset)

Reactivated sections of the lower thrust

Displacement to north

 (into plane of figure)

Displacement to south

 (out of plane of figure)

W E

Propagation of

high-angle

W fault (no offset) E

W E

Figure 24. Schematic cross section illustrating the sequence of brittle deformation events, looking 

north.
Structural Transition and Comparison to Neighboring Orebodies 393

Fault block offset

to the north

Fault block offset

to the south

Fault zone intensely 

fractured

Propagation of

high-angle

fault (no offset)

Displacement to north

Displacement to south

 (size of symbol indicates relative

 magnitude of displacement)

N

Figure 25. Block diagram representing two fault blocks of massive sulfide of the Lower Southwest orebody offset 

across right-slip faults, with an intensely fractured fault zone.

A simplification of the structural similarities and differences (table 4) shows that bedding, F2/L2, and F3/L3 orientations are similar in all of the examined orebodies (figs. 27, 

28). The S2 foliation (fig. 29) and S3 cleavage (fig. 30) have 

consistent dips in the Lower Southwest and 200 South orebodies. In contrast, S2 foliation and S3 cleavage in the Upper 

Southwest and 224 West Bench orebodies have variable strikes 

and dips.

The author uses a modified schematic representation 

of polyharmonic folds (fig. 31) after Ramsay and Huber 

(1987) to explain the difference in orientation of S3 cleavage between the orebodies as a function of the relative 

competency of the orebody. The schematic representation 

of polyharmonic folds suggests that during ductile deformation of the Greens Creek deposit, the effect of folding was 

more pronounced in relatively less competent, thin orebody 

sections, resulting in higher frequencies and amplitudes of F2 

and F3 folds and variable orientations of S2 foliation and S3 

cleavage. In contrast, relatively competent, thick orebodies 

formed consistently oriented folds, with consistently oriented 

S2 foliation and S3 cleavage. The fold structure, therefore, is 

more complex in the thinner orebodies. The least competent 

rocks, slaty argillite and sericitic phyllites, show the highest 

degree of deformation.
394 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

F2 hinge lines

Schematic cross section 

of the Lower Southwest 

orebody on XS 2400

Schematic plan 

view of the Upper

Southwest orebody

on the 464 level

Phyllite

N

E

Down

300 level

(approx.)

464 level

XS 2700

(approx.)

Argillite

Schematic cross

section of the 224

West Bench orebody

on XS 2400

90 m

50 m

Figure 26. Schematic model for the transition from the Lower Southwest to the Upper Southwest and 224 West Bench orebodies based 

on F2 fold geometry. F3 folds, which have a similar trend to F2 folds, are unfolded to simplify the model (thin black lines contour the 

surface of footwall phyllites).
Structural Transition and Comparison to Neighboring Orebodies 395

Table 3. Comparison of orientations of structural features in the Lower Southwest, Upper Southwest, 224 West Bench and 200 South 

orebodies. The notations “thick” and “thin” refer to relative thickness (greater than 10 meters and less than 3 meters, respectively) of 

the orebodies.

Structural feature Lower Southwest (thick) Upper Southwest (thin) 224 West Bench (thin) 200 South (thick)

Bedding F2/F3 p-axes similar No data No data

F2/L2 Similar orientation, trend generally to southeast, variable plunge No data No data

S2 General strike northwest, 

general dip to southwest Varied strike and dip No data

F3 5–55° to southeast, minor 

northwest trend 10–66° to southeast No data 10–40° to southsoutheast

L3 5–50° to southeast, minor 

northwest trend 10–50° to southeast 10° to southsoutheast 45° to southeast

S3 Consistent dip of 40–90° to 

east

Variable dip of 40–90° to east,

southeast, south and southwest

Consistent dip of 

50–65° to east

Table 4. Comparison of orebody thickness and orientations of structural features.

Structural feature Thick orebody (Lower Southwest, 200 South 

orebodies)

Thin orebody

(Upper Southwest, 224 West Bench orebodies)

Bedding Same

F2/L2 Same

S2 Dip to the west Variable dip direction to northeast or southwest

F3 Same

L3 Same

S3 Moderate to steep dip to east Variable—east-northeast and southeast dips dominant
396 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

(a) (b)

Lower Southwest Upper Southwest

200 South

F3 fold axes

Figure 27. Lower hemisphere equal area projections of F3 fold axes of the (a) Lower Southwest (circles; 

n=26) and (b) Upper Southwest (triangles; n=25) and 200 South (stars; n=2) orebodies.

(a) (b)

Lower Southwest Upper Southwest

224 West Bench

200 South L3 crenulations

Figure 28. Lower hemisphere equal area projections of L3 crenulation lineations of the (a) Lower Southwest (n=22) 

and (b) Upper Southwest (triangles; n=16), 224 West Bench (square; n=1), and 200 South (star; n=1) orebodies.
Structural Transition and Comparison to Neighboring Orebodies 397

Poles to S2 foliation in footwall

Lower Southwest Upper Southwest

224 West Bench

(a) (b)

(c)

Figure 29. Lower hemisphere equal-area projections of poles to S2 foliation planes measured in footwall rocks of the (a) 

Lower Southwest (circles; n=13), (b) Upper Southwest (triangles; n=42), and (c) 224 West Bench (squares; n=18) orebodies.
398 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Poles to S3 cleavage

Lower Southwest

200 South

Upper Southwest

224 West Bench

(a) (b)

(c)

Figure 30. Lower hemisphere equal area projections of poles to S3 cleavage in the (a) Lower Southwest (circles; n=21), 200 

South (squares; n=4), (b) Upper Southwest (triangles; n=22), and (c) 224 West Bench (stars; n=13) orebodies.
Model of the Structural and Tectonic Evolution of the Greens Creek Deposit 399

Figure 31. Schematic representation of polyharmonic folds developed in competent layers of varying thickness (black) and 

incompetent host materials (grey) showing the effect of the thickness of the mineralized horizon during folding (modified after

Ramsay and Huber, 1987).

Thick competent layer such as the 

Lower Southwest orebody

Thin competent layer such as the

Upper Southwest orebody

Incompetent host rocks such as the

slaty argillite or sericite phyllite

Model of the Structural and Tectonic 

Evolution of the Greens Creek Deposit

The following model outlines the structural evolution of 

the Greens Creek deposit on both a local and regional scale 

(fig. 32). The basis for the model is structural data from, and 

interpretations of, the Lower Southwest orebody and limited 

data from adjacent orebodies (Upper Southwest, 224 West 

Bench, and 200 South orebodies).

A Late Triassic, inferred structural event (Dmineral) is 

interpreted to have formed pre- to synmineralization, normal 

(?) faults in a back-arc basin environment. Subsequent to 

sulfide, carbonate, and argillite deposition, compaction during diagenesis (D0) led to the formation of quartz-carbonate 

“ladder” veins oriented perpendicular to massive argillite beds 

and offset by S0 pressure solution seams.

Late Jurassic to Early Cretaceous small-scale thrust faults, 

which offset massive argillite beds and are attributed to a D1 

deformation event by the author, may have formed during 

partial subduction of the Alexander terrane under the North 

American plate along an east-dipping subduction zone (Plafker 

and Berg, 1994). Late Cretaceous to early Tertiary accretion 

of the Alexander terrane to the North American plate (Gehrels 

and Saleeby, 1987) folded the Greens Creek deposit into early 

open to isoclinal F2 and later open to closed F3 folds. Both F2 

and F3 folds have northerly oriented fold hinges, indicating 

east-west contraction. F3 folds whose axial planes dip easterly 

are interpreted to have formed during back-thrusting of the 

Alexander terrane during later stages of accretion. The F2 and 

F3 folds at Greens Creek may reflect two regionally recognized fold generations along the eastern edge of the Alexander 

terrane. The earlier folds (probably correlative to F2 folds 

at Greens Creek) are tight to isoclinal, with attenuated fold 

limbs, moderately southeast-plunging fold axes, and associated, steeply (70o to 90o) northeast-dipping foliation planes (for 

example, Rubin and Saleeby, 1992). These were crenulated by 

a northeast-trending, spaced cleavage and folded by west- to 

northwest-vergent folds (probably correlative to F3 folds at 

Greens Creek) (for example, Rubin and Saleeby, 1992).

A change in the stress regime from east-west to northeast-southwest and from ductile to brittle deformation resulted 

in the development of low-angle D4 faults (Klaus and Lower 

Southwest thrust fault systems), which offset the Greens Creek 

deposit to the north, and gentle F4 folds, which have eastwest-trending fold axes. Finally, dextral transpression along 

the transform plate margin of southeastern Alaska resulted 

in right-slip faulting, starting in Eocene time, and probably 

formed high-angle, strike-slip faults (for example, Maki fault) 

at Greens Creek.
400 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Quartz-carbonate 

ladder vein Stylolite

Dmineral

pre- to synmineralization

normal (?) faults

Diagenesis

Rifting in a back-arc

environment

(Late Triassic)

D5

right-slip faults, reactivation 

of D4 thrust faults

Subduction and

 accretion

(Late Jurassic to

early Tertiary)

D1 

thrust 

faulting

D2

open to isoclinal

folds and local

axial plane shears

D3

open to closed

 folds

Wrench tectonics

(Eocene to present)

W E

D4 

northerly directed thrust faulting, gentle folds

N S

W E

Thrust faulting

(sometime during

Tertiary ?)

D0

compaction

Sea floor

Sea floor

100 m

2 mm

1 m 30 m 3 m

100 m

Approx. scale

Direction of principal stress

EXPLANATION

Figure 32. Model of the structural and tectonic evolution of the Greens Creek deposit. All views are cross sectional.
References Cited 401

Summary and Conclusions

Detailed mapping of the Lower Southwest orebody 

revealed structural elements throughout the Greens Creek 

deposit, including F2 folds, S2 foliation, L2 lineation, F3 

folds, S3 cleavage, L3 lineation, and brittle faults. However, 

L1 lineations and D4 fabrics were not recognized. Analysis 

of structural elements led to a structural model for the Lower 

Southwest orebody and a tectonic model for the Greens 

Creek deposit.

Pre- to syndepositional faults are inferred from reconstructed ore lithology morphologies and may have formed 

in an extensional back-arc basin environment. The faults are 

inferred to have focused hydrothermal fluids, resulting in 

separate accumulations of massive sulfide and mineralized 

dolomite. Burial and diagenesis of the deposit are recognized 

in diagenetic quartz-carbonate “ladder” veins and stylolites 

in massive argillite beds and were followed by early postdepositional thrust faulting during Late Jurassic (?) subduction of the Alexander terrane, determined in offset of massive 

argillite beds. Ductile deformation features of the Lower 

Southwest orebody, including open to isoclinal F2 and open 

to closed F3 folds, probably developed during Late Jurassic to early Tertiary accretion of the Alexander terrane to 

the North American continent. Major F2 fold hinges, which 

coincide with the inferred syndepositional faults, is interpreted to have developed in zones of weakness created by 

these inferred early faults. Ore type, thickness of orebodies, 

and silicification of the stratigraphic footwall rocks determined the geometry of F2 folds. Tight to isoclinal F2 folds 

deformed and structurally thickened the relatively ductile 

massive sulfide layers and, locally, isoclinal F2 anticlines 

developed into D2 shear zones along the F2 axial planes. 

Open F2 folds formed where stratigraphic footwall argillites 

were silicified and where competent mineralized dolomite 

was the predominant ore lithology. The F3 folds, prevalent in 

thin (less than 2.5 m) massive sulfide layers, refolded open to 

isoclinal F2 folds. Because F3 axial planes are inclined to the 

east, these may have formed during back-thrusting in later 

stages of accretion. The S2 stylolitic foliation, S3 stylolites, 

and locally remobilized ductile sulfide and sulfosalt minerals 

indicate that pressure solution was an important mechanism 

during both F2 and F3 folding.

The main structural features of the D4 event are the 

Lower Southwest thrust faults, which show small offsets 

(generally to the northwest), and gentle F4 folds oriented 

perpendicular to the F2 and F3 axial planes. These D4 structures represent a change from ductile to brittle deformation 

and a change from east-west compression during accretion to 

northeast oriented, dextral transpression along the transform 

plate margin of southeastern Alaska. The youngest D5 deformation features are high-angle, strike-slip faults that locally 

reactivated D4 thrust faults.

Acknowledgments

This paper formed a major part of my Ph.D. dissertation 

and is the result of fieldwork done at the Greens Creek mine 

and research undertaken at the Colorado School of Mines. 

I acknowledge my thesis advisors, M.W. Hitzman and E.P. 

Nelson, for their support and guidance throughout the study. I 

thank the Kennecott Greens Creek Mining Company for supporting my fieldwork and the mine geologists for their input on 

my interpretations. Invaluable discussions on the geology and 

structure of the Lower Southwest orebody and the Greens Creek 

deposit in general were provided by P. Lindberg, J. Proffett, 

C. Taylor, and N. Duke. Financial support came from an SEG 

Student Research Grant. Rick Allmendinger is acknowledged 

for the use of his Stereonet program. Finally, I thank the reviewers C. Thorman and P. Haeussler for their constructive criticism, 

which resulted in a much improved final manuscript.

References Cited

Freitag, Katja, 2000, Geology and structure of the Lower 

Southwest orebody, Greens Creek mine, Alaska: Golden, 

Colorado School of Mines, Ph.D. dissertation, 248 p.

Gehrels, G.E., and Saleeby, J.B, 1987, Geologic framework, 

tectonic evolution and displacement history of the Alexander Terrane: Tectonics, v. 6, no. 2, p. 151–173.

Newberry, R.J., Crafford, T.C., Newkirk, S.R., Young, L.E., 

Nelson, S.W., and Duke, N.A., 1997, Volcanogenic massive 

sulfide deposits of Alaska: Economic Geology Monograph 

9, p. 120–150.

Passchier, C.W., and Trouw, R.A.J., 1996, Microtectonics: 

Berlin, Springer-Verlag, 289 p.

Plafker, George, and Berg, H.C., 1994, Overview of the geology 

and tectonic evolution of Alaska, in Plafker, George, and Berg, 

H.C., eds., The geology of Alaska: Geological Society of 

America, The geology of North America G–1, p. 989–1021.

Ramsay, J.G., and Huber, M.I., 1987, The techniques of 

modern structural geology, volume 2—folds and fractures: 

London, Academic Press, 400 p.

Rubin, C.M., and Saleeby, J.B., 1992, Tectonic history of the 

eastern edge of the Alexander terrane, southeast Alaska: 

Tectonics, v. 11, no. 3, p. 586–602.

Sutley, S.J., Goldfarb, R.J., O’Leary, R.M., and Tripp, R.B., 1990, 

A comparison of geochemical exploration techniques and 

sample media within accretionary continental margins—An 

example from the Pacific Border Ranges, Southern Alaska, 

USA: Journal of Geochemical Exploration, v. 37, p. 255–275.

Three-Dimensional Modeling and 

Visualization of Greens Creek Drill-Hole 

Data

By Gregory K. Lee and Cliff D. Taylor

Chapter 14 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract.......................................................................................................................................................405

Introduction.................................................................................................................................................405

Description of the Dataset........................................................................................................................405

Data-Processing Procedures ..................................................................................................................405

Modeling......................................................................................................................................................406

Minimum-Tension Gridding.............................................................................................................406

Topographic Model...........................................................................................................................408

Ore Model...........................................................................................................................................408

Geochemical Models .......................................................................................................................408

Geologic Structure Models.............................................................................................................410

Visualization................................................................................................................................................410

Conclusions.................................................................................................................................................416

Reference Cited..........................................................................................................................................416

Figures

1. Drill-hole locations, Greens Creek mine area......................................................................407

2. Greens Creek mine orebodies, showing major workings..................................................409

3. Faults, shear zones, and gold distribution within orebodies, Greens Creek mine.........410

4. Chair cut display of silver in orebodies, Greens Creek mine.............................................411

5. Isovalue shell display of silver greater than 10 parts per million in orebodies,

Greens Creek mine ...................................................................................................................412

6. Isovalue shell display of zinc greater than 10 percent in orebodies, Greens

Creek mine .................................................................................................................................413

7. Isovalue shell display of antimony greater than 600 parts per million in

orebodies, Greens Creek mine ...............................................................................................414

8. Isovalue shell display of arsenic: antimony ratios greater than 10 in orebodies,

Greens Creek mine ...................................................................................................................415
Abstract

Three-dimensional modeling and visualization provide 

powerful tools for evaluating and interpreting chemical and 

physical properties in space, including subsurface domains. 

These tools were applied to drill-hole data provided by the 

Kennecott Greens Creek Mining Company for the Greens 

Creek mine on Admiralty Island, southeast Alaska. Threedimensional models of subsurface data from drill-core chemical assays, ore lithology logs, mine workings, digitized faults, 

and digital terrain were produced and combined to create 

visual displays that could be manipulated and rendered as 

images for this report. The validity of the model showing the 

distribution of orebodies is confirmed by comparisons with 

plan and cross-section drawings produced by geologists at 

the mine. The three-dimensional models should therefore be 

useful to guide mining development efforts and could also be 

effectively used to revisit previously developed mine areas to 

determine where additional production might be targeted.

Introduction

This chapter describes methods that were used to render 

Greens Creek mine drill-hole information into three-dimensional models of the distribution of orebodies and of geochemical concentrations within the orebodies. Geologic structures, 

mine workings, and a topographic surface were also modeled 

and were integrated with the other models for purposes of 

scientific visualization. Data descriptions, coordinate transformation procedures, and modeling techniques are included. 

Dynamic Graphics, Inc., EarthVision software was used to 

successfully calculate and display the three-dimensional models, and several graphical images of the modeling results are 

included in this report.

Description of the Dataset

In 1997, the Kennecott Greens Creek Mining Company 

provided core log data for 1,895 exploration drill holes in 

the Greens Creek mine vicinity. There are 12,764 deviated 

segments in these holes and more than a million observations 

and analytical determinations at 75,291 locations along the 

core segments. These data include measured depths, geochemical concentrations, lithologic and ore-type classifications, and inclinations and orientations of drill-hole segments. 

The spatial coordinates of the drill-hole collars (origins) and 

the azimuths of the holes were relative to a local surface grid 

of northings and eastings, measured in feet. The origin of this 

grid, relative to the Alaska State Plane projection, Zone 1, 

Clarke 1866 spheroid, NAD 1927 datum, also in units of feet, 

is 2262748.50N; 2479273.89E. These coordinates correspond 

to lat 58.0234985°N., long 134.7311267°W.

The spatial reference for the mine workings, however, is a 

local grid of cross-section (XS) and long-section (LS) coordinates whose origin is given as northing 12635.93 ft and easting 

17438.42 ft in terms of the surface grid coordinates. Therefore, 

the mine grid origin is at Alaska State Plane Zone 1 coordinates of 2275384.43N and 2496712.31E. The mine grid is 

rotated 26.5651 degrees counterclockwise from due north. The 

mine coordinate elevations are 60 ft higher than true abovesea-level elevations (chap. 7).

Data-Processing Procedures

Although the data were provided with spatial coordinates 

in terms of the local surface grid, it was felt that three-dimensional modeling and visualization of the subsurface data would 

be most useful if rendered in terms of the mine coordinates. 

This necessitated the task of mathematically describing the 

paths of every drill hole in mine-coordinate space. From a 

computational perspective, there are complicating factors presented by the Greens Creek drill-hole data in addition to the 

offset and rotation of the mine grid relative to the surface grid. 

First, the paths of the drill holes are deviated. That is, each 

hole may be composed of numerous segments with varying 

azimuths and inclinations. Furthermore, because the origins of 

most of the drill holes are underground, the inclinations of the 

many boreholes vary from downward to upward (fig. 1).

Path calculations were performed by first converting the 

surface grid northing and easting coordinates, given for the 

collar (origin) locations of the drill holes, into mine cross section and long section coordinates, respectively. After revisiting 

Three-Dimensional Modeling and Visualization of Greens 

Creek Drill-Hole Data

By Gregory K. Lee and Cliff D. Taylor
406 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

previous lessons in geometry and trigonometry, the following 

formulas were derived:

XS N N E E = − − −  ( )  

 ( ) tan cos 0 0 a a , (1)

and

LS

E E = N N E E − + − − −  ( )  



( )

cos

( ) tan sin 0

0 0 a

a a , (2)

where E0 is the surface grid easting of the origin of the mine 

grid,

E is the surface grid easting coordinate of the drill-hole 

collar (origin),

N0 is the surface grid northing of the origin of the mine 

grid,

N is the surface grid northing coordinate of the drillhole collar (origin),

a is the angle of axis rotation.

The next step was to calculate the three-dimensional location of each deviation in every drill hole, given the measured 

downhole depth of each inflection and the inclination and 

azimuth of the drill hole at each of these points. The following 

calculation framework was derived:

LS LS MD n = + ( ) 0 cos sin φ θ , (3)

XS XS MD = + ( ) 0 cos cos φ θ , (4)

TVDSS Z MD = + − [ ( sin )] 0  60 , (5)

where MD is the measured downhole distance from the origin 

of the core segment,

LS0 is the long section coordinate of the origin of the 

core segment,

XS0 is the cross-section coordinate of the origin of the 

core segment,

Z0 is the mine elevation coordinate,

	 f is the inclination of the drill-hole segment from 

horizontal, in radians,

	 q is the azimuth (relative to LS-XS axes) of the drillhole segment, in radians,

TVDSS is true vertical distance above sea level 

(elevation).

Because the azimuths and inclinations of the boreholes 

change at inflection points, or deviations, along the paths, the 

application of these formulas is somewhat involved. Each time 

a point of inflection is encountered along a hole, the 3-D coordinates must be calculated for the inflection point and then 

reintroduced into formulas 3–5 as a new origin for the next 

section of core, until another deviation is encountered, and so 

on. To apply the required series of successive calculations for 

each of the drill holes with thousands of deviated segments, 

Robert McFaul of Dynamic Graphics, Inc. (DGI), wrote and 

provided programming code to accomplish the task. Bob 

Belcher of DGI also assisted with subsequent modeling tasks.

The log and assay data were recorded for core segments 

defined by a top (first) measured downhole depth and a bottom 

(second) measured depth. It was felt that a reasonable single 

measured distance to attach to each data point is the midpoint 

of the core segment from which the data were obtained. This 

midpoint was calculated for each core segment and was used 

as the measured downhole depth for each data point.

Modeling

For three-dimensional modeling of the drill-hole data, 

it was necessary to calculate the coordinates of each of the 

observation locations in three-dimensional space, in this case 

LS, XS, and TVDSS (elevation). This task was performed using 

Dynamic Graphics, Inc., EarthVision software. By incorporating core logs and assay data with the drill-hole paths, the 

software calculated the three-dimensional coordinates of each 

data point. The result was a file of data with associated drillhole identifiers, three-dimensional coordinates, and associated 

physical and chemical properties. These property data were 

used as input for three-dimensional EarthVision modeling 

calculations.

This procedure produces a three-dimensional grid 

depicting the calculated distribution of the measured property 

throughout a defined volume. The calculated models are grids 

in the shape of rectangular prisms containing grid nodes at 

regularly spaced intervals in each dimension. The calculated 

value of the property being modeled is stored for each grid 

node location and used for subsequent display and analysis. 

The drill-hole data locations (fig. 1) are most densely distributed within a volume bounded by cross-section coordinates of 

2000 to 5200, long-section coordinates of 4200 to 7100, and 

true elevations between –400 and 3,000 feet. The rest of the 

three-dimensional models produced in this study are confined 

to the rectangular prism defined by those limits. The displays 

of these models were also clipped by the two-dimensional 

topographic surface grid discussed below.

Minimum-Tension Gridding

To produce spatially continuous two- and three-dimensional models that are representative of data associated with 

scattered points along drill holes, topographic maps, and 

digitized cross sections, interpolated grid values were calculated using 2-D and 3-D minimum-tension gridding algorithms 

in the EarthVision software suite. The following discussion is 

derived from EarthVision documentation by Dynamic Graphics, Inc. (Dynamic Graphics, Inc., 1997).
Greens Creek mine area

Drill holes

Big Sore Ridge Greens Creek Big Sore Creek Gallagher Creek

Long section

Cross section

Figure 1. Drill-hole locations, Greens Creek mine area. The bearing of the cross-section axis is N. 26.5651° W. Cross-section and long-sectshown in feet.
408 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

The main goals of representational gridding are to honor 

the values of the input data as closely as possible and to calculate a reasonable-looking model for grid nodes that are not on 

or adjacent to input data points. Minimum tension is the distribution of the second derivative or curvature of the property 

variation among the nodes such that the sum of the squares of 

the second derivative (tension) is minimized.

The EarthVision two-stage minimum-tension gridding 

method reconciles these two, sometimes conflicting, goals. 

The two stages of minimum-tension gridding are (1) the initial 

estimate, and (2) cubic iteration functions with scattered data 

feedback.

The initial grid estimation process calculates a property 

value for every grid node in an extremely coarse grid that is 

used in the initial stages of gridding. Next, iterations begin, 

each a calculation of a new property value for each grid node 

with neighboring grid nodes providing input values to a cubic 

function that determines the new value. Once the new value is 

calculated for a node, the scattered data are used for the feedback process. Each set of iterations produces a finer grid, and 

this process is repeated until the desired grid size is produced.

To ensure that the original data values are honored, each 

iterative reevaluation of grid nodes is followed by a feedback 

process that compares the calculated property values to the 

input scattered data values that fall within a one-cell zone 

around the grid nodes. If the difference is less than with the 

preceding iteration, the program accepts the new functionderived grid node value and proceeds to recalculate the next 

grid node. If, however, the difference has increased, the node 

is reset to a value closer to the input scattered data point. 

Through this process, the scattered data feedback keeps grid 

nodes tied to neighboring scattered data while allowing the 

cubic function to distribute tension in a reasonable fashion. 

The result of these operations is a continuous data distribution 

that honors the values of the original scattered points and that 

can be displayed and manipulated in 2- and 3-D visualizations.

Topographic Model

Terrain data were digitized from topographic contour 

maps by the Kennecott Greens Creek Mining Company and 

were made available in Alaska State Plane Zone 1 coordinates 

by Andy West. The State Plane coordinates were first translated to the Greens Creek mine local surface grid reference 

system by subtracting the 2262748.50N, 2479273.89E grid 

origin offsets described earlier. The resulting local surface grid 

coordinates were then transformed to mine grid long-section 

and cross-section coordinates by applying equations 1 and 2, 

so that a terrain model calculated from the data would be correctly geographically referenced with respect to the subsurface 

ore, geochemical, and structural models. EarthVision twodimensional minimum-tension gridding was applied to the 

transformed data to produce the topographic surface model 

that is included in figures 1–4. It can be seen that this model, 

when rendered in three-dimensional space, appears as a thin 

floating wafer, similar to the fault planes in this respect.

The topographic surface was also used to constrain, or 

clip, the ore, geochemical, and fault models at the ground 

surface. Otherwise, the models would be unrealistically 

extrapolated to fill the entire extent of the volume defined by 

the model limits of LS, XS, and TVDSS.

Ore Model

The core log data include lithologic codes that permit 

the identification of five types of ore in the Greens Creek 

mine. Because goals of the three-dimensional modeling in 

this study were not only to model and visualize the distribution of orebodies, but also to depict geochemical distributions 

within those orebodies, it was necessary to derive a numeric 

variable to designate each lithologic log observation as ore or 

“non-ore.” The samples designated as ore were given an ore 

value of 1; non-ore samples were assigned an ore value of 0. 

A three-dimensional minimum-distance gridding algorithm 

was first applied to the derived ore value variable, by which 

grid cells within a prescribed distance from data points were 

assigned the value of the nearest data point. The appearance of 

this ore model, however, was found to be somewhat unsatisfactory because the display routine imposed continuously 

varying ore values to the desired binary distribution. Instead, 

although minimum-tension gridding is more typically used for 

continuously varying properties, a somewhat unconventional 

application of the technique was used in this study to create 

3-D models of ore distribution (fig. 2).

Minimum-tension gridding calculations were applied to 

the ore value variable, and the resulting continuously varying 

model values were converted to binary form. All model values 

of 0.5 or greater were converted to 1. All model values less 

than 0.5 were converted to 0.

The validity of the results was tested by comparing this 

binary ore model with views of various cross sections and 

plan views of ore distributions as shown by Proffett (chap. 7) 

and other maps created and provided by the Kennecott Greens 

Creek Mining Company. Close agreement was noted between 

the results of the three-dimensional ore model and geologistdrawn cross sections showing ore delineation. Although the 

cross-section profiles of orebodies mapped by geologists 

were rendered in greater detail, the 3-D model shows similar 

orebody shapes and precise spatial concordance at locations 

where comparative drawings are available to be examined.

Geochemical Models

EarthVision minimum-tension 3-D gridding was applied 

to geochemical variables in the scattered point data of the 

drill-core assays, and to derived variables such as element 

concentration ratios. To produce models that could readily 

be related to modeled orebody distributions derived from 

geologic interpretations rendered by mine geologists, the 

three-dimensional geochemical grids were constrained 

by the interpreted orebodies (fig. 2). To do so, each of the 
Modeling 409

Greens Creek mine

Orebodies and major workings

Figure 2. Greens Creek mine orebodies, showing major workings. The bearing of the cross-section axis is N. 26.5651° W. 

Cross-section and long-section coordinates and elevation shown in feet.

three-dimensional geochemical grids was multiplied by the 

binary ore grid to produce models of geochemical variables 

within interpreted orebodies. The multiplication operation left 

the geochemical distributions unchanged in the presence of ore 

(ore value=1) but changed the geochemical grid values to 0 in 

the presence of non-ore (ore value=0). Some of the resulting 

geochemical models are shown in figures 3–8.

It had also been intended to model the lithologic horizons 

of the mine and to conformably model geochemical distributions among these units as well, but intractable difficulties were 

encountered in the form of numerous discontinuous repetitions 

of lithologies down the same drill holes. Additional information 

pertaining to dip and azimuth of the bedding planes would have 

been required to successfully create lithologic horizon models.
410 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Geologic Structure Models

Several of the most important geologic structures in the 

area were modeled to provide three-dimensional visualization 

of these features. Cross sections and surface maps produced 

by Proffett (chap. 7) were used to digitize locations along the 

Klaus shear, the Maki and Little Maki faults, and the Upper 

Shear Zone. The LS, XS, and TVDSS coordinates of plan and 

cross-section traces of these structures were recorded and used 

as input to EarthVision’s fault-modeling program. The modeled 

structures appear as thin wafers, floating in space, and can be 

combined with geochemical and ore models as shown in fig. 3.

Little Maki fault

upper shear zone

Maki fault

Klaus shear

Big Sore Ridge

topographic 

surface

Cross section

Long section

Elevation

Greens Creek mine

Gold in orebodies

(major faults shown)

Figure 3. Faults, shear zones, and gold distribution within orebodies, Greens Creek mine. Only gold concentrations greater 

than 0.05 part per million are shown. The bearing of the cross-section axis is N. 26.5651° W. Cross-section and long-section 

coordinates and elevation shown in feet.

Visualization

A significant advantage of three-dimensional modeling 

is that it makes available practically unlimited perspectives 

from which to view or visualize the results. The models may 

be sliced, rotated, panned, and zoomed in countless ways. 

Isovalue shells, equivalent to three-dimensional contour 

surfaces and analogous to two-dimensional contour lines, may 

be chosen for display, and volumetric statistics can be readily calculated and displayed for each variation of the property 

models. In addition, various 3-D models may be combined for 

simultaneous display and visualization.
Visualization 411

A few of the myriad visualization possibilities for the 

three-dimensional models produced for the Greens Creek 

mine are included here. Figure 4 shows a chair cut display of 

the three-dimensional distribution of silver within ore bodies, 

clipped by the topographic surface above. It can be seen that 

Figure 4. Chair cut display of silver in orebodies, Greens Creek mine. The bearing of the cross-section axis is N. 26.5651° W. 

Cross-section and long-section coordinates and elevation shown in feet.

Greens Creek mine

Silver in orebodies

Elevation

Cross section

Long section

topographic

surface

main haulage

36 decline

parts of five different cross sections are shown in the same 

image, and that a sixth is possible if the top slice of the model 

were lowered to be below the topography. Figures 5–7 show 

isovalue shells of silver, zinc, and antimony, and figure 8 

shows isovalue shells of the arsenic:antimony ratios.
412 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Greens Creek mine

Silver in orebodies

Long section

Cross section

Elevation

main haulage

1350 drift

59 development

Volume

53, 819, 478, 13965

Figure 5. Isovalue shell display of silver greater than 10 parts per million in orebodies, Greens Creek mine. Volume calculated in cubic 

feet. The bearing of the cross-section axis is N. 26.5651° W. Cross-section and long-section coordinates and elevation shown in feet.
Modeling 413

Figure 6. Isovalue shell display of zinc greater than 10 percent in orebodies, Greens Creek mine. Volume calculated in cubic feet. 

The bearing of the cross-section axis is N. 26.5651° W. Cross-section and long-section coordinates and elevation shown in feet.

36 decline

main haulage

1350 drift

Elevation

Cross section

Long section

Greens Creek mine

Zinc in orebodies

Volume

48, 908, 212, 444328
414 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Figure 7. Isovalue shell display of antimony greater than 600 parts per million in orebodies, Greens Creek mine. Volume calculated in 

cubic feet. The bearing of the cross-section axis is N. 26.5651° W. Cross-section and long-section coordinates and elevation shown in 

feet.

Cross section

Long section

Elevation

36 decline

main haulage

1350 drift

Greens Creek mine

Antimony in orebodies

Volume

38, 188, 102, 379023

,

,

,

,

,

,
Modeling 415

Figure 8. Isovalue shell display of arsenic: antimony ratios greater than 10 in orebodies, Greens Creek mine. Volume calculated 

in cubic feet. The bearing of the cross-section axis is N. 26.5651° W. Cross-section and long-section coordinates and elevation 

shown in feet.

Elevation

Cross section

Long section

main haulage

1350 drift

36 decline

Greens Creek mine

As/Sb in orebodies

Volume

50, 336, 079, 005927
416 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Conclusions

The modeling efforts have been successful in producing reasonable three-dimensional renderings of the ore and 

geochemical information included in the drill-hole data. 

Verification has been obtained from geologist-drawn plan and 

cross-section views of the mine. Although the drawn cross 

sections may provide greater detail in delineating the shapes 

of the orebodies, the 3-D models provide great flexibility in 

readily displaying and manipulating unlimited perspectives 

of the locations, shapes, and volumes of orebodies along with 

their associated metal content throughout the region of data. 

These capabilities are potentially valuable tools for examining 

issues of not only scientific interest, but also of mining development and redevelopment strategies. The three-dimensional 

models and visualization can be used to guide development 

as it progresses but might also be used to consider and devise 

effective strategies for revisiting previously explored areas 

for the purpose of ancillary production efforts if warranted by 

changing economic conditions.

Reference Cited

Dynamic Graphics, Inc., 1997, EarthVision user’s guide 5.1: 

Alameda, Calif., Dynamic Graphics, Inc.
A Genetic Model for the Greens Creek 

Polymetallic Massive Sulfide Deposit, 

Admiralty Island, Southeastern Alaska

By Cliff D. Taylor, Kerry G. Lear, and Steven R. Newkirk

Chapter 15 of

Geology, Geochemistry, and Genesis of the Greens Creek Massive 

Sulfide Deposit, Admiralty Island, Southeastern Alaska

Edited by Cliff D. Taylor and Craig A. Johnson

Professional Paper 1763

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract.......................................................................................................................................................419

Introduction.................................................................................................................................................419

Genetic Model for the Greens Creek Deposit.......................................................................................420

Tectonic Setting ................................................................................................................................420

Style and Timing of Mineralization.................................................................................................421

Post-Mineral Modifications to the Greens Creek Orebodies....................................................424

Discussion...................................................................................................................................................425

References Cited........................................................................................................................................427

Figure

1. Graphic illustrations of the: (a) early, (b) main-stage, and (c) late periods of the

development, growth, and death of the Greens Creek ore-forming environment.........422
A Genetic Model for the Greens Creek Polymetallic 

Massive Sulfide Deposit, Admiralty Island, Southeastern 

Alaska

By Cliff D. Taylor,1 Kerry G. Lear,2 and Steven R. Newkirk2*

1

U.S. Geological Survey, Denver, Colorado, USA.

2

 Kennecott Greens Creek Mining Company, Juneau, Alaska, USA.

*

Present address: Department of Earth Sciences, University of Memphis,

Memphis, Tennessee, USA 38152.

Abstract

The Greens Creek deposit (global resource of 24.2 million tons at an average grade of 13.9 percent zinc, 5.1 percent 

lead, 0.15 troy ounce per ton gold, and 19.2 troy ounces per 

ton silver at zero cutoff) formed in latest Triassic time during 

a brief period of rifting of the Alexander terrane. The deposit 

exhibits a range of syngenetic, diagenetic, and epigenetic 

features that are typical of volcanogenic (VMS), sedimentary 

exhalative (SEDEX), and Mississippi Valley-type (MVT) 

genetic models. In the earliest stages of rifting, formation of 

precious-metal-rich silica-barite-carbonate white ores began at 

low temperature in a shallow, subaqueous setting, probably a 

thin carbonate shelf on the flanks of the Alexander landmass. 

Epigenetic carbonate replacement textures in the footwall 

dolostones are overlain by stratiform silica-carbonate-bariterich ores and indicate that early mineralization formed at 

and just beneath the paleo sea floor by mixing of a reduced, 

precious-metal-rich, base-metal-poor hydrothermal fluid with 

oxygenated seawater. As rifting intensified, the shelf was 

downfaulted and isolated as a graben. Isolation of the basin 

and onset of starved-basin shale sedimentation was concurrent 

with emplacement of mafic-ultramafic intrusives at shallow 

levels in the rift, resulting in an increasingly higher temperature and progressively more anoxic ore-forming environment. The formation of the main stage of massive sulfide ores 

began as the supply of bacterially reduced sulfur increased 

in the accumulating shales. As the main-stage mineralization 

intensified, shale sedimentation inundated the hydrothermal 

system, eventually forming a cap. Biogenic sulfate reduction 

supplied reduced sulfur to the base of the shales where mixing 

occurred with hot, base-metal-rich hydrothermal fluids. Ore 

deposition continued by destruction and epigenetic replacement of the early white ores in proximal areas and by inflation 

and diagenetic replacement of unlithified shale at the interface 

between the white ores and the base of the shale cap. Ore 

deposition waned as the shales became lithified and as the supply of bacterially reduced sulfur to the site of ore deposition 

ceased. The final stages of rifting resulted in the emplacement 

of mafic-ultramafic intrusive rocks into the Greens Creek system and extrusion of voluminous basaltic flows at the top of 

the Triassic section. Greenschist facies metamorphism during 

the Jurassic-Cretaceous accretion of the Alexander terrane to 

the continental margin resulted in recrystallization, remobilization, and significant upgrading of the Greens Creek orebody.

Current ore-genetic models are inadequate to explain 

the diverse characteristics of the Greens Creek deposit. We 

suggest that Greens Creek represents a transitional type of 

deposit that formed as a result of its evolving metallogenic 

setting in a propagating intra-arc rift. It is therefore a hybrid 

deposit within a spectrum of exhalative to replacement-style 

deposits.

Introduction

The Greens Creek deposit provides an opportunity to 

examine the relationship between VMS, SEDEX, and MVT 

massive sulfide genetic models. VMS characteristics (Hutchinson, 1973; Franklin and others, 1981; Large, 1992) of the 

Greens Creek deposit include a zinc-lead-silver-gold-copper 

metal endowment similar to the Kuroko-type, a mafic volcanic 

footwall, a zoned alteration profile, and mineralogy similar 

to that of white smoker systems of the southwestern Pacific 

Ocean (Halbach and others, 1993). However, the deposit 

also has numerous characteristics usually associated with the 

SEDEX class (Goodfellow and others, 1993; Solomon and 

Groves, 1994) including: a metal assemblage dominated by 

zinc, lead, and silver; the absence of felsic igneous rocks and 

the presence of altered mafic-ultramafic intrusives in the footwall; lack of a focused feeder system and presence of a huge 

alteration envelope containing chromium and barium-rich silicates and complex carbonate alteration mineralogy; a hanging 

wall consisting of graphitic, pyritic argillites; geochronologic 

and isotopic evidence suggesting that ore formation occurred 

during and after deposition of the shale cap; and location in an 
420 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

intra-arc setting consistent with the rift tectonics model common to most SEDEX deposits. Crosscutting relationships and 

ore textures are consistent with growth by inflation beneath, 

and syndiagenetic replacement of, the shales during sedimentation. Additionally, MVT mineral-forming processes (Leach 

and Sangster, 1993) are suggested by the presence of a thin, 

discontinuous, platform carbonate unit in the footwall. The 

footwall carbonate is host to an epigenetic ore and gangue 

mineral assemblage that occurs in veins, replacements, and 

open space fillings similar to the carbonate-hosted deposits of 

the Irish Midlands and the U.S. Midcontinent regions. Sulfur 

isotope values are unusually low and are unlike sulfur isotope 

compositions typical of either VMS or SEDEX deposits. They 

most closely resemble the range of values exhibited by a subset of deposits in the Irish Midlands. Greens Creek, therefore, 

is a hybrid or transitional type of mineral deposit, with characteristics of VMS, MVT, and SEDEX deposits.

In this chapter we present an interpretive genetic model 

for the formation of the deposit based on the cumulative information presented in the preceding chapters of this volume. We 

then discuss the genetic model with regard to the proposed 

tectonic setting and examine whether the Greens Creek deposit 

fits into existing ore-genetic classification schemes.

Genetic Model for the Greens Creek 

Deposit

Tectonic Setting

Development of a genetic model for the Greens Creek 

deposit requires the consideration of the data presented in the 

preceding chapters in the context of the tectonic environment 

that was extant at the time of mineralization. The well-established age of the immediate hanging-wall argillites of 220.7 

± 4.4 Ma (latest Carnian-earliest Norian stages of the latest 

Triassic; chap. 11) places Greens Creek into the allochthonous, 

oceanic portion of the Alexander terrane’s history prior to the 

Jurassic-early Tertiary accretion to the continental margin. The 

geologic history of the Alexander terrane from middle Paleozoic 

through Middle (?) Permian is thought to have been largely 

a period of relative quiescence marked by erosion of uplifts 

formed during the Middle Silurian to earliest Devonian Klakas 

orogeny, development of large areas of platform carbonates, and 

shale sedimentation in open marine depositional basins (Gehrels and Berg, 1994). Minor mafic volcanism and tectonism 

during Early Permian (?) time is marked by the volumetrically 

minor and poorly preserved Halleck Formation. This unit occurs 

between the Mississippian to Permian Cannery Formation 

shales and the Lower to Upper Permian Pybus dolomite.

The Permian depositional setting is marked by progressive emergence of the Alexander terrane. The siliceous black 

shales and interbedded cherts of the Cannery Formation, 

indicative of sedimentation below the carbonate compensation 

depth, are overlain by shallow-water, dolomitic carbonates 

of the Pybus Formation. Preservation of ooid grainstones and 

fossil debris provides evidence that the Pybus Formation was 

deposited at or close to wave base. Nondeposition (erosion) is 

indicated by the absence of Late (?) Permian through Middle 

Triassic strata throughout southeastern Alaska. This hiatus is 

significant and probably indicates emergence of the Alexander 

landmass. However, it is surprising that there is no evidence 

for prolonged exposure in the form of extensive karsting of 

the Pybus Formation or the development of a regolith horizon. 

These lines of evidence may suggest that the hiatus was a 

prolonged period of exposure marked by erosion and removal 

rather than nondeposition of pre-Late Permian units (chap. 2).

Deposition of the polymictic conglomerates at the base 

of the Hyd Group provides the earliest indication of the 

onset of rift tectonic activity that ultimately resulted in the 

formation of the Greens Creek deposit. Although not directly 

dated, their presence immediately underlying the 225±3 Ma 

Puppets Formation rhyolite (uranium-lead zircon, Gehrels 

and others, 1987) on Gravina Island provides a minimum 

age for the initiation of graben formation and rift-filling 

volcano-sedimentary activity in southeastern Alaska. The 

earliest known intrusive rocks related to rifting in southeastern Alaska are mafic-ultramafic intrusions on Duke Island 

that yield a similar age of 226±3 Ma (uranium-lead zircon, 

Gehrels and others, 1987). The absence of a well-defined 

basal conglomerate horizon at the latitude of Greens Creek 

indicates that the mine area was distal to the locations 

where normal faulting first occurred. This period of tectonic 

readjustment and associated gravity sliding was immediately 

followed by the extrusion of the first of two major pulses 

of volcanic rocks into the nascent rift; the first pulse was 

bimodal and consists of voluminous rhyolites in the southern 

part of the rift and relatively minor basaltic volcanic rocks 

in the central and northern portions (where Greens Creek is 

located). The second pulse consists of voluminous basaltic 

flows that cap most exposures of Late Triassic rocks throughout southeast Alaska. The geochemical character of these 

volcanic rocks changes northward from arc-contaminated 

calc alkaline rhyolites to peralkaline rhyolites and then to 

arc-contaminated tholeiites and minor alkaline basalts by the 

latitude of Admiralty Island. This geochemical evolution of 

the volcanic rocks, coupled with the northward thinning of 

the underlying conglomerates, suggests that the developing 

rift may have been oblique to, and propagating southward 

into, the Alexander terrane landmass (Taylor, 1997; Taylor, 

Philpotts, Sutley, and others, 1995; Taylor, Philpotts, Hall, 

and Wakeman, 1995; Taylor, Premo, and Meier, 1999; Taylor 

2000; chap. 2). Indications of the depositional setting at the 

time of extrusion of the bimodal first pulse of volcanic rocks 

are scarce due to their predominantly volcaniclastic character; however, minor pillow basalts exposed on Admiralty 

Island indicate that at least at the latitude of Greens Creek 

the environment was subaqueous. Conodont data from the 

overlying Hyd Group argillites at Greens Creek constrain the 

cessation of the first extrusive episode to sometime before 

the onset of shale sedimentation at 220.7±4.4 Ma (chap. 12).
Genetic Model for the Greens Creek Deposit 421

Following the first period of magmatism, a period of 

quiescence ensued during which a thin carbonate platform 

developed in the newly formed rift. On Annette, Gravina, and 

Kuiu Islands (see fig. 1 in chap. 2) this unit consists primarily 

of a light gray, fossiliferous, massive, fine to coarse crystalline, cliff-forming, dolomitic metalimestone with minor reefforming communities (George Stanley, oral commun., 2000) 

and oolitic shoals (Muffler, 1967; Berg, 1973) that indicate 

a shallow-water depositional setting. The carbonate platform 

thins northward to Gambier Bay on southern Admiralty Island 

where it is discontinuously exposed as hackly textured thickbedded blocks of alternating limestone and dolomite. Discontinuous bodies of heavily altered, coarse crystalline dolomite 

and dolomitic breccia rest on the phyllites in the immediate 

footwall of the Greens Creek deposit and contain relict fragments of Halobia and crinoid stems. Their presence indicates 

that the depositional environment just prior to mineralization 

was a shallow-water carbonate platform or possibly a proximal 

carbonate ramp setting.

Resumption of rifting resulted in the cessation of carbonate deposition and the initiation of hydrothermal fluid flow at 

Greens Creek. Foundering of the carbonate platform and tectonic readjustment of various subbasins within what was probably a segmented rift is indicated by the localized presence 

of carbonate debris flows and more distal, graded, carbonate 

turbidites. Carbonate breccias in the footwall at Greens Creek 

are highly altered, which makes it difficult to distinguish 

between tectonic and sedimentary origins. However, a subset 

of the carbonate breccias displays rounded clasts, suggesting 

that carbonate debris flows are present.

Style and Timing of Mineralization

As described in detail in chapters 6 and 9, ore lithologies 

at Greens Creek are divided into two major groups. The first 

group of early white ores, consisting of silica-, carbonate-, and 

barite-rich subtypes, rests on the footwall phyllite and platform 

carbonate units beneath and(or) distal to the second group of 

main stage, massive, pyritic and base-metal-rich sulfides. The 

gradation from white ores into massive ores is fairly abrupt, 

and the metal endowments are distinct. White ores are basemetal-poor and precious-metal-rich with a gangue-rich mineral 

assemblage marked by a distinctive yellow, low-iron sphalerite, 

pyrite, galena, tetrahedrite, pyrargyrite, free gold, and a host of 

lead-antimony-sulfosalt minerals, whereas the massive ores are 

markedly enriched in base metals in addition to significantly 

elevated precious-metal concentrations. The main-stage ores 

are dominated by pyrite, sphalerite, galena, and tetrahedrite and 

contain chalcopyrite, arsenian pyrite/arsenopyrite, free gold, 

and electrum in proximal areas of the deposit.

In the absence of any direct geochronological evidence 

from this ore assemblage, the timing of the onset of mineralization is an arguable point. The ore stratigraphic succession 

from the basal and peripheral early white ores up into massive 

sulfides, and the silica-carbonate-barite-dominated mineral 

assemblage of the early white ores, indicate that mineralization 

began by exhalation of low-temperature, hydrogen sulfidedominated hydrothermal fluids onto or near the sea floor (fig. 

1A). The presence of epigenetic mineral textures dominated 

by low iron sphalerite, lead-antimony, and silver sulfosalts 

associated with dolomite and quartz-infilled solution cavities 

is consistent with percolation of hydrothermal fluids through, 

and replacement of, the footwall sedimentary carbonate units. 

Precipitation of the baritic ores as blankets occurred at or just 

below the sediment/water interface. Sulfur isotopic values 

from these baritic ores are equivalent to Triassic seawater 

values and suggest that initially the hydrothermal fluids mixed 

with oxygenated marine water (chap. 10). The high arsenic, 

antimony, and mercury content of the white ores in the form 

of minor realgar, arsenian pyrite, and mercurian tetrahedrites 

and electrum represents additional evidence of the low-temperature, reduced state of the initial ore fluid. Recent studies of active shallow and(or) low-temperature white smoker 

systems on the sea floor (Hannington and others, 1986; 

Halbach and others, 1993; Binns and others, 1993; Fouquet 

and others, 1993; Stoffers and others, 1999) have documented 

the existence of mineral assemblages and metal endowments 

very similar to those observed in the early white ores at 

Greens Creek. The very large size of the footwall alteration 

envelope (Taylor, Newkirk, and others, 1999; Anderson and 

Taylor, 2000; Anderson and Taylor, unpub. data, 2000) and the 

absence of any evidence suggestive of white smoker chimneys 

or focused upflow zones indicate that fluid upwelling was 

diffuse and occurred over a large area of the sea floor. Another 

feature that suggests fluid upwelling occurred by diffuse flow 

over a relatively large area is the dominantly volcaniclastic 

nature of the footwall. Mafic volcaniclastic rocks extruded 

during the first period of rift-related tectonic activity, overlain 

by sedimentary carbonate breccias in the mine area, resulted 

in a permeable substrate through which hydrothermal fluids 

passed. The presence of a highly permeable footwall at Greens 

Creek precluded the development of a focused feeder system and probably contributed to the large size of the deposit. 

Similar relationships have been observed in Canada, where 

many of the larger massive sulfide deposits are associated with 

volcaniclastic sequences (Morton and Franklin, 1987; Kerr 

and Gibson, 1993; Hannington and others, 1999).

As rifting progressed, the graben continued to deepen, 

resulting in shale sedimentation and the gradual isolation of 

the immediate Greens Creek depositional system (fig. 1B). 

A variety of evidence suggests that the accumulation of the 

shales over the diffuse vent system happened rapidly enough 

to prevent vertical growth of the orebody through the unlithified sediments. As the rising hydrothermal fluids came in 

contact with the growing shale cap, physical and(or) chemical 

conditions were such that ore precipitation occurred at the 

contact between the footwall greenstones and carbonates and 

the overlying shales. The absence of significant shale interbedding at the top of the orebodies and the lack of stacked massive sulfide lenses in the shales suggest that the majority of ore 

formation occurred by inflation beneath and replacement of 

the shales at the base of the sedimentary pile. The shales also 
422 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Paleozoic island arc

hypabyssal mafic/

ultramafic intrusions

Late Triassic basalts

Continued sedimentation and lithification of shales shuts down Greens Creek

hydrothermal system. Cessation of rifting following extrusion of basalts.

Paleozoic island arc

hypabyssal mafic/

ultramafic intrusions

extension extension

anoxic unlithified shales

massive sulfide formation by

inflation beneath, and replacement

of, shales at base of cap

Continued rifting results in deeper water and starved basin sedimentation.

Shallow crustal emplacement of mafic/ultramafic intrusions drive sea water/pore

water convection at increasingly higher temperature and lower oxygen fugacity. 

H2O

+ metals

H2O 

+ metals

Paleozoic island arc

shallow arc shelf

hypabyssal mafic/

ultramafic intrusions

normal faults and rift-fill conglomerates

silica-barite exhalite

Onset of Greens Creek mineralization during the early phases

of intra- or back-arc rifting in latest Triassic time. 

extension extension

biogenic SO4

reduction

B

C

A

Figure 1A–C. Graphic illustrations of the: (A) early, (B) main-stage, and (C) late periods of the development, growth, and death of the 

Greens Creek ore-forming environment.
Genetic Model for the Greens Creek Deposit 423

are characterized by high organic carbon content and contain 

abundant diagenetic pyrite. These features indicate that, as 

the bottom dropped out of the rift basin, the local depositional 

setting at Greens Creek quickly evolved into a restricted, 

anoxic marine basin (chap. 8). Although direct indications of 

water depth are lacking, the conodont assemblages recovered 

from the hanging-wall shales are consistent with a shallow 

marine shelf or possibly of a shelf-slope setting (chap. 12). 

The interbedded massive and slaty argillites were originally 

deposited as relatively quiescent silty, organic-rich dolomitic 

muds above the carbonate compensation depth, which received 

periodic influxes of very fine grained clastic sediments.

Once restricted, anoxic, bottom-water conditions were 

established, the Greens Creek area became a locus of intense 

microbial activity. Supporting evidence of bacterial sulfate 

reduction includes the high organic carbon content and the 

locally enriched sulfur and carbonate content of the shales, 

as well as the anomalously light sulfur and carbon isotope 

values of sulfides and carbonates in the shales (chaps. 8, 10). 

This supplied a steadily increasing component of biogenically reduced sulfur to the ore-forming system at the base of 

the shales. As the pore water being supplied at the base of the 

shales became dominated by biogenically reduced hydrogen 

sulfide (H2

S), barite precipitation ceased, marking the onset of 

the main stage of sulfide ore formation. Concurrent with the 

change of the pore fluids in the shales to more reduced conditions, the accumulation of the shale cap acted as an insulating 

blanket to the hydrothermal system. As the shale cap grew and 

the hydrothermal system intensified, temperatures in the footwall rose to the point where significant quantities of iron, lead, 

and zinc were carried in the ore fluid as chloride complexes. 

The striking ore stratigraphic shift from early precious-metalrich and base-metal-poor white ores to the main-stage massive 

pyritic and base-metal-rich ores requires the shift from an 

initial low-temperature ore fluid with H2

S-complexed metals 

to a higher temperature fluid in which base metals, carried as 

chloride complexes, predominate. The presence of sedimentary carbonate bodies in the footwall and the abundance of carbonate alteration at Greens Creek further require that the fluid 

was buffered to near neutral pH. Numerous studies on metal 

solubility in volcanogenic massive sulfide deposits and recent 

sea-floor hydrothermal systems indicate that the cross-over 

temperature of H2

S-complex-dominated to Cl- -complex-dominated fluids at salinities and H2

S contents typical of volcanogenic massive sulfide deposits, occurs at roughly 300o

C (Hannington and Scott, 1989; Huston and Large, 1989; Large and 

others, 1989; Herzig and others, 1993). A variety of indirect 

constraints on temperature (40Ar/39Ar closure temperature of 

2M1

 muscovite, conodont CAIs of 5 to 5.5, lack of carbonate 

and organic carbon isotopic re-equilibration, sphalerite-galena 

sulfur isotope pairs; chaps. 8, 10, 12) at Greens Creek suggest that maximum temperature during either the mineralizing 

event or Cretaceous regional metamorphism was no greater 

than about 275–350o

C.

As the temperature of the ore fluid increased, a greater 

dissolved load of base metals percolated upward to the base 

of the shale cap where it mixed with much cooler pore water 

containing abundant biogenically reduced sulfur. During this 

main stage of massive sulfide formation, massive pyritic and 

base-metal-rich sulfides grew by inflation beneath the shales. 

The very low aspect ratio of the deposit (great length to thickness) and the exceptionally large and diffuse nature of the 

footwall alteration zone (Taylor, Newkirk, and others, 1999; 

Anderson and Taylor, 2000; Anderson and Taylor, unpub. 

data, 2000), suggest that the precipitation of massive sulfides 

by mixing and cooling occurred over a broad area. Thus, the 

tabular, sheetlike morphology of the orebodies is a result of 

unfocused upflow of the hydrothermal fluids and probably 

multiple centers of thermal activity.

As described for the West orebody (chap. 6), areas with 

the hottest temperatures and greatest fluid flow are characterized by greater accumulations of copper-arsenic-rich pyritic 

ores centered over thick footwall sections of intensely silicasericite flooded proximal alteration. Within these higher 

temperature centers, mineral textures and metal zonation 

suggest that any early white ores were completely destroyed 

and that zone refining of metals within the growing sulfide 

blanket occurred (chap. 9). The presently observed footwall 

to hanging-wall progression of white, to massive pyritic, 

to massive base-metal-rich ore types, therefore, reflects the 

transgression and destruction of the early white ores by the 

main-stage sulfide ores as the hydrothermal system reached 

its thermal maximum. Such a progression is consistent with 

an early, H2

S-dominated, precious-metal and barium-rich fluid 

evolving to a higher temperature main-stage fluid characterized by much higher base-metal and lower precious-metal 

contents. The steady increase in the proportion of biogenically 

reduced sulfur supplied to the locus of sulfide precipitation is 

supported by the upward progression from isotopically heavy 

to light d34S values through the ore stratigraphy (chap. 10). As 

peak thermal conditions were attained, metals such as Au, Sb, 

Hg, Tl, Mo, and Ag were zone refined upward and outward 

into the base-metal-rich massive sulfides against the hanging 

wall, leaving proximal pyritic massive sulfides enriched in 

copper, arsenic, nickel, and cobalt (chap. 9). Mineralogically, 

this resulted in the development of subhedral to euhedral arsenian pyrite-arsenopyrite along the fringes of clasts and in areas 

of greater permeability in the proximal ores and expulsion of 

the base-metal sulfides outward in the pile.

As the Greens Creek hydrothermal system matured, 

ongoing sedimentation and lithification of the shales, coupled 

with precipitation of gangue minerals, gradually choked off 

fluid flow through the accumulated sulfide body (fig. 1C). 

Additionally, the eventual depletion of palatable organic matter in the hanging-wall shales may have decreased the supply 

of organically reduced sulfur. A combination of these factors led to the final decline in ore formation. As temperatures 

decreased after peak ore deposition, the system was swamped 

with paragenetically late hydrothermal carbonate gangue. Outward zonation from stochiometric dolomite to more iron- and 

manganese-rich dolomite (Taylor, Newkirk, and others, 1999; 

Anderson and Taylor, 2000; Anderson and Taylor, unpub. 
424 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

data, 2000) occurred as the supply of H2S to the hydrothermal 

system waned. In the final stages of Late Triassic rifting, tapping of the underlying mafic-ultramafic heat sources occurred, 

resulting in the voluminous extrusion of the Hyd Group basalt 

flows onto the argillites.

Although efforts to establish an absolute age of mineral 

formation at Greens Creek failed, an age of alteration of an 

ultramafic sill with associated Greens Creek-like mineralogy 

and metal geochemistry was obtained for an occurrence in 

the Triassic belt on the south end of Admiralty Island. The 

210.7±0.3 Ma (40Ar/39Ar – fuchsite) age of alteration at this 

occurrence (Taylor, Philpotts, Sutley, and others, 1995; Taylor, 

Philpotts, Hall, and Wakeman, 1995; chaps. 2, 12) represents 

the closest available estimate for the age of main-stage hydrothermal fluid flow at Greens Creek. Our best constraint for 

the age of extrusion of the Hyd basalts onto the Hyd argillites 

comes from whole-rock radiogenic isotope data and indicates 

an approximately 215 Ma age of emplacement (chap. 12). Figures 1A–C represent graphic illustrations of the early, mainstage, and late periods of the development, growth, and death 

of the Greens Creek ore-forming environment.

Post-Mineral Modifications to the Greens Creek 

Orebodies

The final event to affect the Greens Creek deposit was 

the Jurassic through Cretaceous regional mid-greenschist 

facies metamorphism that occurred during accretion of the 

Alexander terrane to the North American margin. During this 

event the morphology, mineralogy, and tenor of the orebody 

was significantly modified. Tight isoclinal F2 folding resulted 

in significant shortening and local thickening of the orebody. 

These were followed by open F3 folds, which further thickened ore in fold axes (see chap. 7). The absolute age of 

these two deformation events is unknown; however, folding 

is clearly younger than the Norian Triassic argillites of the 

hanging wall. The orientation of these fabrics is consistent 

with regional northwest-vergent thrust faults that are thought 

to have formed during Jurassic-Cretaceous collision of the 

Alexander terrane with the continental margin (Haeussler 

and others, 1999). High-angle strike-slip movement along the 

Maki fault and its subsidiaries is generally thought to have 

occurred during transcurrent movement of the terrane during 

early Tertiary time. Although Maki faulting significantly 

complicated the morphology of the deposit, little modification 

of the mineralogy or tenor of the ore occurred.

Textural studies indicate that semiductile shearing of the 

ores occurred during Jurassic-Cretaceous metamorphism. Rigid 

blocks of massive pyritic ore acted as buttresses around which 

the more ductile base-metal-rich ores flowed. This resulted in 

near-complete (about 70 percent) recrystallization of pyrite 

and base-metal sulfides and imparted a tectonic banding to 

the base-metal-rich ores. Brittle failure occurred within the 

rigid blocks of massive pyritic ore, producing breccia textures 

consisting of angular clasts of massive pyrite in matrix of 

pyrite, base-metal sulfides, and gangue. Recrystallization of the 

sulfides also occurred within the sulfide clasts, but to a much 

lesser degree than in the plastically deformed and banded basemetal-rich ores. Thus, a full range of primary, partially recrystallized, fully recrystallized, and remobilized sulfide textures 

are preserved (chap. 9).

Mineralogically, the primary ores consist of very fine 

grained, framboidal, colloform, dendritic, and botryoidal, 

brassy-colored pyrite intimately intergrown with sphalerite, 

galena, tetrahedrite, rarely chalcopyrite, and an unidentified and probably variable suite of lead-antimony sulfosalts. 

Partial recrystallization results in an increase in crystal size 

and coalescence of the primary pyrite into large, spongy-textured masses. The base-metal sulfides begin to form mineralogically discrete anhedral masses, and pyrite aggregates 

form subhedral masses of pyrite with spongy interiors and 

inclusion-free, growth-zoned margins. Complete recrystallization results in a metamorphic “cleaning” of the primary- and 

spongy-textured pyrite and formation of very large, brightcolored, inclusion-free, euhedral pyrites in matrix of anhedral 

tetrahedrite, sphalerite, chalcopyrite, and galena, argentite, 

and acanthite. In the extreme case, polygonal aggregates 

of near-monomineralic pyrite are formed. Grains of yellow 

gold appear entirely included within pyrite masses or on the 

margins of crystals, and the exotic lead-antimony sulfosalts are 

absent. Metamorphic remobilization is characterized by crosscutting veinlets and fractures filled with chalcopyrite, sphalerite, galena, tetrahedrite, pyrargyrite, argentite, acanthite, free 

gold, and electrum and an increased abundance of quartz and 

dolomite gangue.

The process of metamorphic recrystallization and remobilization of the primary ores is reflected in the correlation 

between the variety and abundance of trace metals in sulfides 

and the textural state of the sulfides. The primary-textured 

ores, and specifically pyrite, contain elevated abundances of 

Sb, As, Hg, Mo, Tl, Ni, Co, V, Ag, and Au, whereas in the 

recrystallized and remobilized ores, the number of trace metals in pyrite decreases and the post-recrystallization mineral 

residence of a given trace metal becomes predictable based 

on the stochiometry of the major sulfide phases. For example, 

pyrite becomes almost trace-metal free; mercury resides in 

sphalerite; antimony, arsenic, and silver reside predominantly 

in tetrahedrite and pyrargyrite; and gold forms discrete grains.

Although the Jurassic-Cretaceous metamorphism is not 

related to the genetic origin of the Greens Creek deposit, it is 

of major importance with regard to the distribution of metal 

grades throughout the deposit as well as the recoverability of 

those metals during the beneficiation process. The highestgrade ore intercepts in the mine occur where high-grade 

primary-textured ores are shot through with densely packed, 

remobilized veinlets consisting of electrum and silver sulfosalt 

minerals. Recrystallization of the ores greatly improves the 

recovery of metals in the mill and allows for blending of ore 

types, which decreases the content of deleterious trace metals 

in the resulting concentrates. Unblended primary ores result in 

concentrates with high trace-metal contents and poor recovery 

of precious metals.
Discussion 425

Discussion

Greens Creek presents an interesting case of a polymetallic massive sulfide deposit at which the immediate 

footwall was a cold, basaltic volcaniclastic pile irregularly 

mantled by carbonate rocks at the time of ore formation. In 

contrast to the commonly modeled case in VMS deposits 

where the heat source is attributed to subvolcanic intrusions and related active volcanism, at Greens Creek the 

heat source(s) for the hydrothermal system were hypabyssal mafic-ultramafic intrusions associated with Late Triassic 

rifting (chap. 12). The rift succession in southeastern Alaska 

contains a number of Triassic-aged trondhjemite and gabbroperidotite intrusions (Gehrels and Berg, 1992; Haeussler 

and others, 1999), and there is a striking spatial correlation 

between mafic-ultramafic dikes, sills, serpentinite bodies, and 

mineral occurrences in the Late Triassic mineral belt (Taylor and others, 2000). Several of these occurrences provide 

evidence that some of the mafic-ultramafic intrusions were 

emplaced at very shallow levels. A basaltic dike of probable 

Late Triassic age associated with the Keku Inlet Ladder Vein 

occurrence (see fig. 2 in chap. 2) has peperitic margins indicative of intrusion into wet sediments. Similarly, mineralized 

basaltic dikes in Gambier Bay (see fig. 2 in chap. 2) display a 

composite texture in the form of chilled margins and vesicular 

interiors. One dike pinches from about 2-m thickness down to 

0.2-m thickness, at which point the dike spreads horizontally 

to the enclosing host rocks and forms bulbous structures similar to pillow basalts. Presumably the dike rose to a position at 

or very near the paleo sea floor where it then spread laterally 

due to a lack of confinement.

Both of these examples suggest that during Late Triassic rifting, mafic-ultramafic intrusives were emplaced near 

the sediment/water interface. We believe that gabbroic sills 

significantly thicken the footwall phyllite at Greens Creek, 

and both altered and fresh serpentinites are present in the 

immediate footwall and at depth. Significantly, compared to 

other Late Triassic mineral occurrences, outcrop (chap. 4) and 

geophysical data (chap. 5) indicate that the Greens Creek mine 

area contains a high concentration of gabbro and serpentinite 

intrusive bodies. The gabbros are linked geochronologically and geochemically to Late Triassic igneous suites, as 

are the altered ultramafic bodies underground and on Mariposite Ridge (see fig. 1 in chap. 2) immediately north of the 

mine (chaps. 11, 12). The combination of the concentration 

of intrusive heat sources emplaced into a locally restricted, 

anoxic, organic-rich, shale-filled rift basin may represent the 

key conditions required for the development of a world-class 

deposit at Greens Creek.

Taking into account the wide error bars, we note that 

the available geochronological constraints on the timing of 

mineralization and emplacement of both the igneous and sedimentary rocks are broadly consistent with the progression of 

events previously outlined. The onset of rifting at 225±3 Ma, 

as established by the first extrusive event, and sedimentation of 

the hanging wall shales at 220.7±4.4 Ma (based on conodonts) 

followed by alteration of serpentinite at 210.7±0.3 Ma (Taylor, 

Philpotts, Sutley, and others, 1995; Taylor, Philpotts, Hall, and 

Wakeman, 1995) provides the window of time during which 

the Greens Creek deposit must have formed (chap. 12). Considered independently of geologic constraints, our strontiumneodymium-lead isotopic age data are not precise enough to 

provide resolution to the emplacement sequence of the gabbros and serpentinites into the footwall and extrusion of the 

Hyd Group basalts above the argillites. Geologic relationships 

are consistent with emplacement of gabbros into the footwall 

as sediments accumulated, causing leaching and alteration of 

associated serpentinites. Extrusion of the Hyd basalts marks 

the end of sediment accumulation. Igneous activity ceased following stoping of the gabbros up to the base of the Hyd basalt 

flows. Our mineral and whole-rock samarium-neodymium 

data on gabbros in the mine area and the ~215-Ma age of 

extrusion of the Hyd basalts at the top of the section (chap. 12) 

are broadly consistent with geologic relationships.

Another enigmatic feature of the Greens Creek deposit 

that is contrary to conventional thinking is the relationship 

between the tectonic setting, the geochemical nature of the 

observed host rocks, and the metal endowment of the ores. 

Comparisons of metal content at Greens Creek to other 

volcanic-associated massive sulfide deposits worldwide suggest that the zinc-lead-rich polymetallic metal suite present 

at Greens Creek is most like the metal suites found in the 

Kuroko district of Japan, the Bathurst district of Canada, 

and the deposits of the Mt. Read volcanic belt in Tasmania (Franklin and others, 1981; Large, 1992). However, in 

marked contrast to Greens Creek, which has a dominantly 

basaltic footwall, all of these districts are dominated by the 

presence of thick rhyolitic volcanic piles and associated 

felsic subvolcanic intrusions that are generally considered to 

be the major sources of metals. Long-established classification schemes, based on metal endowments of VMS deposits 

of all ages, equate high zinc/copper and lead/copper ratios 

to felsic igneous source rocks. Copper-rich deposits with 

high gold/silver ratios are attributed to basaltic source rocks 

(Hutchinson, 1973; Franklin and others, 1981; Ohmoto and 

others, 1983). Similarly, a recently suggested classification 

scheme based on dominant host-rock compositions (Barrie 

and Hannington, 1999) does not apply well to Greens Creek. 

All three of the host-rock classes that involve a major mafic 

component (their mafic, bimodal-mafic, and mafic siliciclastic divisions) are characterized by districts and deposits that 

contain copper- or copper-zinc-rich metal assemblages. It is 

noteworthy that the mafic siliciclastic division describes the 

major host-rock lithologies present at Greens Creek. Further, 

the mafic siliciclastic division includes the Windy Craggy 

deposit (the world’s largest Besshi-type deposit; Peter and 

Scott, 1999), which we suggest is metallogenically related 

to Greens Creek and occupies a position in the northernmost, deepest portion of the Late Triassic rift. However, 

Greens Creek is out of place in a division that is dominated 

by copper-rich deposits characterized by the Besshi-type of 

volcanic-associated massive sulfides.
426 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Perhaps the reason for the unusual nature of the Greens 

Creek deposit is that the hydrothermal fluids may have derived 

the majority of their metals from the mafic-ultramafic intrusive rocks in the footwall and from the immediately overlying 

shales, rather than from the cold basaltic volcaniclastic pile. 

Available trace metal (chap. 9) and sulfur and lead isotopic data 

(chap. 10) appear to suggest this possibility. The extreme alteration of serpentinites in the mine area and the cobalt-nickelchromium enrichments of the massive pyritic ores point to 

leaching of the mafic-ultramafic intrusive rocks. Sulfur isotopic 

studies implicate a major contribution of reduced sulfur-bearing 

fluids from the hanging-wall shales, as do the strong arsenic, 

antimony, mercury, molybdenum, and vanadium enrichments 

of the ores. Finally, the radiogenic isotopic data show that ore 

metals were derived from two major sources, an unradiogenic 

source similar to the mafic-ultramafic rocks in the mine area, 

and an undetermined radiogenic source. The ore-lead isotopic 

array clearly shows derivation of unradiogenic lead from a 

field of whole-rock lead determinations defined by the comagmatic, Late Triassic gabbros and basalts of the Hyd Group 

(chap. 10). Samarium-neodymium isotopic data also suggest a 

comagmatic relationship for the entire mafic-ultramafic suite 

(chap. 11). Derivation of the radiogenic lead component of 

the ores remains inconclusive. The data are permissive of the 

contribution of radiogenic lead from the hanging-wall argillites. 

However, contributions from serpentinites, the Permian Cannery Formation shales, or from older Paleozoic rocks lower in 

the section cannot be ruled out at this time.

We believe the major reason why Greens Creek is difficult 

to reconcile with currently favored models for VMS deposits 

is because it represents a transitional type of massive sulfide 

(Taylor, Newkirk, and others, 1999). Early genetic descriptions for Greens Creek included proponents of a SEDEX 

model (Dressler and Dunbire, 1981) as well as of a VMS 

model (Newberry and others, 1997). As previously discussed, 

attempts to classify Greens Creek based on metal ratios or on 

composition of the host rocks leads to ambiguities. A review 

of the major features of the Greens Creek deposit shows that 

many of its distinctive characteristics can be placed in either the 

VMS or SEDEX classes. VMS characteristics include a zinclead-silver-gold-copper-rich metal endowment similar to the 

Kuroko-type in an essentially continuous, single orebody. Ore 

types display distinct lateral and vertical zonation that indicate 

thermal and geochemical evolution of a fluid during a single 

mineralizing event. The thickest portions of the orebody are 

dominated by massive pyritic ores that retain primary textures 

indicative of growth by zone refining and replacement of earlier formed minerals. Further, both the ore and gangue mineral 

assemblages at Greens Creek are strikingly similar to recent 

descriptions of active sea-floor systems generally described as 

modern analogues to the Kuroko-type of deposits.

Although volcanism was not active immediately before 

or during ore formation, Greens Creek sits on an intensely 

altered mafic volcanic footwall that has a zoned alteration 

profile typical of VMS systems (Taylor, Newkirk, and others, 

1999; Anderson and Taylor, 2000; Anderson and Taylor, 

unpub. data, 2000). However, the deposit also has numerous characteristics usually associated with the SEDEX class. 

The complete absence of felsic igneous rocks is striking, and 

the intrusion of mafic-ultramafic stocks and sills into a cold 

footwall is more typical of SEDEX deposits. Similarly, the lack 

of a focused feeder system and presence of a huge alteration 

envelope containing chromium and barium-rich silicates such 

as fuchsite, oellacherite, and celsian, and a complexly zoned 

carbonate alteration assemblage are more typical of SEDEX. 

Perhaps even more striking is the abundant evidence that suggests Greens Creek formed primarily during diagenesis of the 

graphitic, pyritic, hanging-wall argillite; geochronologic and 

isotopic evidence suggests that ore formation occurred during 

and after deposition of the shale cap. Crosscutting relationships and ore textures are consistent with growth by inflation 

beneath, and diagenetic replacement of, the shales during 

sedimentation. Additionally, sulfur isotope values are unusually low and are unlike either VMS or SEDEX values. Indeed, 

the epigenetic replacement textures in the footwall sedimentary 

carbonate bodies and the sulfur isotopic characteristics of the 

ores are most similar to the carbonate-hosted massive sulfide 

deposits of the Irish Midlands ore field and of the MVT deposits of the U.S. Midcontinent. Greens Creek, therefore, exhibits 

a hybrid set of characteristics that places it within a spectrum 

of exhalative- to replacement-style deposits rather than within a 

single general category.

A major reason for the hybrid characteristics of the 

Greens Creek deposit may be reconciled by examination of the 

Late Triassic tectonic setting. If, as proposed, the Late Triassic 

rift in southeastern Alaska formed by oblique propagation into 

the Alexander terrane (Taylor, 1997; Taylor, Philpotts, Sutley, 

and others, 1995; Taylor, Philpotts, Hall, and Wakeman, 1995; 

Taylor, Premo, and Meier, 1999; Taylor, 2000), then a metallogenic environment would have existed that is common to 

both VMS and SEDEX environments. Recent work relating the 

specific nature of both ancient (Barrett and MacLean, 1999) 

and modern (Hannington and others, 1986; Halbach and others, 

1993; Binns and others, 1993; Fouquet and others, 1993; Stoffers and others, 1999) VMS deposits to the location (continental margin, oceanic) and maturity level of the rift basin may 

explain the variation in the mineral occurrences of the Late 

Triassic belt in southeastern Alaska. For example, deposits that 

form at the tip of rifts propagating into mature arcs (Binns and 

others, 1993; Fouquet and others, 1993) or where nascent intracontinental rifts split arcs, such as Japan, are generally Kurokotype and are associated with arc-type or heavily calc-alkalinecontaminated tholeiitic lavas (Barrett and MacLean, 1999). 

Deposits that form in this setting correspond to the bimodalmafic division of Barrie and Hannington (1999). Deposits 

that form landward from the propagating rift or on land in the 

early stages of rifting have an epithermal or hot springs style 

of expression (for example, Stoffers and others, 1999; deposits 

of the Taupo volcanic zone). Deposits that form in the deeper, 

seaward portion of propagating rifts or in mature rifts are more 

likely to be copper-zinc-rich and may be associated with distal 

clastic sediments such as Windy Craggy (Peter and Scott, 
References Cited 427

1999) and the Besshi deposits. The deposits in the mature rift 

settings are usually associated with primitive mafic melts that 

are forming segments of new oceanic crust that may or may 

not show contamination by melting and incorporation of the 

rifted crust (Barrett and MacLean, 1999; the mafic-siliciclastic 

division of Barrie and Hannington, 1999). That such a variation 

of deposit styles, associated with predictably varying suites of 

igneous rocks, can be found in a single rift propagating into a 

mature arc or continental margin provides confirmation for the 

lithogeochemical and deposit variability of the occurrences in 

southeastern Alaska.

The segment of a propagating rift that we feel is analogous 

to the Greens Creek tectonic setting is that portion seaward of 

the propagating tip of the rift basin and landward of the point at 

which new oceanic crust begins to form. Within this segment, 

bimodal volcanism is characterized by peralkaline rhyolites and 

tholeiitic basalts that exhibit varying degrees of crustal contamination (chap. 2). Moving seaward, the rhyolites disappear from 

the section and the mafic melts become less arc-contaminated 

and more similar to ocean-ridge basalts, commonly EMORB 

or “transitional” basalts. The seaward transition may or may 

not evolve into a sediment-covered ridge; however, the transition represents the change from a bimodal-mafic to a maficsiliciclastic metallogenic environment. This transition is exactly 

like the observed changes in the tectonostratigraphic setting 

described between the Keku Inlet, where Greens Creek-like 

occurrences are hosted in dolomitic limestone overlying peralkaline rhyolites, and Greens Creek, where rhyolites are absent, 

the rift has become sediment-covered, and mafic-ultramafic 

melts are still heavily contaminated by the Alexander terrane 

basement that they rise through (chap. 2).

We suggest that the specific portion or period of 

an evolving rift—where lithologies have transitioned to 

mafic-ultramafic rocks intruding through and being heavily 

contaminated by a mature arc, covered by distal clastic 

sedimentation—is strikingly similar to the failed epicontinental rift tectonic setting common to most SEDEX deposits. 

At the time of Late Triassic rifting, the Alexander terrane 

was an inactive continent-sized landmass of wholly oceanic 

affinities, cored by sialic Proterozoic and lower Paleozoic 

crust. At the latitude of Greens Creek, rifting resulted in the 

formation of a small (second order?), restricted, anoxic, and 

very organic rich sedimentary basin, which was intruded by 

rift-related mafic-ultramafic intrusive rocks. This specific, 

SEDEX-like metallogenic setting occurred within a propagating rift, which on a larger scale is more akin to the 

metallogenic setting common to many VMS deposits.

References Cited

Anderson, V.M., and Taylor, C.D., 2000, Alteration mineralogy and zonation in host rocks to the Greens Creek deposit, 

southeastern Alaska: Geological Society of America Cordilleran Section Meeting, Abstracts with Programs, v. 32, no. 

6, p. A–2.

Barrett, T.J., and MacLean, W.H., 1999, Volcanic sequences, 

lithogeochemistry, and hydrothermal alteration in some 

bimodal volcanic-associated massive sulfide systems, in

Barrie, C.T., and Hannington, M.D., eds., Volcanic-associated massive sulfide deposits—Processes and examples in 

modern and ancient settings: Society of Economic Geologists Reviews in Economic Geology, v. 8, p. 101–127.

Barrie, C.T., and Hannington, M.D., 1999, Classification 

of volcanic-associated massive sulfide deposits based on 

host-rock composition, in Barrie, C.T., and Hannington, 

M.D., eds., Volcanic-associated massive sulfide deposits—

Processes and examples in modern and ancient settings: 

Society of Economic Geologists Reviews in Economic 

Geology, v. 8, p. 1–11.

Berg, H.C., 1973, Geology of Gravina Island, Alaska: U.S. 

Geological Survey Bulletin 1373, 41 p.

Binns, R.A., Scott, S.D., Bogdanov, Y.A., Lisitzin, A.P., Gordeev, V.V., Gurvich, E.G., Finlayson, E.J., Boyd, T., Dotter, 

L.E., Wheller, G.E., and Muravyev, K.G., 1993, Hydrothermal oxide and gold-rich sulfate deposits of Franklin 

Seamount, western Woodlark basin, Papua New Guinea: 

Economic Geology, v. 88, p. 2122–2153.

Dressler, J.S., and Dunbire, J.C., 1981, The Greens Creek ore 

deposit, Admiralty Island, Alaska: Canadian Institute of 

Mining and Metallurgy Bulletin, v. 74, no. 833, p. 57.

Fouquet, Yves, Von Stackelberg, U., Charlou, J.L., Erzinger, 

J., Herzig, P.M., Muhe, R., and Wiedicke, M., 1993, Metallogenesis in back-arc environments—The Lau basin example: Economic Geology, v. 88, p. 2154–2181.

Franklin, J.M., Lydon, J.W., and Sangster, D.F., 1981, Volcanic-associated massive sulfide deposits, in Skinner, B.J., 

ed., Economic geology: Seventy-fifth anniversary volume, 

1905–1980, p. 485–627.

Gehrels, G.E., and Berg, H.C., 1992, Geologic map of southeastern Alaska: U.S. Geological Survey Miscellaneous 

Investigations Series Map I–1867, scale 1:600,000.

Gehrels, G.E., and Berg, H.C., 1994, Geology of southeastern Alaska, in Plafker, George, and Berg, H.C., eds., The 

geology of Alaska: Boulder, Colorado, Geological Society 

of America, Decade of North American Geology, v. G1, 

p. 451–468.

Gehrels, G.E., Saleeby, J.B., and Berg, H.C., 1987, Geology of 

Annette, Gravina, and Duke Islands, southeastern Alaska: 

Canadian Journal of Earth Sciences, v. 24, p. 866–881.

Goodfellow, W.D., Lydon, J.W., and Turner, R.J.W., 1993, 

Geology and genesis of stratiform sediment-hosted 

(SEDEX) zinc-lead-silver sulphide deposits, in Kirkham, 

R.V., Sinclair, W.D., Thorpe, R.I., and Duke, J.M., eds., 

Mineral deposit modeling: Geological Association of 

Canada, Special Paper 40, p. 201–251.
428 Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Alaska

Haeussler, P.J., Karl, S.M., Mortensen, J.K., Layer, Paul, and 

Himmelberg, G.R., 1999, Permian and mid-Cretaceous deformation of the Alexander terrane on Admiralty and Kupreanof 

Islands, southeastern Alaska [abs.]: Geological Society of 

America Abstracts with Programs v. 31, no. 6, p. A–60.

Halbach, Peter, Pracejus, B., and Marten, A., 1993, Geology 

and mineralogy of massive sulfide ores form the central 

Okinawa trough, Japan: Economic Geology, v. 88, p. 

2210–2225.

Hannington, M.D., Bleeker, W., and Kjarsgaard, I., 1999, Sulfide mineralogy, geochemistry, and ore genesis of the Kidd 

Creek deposit—Part I, North, Central, and South orebodies: 

Economic Geology Monograph 10, p. 163–224.

Hannington, M.D., Peter, J.M., and Scott, S.D., 1986, Gold in 

sea-floor polymetallic sulfide deposits: Economic Geology, 

v. 81, p. 1867–1883.

Hannington, M.D., and Scott, S.D., 1989, Gold mineralization in volcanogenic massive sulfides—Implications of data 

from active hydrothermal vents on the modern sea floor: 

Economic Geology Monograph 6, p. 491–507.

Herzig, P.M., Hannington, M.D., Fouquet, Y., Von Stackelberg, U., and Petersen, S., 1993, Gold-rich polymetallic 

sulfides from the Lau back-arc and implications for the geochemistry of gold in sea-floor hydrothermal systems of the 

southwest Pacific: Economic Geology, v. 88, p. 2182–2209.

Huston, D.L., and Large, R.R., 1989, A chemical model for 

the concentration of gold in volcanogenic massive sulphide 

deposits: Ore Geology Reviews, v. 4, p. 171–200.

Hutchinson, R.W., 1973, Volcanogenic sulfide deposits and 

their metallogenic significance: Economic Geology, v. 68, 

p. 1223–1246.

Kerr, D.J., and Gibson, H.L., 1993, A comparison of the 

Horne volcanogenic massive sulfide deposit and intracauldron deposits of the mine sequence, Noranda, Quebec: 

Economic Geology, v. 88, p. 1419–1442.

Large, R.R., 1992, Australian VHMS deposits—Features, 

styles, models: Economic Geology, v. 87, p. 471–510.

Large, R.R., Huston, D.L., McGoldrick, P.J., and Ruxton, P.A., 

1989, Gold distribution and genesis in Australian volcanogenic 

massive sulfide deposits and their significance for gold transport models: Economic Geology Monograph 6, p. 520–536.

Leach, D.L., and Sangster, D.F., 1993, Mississippi Valley-type 

lead-zinc deposits, in Kirkham, R.V., Sinclair, W.D., Thorpe, 

R.I., and Duke, J.M., eds., Mineral deposit modeling: Geological Association of Canada, Special Paper 40, p. 289–314.

Morton, R.L., and Franklin, J.M., 1987, Two-fold classification of Archean volcanic-associated massive sulfide deposits: Economic Geology, v. 82, p. 1057–1064.

Muffler, L.J.P., 1967, Stratigraphy of the Keku Islets and 

neighboring parts of Kuiu and Kupreanof Islands southeastern Alaska: U.S. Geological Survey Bulletin 1241–C, 

52 p.

Newberry, R.J., Crafford, T.C., Newkirk, S.R., Young, L.E., 

Nelson, S.W., and Duke, N.A., 1997, Volcanogenic massive 

sulfide deposits of Alaska, in Goldfarb, R.J., and Miller, 

L.E., eds., Mineral deposits of Alaska: Economic Geology 

Monograph 9, p. 120–150.

Ohmoto, Hiroshi, Mizukami, M., Drummond, S.E., Eldridge, 

C.S., Pisutha-Arnond, V., and Lenagh, T.C., 1983, Chemical processes of Kuroko formation, in Ohmoto, Hiroshi, and 

Skinner, B.J., eds., The Kuroko and related volcanogenic 

massive sulfide deposits: Economic Geology Monograph 5, 

p. 570–604.

Peter, J.M., and Scott, S.D., 1999, Windy Craggy, northwestern British Columbia—The world’s largest Besshitype deposit, in Barrie, C.T., and Hannington, M.D., eds., 

Vocanic-associated massive sulfide deposits—Processes 

and examples in modern and ancient settings: Society of 

Economic Geologists Reviews in Economic Geology, v. 8, 

p. 261–295.

Solomon, Michael, and Groves, D.I., 1994, The geology and 

origin of Australia’s mineral deposits: Oxford, Oxford Science Publications, 951 p.

Stoffers, Peter, Hannington, M., Wright, I., Herzig, P., de 

Ronde, C., and Shipboard Scientific Party, 1999, Elemental 

mercury at submarine hydrothermal vents in the Bay of 

Plenty, Taupo volcanic zone, New Zealand: Geology, v. 27, 

no. 10, p. 931–934.

Taylor, C.D., 1997, An arc-flank to back-arc transect—

Metallogeny of Late Triassic volcanogenic massive sulfide 

occurrences of the Alexander terrane, southeastern Alaska 

and British Columbia: [extended abs.] in Society of Economic Geologists Neves Corvo Field Conference, May 

7–17, 1997, Lisbon, Portugal, Abstracts and Programs 

volume, p. 68.

Taylor, C.D., Newkirk, S.R., Hall, T.E., Lear, K.G., Premo, 

W.R., Leventhal, J.S., Meier, A.L., Johnson, C.A., and 

Harris, A.G., 1999, The Greens Creek deposit, southeastern Alaska—A VMS-SEDEX hybrid, in Stanley, C.J., and 

others, eds., Mineral deposits—Processes to processing: 

Rotterdam, Balkema, v. 1, p. 597–600.

Taylor, C.D., Philpotts, J.A., Hall, T.E., and Wakeman, 

B.W., 1995, New information on the geochemistry, age, 

and tectonic history of Late Triassic volcanic host rocks 

and associated massive sulfide occurrences of the Alexander terrane, southeast Alaska [abs.]: Alaska Miners 

Association Conference, Juneau, Program with Abstracts, 

p. 31–32.
References Cited 429

Taylor, C.D., Philpotts, J., Sutley, S., Gent, C., Harlan, S., 

Premo, W., Tatsumoto, M., Emsbo, P., and Meier, A., 1995, 

Geochemistry of Late Triassic volcanic rocks and age of 

alteration associated with volcanogenic massive sulfide 

occurrences, Alexander terrane, southeast Alaska, in Geology and ore deposits of the American Cordillera, A Symposium, Reno, Nev., 1995: Reno, Nev., Geological Society of 

Nevada, p. A74.

Taylor, C.D., Premo, W.R., and Lear, K.G., 2000, The Greens 

Creek massive sulfide deposit—Premier example of the Late 

Triassic metallogeny of the Alexander terrane, southeastern 

Alaska and British Columbia [abs.]: Geological Society of 

America Abstracts with Programs, v. 32, no. 6, p. A–71.

Taylor, C.D., Premo, W.R., and Meier, A.L., 1999, The Late 

Triassic metallogeny of the Alexander terrane, southeastern 

Alaska and British Columbia [abs.]: Geological Society of 

America Abstracts with Programs, v. 31, no. 6, p. A–101.

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