U.S. Department of the Interior

Bureau of Land Management

BLM Alaska Open File Report 103

BLM/AK/ST-06/001+3090+942

November 2005

An Investigation of the Geology and Gold 

Mineralization in the Nyac District, 

Southwest Alaska

Zachary John Wenz

���

Alaska

U.S. DEPARTMENT OF THE INTERIOR BUREAU OF LAND MANAGEMMENT
Mission Statement

The Bureau of Land Management (BLM) sustains the health, diversity and productivity of the public lands 

for the use and enjoyment of present and future generations.

Author

Zachary John Wenz

This report is the outcome of a thesis completed by the author in partial fulfillment of the requirements for 

a Masters of Science degree at the University of Alaska, Fairbanks. The project was supported in part by 

the BLM as part of the Aniak Mining District study.

Cover

Geologists Jeff Foley (left) and Zach Wenz examine a gold-bearing sericite-altered quartz-calcite vein 

zone on Bonanza Ridge, NYAC District, Southwest, Alaska (photo by Nick Enos).

Open File Reports

Open file reports present the results of inventories or other investigations published outside the formal 

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are not published and distributed in quantity. 

Reports are available while supplies last from BLM External Affairs, 222 West 7th Avenue, #13, 

Anchorage, Alaska 99513 (907) 271-5555 and from the Juneau Minerals Information Center, 100 Savikko 

Road, Mayflower Island, Douglas, AK 99824, (907) 364-1553. Copies are also available for inspection 

at the Alaska Resource Library and Information Service (Anchorage), the United States Department of 

the Interior Resources Library in Washington D.C., various libraries of the University of Alaska, the BLM 

National Business Center Library (Denver), and other selected locations. 

A complete bibliography of all BLM-Alaska scientific reports can be found on the Internet at:

http://www.ak.blm.gov/affairs/sci_rpts.html

Related publications are also listed at: http://juneau.ak.blm.gov. 
An Investigation of the Geology and Gold 

Mineralization in the Nyac District, 

Southwest Alaska

By

Zachary John Wenz

BLM Open File Report 103

November 2005

U.S. Department of the Interior

Bureau of Land Management

Alaska State Office

222 W. 7th Ave., #13

Anchorage AK 99513

i

Abstract 

The Nyac district, southwest Alaska, contains multiple felsic to mafic plutons and dikes intruding 

the volcano-sedimentary package of the Nyac terrane. Dated plutons and dikes in the Nyac terrane record 

Early Cretaceous ages; other plutons in southwest Alaska are Late Cretaceous and Tertiary. The Nyac 

district contains high-temperature and low-temperature gold mineralization. The age of high-temperature 

and low-temperature mineralization is concordant with plutonism. The high-temperature mineralization 

occurs in the Bonanza pluton and associated gray granodiorite porphyry dikes. Bonanza pluton 

mineralization consists of gold-bearing quartz veins with pyrite-chalcopyrite-magnetite-bismuthinitemolybdenite. Fluid inclusions from mineralized quartz veins record trapping temperatures up to 560o

 C and 

salinities up to 60 wt% NaCl. Mineralization in the grey granodiorite porphyry dikes consists of goldbearing quartz veins with tellurobismuthite-tetradymite-chalcopyrite. Fluid inclusions from mineralized 

quartz veins record trapping temperatures up to 370o

 C, salinities up to 5 wt% NaCl, and CO2

concentrations up to 80 vol%. Both types display sericite-chlorite-albite alteration, and the Bonanza Pluton 

also displays potassic alteration. The low-temperature mineralization occurs at the Bonanza Creek Color 

Anomaly and along high-angle faults. This type contains anomalous Au and Hg. The alteration assemblage 

is sericite-kaolinite, indicating low temperature (<240o

 C) and acidic fluids. 
ii

TABLE OF CONTENTS 

Abstract ............................................................................................................................................................i 

Table of Contents ............................................................................................................................................ii 

List of Figures .................................................................................................................................................v 

List of Tables.................................................................................................................................................vii 

List of Appendices ........................................................................................................................................vii 

Chapter 1: Introduction................................................................................................................................1

1.1 Regional Geology.....................................................................................................................................1 

1.2 Previous Exploration................................................................................................................................4 

1.3 Purpose of Study ......................................................................................................................................6 

1.4 Methods....................................................................................................................................................6 

1.4.1 Chemical Analysis ..........................................................................................................................6 

1.4.2 Petrography .....................................................................................................................................7 

1.4.3 Magnetic Susceptibilities ................................................................................................................7 

1.4.4 Feldspar Staining.............................................................................................................................8 

1.4.5 Microprobe Analysis.......................................................................................................................8 

1.4.6 Fluid Inclusion Microthermometry .................................................................................................8 

1.4.7 Radiometric 40Ar/39Ar Dating..........................................................................................................8 

Chapter 2: Geology and Geophysics..........................................................................................................10

2.1 Jurassic Volcano-Sedimentary Rocks .....................................................................................................10 

2.1.1Metavolcanic Rocks................................................................................................................15 

2.1.2 Metasedimentary Rocks.........................................................................................................18 

2.2 Introduction to Plutonic Rocks................................................................................................................20 

2.3 Jurassic (?) Plutonic Rocks......................................................................................................................20 

2.3.1 Rex Creek Pluton ...................................................................................................................21 

2.3.2 Altered Granodiorite ..............................................................................................................26 

2.3.3 Diorite Hornfels .....................................................................................................................29 

2.3.4 Gabbro....................................................................................................................................29 

2.4 Early Cretaceous Plutonic Rocks ............................................................................................................29 

2.4.1 Nyac Batholith .......................................................................................................................30 

2.4.2 Bonanza Pluton ......................................................................................................................32 

2.4.3 Sawpit Pluton .........................................................................................................................33 

2.4.4 Gray Dikes .............................................................................................................................33 
iii

2.4.5 Red Dikes...............................................................................................................................34 

2.5 Tertiary (?) Dikes ....................................................................................................................................34 

2.5.1 Mafic Dikes............................................................................................................................34 

2.5.2 Pink Dikes..............................................................................................................................35 

2.5.3 Undifferentiated Dikes...........................................................................................................35 

2.6 Regional Geophysics and Structural Geology.........................................................................................35 

Chapter 3: Gold Mineralization.................................................................................................................41

3.1 The Wallace Occurrence .........................................................................................................................41 

3.2 VABM Bonanza Lobe.............................................................................................................................49 

3.3 Bonanza Creek Color Anomaly...............................................................................................................58 

3.3.1 High-T Mineralization ...........................................................................................................58 

3.3.2 Low-T Mineralization ............................................................................................................65 

3.4 Other Styles of Mineralization ................................................................................................................67 

3.5 Placers .....................................................................................................................................................70 

3.6 Relationship of the Placer to Bedrock Gold ............................................................................................72 

3.7 Classification of Mineralization ..............................................................................................................75 

Chapter 4: Geochronology .........................................................................................................................78

4.1 Sample Selection .....................................................................................................................................79 

4.2 Volcanic Rock Ages................................................................................................................................80 

4.3 Plutonic Rock Ages.................................................................................................................................80 

4.3.1 Nyac Batholith .......................................................................................................................84 

4.3.2 Bonanza Creek Lobe..............................................................................................................90 

4.3.3 VABM Bonanza Lobe............................................................................................................90 

4.3.4 Spruce Creek Lobe.................................................................................................................95 

4.3.5 Grey Dikes .............................................................................................................................95 

4.3.6 Red Dikes.............................................................................................................................102 

4.4 40Ar/39Ar Rock Age Summary............................................................................................................102 

Chapter 5: Mineralization Model ............................................................................................................109

5.1 Jurassic (?) Plutonism............................................................................................................................109 

5.2 Early Cretaceous Plutonism ..................................................................................................................109 

5.3 Tertiary (?) Hydrothermal Activity .......................................................................................................113 

5.4 Mineralization Model............................................................................................................................113 
iv

Chapter 6: Conclusions.............................................................................................................................116

6.1 Recommended Work.............................................................................................................................117 

References ..................................................................................................................................................118 

Appendices .................................................................................................................................................123 
v

List of Figures 

Figure 1.1: Regional geologic map of southwest Alaska ................................................................................2 

Figure 1.2: USGS 1:250,000-scale geologic map of the Nyac area ................................................................3

Figure 1.3: Topographic map of the study area...............................................................................................5 

Figure 2.1: Interpretive bedrock geology map of the Nyac district...............................................................11 

Figure 2.2: TAS diagram for volcanic rocks from the metasedimentary and metavolcanic rock units and the 

mafic dike .............................................................................................................................................13 

Figure 2.3: Winchester and Floyd (1977) trace element volcanic rock classification diagram for volcanic 

rocks from the metavolcanic and metasedimentary rock units and the mafic dike...............................14 

Figure 2.4: Winchester and Floyd (1977) trace element basalt origin diagram for metavolcanic and 

metasedimentary rock units and the mafic dike....................................................................................16 

Figure 2.5: Pearce and Cann (1973) Zr vs. Ti discrimination diagram for the origin of basalts and 

basalt/andesites .....................................................................................................................................17 

Figure 2.6: Cordierite in pyritic metavolcanic rocks from the BCCA...........................................................19

Figure 2.7: R1-R2 chemical classifications for plutons and dikes................................................................22 

Figure 2.8: IUGS modal igneous classification scheme for igneous rocks ...................................................23 

Figure 2.9: AFM classification diagram for the alkalinity of igneous rocks ................................................24 

Figure 2.10: Trace element origin classification for felsic to intermediate plutonic rocks............................25 

Figure 2.11: Triangular trace element plutonic discrimination diagram for all plutonic rocks ....................27 

Figure 2.12: Trace element discrimination diagrams for plutonic rocks .......................................................28 

Figure 2.13: Aplite compositional geobarometry for the albite-quartz-orthoclase-H20 system ....................31 

Figure 2.14: Trace element discrimination diagram for plutonic bodies and red dikes.................................36 

Figure 2.15: Boxplot of the magnetic susceptibilities for the rock units in the study area............................38 

Figure 2.16. Aero-magnetic map of the study area with some ground-based geologic contacts...................39 

Figure 3.1: Topographic map showing historic and current placer mining locations....................................42 

Figure 3.2: Map of locations and sample numbers for important assays from this study..............................43 

Figure 3.3: Quartz-chlorite-calcite veining and associated tellurobismuthite and native gold from the 

Wallace Occurrence..............................................................................................................................44 

Figure 3.4: Stained grey dike samples from the Wallace occurrence............................................................46

Figure 3.5: Fluid inclusion in mineralization associated quartz veining from the Wallace occurrence ........48 

Figure 3.6: Geologic map of VABM Bonanza lobe......................................................................................50 

Figure 3.7: Sr vs. Rb plot for altered and unaltered granodiorite samples from VABM Bonanza lobe ........52 

Figure 3.8: Mineralization in quartz veining from VABM Bonanza lobe.....................................................54 

Figure 3.9: Fluid inclusion from a quartz vein hosting mineralization in the VABM Bonanza Pluton.........57 

Figure 3.10: Oxidation State vs. Temperature mineral stability diagram at 500 bars ...................................59 

Figure 3.11: Two pictures of the limonite stained pyritic metavolcanic rocks at the BCCA ........................60 
vi

Figure 3.12: Geologic map of the BCCA showing the location of different styles of alteration...................61 

Figure 3.13: Quartz vein mineralization from the high-T mineralization at the BCCA................................62 

Figure 3.14: Fluid inclusions in quartz veins from the high-T mineralization at the BCCA.........................64 

Figure 3.15: Pictures of sericitic-kaolinite altered dikes, chalcedonic veining and quartz veined carbonate 

breccia from the low-T mineralization at the BCCA............................................................................66

Figure 3.16: Linear regression plot for Au and Hg from low-T (epithermal) mineralization at the BCCA..68 

Figure 3.17: Photomicrographs of placer gold from the study area ..............................................................71 

Figure 3.18: Map of sample location and gold fineness for bedrock, placer and production average...........74 

Figure 3.19: Triangular plot of mineralization factors ..................................................................................76 

Figure 3.20: Map of samples with Au concentrations >200 ppb and their factor classification....................77 

Figure 4.1: Map of sample location for all rock ages....................................................................................81 

Figure 4.2: Age, Ca/K and Cl/K spectrum diagram for whole rock basalt....................................................82 

Figure 4.3: Age, Ca/K and Cl/K spectrum diagram for the second whole rock basalt analysis ....................83 

Figure 4.4: Age, Ca/K and Cl/K spectrum diagram for hornblende from the Nyac batholith.......................85 

Figure 4.5: Age, Ca/K and Cl/K spectrum diagram for hornblende from the Nyac batholith.......................86 

Figure 4.6: Age, Ca/K and Cl/K spectrum diagram for biotite from the Nyac batholith...............................87 

Figure 4.7: Age, Ca/K and Cl/K spectrum diagram for biotite from the Nyac batholith...............................88 

Figure 4.8: Age, Ca/K and Cl/K spectrum diagram for biotite from the Nyac batholith...............................89 

Figure 4.9: Age, Ca/K and Cl/K spectrum diagram for hornblende from the Bonanza Creek lobe ..............91 

Figure 4.10: Age, Ca/K and Cl/K spectrum diagram for biotite from the Bonanza Creek lobe....................92 

Figure 4.11: Age, Ca/K and Cl/K spectrum diagram for biotite from the VABM Bonanza lobe .................93 

Figure 4.12: Age, Ca/K and Cl/K spectrum diagram for muscovite from the VABM Bonanza lobe ...........94 

Figure 4.13: Spruce Creek mineral aggregate separate .................................................................................96 

Figure 4.14: Age, Ca/K and Cl/K spectrum diagram for hornblende from the Spruce Creek lobe ...............97 

Figure 4.15: Age, Ca/K and Cl/K spectrum diagram for biotite from the Spruce Creek lobe.......................98 

Figure 4.16: Age, Ca/K and Cl/K spectrum diagram for hornblende from the gray dike .............................99 

Figure 4.17: Age, Ca/K and Cl/K spectrum diagram for hornblende from the gray dike ...........................100 

Figure 4.18: Photomicrographs of hornblende (a) and biotite (b) from the grey dike at the Wallace 

occurrence...........................................................................................................................................101 

Figure 4.19: Age, Ca/K and Cl/K spectrum diagram for biotite from the gray dike ...................................103 

Figure 4.20: Age, Ca/K and Cl/K spectrum diagram for biotite from the gray dike ...................................104 

Figure 4.21: Age, Ca/K and Cl/K spectrum diagram for biotite from the red dike .....................................105 

Figure 4.22: Age, Ca/K and Cl/K spectrum diagram for muscovite from a mineralized red dike ..............106 

Figure 4.22: Figure of dated samples illustrating two distinct age suites....................................................107 

Figure 5.1: pH vs. Temperature diagram for Al alteration minerals ...........................................................112

Figure 5.2: Schematic cross section through the Bonanza Pluton...............................................................115 
vii

List of Tables 

Table 2.1: Magnetic susceptibility (x10-3 SI) ranges and averages for each of the rock units.......................12 

Table 2.2: Classification results of discriminant analysis for plutonic rocks ................................................21

Table 3.1: Partial chemistry of altered and unaltered grey dikes from the Wallace occurrence....................45 

Table 3.2: Microprobe analysis averages for Bi-Te minerals from the Wallace occurrence.........................47 

Table 3.3: Correlation table for elements from mineralized gray dikes ........................................................47

Table 3.4: Primary fluid inclusion measurements from the Wallace occurrence ..........................................49 

Table 3.5: Partial chemistry for granodiorite samples from the VABM Bonanza lobe.................................53 

Table 3.6: Correlation table for all mineralized samples from the VABM Bonanza lobe.............................55 

Table 3.7: Correlation table for samples with >100 ppb Au from the VABM Bonanza lobe .......................55 

Table 3.8: Primary and secondary fluid inclusion measurement data from the VABM Bonanza lobe .........56 

Table 3.9: Primary fluid inclusion measurement data from high-T mineralization at the BCCA .................63 

Table 3.10: Partial chemistry for altered and unaltered red dikes .................................................................65 

Table 3.11: Partial assays for Spruce Creek skarn specimens.......................................................................69 

Table 3.12: Partial assays for Rex Creek pluton associated mineralization ..................................................69 

Table 3.13: SEM morphology of placer gold from the study area ................................................................70

Table 3.14: Placer gold microprobe and dredge average placer fineness data ..............................................72 

Table 3.15: Summarized table of all gold fineness data from the study area ................................................73 

Table 4.1: Typical atomic Ca/K and Cl/ K ratio ranges for dated minerals ..................................................79 

Table 4.2: Abbreviated 40Ar/39Ar age data for all dated samples ..................................................................84

List of Appendices 

Appendix A: List of samples, location, rock type, veining style, 

 ore mineralogy and magnetic susceptibility.........................................................123 

Appendix B: Compositional chemical data and analysis technique..............................................134 

Appendix C: List of quartz -plagioclase-K-feldspar modal estimates............................................144 

Appendix D: Microprobe analysis data .............. ................................................................145 

Appendix E: 40Ar/39Ar analytical data................................................................................147 

1

1. Introduction 

 The Nyac district is located approximately 100 kilometers northeast of Bethel in the Kilbuck 

Mountains, southwest Alaska (Figure 1.1). Calista Corporation, an Alaska native corporation founded 

under the Alaska Native Claims Settlement Act, owns the surface and subsurface rights to 186 square 

kilometers in the Nyac area, covering nearly all of the historical placer mining operations in the district. 

The Nyac district lies in the northeast portion of the Nyac terrane (as defined by Decker et al., 1994). The 

Nyac terrane is arguably the least understood terrane in southwest Alaska. The only published geologic 

maps (Box et al., 1993; Hoare and Coonrad, 1959) are highly generalized (1:250,000 scale) and 

accompanied by a few K-Ar, U-Pb dates, geochemical analyses and major oxide analyses (Box et al., 1993; 

Robinson and Decker, 1986; and Wilson, 1977). No detailed study of the geology and particularly of the 

lode gold mineralization is available. 

From the early 1900’s to 2000, a minimum 500,000 oz. of placer gold has been produced from the 

Nyac district (Foley, 2000). Despite this enormous placer gold production, no significant lode gold 

prospects are known. Although known bedrock gold anomalies occur in the district (Gierymski and 

Werdon, 1997; Frost et al., 1993; RAA, 1975; and Wallace, 1945), no particular lode source or system has 

been identified as responsible for the accumulation of gold in the streams. Lack of lode gold discovery is 

related to limited exploration, lack of detailed mapping, and inadequate models for potential mineralization. 

Therefore the purpose of this study is to produce an accurate geologic map and combine all geochemical 

data to produce a local model for gold deposition in the study area. 

1.1 Regional Geology 

Southwestern Alaska is comprised of various tectonostratigraphic terranes, including the Farewell, 

Goodnews, Nyac, Kilbuck, and Togiak terranes largely overlain by the Cretaceous Kuskokwim Group and 

unconsolidated Tertiary sediments (Figure 1.1; Decker et al., 1994). The Nyac terrane consists of volcanic 

and volcaniclastic rocks of Middle and Late Jurassic age intruded by Early Cretaceous felsic to 

intermediate plutons. The volcanic rocks possess high La/Nb ratios, characteristic of volcanic arc-related 

magmatism. The volcaniclastic rocks are dominantly epiclastic tuffaceous marine sandstone, shale and 

conglomerate. Pelecypod fossils found in sedimentary beds are of Bajocian (Early Jurassic) and Tithonian 

(Late Jurassic) age; the latter are present in the upper sequences outside the study area. Unlike other 

terranes in southwest Alaska, the Nyac terrane is nowhere overlain by the Kuskokwim Group rocks (Box et 

al., 1993). The Nyac terrane is also unique among the SW Alaska terranes in that it contains Early 

Cretaceous plutons whereas plutons in adjacent terranes are latest Cretaceous and early Tertiary in age 

(Decker et al., 1994). 
2

Iditarod-Nix

lt

on Fork Fau

Denali-Farewell Fault

Sawpit Fault

YUKON R.

KUSKOKWIM R.

SOUTHWEST ALASKA

Aniak-Thompson Creek fault

gsj_geo.cdr oct 95revised 7/96

AN

FA

NYAC

study area

HORN MTN.

DONLIN

DeCOURSEY

RED DEVIL

VINASALE

GANES CREEK

NIXON FORK

CHICKEN MTN

GOLDEN HORN

Bethel

KuskokwimBay

Aniak

McGrath

COLORADO CREEK

Norton Sound

MAP

AREA

Tertiary sedVolcanic-plu(LK-ET)Volcanic fieGranite porp(LK-ET)Kuskokwim Yukon-Koyu

GranodioritComplexes 

Nyac terran

Other SW A

EXPLANAT

PAST PRODLODE GOL

LODE GOLD 

WITH DRILLED 

LODE GOLD 

PAST PRODMERCURY 

SELECTED OCCUREN

100 km

61o

63o

162o 156o

INDEPENDENCE

Figure 1.1: Regional geologic map of southwest Alaska. Modified after Bundtzen and Miller (1997).
3

Tuluksak

River

Bear

Creek

California

Ck.

Rocky

Ck.

Bonanza Ck.

Nugget Ck.

Sabula

Ck.

Spruce Ck.

Granite Ck.

Nyac

Batholith

Cale Ck.

Eagle Ck.

East Fork

Bear Ck.

Slate Ck.

Fox Ck.

Marvel

Dome

Fault

Fault

Fault

Golden

Gate

Sawpit

Karl

Creek

Nyac

Fault zone, dashed where inferred 2 miles

Quaternary alluvial and terrace deposits

Quaternary glacial till and moraine deposits

Early Tertiary - Late Cretaceous granodiorite

Altered intrusive rhyolite and dacite

Mafic plutonic rocks, including diorite and gabbro

Kuskokwim Group Upper Cretaceous marine turbidite sequence

Early Cretaceous granite and quartz monzonite

Middle Jurassic andesitic flows and marine epiclastic rocks

Silica-carbonate altered serpentinite

Late and Middle Jurassic volcaniclastic rocks

Study Area

61o

60 55’ o

160o159 50’ o

61 05’ o

Figure 1.2: USGS 1:250,000-scale geologic map of the Nyac area after Box et al. (1993). Study area 

enclosed by the outlined box. 
4

Southwest Alaska is dominated by the right-lateral Iditarod-Nixon Fork and Denali-Farewell Fault 

systems (Figure 1.1). In the Nyac area, the Nyac terrane is bounded on the SE by the right-lateral Golden 

Gate-Sawpit Fault (Figure 1.2). The Golden Gate-Sawpit Fault is inferred to be a continuation of the 

Iditarod-Nixon Fork Fault system, offset by the left lateral Aniak-Thompson Creek Fault (Figure 1.1). 

Miller et al. (2002) found the Iditarod-Nixon Fork Fault system became active in Late Cretaceous time. The 

Aniak-Thompson Creek Fault appears to offset the Iditarod-Nixon Fork Fault system, but the timing of that 

movement is uncertain. 

1.2 Previous Exploration 

Robert E. Wallace made the first documented discovery of lode gold in the Nyac district (Wallace, 

1945). He found free gold in quartz-chlorite veins hosted in a granitic porphyry dike at the confluence of 

California Creek and the Tuluksak River (Figure 1.3). More abundant and occurring with the gold was a 

soft, silver-gray mineral with laminar cleavage later believed to be a telluride (Gates, 1945a, unpublished 

letter). Early assays of this occurrence reported gold values up to 1.3 opt/Au (Gates, 1945b, unpublished 

letter). 

 Resource Associates of Alaska (RAA; 1975) conducted the first comprehensive exploration study in 

the Nyac area from 1974 to 1975. RAA conducted 1:63,630 scale mapping and sampling of over 675 

square miles in a one and a half month period. RAA documented five areas of anomalous gold values: the 

Wallace occurrence, a fault zone north of Bonanza Creek, Marvel Creek, Fisher Dome and the Cripple 

Mountain. Two of these areas, the Wallace occurrence and fault-hosted mineralization north of Bonanza 

Creek (Figure 1.3), lie in the study area. The mineralization north of Bonanza Creek, as described by RAA, 

is a 20-foot-wide zone of brecciated, quartz-veined, iron-stained hornfels. RAA believed the anomalous 

gold was constrained to quartz-dolomite veins with values up to 15.1 ppm Au (J. Foley, written comm., 

2004). 

Frost (1990) discovered anomalous Hg (up to 2.28 ppm) values associated with gold-bearing, quartz 

veins, suggesting an epithermal component to some of the mineralization. Frost et al. (1993) later 

speculated that the spatial association of the mineralized veins with the plutons suggests that the plutons at 

least supplied a heat source for circulation of hydrothermal fluids. 

In 1996 and 1997 Placer Dome Exploration (PDX; Gierymski and Werdon, 1997) conducted the most 

thorough exploration program in the district. In 1996 an eleven-hole, reverse circular drilling program and 

nine ground-VLF-resistivity profiles were completed. All efforts were constrained to the Bear Creek and 

Tuluksak River valleys, in belief that the placers directly overlay their lode sources. Of a total 742 meters 

of drilling the highest anomalous gold values were eight meters of 30 to 70 ppb Au. The 1997 exploration 

began with compilation of all the old churn drill and dredging records for the district. PDX geologists 

determined the data were too limited in extent to be spatially useful, but the old reports did provide 
5

Wallace

Occurrence

RAA

discovery

Rich Placer

Placer Dome

discoveries

159 41’ 0

 61 04’ 0

 61 07’ 0

159 41’ 0

159 56’ 0

 61 01’

159 56’ 0

ANCHORAGE

FAIRBANKS Study Area

Russian Mission A-3 Russian Mission A-2

Mission

Gulch

Spruce Cree

H

k

appy Creek

Bonanza

Pluton

Altered

dikes

Tuluksak River

Figure 1.3: Topographic map of the study area. Map depicts previously discovered bedrock gold 

occurrences and rich placer locations. 
6

references to high-grade placers in Rocky and California Creek drainages (Figure 1.3). PDX geologists 

mapped and sampled approximately 200 square kilometers at a 1:12000 scale in 200 days. New discoveries 

found during this exploration included anomalous gold values in the Bonanza pluton and altered dikes 

north of Bonanza Creek (Figure 1.3; Gierymski and Werdon, 1997). 

1.3 Purpose of Study 

The main goal of this study is to determine the source of the 500,000 oz of placer gold. To determine 

the source of the gold, this investigation is focused on two aspects. The first aspect is to better understand 

and document the geology of the area, especially the intrusions. The second aspect is to better understand 

and tie together the various prospects and bedrock geochemical anomalies in the area. Thus, the principal 

goal was to construct an accurate geologic map at 1:25,000 scale employing a combination of field, 

petrographic, petrologic and dating techniques. Using this map and characteristics of the 

mineralization/alteration (deduced from field and laboratory observations and statistical analysis in the 

study area), this study ultimately produced a model for gold mineralization in the region that accounts for 

the placer deposits. 

1.4 Methods 

During June and July of 2003 field research was conducted that included geologic mapping and 

sampling in the Nyac district. The study area is bounded by UTM easting 449000, 463000, UTM northing 

6775900 (zone 4 NAD27 datum, Clarke 1866 spheroid) and Bear Creek to the south (Figure 1.2). The 

terrain is steeply rising foothills covered by talus and vegetation on the lower portions. Outcrop is only 

exposed on ridge tops. The valleys are entirely covered with vegetation. Access to the base of the ridge tops 

was made possible by ATV-accessible mining roads. A total of 499 sample locations were collected and 

recorded using a Garmin 12 GPS unit. Field mapping was aided in part a by regional magnetics map 

(ADGGS staff et al., 1994). Abbreviated rock sample descriptions and locations are in Appendix A. 

1.4.1 Chemical Analysis 

A total 204 rock samples were submitted to ALS Chemex Laboratories1 for trace element and major 

oxide analysis. The 204 rock samples were sent in two different sets and were analyzed by different 

techniques. Both sets were prepared for analysis by fine crushing (70% <2 mm), then a split sample (riffle 

splitter) was pulverized to < 75 microns (85% of sample). Analyses of the first set involved Aqua Regia 

digestion of the powdered sample followed by ICP-MS analysis for 50 elements. In addition, Ba, W and Sn 

 

1 Mention of ALS Chemex Labortories does not signify any specific BLM endorsement.
7

were analyzed by XRF wavelength dispersive methods, Hg by cold-vapor atomic absorption spectroscopy 

and Au by fire assay with ICP-AES. Analysis of the second set of samples involved a triple acid digestion 

(HF, HNO3 and HClO4) and HCl leach followed by ICP-MS analysis. In addition, Au was analyzed by fire 

assay atomic absorption spectroscopy, Hg by cold-vapor atomic absorption spectroscopy and major oxide 

analysis of lithium borate fused discs by XRF wavelength dispersive techniques. The triple acid technique 

was used for all the samples from mineralized areas suspected to have significant tellurium values since 

this method is more accurate in determining tellurium concentration. Partial digestion, especially for 

samples treated with aqua regia, make many of the elemental values low. Only results for elements known 

to completely dissolve are reported here. 

Some powders returned from the ALS Chemex were used to prepare pressed pellets for major oxide 

and trace element analysis at the University of Alaska Fairbanks (UAF). The rock powders were mixed 

with 0.5 mL polyvinyl (2M) binding agent. The samples were then compressed under 20,000 psi and 

allowed to dry for 24 hours before analysis. Trace and major element analysis were performed at UAF on a 

Rigaku 3064 XRF using a program created by Dr. Rainer Newberry (described in Cameron, 2000). 

Analytical accuracy for commercial and UAF XRF analyses are ± 2% amount present for major 

oxides and ± 5-10% amount present for trace elements (Cameron, 2000). Duplicate samples were 

submitted to ALS Chemex. Since heterogeneity and the nugget effect could affect duplicate results, only a 

general sense of accuracy can be obtained. Duplicate samples varied no more than 12% of the amount 

present. Appendix B lists chemical data and analytical techniques. 

1.4.2 Petrography 

Polished and covered thin sections of 34 rock samples were prepared commercially by Spectrum 

Petrographics. An additional 50 polished and covered thin sections were prepared at UAF. All were 

examined by standard reflected and transmitted light techniques in conjunction with feldspar staining and 

major oxide analysis. Thin section petrography was used to determine which samples were good candidates 

for 40Ar/39Ar dating, microprobe analysis and fluid inclusion microthermometry. Anorthite content was 

calculated using the Michel-Levy technique (Deer et al., 1966). 

1.4.3 Magnetic Susceptibilities 

Magnetic susceptibilities were taken for all samples collected in the field. Normally three 

measurements were taken at each station and averaged. For those samples taken from Bonanza Pluton, ten 

measurements were averaged. All measurements were taken with a Kappameter model KT-6 magnetic 

susceptibility meter. The meter was held normal to a fresh, smooth surface of the rock. Magnetic 

susceptibility data are given in Appendix A. 
8

1.4.4 Feldspar Staining 

Thirty seven igneous rock samples were etched using HF acid and then stained with sodium 

cobaltinitrate following the procedure of Ruperto et al. (1964). Using this technique K-feldspar stains 

yellow, plagioclase etches milky white and quartz is unaffected. Modal abundances of quartz, K-feldspar 

and plagioclase were estimated using standard abundance charts. In general the modal estimations agree 

with chemically derived names for the same specimen. Modal data are presented in Appendix C. 

1.4.5 Microprobe Analysis 

Microprobe analyses were conducted on native gold, Bi and Bi-Te minerals. The analyses were 

performed at the UAF on a Cameca SX-50 microprobe with a 25 micron beam set at 25kV and 30 mA. On 

peak was counted for 10 seconds and off peaks for 5 seconds. Working standards were used to ensure data 

quality. Microprobe data are given in Appendix D. 

1.4.6 Fluid Inclusion Microthermometry 

Fluid inclusion studies were conducted at UAF on a Fluid Inc. model (Reynold) stage. All samples 

were doubly polished quartz veins with a thickness of approximately 100 microns. Due to the inability to 

control low temperatures on this setup, few freezing temperatures were determined and no CO2 freezing 

temperatures were attempted. Final homogenization temperatures were the last value measured. A final 

standardization was run to ensure data quality. The standard used was a pure water inclusion that froze at 

0.2 C o . Accurate measurements were acquired by cycling back and forth through phase transitions and 

averaging the results. In general, repeated measurements varied by <1 degree Celsius. Salinities and vol% 

CO2 were calculated using the Macintosh FLINCOR (Brown, 1989) program. Trapping temperatures were 

estimated after Potter (1997). Fluid inclusion data are presented in Chapter 3. 

1.4.7 Radiometric 40 Ar/ 39 Ar Dating 

 For 40Ar/39Ar analysis, mineral separates and whole rock chips (7 hornblende, 1 muscovite, 9 

biotite and 2 whole rock) were submitted to the Geochronology Laboratory at UAF. Mineral separates 

were obtained from a crushed rock sample by hand-picking. The monitor mineral MMhb-1 (Samson and 

Alexander, 1987) with an age of 513.9 Ma (Lanphere and Dalrymple, 2000) was used to monitor neutron 

flux (and calculate the irradiation parameter, J). The samples and standards were wrapped in aluminum foil 

and loaded into aluminum cans of 2.5 cm diameter and 6 cm height. The samples were irradiated in 

position 5c of the uranium enriched research reactor of McMaster University in Hamilton, Ontario, Canada 

for 20 megawatt-hours. 
9

 Upon their return from the reactor, the sample and monitors were loaded into 2 mm diameter holes 

in a copper tray that was then loaded into an ultra-high vacuum extraction line. The monitors were fused, 

and samples heated, using a 6-watt argon-ion laser following the technique described in York et al. (1981), 

Layer et al. (1987) and Layer (2000). Argon purification was achieved using a liquid nitrogen cold trap 

and a SAES Zr-Al getter at 400 degrees Celsius. The samples were analyzed in a VG-3600 mass 

spectrometer at the Geophysical Institute, UAF. The argon isotopes measured were corrected for system 

blank and mass discrimination, as well as calcium, potassium and chlorine interference reactions following 

procedures outlined in McDougall and Harrision (1988). 

The detailed analyses are given in Appendix E. Ages are quoted at the ± 1 sigma level and calculated 

using the constants of Steiger and Jaeger (1977). 
10

2. Geology and Geophysics 

Rock types present in a given district are a good initial indicator of where and how the gold 

occurs. Since both volcanic and plutonic rocks can produce and host gold deposits (e.g., volcanogenic 

massive sulfide or copper porphyry type deposits), it is important to characterize these different rock types 

and determine their relation to gold mineralization. The rocks of the study area are of four major types: (1) 

variably metamorphosed Jurassic volcano-sedimentary rocks, (2) Jurassic (?) plutonic rocks, (3) Early 

Cretaceous plutonic rocks and (4) Tertiary (?) dikes. Discrimination between these rock types is based on 

statistical analysis, cross-cutting relationships, compositional data, Ar dating (discussed in chapter 4) and 

textural features. 

The magnetic susceptibility of a particular rock type can be a useful discriminating characteristic 

of any rock unit. When surface magnetic susceptibilities are used in conjunction with magnetic surveys an 

indication of the depth of the rock cover can be estimated. This is useful to understand if the rocks exposed 

at the surface continue at depth. Table 2.1 lists the magnetic susceptibility range and average for each of the 

rock units. 

The interpretive geologic map of the study area (Figure 2.1), is the most detailed map to date of 

the Nyac district. The previous most detailed published map is a USGS 1:250,000 scale map (Figure 1.2; 

Box et al, 1993). The USGS map has no bedding measurements in the Jurassic volcanic rocks, does not 

have any high-angle faults (besides the Golden Gate-Sawpit Fault) and the plutonic rocks mapped in the 

study area are the same unit as the Nyac Batholith. The map produced as a result of this study includes 

bedding measurements in the Jurassic volcanic rocks, identifies six different igneous bodies and four 

different dike types. This map also includes two fault sets with northeast-southwest and north-south 

orientations. The northeast-southwest faults include the high-angle, right-lateral Golden Gate-Sawpit fault 

system and its related faults. The north-south trending high-angle, left-lateral faults, are presumably related 

to the Aniak-Thompson Creek Fault. This chapter includes a complete description of each rock unit shown 

on the interpretive bedrock geology map (Figure 2.1). 

2.1 Jurassic Volcano-Sedimentary Rocks 

 The volcano-sedimentary rock group includes two rock units: (1) metavolcanic rocks and (2) 

metasedimentary rocks. The volcano-sedimentary rocks are most important for determining the stratigraphy 

in the study area. Although some anomalous mineralization occurs in these rocks, they are relatively 

unmineralized in comparison to the plutonic rocks. The Jurassic volcano-sedimentary rocks are contact 

metamorphosed to various hornfels facies depending on proximity to a heat source and initial composition. 
11

4

43

13

16

28

21

27

37

22

19

20

22

14

25

36

24

20

17

60

50

40

35

0 1,000 2,000 3,

500

Explanation

FaultsBrecciaMafic DikePink DikeAltered Red Dikes Red DikeGrey DikeBonanza PlutonSawpit Pluton

Nyac Batholith

Rex Creek PlutonIntrusive BrecciaAltered GranodioritDiorite HornfelsMetasedimentary RLimonite-stained MMetavolcanic RockGabbroInferred Rock Unit Rock Unit Contact

450000 452500 455000 457500 460000 462500

6775000 6772500 6770000 6767500 6765000

450000 452500 455000 457500 460000 462500

6775000 6772500 6770000 6767500 6765000 Inclined Bedding

Golden Gate -Sawpit

Fault

D

U

D

U

Bonanza Creek

lobe

Spruce Creek

lobe

VABM

Bonanza lobe

159 56’ O

 61 07’ O

159 41’ O

 61 01’ O

InferredFaults

Kkg Kuskokwim Group

Ard

Kbp

Ksp

Knb

Jrc

Jib

Jag

Jdh

Jms

Lm

Jmv

Jg

Jg

Jmv

Jmv

Jmv

Lm

Jms

Jdh

Jag

Jib

Jrc

Knb

Csp

Ksp

Ksp

Ksp

Kbp

Kbp

Ard

Kkg

Figure 2.1: Interpretive bedrock geology map of the Nyac district. Geology southeast of dashed and dotted line is from Gierymski and (1997). 
12

Table 2.1 Magnetic susceptibility (x10-3 SI) ranges and averages for each of the rock units. 

Map Unit Average Range Number 

Mafic Dike 13.3 1 

Pink Dike 4.21 1.39-7.96 16 

Bonanza Pluton 8.43 0.14-30.8 54 

Gray Dike 3.16 0.19-13.8 16 

Red Dike 14.0 1 

Nyac Batholith 8 4.0-12.0 13 

Sawpit Pluton 3.64 0.11-16.2 8 

Rex Creek Pluton 6.75 0.3-25.0 19 

Altered Granodiorite 4.88 4.54-5.23 2 

Diorite Hornfels 2.29 0.26-16.3 16 

Undifferentiated Dikes 2.47 0.01-14.4 17 

Metasedimentary Rocks 0.94 0.06-8.76 45 

Metavolcanic Rocks 9.61 0.02-108 185 

Gabbro 27.5 17.2-37.7 2 

Figure 2.2 shows the compositional names for analyzed volcanic rocks using a TAS diagram. 

Because all of the volcanic rocks have experienced various degrees and types of metamorphism and 

alteration, the TAS classification may not accurately classify the rocks. The TAS method depends upon Na 

and K concentrations, which are relatively mobile elements. 

TAS volcanic rock classifications were confirmed for samples with trace element data using the 

Nb/Y vs. Zr/TiO2 scheme of Winchester and Floyd (1977) (Figure 2.3). These trace element classifications 

variably agree with the TAS classifications. Most importantly, the trace element classification illustrates 

that the apparent bimodal volcanic assemblage (basalts and rhyolite) is not accurate and in fact there is a 

continuum of volcanic compositions (basalt, andesite and rhyodacite). Using the trace element 

classification scheme none of the volcanic rocks plot as alkali-rich types, suggesting that the volcanic rocks 

either experienced alkali enrichment by syn-eruptive hydrothermal activity or post-eruptive alteration. 

Hydrothermal alkali enrichment of volcanic rocks is a common phenomenon for marine volcanic rocks; the 

resulting alteration is called spilitization (Blatt and Tracy, 1995). Spilitization results in the addition of 

alkalis from seawater into hot rocks. Since the Nyac terrane is a volcanic-arc and there are fossil beds 

layered with the flows, it is conceivable that some of the flows were submarine and may have experienced 

hydrothermal alteration and spilitization. However, since no unaltered varieties of volcanic rocks were 

identified, and thus analyzed, it is difficult to distinguish between spilitization and post-eruptive alteration 

as the cause for alkali enrichment. 

Trace element data can also provide a means to determine the tectonic setting. Figures 2.4 and 2.5 

show trace element based tectonic settings of basaltic composition rocks. In Figure 2.4 all of the basalts 

plot in the MORB, island-arc tholeiite and calc-alkali basalt field while Figure 2.5 illustrates that all but 
13

35 40 45 50 55 60 65 70 75

0

2

4

6

8

10

12

14

16

Na

2O+K2

O

SiO2

Picrobasalt

Basalt

Basaltic

andesite

Andesite

Dacite

Rhyolite

Trachyte

Trachydacite Trachyandesite

Basaltic

trachyandesite

Trachybasalt

Tephrite

Basanite

PhonoTephrite

Tephriphonolite

Phonolite

Foidite A

B

C

D

E

Mafic Dike

Metasedimentary Rock Unit

Metavolcanic Rock Unit

F1

2

3

1

1

2 2

Figure 2.2: TAS diagram for volcanic rocks from the metasedimentary and metavolcanic rock units. 

and the mafic dike. Lettered samples are those with trace element data that is used on Figure 2.3 for 

trace element classification. Data are from this study; (1) Gierymski and Werdon (1997), (2) J. Foley 

written comm. (2004) and (3) T. P. Frost, written comm. (2004). Classification after LeMaitre et al. 

(1989). 
14

.01 .1 1 10

.001

.01

.1

1

Zr/TiO2

Nb/Y

SubAlkaline Basalt

Andesite/Basalt

Andesite

Rhyodacite/Dacite

Rhyolite

Alkaline-Basalt

TrachyAndesite

Pantellerite

Mafic Dike

Metasedimentary Rock Unit

Metavolcanic Rock Unit

A

B D

E

C

F

1

1

1

2

Figure 2.3: Winchester and Floyd (1977) trace element volcanic rock classification diagram for 

volcanic rocks from the metavolcanic and metasedimentary rock units and the mafic dike. Data are 

from this study, (1) Gierymski and Werdon (1997), and (2) J. Foley, written comm. (2004). 
15

two of the samples are calc-alkaline basalts. All of the basaltic rocks have trace element characteristics of a 

volcanic-arc setting; andesite is characteristically of arc origin. 

2.1.1 Metavolcanic Rocks 

 The metavolcanic rock unit is one of the oldest rock units in the study area. Since the bottom 

contact of this unit is not exposed and due to variable bedding measurements a minimum approximate 

thickness of 500 meters can be estimated. The unit contains approximately equal parts of volcaniclastic 

rocks and lava flows. Due to extensive compositional variation and degree of thermal metamorphism, the 

magnetic susceptibility for this unit is extremely variable (Table 2.1). Only one stratigraphic layer, a 

wackestone pelecypod-bearing bed, was found to continue across ridges. 

The volcaniclastic rocks are extremely variable in composition and texture. The volcaniclastic 

rocks are dominantly clast supported, but some matrix supported beds exist. Clast supported beds are 1-10 

meters thick; matrix supported beds are approximately 2 to <1 meter thick. In clast supported beds the 

clasts are generally angular and range in size from 2 mm to 10 cm in diameter and account for >50% of the 

rock volume. Matrix supported beds have more visible quartz grains and rare rounded to sub-angular clasts 

(2-40 mm in diameter) that account for >10% of the rock volume. In many cases correct classification 

between volcaniclastic and flow is only possible upon petrographic inspection. Most original volcaniclastic 

textures are lost due to recrystallization during thermal metamorphism (e.g., porphyritic flows look 

identical to crystal tuffs). 

The flow rocks vary in composition from basalt to andesite with <1% dacite and rhyolite (Figure 

2.3). The flows are 2-20 meters thick and presumably represent multiple flows. Flows are gray to gray 

green, purple and black, variably aphanitic to fine-grained or porphyritic, and/or amygdaloidal fine-grained. 

Porphyritic flows contain 1-10% plagioclase (1-8 mm) and 0-5% pyroxene (1-5 mm) as phenocrysts, and 

rarely hornblende. Amygdules are filled with epidote, actinolite or ringed chalcedony. Dacites are typically 

medium to coarse-grained, follow bedding planes, and may represent sills in the metavolcanic package. A 

single identified rhyolite is a plagioclase and quartz porphyry with an aphanitic matrix. 

In addition to the volcanic and volcaniclastic rocks, other lithologies are present in this unit. They 

include: a few calcareous beds, a wackestone pelecypod fossil bed, and a clinopyroxenite dike. The 

calcareous beds are <1 to 20 meters thick and consist of dominantly argillaceous limestone beds, but rare 

pure limestone is also seen. One calcareous bed located north of Spruce Creek is almost entirely replaced 

by calc-silicate minerals (described in greater detail in Chapter 3: Gold Mineralization). The wackestone 

pelecypod-bearing bed consists of rounded to sub-rounded, medium-grained rock fragments in a chlorite 

altered matrix. Box et al. (1993) reported the pelecypod fossils are Bajocian (Middle Jurassic) in age. A 

single pyroxenite dike (03ZW328) has a cumulate, coarse-grained texture. Interstitial material is entirely 

chloritized. 
16

A= island- arc tholeiite

B= island-arc tholeiite

 calc-alkali basalt and MORB

C= calc-alkali basalt

D= within-plate basalt

Zr Y*3

Ti/100

C

D A

B

Mafic Dike

Metasedimentary Rock Unit

Metavolcanic Rock Unit

1

2

Figure 2.4: Winchester and Floyd (1977) trace element basalt origin diagram for metavolcanic and 

metasedimentary rock units and the mafic dike. Data are from this study, (1) Gierymski and Werdon 

(1997), and (2) J. Foley, written comm. (2004). 
17

0 50 100 150 200

0

5000

10000

15000

20000

Ti ppm

Zr ppm

A= island-arc tholeiite

B= MORB, calc-alkali basalt

 and island-arc tholeiite

C= calc-alkali basalt

D= MORB

D

C

B

A

Mafic Dike

Metasedimentary Rock Unit

Metavolcanic Rock Unit

1

2

Figure 2.5: Pearce and Cann (1973) Zr vs. Ti discrimination diagram for the origin of basalts and 

andesites. Data are from this study, (1) Gierymski and Werdon (1997); and (2) J. Foley, written comm. 

(2004). 
18

In thin section the clast supported volcaniclastic rocks contain approximately 40-85% angular 

volcanic rock clasts (>2 cm-4 mm diameter), 10-25% feldspar crystals (1-4 mm), <1% quartz (<1mm) and 

5-65% fine-grained material. The feldspar crystals are approximately 95% plagioclase and 5% K-feldspar. 

Feldspar crystals are variably altered to chlorite, epidote and minor sericite (0-10%). The fine-grained 

material is altered to chlorite and epidote. Matrix supported volcaniclastic rocks are fine grained, occur in 

5-mm to 15-cm-sized beds and contain round to sub-angular rock clasts. Some of these clasts form obvious 

depressions in the bedding and may be bombs. These volcaniclastic rocks contain fine-grained feldspar, 

minor quartz (80-90%) and larger (2-7 mm) feldspar crystals. 

 In thin section the volcanic flow rocks are generally porphyrititc and amygdaloidal with a finegrained to aphanitic groundmass. Plagioclase phenocrysts are most common; pyroxene and hornblende 

phenocrysts also occur. The pyroxene and hornblende phenocrysts are commonly pseudomorphs replaced 

by a combination of epidote and actinolite. Amygdules are filled with epidote, actinolite, zeolites and 

chalcedony. Fine-grained groundmass is altered similar to the phenocrysts. Basalt contains up to 7% 

magnetite, although it is unclear how much of the magnetite was formed during thermal metamorphism. 

 In thin section the clinopyroxenite dike contains pyroxene pseudomorphs (2-5 mm, 30-100%) 

entirely altered to chlorite (50%), actinolite (40%) and epidote (10%). Plagioclase crystals make up 5-10% 

of the rock, are 10-20 microns in length and, and have been altered to chlorite (85%), epidote (10%) and 

sericite (5%). Plagioclase has an anorthite content of ~55%. 

The volcanic and volcaniclastic rocks generally exhibit albite-epidote hornfels facies mineral assemblages. 

Higher grade hornblende hornfels and pyroxene hornfels facies are seen locally around the plutons. 

Metavolcanic rocks in the altered red dikes in metavolcanic rocks unit and near the altered granodiorite 

contain cordierite (Figure 2.6). Low-grade zeolite facies are present north of Spruce Creek. 

2.1.2 Metasedimentary Rocks 

 This unit occurs in the north and northeastern portion of the study area (Figure 2.1). The 

metasedimentary unit may be traced from the study area north to the boundary of the Nyac terrane (Box et 

al, 1993). This unit appears to conformably overlie the metavolcanic unit. The unit is dominantly composed 

of mudstone/siltstone (55%), conglomerate (35%), volcaniclastic rocks (10%) and flows (<1%) all of which 

are now hornfels. The mudstone and siltstone beds are tens of meters thick, finely layered (mm’s to 2 cm) 

and characteristically have a purple, biotite-hornfels color. Conglomerates are both clast supported (80%) 

and matrix supported (20%). The matrix is a fine-grained to aphanitic, quartz poor clay material, now 

entirely altered to chlorite. The clasts are sand to cobble-sized dominantly porphyritic, medium to finegrained volcanic rocks with rare (<5%) sedimentary and granitic textured clasts. 
19

Figure 2.6: Cordierite in pyritic metavolcanic rocks from the BCCA. 

In thin section volcaniclastic rocks in the unit have fine layers of feldspar and rock fragment clasts 

in a fine-grained matrix. In one sample the fine-grained matrix was thermally metamorphosed resulting in a 

2/3 scapolite assemblage. The same rock also contains randomly oriented clinopyroxene and hornblende 

porphyroblasts indicating pyroxene hornfels facies metamorphism. Along the metasedimentary unit and 

Nyac Batholith contact, many metasedimentary rocks contain calc-silicate veins with sulfides (pyrite, 

pyrrhotite, chalcopyrite and marcasite) enveloped by garnet, pyroxene, hornblende, epidote, calcite and 

quartz. This local development of skarn indicates that the sedimentary beds originally contained 

appreciable calcite. 
20

2.2 Introduction to Plutonic Rocks and Dikes 

The correct name for a plutonic igneous rock is determined by IUGS modal abundance (quartz, 

alkali feldspar and plagioclase; Streckheisen, 1973). A secondary technique uses major oxide composition 

plotted on a chemical classification diagram (e.g., Streckheisen or R1-R2). The plutonic rocks and dikes 

were classified using the R1-R2 classification scheme of De la Roche et al. (1980). This method uses most 

major oxide data (excluding MnO and P2O5) from a typical major oxide analysis. The two parameters (R1 

and R2) are calculated using the millication proportions of the elements. The formulas for calculating these 

factors are: R1=[ 4Si - 11(Na+K) - 2(Fe+Ti) ] and R2=(Al + 2Mg + 6Ca). This method does not use 

normative based methods so a broad comparison of modal abundance versus chemical classification can be 

made. The R1-R2 diagram then displays mineral compositions relative to major oxide compositions. R1-R2 

chemical classifications for plutonic rocks and dikes are given in Figures 2.7a and b. Modal classifications 

are shown on Figure 2.8. 

 Statistical methods can be used to group rocks of similar composition. Using discriminant analysis 

of trace element and major oxide data, the rock units in the study area are statistically distinguishable. 

Table 2.2 illustrates that 97.8% of the analyzed samples can be statistically distinguished on the basis of 

composition. Only one specimen from the Bonanza pluton is incorrectly classified. 

The oxidation state of a pluton has implication for gold favorability and the type of associated 

fluids (Thompson and Newberry, 2000). Figure 2.9 shows that all of the Nyac Batholith and Bonanza 

Pluton rocks are calc-alkaline, relatively high oxidation state felsic rocks. Implications of this will be 

discussed in greater detail in Chapter 5. Figure 2.10 shows that all the granitic rocks have volcanic-arc trace 

element signatures. 

2.3 Jurassic (?) Plutonic Rocks 

 This group includes the Rex Creek pluton, altered granodiorite, diorite hornfels and gabbro 

(Figure 2.1). These plutonic bodies were grouped together due to intense pervasive alteration, composition 

and unique trace element chemistry. Plutonic rocks grouped in this category have experienced intense 

thermal metamophism and/or epidote-chlorite-calcite-sericite alteration. The Rex Creek pluton and altered 

granodiorite display intense epidote-chlorite-calcite-sericite alteration. This alteration has entirely 

destroyed the original mafic mineralogy. These pervasive alteration types do not occur in the Early 

Cretaceous plutonic rocks, indicating a different and perhaps longer history of alteration for the Jurassic (?) 

plutonic rocks. 
21

Table 2.2 Classification results of discriminant analysis for plutonic rocks. 

22 0 0 0 0 0 22

1 17 0 0 0 0 18

0 0 1 0 0 01

0 0 0 2 0 02

0 0 0 0 1 01

0 0 0 0 0 22

100.0 .0 .0 .0 .0 .0 100.0

5.6 94.4 .0 .0 .0 .0 100.0

.0 .0 100.0 .0 .0 .0 100.0

.0 .0 .0 100.0 .0 .0 100.0

.0 .0 .0 .0 100.0 .0 100.0

.0 .0 .0 .0 .0 100.0 100.0

Rock Unit

Nyac Batholith

Bonanza Pluton

Sawpit Pluton

Rex Creek Pluton

Hornfels Diorite

Altered Granodiorite

Nyac Batholith

Bonanza Pluton

Sawpit Pluton

Rex Creek Pluton

Hornfels Diorite

Altered Granodiorite

%

Count

Original

Nyac Batholith

Bonanza

Pluton Sawpit Pluton

Rex Creek

Pluton

Hornfels

Diorite

Altered

Granodiorite

Predicted Group Membership

Total

*The statistical analysis includes all major oxide and trace element data. The table shows 97.8% of the groups are classified correctly.

The Jurassic (?) plutonic rocks have variable compositions (Figures 2.7a and 2.8). In general these 

rocks contain significantly more mafic compositions (diorite) in comparison to the Early Cretaceous 

plutons. It is possible that some of these rocks may have been the feeders for the volcanic rocks in the 

district. The Jurassic (?) plutonic rocks appear to be more yttrium enriched than the early Cretaceous 

plutons (Figure 2.11). This difference in yttrium suggests a compositional variation inherent in the source 

for the two rock groups; thus, the Early Cretaceous plutons likely have originated from a different source. 

The final evidence for separating the Jurassic (?) plutonic rocks from the other plutons is 

illustrated by their fractionation patterns. Since three of the Jurassic (?) plutonic bodies exhibit yttrium 

enrichment (relative to niobium), their analyses can be grouped together to display a fractionation pattern 

of trace elements changing with silica content. Figure 2.12 illustrates that the Jurassic (?) plutonic rocks 

have opposite fractionation patterns from the Early Cretaceous rocks with respect to Ce, Y and Zr. These 

three elements increase in concentration with increasing silica for the Jurassic (?) plutonic rocks, while for 

the Early Cretaceous plutonic rocks Ce, Y and Zr concentrations decrease with increasing silica content. 

2.3.1 Rex Creek Pluton 

 The Rex Creek pluton occurs in the southwest portion of the field area (Figure 2.1). The 

pluton intrudes the metavolcanic unit and is inferred to underlie >4 km2

 of surface area. It is sporadically 

covered with erosional remnants of metavolcanic rocks a few meters thick. The Rex Creek pluton is a 
22

Or

Ab

An50

R2

R1

2000

1000

1000 2000 3000

Gabbro

Syenite

Diorite

Essexite

Tonalite

Monzonite

Monzogabb

Syenogabbro ro

Gabbronorite

Alkaligabbro

Syenodiorite

Monzodiorite

Granodiorite

Monzogranite

Syenogranite

Qtz Monzonite

Quartz Diorite

Olivine Gabbro

Quartz Syenite

Alkali Granite

Qtz Monzodiorite

Nepheline Syenite

Bonanza Pluton

Nyac Batholith

Sawpit Pluton

Rex Creek Pluton

Altered Granodiorite

Diorite Hornfels

Gabbro

Or

Ab

An50

R2

R1

2000

1000

1000 2000 3000

Gabbro

Syenite

Diorite

Essexite

Tonalite

Monzonite

Monzogabb

Syenogabbro ro

Gabbronorite

Alkaligabbro

Syenodiorite

Monzodiorite

Granodiorite

Monzogranite

Syenogranite

Qtz Monzonite

Quartz Diorite

Olivine Gabbro

Quartz Syenite

Alkali Granite

Qtz Monzodiorite

Nepheline Syenite

Pink Dike

Red Dike

Mafic Dike

Gray Dike

Undifferentiated Dikes

a

b

Alkalic

Sub-alkalic

Alkalic

Sub-alkalic

1

2

3 1

1

1

1

1

1

1

1

1

1 1

1

2

2

2

2

2

2

2

2

2

3

3

3

3 3

3 3

3 3 3

3 3

3

3

2

3

Figure 2.7: R1-R2 chemical classifications for plutons (a) and dikes (b). The two parameters (R1 and 

R2) are calculated using the millication proportions of the elements, R1=[ 4Si - 11(Na+K) - 2(Fe+Ti) ] 

and R2=(Al + 2Mg + 6Ca ). Data are a compilation from this study; (1) Gierymski and Werdon (1997), 

(2) J. Foley, written comm. (2004), and (3) T. P. Frost, written comm. (2004). Diagram modified after 

De la Roche et al. (1980). 
23

K-feldspar Plagioclase

Quartz

Monzogranite Granodiorite

Quartz Monzonite Quartz Monzodiorite

Monzonite

Monzodiorite

Tonalite

Quartz Diorite

Diorite

Quartz Syenite

Syenogranite

Syenite

Alkali Feldspar Granite

Alkali Feldspar

Quartz

Syenite

Alkali Feldspar

Syenite

Bonanza Pluton

Sawpit Pluton

Rex Creek Pluton

Diorite Hornfels

Figure 2.8: IUGS modal igneous classification scheme for igneous rocks. Estimated modal 

abundances from stained rock slabs containing at least 100 mineral grains. Figure after Strekheisen 

(1973). Data from this study.
24

Alk MgO

FeO*

Calc-Alkaline

Tholeiitic

Low oxidation

state

High oxidation

state

Bonanza Pluton

Nyac Batholith

Sawpit Pluton

Rex Creek Pluton

Diorite Hornfels

Altered Granodiorite

Figure 2.9: AFM classification diagram for the alkalinity of igneous rocks. Tholeiitic rocks have 

lower oxidation states than calc-alkaline rocks (FeO*= total Fe as Fe2+, Alk= Na2O + K2O). Figure is 

modified after Irvine and Baragar (1971). Data are from this study, Gierymski and Werdon (1997), J. 

Foley, written comm. (2004), and T. P. Frost, written comm. (2004). 
25

10 100 1000

1

10

100

1000

Rb ppm

Y+Nb ppm

Syn-Collisional

Within-plate

Volcanic-arc

Orogenic

Bonanza Pluton

Nyac Batholith

Sawpit Pluton

Rex Creek Pluton

Altered Granodiorite

Figure 2.10: Trace element origin classification for felsic to intermediate plutonic rocks. Data are 

from this study; Gierymski and Werdon (1997), J. Foley, written comm. (2004) and T. P. Frost, written 

comm. (2004). Figure after Pearce et al. (1984). 
26

medium-grained, generally equigranular, quartz monzodiorite to quartz-diorite and granodiorite body 

(Figure 2.7a and 2.8). Based on limited exposures, no compositional zoning is seen, but the variation of 

rock composition suggests that zoning does occur. The pluton displays pervasive epidote-chlorite-calcitesericite alteration. Epidote veins (1- 20mm wide) comprise <1% of the rock volume, but some areas contain 

up to 5% veining. Much larger (5-15 cm wide) epidote-magnetite veins are rare. Measured magnetic 

susceptibilities range from 0.3 to 25.03. The variation is presumably the result of different degrees of 

magnetite formation during alteration as well as variation in original rock composition (more magnetite 

present in more mafic rocks). 

 In thin section, all the original mafic minerals (~ 15-20% of the original volume) are replaced by a 

combination of epidote, chlorite, calcite, magnetite ± rutile ± pyrite. Evidence of the original mafic 

mineralogy appears as epidote-chlorite pseudomorphs after hornblende. Plagioclase is 30-80% altered to a 

combination of epidote + sericite + calcite and minor chlorite. Less altered plagioclase crystals display 

albite twinning and some are concentrically zoned. K-feldspar crystals are relatively unaffected by the 

alteration. Trace amounts of apatite and zircon are visible in the feldspars and altered mafics. 

2.3.2 Altered Granodiorite 

The altered granodiorite, located east of the Rex Creek Pluton, is an inferred 1.5 km2 body. It is a 

gray-green, medium to coarse-grained, equigranular granodiorite (Figure 2.7a). All the mafics have been 

altered to a combination of chlorite and epidote. The top of the body is an intrusive breccia intruded by 

sericitically altered felsic porphyry dikes. 

 In thin section all the mafic minerals have been entirely replaced by a combination of epidote, 

chlorite and calcite. The original mafic minerals constitute approximately 12% of the rock volume. The 

feldspars are 20-80% replaced by a combination of epidote and sericite. Accessory minerals include apatite 

and zircon. Chemically, the rock is a granodiorite with a relatively small LOI, indicating that epidote (low 

water content) is the principal alteration mineral. However, considering the degree of alteration, the original 

rock composition is uncertain. 

 The altered dikes in the intrusive breccia have yttrium and niobium concentrations similar to those 

of the altered granodiorite, but the dikes are slightly more enriched in zirconium. This indicates the altered 

dikes are likely derived from the altered granodiorite. Similar composition, trace element chemistry, 

fractionation trends and similar alteration style suggest the altered granodiorite may be part of the Rex 

Creek pluton. 
27

Y Nb

Zr/10

Jurassic Plutonic Group

Bonanza Pluton

Nyac Batholith

Sawpit Pluton

Rex Creek Pluton

Diorite Hornfels

Altered Granodiorite

Figure 2.11: Triangular trace element plutonic discrimination diagram for all plutonic rocks. Data are 

from this study, Gierymski and Werdon (1997), and T. P. Frost, written comm. (2004). 
28

20

40

60

80

100

120

Ce ppm 0

10

20

30

40

Y ppm

50 60 70 80 100

300

500

700

900

Sr ppm

SiO wt% 2

0

50

100

150

200

Rb ppm 0

10

20

30

Nb ppm

50 60 70 80 0

100

200

300

Zr ppm

SiO wt% 2

Bonanza Pluton

Nyac Batholith

Sawpit Pluton

Rex Creek Pluton Diorite Hornfels

Altered Granodiorite

Figure 2.12: Trace element discrimination diagrams for plutonic rocks. Arrows indicate the 

fractionation trend with increasing silica content. The solid arrow indicates the trend direction for 

the Nyac Batholith and Bonanza Plutons and the dashed arrow indicates the trend for the Jurassic 

(?) Plutonic Rocks. Data are from this study, Gierymski and Werdon (1997), J. Foley, written comm. 

(2004) and T. P. Frost, written comm. (2004). 
29

2.3.3 Diorite Hornfels 

 The diorite hornfels occurs sporadically in the metasedimentary rock unit (Figure 2.1). It probably 

is a series of sills and small intrusive bodies, most likely related to Jurassic volcanism. The largest body is 

located along the metasedimentary contact with the Nyac Batholith. The hornfelsed diorite contains 40-

60% plagioclase and 40-60% hornblende and pyroxene (pyroxene is less abundant than hornblende). The 

plagioclase has a characteristic gray-blue color. The hornblende and pyroxene are partially altered to 

chlorite and epidote. 

 In thin section the diorite hornfels does not display epidote-chlorite-calcite-sericite alteration. 

Instead, the mafics are entirely recrystallized into fine-grained, randomly oriented masses of biotite and 

hornblende. The plagioclase crystals contain hornblende inclusions. It is unclear whether some plagioclase 

crystals originally enclosed the hornblende or if this texture is the result of thermal metamorphism. The 

biotites are light brown, 1-3 mm euhedral grains that form as aggregate masses. The hornblende crystals are 

green to green-blue, 1-2 x 3-8 mm and elongate with a sub-acicular habit. Within these mafic masses are 

rare sphene and opaque minerals (presumably magnetite based on crystal shape). This hornfels texture is 

the best evidence in the study area for pre-Cretaceous plutonism. 

2.3.4 Gabbro 

 Gabbro occurs in two areas on the map. A large body (approximately 2 km 2 ) is located in the 

eastern center of the map and a much smaller body is near the Rex Creek Pluton (Figure 2.1). The 

relationship between these two occurrences is unclear. The largest body is dark green (mafic minerals) and 

white (plagioclase), coarse-grained and equigranular, approximately 50% plagioclase and 50% pyroxene 

with zones of up to 60-70% plagioclase. The gabbro also contains few fine-grained mafic enclaves of 

clinopyroxenite. The gabbro body near Rex Creek pluton appears to intrude the metavolcanic rocks. It is 

unclear whether this body is associated with the Rex Creek pluton or the large gabbroic body. The small 

body is dark green and grey in color consisting of 30-40% plagioclase and 70-60% pyroxene. 

2.4 Early Cretaceous Plutonic Rocks 

 The Cretaceous plutonic rocks include: the Nyac batholith, Bonanza pluton, Sawpit pluton, gray 

dikes and red dikes. Except for the Sawpit pluton, each unit is dated as Early Cretaceous (discussed in 

Chapter 4). I have grouped the Sawpit Pluton with the Early Cretaceous plutonic rocks because there is no 

evidence that the Sawpit Pluton cuts any of the Early Cretaceous rocks, it appears to intrude the Rex Creek 

Pluton (Figure 2.1) and Maddren (1915) reports diabase dikes cut it. 

In addition to composition, textures and mineralogy, another factor that can be used to 

discriminate between igneous bodies is their emplacement depth. The minimum melting 
30

point/crystallization temperature and composition of granite under water saturated conditions is fixed by 

pressure, so aplite compositions can be used to estimate pressure of crystallization. If the aplite has low 

calcium concentrations (< 1 wt% CaO), was crystallized under water saturated conditions, and represents 

the end product of magmatic fractionation, the normative quartz-orthoclase-albite values are a function of 

pressure (Tuttle and Bowen, 1958). Figure 2.13 shows normative data for the Nyac batholith and Bonanza 

pluton aplites projected onto the granite ternary diagram. The Nyac batholith aplites plot on the 

experimental curve at ~1.25 kb (9TF003). A second sample (9TF028B) plots to the right of this value and 

below the curve. Projecting this value onto the curve yields a pressure of ~1 kb. The third Nyac Batholith 

value (03ZW357C) plots at the end of the curve near 0.5 kb. This sample displays sericitic alteration and 

hence the composition does not represent the true pressure. Since one value (9TF003) plots on the expected 

curve at ~1.25 kb this is the best estimate for the crystallization pressure of the Nyac batholith and 

represents a depth of ~3 km. 

Two samples from Bonanza pluton (8TF036 and 03ZW374B) plot off the experimental curve. 

Sample 8TF036 is enriched in CaO and therefore does not plot accurately on this projection. Sample 

03ZW374B is ~1-3% sericite-chorite-carbonate altered and therefore does not represent the true original 

composition. Compensation for the alteration effect was calculated by estimating K2O enrichment and 

Na2O depletion in the sample. This calculation yields normative values that plot closer to the experimental 

curve (Figure 2.13); the crystallization pressure is low, but uncertain. Considering the textures 

(subporphyritic) in the pluton and the ambiguous aplite compositions, it is reasonable to estimate a pressure 

of ~0.5 kb or 1.5 km depth for the crystallization of Bonanza pluton. 

Despite spatial and compositional variation in Bonanza pluton, trace-element chemistry and age 

data (discussed in Chapter: 4) indicate that the Bonanza pluton at the three different locations (VABM 

Bonanza, Spruce and Bonanaza Creek lobes; Figure 2.1) are parts of a single body. Trace element 

chemistry from Bonanza pluton and the Nyac batholith show a clear pattern of trace element enrichment 

with decreasing silica content for cerium, yttrium, strontium, niobium and zirconium (Figure 2.12). 

2.4.1 Nyac Batholith 

 The Nyac batholith is located in the northwest corner of the study area (Figure 2.1). The batholith 

is an approximately 200 km2

 (Box et. al, 1993), elliptical body elongate parallel to the Golden Gate-Sawpit 

fault. The portion of the batholith that lies in the study area is small, but samples from outside of the map 

area were collected for comparison to other plutonic rocks. 

The Nyac batholith appears to be zoned, with a tonalite and monzodiorite rim grading into a 

granodiorite center. The batholith is generally equigranular and coarse-grained (locally seriate or 

porphyritic) with medium and fine-grained textures near the rim. Where porphyritic, the phenocrysts are 1-

3 cm K-feldspar. The batholith is cut by numerous aplite dikes and rare medium-grained dikes 
31

Ab Or

Qtz

0.5kb

1 kb

2 kb

3 kb

4 kb

5 kb

10 kb

20 kb

30 kb

Bonanza Pluton

Nyac Batholith

1 1 1

Figure 2.13: Aplite compositional geobarometry for the albite-quartz-orthoclase-H20 system. Arrow 

points towards the most likely formation pressure for the Bonanza Pluton at ~0.5 kb equivalent to 

~1.5 km depth. Experimental data from Tuttle and Bowen (1958), Steiner et al. (1975), Luth et al. 

(1964) and Huang and Wyllie (1975). Aplite data is from this study and (1) T. P. Frost, written comm. 

(2004). 
32

(03ZW357B) similar in composition to the batholith cut the batholith. The medium-grained dikes have 

slightly more K-feldspar than the granodiorite portions of the batholith they intrude. 

 In thin section the Nyac batholith displays common plutonic characteristics including randomly 

oriented, coarse, equigranular crystal grains and concentric zoning of plagioclase. The orthoclase crystals 

display weak perthitic texture and Carlsbad twinning. Plagioclase crystals display both polysynthetic and 

Carlsbad twins. Plagioclase anorthite contents range from 23 to 27%. Plagioclase crystals contain 2-5% 

sericite. In contrast, K-feldspar contains 0-<1% sericite. Samples displaying the most intense sericitization 

also have intergranular euhedral quartz. Granodiorite portions of the Nyac batholith contain 10-15% mafic 

minerals with sub-equal biotite and hornblende. Biotite and hornblende are slightly altered along their 

margins to chlorite; some biotites display up to 5% chloritization. Accessory minerals include allanite, 

apatite, sphene, and zircon. 

2.4.2 Bonanza Pluton 

Bonanza pluton is centered on VABM Bonanza peak and extends southeast towards Spruce Creek. 

A small portion of the pluton is exposed on a ridge north of the main body (Figure 2.1). Bonanza Pluton is 

dominantly granodiorite with local quartz monzonite and monzonite portions and marginal diorite, quartz 

diorite, tonalite and monzodiorite (Figures 2.7a and 2.8). The body is typically medium-grained (finegrained at margins) with central areas exhibiting sub-porphyritic textures. The majority of the Bonanza 

pluton has lower magnetic susceptibilities than the Nyac Batholith. The higher magnetic susceptibility 

values for Bonanza pluton are from the mafic (monzodiorite and tonalite) margins of the pluton, which 

presumably contains more magnetite. Aplite dikes are abundant in portions of the pluton, some are as wide 

as 10 cm. 

In thin section, the Bonanza pluton displays common plutonic characteristics such as, randomly 

oriented crystal grains and concentrically zoned plagioclase. Orthoclase crystals exhibit Carlsbad twins and 

microperthitic textures. Plagioclase crystals display both polysynthetic and Carlsbad twins and minor 

myrmekite. Plagioclase anorthite content ranges from 23 to 40%. The higher anorthite contents are from the 

more mafic part of the pluton (diorite, quartz-diorite). Sericitic alteration is pervasive. Both feldspars are 5-

15% sericitically altered; the plagioclase is more altered than the K-feldspar. 

The pluton contains 10-25% mafic minerals. Mafic minerals commonly include biotite and 

hornblende; minor amounts of pyroxene are also present. A straightforward crystallization order is seen in 

the granodiorite portion of the pluton where pyroxene grains are entirely enclosed by hornblende rims. The 

hornblende rim in turn is partially rimmed by biotite, indicating a crystallization order of pyroxenehornblende-biotite. 

The crystallization sequence of the mafic minerals in the monzodiorite portions of the pluton is 

different. In monzodiorite, pyroxene contains biotite inclusions. The pyroxene is similarly rimmed with 
33

hornblende, but the hornblende rarely entirely encloses pyroxene. Hornblende crystals also occur by 

themselves, with no pyroxene attached. 

The mafic portions of the pluton contain up to 1% apatite. All the rocks contain zircon, but the 

more mafic varieties have approximately twice as much. Granodiorite portions of pluton contain less 

apatite and zircon and have trace amounts of sphene. The presence of pyroxene in the pluton indicates that 

at least initially the pluton had a low water content. All mafics are partially chloritized. Samples displaying 

the most intense feldspar sericitization also have the most chloritization. 

2.4.3 Sawpit Pluton 

 The Sawpit pluton consists of multiple exposures, all of which lie near or within the Golden GateSawpit fault zone in the study area. The Sawpit pluton lies outside the study area as well and covers 

approximately 35 km2

 in its entirety (Box et al., 1993). The pluton is a seriate to coarse-grained biotite 

granite (Figure 2.7a). Portions of the pluton have miarolitic texture. The cavities are filled with chlorite and 

epidote or quartz. Veinlets of epidote and chlorite 1-3 mm in width cut the pluton, which locally contain 

pyrite. The pluton has lower average magnetic susceptibility than either the Nyac batholith or the Bonanza 

pluton (Table 2.1). 

 In thin section, orthoclase and rare plagioclase are sericitically altered (5-10%). All the mafics are 

entirely altered to a combination of chlorite (75%), epidote (20%), sphene and magnetite (5%). The 

feldspars are euheral to subhedral and enclosed by larger optically continuous anhedral quartz crystals. 

Accessory minerals include apatite, zircon and sphene. 

2.4.4 Gray Dikes 

 The gray dikes are a granodiorite porphyry characterized by their gray color and porphyritic 

texture. These dikes intrude both the metasedimentary and metavolcanic rocks. The dikes are typically 1-5 

meters wide and occur in greatest abundance northwest of the Bonanza pluton (Figure 2.1). The dikes are 

feldspar-biotite-hornblende-quartz porphyritic and have a gray aphanitic groundmass. The composition is 

dominantly granodiorite although tonalitic and monzodioritic varieties are also found (Figure 2.7b). Despite 

compositional variation, the feldspar-biotite-quartz porphyry texture is consistent. Rare (<1% of the rock 

volume) 5-mm-to 1-cm-sized, amoeba-shaped mafic inclusions occur in some of the dikes. The mafic 

inclusions consist of fine-grained plagioclase and mafic minerals (pyroxene and hornblende?). 

 In thin section, phenocrysts include plagioclase (2-15 mm, 10-30%), hornblende (2x1 to 10x3 mm, 

1-3%), biotite (1x8 to 4x10 mm, 1-5%), resorbed quartz with groundmass inclusions (2-10 mm, 1-3%) and 

K-feldspar (5-15 mm, 0-1%) with inclusions of hornblende and biotite. Hornblende and biotite are variably 

(0-10%) altered to chlorite. The groundmass consists of feldspar and quartz grains both <1 mm in size. 

Anorthite content of the plagioclase phenocrysts is 27-29%. 
34

2.4.5 Red Dike 

Red dikes are quartz monzonite porphyry dikes were seen only as rubble, not in outcrop. Red dike 

rubble is most abundant on the talus slope north of the limonite-stained metavolcanic rocks (Figure 2.1). 

The dikes are a biotite-feldspar porphyry with a red fine-grained groundmass. The majority of these dikes 

are intensely sericite-kaolinite altered. In altered varieties phenocrysts are entirely altered to muscovite, and 

limonite-sericite lined vugs account for 5-10% of the rock volume. 

In thin section, phenocrysts include plagioclase (1-5 mm, 1-3%), K-feldspar (1-3 mm, 1%) and 

biotite (1-2 mm, 1-2%). Plagioclase is albitically twinned and sometimes concentrically zoned. Plagioclase 

phenocrysts have anorthite contents of 26-35%. Some K-feldspar crystals display Carlsbad twining. The 

groundmass is a mixture of <1 mm feldspars, biotite, opaque minerals and minor quartz. Accessory 

minerals include apatite and zircon. Least altered varieties display weak chlorite alteration of biotite 

phenocrysts and ~1% sericitic alteration of feldspars. Strongly altered varieties display muscovite rimming 

vugs and biotite and feldspar phenocrysts entirely altered to muscovite and kaolinite. Complete loss of Ca, 

Na, Fe and Mg from conversion of the groundmass into sericite, kaolinite and quartz results in the volume 

loss (vugs). 

 Trace element analysis indicates altered and unaltered varieties are much more enriched in a 

variety of elements than the rest of the dikes and plutons (Figure 2.14). 

2.5 Tertiary (?) Dikes 

 The Tertiary (?) dikes are of uncertain age. They include the mafic and pink dikes. Each of these 

dikes cut the Bonanza pluton, so they are at least younger than that body. Also categorized in this group are 

some undifferentiated dikes. These dikes include a variety of different textures and compositions and are 

common in the district. They may represent previously classified dikes, but textural differences and 

variable compositions make it difficult to categorize these dikes. 

2.5.1 Mafic Dikes 

 Mafic dikes are located in the Bear Creek valley (Maddren, 1915) and on the ridge immediately 

west of Spruce Creek. Mafic dikes are black, diabasic textured gabbro. A single mafic dike was found at 

only one location cutting the Bonanza Pluton at Spruce Creek (Figure 2.1). 

 In thin section the mafic dike is composed of 70% plagioclase (0.1-1 mm), 5% pyroxene (0.1-1.5 

mm) and 25% alteration and vesicles. The plagioclase crystals are albitically twinned and weakly (1-5%) 

altered to sericite. The pyroxenes are concentrically zoned and weakly altered to clinozoisite and chlorite 

around their rims. The remaining rock is an alteration assemblage of oxy-chlorite, chlorite, biotite, 

clinozoisite and quartz. This peculiar assemblage is presumably the result of glass recrystallization, because 
35

basaltic glass and this assemblage have roughly equivalent composition. Clinozoisite also rims open 

cavities. 

 The mafic dike has trace element signature of continental basalt, suggesting they formed during an 

extensional event (Figure 2.4). 

2.5.2 Pink Dikes 

The pink dikes are a granodiorite porphyry found throughout the study area. The dikes are 

generally 1-5 meters wide and intrude the Bonanza pluton (Figure 2.1). The dikes are feldspar-biotitehornblende-quartz porphyry with a pink aphanitic groundmass. Pink dikes are dominantly granodiorite in 

composition, but monzogranite and syenogranite varieties exist (Figure 2.7b). 

In thin section, phenocrysts include plagioclase (2x3 to 4x6 mm, 10-20%), biotite (1x2 to 3x3, 2-

5%), hornblende (1x2 to 4x8, 1-3%) and resorbed quartz (1-5 mm, 0-7%). The groundmass is a finegrained mixture of similar composition which presumably contains some K-feldspar. Despite a relatively 

unaltered appearance in hand specimen, upon petrographic inspection it is evident that these dikes are 

strongly altered. Feldspar phenocrysts are altered to a combination of equal parts sericite and calcite with 

minor chlorite. Hornblendes are altered to a combination of chlorite (70%), calcite (25%), and opaque 

minerals (5%). Calcite commonly replaces the center of the crystal. Biotites are altered to a combination of 

chlorite (50%), muscovite (40%), calcite (10%) and trace sphene and opaque minerals (<1%). The 

groundmass is similarly altered. It is unclear how much of the sphene and opaque minerals are primary. 

2.5.3 Undifferentiated Dikes 

 A considerable number of low volume dikes that were not identified enough to be 

included on the geologic map occur in the field area. Analyzed samples have variable compositions (Figure 

2.7a) and textures. Some of these dikes may be Jurassic while others could be related to Early Cretaceous 

or Tertiary magmatism. 

2.6 Regional Geophysics and Structural Geology 

 In 1994 the Alaska Division of Geological and Geophysical Surveys published a regional 

magnetic map (ADGGS et al., 1994) of the Nyac area. The flight lines were spaced at quarter-mile intervals 

with a NW-SE orientation. The magnetic map is useful for identifying the large-scale faults and 

approximating some lithologic contacts in areas of poor exposure. Mapping in the area is difficult due to 

limited exposure (outcrops areconstrained mainly to ridges) and limited geophysics (no resistivity maps are 

available). Without resistivity data it is difficult to determine the number and orientation of faults in the. 
36

0 10 20 30 40 50 60

0

100

200

300

400

500

Zr

Nb+Y

Red Dikes

Bonanza Pluton

Nyac Batholith

Sawpit Pluton

Rex Creek Pluton

Diorite Hornfels

Altered Granodiorite

Figure 2.14: Trace element discrimination diagram for plutonic bodies and red dikes. Data 

are from this study, Gierymski and Werdon (1997), and T. P. Frost, written comm. (2004). 
37

study area. An area so close to the Golden Gate-Sawpit will potentially contain a significant number of 

subsidiary faults, which could have significant displacement. Many small faults cut the ridges in the study 

area, but their orientation is difficult to interpret without resistivity data, especially the smaller scale 

structures that could be locally important in interpreting the stratigraphy 

Magnetic susceptibilities vary considerably within and between units (Table 2.1, Figure 2.15). 

Since no geologic unit has a unique magnetic susceptibility, using the magnetic map to interpret lithologic 

units in areas of no exposure is problematic. Figure 2.16 shows that magnetic susceptibilities measured on 

surface samples generally correlate with the magnetic map. This indicates that where the magnetic 

susceptibilities measured at the surface coincide with magnetic intensity the exposed rock continues at 

depth or no drastic changes in magnetic character occur. The only obvious rock unit that matches a 

magnetic signature is the Rex Creek pluton. The body is a magnetic high in surrounding magnetic lows 

(Figure 2.16). The metasedimentary rocks display an average low magnetic signature except where in 

contact with the Nyac batholith (Figure 2.16). The high magnetic signature there is probably due to thermal 

metamorphism (producing secondary magnetite) and an apparent SE dip to the batholith. 

Southeast and east of the metasedimentary rocks are the metavolcanic rocks. This unit displays a 

generally higher magnetic signature than the metasedimentary rocks. Included in the metavolcanic package 

are areas dominantly composed of metabasalt (>70 of the rock volume). These metabasalt rich areas have 

average higher magnetic susceptibilities than the other metavolcanic rocks and are easily identifiable on the 

magnetic map (Figure 2.16). However, their exposure is never seen as a continuous stratigraphic layer in 

the study area. This is due largely to no exposure in the Bear Creek Valley and possible significant 

displacment on unidentified faults. If there was exposure in the Bear Creek Valley the magnetic highs seen 

there may correlate with the metabasaltic unit and would suggest that the metabasalts represent a 

stratigraphic layer and are likely the lowest and oldest rocks in the study area. 

Despite significant surface exposure, the Bonanza pluton displays no unique magnetic anomaly 

(Figure 2.16). Magnetic susceptibilities taken from the surface span a range of 0.14-30.83 x10-3 SI (Table 

2.1). Since significant compositional variations exist at different locations in Bonanza pluton and 

mineralization is focused in two areas, a naming scheme will be used to divide the Bonanza pluton into 

three different lobes. Thee lobes are, VABM Bonanza lobe (near VABM Bonanza Peak), Spruce Creek 

lobe and Bonanza Creek lobe (Figure 2.16). The Bonanza pluton appears to be displaced along high angle, 

north-south faults. Carbonate fault breccia located between the Spruce Creek lobe and VABM Bonanza 

lobe (Figure 2.1) suggests there is a fault between these two bodies, although the azimuthal orientation is 

unclear. Recent unroofing is evident at the Spruce lobe where a small metavolcanic raft lies on top of the 

pluton (Figure 2.1) indicating that this lobe was down-dropped relative to VABM Bonanza lobe. The 

Bonanza Creek lobe is left laterally displaced north approximately three miles from the Spruce Creek lobe. 
38

N = 13 54 8 19 16 2 1 16 16 1 17 2 185 45

3

2

1

0

-1

-2

-3

Metasedimentary RocksMetavolcanic RocksDikes UndiffGabbro

erentiated

Diabase DikeGrey DikePink DikeRed DikeAltered GranodioriteHornfelsed DioriteRex Creek PlutonSawpit PlutonBonanza Pluton

Nyac Batholith

Lo

g

m

a

g

n

et ci su

sc

e

pt bi ility (x10

^ -3

SI) Figure 2.15: Boxplot of the magnetic susceptibilities for the rock units in the study area. Bold lines 

represent median values and the circles and asterisks represent outside and far outside values, 

respectively. Data from this study. 
39

Explanation

FaultsKuskokwim Group cBonanza Pluton conNyac Batholith contaRex Pluton ContactMetasedimentary-voMetabasalt outline in 

Magnetic Susceptibility x10^

0.02 - 1>1 - 1010 - 108

450000 452500 455000 457500 460000 462500

6775000 6772500 6770000 6767500 6765000

450000 452500 455000 457500 460000 462500

6775000 6772500 6770000 6767500 6765000 0 1,000 2,000 3,00

500 

Bonanza Creek lobe VABM Bonanza lobe Spruce Creek lobe

159 56’ O

 61 07’ O 159 41’ O

 61 01’ O

Figure 2.16: Aero-magnetic map of the study area with some ground-based geologic contacts. Map shows the location of the three lo

Bonanza Pluton. The red and purple correspond to 54,800-54,500 nT, yellow 54,500-54,480 nT, green 54,480-54,300 nT, and blue 54

54,225 nT. Magnetic data from ADGGS staff et al. (1994).

Unmetamorphosed

Basalts
40

The Spruce and Bonanza Creek lobes are more mafic in composition and likely represent the near contact 

surface of the pluton. 

The sub-parallel alignment of the Nyac Batholith with the Golden Gate-Sawpit Fault suggests that 

the batholith occupies an old fault parallel to the Golden Gate-Sawpit Fault. No evidence of crystal 

deformation was found in the batholith, indicating that its shape is not the result of syn-magmatic 

deformation. The other possibility for this orientation is brittle deformation of the body by NE-SW trending 

faults. Detailed mapping of the batholith contact might indicate why the batholith has this orientation. 

The faults on the magnetic maps appear as linear magnetic lows or obviously offset anomalous 

magnetic bodies. Along the contact of the Nyac terrane with the Kuskokwim Group rocks in the southeast 

part of the study area, a N-S trending fault obviously bisect the northeast trending Golden Gate-Sawpit 

Fault (Figure 2.16). The Golden Gate-Sawpit Fault must therefore predate the N-S faults. 

Metabasalts north of Spruce Creek are the least thermally altered rocks in the study area. During intrusion 

of the Nyac batholith these rocks were presumably located further to the south and have been displaced left 

laterally along a north-south trending fault, the same fault that offsets Bonanza pluton (Figure 2.1). The 

thermal metamorphism effect is weakly imprinted on these rocks because they were presumably located 

further from the Nyac batholith. 
41

3. Gold Mineralization

 The Nyac district is a historically significant placer gold producer. Figure 3.1 shows all the 

drainages that have been placer mined. Placer mining and exploration are currently taking place on Bear 

and Shamrock Creeks (Figure 3.1). As of 2000, total placer gold production from the Nyac district is 

>500,000 oz (Foley, 2000). Placer gold is found in nearly all of the drainages in the study area, and it is 

important to determine the bedrock source for the gold in order to produce a model for local gold 

mineralization in the area. Over the years some bedrock gold occurrences have been identified in the 

district by intensive sample collection and chemical analyses. Over 2,500 rock and soil specimens from the 

study area have been analyzed for trace elements; however, other than plotting anomalous value locations 

nothing has been done with this large geochemical database. 

Only broad generalizations regarding the styles of mineralization have been made for the Nyac 

district (RAA 1975, Gierymski and Werdon, 1997). This study uses statistical analysis techniques with the 

geochemical database to classify the different styles of mineralization. Classification of the styles of 

mineralization was augmented by field observations, petrographic techniques, fluid inclusion analyses, 

trace and major oxide data comparisons and microprobe techniques. Three areas were identified within the 

study area that host the most significant gold mineralizations: the Wallace Occurrence, VABM Bonanza 

lobe and the Bonanza Creek color anomaly (BCCA) (Figure 3.1). Figure 3.2 is a simplified geologic map 

showing the location and sample number for each important assay. This chapter focuses on characterizing 

the different types of alteration and mineralization at each of these locations and uses factor analysis to 

classify the different types of gold mineralization. 

 

3.1 The Wallace Occurrence 

 USGS geologist Robert E. Wallace reported finding lode gold along the ridge at the confluence of 

the Tuluksak River and California Creek (Wallace, 1945; Figure 3.1). The ridge is covered by vegetation 

making it difficult to find any exposure. The location of the mineralization is only evident from a pile of 

rubble bull-dozed in the 1970’s. Gold mineralization occurs in altered gray dikes. Exposed gold bearing 

rocks occur over an approximately 10x8 meter area. 

 The gold occurs in open-spaced quartz-chlorite-calcite veinlets 1 to 8 mm thick that extend for 

>20 cm (vein dimensions are limited by rubble size). The veining accounts for approximately 1 % of the 

rock volume. The vein material is approximately 75% quartz, 10% chlorite, 5% calcite and 10% cavities 

and ore minerals (Figure 3.3). Due to the weathered nature of the mineralized rock the amount of original 

calcite is uncertain (i.e., the open-spaces in the veins may have once been filled with calcite). The quartz 
42

159 41’ 0

 61 04’ 0

 61 07’ 0

159 41’ 0

159 56’ 0

 61 01’

159 56’ 0

ANCHORAGE

FAIRBANKS

Study Area

Russian Mission A-3 Russian Mission A-2

Mission

Gulch

Spruce Creek

Happy Creek

Current Placer 

Mining

Current Drilling

Previously Placer Mined

Previously Placer Mined

Wallace

Occurrence

VABM Bonanza

lobe

Bonanza Creek

Color Anomaly

Tuluksak River

Figure 3.1: Topographic map showing historic and current placer mining locations. The three areas 

of most significant bedrock gold mineralization are also indicated. 
43

Explanation

Faults

Important As

Bonanza Pl

450000 452500 455000 457500 460000 462500

450000 452500 455000 457500 460000 462500

6775000 6772500 6770000 6767500 6765000

6775000 6772500 6770000 6767500 6765000 0 1,000 2,000 

500 

03ZW219 03ZW257 03ZW256 03ZW344 03ZW33903ZW499 03ZW434 03ZW441 03ZW383 03ZW292 03ZW351 03ZW386 03ZW382 03ZW369 03ZW353 03ZW387 03ZW093 03ZW088

159 56’ O

 61 07’ O 159 41’ O

 61 07’ O

Figure 3.2: Map location and sample number for important assays from this study.
Figure 3.3: Quartz-chlorite-calcite veining and associated tellurobismuthite and native gold from the 

Wallace occurrence. Figure 3.3b is a higher magnification picture of the top right portion (dotted line) 

of figure 3.3a. Figure 3.3c is from a different vein.

44
45

crystals are euhedral and up to 6 mm wide. The quartz crystals often terminate on adjacent sides of the 

vein. The chlorite crystals are rosettes 1-6 mm in diameter. In thin section the chlorite is length fast and has 

anomalous purple blue interference colors indicating a high Fe content. There is no evidence indicating that 

the cavities in the veins were at one time filled, indicating low pressure during mineralization. 

 No alteration envelopes were observed adjacent to the quartz veins; instead, the dikes hosting 

gold-quartz veins are pervasively altered. Feldspar phenocrysts are 10-90% altered to sericite (15-85%), 

albite (5-15%) and chlorite (<1%). Hornblende phenocrysts are 75-100% altered to a combination of 

chlorite (85%), calcite (10%), magnetite (2-10%) and rutile (2-3%). Biotite phenocrysts are 90-100% 

altered to a combination of chlorite (75-80%), magnetite (5-20%) and rutile (2-3%). The groundmass of the 

dike is almost entirely altered to sericite (40%), albite (30%), quartz (20%) and chlorite (10%). 

A standard means of assessing elemental changes during alteration processes is to model them 

based on Al2O3 immobility (Krauskopf and Bird, 1995). Table 3.1 shows composition of altered and 

unaltered gray dikes. Chemically the altered varieties have experienced CaO, Fe2O3, K2O, MgO, MnO, 

Na2O, P2O5, SiO2, Ba and Sr loss and Rb gain. These findings are consistent with the mineralogical 

alteration. CaO, Fe2O3, K2O, MgO, MnO, Ba and Sr are lost by the replacement of hornblende, biotite, 

plagioclase and K-feldspar by muscovite, chlorite, epidote and albite. Figure 3.4 shows stained versions of 

both altered and unaltered varieties of the grey dikes. The unaltered variety has a significant amount of Kfeldspar while the altered version has no K-feldspar. The chemistry also reflects this alteration in that the 

unaltered variety has more K2O than the less altered variety (Table 3.1) The altered variety has experienced 

significant CaO loss and relatively little Na2O loss, so the feldspar in the groundmass must be largely 

albitic. The higher LOI values for the altered gray dike indicates the presence of CO2 and water. Therefore 

the alteration at the Wallace occurrence is sericite-chlorite-carbonate-albite alteration. 

Ore minerals identified by reflected light and microprobe analysis include (in order of descending 

abundance): tellurobismuthite, gold, tetradymite and minor chalcopyrite (Table 3.2). As indicated by 

microprobe analysis the tetradymite occurs as fine interlayers in the tellurobismuthite. Chalcopyrite was 

only identified in one slide and was a <1 mm diameter grain. 

Table 3.1 Partial chemistry of three variably altered gray dikes from the Wallace occurrence. 

Sample Al2O3 CaO Fe2O3 K2O MgO MnO Na2O P2O5 SiO2 BA RB SR LOI alteration

03ZW474 15.6 3.5 4.67 2.92 1.66 0.09 3.44 0.18 65.2 1548 38 533 0.97 none 

7SB020B 16.29 3.74 4.50 1.94 1.46 0.06 4.02 0.19 67.57 815 47 340 4.89 weak 

03ZW369 15.94 1.99 4.01 2.11 0.98 0.05 3.89 0.20 70.28 712 53 347 strong 

% change 0% -44% -16% -29% -42% -43% -11% -8% -5% -55% 38% -36% 

* Ba, Rb, Sr values are ppm; all other data are wt%. % change calculated from least altered (03ZW474) and most altered 

(03ZW369) assuming Al immobility. Data are from this study and T. P. Frost (written comm., 2004). 
46

Figure 3.4: Stained gray dike samples from the Wallace occurrence. Figure 3.4a is from an intensely 

mineralized specimen and Figure 3.4b is from an unmineralized specimen. 
47

Although there are limited data from the Wallace occurrence, mineralized gray dikes throughout 

the study area can be used to investigate the elemental correlations. Table 3.3 shows the highest 

correlations are for Sb-As (.736), Bi-Ag (.685), Cu-Zn (.642), and Bi-Au (.630). Au and Ag have either 

negative or weak correlations with As, Cu, Sb and Zn, demonstrating that while those elements (As, Cu, Sb 

and Zn) have high correlations with one another they are not associated with Au and Ag. Tellurium data is 

too limited to determine its correlation with gold; however, visually the gold is attached to and intergrown 

with tellurobismuthite and tetradymite. Given this physical evidence, it is reasonable to assume that, given 

more data, Au would correlate well with Te. 

Both primary and secondary fluid inclusions are present in quartz veins. Measured primary 

inclusions (sample 03ZW369) are 9-15 microns in size, have negative crystal shapes, are generally isolated 

and always have double bubbles (Figure 3.5). The double bubbles indicate the fluids contain high levels of 

carbon dioxide. The secondary inclusions are 1-4 microns in size, irregularly shaped and define planes in 

Table 3.2 Microprobe analysis averages for Bi-Te minerals from the Wallace occurrence. 

Sample Bi % Te % S % Totals

Bi atomic 

wt% 

Te atomic 

wt% 

S atomic 

wt% Mineral 

03ZW369 51.73 47.9 0.02 99.64 39.7 60.2 0.08 Tellurobismuthite (Bi2Te3) 

03ZW369 58.35 36.64 4.49 99.48 39.5 40.7 19.8 Tetradymite (Bi2Te2S) 

Table 3.3 Correlation table for elements from mineralized gray dikes. 

.390

.066

23

.493* -.083

.017 .707

23 23

.685** .114 .630**

.000 .604 .001

23 23 23

.380 .168 -.087 -.030

.074 .445 .694 .892

23 23 23 23

.540** .209 .104 .320 .379

.008 .338 .636 .137 .074

23 23 23 23 23

.574** .736** .047 .500* .190 .545**

.004 .000 .830 .015 .386 .007

23 23 23 23 23 23

.134 .211 -.281 -.271 .642** .300 .109

.541 .334 .195 .212 .001 .164 .620

23 23 23 23 23 23 23

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

LOG_AS

LOG_AU

LOG_BI

LOG_CU

LOG_PB

LOG_SB

LOG_ZN

LOG_AG LOG_AS LOG_AU LOG_BI LOG_CU LOG_PB LOG_SB

Correlation is significant at the 0.05 level (2-tailed). *. 

Correlation is significant at the 0.01 level (2-tailed). **. 
48

Figure 3.5: Fluid inclusion in mineralization associated quartz veining from the Wallace occurrence. 

Double bubble is due to the presence of water and liquid CO2. Sample 03ZW369. 
49

 the quartz vein and quartz phenocrysts. The secondary fluid inclusions variably have double bubbles. No 

measurements were taken on the secondary fluid inclusions. 

Upon heating, the vapor bubble and the carbon dioxide bubble expanded to a vapor. This indicates 

the fluids were under low pressures. Since there is no direct evidence for the exact pressure under which 

these fluid inclusions formed under exists, an estimate of 0.5 kilobars was used to calculate the trapping 

temperature. Fluid inclusions from the Wallace occurrence record homogenization temperatures of 301-

325 o C, trapping temperatures of 346-370 o C, salinities of 2-5 wt % NaCl, and 45-80 vol% carbon dioxide 

(Table 3.4). 

Table 3.4 Primary fluid inclusion measurements from the Wallace 0ccurrence. 

Sample Th Tt wt% NaCl Tclath TCO2 xCO2

03ZW369 325 370 2 9 30 45 

 311 356 5 8 30 75 

 324 369 4 8 30 80 

 315 360 5 7 24 45 

 301 346 3 9 31 55 

* Th = final homogenization temperature, Tt = trapping temperature, Tclath= clathrate melting temperature, TCO2 = CO2

bubble homogenization and xCO2 = volume percent CO2. 

The oxidation and sulfidation of the mineralizing system at the Wallace occurrence can only be roughly 

estimated. However, because the dominant ore mineral is tellurobismuthite the system must be at relatively 

low sulfidation state in comparison to the activity of Te. If the sulfidation were higher one would expect 

more tetradymite or bismuthinite. 

3.2 VABM Bonanza Lobe 

 Placer Dome geologists discovered gold mineralization at VABM Bonanza lobe (Gierymski and 

Werdon, 1997). The mineralization is hosted in the Bonanza Pluton and north-south trending high angle 

fault zones adjacent to the pluton. For this study the area was resampled and more thorough chemical 

analyses were performed on the samples. Of particular interest was tellurium, for which no samples had 

been previously analyzed. 

 Mineralized rock in the VABM Bonanza lobe occurs throughout the entire body and partly into 

the Spruce Creek lobe. The bulk of the intense gold mineralization is constrained to the west side of the 
50

454000 455000454000 455000

67710006772000

6771000 6772000 Apl

Explanat

FauPink GraBonMetMet

25

0

Intense sericite-chlorite-carbonate alteration

Potassic alteration

Potassic alteration

x

x

Figure 3.6: Geologic map of the VABM Bonanza lobe showing the location of different styles of alteration and aplite dikes.
51

pluton (mineralized sample specimens; Figure 3.6). Rock exposure at the VABM Bonanza lobe is limited 

to boulder fields. Due to the tendency for the veins to weather and the boulders to break along quartz veins, 

it is difficult to estimate the actual amount of veining and to find unoxidized sulfide specimens. Areas of 

the most intense veining constitute approximately 1-2% volume of the rock. Ore minerals are more 

concentrated in or near quartz veins, but significant alteration and mineralized rock do occur were no 

veining is visible. 

 Types of alteration in the VABM Bonanza lobe include potassic and sericite-chlorite-carbonate 

(Figure 3.6). Significant gold mineralization is only found associated with the sericite-chlorite-carbonate 

alteration. 

 The potassic alteration consists of <1-3 mm wide quartz veinlets (length is limited by specimen 

size up to ~15 cm) that have narrow K-feldspar envelopes (<1-1mm) and rare (found at one location) 1-cmwide K-feldspar veins (length is limited by specimen size up to ~5 cm). Pyrite, magnetite and chalcopyrite 

are the only opaque minerals found in or near these veins. Potassic alteration is also present in one sample 

from the Bonanza Creek lobe (03ZW293). 

 The entire Bonanza pluton exhibits variable sericitic alteration of feldspars (Chapter 2). At the 

VABM Bonanza lobe an area of intense sericitic-chlorite-carbonate alteration consisting of 2-20 mm wide 

and >1m long sized quartz -calcite- chlorite-sericite veins with sericite envelopes occurs over a 400x900 

meter area (Figure 3.6). The vein material is approximately 80% quartz, 5% calcite, 2-3% chlorite, 2-3% 

sericite and 1-2% ore minerals. Feldspars within 4 cm of the veins are 5-90% replaced by sericite. All the 

mafic minerals are 75-100% replaced by a combination of chlorite (85-90%), calcite (5-10%) and rutile 

(<1%). Under the petrographic microscope the chlorite has green-brown anomalous interference colors and 

is length slow indicating low to moderate Fe contents. 

 Chemically the effects of the alteration are obvious. Table 3.5 shows geochemical data for 

mineralized and unmineralized granodiorite from VABM Bonanza. Altered granodiorite exhibits CaO, 

Fe2O3, MgO, MnO, Na2O, P2O5 and Sr loss and K2O and Rb gain. The K2O enrichment is expected with 

sericitic alteration since K is a significant component in sericite. The loss of CaO, Fe2O3, MgO, MnO and 

Na2O can be explained by the replacement of plagioclase and biotite by sericite and albite. Since CaO is 

depleted in altered samples and Na2O is relatively unchanged, the dominant non-potassic feldspar must be 

albite. Therefore the alteration at VABM Bonanza is sericite-chlorite-carbonate-albite assemblage. 

Rb is a relatively incompatible element and is concentrated in the residual melt as a pluton cools. 

If the Rb is concentrated in the residual melt and thus in the fluids inherent to the pluton, one would expect 

increased Rb concentrations in the altered and mineralized parts of the pluton if in fact magmatic fluids are 

responsible for the mineralization. The fact that this phenomenon is seen is direct evidence that the fluids 

responsible for the mineralization are magmatic. For this style of alteration, a direct inverse correlation 

between Sr and Rb can be used to evaluate the extent of alteration. Figure 3.7 shows increased Rb/Sr ratios
52

Figure 3.7: Sr vs. Rb plot for altered and unaltered granodiorite samples from VABM Bonanza lobe. 

Increasing Rb/Sr ratios indicate stronger alteration. 

increasing with alteration. Table 3.5 ranks the rocks by this method, and it illustrates that rocks with higher 

Rb/Sr ratios similarily have lower CaO, Fe2O3, MgO, MnO, Na2O concentrations. 

Identified ore minerals in sericite-enveloped veins include (in order of decreasing abundance): 

pyrite, chalcopyrite, magnetite, bismuthinite, molybdenite, native gold, arsenopyrite, pyrrhotite and 

bismuth. Chalcopyrite and pyrite are by far the most common minerals in the quartz veins. Pyrite is roughly 

twice as abundant as chalcopyrite. Although no Te-bearing minerals were identified, Te concentrations in 

excess of 3 ppm indicate some Te-bearing minerals must be present. The mineral assemblage in the zone of 

intense sericite-chlorite-carbonate alteration is pyrite, chalcopyrite, bismuthinite, molybdenite and native 

gold (Figure 3.8). Arsenopyrite was only observed in one specimen (03ZW349) from Spruce Creek. 
53

Neither of the samples containing pyrrhotite (03ZW142) or bismuth (03ZW496) contain significant Au; 

both are located outside of the zone of intense sericite-chlorite-carbonate alteration (Figure 3.6). At these 

two occurrences chlorite is more abundant than sericite and there is essentially no sericitic envelope. 

Table 3.5 Partial chemistry for granodiorite samples from the VABM Bonanza lobe. 

Sample Al2O3 CaO Fe2O3 K2O MgO MnO Na2O P2O5 Rb Sr Alteration

03ZW378 16.2 3.5 3.8 3.6 1.8 0.06 3.3 0.19 133 578 0 

03ZW391 15.6 3.4 3.6 3.7 1.7 0.06 3.2 0.18 140 519 0 

03ZW395 16.0 3.0 3.8 3.7 1.8 0.05 3.2 0.19 161 563 0 

03ZW482 15.7 3.2 3.6 3.8 1.6 0.05 3.2 0.17 154 517 0 

03ZW382 16.0 2.7 3.4 3.2 1.7 0.04 3.4 0.19 151 497 1 

03ZW386 15.8 2.2 3.2 3.7 1.5 0.04 3.3 0.16 167 453 2 

03ZW379 16.5 1.3 3.4 3.9 1.6 0.05 3.3 0.19 191 385 3 

03ZW387 15.8 2.6 3.1 3.5 1.3 0.04 3.3 0.18 169 364 4 

03ZW340 15.3 1.4 2.9 4.0 1.2 0.05 3.1 0.16 159 320 5 

03ZW339 15.1 1.1 2.9 3.5 1.3 0.03 2.9 0.16 178 252 6 

03ZW377 17.4 0.3 2.6 4.1 1.0 0.03 3.0 0.19 234 206 7 

%change 0% -92% -36% 7% -49% -52% -14% -5% 64% -67% 

* Rb and Sr data are ppm; all other data are wt%. % change calculated from least altered (03ZW378) and most altered 

(03ZW377) assuming Al immobility. Alteration increases from 0 (unaltered) to 7 (most altered). Unaltered samples (0) are 

unmineralized.

 

Due to limited exposure and the inability to properly sample the anomaly, bulk grades from the 

VABM Bonanza lobe are uncertain. However, hand specimens collected from the most altered zone are 

generally anomalous in gold. Mineralized hand specimens assay up to 20.8 ppm Au. 

 Regression of all mineralized samples from the VABM Bonanza lobe show gold correlates best 

with tellurium (.822) and bismuth (.581) (Table 3.6). Samples containing >100 ppb Au report correlation 

coefficients of .812, .737 and .712 for Bi, Ag and Cu, respectively (Table 3.7). For strongly mineralized 

samples (>200 ppb Au) Au correlates best with Te (.919). It appears that, the higher the Au concentration, 

the greater the Au correlation with Bi and Te, and the lower the Au concentration, the better the correlation 

with Cu. 

Primary fluid inclusions (Figure 3.9) were identified only in one vein sample (03ZW339) from 

VABM Bonanza. They are 3.75-15 microns in size, have roughly negative crystal shapes, are generally 

isolated and variably contain daughter minerals. The infrequency of primary inclusions is presumably the 

result of their destruction by later secondary inclusions. The secondary inclusions are much more abundant 

and are found both in the quartz veins and in quartz crystals in the pluton. Measured inclusions are 4-6.5 

microns in size, irregular in shape, define planes and lack daughter minerals. 
54

Figure 3.8: Mineralization in quartz veining from VABM Bonanza lobe. Bottom pictures (b and c) are 

photomicrographs from polished thin sections of vein material. 
55

Table 3.6 Correlation table for all mineralized samples from the VABM Bonanza lobe. 

.348**

.010

54

.526** .233

.000 .089

54 54

.518** .129 .581**

.000 .354 .000

54 54 54

.717** .141 .481** .429**

.000 .309 .000 .001

54 54 54 54

.234 -.171 .022 .029 .150

.105 .240 .881 .844 .302

49 49 49 49 49

.425** .412** .015 .215 .037 -.057

.001 .002 .911 .119 .793 .698

54 54 54 54 54 49

.496** .311* .104 .350** .260 .506** .464**

.000 .022 .456 .009 .057 .000 .000

54 54 54 54 54 49 54

.211 -.083 .822** .764** .195 -.103 -.127 .130

.416 .751 .000 .000 .454 .693 .626 .619

17 17 17 17 17 17 17 17

.303* .373** -.022 .085 .252 .337* .569** .628** -.340

.026 .005 .874 .539 .066 .018 .000 .000 .182

54 54 54 54 54 49 54 54 17

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

AS

AU

BI

CU

HG

PB

SB

TE

ZN

AG AS AU BI CU HG PB SB TE

Correlation is significant at the 0.01 level (2-tailed). **. 

Correlation is significant at the 0.05 level (2-tailed). *. 

Table 3.7. Correlation table for samples with >100 ppb Au from the VABM Bonanza lobe. 

.423

.080

18

.737** .152

.000 .548

18 18

.734** .117 .812**

.001 .644 .000

18 18 18

.901** .310 .712** .753**

.000 .210 .001 .000

18 18 18 18

.332 .206 .238 .149 .184

.178 .412 .341 .555 .466

18 18 18 18 18

.737** .471* .541* .525* .631** .218

.000 .049 .021 .025 .005 .386

18 18 18 18 18 18

.706** .729** .421 .391 .461 .444 .645**

.001 .001 .082 .108 .054 .065 .004

18 18 18 18 18 18 18

-.304 .198 .600 .491 -.464 -.749 -.446 .402

.507 .671 .154 .263 .295 .053 .316 .372

77777777

.644** .610** .348 .374 .563* .560* .725** .741** -.584

.004 .007 .157 .126 .015 .016 .001 .000 .168

18 18 18 18 18 18 18 18 7

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

AS

AU

BI

CU

HG

PB

SB

TE

ZN

AG AS AU BI CU HG PB SB TE

Correlation is significant at the 0.01 level (2-tailed). **. 

Correlation is significant at the 0.05 level (2-tailed). *. 
56

Primary fluid inclusions from quartz veins (sample 03ZW339) record final homogenization 

temperatures of 221-486 o C, trapping temperatures 266-536 o C and salinities of 21-55 wt% NaCl (Table 

3.8). Secondary fluid inclusions from quartz veins (sample 03ZW382) report final homogenization 

temperatures of 87-146 o C, trapping temperatures of 132-191 o C, and salinities of 5-9 wt% NaCl. The 

secondary fluid inclusions most likely represent younger cooler fluids unrelated to mineralization. The 

mineral assemblage of pyrite-chalcopyrite-magnetite allows an estimate of the oxidation and sulfidation 

state of the system. In reflected light these three minerals and native gold were observed in a single quartz 

vein. Figure 3.10 shows the possible range of oxidation and sulfidation state conditions for the mineralizing 

system. 

Table 3.8 Primary and secondary fluid inclusion measurement data from the VABM Bonanza lobe. 

Sample Th Tt Ts Tfd wt% NaCl 

03ZW339 220 536 486 55 

 207 529 479 54 

 204 522 472 53 

 211 477 427 49 

 425 470 332 40 

 362 407 227 33 

 346 391 337 41 

 320 365 

 212 350 305 38 

 226 334 289 37 

 261 306 

 256 301 

 255 300 

 252 297 -19 21 

 247 292 

 247 292 -20 23 

 246 291 

 244 289 

 240 286 -20 22 

 221 266 

03ZW382 146 191 -6 9 

 133 178 -3 5 

 87 132 -3 5 

* Th = liquid homogenization temperature, Tt = trapping temperature, Ts = solid homogenization temperature and Tfd = 

freezing point depression. 
57

Figure 3.9: Fluid inclusion from a quartz vein hosting mineralization in the VABM Bonanza lobe. The 

primary fluid inclusion is large, has negative crystal shape and a daughter mineral (halite). In 

contrast, secondary fluid inclusions are smaller and occur in lines. Sample 03ZW339. 
58

3.3 Bonanza Creek Color Anomaly 

 A prominent altered zone, informally named the Bonanza Creek Color Anomaly (BCCA; Figure 

3.1) is an area of extensive limonite stained pyritic metavolcanic hornfels, easily seen from miles away 

(Figure 3.11). The pyritic hornfels contains up to 10% pyrite, but does not contain appreciable gold 

concentrations (generally < 20 ppb Au). The pyritic rocks do contain variably high tellurium contents (up to 

5 ppm). However, no tellurium minerals were observed in reflected light, presumably because the Te 

replaces sulfur in pyrite (Fe (S,Te)2). Much of the pyritic hornfels at the BCCA is brecciated, indicating 

faulting, which facilitated supergene fluid flow to produce limonite by oxidation of pyrite. Within the 

pyritic hornfels are isolated areas containing calc-silicate veinlets. The calc-silicate veinlets have garnet 

cores with pyroxene and epidote envelopes. Opaque minerals associated with the veinlets include pyrite, 

chalcopyrite and pyrrhotite. The veinlets do not occur in great enough frequency to be economically 

important, but they do demonstrate that some of the mineralization at the BCCA is plutonic-related. 

Anomalous gold values at the BCCA include high-T and low-T mineralization. 

3.3.1 High-T Mineralization 

 The high-T mineralization at the BCCA is of two types: Au-Bi and Cu-Au. The Au-Bi 

mineralization is restricted to two samples collected by PDX geologists. The specimens include a limonite 

gossan and a granitic rock cut by quartz-chlorite-limonite veins. This mineralization is presumably related 

to the Bonanza Creek lobe at the BCCA. 

The high temperature Cu-Au mineralization occurs near the contact of the Bonanza Creek lobe 

with the metavolcanic rock unit (Figure 3.12). The Cu-Au mineralization extends for approximately 100 

meters from the contact; the most intense veining is within ten meters of the contact. This mineralization 

consists of quartz-chlorite-calcite veins with associated magnetite, chalcopyrite and native gold (Figure 

3.13). The quartz veins are up to 3 cm wide, >30 cm long and composed of approximately 70% quartz, 

10% chlorite, 5% calcite, 10% magnetite, 5% chalcopyrite and <1% pyrite. Total veining near the contact 

constitutes approximately 2-5% of the rock volume. Metabasalt that hosts the veining is pervasively 

altered. Plagioclase phenocrysts in the metabasalt are 5-15% sericitized. The groundmass is ~75% altered 

to 75% biotite, 15% chlorite, 10% sericite and 10% magnetite. Chlorite in the veins has anomalous greenbrown interference colors and is length fast. Biotite (<1%) is also present in and surrounding mineralized 
59

-48 -46 -44 -42 -40 -38 -36 -34 -32

160

180

200

220

240

260

280

300

log f O2(g)

T (

d

e

g

rees C)

Daphnite

14A

Magnetite

Troilite

FeSO4 Nontronite-Na

,

Beidelite

Kaolinite

BCCA low-T (epithermal)

mineral assemblage stability

field

Hematite

VABM Bonanza lobe and BCCA high-T 

(proximal) mineral assemblage stability field

Water Unstable

Figure 3.10: Oxidation vs. Temperature mineral stability diagram at 500 bars. The diagram includes 

the presence of quartz, pyrite, chalcopyrite, muscovite, K-feldspar and albite. The diagram illustrates 

the possible range of temperature and oxidation state for the mineral assemblage of pyrite, 

chalcopyrite and hematite for the low-T mineralization at the BCCA. In contrast, the pyritechalcopyrite-magnetite mineral assemblage at the VABM Bonanza lobe and high-T (proximal) 

mineralization at the BCCA is higher temperature and presumably lower oxidation than the BCCA 

low-T (epithermal) mineralization. Diagram calculated using Geochemist’s Workbench (Bethke, 1998) 

and thermodynamic data of Delany and Lundeen (1990). 
60

Figure 3.11: Two pictures of the limonite stained pyritic metavolcanic rocks at the BCCA. Figure 

3.11a is looking east from Spruce Creek and Figure 3.11b is looking southeast down the ridge north 

of the color anomaly. 
61

458000 459000458000 459000

6774000 6773000

6774000 6773000 Explanation Faults Breccia Red Dike Altered Red Dikes 

Bonanza Pluton Metasedimentary RLimonite-stained MMetavolcanic Rock

0 250 

Potassic alteration overprinted bychlorite-carbonate-sericite (03ZW353)

Sericite-kaolinitealteration ofred dikes

Figure 3.12: Geologic map of the BCCA showing the location of different styles of alteration. Faults mapped in part by regional geophy
62

Figure 3.13: Quartz vein mineralization from the high-T mineralization at the BCCA. Figure 3.13a is a 

mineralized metavolcanic rock near the contact with the Bonanza Creek lobe. Figures 3.13a and b 

are photomicrographs of quartz veins from polished thin sections in reflected light. 
63

quartz veins. The appearance of secondary biotite is the only evidence for mineralization associated with 

potassic alteration in the study area. Figure 3.13: Quartz vein mineralization from the high-T mineralization 

at the BCCA. Figure 3.13a is a mineralized metavolcanic rock near the contact with the Bonanza Creek 

lobe. Figures 3.13a and b are photomicrographs of quartz veins from polished thin sections in reflected 

light. 

On the aeromagnetic map (Figure 2.16) the BCCA is a large magnetic high. The highest magnetic 

anomaly measurement is at this mineralization locality. The high magnetic signature is likely related to the 

significant amount of magnetite at the occurrence. This suggests that the mineralization may continue to 

significant depths. A single mineralized specimen (03ZW353) from this area assayed 10.9 ppm Au and 

1,860 ppm Cu. 

Analyzed primary fluid inclusions from mineralized quartz veins (03ZW353) are 3-17.5 microns 

in size, have negative crystal shapes, and approximately 90% have NaCl daughter minerals (Figure 3.14). 

The fluid inclusions record final homogenization temperatures of 237-507 degrees C, trapping temperatures 

of 282-557 degrees Celsius, and salinities of 17-57 wt% NaCl (Table 3.9). The lower homogenization 

temperatures typically have low salinities as well and presumably indicate conditions when the system was 

cooling. The wide range of trapping temperature is reflected in the alteration-associated minerals, chlorite 

Table 3.9 Primary fluid inclusion measurement data from high-T mineralization at the BCCA. 

Sample Th Tt Ts Tfd wt% NaCl 

03ZW353 232 557 507 57. 

 225 543 493 56 

 398 443 331 40 

 291 415 370 43 

 302 358 313 39 

 258 357 312 39 

 257 355 310 39 

 270 351 306 38 

 268 349 304 38 

 271 339 294 38 

 208 320 275 36 

 275 320 245 34 

 244 311 266 36 

 195 310 265 36 

 207 293 248 35 

 246 291 214 33 

 244 289 -20 23 

 237 282 -13 17 

Th = liquid homogenization temperature, Tt = trapping temperature, Ts = solid homogenization temperature and Tfd = 

freezing point depression. 
64

Figure 3.14: Fluid inclusions in quartz veins from the high-T mineralization at the BCCA. Primary 

fluid inclusions exhibit negative crystal shapes, are generally isolated and have daughter minerals 

(halite). Secondary fluid inclusions are generally irregular in shape, occur along fractures and 

variably contain daughter minerals. Sample 03ZW353. 
65

and biotite. The biotite presumably formed during high temperatures and chlorite replaced biotite (evident 

from significant sphene in the chlorite) during cooling. A continuum of trapping temperatures also suggests 

this is the case. 

The combination of pyrite-chalcopyrite-magnetite is a similar assemblage to the mineralization at 

the VABM Bonanza lobe. Again this assemblage defines a range of oxidation-sulfidation state conditions 

for the mineralizing system (Figure 3.10). 

3.3.2 Low-Temperature Mineralization 

The low-temperature mineralization at the BCCA occurs in a variety of different forms including 

vuggy chalcedonic veining, sericitically altered red dikes, and mineralized fault (hydrothermal?) breccia 

(Figure 3.15). 

Vuggy chalcedonic veining is found in the limonite stained pyritic hornfels and in close proximity 

to the sericitically altered dikes. The chalcedonic veins are up to 15 cm wide and their length is limited to 

20 cm by rubble occurrence. Open cavities account for approximately 5% of the rock by volume. Of two 

specimens analyzed in this study the highest ore element values were 0.723 ppm Au, 9.88 ppm Ag and 0.28 

ppm Hg. 

Sericitically altered red dikes are concentrated on the ridge north of the BCCA (Figure 3.12). The 

sericitically altered dikes are characteristically pink to orange in color with open vugs accounting for 5-

15% of the rock volume. The vugs are lined with sericite, kaolinite and oxidized sulfides. The original 

feldspar and biotite phenocrysts of the dikes are entirely altered to muscovite. The groundmass is a 

combination of 40% quartz, 35% sericite, 15% feldspar (albite?) and 10% kaolinite. No visible ore minerals 

were observed in the dikes. However, some of the altered dikes exhibit square shaped cavities were pyrite 

presumably occurred. Table 3.10 shows chemistry for the altered and unaltered varieties of the red dikes. 

The red dikes have experienced loss for all of the major oxides and some trace elements. The loss of most 

major elements is apparent in the vuggy nature of the dikes. The increased Al2O3 and SiO2 in the altered 

Table 3.10: Partial chemistry for altered and unaltered red dikes. 

Sample Al2O3 CaO Fe2O3 K2O MgO MnO Na2O P2O5 SiO2 TiO2 Ba Rb Sr 

03ZW297 16.84 1.70 4.27 5.15 0.94 0.11 4.13 0.19 64.49 0.61 1449 217 354 

03ZW427 17.95 0.06 1.57 4.31 0.15 0.01 4.25 0.03 71.49 0.18 1514 78 117 alt

03ZW434 17.80 0.12 3.19 4.21 0.37 0.01 4.27 0.07 69.67 0.29 1328 69 157 alt

03ZW435 17.52 0.08 3.25 4.08 0.38 0.01 4.43 0.07 69.90 0.27 1204 69 141 alt

03ZW351 21.90 0.01 2.99 3.76 0.51 0.01 1.16 0.02 69.45 0.21 1186 76 55 alt

%change 0% -100% -46% -44% -58% -96% -78% -91% -17% -74% -37% -73% -88% 

* Ba, Rb and Sr are ppm; all other data are wt%. % change calculated from least altered (03ZW297) and most altered 

(03ZW351) assuming Al immobility. Data are from this study. 
66

Figure 3.15: Pictures of sericitic-kaolinite altered dikes, chalcedonic veining and quartz veined 

carbonate breccia of the low-T mineralization at the BCCA. Figure 3.15a and b are examples of the 

altered red dikes in hand specimen (a) and thin section (b). Figure 3.15c shows carbonate breccia 

and quartz-hematite veining from low-T (epithermal) mineralization. Figure 3.15d is a 

photomicrograph of pyrite with chalcopyrite inclusions from the hydrothermal breccia. Figure 3.15e 

shows limonite filled vugs in a chalcedonic vein. 
67

varieties is the result of intense sericite-kaolinite-silica alteration. The lack of Rb enrichment suggests the 

major alteration mineral is kaolinite rather than sericite (as seen at VABM Bonanza). 

The mineralized fault breccia (sample 03ZW292) is located on top of the ridge north of the 

limonite stained metavolcanic rocks. The breccia consists of carbonate-replaced metabasalts cut by quartz 

veins. The carbonate-replaced breccia contains minor pyrite and chalcopyrite (Figure 3.15). The quartz 

veins contain clasts of carbonate-replaced breccia and 1-5% specular hematite. Despite the apparent lack of 

abundant ore minerals the breccia assays up to 15.1 ppm Au (J. Foley, written comm., 2004) and 1.6 ppm 

Hg. 

Regression of Au values >200 ppb from the low-T mineralization do not show any significant 

correlation with other ore elements. However, if some data points are removed Au correlates well with Hg 

.987 (Figure 3.16). The reason for not seeing any significant correlations with the unedited data is due to 

limited sample analyses from this style of mineralization or poor chemical analysis for data not from this 

study. 

The mineral assemblage of pyrite-chalcopyrite and hematite can be used to approximate the 

oxidation-sulfidation state conditions for the mineralizing system (Figure 3.10). The presence of kaolinite 

allows a maximum temperature estimate to be made, since at higher temperatures kaolinite dehydrates into 

pyrophyllite. Figure 3.10 illustrates that under quartz saturated conditions the maximum temperature for 

kaolinite formation is 240 degrees Celsius. 

3.4 Other Styles of Mineralization 

 In addition to the three main gold mineralized areas described above, two additional areas of weak 

gold mineralized areas occur in the study area. These are the Spruce Creek skarn and Cu-mineralization 

near the Rex Creek pluton. Although neither of these types contain significant gold, they are important to 

the mineralization history. 

 The skarn consists of approximately 50% epidote, 30% calcite, 5-7% hornblende, 5% garnet, 5% 

scapolite and 2-3% pyroxene. The garnet, pyroxene and scapolite minerals represent the prograde 

assemblage while the calcite, epidote and hornblende represent the retrograde assemblage. Sulfides 

observed in the skarn include pyrite (85%), chalcopyrite (10%), pyrrhotite (5%) and covellite (<1%). The 

pyrrhotite always occurs as inclusions in the pyrite, indicating low oxidation-sulfidation conditions 

progressing to more oxidized conditions during mineralization. Covellite rims chalcopyrite and represents 

supergene alteration. Of the three samples analyzed, none contained Au in excess of 100 ppb, but all 

contained anomalous Cu and one sample reported 96 ppm W (Table 3.11). 
68

R2 = 0.9873

-1.50

-1.00

-0.50

0.00

0.50

1.00

-1.00 -0.50 0.00 0.50 1.00 1.50

log Au (ppm)

log Hg (ppm)

Figure 3.16: Linear regression plot for Au and Hg from low-T (epithermal) mineralization at the BCCA 

(samples plotted have >200 ppb Au). The squares are data from this study while the triangles are 

from Gierymski and Werdon (1997). The data as a whole indicate a poor correlation between Au and 

Hg. Regression of the four samples from this study, however, result in a strong correlation between 

Au and Hg. 
69

Table 3.11: Partial assays for Spruce Creek skarn specimens; values are ppm. 

Sample Ag Au Bi Cu Hg Mo Pb Sb Te W Zn 

03ZW256 0.27 0.02 0.02 193 0.01 0.52 5.4 0.76 0.01 10 39 

03ZW257 0.32 0.04 2.97 580 0.05 6 2.9 6.41 0.14 96 33 

03ZW344 0.88 0.09 0.83 658 0.01 1.03 0.9 1.42 0.14 <10 29 

Originally, the Spruce Creek skarn (Figure 3.2) was a carbonate rich bed approximately 10-15 

meters wide. Volcaniclastic textures (volcanic rock and plagioclase crystal fragments in a fine-grained 

matrix) are evident in thin section from portions of the skarn, presumably at the boundary of the carbonate 

bed. 

The Rex Creek pluton does not appear to be related to the mineralization in the VABM Bonanza 

lobe. The alteration mineral assemblage at the Rex Creek pluton is epidote-chlorite-carbonate-sericite. Ore 

minerals associated with the alteration include malachite, chalcopyrite, magnetite and pyrite. Where 

metavolcanic rocks shallowly overlie the pluton there are rare, open-spaced, malachite-stained quartz veins 

with chalcopyrite (samples 03ZW219, 03ZW093). These veins have associated anomalous Cu and Ag 

values (Table 3.12). The open-spaced nature of the quartz veins indicates that the mineralization formed 

under low-pressure conditions. An intensely malachite stained portion of the metavolcanic rocks 

(03ZW088) exists at the NE end of the Rex Creek pluton (Figure 3.1). This zone is approximately 10 

meters in width and assays over 1% Cu (Table 3.12). The pluton itself exhibits 1-150 mm sized epidote 

veins that variably contain up to 1-5% pyrite and magnetite. Mafic minerals are 0-100% replaced by pyrite. 

Pyrite that replaces mafic minerals is accompanied by epidote, chlorite, calcite and magnetite. Pyrite is 

largely restricted to the pluton, while chalcopyrite is dominantly found outside the pluton. 

Table 3.12. Partial assays for Rex Creek pluton associated mineralization; values are ppm. 

SAMPLE Ag As Au Bi Cu Hg Mo Pb Sb Te Zn 

03ZW219 0.03 1 <0.001 <0.01 244 <0.01 0.51 1.2 0.08 <0.01 15 

03ZW088 1.16 0.6 0.002 1.16 13200 <0.01 0.61 11 0.13 0.51 393 

03ZW093 0.6 1.8 0.008 0.19 676 0.01 1.66 50.1 0.14 0.1 40 

Fluid inclusions in quartz veins from the Rex Creek pluton are irregular in shape and generally <2 

microns in size and always define planes. The morphology and geometry of these fluid inclusions indicate 

they are all secondary. If primary inclusions did exist the likelihood of finding any unaffected by the 

secondary inclusions is doubtful. 

 
70

3.5 Placers 

The location of historic and current placer mining operations include Bear Creek, the Tuluksak 

River and most of their tributaries (Figure 3.1). In the early 1900’s high grade placers were found at the 

mouths of California and Rocky Creeks (Figure 3.1; Gierymski and Werdon, 1997). In the mid 1990’s the 

most productive placer mining was on Spruce Creek; a minimum 25,000 oz. of gold was produced from 

that drainage (J. Foley, written comm., 2004). Bear Creek was being mined in 2003 and Shamrock Creek is 

expected to be mined soon. 

Despite a long history of placer mining, limited data exist on the placer gold from the Nyac 

district. A preliminary SEM placer gold study by Dan McCoy (in Gierymski and Werdon, 1997) focused 

on the morphology and leached rims of placer grains from the Nyac district. These data (Table 3.13) show 

that placer gold from Spruce and Happy Creeks is irregular in shape and has thin (5-10 micron) partially 

concentric (15-20%) rims. Placer gold from Bear Creek is craggy and fully rimmed (10-40 microns). 

In reflected light the placer grains appear homogenous (Figure 3.17a-d). No pores or dark yellow 

rims are visible which would indicate that the gold was leached of Ag and thus had traveled a significant 

distance. Placer gold is occasionally attached to quartz and tetradymite (Figure 3.17c and 3.17d). 

Gold occurs in nature as a solid solution of Ag and Au, known as electrum. Traditional 

measurements of Au composition are reported as fineness (= (Au/Au+Ag)*1000). As gold travels in a 

stream environment, the Ag in solid solution becomes oxidized and is leached from the gold grain (Knight 

et al., 1999; Figure 3.17e). Removing Ag from the electrum results in gold enrichment, hence increasing 

fineness. 

Microprobe analyses of placer grains prepared for SEM study (Table 3.14) show both leached and 

unleached rims. Placer grains from Spruce and Happy Creeks show no compositional rimming, indicating 

minimal transport. In contrast, nearly pure gold rims (indicative of Ag-leaching) are present on gold grains 

from Bear Creek. These grains experienced significant stream transport. 

Table 3.14 also lists average gold finenesses for Bear and Bonanza Creeks and the Tuluksak 

River. The production average finenesses must be carefully interpreted since they could represent the 

Table 3.13. SEM morphology of placer gold from the study area. 

Sample Location 

Size 

(microns) Shape 

Leached Rim 

(% of 

Circumference) 

Rim 

Width 

(microns)

Average 

Width 

975727 Spruce Creek 500x200 craggy, attached quartz 20 1-5 2 

975842 Happy Creek 50x50 craggy 15 1-10 3 

975721 Bear Creek 100x100 craggy 100 10-40 25 

* Data in Gierymski and Werdon (1997). 
71

Figure 3.17: Photomicrographs of placer gold from the study area. Samples are from: (a) Bear Creek 

(975721), (b) Happy Creek (975842), (c) and (d) Spruce Creek (975727 and placer sample), and (e) 

weathered gold grain (courtesy of R. Newberry). Figure 3.17e is a weathered gold grain exhibiting a 

porous appearance where Ag has been leached out. None of the grains from the study area exhibit 

visible Ag-leached rims and are irregular in shape or are attached to quartz (c) or tetradymite (d) 

indicative of minimal stream transport. 
72

average of several gold populations. Figure 3.18 shows the location for each of the placer grains and 

production average finenesses. The average fineness location for Bonanza Creek is constrained to the 

mouth of the creek since placer operations stopped approximately 1000 meters upstream. The location of 

the Bear Creek production average fineness could have come from anywhere from the mouth of Bear Creek 

to approximately 1000 m upstream from the Bonanza Creek confluence. The production average fineness 

for the Tuluksak River is the most problematic. Historic placer mining began on the Tuluksak River outside 

of the study area and continued along it until the confluence of California Creek. So this bulk average 

fineness could be located anywhere along the river to the confluence of California Creek. 

Table 3.14 Placer gold microprobe and production average placer fineness data. 

Sample Location %Ag %Au total Fineness Grain

Measurement 

location 

975727 Spruce Creek 10.2 88.8 98.9 897 1 center 

 10.3 88.8 99.1 896 1 center 

 9.8 87.9 97.7 899 1 rim 

975842 Happy Creek 3.8 93.4 97.2 961 1 center 

 3.9 93.6 97.5 960 1 rim 

 3.6 93.0 96.6 962 1 rim 

975629 Tiny Gulch 4.6 94.4 99.0 954 1 center 

 0.3 97.9 98.2 997 1 rim 

 4.2 94.5 98.7 957 2 center 

975121 Bear Creek 8.4 88.9 97.3 914 1 center 

 0.5 94.9 95.4 994 1 rim 

 0.3 94.4 94.6 997 1 rim 

Spruce Placer Spruce Creek 6.0 93.2 99.3 939 1 rim 

 5.9 95.2 101.1 942 1 center 

 6.3 94.9 101.3 938 1 rim 

 Bonanza Creek 893 placer average 

 Tuluksak River 922 placer average 

 Bear Creek 931 placer average 

*Microprobe fineness data from this study; placer average data from Metz and Hawkins (1981). 

3.6 Relationship of the Placer and Bedrock Gold

Maddren (1915) first postulated that the gold in Bear Creek was locally derived. This study used 

microprobe analysis to measure gold fineness from placer and bedrock in the study area to determine if the 

gold is truly locally derived and the extent of fineness variations. 

A summary of gold fineness data is listed on Table 3.15. For placer grains the reported values are 

single measurements or averages from the center of the grain and bedrock values are the average of 

multiple measurements. More than one style of mineralization is present in the study area, so it is 
73

conceivable that the gold fineness could be quite variable. Of the styles of mineralization classified bedrock 

gold fineness data exists for the Wallace occurrence, VABM Bonanza lobe and the high-T Cu-Au 

mineralization at the BCCA. These fineness values are 937, 875 and 913, respectively (Table 3.15). These 

three occurrences likely represent the same mineralization event; and the fineness variation depicts a 

typical natural range. 

Table 3.15. Summarized table of all gold fineness data from the study area. 

Sample Location fineness type 

975721 Bear Creek 914 placer grain 

975727 Spruce Creek 897 placer grain 

975842 Happy Creek 961 placer grain 

Spruce Placer Spruce Creek 940 placer grain 

03ZW353 Bonanza Creek lobe (high-T, BCCA) 913 outcrop 

03ZW369 Wallace occurence 937 outcrop 

03ZW382 VABM Bonanza lobe 875 outcrop 

 Bonanza Creek 893 placer average 

 Tuluksak 922 placer average 

 Bear Creek 931 placer average 

* Microprobe analyses fineness values have analytical uncertainties of ~ +/- 5 parts/thousand. Microprobe fineness data 

from this study; placer average data from Metz and Hawkins (1981). 

Interestingly, the high fineness gold from the Wallace occurrence (937) is essentially the same as a 

placer grain with attached tetradymite (940) taken from Spruce Creek. There may be a mineralogical link 

between Bi-Te minerals and associated high fineness gold in the district. 

Placer grain sample 975727 and the Spruce placer sample are essentially outcrop values. The 

Spruce placer 940 fineness gold grain is attached to tetradymite, a very soft mineral (hardness of 1.5-2) 

with a perfect cleavage, which would be destroyed quickly in a stream environment. Sample 975727 

finenesses were obtained from a placer specimen with gold enclosed in quartz. 

Since the gold finenesses reported in Table 3.15 represent either unweathered gold from bedrock 

or the center of placer grains (unaffected by Ag-leaching), a direct comparison between Au-source and 

placer location can be made. Fineness of placer grains is both higher and lower than those from outcrop 

(Figure 3.18). Excluding sample 975842 the placer gold from the study area is all within error of the 

predicted bedrock fineness range. The highest placer fineness value (961) comes from a homogeneous, 

apparently unleached placer grain (Figure 3.17b). This sample comes from a small drainage (Happy Creek) 

and could not have traveled far. The most likely source for this gold is from the headwaters of Happy Creek 

(Figure 3.1), which is in Bonanza Pluton. The bulk average fineness of gold from Bonanza Creek is 

especially significant. Only approximately 1000 meters of Bonanza Creek were mined from its confluence 
74

450000 452500 455000 457500 460000 462500

6775000 6772500 6770000 6767500 6765000

450000 452500 455000 457500 460000 462500

6775000 6772500 6770000 6767500 6765000 913 931 922 893 875 940 937 961 897 914 Explanation Gold Location Bedrock Micropro

Placer Microprobe Placer– Average fr

0 1,000 2,000 

500 

Spruce Creek Bear Creek Tuluksak River Bonanza Creek Bear Creek Happy Creek Bonanza Pluton 

Bonanza Creek lobe Spruce Creek lobe VABM Bonanza lobe

159 56’ O

 61 07’ O

159 41’ O

 61 01’ O

Figure 3.18: Map of sample location and gold fineness for bedrock, placer and production average. Line markers indicate the possible 

production average values.
75

with Bear Creek (Figure 3.1). The gold fineness average there reflects the fineness of a relatively small 

area. Upstream sources for this gold have high finesses (913) suggesting that this production average is 

possibly a mixture of low-T (lower fineness) and high-T (high fineness, 913) gold from the BCCA. The 

remaining bulk Au fineness values do not provide any direct evidence to provenance except that they are 

likely of local derivation. The highest and lowest placer grains with finesses of 915 (Bear Creek) and 961 

(Happy Creek) indicate that a significant compositional range exists in the district. Beside the 961 fineness 

sample all of the other Au finenesses fall in the natural range of the mineralizing system and thus are 

clearly of local derivation. 

3.7 Classification of Mineralization Style

 Classification of the types of mineralization was characterized by principal component factor 

analysis (Davis, 2002). Factor analysis is a data reduction process that takes many variables (in this case 

element concentrations) and determines their correlations to one another. Factor analysis combines 

variables that correlate well with one another into a factor, hence this process thus reduces the number of 

variables. All rock samples that contained >200 ppb Au from the compiled data set (Gierymski and 

Werdon, 1997; J. Foley, written comm., 2004; and this study) were used to perform the analysis. Elements 

included in the analysis are Ag, As, Au, Bi, Cu, Hg, Pb, Sb and Zn. Figure 3.19 shows the statistical results 

of the factor analysis. The factor analysis identified three factors with eigen values greater than one, that 

explain 77% of the variance of the data. Elements that have high loading values for each factor indicate 

they correlate with one another. The three factors can be geologically classified as distal, proximal and 

epithermal style mineralization (Figure 3.19). 

 Factor 1 has high loading values for Pb-Ag-Zn-As-Sb. These elements have relatively high 

solubilities, particularly Pb, Zn and Sb, and thus do not precipitate as readily as Au or Bi. Therefore factor 

1 is called a distal mineralization factor because these elements and the minerals they form are typically 

found distal to the mineralizing source. This type of mineralization in the Nyac area is often found in fault 

breccia. 

 Factor 2 has high loading values for Bi, Au, Cu and Ag. Wood et al. (1987) found Bi has a lower 

solubility than Ag, Pb, Zn and Sb and thus precipitates near the hydrothermal source. Therefore, factor 2 is 

called the proximal mineralization factor. 

 Factor 3 has high loadings for Au and Hg. Hg mineralization is commonly associated with low 

temperature hydrothermal systems. Since Hg is a significant attribute to this type of mineralization, factor 3 

is classified as an epithermal mineralization factor. 
76

Figure 3.20 shows the location and dominant geologic factor for the 41 samples at each of the 

three anomalous gold occurrences: the Wallace occurrence, VABM Bonanza lobe and the BCCA. The 

Wallace occurrence and VABM Bonanza lobe are characterized by proximal mineralization. The BCCA 

contains both proximal and epithermal style mineralization. 

The end result of the factor analysis shows that mineralization at VABM Bonanza lobe, the 

Wallace Occurrence and Bi-Au mineralization at the BCCA are similar geochemically and thus likely 

represent similar origins. The low-T type mineralization at the BCCA anomaly and a few scattered 

locations throughout the study area are classified as epithermal type mineralization.

Proximal Epithermal

Distal

Factor 1: Pb-Ag-Zn-As-Sb Distal Mineralization

Factor 2: Bi-Au-Cu Proximal Mineralization

Factor 3: Au-Hg Epithermal mineralization

2

1

2

1

1

1 1

1 1 1

1

1 1

1

1

1

1

1

1 1

1

1

1

1 1

1

1 1 1 1

Figure 3.19: Triangular plot of mineralization factors. Diagram illustrates three types of 

mineralization in the study area: distal mineralization, proximal mineralization, and epithermal 

mineralization. Data are from this study, (1) Gierymski and Werdon (1997), and (2) J. Foley, written 

comm. (2004). 
77

0 

500

Legend

Bon

Mineraliza

Distal FProximaEpitherm

450000 452500 455000 457500

6772500 6770000 6767500

450000 452500 455000 457500

6772500 6770000 6767500 Wallace occurrence

BCCA

VABM Bonanza

lobe

Figure 3.20: Map of samples with Au concentrations >200 ppb and their factor classification.
78

4. Geochronology

 The Nyac terrane contains a tremendous number of plutonic bodies and dikes that intrude the 

Jurassic volcano-sedimentary rock package. Because textural variations and chemistry can vary 

significantly in a single pluton or series of dikes, other criteria must be to group the different igneous 

bodies. The most definitive way to accomplish this is by isotope geochronology. 

 Previously dated igneous bodies from the Nyac terrane are Early Cretaceous ages (Box et al., 

1993; Robinson and Decker, 1986; and Wilson, 1977). Most of the plutonic complexes in SW Alaska have 

ages of Late Cretaceous and early Tertiary (Bundtzen and Miller, 1997). Previous determinations from the 

Nyac terrane have large analytical uncertainties ( ± 5 Ma), and were obtained by K-Ar and U-Pb methods. 

Ages for this study were determined by 40Ar/39Ar laser step-heating of a mineral separate or whole rock 

chip (York et al., 1981; Layer et al.; 1987; and Layer 2000). 

This technique is based on the ratio of 40Ar to 39Ar. Samples are irridated in a reactor to produce 

39Ar from 39K. The ratio of 40Ar to 39Ar increases with the age of the rock. Because Ar is a gas, it diffuses 

from and into minerals, especially at high temperatures. Different minerals have different temperatures at 

which the mineral retains Ar called the closure temperature. The three minerals measured in this study are 

hornblende, muscovite and biotite. These minerals have closure temperatures of approximately 450, 350 

and 300 o C, respectively (McDougall and Harrison, 1988). After the mineral cools to its closure 

temperature it has locked a finite amount of 40K into its crystal lattice. The radiogenic 40K decays into 40Ar. 

The 40Ar/39Ar method requires using a standard irridated under the same conditions as the samples to 

determine the age. The step heating technique results in an age spectrum. The age spectrum is a series of 

steps (increasing temperature with each step). The Ar released at a given step yields an apparent age. 

Consecutive steps produce an age spectra. A weighted average of all steps is equivalent to a K-Ar date. 

Three consecutive steps that account for >60% of argon released within ± 2σ of one another define a 

plateau. A plateau gives the most reliable age. 

 The 40Ar/39Ar laser step-heating technique provides insight into the thermal history of the material 

dated. Two different geologic processes can affect a mineral’s Ar concentration: reset heating and argon 

addition. After a mineral cools below its closure temperature and is reheated, raising the temperature above 

the mineral’s closure temperature, Ar is lost by diffusion out of the mineral. Ar can be added to a mineral 

by remobilization of Ar in a hydrothermal system and depositing Ar into the mineral. In both cases a K-Ar 

age will be erroneous. The 40Ar/39Ar laser step-heating technique step releases Ar from increasingly tightly 

held sites; at higher temperatures the Ar released comes from the most tightly held sites. This is 

advantageous because alteration typically occurs on the outside portion of a crystal grain. In such a case, 

the first few heating steps can be ignored due to Ar loss, while Ar released at higher temperature gives the 

closure age of the mineral. 
79

In addition to the 40Ar/39Ar age spectrum this method also provides atomic Ca/K and Cl/K spectra 

through reactor-produced 37Ar from 40Ca and 38Ar from 35Cl. These spectra are useful in determining the 

composition of the mineral that released Ar at each of the heating steps. Table 4.1 shows typical atomic 

Ca/K and Cl/K ratios for the minerals of interest. 

 

Table 4.1: Typical atomic Ca/K and Cl/ K ratio ranges for dated minerals. Pyroxene and hornblende 

data is from Deer et al. (1997a and 1997b) and biotite and muscovite data is from Middelaar and Keith 

(1990). 

Mineral Ca/K Cl/K 

Muscovite .001-.002 [.001]-.006

Biotite .001-.005 .005-.016

Hornblende 4.8-76 .01-.21 

Pyroxene 45->300 [.02-.1] 

 * Bracketed values used .0025 for Cl %. 

Previous K-Ar and U-Pb data will not be discussed because those techniques do not offer means 

of assessing Ar or Pb loss or gain, whereas the 40Ar/39Ar spectra approach will. In one case the biotite K-Ar 

age is older than the hornblende age from a sample taken from the Nyac batholith. Hornblende has a higher 

closure temperature and it should yield an older age than biotite from the same sample. Opposite results (as 

in this case) indicates open system behavior in the K-Ar data or serious analytical uncertainties. 

 The following presents interpretations for the different 40Ar/39Ar, Ca/K and Cl/K age spectra. 

4.1 Sample Selection 

 A large number of rock types exist in the study area, samples selected for this study include: 

metabasalts in the metavolcanic rock unit, Nyac batholith, Spruce Creek lobe, Bonanza Creek lobe, grey 

dike and red dike. Besides the fossil age in the metavolcanic rocks no other dates exist for the volcanic 

rocks. Although radiometric ages already existed for the Nyac batholith the previous data had associated 

large errors, were measured by less precise methods and the biotite ages are older than the hornblende 

indicating that the methods used were not producing correct ages. Both the Spruce creek and Bonanza 

creek lobes of the Bonanza Pluton were dated to determine whether they are the same age as the VABM 

Bonanza lobe. Since significant mineralization is hosted in the gray dikes, it is important to determine their 

age to indicate their relationship to any of the plutons. Muscovite from a mineralized red dike was dated to 

determine the age of epithermal mineralization from the BCCA. 

 Placer Dome previously submitted three samples to the UAF Geochronology lab for 40Ar/39Ar 

dating, and these data were made available for this thesis. These samples include a biotite age from VABM 
80

Bonanza lobe, a muscovite age from VABM Bonanza alteration and a biotite age from the red dike. 

Interpretation of those ages will be included in this chapter. Locations for all of the dated samples are 

illustrated in Figure 4.1. The age data are tabulated on Table 4.2. 

 

4.2 Volcanic Rock Ages 

 While mapping in the field, an area of apparently unaltered basalts were identified. It appeared 

that these basalts might represent post-Cretaceous magmatism. In thin section the basalt is weakly altered, 

but otherwise unmetamorphosed. The groundmass is composed of fine-grained plagioclase and pyroxene. 

Phenocrysts include pyroxene and plagioclase. The pyroxene crystals have a small rim of chlorite-epidote 

alteration along their rims. Two samples of basalt rock chips (03ZW232) were analyzed. The age spectra 

(Figures 4.2, 4.3) are complex and show that basalt is reset at ~119 Ma, but a high Ca phase, presumably 

pyroxene, preserves an older age as a pseudo-plateau. The best eruption age is the variance-averaged results 

of the two pseudo-plateaus, of 180 ± 7 Ma. These two pseudoplateaus only account for 23.1% and 24.2% 

of the total Ar released and thus only serve as a minimum estimate of the original age. The reset pseudoplateaus account for 45.9% and 56.5% of the total Ar released. The best age for reset is the varianceaveraged results of these pseudo-plateaus, 119 ± 3 Ma. 

4.3 Plutonic Rock Ages 

 The plutonic rocks can be divided into two different age suites: the Nyac batholith and Bonanza 

pluton group. Most of the mineral separates contain inclusions of other minerals and such inclusions can 

have a dramatic effect on the age spectrum. There are two characteristics found in nearly all of the plutonic 

rock age spectra. First, most of the age spectra display Ar gain followed by Ar loss. The Ar loss is likely 

attributed to alteration during a younger event, which will be described in greater detail later in this chapter. 

The Ar gain is extraneous Ar normally concordant with the biotite phase. Biotite has a lower closure 

temperature than other phases (in particular hornblende), and as a pluton cools Ar from other phases is 

released. If biotite has not yet reached its closure temperature it can take the released Ar into its crystal 

lattice. The extraneous Ar contributed by this process will result in a hump in the age spectrum and result in 

an erroneously old age. The second characteristic has to do with initial high Ca/K and/or Cl/K ratios for 

most of the spectra. The initial high Ca/K ratios are the result of alteration of biotite and hornblende to 

epidote and/or calcite. The initial high Cl/K ratios are likely the result of Cl released from inclusions. 
81

Explanatio

Bonanz

Dated Sa

0 1,000 2,000 

500

450000 452500 455000 457500 460000 462500

6775000 6772500 6770000 6767500 6765000

450000 452500 455000 457500 460000 462500

6775000 6772500 6770000 6767500 6765000

Bonanza Creek lobe03ZW295113+/- 1 Ma

(1) Red Dike977056113+/- 1 Ma

Basalt03ZW232180+/- 7 Ma119+/- 3 Ma reset

Spruce Creek lobe03ZW471113+/-1 Ma

Gray Dike03ZW474113.1+/- 0.4 Ma

(1) VABM Bonanzalobe 975960113+/- 1 Ma

(1) VABM Bonanzalobe sericite 976864109+/- 1 Ma

Nyac Batholith03ZW365118+/- 1 Ma

Red Dike Sericite03ZW351112+/- 1 Ma

Figure 4.1: Map of sample location for all rock ages. Listed ages are best estimate. Data are from this study and (1) Gierymski and W

(1997). See Table 4.2.

159 56’

O

 61 01’ O

159 41’

O

 61 07’ O
82

Reset Age

117+ /- 5 Ma

Clinopyroxene

Eruption Age

173 + /- 11 Ma

Hbl+ Cpx Hornblende

Biotite+ Hbl

Excess Ar

Minor contribution of Ar from plagioclase

for all steps

Figure 4.2: Age, Ca/K and Cl/K spectrum diagram for whole rock basalt sample 03ZW232. Age 

spectrum depicts two pseudo-plateaus, an original age (black steps) and a reset age (grey steps). A 

high calcium phase (pyroxene and/or plagioclase?) has retained the initial Ar concentration in the 

basalt. 
83

Reset Age

120. + /- 3 Ma

Eruption Age

183 + /- 8 Ma

Clinopyroxene

Hbl+ Cpx

Hornblende

Excess Ar

Biotite+ Hbl

Minor Ar contribution from plagioclase

for all steps

Figure 4.3: Age, Ca/K and Cl/K spectrum diagram for the second whole rock basalt sample 03ZW232. 

Age spectrum depicts two pseudo-plateaus, an original age (black steps) and a reset age (grey 

steps). A high calcium phase (pyroxene and/or plagioclase) has retained the initial Ar concentration 

in the basalt. 
84

Table 4.2: Abbreviated 40Ar/39Ar age data for all dated samples. 

Sample Location Rock Type Mineral 

Integrated 

Age (Ma) 

Plateau Age 

(Ma) 

# 

Fractions 

% 

39Ar MSWD Best Age (Ma) 

03ZW232 Spruce Ck A Basalt WR 133.3+/ 4.6 173.4+/- 11.3 3 23.1 0.66 180+/- 7 

03ZW232 Spruce Ck B Basalt WR 142.9+/- 2.8 182.8+/- 8.2 7 24.2 0.61 

03ZW232 Spruce Ck A Basalt WR 133.3+/ 4.6 116.8+/- 4.9 5 56.5 0.42 119+/- 3 

03ZW232 Spruce Ck B Basalt WR 142.9+/- 2.8 119.6+/- 3.4 4 45.9 2.42 

03ZW295 Bonanza Ck QtzMzDi B 110.6+/- 0.5 111.0+/- 0.5 10 97.6 0.75 

03ZW295 Bonanza Ck QtzMzDi H 112.8+/- 0.8 113.4+/- 0.8 8 95.1 0.79 ~113 

03ZW365 Nyac Batholith Grd B 110.7+/- 0.4 113.2+/- 0.4 9 96.7 9.49 

03ZW365 Nyac Batholith Grd B 111.3+/- 0.4 113.3+/- 0.4 8 94.2 5.83 

03ZW365 Nyac Batholith Grd B 112.1+/- 0.4 116.3+/- 0.4 5 79 0.59 

03ZW365 Nyac Batholith Grd H 109.8+/- 0.8 112.7+/- 1.0 3 69.2 0.9 

03ZW365 Nyac Batholith Grd H 105.8+/- 4.5 117.8+/- 0.7 3 76.1 0.28 118+/- 1 

03ZW471 Spruce Ck QtzMzDi B 110.9+/- 0.4 111.0+/- 0.4 6 80.3 0.36 

03ZW471 Spruce Ck QtzMzDi H 114.2+/- 0.6 115.1+/- 0.8 6 65.9 0.93 113+/- 1 

03ZW474 Wallace Grd Dike B 98.6+/- 1.1 109.1+/- 1.2 7 81.7 10.1 

03ZW474 Wallace Grd Dike B 112.8+/- 0.5 

03ZW474 Wallace Grd Dike H 112.2+/- 0.8 113.5+/- 0.7 8 95.6 3.83 113.1+/- 0.4 

03ZW474 Wallace Grd Dike H 110.2+/- 0.8 112.5+/- 0.8 3 90.1 0.78 

975960 VABM Grd B 108.5+/- 0.5 108.8+/- 0.5 8 61.3 2.43 ~113 

976864 VABM Grd M 109.4+/- 0.9 109.2+/-1.2 6 68.9 0.21 ~111 

977056 BCCA QtzMz Dike B 110.4+/- 0.5 111.2+/- 0.5 9 81.8 1.11 ~113 

03ZW351 BCCA QtzMz Dike M 112.1+/-0.6 111.9+/-0.6 6 80 0.5 112+/-1 

 

4.3.1 Nyac Batholith 

 Two hornblende and three biotite separates were dated from a granodiorite sample (03ZW365) 

from the Nyac batholith. Of the two hornblende age spectra, the second yields the most precise age (Figure 

4.4). The Ca/K ratio for the first split (Figure 4.5) is low throughout the spectrum and gradually increases. I 

interpreted this to indicate that the hornblende from the first analysis have a significant amount of biotite 

inclusions. In thin section some of the hornblendes have obvious biotite inclusions. Since biotite has an 

order of magnitude more K than hornblende, the biotite age will dominate the age spectrum and will not 

yield an accurate hornblende age. The second split yielded a higher Ca/K ratio and represents the best 

hornblende age for the pluton. Of the three biotites analyzed, the first two analyses exhibit age spectra that 

gradually step to a peak and then decline from the peak (Figures 4.6 and 4.7). The peak is likely the closure 

age of the biotite and the decreased values represent diffusion of Ar out of the crystal from alteration. The 

third biotite split produced an age spectrum without a hump (Figure 4.8). The third split yields the best 
85

Plateau Age

117.8+ /- 0.7

Typical hornblende Ca/K ratio

Ar loss

Biotite

Excess Ar

Figure 4.4: Age, Ca/K and Cl/K spectra for hornblende from the Nyac batholith (03ZW365). Despite 

the majority of the Ar being released in one step, the Ca/K spectrum is typical of a hornblende 

composition. 
86

Plateau Age

112.7 + /- 1.0 Ma

Hornblende+ biotite

Excess Ar

Ar loss

Biotite

Figure 4.5: Age, Ca/K and Cl/K spectrum diagram for hornblende from the Nyac batholith (03ZW365). 

The Ca/K spectrum gradually steps up and never reaches a Ca/K ratio higher than the first 

(03ZW365) hornblende sample. 
87

Pseudo-plateau Age

113.2 + /- 0.4 Ma

Ar-loss

Ar diffusion?

Biotite

Biotite> > Hornblende

Figure 4.6: Age, Ca/K and Cl/K spectrum diagram for biotite from the Nyac batholith (03ZW365). The 

age spectrum exhibits a convex shape indicating Ar loss by diffusion. 
88

Pseudo-plateau Age

113.3 + /- 0.4

Ar loss

Biotite

Biotite> > Hornblende

Figure 4.7: Age, Ca/K and Cl/K spectrum diagram for biotite from the Nyac batholith (03ZW365). The 

age spectrum exhibits a convex shape indicating Ar loss or Ar recoil. 
89

Plateau Age

116.3 + /- 0.4

Ar loss

Biotite

Biotite> > Hbl

Figure 4.8: Age, Ca/K and Cl/K spectrum diagram for biotite from the Nyac batholith (03ZW365). The 

age spectrum levels out into a true plateau and gives the best biotite age for the Nyac batholith. 
90

biotite age for the Nyac batholith since it levels into a true plateau. All of the biotite Ca/K and Cl/K spectra 

display ratios expected for biotite. 

The most precise hornblende and biotite analyses from the Nyac batholith record ages of 117.8 ±

0.7 and 116.3 ± 0.4 Ma, respectively. Both of the age spectra level off into flat plateaus accounting for 

more than 75% of the total argon released and have plateau MSWDs of less than 0.6. Although, 

approximately 60% of the 39Ar for the first hornblende analysis was released in a single step, the Ca/K ratio 

remained high, indicating that the hornblende crystal is homogenous. Since hornblende traps Ar at much 

higher temperatures than biotite, the best estimate for emplacement of the Nyac batholith is 118± 1 Ma. 

4.3.2 Bonanza Creek Lobe 

 One hornblende and one biotite separate were dated from a quartz diorite sample (03ZW295) from 

the Bonanza Creek lobe. In thin section hornblende, pyroxene and biotite are generally separate from one 

another. The Ca/K spectra for the hornblende and biotite (Figures 4.9 and 4.10) indicate the samples 

analyzed were nearly pure. Some, often high temperature, Ar released from the biotite sample reveals high 

Ca/K ratios (Figure 4.10), which likely represent small inclusions of hornblende. 

 The hornblende and biotite dates from the Bonanza Creek lobe yield ages of 113.4± 0.8 and 

111.0 ± 0.5 Ma, respectively (Figures 4.9 and 4.10). Both age plateaus account for over 95% of the total Ar 

released and have MSWD less than 0.8. The best estimate emplacement age for the Bonanza Creek lobe is 

113 ± 1 Ma. 

4.3.3 VABM Bonanza Lobe 

 One biotite and one muscovite separate were dated from theVABM Bonanza lobe. The biotite 

came from a least altered portion of the pluton. In thin section the biotites are unaltered. The muscovite 

sample was taken from a gold mineralized quartz vein (Gierymski and Werdon, 1997). 

The biotite (Figure 4.11) and muscovite (Figure 4.12) samples from VABM Bonanza lobe yield 

ages of 109.0 ± 0.5 and 110.9 ± 0.7 Ma, respectively. The muscovite Ca/K spectrum has unusually high 

values, most likely due to remnant plagioclase inclusions in the sericite. Both of the age spectra level off 

into flat plateaus accounting for more than 70% of the total argon released and have plateau MSWDs of 

less than 0.6. Since no hornblende age exists for VABM Bonanza Pluton the best estimate for 

emplacement is ~111 Ma (the estimated age is 2 Ma older than the biotite age, consistent with the Bonanza 

Creek lobe). The best age for the muscovite and thus the age of mineralization is also ~111 Ma. The older 

age for the muscovite is not necessarily due to being older, but from having a higher closure temperature 

than biotite. 
91

Plateau Age

113.4 + /- 0.8 Ma

Ar loss

Hornblende

Figure 4.9: Age, Ca/K and Cl/K spectrum diagram for hornblende from the Bonanza Creek lobe 

(03ZW295). 
92

Plateau Age

111.0 + /- 0.5 Ma

Ar loss

Biotite> > Hornblende

Biotite

Figure 4.10: Age, Ca/K and Cl/K spectrum diagram for biotite from the Bonanza Creek lobe 

(03ZW295). 
93

Plateau Age

108.8 + /- 0.5 Ma

Ar loss

Excess Ar

Biotite> > Hornblende

Figure 4.11: Age, Ca/K and Cl/K spectrum diagram for biotite from VABM Bonanza lobe (975960). 
94

Plateau Age

Excess Ar 109.2 + /- 1.2 Ma

Ar loss

Muscovite

Muscovite> > Hornblende

Figure 4.12: Age, Ca/K and Cl/K spectrum diagram for muscovite from VABM Bonanza lobe (976864). 

The age plateau for muscovite is a good estimate for the time of mineralization. 
95

4.3.4 Spruce Creek Lobe 

 One hornblende and one biotite separate were dated from a quartz diorite sample (03ZW471) from 

the Spruce Creek lobe. Petrographic examination of the mineral separates revealed that the dated crystals 

were a combination of biotite, hornblende, and pyroxene (Figure 4.13). Hornblende rims pyroxene, and the 

biotite both occurs as small inclusions in pyroxene and rims around hornblende. The hornblende Ca/K 

(Figure 4.14) spectrum shows extreme variations in Ca/K ratios. Since the age spectrum reflects a 

combination of minerals, the Ca/K spectrum can be used to determine which heating steps represent Ar 

released from the three different minerals. Biotite has the lowest Ca/K ratio (nearly zero), and since it has 

the lowest Ar-retention temperature it should release its Ar first. The Ca/K spectrum shows that the early 

heating steps released Ar from a low Ca mineral. With increasing laser energy the Ca/K ratio rises, 

indicating Ar released from both hornblende and biotite. At higher energy high Ca/K ratios indicate 

hornblende released Ar with a small contribution from clinopyroxene. Finally, at the highest heating 

temperature very high Ca/K ratios indicate clinopyroxene released its Ar (Figure 4.14). In contrast, the 

biotite analysis (Figure 4.15) resulted in a near perfect age plateau and a flat and low Ca/K spectrum 

indicating the biotite separate was nearly pure biotite. 

The hornblende and biotite from the Spruce Creek lobe yield ages of 115.2 ± 0.8 and 111.2 ± 0.4 

Ma, respectively. For the hornblende age spectrum, Ar was primarily released from hornblende for steps 

seven through twelve (Figure 4.14). The plateau accounts for 65.9% of the total Ar released and has a 

MSWD of 0.93. The biotite plateau (Figure 4.15) accounts for 98.1% of the total Ar released and has a 

MSWD of 1.22. The hornblende age is older than expected (relative to the biotite) and is probably the 

result of extraneous Ar in biotite inclusions in the dated mineral grain. Since the biotite occurs as inclusions 

and attached to hornblende and pyroxene, Ar released from those minerals can still enter the biotite since it 

has a lower closure temperature. Considering this problem and consistent with a typical 2 Ma difference 

between biotite and hornblende ages the best estimate emplacement age for the Spruce Creek lobe is ~113 

Ma, similar to that of the Bonanza Creek lobe. 

4.3.5 Gray Dikes 

 Two hornblende and two biotite samples were dated from a gray dike (03ZW474) at the Wallace 

Occurrence. All of the age, Ca/K and Cl/K spectra (Figure 4.16 and 4.17) are similar for each hornblende 

analysis. The hornblende crystals are large (dated specimens >1x1 mm), weakly chloritized along their 

margins, and have rare biotite inclusions (Figure 4.18). The defined plateaus account for over 
96

Figure 4.13: Spruce Creek lobe mineral aggregate separate (sample 03ZW471). The majority of the 

grain is clinopyroxene with biotite, hornblende and Fe-Ti oxide inclusions with a partial hornblende 

rim. 
97

Plateau Age

115.1 + /- 0.8 Ma Excess Ar

Ar loss

Clinopyroxene

Biotite> > Hbl Biotite> Hbl

Hbl+ Cpx?

Figure 4.14: Age, Ca/K and Cl/K spectrum diagram for hornblende from the Spruce Creek lobe 

(03ZW471). The analyzed samples were mineral aggregates. Only heating steps 7-12 have Ca/K 

ratios diagnostic of hornblende. 
98

Plateau Age

111.0 + /- 0.4 Ma Excess Ar

Ar loss

Biotite

Figure 4.15: Age, Ca/K and Cl/K spectrum diagram for biotite from the Spruce Creek lobe (03ZW471). 
99

Pseudo-plateau Age

113.5 + /- 0.7

Ar loss

Hornblende> > Biotite Biotite

Figure 4.16: Age, Ca/K and Cl/K spectrum diagram for hornblende from the gray dike (03ZW474). 
100

Pseudo-plateau Age

112.5 + /- 0.8

Ar loss

Excess Ar

Hornblende> > Biotite

Figure 4.17: Age, Ca/K and Cl/K spectrum diagram for hornblende from the gray dike (03ZW474). 
101

Figure 4.18: Photomicrographs of hornblende (a) and biotite (b) from the gray dike at the Wallace 

occurrence. Figure 4.18 (a) shows an extreme example of biotite inclusions in hornblende grains and 

Figure 4.18 (b) shows extensive chloritization of biotite. Biotite photomicrograph is rotated 90 

degrees. 
102

95.6% and 90.1% of the total Ar released. The plateaus have MSWDs of 3.81 and 0.78. The two plateau 

ages weighted by variance and averaged report a hornblende age of 113.1 ± 0.4. 

Biotites from the grey dike are variable chloritized. The grains separated were visibly altered to 

chlorite apparent in their green discoloration; only the grains with minimal chlorite alteration were selected 

for dating. In thin section it is obvious that the biotites are altered (Figure 4.18), but in some grains the 

alteration is not as intense. Both biotite samples analyzed yielded complex results. The first biotite age 

spectrum is very noisy (Figure 4.19). The age spectrum never levels off into a true plateau. A pseudoplateau gives a biotite age of 109.1 ± 1.2 Ma. A second analysis, with the hope of obtaining a better 

plateau, was no better: no plateau was ever reached (Figure 4.20). The last two steps, which each account 

for approximately 25% of the total argon released, differ in age by more than 15 Ma. All of the previous 

steps gradually increase in age with successive heating steps. The biotite age spectra from the second 

analysis records 39Ar recoil. The biotite analyzed in the second analysis was presumably more altered and 

thus 39Ar was easily redistributed in the crystal during irridation. Due to the unreliability of the biotite 

analyses from this dike it is unclear whether the 109.1 ± 1.2 Ma age reflects the magmatic cooling biotite 

age or rather a later mineralizing event at the Wallace occurrence. The best crystallization age for the gray 

dike is 113.1 ± 0.4 Ma. 

 

4.3.6 Red Dikes 

 One biotite and one muscovite sample were dated from the red dike at the BCCA. The biotite 

came from an unaltered variety of the dike and the muscovite from the most altered variety which hosts 

gold mineralization. Biotites from the unaltered variety display weak chlorite alteration along their rims 

(Gierymski and Werdon, 1997). The biotite records an age of 111.2 ± 0.5 Ma (Figure 4.21). The variation 

of the Ca/K ratio is likely the result of hornblende or sphene present as inclusions in the biotite. 

Nonetheless, the Ca/K ratio is low indicating nearly pure biotite. The muscovite grains are large (up to 

4mm diameter) and coherent crystals. The muscovite appears to have completely replaced former biotite 

grains. The age spectrum for the muscovite sample records a mineralization age of 111.9 ± 0.6 Ma (Figure 

4.22). 

4.4 40Ar/ 39Ar Rock Age Summary 

All the plutonic and volcanic age data are illustrated on Figure 4.23. I propose that there were four 

different geologic events in the study area: Jurassic volcanic-arc formation, Nyac Batholith plutonism, 

Bonanza Pluton plutonism and Tertiary hydrothermal activity. 

The first event is the formation of the volcanic arc. The basalt dated in this study records an age of 

180 ± 7 Ma. This age is similar to the Bajocian age of the pelycypod fossils (Box et al., 1993). Several 
103

Pseudo-plateau Age

109.1 + /- 1.2 Ma

Ar loss

Biotite> > hornblende

Figure 4.19: Age, Ca/K and Cl/K spectrum diagram for biotite from the gray dike (03ZW474). The age 

spectrum indicates substantial Ar loss, but a pseudo-plateau does give an indication of either the 

biotite age or time of alteration. 
104

Ar loss

Ar recoil?

Biotite> > hornblende

Figure 4.20: Age, Ca/K and Cl/K spectrum diagram for biotite from the gray dike (03ZW474). The age 

spectrum never levels off into a plateau. The appearance of the age spectrum is the result of either 

Ar gain followed by Ar loss or more likely Ar recoil since the integrated age is similar to the other 

biotite age (Table 4.1). 
105

Plateau Age

111.2 + /- 0.5 Ma

Excess Ar

Ar loss

Biotite

Figure 4.21: Age, Ca/K and Cl/K spectrum diagram for biotite from the red dike (977056). 
106

150

100

50

.02

.01

0

-.01

.002

.001

0

0.0 0.2 0.4 0.6 0.8 1.0

Age in Ma Ca/

K Cl/

K

Excess Argon

Ar loss

Plateau Age

111.9+ /- 0.6 Ma

Muscovite

Figure 4.22: Age, Ca/K and Cl/K spectrum diagram for muscovite from a mineralized red dike 

(03ZW351). 
107

Figure 4.23: Figure of dated samples illustrating two distinct age suites. The old suite is the Nyac batholith. The young suite incluportions of the Bonanza pluton, the gray dikes and the red dikes (bars represent 1 sigma error).

Gray dike

Bona

Red dike Bonanza Ck

lobe

Spruce Ck

lobe

Nyac

Batholith
108

plutons (diorite hornfels, Rex Creek pluton, and altered granodiorite; discussed in Chapter: 2) also appear 

to be related to this event. 

The second event is the intrusion of the Nyac batholith into the volcanic-arc complex. The Nyac 

batholith is 118 ± 1 Ma. The reset age of the metavolcanic rock unit (119 ± 3 Ma) is statistically the same 

(at ± 1σ ) as the hornblende age from the Nyac Batholith (Figure 4.22). The Nyac Batholith is thus 

responsible for the regional thermal metamorphism in the study area and perhaps the entire northern portion 

of the Nyac terrane. 

The third event is Bonanza pluton plutonism. This event includes the Bonanza pluton, grey dikes, 

red dikes, mineralization at the VABM Bonanza lobe at ~111 Ma, and mineralization at the BCCA at ~112 

Ma . The biotite age from Bonanza Pluton was likely affected by the mineralization event and Ar loss 

resulting in a younger age. Biotite from the Bonanza Creek and Spruce Creek lobes, red dike and the grey 

dike are statistically indistinguishable (Figure 4.22). Similarly, the hornblende ages from Bonanza Pluton 

and the grey dike are statistically indistinguishable at the ± 2σ confidence level. The muscovite age from 

the VABM Bonanza lobe is statistically indistinguishable from the biotite age of the Bonanza pluton. 

Therefore, the Bonanza pluton is most likely responsible for the mineralization at VABM Bonanza lobe. 

The later mineralization age at the BCCA likely reflects the later stages of mineralization. This topic will 

be futher discussed in Chapter 5. 

The fourth event is a widespread heating event. All of the mineral samples analyzed yield an 

initial Ar loss. This Ar loss is most likely due to hydrothermal activity related to a regional Tertiary heating 

event. The undated mafic dikes may be responsible for this event. 
109

5. Mineralization Model

This study presented mineralogical and petrological data of the rocks, evidence for alteration 

styles, ore mineralogy, and fluid chemistry and age data from the study area. All of these aspects provide 

the information needed to produce a geological model that explains the mineralization in the study area. 

Mineralization in the study area accompanied three separate events: Jurassic (?) plutonism, Early 

Cretaceous plutonism and Tertiary hydrothermal activity. 

5.1 Jurassic (?) Plutonism 

 The timing of the earliest mineralizing event can only be inferred because the causative pluton 

(Rex Creek pluton ?) age cannot be determined with certainty. Biotite and hornblende in the pluton are 

altered to a combination of epidote-chlorite-calcite-magnetite-rutile rendering 40Ar/39Ar dating useless. As 

evidenced by intense alteration and similar trace element chemistry to the diorite hornfels the Rex Creek 

pluton is at least older than 118 Ma, because the large scale thermal metamorphism in the study area is 

likely the result of Nyac batholith plutonism. Mineralization associated with this pluton includes quartzchalcopyrite veining, disseminated chalcopyrite in volcanic rocks now replaced by malachite, and 

pyritization of mafics in and around the Rex Creek pluton. 

 This style of alteration and mineralization is different from that at VABM Bonanza lobe in that it 

has no associated anomalous Au, Bi or Te and a different alteration assemblage of epidote-chloritecarbonate-sericite. This pluton also hosts epidote veins not seen at VABM Bonanza. 

5.2 Early Cretaceous Plutonism 

The Early Cretaceous event includes mineralization resulting from the intrusion of the Nyac 

batholith and Bonanza pluton. Before discussing the source and relationship between the two igneous 

bodies it is important to review the chemical processes responsible for plutonic-related mineralization. 

First, both the Nyac batholith and Bonanza pluton are volcanic-arc plutons with high oxidation states 

(Figures 2.9 and 2.10). Plutons with original high oxidation states are not gold favorable because at these 

conditions gold is in the Au3+ valence state and thus goes into magmatic magnetite. If the oxidation state is 

too low gold will be in the Au1+ valence state and will be lost to magmatic sulfide (Mirsa, 2000). The 

Bonanza pluton contains both native gold and magmatic magnetite, indicating it was relatively oxidized, 

but the oxidation state was not high enough for all the gold to be lost to magmatic magnetite. Another 

implication of volcanic-arc high oxidation plutons is their fluid chemistry. HS − and Cl − are the two most 

common complexing agents for Au (Mirsa, 2000). High oxidation fluids cannot contain significant 
110

amounts of HS − (sulfur is instead present as SO 2−

4 ). Hence, in such fluids, if metal complexing occurs, it 

is through Cl − complexation. The Bonanza pluton’s high oxidation state, high salinities and high 

temperature fluid inclusions indicate that the Au complexing agent at Bonanza pluton was Cl − ion. The 

low salinities calculated from fluid inclusions at the Wallace occurrence suggest instead a HS − complex. 

 The Nyac batholith is most likely responsible for the large-scale thermal metamorphism 

throughout the study area. During cooling it is likely that fluids were released from the crystallizing 

batholith. It is these far-reaching fluids that are likely responsible for most of the uneconomic 

mineralization in the volcano-sedimentary package. The majority of the calc-silicate veinlets that have 

associated sulfides are located on the metasedimentary-Nyac batholith contact (discussed in Chapter 4). 

These sulfide occurrences are likely the result of fluids from the Nyac batholith traveling through the 

wallrocks, locally mobilizing Fe and Cu, to be later precipitated as pyrite, pyrrhotite and chalcopyrite. The 

magmatic fluids could have also contained inherent appreciable amounts of Cu and Fe. The mineralization 

is dominantly small calc-silicate veinlets with associated pyrite, pyrrhotite, chalcopyrite and marcasite. 

Rocks of the volcano-sedimentary package ubiquitously contain pyrite, pyrrhotite and chalcopyrite with no 

associated calc-silicates. It is unclear whether the sulfides with no associated calc-silicates are related to the 

Nyac batholith or earlier Jurassic volcanism. 

It is unclear whether the skarn at Spruce Creek is the result of the regional thermal event (Nyac 

batholith plutonism)or the later intrusion of the Bonanza pluton. The abundance of scapolite, a Cl-rich 

mineral, in the Spruce Creek skarn is a strong indication that the responsible fluids had high salinities. Fluid 

inclusions from Bonanza pluton have high salinities, indicating that the Bonanza pluton is possibly 

responsible for the Spruce Creek skarn. However, scapolite also occurs in unmineralized hornfels along the 

contact of the metasedimentary rocks and the Nyac batholith. The scapolite here has small pyroxene 

inclusions (hence, high temperature) indicating that the close proximity of the Nyac batholith must be 

responsible for the scapolite at this locality. This evidence indicates the Nyac Batholith may be responsible 

for the Spruce Creek skarn. 

 Mineralized rock in and around the Bonanza pluton have the highest gold concentrations of lode 

prospects in the study area. There are four different subtypes of mineralization: the proximal Bi-Cu-Au 

mineralization in and around the VABM Bonanza lobe, proximal Cu-Au mineralization at the BCCA, 

epithermal Au-Hg mineralization at the BCCA and proximal Te-Bi-Au mineralization at the Wallace 

occurrence. All four subtypes of mineralization are likely to be related to the Bonanza Pluton. Each subtype 

has its own unique alteration and mineralization characteristics. 

The VABM Bonanza lobe displays sericite-chlorite-carbonate alteration with associated pyrite, 

chalcopyrite, bismuthinite, molybdenite and native gold. The chlorites associated with this style of 

mineralization are length fast and have anomalous green-brown interference colors, characteristic of 
111

moderate to low Fe composition. The fluid inclusions from VABM Bonanza lobe yield trapping 

temperatures from 536 to 266 degrees Celsius and have salinities of 55-21 wt% NaCl. 

BCCA high-T, Cu-Au mineralization displays potassic alteration (secondary biotite) overprinted 

by chlorite-sericite-carbonate alteration with associated magnetite, chalcopyrite, pyrite and native gold. The 

chlorite associated with the mineralization is optically indistinguishable from chlorite at VABM Bonanza 

Pluton. Fluid inclusions from the high-T Cu-Au mineralization yield trapping temperatures from 557 to 282 

degrees Celsius and salinities of 57-13 wt% NaCl. The high-T BCCA mineralization is different from the 

VABM Bonanza Pluton mineralization in that Bi contents are low, chlorite is more abundant than sericite, 

and the mineralization occurs outside of the pluton. 

BCCA epithermal mineralization is older than VABM Bonanza lobe mineralization (112 Ma) and 

likely represents a later stage of Bonanza pluton mineralization as the system was cooling. Epithermal-type 

mineralization is seen throughout the entire study area but is concentrated at the BCCA. The sporadic 

occurrences of epithermal mineralization in the study area are localized along faults, which serve as major 

fluid conduits. At the BCCA, epithermal mineralization is hosted in the red dikes and fault breccia and also 

occurs in vuggy chalcedonic quartz veins. This style of mineralization is different from VABM Bonanza 

mineralization in its elemental association, oxidation-sulfidation conditions and alteration assemblage. The 

epithermal mineralization has associated high levels of Hg, higher than any other style of mineralization in 

the study area. The oxidation and sulfidation conditions are higher than that of the Bonanza pluton 

mineralization. The most defining different characteristic of this style of mineralization is the sericitekaolinite alteration assemblage. This assemblage indicates both lower temperature and more acidic 

conditions than sericite-chlorite alteration (Figure 5.1). 

The Wallace occurrence displays sericite-chlorite-carbonate-albite alteration with associated 

tellurobismuthite, tetradymite, native gold and minor chalcopyrite. The chlorites associated with this style 

of mineralization have purple-blue anomalous interference colors and are length slow, indicating high Fe 

content. Fluid inclusions from the Wallace occurrence yield trapping temperatures from 370 to 346 o C, 

salinities of 2 wt% NaCl and high CO 2 concentrations. The Wallace occurrence is different from Bonanza 

Pluton mineralization in its alteration assemblage, ore mineralogy, chlorite composition and fluid 

chemistry. The Wallace occurrence exhibits the most intense albite alteration, has higher Fe chlorites, a 

greater abundance of Bi-Te bearing minerals and a much lower abundance of chalcopyrite. The fluid 

inclusions have much lower salinities and much higher CO 2 concentrations than VABM Bonanza Pluton 

mineralization. 

 
112

3.5 4 4.5 5 5.5 6 6.5 7 7.5

0

50

100

150

200

250

300

pH

T (degrees 

C)

Albite

Albite low

Beidellit-H

Kaolinite

Maximum

Microcline

Muscovite

Figure 5.1: pH vs. Temperature diagram for Al alteration minerals. The diagram illustrates that 

kaolinite is the stable species at low pH. Conditions are under quartz saturation, K+

 activity of 0.01 

and Na+ activity of 0.3. Increasing K+ activity by a factor of ten shifts all boundaries 1 pH unit lower. 

Diagram calculated using Geochemist’s Workbench (Bethke, 1998) and thermodynamic data of 

Delany and Lundeen (1990). 
113

5.3 Tertiary (?) Hydrothermal Activity 

 Tertiary (?) hydrothermal activity likely occured in the district. Although, no igneous body was 

identified that is responsible for this mineralization; the mafic dikes that cut the Bonanza and Sawpit 

plutons (Maddren, 1915) could be responsible for this event. The Ar loss seen in all age spectra in the 

study area supports this hypothesis. The single analyzed mafic dike has continental trace element signatures 

suggesting that it originated from an extensional event (Figure 2.4). 

5.4 Mineralization Model

Figure 5.2 is a schematic cross section through Bonanza pluton that illustrates the structural 

history and location of the most significant mineralization in the study area. 

Originally the volcano-sedimentary package overlay all of the Bonanza pluton. Movement on the 

N-S faults uplifted the pluton at VABM Bonanza and the Spruce and Bonanza lobes. At the Wallace 

occurrence the metasedimentary rocks presumably still overlie the pluton. Here the gray dikes may be 

related to the underlying Bonanza pluton (the grey dikes have similar age and composition as the Bonanza 

pluton). The Spruce lobe is likely down dropped from the VABM Bonanza lobe as is evident from the 

small raft of metavolcanic rocks that lie on top of the pluton and more mafic compositions here (Figure 

2.1). The Bonanza Creek lobe is roughly at the same exposure level as the Spruce Creek lobe, but is leftlaterally displaced north along N-S faults. 

The differences in the type of mineralization can be explained by a phase separation of fluids 

expelled from Bonanza pluton resulting in an aqueous phase and a gas-rich phase. Several authors (Candela 

and Piccoli, 1995; Hedenquist, 1995; and Gammons and Williams-Jones, 1997) have proposed a similar 

phase separation resulting in a gas-rich phase and a hypersaline liquid. In this case, the aqueous phase is a 

high temperature, high salinity, and low CO 2 phase with an associated Cu-Bi-Au mineralization (eg. 

VABM Bonanza lobe). The gas-rich phase is a lower temperature, low salinity, and high CO 2 phase with 

an associated Te-Bi-Au mineralization (eg. Wallace occurrence). 

 The aqueous phase is responsible for the proximal mineralization at VABM Bonanza lobe and the 

high temperature Cu-Au mineralization at the BCCA. The high salinity of this style of mineralization 

suggests that the ore minerals were dominantly complexed with Cl − . At high temperature and oxidation 

state Au can complex with Cl − (Wood et al., 1987; and Hayashi and Ohmoto, 1991). 

 In contrast, the gas-rich phase is responsible for the mineralization at the Wallace occurrence. Au 

transport as a chloride complex dominates bisulfide complex, but at lower temperatures bisulfide dominates 

Au complexing (Hiyashi and Ohmoto, 1991). Since chloride complexes dominate at high temperature and 
114

their solubility is strongly affected by temperature, at lower temperature all available Cu could have already 

precipitated and thus is not seen with the gas-rich phase. 

Magmatic fluids were concentrated as the magma body (Bonanza Pluton) crystallized and then 

were subsequently expelled. At some point lower pressure resulted in a phase separation (aqueous and gasrich) of the magmatic fluid. The gaseous phase being less dense would ascend with the dikes or use them as 

conduits. It is more likely that the dikes acted as conduits since early crystallization of Bonanza pluton (the 

mafic outer zone) yielded mostly plagioclase and pyroxene, indicating that water contents were initially 

low and it was not until later that H2O was sufficiently concentrated to be expelled from the pluton. If the 

fluids were expelled from the pluton after a significant amount of crystallization, the dikes would likely 

have been in place and thus serve as conduits for the fluids. 

The reason both fluid phases resulting styles of mineralization are seen on the surface is due to 

significant vertical displacement along the high-angle N-S faults. At the Wallace occurrence gray dikes 

intrude the metasedimentary rocks and host the gas-rich mineralization style. In contrast, the uplifted, 

VABM Bonanza lobe hosts the aqueous mineralization. It is possible that beneath the surface at the 

Wallace occurrence the Bonanza pluton would contain the aqueous style of mineralization. 

The epithermal mineralization at the BCCA likely represents a largely meteoric fluid dominating 

late, low temperature circulation through the uppermost part of the Nyac system. A later epithermal 

mineralization could be related to a regional Late Cretaceous and early Tertiary magmatic arc and 

extensional event in SW Alaska (Gray et al., 1997). The mafic dikes with continental signatures that cut the 

Bonanza pluton are direct evidence for such a magmatic event. 
115

Wallace Occurrence VABM Bonanza lobe

Spruce Creek Lobe

Bonanza Creek Lobe

BC

Granodiorite

Gas-rich, CO rich, low salinity phase (Te-Bi-Au)

2

Liquid, CO -poor, high salinity phase (Cu-Bi-Au)

2

Phase Separation

Grey Dikes

Bonanza Pluton associated Qtz-Chl (mt-cp-Au) veining

Diabase Dikes

Qtz Monzodiorite

Epithermhosted in Hydroth

T A

Metavolcanics Granodiorite

Granodiorite

Granodiorite

?

?

?

? ? ? ?

?

?

?

SW 

Figure 5.2: Schematic cross section through Bonanza pluton.
116

6. Conclusions

 During the field and analytical portions of this study six important conclusions were determined. 

1. Placer gold mined from the study area is definitely locally derived. All of the placer grain 

(excluding sample 975842) finenesses and placer averages fall within the range of finenesses 

taken from outcrop. All analyzed placer grains were either attached to tetradymite (a soft mineral 

which would be destroyed quickly in a stream environment), had experience little Ag-leaching or 

had irregular shapes indicating local derivation. 

2. The Nyac batholith is significantly older than Bonanza pluton and dated mineralization. The Nyac 

batholith is thus unrelated to any of the mineralization in the study area. The hornblende age for 

the gray dikes at the Wallace occurrence are younger than the hornblende age of the Nyac 

Batholith, illustrating that the batholith cannot be responsible for this mineralization. 

3. All portions of the Bonanza pluton have statistically indistinguishable biotite ages, distinct trace 

element fractionation patterns and similar mineralogy. All these lines of evidence indicate that the 

VABM Bonanza lobe, Spruce Creek lobe and Bonanza Creek lobe are part of the same pluton. 

The differences in composition are likely the result of different levels of exposure of the zoned 

pluton. Mineralization from mineralized quartz muscovite veins at VABM Bonanza lobe yield an 

age slightly older than the biotite, but definitely younger than hornblende. The closure temperature 

of muscovite is higher than biotite and lower than hornblende, thus the mineralization occurred 

during cooling of the Bonanza pluton. 

4. The gray dikes yield statistically indistinguishable ages from dated hornblende (and biotite?) from 

Bonanza pluton, and the red dikes have a statistically indistinguishable biotite age from that of the 

Bonanza pluton. The similar ages suggest that the grey dikes, the Bonanza pluton and possibly the 

red dikes were derived from a common magmatic body. The extreme trace element enrichment of 

the red dikes suggests they are not compositionally related to the Bonanza pluton. It is possible 

that multiple magma bodies existed at ~113 Ma ago. 

5. Bedding measurements indicate that the metasedimentary rocks overlie the metavolcanic rocks. 

This finding is consistent with dated fossils (Box et al., 1993). Variable bedding measurements are 

likely due to the significant movement along faults and original non-horizontal bedding due to an 

active volcanic-arc formation. 

6. The high temperature Cu-Bi-Au mineralization in the study area is unique to the Nyac terrane in 

SW Alaska. The dated mineralization is older than all other dated Au occurrences of the region. 

The style of mineralization is also different with respect to high salinities, essentially no 

arsenopyrite and the association of chalcopyrite. Since this is the first documentation of this style 
117

of mineralization in southwest, Alaska the economic potential for this type of mineralization is 

unknown. 

6.1 Recommended Work

 It is the author’s hope that the results presented in this study will provide a solid basis for 

continued exploration in the Nyac district. The following is a summary of recommendations for further 

study and exploitation. 

1. Due to poor exposure, geologic mapping in the Nyac terrane is difficult. There appears to be a 

tremendous number of faults that cut the study area. Producing a more accurate map requires more 

geophysical data. Tighter flight lines for a magnetic survey and a resistivity survey would make 

mapping the geology simpler and more accurate. 

2. Three areas of the most intense gold mineralization have been outlined: the Wallace occurrence, 

the VABM Bonanza lobe and the BCCA. Continued work should be focused on these areas. 

Gridded soil sampling, trenching, and drilling these targets should be conducted to estimate the 

economic potential of the Nyac district. 

3. What role do the pink dikes play in Au mineralization in the Nyac district? Although no 

mineralization was ever found in the pink porphyry dikes significant mineralization occurs in 

close proximity to these dikes. The closest spatially associated mineralized areas are at the 

Bonanza pluton contact with the metavolcanic rocks at Spruce Creek and in the center of VABM 

Bonanza lobe. A sample should be dated to see if the age is similar to that of the muscovite from 

VABM Bonanza lobe mineralization. 

4. Obtain a U-Pb date of the Rex Creek pluton to determine its true age. 

5. Dating the scapolite from the contact at the Spruce Creek skarn and from the metasedimentary 

rock unit will indicate which igneous body is responsible for the skarn mineralization. 

6. Dating of secondary biotite from the High-T, Cu-Au mineralization at the BCCA, and dating 

sericite from the Wallace occurrence would show if all these styles of mineralization are related to 

a single event (Bonanza Pluton) and give a time constraint on how long the system lasted. 

7. Are the mafic dikes in the study area responsible for the Ar loss seen in all the age spectra and 

later epithermal mineralization? Dating the mafic dike from the Spuce Creek lobe will answer part 

of this question. 
118

References 

ADGGS, WGM, Dighem, 1994, Digital gridded data of total field magnetics for entire survey of Nyac 

mining district: Alaska Division of Geological & Geophysical Surveys, Public Data File 94-34, 1 disk. 

Bethke, C.M., 1998, The Geochemist’s Workbench (computer program). University of Illinois, Urbana. 

Box, S.E., Moll-Stalcup, E.J., Frost, T.P., and Murphy, J.R., 1993, Preliminary geologic map of the Bethel

 and southern Russian Mission quadrangles, southwestern Alaska: U.S. Geological Survey

 Miscellaneous Field Studies Map MF-2226-A, scale 1:250,000, 20 p. 

Blatt, H., and Tracy, R.J., 1995, Petrology Igneous, Sedimentary, and Metamorphic, Houndsmills,

 Basingstoke, England, 2nd edition: W. H. Freeman and Company, 529 p. 

 

Brown, P.E., 1989, FLINCOR: A microcomputer program for the reduction and investigation of fluid

 inclusion data: American Mineralogist, v. 74, p. 1390-1393. 

Bundtzen, T.K., and Miller, M.L., 1997, Precious metals associated with Late Cretaceous-Early Tertiary

 igneous rocks of southwestern Alaska: Economic Geology Monograph 9, p. 242-295. 

Cameron, C.E., 2000, Fault-hosted Au Mineralization, Ester Dome, Alaska: M.S. Thesis, University of

 Alaska, Fairbanks, 115 p. 

Candela, P.A., and Piccoli, P.M., 1995, Model ore-metal partitioning from melts into vapor and vapor/brine

 mixtures, in Thompson, J. F. H., ed., Magmas, Fluids, and Ore Deposits: Mineralogical

 Association of Canada Short Course, v. 23, p. 101-127. 

Davis, J.C., 2002, Statistics and Data Analysis in Geology: New York, John Wiley & Sons, 638 p. 

Decker, J., Bergman, S.C., Blodgett, R.B., Box, S.E., Bundtzen, T.K., Clough, J.G., Coonrad, W.L.,

 Gilbert, W.G., Miller, M.L., Murphy, J.M., Robinson, M.S., and Wallace, W.K., 1994, Geology of

 Southwestern Alaska, in Plafker, G., and Berg, H.C., eds., v. G1, The Geology of Alaska: Boulder,

 Colorado, Geological Society of America, Geology of North America, p. 285-310. 

Deer, W.A., Howie, R.A., and Zussman, J., 1997a, Rock-Forming Minerals: Single Chain Silicates, 2nd ed,

 Oxford UK, Alden Press, Osney Mead, v. 2A, 668 p. 

Deer, W.A., Howie, R.A., and Zussman, J., 1997b, Rock-Forming Minerals: Double Chain Silicates, 2nd ed,

 Oxford UK, Alden Press, Osney Mead, v. 2B, 758 p. 

Deer, W.A., Howie, R.A., and Zussman, J., 1966, An Introduction to the Rock-Forming Minerals:

 Longman Group Limited, London, 528 p. 

Delany, J.M., and Lundeen, S.R., S.R., 1990, The LLNL thermodynamic database: Lawrence Livermore

 National Laboratory Report UCRL-21658, 150 p. 

De la Roche, H., Leterrier, J., Grande Claude, P., and Marchal, M., 1980, A classification of volcanic and

 plutonic rocks using R1-R2 diagrams and major element analyses—its relationships and current

 nomenclatures: Chemical Geology, v. 29, 183-210. 
119

Foley, J., 2000, The Nyac mining district, southwestern Alaska: Calista Corporation, unpublished company

 report, 13 p. 

Frost, T.P., Box, S.E., and Moll-Stalcup, E.J., 1993, Summary of results of the mineral resource assessment

 of the Bethel and southeastern part of the Russian Mission 1 o and 3 o quadrangles, Alaska: U.S.

 Geological Survey Bulletin 2041, p. 30-48. 

Frost, T.P., 1990, Geology and geochemistry of mineralization in the Bethel quadrangle, southwestern

 Alaska, in Goldfard, R.J., Nash, J.T., and Stoeeser, J.W., eds., Geochemical studies in Alaska by

 the U.S. Geological Survey: U.S. Geological Survey Bulletin 1950, p. C1-C10. 

Gammons, C.H., and Williams-Jones, A.E., 1997, Chemical mobility of gold in the porphyry-epithermal

 environment: Economic geology, v. 92, p. 45-59. 

Gates, G., 1945a, Letter from USGS geologist George Gates to USGS geologist Robert Wallace, July 9,

 1945. (Calista Corporation holdings) 

Gates, G., 1945b, Letter from USGS geologist George Gates to USGS geologist Robert Wallace, July 17,

 1945. (Calista Corporation holdings) 

Gierymski, C., and Werdon, M. B., 1997, 1997 Summary report: Placer Dome Exploration, unpublished

 company report, Nyac- project 8A-25, 2 volumes. 

Gray, J.E., Gent, C.A., Snee, L.W., and Wilson, F.H., 1997, Epithermal mercury-antimony and gold

 bearing vein lodes of southwestern Alaska: Economic Geology Monograph 9, p. 287-305. 

Hayashi, K-I., and Ohmoto, H., 1991, Solubility of gold in NaCl- and H2S-bearing aqueous solutions at

 250-350 o C: Geochemica et Cosmochemica Acta, v. 55, p. 2111-2126. 

Hedenquist, J.W., 1995, The ascent of magmatic fluid: discharge versus mineralization, in Thompson, J. F.

 H., ed., Magmas, Fluids, and Ore Deposits: Mineralogical Association of Canada Short Course, v.

 23, p. 101-127. 

Hoare, J.M., and Coonrad, W.L., 1959, Geology of the Russian Mission quadrangle, Alaska: U.S.

 Geological Survey Miscellaneous Investigations Map I-292, scale 1:250,000. 

Huang, W-L., and Wyllie, P.J., 1975, Melting relations in the system NaAlSi 3 O 8 -KAlSi 3 O 8 -SiO 2 to 35

 kilobars, dry and excess water: Journal of Geology, v. 83, p. 737-748. 

Irvine, T.N., and Baragar, W.R.A., 1971, A guide to the chemical classification of the common volcanic

 rocks: Canadian Journal of Earth Science, v. 8, p. 523-548. 

Knight, J.B., Morison, S.R., and Mortensen, J.K., 1999, The relationship between placer gold particle

 shape, rimming, and distance of fluvial transport as exemplified by gold from the Klondike

 district, Yukon Territory, Canada: Economic Geology, v.94, p. 635-648. 

Krauskopf, K.B., and Bird, D.K., 1995, Introduction to Geochemistry: New York, Mc-Graw Hill, 647 p. 

Lanphere, M.A., and Dalrymple, G.B., 2000, First-principles calibration of 38Ar tracers: Implications for

 the ages of 40Ar/39Ar fluence monitors: U.S. Geological Survey Professional Paper 1621, 10 p. 
120

Layer, P.W., 2000, 40 Ar/ 39 Ar age of the El’gygytgyn impact event, Chukotka, Russia: Meteoritics and

 Planetary Science, v. 35, p. 591-600. 

Layer P. W., Hall C. M. and York D., 1987, The derivation of 40 Ar/ 39 Ar age spectra of single grains of

 hornblende and biotite by laser step heating: Geophysical Research Letters, v. 14, p. 757-760. 

 

LeMaitre, R.W.[ed.], Bateman, P., Dudek, A., Keller, J., Lemeyre, J., Le Bas, M.J., Sabine, P.A., Schmid,

 R., Sorenson, H., Sreckheisen, A., Wooley, A.R., and Zanettin, B., 1989, A classification of

 igneous rocks and glossary of terms: Blackwell Science Publishing, Oxford, 193 p. 

Luth, W.C., Jahns, R.H., and Tuttle, O.F., 1964, The granite system at pressures of 4-10 kbar: Journal of

 Geophysical Research, v. 69, p. 759-773. 

Maddren, A.G., 1915, Gold placers of the lower Kuskokwim, with a note on copper in the Russian

 mountains, in Brooks, A.H. ed., Mineral Resources of Alaska: U.S. Geological Survey Bulletin

 622, p. 292-355. 

McDougal, I., and Harrison, T.M., 1988, Geochronology and Thermochronolgy by the 40Ar/39Ar Method:

 New York, Oxford University Press, 212 p. 

Metz, P.A. and Hawkins, D.B., 1981, A summary of gold fineness values from Alaska placer deposits,

 University of Alaska, Mineral Industry Research Lab, Report No. 45, 63 p. 

Middelaar, W.T. van, and Keith, J.D., 1990, Mica chemistry as an indicator of oxygen and halogen

 fugacities in the CanTung and other W-related granitoids in the North American Cordillera, in

 Stein, H.J., and Hannah, J.L., eds.: Geological Society of America Special Paper 246, p. 205-220. 

Miller, M.L., Bradley, D.C., Bundtzen, T.K., and McClelland, W., 2002, Late Cretaceous through Cenozoic

 strike-slip tectonics of southwestern Alaska: Journal of Geology, v. 110, p. 247-270. 

Mirsa, K.C., 2000, Understanding Mineral Deposits: Dordrecht Netherlands, Kluwer Academic Publishers,

 845p. 

Pearce, J.A., and Cann, J.R., 1973, Tectonic setting of basic volcanic rocks determined using trace element

 analyses: Earth and Planetary Science Letters, v. 19, p. 290-300. 

Pearce, J.A., Harris, N.B.W., and Tindle, A.G., 1984, Trace element discrmination diagrams for the

 tectonic interpretation of granitic rocks: Journal of Petrology, v. 25, p. 956-983. 

Potter, R.W, II, 1977, Pressure corrections for fluid inclusion homogenization temperatures based on the

 volumetric properties of the system H2O-NaCl: U.S. Geological Survey Journal of Research, v.

 5, p. 603-607. 

Resource Associates of Alaska (RAA), 1975, Mineral resource evaluation for Calista Corporation: Final

 report of exploration activities during 1975, unpublished report, 29p. 

Robinson, M.S., and Decker, J., 1986, Preliminary age dates and analytical data for selected igneous rocks

 from the Sleetmute, Russian Mission, Taylor Mountains, and Bethel quadrangles, southwestern:

 Alaska Division of Mining and Geological and Geophysical Surveys, Public Data File 86-99, 3 p. 
121

Ruperto, V.L., Stevens, R.E., and Norman, M.B., 1964, Staining of plagioclase feldspar and other minerals

 with F.D. and C. Red No. 2: U.S. Geological Survey Professional Paper 501B, p. 152-153. 

Samson S. D., and Alexander E. C., 1987, Calibration of the interlaboratory 40Ar/39Ar dating standard,

 MMhb-1: Chemical Geology, v. 66, p. 27-34. 

Streckheisen, A.L., 1973, Classification and nomenclature recommended by the IUGS Subcommission on

 the systematics of igneous rocks: Geotimes, v. 18, p. 26-30. 

Steiger, R.H. and Jaeger, E., 1977, Subcommission on geochronology: Convention on the use of decay

 constants in geo and cosmochronology: Earth and Planetary Science Letters, v. 36, p. 359-362. 

Steiner, J.C., Jahns, R.H., and Luth, W.C., 1975, Crystallization of alkali feldspars and quartz in the

 haplogranite system NaAlSi 3 O 8 -KAlSi 3 O 8 -SiO 2 -H 2 O at 4 kb: Bulletin of the Geological

 Society of America, v. 86, p. 83-98. 

Thompson, J.F.H. and Newberry, R.J.J., 2000, Low fO 2 intrusion-related gold deposits: An important

 class of Phanerozoic ores: Reviews in Economic Geology, v. 14, p. 12-38. 

Tuttle, O.F., and Bowen, N.L., 1958, The origin of granite in the light of experimental studies in the system

 NaAlSi 3 O 8 -KAlSi 3 O 8 -SiO 2 - H 2 O: Geological Society of America Memoir, no. 74. 

Wallace, R.E., 1945, Free-gold lode deposit on Tuluksak River, Kuskokwim Region, Alaska: US

 Department of the Interior Press Release, August 4, 1945. 

Wilson, F.H., 1977, Some plutonic rocks of southwestern Alaska, a data compilation: U.S. Geological

 Survey Open-File Report 77-501. 

Winchester, J.A., and Floyd, P.A., 1977, Geochemical discrimination of different magma series and their

 differentiation products using immobile elements: Chemical Geology, v. 20, p. 325-343. 

Wood, S.A., Crear, D.A., and Borcsik, M.P., 1987, Solubility of the assemblage, pyrite-pyrrhotite

 magnetite-sphalerite-galena-gold-stibnite-bismuthinite-argentite-molybdenite in H 2 O-NaCl-CO 2

 solutions from 200 o to 350 o C: Economic Geology, v. 82, p. 1864-1887. 

York, D., Hall, C.M., Yanase, Y., Hanes, J.A., and Kenyon, W.J., 1981, 40 Ar/ 39 Ar dating of terrestrial

 minerals with a continuous laser: Geophysical Research Letters, v. 8, p. 1136-1138. 

123 

Appendices 

Appendix A: List of samples, location, rock type, veining style, 

ore mineralogy and magnetic susceptibility. 

Abbreviations are as follows: asp= arsenopyrite, cc= calcite, chl= chlorite, co= chalcopyrite, bis= bismuthinite, 

ep=epidote, hm= hematite, il= ilmenite, lim= limonite, mal= malachite, mg=magnetite, musc= muscovite, po= 

pyrrhotite, py=pyrite, qtz= quartz, rt= rutile, ser= sericite, tebis= tellurobismuthite and tet= tetradymite. 

Sample UTM E UTM N Lithology Ore Minerals Veins Magnetic Susceptibility 

03ZW001 460927 6771453 Conglomerate Hornfels py 0.90 

03ZW002 460929 6771463 Andesite Hornfels py 0.46 

03ZW003 461899 6771273 Gabbro mg,il 17.23 

03ZW004 462537 6771678 Andesite Hornfels py,co ep 0.31 

03ZW005 462278 6772703 Granodiorite Dike 0.45 

03ZW006 449959 6769116 Andesite Hornfels co,py chl(2%) 0.57 

03ZW007 455115 6768387 Basalt Hornfels py chl 6.17 

03ZW008 455169 6768473 Andesite Hornfels chl 5.57 

03ZW009 455189 6768578 Volcaniclastic Hornfels py qtz-chl 0.35 

03ZW010 455151 6768405 Basalt Hornfels co,py ep-chl-qtz 2.04 

03ZW011 455369 6768066 Basalt Hornfels 8.50 

03ZW012 455353 6768078 Basalt Hornfels co 11.55 

03ZW013 455293 6768198 Basalt Hornfels 4.94 

03ZW014 455291 6768209 Volcaniclastic Hornfels mg 20.43 

03ZW015 455234 6768305 Volcaniclastic Hornfels co,py chl-ep-qtz(80%) 1.22 

03ZW016 455216 6768337 Andesite Hornfels 0.43 

03ZW017 454998 6768516 Basalt Hornfels py ep 14.03 

03ZW018 455015 6768481 Breccia lim qtz,lim 0.44 

03ZW019 454962 6768320 Pink Dike 5.04 

03ZW020 454953 6768322 Volcaniclastic Hornfels chl 0.31 

03ZW021 454925 6768303 Basalt Hornfels 16.73 

03ZW022 454839 6768229 Volcaniclastic Hornfels ep-chl-qtz(2%) 0.41 

03ZW023 454816 6768210 Volcaniclastic Hornfels ep 0.64 

03ZW024 454719 6768122 Dacite Sill Hornfels 0.79 

03ZW025 454651 6768087 Basalt Hornfels 5.73 

03ZW026 454617 6768030 Volcaniclastic Hornfels po 0.52 

03ZW027 454348 6768150 Volcaniclastic Hornfels py 0.44 

03ZW028 454393 6768124 Breccia lim 0.33 

03ZW029 454507 6767881 Dacite Sill Hornfels 0.72 

03ZW030 454505 6767869 Breccia lim 0.25 

03ZW031 454474 6767820 Volcaniclastic Hornfels py 0.62 

03ZW032 454456 6767618 Andesite Hornfels lim 0.51 

03ZW033 454449 6767549 Felsic Dike py(15%) 0.87 

03ZW034 453985 6767638 Volcaniclastic Hornfels py 

qtz-ep-chlcc(5%) 0.61 

03ZW035 454052 6767662 Breccia lim lim-cc 0.48 
124 

Sample UTM E UTM N Lithology Ore Minerals Veins Magnetic Susceptibility 

(pervasive) 

03ZW036 454080 6767687 Volcaniclastic Hornfels 0.88 

03ZW037 454428 6767467 Dacite Sill Hornfels 0.41 

03ZW038 454420 6767364 Volcaniclastic Hornfels 0.25 

03ZW039 454404 6767048 Volcaniclastic Hornfels py,co ep (pods) 5.31 

03ZW040 450992 6763935 Siltstone Hornfels py,lim ep-qtz-cc 0.58 

03ZW041 459579 6770483 Sawpit Pluton qtz-ep-Na-spar 1.45 

03ZW042 459579 6770483 Volcaniclastic Hornfels 0.58 

03ZW043 452626 6767767 Basalt Hornfels co,hm ep-cc 30.40 

03ZW044 452632 6767704 Basalt Hornfels ep-cc 17.47 

03ZW045 452641 6767636 Basalt Hornfels hm? ep-cc (5%) 12.77 

03ZW046 452649 6767587 Altered Porphyry (Dike?) lim 0.69 

03ZW047 452652 6767567 Basalt Hornfels hm? ep-cc 1.54 

03ZW048 452682 6767402 Basalt Hornfels ep-qtz-cc (10%) 1.55 

03ZW049 452718 6767350 Volcaniclastic Hornfels hm? ep-cc (2%) 6.55 

03ZW050 452749 6767283 Altered Porphyry (Dike?) lim 0.29 

03ZW051 452790 6767199 Altered Porphyry (Dike?) lim 0.40 

03ZW052 452808 6767067 Volcaniclastic Hornfels ep-cc 0.43 

03ZW053 452806 6767020 Alt Metavolcanic Hornfels lim,py 0.26 

03ZW054 452795 6766961 Breccia lim 0.39 

03ZW055 452799 6766816 Tonalite Hornfels lim 0.61 

03ZW056 452885 6766555 Monzogranite 2.26 

03ZW057 452901 6766505 Altered Diorite Hornfels lim 0.35 

03ZW058 452931 6766480 Volcaniclastic Hornfels ep-cc 0.85 

03ZW059 452921 6766261 Basalt Hornfels 2.39 

03ZW060 453089 6765687 Andesite Hornfels py 0.48 

03ZW061 450236 6768195 Volcaniclastic Hornfels 0.29 

03ZW062 450385 6767749 Andesite Hornfels 0.61 

03ZW063 450872 6767990 Andesite Hornfels py 0.76 

03ZW064 450933 6767985 Volcaniclastic Hornfels py (2-3%) 0.83 

03ZW065 451010 6767984 Basalt Hornfels 17.43 

03ZW066 451108 6767987 Basalt Hornfels py ep-cc 7.74 

03ZW067 451197 6767981 Basalt Hornfels py (2%) 18.30 

03ZW068 451296 6767961 Quartz Diorite Hornfels 25.03 

03ZW069 451364 6767905 Altered Porphyry (Dike?) lim 0.37 

03ZW070 451441 6767916 Diorite Hornfels ep 3.36 

03ZW071 451626 6767843 Volcaniclastic Hornfels ep-cc (5%) 0.88 

03ZW072 451541 6767900 Diorite Dike Hornfels 1.40 

03ZW073 451402 6768220 Basalt Hornfels py ep-chl-cc 37.47 

03ZW074 451373 6768288 Andesite Hornfels py, lim (3%) lim 0.45 

03ZW075 451349 6768376 Andesite Hornfels py(3%) 1.91 

03ZW076 451324 6768514 Volcaniclastic Hornfels 0.42 

03ZW077 453156 6768868 Quartz Veined Breccia py,lim silica 0.20 

03ZW078 453054 6768913 Basalt Hornfels ep 35.10 

03ZW079 453010 6768852 Basalt Hornfels py ep 21.67 

03ZW080 452970 6768832 Basalt Hornfels py 9.08 
125 

Sample UTM E UTM N Lithology Ore Minerals Veins Magnetic Susceptibility 

03ZW081 452905 6768750 Volcaniclastic Hornfels 0.34 

03ZW082 452836 6768674 Andesite Hornfels py ep 0.55 

03ZW083 452714 6768574 Basalt Hornfels ep 12.36 

03ZW084 452648 6768549 Basalt Hornfels 25.80 

03ZW085 452589 6768516 Basalt Hornfels qtz-ep 21.00 

03ZW086 453180 6768847 Breccia lim,cc(30%) 

03ZW087 451262 6765472 Epidote-Quartz Vein 0.46 

03ZW088 452421 6767968 Alt Metavolcanic Hornfels mal(5%) 0.51 

03ZW089 452557 6768430 Dacite Hornfels 0.41 

03ZW090 452554 6768438 Diorite Dike Hornfels 2.41 

03ZW091 452467 6768095 Andesite Hornfels cc 0.50 

03ZW092 452459 6768054 Andesite Hornfels py cc-qtz 0.58 

03ZW093 452425 6767969 Quartz Vein lim,co qtz-cc-mal 0.21 

03ZW094 452409 6767945 Andesite Hornfels py cc 0.34 

03ZW095 452365 6767886 Alt Metavolcanic Hornfels hm,py,mal ep-qtz-cc(5%) 0.51 

03ZW096 453040 6769173 Andesite Hornfels ep-qtz-cc 0.59 

03ZW097 453045 6769117 Andesite Hornfels py ep-qtz-cc-chl 0.76 

03ZW098 452574 6768393 Andesite Hornfels ep 1.67 

03ZW099 452391 6767901 Alt Metavolcanic Hornfels lim,py? 0.51 

03ZW100 452333 6767870 Andesite Hornfels py,lim qtz 1.01 

03ZW101 452249 6767856 Andesite Hornfels py 0.38 

03ZW102 452143 6767873 Breccia py,lim qtz 0.20 

03ZW103 452111 6767879 Dacite Hornfels 5.06 

03ZW104 451950 6767867 Quartz Diorite Hornfels ep (2%) 6.65 

03ZW105 451909 6767850 Diorite Hornfels ep (2%) 17.07 

03ZW106 451886 6767855 Pink Dike 4.74 

03ZW107 451824 6767817 Diorite Hornfels lim 11.40 

03ZW108 451669 6767780 Quartz Monzodiorite H ep-qtz 7.81 

03ZW109 451650 6767835 Intrusive Breccia lim qtz-cc 3.06 

03ZW110 452110 6767853 Dacite Hornfels 4.85 

03ZW111 452292 6767716 Quartz Veined Breccia lim 0.12 

03ZW112 452319 6767614 Basalt Hornfels 13.57 

03ZW113 452445 6767837 Gabbro 37.73 

03ZW114 452570 6767805 Quartz Veined Breccia lim qtz 0.08 

03ZW115 460143 6772174 Andesite Hornfels 0.19 

03ZW116 460126 6772171 Monzogranite 0.11 

03ZW117 460036 6772223 Monzogranite 0.37 

03ZW118 459741 6772908 Dacite Hornfels 11.10 

03ZW119 460222 6773629 Alt Metavolcanic Hornfels lim qtz-ser 0.27 

03ZW120 460224 6773681 Alt Metavolcanic Hornfels lim qtz-ser 0.29 

03ZW121 460317 6773963 Dacite Hornfels 10.42 

03ZW122 460219 6773976 Shear lim qtz-ser 0.18 

03ZW123 453638 6769305 Breccia lim silica 0.06 

03ZW124 453672 6769328 Pink Dike 3.21 

03ZW125 453803 6769439 Alt Metavolcanic Hornfels chl-qtz-cc 0.42 

03ZW126 453868 6769470 Volcaniclastic Hornfels 4.35 
126 

Sample UTM E UTM N Lithology Ore Minerals Veins Magnetic Susceptibility 

03ZW127 453997 6769592 Quartz Vein lim, py qtz-chl 0.07 

03ZW128 454045 6769695 Mudstone Hornfels lim silica 0.14 

03ZW129 454097 6769696 Pink Dike 7.60 

03ZW130 454145 6769719 Mudstone Hornfels py(2%),co chl 0.77 

03ZW131 454184 6769731 Basalt Hornfels qtz-ep-chl-cc 40.97 

03ZW132 454379 6769551 Alt Metavolcanic Hornfels py(2%),lim ep-qtz-cc-chl 8.11 

03ZW133 454317 6769638 Alt Metavolcanic Hornfels lim,py,co silica 0.29 

03ZW134 455188 6768566 Volcaniclastic Hornfels 0.52 

03ZW135 455171 6768805 Alt Metavolcanic Hornfels lim silica 16.80 

03ZW136 455225 6768954 Diorite Hornfels py(2%) 13.73 

03ZW137 455199 6769078 Alt Metavolcanic Hornfels py(3%) 7.05 

03ZW138 455211 6769095 Andesite Hornfels qtz-cc-ep 22.33 

03ZW139 455224 6769168 Alt Metavolcanic Hornfels py,po 23.37 

03ZW140 455232 6769210 Basalt Hornfels 16.67 

03ZW141 455232 6769321 Volcaniclastic Hornfels py(2%) 50.23 

03ZW142 455124 6769795 Granodiorite py, bis qz-chl-py-po-bth 4.54 

03ZW143 453819 6773447 Diorite Hornfels py 0.63 

03ZW144 453853 6773622 Mudstone Hornfels py,po 0.43 

03ZW145 453946 6773723 Mudstone Hornfels py,po, lim 1.01 

03ZW146 453908 6773724 Mudstone Hornfels 0.24 

03ZW147 453970 6773777 Gray Dike 4.44 

03ZW148 453992 6773809 Diorite Hornfels py 0.52 

03ZW149 454053 6773990 Mudstone Hornfels py silica 0.99 

03ZW150 454072 6774212 Gray Dike 0.37 

03ZW151 453915 6774303 Mudstone Hornfels qtz-chl 0.44 

03ZW152 453933 6774309 Conglomerate Hornfels 0.48 

03ZW153 454142 6774130 Andesite Hornfels 8.76 

03ZW154 454203 6774126 Dacite Hornfels 0.23 

03ZW155 454251 6774116 Monzonite Hornfels 0.81 

03ZW156 454093 6773420 Mudstone Hornfels py 0.38 

03ZW157 452268 6771755 Diorite Hornfels 11.10 

03ZW158 452214 6771810 Mudstone Hornfels py 0.82 

03ZW159 452074 6771988 Volcaniclastic Hornfels py 1.74 

03ZW160 452038 6772272 Diorite Hornfels chl 0.55 

03ZW161 452044 6772597 Pink Dike 2.83 

03ZW162 451914 6772775 Diorite Hornfels 1.27 

03ZW163 452284 6772813 Mudstone Hornfels chl-qtz-cc(2%) 0.50 

03ZW164 452343 6772891 Diorite Hornfels 0.34 

03ZW165 452398 6772980 Mudstone Hornfels py chl-qtz-cc,silica 0.69 

03ZW166 452475 6773058 Mudstone Hornfels chl-qtz(3%) 0.27 

03ZW167 452475 6773058 Diorite Hornfels chl-qtz(3%) 0.26 

03ZW168 452503 6773109 Gray Dike 0.25 

03ZW169 452582 6773149 Conglomerate Hornfels 0.46 

03ZW170 452880 6774216 Mudstone Hornfels chl-qtz(15%) 0.19 

03ZW171 452667 6774311 Mudstone Hornfels py silica 0.30 

03ZW172 452536 6774276 Dacite Hornfels 0.98 
127 

Sample UTM E UTM N Lithology Ore Minerals Veins Magnetic Susceptibility 

03ZW173 452377 6774063 Peraluminous Aplite Dike 1.46 

03ZW174 453393 6774348 Mudstone Hornfels py chl-qtz 0.54 

03ZW175 453358 6773978 Breccia cc(20%) 13.55 

03ZW176 456487 6772736 Granodiorite Dike 3.06 

03ZW177 456399 6772687 Volcaniclastic Hornfels py? 0.47 

03ZW178 456325 6772692 Breccia lim cc(5%) 0.34 

03ZW179 456220 6772668 Granodiorite Dike 4.46 

03ZW180 456120 6772672 Quartz Vein qtz 0.14 

03ZW181 455955 6772712 Aplite Dike qtz 0.16 

03ZW182 455902 6772732 Mudstone Hornfels 0.26 

03ZW183 455819 6772778 Breccia lim 0.22 

03ZW184 455746 6772828 Aplite Dike 0.69 

03ZW185 455391 6772889 Volcaniclastic Hornfels 0.54 

03ZW186 453790 6773047 Mudstone Hornfels py,lim chl(2%) 0.50 

03ZW187 454519 6773022 Conglomerate Hornfels cc-chl 0.63 

03ZW188 454944 6773103 Mudstone Hornfels py 0.58 

03ZW189 455143 6773134 Tonalite? 0.66 

03ZW190 455098 6773431 Mudstone Hornfels 0.58 

03ZW191 455403 6774344 Conglomerate Hornfels 0.62 

03ZW192 455586 6774424 Gray Dike 4.11 

03ZW193 455985 6774203 Pink Dike 1.98 

03ZW194 456757 6773963 Volcaniclastic Hornfels py 0.61 

03ZW195 456044 6774108 Tonalite Dike 0.37 

03ZW196 455980 6774194 Pink Dike 2.16 

03ZW197 455292 6774155 Gray Dike 0.45 

03ZW198 452085 6765630 Volcaniclastic Hornfels 0.39 

03ZW199 451985 6765800 Intrusive Breccia py? 2.67 

03ZW200 451595 6767669 Quartz Diorite Hornfels py ep-qtz(2%) 12.87 

03ZW201 451560 6767647 Diorite Hornfels 6.85 

03ZW202 451560 6767647 Basalt Hornfels py ep-qtz(3%) 19.23 

03ZW203 451526 6767580 Andesite Hornfels py ep-qtz(2%) 0.82 

03ZW204 451512 6767531 Altered Diorite Hornfels lim 0.31 

03ZW205 451459 6767474 Volcaniclastic Hornfels py(2%) qtz-ep 0.47 

03ZW206 451431 6767375 Alt Metavolcanic Hornfels lim 0.02 

03ZW207 451400 6767219 Diorite Hornfels 0.61 

03ZW208 451360 6767127 Altered Porphyry (Dike?) lim 0.52 

03ZW209 451355 6767115 Altered Porphyry (Dike?) lim(25%) 0.21 

03ZW210 450542 6766921 Andesite Hornfels py 1.35 

03ZW211 451218 6767013 Diorite Hornfels py ep(2%) 0.30 

03ZW212 451396 6766765 Quartz Diorite Hornfels 10.94 

03ZW213 451425 6766700 Granodiorite ep-qtz 5.47 

03ZW214 451550 6766427 Granodiorite Hornfels 0.48 

03ZW215 451583 6766159 Diorite Hornfels 3.74 

03ZW216 451540 6765339 Volcaniclastic Hornfels mg cc(2%) 8.14 

03ZW217 451222 6765452 Volcaniclastic Hornfels py ep-qtz-cc(2%) 0.48 

03ZW218 451234 6765691 Basalt Hornfels py cc 0.59 
128 

Sample UTM E UTM N Lithology Ore Minerals Veins Magnetic Susceptibility 

03ZW219 451245 6765742 Quartz Vein co, mal qtz-chl(95-5%) 0.08 

03ZW220 451241 6765840 Quartz Diorite Hornfels lim 8.28 

03ZW221 451421 6765952 Alt Metavolcanic Hornfels mg 0.28 

03ZW222 450645 6765696 Andesite Hornfels py 0.93 

03ZW223 459892 6771320 Epidote Rock py(2%) 0.71 

03ZW224 459718 6771209 Alt Metavolcanic Hornfels py(2%) ep-qtz(3%) 0.13 

03ZW225 459411 6771198 Chlorite Rock co,py 0.92 

03ZW226 459312 6771149 Volcaniclastic Hornfels py chl(5%) 0.49 

03ZW227 459605 6770283 Quartz Vein co, py 

03ZW228 459601 6770283 Quartz Monzonite qtz-Kspar-ep 

03ZW229 459601 6770283 Altered Quartz Monzonite py qtz-Kspar-ep 

03ZW230 459483 6770272 Sawpit Pluton 8.20 

03ZW231 459188 6770080 Sawpit Pluton py 0.25 

03ZW232 458123 6771026 Basalt Hornfels qtz-chal 14.93 

03ZW233 458034 6771189 Basalt Hornfels qtz-chal 23.63 

03ZW234 457744 6771285 Basalt Hornfels 8.58 

03ZW235 457654 6771322 Basalt Hornfels 16.83 

03ZW236 457567 6771319 Altered Metabasalt 5.01 

03ZW237 457294 6771495 Basalt Hornfels 11.01 

03ZW238 456775 6771456 Volcaniclastic Hornfels mg qtz-chl 1.64 

03ZW239 456738 6771430 Andesite Hornfels 1.73 

03ZW240 456735 6771429 Breccia lim(10%) 0.57 

03ZW241 456722 6771415 Alt Metavolcanic Hornfels lim 0.15 

03ZW242 456710 6771401 Volcaniclastic Hornfels py chl-qtz(2%) 0.56 

03ZW243 456630 6771314 Volcaniclastic Hornfels py 

chl-qtzmusc(3%) 5.13 

03ZW244 456538 6771280 Volcaniclastic Hornfels ep-qtz-chl-musc 1.76 

03ZW245 456457 6771336 Volcaniclastic Hornfels ep-qtz-chl-musc 0.53 

03ZW246 456439 6771326 Volcaniclastic Hornfels ep-qtz-chl(5%) 0.82 

03ZW247 456429 6771327 Pink Dike 4.82 

03ZW248 456372 6771302 Basalt Hornfels chl(2%) 4.33 

03ZW249 456385 6771341 Volcaniclastic Hornfels qtz-chl(2%) 0.34 

03ZW250 456376 6771341 Basalt Hornfels mg 3.12 

03ZW251 456355 6771305 Pink Dike 1.97 

03ZW252 456306 6771313 Andesite Hornfels mg(2%) qtz-chl-musc-mg 42.40 

03ZW253 456277 6771292 Alt Metavolcanic Hornfels py, lim(2%) 0.16 

03ZW254 456231 6771263 Dacite Hornfels mg(2%) 19.57 

03ZW255 456168 6771213 Basalt Hornfels mg(2%) 107.97 

03ZW256 456081 6771199 Skarn mg, co, cv, py qtz 8.75 

03ZW257 456075 6771204 Skarn 

pypo(3%),co,mg 3.07 

03ZW258 456113 6771212 Alt Metavolcanic Hornfels lim(5%) 0.14 

03ZW259 459564 6770310 Sawpit Pluton ep 16.23 

03ZW260 452349 6771400 Quartz Diorite Hornfels 1.00 

03ZW261 452349 6771399 Andesite Hornfels py chl-qtz 0.15 

03ZW262 456708 6771401 Epidote-Chlorite vein py(2%) ep-chl(90%) 4.18 

03ZW263 456005 6771205 Andesite Hornfels py chl-ep 2.95 

03ZW264 455993 6771201 Alt Metavolcanic Hornfels py(2%),lim 0.41 
129 

Sample UTM E UTM N Lithology Ore Minerals Veins Magnetic Susceptibility 

03ZW265 455955 6771194 Pink Dike 5.70 

03ZW266 455896 6771173 Basalt Hornfels py(2%) 4.45 

03ZW267 455836 6771161 Pink Dike 1.39 

03ZW268 455804 6771164 Volcaniclastic Hornfels py qtz-chl 0.42 

03ZW269 455733 6771125 Quartz Vein qtz(99%) 0.21 

03ZW270 455733 6771125 Gray Dike 13.77 

03ZW271 455704 6771134 Alt Metavolcanic Hornfels mg(5%),py(2%) 

qtz-ep-chlser(2%) 9.89 

03ZW272 455607 6771045 Monzodiorite 10.25 

03ZW273 455603 6770976 Diorite 16.90 

03ZW274 455774 6770835 Granodiorite lim(10%) 0.22 

03ZW275 455799 6770823 Quartz Diorite co qtz-chl 13.53 

03ZW276 455812 6770796 Tonalite Dike 14.40 

03ZW277 455824 6770773 Granodiorite 5.18 

03ZW278 455850 6770697 Tonalite 18.17 

03ZW279 455938 6770568 Monzodiorite 16.77 

03ZW280 456191 6770296 Granodiorite lim(5%), hem 0.14 

03ZW281 456261 6770172 Monzodiorite mg chl-py 17.23 

03ZW282 456225 6770254 Gabbro mg 20.07 

03ZW283 456075 6770466 Quartz Diorite 11.40 

03ZW284 456047 6770481 Diabase Dike 13.27 

03ZW285 458179 6773669 Basalt Hornfels chl 22.90 

03ZW286 458176 6773690 Basalt Hornfels mg chl-mg 49.10 

03ZW287 458190 6773709 Alt Metavolcanic Hornfels mg chl-mg 32.13 

03ZW288 458171 6773765 Alt Metavolcanic Hornfels mg chl-mg(80%) 34.40 

03ZW289 458148 6773831 Basalt Hornfels mg chl-mg(3%) 66.87 

03ZW290 458131 6773965 Basalt Hornfels mg 71.20 

03ZW291 458125 6773999 Breccia py 0.69 

03ZW292 458140 6774021 Breccia lim(15%), hem 0.30 

03ZW293 458150 6774125 Monzodiorite 30.83 

03ZW294 458135 6774201 Tonalite 14.70 

03ZW295 458152 6774259 Monzodiorite 29.50 

03ZW296 458196 6774408 Quartz Monzodiorite 19.60 

03ZW297 458355 6774558 Quartz Monzonite Dike 13.97 

03ZW298 458914 6774673 Volcaniclastic Hornfels py qtz-ep 12.63 

03ZW299 459519 6774652 Breccia lim(10%) 0.68 

03ZW300 458377 6772530 Volcaniclastic Hornfels lim(5%) 13.34 

03ZW301 458636 6772231 Basalt Hornfels 0.60 

03ZW302 458619 6772342 Alt Metavolcanic Hornfels lim(10%) 0.62 

03ZW303 458601 6772509 Basalt Hornfels lim(5%) 0.98 

03ZW304 458576 6772951 Basalt Hornfels py 24.33 

03ZW305 459034 6773055 Basalt Hornfels chl-qtz(2%) 21.97 

03ZW306 458992 6773280 Alt Metavolcanic Hornfels py(3%) 11.21 

03ZW307 458976 6773640 Monzodiorite 5.40 

03ZW308 458961 6773649 Andesite Hornfels 34.00 

03ZW309 458739 6773535 Alt Metavolcanic Hornfels py(5%) 0.71 

03ZW310 453236 6771760 Conglomerate Hornfels 0.27 
130 

Sample UTM E UTM N Lithology Ore Minerals Veins Magnetic Susceptibility 

03ZW311 452024 6769705 Basalt Hornfels 18.47 

03ZW312 452069 6769746 Gray Dike 4.17 

03ZW313 452183 6769814 Mudstone hornfels py qtz-chl-py 1.01 

03ZW314 452317 6769917 Siltstone Hornfels 0.52 

03ZW315 452406 6770007 Diorite Hornfels py? qtz-cc-chl 0.48 

03ZW316 452419 6770016 Alt Metavolcanic Hornfels py 0.09 

03ZW317 452433 6770025 Pink Dike 3.02 

03ZW318 452488 6770066 Andesite Hornfels py qtz-chl-cc 17.03 

03ZW319 452522 6770068 Breccia lim(10%) 0.63 

03ZW320 452555 6770067 Diorite Hornfels py chl 0.67 

03ZW321 452596 6770066 Basalt Hornfels py chl(10%) 1.61 

03ZW322 454177 6771867 Dacite Hornfels lim qt-cc-mus 0.22 

03ZW323 454258 6771891 Aplite Dike 0.33 

03ZW324 454322 6769755 Andesite Hornfels py 3.31 

03ZW325 454328 6769768 Intrusive Breccia py 2.09 

03ZW326 454358 6769806 Intrusive Breccia py(2%) 0.16 

03ZW327 454404 6769884 Intrusive Breccia py 0.66 

03ZW328 454421 6769898 Clinopyroxenite Hornfels 36.73 

03ZW329 454462 6769978 Intrusive Breccia py(3%) 0.33 

03ZW330 454188 6770244 Volcaniclastic Hornfels 18.57 

03ZW331 454384 6770159 Pink Dike 7.96 

03ZW332 454536 6770154 Intrusive Breccia py(2%) 0.68 

03ZW333 454586 6770173 Altered Felsic Dike py(2%) 0.42 

03ZW334 454650 6770211 Intrusive Breccia red lim(2%) 0.02 

03ZW335 454736 6770235 Volcaniclastic Hornfels py chl(4%) 2.40 

03ZW336 454803 6770316 Intrusive Breccia mg, py chl(3%) 11.17 

03ZW337 454819 6770392 Basalt Hornfels py 35.33 

03ZW338 454802 6770517 Mudstone hornfels chl 0.63 

03ZW339 454510 6771275 Quartz Monzodiorite co,py,mo,rt qtz-ser-sul 0.34 

03ZW339B 454510 6771275 Aplite Dike 

03ZW340 454569 6770918 Quartz Monzodiorite co,py, bis qtz-ser-sul 4.73 

03ZW341 454395 6769384 Granodiorite py 5.23 

03ZW342 454138 6769321 Aplite Dike 0.19 

03ZW343 456012 6771285 Pink Dike 7.41 

03ZW344 456060 6771220 Skarn co,py,po 4.31 

03ZW345 455805 6771159 Basalt Hornfels py(3%) 0.76 

03ZW346 455709 6771094 Basalt Hornfels mg,py(2%) 22.90 

03ZW347 455521 6771006 Diorite lim, co, bis qtz 7.46 

03ZW348 455327 6770960 Quartz Diorite? co,py, bis qtz 10.14 

03ZW349 455824 6770769 Granodiorite co,py,asp qtz-musc 2.98 

03ZW350 455689 6770947 Diorite? co,py qtz-chl 2.83 

03ZW351 458480 6773677 Quartz Monzonite Dike lim(3%) 0.09 

03ZW352 458532 6773613 Skarn py(2%) 4.46 

03ZW353 458135 6774036 Basalt Hornfels py,co,mg, Au 

qtz-chlsulfide(3%) 92.27 

03ZW354 458141 6774016 Breccia 0.64 

03ZW355 454402 6775667 Tonalite qtz 4.00 
131 

Sample UTM E UTM N Lithology Ore Minerals Veins Magnetic Susceptibility 

03ZW356 456142 6776399 Tonalite 

qtz and qtzKspar 10.00 

03ZW357 454785 6777734 Granodiorite 5.00 

03ZW358 453706 6779070 Granodiorite qtz-Kspar 7.00 

03ZW359 453175 6777346 Granodiorite 5.00 

03ZW360 449666 6778440 Monzodiorite qtz-Kspar 12.00 

03ZW361 446934 6775776 Granodiorite 7.00 

03ZW362 450099 6773992 Granodiorite 9.00 

03ZW363 445813 6772869 Granodiorite 8.00 

03ZW364 444359 6771884 Granodiorite 7.00 

03ZW365 443643 6769271 Granodiorite 8.00 

03ZW366 446620 6769360 Granodiorite 11.00 

03ZW367 447902 6771398 Granodiorite 11.00 

03ZW368 449815 6768948 Gray Dike 0.25 

03ZW369 449896 6768969 Gray Dike tebis,tet,Au,co qtz-chl 0.19 

03ZW370 450411 6769796 Diorite Hornfels chl 0.48 

03ZW371 450591 6769883 Limestone 0.29 

03ZW372 450492 6770593 Volcaniclastic Hornfels 0.54 

03ZW373 454033 6771560 Quartz Diorite 6.08 

03ZW374 454112 6771435 Quartz Monzonite 

03ZW374B 454112 6771435 Aplite Dike 7.20 

03ZW375 454155 6771357 Granodiorite co 2.44 

03ZW376 454176 6771288 Granodiorite py,co qtz 0.82 

03ZW377 454175 6771252 Granodiorite py,co qtz 0.49 

03ZW378 454191 6771174 Granodiorite 4.82 

03ZW379 454222 6771086 Quartz Monzodiorite lim qtz-ser 3.97 

03ZW380 454294 6771008 Granodiorite qtz 1.90 

03ZW381 454367 6771039 Quartz Monzodiorite py,lim 2.10 

03ZW382 454384 6771047 Quartz Monzodiorite co,Au,py, bis qtz-ser-chl-cc 0.38 

03ZW383 454511 6771039 Quartz Vein qtz-cc-ser 

03ZW384 454508 6770122 Altered Felsic Dike py(3%) 0.42 

03ZW385 454768 6770268 Intrusive Breccia py 1.31 

03ZW386 454058 6771326 Granodiorite co,py, bis, Au qtz 1.43 

03ZW387 454479 6771019 Quartz Monzodiorite co,py, bis, Au qtz 2.15 

03ZW388 454782 6770720 Aplite Dike lim 

03ZW389 454865 6770887 Gabbro qtz-Kspar 13.63 

03ZW390 454828 6770899 Altered Igneous lim(15%) 0.34 

03ZW391 454716 6770930 Granodiorite 7.84 

03ZW392 454682 6770998 Tonalite co,py qtz-co-py 1.25 

03ZW393 454467 6771538 Granodiorite 2.39 

03ZW394 454479 6771636 Quartz Diorite 2.69 

03ZW395 454483 6771655 Granodiorite 4.74 

03ZW396 454976 6772391 Tonalite 1.42 

03ZW397 454897 6772289 Quartz Monzodiorite 4.25 

03ZW398 454811 6772207 Altered Igneous lim(10%) qtz 0.19 

03ZW399 454760 6772141 Quartz Monzodiorite 10.73 

03ZW400 454594 6772005 Quartz Monzodiorite lim qtz 11.92 
132 

Sample UTM E UTM N Lithology Ore Minerals Veins Magnetic Susceptibility 

03ZW401 454473 6771951 Quartz Monzodiorite 10.10 

03ZW402 454366 6771882 Quartz Monzodiorite 11.12 

03ZW403 454398 6771723 Quartz Diorite 11.41 

03ZW404 454028 6771881 Gray Dike py qtz-chl-sulfide 0.22 

03ZW405 453934 6772424 Altered Metaconglomerate py(2%) 0.16 

03ZW406 454078 6772299 Altered Metaconglomerate py 0.06 

03ZW407 454081 6771895 Mudstone hornfels qtz-chl-sul? 0.27 

03ZW408 452586 6770172 Breccia lim 0.46 

03ZW409 452628 6770198 Breccia lim 0.71 

03ZW410 452694 6770238 Breccia lim 0.31 

03ZW411 452677 6770377 Conglomerate Hornfels chl 0.42 

03ZW412 452873 6770652 Quartz Diorite Hornfels py chl-qtz 0.70 

03ZW413 453066 6771011 Grey Dike 0.20 

03ZW414 453108 6771104 Conglomerate Hornfels py 0.92 

03ZW415 458400 6772836 Basalt Hornfels py 3.72 

03ZW416 458620 6772980 Alt Metavolcanic Hornfels lim 0.18 

03ZW417 458809 6773117 Altered Metabasalt lim 0.34 

03ZW418 458805 6773131 Altered Metabasalt lim 0.24 

03ZW419 458802 6773149 Altered Metabasalt lim, py(2-3%) 0.13 

03ZW420 458818 6773207 Altered Metabasalt lim, py(2-3%) 0.21 

03ZW421 458844 6773272 Altered Metabasalt lim 0.44 

03ZW422 459136 6772758 Basalt Hornfels 25.57 

03ZW423 459100 6772941 Altered Metabasalt lim 0.22 

03ZW424 459006 6773144 Altered Metabasalt lim 0.60 

03ZW425 458915 6773317 Breccia lim 0.08 

03ZW426 458852 6773348 Basalt Hornfels 30.60 

03ZW427 458624 6773630 Quartz Monzonite Dike py, lim 0.22 

03ZW428 458611 6773664 Breccia lim 0.36 

03ZW429 458583 6773692 Quartz Monzonite Dike 4.80 

03ZW430 458566 6773724 Quartz Monzonite Dike 0.55 

03ZW431 458541 6773734 Basalt Hornfels co,py 29.60 

03ZW432 458482 6773727 Quartz Monzonite Dike 0.28 

03ZW433 458453 6773631 Quartz Monzonite Dike 0.68 

03ZW434 458421 6773571 Quartz Monzonite Dike 0.34 

03ZW435 458456 6773545 Quartz Monzonite Dike 0.24 

03ZW436 458712 6773532 Altered Metabasalt lim 0.25 

03ZW437 458708 6773468 Altered Metabasalt lim 0.07 

03ZW438 458756 6773419 Breccia lim 0.16 

03ZW439 458826 6773545 Altered Metabasalt lim 0.28 

03ZW440 458767 6773590 Altered Metabasalt lim 1.99 

03ZW441 458730 6773523 Quartz Vein 

lim, Ag-Pb 

sulfide 0.37 

03ZW442 458752 6773173 Altered Dike? lim 0.72 

03ZW443 458421 6772822 Quartz Vein 0.56 

03ZW444 451339 6770833 Volcaniclastic Hornfels chl(5%) 0.45 

03ZW445 451827 6772067 Diorite Hornfels chl(2%) 16.30 

03ZW446 451724 6771993 Gray Dike 11.33 
133 

Sample UTM E UTM N Lithology Ore Minerals Veins Magnetic Susceptibility 

03ZW447 451661 6771922 Volcaniclastic Hornfels chl(2%) 0.56 

03ZW448 451647 6771841 Breccia chl 0.13 

03ZW449 451632 6771672 Mudstone hornfels chl 3.09 

03ZW450 451647 6771598 Breccia lim 0.21 

03ZW451 451674 6771527 Gray Dike 0.47 

03ZW452 451662 6771471 Gray Dike 0.56 

03ZW453 451585 6771303 Diorite Hornfels chl(2%) 0.86 

03ZW454 451439 6771053 Mudstone Hornfels chl 1.07 

03ZW455 451234 6770802 Alt Metavolcanic Hornfels qtz 0.38 

03ZW456 460756 6772670 Sawpit Pluton 0.21 

03ZW457 460776 6772694 Volcaniclastic Hornfels py 1.12 

03ZW458 458840 6771263 Dacite Sill Hornfels lim 0.56 

03ZW459 457713 6769890 Alt Metavolcanic Hornfels lim 2.41 

03ZW460 457602 6769770 Basalt Hornfels 5.52 

03ZW461 457606 6770172 Volcaniclastic Hornfels 6.75 

03ZW462 457569 6770247 Basalt Hornfels 32.37 

03ZW463 456195 6770410 Quartz Monzonite 21.17 

03ZW464 456216 6770329 Altered Igneous lim 0.66 

03ZW465 456218 6770306 Quartz Vein Ag-Pb sulfide 

03ZW466 456226 6770292 Altered Igneous 0.01 

03ZW467 456256 6770255 Altered Igneous 0.24 

03ZW468 456256 6770168 Monzodiorite 19.60 

03ZW469 456402 6770009 Quartz Diorite 7.30 

03ZW470 456382 6769727 Pink Dike 4.65 

03ZW471 456437 6769356 Monzodiorite 13.73 

03ZW472 456398 6768692 Basalt Hornfels 37.37 

03ZW473 449884 6769030 Gray Dike 0.60 

03ZW474 450156 6769640 Gray Dike 12.93 

03ZW475 452245 6768815 Quartz Monzodiorite 0.68 

03ZW476 452519 6768734 Diorite Hornfels 5.66 

03ZW477 452389 6768743 Quartz Monzodiorite py 0.45 

03ZW478 452170 6768836 Pink Dike 2.94 

03ZW479 457594 6770920 Basalt Hornfels 0.71 

03ZW480 454295 6771361 Granodiorite 0.72 

03ZW481 454500 6771604 Altered Igneous 0.29 

03ZW482 454489 6771594 Granodiorite 6.51 

03ZW483 454476 6771557 Quartz-Feldspar veins 

03ZW484 454496 6771396 Altered Igneous 0.34 

03ZW485 454638 6771162 Monzogranite co,py,mo qtz-ser 0.68 

03ZW486 453348 6771738 Granodiorite Dike 0.27 

03ZW487 453327 6771846 Siltstone Hornfels py 0.28 

03ZW488 453368 6771783 Quartz-Sulfide vein sulfide 

03ZW489 453832 6772676 Conglomerate Hornfels qtz-chl 8.10 

03ZW490 453838 6772839 Altered Metaconglomerate py,lim 0.26 

03ZW491 452126 6771252 Diorite Hornfels 0.65 

03ZW492 453127 6771195 Conglomerate Hornfels 2.83 
134 

Sample UTM E UTM N Lithology Ore Minerals Veins Magnetic Susceptibility 

03ZW493 452874 6771194 Granodiorite Dike 5.14 

03ZW494 452992 6771136 Dacite Hornfels 0.61 

03ZW495 453523 6771807 Granodiorite Dike 8.70 

03ZW496 453647 6772164 Gray Dike py, co, bis qtz-chl 0.34 

03ZW496B 453647 6772164 Volcaniclastic Hornfels 

03ZW497 450971 6765276 Altered Quartz Diorite 0.19 

03ZW498 454687 6770998 Quartz Monzodiorite mo, mal 

03ZW499 454777 6770916 Quartz Monzodiorite co qtz 7.16 

Appendix B: Compositional chemical data and analysis technique. 

I. XRF major oxide data as wt%. Lab number signifies (1) ALS Chemex or (2) UAF analysis 

Sample SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O Cr2O3 TiO2 MnO P2O5 SrO BaO LOI Total Lab 

03JF018 50.2 18.5 12.8 4.81 6.99 5.75 0.47 1 0.25 0.07 101 2 

03ZW006 56.6 16 11.1 7.11 6.26 3.74 1.11 0.97 0.24 0.18 103 2 

03ZW012 54.4 18.2 9.42 6.72 4.77 3.02 0.57 0.01 0.88 0.19 0.12 0 0.1 1.4 99.8 1 

03ZW068 58.6 16.6 6.53 4.6 3.49 4.17 1.61 <0.01 0.71 0.09 0.11 0 0.1 3.3 99.9 1 

03ZW121 66.6 15.1 4.31 1.64 1.94 3.93 2.77 0.01 0.48 0.08 0.11 0 0.1 2.6 99.7 1 

03ZW142 73.4 16.3 3.74 1.7 1.11 5.35 1.48 0.4 0.08 0.07 104 2 

03ZW147 59 15.2 7.05 5.01 3.51 3.46 1.6 0.01 0.72 0.1 0.2 0.1 0.1 3.7 99.8 1 

03ZW176 64.6 15.3 3.53 3.36 1.59 3.35 2.85 0.01 0.59 0.07 0.17 0.1 0.2 4 99.6 1 

03ZW179 61.8 16.1 5.06 4.63 2.79 3.25 3.11 0.01 0.73 0.08 0.23 0.1 0.1 1.3 99.2 1 

03ZW189 66.5 15 2.5 3.72 0.97 2.62 2.75 <0.01 0.34 0.05 0.1 0 0.1 5 99.6 1 

03ZW195 56.5 16.5 5.33 5.19 2.01 4.01 1.99 <0.01 0.79 0.12 0.25 0.1 0.1 6.2 99.1 1 

03ZW196 67.7 15.4 2.77 1.91 1.13 4.01 2.9 0.01 0.38 0.06 0.12 0.1 0.2 2.9 99.5 1 

03ZW213 66.4 15.6 4.67 3.35 1.55 4.04 1.39 <0.01 0.52 0.07 0.1 0 0.1 2.1 99.9 1 

03ZW265 65 15.4 3.65 2.76 1.76 3.86 2.99 0.01 0.56 0.07 0.17 0.1 0.2 3.3 99.7 1 

03ZW267 63.8 15.1 3.44 3.59 1.59 3.05 2.92 0.01 0.58 0.06 0.17 0.1 0.2 5 99.5 1 

03ZW273 57 18.2 6.48 6.21 3.4 3.41 2.73 0.01 0.94 0.1 0.33 0.1 0.2 0.4 99.4 1 

03ZW276 57.7 15.9 7.45 3.82 3.65 3.8 2.66 0.01 1.25 0.12 0.28 0.1 0.1 2.8 99.7 1 

03ZW277 68.9 15 4.14 1.42 2.26 4.21 1.62 0.01 0.45 0.09 0.09 0 0.1 1.4 99.6 1 

03ZW279 59.9 16.8 5.81 4.79 2.62 3.4 3.81 0.01 0.99 0.09 0.33 0.1 0.2 0.4 99.1 1 

03ZW282 53.1 17.4 7.69 7.46 5.46 3.1 1.4 0.01 1.09 0.13 0.36 0.1 0.1 2.2 99.7 1 

03ZW283 60.1 16.9 5.83 5.37 3.39 3.16 2.98 0.01 0.8 0.09 0.25 0.1 0.1 0.8 99.8 1 

03ZW284 51.6 16.2 8.28 5.21 7.01 3.41 1.87 0.02 1.36 0.15 0.44 0.1 0.1 4 99.7 1 

03ZW285 52 18 11.4 5.45 5.46 2.63 0.7 <0.01 1.03 0.22 0.15 0 0 2.8 100 1 

03ZW293 57.3 17.5 7.11 5.1 3.14 3.5 3.24 0.01 0.94 0.1 0.42 0.1 0.2 1.1 99.7 1 

03ZW294 61.8 17 4.95 4.73 2.28 3.6 2.86 0.01 0.77 0.08 0.29 0.1 0.2 0.8 99.4 1 

03ZW297 64.5 16.8 4.27 1.7 0.94 4.13 5.15 0.01 0.61 0.11 0.19 0 0.2 1 99.7 1 

03ZW298 56 18.2 7.75 5.22 3.71 3.26 0.7 0.01 1.08 0.1 0.15 0 0 3.7 100 1 

03ZW317 65 15.6 3.6 3.63 1.94 3.18 2.97 0.01 0.56 0.07 0.16 0.1 0.1 2.7 99.6 1 

03ZW331 65.7 14.9 3.27 2.69 1.62 3.17 3.42 0.01 0.51 0.06 0.16 0.1 0.2 3.9 99.7 1 

03ZW333 73.4 16.7 3.04 0.19 0.24 5.2 2.08 0.49 0.02 0.03 101 2 

03ZW337 52 16.3 9.22 8.26 6.22 3.03 0.73 0.03 1.59 0.17 0.27 0.1 0.1 1.6 99.4 1 

03ZW341 68.6 15.3 4.19 1.41 1.57 4.49 1.51 0.01 0.48 0.07 0.09 0 0.1 1.8 99.6 1 

03ZW347B 58.7 16.8 5.98 5.64 3.73 3.12 3.26 0.02 0.89 0.09 0.27 0.1 0.1 0.9 99.6 1 

03ZW351 72.4 21.5 3.37 0.03 0.52 0.96 4.03 0.22 0.02 0.03 103 2 

03ZW355 62.3 16.2 4.86 4.89 2.88 3.23 2.94 0.01 0.73 0.08 0.21 0.1 0.1 0.7 99.2 1 

03ZW356 63.4 15.9 4.64 4.48 2.74 3.49 3.13 0.01 0.68 0.07 0.2 0.1 0.1 0.8 99.7 1 

03ZW357 66.7 15.5 3.65 3.81 1.88 3.29 2.98 0.01 0.58 0.05 0.17 0.1 0.1 0.6 99.5 1 

03ZW357B 66.8 15.6 3.6 3.72 1.83 3.27 3.03 0.01 0.55 0.05 0.14 0.1 0.2 0.5 99.3 1 

03ZW357C 77.7 12.1 0.79 0.54 0.12 3 5.03 0.01 0.1 0.01 0.02 0 0.1 0.3 99.8 1 

03ZW358 66.7 15.7 3.68 3.92 1.88 3.51 2.83 0.01 0.54 0.07 0.16 0.1 0.1 0.5 99.6 1 

03ZW359 68.6 15.5 3.11 3.08 1.46 3.29 3.31 0.01 0.47 0.05 0.13 0.1 0.2 0.7 99.9 1 

03ZW359B 68.6 15.5 3.1 3.05 1.41 3.24 3.29 0.01 0.46 0.05 0.13 0.1 0.2 0.7 99.8 1 
135 

03ZW360 57.2 17.5 6.64 5.77 3.21 3.1 3.87 0.01 1.03 0.11 0.34 0.1 0.2 0.5 99.5 1 

03ZW361 68 15.3 3.37 2.9 1.4 3.63 3.34 0.01 0.53 0.07 0.16 0.1 0.2 0.6 99.5 1 

03ZW362 68.6 14.9 3.11 2.73 1.31 3.24 3.81 0.01 0.46 0.07 0.14 0.1 0.1 0.8 99.4 1 

03ZW363 69.8 15 2.74 2.49 1.08 3.47 3.62 0.01 0.42 0.06 0.13 0.1 0.1 0.5 99.4 1 

03ZW364 69.2 15.2 2.69 2.29 1.03 3.63 3.67 0.01 0.41 0.07 0.11 0.1 0.2 0.7 99.2 1 

03ZW365 70.2 14.9 2.48 2.27 0.97 3.53 3.84 0.01 0.36 0.05 0.1 0.1 0.1 0.4 99.3 1 

03ZW366 66 16 3.86 3.54 1.78 3.6 3.12 0.01 0.57 0.07 0.18 0.1 0.2 0.6 99.6 1 

03ZW367 65.9 15.9 3.88 3.44 1.71 3.5 3.22 0.01 0.58 0.07 0.18 0.1 0.2 0.6 99.2 1 

03ZW369 72.2 16.2 4.39 2.18 0.93 3.96 2.24 0.54 0.07 0.18 103 2 

03ZW373 61 16.7 5.39 4.56 2.67 3.28 3.66 0.01 0.81 0.09 0.28 0.1 0.2 0.7 99.4 1 

03ZW374 72.7 11.8 0.55 0.36 0.08 2.66 6 0.08 0.02 0 94.2 2 

03ZW378 65.8 16.2 3.8 3.49 1.81 3.3 3.59 0.01 0.57 0.06 0.19 0.1 0.2 0.6 99.7 1 

03ZW389 56.3 16.6 7.2 6.38 4.35 3.09 3.36 0.02 1.05 0.12 0.36 0.1 0.2 0.6 99.6 1 

03ZW391 65.8 15.6 3.57 3.43 1.68 3.22 3.72 0.01 0.59 0.06 0.18 0.1 0.1 0.6 98.6 1 

03ZW394 57.3 15.7 7.11 5.05 3.64 2.97 3.07 0.01 1.12 0.1 0.38 0.1 0.2 2.6 99.3 1 

03ZW395 66.1 16 3.8 2.95 1.84 3.21 3.68 0.01 0.56 0.05 0.19 0.1 0.2 1.1 99.7 1 

03ZW396 62.9 16.2 4.6 5.04 3.08 3.36 2.26 0.02 0.61 0.08 0.19 0.1 0.1 0.6 99.1 1 

03ZW403 59.8 17.2 5.79 5.12 3.04 3.36 3.23 0.01 0.84 0.09 0.28 0.1 0.2 0.6 99.6 1 

03ZW404 69.4 15 4.81 3.73 1.67 3.99 2.59 0.64 0.1 0.21 102 2 

03ZW412 62.8 15.5 8.16 4.25 5.17 3.44 2.69 0.68 0.14 0.11 103 2 

03ZW427 74.3 17.9 1.85 0.09 0.21 4.36 4.56 0.19 0.03 0.03 104 2 

03ZW434 70.6 17.7 3.52 0.15 0.4 4.35 4.42 0.3 0.02 0.07 102 2 

03ZW435 70.9 17.5 3.58 0.1 0.41 4.53 4.3 0.28 0.02 0.07 102 2 

03ZW458 65.8 16.7 5.32 3.44 1.72 2.06 1.56 0.52 0.07 0.09 97.2 2 

03ZW466 74.4 18.3 1.44 0.04 0.45 2.93 5.73 0.44 0.02 0.06 104 2 

03ZW467 76.2 18.1 3.12 0.75 1.09 3.67 1.27 0.23 0.07 0.05 104 2 

03ZW469 61.6 16.9 5.29 5.43 3.04 3.34 2.65 0.01 0.76 0.08 0.22 0.1 0.1 0.2 99.7 1 

03ZW474 65.2 15.6 4.67 3.5 1.66 3.44 2.92 0.01 0.57 0.09 0.18 0.1 0.2 1 99.1 1 

03ZW478 65.6 15.8 3.68 2.54 2 3.73 3.66 0.01 0.56 0.07 0.17 0.1 0.2 1.6 99.6 1 

03ZW479 52.1 16.8 9.52 2.61 5.65 5.67 0.19 <0.01 0.9 0.12 0.14 0 0 5.8 99.5 1 

03ZW481 68.2 18.4 3.21 4.17 0.63 2.67 3.41 0.38 0.07 0.1 101 2 

03ZW482 66.1 15.7 3.58 3.23 1.64 3.21 3.84 0.01 0.53 0.05 0.17 0.1 0.2 1.2 99.5 1 

137 

II. Triple acid digestion followed by ICP-AES analysis. ALS Chemex analysis. 

SAMPLE Ag Al As Au Ba Be Bi Ca Cd Ce Co Cr Cs Cu Fe Ga Ge Hf Hg In K La Li Mg Mn Mo Na Nb Ni P Pb 

03ZW006 0.3 9.3 8.2 0.1 300 0.6 0.1 4.8 0.6 24 21 42 0.8 86.4 5.7 18 0.2 0.9 0 0.1 1 11 12 2.4 1600 0.9 3.2 1.4 15 780 15.1 03ZW028 0 7.4 98 <0.01 640 0.6 0.1 0.1 0.1 32 5 9 1.1 8.4 2.6 15 0.1 0.4 0 0.1 2.1 15 16 0.2 503 4.2 0.1 3 2.7 130 5 03ZW142 0.1 7.5 14 0 200 0.6 3.4 1 0.1 23 4.6 26 2 39.1 1.9 13 0.1 1.4 <0.01 0 1 11 7.6 0.6 385 0.8 3.4 2.6 2.6 260 3.4 03ZW171 0.2 7.3 50 <0.01 480 0.6 0.2 4.5 0.8 21 12 62 0.8 34.8 4.9 15 0.1 0.9 0 0.2 1.3 10 4.8 1.4 1620 1.1 2.3 1.8 18 640 31.5 03ZW225 0.1 7.9 3.4 <0.01 120 0.7 0.2 5.2 0.1 30 19 21 0.6 6.4 18 20 0.3 1 0 0.2 0.5 12 6.8 2.1 5610 0.7 0.6 3.3 5.3 450 2.6 03ZW227 0.1 0.8 0.6 <0.01 10 0.1 0 0.3 <0.02 2.7 0.8 103 <0.05 540 0.5 1.4 <0.05 0.2 <0.01 <0.005 0 1.2 1.4 0.1 63 1.4 0.2 0.4 3.3 20 0.8 03ZW257 0.3 6.4 72 0 10 0.6 3 10 0 17 48 38 2 580 12 17 0.2 1.5 0.1 0.6 0.1 8.1 15 1.3 1270 6 0.5 2.9 16 630 2.9 03ZW271 0.1 11 3.8 <0.01 580 1 0.1 0.9 0 37 24 43 4.9 34.2 5.5 26 0.2 0.3 0 0 3.6 15 36 1 767 6.2 1.2 4.2 20 990 4 03ZW274 0.1 11 14 <0.01 780 0.9 0.1 1.1 <0.02 31 5.7 36 5.8 19.8 5.7 24 0.2 0.2 0 0 1.8 14 20 1.6 497 2.8 3 1 5.9 680 5.2 03ZW280 0.3 8.7 6.6 0 570 3.2 0.6 0 0.1 178 1.4 36 2.3 4.5 1.2 19 0.2 1.3 0.5 0 3.5 121 12 0.3 61 47 0 9.3 4.9 200 27.7 03ZW281 <0.02 9.9 5.2 0 1410 2 0.1 4.1 0.1 73 22 46 3.1 10.9 3.7 20 0.2 1.6 <0.01 0 2.7 42 16 2 675 1.3 2.9 8.1 41 1090 13.6 03ZW288 0.2 9 18 0.1 340 1 0.1 5.8 0.2 23 37 42 3.3 218 8.2 22 0.2 1.2 0 0.4 1.1 11 22 5 3050 4.4 1.1 2 21 710 23.1 03ZW292 0.2 2.8 12 1.4 10 0.4 0 5.8 0.1 5.6 7.3 27 0.7 28.6 2.7 5.2 0.1 0.2 1.2 0 0.2 3 20 2 644 11 0 0.2 6.9 200 7 03ZW313 0.1 9.2 27 <0.01 320 0.5 0.3 3 0.2 14 40 51 0.7 105 8.5 18 0.2 1 0 0 0.6 6.7 18 2.7 1835 2.2 2.9 0.9 31 620 4.3 03ZW333 <0.02 8.1 2.1 <0.01 50 0.4 0.7 0.1 <0.02 33 22 32 0.8 3.2 2 15 0.1 2.9 <0.01 0 1.5 15 3.3 0.1 15 7.2 3.6 1.2 2.9 130 2.3 03ZW339 1 8 20 0.1 950 2.3 30 0.8 0.1 70 8 37 7.5 148 2.1 17 0.2 0.7 0 0.1 2.9 39 15 0.8 204 1.9 2.2 4.5 12 720 10.1 

03ZW339B 0.7 6.2 11 0 710 2.2 0.3 0.2 0.1 37 2.4 42 6.5 66.8 0.8 13 0.1 0.9 <0.01 0 4.7 20 7.3 0.2 67 1 1.5 4.4 4.5 150 24.8 

03ZW340 6.2 8.1 15 0.1 1080 2.8 40 1 0.6 80 7.2 59 7.8 1005 2 18 0.2 0.7 0 0.1 3.3 46 19 0.7 391 2.3 2.3 5.9 14 680 64 03ZW347 0.1 8.5 11 <0.01 1140 2.2 3.7 2.6 0.1 91 18 71 11 60.6 3.6 18 0.2 1.2 0 0 2.9 51 26 1.8 541 8.5 2.3 10 42 1180 19 03ZW348 0.9 9 8.7 0 1230 2.2 4.6 3.3 0.2 97 19 46 7.1 380 3.8 19 0.3 1.3 0 0.1 3 54 30 1.9 596 2.7 2.6 12 35 1320 21.1 03ZW349 2.4 7.7 237 0.1 560 0.8 0.9 1.5 16 32 8.9 41 2.2 112 2.5 14 0.2 0.9 0.1 0.1 1.9 16 10 0.7 626 1.3 1.9 2.9 3 330 168 03ZW350 0.2 7.5 33 0.1 710 1.4 0.2 2.8 0.1 66 24 46 6.5 90.9 4.4 18 0.2 0.4 0 0 1.6 37 30 1.7 499 9 2 7 35 1140 9 03ZW354 0.3 5.1 28 0.2 10 0.7 0.1 6.1 0.2 8.1 17 26 0.6 101 3.1 8.2 0.1 0.1 1.2 0 0.1 3.8 39 2.3 543 0.5 0 0.2 12 370 8.1 03ZW369 0.2 8.5 2.9 6.9 790 1.8 156 1.3 0.1 74 7.8 19 1.5 2.4 2.4 17 0.2 2.3 <0.01 0 1.7 45 8.5 0.8 362 1.2 2.6 3.7 6.2 790 4.7 03ZW377 1.4 9.2 31 0.2 1150 2.7 0.9 0.2 0.1 72 5.7 35 13 183 1.8 21 0.2 1 0 0.1 3.4 44 15 0.6 242 1.5 2.3 6.4 11 850 23.1 03ZW379 0.9 8.7 12 0 1280 2.7 0.6 0.9 0.3 85 8.4 48 6.7 259 2.4 19 0.2 0.9 <0.01 0.1 3.3 48 25 1 363 2.9 2.5 7.9 16 820 14 03ZW382 0.3 8.5 4.1 3.1 1320 2.5 19 1.9 0.1 74 8.7 44 7.4 158 2.4 19 0.2 0.9 <0.01 0 2.7 43 25 1 315 0.9 2.6 6.7 13 850 13.2 03ZW383 0.6 1.4 20 1.3 160 0.4 3.6 0.2 0.1 12 2.7 105 1.6 25.9 0.6 3.2 0.1 0.2 <0.01 0 0.5 6.7 6.6 0.1 77 4.1 0.3 1.1 4.5 70 7.7 03ZW386 1.2 8.4 24 2 1540 2.4 50 1.5 0.4 75 8.8 45 9.9 432 2.3 18 0.2 1.2 0 0.1 3.1 46 21 0.9 278 1.2 2.5 7 13 720 23 03ZW387 1.5 8.3 8.7 6.7 1090 2.6 23 1.9 0.3 78 8.2 39 7.7 288 2.2 19 0.2 1 0 0 2.9 46 23 0.8 294 2 2.4 5 12 770 17.3 03ZW390 0.2 10 6.2 0 590 1.6 0.2 8.9 0.2 157 22 62 2.9 76.3 4.6 23 0.3 2.1 0 0.1 1.2 90 18 0.3 1040 2.2 0.1 6.2 51 1800 29.1 03ZW398 <0.02 11 5.9 0 70 2.1 0.3 0.1 0.3 132 14 48 2.2 30.1 3.2 20 0.2 1.3 0 0.1 0.6 63 47 0.3 432 0.6 0 9.5 44 1190 24.7 
138 

03ZW400 0.1 9.2 21 <0.01 1770 3 0.5 3 0.6 121 17 52 11 30.2 3.9 20 0.3 0.9 0 0.1 3.2 69 31 1.8 777 1.8 2.5 13 31 1380 28.9 03ZW404 0 8.8 3.1 <0.01 1540 2 0.1 2.6 0.2 68 11 26 1.4 43.4 2.7 18 0.2 1.8 0 0 2.1 37 15 1.1 557 1.4 3 7.4 11 790 14.9 03ZW464 <0.02 8.8 5.7 <0.01 690 3.7 0.1 0.1 0.1 152 4.7 52 3.3 5.1 2.3 21 0.3 0.3 0 0 4.6 89 9.5 0.2 224 1 2.2 6.4 11 470 10.9 03ZW465 22 1.6 21 0 210 0.7 1.1 0 0.8 16 3 179 0.8 20 1 3.8 0.1 0.3 2 0 0.7 9.4 28 0.1 403 6.5 0 0.2 8.8 120 65603ZW466 <0.02 7.7 4.1 <0.01 1070 3 0.3 0 0.1 152 0.4 27 2.1 2.4 0.8 18 0.2 5.1 0.5 0 4 87 6.5 0.2 16 0.7 1.8 15 3.4 260 15.7 03ZW467 0.3 7.3 2.3 0 320 0.6 0 0.4 0.1 17 4.4 40 0.9 172 1.6 13 0.1 0.2 0 0 0.8 7.8 16 0.8 304 2.9 1.8 1 4.7 170 10.1 03ZW481 <0.02 8.3 3.5 <0.01 940 1.6 0 2.4 0.1 34 4.3 14 5.4 3 1.6 17 0.1 2.3 0 0 2.4 21 12 0.3 357 1 2.1 3.6 3.2 450 14.3 03ZW483 0.1 3.6 24 0.1 540 1 0.1 0.1 0.1 29 1.9 41 2.6 6 0.6 7.6 0.1 0.8 <0.01 0 2.2 17 7.9 0.2 81 1.9 0.8 2 5.1 110 8.5 03ZW484 <0.02 8.1 4.3 <0.01 850 2 0 1.8 0.1 34 4.7 22 4.9 5 1.8 17 0.1 2.4 0 0 2.4 20 23 0.3 350 1.2 0 3.4 4.5 530 10.9 03ZW485 0.8 8 11 0 1110 2.4 0.4 1.2 0.1 68 4.8 42 6.9 175 1.7 18 0.2 2.5 0 0 3.4 39 20 0.6 225 2.4 1.5 4.8 8.1 540 11.7 03ZW488 0.1 8 133 <0.01 1040 0.7 0.2 0.2 0.3 27 9.2 47 2 26.9 7.3 22 0.2 1.7 0 0.1 1.9 12 26 2.9 1375 0.8 0.1 3.4 18 680 13 03ZW496 0.1 8.8 5.5 <0.01 1250 2.3 23 2.7 0.1 80 11 25 5.1 58.7 3 19 0.2 3.2 0 0 2.3 47 22 1.3 558 0.7 2.8 9 10 960 15 

03ZW496B 0 8.8 6.7 <0.01 1100 1.4 0.6 1.4 0.1 44 10 18 8.6 21.4 3.2 18 0.2 1.1 0 0 2.7 23 17 1.2 568 1 2.2 4 12 740 6.6 

03ZW499 1.2 9.2 5 0.2 1530 2.8 2.9 3 0.3 93 16 55 11 421 3.9 21 0.3 0.9 0 0.1 2.8 55 37 2 572 1.9 2.6 12 31 1200 18.3 
139 

III. Aqua regia digestion followed by ICP-AES analysis. ALS Chemex analysis. 

SAMPLE Ag As Au Ba Bi Cd Co Cs Cu Hg Li Mn Mo Ni P Pb Sb Se T

03ZW015 0.78 3.9 0.029 570 0.25 0.31 11.1 0.79 499 0.02 7.2 760 4.26 13.9 270 5.2 1.04 0.7 103ZW018 0.05 15.8 0.003 70 0.4 0.15 18 0.11 25.2 1.09 3.4 625 1.97 17.7 480 3.5 0.53 0.3 003ZW030 0.03 4.3 <0.001 290 0.08 0.08 5.2 0.09 12.4 0.04 3.8 339 1.01 3.3 260 4.4 0.54 0.6 003ZW033 0.03 3.1 <0.001 110 0.07 0.02 22 0.3 6.8 0.01 8.5 406 0.91 11 670 0.8 0.1 2.2 003ZW035 0.09 30.2 0.001 520 0.05 0.2 17.6 0.48 53.5 <0.01 5.3 1405 2.37 13.6 420 9.5 1.76 0.8 003ZW046 0.04 6.9 0.003 330 0.74 0.04 10.6 0.15 83.2 0.01 5.8 340 0.48 6.9 620 2.2 0.13 3.3 003ZW048 0.02 3.1 <0.001 440 <0.01 0.02 23.9 0.37 11.6 <0.01 14.2 717 0.25 28.9 530 0.6 0.17 0.4 003ZW050 0.01 0.5 <0.001 520 <0.01 0.06 1.8 0.57 2.9 0.01 0.2 259 0.44 3 500 4.1 0.07 0.4 <003ZW053 0.06 3.2 0.001 70 0.1 0.11 14.7 <0.05 120.5 0.01 2 473 0.79 11.2 570 3.6 0.32 1.4 003ZW057 0.04 7.6 0.001 180 0.1 0.11 8 0.23 41.4 0.01 0.7 484 2.06 4.8 380 1.8 0.09 0.5 003ZW074 0.01 3.8 0.038 520 0.02 0.04 5.4 0.18 11.6 <0.01 5 142 0.91 4.5 380 1.5 0.16 0.6 003ZW077 0.17 14.6 0.011 250 0.12 0.15 3.5 0.25 16.6 0.01 2.6 287 11.1 4.8 180 12.6 0.85 0.3 003ZW086 0.08 7 <0.001 150 <0.01 0.24 8.8 0.31 6.6 0.01 0.7 2320 2.92 8.4 240 17.4 1.1 0.6 003ZW087 0.06 0.9 0.001 40 0.06 0.11 16 <0.05 123 <0.01 2.9 651 0.94 12 490 3.4 0.5 0.4 003ZW088 1.16 0.6 0.002 320 1.16 1.98 73.3 1.44 132000 <0.01 13.2 1385 0.61 6.8 500 11 0.13 0.8 003ZW093 0.6 1.8 0.008 200 0.19 2.22 3.3 0.17 676 0.01 2 550 1.66 6.6 60 50.1 0.14 0.3 003ZW102 0.03 3.5 <0.001 230 0.21 0.01 5.1 0.06 32.3 0.01 1.1 47 0.47 4.6 460 2 0.1 2.8 003ZW111 0.09 2.1 0.091 250 0.02 0.38 5.6 0.55 24.4 <0.01 0.5 631 1.6 9.8 150 8.5 0.5 0.2 003ZW114 0.01 0.3 <0.001 190 <0.01 0.05 2.2 0.13 5.8 <0.01 0.6 210 0.6 5.4 90 2.5 0.08 <0.2 <003ZW119 0.15 13 <0.001 1160 0.28 0.05 1 0.17 3.2 0.3 0.4 60 3.03 2.2 280 15.2 0.49 0.3 003ZW120 0.05 5.9 0.002 1640 0.43 0.05 0.6 0.39 3 0.16 0.7 50 2.36 2.9 300 24.4 0.53 0.3 003ZW122 0.32 92.9 0.001 50 0.14 0.08 0.7 0.31 8 0.11 3.5 62 2.01 3.1 80 57.3 2.29 0.3 003ZW123 0.38 31.6 0.013 3370 <0.01 0.18 1.7 0.47 41.2 0.04 3.8 190 2.99 3.3 150 65.5 2.3 0.2 <003ZW127 0.08 3.5 0.029 70 <0.01 0.21 5.3 0.23 41.5 0.01 1.2 347 1.93 10.1 130 0.7 3 0.2 <003ZW130 0.07 26 0.003 480 0.1 0.04 13 0.95 44.5 <0.01 17 274 1.28 15.3 870 2.6 1.1 1.5 003ZW132 0.16 5.5 <0.001 140 0.12 0.07 37.4 0.31 252 <0.01 5.9 826 2.99 13.8 870 1.6 0.62 4.2 003ZW137 0.35 6.7 0.015 190 0.15 0.08 21.9 0.25 221 <0.01 6.9 183 4.3 18.7 400 2.2 0.29 1.9 003ZW139 0.02 1.7 <0.001 50 0.01 0.01 11.6 0.09 41.4 <0.01 1.2 76 0.73 14.6 1250 0.6 0.16 0.5 003ZW145 0.18 58.3 0.005 420 0.13 0.06 15 0.34 62.9 <0.01 10.2 673 3.03 19.2 510 6.7 1.56 1 003ZW165 0.09 5.7 0.002 520 0.12 0.28 4.8 1.04 15.3 <0.01 7.3 230 1.72 10 420 7.3 1.26 0.7 003ZW175 0.02 20 0.003 660 0.04 0.26 21.1 1.08 4.5 0.01 8.5 1365 0.13 58.9 450 2 0.59 0.4 003ZW178 0.11 16 0.002 60 0.05 0.1 7.3 0.51 15 <0.01 1.1 1075 4.15 10.4 240 16.1 4.12 0.5 003ZW180 0.02 1 <0.001 670 <0.01 0.02 2 0.29 6.1 <0.01 4.6 116 2.12 12.5 50 1.6 0.17 <0.2 <003ZW183 0.07 28.2 0.002 80 0.05 0.09 11 0.28 33 0.04 8.3 171 1.75 19.8 660 6.9 1.69 0.6 003ZW186 0.05 8 0.002 600 0.09 0.09 10 4.15 13.4 <0.01 12.4 439 1.28 6.5 1520 3.7 0.45 0.7 <003ZW204 0.03 2.6 <0.001 510 0.03 0.09 17.6 0.61 20.1 0.01 10.4 419 0.64 7.5 440 1.7 0.31 0.3 <003ZW205 0.04 9.5 0.018 160 0.04 0.05 26.1 0.29 47 <0.01 6.1 303 1.52 15.4 650 0.6 0.13 0.7 003ZW206 0.79 29.5 0.002 500 <0.01 59.4 11.2 0.66 99.6 0.02 1.9 1050 0.28 8.2 430 124 5.12 0.8 0
140 

SAMPLE Ag As Au Ba Bi Cd Co Cs Cu Hg Li Mn Mo Ni P Pb Sb Se T

03ZW209 0.11 6.9 <0.001 630 0.06 0.25 9 0.42 15.7 0.01 0.7 1105 1.77 5.4 420 7.8 2.13 0.8 <003ZW219 0.03 1 <0.001 90 <0.01 0.11 3.2 0.17 244 <0.01 1.4 168 0.51 6 150 1.2 0.08 0.2 <003ZW223 0.09 2.9 0.002 50 <0.01 0.15 9.8 <0.05 6.2 <0.01 0.5 292 0.54 8 190 6.6 0.56 1 003ZW224 0.06 4.1 <0.001 310 0.04 0.13 18 <0.05 44.8 <0.01 2.5 291 0.72 10.4 810 3.8 0.26 0.9 003ZW240 0.03 236 0.001 80 <0.01 0.06 5.8 0.28 14.8 <0.01 1.4 1825 4.81 3.6 220 4.8 2.64 0.6 003ZW252 0.13 1.6 0.004 620 <0.01 0.36 12.8 2.02 51.3 0.01 9.3 399 0.33 6.8 140 4.5 0.61 0.3 <003ZW253 0.09 41.1 0.007 120 0.23 0.02 3.6 1.15 128 <0.01 5.4 96 0.59 2.4 410 1.4 0.79 1.4 003ZW256 0.27 7.6 0.02 350 0.02 0.3 5.1 10.2 193 0.01 4.3 229 0.52 8.1 740 5.4 0.76 0.6 003ZW258 0.11 235 0.014 170 0.84 0.21 8.3 1.64 29.5 <0.01 2.3 78 12.3 3 950 5.1 2.12 2.7 003ZW261 0.12 4.5 0.002 170 0.1 0.09 4.5 0.5 37.9 <0.01 3.9 349 0.97 4.4 330 6 0.53 0.8 003ZW262 0.18 7.5 0.001 120 0.17 0.21 12.8 0.11 11.8 <0.01 6.7 1280 0.18 3.2 950 3.9 0.55 0.8 003ZW269 0.03 6.7 0.002 30 <0.01 0.04 15.6 0.38 32.6 <0.01 2.4 320 1.54 7.3 50 0.4 0.13 <0.2 <003ZW299 0.03 <2.0 0.003 310 <0.01 0.3 4.5 0.16 9.6 0.04 2.2 791 0.18 2.5 140 13.4 0.4 0.4 003ZW302 0.03 2.5 0.001 570 0.03 1.14 11 0.21 40.4 0.31 3.6 754 0.85 6.5 440 29.6 0.12 0.3 <003ZW306 2.19 21.6 0.004 520 0.67 10.5 19.4 1.3 36.6 0.04 15.2 647 2.36 5.9 480 913 3.44 2.5 103ZW309 1.1 14.6 0.066 1240 <0.01 0.18 24.3 0.19 45.2 0.01 8.5 481 1.28 19.9 550 11.7 0.56 11.6 403ZW319 0.06 25.4 0.001 180 0.01 0.06 16.7 0.22 4.1 0.11 14.6 526 0.38 4.2 800 5.9 0.34 0.7 003ZW326 0.08 4.3 0.003 210 0.21 0.1 14.6 0.51 10.6 <0.01 7.5 328 6.37 3.7 240 4.4 0.38 4.1 203ZW329 0.05 3.5 0.006 270 0.69 0.16 10.7 0.92 4 <0.01 6.9 154 3.05 2.8 350 3.7 0.45 1.4 003ZW332 0.08 1.6 0.003 100 0.04 0.1 6.1 0.89 4 <0.01 11.1 243 2.49 3.9 390 4.1 0.28 0.4 003ZW334 0.12 5.9 0.001 460 0.25 0.04 0.5 0.76 4 <0.01 2.9 30 1.78 1.4 140 1.9 0.47 1.7 003ZW344 0.88 9.4 0.091 50 0.83 0.18 11.6 1.48 658 0.01 4.4 1200 1.03 8 570 0.9 1.42 0.5 003ZW345 0.04 2.6 0.001 490 0.11 0.11 11.2 2.39 104.5 <0.01 17.1 198 3.16 12.8 880 0.5 0.33 0.4 003ZW346 0.08 3.3 0.003 290 0.11 0.16 27.2 3.91 70.9 <0.01 22.1 469 1.58 21.2 1190 3.7 0.54 1.1 003ZW351 0.23 51.5 1.735 1520 0.41 0.17 1.5 0.14 33.2 1.96 0.8 19 3.77 1.1 120 2.4 5.12 0.8 003ZW352 2.3 64.1 0.174 2510 0.33 1.35 26 1.6 98.3 0.01 14.3 960 1.56 12.8 490 27.2 1.94 1.4 003ZW353 0.9 2.7 10.9 560 0.04 0.1 21.1 5.44 1860 0.02 25.4 408 2.35 29 660 1.2 0.28 1 <003ZW384 0.09 0.8 0.012 1150 0.09 0.04 3 0.18 14.8 <0.01 0.4 10 2.5 2.3 40 1 0.14 0.7 003ZW405 0.2 40.4 0.011 460 0.09 0.04 7.6 2.92 15.1 0.05 9.6 472 2.85 2.3 390 9.6 2.32 <0.2 003ZW406 8.41 24.2 0.024 >10000 0.09 0.19 0.6 0.32 30.8 0.09 1.7 18 2.42 1.3 260 126 1.92 <0.2 003ZW408 0.14 20 0.003 6360 0.19 0.11 17.1 0.48 63.7 0.07 4.7 1375 0.87 15.6 700 7.3 1.44 0.5 003ZW409 0.29 37 0.001 360 0.18 0.33 14.4 0.52 30.8 0.02 3.2 2670 0.86 22.3 330 28 1.55 0.4 <003ZW410 0.1 14.8 0.001 230 0.06 0.2 11.8 0.48 24.5 0.02 5.5 1215 0.7 7.2 450 5.3 0.32 0.4 <003ZW412 0.09 6.2 0.002 890 0.05 0.08 16.2 2.14 40.2 <0.01 13.4 807 0.45 8.8 440 1.5 0.46 0.4 003ZW416 0.33 23.2 0.011 310 0.04 0.04 2.3 0.27 21.3 0.01 10.5 987 1.64 4.1 270 56.5 0.99 1.6 003ZW417 0.87 21.4 0.013 150 0.52 0.15 8.2 0.69 50.1 0.02 16.9 533 0.56 3.7 300 16.2 4.3 1.3 203ZW418 0.32 17.2 0.006 320 0.25 0.07 1.3 0.26 27.2 0.02 14.2 349 1.86 1.1 560 26 2.36 1 103ZW419 0.4 21.8 0.01 160 1.1 0.22 21.9 0.39 37.9 0.04 20 841 1.04 5.9 440 29.8 5.8 3.4 203ZW420 0.5 31.1 0.003 580 0.39 3.63 16.3 0.25 25.3 0.03 18.6 775 1.32 4.4 530 136 2.82 1.1 203ZW421 2.3 47.9 0.016 430 0.07 0.22 4.5 0.61 108 0.02 34.4 1075 0.62 11 260 323 5.53 1.2 103ZW423 0.05 100 0.002 740 0.02 0.27 4.6 0.2 15.8 0.11 1 318 1.9 1.8 1440 22.2 5.26 0.4 0
141 

SAMPLE Ag As Au Ba Bi Cd Co Cs Cu Hg Li Mn Mo Ni P Pb Sb Se T

03ZW424 0.52 32.3 0.013 470 0.22 1.7 25 0.49 26.9 0.07 9.9 366 1.65 7 530 95.8 4.7 3.4 403ZW425 0.31 20.9 0.004 90 0.1 0.14 0.6 0.16 7.6 0.01 0.7 19 1.42 2.9 160 35.2 0.76 0.8 103ZW427 0.08 16.8 0.025 1940 0.16 0.03 3.3 0.12 61.1 0.06 0.3 47 1.24 2.9 150 7.5 0.99 0.4 003ZW428 0.09 481 0.06 210 0.06 0.09 10.4 0.07 20.4 0.74 1.4 1330 13.8 6.6 110 26.9 24 0.4 003ZW430 0.02 4.1 0.01 520 0.05 0.01 0.5 0.1 3.3 0.72 0.2 18 3.23 2.3 110 2.3 1.02 0.2 <003ZW432 0.05 5.2 0.017 720 0.11 <0.01 0.6 0.14 3.9 0.12 0.3 17 4.45 2.6 100 4.1 0.89 0.6 003ZW434 0.12 8.3 0.329 1600 0.55 0.02 0.5 0.1 12.2 0.09 0.2 24 3.23 2.2 280 5.7 2.59 0.4 003ZW435 0.04 7.6 0.033 1430 0.41 0.01 0.3 0.1 4.3 0.04 0.2 18 2.44 1.8 270 4.2 0.52 0.2 003ZW436 4.03 19.4 0.093 1520 0.19 0.09 8.9 0.19 48.9 0.07 2.7 217 5.66 6 190 28 0.98 5.7 303ZW437 0.05 8.1 0.014 1370 0.46 0.01 0.5 0.1 5.4 0.05 0.3 24 2.91 3.2 280 4.6 0.56 0.3 003ZW438 0.16 14.6 0.005 100 0.01 0.01 0.8 <0.05 68.9 0.04 0.2 11 1.42 2.9 740 1.6 0.76 27 503ZW439 2.56 24.3 0.064 1110 1.12 0.09 14.6 0.43 79.6 0.12 6.1 301 5.09 14 390 139 1.44 9.8 203ZW440 0.4 6 0.01 540 0.06 0.11 12.2 0.42 82.8 <0.01 38.1 299 1.5 18.5 310 7.1 0.21 3.6 003ZW441 9.88 53.8 0.723 150 0.14 0.05 0.7 0.11 31.5 0.28 0.2 23 3.23 4.6 40 31.9 10.1 1.7 003ZW443 0.29 2.1 0.034 60 0.05 <0.01 0.8 <0.05 4 0.03 0.2 20 1.42 4.6 20 5 0.3 0.2 003ZW450 0.21 32.7 0.014 110 0.42 0.13 14.8 0.13 121.5 0.03 1.2 268 1.54 9.5 480 8.3 0.68 0.5 003ZW455 0.1 203 0.005 360 0.33 0.35 9.6 0.19 23.4 0.01 2.8 421 1.73 6.1 280 5.5 0.41 0.2 003ZW458 0.02 19.2 0.001 90 0.01 0.1 6 0.26 56.9 0.04 1.6 320 0.59 5.5 230 1.8 1.56 0.3 <003ZW459 0.01 6.9 0.001 610 0.02 0.06 8.6 0.09 17.2 <0.01 6.8 425 0.49 2.2 510 2.2 0.07 0.3 <003ZW490 0.09 36.2 0.002 210 0.19 0.36 12 0.87 42.3 0.05 6.5 410 11.8 12.2 450 11.8 1.12 0.3 0

143 

IV. Trace element chemical data. UAF analysis. 

Sample BA CE NB RB SR Y ZR 

 03JF018 137 21 2 11 258 17 46 

 03JF020 570 38 2 23 162 23 162 

 03ZW006 381 26 4 15 322 29 89 

 03ZW012 394 29 3 11 360 20 64 

 03ZW068 470 33 3 32 332 22 91 

 03ZW121 660 33 4 38 238 28 147 

 03ZW142 232 35 3 31 163 31 149 

 03ZW147 1159 56 7 32 743 16 128 

 03ZW176 1240 43 7 91 480 15 128 

 03ZW179 1196 84 12 119 617 20 188 

 03ZW189 549 28 4 93 170 14 101 

 03ZW195 1016 85 12 60 596 21 153 

 03ZW196 1444 33 4 91 406 12 109 

 03ZW213 572 35 3 20 319 25 132 

 03ZW265 1237 54 8 91 526 14 136 

 03ZW267 1226 51 7 88 395 15 124 

 03ZW273 1547 85 11 88 825 19 143 

 03ZW276 1109 59 9 64 578 18 120 

 03ZW277 597 35 3 24 183 21 131 

 03ZW279 1412 129 17 167 662 27 252 

 03ZW282 788 52 4 57 953 19 72 

 03ZW283 1123 88 12 129 608 20 182 

 03ZW284 866 66 14 55 557 20 142 

 03ZW285 299 25 3 14 263 25 69 

 03ZW293 1653 133 17 112 840 25 209 

 03ZW294 1344 69 10 99 711 16 150 

 03ZW297 1448 166 25 217 352 29 420 

 03ZW317 1186 63 8 85 509 14 136 

 03ZW331 1360 64 7 109 379 14 119 

 03ZW333 337 43 3 29 89 30 172 

 03ZW341 495 42 4 24 251 28 133 

 03ZW347 1281 96 12 133 683 22 187 

 03ZW351 1185 128 22 76 64 20 337 

 03ZW355 1156 72 10 106 557 17 149 

 03ZW356 945 64 11 119 480 19 148 

 03ZW357 1207 47 8 105 470 14 123 

03ZW357B 1302 53 7 111 476 13 126 

 03ZW358 1121 60 7 92 484 14 119 

 03ZW359 1456 44 7 115 420 14 121 

03ZW359B 1323 52 7 109 458 13 119 

 03ZW360 1467 91 13 136 691 24 167 

 03ZW361 1172 66 9 114 501 16 133 

 03ZW362 1092 70 8 126 458 14 120 

 03ZW363 1033 62 7 126 405 14 127 

 03ZW364 1313 62 8 129 399 15 147 

 03ZW365 1041 49 8 128 379 15 119 

 03ZW366 1268 81 9 106 577 16 133 

 03ZW367 1245 71 8 107 546 16 128 

 03ZW369 712 73 8 53 346 15 130 

 03ZW373 1341 110 14 141 636 21 194 

 03ZW378 1329 79 11 133 569 18 161 

 03ZW389 1375 110 16 139 747 25 164 

 03ZW391 1188 81 10 140 512 17 161 

 03ZW394 1641 106 15 137 584 26 239 

 03ZW395 1378 86 11 161 554 18 164 

 03ZW396 1068 60 7 78 591 15 128 

 03ZW403 1310 100 12 124 689 21 177 

 03ZW404 1421 51 8 65 728 15 132 

 03ZW412 847 25 3 46 275 26 118 

 03ZW427 1513 100 20 78 123 22 338 
144 

Sample BA CE NB RB SR Y ZR 

 03ZW434 1327 130 20 69 162 15 346 

 03ZW435 1203 127 19 69 147 19 331 

 03ZW458 116 38 3 27 333 35 153 

 03ZW466 934 126 18 150 173 19 249 

 03ZW467 323 27 1 27 190 14 83 

 03ZW469 1230 73 9 97 615 18 156 

 03ZW474 1547 64 9 38 525 15 142 

 03ZW478 1517 48 7 117 492 15 136 

 03ZW479 104 24 3 4 178 24 70 

 03ZW481 873 31 4 96 285 12 99 

 03ZW482 1341 80 11 154 510 18 152 

Appendix C: List of quartz-plagioclase-K-feldspar modal 

estimates

Estimated modal abundances from stained rock slabs. 

Sample Rock Unit Qtz Plag Kspar 

03ZW055 Rex Creek Pluton 36 64 0 Tonalite 

03ZW056 Sawpit Pluton 32 26 42 Monzogranite 

03ZW104 Rex Creek Pluton 19 77 4 Quartz Diorite 

03ZW108 Rex Creek Pluton 16 83 1 

Quartz 

Monzodiorite 

03ZW117 Sawpit Pluton 22 44 33 Monzogranite 

03ZW148 Hornfels Diorite 4 94 1 Diorite 

03ZW155 Hornfels Diorite 2 43 55 Monzonite 

03ZW157 Hornfels Diorite 1 99 0 Diorite 

03ZW200 Rex Creek Pluton 7 92 1 Quartz Diorite 

03ZW214 Rex Creek Pluton 24 76 0 Granodiorite 

03ZW220 Rex Creek Pluton 19 81 0 Quartz Diorite 

03ZW260 Hornfels Diorite 7 91 1 Quartz Diorite 

03ZW272 Bonanza Pluton 4 74 21 Monzodiorite 

03ZW281 Bonanza Pluton 1 88 12 Monzodiorite 

03ZW295 Bonanza Pluton 4 82 14 Monzodiorite 

03ZW296 Bonanza Pluton 6 77 18 

Quartz 

Monzodiorite 

03ZW307 Bonanza Pluton 3 78 20 Monzodiorite 

03ZW374 Bonanza Pluton 19 51 30 

Quartz 

Monzonite 

03ZW375 Bonanza Pluton 26 50 24 Granodiorite 

03ZW376 Bonanza Pluton 25 67 8 Granodiorite 

03ZW377 Bonanza Pluton 28 55 17 Granodiorite 

03ZW380 Bonanza Pluton 23 63 15 Granodiorite 

03ZW386 Bonanza Pluton 24 53 23 Granodiorite 

03ZW392 Bonanza Pluton 27 67 6 Tonalite 

03ZW393 Bonanza Pluton 27 55 18 Granodiorite 

03ZW397 Bonanza Pluton 20 65 15 

Quartz 

Monzodiorite 

03ZW399 Bonanza Pluton 8 82 10 

Quartz 

Monzodiorite 

03ZW400 Bonanza Pluton 7 76 17 

Quartz 

Monzodiorite 

03ZW401 Bonanza Pluton 10 68 23 

Quartz 

Monzodiorite 

03ZW402 Bonanza Pluton 6 69 25 

Quartz 

Monzodiorite 

03ZW463 Bonanza Pluton 5 58 37 

Quartz 

Monzonite 

03ZW468 Bonanza Pluton 3 84 14 Monzodiorite 

03ZW471 Bonanza Pluton 1 76 22 Monzodiorite 
145 

Sample Rock Unit Qtz Plag Kspar 

03ZW475 Rex Creek Pluton 12 58 30 

Quartz 

Monzodiorite 

03ZW477 Rex Creek Pluton 12 58 30 

Quartz 

Monzodiorite 

03ZW480 Bonanza Pluton 27 60 13 Granodiorite 

03ZW485 Bonanza Pluton 30 32 38 Monzogranite 

Appendix D: Microprobe analysis data. 

UAF analysis. DL=detection limit 

Sample %Ag %Au %total Fineness Ag DL Au DL Grain Location 

03ZW353 8.4 91.0 99.4 916 0.16 0.17 1 

 8.4 90.1 98.6 914 0.16 0.17 1 

 8.9 89.8 98.7 910 0.18 0.16 1 

03ZW369 5.9 93.8 99.7 941 0.16 0.17 1 

 6.2 93.5 99.7 938 0.16 0.17 1 

 6.6 91.4 98.0 933 0.17 0.17 1 

03ZW382 12.3 86.1 98.4 875 0.15 0.17 1 

 13.2 88.9 102.1 871 0.16 0.17 1 

 12.1 87.5 99.7 879 0.16 0.17 1 

Spruce Placer 6.0 93.2 99.3 939 0.16 0.17 1 rim 

 5.9 95.2 101.1 942 0.15 0.17 1 center 

 6.3 94.9 101.3 938 0.16 0.17 1 rim 

975727 10.2 88.8 98.9 897 0.16 0.17 1 

 10.3 88.8 99.1 896 0.15 0.17 1 

 9.8 87.9 97.7 899 0.15 0.17 1 

975721 8.4 88.9 97.3 914 0.16 0.17 1 center 

 0.5 94.9 95.4 994 0.17 0.17 1 rim 

 0.3 94.4 94.6 997 0.16 0.17 1 rim 

975842 3.8 93.4 97.2 961 0.16 0.17 1 center 

 3.9 93.6 97.5 960 0.16 0.17 1 edge 

 3.6 93.0 96.6 962 0.17 0.17 1 edge 

 %Bi %Te %S %total Bi DL Te DL S DL Mineral 

03ZW369 52.1 48.1 0.0 100.2 0.34 0.08 0.03 Tellurobismuthite 

 51.2 48.2 0.0 99.4 0.34 0.08 0.03 Tellurobismuthite 

 58.4 36.6 4.5 99.5 0.34 0.08 0.03 Tetradymite 

 52.0 47.7 0.0 99.8 0.34 0.08 0.03 Tellurobismuthite 

 52.2 48.2 0.0 100.4 0.34 0.08 0.03 Tellurobismuthite 

 51.4 47.7 0.0 99.1 0.34 0.08 0.03 Tellurobismuthite 

 51.4 47.4 0.0 98.9 0.34 0.08 0.03 Tellurobismuthite 

 51.9 47.0 0.0 99.0 0.35 0.08 0.03 Tellurobismuthite 

 51.6 48.4 0.0 100.0 0.34 0.08 0.03 Tellurobismuthite 

 51.9 48.4 0.0 100.3 0.33 0.08 0.03 Tellurobismuthite 

 51.6 47.8 0.0 99.5 0.35 0.08 0.03 Tellurobismuthite 

Spruce Placer 52.2 33.9 4.1 90.2 0.33 0.07 0.03 Tetradymite 

 58.9 35.9 4.8 99.6 0.34 0.08 0.03 Tetradymite 

 59.9 36.7 4.9 101.4 0.34 0.08 0.03 Tetradymite 

 59.9 36.1 4.7 100.7 0.34 0.08 0.03 Tetradymite 

03ZW339 73.0 0.0 17.6 90.6 0.38 0.09 0.03 Bismuthinite 

 71.3 0.0 18.1 89.4 0.37 0.09 0.03 Bismuthinite 

 94.5 0.0 0.0 94.5 0.36 0.11 0.02 Bismuth 

147 

Appendix E: 40Ar/39Ar analytical data. UAF Geophysical Institute Analysis. UAF106-27 03ZW232 WR#1 Weighted average of J from standards = 0.002512 +/- 0

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK (mW) 39Ar meas. meas. meas. 40Ar 300 0.206 75.6526 2.0186 4.6844 0.1194 0.15396 0.00867 59.7 8.622 0.220 0.00527 0.00079 30.57 2600 0.353 73.8210 0.9264 9.3107 0.1387 0.16716 0.00650 66.0 17.188 0.258 0.00950 0.00117 25.25 1900 0.482 63.1966 0.7425 17.6998 0.2153 0.12858 0.00644 58.0 32.855 0.404 0.01097 0.00161 26.81 11200 0.584 41.6213 0.5387 17.5389 0.2267 0.06249 0.00877 41.2 32.553 0.426 0.01181 0.00183 24.73 21500 0.668 41.3980 0.4509 17.1959 0.1877 0.04697 0.01481 30.4 31.909 0.352 0.01174 0.00186 29.11 42000 0.772 46.3930 0.5466 23.0454 0.2729 0.06888 0.00890 40.2 42.929 0.516 0.00775 0.00286 28.16 22500 0.838 57.0671 0.9347 28.9640 0.4743 0.06672 0.02197 30.8 54.166 0.904 0.00462 0.00464 40.26 63000 0.889 59.5541 1.3658 51.0776 1.1792 0.09944 0.01879 42.9 96.944 2.315 0.00984 0.00507 35.15 59000 1.000 60.8574 0.6482 43.2494 0.4645 0.07732 0.00983 32.2 81.656 0.902 0.00888 0.00230 42.42 3Integrated 60.6584 0.4368 19.6971 0.1074 0.10820 0.00347 50.3 36.611 0.202 0.00869 0.00069 30.53 1

03ZW232 WR#2 Weighted average of J from standards = 0.002512 +/- 0

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK (mW) 39Ar meas. meas. meas. 40Ar 300 0.103 100.0266 1.1113 3.2695 0.0387 0.24082 0.00474 70.9 6.012 0.071 0.00220 0.00160 29.14 600 0.251 65.6510 0.5526 4.8098 0.0424 0.10200 0.00274 45.4 8.853 0.078 0.00181 0.00119 35.96 900 0.378 65.7001 0.7643 13.1717 0.1534 0.13327 0.00350 58.5 24.377 0.286 0.00515 0.00139 27.51 1200 0.551 45.7733 0.4987 14.0257 0.1643 0.07269 0.00236 44.7 25.972 0.307 0.00590 0.00096 25.55 1500 0.637 41.6522 1.5924 15.3775 0.5966 0.04012 0.00842 25.7 28.501 1.117 0.00043 0.00583 31.24 1800 0.710 46.7229 0.3842 14.6312 0.1294 0.07369 0.00925 44.3 27.104 0.242 0.00596 0.00219 26.27 2100 0.760 51.7352 0.6202 19.4694 0.2321 0.06076 0.01444 31.9 36.182 0.437 0.00489 0.00307 35.67 2400 0.798 66.0131 0.8171 20.9835 0.2658 0.09273 0.01794 39.1 39.035 0.501 0.00703 0.00384 40.71 2700 0.829 71.0565 1.3003 23.3292 0.4229 0.10244 0.02278 40.2 43.466 0.800 0.00413 0.00507 43.16 3000 0.840 75.5687 8.6932 24.5350 2.8221 0.08095 0.07806 29.2 45.749 5.348 0.00419 0.04310 54.33 3300 0.858 73.9765 1.7694 26.0333 0.6223 0.12584 0.02520 47.6 48.591 1.182 0.00461 0.00413 39.38 3700 0.869 67.8215 2.6739 27.1328 1.0687 0.11803 0.03654 48.4 50.680 2.032 0.00201 0.00653 35.58 4200 0.885 65.4366 1.4628 28.1469 0.6264 0.11684 0.02219 49.6 52.610 1.193 0.00778 0.00441 33.61 9000 1.000 67.8465 0.3835 32.9854 0.1859 0.09205 0.00514 36.5 61.852 0.356 0.00880 0.00223 44.04 Integrated 62.3143 0.2969 15.3631 0.0750 0.10475 0.00221 47.8 28.474 0.140 0.00457 0.00088 32.81 
148 

03ZW295 BI Weighted average of J from standards = 0.002512 +/- 

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK (mW) 39Ar meas. meas. meas. 40Ar 250 0.002 39.8589 1.1328 0.3346 0.0295 0.13242 0.02247 98.2 0.614 0.054 0.02418 0.00448 0.72 500 0.006 26.3389 0.4050 0.3428 0.0182 0.01922 0.01271 21.5 0.629 0.033 0.03079 0.00294 20.66 750 0.024 26.4071 0.1740 0.0915 0.0056 0.01183 0.00281 13.2 0.168 0.010 0.03041 0.00116 22.89 1000 0.089 25.5182 0.0466 0.0152 0.0009 0.00123 0.00088 1.4 0.028 0.002 0.03010 0.00024 25.13 1250 0.223 25.4256 0.2565 0.0078 0.0007 0.00013 0.00045 0.1 0.014 0.001 0.02951 0.00013 25.36 1500 0.327 25.4824 0.2974 0.0260 0.0088 -0.00010 0.00089 -0.1 0.048 0.016 0.02915 0.00023 25.49 1750 0.392 25.3971 0.0463 0.0294 0.0026 -0.00073 0.00143 -0.9 0.054 0.005 0.02938 0.00031 25.59 2000 0.449 25.4222 0.0492 0.0786 0.0022 0.00022 0.00108 0.2 0.144 0.004 0.03033 0.00030 25.34 2300 0.543 25.4553 0.0885 0.1134 0.0017 -0.00138 0.00122 -1.6 0.208 0.003 0.03248 0.00027 25.85 2600 0.701 25.1113 0.1191 0.0652 0.0007 -0.00023 0.00041 -0.3 0.120 0.001 0.03021 0.00019 25.16 3000 0.869 24.9295 0.2428 0.0512 0.0008 0.00027 0.00046 0.3 0.094 0.001 0.02912 0.00013 24.83 4000 0.990 25.2634 0.2451 0.1611 0.0104 0.00028 0.00142 0.3 0.296 0.019 0.03544 0.00302 25.17 9000 1.000 25.2905 0.2580 0.0515 0.0117 0.00121 0.00509 1.4 0.095 0.021 0.02841 0.00159 24.91 Integrated 25.3310 0.0717 0.0644 0.0016 0.00050 0.00030 0.6 0.118 0.003 0.03059 0.00037 25.16 

03ZW295 HO Weighted average of J from standards = 0.002512 +/- 

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK (mW) 39Ar meas. meas. meas. 40Ar 400 0.004 564.9709 15.1458 10.2205 0.2796 1.79286 0.05227 93.6 18.879 0.520 0.45839 0.01385 36.16 800 0.011 154.1140 1.6363 30.9058 0.3320 0.46187 0.01121 87.1 57.872 0.634 0.24487 0.00392 20.33 1200 0.022 94.8731 1.2870 51.0288 0.6923 0.26747 0.00793 79.3 96.848 1.359 0.11038 0.00222 20.31 1500 0.048 59.1746 0.2832 16.2589 0.0798 0.12822 0.00344 62.0 30.152 0.149 0.06935 0.00078 22.72 1800 0.084 44.9492 0.2460 14.9633 0.0899 0.07002 0.00238 43.6 27.726 0.168 0.13716 0.00110 25.60 2100 0.161 36.3755 0.1055 9.1649 0.0326 0.03940 0.00126 30.1 16.917 0.061 0.21032 0.00073 25.55 2500 0.260 34.8002 0.0995 6.5301 0.0280 0.03095 0.00086 24.9 12.033 0.052 0.17059 0.00083 26.23 3000 0.388 30.5455 0.0807 8.2769 0.0292 0.01691 0.00119 14.3 15.269 0.054 0.21117 0.00089 26.28 3500 0.488 31.0672 0.1823 8.3461 0.0555 0.01982 0.00086 16.8 15.398 0.103 0.18329 0.00127 25.95 4000 0.564 32.1592 0.2062 9.8554 0.0780 0.02554 0.00107 21.2 18.200 0.145 0.25451 0.00229 25.49 5000 0.950 28.4972 0.3797 7.9813 0.0619 0.01181 0.00030 10.2 14.721 0.115 0.20580 0.00155 25.71 9000 1.000 30.4751 0.2243 16.6869 0.1315 0.02105 0.00187 16.3 30.954 0.247 0.27169 0.00205 25.76 Integrated 35.7210 0.1573 9.6986 0.0290 0.03686 0.00034 28.5 17.909 0.054 0.20225 0.00066 25.69 
149 

03ZW365 BI#1 Weighted average of J from standards = 0.002512 +/- 0

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK +(mW) 39Ar meas. meas. meas. 40Ar 250 0.001 30.7215 0.9824 0.8598 0.0590 0.09031 0.04293 86.7 1.578 0.108 0.02019 0.00881 4.07 12500 0.006 10.7363 0.1199 0.6972 0.0139 0.02838 0.00717 77.8 1.280 0.025 0.03092 0.00293 2.37 2750 0.017 6.8019 0.0357 0.3160 0.0065 0.01727 0.00299 75.0 0.580 0.012 0.02932 0.00109 1.69 01000 0.033 19.3270 0.0747 0.1304 0.0040 0.01441 0.00333 22.0 0.239 0.007 0.02288 0.00077 15.05 01250 0.083 25.1995 0.0677 0.0326 0.0013 0.00273 0.00063 3.2 0.060 0.002 0.02166 0.00030 24.37 01500 0.158 25.5526 0.0532 0.0228 0.0010 0.00099 0.00088 1.1 0.042 0.002 0.02167 0.00020 25.23 01750 0.235 25.8971 0.2802 0.0312 0.0011 0.00076 0.00050 0.9 0.057 0.002 0.02208 0.00018 25.65 02000 0.317 25.8859 0.4307 0.0403 0.0014 0.00064 0.00095 0.7 0.074 0.003 0.02238 0.00026 25.67 02300 0.410 26.4121 0.1658 0.0649 0.0010 0.00139 0.00040 1.5 0.119 0.002 0.02292 0.00014 25.98 02600 0.512 26.9304 0.1687 0.0961 0.0009 0.00136 0.00038 1.5 0.176 0.002 0.02340 0.00018 26.51 03000 0.642 26.5503 0.1912 0.1138 0.0008 0.00098 0.00025 1.1 0.209 0.001 0.02353 0.00013 26.24 04000 0.873 25.9742 0.1476 0.1268 0.0008 0.00057 0.00023 0.6 0.233 0.001 0.02290 0.00011 25.79 09000 1.000 25.7810 0.1608 0.0481 0.0009 0.00085 0.00061 1.0 0.088 0.002 0.02082 0.00016 25.50 0Integrated 25.7044 0.0669 0.0850 0.0003 0.00163 0.00019 1.9 0.156 0.001 0.02261 0.00006 25.20 0

03ZW365 BI#2 Weighted average of J from standards = 0.002512 +/- 0.0

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK +(mW) 39Ar meas. meas. meas. 40Ar 250 0.002 22.2670 0.3994 0.9424 0.0203 0.07114 0.00817 94.2 1.730 0.037 0.02189 0.00160 1.29 2.500 0.006 7.5124 0.1160 0.6806 0.0112 0.01933 0.00254 75.6 1.249 0.021 0.02944 0.00071 1.82 0.750 0.015 9.1814 0.1062 0.2640 0.0040 0.01137 0.00158 36.5 0.485 0.007 0.02625 0.00057 5.81 0.1000 0.030 20.1603 0.4075 0.1129 0.0038 0.00363 0.00285 5.3 0.207 0.007 0.02427 0.00065 19.07 0.1250 0.058 25.0085 0.1183 0.0417 0.0008 0.00331 0.00050 3.9 0.077 0.002 0.02415 0.00013 24.00 0.1500 0.102 25.7118 0.2547 0.0361 0.0005 0.00139 0.00144 1.6 0.066 0.001 0.02467 0.00035 25.28 0.1750 0.159 26.3218 0.2677 0.0470 0.0006 0.00133 0.00018 1.5 0.086 0.001 0.02507 0.00018 25.91 0.2000 0.223 26.2631 0.2335 0.0683 0.0004 0.00096 0.00020 1.1 0.125 0.001 0.02527 0.00014 25.96 0.2300 0.300 26.7125 0.2239 0.0975 0.0006 0.00071 0.00016 0.8 0.179 0.001 0.02572 0.00018 26.48 0.2600 0.397 26.5772 0.3305 0.1094 0.0007 0.00064 0.00016 0.7 0.201 0.001 0.02570 0.00019 26.37 0.3000 0.525 26.1242 0.1499 0.1079 0.0003 0.00034 0.00009 0.4 0.198 0.001 0.02598 0.00011 26.00 0.4000 0.779 25.8257 0.1261 0.1038 0.0004 0.00037 0.00007 0.4 0.191 0.001 0.02601 0.00010 25.70 0.9000 1.000 25.4317 0.0889 0.0835 0.0003 0.00022 0.00006 0.2 0.153 0.001 0.02637 0.00008 25.35 0.Integrated 25.6262 0.0612 0.0951 0.0002 0.00095 0.00009 1.1 0.174 0.000 0.02581 0.00005 25.33 0.
150 

03ZW365 BI#3 Weighted average of J from standards = 0.002512 +/- 0

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK +(mW) 39Ar meas. meas. meas. 40Ar 250 0.002 25.5004 0.4456 0.9193 0.0254 0.07288 0.01033 84.3 1.688 0.047 0.01786 0.00253 4.01 3.500 0.008 6.1012 0.1143 0.3836 0.0091 0.00583 0.00319 27.9 0.704 0.017 0.02784 0.00080 4.38 0.750 0.019 12.6330 0.1573 0.2216 0.0045 0.00651 0.00158 15.1 0.407 0.008 0.02490 0.00046 10.70 0.1000 0.038 19.5382 0.1794 0.1504 0.0022 0.00194 0.00097 2.9 0.276 0.004 0.02466 0.00043 18.95 0.1250 0.064 20.7693 0.1199 0.1190 0.0016 0.00078 0.00066 1.1 0.218 0.003 0.02481 0.00022 20.52 0.1500 0.101 22.2125 0.1156 0.0738 0.0011 0.00053 0.00049 0.7 0.135 0.002 0.02410 0.00024 22.03 0.1750 0.148 24.8559 0.5701 0.0492 0.0013 0.00173 0.00053 2.0 0.090 0.002 0.02421 0.00028 24.32 0.2000 0.210 25.8653 0.3054 0.0484 0.0009 0.00160 0.00085 1.8 0.089 0.002 0.02400 0.00015 25.37 0.2300 0.288 26.5677 0.3671 0.0503 0.0008 0.00055 0.00031 0.6 0.092 0.001 0.02404 0.00018 26.38 0.2600 0.386 26.3385 0.2143 0.0665 0.0007 0.00024 0.00022 0.2 0.122 0.001 0.02425 0.00014 26.25 0.3000 0.503 26.6966 0.1948 0.0817 0.0005 0.00044 0.00016 0.5 0.150 0.001 0.02442 0.00009 26.55 0.4000 0.748 26.6372 0.1374 0.1144 0.0005 0.00034 0.00007 0.3 0.210 0.001 0.02416 0.00014 26.52 0.9000 1.000 26.6896 0.1192 0.1949 0.0005 0.00019 0.00011 0.2 0.358 0.001 0.02428 0.00008 26.62 0.Integrated 25.7515 0.0703 0.1176 0.0003 0.00073 0.00009 0.8 0.216 0.000 0.02426 0.00005 25.52 0.

03ZW365 HO#1 Weighted average of J from standards = 0.002512 +/- 0

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK (mW) 39Ar meas. meas. meas. 40Ar 200 0.003 156.3811 3.8617 4.2263 0.1100 0.51676 0.01809 97.5 7.776 0.203 0.08812 0.00487 3.98 400 0.020 32.9931 0.2053 1.3442 0.0109 0.10169 0.00391 90.8 2.469 0.020 0.06195 0.00089 3.02 600 0.039 34.4551 0.3463 1.5310 0.0159 0.08364 0.00323 71.5 2.812 0.029 0.06593 0.00142 9.84 900 0.077 35.6017 0.1235 0.7381 0.0045 0.05190 0.00164 43.0 1.355 0.008 0.03924 0.00041 20.30 1200 0.117 31.8273 0.1391 0.6529 0.0042 0.01834 0.00212 16.9 1.198 0.008 0.03207 0.00047 26.44 1500 0.174 32.9104 0.1873 2.3174 0.0162 0.01840 0.00304 16.0 4.259 0.030 0.04868 0.00149 27.66 2000 0.309 28.4881 0.2902 6.4944 0.0714 0.00819 0.00077 6.8 11.967 0.132 0.11642 0.00133 26.64 2500 0.484 27.3859 0.2300 7.6810 0.0786 0.00740 0.00120 5.9 14.164 0.146 0.13246 0.00150 25.88 3000 0.716 27.5574 0.3178 8.5827 0.0620 0.00819 0.00112 6.5 15.837 0.115 0.13657 0.00095 25.90 9000 1.000 27.2618 0.2474 10.0417 0.0170 0.00944 0.00033 7.5 18.546 0.032 0.13981 0.00036 25.36 Integrated 29.0098 0.1184 7.3226 0.0223 0.01576 0.00043 14.2 13.500 0.041 0.11843 0.00040 24.99 
151 

03ZW365 HO#2 Weighted average of J from standards = 0.002512 +/- 0

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK (mW) 39Ar meas. meas. meas. 40Ar 400 0.003 147.8383 7.9163 4.9664 0.2767 0.50594 0.05170 100.9 9.142 0.511 0.08906 0.01238 -1.33 800 0.009 95.5976 2.8543 3.7484 0.1159 0.33801 0.03281 104.2 6.895 0.214 0.11069 0.00650 -4.04 1200 0.018 48.2646 0.9220 2.8975 0.0574 0.16226 0.01309 99.0 5.326 0.106 0.09196 0.00268 0.51 1500 0.041 19.2639 0.1829 1.1146 0.0150 0.07066 0.01196 108.1 2.047 0.028 0.07705 0.00173 -1.56 1800 0.067 16.6906 3.7314 1.1181 0.4508 0.17551 0.13654 310.8 2.053 0.828 0.09350 0.04107 -35.14 2100 0.083 36.8010 0.2951 2.3478 0.0223 0.04020 0.00698 31.8 4.314 0.041 0.05759 0.00155 25.11 2500 0.124 28.1589 0.1283 2.5899 0.0131 0.01542 0.00255 15.5 4.760 0.024 0.06004 0.00055 23.81 3000 0.185 30.2824 0.0781 5.9982 0.0219 0.00895 0.00228 7.3 11.049 0.040 0.09572 0.00063 28.17 3500 0.240 30.4470 0.2205 9.1058 0.0813 0.01201 0.00193 9.4 16.807 0.151 0.13012 0.00119 27.72 4000 0.300 29.4191 0.1071 10.5750 0.0619 0.01289 0.00192 10.3 19.538 0.115 0.15401 0.00085 26.56 5000 0.418 28.5440 0.2202 11.6792 0.0955 0.00863 0.00090 5.9 21.594 0.178 0.17840 0.00156 27.05 9000 1.000 28.4315 0.1738 13.0757 0.0545 0.00931 0.00024 6.2 24.198 0.102 0.19430 0.00099 26.86 Integrated 29.2579 0.2023 10.7597 0.0709 0.02082 0.00347 18.3 19.882 0.132 0.16571 0.00147 24.05 

03ZW471 BI Weighted average of J from standards = 0.002512 +/- 0

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK +(mW) 39Ar meas. meas. meas. 40Ar 250 0.001 46.2154 1.5113 0.3110 0.0477 0.12908 0.02860 82.5 0.571 0.088 0.02396 0.00773 8.07 8.500 0.005 23.9526 0.2399 0.1402 0.0084 0.03852 0.00411 47.5 0.257 0.015 0.03029 0.00184 12.55 1.750 0.019 28.1005 0.2075 0.0428 0.0033 0.01224 0.00145 12.9 0.078 0.006 0.02967 0.00074 24.46 0.1000 0.049 26.4388 0.0658 0.0161 0.0013 0.00467 0.00066 5.2 0.029 0.002 0.02996 0.00025 25.03 0.1250 0.090 25.7881 0.1506 0.0118 0.0008 0.00005 0.00058 0.1 0.022 0.001 0.03031 0.00026 25.74 0.1500 0.142 26.2426 0.3603 0.0127 0.0008 0.00109 0.00044 1.2 0.023 0.001 0.03030 0.00029 25.89 0.1750 0.198 25.8703 0.5652 0.0126 0.0011 0.00110 0.00030 1.3 0.023 0.002 0.03034 0.00040 25.52 0.2000 0.257 25.8953 0.2127 0.0137 0.0006 0.00198 0.00075 2.3 0.025 0.001 0.03034 0.00026 25.28 0.2300 0.323 25.4041 0.3412 0.0152 0.0006 0.00032 0.00040 0.4 0.028 0.001 0.03091 0.00048 25.28 0.2600 0.404 25.5211 0.2529 0.0285 0.0005 0.00117 0.00020 1.3 0.052 0.001 0.03057 0.00011 25.15 0.3000 0.521 25.5045 0.1758 0.0382 0.0004 0.00030 0.00016 0.3 0.070 0.001 0.03072 0.00019 25.39 0.4000 0.762 25.4150 0.1441 0.0176 0.0002 0.00030 0.00007 0.3 0.032 0.000 0.03002 0.00011 25.30 0.9000 1.000 25.2564 0.0994 0.0684 0.0003 0.00026 0.00006 0.3 0.126 0.001 0.02985 0.00012 25.16 0.Integrated 25.5915 0.0682 0.0330 0.0002 0.00114 0.00008 1.3 0.061 0.000 0.03022 0.00007 25.23 0.
152 

03ZW471 HO Weighted average of J from standards = 0.002512 +/- 0

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39Ar(mW) 39Ar meas. meas. meas. 40Ar 300 0.004 151.1691 3.8241 2.0504 0.0612 0.50715 0.02217 99.1 3.767 0.113 0.05239 0.00723 1.43 600 0.027 19.3243 0.0882 0.5842 0.0121 0.03732 0.00369 56.9 1.072 0.022 0.04517 0.00129 8.31 900 0.058 34.1396 0.1134 0.5106 0.0047 0.03048 0.00238 26.3 0.937 0.009 0.02973 0.00050 25.15 1200 0.114 32.1831 0.0861 0.4034 0.0021 0.01620 0.00075 14.8 0.740 0.004 0.03054 0.00031 27.41 1500 0.195 28.9786 0.0795 0.6684 0.0025 0.00612 0.00051 6.1 1.227 0.005 0.03251 0.00022 27.20 1800 0.299 28.5823 0.0858 0.9404 0.0036 0.00277 0.00055 2.6 1.727 0.007 0.03925 0.00024 27.82 2100 0.438 27.3313 0.4998 0.8845 0.0043 0.00249 0.00043 2.5 1.624 0.008 0.03750 0.00024 26.65 2500 0.669 26.6322 0.2787 1.1869 0.0049 0.00226 0.00017 2.2 2.180 0.009 0.03469 0.00015 26.04 2900 0.857 26.5293 0.3246 3.4860 0.0157 0.00270 0.00026 2.0 6.411 0.029 0.03628 0.00020 26.02 3300 0.929 26.3992 0.1690 13.8551 0.0905 0.00321 0.00080 -0.4 25.654 0.169 0.03602 0.00037 26.70 3700 0.952 26.7535 0.1971 19.1216 0.1659 0.00920 0.00200 4.8 35.528 0.312 0.03804 0.00062 25.76 4100 0.959 26.3193 0.4124 20.4987 0.3167 0.00597 0.00523 0.9 38.121 0.597 0.04215 0.00238 26.42 5000 0.974 27.0794 0.1845 44.5961 0.3118 0.01490 0.00316 3.9 84.274 0.607 -0.03645 0.10490 26.77 9000 1.000 28.2916 0.2584 138.6763 0.5970 0.04749 0.00162 12.8 279.703 1.324 0.05556 0.00069 27.09 Integrated 27.9411 0.1144 7.4754 0.0116 0.00872 0.00021 7.2 13.783 0.022 0.03533 0.00154 26.02 

03ZW474 BI#1 474B_1 Weighted average of J from standards = 0.002512 +/- 0

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK +(mW) 39Ar meas. meas. meas. 40Ar 250 0.005 51.1107 1.2448 2.8473 0.0755 0.17564 0.01958 101.2 5.234 0.139 0.01883 0.00621 -0.61 5.500 0.020 12.1118 0.1515 1.5419 0.0210 0.02475 0.00571 59.6 2.832 0.039 0.04041 0.00138 4.89 1.750 0.054 8.3198 0.0392 0.6493 0.0048 0.01383 0.00247 48.7 1.192 0.009 0.03507 0.00065 4.25 0.1000 0.093 15.2832 0.0411 0.5336 0.0037 0.02158 0.00199 41.5 0.979 0.007 0.02699 0.00069 8.92 0.1250 0.153 21.0347 0.2471 0.3291 0.0061 0.01727 0.00130 24.2 0.604 0.011 0.02517 0.00053 15.93 0.1500 0.263 25.6434 0.2897 0.2093 0.0029 0.00436 0.00162 5.0 0.384 0.005 0.02307 0.00051 24.34 0.1750 0.377 27.1175 0.1163 0.4038 0.0023 0.00222 0.00088 2.3 0.741 0.004 0.02437 0.00037 26.47 0.2000 0.463 24.6891 0.1611 0.6133 0.0040 0.00463 0.00098 5.4 1.126 0.007 0.02567 0.00029 23.35 0.2300 0.555 25.6667 0.2706 0.7050 0.0075 0.00044 0.00112 0.3 1.294 0.014 0.02980 0.00280 25.57 0.2600 0.625 26.6327 0.3033 1.1161 0.0246 0.00551 0.00757 5.8 2.049 0.045 0.03262 0.00066 25.08 2.3000 0.712 24.4586 0.0931 0.8552 0.0071 0.00534 0.00508 6.2 1.570 0.013 0.02259 0.00065 22.93 1.4000 0.970 25.4847 0.2413 1.3776 0.0058 0.00167 0.00058 1.5 2.530 0.011 0.02274 0.00015 25.09 0.9000 1.000 20.0232 0.0833 0.2541 0.0055 0.00233 0.00235 3.4 0.466 0.010 0.00567 0.00077 19.33 0.Integrated 24.1193 0.0801 0.8009 0.0024 0.00606 0.00077 7.2 1.470 0.004 0.02501 0.00029 22.37 0.
153 

03ZW474 BI#2 474B_2 Weighted average of J from standards = 0.002512 +/- 0

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK +(mW) 39Ar meas. meas. meas. 40Ar 250 0.002 69.8515 2.3169 4.2912 0.1580 0.19586 0.03073 82.4 7.896 0.292 0.01523 0.01157 12.30 8.500 0.011 11.8359 0.1121 1.9794 0.0224 0.04111 0.00816 101.6 3.637 0.041 0.04125 0.00265 -0.19 2.750 0.041 5.0075 0.0194 0.6341 0.0042 0.01360 0.00211 79.8 1.164 0.008 0.03279 0.00087 1.01 0.1000 0.075 8.0687 0.0247 0.5512 0.0032 0.01252 0.00194 45.5 1.012 0.006 0.02788 0.00071 4.38 0.1250 0.113 14.3929 0.0506 0.5126 0.0047 0.01434 0.00175 29.2 0.941 0.009 0.02620 0.00072 10.17 0.1500 0.155 18.1120 0.0640 0.5768 0.0034 0.01272 0.00184 20.5 1.059 0.006 0.03140 0.00061 14.37 0.1750 0.206 19.4121 0.0534 0.4078 0.0021 0.01032 0.00074 15.6 0.748 0.004 0.03057 0.00021 16.37 0.2000 0.269 22.9870 0.0520 0.3084 0.0020 0.01084 0.00062 13.8 0.566 0.004 0.02879 0.00017 19.78 0.2300 0.349 27.3967 0.0673 0.2914 0.0016 0.00974 0.00051 10.4 0.535 0.003 0.02792 0.00013 24.52 0.2600 0.431 30.4630 0.2310 0.4119 0.0040 0.01030 0.00091 9.9 0.756 0.007 0.03096 0.00053 27.43 0.3000 0.505 33.1919 0.1814 0.5815 0.0036 0.01030 0.00079 9.0 1.067 0.007 0.03300 0.00052 30.18 0.4000 0.749 35.3138 0.2110 1.0790 0.0030 0.00349 0.00032 2.7 1.981 0.006 0.03906 0.00011 34.36 0.9000 1.000 30.5946 0.2839 0.9636 0.0020 0.00141 0.00011 1.1 1.769 0.004 0.04186 0.00030 30.24 0.Integrated 27.8684 0.0904 0.7539 0.0011 0.00749 0.00022 7.8 1.384 0.002 0.03527 0.00012 25.69 0.

03ZW474 HO#1 474H_1 Weighted average of J from standards = 0.002512 +

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK (mW) 39Ar meas. meas. meas. 40Ar 400 0.003 126.1942 15.5943 3.6072 0.5172 0.43480 0.14485 101.6 6.634 0.953 0.19972 0.03627 -2.05 800 0.009 71.5232 2.5524 2.3572 0.0882 0.20813 0.01980 85.8 4.332 0.162 0.19925 0.00955 10.18 1200 0.024 39.8303 0.6293 1.0881 0.0203 0.06204 0.00816 45.9 1.998 0.037 0.06518 0.00183 21.56 1500 0.044 32.4310 0.3836 0.9420 0.0126 0.03338 0.00546 30.2 1.730 0.023 0.05573 0.00118 22.62 1800 0.064 28.8942 0.3463 2.3113 0.0377 0.01078 0.00755 10.4 4.247 0.069 0.14441 0.00218 25.89 2100 0.089 29.0386 0.2374 4.4569 0.0382 0.01508 0.00285 14.2 8.202 0.070 0.19404 0.00238 24.96 2500 0.138 26.9725 0.0980 6.4620 0.0286 0.00408 0.00178 2.7 11.907 0.053 0.16712 0.00119 26.33 3000 0.226 26.1070 0.1253 6.8622 0.0384 0.00402 0.00092 2.6 12.648 0.071 0.14357 0.00079 25.52 3500 0.354 25.9291 0.2656 6.8610 0.0810 -0.00146 0.00245 -3.7 12.646 0.150 0.13479 0.00144 26.97 4000 0.440 25.9094 0.1027 7.1245 0.0300 -0.00042 0.00201 -2.5 13.133 0.056 0.13633 0.00085 26.66 5000 0.563 26.1880 0.1677 7.2157 0.0465 0.00282 0.00065 1.1 13.302 0.086 0.15227 0.00098 25.99 9000 1.000 25.7457 0.0914 8.3899 0.0123 0.00376 0.00018 1.9 15.479 0.023 0.17991 0.00026 25.37 Integrated 26.9822 0.0615 7.1840 0.0146 0.00701 0.00060 5.7 13.244 0.027 0.15875 0.00032 25.54 
154 

03ZW474 HO#2 474H_2 Weighted average of J from standards = 0.002512 +/- 

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK (mW) 39Ar meas. meas. meas. 40Ar 400 0.001 382.9427 45.7143 10.6323 1.2838 1.42350 0.19184 109.6 19.645 2.389 0.12268 0.02771 -37.19 800 0.003 198.8530 7.3563 5.7575 0.2235 0.65949 0.03722 97.8 10.604 0.413 0.26464 0.01245 4.39 1200 0.008 50.5309 0.7827 4.0452 0.0687 0.14812 0.01653 86.1 7.442 0.127 0.11352 0.00426 7.05 1500 0.014 31.7665 0.5164 3.0699 0.0586 0.06957 0.00958 64.0 5.644 0.108 0.06115 0.00318 11.43 1800 0.021 30.7688 0.4466 5.6431 0.0880 0.06307 0.00888 59.3 10.392 0.163 0.04727 0.00293 12.57 2100 0.028 31.2588 0.7194 6.5804 0.1662 0.07012 0.01735 64.8 12.126 0.308 0.04263 0.00488 11.05 2500 0.038 34.8768 0.5746 4.6697 0.0833 0.07227 0.01315 60.3 8.594 0.154 0.06660 0.00322 13.89 3000 0.054 32.7345 0.2516 4.4529 0.0396 0.03341 0.00728 29.2 8.194 0.073 0.09699 0.00210 23.23 3500 0.099 30.5007 0.2397 5.7580 0.0492 0.01277 0.00262 11.0 10.605 0.091 0.13748 0.00127 27.23 4000 0.216 26.7690 0.1974 6.9191 0.0557 0.00473 0.00086 3.3 12.753 0.103 0.14354 0.00116 25.98 5000 0.423 26.2303 0.3430 6.7232 0.0935 0.00369 0.00062 2.2 12.390 0.173 0.13800 0.00191 25.73 9000 1.000 26.3273 0.2483 8.0833 0.0536 0.00519 0.00015 3.5 14.910 0.099 0.14934 0.00098 25.51 Integrated 27.6047 0.1647 7.3878 0.0367 0.01076 0.00034 9.5 13.621 0.068 0.14217 0.00070 25.07 

975960 BI Weighted average of J from standards = 0.002512 +/- 0

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK +(mW) 39Ar meas. meas. meas. 40Ar 100 0.004 17.3942 0.1629 0.1622 0.0062 0.05188 0.00207 88.2 0.298 0.011 0.09342 0.00184 2.05 0.150 0.007 6.9854 0.0823 0.0888 0.0071 0.01594 0.00201 67.6 0.163 0.013 0.09232 0.00169 2.25 0.200 0.015 8.3159 0.0616 0.0581 0.0033 0.00979 0.00047 34.9 0.107 0.006 0.08008 0.00106 5.40 0.300 0.042 7.8983 0.0396 0.0308 0.0010 0.00325 0.00036 12.2 0.057 0.002 0.08019 0.00058 6.91 0.450 0.115 7.4533 0.0300 0.0177 0.0003 0.00068 0.00007 2.7 0.032 0.001 0.07753 0.00073 7.23 0.600 0.219 7.3427 0.0482 0.0261 0.0003 0.00008 0.00007 0.3 0.048 0.001 0.07752 0.00055 7.29 0.750 0.387 7.2444 0.0253 0.0518 0.0002 0.00012 0.00004 0.4 0.095 0.000 0.07783 0.00027 7.19 0.900 0.538 7.1933 0.0306 0.0761 0.0005 0.00010 0.00005 0.3 0.140 0.001 0.07472 0.00027 7.14 0.1050 0.683 7.1718 0.0194 0.0688 0.0007 0.00021 0.00007 0.8 0.126 0.001 0.06208 0.00011 7.09 0.1200 0.747 7.1774 0.0450 0.0656 0.0010 0.00023 0.00013 0.9 0.120 0.002 0.06057 0.00045 7.09 0.1500 0.808 7.2432 0.0355 0.0393 0.0006 0.00038 0.00014 1.5 0.072 0.001 0.06616 0.00027 7.11 0.2000 0.836 7.2849 0.0305 0.0315 0.0010 0.00090 0.00030 3.6 0.058 0.002 0.06336 0.00054 6.99 0.2500 0.844 7.8406 0.0670 0.0130 0.0029 0.00151 0.00107 5.7 0.024 0.005 0.05873 0.00093 7.37 0.3000 0.856 7.7187 0.0537 0.0213 0.0013 0.00312 0.00053 12.0 0.039 0.002 0.05930 0.00045 6.77 0.8000 1.000 7.4412 0.0393 0.0324 0.0006 0.00061 0.00005 2.4 0.059 0.001 0.06823 0.00036 7.23 0.Integrated 7.3519 0.0112 0.0489 0.0002 0.00074 0.00003 3.0 0.090 0.000 0.07124 0.00012 7.11 0.
155 

976864 M Weighted average of J from standards = 0.002512 +/- 0

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK +(mW) 39Ar meas. meas. meas. 40Ar 100 0.003 7.4673 0.0577 0.0378 0.0015 0.01328 0.00075 52.7 0.069 0.003 0.00176 0.00010 3.52 0.150 0.007 7.9195 0.0422 0.0326 0.0015 0.00850 0.00060 31.8 0.060 0.003 0.00172 0.00010 5.38 0.200 0.014 8.1926 0.0402 0.0258 0.0006 0.00489 0.00036 17.7 0.047 0.001 0.00103 0.00009 6.72 0.300 0.029 8.1921 0.0403 0.0174 0.0006 0.00253 0.00009 9.1 0.032 0.001 0.00077 0.00004 7.42 0.450 0.056 7.8696 0.0164 0.0122 0.0002 0.00140 0.00012 5.3 0.022 0.000 0.00066 0.00002 7.43 0.600 0.114 7.5424 0.0472 0.0074 0.0001 0.00063 0.00007 2.5 0.014 0.000 0.00049 0.00003 7.33 0.750 0.173 7.4774 0.0123 0.0073 0.0001 0.00055 0.00006 2.2 0.013 0.000 0.00049 0.00002 7.29 0.900 0.237 7.4007 0.0097 0.0159 0.0002 0.00048 0.00007 1.9 0.029 0.000 0.00049 0.00002 7.23 0.1050 0.311 7.3907 0.0241 0.0109 0.0001 0.00056 0.00003 2.2 0.020 0.000 0.00052 0.00003 7.20 0.1200 0.391 7.3487 0.0305 0.0107 0.0001 0.00052 0.00003 2.1 0.020 0.000 0.00050 0.00002 7.17 0.1500 0.473 23.4563 0.4503 0.0165 0.0003 0.05442 0.00064 68.6 0.030 0.001 0.00061 0.00006 7.35 0.2000 0.546 7.3536 0.0570 0.0362 0.0002 0.00053 0.00004 2.1 0.066 0.000 0.00076 0.00001 7.17 0.2500 0.624 7.4541 0.1587 0.0332 0.0004 0.00080 0.00006 3.1 0.061 0.001 0.00074 0.00003 7.19 0.3500 0.731 7.3396 0.1347 0.0640 0.0007 0.00084 0.00004 3.3 0.118 0.001 0.00101 0.00004 7.07 0.8000 1.000 7.3658 0.1068 0.0741 0.0007 0.00078 0.00004 3.1 0.136 0.001 0.00111 0.00004 7.11 0.Integrated 8.7442 0.0492 0.0379 0.0002 0.00524 0.00004 17.7 0.070 0.000 0.00079 0.00001 7.17 0.

977056 BI Weighted average of J from standards = 0.002512 +/- 

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar*/39ArK (mW) 39Ar meas. meas. meas. 40Ar 100 0.003 16.1099 0.1010 0.1236 0.0039 0.05068 0.00248 93.1 0.227 0.007 0.02361 0.00055 1.12 150 0.007 4.9061 0.0428 0.0791 0.0044 0.00989 0.00106 59.8 0.145 0.008 0.02347 0.00034 1.96 200 0.014 8.4727 0.0490 0.0506 0.0026 0.01121 0.00131 39.2 0.093 0.005 0.02115 0.00039 5.14 300 0.036 8.2456 0.0264 0.0207 0.0006 0.00537 0.00031 19.3 0.038 0.001 0.02013 0.00017 6.63 450 0.104 7.6743 0.0232 0.0066 0.0003 0.00090 0.00008 3.5 0.012 0.000 0.02040 0.00009 7.38 600 0.182 7.5224 0.0667 0.0080 0.0003 0.00013 0.00007 0.5 0.015 0.001 0.02058 0.00024 7.46 750 0.251 7.4474 0.0300 0.0240 0.0004 0.00038 0.00012 1.5 0.044 0.001 0.02038 0.00012 7.31 900 0.346 7.3880 0.0331 0.0550 0.0007 0.00013 0.00009 0.5 0.101 0.001 0.02030 0.00014 7.33 1050 0.490 7.3139 0.0188 0.0610 0.0003 -0.00007 0.00004 -0.4 0.112 0.001 0.01999 0.00010 7.31 1200 0.573 7.3232 0.0263 0.0285 0.0003 0.00005 0.00006 0.2 0.052 0.000 0.02020 0.00009 7.28 1500 0.658 7.3531 0.0184 0.0150 0.0002 0.00008 0.00010 0.3 0.027 0.000 0.02063 0.00008 7.30 2000 0.816 7.2584 0.0142 0.0395 0.0003 -0.00004 0.00006 -0.2 0.072 0.001 0.02121 0.00008 7.25 2500 0.854 7.3192 0.0168 0.0614 0.0007 0.00018 0.00027 0.7 0.113 0.001 0.02111 0.00018 7.24 3500 0.949 7.3032 0.0281 0.0203 0.0003 -0.00015 0.00010 -0.6 0.037 0.000 0.02031 0.00009 7.32 8000 1.000 7.2462 0.0165 0.0232 0.0002 -0.00001 0.00015 -0.1 0.042 0.000 0.01993 0.00013 7.22 Integrated 7.4038 0.0085 0.0336 0.0001 0.00048 0.00003 1.9 0.062 0.000 0.02049 0.00004 7.24 
156 

03ZW351 M Weighted average of J from standards = 0.002512 

Laser Cum. 40Ar/39Ar +/- 37Ar/39Ar +/- 36Ar/39Ar +/- % Atm. Ca/K +/- Cl/K +/- 40Ar

(mW) 39Ar measured measured measured 40Ar 

200 0.0014 25.285 0.152 0.0127 0.0127 0.05663 0.00170 66.2 0.0232 0.0234 0.00301 0.00031 8400 0.0068 30.109 0.199 0.0065 0.0034 0.03536 0.00060 34.7 0.0119 0.0063 0.00259 0.00008 19600 0.0172 28.707 0.155 0.0019 0.0017 0.01336 0.00025 13.8 0.0036 0.0031 0.00148 0.00003 24800 0.0365 27.578 0.174 0.0021 0.0014 0.00517 0.00015 5.5 0.0039 0.0025 0.00109 0.00004 26

1000 0.0636 26.778 0.133 0.0020 0.0008 0.00254 0.00008 2.8 0.0037 0.0014 0.00095 0.00002 251250 0.1030 26.102 0.132 -0.0003 0.0005 0.00112 0.00006 1.3 -0.0006 0.0010 0.00097 0.00002 251500 0.1472 25.759 0.121 -0.0010 0.0004 0.00066 0.00005 0.8 -0.0019 0.0008 0.00098 0.00002 251750 0.1994 25.662 0.121 -0.0008 0.0003 0.00067 0.00005 0.8 -0.0014 0.0006 0.00099 0.00002 252000 0.2581 25.507 0.112 -0.0005 0.0003 0.00060 0.00004 0.7 -0.0009 0.0005 0.00100 0.00002 252500 0.3465 25.431 0.131 -0.0007 0.0002 0.00046 0.00003 0.5 -0.0012 0.0004 0.00105 0.00002 253000 0.4685 25.392 0.116 -0.0002 0.0001 0.00046 0.00001 0.5 -0.0004 0.0002 0.00108 0.00002 254000 0.6723 25.316 0.115 -0.0003 0.0001 0.00044 0.00001 0.5 -0.0005 0.0002 0.00115 0.00001 255000 0.8962 25.322 0.118 -0.0003 0.0001 0.00047 0.00001 0.6 -0.0006 0.0001 0.00126 0.00002 258000 1.0000 25.313 0.116 -0.0004 0.0002 0.00062 0.00003 0.7 -0.0007 0.0003 0.00168 0.00002 25

Integrated 25.561 0.044 -0.0002 0.0001 0.00108 0.00001 1.2 -0.0004 0.0001 0.00119 0.00001 25