Geochemical Studies in Alaska 

by the U.S. Ge )logical Survey, 1989 

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ERRATA 

U.S. Geological Survey Bulletin 1950, Geochemical studies in Alaska by the U.S. Geological Survey, 1989. 

The names "Windfall Creek" and "Windfall Creek area" are incorrect in the text of chapter A and in figure 

4 and table 3 of chapter A. The correct names are "Ward Creek" and "Ward Creek area." 

Geochemical Studies in Alaska 

by the U.S. Geological Survey, 1989 

Edited by RICHARD J. GOLDFARB, J. THOMAS NASH, 

and J.W. STOESER 

This volume is published as chapters A-F. 

Chapter titles are listed in volume contents. 

These chapters are not available separately 

U.S. GEOLOGICAL SURVEY BULLETIN 1950 
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government. 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1990 

For sale by the 

Books and Open-File Reports Section 

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Library of Congress Cataloging-in-Publication Data 

Geochemical studies in Alaska by the U.S. Geological Survey, 1989 I edited by Richard J. 

Goldfarb, J. Thomas Nash, and J.W. Stoeser. 

p. em. - (U.S. Geological Survey bulletin ; 1950) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.3:1950 

1. Geochemistry-Alaska. 2. Ore deposits-Alaska. I. Goldfarb, R. J. II. Nash, J. 

Thomas (John Thomas), 1941-. Ill. Stoeser, J. W. IV. Series. 

OE75.B9 no. 1950 

[QE515] 

557.3 s-dc20 9Q-14099 

[551.9'09798] CIP 
VOLUME CONTENTS 

[Letters designate the chapters] 

(A) Interpretation of geochemical data from Admiralty Island, Alaska-Evidence for 

volcanogenic massive sulfide mineralization, by Karen Duttweiler Kelley. 

(B) Geochemical orientation study for identification of metallic mineral resources in 

the Sitka quadrangle, southeastern Alaska, by E. Lanier Rowan, Elizabeth A. 

Bailey, and Richard J. Goldfarb. 

(C) Geology and geochemistry of mineralization in the Bethel quadrangle, southwestem Alaska, by Thomas P. Frost. 

(D) Gold associated with cinnabar- and stibnite-bearing deposits and mineral occurrences in the Kuskokwim River region, southwestern Alaska, by John E. Gray, 

Thomas P. Frost, Richard J. Goldfarb, and David E. Detra. 

(E) Stable isotope systematics of epithermal mercury-antimony mineralization, southwestern Alaska, by Richard J. Goldfarb, John E. Gray, William J. Pickthom, 

Carol A. Gent, and Barrett A. Cieutat. 

(F) Gold anomalies and newly identified gold occurrences in the Lime Hills quadrangle, Alaska, and their association with the Hartman sequence plutons, by 

Michael S. Allen. 

Volume Contents Ill 

Chapter A 

Interpretation of Geochemical Data from 

Admiralty Island, Alaska-Evidence for 

Volcanogenic Massive Sulfide Mineralization 

By KAREN DUTTWEI LER KELLEY 

U.S. GEOLOGICAL SURVEY BULLETIN 1950 

GEOCHEMICAL STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1989 
CONTENTS 

Abstract Al 

Introduction Al 

Geology of Admiralty Island Al 

Mineral deposits A3 

Geochemical studies A4 

Methods and data evaluation A4 

Interpretation A4 

Conclusions AS 

References cited AS 

FIGURES 

1-4. Maps showing: 

1. Distribution of volcanogenic massive sulfide occurrences in the area of 

Admiralty Island A2 

2. Geology of Admiralty Island A3 

3. Distribution of Ag, Au, Sb, and Win sediment samples from Admiralty 

Island A6 

4. Basin areas containing samples having anomalous scores for factors 3 

and 5 AS 

TABLES 

1. Univariate statistical estimates for 380 sediment samples, Admiralty Island AS 

2. Five-factor geochemical model for sediment samples, Admiralty Island A6 

3. Concentrations of As, Au, Ba, Ni, Sb, and Zn in samples having anomalous scores 

for factor 3 (As-Ba-Ni-Zn), Admiralty Island A7 
Interpretation of Geochemical Data from 

Admiralty Island, Alaska-Evidence for 

Volcanogenic Massive Sulfide Mineralization 

By Karen Duttweiler Kelley 

Abstract 

Late Triassic sedimentary and intermediate to mafic volcanic rocks 

of the Alexander terrane on Admiralty Island host the Greens Creek and 

Pyrola Ag-Au-Pb-Zn syngenetic volcanogenic massive sulfide deposits. 

Other Au-Cu-Pb-Zn mineral occurrences and prospects are northeast of 

Greens Creek on the northernmost part of Admiralty Island. 

Reconnaissance geochemical surveys conducted during the 

National Uranium Resource Evaluation (NURE) program included 

collection of 416 sediment samples from Admiralty Island. Results of 

factor analysis of the multi-element data include two geochemical 

associations-As-Ba-Ni-Zn and Pb-Zn-Cu-most likely indicative of 

volcanogenic massive sulfide mineralization. Three geographically 

distinct regions, underlain by Triassic volcanic and sedimentary rocks, are 

delineated as geochemically favorable areas for mineral occurrences: (1) 

the Greens Creek area surrounding the Greens Creek deposit and other 

nearby Au-Cu-Pb-Zn occurrences, (2) a large area southeast of the 

Pyrola deposit that includes most of the tributaries to Windfall Creek and 

adjacent drainage basins to the east and southeast, and (3) drainage 

basins north and south of Gambier Bay. 

These three regions define a northwesterly trend from Gambier 

Bay in the southeast to the Greens Creek area in the northwest. This 

trend is consistent with a regional northwest-trending belt of syngenetic 

massive sulfide occurrences of Permian and Triassic age in southeastern 

Alaska. 

INTRODUCTION 

Admiralty Island is located 15 km south of Juneau in 

parts of the Sitka, Sumdum, and Juneau quadrangles (fig. 1). 

In 1982 the U.S. Department of Energy completed 

reconnaissance geochemical surveys of these quadrangles 

as part of the National Uranium Resource Evaluation 

(NURE) program. Stream- and lake-sediment samples and 

water samples were collected and analyzed for a variety of 

trace elements. 

Manuscript approved for publication, June 26, 1990. 

An initial evaluation of the data from the Sitka 

quadrangle was conducted by the U.S. Geological Survey 

during a preliminary mineral resource assessment. Data 

from the area of Admiralty Island within the Juneau and 

Sumdum quadrangles were subsequently added. This paper 

presents an evaluation and interpretation of the sediment 

geochemical data from Admiralty Island. The geochemical 

signature in sediment samples from streams draining the 

Greens Creek deposit is distinctive. Other possible 

mineralized areas are suggested based on similar geochemical anomalies and associations. 

Acknowledgments.-! thank Rich Goldfarb, Bob 

Eppinger, and Tom Nash for their helpful reviews of this 

paper. Discussions with Sue Karl and Art Ford regarding the 

regional setting, stratigraphy, and structure of Admiralty 

Island greatly improved my understanding of the area. I also 

thank Karen Slaughter, who helped with the drafting. 

GEOLOGY OF ADMIRALTY ISLAND 

Admiralty Islam( is made up mostly of sedimentary, 

volcanic, and plutonic rocks (fig. 2) of the Alexander 

terrane of Silberling and Jones (1984). These rocks have 

been interpreted to represent . intermittent volcanic arc 

activity along a convergent continental margin (Gehrels and 

Saleeby, 1987). 

The oldest rocks on Admiralty Island are black 

radiolarian chert (Karl, 1989), argillite, graywacke, and 

minor altered volcanic rocks of the Ordovician Hood Bay 

Formation (Carter, 1977) and unnamed Silurian 

sedimentary rocks (Lathram and others, 1965). Thick 

carbonate sequences of Devonian age unconformably 

overlie the Silurian rocks. These are overlain by siliceous 

argillite, graywacke, and chert of the Permian Cannery 

Formation (Jones and others, 1981). Two different 

sequences of Late Triassic rocks have been recognized on 

Admiralty Island. The Hyd Group (Loney, 1964) consists of 

pillow lava flows, tuff, andesitic and basaltic breccia, and 

Interpretation of Geochemical Data from Admiralty Island, Alaska A1 
& Mt. Henry Clay 

£ Orange Point 

& Greens Creek 

& Pyrola 

£ Cornwallis Peninsula 

& Castle Island 

' 

~~-9 ')l,Z, 

G- ~ -9<> 

d\-9, -9 

50 0 50 

KILOMETERS 

Figure 1. Distribution of volcanogenic massive sulfide occurrences of Permian and Triassic age within the Alexander terrane in the area 

of Admiralty Island. Modified from Goldfarb and others (1987). 

fine-grained clastic and carbonate rocks, and the Retreat 

Group consists of deeper water volcanic and sedimentary 

rocks. The Retreat Group was originally considered to be 

Late Triassic (?) to Early Cretaceous (?) in age (Barker, 

1957); its age was subsequently revised to Middle (?) 

Devonian (Lathram and others, 1965). Recent evidence, 

however, indicates that its age is Late Triassic (Ford and 

others, 1989). Chlorite-epidote-calcite phyllite and schist of 

the Gambier Bay Formation (Lathram and others, 1965) 

may be correlative with the Retreat Group on northern 

Admiralty Island (Ford and others, 1989). 

Jurassic and Cretaceous graywacke turbidite and 

massive conglomerate of the Seymour Canal Formation and 

A2 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

basaltic (Ford and Brew, 1988) or andesitic flow breccia 

(Lathram and others, 1965) of the Douglas Island Volcanics 

comprise the Stephens Passage Group, which disconformably overlies Triassic rocks on northeastern Admiralty 

Island. The Paleozoic and Mesozoic rocks· were intruded by 

Cretaceous plutonic rocks of intermediate, mafic, and ultramafic composition. The largest intrusive body in the central 

part of the island is a batholith composed dominantly of 

granodiorite and tonalite. Tertiary sedimentary and volcanic 

rocks include the Kootznahoo Formation and the Admiralty 

Island Volcanil(s (Lathram and others, 1965). The Kootznahoo Formation consists of pebble to cobble conglomerate, 

sandstone, carbonaceous shale, and sub-bituminous coal. 
58° 

(/') 

-1 

:0 

)> 

:; 

134° 30' 

· .. : /, .. ,·: . ' .. :·-: ·: .: 

Kootznahoo : 

Inlet 

134° 

0 

~ 

10 

KILOMETERS 

57°L_ __________________ L_ ______________ L_ ______ ~ 

Figure 2. Geologic map of Admiralty Island. Generalized from Lathram 

and others (1965) and Ford and others (1989). 

The Admiralty Island Volcanics consist of massive 

porphyritic andesitic basalt flows that unconformably 

overlie pre-Tertiary rocks on the southern part of the island. 

MINERAL DEPOSITS 

The Greens Creek and Pyrola deposits are AgAu-Pb-Zn volcanogenic massive sulfide deposits hosted by 

Late Triassic volcanic and sedimentary rocks (fig. 2). 

Several other Au-Cu-Pb-Zn occurrences are northeast of the 

Greens Creek deposit (Lathram and others, 1965), and 

syngenetic sulfide-barite mineral occurrences have been 

reported in the Pybus Bay area of southern Admiralty Island 

B . 

. 

5] 

D 

• 

~ 

[] 

[ll] 

• 

EXPLANATION 

Tertiary rocks-Andesitic basalt flows: Admiralty Island Volcanics 

Tertiary rocks-Conglomerate, sandsto ne. shale, coal; Kootznahoo 

Formation 

Cretaceous rocks-Intermediate, mafic, and ultramafic plutonic rocks 

Cretaceous and Jurassic rocks-Argillite, conglomerate, and graywacke; Seymour Canal Formation 

Cretaceous and Jurassic rocks-Basaltic or andesitic flow breccia; 

Douglas Island Volcanics 

Triassic and Permian rocks-Volcanic and sedimentary rocks 

Triassic rocks-Chert, argillite, graywacke, carbonate rocks, and 

intermediate to mafic volcanic rocks. Consists of the Hyd Group, as 

mapped, and the Retreat Group and Gambier Bay Formation 

Mississippian and Devonian rocks-Argillite, graywacke, chert, and 

minor co nglomerate, limestone, and volcan ic rocks; Canne ry 

Formation 

Devonian rocks-Marble enclosed tectonically within Gambier Bay 

Formation 

Silurian and Ordovician rocks-Argil lite, chert, graywacke, and 

minor volcanic rocks; includes Ordovic ian Hood Bay Formation and 

sedimentary rocks 

Mesozoic or Paleozoic rocks-Metasedimentary and metaigneous 

rocks 

Ag-Au-Pb-Zn deposit 

Au-Cu-Pb-Zn occurrence 

Au (±Cu) occurrence 

(Van Nieuwenhuyse, 1984). Similar syngenetic massive 

sulfide occurrences in Permian- and Triassic-age rocks of 

the Alexander terrane to the north and south of Admiralty 

Island (Goldfarb and others, 1987) (fig. 1) form a belt 

almost 350 km long. 

The Greens Creek stratiform massive sulfide deposit 

(Dressler and Dunbire, 1981) contains drill-indicated 

reserves of 3.5 million short tons of 23.8 oz/ton Ag, 0.18 

oz/ton Au, 3.9 percent Pb, and 9.7 percent Zn. 

Mineralization is dominantly syngenetic, although remobilization and (or) additional mineralization is indicated by 

sulfide- and gold-bearing quartz veins (Crafford, 1989). The 

main orebody is situated between a structural hanging wall 

of altered mafic volcanic rocks and a footwall of black 

graphitic argillite. Recently discovered fossils in argillite 

fragments within the massive sulfide ore suggest a Late 

Triassic age for the mineralization (Crafford, 1989). The 

dominant ore minerals are sphalerite, galena, freibergite, 

and chalcopyrite; native gold and silver-sulfide and silversulfosalt minerals occur in lesser amounts. Quartz and barite 

are the primary gangue minerals (Crafford, 1989). 

The Pyrola deposit, which lies at the contact between 

volcanic rocks and fine-grained clastic and carbonate rocks, 

consists of interbedded massive sulfide minerals and barite 

and an underlying siliceous stockwork zone containing 

auriferous pyrite. Sulfide minerals are pyrite, sphalerite, 

galena, and minor chalcopyrite; other minerals include the 

Interpretation of Geochemical Data from Admiralty Island, Alaska A3 
lead-antimony sulfosalt minerals jamesonite and boulangerite (Van Nieuwenhuyse, 1984 ). 

A nickel-copper deposit near Punter Bay (fig. 1) is 

hosted in a pipelike intrusive body of gabbroic and noritic 

composition. The ore minerals, chiefly pentlandite and 

chalcopyrite, are in veinlets or lenses and bands of sulfide 

ore (Reed, 1942; Lathram and others, 1965). 

Six gold (±copper) prospects are reported on 

Admiralty Island (fig. 2). These are gold-bearing quartz 

veins in schistose rocks and disseminated gold in brecciated 

limestone and calcareous schist (Lathram and others, 1965; 

Cobb, 1972, 1978). In addition, dolomite breccia 

immediately north of Gambier Bay locally contains chalcopyrite and trace amounts of gold (Herbert and Race, 1965; 

Berg and Cobb, 1967). 

GEOCHEMICAL STUDIES 

Methods and Data Evaluation 

During the course of the NURE program, 416 streamand lake-sediment samples were collected from Admiralty 

Island. All samples were sieved to -100 mesh and analyzed 

for 44 elements using X-ray fluorescence and neutron 

activation methods (Los Alamos National Laboratories, 

1982a, b, c). 

Univariate statistics (table 1) and multivariate 

analysis were used to (1) evaluate the NURE geochemical 

data, (2) identify anomalous samples, and (3) relate 

anomalies to particular types of mineral deposits. Prior to 

data evaluation, 36 samples were eliminated due to the lack 

of analyses for As, Cu, Pb, and Zn. The remaining 380 

sediment samples include 297 stream-sediment samples and 

83 lake-sediment samples. Although stream- and lakesediment samples may be considered two distinctly 

different sample media, data for the two media were 

combined prior to multi-element data analysis; initial 

evaluation of the two as separate data populations revealed 

that within each most elements show similar concentration 

ranges, geometric means, and interelement correlation. 

Prior to multi-element data evaluation and 

interpretation, many elements were removed from the data 

set because of the large percentages of qualified values 

(concentrations below the lower determination limit). 

Although data for Au, Ag, Sb, and W were thereby 

removed, the few samples contammg anomalous 

concentrations of one or more of these elements are noted 

on figure 3. 

Correlation and R-mode factor analysis (Davis, 1986) 

were used to identify the major element associations in the 

sediment data set. R-mode factor analysis groups elements 

that tend to behave similarly into multi-element 

associations, or factors, based on their mutual linear 

A4 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

correlation coefficients. Different types of mineral deposits 

and rock types have distinct geochemical signatures that can 

be identified as factors. 

The contribution of each variable to each factor is 

represented by a factor loading. The effect a particular 

factor may have on each sample site is represented by a 

factor score. When presented in map form, factor scores 

portray the areal variation of the interpreted geological and 

geochemical features or processes. 

Interpretation 

A five-factor model accounts for 71 percent of the 

total data variance and was selected as the geochemically 

most meaningful model to describe the major associations 

(table 2). Two of the factors reflect the dominant bedrock 

geochemistry. Factor 1 has high loadings for Mg, Sc, V, Cr, 

Fe, AI, Ca, Co, Ni, Na, Ti, Cu, and Mn. Samples having 

anomalous scores correlate with basaltic or andesitic flow 

breccias of the Douglas Island Volcanics or undivided 

Mesozoic or Paleozoic metamorphic rocks. Factor 2, which 

has high loadings for Hf, Zr, Ce, Lu, Eu, Th, Ti, Dy, AI, Na, 

U, and Fe, characterizes Cretaceous plutonic rocks of 

intermediate composition and andesitic basalt flows of the 

Admiralty Island Volcanics. 

High positive loadings for Mn, Co, and Fe 

characterize factor 4. This factor association most likely 

represents an abundance of iron-manganese oxides in 

sediment samples produced during weathering and 

oxidation. Anomalous samples are widely scattered and are 

not associated with any particular rock unit. 

Factors 3 (As, Ba, Ni, Zn) and 5 (Pb, Zn, Cu) are 

indicative of mineralization. Drainage basin areas 

characterized by samples having anomalous scores for these 

factors are shown on figure 4. Three relatively large regions 

are delineated: ( 1) the Greens Creek area surrounding the 

Greens Creek deposit and other nearby Au-Cu-Pb-Zn 

prospects, (2) the area southeast of the Pyrola deposit, 

which includes most of the ttibutaries to Windfall Creek and 

adjacent drainage basins to the east and southeast, and (3) 

drainage basins north and south of Gambier Bay. The 

concentrations of As, Ba, Ni, and Zn in samples having 

anomalous scores ( ;;::: 1.31) for factor 3 from these areas are 

shown in table 3. Concentrations of Au and Sb are also 

shown. More than half of the samples have anomalous Ba 

concentrations (;:::1,200 ppm); ~wo samples from the Gambier Bay area have concentrations of 7,118 and 9,090 ppm, 

respectively. Many of the samples have anomalous 

concentrations of As (35-216 ppm), Ni (84-749 ppm), Sb 

(2-28 ppm), and (or) Zn (300-694 ppm). Barite, sphalerite, 

pyrite, sulfosalt minerals, or oxides derived from these 

minerals are the most likely sources for these highly 

anomalous concentrations. 

Samples having scores greater than or equal to 1.25 

for factor 5 are considered anomalous. Many of these 
Table 1. Univariate statistical estimates for 380 sediment samples, Admiralty Island, Alaska 

[Values in parts per million unless otherwise indicated. Analysis by neutron activation methods unless otherwise indicated. 

Leaders (--)indicate too many qualified values (below lower detection limit) to calculate accurate or meaningful statistics] 

Minimum Geometric 90th 99th Maximum 

Element Valid2 NA3 concentration mean4 ~ercentile ~ercentile concentration 

Ag 3 116 5 7 

Al% 378 0 0.6 6.0 8.3 9.1 9.5 

As1 299 0 5 11 35 131 216 

Au 1 0 1.07 1.07 

Ba 243 0 271 435 1,115 3,101 9,090 

Bil 18 116 5 10 

Ca% 357 0 0.3 1.7 4.7 7.5 16.8 

Cd1 7 0 5 11 

Ce 353 0 13 40 69 99 137 

Cl 99 0 140 11,700 

Co 362 0 3.3 20 43 61 106 

Cr 352 0 23 109 277 440 1,772 

Cs 47 0 2.1 18.7 

cul 377 0 10 44 94 204 275 

Dy 340 0 2 4 7 9 11 

Eu 356 0 0.6 1.2 1.8 2.4 8.2 

Fe% 376 0 0.3 4.7 7.6 9.6 13.0 

Hf 307 0 1.5 3.3 6.2 10.1 12.8 

K% 198 0 0.5 0.8 1.6 2.3 2.9 

La 171 0 12 14.6 33 54 126 

I.n 289 0 0.1 0.3 0.5 0.8 0.8 

Mg% 344 0 0.4 1.3 2.7 4.1 6.1 

Mn 380 0 40 1,288 2,836 6,340 13,370 

Na% 380 0 0.07 1.5 2.3 32.9 3.5 

Nb 0 116 

Nil 290 0 15 29 70 160 749 

Pbl 138 0 5 5 10 52 132 

Rb 3 0 54 81 

Sb 17 0 2 28 

Sc 379 0 0.9 18 31 46 54 

Se 8 0 5 13 

Sm 300 1 1.6 3.0 6.3 9.2 14.8 

snl 1 116 10 10 

Sr 12 5 357 1,055 

Ta 4 0 2 3 

Tb 17 8 1 3 

Th 281 0 1.4 3 6 10 12.2 

Ti% 350 0 0.12 0.45 0.8 1.2 1.4 

u 380 0 0.26 2.5 5.1 18.0 129 

v 372 0 17 286 286 383 530 

w 26 0 15 40 

Yb 134 0 1.7 2.4 4.9 7.3 9.1 

Zn 164 0 49 84 227 470 857 

Zrl 380 0 5 118 221 372 461 

1 Analyzed by X-ray fluorescence spectrography. 2Number of samples that have concentrations above the lower determination limit (unqualified values). 

3

Number of samples not analyzed; sediment samples from the Juneau and Sumdum surveys (116 samples) were not analyzed for 

Ag, Bi, Nb, or Sn. 

4Calculated on samples subsequent to log transformation of the data; values less than the detection limit were replaced with 

one-half the value of the lower limit of determination. Lower limit may vary for neutron activation analysis. 

Interpretation of Geochemical Data from Admiralty Island, Alaska A5 
Greens 

Creek 

() 

\ 

134° 30' 

0 10 L.,_,.___...j 

KILOMETERS 

57°~----------------~------------~--------~ 

EXPLANATION 

0 Sb, 2-28 ppm 

& w. 15-40 ppm 

• A g. 5-7 ppm 

0 Au, 1.07 ppm 

Sediment sample 

site 

• Au-Ag-Pb-Zn 

deposit 

• Au-Cu-Pb-Zn 

occurrence 

• Au (±Cu) 

occurrence 

Figure 3. Distribution of anomalous concentrations of Ag, Au, Sb, and 

W in sediment samples from Admiralty Island. 

A6 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

Table 2. Five-factor geochemical model for sediment 

samples, Admiralty Island, Alaska 

[Number of samples, 380. Total variance explained by the model is 

71 percent; loadings greater than 0.4 shown in boldface type] 

V ARIMAX FACfOR LOADINGS 

Factor 

Element 1 2 3 4 5 

Al 0.67 0.61 0.03 -0.03 -0.08 

As 0.10 0.19 0.73 0.21 -0.06 

Ba 0.15 0.15 0. 71 -0.31 0.05 

Ca 0.67 0.06 -0.32 0.22 -0.12 

Ce 0.31 0.78 0.17 0.20 0.06 

Co 0.63 0.24 0.11 0.60 0.04 

Cr 0.81 0.01 0.33 -0.02 -0.01 

Cu 0.49 -0.12 0.38 0.35 0.40 

Dy 0.36 0.61 0.12 0.06 0.31 

Fn 0.38 0.65 0.15 0.20 0.26 

Fe 0.70 0.43 0.08 0.40 -0.04 

Hf -0.02 0.86 0.01 0.05 -0.09 

l.ll 0.03 0.65 0.03 0.22 0.32 

Mg 0.90 0.13 0.10 0.12 0.08 

Mn 0.41 0.25 0.08 0. 71 -0.16 

Na 0.62 0.56 -0.09 -0.16 -0.24 

Ni 0.63 -0.18 0.49 0.16 0.14 

Pb -0.05 0.10 0.04 -0.16 0.80 

Sc 0.87 0.31 0.02 0.18 0.05 

Th -0.03 0.63 0.38 -0.05 0.01 

Ti 0.60 0.63 -0.07 -0.01 0.07 

u 0.05 0.48 0.37 0.17 0.14 

v 0.83 0.32 0.19 0.12 0.05 

Zn -0.04 0.09 0.48 0.22 0.41 

'h 0.32 0.86 -0.04 -0.05 -0.14 

Percent of 

total variance 41 12 10 5 4 

INI'ERPRETATION OF MODEL 

Factor 1 (Mg-Sc-V -Cr-Fe-Al-Ca-Co-Ni-Na-Ti-Cu-Mn)-

Jurassic and Cretaceous Douglas Island Volcanics; Mesozoic 

or Paleozoic metamorphic rocks. 

Factor 2 (Hf-Zr-Ce-Lu-Eu-Th-Ti-Dy-Al-Na-U-Fe)-Cretaceous 

plutonic rocks; Tertiary Admiralty Island Volcanics. 

Factor 3 (As-Ba-Ni-Zn)-Triassic volcanic and sedimentary 

rocks; base-metal sulfide and barite mineral occurrences. 

Factor 4 (Mn-Co-Fe)-Iron and manganese oxide minerals; 

weathering and oxidation products. 

Factor 5 (Pb-Zn-Cu)-Triassic volcanic and sedimentary 

rocks; base-metal sulfide mineral occurrences. 

samples contain 200-385 ppm Zn and associated anomalous 

Cu (103-123 ppm) and Pb (20-132 ppm). 

The anomalous concentrations and consistent 

association of these elements in samples from restricted 

geographic areas is good evidence that factors 3 and 5 are 

indicative of mineralization. Specifically, the data indicate 
Table 3. Concentrations of As, Au, Ba, Ni, Sb, and Zn in samples having anomalous scores for factor 3 (As-Ba-Ni-Zn), 

Admiralty Island, Alaska 

[In parts per million. Boldface type indicates anomalous concentrations (approximately 90th percentile or greater; table 1); L indicates value 

less than the lower determination limit] 

Samele1 Score2 As Au Ba Ni Sb Zn 

GREENS CREEK. AREA 

3071535 2.16 47 L 2, 712 222 L L 

3071536 2.15 47 L 1,612 89 L 250 

3071537 1.40 26 L 1,450 84 5 238 

3071541 1.55 39 L 1,556 55 L 299 

3071543 2.03 47 L 2,944 66 L 183 

3071544 2.64 101 1.07 2,628 48 7 368 

3071545 2.56 51 L 4,217 61 7 267 

3071547 1.44 26 L 2,623 46 2 L 

3071548 1.70 27 L 1,119 58 L 153 

3071640 2.72 42 L 3,259 66 5 694 

3071836 2.40 81 L 1,041 67 28 176 

3071840 1.46 11 L 542 749 L L 

3071841 1. 78 72 L 1 216 50 L 359 

WINDFALL CREEK AREA 

3080271 1.35 39 L 1,451 34 L L 

3080274 1.94 44 L 896 118 L 358 

3080275 1.49 156 L 1,271 16 L 236 

3080278 1.80 47 L 1 '133 42 L 322 

3080305 1.36 34 L 1 '774 39 L L 

3080339 1.86 33 L 1,392 106 L 158 

3080428 1.31 16 L 657 96 L 296 

3080429 2.58 88 L 679 202 L 517 

3080430 3.00 196 L 623 58 L 202 

3080431 2.71 216 L 946 50 L 205 

GAMBIER BAY AREA 

3080111 1.63 14 L 

3080113 1. 78 8 L 

3080115 1.57 23 L 

3080131 1.84 19 L 

3080230 1.83 55 L 

3080313 1.65 41 L 

3080415 1.53 19 L 

1 Location given in Los Alamos National Laboratory (1982a, b, c). 

2Score greater than or equal to 1.31 considered anomalous. 

favorability for volcanogenic massive sulfide mineralization 

based on the following observations: 

1. Most samples from the drainage basin of the 

Greens Creek deposit and other small Au-Cu-Pb-Zn 

prospects are anomalous in As, Ba, and Zn and 

corresponding scores for factors 3 (As-Ba-Ni-Zn) and 5 

(Pb-Zn-Cu). The Pyrola deposit is not delineated; however, 

the only samples collected along the creek that drains the 

deposit are 10 km downstream, below a lake (fig. 3). 

2. Barite, the most likely source of anomalous Ba in 

the sediment samples, is a common constituent in both the 

Greens Creek and Pyrola deposits (Van Nieuwenhuyse, 

1984; Crafford, 1989). 

3. Freibergite [(Ag, Cu) 12(Sb,As)4S13] is a common 

ore mineral at Greens Creek, and many of the samples in the 

Greens Creek area contain correspondingly anomalous Sb 

(fig. 3). Similar anomalous concentrations of Sb are in 

samples from the Gambier Bay area. 

2,672 25 L L 

7,118 98 L 100 

1,811 45 L 164 

9,090 37 5 423 

2,366 84 9 361 

2,175 100 L 182 

688 17 L 198 

4. Except for the area north and southwest of Pybus 

Bay, samples having anomalous scores are associated with 

rocks of similar lithology and age as those that host the 

Greens Creek and Pyrola deposits. 

The Greens Creek, WindfalJ Creek, and Gambier Bay 

areas form a northwest-trending belt (fig. 4). This trend is 

consistent with the regional northwest trend of syngenetic 

massive sulfide occurrences of Permian and Triassic age in 

southeastern Alaska (fig. 1) (Goldfarb and others, 1987). 

Although the data are useful in targeting areas having 

high favorability for volcanogenic massive sulfide 

occurrences, evaluation of other types of deposits is not 

possible because of the lack of data for Au, Ag, Bi, Mo, Sn, 

and W. For instance, although six gold prospects are 

reported on Admiralty Island, they are not reflected by 

geochemical anomalies other than anomalous tungsten in 

one sediment sample (fig. 3). 

Interpretation of Geochemical Data from Admiralty Island, Alaska A7 
134° 30' 134• 

0 10 &...-...l.-...-

KILOMETERS 

"Greens Creek area" 

ss· 

5?·~----------------~------------~------~ 

EXPLANATION 

ttl Triassic and Permian volcanic and sedimentary rocks 

/" ....... 

~ ' Basin area containing samples having scores >90th 

_./ percentile for factor 3 (As·Ba-Ni·Zn) 

0 Basin area containing samples having scores >90th 

percentile for factor 5 (Pb-Zn·Cu) 

• Ag·Au·Pb-Zn deposit 

® Au·Cu-Pb-Zn occurrence 

• Au (±Cu) occurrence 

Figure 4. Basin areas containing samples having anomalous scores for 

factors 3 and 5. Single-sample anomalies are not shown unless the 

sample was anomalous in both factor 3 and factor 5 scores. Areas 

labelled refer to text and table 3. 

A8 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

CONCLUSIONS 

Factor analysis of the geochemical data from the 

NURE program is useful in determining the geochemical 

associations in sediment samples that are characteristic of 

the Late Triassic volcanogenic massive sulfide deposit at 

Greens Creek. These associations are reflected by factors 3 

and 5 and consist of As-Ba-Ni-Zn and Pb-Zn-Cu, 

respectively. Based on these associations, two additional 

geochemically favorable areas underlain by Triassic 

volcanic and sedimentary rocks containing no known 

occurrences are outlined: the Windfall Creek and Gambier 

Bay areas. The Pyrola deposit could not be delineated 

because of insufficient sampling in the basin containing the 

deposit. 

Sediment samples from the Greens Creek drainage 

have anomalous concentrations of Sb (5-28 ppm), As 

(35-101 ppm), Ba (1,200-4,217 ppm), Cu (106 ppm), Pb 

(as much as 132 ppm), and Zn (270--694 ppm). These are 

likely the result of concentrations of ore-related minerals 

such as barite, chalcopyrite, galena, sphalerite, and 

antimony- and arsenic-bearing sulfide and sulfosalt 

minerals. Sediments from Windfall Creek and Gambier Bay 

contain concentrations similar to or higher than those at 

Greens Creek. Concentrations of 7,118-9,090 ppm Ba are 

in sediment samples from near Gambier Bay. The Windfall 

Creek area is characterized by one or more samples 

containing as much as 216 ppm As and 123 

ppm Cu. 

The highly anomalous concentrations of ore-related 

elements in sediment samples from Windfall Creek and 

Gambier Bay indicate that these areas have been 

mineralized. Furthermore, the As-Ba-Ni-Zn and Pb-Zn-Cu 

geochemical associations that delineate these areas suggest 

that syngenetic volcanogenic massive sulfide mineralization 

similar to that at Greens Creek is most likely. 

REFERENCES CITED 

Barker, Fred, 1957, Geology of the Juneau (B-3) quadrangle, 

Alaska: U.S. Geological Survey Map GQ-100, scale 

1:63,360. 

Berg, H.C., and Cobb, E.H., 1967, Metalliferous lode deposits of 

Alaska: U.S. Geological Survey Bulletin 1246, 254 p. 

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. 117-118. 

Cobb, E.H., 1972, Metallic mineral resources map of the Sitka 

quadrangle, Alaska: U.S. Geological Survey Miscellaneous 

Field Studies Map MF-467, scale 1 :250,000. 
___ 1978, Summary of references to mineral occurrences 

(other than mineral fuels and construction materials) in the 

Sitka quadrangle, Alaska: U.S. Geological Survey OpenFile Report 78-450, 124 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, April, 

1989, p. 27-29. 

Davis, J.C., 1986, Statistics and data analysis in geology (2nd ed.): 

New York, John Wiley and Sons, 646 p. 

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. 

Ford, A.B., and Brew, D.A., 1988, The Douglas Island volcanics; 

basaltic-rift-not andesitic-arc-volcanism of the "GravinaNutzotin belt," northern southeastern Alaska: Geological 

Society of America Abstracts with Programs, v. 20, no. 7, 

p. 111. 

Ford, A.B., Karl, S.M., Duttweiler, K.A., Sutphin, D.M., Finn, 

C.A., and Brew, D.A., 1989, Sitka Quadrangle, Alaska-An 

AMRAP preassessment planning document: U.S. 

Geological Survey Administrative Report, 92 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. 

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 Alaskan Cordillera, in 

Elliot, I.L., and Smee, B.W., eds., Geoexpo/86-

Exploration in the North American Cordillera: Association 

of Exploration Geochemists, p. 19-41. 

Herbert, C.F., and Race, W.H., 1965, Geochemical investigations 

of selected areas in southeastern Alaska: Alaska Division of 

Mines and Minerals Geochemical Report 1, 45 p. 

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, in Albert, N.R.D., and 

Hudson, T., eds., The United States Geological Survey in 

Alaska-Accomplishments during 1979: U.S. Geological 

Survey Circular 823-B, p. 109-112. 

Karl, S.M., 1989, Paleoenvironment implications of Alaskan 

siliceous deposits, in Hein, J.R., and Obradovich, J.D., eds., 

Siliceous deposits of the Tethys and Pacific regions: New 

York, Springer-Verlag, p. 169-200. 

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 area, Admiralty Island, Alaska: U.S. Geological 

Survey Bulletin 1178, 103 p. 

Los Alamos National Laboratory, 1982a, Hydrogeochemical and 

stream sediment reconnaissance basic data for the Juneau 

quadrangle, Alaska: U.S. Department of Energy Report 

GJBX-90(82). 

___ 1982b, Hydrogeochemical and stream sediment 

reconnaissance basic data for the Sitka quadrangle, Alaska: 

U.S. Department of Energy Report GJBX-128(82). 

___ 1982c, Hydrogeochemical and stream sediment 

reconnaissance basic data for the Sumdum quadrangle, 

Alaska: U.S. Department of Energy Report GJBX-47(82). 

Reed, J.C., 1942, Nickel-copper deposit at Punter Bay, Admiralty 

Island, Alaska: U.S. Geological Survey Bulletin 936-0, 

p. 349-361. 

Silberling, N.J., and Jones, D.L., eds., 1984, Lithotectonic terrane 

maps of the North American Cordillera: U.S. Geological 

Survey Open-File Report 84-523. 

Van Nieuwenhuyse, R.E., 1984, Geology and geochemistry of the 

Pyrola massive sulfide deposit, Admiralty Island, Alaska: 

Tucson, University of Arizona, M.S. thesis, 170 p. 

Interpretation of Geochemical Data from Admiralty Island, Alaska A9 

Chapter B 

Geochemical Orientation Study for 

Identification of Metallic Mineral Resources 

in the Sitka Quadrangle, Southeastern Alaska 

By E. LANIER ROWAN, ELIZABETH A. BAILEY, 

and RICHARD J. GOLDFARB 

U.S. GEOLOGICAL SURVEY BULLETIN 1950 

GEOCHEMICAL STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1989 
CONTENTS 

Abstract Bl 

Introduction Bl 

Tectonic-geologic setting B3 

Description of sampling and analytical methods B3 

Sample collection B3 

Sample preparation B3 

Analytical techniques B3 

Volcanogenic massive sulfide deposits B4 

Gold-quartz vein deposits B7 

Ultramafic-hosted nickel-copper sulfide deposits BS 

Chromite deposits BlO 

Discussion and summary Bll 

References cited Bll 

FIGURES 

1-2. Maps showing locations of: 

1. Sitka quadrangle, Alaska Bl 

2. Mining districts and deposits and tectonostratigraphic terranes, Sitka 

quadrangle B2 

3-6. Maps showing sample localities in vicinity of: 

3. Pyrola volcanogenic massive sulfide deposit, Admiralty Island BS 

4. Lucky Chance gold-quartz vein deposit, Baranof Island B7 

5. Bohemia Basin magmatic nickel-copper sulfide deposits, southern Yakobi 

Island BS 

6. Chromite occurrences, central Baranof Island BlO 

TABLES 

1-3. Lower limits of determination for: 

1. Semiquantative emission spectrographic analysis of stream-sediment, heavymineral concentrate, and rock samples B4 

2. Analysis of stream-sediment and rock samples by ICP-10 BS 

3. ICP-40 analysis of stream-sediment and rock samples BS 

4-5. Comparison of concentrations of selected elements in: 

4. Three stream-sediment size fractions and three magnetic fractions of the 

heavy-mineral concentrates from the Pyrola volcanogenic massive sulfide 

deposit B6 

5. Three stream-sediments size fractions from of the Lucky Chance goldquartz vein deposit BS 

6. Element concentrations determined by emission spectrography for rock samples 

from the Bohemia Basin nickel-copper sulfide deposits B9 

7. Comparison of ore and pathfinder element concentrations in three streamsediment size fractions from the Bohemia Basin nickel-copper sulfide 

district B9 

8. Comparison of chromium concentrations in fine, medium, and coarse streamsediment samples, and in magnetic, weakly magnetic, and nonmagnetic 

fractions of heavy-mineral concentrates from the chromite district of central 

Baranof Island BlO 
Geochemical Orientation Study for Identification of 

Metallic Mineral Resources in the Sitka Quadrangle, 

Southeastern Alaska 

By E. Lanier Rowan, Elizabeth A. Bailey, and Richard J. Goldfarb 

Abstract 

Stream-sediment and rock samples were collected from the vicinity 

of four mineralized areas representative of the known principal ore 

deposit types in the Sitka region of southeastern Alaska. Results of 

chemical analyses of the samples provide information to guide future 

geochemical exploration programs in this region. Three size fractions of 

the stream-sediment samples were analyzed by semiquantitative 

emission spectrography (SQS), induction coupled plasma (ICP), and 

atomic absorption (AA) techniques. In addition, three magnetic fractions 

of heavy-mineral concentrates from stream-sediment samples were 

analyzed by SQS to determine the optimal sample media and analytical 

methods. 

Four principal deposit types are known in the region of the Sitka 

quadrangle: (1) Kuroko-type volcanogenic massive sulfide deposits, (2) 

gold-quartz vein deposits, (3) chromite deposits hosted by ultramafic 

rocks, and (4) magmatic nickel-copper sulfide deposits in ultramafic 

rocks. Dispersion from the first three deposit types is readily identified 

through chemical analyses of the stream-sediment samples alone; 

however, the heavy-mineral concentrate samples provide additional 

mineralogical information and, at some localities, give better anomaly to 

background contrast. 

Emission spectrography is adequate for recognition of dispersion 

trails from the volcanogenic massive sulfide and chromite deposit types. 

The more sensitive AA and ICP techniques, however, are required to 

detect arsenic, gold, cadmium, and antimony anomalies in streamsediment samples downstream from gold-quartz vein deposits. The 

nickel-copper deposits were not detected at a distance greater than 

approximately 0.8 km downstream using any of the sample media or 

analytical methods tested. Identification of new nickel-copper 

occurrences will require detailed field investigation of ultramafic intrusive 

bodies that may be delineated by stream-sediment geochemistry. 

INTRODUCTION 

This study was undertaken to determine the streamsediment sample types and analytical methods most 

effective in locating mineralized rocks in the Sitka 

quadrangle and in the surrounding region of southeastern 

Alaska (figs. 1, 2). Numerous operating or historic mines 

500 

ALASKA 

PACIFIC OCEAN 

Figure 1. Location of the Sitka quadrangle, Alaska. 

and prospects within or close to the Sitka quadrangle 

represent four different types of mineral deposits and 

present an unusual opportunity to conduct a pilot geochemical study. The results of this study provide guidelines 

for future geochemical exploration and assessment of 

metallic mineral resources in the Sitka quadrangle and in 

geologically similar regions in Alaska. 

The principal mineral deposit types known in the 

Sitka quadrangle or just outside its boundaries are (fig. 2): 

( 1) gold-quartz veins exemplified by the Chichagof and 

Apex-El Nido districts and the Lucky Chance deposit 

(Knopf, 1912; Reed and Coats, 1941; Rossman, 1959), (2) 

Kuroko-type volcanogenic massive sulfide mineralized 

rocks at Pyrola (Van Nieuwenhuyse, 1984), (3) lenses of 

chromite hosted by serpentinized ultramafic rocks on 

central Baran of Island (Kennedy and Walton, 1946a; Loney 

and others, 1975), and (4) magmatic nickel-copper sulfide 

Metallic Mineral Resources in the Sitka Quadrangle, Southeastern Alaska 81 
0 

I 

Chichagof 

30 

KILOMETERS 

Explanation 

[i.;--1J Chugach terrane 

Wrangellia terrane 

~ Alexander terrane 

~ Gravina-Nutzotin belt 

Figure 2. Mining districts and deposits (arrows) and tectonostratigraphic terranes in the Sitka quadrangle. Modified from Berg and others (1978) and 

Ford and others (1989). 

segregations hosted by ultramafic rocks at Bohemia Basin 

and Mirror Harbor (Reed and Dorr, 1942; Kennedy and 

Walton, 1946b; Loney and others, 1975; Bundtzen and 

others, 1984; Still, 1988). 

Thirty-one samples of stream sediments and heavymineral concentrates from stream sediments and seventeen 

rock samples were collected from localities believed to be 

typical of the four principal types of mineral deposits in the 

Sitka quadrangle. Coarse, medium, and fine fractions of 

each stream-sediment sample and the magnetic, weakly 

magnetic, and nonmagnetic fractions of heavy-mineral 

concentrates were analyzed by four techniques (emission 

82 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

spectrography, atomic absorption, and inductively coupled 

plasma emission spectroscopy using two different digestion 

methods). Results were compared to determine optimal 

sampling media and analytical methods. For each deposit 

type except chromite, rock samples were used to define the 

characteristic suite of elements, including potential 

pathfinder elements. 

Acknowledgments.-The authors gratefully 

acknowledge P.H. Briggs, J.R. Motooka, and R. O'Leary, 

who carried out some chemical analyses of the samples. We 

are also grateful to R.B. Tripp, who identified mineral grains 

in the heavy-mineral concentrates. 
TECTONIC-GEOLOGIC SETIING 

The rocks of the Sitka quadrangle constitute parts of 

three distinct tectonostratigraphic terranes-the Chugach, 

Wrangellia, and Alexander-and the Gravina-Nutzotin belt 

overlap assemblage (fig. 2) (Ford and others, 1989). The 

Chugach terrane consists of flysch and melange formed in a 

subduction complex; this terrane was accreted to and 

subducted below the Wrangellia and Alexander terranes in 

Late Cretaceous to early Tertiary time (Plafker and others, 

1977). The Cretaceous Sitka Graywacke within the Chugach terrane hosts most of the gold-bearing quartz deposits. 

Mafic igneous rocks intruding metasedimentary units of the 

Chugach terrane are hosts for the nickel-copper and 

chromium occurrences. 

Pre-Middle Pennsylvanian island-arc volcanic and 

sedimentary rocks overlain by Triassic rift-fill tholeiitic 

basalt and limestone make up the Wrangellia terrane 

(MacKevett, 1978; Nokleberg and others, 1985). The Alexander terrane is comprised of igneous, volcanic-arc, and 

sedimentary rocks of Precambrian (?) to Middle Jurassic 

age (Eberlein and others, 1983; Gehrels and Saleeby, 1987a, 

b). The Wrangellia and Alexander terranes were accreted to 

the craton by Late Cretaceous to early Tertiary time. The 

Gravina-Nutzotin overlap assemblage on the northwestern 

part of Admiralty Island consists of basaltic volcanic rocks 

(Ford and Brew, 1988), argillite, graywacke turbidite, and 

conglomerate (Loney, 1964) deposited in a basin formed 

between the amalgamated Alexander-Wrangellia terranes 

and previously accreted terranes to the east. The syngenetic 

Pyrola volcanogenic massive sulfide deposit is in argillite 

and volcanic rocks of the Triassic Retreat Group in the 

Alexander terrane (Van Nieuwenhuyse, 1984). 

DESCRIPTION OF SAMPLING AND 

ANAL VTICAL METHODS 

Sample Collection 

A total of 17 rock samples were collected from the 

vicinity of the four deposits or mining districts. In the 

Bohemia Basin, nickel-copper-rich samples were collected 

from mine waste piles. Mineralized float samples were 

collected from the stream channel approximately 200 m 

downstream from Pyrola. At the Lucky Chance deposit; 

samples were collected from ore or tailings piles within a 

few meters of the main mine portal. Most samples collected 

in these three areas contain visible sulfide minerals. No 

mineralized rock samples were collected from the chromite 

district. 

At stream sample sites, sediment was collected from 

the active part of the stream channel and passed through a 

10-mesh (2.0 mm) seive to remove pebbles. In addition to a 

stream-sediment sample, a heavy-mineral concentrate was 

obtained by panning additional sediment until most of the 

quartz, feldspar, organic material, and clay-size material 

was removed. 

Sample Preparation 

Rock samples were crushed and then pulverized to 

-0.15 mm using ceramic plates. Each rock was 

analyzed by all four methods of analysis (discussed below). 

Stream sediments were air dried, then sieved to three 

fractions: -10 to +60 mesh (2.0-0.25 mm), -60 to +200 

mesh (0.25-0.075 mm), and -200 mesh (0.075 mm). These 

three fractions correspond to coarse to medium sand, fine to 

very fine sand, and very fine sand to silt, respectively. All 

fractions were pulverized and then analyzed using all four 

analytical techniques. 

Heavy-mineral concentrate samples were air dried 

then passed through a 30-mesh (0.59 mm) sieve. Any 

remaining quartz, feldspar, organic material, or clays less 

than 30 mesh were removed by allowing the heavy material 

in each sample to settle through bromoform (sp gr 2.85). 

The heavy fraction was then separated into magnetic, 

weakly magnetic, and nonmagnetic fractions using a Frantz 

Isodynamic Separator. The magnetic fraction (primarily 

magnetite), weakly magnetic fraction (mostly ferromagnesian silicate and oxide minerals), and nonmagnetic 

fractions (mostly ore minerals, rutile, zircon, sphene, and so 

on) were split again if enough sample was available. One 

split was saved for identification of mineral grains using a 

binocular microscope. The other split was handground for 

chemical analysis. The relatively small sample volumes 

restricted heavy-mineral concentrate analysis to the semiquantitative emission spectrographic technique. 

Analytical Techniques 

The four methods of analysis used were atomic 

absorption spectrometry (AA) for gold, semiquantitative 

emission spectrography (SQS) for 35 elements (rock and 

stream-sediment samples) and 37 elements (heavy-mineral 

concentrates), and inductively coupled plasma atomic 

emission spectroscopy for 10 elements (ICP-10) and for 40 

elements (ICP-40) using two different digestion methods. 

The stream-sediment and rock samples were analyzed 

for gold by atomic absorption (AA) following a hydrobromic acid and bromine digestion and an MIBK extraction 

(Thompson and others, 1968). The lower limit of 

determination for gold is 0.05 ppm. 

All sample media were analyzed for 35 or 37 

elements using the six-step semiquantitative emission spectrographic (SQS) method of Grimes and Marranzino ( 1968). 

The elements and their lower limits of determination are 

Metallic Mineral Resources in the Sitka Quadrangle, Southeastern Alaska 83 
listed in table 1. Spectrographic results were obtained by 

visual comparison of spectra derived from the sample with 

spectra obtained from standards made from pure oxides and 

carbonates. The analytical values are geometrically spaced 

over any given order of magnitude of concentration (10, 7, 

5, 3, 2, 1.5, and multiples of these numbers). The precision 

of this method is approximately plus or minus one reporting 

interval at the 83 percent confidence level and plus or minus 

two reporting intervals at the 96 percent confidence level 

(Motooka and Grimes, 1976). 

The stream-sediment and rock samples were analyzed 

by two ICP methods. The first, ICP-10, employs the method 

of Motooka (1988). Silver, arsenic, gold, bismuth, 

cadmium, copper, molybdenum, lead, antimony, and zinc 

were extracted into the organic phase of 10 percent Aliquot 

336 (tricaprylylmethylammonium chloride) DIBK (di-isobutyl ketone) in the presence of ascorbic acid and potassium 

iodide in 6N HCl. The organic phase was then separated for 

aspiration into the plasma, and the concentrations of the 10 

elements were determined simultaneously. The lower limits 

of determination are listed in table 2. 

The second method, ICP-40, employs a digestion 

without subsequent extraction into an organic phase. The 

samples were dissolved in HF, aqua regia, and HC104 and 

then dried (Crock and others, 1983; Lichte and others, 

1987). The residues were redissolved in aqua regia and 

diluted to 10 mL with 1 percent HN03• The solution was 

then introduced into the plasma and the concentrations of 40 

elements measured simultaneously. The 40 elements and 

their lower limits of determination are shown in table 3. The 

dissolution procedure described volatilizes silicon and 

boron and does not dissolve minerals such as zircon, 

tourmaline, cassiterite, rutile, and chromite. 

VOLCANOGENIC MASSIVE SULFIDE DEPOSITS 

The Pyrola deposit on Admiralty Island is the only 

known Kuroko-type volcanogenic massive sulfide deposit 

in the Sitka quadrangle, although the Greens Creek deposit 

to the north on Admiralty Island (in the Juneau quadrangle) 

is of the same type (Crafford, 1989). Similar mineralized 

rocks are associated with Triassic volcanic rocks throughout 

the length of southeastern Alaska (Goldfarb and others, 

1987). The Pyrola deposit is at the contact between mafic 

volcanic rocks and fine-grained clastic and carbonate units 

of the Retreat Group. Massive pods of pyrite and sphalerite 

and adjacent lenses of silver-rich barite make up most of the 

deposit. Galena and lesser chalcopyrite, boulangerite, and 

jamesonite are additional sulfide phases. Chemical analyses 

of barite-rich float indicate significant arsenic and antimony 

concentrations associated with some of the ore (E.L. Rowan 

and others, unpub. data). Local sericite-pyrite-quartz 

alteration is superimposed on a broad chlorite-carbonate 

alteration halo (Van Nieuwenhuyse, 1984). 

84 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

Table 1. Lower limits of determination for semiquantitative 

emission spectrographic (SQS) analysis of streamsediment, heavy-mineral concentrate, and rock samples 

[Values for rock and stream-sediment samples are based on a 10-mg 

sample and for heavy-mineral concentrate samples on a 5-mg sample. 

Stream -sediment and rock samples were not analyzed for platinum and 

palladium] 

Sream-sediment 

Element and rock samples 

PERCENT 

Calcium (Ca) ....................... 0.05 

Iron (Fe) ............................. 0.05 

Magnesium (Mg) .................. 0.02 

Sodium (Na) ........................ 0.2 

Phosphorus (P) .................... 0. 2 

Titanium (fi) ....................... 0.002 

PARTS PER MilliON 

Manganese (Mn) ................ 10 

Silver (Ag) .......................... 0.5 

Arsenic (As) ..................... 200 

Gold (Au) .......................... 10 

Barium (Ba) ....................... 20 

Boron (B) ......................... 10 

Beryllium (Be) ..................... 1 

Bismuth (Bi) ..................... 10 

Cadmium (Cd) .................... 20 

Cobalt (Co) ....................... 10 

Chromium (Cr) ................... 10 

Copper (Cu) ........................ 5 

Gallium (Ga) ........................ 5 

Germanium (Ge) ................. 10 

Lanthanum (La) .................. 50 

Molybdenum (Mo) ................ 5 

Niobium (Nb) .................... 20 

Nickel (Ni) .......................... 5 

Palladium (Pd) .................... _ 

Platinum (Pt) ..................... _ 

Lead (Pb) ........................... 10 

Antimony (Sb) .................. 100 

Scandium (Sc) ...................... 5 

Tin (Sn) ........................... 10 

Strontium (Sr) ................... 100 

Vanadium (¥) ..................... 10 

Tungsten (W) ..................... 20 

Yttrium (Y) ....................... 10 

Zinc (Zn) ......................... 200 

Zirconium (Zr) ................... 10 

Thorium (fh) .................... 1 00 

Heavy-mineral 

concentrates 

0.1 

0.1 

0.05 

0.5 

0.5 

0.005 

20 

1 

500 

20 

50 

20 

2 

20 

50 

20 

20 

10 

10 

20 

100 

10 

50 

10 

2 

10 

20 

200 

10 

20 

200 

20 

50 

20 

500 

20 

200 

Stream-sediment and heavy-mineral concentrate 

samples were collected in a small, unmineralized watershed 

about 1.5 km east of Pyrola, on a small tributary 

approximately 0.3 km downstream from Pyrola, and on a 

major stream approximately 1.5, 5, and 8 km below the 

orebody (fig. 3). Emission spectrographic data for stream-
Table 2. Lower limits of determination for analysis of 

stream-sediment and rock samples by ICP-1 0 (and atomic 

absorption for gold) 

[In parts per million] 

Element Lower limit Element Lower limit 

Ag ............. 0.045 Cu .............. 0.05 

As ............. 0.60 Mo ............. 0.09 

Au ............. 0.15 Pb .............. 0.60 

Au1 ••••••.••••• 0.05 Sb .............. 0.60 

Bi .............. 0.60 Zn .............. 0.03 

Cd ............. 0.03 

1 Atomic absorption analysis. 

Table 3. Lower limits of determination for ICP-40 analysis 

of stream-sediment and rock samples 

Limit 

Element (percent) 

AI. ...... 0.05 

Ca ...... 0.05 

Fe ....... 0.05 

K ........ 0.05 

Mg ..... 0.005 

Na ...... 0.005 

P ........ 0.005 

Ti ....... 0.005 

Limit 

Element (ppm) 

Ag ......... 2 

As ....... 10 

Au ......... 8 

Ba ......... 1 

Be ......... 1 

Bi ........ 10 

Cd ......... 2 

Ce ........ .4 

Co ......... 1 

Cr. ......... 1 

Cu ......... 2 

Eu .......... 2 

Ge ....... 20 

Ga ........ .4 

Ho ......... 4 

La .......... 2 

Limit 

Element (ppm) 

Li .......... 2 

Mn ...... 10 

Mo ........ 2 

Nb ......... 4 

Ni ....... 20 

Ni .......... 2 

Pb ......... 4 

Sc .......... 2 

Sn ........ .4 

Sr .......... 2 

Th ......... 4 

U ........ 100 

v ........... 2 

Y ........... 2 

Yb ......... 1 

Zn ........ .4 

sediment samples indicate dispersion trains for silver, 

barium, molybdenum, lead, and zinc in all three size 

fractions (table 4). Copper and iron distributions also show 

dispersion trains downstream from Pyrola, but only in the 

coarse sediment size fraction. Silver, barium, and lead show 

the broadest dispersion halos for the three stream-sediment 

size fractions. Anomalous values for these three elements 

persist to the sample site 8 km downstream from Pyrola. 

Anomaly to background contrast for the Pyrola area is 

strongest for silver and barium, especially in the fine ( -200 

mesh) size fraction. Silver values in the -200 mesh 

sediments range from not detected at a 0.5 ppm lower 

determination limit to 20 ppm, and barium values range 

from a 500 ppm background level at sites to the east of 

Pyrola, to greater than 5,000 ppm just below Pyrola, and 

2,000 ppm 8 km downstream. 

Semiquantitative emission spectrographic (SQS) 

analysis of stream-sediment samples is clearly adequate for 

use in regional exploration surveys in the Sitka area for 

massive sulfide deposits similar to Pyrola. It is possible, 

however, to determine a more complete suite of anomalous 

+ 

Explanation 

• Deposit 

8 Sample site 

0 2 

58° 00' + 

134° 30' 

3 KILOMETERS I 

Figure 3. Sample localities in vicinity of Pyrola volcanogenic massive 

sulfide deposit, Admiralty Island. 

metals, including arsenic, cadmium, and antimony, if SQS 

is combined with the more sensitive ICP-1 0 technique. 

ICP-1 0 data for all three elements from all three size 

fractions show enrichment relative to local background 

values at the site farthest below Pyrola; anomalies are 

strongest for antimony. Analytical values for antimony for 

all size fractions collected 8 km downstream from Pyrola 

are from 1.3 to 1.7 ppm, relative to background values of 

less than 0.6 ppm. Narrower dispersion halos also exist for 

potassium (determined by ICP-40) within all streamsediment size fractions. The potassium enrichment most 

likely reflects sericitic alteration ~f the host rocks. 

Background barium values for nonmagnetic heavymineral concentrate samples from streams underlain by 

rocks of the Retreat Group are approximately 2,000 ppm. 

All nonmagnetic heavy-mineral concentrate samples 

collected downstream from Pyrola contain more than 

10,000 ppm Ba. Barite is, however, a common accessory 

mineral in unmineralized areas underlain by various facies 

of the Retreat Group; therefore, abundant barite in nonmagnetic concentrates, flagged by barium values above 10,000 

ppm in the analytical data, does not necessarily signify 

terranes favorable for Kuroko-type massive sulfide 

Metallic Mineral Resources in the Sitka Quadrangle, Southeastern Alaska 85 
Table 4. Comparison of concentrations of selected elements in three stream-sediment size fractions and three magnetic 

fractions of the heavy-mineral concentrates from the Pyrola volcanogenic massive sulfide deposit 

[Sample locations (fig. 3) in relation to mineralized rocks are as follows: 040 is from unmineralized rocks (background), 041 is immediately 

below Pyrola, 042 is 1.5 km downstream, 043 is 5 km downstream, and 044 is 8 km downstream. Potassium values are in percent, all other 

values are in parts per million. I indicates analysis by ICP: potassium obtained using ICP-40, other elements using ICP-10. S indicates 

analysis by emission spectrography. N, not detected; L, value less than lower limit of determination; G, value greater than upper limit of 

determination] 

Sam~le S-Fe S-Ag S-Ba S-Mo S-Cu S-Pb S-Zn 1-K l-As 1-Cd 1-Sb 

-10 TO +60 MESH 

040 1.5 N 300 N 20 lOL 200N 1.3 8 0.1 0.6L 

041 7 15 5,000 20 50 1,000 2,000 2.8 230 3.7 37 

042 5 3 5,000 7 50 100 300 1.7 40 0.7 6 

043 2 0.5 1,500 5L 30 20 200L 1.6 18 0.5 3 

044 3 0.7 700 5N 20 30 200N 1.3 13 0.2 1.5 

-60 TO +200 MESH 

040 5 N 500 N 50 L N 1.3 13 0.1 0.6L 

041 3 15 5,000G 10 50 500 2,000 2.6 200 6 34 

042 7 3 5,000 L 70 100 500 2.0 51 1.4 8 

043 5 0.5 5,000 N 30 20 200 1.5 20 0.5 3 

044 5 L 1,500 N 20 20 N 1.4 13 0.1 1.3 

-200MESH 

040 7 N 500 N 70 

041 7 20 5,000G 20 70 

042 7 7 5,000 7 70 

043 5 1.5 2,000 N 20 

044 5 0.5 2,000 N 30 

NONMAGNETIC 

S-Ag S-Ba S-Mo S-Pb S-Sr 

040 L 2,000 N 30 200 

041 50 10,000G 20 1,000 7,000 

042 15 10,000G 10 700 5,000 

043 5 10,000G N 50 3,000 

044 N lO,OOOG N 20 700 

WEAKLY MAGNETIC 

S-Ag S-Ba S-Mo S-Pb S-Zn 

040 N 300 N L N 

041 100 lO,OOOG 70 1,500 5,000 

042 15 5,000 20 200 1,000 

043 2 1,000 N 70 N 

044 N 700 N 50 N 

deposits. The absence of anomalous barium may help, 

however, to · eliminate areas as potential massive sulfide 

targets. 

For the nonmagnetic concentrate sample medium, 

emission spectrographic analyses for silver, molybdenum, 

lead, strontium, and zinc, in addition to barium, adequately 

identify upstream Kuroko-type occurrences. Below Pyrola, 

strong molybdenum, lead, and zinc anomalies extend at 

least as far as 1.5 km downstream, silver at least as far as 5 

km, and strontium at least as far as 8 km. The anomalous 

strontium is most likely due to high concentrations of this 

element in barite. Excluding the anomalous barium and 

strontium, dispersion trains are generally narrower for 

nonmagnetic concentrates than for stream-sediment 

samples. This suggests that a significant amount of hydro86 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

10 N 1.4 18 0.5 0.6L 

700 3,000 2.2 180 8 28 

100 500 1.9 54 2 8 

30 200 1.7 17 0.8 3 

20 N 1.5 18 0.3 1.7 

S-Zn 

N 

15,000 

5,000 

N 

N 

MAGNETIC 

S-Ag S-Ba S-Pb S-Zn 

N 300 L N 

20 7,000 200 2,000 

5 5,000 100 1,000 

N 300 L 700 

N 300 L 700 

morphic dispersion may characterize erosion of these 

Kuroko-type systems, and that geochemical surveys 

designed solely for massive sulfide exploration need not 

include nonmagnetic heavy-mineral concentrate samples. 

The weakly magnetic and magnetic fractions of the 

heavy-mineral concentrate samples were also analyzed by 

emission spectrography. Silver, barium. molybdenum, lead, 

and zinc in the weakly magnetic samples and silver, barium, 

lead, and zinc in the magnetic samples are present in 

anomalous concentrations downstream from Pyrola (table 

4). Barium and lead in the former medium and zinc in the 

latter are still significantly enriched in samples 8 km below 

Pyrola. Therefore, in some situations, the weakly magnetic 

and magnetic heavy-mineral concentrate fractions may 

prove useful in exploration. 
GOLD-QUARTZ VEIN DEPOSITS 

Several small gold mines and prospects are southeast 

of Silver Bay, within approximately 7 km of the southern 

boundary of the Sitka quadrangle (fig. 4). These gold-quartz 

lode occurrences, briefly described by Knopf (1912), are 

generally along slate-graywacke contacts within the Sitka 

Graywacke. Quartz veins are as wide as 2.5 m and contain 

free gold, pyrite, and (or) pyrrhotite (Knopf, 1912). Many 

rock samples that we collected from the vicinity of the 

Lucky Chance deposit (fig. 4) contain arsenopyrite. 

Chemical analyses of four vein samples indicate as much as 

63 ppm Au, 16 ppm Ag, 1,600 ppm As, 0.47 ppm Cd, and 

2.1 ppm Sb. No other elements are anomalous. 

Two stream-sediment and two heavy-mineral 

concentrate samples were collected at sites about 0.5 and 7 

km below the Lucky Chance deposit on Salmon Creek. An 

additional two stream-sediment and concentrate samples 

were collected nearby on an unnamed stream draining Pinta 

Lake. This drainage basin contains a number of other small 

gold occurrences (Knopf, 1912). 

Stream-sediment data from the four sites indicate that 

arsenic and antimony are the most consistently anomalous 

pathfinder elements and that gold and cadmium are less 

useful ore indicators (table 5). Concentrations for all four 

elements at all sites are below the lower determination 

limits for emission spectrography and ICP-40 methods, but 

anomalous values are clearly defined using ICP-10 and AA 

56° 55' 

+ 135° 10' 

0 

I 

2 3 KILOMETERS 

I 

+ 57° 00' 

135° 05' 

Lucky Chance 

Explanation 

• Deposit 

D Occurrence 

e Sample site 

Figure 4. Sample localities in vicinity of Lucky Chance gold-quartz vein 

deposit, Baranof Island. Sample sites are within approximately 7 km of 

the southern boundary of the Sitka quadrangle. 

methods. Atomic absorption analysis is the only technique 

sensitive enough to detect gold, b:it ICP-10 is adequate for 

determination of arsenic, cadmium, and antimony in the 

stream-sediment samples. 

The -200 mesh stream-sediment fraction was the 

most useful of the fractions; arsenic values are between 29 

and 270 ppm, cadmium between 0.12 and 0.47 ppm, and 

antimony between 1.1 and 2.3 ppm. Gold was detected in 

two -200 mesh samples, one near the Lucky Chance deposit 

(008) and the other farthest downstream from Pinta Lake 

(026) (fig. 4). Silver was not detected. 

The coarsest sediment fraction contains 83 ppm As at 

the site below the Lucky Chance deposit and 0.61-0.73 ppm 

Sb at the other three sites. Although not as obvious as in the 

finest sediment fraction, the coarse sediment fraction 

indicates that mineralized rocks are upstream. Two samples 

from the medium size fraction contain anomalous arsenic 

but no anomalous antimony. These data suggest preferential 

breakdown of many of the ore-related minerals into finegrained stream sediment and perhaps some hydromorphic 

dispersion of antimony. The -200 mesh stream-sediment 

fraction is therefore recommended for exploration for goldquartz veins in the Sitka quadrangle. 

Arsenopyrite, pyrite, and scheelite were observed 

during microscopic examination of the nonmagnetic heavymineral concentrate samples from two sites, 008 and 025 

(fig. 4). Gold grains were also found in the concentrate from 

site 008 below the Lucky Chance mine. Samples from both 

sites contain highly anomalous arsenic concentrations 

that reflect the observed arsenopyrite; the sample 

downstream from the Lucky Chance deposit contains 

10,000 ppm As and that closest to Pinta Lake contains 5,000 

ppm As. The former also contains 700 ppm Pb and 2,000 

ppm Sn, but these values are believed to reflect 

contamination from old mining activities. 

The broadest dispersion halos were identified using 

ICP-10 and AA analytical methods on the fine-grained 

stream-sediment samples; however, collection of 

concentrate samples at each sample site is still 

recommended for gold exploration. Microscopic 

observation of the nonmagnetic concentrates provides 

information that is not available from the chemical analyses 

alone. Tripp and others (1985), in a study of the Valdez 

Group of south-central Alaska (stratigraphically equivalent 

to the Sitka Graywacke), noted that arsenopyrite is much 

more widespread than gold. Therefore, anomalous arsenic 

values in stream-sediment and concentrate samples may not 

always be indicative of upstream gold deposits. Also, 

because antimony-dominant sulfide mineral phases are not 

common in this type of gold-bearing system (Goldfarb and 

others, 1987), antimony may not be a consistently reliable 

pathfinder element. Therefore, both ICP-10 or AA analyses 

Metallic Mineral Resources in the Sitka Quadrangle, Southeastern Alaska 87 
Table 5. Comparison of concentrations of selected elements in three stream-sediment size fractions from the Lucky 

Chance gold-quartz vein deposit 

[In parts per million. Observations made on the nonmagnetic fraction of the heavy-mineral concentrates are also shown. Sample locations 

in relation to mineralized rocks: 008 and 009 are 0.5 and 7 km below the Lucky Chance mine, respectively; 025 and 026 are in a basin 

draining several small gold prospects (fig. 4). N, not detected; L, value less than lower limit of determination] 

Stream-sediment samgles 

-1 0 to +60 mesh -60 to +200 mesh 

Samele As Cd Sb Au As Cd Sb Au 

008 83 0.16 L N 160 0.15 N N 

009 13 0.09 0.73 N 12 0.07 N N 

025 21 0.08 0.65 N 42 0.11 N N 

026 12 0.04 0.61 N 17 0.03 N N 

*Insufficient sample for analysis. 

of stream-sediment samples for gold and microscopic 

examination of concentrate samples for coarser gold grains 

are recommended for targeting areas that may contain vein 

gold deposits. 

ULTRAMAFIC-HOSTED NICKEL-COPPER 

SULFIDE DEPOSITS 

Two nickel-copper sulfide deposits have been 

recognized in the Sitka quadrangle: Bohemia Basin 

(sampled in this study), on Yakobi Island, and Mirror 

Harbor, on the west coast of Chichagof Island (fig. 2). These 

deposits formed as segregations of sulfide minerals, 

primarily pyrrhotite, pentlandite, and chalcopyrite, from a 

norite magma (Kennedy and Walton, 1946b). They are 

hosted by Tertiary (?) norite plutons that generally have 

intruded Mesozoic sedimentary rocks (Loney and others, 

1975). 

Several small, abandoned mine workings, trenches, 

and prospect pits are on the north and south sides of 

Bohemia Basin. Six rock samples were collected from the 

mine dumps. A total of nine stream-sediment samples was 

collected from the immediate vicinity of the mine workings 

and from approximately 0.8, 1.6, 2.8, and 4 km downstream 

of the mines (fig. 5). 

All but one rock sample contains visible sulfide 

minerals, and all are characterized by high levels of nickel, 

copper, silver, cobalt, and chromium (table 6). Comparison 

of the concentrations of these elements with background 

levels for mafic and ultramafic rocks (Rose and others, 

1979) indicates that metal concentrations are anomalous for 

nickel, copper, silver, and cobalt. High levels of chromium 

in various media may only indicate the presence of mafic or 

ultramafic rocks, and thus chromium probably is not useful 

as an ore pathfinder element. Silver was detected by SQS in 

four of the rock samples but was not detected by ICP-40 in 

any of the samples. Silver values were confirmed by 

ICP-10, which has the lowest detection limit of the three 

methods, although the SQS detection limits are adequate. 

88 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

-200 mesh 

As Cd Sb Au 

270 0.46 1.2 0.20 

29 

140 

49 

0.31 1.1 N 

0.47 2.3 

0.12 1.2 

Explanation 

• Deposit 

* 

[J Occurrence 

e Sample site 

57° 55' 

+ 136° 30' 

0 

Nonmagnetic concentrate sameles 

10,000 ppm As; pyrite, gold, 

scheelite. 

5,000 ppm As; pyrite, scheelite, 

arsenopyrite, malachite. 

Bohemia Basin 

2 3 KILOMETERS 

Figure 5. Sample localities in vicinity of Bohemia Basin magmatic 

nickel-copper sulfide deposits, southern Yakobi Island. 

Stream-sediment samples were examined with 

particular attention to the four elements anomalous in rock 

samples (nickel, copper, silver, and cobalt). Concentrations 

of silver and copper are slightly higher in the -200 mesh 

stream-sediment fraction, whereas concentrations of nickel 

and cobalt are higher in the two coarser fractions (table 7). 

Sample 010, collected in the immediate vicinity of a mine, 

contains anomalous concentrations of silver and copper in 

the fine fraction (0.5 ppm and 1,500 ppm, respectively) and 

of cobalt and nickel in the coarser size fractions ( 100 ppm 

and 1,000 ppm, respectively) relative to the other streamsediment samples. In a sample collected only 0.8 km 

downstream, however, concentrations are at background 

levels (<0.5, ~100, ~70, and ~100 ppm for silver, copper, 

cobalt, and nickel, respectively) in all stream-sediment size 

fractions, and they remain unchanged with increasing distance downstream from the mine (fig. 5). 
Table 6. Element concentrations determined by emission spectrography for rock samples from the Bohemia Basin nickelcopper sulfide deposits 

[In parts per million. Sulfide minerals were visible in each sample except 6A. Background values for ultramafic and mafic rocks are given 

in the last two columns. Data from Rose and others (1979). N, not detected] 

Element SA SB sc 6A 

Ag ..................... 0.7 N 1 N 

Co .................. 700 150 200 50 

Cr ................ 1,000 700 1,000 200 

Cu ............... 1,500 1,000 1,500 20 

Ni ................ 5,000 2,000 >5,000 100 

Table 7. Comparison of ore and pathfinder element 

concentrations in three stream-sediment size fractions 

from the Bohemia Basin nickel-copper sulfide district 

[In parts per million. N, not detected; L, value less than lower limit 

of determination] 

Sample Ag Co Cu Ni 

-200MESH 

010 0.5 50 1,500 500 

011 N 70 50 50 

012 N 70 100 100 

013 N 30 70 30 

014 N 100 100 50 

015 N 70 70 70 

016 N 70 70 70 

017 N 50 100 50 

018 N 100 70 100 

-60 TO +200 MESH 

010 L 100 1,000 1,000 

011 N 70 50 70 

012 N 70 100 100 

013 N 20 50 20 

014 N 50 70 50 

015 N 30 50 100 

016 N 70 50 50 

017 N 50 70 50 

018 N 50 30 70 

-10 TO +60 MESH 

010 L 100 1,000 1,000 

011 N 50 50 50 

012 N 30 50 100 

013 N 20 50 20 

014 N 30 50 50 

015 N 50 50 100 

016 N 50 20 50 

017 N 30 30 30 

018 N 30 50 50 

Heavy-mineral concentrates were equally unsatisfactory for defining any significant dispersion train. 

Concentrations of copper and nickel are higher in the 

sample collected nearest the mine but are at background 

levels just 0.8 km downstream. Silver was detected only in 

the magnetic fraction of sample 010, at a level below the 

quantifiable detection limit of 1.0 ppm. 

Sam le 

6B 6C Ultramafic Mafic 

1 0.7 0.06 0.1 

300 150 110 48 

2,000 2,000 2,980 170 

2,000 100 42 72 

>5,000 5,000 2,000 130 

Difficulty in exploring for nickel-copper deposits 

such as those at Bohemia Basin and Mirror Harbor was 

discussed by Ford and others (1989). They reported that a 

regional reconnaissance stream-sediment survey failed in 

both districts to identify either the ultramafic rocks hosting 

mineralized rocks or the deposits themselves because 

copper and nickel concentrations do not significantly 

exceed background in the unmineralized, surrounding mafic 

rocks. The mafic rocks of the Goon Dip Greenstone on 

Yakobi Island, for example, have background nickel and 

copper values of 100-150 ppm and 100-200 ppm, 

respectively (Johnson and Elliot, 1984). These values 

exceed the stream-sediment values determined in this study 

for all Bohemia Basin samples, except for sample 010 

collected adjacent to a mine (fig. 5). Ford and others (1989) 

found that the element association Cr-Nr-Mg-Cu-Co-VSc-Ca-Mn-Fe generally coincides with mafic rock types but 

is not reliable in identifying magmatic nickel-copper 

deposits. The stream-sediment sample density for the 

reconnaissance surveys discussed by Ford and others (1989) 

is approximately one per two square kilometers. Our more 

detailed orientation survey, which includes one sample site 

in a drainage only meters below a mine, permits 

unambiguous conclusions to be drawn on the difficulties 

detecting this deposit type using stream-sediment samples. 

Given that groups of existing mines (whose ore and 

tailings dumps expose large quantities of sulfide minerals to 

surface weathering) are not detectable more than 

approximately 0.8 km downstream, we conclude that 

conventional exploration geochemistry using streamsediment samples or heavy-mineral concentrates will be 

ineffective in locating new, undeveloped deposits of this 

type. In nonmafic rocks that have relatively low FeMg-Cr-Ni-Cu background, stream-sediment geochemistry 

should be useful in delineating previously unrecognized 

mafic intrusive bodies. Detailed followup mapping, field 

examination, and geochemical sampling of these bodies 

might lead to further discoveries of ultramafic intrusive 

bodies of the type that host nickel-copper sulfide deposits. 

Metallic Mineral Resources in the Sitka Quadrangle, Southeastern Alaska 89 
CHROMITE DEPOSITS 

Chromite lenses hosted by small, sheared, lenticular 

serpentinite bodies occur on central Baranof Island in a belt 

trending southeast from Silver Bay (fig. 6). These serpentinite bodies were emplaced in Mesozoic and Tertiary 

metasedimentary rocks (Loney and others, 1975). Thirteen 

stream-sediment samples were collected from within and 

near this belt of mineralized serpentinites, within 

approximately 10 km of the southern boundary of the Sitka 

quadrangle (fig. 6). No mineralized rock samples were 

collected. 

Two samples (001 and 002) were collected from 

first-order streams within drainage basins that do not 

contain known chromite occurrences (fig. 6). These two 

samples are assumed to contain background concentrations 

of possible pathfinder elements for chromite occurrences. 

Drainage basins for the remaining 11 samples contain small 

chromite occurrences (Kennedy and Walton, 1946a). 

In this study, chromium was found to be the best 

pathfinder element in exploration for chromite occurrences. 

In the stream-sediment samples, chromium is anomalously 

high relative to background samples (001 and 002) in all 

three stream-sediment size fractions for each of the other 11 

samples (table 8). The highest chromium concentration is in 

sample 003, the sample closest to a chromite occurrence. 

The intensity of the chromium anomaly is strongest in the 

medium size fraction ( -60 mesh) and weakest in the fine 

(-200 mesh) fraction (table 8). 

The heavy-mineral concentrates show a similar 

chromium enrichment pattern in that the weakly magnetic 

fraction provides the clearest distinction between the 

anomalous and background samples. Chromium values are 

150-300 ppm in the background samples and 1,500-10,000 

ppm in the remaining samples (table 8). Relatively high iron 

0 2 3 KILOMETERS I I I 

a 

a 

Figure 6. Sample localities in vicinity of chromite occurrences, central 

Baranof Island. Sample sites are within approximately 1 0 km of the 

southern boundary of the Sitka quadrangle. 

810 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

Table 8. Comparison of chromium concentrations in fine, 

medium, and coarse stream-sediment samples, and in 

magnetic, weakly magnetic, and nonmagnetic fractions of 

heavy-mineral concentrates from the chromite district of 

central Baranof Island 

[In parts per million] 

SlREAM-SEDIMENT SAMPLES 

Sam~le -200 mesh -60 to +200 mesh -1 0 to +60 mesh 

001 70 100 70 

002 100 100 70 

003 700 2,000 1,000 

004 700 1,500 200 

005 700 500 200 

006 200 700 150 

007 200 1,000 300 

019 100 700 150 

020 100 200 100 

021 200 500 200 

022 100 150 100 

023 150 200 200 

024 150 300 300 

HEAVY-MINERAL CONCENIRA TES 

Sam~le Magnetic Weakly magnetic Nonmagnetic 

001 100 150 70 

002 150 300 150 

003 5,000 10,000 2,000 

004 2,000 10,000 500 

005 3,000 10,000 2,000 

006 2,000 10,000 100 

007 5,000 7,000 150 

019 5,000 5,000 1,000 

020 3,000 1,500 200 

021 2,000 2,000 500 

022 5,000 2,000 3,000 

023 3,000 7,000 1,500 

024 5,000 2,000 2,000 

content in the chromite (Guild and Balsley, 1942) is 

responsible for the magnetic properties of the chromite and 

the concentration of chromite in the weakly magnetic 

fraction. Concentrate samples do not show a consistent 

dispersion pattern downstream. 

The anomaly to background ratio is smaller for 

stream-sediment samples than for heavy-mineral 

concentrates. The concentrates thus provide a slightly more 

distinct dispersion halo than do the stream sediments (table 

8). Of the two sample media, the concentrates should be 

more useful in identifying chromium mineralization. In the 

weakly magnetic and magnetic concentrates, chromium 

enrichment of as much as 50 times background persists as 

far as 11 km downstream from known chromite 

occurrences, whereas chromium values in stream-sediment 

samples were only 3-10 times background. Concentrations 

of chromium in both stream-sediments and heavy-mineral 

concentrates are high enough for easy detection by emission 

spectrography, even in the background samples. Therefore, 

more sensitive analytical techniques are not required in the 

exploration for this mineral deposit type. 
Anomalous concentrations of nickel, arsenic, 

antimony, silver, and gold in the stream-sediment samples 

and heavy-mineral concentrates collected in this region are 

not believed to be related to chromite occurrences. Silver, 

arsenic, gold, and antimony likely reflect gold-quartz vein 

deposits similar to those at the Lucky Chance deposit, 5-8 

km to the east. The mineral phase contributing as much as 

2,000 ppm Ni in magnetic heavy-mineral concentrates is 

unknown, but serpentine, pyroxene, magnetite, and other 

minerals derived from the serpentinized peridotite bodies 

and identified in the heavy-mineral concentrates likely 

contribute to a high nickel background (see table 6). 

Nickel-bearing minerals have not been described in 

association with the chromite occurrences (Kennedy and 

Walton, 1946a). 

DISCUSSION AND SUMMARY 

The origins and host rock types of ore deposits in the 

Sitka quadrangle are diverse. An efficient stream-sediment 

geochemical exploration program aimed at identifying all 

deposit types described herein must make compromises. Of 

the gold-quartz vein, massive sulfide, chromite, and 

magmatic nickel-copper deposits examined in this study, all 

except nickel-copper deposits show clearly recognizable 

geochemical signatures dispersed over distances of several 

kilometers downstream in stream-sediment samples and 

heavy-mineral concentrates. The difficulty in identifying 

nickel-copper sulfide deposits, noted by Ford and others 

(1989) based on a large-scale reconnaissance survey, has 

not been resolved by our more detailed survey. The nickelcopper occurrences were not detected more than about 0.8 

km downstream using any of the sample media. Apparently, 

the rapid breakdown of nickel and copper sulfide minerals 

produces a small anomaly close to the deposit that drops to 

background levels less than a kilometer downstream. 

The -200 mesh fraction of the stream-sediment 

samples generally yields the highest concentrations and the 

highest anomaly to background ratios for ore and pathfinder 

elements. For chromite deposits, however, analyses of the 

fine fraction did not identify several sites where anomalous 

chromium was detected in the medium size fraction ( --60 to 

+200 mesh); the medium size fraction was significantly 

more sensitive than either the coarse or the fine streamsediment fraction. Emission spectrography adequately 

identified ore and pathfinder elements for the chromite and 

massive sulfide deposits; however, the gold-quartz lodes 

require more sensitive techniques to detect ore and 

pathfinder elements. Atomic absorption analysis was 

necessary for gold analyses and ICP-10 was required for 

adequate sensitivity to detect the pathfinder elements 

arsenic, cadmium, and antimony. 

Emission spectrographic analyses of the heavymineral concentrates adequately detected dispersion halos 

downstream of mineralized rocks. The nonmagnetic 

fraction of heavy-mineral concentrates best revealed ore and 

pathfinder anomalies for massive sulfide deposits, although 

analyses from the magnetic and weakly magnetic fractions 

also revealed anomalies for many of the same elements. 

Analyses from stream sediments provided a broader 

dispersion halo and should therefore be more useful in 

exploratation for massive sulfide deposits. For the chromite 

deposits, the weakly magnetic fraction provided the 

strongest anomalies, but the stream-sediment samples alone 

would have sufficiently identified the mineralized region. 

For the gold-quartz vein deposits, -200 mesh streamsediment samples were useful in delineating a dispersion 

halo, but heavy-mineral concentrates generally were not as 

consistently anomalous in ore or pathfinder elements. 

In summary, the stream-sediment samples were 

adequate to identify dispersion from three major deposit 

types in the Sitka quadrangle: volcanogenic massive sulfide, 

chromite, and gold-quartz vein deposits. Although not 

required to identify these types of deposit, heavy-mineral 

concentrates may provide higher anomaly to background 

contrasts than stream sediments (as for the chromite 

deposits). Of the analytical techniques tested, emission 

spectrography was adequate for recognition of the massive 

sulfide and chromite deposits, but atomic absorption and 

ICP-1 0 techniques were necessary to identify gold-quartz 

vein deposits. Atomic absorption, the most sensitive of the 

techniques available, was required to detect gold in stream 

sediments below gold-quartz vein deposits, and ICP-1 0 

techniques were required to detect the pathfinder elements 

arsenic, antimony, and cadmium. 

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pre-Cenozoic tectonostratigraphic terranes of southeastern 

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Bundtzen, T.K., Eakins, G.R., Clough, J.G., Lueck, L.L., Green, 

C.B., Robinson, M.S., and Coleman, D.A., 1984, Alaska's 

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sulfide deposit, Admiralty Island, southeast Alaska: Alaska 

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Mineral Development in Southeast Alaska, the Yukon, and 

British Columbia, Abstracts of Professional Papers, p. 

27-29. 

Crock, J.G., Lichte, F.E., and Briggs, P.H., 1983, Determination of 

elements in National Bureau of Standards geological 

reference materials SRM 278 obsidian and SRM 688 basalt 

by inductively coupled argon plasma-atomic emission 

spectroscopy: Geostandards Newsletter, v. 7, no. 2, 

p. 335-340. 

Eberlein, G.D., Churkin, M., Carter, C., Berg, H.C., and Ovenshine, A.T., 1983, Geology of the Craig Quadrangle, 

Alaska: U.S. Geological Survey Open-File Report 83-91, 

28 p. 

Metallic Mineral Resources in the Sitka Quadrangle, Southeastern Alaska 811 
Ford, A.B., and Brew, D.A., 1988, Major-element geochemistry of 

metabasalts of the Juneau-Haines region, southeastern 

Alaska, in Galloway, J.P., and Hamilton, T.D., eds., 

Geologic studies in Alaska during 1987: U.S. Geological 

Survey Circular 1016, p. 150-155. 

Ford, A.B., Karl, S.M., Duttweiler, K.A., Sutphin, D.M., Finn, 

C.A., and Brew, D.A., 1989, Sitka Quadrangle, Alaska-An 

AMRAP preassessment planning document: U.S. 

Geological Survey Administrative Report, 92 p. 

Gehrels, G.E., and Saleeby, J.B., 1987a, Geology of southern 

Prince of Wales Island, southeastern Alaska: Geological 

Society of America Bulletin, v. 98, p. 123-137. 

___ 1987b, Geologic framework, tectonic evolution, and 

displacement history of the Alexander terrane: Tectonics, v. 

6, no. 2, p. 151-173. 

Goldfarb, R.J., Nelson, S.W., Berg, H.C., and Light, T.V., 1987, 

Distribution of mineral deposits in the Pacific Border 

Ranges and Coast Mountains of the Alaskan Cordillera, in 

Elliot, I.L., and Smee, B.W., eds., Geoexpo/86---

Exploration of the North American Cordillera: Association 

of Exploration Geochemists, p. 19-41. 

Grimes, D.J., and Marranzino, A.P., 1968, Direct-current arc and 

alternating-current spark emission spectrographic field 

methods for the semiquantitative analysis of geologic 

materials: U.S. Geological Survey Circular 591, 6 p. 

Guild, P.W., and Balsley, J.R., 1942, Chromite deposits of Red 

Bluff Bay and vicinity, Baranof Island, Alaska: U.S. 

Geological Survey Bulletin 936-G, p. G171-G187. 

Johnson, B.R., and Elliot, G.S., 1984, Map showing the 

distribution and abundance of copper in bedrock samples, 

Western Chichagof-Yakobi Islands Wilderness Study Area, 

southeastern Alaska: U.S. Geological Survey Open-File 

Report 81-27-D, scale 1:125,000. 

Kennedy, G.C., and Walton, M.S., 1946a, Geology and associated 

mineral deposits of some ultrabasic rock bodies in 

southeastern Alaska: U.S. Geological Survey Bulletin 

947-D, p. 65-84. 

___ 1946b, Nickel investigations in southeast Alaska: U.S. 

Geological Survey Bulletin 947-C, p. 39-64. 

Knopf, A., 1912, The Sitka mining district, Alaska: U.S. 

Geological Survey Bulletin 904, 32 p. 

Lichte, F.E., Golightly, D.W., and Lamothe, P.J., 1987, 

Inductively coupled plasma-atomic emission spectrometry, 

in Baedecker, P.A., ed., Methods for geochemical analysis: 

U.S. Geological Survey Bulletin 1770, p. B1-Bl0. 

Loney, R.A., 1964, Stratigraphy and petrography of the PybusGambier area, Admiralty Island, Alaska: U.S. Geological 

Survey Bulletin 1178, 103 p. 

812 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

Loney, R.A., Brew, D.A., Muffler, L.J.P., and Pomeroy, J.S., 

1975, Reconnaissance geology of Chichagof, Baranof, and 

Kruzof Islands, southeastern Alaska: U.S. Geological 

Survey Professional Paper 792, 105 p. 

MacKevett, E.M., 1978, Geologic map of the McCarthy 

quadrangle, Alaska: U.S. Geological Survey Miscellaneous 

Investigations Series Map I-1 032, scale 1 :250,000. 

Motooka, J.R., 1988, An exploration geochemical technique for 

the determination of preconcentrated organometallic halides 

by ICP-AES: Applied Spectroscopy, v. 42, no. 7, p. 

1293-1296. 

Motooka, J.R., and Grimes, D.J., 1976, Analytical precision of 

one-sixth order semiquantitative spectrographic analyses: 

U.S. Geological Survey Circular 738, 25 p. 

Nokleberg, W.J., Jones, D.L., and Silberling, N.J., 1985, Origin 

and tectonic evolution of the Maclaren and Wrangellia 

terranes, eastern Alaska Range, Alaska: Geological Survey 

of America Bulletin, v. 96, p. 1251-1270. 

Plafker, G., Jones, D.L., and Pessagno, E.A., 1977, A Cretaceous 

accretionary flysch and melange terrane along the Gulf of 

Alaska margin, in Blean, K.M., ed., The U.S. Geological 

Survey in Alaska-Accomplishments during 1976: U.S. 

Geological Survey Circular 751-B, p. B41-B43. 

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Chichagof mining district, Alaska: U.S. Geological Survey 

Bulletin 929, 148 p. 

Reed, J.C., and Dorr, J.V.N., 1942, Nickel deposits of Bohemia 

Basin and vicinity, Yakobi Island, Alaska: U.S. Geological 

Survey Bulletin 931-F, p. 105-138. 

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mineral exploration: New York, Academic Press, 657 p. 

Rossman, D.L., 1959, Geology and ore deposits of northwestern 

Chichagof Island, Alaska: U.S. Geological Survey Bulletin 

1058-E, p. E139-E216. 

Still, J.C., 1988, Distribution of gold, platinum, palladium, and 

silver in selected portions of the Bohemia Basin deposits, 

southeast Alaska (with an appendix on Mirror Harbor): U.S. 

Bureau of Mines Open-File Report 10-88, 10 sheets, 42 p. 

Tripp, R.B., Goldfarb, R.J., and Pickthorn, W.J., 1985, Geochemical map showing distribution of gold within Chugach 

National Forest, Alaska: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1645-D, scale 

1:250,000. 

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Rapid analysis for gold in geologic materials, in Geological 

Survey Research 1968: U.S. Geological Survey 

Professional Paper 600-B, p. B 130-B 132. 

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Pyrola massive sulfide deposit, Admiralty Island, Alaska: 

Tucson, University of Arizona, M.S. thesis, 170 p. 
Chapter C 

Geology and Geochemistry of Mineralization 

in the Bethel Quadrangle, 

Southwestern Alaska 

By THOMAS P. FROST 

U.S. GEOLOGICAL SURVEY BULLETIN 1950 

GEOCHEMICAL STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1989 
CONTENTS 

Abstract Cl 

Introduction Cl 

Mineral deposits and occurrences C3 

Gold veins in the N yac terrane C3 

Silica-carbonate and serpentinite zones C4 

Tourmaline-quartz replacement zones C4 

Mercury-antimony deposits CS 

Gold Lake "red spots" CS 

Other gold occurrences C8 

Summary C9 

References cited C9 

FIGURE 

1. Map showing regional geology and mineral occurrences in the Bethel quadrangle 

and parts of the Russian Mission and Goodnews quadrangles, southwestern 

Alaska C2 

TABLE 

1. Analytical results for selected samples from the Bethel quadrangle and surrounding 

areas C6 
Geology and Geochemistry of Mineralization in the 

Bethel Quadrangle, Southwestern Alaska 

By Thomas P. Frost 

Abstract 

Geologic and geochemical data indicate the presence of several 

types of lode deposits in the Bethel 1 °X2° quadrangle in southwestern 

Alaska. Hydrothermally mineralized rocks include gold-bearing quartz 

veins apparently associated with Early Cretaceous plutonism west of the 

Golden Gate fault; mercury- and antimony-rich veins that may have 

anomalous gold and silver and are present for the most part in areas 

underlain by sedimentary rocks of the Kuskokwim Group or in rhyolite 

domes; and quartz veins that have anomalous Ag, As, Au, and Pb in 

clastic rocks and chert in the older terranes of the southeastern part of 

the quadrangle. Quartz veins containing gold are also associated with 

several 60- to 70-million-year-old granitoid plutons that cut Cretaceous 

sedimentary rocks of the Kuskokwim Group. Localized boron metasomatism in Upper Cretaceous volcanic and volcaniclastic rocks in the 

northeastern part of the quadrangle has resulted in quartz-tourmaline 

replacement zones that are anomalous in Ag, Au, Hg, Pb, Sn, and Zn. 

INTRODUCTION 

The Bethel 1 °X2° quadrangle in southwestern Alaska 

contains numerous gold placer deposits and occurrences and 

lode occurrences that contain anomalous Au, Ag, Hg, and 

Sb. Several anomalies identified from stream-sediment and 

panned-concentrate samples suggest additional areas 

favorable for these mineral deposit types. This report 

describes the geology and geochemistry of these new areas 

and offers interpretations for the source of the metal 

anomalies. 

The western third of the Bethel quadrangle is covered 

by thick, unconsolidated Quaternary deposits of the YukonKuskokwim delta. The remainder of the quadrangle is 

underlain by at least five distinct accreted tectonostratigraphic terranes (Box and Murphy, 1987; Jones and 

others, 1987) that are made up of rocks of Precambrian 

through Early Cretaceous age (fig. 1). Deposited unconformably on most of the older terranes is a thick sequence of 

highly deformed, predominantly turbiditic sedimentary 

rocks of the Lower and Upper Cretaceous Kuskokwim 

Group (Hoare and Coonrad, 1959a, b). Cretaceous and 

Tertiary high-level granitoid plutons, basaltic through 

dacitic volcanic fields, and hypabyssal rhyolite intrusions 

and extrusive (?) domes were intruded through and (or) 

deposited on all older rock units. 

Rocks of the Tikchik terrane crop out in the 

southeastern comer of the quadrangle (fig. 1) and consist of 

a structurally complex assemblage of Paleozoic and Mesozoic chert and Permian limestone, basalt, and clastic rocks 

(Mertie, 1938; Hoare and Coonrad, 1959a, 1978; Hoare and 

Jones, 1981). The original nature of the boundary between 

the Tikchik terrane and the Togiak terrane to the west is 

uncertain but is presently marked in part by the active 

right-lateral Togiak fault (Box and Murphy, 1987). 

The Togiak terrane is composed of complexly 

deformed andesitic volcanic and volcaniclastic rocks that 

have yielded Late Triassic through Early Cretaceous fossils 

from the Goodnews quadrangle to the south (Hoare and 

Coonrad, 1978). The boundary between the rocks of the 

Togiak terrane and the Goodnews terrane to the west is 

covered by the Lower and Upper Cretaceous sedimentary 

rocks of the Kuskokwim Group in the Bethel quadrangle 

(Box and Murphy, 1987). It is uncertain whether the 

Kuskokwim Group depositionally overlies or is faulted 

against the rocks of the Togiak terrane. 

Rocks of the Goodnews terrane are exposed in 

erosional windows through the overlying Kuskokwim 

Group. The Goodnews terrane consists of a structurally 

complex assemblage of variably foliated metabasalt, lowgrade schist, marble, chert, graywacke, and slate (Hoare and 

Coonrad, 1959a, 1978; Box and Murphy, 1987). Box and 

Murphy (1987) reported a K-Ar metamorphic age of 146 

Ma from an actinolite-bearing schist. Fossils are Permian to 

Early Cretaceous in age (Murphy, 1987). The structural 

relationship between the rocks of the Goodnews terrane and 

Precambrian rocks to the west is uncertain, although both 

groups of rocks are overlain by basal conglomerate of the 

Kuskokwim Group that contains clasts derived in part from 

both terranes (Box and Murphy, 1987). 

Precambrian orthogneiss, amphibolite, and quartzmica schist of the Kilbuck terrane crop out in a narrow 

tectonic sliver in the southern part of the Bethel quadrangle 

Mineralization in the Bethel Quadrangle, Southwestern Alaska C1 
Russian 

60o MISSIOn 

0 

161° 

.....__ _____ --J 20 KILOMETERS 

Qs 

I 

160° 

/ .,....-----~ 

-.. 

I 

e1 Qs 

Figure 1 (above and facing page). Regional geology and mineral occurrences in the Bethel quadrangle and parts of the Russian Mission and 

Goodnews quadrangles, southwestern Alaska. Geology adapted from Hoare and Coonrad (1959a, b, 1978) and Box and Murphy (1987). 

C2 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 
EXPlANATION 

Overlap sequences 

Os Surficial deposits (Quaternary) 

v VTK V v v v o I canic rocks (early Tertiary and Late Cretaceous)-

Basalt to rhyolite flows and domes, includes some 

hypabyssal rocks. 

j;TKgZI Granitic to granodioritic plutonic rocks (early Tertiary 

to Late Cretaceous) 

I' '-' K'g ~' ,, G ramt1c · · to grano d ioritic p I utonic rocks (Early Cretaceous) 

:·: ·~ k :_. Kuskokwim Group (late and Early Cretaceous) 

Pre-mid-Cretaceous terranes 

~ 

~ 

IMzPzgJ 

tMzflZ] 

[@t~ 

Togiak terrane (Early Cretaceous to Late Triassic)-

Andesitic volcanic rocks, volcaniclastic rocks, and tuf· 

faceous argillite 

Nyac terrane (Middle Jurassic)-Andesitic volcanic rocks 

and minor volcaniclastic sedimentary rocks 

Goodnews terrane (Mesozoic and Paleozoic)-Tuffaceous 

argillite, chert, basalt, metabasite, metachert, and marble 

Tikchik terrane (Mesozoic and Paleozoic)-Metavolcanic 

rocks, metachert, graywacke, and limestone 

Kilbuck terrane (Precambrian)-Amphibolite facies 

orthogneiss and minor amphibolite and quartz-mica schist 

---- Contact-Dashed where inferred 

---- Fault-Dashed where approximate, dotted where inferred 

6 6 Thrust fault-Teeth on upper plate 

t Syncline axis 

40 ~ Locality or area described in text; number refers to text 

12 ~ and table 1 

and in the Goodnews quadrangle west of the Goodnews 

terrane (Turner and others, 1983; S.E. Box, U.S. Geological 

Survey, written commun., 1989). 

Middle Jurassic andesitic volcanic rocks and volcaniclastic sandstones of the Nyac terrane are the westernmost 

basement rocks exposed in the Bethel quadrangle (Box and 

Murphy, 1987). The contact between the Nyac terrane and 

rocks to the east is not exposed but probably is marked in 

part by the Golden Gate fault or its equivalent in the 

northern part of the Bethel quadrangle (Hoare and Coonrad, 

1959a). 

The Kuskokwim Group is represented by a thick 

sequence of shale, siltstone, sandstone, and minor basal 

conglomerate that was deposited unconformably on all 

older rocks except those of the Nyac terrane (Box and 

Murphy, 1987). The Kuskokwim Group is composed 

predominantly of marine turbidite, with the exception of 

shallow marine and nonmarine sedimentary rocks in the 

southwestern part of the quadrangle (Box and Murphy, 

1987). Albian to Coniacian fossils have been recovered 

from the Kuskokwim Group in different parts of the 

quadrangle (Hoare and Coonrad, 1959a, 1978; Box and 

Murphy, 1987; Murphy, 1987), but regional age control is 

poor. The Kuskowkim sedimentary rocks host a wide 

variety of granitoid intrusions, volcanic fields, and 

intermediate to silicic dikes, which are common in many 

parts of the quadrangle. 

Early Cretaceous (125-120 Ma) granitoid plutons are 

restricted to the Nyac terrane west of the Golden Gate fault; 

granitoid plutons and volcanic fields in other terranes and 

the Kuskokwim Group are Late Cretaceous to early Tertiary 

(72-65 Ma) in age (Shew and Wilson, 1981; Robinson and 

Decker, 1986; Frost and others, 1988). Most plutons are 

elliptical in outline and surrounded by a biotite-bearing 

hornfels zone as wide as a kilometer. The plutons are 

porphyritic or coarse grained; many have small miarolytic 

cavities. The most common plutonic rock types are 

hornblende-biotite granodiorite through granite, although 

augite-biotite diorite and gabbro are present in some plutons 

(Robinson and Decker, 1986; Frost and others, 1988). 

Late Cretaceous to early Tertiary volcanic rocks crop 

out in the northeastern comer of the quadrangle on both 

sides of the Kipchuk River and in an elongate northeasttrending belt in the lowlands west of the Golden Gate fault 

(fig. 1 ). These rocks consist mainly of bedded basaltic to 

dacitic flows and tuffs, and some volcaniclastic sedimentary 

rocks. Platy to massive felsic domes, at least some of which 

are intrusive along their upper contacts, are scattered 

through all the volcanic fields. The felsic domes are 

composed, for the most part, of biotite rhyolite containing 

partially resorbed quartz phenocrysts. Some rocks have a 

glassy groundmass, but in most rocks the glass has devitrified. Intermediate to felsic dikes cut all older rock types in 

many parts of the quadrangle. 

Acknowledgments.-This manuscript profited from 

reviews by Stephen E. Box, Richard J. Goldfarb, and John 

Galloway. Analytical work was provided by Richard M. 

0 'Leary, David E. Detra, Leon A. Bradley, Betty Bailey, 

Floyd Brown, Zoe A. Brown, D. Fey, P. Hageman, J. 

Motooka, K. Romine, and E.P. Welsch. 

MINERAL DEPOSITS AND OCCURRENCES 

Placer gold has been the major mineral commodity 

produced in southwestern Alaska, and mercury has been 

produced predominantly from small scattered lode deposits 

(Sainsbury and MacKevett, 1965; Hoare and Cobb, 

1977). Field work and petrographic interpretation, 

supported by geochemical data, have identified several 

previously unknown, or at least undocumented, mineral 

occurrences and additional drainage basins favorable for the 

discovery of new occurrences. This report also provides 

new, detailed information on known mineral occurrences. 

Gold Veins in the Nyac Terrane 

Placer gold has been produced from the headwaters of 

the Tuluksak River since the 1910's (Hoare and Coonrad, 

Mineralization in the Bethel Quadrangle, Southwestern Alaska C3 
1959a). No data on lode gold in the Bethel quadrangle 

has been published to date. Anomalous gold concentrations 

have been identified by atomic absorption spectroscopy of 

samples of pyrite- and iron-oxide-bearing quartz and calcite 

veins from several old prospect pits in the Russian Mission 

and the Bethel quadrangles (fig. 1, locs. 1-4, table 1). Most 

of the gold-bearing veins cut hornfelsed and sericitized 

pyroxene andesite or volcaniclastic rocks of the Nyac 

terrane, although one gold-bearing vein (fig. 1, loc. 4) cuts 

sericitized quartz porphyry that may be part of the Early 

Cretaceous plutonic system. The veins are characterized by 

euhedral quartz prisms that have abundant open space 

between crystals; quartz, calcite, and chlorite are the most 

common gangue minerals. Several generations of quartz 

veins may be present at any locality, and they all may 

contain gold. 

At one locality (fig. 1, loc. 3) the oldest veins occupy 

en echelon fractures and contain as much as 20 ppm Au. 

Later quartz veins are coarsely brecciated and contain as 

much as 4.5 ppm Au. Gold-bearing quartz vein samples 

from the Nyac terrane contain 0.6-2.3 ppm Hg; one sample 

contains 500 ppm As and 10 ppm Ag (table 1). Streamsediment samples from several drainages in the Nyac 

terrane that contain as much as 180 ppm As (T.P. Frost, 

unpub. data) suggest additional undiscovered lode 

occurrences in the Nyac terrane. The known lode gold 

occurrences are located near Early Cretaceous granitoid 

plutons that cut the Jurassic volcanic and volcaniclastic 

rocks of the Nyac terrane. The spatial association between 

veins and plutons suggests that the plutons provided at least 

a heat source to circulate hydrothermal fluids that deposited 

the gold. The field relations, petrography, and geochemistry 

indicate that the gold-bearing quartz veins in the Nyac 

terrane are epithermal or mesothermal. 

Silica-Carbonate and Serpentinite Zones 

Small areas of bright-red-orange-weathering and 

unvegetated silica-carbonate rock are scattered through the 

tundra along the topographic break at the foot of the 

Kuskokwim Mountains in the Bethel and the Goodnews 

quadrangles (fig. 1, table 1, locs. 5, 6). North of the Kisarilik 

River, these areas are along what is probably the trace of the 

Golden Gate fault or its equivalent (Hoare and Coonrad, 

1959a, b, 1978). Silica-carbonate rock, sheared and 

unsheared serpentinite, and lesser gabbro, dunite, and 

pyroxenite blocks are in the rubble outcrops. Silicacarbonate rock is the most common rock type and consists 

of quartz and several crosscutting generations of carbonate 

veins, in many cases containing relicts of serpentinite; 

Chromium and nickel contents as high as 0.5 percent and 

1,500 ppm, respectively, reflect the original mafic to ultramafic compositions of the protoliths. Several silicacarbonate samples contain as much as 1 ,500 ppm Zn and 

1,500 ppm As. Silica-carbonate rock at Slate Creek (fig. 1, 

C4 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

table 1, loc. 5) is anomalous in mercury, one sample 

contains more than 36 ppm Hg. Football-sized dunite and 

gabbro blocks in sheared serpentinite from south of the Fog 

River (fig. 1, table 1, loc. 6) have gold contents of 0.05 and 

0.10 ppm. Geology, geochemistry, and tectonic setting 

suggest that the ultramafic and mafic rocks and their altered 

equivalents along the Golden Gate fault may be similar in 

origin to the rocks of the ultramafic complex 70 km south of 

the southern edge of the Bethel quadrangle at Goodnews 

Bay (Mertie, 1976; Southworth, 1986). The ultramafic 

complex at Goodnews Bay is an important source for 

platinum group elements (PGE), and therefore the ultramafic 

rocks along the Golden Gate fault may have PGE resource 

potential. The silica-carbonate alteration is similar to hydrothermal alteration common to many epithermal lodes in 

southwestern Alaska (Sainsbury and MacKevett, 1965). 

Tourmaline-Quartz Replacement Zones 

Tourmaline-quartz replacement of volcanic rocks and 

waterlain tuffs occurred at two localities near the base of the 

Kipchuk volcanic field flanking the Kipchuk River in the 

northeastern corner of the Bethel quadrangle (fig. 1, locs. 7, 

8). The altered rocks are brownish red to black; weathered 

surfaces commonly are bright red. Vegetation in the altered 

areas is restricted for the most part to sparse lichens and 

mosses. 

At the northern tourmaline-quartz replacement zone 

(fig. 1, loc. 7), a small pluton of biotite-orthopyroxene 

quartz diorite cuts Kuskokwim sedimentary rocks 

stratigraphically below the altered volcaniclastic rocks. The 

pluton is itself mostly unaltered; samples from the pluton 

and surrounding metasedimentary hornfels lack anomalous 

geochemical values. The northern tourmaline-quartz 

replacement zone is restricted to a waterlain tuff unit at the 

local base of the overlying volcanic field. 

At the southern tourmaline-quartz replacement zone, 

no plutons or dikes have been identified (fig. 1, Joe. 8). The 

southern tourmaline-quartz replacement zone is at least 100 

m above the base of the volcanic section. Tourmaline-quartz 

replacement of plagioclase porphyry is gradational over 

several hundred meters along the eastern contact, although 

the southern contact is no greater than 20 m wide. In 

incipiently altered rocks, tourmaline replaces phenocrysts in . 

the rock, whereas quartz replaces groundmass. With 

increasing alteration, the original texture is completely 

obscured and the rock consists of a granular aggregate of 

fine-grained quartz and clumps of prismatic tourmaline. 

Some rocks are distinctly layered or "orbicular" and are 

made up of alternating layers rich in quartz and tourmaline. 

Many orbs have a coarse-grained vuggy core of prismatic 

tourmaline, quartz, and iron oxide minerals. Very small 

cassiterite (?) crystals line some vugs. 

In addition to boron, the tourmaline-quartz rocks are 

high in Ag, As, Ba, Pb, Sb, and Sn, and less consistently in 
Bi, Cu, and Zn. One sample contains 0.10 ppm Au, and the 

mercury content in most samples is 0.10-3 ppm; one sample 

contains greater than 36 ppm Hg. Little or no correlation 

between anomalous elements from sample to sample 

suggests that mineralization occurred erratically in the 

altered zones. Gold, cinnabar, scheelite, tourmaline, barite, 

arsenopyrite, pyrite, and an unidentified brown mineral 

(probably cassiterite) are present in heavy-mineral 

concentrates downstream from the northern tourmalinized 

area and in streams draining the entire volcanic field north 

and east of the Kipchuk River (R. Tripp, U.S. Geological 

Survey, written common., 1988). The quartz-tourmaline 

occurrences result from hydrothermal replacement. 

Available data suggests that these occurrences may have 

affinities to syngenetic. exhalative or skarn deposits. 

Mercury-Antimony Deposits 

Mercury and (or) antimony deposits and occurrences 

are widely scattered through southwestern Alaska (Sainsbury and MacKevett, 1965). Occurrences in the Bethel 

region include simple quartz-stibnite veins, quartzcinnabar-stibnite veins, realgar-quartz veins, composite 

tourmaline-quartz-cinnabar-stibnite-realgar veins, and rhyolite domes and dikes having anomalous mercury contents. 

In the Bethel quadrangle, veins, fault zones, felsic intrusive 

bodies cut by veins, and altered rhyolite containing 

anomalous mercury for the most part are restricted to areas 

underlain by or adjacent to sedimentary rocks of the 

Kuskokwim Group. 

At Fisher Dome (fig. 1, loc. 9) in the north-central 

part of the Bethel quadrangle, quartz-stibnite veins as wide 

as 10 em cut a mildly peraluminous hypabyssal biotite 

quartz prophyry (Hoare and Coonrad, 1959a; Frost and 

others, 1988; T.P. Frost, unpub. data). Known stibnitebearing veins are restricted to an area of less than 100 m2• 

Stibnite is present as coarse blades as long as 5 em and 

may comprise 50 percent of a given vein. Mercury content 

in the veins is less than 10 ppm, but as much as 1.0 ppm Au 

is present (table 1). 

Mercury and antimony are present in two types of 

distinctly textured veins at Rainy Creek (Rutledge, 1948; 

Hoare and Coonrad, 1959a; Sainsbury and MacKevett, 

1965) (fig. 1, loc. 1 0) at the southern boundary of the Bethel 

quadrangle. The first type consists of irregular mineralized 

breccias that cut and locally silicify Kuskokwim shale. The 

breccia matrix is composed of granular aggregates of 

realgar and lesser amounts of euhedral quartz, orpiment, 

cinnabar, and stibnite and clasts of country rock. Individual 

breccia zones are as wide as 1 m, but few can be traced more 

than a few meters. As much as 0.05 ppm Au is present in 

some samples of this type. The second type is near vertical, 

N. 20° E. striking, massive quartz veins that contain less 

than 5 percent cinnabar and stibnite. Some vein surfaces 

have two sets of slickensides, plunging 45° N. and 80° S. 

The order of emplacement and relationship between the two 

textural types of veins is not clear. 

East of Kagati Lake in the Goodnews quadrangle (fig. 

1, loc. 11 ), composite quartz-calcite-cinnabar-stibnitetourmaline veins cut a hornblende-biotite granite and granodiorite pluton (Sainsbury and MacKevett, 1965). The veins 

are vertical and strike N. 20° W. Individual veins are as 

wide as 15 em; most are gently anastomosing or en echelon. 

The veins are zoned and have a margin of blue-green to 

brown tourmaline needles growing into a core of coarse 

quartz and calcite. Faceted cinnabar crystals and bladed 

stibnite as large as 2 mm and minor realgar and orpiment are 

scattered through the quartz at the cores of the veins. The 

textures of the veins suggest that tourmaline and quartz 

were the earliest minerals to crystallize and that additional 

quartz, calcite, stibnite, cinnabar, realgar, and orpiment 

were deposited later, probably in a different hydrothermal 

event. Gold content of individual vein samples is as high as 

2.9 ppm (table 1). Hornblende and biotite in the host granite 

are partially replaced by chlorite and calcite, and plagioclase 

is partially altered to sericite within 5 em of the veins. 

Numerous silicic volcanic rocks emplaced through 

the sedimentary rocks of the Kuskokwim Group have 

anomalous mercury and (or) gold contents. Samples from 

prominent white to pinkish-white rhyolite and rhyodacite 

domes and dikes in the Kipchuk-Tulip area (fig 1, loc. 12) 

have mercury contents as high as 14.4 ppm, gold contents as 

high as 0.30 ppm, and arsenic contents as high as 140 ppm 

(table 1). Quartz and (or) plagioclase rhyolite and rhyodacite porphyries have been extensively altered to 

assemblages of quartz, fine-grained white mica or clays, and 

hematite and limonite. Hematite-bearing quartz veins are 

also present in many of the rhyolites. The available data do 

not conclusively indicate whether mercury and (or) gold are 

disseminated in the altered rhyolite, in quartz veins, or in 

both. Stream-sediment samples from streams draining 

volcanic rocks of the Kipchuk-Tulip area have as much as 

5.2 ppm Hg, 238 ppm As, and 17 ppm Sb (T.P. Frost, 

unpub. data). The widely scattered anomalies suggest that 

the Kipchuk-Tulip volcanic field has potential for epithermal mercury-gold mineralization. 

Gold Lake "Red Spots" 

Many prominant "red spots" scattered through the 

rugged higher elevations in the southeastern part of the 

Bethel quadrangle are areas of oxidized pyrite-bearing 

rhyolite dikes and sulfide-bearing quartz veins that cut 

argillite, sandstone, and volcanic and volcaniclastic rocks of 

the Tikchik and Togiak terranes (fig. 1 ). Most of the rhyolite 

dike-quartz vein zones are exposed over areas of less than a 

few tens of square meters, but some larger zones extend 

erratically over several square kilometers. The dike-vein 

Mineralization in the Bethel Quadrangle, Southwestern Alaska C5 
Table 1. Analytical results for selected samples from the Bethel quadrangle and surrounding areas 

[Location shown by number in figure 1. Latitude and longitude in degrees, minutes, and seconds, north and west, respectively. Abbreviations 

for sample types: ss, sandstone; qtz, quartz; carb, carbonate; tour, tounnaline; cin, cinnabar; alt'd, altered; orp, orpiment. Most analyses by 

semiquantitative spark-source emission spectrography, except Au (flame atomic absorption), Hg (cold-vapor atomic absorption), and As, Bi, 

Cd, Sb, and Zn (inductively coupled plasma emission spectroscopy; where results of the last two methods are not yet available, semiquantitative 

spectroscopy data is shown in parentheses. All values in parts per million. N, not detected at level shown: L, detected but not quantifiable; G, 

greater than value shown; H, no data due to interference from other elements: ND, no data] 

Map location 

and sam~le no. Sam~le t~~e Latitude Longitude Ag As Au B Ba Bi Cr 

NY AC TERRANE QUAR1Z VEINS 

1. 9TF042B ... Qtz vein ......... 61 13 27 159 47 47 10.0 (500) 12.00 15 300 (NlO) LlO 

2. 8TF034A ... Qtz vein ......... 61 06 01 159 46 32 N0.5 2.1 20.00 30 30 Nl LIO 

8TF034C ... Qtz vein ......... 61 06 01 159 46 32 N0.5 NlO 4.50 30 30 Nl 10 

8TF034D ... Qtz vein ......... 61 06 01 159 46 32 N0.5 2.4 0.25 NlO N20 Nl 20 

3. 7SB20 ...... Qtz vein ......... 61 03 20 159 55 40 N0.5 NlO 4.90 20 700 21 15 

4. 7YB14A .... Ss w/ gtz vein .. 60 37 15 160 41 54 N0.5 NlO 0.40 20 150 Nl 30 

GOIDENGATEFAULTZONE 

5. 9TF073A ... Silica-carb rk ... 60 57 00 159 55 15 N0.5 (200) N0.05 NlO N20 (NlO) 1,000 

9TF073E ... Silica-carb rk ... 60 57 00 159 55 15 N0.5 (N200) N0.05 NlO 30 (NlO) 700 

9TF073E ... Breccia .......... 60 57 00 159 55 15 N0.5 (1,500) N0.05 10 50 (NIO) 1,500 

9TF116B ... Silica-carb rk ... 61 03 36 159 44 33 0.7 (1,500) N0.05 20 150 (NIO) 150 

6. 7SB102H .. Pyroxenite ...... 60 47 08 160 07 47 N0.5 NlO N0.05 30 L20 Nl 700 

7SB1021 ... Dunite ........... 60 47 08 160 07 47 N0.5 NlO 0.05 LlO 70 Nl G5,000 

7SB102L ... Gabbro .......... 60 47 08 160 07 47 N0.5 NlO 0.10 10 L20 Nl 5,000 

KIPCHUK AREA 

7. 89ML227 .. Altered tuff(?) .. 60 50 10 159 17 00 70.0 (1,500) L0.05 500 300 (300) 700 

89TF32B ... Qtz-tour rock ... 60 49 51 159 16 45 1.5 (200) N0.05G2,000 150 (10) 150 

89TF32C ... Qtz-tour rock ... 60 49 51 159 16 45 7.0 (200) N0.05G2,000 300 (30) 100 

8. 9TF67C .... Qtz-tour rock ... 60 44 59 159 07 10 30.0 (1,000) N0.05G2,000 500 (30) 70 

9TF67D .... Qtz-tour rock ... 60 44 59 159 07 10 5.0 (1,500) O.IOG2,000 150 (NlO) 200 

9TF67J ..... Qtz-tour rock ... 60 44 59 159 07 10 70.0 {2,000} N0.05G2,000 100 {30} 200 

FISHER DOME STIBNITE VEINS 

9. 8TF058 .... Stibnite-qtz ..... 60 50 01 159 44 15 7.0 (1,500) 1.00 300 100 (NIO) NIO 

FD-4 ........ Stibnite-gtz ..... 60 50 01 159 44 15 N0.5 {300} 0.20 30 30 (NIO} LIO 

RAINY CREEK VEINS 

10. 7B031Rl .. Realgar-orp ..... 60 00 08 160 12 46 N0.5 17,000 0.05 50 70 Nl 15 

7B034Rl .. Qtz-cin .......... 60 01 37 160 07 59 N0.5G20,000 N0.05 70 150 Nl 30 

KAGA TI lAKE VEINS 

11. 8TF07l. .... Qtz-cin-tour .... 59 54 50 159 54 54 3.0 {2,000} 2.90 300 100 {NIO} NIO 

RHYOLITE DIKES AND OOMES-KIPCHUK/TULIP AREA 

12. 9SB137A .. Rhyolite ........ 60 44 52 159 15 05 N0.5 (N200) N0.05 700 150 (NIO) 70 

8-238 ....... Rhyolite ........ 60 37 24 159 17 10 N0.5 140 0.30 200 1,500 6 L0.6 

7CZOOI .... Rhyolite ........ 60 33 22 159 26 35 N0.5 10 N0.05 70 700 Nl LIO 

GOLD LAKE AREA 

13. 7SB143A .. Qtz vein ......... 60 13 25 159 23 18 7.0 7,000 1.10 50 150 30 LIO 

7SB143B .. Rhyolite ........ 60 13 25 159 23 18 7.0 1,500 L0.05 500 300 15 LlO 

7SB143D .. Breccia .......... 60 13 25 159 23 18 5.0GIO,OOO 0.15 10 70 15 LIO 

9TF080L ... Breccia .......... 60 13 25 159 23 18 7.0G10,000 2.00 NlO 700 {70} LIO 

KISARlllK LAKE AREA 

14. 8CZ039D .. Qtz vein ......... 60 21 10 159 18 00 1.5 (7,000) 0.41 300 200 Nl 70 

8CZ039E .. Rhyolite ........ 60 21 10 159 18 00 1.5 (3,000) 0.23 200 300 Nl NlO 

15. 9TFI07B .. Rhyolite ........ 60 17 10 159 01 26 3.0 {N200} {NlO} 15 05,000 {LlO} LIO 

aniER GOLD REPORTS 

16. 7TF003 .... Alt'd ss .......... 60 57 28 159 39 00 0.5 8.00 0.10 15 70 L2 300 

17. 7JM36B .... Qtz vein ......... 60 09 08 159 56 11 N0.5 20.00 0.35 30 700 31 150 

networks have anomalous concentrations of various 

combinations of Ag, As, Au, Cu, Hg, Mo, Pb, Sb, and W 

(table 1). The highest anomalous values for Au, Ag, and As 

are from red spots where both rhyolite dikes and quartz 

veins are present, although anomalies are also present in 

spots in which only one or the other rock type has been 

identified. 

C6 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

The largest and best exposed of the dike-vein 

networks crops out in ridges and valleys east of Gold Lake 

in the northeastern comer of the Bethel A-2 quadrangle (fig. 
Table 1. Continued 

Sam~le no. Cu Mn Mo Ni Pb Sb Sn w Zn Hg 

NYAC TERRANE QUAR1Z VEINS 

9TF042B ........... 7 200 15 5 30 (N100) N10 N20 (N200) N0.02 

8TF034A .......... 70 700 5 7 N10 1.6 N10 N20 N0.05 0.84 

8TF034C .......... 70 700 30 10 N10 N1 N10 N20 5.8 0.60 

8TF0340 ......... .30 1,500 N5 10 N10 1.7 N10 N20 42.0 2.28 

7SB20 ............. L5 1,000 N5 7 L10 N2 N10 N20 20.0 0.08 

7YB14A ........... 15 1,500 10 30 20 N2 N10 70 40.0 0.02 

GOlDEN GATE FAULT ZONE 

9TF073A .......... 10 700 N5 700 N10 (N100) N10 N20 (N200) 4.20 

9TF073E ......... .30 700 N5 500 N10 (N100) N10 N20 (N200) 1.90 

9TF073E .......... 50 700 N5 1,500 15 (N100) N10 N20 (N200) 036 

9TF116B .......... 20 300 N5 700 50 (N100) 20 N20 (1500) 4.00 

7SB102H ....... 100 1,000 N5 70 N10 N2 N10 N20 10.0 0.12 

7SB 1021. .......... 7 500 N5 1,000 N10 N2 NlO N20 25.0 0.04 

7SB 1 02L. ....... 150 1,500 N5 700 N10 N2 N10 N20 10.0 0.52 

KIPCHUK AREA 

89ML227 .... 1,000 300 N5 200 2,000 (1,500) 100 N20 (010,000) 036 

89TF32B .......... 15 150 N5 30 70 (L100) 15 N20 (N200) 1.20 

89TF32C .......... 10 150 N5 30 100 (N100) 30 N20 (N200) 2.40 

9TF67C ......... 500 300 7 30 7,000 (5,000) 30 N20 (N200) 1.80 

9TF67D ........... 15 300 5 50 50 (500) 20 N20 (1,000) 0.60 

9TF67J ............ 70 300 5 30 5,000 (7,000} 30 N20 (N200} 4.40 

FISHER OOME STIBNITE VEINS 

8TF058 ........... 30 500 N5 7 50 (010,000) N10 N20 (N200) ND 

FD-4 ............... L5 70 L5 L5 70 (010,000} N10 N50 (N200} 4.80 

RAINY CREEK VEINS 

7B031R1 ......... 15 70 N5 5 10 11,000 N10 N20 50.0 ND 

7B034R1 ......... 70 700 N5 20 L10 8,200 NlO L20 85.0 160 

KAGA 11 LAKE VEINS 

8TF071 ........... .30 500 N5 7 50 (020,000} N10 N20 (N200} ND 

RHYOUTE DIKES AND OOMES-KIPCHUK{IULIP AREA 

9SB137A ........ .30 300 N5 30 30 (N100) N10 N20 (N200) 14.40 

8-238 .............. 20 700 7 N5 30 3.8 NlO N20 65.0 3.24 

7CZ001 ............ 5 30 N5 L5 15 2.0 N10 N50 100.0 11.00 

GOlD LAKE AREA 

7SB143A ....... 100 2,000 20 L5 300 150.0 NlO N20 20.0 0.14 

7SB143B ......... 70 50 30 N5 100 24.0 N10 N20 15.0 0.04 

7SB143D ......... 15 100 N5 L5 30 10.0 15 N20 15.0 0.02 

9TF080L .......... 70 30 N5 L5 10 (L100} 10 N20 (N200} 0.06 

KISARILIK lAKE AREA 

8CZ039D ........ N5 500 7 7 N10 20.0 15 70 15.0 H 

8CZ039E ....... 200 70 15 N5 10 100.0 15 30 20.0 0.40 

9TF107B ......... 30 70 100 5 50 (N100} NlO N20 (N200} 0.08 

OTIIER GOlD REPORTS 

7TF003 ......... 200 1,500 N5 50 NlO L2 70 N20 6.0 0.32 

7JM36B ........... 70 700 10 70 15 8.0 NlO N20 30.0 0.32 

1, loc. 13). The Gold Lake occurrence was first visited by 

U.S. Geological Survey geologists in 1987; it also was 

found by Cominco geologists and staked by them in 

September of 1988. The ridges on the north side of Kisarilik 

Lake (fig. 1, loc. 14) also host a prominent Au-AgAs-Sb-bearing dike-vein network. Pyrite-bearing rhyolite 

Mineralization in the Bethel Quadrangle, Southwestern Alaska C7 
dikes and quartz veins east of the Togiak fault in volcanic 

rocks of the Tikchik terrane (fig. I, Joe. 15) contain 

anomalous amounts of Ag, Pb, and Mo. Other red spots 

scattered through the Tikchik and Togiak terranes yield 

anomalies in some or all the metals of the Gold Lake-type 

veins but are not shown on figure 1 (T.P. Frost, unpub. 

data). 

Altered rhyolite dikes containing partially resorbed 

quartz phenocrysts and pyrite cubes as large as 2 mm are 

prominent at the Gold and Kisarilik Lake occurrences and at 

most other red spots. The rhyolite is white to pale yellowish 

white on unweathered surfaces; oxidation of pyrite on 

weathered surfaces produces the bright-red color of most 

spots. The dikes are as wide as 3 m and are relatively 

resistant to erosion; in many areas they hold up ridges. The 

groundmass of most rhyolite is replaced by sericite or illite 

and quartz. Relict plagioclase phenocrysts are present and 

are partially replaced by albite and sericite. Samples of 

rhyolite contain as much as 7 ppm Ag, 3,000 ppm As, 0.23 

ppm Au, I 00 ppm Mo, and I 00 ppm Sb. It is uncertain 

whether the metals are disseminated in the rhyolite or are 

present in quartz veins. 

At the Gold Lake locality, several generations of 

zoned quartz veins containing as much as 20 percent galena 

cut all rock types. Common vein assemblages are quartz, 

quartz+calcite, quartz+(chlorite), quartz+iron (?) oxides, 

quartz+pyrite, and quartz+galena. Argillite and sandstone 

wall rocks and rhyolite dikes are incipiently to extensively 

altered to quartz, sericite, calcite, and iron oxide minerals 

near quartz veins. Most veins are less than 2 em wide, 

although some may be as wide as 12 em. Quartz is present 

as euhedral prisms as long as 1 em. The prisms have clear 

cores, but the outer third of most crystals contains very fine 

grained fluid and mineral inclusions in concentric layers. 

The quartz in the layered rims has irregular extinction. Two 

generations of carbonate are present in the veins, both of 

which postdate crystallization of most of the quartz. The 

earliest carbonate is a brown, fine-grained aggregate that is 

intergrown with fine-grained quartz and galena. A later 

generation of coarse-grained, clear calcite fills in remaining 

space. Quartz veins contain as much as 7 ppm Ag, 7,000 

ppm As, 1.1 ppm Au, 30 ppm Bi, 300 ppm Pb, 150 ppm Sb, 

and 70 ppm W (table 1). Hydrothermal breccia dikes or 

veins composed of pale-greenish-gray clays, quartz clasts, 

and oxide minerals have gold contents as high as 2.0 ppm 

(table 1). Coarse calcite veins at the Gold Lake locality have 

black alteration halos and contain as much as 0.05 ppm Au 

(T.P. Frost, unpub. data). 

The rhyolite dike-quartz vein association at Gold 

Lake is dominated by anomalous arsenic and antimony 

concentrations and less consistent, but locally significant, 

enrichments in Ag, Au, Ba, and Pb. The veins are probably 

best classified as deep epithermal or shallow mesothermal 

polymetallic veins. Similar dike-vein associations are 

scattered through the southeastern comer of the Bethel 

C8 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

quadrangle in rocks of the Togiak and Tikchik terranes, but 

most that were located in this study have small surface 

expressions. Analytical values for arsenic and antimony as 

high as 180 ppm and 28 ppm, respectively, for streamsediment samples in many drainages in the Togiak terrane 

and to a lesser extent the Tikchik terrane (T.P. Frost, unpub. 

data) suggest that there may be other rhyolite-quartz vein 

occurrences in the southeastern part of the Bethel 

quadrangle. Heavy-mineral concentrate samples from the 

same areas also yield anomalous As (to 5,000 ppm) and Sb 

(to 15,000 ppm), as well as locally anomalous Pb (to 200 

ppm), W (to 5,000 ppm), and Zn (to 2,000 ppm) (T.P. Frost, 

unpub. data). Anomalous As, Au, Ag, Hg, and Pb contents 

in rock and stream-sediment samples in areas underlain by 

the Togiak and Tikchik terranes in the Goodnews, Taylor 

Mountains, and Dillingham quadrangles (Coonrad and 

others, 1978; Hessin and others, 1978a, b) suggest that 

mineralized rocks similar to those at Gold Lake may be 

present throughout these terranes. 

Other Gold Occurrences 

Gold was detected in red-weathering quartz veins in 

hornfelsed volcaniclastic sandstone in the vicinity of the 

Marvel Dome and Mt. Plummer plutons (fig. 1, Joe. 16),just 

upstream from the Marvel Creek gold placer east of the 

Golden Gate fault (Hoare and Coonrad, 1959a; Hoare and 

Cobb, 1977). The sandstone contains ameoboid opaque 

minerals that probably grew in place. The sample also 

contains anomalous tin (table 1). The gold is probably in the 

quartz veins, although the source of the tin is less certain. 

The Mt. Plummer and Marvel Dome plutons probably are 

continuous below the present level of exposure. The plutons 

intrude sedimentary rocks of the Kuskokwim Group and 

have yielded a biotite K-Ar age of 70 Ma (S.E. Box, written 

commun., 1988). 

Quartz veins cut hornfelsed argillite and fine-grained 

sandstone of the Togiak terrane in the vicinity of the 

Canyon Creek pluton (fig. 1, Joe. 17) and contain as much 

as 0.35 ppm Au. Placers downstream from the pluton have 

produced significant gold (Hoare and Coonrad, 1959a; 

Hoare and Cobb, 1977). Stream-sediment and heavymineral concentrate samples downstream from the pluton 

contain anomalous As, Au, Cu, Hg, Pb, Sb, and W (T.P. 

Frost, unpub. data). 

Gold was observed in pan concentrate samples or 

detected analytically (T.P. Frost, unpub. data) in at least one 

first- or second-order stream draining every pluton in the 

Bethel quadrangle. The granitoid plutons in the Bethel 

quadrangle provide favorable targets for additional 

undiscovered gold-bearing veins or related placer 

occurrences. 
SUMMARY 

The Bethel quadrangle contains several types of lode 

mineralization having potential for gold and mercury and 

lesser potential for silver and lead as byproducts. Goldbearing quartz veins spatially associated with Early 

Cretaceous felsic granitic plutons are in Jurassic andesitic 

and volcaniclastic rocks of the Nyac terrane. Gold placers 

east of the the Nyac terrane in the the Bethel quadrangle and 

in the southern part of the Russian Mission quadrangle 

apparently are derived from quartz veins and hornfels 

surrounding 60-- to 72-million-year-old granitic plutons. 

Mercury- and antimony-bearing quartz veins predominantly 

in Kuskowkim sedimentary rocks contain gold at significant 

levels. Base- and precious-metal-bearing rhyolite and 

quartz veins are scattered through the Paleozoic and Mesozoic volcanic and sedimentary rocks of the Togiak and 

Tikchik terrane in the southeastern part of the quadrangle. 

Small areas of quartz-tourmaline replacement in Upper 

Cretaceous volcanic and volcaniclastic rocks near the Kipchuk River contain variable but anomalous amounts of 

silver, gold, lead, and zinc. 

REFERENCES CITED. 

Box, S.E., and Murphy, J.M., 1987, Late Mesozoic structural and 

stratigraphic framework, eastern Bethel quadrangle, 

southwestern Alaska, in Hamilton, T.D., and Galloway, 

J.P., eds., Geologic studies in Alaska by the U.S. Geological 

Survey during 1986: U.S. Geological Survey Circular 998, 

p. 78-82. 

Coonrad, W.L., Hoare, J.M., Taufen, P.M., and Hessin, T.D., 

1978, Geochemical analyses of rock samples in the Goodnews and Hagemeister Island quadrangles region, 

southwestern Alaska: U.S. Geological Survey Open-File 

Report 78-9-H, 1 sheet, scale 1:250,000. 

Frost, T.P., Calzia, J.P., Kistler, R.W., and Vivit, D.V., 1988, 

Petrogenesis of the Crooked Mountains pluton, Bethel 

quadrangle-A preliminary report, in Galloway, J.P., and 

Hamilton, T.D., eds., Geologic studies in Alaska by the U.S. 

Geological Survey during 1987: U.S. Geological Survey 

Circular 1016, p. 126-131. 

Hessin, T.D., Taufen, P.M., Seward, J.C., Quintana, S.J., Clark, 

A.L., Grybeck, Donald, Hoare, J.M., and Coonrad, W.L., 

1978a, Geochemical and generalized geological map 

showing distribution and abundance of lead in the Goodnews and Hagemeister Island Island quadrangles region, 

southwestern Alaska: U.S. Geological Survey Open-File 

Report 78-7-N, scale 1 :250,000. 

___ 1978b, Geochemical and generalized geological map 

showing distribution and abundance of arsenic, gold, silver, 

and platinum in the Goodnews and Hagemeister Island 

quadrangles region, southwestern Alaska: U.S. Geological 

Survey Open-File Report 78-7-R, scale 1:250,000. 

Hoare, J.M., and Cobb, E.H., 1977, Mineral occurrences (other 

than mineral fuels and construction materials) in the Bethel, 

Goodnews, and Russian Mission quadrangles, Alaska: U.S. 

Geological Survey Open-File Report 77-156, 98 p. 

Hoare, J.M., and Coonrad, W.L., 1959a, Geology of the Bethel 

quadrangle, Alaska: U.S. Geological Survey Miscellaneous 

Investigations Map 1-285, scale 1 :250,000, 

___ 1959b, Geology of the Russian Mission Quadrangle, 

Alaska: U.S. Geological Survey Miscellaneous 

Investigations Map 1-292, scale 1 :250,000. 

___ 1978, Geologic map of the Goodnews and Hagemeister 

Island quadrangles, Alaska: U.S. Geological Survey OpenFile Report 78-9-B, scale 1 :250,000. 

Hoare, J.M., and Jones, D.L., 1981, Lower Paleozoic radiolarian· 

chert and associated rocks in the Tikchik Lakes area, 

southwestern Alaska, in Albert, N.R.D., and Hudson, 

Travis, eds., The United States Geological Survey in AlaskaAccomplishments during 1979: U.S. Geological Survey 

Circular 823-B, p. B44-B45. 

Jones, D.L., Silberling, N.J., Coney, P.J., and Plafker, George, 

1987, Lithotectonic terrane map of Alaska (west of the 

141 st meridian): U.S. Geological Survey Miscellaneous 

Field Studies Map MF-1874-A, scale 1:2,500,000. 

Mertie, J.B., Jr., 1938, The Nushagak district, Alaska: U.S. 

Geological Survey Bulletin 903, 96 p. 

___ 1976, Platinum deposits of the Goodnews Bay District, 

Alaska: U.S. Geological Survey Professional Paper 938, 

42 p. 

Murphy, J.M., 1987, Early Cretaceous cessation of terrane 

accretion, northern Eek Mountains, southwestern Alaska, in 

Hamilton, T.D., and Galloway, J.P., eds., Geologic studies 

in Alaska by the U.S. Geological Survey during 1986: U.S. 

Geological Survey Circular 998, p. 83-85. 

Robinson, M.S., and Decker, John, 1986, Preliminary age data and 

analytical data for selected igneous rocks from the Sleetmute, Russian Mission, Taylor Mountain, and Bethel 

quadrangles, southwestern Alaska: Alaska Division of 

Mining and Geological and Geophysical Surveys PublicData File 86-98, 9 p. 

Rutledge, F.A., 1948, Investigation of the Rainy Creek mercury 

prospect, Bethel district, Kuskokwim region, southwestern 

Alaska: U.S. Bureau of Mines Report of Investigations 

4361, 7 p. 

Sainsbury, C.L., and MacKevett, E.M., Jr., 1965, Quicksilver 

deposits of southwestern Alaska: U.S. Geological Survey 

Bulletin 1187, 89 p. 

Shew, Nora, and Wilson, F.H., 1981, Map and table showing 

radiometric ages of rocks in southwestern Alaska: U.S. 

Geological Survey Open-File Report 81-866, 26 p. 

Southworth, D.D., 1986, Geology of the Goodnews Bay ultramafic 

complexes: Fairbanks, University of Alaska, M.S. thesis, 

114 p. 

Turner, D.L., Forbes, R.B., Aleinikoff, J.N., Hedge, C.E., and 

McDougall, Ian, 1983, Geochronology of the Kilbuck 

terrane of southwestern Alaska: Geological Society of 

America Abstracts with Programs, v. 15, p. 407. 

Mineralization in the Bethel Quadrangle, Southwestern Alaska C9 

Chapter D 

Gold Associated with Cinnabar- and 

Stibnite-Bearing Deposits and 

Mineral Occurrences in the Kuskokwim River 

Region, Southwestern Alaska 

By JOHN E. GRAY, THOMAS P. FROST, 

RICHARD J. GOLDFARB, and DAVID E. DETRA 

U.S. GEOLOGICAL SURVEY BULLETIN 1950 

GEOCHEMICAL STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1989 
CONTENTS 

Abstract Dl 

Introduction D 1 

Geology Dl 

Geochemical results for mineralized vein samples D2 

Significance of gold associated with mercury-antimony deposits D4 

Summary DS 

References cited DS 

FIGURE 

I. Map showing cinnabar- and stibnite-bearing deposits and mineral occurrences in 

the Kuskokwim River region, southwestern Alaska D2 

TABLES 

I. Geochemical results of ores from cinnabar-stibnite deposits, southwestern 

Alaska D3 

2. Geochemical results of cinnabar and stibnite separates from deposits and mineral 

occurences, southwestern Alaska D4 
Gold Associated with Cinnabar- and Stibnite-Bearing Deposits and 

Mineral Occurrences in the Kuskokwim River Region, 

Southwestern Alaska 

By John E. Gray, Thomas P. Frost, Richard J. Goldfarb, and David E. Detra 

Abstract 

Several epithermal mercury-antimony vein deposits in the Kuskokwim River region of southwestern Alaska contain anomalous gold 

concentrations. Gold contents in vein samples containing cinnabar and 

stibnite are 0.05-6.9 ppm; samples are from the Red Devil, Mountain 

Top, White Mountain, Cinnabar Creek, Fisher Dome, Kagati Lake, and 

Snow Gulch deposits. In addition, analyses of cinnabar separates from 

Red Devil and stibnite separates from Fisher Dome and Snow Gulch 

contain as much as 10 ppm Au. 

Gold concentrations in the ores exposed at the surface of these 

deposits are significant. These concentrations suggest that gold may be 

a byproduct of some of these epithermal systems, which previously were 

recognized only as mercury and antimony bearing. Gold-rich veins and 

stockworks may have also formed below these epithermal mercuryantimony deposits. These gold-rich zones may be found in deeper, hotter 

parts of the systems in southwestern Alaska by processes analogous to 

those operating in vertically zoned deposits in other parts of the world. 

The gold anomalies indicate that analytical methods for gold that are 

sensitive to parts per billion should be part of regional exploration 

programs in Alaska in order to target precious-metal occurrences. 

INTRODUCTION 

Epithermal cinnabar and stibnite lodes are scattered 

over several hundred thousand square kilometers in the 

Kuskokwim River region of southwestern Alaska (fig. 1). 

Cinnabar and stibnite are the dominant ore minerals; lesser 

amounts of realgar, orpiment, native mercury, pyrite, 

limonite, and hematite are present (Sainsbury and MacKevett, 1965). Dickite is a common alteration mineral at many 

of these deposits. Ore minerals are typically in quartzcarbonate veins hosted within and adjacent to mafic dikes, 

carbonate rock, graywacke, rhyolite, or monzonite to granodiorite bodies. Commonly, mineralized veins are localized 

where bedding-plane faults in the surrounding sedimentary 

rocks intersect these more competent units (Sainsbury and 

MacKevett, 1960). Approximately 41,000 flasks of mercury 

have been produced from the region, mostly from mines in 

the Red Devil area where about 35,000 flasks were 

recovered (Miller and others, 1989). 

Although geological evaluations have been conducted 

on many of these mercury-antimony deposits (for example, 

Webber and others, 1947; Rutledge, 1950; Sainsbury and 

MacKevett, 1965), few studies report the presence of gold. 

The lack of reported gold is due in part to the relatively high 

limit of determination for gold in analytical techniques 

utilized in these studies. For example, in the most 

comprehensive study of the mercury-antimony systems in 

southwestern Alaska, Sainsbury and MacKevett (1965) 

reported that ores from several cinnabar-stibnite deposits in 

southwestern Alaska were below the emission spectrography lower limit of determination of 20 ppm for gold. In this 

paper, we present gold analyses of mineralized vein samples 

determined by atomic absorption (AA) or inductively 

coupled plasma-atomic emission spectroscopy (ICP-AES), 

techniques that have lower limits of determination of 0.05 

ppm and 0.15 ppm, respectively. We also report emission 

spectrographic results of Au, Ag, Sb, and As of cinnabar 

and stibnite separates from the deposits. 

Acknowledgments.-The authors would like to 

thank Bruce Roushey, Randy Hill, Phil Hageman, and Jerry 

Motooka for chemical analyses of samples. Assistance with 

field work was provided by Robert Eppinger and James 

Kilburn. We also recognize the assistance of Karen E. 

Slaughter with drafting. We gratefully acknowledge Bruce 

Hickock of the Calista Corporation for helpful discussions 

and permission to visit several deposits and mineral 

occurrences during this study. The manuscript was 

strengthened by technical reviews by Robert Eppinger, Cliff 

Taylor, Tom Nash, Jim Dover, and John Galloway. 

GEOLOGY 

Rocks of the Cambrian to Devonian Holitna Group 

are the oldest known to host mercury-antimony deposits in 

the Kuskokwim River region. Strata of the Holitna Group 

Gold Associated with Cinnabar· and Stibnite-Bearing Deposits 01 
0 50 

EXPLANATION 

GEOLOGY 

100 KM 

1:::::::::::1 Kk Cretaceous Kuskokwim Group 

ltt=rtrl KTrg Triassic and Lower Cretaceous 

Gemuk Group 

~ Pzl Cambrian to Devonian 

Holitna Group 

DEPOSITS AND 

MINERAL OCCURRENCES 

1 Cinnabar Creek 

2 Fisher Dome 

3 Kagati Lake 

4 Mountain Top 

5 Red Devil 

6 Snow Gulch 

7 White Mountain 

Figure 1. Cinnabar- and stibnite-bearing deposits and mineral 

occurrences in the Kuskokwim River region, southwestern Alaska. 

Geology modified from Decker and others (Alaska Division of Geological 

and Geophysical Surveys, written commun., 1989). 

consist of massive to thinly bedded limestone and dolomite 

and minor, local conglomerate (Cady and others, 1955). 

Mineral occurrences in the White Mountain area are found 

in rocks of the Holitna Group. 

02 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

Cinnabar- and stibnite-bearing deposits are also found 

in rocks of the Triassic and Lower Cretaceous Gemuk 

Group. The Gemuk Group is composed of massive siltstone 

interbedded with lesser amounts of chert, volcanic rock 

(tuffs and lavas), limeston«:', and graywacke (Cady and 

others, 1955). The Cinnabar Creek area, the type locality for 

the Gemuk Group, hosts a number of epithermal cinnabar 

and stibnite mineral occurrences. Mercury- and antimonybearing quartz veins are also found in Cretaceous-Tertiary 

quartz monzonite and granodiorite bodies that intrude rocks 

of the Gemuk Group; for example, at the Kagati Lake 

mineral occurrence (Sainsbury and MacKevett, 1965). 

Many of the cinnabar and stibnite deposits are hosted 

in rocks of the Cretaceous Kuskokwim Group. The Kuskokwim Group consists primarily of marine turbidites 

composed of interbedded graywacke, siltstone, shale, minor 

conglomerate, and occasional thin coal seams (Miller and 

others, 1989). These rocks unconformably overly other rock 

units in the region including those of the Gemuk and 

Holitna Groups. Cretaceous to Tertiary dikes of 

intermediate to mafic composition intrude rocks of the 

Kuskokwim Group and commonly host quartz-carbonate 

veins containing cinnabar and stibnite. At Red Devil and 

Mountain Top, mineralized veins are found in mafic dikes, 

in graywacke and shale of the Kuskokwim Group, and at 

contacts between the dikes and sedimentary rocks. 

Similarly, at Fisher Dome, quartz-stibnite veins are present 

in a Cretaceous-Tertiary granite pluton that intrudes rocks 

of the Kuskokwim Group (Hoare and Coonrad, 1959). At 

the Snow Gulch deposit in the Donlin Creek area, cinnabar 

and stibnite are present in rhyolite where hypabyssal rhyolite dikes intrude graywacke and shale of the Kuskokwim 

Group. 

GEOCHEMICAL RESULTS FOR 

MINERALIZED VEIN SAMPLES 

Utilizing the AA and ICP-AES methods we were 

able to identify the presence of significant gold in several 

cinnabar- and stibnite-bearing deposits in the Kuskokwim 

River region (table 1). Our results indicate anomalous 

concentrations of gold in mineralized samples from the Red 

Devil, Cinnabar Creek, Mountain Top, and White Mountain 

deposits. In addition, McGimsey and others (1988) reported 

anomalous gold in ore samples from the Snow Gulch 

deposit (table 1). Mineralized vein samples from the Fisher 

Dome and Kagati Lake mineral occurrences are also 

. anomalous in gold (Frost, this volume). Geochemical 

studies of rocks that host cinnabar and stibnite deposits 

throughout the Kuskokwim River region indicate that 

background gold concentrations are less than 0.05 ppm 

(McGimsey and others, 1988; J.E. Gray, unpub. data). 

Therefore, it is noteworthy that many of the deposits in the 

Kuskokwim River region contain anomalous amounts of 

gold of greater than 0.05 ppm. 
Table 1. Geochemical results of ores from cinnabar-stibnite deposits and mineral occurrences, southwestern Alaska 

[All values are in parts per million. Leaders(--), not detennined; N, not detected at the value shown; L, detected but not quantifiable; G, greater 

than the value shown] 

location Sample Au 

Red Devi11 •••••••••••••••••••••• RDtca ....................... 4.4 

Red Devi11 •••••••••••••••••••••• RDI[)b ....................... 1.1 

Red Devi12 ...................... 88A TF043A • ............... 0.1 0 

Red DeviJ2 ...................... 88ATF043B1 ••••••••••••••• 0.4 

Red Devi12 ...................... 88ATF043Cb ............... 1.3 

Red Devi12 ...................... 88ATF043Dh ............... 0.05N 

Mountain Top1 •••••••••••••••• .MTtc• ....................... 0.32 

White Mountain1 •••••••••••••• WM1A1 •••••••••••••••••••••• 0.37 

White Mountain2 .............. 88ATF0471 ••••••••••••••••• 0.05 

Cinnabar Creek2 ............... 88ATF049c ................. 0.1 0 

Cinnabar Creek2 ............... 88ATF05od ................. 0.40 

Cinnabar Creek2 ............... 88ATF05td ................. 0.20 

Ag 

0.26 

0.45 

0.5L 

0.5L 

0.5 

0.5N 

0.12 

0.09 

0.5N 

0.5N 

0.5N 

0.5N 

Hg 

360 

360 

360 

360 

Sb As 

8,0000 4,463 

8,0000 387 

tOOL 1,500 

10,0000 7,000 

10,0000 7,000 

300 2,000 

3.8 7.3 

18 20 

150 200N 

5,000 1,500 

10,0000 7,000 

500 2,000 

Fisher Dome2 ................... 88ATF058b ................. 1.0 7 10,0000 1,500 

Fisher Dome2 ................... FD-4b ........................ 0.20 0.5N 4.8 10,0000 300 

Kagati Lake2 .................... 88ATF071Ac ............•.. 2.9 3 10,0000 2,000 

Kagati Lake2 .................... 88ATF071Bc ............... 1. 7 2 10,0000 2,000 

Snow Gulch3 ••••••••••••••••••• .10337RAb ................... 6.9 38 lOG 1,0000 1,600 

Snow Gulch3 ................... J0337RBh .................. .4.1 13 lOG 1,0000 2,000G 

1Concentrations of Au, Ag, Sb, and As were detennined by inductively coupled plasma atomic emission spectrometry; Hg by cold-vapor 

atomic absorption. 2Concentrations for Au were detennined by atomic absorption; Ag, Sb, ~d As by semiquantitative emission spectrography; Hg (when 

listed) by cold-vapor atomic absorption. 3Results from McGimsey and others (1988). Concentrations of Au, Ag, Sb, and As were determined by atomic absorption; Hg by coldvapor atomic absorption. 

•ore sample containing predominantly cinnabar. 

bore sample containing predominantly stibnite. 

core sample containing cinnabar and stibnite. 

dare sample containing abundant cinnabar and native mercury, abundant cinnabar and native mercury, and minor stibnite. 

At the Red Devil mine, both vein samples containing 

abundant cinnabar and those containing predominantly 

stibnite are anomalous in gold (table 1 ). Quartz-carbonate 

veins hosted in graywacke of the Kuskokwim Group at Red 

Devil contain cinnabar and minor stibnite and 0.40-4.4 ppm 

Au. Other mineralized vein and breccia samples from Red 

Devil that are hosted in altered mafic dikes and Kuskokwim 

graywacke, but contain vug fillings of abundant stibnite, have 

as much as 1.3 ppm Au. At the Mountain Top deposit, 

high-grade mercury ore having anomalous gold 

concentrations is found in brecciated mafic dikes that cut 

graywacke and shale of the Kuskokwim Group. A sample of 

quartz-carbonate vein from Mountain Top contains 

abundant cinnabar open-space filling and 0.32 ppm Au 

(table 1). 

Two samples of high-grade mercury ore from the 

White Mountain deposit contain 0.05 and 0.37 ppm Au. 

These vein samples contain vug fillings of cinnabar that cut 

brecciated and silicified dolomite of the Holitna Group. In 

the Cinnabar Creek area, two samples of silicified and 

brecciated siltstone and graywacke of the Gemuk Group are 

cut by numerous stockworks containing cinnabar, stibnite, 

and abundant free mercury. These samples contain 0.20 and 

0.40 ppm Au. Another sample of brecciated siltstone from 

the Gemuk Group in the Cinnabar Creek area contains 

cinnabar and stibnite in quartz stockworks and 0.10 ppm 

Au. 

Two quartz-stibnite vein samples that cut a hypabyssal biotite quartz porphyry at the Fisher Dome mineral 

occurrence contain 0.20 and 1.0 ppm Au (Frost, this 

volume) (table 1). Frost also reports as much as 2.9 ppm Au 

in quartz-calcite-cinnabar-stibnite veins in a hornblendebiotite granite stock from the Kagati Lake locality. 

Anomalous gold is present in two samples of quartz vein 

with abundant stibnite cutting rhyolite at Snow Gulch 

(McGimsey and others, 1988) (table 1). These samples 

contain 4.1 and 6.9 ppm Au, some of the highest 

concentrations yet determined for any of the mercuryantimony lodes in the region. 

Native gold was recognized in a heavy-mineral 

separate of Red Devil ore. Semiquantitative spectrographic 

analysis indicates that cinnabar and stibnite separates from 

Red Devil, Fisher Dome, and Snow Gulch contain 10 ppm 

Au (table 2). In addition, heavy-mineral-concentrate 

samples collected downstream from the Fisher Dome, 

White Mountain, and Mountain Top deposits contain finely 

Gold Associated with Cinnabar- and Stibnite-Bearing Deposits D3 
Table 2. Geochemical results of cinnabar and stibnite separates from deposits and mineral occurrences, 

southwestern Alaska 

[All determinations were made by semiquantitative emission spectrography. Values are in parts per million. N, not detected at the 

value shown; L, detected at the value shown, but not quantifiable; G, greater than the value shown] 

Location 

Red Devil 

Mountain Top 

White Mountain 

White Mountain 

Cinnabar Creek 

Fisher Dome 

Fisher Dome 

Snow Gulch 

Snow Gulch 

Sample 

RDlCa 

MTlCa 

WMlAa 

WM2a 

CCAa 

FDlb 

FD2b 

SGlb 

SG2b 

acinnabar mineral separate, 95-99 percent pure. 

bStibnite mineral separate, 95-99 percent pure. 

Au 

10 

lON 

lON 

lON 

lON 

lOL 

10 

10 

10 

particulate free gold (Gray and others, 1990; T.P. Frost, 

unpub. data). These results suggest that the gold in the 

cinnabar-stibnite deposits is native gold. 

Placer gold deposits below stibnite lodes in the 

Donlin Creek area (which includes Snow Gulch) also 

provide evidence that gold is derived from upstream 

mercury-antimony lodes. Cady and others (1955) reported 

cinnabar and stibnite, as well as gold, in placer concentrates 

in the Donlin Creek area. Gold in cinnabar nuggets from 

placers in the Donlin Creek area (Cady and others, 1955) is 

evidence that some gold is associated with mercuryantimony lodes. These findings led Cady and others ( 1955) 

to suggest that cinnabar and stibnite lodes were the source 

of placer gold in the Donlin Creek area. 

In addition to the gold anomalies discussed 

previously, many cinnabar- and stibnite-bearing veins in the 

Kuskokwim River region contain appreciable Hg, Sb, As, 

and Ag (table 1). Anomalous Hg, Sb, and As reflect the 

presence of cinnabar, stibnite, and realgar, which are 

common in these mineral systems. The presence of "a small 

amount of silver" was previously reported in the Donlin 

Creek area by Cady and others (1955); however, silver has 

not been previously reported from the other mercuryantimony deposits in this study. Appreciable silver was 

found in mineralized vein samples from Snow Gulch 

(13-38 ppm), Fisher Dome (7 ppm), and Kagati Lake (2-3 

ppm) (table 1 ). Silver concentrations of 50-200 ppm were 

also found in stibnite separates from Fisher Dome and Snow 

Gulch (table 2). The association of anomalous Au, Ag, and 

Sb in mineralized samples from these deposits is suggestive 

of silver association with gold in electrum, or silver 

enrichment in stibnite. 

SIGNIFICANCE OF GOLD ASSOCIATED WITH 

MERCURY-ANTIMONY DEPOSITS 

Our results are important because they are the first 

gold anomalies reported for many of the cinnabar and 

stibnite deposits in ihe Kuskokwim River region. The 

04 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

Ag 

2 

1 

.5N 

.5N 

.5N 

50 

50 

200 

150 

Sb 

1,000 

lOON 

300 

100 

300 

10,0000 

10,0000 

10,0000 

10,0000 

As 

10,0000 

1,000 

200 

200N 

200N 

200N 

200L 

1 0~000 

10,0000 

discovery of these anomalies indicates that regional 

exploration programs should include parts per billion level 

determinations for gold, such as those obtained using AA or 

ICP-AES techniques. The low-level gold determinations 

should be useful for identifying epithermal mercuryantimony systems that are also favorable for precious-metal 

resources. 

These findings indicate that gold may be a significant, 

yet unrecognized, byproduct in these mercury-antimony 

deposits. The data shown in table 1 indicate that gold was 

deposited along with the other trace metals. However, the 

geochemical studies presented here were conducted on grab 

samples of high-grade mercury and antimony ore, and 

additional studies are needed to more precisely determine 

gold ore grades and the lateral and vertical extent of gold. 

Although the gold content in samples of some of these 

deposits is high, mineralized veins are commonly small and 

discontinuous, and thus ore tonnages are generally low. 

Perhaps more importantly, our results suggest that 

more gold may be found in deeper environments below 

these deposits. The presence of such concealed gold 

deposits is dependent on a number of factors including the 

thermal gradient of the hydrothermal systems and the lateral 

and vertical extent of veining. 

The light stable isotope (Goldfarb and others, this 

volume) and fluid inclusion (Roedder, 1963; Miller and 

others, 1989) compositions of the ore fluids from these 

epithermal mercury-antimony deposits are compatible with 

an origin from dehydration of surrounding sedimentary 

rocks by igneous activity or burial metamorphism. Fluid 

inclusion data from the Red Devil deposit indicate that the 

Kuskokwim deposits formed at temperatures of 

approximately 150-210 °C (Miller and others, 1989). Such 

low ore-fluid temperatures commonly hinder the 

mobilization of gold because the solubility of gold bisulfide 

decreases sharply between 300 and 200 °C (Seward, 1984 ). 

Therefore, assuming that the Kuskokwim ore fluids were 

hot enough at some depth to have carried significant gold 
and the gold was transported as bisulfide complex, much of 

the gold would have been precipitated from the fluids 

before they reached the low-temperature, near-surface 

environment. 

The presence of dickite and hematite at many of the 

Kuskokwim deposits indicates acidification and oxidation 

of ore fluids near the surface. Acidic and oxidizing 

conditions further limit gold bisulfide complex stability 

(Seward, 1984). Significant gold deposition is more 

probable under more reducing and neutral pH fluid 

conditions. Such physicochemical conditions are more 

common below the near-surface environment. 

Higher gold concentrations are more likely at deeper 

levels of these hydrothermal systems, where fluid 

temperatures were 250 °C or more. Without additional 

subsurface data it is not possible to determine whether fluid 

flow and fluid temperatures were adequate to form gold-rich 

zones below any of the Kuskokwim epithermal systems. 

However, assuming similar ore fluid oxygen isotopic 

composition for all of these Kuskokwim deposits, the 

relatively light o180 value for quartz from Fisher Dome 

(Goldfarb and others, this volume) suggests that stibniterich quartz was deposited under higher temperature 

conditions than those of the other, more cinnabar-rich quartz 

veins within the Kuskokwim region. This interpretation is 

also supported by the slighter higher formation temperature 

of stibnite versus that of cinnabar reported in many hydrothermal ore deposits (Buchanan, 1981). Thus, the stibniterich Fisher Dome mineral occurrence could have formed 

closer to a gold-rich zone than many of the other deposits. 

The relatively large hydrothermal system at Red Devil 

could be representative, however, of the upper levels of a 

concealed gold system and may be a more viable target 

because of its size. 

In other Hg-Sb-Au systems, antimony commonly 

occupies a position intermediate to that of mercury systems 

(above) and gold (below). In the Marlborough schists of 

New Zealand, vein systems are stibnite dominant in the near 

surface and gold bearing without stibnite at depths of 400 m 

(Pirajno, 1979). Similarly, quartz veins evolve from 

antimony rich to gold rich with increasing depth at Carbon 

Hill in the southern Yukon Territory (Craig Hart, Aurum 

Consultants, written commun., 1989). Economic 

concentrations of gold in the mercury-rich hot spring 

deposits at McLaughlin and Wilbur Springs in northern 

California suggest telescoping of mercury- and gold-rich 

parts of these deposit types. In many large antimony-bearing 

districts, such as those in the Iberian Peninsula of southern 

Europe (Gumiel and Arribas, 1987), stibnite is found in 

simple quartz veins, as well as in veins containing cinnabar 

or gold. At Red Devil, there is a transition from cinnabar 

without stibnite near the surface, to both phases at 

intermediate depths, and to stibnite without cinnabar at 

deepest levels (about 200 m). Perhaps the Kuskokwim 

deposits represent surface expressions of deeper, more goldrich deposits. 

SUMMARY 

Anomalous gold concentrations in several epithermal 

mercury-antimony deposits in the Kuskokwim River region 

of southwestern Alaska are the first reported for many of 

these deposits. These gold anomalies indicate the potential 

for byproduct gold in some of these deposits. Although 

many of the gold concentrations associated with these 

deposits in surface exposures are somewhat low, the gold 

anomalies may target more significant gold deposits below 

one or more of these mercury-antimony systems. Our results 

suggest that low-level gold analyses at the parts per billion 

level should be carried out during regional programs for 

gold exploration. 

REFERENCES CITED 

Buchanan, L.J ., 1981, Precious metal deposits associated with 

volcanic environments in the southwest, in Dickinson, 

W.R., and Payne, W.D., eds., Relations of tectonics to ore 

deposits in the Southern Cordillera: Arizona Geological 

Society Digest 14, p. 237-262. 

Cady, W.M., Wallace, R.E., Hoare, J.M., and Webber, E.J., 1955, 

The central Kuskokwim region, Alaska: U.S. Geological 

Survey Professional Paper 268, 132 p. 

Gray, J.E., Detra, D.E., Hill, R.H., Slaughter, K.E., and Sutley, 

S.J., 1990, Geochemical data and sample locality maps for 

stream-sediment and heavy-mineral-concentrate samples, 

and mineralogical data of nonmagnetic, heavy-mineralconcentrate samples, collected near five cinnabar-stibnite 

mineral occurrences in the Kuskokwim River region, 

southwestern Alaska: U.S. Geological Survey Open-File 

Report 90-299A. 

Gumiel, P., and Arribas, A., 1987, Antimony deposits in the 

Iberian Peninsula: Economic Geology, v. 82, p. 1453-1463. 

Hoare, J.M., and Coonrad, W.L., 1959, Geology of the Bethel 

quadrangle, Alaska: U.S. Geological Survey Miscellaneous 

Geological Investigations Series Map 1-285, scale 

1:250,000. 

McGimsey, R.G., Miller, M.L., and Arbogast, B.F., 1988, Paper 

version of analytical results, and sample locality map for 

rock samples from the lditarod quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 88-421-A, 110 p., 

1 plate. 

Miller, M.L., Belkin, H.E., Blodgett, R.B., Bundtzen, T.K., Cady, 

J.W., Goldfarb, R.J., Gray, J.E., McGimsey, R.G., and 

Simpson, Shirley, 1989, Pre-field study and mineral 

Gold Associated with Cinnabar· and Stibnite-Bearing Deposits 05 
resource assessment of the Sleetmute quadrangle, 

southwestern Alaska: U.S. Geological Survey Open-File 

Report 89-363, 115 p., 3 plates. 

Pirajno, Franco, 1979, Geology, geochemistry, and mineralization 

of the Endeavour Inlet antimony-gold prospect, Marlborough Sounds, New Zealand: New Zealand Journal of 

Geology and Geophysics, v. 22, p. 227-237. 

Roedder, Edwin, 1963, Studies of fluid inclusions 11-Freezing 

data and their interpretation: Economic Geology, v. 58, 

p. 167-211. 

Rutledge, F.A., 1950, Investigation of mercury deposits, Cinnabar 

Creek area, Georgetown and Aniak districts, Kuskokwim 

region, southwestern Alaska: U.S. Bureau Mines Report of 

Investigation 4719, 9 p. 

06 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

Sainsbury, C.L., and MacKevett, E.M., Jr., 1960, Structural control 

in five quicksilver deposits in southwestern Alaska, in 

Geological Survey Research 1960: U.S. Geological Survey 

Professional Paper 40~B. p. B35-B38. 

___ 1965, Quicksilver deposits of southwestern Alaska: U.S. 

Geological Survey Bulletin 1187, 89 p. 

Seward, T.M., 1984, The transport and deposition of gold in 

hydrothermal systems, in Gold 82-The geology, geochemistry, and genesis of gold deposits: Geological Society 

of Zimbabwe Special Publication 1, p. 165-181. 

Webber, B.S., Bjorklund, S.C., Rutledge, F.A., Thomas, B.l., and 

Wright, W.S., 1947, Mercury deposits of southwestern 

Alaska: U.S. Bureau of Mines Report oflnvestigation 4065, 

57 p. 
Chapter E 

Stable Isotope Systematics of 

Epithermal Mercury-Antimony 

Mineralization, Southwestern Alaska 

By RICHARD J. GOLDFARB, JOHN E. GRAY, 

WILLIAM J. PICKTHORN, CAROL A. GENT, 

and BARRETT A. CIEUTAT 

U.S. GEOLOGICAL SURVEY BULLETIN 1950 

GEOCHEMICAL STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1989 
CONTENTS 

Abstract El 

Introduction El 

Geological setting and character of the Kuskokwim mercury-antimony deposits E2 

Stable isotope studies E3 

Oxygen isotopes E3 

Hydrogen isotopes E5 

Sulfur isotopes E5 

Stable isotope implications for ore genesis E6 

Origin of the Kuskokwim deposits E7 

References cited E8 

FIGURES 

1. Map showing location of cinnabar-and stibnite-bearing deposits, Kuskokwim 

Mountains, southwestern Alaska El 

2. Plot of OD versus o180 for ore fluids from the Kuskokwim region and for other 

studied hydrothermal systems E4 

TABLE 

1. Stable isotope data for ore-related minerals from mercury-antimony deposits, 

southwestern Alaska E3 
Stable Isotope Systematics of Epithermal Mercury-Antimony 

Mineralization, Southwestern Alaska 

By Richard J. Goldfarb, John E. Gray, William J. Pickthorn, Carol A. Gent, and Barrett A. Cieutat 

Abstract 

Epithermal mercury-antimony lode deposits and occurrences are 

in rocks of the Kuskokwim Group, Gemuk Group, and Holitna Group of 

southwestern Alaska. Vein quartz, probably coeval with much of the 

sulfide deposition, generally has 8180 compositions of 23-30°/oo (per mil) 

indicative of ore-forming fluids of 11-18°/oo. Hydrothermal dickite from the 

Red Devil deposit has a measured oD value of -127°/oo, whereas fluid 

inclusion waters from host quartz are at least 23°/oo lighter. The 834S 

values for cinnabar, stibnite, realgar, and orpiment for most of the 

deposits range from -3.0 to --6.7°/oo. 

Oxygen isotope data are most compatible with oxygen in the ore 

fluids being derived from dehydration of sedimentary rocks due to simple 

burial metamorphism or localized igneous activity. The relatively 

deuterium-depleted ore fluids suggest that much of the hydrogen was 

derived from breakdown of organic material. The sulfur in these deposits 

was generally derived from a similar organic source in the sedimentary 

rocks. Enrichment of sulfide minerals in 32S at Mountain Top and Snow 

Gulch suggests that a more local sulfur reservoir may have contributed 

to these hydrothermal systems. 

INTRODUCTION 

Cinnabar- and stibnite-bearing quartz-filled fractures 

are present at many locations throughout the Kuskokwim 

Mountains region of southwestern Alaska (fig. 1). The 

veinlets are within the Cambrian to Devonian Holitna 

Group, the Triassic and Lower Cretaceous Gemuk Group, 

and the Cretaceous Kuskokwim Group. Many of the 

mineralized fractures are within or adjacent to silicacarbonate-altered mafic dikes that cut through these 

sedimentary rocks. Red Devil, the largest of these epithermal systems, has produced about 35,000 flasks of 

mercury since World War II (Miller and others, 1989). 

Detailed descriptions of the geology, mineralogy, and 

structural controls on mineralization for the more significant 

epithermal deposits and occurrences are given by Sainsbury 

and MacKevett ( 1965). 

This paper presents the results of a stable isotope 

investigation of this group of mineral deposits and 

occurrences. These data provide new information that have 

50 100 KILOMETERS 

60' 

EXPLANATION 

DEPOSITS AND OCCURRENCES GEOLOGY 

1 Cinnabar Creek 6 Mountain Top FW Farewell terrane 

2 DeCourcy 7 Rainy Creek TG Togiak terrane 

3 Fairview 8 Red Devil GN Goodnews terrane 

4 Fisher Dome 9 Snow Gulch NY Nyac terrane 

5 Kagati Lake 1 0 White Mountain Kk Kuskokwim Group 

Figure 1. Cinnabar- and stibnite-bearing deposits in the Kuskokwim 

Mountains region, southwestern Alaska. Geology modified from Decker 

and others (Alaska Division of Geological and Geophysical Surveys, 

written commun., 1989). 

significant implications for development of a genetic model. 

Hydrogen and oxygen isotope data constrain possible sources for the ore fluids and provide information regarding 

processes of mineral precipitation. Sulfur isotope data aid in 

defining physiochemical conditions of ore deposition and in 

Epithermal Mercury-Antimony Mineralization, Southwestern Alaska E1 
identifying sources for the sulfur within the hydrothermal 

systems. These new isotopic data, when applied to the 

conceptual ore deposit model for cinnabar- and stibnitebearing mineral occurrences within southwestern Alaska, 

may improve our ability to predict favorable exploration 

target areas within the Kuskokwim Mountains region. 

Acknowledgments.-This paper benefited from 

critical reviews by John Galloway, Albert Hofstra, Tom 

Nash, and Ian Ridley. Marti Miller kindly provided samples 

of mafic dikes, and Tom Frost contributed samples from 

Kagati Lake and Fisher Dome. 

GEOLOGICAL SETTING AND CHARACTER OF 

THE KUSKOKWIM MERCURY-ANTIMONY 

DEPOSITS 

Miller and others (1989) and Decker and others 

(Alaska Division of Geological and Geophysical Surveys, 

written commun., 1989) have provided the most recent 

detailed descriptions of the rocks of southwestern Alaska 

that host cinnabar and stibnite mineralization. The 

Cambrian to Devonian Holitna Group, forming part of what 

presently is referred to as the Farewell tectonostratigraphic 

terrane, consists dominantly of partly dolomitized 

limestone. The Triassic and Lower Cretaceous Gemuk 

Group, accreted to the Alaskan margin as part of the Togiak 

terrane in late Early Cretaceous time, is comprised of 

massive siltstone and lesser chert and volcanic rocks. 

Cretaceous marine turbidite, forming the Kuskokwim 

Group, filled an extensional basin between the above 

Farewell and Togiak accretionary terranes. Widespread 

igneous activity occurred during the Late Cretaceous and 

early Tertiary in southwestern Alaska, subsequent to terrane 

accretion. Volcano-plutonic complexes of varied 

compositiOn; rhyolite sheets, dikes, and sills; and 

intermediate to mafic dikes and sills are scattered 

throughout much of the region. 

The majority of the known cinnabar (±-stibnite)-

bearing deposits and occurrences are within rocks of the 

Kuskokwim Group. Ore-bearing veinlets at Red Devil, 

DeCourcy, and Mountain Top are spatially associated with 

altered mafic dikes. Cady and others (1955) and Sainsbury 

and MacKevett ( 1965) emphasized that mineralized rocks 

are concentrated at the intersection of the dikes and 

bedding-plane faults. Also within the Kuskokwim Group, 

mineralized rocks at Fairview and Rhyolite crosscut rhyolite 

porphyry dikes and sills. Stibnite-bearing quartz veins, 

lacking cinnabar, cut a granitic stock and rhyolite dikes at 

Fisher Dome and Snow Gulch, respectively. At the Rainy 

Creek occurrence, cinnabar- and realgar-bearing quartz 

veinlets fill fractures in a more competent graywacke unit 

within interbedded graywacke and shale of the Kuskokwim 

Group. 

E2 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

Mineralized rocks are also hosted by the Gemuk and 

Holitna Groups. Deposits at Red Top and Cicnabar Creek 

are hosted in siltstone-dominant sequences of the Gemuk 

and localized in the more competent graywacke. Quartz 

veins at Kagati Lake that contain cinnabar, stibnite, and 

realgar (Sainsbury and MacKevett, 1965) are hosted in 

quartz monzonite and granodiorite that intrude Gemuk 

sedimentary rocks. The White Mountain deposit is the only 

mercury-antimony epithermal system that is known to be 

hosted by carbonate units of the Holitna Group. It may be 

significant, however, that this deposit is only a few 

kilometers southeast of the clastic rocks of the Kuskokwim 

Group. In addition, clastic rocks of unknown affinity, but 

perhaps belonging to the Kuskokwim Group, crop out much 

closer to White Mountain (Tom Bundtzen, Alaska Division 

of Geological and Geophysical Surveys, oral commun., 

1989). 

Cinnabar-bearing quartz veinlets, disseminated 

cinnabar grains, and cinnabar-quartz cement of brecciated 

wall rock were found at all deposits and occurrences shown 

on figure 1 except Fisher Dome. Stibnite is closely 

associated with the cinnabar at about two-thirds of these. At 

Fisher Dome, quartz-bearing fractures contain stibnite but 

not cinnabar. Minor pyrite, realgar, orpiment, hematite, and 

limonite are in a few systems. Samples of high-grade 

mercury-antimony ore from some of the deposits and 

occurrences contain as much as 6.9 ppm Au (Gray and 

others, this volume). Free mercury is associated with much 

of the cinnabar-rich ore at the Cinnabar Creek deposit. 

Quartz and dolomite are the main gangue minerals in 

all systems. Petrographic examination of polished thin 

sections from a number of the deposits and occurrences 

indicates that vein quartz and much of the cinnabar are 

paragenetica11y coeval. Hydrothermal dickite is also 

common at many of the occurrences. Sainsbury and MacKevett (1965) noted that dickite formed prior to the sulfide 

minerals at some occurrences and subsequent to the ore 

minerals at other occurrences. Most likely, the dickite 

represents an ore-stage alteration phase. Calcite veinlets are 

common in a number of the occurrences but probably 

postdate precipitation of sulfide minerals, quartz, dolomite, 

and dickite. 

A limited amount of fluid inclusion data has been 

published for quartz and cinnabar samples from the Red 

Devil deposit. Roedder (1963) described primary threephase C02-rich fluid inclusions in quartz from Red Devil. 

Melting of clathrate compounds at 11.1 °C in these 

inclusions suggests that hydrocarbons are present in the 

vein-forming fluids. Roedder described evidence for fluid 

immiscibility and was the first to point out that these high 

gas contents at Red Devil are uncharacteristic of shallow 

epithermal systems. Measurements by Belkin (in Miller and 

others, 1989) show homogenization temperatures of 158-

164 °C for fluid inclusions in cinnabar and 169-210 °C for 

those in cinnabar-bearing quartz. Ice-melting data suggest 
Table 1. Stable isotope data for ore-related minerals from epithermal mercury-antimony deposits, southwestern 

Alaska 

[All isotope data in standard per mil notation. Abbreviations: c, cinnabar; d, dickite; fi, fluid inclusion waters; o, orpiment; r, realgar; s, 

stibnite] 

Deposit Regional host unit Host I ithology o 18o (quartz) oo 

Red Devil ............... Kuskokwim Group ...... Clastic rocks, mafic dike .............. 24.4-26.41 -152(fi)1 -3.7(c) 

26.2-27.42 

19.1 

-191(fi)2 

-127(d) 

-4.2(s) 

Fairview ................. Kuskokwim Group ...... Rhyolite si11 ............................. 24.6 -3.4(c) 

-3.7(s) 

DeCourcy ............... Kuskokwim Group ...... Clastic rocks, mafic dike .............. 29.3-29.5 -4.5(c) 

-4.0(s) 

Mountain Top .......... Kuskokwim Group ...... Clastic rocks, mafic dike ....................................................... -16.5(c) 

Snow Gulch ............. Kuskokwim Group ...... Rhyolite dikes, clastic rocks ......... 24.5 -23.2(s) 

-25.0(s) 

Fisher Dome ............ Kuskokwim Group ...... Rhyolite .................................. 14.6 -6.2(s) 

Rainy Creek ............ Kuskokwim Group ...... Clastic rocks ............................. 24. 6 -6.7 (r) 

White Mountain ....... Holitna Group ........... Carbonate rocks ................................................................... +6 .0( c) 

Cinnabar Creek ........ GemukGroup ............ Clastic rocks ............................. 22.8 -5.2(c) 

Kagati ................... GemukGroup ............ Granitic stock ........................... 12.6 -3.0(o) 1 For cinnabar-rich quartz. 

2For stibnite-rich quartz. 

that inclusions within both minerals have a salinity of about 

3. 7 equivalent weight percent NaCl. Trapping pressures 

estimated by Belkin to be between 150 and 200 bars 

indicate depths of vein formation of at least 500-700 m. 

STABLE ISOTOPE STUDIES 

In this study we measured oxygen isotope 

compositions of quartz, dickite, and mafic dikes; hydrogen 

isotope compositions of dickite and fluid inclusion waters; 

and sulfur isotope compositions of sulfide minerals. Standard techniques for extraction and analysis were used as 

described by Clayton and Mayeda (1963), Craig (1961), 

Fritz and others (1974), Godfrey (1962), Grinenko (1962), 

Savin and Epstein (1970), and Taylor and Epstein (1962). 

Isotope data are reported in standard 8 notation relative to 

the Vienna SMOW standard for oxygen and hydrogen and 

the Canyon Diablo triolite (CDT) standard for sulfur. The 

standard error of each analysis is approximately ±0.2°/oo for 

sulfur and oxygen and ±1.0°/oo for hydrogen. Results from 

analyses are summarized in table 1. 

Oxygen Isotopes 

The 8180 values of cinnabar- and stibnite-bearing 

quartz are among the highest values measured from any 

mineralized system in western North America. All of the 

quartz values are between 23°/oo and 29.5°/oo, except for a 

value of 14.6°/oo for stibnite-bearing quartz from Fisher 

Dome and a value of 12.6°/oo for realgar-orpiment-bearing 

quartz collected from Kagati (table 1). The quartz-water 

fractionation equation of Clayton and others (1972) 

indicates a fractionation of 11. 7%o at 200°C. Fluid inclusion 

homogenization temperatures for quartz at Red Devil are 

about 200 °C, and C02 density data suggest that little, if 

any, correction for pressure is required for estimating fluid 

trapping temperatures (Miller and others, 1989). Therefore, 

in most of these systems the ore fluids are calculated to have 

had 8180 values of about 11-18<>/oo. 

A 8180 value of 19.1°/oo for dickite from Red Devil 

indicates a fluid composition of approximately 14°/oo, 

assuming precipitation at 200 oc and using the kaolinitewater fractionation equation of Kulla and Anderson ( 1978). 

MacKevett and Berg (1963) pointed out, however, that the 

dickite at Red Devil most likely postdates sulfide 

deposition. If the dickite formed at 150 °C, a temperature 

just below that of 160 oc estimated for cinnabar deposition 

(Miller and others, 1989), it would have done so from a 

fluid having a 8180 composition of 11.5<>/oo. The 8180 fluid 

values calculated for the dickite are similar to those 

calculated for cinnabar-bearing quartz; thus, both silicate 

phases probably were precipitated from an isotopically 

similar fluid. 

The relative uniformity of the data from all systems, 

excluding Fisher Dome and Kagati Lake, hosted within 

Gemuk and Kuskokwim sedimentary rocks, rhyolite, 

monzonite, and mafic dikes suggests a fluid-dominated ore 

system. The isotopic composition of such a fluid is 

independent of local host rock control (Kerrich, 1987). The 

data are not compatible with a fluid derived from circulation 

of meteoric waters. Meteoric water in the Kuskokwim 

region has a 8180 value of about -200/oo and a shift of more 

than 30°/oo would be required to produce the estimated ore 

fluid range (fig. 2). A calculated meteoric water evolution 

path shows that for a fluid that has an initial 8180 value of 

-200/oo at 200 °C and is migrating through pelitic rocks, 

Epithermal Mercury-Antimony Mineralization, Southwestern Alaska E3 
oxygen shifts under conditions of lowest water to rock ratios 

will result in final values of no greater than 8°/oo (fig. 2). 

Temperatures of at least 400-500 °C are required, under 

conditions of very low water to rock ratios, to produce 

meteoric fluids that have shifted to the heavy () 180 values 

( 11-18°/oo) found in these deposits. 

The oxygen isotope compositions of a silicacarbonate-altered dike and a relatively unaltered mafic dike 

collected near the DeCourcy deposit have ()180 values of 

14.6<>/oo and 11.5°/oo, respectively. Using the complete 

version of the equation of Criss and Taylor (1986) for water 

to rock ratios under closed system conditions, assuming the 

intial fluid near DeCourcy to have a 0180 value of 17.7°/oo, 

and using a quartz-water fractionation of 11.7°/oo at 200 °C, 

calculated water to rock values are approximately 0.1. 

Because the relatively unaltered dike does contains minor 

amounts of secondary quartz and calcite (Marti Miller, U.S. 

Geological Survey, written commun., 1989), the measured 

0180 value may be greater than the true magmatic value. If 

that is the case, then the water to rock ratio of 0.1 must be 

regarded as a minimum estimate. Examination of figure 2 

indicates that even for a ratio as low as 0.1, oxygen isotope 

shifts from meteoric water values to calculated ore fluid 

values are unattainable. 

Ore fluid 0180 values are most compatible with the 

metamorphic water field, although host rocks are relatively 

unmetamorphosed (Marti Miller, oral commun., 1989). 

Therefore, a fluid produced during metamorphic 

dehydration would have been from deeper within the 

0 

--50 0 

~ 0 

-

c 

"'() 

-100 

EXPLANATION 

X Meteoric water composition 

for southwestern Alaska 

•1 Water:rock ratios 

-15 -10 -5 

Kuskokwim basin, where burial metamorphism was 

ongoing or where abnormal geothermal gradients correlate 

with increased igneous activity. Such a scenario is the most 

reasonable explanation for the oxygen data. Ore fluid values 

are significantly heavier than normal magmatic values, 

which commonly are 5.5-1 0°/oo. There also is no consistent 

spatial association between the epithermal systems and a 

specific igneous rock type. Thus, if ore-forming fluids were 

equilibrated with a specific magma, resulting igneous rocks 

must be unexposed below the different epithermal lodes and 

would be among some of the world's most 180-enriched 

igneous rocks. 

The () 180 values of 14.6°/oo for stibnite-bearing quartz 

from Fisher Dome and 12.6°/oo for realgar-orpiment-bearing 

quartz from Kagati Lake are distinctly different from those 

of the other vein systems. These values are more compatible 

with values from mesothermal gold-bearing vein systems 

(Kerrich, 1987) than with those of the other vein systems 

throughout the Kuskokwim region. The relatively light 

value for the Fisher Dome quartz could still reflect a fluid 

derived from a source similar in origin to the other sulfidebearing veins in the Kuskokwim region. Vein formation at 

temperatures higher than those of the cinnabar-bearing 

epithermal vein systems would reduce ~ 180quanz-water and 

precipitate isotopically lighter quartz. Relatively high 

homogenization temperatures of fluid inclusions in Kagati 

Lake quartz, between 280 and 355 °C, and the fact that 

sulfide minerals were only found coating fractures in 

massive quartz suggest that sulfide mineralization is 

I Kuskokwim I 

ore fluids 

5 10 15 

Figure 2. Plot of oD versus o180 for ore fluids from the Kuskokwim region and for other studied hydrothermal systems. A calculated fluid 

evolution path shows that a meteoric fluid, in southwestern Alaska, assumed to be at 200 oc and having an initial 6180 composition of 

-200/oo, cannot be shifted to values of more than about +80/oo even if water to rock ratios are as low as 0.01. (Calculations assume 18

0~= 160/oo and oD~= -600/oo and use plagioclase feldspar-H20 and chlorite-H20 fractionation factors for oxygen and hydrogen ~ R-w• 

respectively.) A crustal source is thus required for the ore fluids. The heavy oxygen and light hydrogen data for the Kuskokwim deposits 

are most compatible with fluid derivation from organic-rich sedimentary rocks containing an abundance of detrital chert grains. 

E4 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 
younger than quartz deposition and that the quartz analyzed 

at Kagati Lake may be unrelated to mineralization. It is 

uncertain whether the sulfide minerals at Kagati Lake 

formed from different, perhaps magmatic, fluids or whether 

they precipitated from later circulating fluids similar to 

those that deposited the epithermal mineralization 

elsewhere in southwestern Alaska. 

The ore-bearing quartz at the Red Devil deposit 

exhibits a vertical zonation in metal content: cinnabar-rich 

ore is nearest the surface and stibnite-rich ore is at a depth 

of 180m (Miller and others, 1989). Our isotope data suggest 

that a simple decreasing temperature gradient was not the 

cause for the shift from an antimony-dominant zone to a 

shallower mercury-dominant zone at Red Devil. 

Compositions of 0180 of 24.4-26.4°/oo were determined for 

cinnabar-rich quartz and 26.6-27.4°/oo for stibnite-rich 

quartz. Because the fractionation between quartz and water 

is inversely correlated with temperature, silica deposition 

simply by declining temperature would have resulted in 

isotopically heavier quartz hosting the mercury-rich ore 

nearer the surface. 

Boiling or fluid immiscibility is a more plausible 

explanation for the observed zoning pattern at Red Devil. 

Roedder (1963) reported evidence from fluid inclusion 

studies for the occurrence of such immiscibility in cinnabarbearing quartz from Red Devil. It is, therefore, reasonable to 

hypothesize that mercury separated from the antimony 

within the ore fluids and was transported to higher levels 

within the vapor phase. Due to differences in vapor 

pressures for the different isotopes, any H20 within the 

vapor phase must be enriched in 160. This is in agreement 

with the relatively 180 depleted, cinnabar-bearing quartz at 

the top of the system. 

Hydrogen Isotopes 

Hydrogen isotope data from dickite at the Red Devil 

deposit suggest the presence of organic water in the ore 

fluids. Dickite is closely associated with the ore minerals at 

Red Devil and has a oD value of -127%o. The most recent 

HID fractionation relationships for hydrous minerals and 

water (Kyser, 1987, p. 51) indicate no fractionation between 

dickite and water at 200 °C. At 160 °C, the approximate 

homogenization temperature of fluid inclusions in Red 

Devil cinnabar (Miller and others, 1989), fractionation data 

show that the clay would have formed from a fluid having 

a oD value of -120o/oo. The dickite-forming fluid was, 

therefore, unquestionably isotopically much lighter than 

typical magmatic or metamorphic waters. Hydrogen isotope 

composition contours in Taylor (1979) suggest that 

meteoric surface waters should have oD values of about 

-150°/oo across much of the Kuskokwim region, a 

composition 30°/oo lighter than that of the calculated dickiteforming fluid. Because the previously described oxygen 

isotope data preclude the predominance of meteoric waters 

within the ore fluids, the oD value is best interpreted as 

representative of a fluid having a strong organic water 

component. Such a deuterium-depleted water, as described 

by Sheppard (1986), is a likely product from dehydration of 

or exchange with organic material in rocks of the Kuskokwim Group. 

Fluid inclusion waters extracted from cinnabar- and 

stibnite-bearing quartz collected at Red Devil are isotopically much lighter than the dickite-forming water. They 

have oD values of -152°/oo and -191<>/oo, respectively, as 

compared with the -120o/oo value estimated for the dickite. 

Inclusion waters from the cinnabar-hosted quartz are 

assumed to be dominantly meteoric in origin. The reason for 

the extremely negative value of the inclusion water from 

stibnite-bearing quartz is uncertain. If any fractionation of 

hydrogen isotopes had occurred during the previously 

described boiling at Red Devil, then the mercurytransporting vapor would contain the more reduced gases 

and the lighter hydrogen. In contrast to what was actually 

observed, heavier deuterium, if fractionated, woilld have 

remained behind in the antimony-bearing liquid. The 

assumption that the fluid inclusion waters accurately show 

ore fluid oD compositions is at best tenuous. Extracted fluid 

inclusion waters are likely to combine crustal fluids trapped 

in many different generations and may result in isotopic 

values that substantially differ from the true ore stage values 

(Pickthom and others, 1987). 

Sulfur Isotopes 

The sulfur isotope compositions of sulfide mineral 

phases are extremely consistent for most epithermal systems 

from southwestern Alaska. Cinnabar, stibnite, realgar, and 

orpiment o34S values generally cluster between -3<>/oo and 

-7°/oo (table 1), suggestive of a similar sulfur source for 

most deposits and occurrences. This source is likely to be 

either disseminated pyrite and (or) organic material 

throughout pelitic sedimentary rocks of the Kuskokwim 

region. Using known cinnabar-H2S and stibnite-H2S 

fractionation relationships (Field and Fifarek, 1985) and 

assuming sulfide precipitation at 200 °C, the o34S 

composition of the ore fluids was about 0°/oo to -3<>/oo. This 

estimate assumes that reduced sulfur is equivalent to total 

sulfur within the ore fluids. This assumption may not be true 

for all deposits, however, because hematite probably was 

coeval with the sulfide minerals in some systems (Sainsbury 

and MacKevett, 1965), indicative of the presence of 

oxidized sulfur species. 

Sulfur data from three of the deposits are noticeably 

anomalous. The o34S composition of ore fluids at White 

Mountain may originally have been equivalent to those 

from the other epithermal systems, but sulfur ratios likely 

shifted during changing physiochemical conditions. 

Cinnabar at the carbonate-hosted White Mountain deposit 

has a o34S value of +6.0o/oo. The presence of ore-related 

Epithermal Mercury-Antimony Mineralization, Southwestern Alaska E5 
dickite at White Mountain, as well as at many of the other 

deposits, suggests that the ore fluids were acidic and pH 

values were no greater than about 4.0. The interaction 

between such fluids, perhaps originating in nearby units of 

the Kuskokwim Group, and carbonate rocks of the Holitna 

Group would rapidly shift fluid pH to more alkaline values. 

As pointed out by Ohmoto (1972), the dissociation of Hz 

and sulfur that accompanies the increase in pH would cause 

an increase in o34S of the sulfide minerals relative to the 

total sulfur in the system. It is, therefore, not surprising that 

the only deposit where Sainsbury and MacKevett ( 1965) 

described cinnabar replacing dickite was at White 

Mountain. The dickite was deposited from an originally 

acidic solution, and the isotopically heavy cinnabar could 

have been deposited following a subsequent shift in fluid 

pH. 

Extremely light o34S values characterize cinnabar 

from the Mountain Top and stibnite from the Snow Gulch 

deposits. Such light values are commonly produced by fluid 

interaction with relatively oxidizing country rocks. Such 

interaction increases SO JHzS ratios and the 3zs 

concentration of subsequently precipitated sulfide minerals 

because the lighter isotope preferentially is concentrated in 

the reduced sulfur species. But, both Mountain Top and 

Snow Gulch probably are within areas of rocks typical of 

the Kuskokwim Group, although rhyolite dikes hosting part 

of the latter occurrence are exceptionally silica rich (Cady 

and others, 1955). Mountain Top, however, is the one 

epithermal system within the Kuskokwim region known to 

contain both liquid and solid hydrocarbons (Sorg and 

Estlund, 1972). The sulfur at Mountain Top may therefore 

have been derived from a more local source, perhaps a 

relatively light petroleum reservoir, than the other Kuskokwim deposits. The o34S value of -23.2°/oo for stibnite at 

Snow Gulch is much lighter than expected for sulfur 

contributed directly from a specific organic reservoir. The 

lack of cinnabar at Snow Gulch could indicate a preferential 

loss of mercury and HzS during boiling off of a vapor phase. 

Such oxidation of the ore fluids is the most likely scenario 

for producing such 3zS-enriched stibnite. 

Both cinnabar and stibnite grains from the Red Devil, 

Fairview, and DeCourcey deposits were analyzed for o34S. 

Previously described fluid inclusion evidence from Roedder 

(1963) shows that boiling took place during ore deposition 

at Red Devil, and our sulfur data are in agreement with such 

a process. Oxidation of the liquid by loss of Hz and HzS 

from the ore fluid into the vapor phase during boiling would 

cause a 

34S depletion in any sulfide phases precipitated 

directly from the liquid. Therefore, the stibnite at Red Devil 

has a o34S value of -4.2°/oo, whereas the cinnabar, mostly 

deposited from the vapor, has a value of -3.7<>/oo. A similar 

situation is possible for the Fairview deposit (table 1 ). At 

Decourcy, isotopically lighter cinnabar could be interpreted 

to indicate a simple temperature decrease rather than boiling 

as the dominant depositional mechanism. Precipitation of 

E6 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

stibnite at relatively higher temperatures would oxidize the 

ore fluids and precipitate isotopically lighter sulfur in 

subsequent cinnabar. Cady and others (1955) pointed out 

that much of the cinnabar within these epithermal systems 

was deposited subsequent to the stibnite. 

STABLE ISOTOPE IMPLICATIONS 

FOR ORE GENESIS 

The oxygen isotope data indicate that ore-forming 

fluids in the Kuskokwim region were different in origin 

from most other hydrothermal fluids responsible for Cenozoic epithermal mineralization in western North America. 

Although oxygen isotopic values of meteoric waters from 

the Basin and Range are similar to those of the Kuskokwim 

region, epithermal vein-forming fluids in the Kuskokwim 

are significantly enriched in 180 (fig. 2). Volcanic-hosted 

epithermal deposits within the Basin and Range formed 

from fluids having o180 compositions between -15°/oo and 

-6°/oo, and sedimentary-hosted gold deposits formed from 

fluids having compositions between -16°/oo and +6°/oo 

(Field and Fifarek, 1985). These results have been 

interpreted by most workers as suggestive of vein formation 

from meteoric fluids under conditions of varied water to 

rock ratios. It is hard to envision how, if a similar oreforming process occurred within the Kuskokwim region, all 

the ore fluids would be shifted by more than 30°/oo from the 

meteoric water line. Rather, oxygen compositions should 

show a wide distribution of o180 compositions between 

about -200/oo and +20°/oo. 

Heavy oxygen data for the mercury- and antimonybearing quartz from southwestern Alaska are more like 

those described for mesothermal gold-bearing systems from 

the western Cordillera (Kerrich, 1989). The o180 values for 

vein-forming fluids for many of these deposits are similar to 

those from the Kuskokwim (fig. 2). The higher temperature 

of vein formation for the Cordilleran fluids is reflected in 

the lighter ratios of the precipitated quartz. Nesbitt and 

others (1987) showed that for the Canadian Cordillera the 

cooling of an ore fluid having a 8180 value of 8-100/oo could 

have precipitated gold-bearing quartz (17 .5°/oo ), then 

stibnite-bearing quartz (21 °/oo), and lastly cinnabar-bearing 

quartz (29°/oo). 

Calculated 8180 values of 11 °/oo-18°/oo for oreforming fluids within the Kuskokwim region are only 

compatible with a fluid derived from dehydration of the 

sedimentary rocks. The ore fluids are slightly more enriched 

in 180 than most other vein-forming fluids also believed to 

have been produced during sediment devolatilization (Kerrich, 1989); however, the abundance of chert fragments and 

lesser limestone fragments in Kuskokwim graywacke (Cady 

and others, 1955) and the clays within Kuskokwim shale 

favor such an 180-enriched fluid. 

The origin of the oD composition of -120°/oo, 

believed to be that of the dickite-forming fluid at Red Devil, 
remains uncertain. The ratio is heavier than local meteoric 

water by about 3(}<>/oo, yet it is also much lighter than that 

expected for a fluid of metamorphic origin. Fluid mixing 

between an isotopically lighter meteoric fluid and a heavier 

metamorphic fluid is one possibility for the dickite value; 

however, the consistently heavy oxygen data for all the 

Kuskokwim region systems do not support the fluid mixing 

hypothesis. Another possibility is that extensive post-ore, 

low-temperature hydrogen exchange occurred between the 

hydrothermal dickite and near-surface meteoric waters. 

Although there are differing opinions, some experimental 

data suggest that such hydrogen isotopic exchanges 

occurred without any accompanying shifts in the 0180 

composition of clay minerals (Longstaffe, 1989). The most 

likely explanation for the light value at Red Devil is that it 

reflects a strong hydrogen contribution to the ore fluids 

from the breakdown of organic material within the 

sedimentary rocks. Sheppard ( 1986) pointed out that such 

organic waters can be strongly depleted in deuterium 

relative to more typical metamorphic fluids. 

The uniform sulfur composition of the epithermal 

deposits in such a large region (except at Mountain Top and 

Snow Gulch) suggests a common sedimentary rock source 

such as sulfur-bearing organic material within the shaley 

units of the Kuskokwim Group. Cady and others ( 1955) 

indicated that approximately one-third of the strata are very 

dark shales that contain relatively large concentrations of 

carbonaceous material. They described thin coaly seams 

and abundant plant remains within outcrops of the Kuskokwim Group at the mouth of the Holitna River, near Red 

Devil. Significant amounts of H2S will be generated during 

late diagenesis of this organic material as burial 

temperatures approach 200 °C (Frey, 1987). 

Occurrences at Rainy Creek and Kagati Lake both are 

within an area mostly underlain by the Gemuk Group, a 

sequence of rocks dominated by black siltstone. Sulfur 

derived from these rocks could have been added into the 

ore-forming fluids; however, sulfur values for orpiment at 

Kagati Lake and cinnabar at Cinnabar Creek are identical to 

those for most of the deposits hosted by rocks of the 

Kuskokwim Group. These two systems within the Gemuk 

Group are within a few kilometers of rocks of the Kuskokwim Group, and sulfur contributions from the latter cannot 

be ruled out. Also, as described above, the White Mountain 

deposit in the carbonate rocks of the Holitna Group is fairly 

close to outcrops of Kuskokwim clastic rocks. Therefore, 

we believe that organic material within the Kuskokwim 

Group, and perhaps within the Gemuk Group, was the 

source for the sulfur in all of the epithermal deposits and 

occurrences. 

ORIGIN OF THE KUSKOKWIM DEPOSITS 

Hot fluids were generated within the Kuskokwim 

basin during both diagenesis and subsequent burial metamorphism. The connate waters expelled from pore spaces 

during sediment compaction were unrelated to the epithermal mineralization. Such fluids would have had 0180 

values much closer to meteoric values than those observed 

for the epithermal systems. In addition, such fluids would 

have been relatively saline; fluid inclusion data from the 

Red Devil deposit suggest salinities of only about 3. 7 

weight percent NaCl equivalent (Miller and others, 1989). 

Very low grade metamorphic reactions, releasing H20-rich 

fluids, began at approximately 150-200 oc during burial 

metamorphism (Frey, 1987). Under a typical geothermal 

gradient of 30 °C/km, temperatures were in excess of 350 

°C in the deeper parts of the Kuskokwim basin, where 

sediment thickness was probably greater than 12 km 

(Decker and others, written commun., 1989). 

Much of the ore fluid responsible for the mineralized 

veins was derived from mineral dehydration reactions 

during very low grade metamorphism of rocks of the 

Kuskokwim Group; the sulfur and some of the hydrogen 

were derived from organic material, and mercury and 

antimony were likely mobilized from organic material and 

clays within shaley beds. If a 30 °C/km geothermal gradient 

is accurate for the Kuskokwim basin, very low grade 

metamorphism would have produced the ore-forming fluids 

at depths of about 5-6 km. Alternatively, the ore fluids 

could have been derived at shallower levels if anomalously 

high heat flow raised the normal gradient. Therefore, 

although ore fluids were derived by devolatilization at 

temperatures in excess of 200 °C, the epithermal systems 

still might show a spatial association with a specific igneous 

rock suite at depth. 

The epigenetic mercury-antimony-bearing lodes in 

southwestern Alaska are most similar to a group of mineral 

deposits that have been termed hot-spring mercury, silicacarbonate mercury, and simple antimony deposits (Bliss and 

Orris, 1986; Rytuba, 1986a, b). These deposits commonly 

are within unmetamorphosed to very low grade metamorphic rocks in basins adjacent to areas of active orogenic 

activity. Like many of the mesothermal vein systems in 

adjacent orogenic belts, these epithermal systems exhibit 

strong carbonate alteration and formed from fluids enriched 

in 180 relative to local meteoric water. 

Three-phase, C02-rich fluid inclusions and readily 

observable clathrate formation indicated to Roedder (1963) 

that the Red Devil deposit was atypical of many wellstudied epithermal vein systems. The relatively high gas 

content for some of the fluid inclusions studied by Roedder 

are more suggestive of ore-fluid compositions commonly 

reported for mesothermal gold vein deposits. White and 

others (1973) have long suggested that many of the springs 

discharging within the relatively unmetamorphosed rocks 

along the western edge of North America represent the 

surface expression of the mercury-antimony ore-forming 

fluids. The anomalous C02 and H2S within the springs, their 

Epithermal Mercury-Antimony Mineralization, Southwestern Alaska E7 
common spatial associatiOn with mercury deposits, and 

their heavy oxygen and hydrogen ratios led White and 

co-workers to suggest a metamorphic source for the spring 

waters. 

REFERENCES CITED 

Bliss, J.D., and Orris, G.J., 1986, Descriptive model of simple Sb 

deposits, in Cox, D.P., and Singer, D.A., eds., Mineral 

deposit models: U.S. Geological Survey Bulletin 1693, p. 

183-184. 

Cady, W.M., Wallace, R.E., Hoare, J.M., and Webber, E.J., 1955, 

The central Kuskokwim region, Alaska: U.S. Geological 

Survey Professional Paper 268, 132 p. 

Clayton, R.N., and Mayeda, T.K., 1963, The use of bromine 

pentafluoride in the extraction of oxygen from oxides and 

silicates for isotopic analyses: Geochimica et Cosmochimica Acta, v. 27, p. 43-52. 

Clayton, R.N., O'Neil, J.R., and Mayeda, T.K., 1972, Oxygen 

isotope exchange between quartz and water: Journal of 

Geophysical Research, v. 77, p. 3057-3067. 

Craig, Harmon, 1961, Isotopic variations in meteoric waters: 

Science, v. 133, p. 1702. 

Criss, R.E., and Taylor, H.P., Jr., 1986, Meteoric-hydrothermal 

systems, in Valley, J.W., Taylor, H.P., Jr., and O'Neil, J.R., 

eds., Stable isotopes in high temperature geological processes: Mineralogical Society of America Reviews in 

Mineralogy, v. 16, p. 373-424. 

Field, C.W., and Fifarek, R.H., 1985, Light stable-isotope 

systematics in the epithermal environment, in Berger, B.R., 

and Bethke, P.M., eds., Geology and geochemistry of 

epithermal systems: Society of Economic Geologists, 

Reviews in Economic Geology, v. 2, p. 99-128. 

Frey, M., 1987, Low temperature metamorphism: Glasgow and 

London, Blackie, 350 p. 

Fritz, P., Drimmie, R.J., and Nowicki, V.K., 1974, Preparation of 

sulfur dioxide for mass spectrometer analyses by 

combustion of sulfides with copper oxide: Analytical 

Chemistry, v. 46, p. 164--166. 

Godfrey, J.D., 1962, The deuterium content of hydrous minerals 

from the east-central Sierra Nevada and Yosemite Nation~l 

Park: Geochimica et Cosmochimica Acta, v. 26, p. 

1215-1245. 

Grinenko, V.A., 1962, Preparation of sulfur dioxide for isotope 

analysis: Zeits. Neorganic. Khimii., v. 7, p. 2478-2483. 

Kerrich, R., 1987, The stable isotope geochemistry of Au-Ag vein 

deposits in metamorphic rocks, in Kyser, T.K., ed., Stable 

isotope geochemistry of low temperature fluids: 

Mineralogical Association of Canada Short Course 

Handbook,v. 13,p. 287-336. 

___ 1989, Geochemical evidence on the source of fluids and 

solutes for shear zone hosted mesothermal Au deposits, in 

Bursnall, J.T., ed., Mineralization and shear zones: 

Geological Association of Canada Short Course Notes, v. 6, 

p. 129-197. 

Kulla, J.B., and Anderson, T.F., 1978, Experimental oxygen 

isotope fractionation between kaolinite and water, in Zartman, R.E., ed., Short papers of the Fourth International 

EB Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

Conference, Geochronology, Cosmochronology, Isotope 

Geology 1978: U.S. Geological Survey Open-File Report 

78-701, p. 234--235. 

Kyser, T.K., 1987, Equilibrium fractionation factors for stable 

isotopes, in Kyser, T.K., ed., Stable isotope geochemistry of 

low temperature fluids: Mineralogical Association of 

Canada Short Course Handbook, v. 13, p. 1-84. 

Longstaffe, F.J., 1989, Stable isotopes as tracers in clastic diagenesis, in Hutcheon, I.E., ed., Short course in burial 

diagenesis: Mineralogical Association of Canada Short 

Course, v. 15, p. 201-277. 

MacKevett, E.M., Jr., and Berg, H. C., 1963, Geology of the Red 

Devil quicksilver mine, Alaska: U.S. Geological Survey 

Bulletin 1142-G, p. G1-G16. 

Miller, M.L., Belkin, H.E., Blodgett, R.B., Bundtzen, T.K., Cady, 

J.W., Goldfarb, R.J., Gray, J.E., McGimsey, R.G., and 

Simpson, S.L., 1989, Pre-field study and mineral resource 

assessment of the Sleetmute quadrangle, southwestern 

Alaska: U.S. Geological Survey Open-File Report 89-363, 

115 p. 

Nesbitt, B.E., Muehlenbachs, K., and Murowchick, J .B., 1987, 

Genesis of Au, Sb, and Hg deposits in accreted terranes of 

the Canadian Cordillera: Geological Association of Canada, 

Programs with Abstracts, v. 12, p. 76. 

Ohmoto, H., 1972, Systematics of sulfur and carbon isotopes in 

hydrothermal ore deposits: Economic Geology, v. 67, p. 

551-579. 

Pickthom, W.J., Goldfarb, R.J., and Leach, D.L., 1987, Comment 

on "Dual origins of lode gold deposits in the Canadian 

Cordillera:" Geology, v. 15, no. 5, p. 471-472. 

Roedder, Edwin, 1963, Studies of fluid inclusions 11-Freezing 

data and their interpretation: Economic Geology, v. 58, p. 

167-211. 

Rytuba, J.J., 1986a, Descriptive model of hot sping Hg, in Cox, 

D.P., and Singer, D.A., eds., Mineral deposit models: U.S. 

Geological Survey Bulletin 1693, p. 178. 

___ 1986b, Descriptive model of silica-carbonate Hg, in Cox, 

D.P., and Singer, D.A., eds., Mineral deposit models: U.S. 

Geological Survey Bulletin 1693, p. 181. 

Sainsbury, C.L., and MacKevett, E.M., Jr., 1965, Quicksilver 

deposits of southwestern Alaska: U.S. Geological Survey 

Bulletin 1187, 89 p. 

Savin, S.M., and Epstein, S., 1970, The oxygen and hydrogen 

isotope geochemistry of clay minerals: Geochimica et 

Cosmochimica Acta, v. 34, p. 25-42. 

Sheppard, S.M.F., 1986, Characterization and isotopic variations 

in natural waters, in Valley, J.W., Taylor, H.P., Jr., and 

O'Neil, J.R., eds., Stable isotopes in high temperature 

geological processes: Mineralogical Society of America, 

Reviews in Mineralogy, v. 16, p. 165-183. 

Sorg, D.H., and Estlund, M.B., 1972, Geologic map of the 

Mountain Top mercury deposit, southwestern Alaska: U.S. 

Geological Survey Miscellaneous Field Studies Map 

MF-449, scale 1 :600. 

Taylor, H.P., Jr., 1979, Oxygen and hydrogen isotope relationships 

in hydrothermal mineral deposits, in Barnes, H.L., ed., 

Geochemistry of hydrothermal ore deposits (2nd ed.): New 

York, John Wiley and Sons, p. 236-277. 
Taylor, H.P., Jr., and Epstein, S., 1962, Relation between 0 18/016 

ratios in coexisting minerals of igneous and metamorphic 

rocks-1. Principals and experimental results: Bulletin of 

the Geological Society of America, v. 73, p. 461--480. 

White, D.E., Barnes, Ivan, and O'Neil, J.R., 1973, Thermal and 

mineral waters of non-meteoric origin, California Coast 

Ranges: Geological Society of America Bulletin, v. 84, 

p. 547-560. 

Epithermal Mercury-Antimony Mineralization, Southwestern Alaska E9 

Chapter F 

Gold Anomalies and Newly Identified Gold 

Occurrences in the Lime Hills Quadrangle, 

Alaska, and Their Association with the 

Hartman Sequence Plutons 

By MICHAEL S. ALLEN 

U.S. GEOLOGICAL SURVEY BULLETIN 1950 

GEOCHEMICAL STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1989 
CONTENTS 

Abstract Fl 

Introduction Fl 

General geology F2 

Methods of study F2 

Drainage-sediment gold anomalies F4 

Fish Creek area F5 

Terra Cotta Mountains F5 

South Fork Kuskokwim River region F5 

Tired Pup pluton region F9 

Styx River region F9 

Identified lode gold occurrences F9 

Three Cub occurrence F9 

Terra Cotta Mountains F12 

Upper Swift River area F12 

Summary and discussion F12 

References cited F15 

FIGURES 

1-7. Maps showing: 

1. Location of study area and the Lime Hills quadrangle, Alaska Fl 

2. Geology of the eastern part of the Lime Hills quadrangle F4 

3: Geochemical anomalies for gold in -80-mesh sediment samples, Lime Hills 

quadrangle F6 

4. Geochemical anomalies for gold in nonmagnetic heavy-mineral concentrate 

samples, Lime Hills quadrangle F7 

5. Mineralogically determined anomalies for gold in nonmagnetic heavymineral concentrate samples, Lime Hills quadrangle FS 

6. Geology and localities of geochemical samples containing anomalous 

amounts of gold, Three Cub occurrence FlO 

7. Geology and localities of geochemical samples containing anomalous 

amounts of gold, Terra Cotta Mountains F14 

TABLES 

1. Whole-rock analyses of rock samples from the Hartman sequence, Lime Hills 

quadrangle, Alaska F3 

2. Geochemical data for rock samples having anomalous metal contents from the 

Three Cub occurrence, Terra Cotta Mountains, and upper Swift River area, Lime 

Hills quadrangle, Alaska Fll 

3. Geochemical data for rock samples from the Kahiltna terrane, Lime Hills 

quadrangle, Alaska F13 
Gold Anomalies and Newly Identified Gold Occurrences in the 

Lime Hills Quadrangle, Alaska, and Their Association with the 

Hartman Sequence Plutons 

By Michael Steven Allen 

Abstract 

A drainage-sediment geochemical survey in the eastern part of the 

Lime Hills quadrangle has identified numerous areas containing 

anomalous gold concentrations. Heavy-mineral concentrates of drainage 

sediment from the Hartman River region also are anomalous in Ag, As, 

B, Ba, Bi, Co, Ni, Sb, and W. Most drainage basins containing anomalous 

samples are underlain by sedimentary rocks of the Kahittna terrane and 

intrusive igneous rocks. The most significant geochemical anomalies for 

gold are associated with gabbroic to granodioritic plutons of the Hartman 

sequence, some of which are alkalic. 

Lode sources for drainage-sediment gold anomalies were 

identified near the Hartman plutons, both southeast of Fish Creek and in 

the Terra Cotta Mountains. Rock samples from outcrop, moraine, and 

talus collected within and around Hartman plutons contain significant 

concentrations of gold (as much as 26 ppm). The highest gold values are 

in pyrite- and arsenopyrite-bearing quartz-carbonate veins that cut 

Kahiltna rocks adjacent to plutons. Alteration generally comprises thin 

selvages of silica and carbonate±sericite±chlorite±barite. Veins are 

generally less than 15 em wide. In addition to gold, anomalous 

concentrations of As, Sb, and Cu and less consistently Ag, Pb, and Zn 

characterize vein samples. Locally, unveined Kahiltna strata contain as 

much as 50 percent disseminated and stratiform pyrite. Sulfide-bearing 

strata are enriched in Ag, Ba, Co, Cr, Cu, Fe, V, Sb, and Zn. 

Carbonaceous graywacke with disseminated pyrite contains 3.5 ppm Au. 

Samples of Hartman igneous rocks cut by thin aplite dikes and quartz 

veins also have anomalous gold contents (0.2-1.3 ppm). The rocks of 

the Kahiltna terrane and the Hartman sequence are considered both 

potential hosts and possible source rocks for gold occurrences. 

INTRODUCTION 

During the summers of 1987 and 1988, a geochemical 

survey was conducted in the eastern part of Lime Hills 

quadrangle, Alaska (fig. 1), as part of the Alaska Mineral 

Resource Appraisal Program (AMRAP). This geochemical 

survey covers an area of approximately 10,000 km2 that 

includes part of the Alaska Range. 

Previous work in the region includes reconnaissance 

geologic mapping, aeromagnetic, and stream-sediment geochemical surveys in the southern Alaska Range undertaken 

LIME HILLS QUADRANGLE 

Figure 1. Location of study area (shaded) and the Lime Hills 

quadrangle, Alaska. 

by the U.S. Geological Survey in the late 1960's (Reed and 

Elliott, 1970). Geologic maps, geochronology, and geochemical data on the Alaska-Aleutian Range batholith have 

been published by Reed and Lanphere (1969, 1972, 1973) 

and Lanphere and Reed (1985). Additional geochemical and 

geophysical surveys in the region were carried out as part of 

the National Uranium Resource Evaluation (NURE) 

program (Jacobsen and others, 1979; Hinderman, 1982). 

The present study was undertaken because of the limitations 

of sampling density, sample type, analytical methods, and 

numbers of elements determined for the previous geochemical surveys (Gamble and others, 1988). 

This report shows the distribution of drainage basins 

containing anomalous gold contents and describes the 

geologic and geochemical character of newly identified 

bedrock gold sources. Anomalous concentrations of other 

metals, including Ag, Ba, Bi, Cu, Mo, Pb, Sn, Th, U, W, Zn, 

and rare-earth elements (REE), occur in many samples 

collected from the study area and indicate potential for the 

discovery of other mineral occurrences. Geochemical 

results are presented by Allen and others (1990), Allen and 

Slaughter (1990), Malcolm and others (1990), and Motooka 

and others (1990). Only data having implications for gold 

resources are discussed here. 

Acknow/edgments.-1 acknowledge the following 

people for their assistance in this study: Elizabeth Bailey, 

Barrett Cieutat, Tracy Delaney, Karen Duttweiler, Richard 

Gold Anomalies and Occurrences, Lime Hills Quadrangle, Alaska F1 
Goldfarb, John Gray, Alfred Hofstra, Gregory Lee, 

Elizabeth Leibold, Molly Malcolm, Jerry Motooka, Scott 

Rose, Karen Slaughter, and Steven Smith. 

GENERAL GEOLOGY 

The major geologic units in the study area include 

rocks of the Dillinger and Kahiltna lithotectonic terranes 

(Jones and others, 1984) and the Alaska Range batholith 

(fig. 2). 

Rocks of the Dillinger terrane, exposed in the 

northwestern part of the study area, consist of Cambrian 

through Devonian graptolitic shale,_basinal carbonate rocks, 

calcareous sandstone, and minor chert and conglomerate. 

These rocks comprise a shallowing-upward sequence 

deposited in basinal, turbidite-fan, and foreslope 

environments (Churkin, 1984; Bundtzen and others, 1987). 

The rocks of this terrane were isoclinally folded prior to the 

Jurassic (Reed and Nelson, 1980). 

The Kahiltna terrane is an Upper Jurassic to Lower 

Cretaceous flysch sequence that consists of graywacke, 

phyllite, and shale and lesser conglomerate, limestone, 

radiolarian chert, ferruginous sandstone, and tuff. The 

present study indicates that some carbonaceous graywacke 

and graphitic schist within the Kahiltna terrane contain as 

much as 50 percent disseminated and stratiform pyrite. The 

rocks of this terrane were deformed and isoclinally folded 

after the Cenomanian (Lanphere and Reed, 1985). 

The Alaska Range batholith includes rocks formed 

during three intervals of igneous activity (Reed and Lanphere, 1973): Middle to Late Jurassic, Late Cretaceous to 

early Tertiary, and middle Tertiary. Jurassic plutonic rocks 

have not been identified in the Lime Hills quadrangle. 

Late Cretaceous to early Tertiary intrusive rocks 

consist of an older suite of gabbro to quartz monzonite 

plutons, which includes the Hartman and Crystal Creek 

sequences and the Mount Estelle pluton, and a younger suite 

of quartz monzonite to granite plutons, which includes the 

Merrill Pass and Tired Pup plutons (Reed and Lanphere, 

1973). Results presented in this study indicate that some 

rocks of the older intrusive suite, particularly the Hartman 

sequence, are alkalic (table.1), ranging in composition from 

monzogabbro to syenite, and display foliation. The alkalic 

pyroxenite listed in table 1 is an oddity; it is present in 

outcrop with borderline subalkalic/alkalic gabbro along 

convoluted gradational contacts, a relationship suggestive 

of magma segregation or mixing. 

Middle Tertiary igneous rocks include quartz monzonite to granite intrusions, such as the Windy Fork pluton. 

Intermediate to felsic volcanic rocks, including flows, 

breccias, and tuffs, in the quadrangle are of uncertain 

Tertiary age. Megabreccias and breccia dikes suggest the 

F2 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

presence of caldera structures near Snowcap Mountain 

(Gamble and others, 1988) and south of the divide 

separating the Styx and Chilligan Rivers (M.S. Allen, 

unpub. data). 

There are no active mines or identified mineral 

resources in the Lime Hills quadrangle. Data for 67 mineral 

occurrences were compiled by Gamble and others (1988). 

Reed and Elliott ( 1970) identified several sites in the 

quadrangle at which float and outcrop samples contain 

detectable gold, including one site (H-10, fig. 6) northwest 

of the Hartman River. Results of the present study define 

areally extensive drainage-basin gold anomalies northwest 

of the Hartman River that are coincident with outcrops of 

Hartman plutons. Previously unreported gold-bearing veins 

are described in this region and near the headwaters of the 

Swift River. 

METHODS OF STUDY 

Drainage-sediment geochemical surveys are a rapid 

means to identify drainage basins that contain significant 

upstream mineralized bedrock, but the effectiveness of 

these surveys is dependent on many factors including the 

use of sample media appropriate for the dominant geochemical dispersion processes. In this part of Alaska, which 

is characterized by pronounced drainage development, steep 

drainage profiles, and active glaciation, mechanical 

dispersion is believed to be the dominant mechanism for 

transportation of eroded metals. Due to the resistate nature 

and high density of many ore minerals, especially gold, 

heavy-mineral fractions of drainage sediment are enriched 

in ore metals relative to bulk sediment. Therefore, this 

reconnaissance survey utilized both -80-mesh (<177 J..Lm) 

and heavy-mineral concentrate fractions of drainage 

sediment. 

Both sample types were ~ollected from approximately 

920 sites. Samples were taken from active stream sediment 

where possible, but moraine and inactive alluvium were 

collected at some localities. The -80-mesh drainagesediment samples were analyzed by a variety of methods for 

36 elements (Motooka and others, 1990). Heavy-mineral 

concentrates were processed through heavy-liquid and 

magnetic separations to obtain a nonmagnetic heavymineral fraction for mineralogical and chemical analysis. 

Mineralogical analyses using stereoscopic microscopy, oilimmersion petrography, and X-ray diffraction were 

performed before chemical analyses (Allen and Slaughter, 

1990). Heavy-mineral concentrates were analyzed for 38 

elements by emission spectrography (Malcolm and others, 

1990). Approximately 400 rock samples were also collected 

and analyzed for 36 elements (Allen and others, 1990). 
G') 

0 

a: 

)> 

::a 

0 

3 

!!!. 

m· 

I» 

a 

§ 

~ ::a 

~ c: 

3 

CD 

Si 

iii 

~ iiJ 

::a 

(Q 

1D 

)> 

iii" 

(I) 

&r 

~ 

Table 1. Whole-rock analyses of rock samples from the Hartman sequence, lime Hills quadrangle, Alaska 

[Samples are listed based on location from north to south in the plutonic belt. Latitude and longitude are in degrees, minutes, and seconds, north and west, respectively. Analytical values are in 

weight percent] 

Sample Rock type1 Affinity2 latitude longitude Si02 AI203 Fe2o33 MgO CaO Na20 

808R ......... Diorite ............... S ........... 61 56 14 153 30 20 56.8 17.1 8.23 2.99 5.58 2.93 

869R ......... Granodiorite ........ S ........... 61 53 38 153 28 49 65.1 14.8 4.30 3.01 3.90 3.03 

871R ......... Diorite ............... S ........... 61 50 36 153 24 14 58.1 16.4 6.91 3.95 6.69 3.24 

821RA ....... Tonalite .............. S ........... 61 46 27 153 37 39 64.1 14.9 4.88 2.83 4.26 2.76 

815RA ....... Granodiorite ........ S ........... 61 45 08 153 41 17 68.6 13.9 3.50 0.49 1.83 3.06 

817RE ....... Tonalite .............. S ........... 61 45 06 153 40 31 63.7 14.7 4.58 3.47 4.48 3.08 

867RA ....... Pyroxenite .......... A~ .......... 61 39 05 153 43 54 40.2 15.4 16.9 6.74 11.9 2.47 

867RB ....... Gabbro ............... SA ......... 61 39 05 153 43 54 52.2 16.9 12.7 2.47 7.67 3.97 

866RA ....... Syenite ............... A ........... 61 38 56 153 39 12 60.8 16.3 3.38 0.68 3.88 5.16 

866RB ....... Monzogabbro ...... A ........... 61 38 56 153 39 12 52.9 19.1 7.85 2.18 8.64 4.00 

865R ......... Monzonite .......... A ........... 61 31 12 153 41 36 60.5 16.3 6.00 1.72 3.82 3.47 

872R ......... Monzodiorite ....... A ........... 61 34 17 153 20 45 57.5 15.8 6.60 4.47 4.82 3.04 

1 Based on the chemical classification for plutonic rocks of De LaRoche and others (1980). 

2Based on the total alkali versus silica discrimination of Irvine and Baragar (1971); S, subalkalic; A, alkalic, SA, borderline subalkalic/alkalic. 

3-rotal iron expressed as Fe:z<>J. 

4Loss on ignition. 

K20 Ti02 P20s MnO l014 

2.75 1.52 0.40 0.18 1.06 

3.39 0.56 0.17 0.06 0.94 

1.59 0.90 0.24 0.11 1.56 

3.70 0.66 0.20 0.08 0.82 

4.78 0.36 0.17 0.05 2.40 

3.22 0.60 0.14 0.07 1.28 

0.23 4.12 2.27 0.22 <.10 

1.14 2.17 0.82 0.26 <.10 

5.45 0.41 0.11 0.10 0.15 

3.14 0.74 0.43 0.21 0.75 

5.94 0.68 0.34 0.12 0;53 

4.86 0.87 0.45 0.11 0.69 
154°30' 

62°00' .------------,---,--,-------------r--rr-T""T"-r--r--.-.--------, 

QJTi KJk 

KJk 

10 20 30 KILOMETERS 

Figure 2 (above and facing page). Geology of the eastern part of the Lime Hills quadrangle, Alaska. Geology from Reed 

and Elliott (1970) and Reed and Lanphere (1973). 

DRAINAGE-SEDIMENT GOLD ANOMALIES 

Figures 3-5 show the distribution of drainage basins 

containing anomalous gold contents (>0.05 ppm in 

F4 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

-80-mesh sediments; :?:20 ppm in concentrates; :?: 1 grain of 

gold detected microscopically). Only the more significant 

multisite anomalies are described here in detail. Of the 

three data sets, the most anomalies are defined 
Tv 

Ti 

Tw 

Tt 

Ttn 

Ts 

Tm J 

Jllil 

~ 

TKc 

TKh 

KJk 

Pzd 

EXPLANATION 

Volcanic rocks (Tertiary) 

Intrusive rocks (Tertiary) 

Windy Fork pluton (Tertiary)-Granite 

Tired Pup pluton (Tertiary)-QIJartz monzonite and granite. 

Northeast prong-Granite 

Snowcap sequence (Tertiary)-Granodiorite to quartz monzonite 

Merrill Pass sequence (Tertiary)-Quartz monzonite and 

granite 

Intrusive rocks (Tertiary and Cretaceous) 

Mount Estelle pluton (Tertiarv and Cretaceous)-Quartz 

diorite to granodiorite 

Crystal Creek sequence (Tertiary and Cretaceous)-Quartz 

monzonite 

Hartman sequence (Tertiary and Cretaceous)-Gabbro to 

granodiorite 

Kahiltna terrane (Cretaceous and Jurassic)-Graywacke, 

slate, and argillite 

Dillinger terrane (Paleozoic)-Shale, limestone, and 

graywacke 

by gold detected microscopically in heavy-mineral 

concentrate samples. Although the anomalies of greatest 

areal extent are revealed by all methods, each method 

defines some anomalies uniquely. J[t is therefore valuable to 

use a variety of sampling and analytical methods in gold 

exploration in the Alaska Range. 

Most of the gold anomalies are in the northeastern 

part of the study area (figs. 3--5), which is underlain 

predominantly by sedimentary rocks of the Kahiltna terrane 

that are intruded by small plutons of the Hartman and 

Merrill Pass sequences. Several anomalies are also along the 

margin of the Tired Pup pluton where it intrudes rocks of 

the Kahiltna terrane. In addition, several anomalies are 

clustered near outcrops of Tertiary volcanic rocks in the 

lower and upper Styx River region and near Snowcap 

Mountain. Few gold anomalies are present within the main 

outcrop areas of the large Merrill Pass and Tired Pup 

plutons or in the region underlain by the carbonate rocks of 

the Dillinger terrane. 

Many gold anomalies are spatially associated with 

areas in which rocks of the Kahiltna terrane were intruded 

by igneous rocks. The most significant of these anomalies, 

in terms of areal extent and gold concentrations, are 

associated with plutons of the Hartman sequence. The most 

significant of the drainage-sediment anomalies are 

discussed below. 

Fish Creek Area 

In the region between the Hartman River and Fish 

Creek, 12 sites have one or more drainage-sediment samples 

containing anomalous gold content (figs. 3-5). One heavymineral concentrate sample (fig. 6, sample locality 29) 

contains 30 grains of gold. The anomalous samples define a 

combined drainage area of more than 60 km2 that is 

underlain by carbonaceous graywacke and shale intruded by 

two large plutons of the Hartman sequence. Other elements 

anomalous in heavy-mineral concentrate samples from this 

area include Ag, As, B, Ba, Bi, Co, Mo, Ni, Sb, and W 

(Malcolm and others, 1990). Concentrate samples contain 

abundant arsenopyrite, barite, and scheelite and rare 

molybdenite (Allen and Slaughter, 1990). Followup of the 

drainage-sediment anomalies led to discovery of goldbearing quartz-carbonate veins between the exposure of the 

two plutons, informally referred to as the Three Cub 

occurrence. Glacial cover in this area obscures much of the 

anomalous area such that significant mineralized rocks may 

be unexposed. Gold in rock from a basal moraine (table 2, 

sample 819) indicates that mineralized rock may also be 

present beneath the glacier in section 8 (T. 19 S., R. 24 W.). 

Terra Cotta Mountains 

In the Terra Cotta Mountains, drainage-sediment 

samples from 14 sites have anomalous gold contents (figs. 

3-5). The combined drainage area, in excess of 70 km2

, is 

underlain by graywacke of the Kahiltna terrane and intruded 

by the Hartman sequence. Heavy-mineral concentrate 

samples containing anomalous gold contents also contain 

anomalous values for Ag, As, B, Ba, Bi, Co, Ni, Sb, Sn, and 

W. Pyrite, arsenopyrite, barite, and scheelite and lesser 

chalcopyrite, cinnabar, stibnite, and tourmaline were also 

observed in the concentrate samples. Gold-bearing veins 

and breccias were discovered in the northern part of the area 

in rocks of the Kahiltna terrane and Hartman sequence. 

South Fork Kuskokwim River Region 

Drainage-sediment samples containing anomalous 

gold contents occur in a broad arcuate area near the 

headwaters of the South Fork of the Kuskokwim River. 

Gold was visible microscopically in almost all heavymineral concentrate samples (fig. 5). In this region, graywacke of the Kahiltna terrane is intruded by two large 

plutons of the Hartman sequence, one on the east side of the 

area and one on the west side. Volcanic rocks crop out in the 

southern part of the area. The source of the gold is not 

known. Additional elements that are anomalous in heavymineral concentrates include Ag, As, B, Ba, Bi, Co, Ni, Pb, 

Sb, and W. These samples contain barite, pyrite, arsenopyrite, chalcopyrite, fluorite, molybdenite, scheelite, and 

stibnite. 

Gold Anomalies and Occurrences, Lime Hills Quadrangle, Alaska F5 
Q)Ti 

Tt 

KJk 

10 20 30 KILOMETERS 

EXPLANATION 

Drainage-basin anomaly for samples containing 0.05-0.5 ppm Au 

Drainage basin anomaly for samples containing more than 0.5 ppm Au 

KJk 

Figure 3. Geochemical anomalies for gold in -80-mesh sediment samples, Lime Hills quadrangle, Alaska. Geology as in 

figure 2. 

F6 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 
154°30' 

62°00' ,--------------,,------,----,-----------r------,------.--r-r-,----,-----------"T 

Q)Ti 

KJk 

10 20 30 KILOMETERS 

EXPlANATION 

Drainage-basin anomaly for samples containing 10-100 ppm of Au 

Drainage basin anomaly for samples containing 100 ppm of Au or more 

KJk 

Figure 4. Geochemical anomalies for gold in nonmagnetic heavy-mineral concentrate samples, Lime Hills quadrangle, 

Alaska. Geology as in figure 2. 

Gold Anomalies and Occurrences, Lime Hills Quadrangle, Alaska F7 
154°30' 

62°00' .-------------.---,--.,------------,---,--.-~-= 

\5Ti 

Tt 

KJk 

10 20 30 KILOMETERS 

EXPlANATION 

Drainage-basin anomaly for samples containing 1-4 grains of gold 

Drainage basin anomaly for samples containing 5 grains or more of gold 

KJk 

Figure 5. Mineralogically determined anomalies for gold in nonmagnetic heavy-mineral concentrate samples, Lime Hills 

quadrangle, Alaska. Geology as in figure 2. 

F8 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 
Tired Pup Pluton Region 

Some drainages around the margin of the Tired Pup 

pluton are anomalous in gold (figs. 3-5). Few isolated 

anomalous drainages are within the outcrop area of the 

pluton. The anomalous basins along the southwestern part 

of the pluton and near the headwaters of the Swift River, 

east of the Revelation Mountains, are underlain by rocks of 

the Kahiltna terrane. Heavy-mineral concentrates from 

drainages along the southwestern part of the pluton contain 

anomalous concentrations of Ag, As, Ba, Cu, Pb, Sb, Sn, 

and W. The bedrock source for the metals is not known. 

Heavy-mineral concentrates from the headwaters of the 

Swift River contain anomalous contents of Ag, As, Ba, Co, 

Cu, Ni, Pb, Sb, and W. In this area, gold- and arsenopyritebearing quartz veins occupy low-angle fault zones that cut 

graphitic schist of the Kahiltna terrane. 

Styx River Region 

On the east side of the Styx River, samples containing 

anomalous gold contents were collected from basins that are 

underlain by graywacke of the Kahiltna terrane that is 

intruded by the Mount Estelle pluton (figs. 3-5). This pluton 

is similar in age and composition to the Hartman sequence. 

Heavy-mineral concentrates also contain anomalous 

contents of Ag, As, B, Ba, Cu, Pb, Sb, and Zn (Malcolm and 

others, 1990). Gold-bearing quartz veins and shear zones 

occur within the granodiorite of Mount Estelle, just east of 

the Lime Hills quadrangle (Reed and Elliott, 1970). A vein 

gold deposit within and adjacent to the pluton has also 

recently been discovered (Northern Miner, 1987). 

Near the headwaters of the Styx River, an anomalous 

area defined by gold in heavy-mineral concentrates 

coincides with exposed volcanic rocks (figs. 4, 5). Thick 

units of ash-flow tuff and agglomerate and megabreccias 

and breccia dikes may be related to a caldera in this area. 

Large zones of pyritic, sericitic, and argillic alteration are 

also present. Anomalous concentrations of Cu, Pb, and Zn 

also occur in heavy-mineral concentrate samples from this 

area. The geologic setting and the primarily base-metal 

geochemical signature distinguish this anomaly from those 

described previously. Polymetallic base-metal veins in 

faults and fractures cut volcanic and intrusive rocks in this 

region (Resource Associates of Alaska, 1976). 

IDENTIFIED LODE GOLD OCCURRENCES 

Field investigations and rock sampling in this study 

identified two lode sources for the drainage-sediment gold 

anomalies spatially coincident with the Hartman plutons. 

One is the Three Cub occurrence southeast of Fish Creek, 

and the second is in the Terra Cotta Mountains. Goldbearing veins also were observed near the headwaters of the 

Swift River, adjacent to the exposure of the Tired Pup 

pluton. These discoveries, resulting from limited followup 

of the reconnaissance geochemical data, suggest that further 

exploration may lead to additional discoveries in other 

anomalous areas. 

Three Cub Occurrence 

In the region between Fish Creek and the Hartman 

River, gold-bearing veins were -discovered along the 

margins and within plutons of the Hartman sequence (fig. 

6). Gold-bearing quartz-carbonate veins cut both 

sedimentary and igneous rocks but are most prevalent in 

carbonaceous graywacke of the Kahiltna terrane and contain 

as much as 26 ppm Au (table 2). The veins are generally less 

than 15 em wide and are spaced a few meters apart. 

Although most veins are simple and have sharp regular 

contacts, a few within the sedimentary rocks are brecciated 

and contain fragments of graywacke. Alteration adjacent to 

the veins is limited to thin selvages of silica and carbonate 

and less commonly chlorite, sericite, and barite. Locally, 

some calc-silicate skarn is developed along the margin of 

the pluton (table 2, samples 817RA and 818). 

The veins contain dominantly quartz, carbonate, 

pyrite, and arsenopyrite and less commonly barite, chalcopyrite, stibnite, galena, and sphalerite. Vein samples taken 

at or near the contact of the northern pluton also contain 

anomalous contents of silver (as much as 170 ppm). Some 

aplite dikes (fig. 6, sample locality 817), quartz veins, and 

pyrite-bearing fracture surfaces in the igneous rocks contain 

scheelite and arsenopyrite. Scheelite is rarely present in 

veins within the sedimentary rocks except where calcsilicate skarn is developed (table 2, sample 817RA). 

The presence of gold (0.2 ppm) and arsenic (> 5,000 

ppm) in an unaltered, granophyric, quartz-albite aplite dike 

(table 2, sample 817RC) suggests that Hartman plutons 

could be gold sources. In places (fig. 6, sample localities 

817 and 824 ), however, abundant xenoliths of mica-rich 

mafic rocks and sedimentary rocks within the Hartman 

sequence indicate possible contamination and assimilation 

of metals and volatiles into Hartman magmas. Samples of 

unaltered rocks of the Hartman sequence contain no 

detectable gold ( < 0.05 ppm). 

Some strata within the Kahiltna terrane in this and 

other parts of the study area weather conspicuously reddish 

brown rather than more typical greyish black and locally 

contain as much as 50 percent pyrite, which is disseminated 

or in conformable lenses. Carbonaceous and pyritiferous 

graywacke units of the Kahiltna terrane are enriched in Fe, 

Ba, Co, Cr, V, Ag, As, Sb, Cu, and Zn relative to average 

shale (table 3). A sample of carbonaceous graywacke with 

disseminated pyrite contains 3.5 ppm Au (table 2, sample 

1 04RA). Anomalous gold and other metals within the 

sulfide-rich rocks suggest that these units might be source 

Gold Anomalies and Occurrences, Lime Hills Quadrangle, Alaska F9 
T 

20 

N 

T 

19 

N 

,, 

I 

\ I ~~----A--~-t---~-

) I 

1os~ 1 

" \ ! 

0 

EXPLANATION 

Geologic contact (dashed where inferred) 

- Dike ------ Glacier 

6 Drainage sample site 

R24W 

A Drainage sample site with anomalous gold content 

X Rock sample site (see table 2) 

R23W 

4 KILOMETERS 

Figure 6. Geology and localtties of geochemical samples containing anomalous amounts of gold, Three Cub occurrence. Location of map area 

shown on figure 2. Geologic units: TKh, Hartman sequence (gabbro to granodiorite); KJk, Kahiltna terrane (graywacke, slate, and argilltte). Sample 

H-10 from Reed and Elliott (1970). 

F10 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 
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Table 2. Geochemical data for rock samples having anomalous metal contents from the Three Cub occurrence, Terra Cotta Mountains, and upper Swift River area, Lime 

'Hills quadrangle, Alaska 

[All values are in parts per million (micrograms/gram). Analytical methods: A, atomic absorption analysis; I, inductively coupled plasma emission spectroscopy. <, element detected but concentration 

below limit of determination listed; N, element not detected at limit listed; >, element concentration greater than limit listed] 

Terrane 

Sample Source or unit Rock t~pe Alteration or vein ~pel Au-A Au-1 Ag-1 As-1 Sb-1 Cu-I Pb-1 Zn-1 

111REE CUB OCCURRENCE 

29RB ....... Float ...... Kahiltna· ... Graywacke ........ Quartz vein ....................... <0.05 0.15N 0.19 560 3.1 36 4.8 32 

34R ......... Float ...... Kahiltna ... Graywacke ........ Quartz veins ........................ 0. 20 0.15N 0.63 230 1.5 320 3.2 74 

102RE ...... Float ...... Hartman .... Monzonite ....... Quartz veins ........................ 0.15 0.15N 13 11 1.8 16 55 13 

104RA ...... Float ...... Kahiltna ... Graywacke ........ Disseminated pyrite ............. .3 .5 1.9 1.4 >3,000 15 140 11 70 

112RB ...... Outcrop ... Hartman .... Monzonite ....... Carbonate veins ................... 1.05 0.15N 0.082 28 4.3 23 7.2 56 

112RC ...... Outcrop ... Hartman .... Monzonite ....... Quartz-carbonate vein ............ 1.9 0.15N 0.095 380 1.8 88. 6.6 27 

639RB ...... Outcrop ... Kahiltna ... Graywacke ........ Quartz vein ......................... 0.25 0.15N 0.11 1700 9.5 5.7 1.8 13 

639RE ...... Outcrop ... Kahiltna ... Graywacke ........ Quartz vein ....................... <0.05 0.15N 0.07 300 8.9 54 0.6N 7.9 

640R ........ Outcrop ... Kahiltna ... Graywacke ........ Quartz vein ......................... 0.10 0.15N 0.045N 52 0.6N 32 0.6N 12 

642R ........ Outcrop ... Kahiltna ... Graywacke ........ Quartz-carbonate vein .......... <0.05 0.15N 0.14 99 15 17 2.1 17 

816RA ...... Talus ...... Kahiltna ... Graywacke ........ Quartz vein ......................... 0.10 0.50 1.4 250 1.9 610 1.0N 24 

817RA ...... Outcrop ... Kahiltna ... Hornfels .......... Calc-silicate vein ................. 0.25 1.8 1.4 90 8.4 440 1.3 66 

817RC ...... Outcrop ... Hartman .... Aplite ...................................................... 0.20 0.25N 0.67 >5,000 3.9 0.22 8.2 7.9 

817RD ...... Outcrop ... Kahiltna ... Graywacke ........ Quartz-carbonate veins ........... 0.30 0.40 0.76 980 44 54 4.0 75 

818RA ...... Outcrop ... Kahiltna ... Graywacke ........ Calc-silicate vein ................. 2 5.9 2.3 1,800 10 870 1.0N >800 

819RA ...... Moraine .. Kahiltna ... Graywacke ........ Quartz-chlorite vein .............. 0 .15 0.58 0.15 140 6.5 28 1.0N 43 

819 RB ...... Moraine .. Kahiltna ... Graywacke ........ Quartz vein ....................... 19 26 3.1 >5,000 35 71 34 68 

823RB ...... Outcrop ... Kahiltna ... Graywacke ........ Quartz vein ......................... 1.3 6.1 110 910 9.6 >2,000 l.ON 150 

824RB ...... Outcrop ... Hartman .... Vein at contact .. Quartz-carbonate-pyrite .......... 1.9 7.8 170 1,500 670 270 1,600 >800 

TERRA COTIA MOUNTAINS 

346RA ...... Float ...... Kahiltna ... Breccia ............ Silicified ............................ 0.40 0.46 0.33 >3,000 41 1.3 2.3 3.9 

346RB ...... Float .......................................... Quartz-sericite-pyrite ............. 0.55 0.65 5.6 570 86 2.4 14 0.77 

809RA ...... Outcrop ... Kahiltna ... Breccia vein ...... Quartz pyrite ....................... 1.0 2.5 130 >5,000 1,300 >2,000 2,100 180 

810RA ...... Outcrop ... Kahiltna ... Graywacke ........ Pyrite veins ........................ 0.05 0.26 2.5 1,600 77 520 7.9 57 

811RA ...... Talus ...... Kahiltna ... Graywacke ........ Carbonate vein .................... 0.05N 1.1 8.6 22 960 7.3 14,000 93 

813RA ...... Outcrop ... Hartman .... Monzonite ....... Quartz vein ....................... <0.05 0.25N 3.2 1,500 17 240 9.3 18 

814RA ...... Outcrop ... Hartman .... Monzonite ....... Quartz vein ......................... 0. 70 1.3 41 63 13 >2,000 LON 96 

UPPER SWIFT RIVER AREA 

1019RA1 ..• Float ...... Kahiltna ... Hornfels .......... Quartz vein ........... , ............ .3 5.6 15 1,900 12 370 LON >800 

1027RA2 ... Float. ..... Kahiltna ... Graphitic schist. Quartz vein ......................... 0.30 0.25N 1.4 69 LON 59 1.1 22 

1027RB2 ... Outcrop ... Kahiltna ... Graphitic schist. Quartz vein ......................... 1.0 2.3 8.1 >5,000 31 66 6.4 380 

lLat 61"40'28"N.,long 154"04'13"W. 

2Lat 61"40'25"N., long 154"04'58"W. 
materials from which metals in the veins were derived and . 

could be hosts to disseminated gold deposits. 

Terra Cotta Mountains 

Mineralization in the Terra Cotta Mountains is similar 

to that at the Three Cub occurrence in that gold-bearing 

quartz-carbonate veins occur in rocks of both the Kahiltna 

terrane and Hartman sequence (fig. 7). Iron staining and 

argillic alteration are more prevalent, however, in the Terra 

Cotta Mountains and are concentrated in east-northeasttrending zones cutting graywacke. Silicified and pyritized 

dikes also occur in these zones. Altered zones are 1-3 m 

wide and are ·spaced about 20 m apart. Gold-bearing 

quartz-carbonate breccia veins (table 2, sample 809) 10-15 

em wide within these altered zones contain pyrite and 

arsenopyrite and lesser stibnite and chalcopyrite. Veins and 

breccias also contain anomalous concentrations of silver (as 

much as 130 ppm). Large zones of iron-stained, silicified 

sedimentary rocks cut by numerous veinlets of pyrite and 

arsenopyrite contain lesser amounts of of Au, As, and Cu. 

Quartz veins (table 2, samples 813 and 814) 

containing anomalous amounts of gold (as much as 1.3 

ppm) occur within a Hartman pluton in the area. The veins, 

similar to those hosted in the sedimentary rocks, contain 

pyrite and arsenopyrite and less commonly chalcopyrite. 

Argillic and sericitic alteration restricted to thin selvages 

immediately adjacent to the veins has resulted in complete 

destruction of mafic minerals and feldpar. Although the 

total extent of veining is unknown, much of the Terra Cotta 

Mountains is indicated to be favorable for gold occurrences 

by gold anomalies in the drainage-sediment survey (fig. 7). 

The newly discovered occurrences described here suggest 

pluton margins may be good targets for exploration. 

Upper Swift River Area 

Another lode source of gold was identified near the 

headwaters of the Swift River, east of the Revelation 

Mountains (fig. 4). Gold-bearing quartz-arsenopyrite veins 

cut graphitic schist and hornfels of the Kahiltna terrane 

adjacent to the Tired Pup pluton. In this area, the 

sedimentary rocks are pyritiferous and weather reddish 

brown. The veins occupy low-angle faults that dip 

westward. No mineralized veins were identified in the 

igneous rocks. The veins are generally less than 15 em wide 

and are concentrated in zones which are themselves widely 

spaced (tens of meters). The veins contain as much as 5.6 

ppm Au and 50 percent arsenopyrite and traces of chalcopyrite and sphalerite. 

SUMMARY AND DISCUSSION 

Reconnaissance geochemical investigations in the 

eastern part of the Lime Hills quadrangle utilizing chemical 

and mineralogical analysis of heavy-mineral concentrate 

F12 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

and -80-mesh fractions of drainage sediments have 

identified numerous basins containing anomalous gold 

contents. Basins containing the most highly anomalous 

samples are underlain by sedimentary rocks of the Kahiltna 

terrane that have been intruded by plutons of the Hartman 

sequence. Gold-bearing quartz-carbonate veins cut Kahiltna 

and Hartman rocks near Fish Creek and in the Terra Cotta 

Mountains. Gold-bearing quartz-arsenopyrite veins also 

occupy low-angle fault zones cutting Kahiltna rocks near 

the margin of the Tired Pup pluton. Followup work of 

reconnaissance data was limited, and exploration within 

other anomalous drainage basins may locate additional lode 

gold occurrences. 

Mineralized veins associated with the Hartman 

sequence are thin and generally widely spaced but locally 

may be extensively brecciated and altered. Vein samples 

contain anomalous contents of As, Cu, and Sb and less 

commonly Ag, Pb, and Zn. Quartz-carbonate veins contain 

pyrite, arsenopyrite, chalcopyrite, stibnite, barite, galena, 

and sphalerite, in decreasing order of abundance. Most 

alteration is restricted to thin selvages of quartz and 

carbonate and less consistently chlorite, sericite, and barite. 

The origin of these vein deposits is unknown, but the 

metalliferous nature of the Kahiltna terrane and the alkalic 

affinity of the Hartman sequence may be important factors 

in the genesis of these occurrences. These rocks may have 

been sources of gold or influenced the nature and action of 

hydrothermal fluids. 

The metalliferous nature of some strata within the 

Kahiltna terrane suggests that these rocks are a potential 

source of gold that was leached by vein-forming hydrothermal fluids. Veins hosted within sedimentary rocks also have 

the highest gold contents; thus, the carbonaceous and 

sulfide-rich sedimentary units may have influenced 

precipitation of metals from hydrothermal fluids through 

reduction. In addition, gold-bearing graywacke containing 

disseminated pyrite may indicate potential for disseminated 

gold deposits. Stratigraphic and geochemical studies of the 

Kahiltna terrane in this region are needed and should focus 

on the identification of metal-rich strata and depositional 

environments favorable for the concentration and 

preservation of sulfides (for example, restricted basins). 

The association between gold-bearing veins and the 

Hartman sequence may indicate a relationship between gold 

mineralization and the petrogenesis of the intrusive rocks. 

The spatial and probable genetic association of certain 

mineral-deposit types to igneous rocks of particular 

chemical affinity is well established in Alaska and elsewhere; 

hence, the petrochemical classification of igneous rocks in 

the Alaska Range batholith can provide a guide to favorable 

environments for ore deposits. Some mafic alkalic rocks are 

notably enriched in gold and may be gold sources (Wedepohl, 1978; Boyle, 1979; Rock and others, 1987). 

Additionally, significant precious-metal deposits are known 
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Table 3. Geochemical data for rock samples from the Kahiltna terrane, Lime Hills quadrangle, Alaska 

[Latitude and longitude in degrees, minutes, and seconds, north and west, respectively. All analytical values are in parts per million, except for Fe which is in weight percent. Analytical methods: S, 

emission spectrography; I, inductively COtJpled plasma emission spectroscopy. <, element detected but concentration below limit of determination listed; N, element not detected at limit listed] 

Sam~le Source Rock type Alteration 1 Latitude Longitude Fe-S B-S Ba-S Co-S Cr-S Ni-S V-S Ag-1 As-1 Sb-1 Cu-I Pb-1 Zn-1 

137RC .... Outcrop .. Graywacke ........ Fresh ..... 61 52 02 153 40 40 3 10 500 15 150 50 150 0.068 14 0.6 73 1.2 52 

310R ...... Outcrop .. Graphitic schist .Fresh ..... 61 38 41 153 31 54 7 70 1,500 30 200 100 200 0.053 0.6N 0.6 12 3.6 130 

639RD .... Outcrop .. Graywacke ........ Fresh ..... 61 45 24 153 40 33 5 20 2,000 20 200 70 200 0.15 16 0.74 39 3.9 81 

703R ...... Float.. .... Graywacke ........ Fresh ..... 61 49 02 153 02 47 3 50 700 15 100 30 100 0.35 0.6N 1.7 20 4.7 75 

805RD .... Outcrop .. Graywacke ........ Fresh ..... 61 56 03 153 29 53 7 300 1,000 30 200 70 300 0.075N LON 2.1 27 13 140 

822RA .... Outcrop .. Graywacke ........ Fresh ..... 61 45 60 153 37 55 5 50 700 15 150 70 150 0.12 17 1.7 41 10 62 

857RA .... Outcrop .. Slate ............... Fresh ..... 61 05 39 154 10 24 7 100 1,000 15 200 70 300 0.075N 16 1.0 26 17 120 

26R ....... Float.. .... Graywacke "'!'"'"'Diss. Py .. 61 54 23 153 32 37 3 10 2,000 15 30 20 70 0.24 5.2 6.6 22 8.4 75 

282RA .... Float. ..... Sandstone ......... Diss. Py .. 61 15 31 153 17 32 5 10 1,000 15 10 <5 30 0.66 0.6N 0.6 140 1.7 21 

886RA .... Float ...... Graywacke ........ Diss. Py .. 61 12 37 153 40 09 10 70 700 15 150 50 300 0.25 1 3.0 98 3.1 140 

888RA .... Float ...... Graywacke ........ Diss. Py .. 61 16 02 153 34 37 10 10 150 30 70 100 200 0.49 26 3.6 210 8.3 130 

906RA .... Moraine .. Slate ............... Diss. Py .. 61 43 42 153 59 58 7 70 700 70 150 150 300 0.48 26 3.7 69 13 110 

1004RA .. Outcrop .. Graywacke ........ Diss. Py .. 61 44 49 153 57 26 7 100 1,000 30 300 100 300 0.27 15 10. 80 1.6 94 

1107R .... Outcrop .. Graphitic schist .Diss. Py .. 61 40 58 154 02 25 3 30 300 15 70 30 70 0.11 3.9 1.9 71 19 140 

1108RB .. Float ...... Graywacke ........ Diss. Py .. 6148 41 15413 28 7 20 1,000 20 70 50 300 0.30 37 1.5 64 8.3 44 

1109R .... Float ...... Graywacke ........ Diss. Py .. 6148 32 154 11 51 3 70 2,000 10 30 150 300 0.20 4.1 1.9 30 22 110 

111 OR .... Float. ..... Graywacke ........ Diss. Py .. 61 46 28 154 12 58 7 150 1,000 20 150 70 300 0.065 3.6 1.1 45 11 110 

1112RA .. Moraine .. Graywacke ........ Diss. Py .. 61 45 11 154 10 15 7 70 3,000 50 200 150 700 1.40 30 3.9 120 5.3 290 

1115RB .. Float ...... Graywacke ........ Diss. Py .. 61 38 39 154 04 55 5 100 500 30 150 70 300 0.51 68 2.6 48 4.5 130 

1117RC .. Float ...... Graywacke ........ Diss. Py .. 6136 30 154 03 00 10 100 500 30 300 70 300 0.075N 38 1.0 68 2.7 120 

1118R .... Float ...... Graywacke ........ Diss. Py .. 61 35 41 154 03 56 3 100 500 15 150 50 200 0.14 LON 1.0 34 1.4 160 

1154R .... Float.. .... Graywacke ........ Diss. Py .. 6146 48 154 19 21 7 100 1,500 30 150 70 300 0.11 LON 1.0 61 9.7 99 

1187RA .. Float. ..... Graywacke ........ Diss. Py .. 61 02 26 153 44 42 5 10 1,000 15 70 20 300 0.47 7.6 1.3 64 11 83 

1191RA .. Float ...... Graywacke ........ Diss. Py .. 61 07 45 153 40 08 5 50 700 20 70 30 300 0.075N 34 1.0 23 1.1 73 

1198RA .. Float. ..... Graywacke ........ Diss. Py .. 61 04 59 153 40 32 2 50 3,000 10 30 20 200 0.33 20 3.8 33 5.3 110 

1217RA .. Float ...... Graywacke ........ Diss. Py .. 61 03 35 153 34 09 7 lON 1,000 15 10 <5 150 0.10 1.9 1.0 19 1.1 64 

826RA .... Moraine .. Graphitic shale .. Strat. Py . 61 45 39 153 38 40 15 lON 70 15 100 70 100 0.20 16 5.3 70 9.3 120 

883RA .... Float ...... Graphitic schist .Strat. Py . 61 14 39 153 43 55 7 20 700 20 150 50 300 0.075N 17 4.0 60 7.9 87 

883RB .... Float ...... Graywacke ........ Strat. Py . 61 14 39 153 43 55 10 ION 150 10 30 30 150 0.16 4.5 3.6 78 1.2 110 

903RD .... Float ...... Graphitic shale .. Strat. Py. 61 48"04 153 58 01 7 70 1,500 50 150 100 700 1.40 41 3.2 120 5.2 350 

1075RA .. Outcrop .. Graphitic schist .Strat. Py . 61 40 20 154 04 34 7 100 1,500 20 300 70 300 0.19 7.1 1.0 55 2.5 160 

1114RA .. Moraine .. Graywacke ........ Strat. Py. 6142 53 154 07 37 5 70 1,500 10 70 30 150 0.24 1.4 1.0 58 1.0 120 

1201RA .. OutcroE .. Slate ............... Strat. Py . 61 05 44 153 40 13 1.5 50 3,000 lON 20 7 150 0.26 13 2.0 18 6.8 100 

Mean ..... 6.1 62 1,100 22 130 61 250 0.29 15 2.4 60 6.8 116 

Tureki~ and Wedepohl {1961} average shale ..... 4. 7 100 580 19 90 68 130 0.07 13 1.~ 45 20 95 

1 Abbreviations: Diss., disseminated; Py, pyrite; Stral, stratiform. 
T 

22 

N 

T 

21 

N 

KJk 

KJk 

0 

EXPLANATION 

Geologic contact (dashed where inferred) 

6 Drainage sample site 

R 23 W R 22 W 

KJk 

4 KILOMETERS 

A Drainage sample site with anomalous gold content 

X Rock sample site (see table 1) 

Figure 7. Geology and localities of geochemical samples containing anomalous amounts of gold, Terra Cotta 

Mountains. Location of map area shown on figure 2. Geologic units: TKh, Hartman sequence (gabbro to 

granodiorite); KJk, Kahiltna terrane (graywacke, slate, and argillite). 

F14 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 
to be related to alkalic rocks within the North American 

Cordillera (Giles, 1983; Mutschler and others, 1985; 

Thompson and others, 1985; Rock and Groves, 1988; Nikic, 

1989; Rebagliati, 1989). 

The recognition of alkalic rocks within early phases 

of the Alaska Range batholith also needs to be addressed in 

the understanding of the genesis and tectonic development 

of the batholiths. Alkalic rocks form under substantially 

different physicochemical conditions (that is, pressure, 

volatile composition) than coeval subalkalic rocks 

(Sorensen, 1979). Reed and Lanphere (1973) suggested 

that, based on AFM trends, the older Cretaceous to Tertiary 

rocks of the Hartman, Crystal Creek, and Mount Estelle 

plutons originated from a different parent than the younger 

igneous rocks, though the character of the source was not 

identified. The alkalic and subalkalic affinities of the 

Hartman sequence (table 1) possibly indicate a need for 

redefinition of the members of the sequence or that the 

sequence is a result of contamination or mixing of alkalic 

and subalkalic magmas. 

REFERENCES CITED 

Allen, M.S., Malcolm, M.J., Motooka, J.M., and Slaughter, K.M., 

1990, Geologic description, chemical analyses and sample 

locality map for rock samples collected from the eastern 

portion of the Lime Hills quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 90-69, 51 p. 

Allen, M.S., and Slaughter, K.E., 1990, Mineralogical data and 

sample locality 'map for nonmagnetic, heavymineral-concentrate samples collected from the eastern 

portion of the Lime Hills quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 90-67, 64 p. 

Boyle, R.W., 1979, The geochemistry of gold and its deposits: 

Geological Survey of Canada Bulletin 280, 584 p. 

Bundtzen, T.K., Kline, J.T., Smith, T.E., and Albanese, M.D., 

1987, Geologic map of the McGrath A-2 quadrangle, 

Alaska: Alaska Division of Geological and Geophysical 

Surveys Professional Report 91, scale 1:63,360. 

Churkin, Michael, Jr., 1984, Nixon Fork-Dillinger terranes-A 

dismembered Paleozoic craton margin in Alaska displaced 

from Yukon Territory: Geological Society of America 

Abstracts with Programs, v. 16, no. 5, p. 275. 

De LaRoche, H., Leterrier, J., Grandclaude, P., and Marchal, M., 

1980, A classification of volcanic and plutonic rocks using 

R1R2-diagram and major-element analyses-Its 

relationship with current nomenclature: Chemical Geology, 

v. 29, p. 183-210. 

Gamble, B.M., Allen, M.S., McCammon, R.B., Root, D.H., Scott, 

W.A., Griscom, A., Krohn, M.D., Ehmann, W.J., and 

Southworth, S.C., 1988, Lime Hills Quadrangle, 

Alaska-An AMRAP planning document: U.S. Geological 

Survey Administrative Report, 167 p. 

Giles, David L., 1983, Gold mineralization in the laccolithic 

complexes of central Montana, in Proceedings of the 

Denver Region Exploration Geologists Society Symposium-The genesis of Rocky Mountain ore deposits; 

changes with time and tectonics: Denver Region 

Exploration Geologists Society, p. 157-162. 

Hinderman, T.K., 1982, National Uranium Resource Evaluation, 

Lime Hills quadrangle, Alaska [National Uranium Resource 

Evaluation program, PGJ/F-057(82)]: Grand Junction, 

Colo., U.S. Department of Energy, 18 p., 14 plates, scale 

1:500,000. 

Irvine, T.N., and Baragar, W.R.A., 1971, A guide to the chemical 

classification of the common volcanic rocks: Canadian 

Journal of Earth Sciences, no. 8, p. 523-548. 

Jacobsen, S.l., Aamodt, P.L., and Sharp, R.R., 1979, Uranium 

hydrogeochemical and stream sediment reconnaissance of 

the Lime Hills and Tyonek NTMS quadrangles, Alaska, 

including concentrations of forty-three additional elements: 

Los Alamos Scientific Laboratory Informal Report LA7348-MS, 224 p. 

Jones, D.L., Silberling, N.J., Coney, P.J., and Plafker, George, 

1984, Lithotectonic terrane map of Alaska west of the 141 st 

meridian, in Silberling, N.J, and Jones, D.L, eds., Lithotectonic terrane maps of the North America Cordillera: U.S. 

Geological Survey Open-File Report 84-523, p. A1-A12. 

Lanphere, M.A., and Reed, B.L., 1985, The McKinley sequence of 

granitic rocks-A key element in the accretionary history of 

southern Alaska: Journal of Geophysical Research, v. 90, 

no. B13, p. 11413-11430. 

Malcolm, M.J., Allen, M.S., and Slaughter, K.E., 1990, Analytical 

results and sample locality map of the nonmagnetic, heavymineral-concentrate samples collected from the eastern 

portion of the Lime Hills quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 90-68, 85 p. 

Motooka, J.M., Allen, M.S., Malcolm, M.J., and Slaughter, K.E., 

1990, Analytical results and sample locality map for streamsediment samples collected from the eastern portion of the 

Lime Hills quadrangle, Alaska: U.S. Geological Survey 

Open-File Report 90-70, 105 p. 

Mutschler, F.E., Griffin, M.E., Stevens, D.S., and Shannon, S.S., 

Jr., 1985, Precious metal deposits related to alkaline rocks in 

the North American Cordillera-An interpretive review: 

Transactions of the Geological Society of South Africa, no. 

88, p. 355-377. 

Nikic, Z.T., 1989, Mount Polley alkalic porphyry copper-gold 

deposit: Northwest Mining Association, Annual 

Convention, 95th, Spokane, Abstracts, p. 3. 

Northern Miner, 1987, Platinova/Cominco in south Alaska 

venture: Northern Miner, v. 73, no. 40, p. 7. 

Rebagliati, Mark, 1989, Mt Milligan-An alkaline intrusive 

related porphyry Au-Cu deposit: Northwest Mining 

Association, Annual Convention, 95th, Spokane, Abstracts, 

p. 3. 

Reed, B.L., and Elliott, R.L., 1970, Reconnaissance geologic map, 

analyses of bedrock and stream sediment samples, and an 

aeromagnetic map of parts of the southern Alaska Range: 

U.S. Geological Survey Open-File Report 70-271 (413), 24 

p., 3 sheets, scale 1:250,000. 

Reed, B.L., and Lanphere, M.A., 1969, Age and chemistry of 

Mesozoic and Tertiary plutonic rocks in south-central 

Alaska: Geological Society of America Bulletin v. 80, 

p. 23-44. 

Gold Anomalies and Occurrences, Lime Hills Quadrangle, Alaska F15 
___ 1972, Generalized geologic map of the Alaska-Aleutian 

Range batholith showing potassium-argon ages of plutonic 

rocks: U.S. Geological Survey Miscellaneous Field Studies 

Map MF-372, 2 sheets, scale 1:100,000. 

__ 1973, Alaska-Aleutian Range batholith-Geochronology, 

chemistry, and relation to circum-Pacific plutonism: 

Geological Society of America Bulletin, v. 84, p. 

2583-2610. 

Reed, B.L., and Nelson, S.W., 1980, Geologic map of the 

Talkeetna quadrangle, Alaska: U.S. Geological Survey 

Investigations Map 1-1174, scale 1:250,000. 

Resource Associates of Alaska, 1976, Geology and geochemistry 

of certain lands within the proposed Lake Clark National 

Park: Contract report (RDF) 10166108 prepared for the U.S. 

Bureau of Mines, 109 p., 6 vols. of analytical data, 13 

sheets, various scales. 

F16 Geochemical Studies in Alaska by the U.S. Geological Survey, 1989 

Rock, N.M.S., Duller, P., Haszeldine, R.S., and Groves, D.l., 1987, 

Lamprophyres as potential gold exploration targets-Some 

preliminary observations and speculations, in Ho, S.E., and 

Groves, D.I., eds., Recent advances in understanding Precambrian gold deposits: Perth, University of Western 

Australia Publication, p. 271-286. 

Rock, N.M.S., and Groves, D.I., 1988, Can lamprophyres resolve 

the genetic controversy over mesothermal gold deposits: 

Geology, v. 16, p. 538-541. 

Sorensen, H., 1979, The alkaline rocks: New York, John Wiley 

and Sons, 622 p. 

Thompson, T.B., Trippel, A.D., and Dwelley, P.C., 1985, 

Mineralized veins and breccias of the Cripple Creek district, 

Colorado: Economic Geology, v. 80, p. 1669-1688. 

Turekian, K.K., and Wedepohl, K.H., 1961, Distribution of the 

element some major units of the Earth's crust: Geological 

Society of America Bulletin, v. 72, p. 175-192. 

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