Platinum Deposits of the 

Goodnews Bay District, 

Alaska 

By JOHN B. MERTIE, JR. 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 938 

Mining history and general and economic 

geology of placer deposits of the district 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1976 
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Srcrrta~ 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Mertie, John Beaver, 1888- 

Platinum deposits of the Goodnews Bay district, Alaska. 

(Geological Survey Professional Paper 938) 

Bibliography: p. 41-42. 

Supt. of Docs. no.: 1.19.16:938. 

1. Platinum ores-Alaska-Goodnews Bay region. 2. Placer deposits-Alaska-Goodnews Bay region. I. Title. 11. Series: 

United States Geological Survey Professional Paper 938. 

TN490.P7M4 553'.422'097984 76-2393 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 

Stock Number 024-001-027844 
CONTENTS 

Page 

Abstract ___--------------------------------------- 1 

Introduction ........................................... 1 . . Location of district ___--_------------------------------ 1 

Early and recent surveys _--_--__---------------------- 1 

Discovery, mining, and prospecting _--------------------- 

Acknowledgments-__----------------------------------- 

Geography -- ------ ------------ -------- -- ---- -------- -- ---- 

General geology-___-__--------------------------------------- 

Bedded rocks -__-____---------------------------------- 

Late Paleozoic(?) rocks __-__-_--______------------- 

Lavas andtuffs__-_________------------------------ 

Intrusive rocks -_____-__------------------------------- 

Ultrabasic rocks -____--_-__----------------------- 

Unconsolidated deposits _-_--_-____--------------------- 

Geomorphology -_-__-_---_----------------------------- 

Economic geology_-__-_------------------------------------ 

Platinum metals _-__-__--_______---------------------- 14 . . Composition -_-___-_-__-_-_-__-------------------- 14 

Analyses _--_-_---------------------------------- 15 

Impurities and dross -_-_-______------------------- 16 

Special chemical investigations __------------------ l7 / 

Page 

Economic geology-Continued 

Platinum placers -_-_---------------------------------- 22 

Analytical data__---------------------------------- 22 

Sieve and chemical analyses -__-__------------------ 23 

Localities of placer deposits -___-____--------------- 23 

Tributaries of Salmon River __-__-______-_------ 23 

Platinum Creek ____-_________-------------- 23 

Fox Gulch and upper Platinum Creek __---- 23 

Squirrel Creek ............................ 24 

Lower Platinum Creek ___----------------- 25 

Last Chance, Boulder, and Dowry Creeks ____ 26 

Clara Creek _----------------------------- 26 

McCann Creek ............................. 27 

Salmon River_--_------------------------------ 27 

Pay streak of valley floor ___--------------- 28 

Bench paystreak __------------------------ 31 

Placer gold -__----------------------------- 34 

Alluvial concentrates --___----------------- 35 

Platinum lodes ____------------------------------------ 39 

Selected references ____-_---------------------------------- 41 

ILLUSTRATIONS 

Page 

FIGURE 1. Sketch map of part of southwestern Alaska showing location of Goodnews Bay district .......................... - 2 

2. Geologic map of the Goodnews Bay platinum district, Alaska -_____-_________--------------------------- 3 

3. Sketch map of placer mining claims in the valley of Salmon River and its tributaries showing path of dredge along pay 

streaks___________-_----------------------- 6 

4-9. Photographs showing: 

4. Panoramic view of west side of Susie Mountain and upper valley of Salmon River ........................ 8 . . 5. Panoramic view of west side of Red Mountain ridge 9 

6. Thorsen Mountain, the upper valley of Platinum Creek, and camp of Goodnews Bay Mining Co. ------------ 9 

7. Camp of Goodnews Bay Mining Co. and the upper valley of Squirrel Creek __------------------------------ 9 

8. Low gravel terrace in lower valley of Salmon River extending from Happy Creek to Chagvan Bay ---------- 10 

9. Lower valley of Smalls River .............................................. 10 

10-14. Graphs showing: 

10. Mean size of platinum grains by claims and production curve for pay streak of valley floor, Salmon River -- 29 

11. Mean analyses of four platinum metals by claims and units for pay streaks of valley floor and bench, Salmon 

River _-_-___-------------------------------------- 30 

12. Mean size of platinum grains by units and production curve for bench pay streak, Salmon River_--_-------- 32 

13. Gold production by claims and units for two pay streaks, Salmon River ___-_----------------------------- 34 

14. Variation in composition of platinum metals from streams that drain Red Mountain ridge 40 

TABLES 

Page 

TABLE 1. Chemical analyses of ultrabasic rocks, Red Mountain ridge .................................................. 1 

2. Chemical analysis of cation of cooperite .......................................... 14 . . 3. Electron microprobe analysis of osmiridium ...........................................

15 
IV CONTENTS 

Page 

TABLE 4. Complete chemical analyses of two samples of platinum metals ........................................ 16 

5. Principal alloy for dredge cleanups of 1943 --_----_-_--_------_--------------------- 18 

6. Osmiridium alloy for dredge cleanups of 1943 ----_----__----------------------------- 18 

7. Principal alloy for dragline excavator cleanups of 1943 ___--___---------__--------------------- 18 

8. Osmiridium alloy for dragline excavator cleanups of 1943 -_-_-__---------__---------------------- 18 

9. Analysis of screened sample of platinum metals, Discovery claim, Salmon River ---_-___-__--_-------------------- 20 

10. Screened sample of platinum metals, recomputed free of gold and impurities, Discovery claim, Salmon River ------ 20 

1l.iMagnetic subfractions of fraction VIII ---------__-_-___----------------------- 20 

12.Chemical data on subfraction VIII-g ---------------_~__---------------------- 20 

13. Computation of principal alloy, fraction VIII _____--~---__--__-_--------------------- 21 

14. Percentages of platinum metals, gold, and impurities, Goodnews Bay district -_-__-_---__-__-_-_----------- 22 

15. Analyses of precious metals, Fox Gulch and upper Platinum Creek ............................................. 24 

16. Analyses of precious metals, Squirrel Creek ----_--__-_-__-------------------------- 25 

17. Analyses of precious metals, valley of Platinum Creek -__------------------------------------------ 26 

18. Analyses of precious metals, Boulder and Dowry Creeks ............................................. 26 

19. Mean analyses of precious metals, Clara Creek _-_-~-----________---------------------- 27 

20. Comparison of platinum metals from streams on east flank of Red Mountain ridge ............................... 27 

21. Mean sizes of platinum grains by claims, pay streak of valley floor, Salmon River ................................ 29 

22. Mean values of platinum analyses by claims, pay streak of valley floor, Salmon River ............................ 29 

23. Mean sizes of platinum grains by units, bench pay streak, Salmon River ........................................ 32 

24. Mean granularity of platinum metals in two pay streaks, valley of Salmon River _-___-__-__--_-_-__--------- 33 

25. Mean values of platinum analyses by units, bench pay streak, Salmon River -----_--_--__--__------------------- 33 

26. Distribution of gold by claims and units two pay streaks, valley of Salmon River _-___~-__-___--~---------------- 34 

27. Mean mineral content of alluvial concentrates ---_-__--_----------------------------------- 38 
PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, 

ALASKA 

ABSTRACT 1 between 0.19 and 0.27 grain of platinum metals per cubic yard of 

Platinum placers were discovered in 1926 in a small area south of 

Goodnews Bay, in southwestern Alaska. Beginning in 1927, the 

placers were worked for 7 years by small-scale mining methods; in 

later years dragline excavators and a dredge were utilized. These 

deposits are important, not only because they are of high grade but 

because they are the only commercial source of platinum metals in the 

United States. 

The bedded rocks of this area are sedimentary and volcanic rocks of 

late Paleozoic(?) age that have been intruded by a variety of ultrabasic 

rocks. The platinum metals of the placers have been derived from a 

mass of dunite and related rocks that constitute the bedrock of Red 

Mountain in the upper valley of the Salmon River. The western 

headwater tributaries ofthis stream are the fluvial conduits that have 

produced all the placers in the valley of the river. 

The principal placers lie in two pay streaks, one in the valley floor of 

the Salmon River and the other in an ancient stream channel along 

the east side of this valley. The stream-channel deposit, called the 

bench pay streak, was formed in early Pleistocene time; its alluvial 

materials consist largely of clay derived from an ancient moraine 

believed to be of Nebraskan age. The valley-floor deposit, called the 

pay streak of the valley floor, consists of alluvial materials of fluvial 

and glaciofluvial origin whose ages range from Yarmouth to 

Holocene. Both channels contain high-grade placers that have yielded 

a large volume of platinum metals. 

The platinum metals of these deposits are contained mainly in two 

alloys intergrown in a pseudoeutectic fabric. The major alloy is mainly 

platinum, with a small amount of iridium, still smaller amounts of 

rhodium and palladium, and probably some osmium and ruthenium. 

The minor alloy is dominantly iridium and osmium with less 

platinum and still less ruthenium and rhodium. The compositions of 

these two alloys are somewhat variable but tend to approach constant 

mean values. A small amount of free gold is recovered with the 

platinum metals. In addition to these two alloys, minute amounts of 

five platinum minerals have been identified. The weighted mean 

percentages of platinum, iridium, osmium, ruthenium, rhodium, 

palladium, and gold, as mined from 1936 to 1972, are respectively 

82.25, 11.32,2.15,0.17, 1.30,0.38,and2.43. 

The lodes from which these placers have been derived are, or have 

been, localized in the Red Mountain ridge, where the principal rocks 

are dunite and serpentinite. No lodes have been recognized, either 

because the platinum metals are sparsely distributed or because a 

large part of the platiniferous rock has been eroded. It is known, 

however, that the amounts of iridium, osmium, and ruthenium, or of 

osmiridium, decrease from south to north. Other generalizations 

regarding the composition and granularity of these metals have been 

deduced. The size and shape of the platinum lodes may have ranged 

from diffuse disseminations to high-grade concentrations in small 

loci. Under certain assumptions, the tenor of platinum metals in the 

dunite can be roughly approximated. Utilizing two totally different 

methods of computation, the mean tenor has been estimated to lie 

dunite, or 0.014 to 0.023 gram per stere. No large low-grade deposits of 

commercial value are likely to be found, but it is possible that some 

small high-grade concentrations occur. 

INTRODUCTION 

LOCATION OF DISTRICT 

Goodnews Bay is an inlet from Bering Sea on the west 

coast of Alaska, about 180 miles northwest of the 

Alaska Peninsula and about 100 miles south of the 

mouth of the Kuskokwim River (fig. 1). The Goodnews 

Bay platinum district is bounded on the west by 

Kuskokwim Bay, on the north by Goodnews Bay, and on 

the east and south by the Kinegnak River and its 

tributaries (fig. 2). The geologic map (fig. 2) covers an 

area of about 242 square miles, lying approximately 

between lat 58"48' and 59'03' N. and long 161'32' and 

161'55' W. This map is essentially the same as that 

published in U.S. Geological Survey Bulletin 918 but is 

assembled on a new base having a scale of 1:63,360. 

EARLY AND RECENT SURVEYS 

The earliest exploration by the Geological Survey in 

this region was in 1898 under the leadership of Spurr 

(1900), who traversed the Kuskokwim River from its 

headwaters to its mouth and continued then up the 

Kanektok River, down the Togiak River, and eastward 

along the coast of the Alaska Peninsula. In 1919, an 

area north and northeast of Goodnews Bay was visited 

and mapped by a Geological Survey party who produced 

topographic and geologic maps on a scale of 1:250,000. 

The geology and mineral resources were described by 

Harrington (1 921). 

Interest in this district was revived in the twenties 

with the discovery of platinum placers south of 

Goodnews Bay, subsequently developed and mined. In 

1937, the ~eblo~ical survey sent a topographic and 

geologic field party into the Goodnews Bay area to 

prepare maps and study the mineral deposits. A 

topographic map on a scale of 1:62,500 was prepared by 

FitzGerald and a geologic map was made by Mertie 
0 100 200 MILES 

FIGURE 1.-Sketch map of part of southwestern Alaska showing location of Goodnews Bay district. 

(1940a), who also described the general geology and 

placers and gave the character and composition of the 

platinum metals. Reconnaissance work was done in this 

region in 1946-53 by Hoare and Coonrad (1961a,b), who 

published geologic maps of the Hagemeister Island and 

Goodnews quadrangles on a scale of 1:250,000. The 

latest contribution to the geology of the Goodnews Bay 

district is a paper by Porter (1967) on the glacial history. 

The dredge now operating in the valley of the Salmon 

River was being built when the fieldwork of 1937 was 

underway. Mining by the dredge and dragline excavators and concurrent underground exploration by 

drilling have produced much additional information on 

these platinum deposits. The mining and subsurface 

data of the report published in 1940 are now outdated 

and obsolete, although the geologic map and the 

descriptions of the geologic formations are still valid. In 

order to bring the economic data up to date, Mertie 

revisited this district in 1966, 1968, and 1969. The 

Goodnews B,ay Mining Co. has cooperated by making 
INTRODUCTION 3 

FIGURE 2.-Geologic map of the Goodnews Bay platinum district. 
4 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

available to the writer all the company's mining records 

since 1934. 

Small quantities of platinum metals have been 

recovered as a byproduct of gold placer mining at 

numerous places in Alaska; the Goodnews deposits are 

important because they are the only placers in Alaska 

or elsewhere in the United States that have been 

worked primarily for their content of the platinum 

metals. A small amount of gold has been recovered with 

the platinum metals. Chemical examination of the 

rocks from which the platinum is derived, as well as the 

concentrates recovered in placer mining, shows the 

presence in bedrock of chromium, copper, and nickel, 

but no commercial lodes of these elements or of the 

platinum metals have yet been found. 

DISCOVERY, MINING, AND PROSPECTING 

The history of the original discovery of platinum in 

the Goodnews Bay district, together with a sketch of 

earlier mining operations, is given by Reed (1933). 

According to his account, platinum was discovered in 

1926 at the mouth of Fox Gulch, a tributary of Platinum 

Creek, by an Eskimo named Walter Smith. Thinking 

that the metal was "white gold," Smith related his 

discovery to another native called Henry Whuya, who 

communicated this information to Charles Thorsen, a 

local resident and miner in this district for many years. 

Thorsen went to the site of the discovery, panned some 

of the metallic material, and sent it to the office of the 

U.S. Bureau of Mines at Fairbanks, where it was 

analyzed and determined to contain platinum. In 1928, 

Thorsen discovered platinum in the gravels of Clara 

Creek, and in the same year Edward St. Clair made the 

first discovery of platinum on Squirrel Creek. 

The complete history of the early mining in this 

district has not been recorded, but small-scale mining 

plants are known to have been operated on Platinum, 

Squirrel, and Clara Creeks and on Fox and Dry Gulches 

intermittently from 1927 to 1934. Numerous details of 

these operations have been recorded elsewhere (Reed, 

1933) and will not be repeated here. 

Most of the earlier mining was done in the headwaters of Platinum and Clara Creeks, where the ground 

was shallow enough for small-scale mining methods, 

such as ground sluicing and shoveling into sluice boxes. 

It soon became evident to the several small operators 

that although this was a promising field, mining would 

have to be done on a large scale to exploit the deeper 

deposits. Consequently, the many mining claims began 

to be consolidated and passed eventually into the 

control of two concerns, the Clara Creek Mining Co. and 

the Goodnews Bay Mining Co. 

The Clara Creek Mining Co., the smaller of these two 

concerns, acquired ownership or leases to about 20 

1 claims located mainly in the valley of Clara Creek and 

' in the valley of the Salmon River between the mouths of 

Clara and Platinum Creeks. This company, using a 

dragline excavator, began in 1936 to work the east end 

of claim 1 above Discovery (1A),1 Clara Creek; they 

worked upstream until this pay streak was mined out. 

Thereafter they mined the pay streak of Dowry Creek, a 

small stream about half a mile south of Clara Creek. 

Some work was done on Dry Gulch, a tributary of 

Platinum Creek, but at the end of 1940 or 1941 all 

mining operations by this company were terminated. 

The Goodnews Bay Mining Co. began work with a 

dragline excavator on Squirrel Creek in August 1934 

and continued such mining for 7 years until most of the 

placers of Platinum Creek, Fox Gulch, and Squirrel 

Creek were worked out. Marginal ground remained, 

however, not worked at that time. Meanwhile, two pay 

streaks were found and staked in the valley of the 

Salmon River, one in the valley floor and the other along 

the eastern wall of the valley. The mining of these. two 

pay streaks has been the principal activity in the 

Goodnews Bay Mining district. 

The Goodnews Bay Mining Co. gradually acquired 

title to most of the claims staked in the valley floor and 

along the bench of the Salmon River, aggregating about 

150 claims, and obtained leases on other claims that it 

did not own. All the mining claims on the Salmon River 

and its tributaries are shown on the sketch map of 

claims, figure 3. From 1942 to 1957, the Goodnews Bay 

Mining Co., starting on the Association bench claim 

opposite claim 9A, worked downstream on the bench 

with a dragline excavator. In 1937, however, the 

company built a dredge on the upper end of claim lB, 

which has operated continuously since that time 

(Sawin, 1938). The path of the dredge from the date of its 

construction to the present time is shown on the claim 

map of figure 3. From its original site, the dredge 

worked upstream to claim lA, then turned, working 

downstream to claim 7B, where in 1942 it turned again 

and worked upstream to claim 6A. In 1947, it turned 

again and worked downstream to claim 2A where in 

1949 it moved eastward onto what is hereinafter 

designated as the bench pay streak. From the Ethel 

bench claim, the dredge moved sinuously but generally 

southward across the Palladium, Osmium, Ruthenium, 

Rhodium, Platinum, and Iridium bench claims to 

Discovery claim of Snow Gulch. From 1955 to 1963, it 

worked southward to the Olson bench claim where, even 

though 40 feet of overburden was being removed by a 

large dragline excavator, the alluvial cover became too 

thick for economic mining and the dredge moved 

westward to the pay streak of the valley floor. From 

claim 10B the dredge worked upstream to the upper end 

'Claims are numbered above (A) or below (B) Discovery 
GEOGRAPHY 5 

of claim 8B, where in 1964 it turned and began working 

downstream. In 1966, at the lower end of claim 15B, the 

dredge turned again and continued upstream in a final 

cut to claim 5B. In 1972, it moved eastward to the bench 

pay streak, where it is now working old tailings and 

areas of unworked marginal ground. 

The bench pay streak south of the Olson bench claim 

has not been abandoned and is being thoroughly 

prospected by drilling in order to outline the southern 

end of the pay streak. Because of the thickness of the 

overburden, new methods will be required for mining 

this deeper ground. 

The feasibility of reworking the bench tailings was 

tested in 1966 by the construction of an experimental 

plant, called the "mudhog," which was installed on the 

bench pay streak opposite claim 4B, Salmon River. This 

unique operation was necessary because many of the 

grains of platinum enclosed in indurated clay of glacial 

origin that had not disintegrated under weathering and 

did not disintegrate in the trommel screen of the dredge 

were not recovered. Hence in the "mudhog" it was 

necessary to crush both the clay and associated gravels, 

as the two were not separable. This was an expensive 

operation, yet the plant, operated for only one summer, 

returned a profit. 

Unworked ground remains in the valley floor from 

claim 6A to claim 11A; this area will probably be mined 

by a dragline excavator. A similar operation started in 

1968 is the mining of the pay streak of Platinum Creek 

from the mouth of Squirrel Creek upstream to and 

possibly beyond the mouth of Dry Gulch. 

The principal source of the platinum metals in this 

district is the mass of ultrabasic rocks that forms the 

ridge known as Red Mountain. All headwater 

tributaries of the Salmon River that drain the east side 

of this ridge were found to be platinum bearing. 

Consequently, the western side of Red Mountain also 

was of interest, and in 1936 and 1937 considerable 

exploratory drilling was done in a triangular area 

bounded by the Smalls River, Red Mountain, and 

Kuskokwim Bay, particularly in the valleys of Seattle 

and Last Chance Creeks. A dozen or more holes were 

drilled by various operators to depths ranging from 30 to 

110 feet; bedrock was reached in only a few of these, and 

no platinum was found. Platinum was reported from one 

of these drill holes, but it was later established that this 

report was false. Small amounts of platinum have been 

found along the beach of Kuskokwim Bay, but no 

workable deposits have been located. 

A little platinum was found and recovered in later 

years from a small cirquelike opening in the west flank 

of the Red Mountain ridge about 1 mile north of the low 

saddle between the head of Platinum Creek and 

Kuskokwim Bay. A drill hole sunk in the valley of the 

Smalls River along the north side of the gravel road, 

about 2.6 miles S. 52" E. of Platinum, reached bedrock at 

a depth of 192 feet and yielded both platinum and gold; 

this discovery did not lead to the location of any 

workable ground. 

The early small-scale mining operations from 1927 

through 1934 are estimated to have yielded about 3,000 

troy ounces of platinum metals. From 1934, when 

large-scale mining began, to the end of 1972, the 

production is believed to have been well over half a 

million ounces, with a maximum yield in 1938 of about 

32,000 ounces. 

ACKNOWLEDGMENTS 

The four principal owners of the Goodnews Bay 

Mining Co. gave every possible service in the preparation of this report. They made available all their data on 

mining and prospecting and furnished a complete 

record of all screen and chemical analyses on cleanups, 

together with the localities corresponding to these 

cleanups. Ed Olson, a vice-president of the company, 

cooperated in many ways, acting not merely as host but 

as a guide and field helper. Charles J. Johnston, 

treasurer of the company, has for 38 years kept the 

writer informed on current mining operations and has 

provided detailed annual reports of the company's 

production, allocated to the six platinum metals and 

gold. Finally I am most grateful to the owners for their 

hospitality at the time of my last visits to the property in 

1966, 1968, and 1969. 

Other officers and employees of the company have 

been equally cooperative. Gene D. Connor, secretary of 

the company, and Mrs. Connor, who has charge of the 

separatory work in the laboratory, have been very 

helpful. The writer is greatly indebted to the company's 

mining engineer, Joseph F. Fisher, for his useful 

suggestions, his cooperation in the acquisition of 

samples, and many other contributions. 

For technical advice and certain analyses mentioned 

in the text, I am greatly indebted to John Cochrane of 

the Cochrane Laboratories, formerly of Tuckahoe, New 

, York. I am also indebted to George E. Desborough and 

I Edward Dwornik, of the U.S. Geological Survey. 

Specific contributions of these men are credited in later 

sections of this report. 

GEOGRAPHY 

The region lying between the southwestern parts of 

the Nushagak and Kuskokwim River valleys (fig. 1) 

may be divided into three physiographic provinces. In 

the central part of this region are high rugged 

mountains like the Tikchik and Ahklun Mountains, 

some of which have altitudes of 5,000 feet or more. This 

alpine province, intensely glaciated during the Pleis- 
PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

161°45' 

FIGURE 3.-Sketch map ofplacer mining claims in the valley of Salmon River and its tributaries showing path of dredge along pay streaks. 
GEOGRAPHY 
8 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

tocene Epoch, was the source of numerous glaciers that 

discharged through the master valleys, mainly to the 

west and south; some of these glaciers reached the coast 

and moved farther west into the Bering Sea. The 

glaciated mountains and deep glacial lakes of the 

Tikchik Mountains have been described by Mertie 

(1938). Between this alpine province and the coast is a 

piedmont province consisting of low and smoother hills 

that attain altitudes of 1,000 to 3,000 feet, decreasing in 

height toward the sea. Valley glaciers have occupied 

these hills, and at an early stage in the Pleistocene 

Epoch, a large part of this province is believed to have 

been covered with ice. Thus the piedmont province 

shows features of both glacial and nonglacial origin. At 

many places, a low foreland, nearly devoid of relief, lies 

between the low hills and Kuskokwim Bay, the third or 

coastal province of the region. 

The Goodnews Bay district lies mostly within the 

piedmont province; a triangular foreland southeast of 

Platinum and a similar area from the mouth of the 

Salmon River into the valley of the Kinegnak River lie 

within the coastal foreland. Red Mountain, altitude 

1,887 feet, is the northern part of a ridge that lies 

between the Salmon River and Kuskokwim Bay, 

extending from Platinum Creek northward to the valley 

of the Smalls River. Susie Mountain (fig. 4), altitude 

1,805 feet, together with its environs, constitutes the 

northern part of another ridge roughly parallel to Red 

Mountain that forms the eastern limit of the valley of 

the Salmon River. 

Red Mountain, the highest part of the ridge and 

closest to the sea, is the most prominent landmark in 

this area. The eastern slopes of the mountain are 

moderately steep, the maximum slope on the spurs 

being about 25-30 percent. The western slopes are much 

steeper; where the mountain rises directly from the sea, 

the slopes are precipitous, rising about 1,500 feet in half 

a mile (fig. 5). Several cirquelike basins are present at 

and near the heads of Last Chance and Seattle Creeks. 

Cirquelike basins border the eastern side of Susie 

Mountain, in the headwaters of Fog Creek; the 

uppermost part of the valley of Susie Creek, which 

drains southeastward from Susie Mountain, is a 

similar, though less well developed, basin. 

Two mountains of lower altitude are conspicuous 

features along the valley of the Salmon River. Thorsen 

Mountain (fig. 6), altitude 1,110 feet, is about 3 miles 

south of Red Mountain. Kemuk Mountain, about 3 

miles S. 16" W. of Susie Mountain and a little higher but 

less prominent than Thorsen Mountain, is merely a flat 

dome on the ridge that forms the eastern boundary of 

the Salmon River. 

The Goodnews River (fig. I), flowing westward to 

Goodnews Bay, is the master stream of this region, and 

one of its tributaries, the Smalls River (fig. 2), bounds 

the Goodnews mining district on the north. The Salmon 

River (fig. 2) heads against the central valley of the 

Smalls River and flows S. 20" W. for about 7 miles, then 

S. 60" W. for about 1 mile, discharging into Kuskokwim 

Bay. The Salmon River has several tributaries from 

both sides of its valley; the most important of these are 

the western headwater tributaries that drain the 

eastern slopes of Red Mountain. These tributaries, from 

south to north, are Platinum Creek with its tributaries 

Fox Gulch, Dry Gulch, and Squirrel Creek, succeeded 

northward by Last Chance, Boulder, Dowry, and Clara 

Creeks. Still farther north is McCann Creek, which 

discharges into the Smalls River. All these streams are 

platinum bearing, and five of them were found to have 

workable placers. Medicine Creek is the only large 

eastern tributary of the Salmon River. 

Goodnews and Chagvan Bays (fig. 2) are shallow tidal 

estuaries that indent the coast of the Bering Sea and 

represent drowned or flooded valleys. Two sand spits, 

FIGURE 4.-Panoramic view of west side of Susie Mountain and upper valley of Salmon River. View northeast. 
GEOGRAPHY 9 

FIGURE 5.-Panoramic view of west side of Red Mountain ridge. View south-southeast. 

FIGURE 6.-Thorsen Mountain, viewed from northeast, showing 

upper valley of Platinum Creek and camp of Goodnews Bay Mining 

Co. 

called the North Spit and South Spit, mark the entrance 

to Goodnews Bay. The settlement of Platinum, at the 

southeast end of the South Spit, is connected with the 

camp of the Goodnews Bay Mining Co. by a 9-mile-long 

gravel road. Another gravel road leads 3 miles 

northward from Platinum to the tip of the South Spit, 

where the company's oil tanks and dock are located. 

Goodnews Bay has a maximum width of 7 miles, an 

entrance 3,700 feet wide, and a devious channel 8-12 

feet deep to the head of the bay. A drill hole, at a site 

about 2,000 feet south of the north shore, was driven 

through clayey sediments reaching bedrock at a depth 

of about 180 feet below water level. Similar conditions 

prevail at Chagvan Bay, where drilling on a sand spit 

west of the bay showed bedrock at a depth of 244 feet. 

These figures indicate that sea level at some time 

during the Pleistocene Epoch was 180-235 feet below 

the present sea level. The maximum depth to bedrock, 

and therefore the maximum lowering of the sea level, 

has not been determined. 

The valley of the Salmon River is nearly straight, and 

its width between the bounding ridges is 3-4 miles. The 

floor of the valley ranges in width from 500 to 2,000 feet; 

it is narrowest about 2,000 feet upstream from the 

mouth of Medicine Creek and widest, except at its 

mouth, in the short stretch between Medicine Creek and 

Snow Gulch. The average gradient of the valley floor, 

from the mouth of Clara Creek to the mouth of Happy 

Creek, is about 32 feet per mile, or about 0.6 percent. 

The western headwater tributaries of the Salmon River 

are of principal economic interest. The largest of these 

tributaries is Platinum Creek with its tributary 

Squirrel Creek. The camp of the Goodnews Bay Mining 

Co. is located in the valley of Squirrel Creek (fig. 7). The 

largest eastern tributary of the Salmon River is 

Medicine Creek. 

The valley of the Salmon River is asymmetrical in 

cross section with a gentle slope on the east side, 

whereas on the west side the river tends to cut against 

FIGURE 7.-Panoramic view showing camp of Goodnews Bay Mining Co. and the upper valley of Squirrel Creek. 
GENERALGEOLOGY 11 

between these two hardrock units is therefore rather 

indefinite. 

The lavas are predominantly basalts with a smaller 

proportion of andesites, and the tuffaceous rocks are 

petrographically similar. Owing to replacement by 

secondary minerals such as chlorite and epidote and to 

albitization of the feldspars, the exact petrographic 

character of the lavas is obscure, although some of the 

basalts are clearly porphyritic. The accessory minerals 

of the lavas are chiefly iron ores altered to iron 

hydroxides but include apatite and sphene. The tuffs are 

greenish fragmental rocks believed to represent volcanic ejectamenta, partly waterlaid and partly of 

subaerial origin. The age of the lavas and tuffs is 

indeterminate, but they appear to lie conformably 

above the argillaceous and siliceous rocks and are 

therefore considered to be probably late Paleozoic in 

age. 

INTRUSIVE ROCKS 

Two principal masses of ultrabasic rocks are present 

in this district. The larger of the masses forms the 

elongate ridge known as Red Mountain, which lies west 

of the headwaters of the Salmon River. This mass trends 

about N. 20" E. and has a length of about 6 miles, a 

maximum width of 1.9 miles, and an area of about 7.3 

square miles. It is the source of practically all the 

platinum metals that have been found on the Salmon 

River and its tributaries. The smaller intrusive body 

crops out in a belt that lies west of Susie Mountain and 

trends N. 40" E. This mass is predominantly perknite 

and is not a major source of the platinum metals in the 

valley of the Salmon River. 

Granitic intrusive rocks along the southeastern side 

of the upper valley ofkhe Smalls River occupy a belt that 

trends N. 57" E. with a known lengths of about 45 

miles. These rocks consist of adamellite (quartz monzonite), granodiorite, and tonalite (quartz diorite); they 

are unrelated to the platinum placers but may be one of 

the sources of the placer gold in the deposits. 

ULTRABASIC ROCKS 

The intrusive body at Red Mountain is essentially a 

dunite with peripheral borders of perknite; it is altered 

surficially to yellowish brown. The unaltered dunite is a 

black to greenish-black rock that consists almost 

entirely of olivine with minor amounts of monoclinic 

pyroxene and iron ores. Some of the olivine is replaced 

by serpentine, at some places to the extent that it may 

be called serpentinite. Disseminated iron ores consisting of magnetite, ilmenite, and chromite are scant in the 

dunite, but concentrations of such ores are locally 

present, as between the heads of Squirrel Creek and Fox 

Gulch, where residual cobbles are found. 

Two complete chemical analyses of the dunite of Red 

Mountain were made by E. T. Erickson, of the U.S. 

Geological Survey: one (A) of a composite sample of 

fresh unaltered dunite, with a representative content of 

marginal perknitic rocks, and one (B) of the oxidized 

shell that forms a veneer on these ultrabasic rocks 

(table 1). 

TABLE l.-Chemzcal analyses, in wezght percent, of ultrabaszc rocks, 

Red Mountazn rzdge 

[Analyst, E T Erlckson, N D = not detected] 

SiOz ---__---------_______-_-__---- 39.20 38.54 

Ah03 ---_-_-----_-_-_____---------- 1.50 .78 

Fez03 ---_-_-------______-_--------- 3.10 5.29 

FeO ________-_____-_--------------_- 7.35 5.99 

MgO __________---___-__--_-------- 37.79 42.29 

CaO ____-_____-_-------------_--_--- 5.66 .34 

NazO __-_________-__-___-------_--_ N.D. N.D. 

KzO_-----__-------_-_-_---_-_------ N.D. N.D. 

H20+ _-__---------______-_--_------ 5.81 5.53 

H20- -_______________-_-----------_ .19 .43 

TiOz ---___ ---- --- _ _______- ------ -- .05 .14 

Cm03 --__-_-------______--- -- ------ .27 .13 

MnO _-___ _ _-_-__ ----_--- ---- --- --- .01 .01 

NiO _______ _______ ---- ----- --- -- -- -- .077 .053 

CuO --_-__----_-__--_-_--- - ---- .007 .004 

Total _--___--~-_--__---__---- 100.014 99.527 

A L'ndltered dun~te and rrknire tcom o,~te sample B. Oxidized illell on ulrrLa3ir rocks o&d ioLnraln. 

Sample A was taken primarily to ascertain the 

composition of the ultrabasic rocks. Although the rock 

was tested for the platinum metals, it was realized that 

the platinum-metal content would probably be too low 

for detection by ordinary analytical methods. For such a 

determination it would be necessary to take a large 

sample of 50-100 pounds, to crush and mill this sample, 

and then concentrate the accessory minerals contained. 

Such a sample, however, might yield an abnormally low 

content, as all the available data indicate that the 

platinum metals are not evenly disseminated throughout the dunite but tend to be concentrated at certain 

loci. 

The presence of chromite (Crz03) shown by the 

chemical analyses is significant, as the placers contain 

platinum nuggets that are intergrown with or have 

adhering chromite. Moreover, chromite constitutes a 

small but significant part of the accessory minerals 

recovered with the platinum metals. In an analysis of 

pebbles of chromite recovered from the placer concentrates made by E. T. Erickson, the tenor in platinum 

metals was found to be 0.05 troy ounce per ton of 

chromite. Ilmenite and chromite are not readily 
12 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

separated magnetically, as the magnetic susceptibility 

of ilmenite is only slightly greater than that of 

chromite. The magnetite is known to contain small 

amounts of the platinum metals, and for these reasons 

all the iron ores are crushed, milled, and concentrated in 

order to recover the contained platinum metals. 

UNCONSOLIDATED DEPOSITS 

Unconsolidated or alluvial deposits of Quaternary 

age are spread over a large part of the district; these 

include morainal, glaciofluvial, fluvial, eluvial, residual, marine, and eolian deposits. The most extensive 

are those of fluvial and glaciofluvial origin and the 

reworked morainal debris. These deposits are not 

mappable genetically but are divided approximately 

into older and younger deposits, essentially of Pleistocene and Holocene age. 

The older alluvial deposits consisting largely of 

glaciofluvial or outwash deposits lie in the valley 

bottoms of the larger streams, such as the Smalls, 

Kinegnak, and Unaluk Rivers, where they are covered 

by younger fluvial deposits, but they extend upward 

onto the lower spurs and ridges to altitudes of 250-500 

feet. Moraines constitute a part of the older deposits; 

included with these are most of the residual and eluvial 

deposits. In the aggregate, the older deposits occupy 

about a fourth of this district. 

Older alluvial deposits occupy a large part of the 

valley of the Salmon River, but the original glacial 

debris has been generally reworked to form both older 

and younger fluvial deposits. An ancient glacier that 

overrode this district left a moraine in the valley of the 

Salmon River; after the retreat of the ice, this morainal 

material was reworked by an ancient stream whose 

channel now occupies an alluvial-filled depression 

along the east wall of the Salmon River. Thi.: channel 

was discovered by drilling and was opened by mining; 

its older fluvial deposits were found to be mainly clay 

with smaller amounts of sand and gravel. These 

reworked morainal deposits are platiniferous and 

constitute what is now designated as the bench pay 

streak. Glaciofluvial deposits of later origin are present 

at the upper and lower ends of the Salmon valley. 

Younger alluvial deposits form the valley floors of all 

the principal rivers and their tributaries; with these 

belong the eolian and marine deposits. The younger 

deposits of the Salmon valley are mainly of fluvial 

origin and consist largely of materials of local origin; 

they include reworked glaciofluvial debris at the head of 

the valley and similar materials at its southern end. 

The alluvial deposits in the valley of Platinum Creek 

and its tributaries consist of gravels and related 

alluvium derived from the ultrabasic rocks of Red 

Mountain and from adjacent sedimentary and igneous 

rocks. The differences in the origin of these deposits are 

reflected in the accessory minerals recovered from the 

alluvial sands and gravels. 

GEOMORPHOLOGY 

Geomorphology deals with the history of surficial 

geologic changes as revealed by the interpretation of 

physiographic landforms and is therefore essential for 

an understanding of the history and formation of 

placers. Within the Goodnews Bay district glaciation 

has been one of the most effective erosional and 

depositional agencies. Eustatic rise and fall of sea level 

during the Pleistocene Epoch also were controlling 

factors. But it is not generally possible to closely 

correlate the erosional events in the Salmon Valley 

with changing base levels of erosion caused by eustatic 

changes in sea level, because local base levels of erosion 

produced by glaciation and glacial deposits had commonly more effect than changing sea levels. Numerous 

statements regarding the geomorphic history will be 

made herein without presenting proof, but these 

statements are adequately substantiated by data that 

are revealed in the description of the two pay streaks in 

the valley of the Salmon River. 

All glaciation in western Alaska was formerly 

referred by geologists, including the writer, to the 

Wisconsin Stage of the Pleistocene Epoch. Multiple 

Pleistocene glaciations were first recognized by the 

writer on Seward Peninsula during the summer of 1940 

and within a month were confirmed at Nome (McNeil 

and others, 1943, p. 6$76). This reopened the entire 

Pleistocene history and led to the recognition of four 

glaciations, generally correlative with those present 

elsewhere in North America. 

Four major glaciations and three major interglaciations have been recognized throughout the world as 

distinctive of the Pleistocene Epoch. Glaciations 

accepted in the United States south of Canada are 

Nebraskan, Kansan, Illinoian, and Wisconsinan; the 

interglaciations, designated in the same order, are 

Aftonian, Yarmouth, and Sangamon. The short span of 

time succeeding the Wisconsin glaciation is now called 

the Holocene Epoch, although this may represent 

merely the beginning of a fourth interglaciation. These 

designations are applied sequentially in the Goodnews 

Bay district merely to indicate the order of the 

glaciations and interglaciations, with no intention of 

correlating closely with the same intervals elsewhere in 

North America. 

The duration of the Pleistocene and Holocene Epochs 

has been variously estimated, but the tendency in 

recent years has been to lengthen the span of time 

accepted in earlier appraisals. In a chronology based 

upon the frequency of Globorotalia menardii in deep-sea 
sediments, proposed by Ericson and Wollin (1968), the 

spans of the four glaciations, from oldest to youngest, 

are charted graphically as approximately 275,000, 

475,000, 175,000, and 180,000 years. The durations of 

the interglaciations, including the post-Wisconsin or 

Holocene Epoch, are 325,000, 360,000, 160,000, and 

50,000 years, a total of 2 m.y. 

The history of the Pliocene Epoch is too obscure to 

warrant any definite statements regarding its climate, 

erosional history, and physiographic development. The 

general altitude of the hills was doubtless much greater 

than that of the present hills, as the available evidence 

suggests a general rate of erosion of about 0.0001 foot 

per year (Dole and Stabler, 1909). This, together with 

the latitude of this region, suggests the existence of 

some alpine glaciation in the high mountains, but no 

glaciers are believed to have reached the sea. There is 

some evidence, however, that a Pliocene river may have 

occupied the valley of the Salmon River; it is definitely 

known that such a stream existed and persisted as the 

principal drainage channel during the Nebraskan 

glaciation and throughout the Aftonian Interglaciation 

in a channel that now occupies a depression in the east 

wall of the valley of the Salmon River. 

The earliest regional glacier, believed to have been of 

Nebraskan age, advanced from the east and not only 

filled the preexisting valley but overrode all but the 

summits of the bounding walls of this valley. Moving 

athwart the course of a narrow valley, this glacier 

probably did not erode to bedrock, and therefore any 

preexisting placer platinum metals that were close to 

bedrock or within the crevices of bedrock were 

undisturbed. Similar conditions are known in certain 

placer deposits south of the Alaskan Range. In melting, 

this glacier left a large valley moraine, which was later 

reworked into a clayey fluvial deposit that has 

persisted, with incipient induration, to the present time 

and now constitutes the principal alluvium in the bench 

channel of the valley of the Salmon River. 

This ancient valley has had a complex history. After 

the retreat of the Nebraskan ice, the valley was drained 

by two streams, one flowing northward, the other 

discharging southward to the Kinegnak River; the 

lower course of Platinum Creek drained northeastward 

to the north-flowing stream, thus producing a backhand 

or "chulitna" drainage. This inference is based upon 

high iridium values in the placers of the bench channel 

north of Medicine Creek. Later, probably during the 

Aftonian, the drainage of the north-flowing stream was 

captured by the south-flowing stream, and the alluvial 

divide between these two streams was obliterated. The 

altitude of the bedrock floor of this ancient valley was 

unrelated to the regional rate of erosion but instead was 

controlled by various local base levels of erosion that 

existed throughout the early Pleistocene, as determined 

both by glaciation and by changing sea levels. Eventually this ancient stream developed a very broad valley, 

with a bedrock gradient higher than that of the present 

valley floor. 

Kansan Glaciation is believed to have existed in this 

region, but its history is obscure because the succeeding 

Illinoian Glaciation destroyed most of its glacial 

deposits. This situation is analogous to the obliteration 

of the evidence for pre-Wisconsin glaciation by Wisconsin ice south of the Alaska Range. One suggestion of the 

presence of Kansan Glaciation and the existence of 

Kansan outwash deposits at the south end of the valley 

of the Salmon River relates to the distribution of gold in 

the placers of the present valley, as later described. 

Kansan ice is believed to have reached the ancient 

oceanic shoreline, both in the valleys of the Smalls 

River and of the Kinegnak River. The total effect of 

Kansan Glaciation is not really known, but one result 

was the creation ofa new stream channel in the valley of 

the Salmon River. Either by damming or by excessive 

alluviation in the old channel, or both, the river in the 

old Aftonian channel was gradually shifted westward 

and was superposed upon its western bedrock wall so 

that a new stream channel began to be carved. The 

resulting stream was ancestral to the present Salmon 

River. A new pay streak, thus begun during the 

Yarmouth Interglaciation, has been continuously in 

process of development since that time. 

Illinoian Glaciation was clearly present in this 

district, and glaciers that reached the sea occupied the 

valleys of the Smalls and Kinegnak Rivers. The valley 

of the Salmon River was not glaciated, yet important 

effects were produced at both ends of the valley. At its 

upper end, the Smalls River lobe of the Goodnews 

glacier deposited erratic boulders at the north end of the 

Red Mountain ridge up to an altitude of 825 feet, but the 

ice was shunted seaward, scouring the west side of Red 

Mountain and removing any platinum deposits that 

may have been present. In the retreat of the Goodnews 

glacier, thick deposits of glaciofluvial materials were 

deposited at the head of the valley of the Salmon River, 

and a considerable part of these deposits have been 

reworked to produce many of the fluvial deposits of the 

present Salmon River. At the lower end of the valley of 

the Salmon River, the Unaluk glacier overrode a hill 

with an altitude of 677 feet south of Kemuk Mountain 

and another hill with an altitude of 575 feet about 2 

miles south of Thorsen Mountain. The most important 

effect of the Unaluk glacier was that it scoured out and 

thereby destroyed the southern end of the valley pay 

streak on claim 15B (fig. 4), north of the mouth of Happy 

Creek. That it did not destroy the old bench pay streak is 

doubtless due to the much greater depth of that channel. 
14 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

The Sangamon Interglaciation appears to have been a 

time of alluviation in the valley of the Salmon River, 

owing to a rising base level of erosion. The materials for 

the fluvial deposits came largely from the hills on both 

sides of the valley but also from the Illinoian glaciofluvial deposits at the head of the valley. These deposits 

contained little or no clay except on claim 4B (fig. 4) 

where, for a short distance, the bench and stream 

deposits are laterally contiguous and clay was contributed by erosion of the bench deposits. 

The Wisconsin Glaciation has not been satisfactorily 

resolved within this district. Porter (1967), from his 

studies of the glacial deposits at the head of the Salmon 

River and in the lower valleys of the Kinegnak and 

Unaluk Rivers, believes that the Wisconsin was 

characterized by an early and a late advance of glacial 

ice separated by a relatively short time interval; to 

these substages he assigned the local names Unaluk 

and Chagvan. It is unlikely that either of these glacial 

lobes reached the ancient shoreline. Erosion and 

sedimentation were more directly controlled by oceanic 

base levels of erosion during the Sangamon, Wisconsin, 

and post-Wisconsin than during the earlier glaciations 

and interglaciations; the overall effect has been the 

broadening and alluvial filling of the valley of the 

Salmon River. 

ECONOMIC GEOLOGY 

PLATINUM METALS 

COMPOSITION 

The precious metals of the Goodnews placers include 

the six platinum metals and gold. Platinum is the 

principal metal recovered; the other platinum metals 

are iridium, osmium, ruthenium, rhodium, and palladium. The average content of gold is only 2.4 percent 

of the output. Detailed data giving the percentages of 

each of the precious metals, as annually produced from 

1936 to 1972, are given in another part of this report. 

The platinum metals occur mainly as two alloys, 

known on the basis of abundance as the principal (or 

major) alloy and the minor alloy. The principal alloy is 

designated by the generic name platinum, although it 

contains the five other platinum metals; the minor alloy 

is called osmiridium. These two alloys were initially 

recognized in polished sections of grains and nuggets 

(Mertie, 1940a), intergrown in a pseudoeutectic fabric. 

They subsequently have been found to contain minute 

inclusions of certain platinum minerals and a number of 

rock-forming minerals; one platinum mineral has been 

found that is not a part of either alloy. Both alloys have 

variable compositions such that specific mineralogical 

names are not warranted. The ratio of these alloys is 

variable within the placers and is inconstant in 

different lodes. They are so intimately intergrown that 

it is almost impossible to obtain samples of each alloy 

suitable for chemical analysis. Electron-probe analyses 

and related disciplines, though less accurate, appear to 

be the most feasible methods for approximate determinations of composition. 

The platinum alloys react differently with inorganic 

acids and other reagents than do the purified metals. 

These reactions are not quantitatively predictable 

because they depend upon the compositions of the alloys 

wherein these metals occur. Pure platinum is not 

attacked by the common inorganic acids but is dissolved 

in aqua regia, though less readily than gold. Pure 

iridium and rhodium are only partly soluble in aqua 

regia, and osmium and ruthenium are quite insoluble. 

Palladium is soluble in aqua regia but is also dissolved 

by hot nitric or sulfuric acid. The platinum alloys, 

however, behave differently. 

The physical and chemical properties of the platinum 

metals were fully described in an earlier publication 

(Mertie, 1969), and a new compilation of some of these 

properties was made by Johnson, Matthey & Co., Ltd. 

(1972). The magnetic susceptibility of the platinum 

metals, especially of the alloys, is an important 

practical criterion, as it bears directly upon the 

separation of these alloys from one another and from the 

accessory black sand recovered in placer mining. In 

general, osmiridium has a much smaller magnetic 

susceptibility than the principal alloy. Theoretically 

this should provide a method for separating very fine 

grains of the two alloys for chemical analyses. Actually, 

this method is impracticable because both alloys 

contain minute inclusions of magnetite, although such 

inclusions are more plentiful in the principal alloy. An 

attempted electromagnetic separation by this method, 

however, yielded a hitherto unrecognized platinum 

mineral, later identified as cooperite. This is an 

iron-gray to black cubic mineral with a metallic luster, 

a density of about 10.0, and a very low magnetic 

susceptibility. It is insoluble in aqua regia and on 

ignition decomposes to a sponge. A chemical analysis of 

its cation is shown in table 2. 

TABLE 2.Ahemical analysis, in percent, of cation 

of cooperite 

[Analyst, John Cochrane, Cochrane Laboratories] 

p~ 

Platinum _____------------------------- 93.77 

Rhodium -_-_ _-__ _- - ----- ---- -- --- -- --- .69 

Palladium _______--------------------- 4.21 

Nickel -____--____--------------------- 1.00 

Copper-____---___--------------------- .15 

Iron -______--____--------------------- Trace 

Cobalt -___________-------------------- Trace 

Silver -___________-------------------- Trace 

Unaccounted for __-------------------- .18 

Total ___-_--_---_--__-------------- 100.00 
ECONOMIC GEOLOGY 15 

The anion was not determined quantitatively but was 

found to consist mainly of sulfur, with a significant 

amount of arsenic and a trace of antimony. The formula 

may therefore be written as (Pt, Pd, Ni) (S, As). This 

differs from Cooper's formula of 1926 in that palladium 

precedes nickel and arsenic is added to sulfur. 

The five least electromagnetic subfractions of the 

sample, as obtained by a Frantz separator, contained 

variable amounts of cooperite and both alloys; from 

these, numerous grains of osmiridium were handpicked 

under the microscope by John Cochrane for study and 

analysis. Two distinct types of osmiridium were 

recognized: 

Type A. Well-formed hexagonal plates ranging generally in diameter from 3.5 to 14.3 microns with a 

maximum diameter of 28 microns. These plates have 

a relatively constant platinum content of about 2.5 

percent and an 1r:Os ratio of about 0.5. An examination under high magnification showed that these 

hexagonal plates occur in parallel sheets separated by 

a lesser number of nonparallel platelets. The preferred orientation of the larger plates appeared to 

coincide with the major orientation of some of the 

included crystals of magnetite. 

Type B. Small to large irregular-shaped grains erratically distributed in the principal alloy, generally 

typified by a platinum content of 10 percent and an 

1r:Os ratio greater than 5.0. This type constitutes on 

the average about 80 percent of the osmiridium 

present in the five subfractions and probably in 

general for the Goodnews product. 

The osmiridium problem was studied in another way 

by Edward Dwornik, of the U.S. Geological Survey. A 

nugget owned by the writer had been cut and polished so 

that it clearly showed the irregular grains of 0smiridium, with a silvery luster and high relief, 

embedded in the principal alloy. The osmiridium 

contained minute inclusions of magnetite, but the 

principal alloy contained more inclusions of magnetite 

and some of chromite. Utilizing electron probe spectroscopy, Dwornik and his assistants made an approximate 

analysis, as show in table 3. The content of platinum in 

TABLE 3.-Electron microprobe analysis, in percent, 

of osmiridium 

[Analyst, Edward Dwornik] 

Platinum .............................. 15 

Iridium --------_--__-_--____----------- 48 

Osmium ----------------__-_----------- 26 

Ruthenium -_-__--_-------__--__------- 1 

Rhodium -----------__-_--_------------ 4 

Paladium -------------_--_-------------Trace 

Iron _-------------_--_---------------- 2 

Copper -----__--__--------------------- 1 

Total ---------_--_-_--_---------- 97 

this analysis correlates fairly well with the type B 

osmiridium as determined by Cochrane, but the 1r:Os 

ratio is 1.85, which is closer to the type A osmiridium. 

Possibly the osmiridium of the nugget was a mixture of 

types A and B. 

Laurite was identified by Leonard, Desborough, and 

Page (1969) in osmiridium contained in a nugget from 

the Goodnews Bay district. This mineral, with a 

formula given as RuS2, is very hard and occurs in 

roundish equant subhedral to irregular grains embedded in osmiridium. Three other minerals of the 

platinum-group metals have been identified by G. A. 

Desborough (written commun., 1970) in the principal 

alloy. One of these is a new iridium-palladium sulfide 

with a composition that is approximately 68 percent 

iridium, 14 percent palladium, and 18 percent sulfur. 

The second mineral consists of a few grains of sperrylite. 

The third is a new mineral to which the name of 

mertieite has been assigned (Desborough and others, 

1973). It has a composition of Pd5(Sb,As)2 and contains 

about 0.5 percent copper. The grains range in size from 

0.10 to 0.50 mm; most are smaller than 0.25 mm. 

Mertieite is a brassy yellow mineral with a density of 

about 11.6 and a hardness comparable to that of 

magnetite. It is distinctly anisotropic with a symmetry 

that suggests a classification in the monoclinic system. 

ANALYSES 

Bulk samples of the platinum metals are prepared for 

analysis and for subsequent refining by treating them 

with hot aqua regia. In this procedure, most of the 

platinum, parts of the iridium and rhodium, and all the 

palladium are dissolved; but the osmium and 

ruthenium, and parts of the platinum, iridium, and 

rhodium that are alloyed with them, are unaffected and 

are rendered soluble by treatment with an alkaline 

oxidizing reagent. The completed analysis invariably 

shows a percentage of so-called impurities, which 

represent the alloyed dross, the mineral inclusions, and 

a part of the black sand that was not completely 

removed from the product before analysis. These 

impurities include also the dross of the gold and any 

lead shot, solder, or similar materials not recognized 

and removed by the producer. Silver, alloyed with the 

gold, is not ordinarily determined and is therefore 

included with the impurities. As recent investigations 

have shown that the two alloys contain minute grains of 

magnetite, ilmenite, chromite, and a number of other 

minerals, the true dross, or alloyed base metals, is 

difficult to determine precisely. 

Chemical analyses of the platinum metals are 

laborious and costly. Matthey-Bishop, Inc., (the American branch of Johnson, Matthey & Co., Ltd.), Baker & 

Co., (now a branch of Englehard Industries, Inc.), D. C. 
16 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

Griffith & Co., and a few other concerns of this caliber 

are competent analysts of the platinum metals. Many 

high-grade analyses have been made by the U.S. 

Bureau of Standards, in particular by Raleigh Gilchrist 

and his, coworkers. But analysts capable of making 

high-grade platinum analyses do not always make 

them, either because they are not needed or because 

the cost may be prohibitive; even if such analyses are 

made, it may not be to the advantage of the producer or 

the buyer to publish them. Relatively few high-grade 

platinum analyses are presented in the foreign literature. 

Chemical analyses of the platinum metals are of 

different orders of dependability and are here divided 

into two general classes, designated as superior and 

inferior analyses. Superior analyses are considered to 

be those wherein the percentages of all six of the 

platinum metals are shown, with or without the dross. 

Hundreds of such analyses have been made by 

Matthey-Bishop, Inc., of the platinum metals produced 

by the Goodnews Bay Mining Co., and some have been 

made by other analysts. Inferior analyses are of several 

types having varying degrees of dependability. 

IMPURITIES AND DROSS 

The platinum metals differ physically from gold in 

many respects. Gold has few if any inclusions of other 

minerals; the platinum metals have many such inclusions. Gold is diamagnetic and may therefore be readily 

separated magnetically or electromagnetically from the 

black sand recovered in placer mining. As most of the 

platinum metals are paramagnetic and some are 

ferromagnetic, the black sand must be separated by 

mechanical methods and a small part remains unseparated. The platinum metals, unlike gold, cannot be 

melted, either by the producer or the refiner, owing 

partly to their high melting points but particularly to 

the fact that osmium sublimates by heating, giving off 

the poisonous gas Os04, thus causing a metallic loss; to 

a lesser degree, ruthenium also sublimates. After all the 

platinum metals are in solution, the solute contains not 

merely the six platinum metals but also their dross and 

inclusions as well as a part of the unseparated black 

sand. 

The true dross of the platinum metals is therefore 

generally indeterminate, and an overall component 

called impurities is tabulated with the analyses. Free of 

black sand, the alloyed dross can be determined 

approximately except for the contained mineral inclusions. For this purpose, Charles J. Johnston handpicked 

two samples of platinum metals free of black sand, and 

these were analyzed completely by Matthey-Bishop, 

Inc. The gold was not removed from these samples, as its 

content of dross would have been negligible. The two 

analyses are shown in two forms, A and B, and are 

recomputed free ofgold and silver as A1 and B1 (table 4). 

The total mean content of iron and copper for these 

two samples is shown to be 8.77 percent; this includes 

not only the amounts of these two elements alloyed with 

the platinum metals but also any increments from 

included iron ores and the minute increment of dross 

from the gold. The stated percentage is therefore a 

maximum value and serves to prove that the principal 

alloy is not the alloy ferroplatinum, which contains 

10-30 percent iron. 

This analysis serves also for obtaining the fineness of 

the gold recovered with the platinum metals. Native 

gold, with alloyed silver, contains a very small 

percentage of alloyed base metals (mainly iron and 

copper), designated as dross (D); the fineness of the gold 

(F) is defined by the equation F=AulAu + Ag + D, 

where F is stated in parts per thousand. Another useful 

ratio, particularly for gold recovered from lodes, is 

AuIAu + Ag, but this fails to show the content of dross 

and is therefore not a proper definition of fineness. 

Accepting the conventional value for the dross of gold as 

1 percent, which is close to its mean content in placer 

gold, a recomputation shows the fineness of this gold to 

be 932. This value is unusually high for placer gold, as 

the mean value for Alaska has been shown by Mertie 

(1940b) to be about 870. The increment is probably due 

to the reduction in size of the grains of gold produced by 

glacial transportation and the resulting solution of 

surficial silver. 

The inclusions that occur in the platinum metals and 

are not properly a part of the true, or alloyed, dross have 

been studies by John Cochrane. In 1963, he separated 8 

TABLE 4.4omplete chemical analyses, in percent, of two samples of 

platinum metals free of black sand 

[Analyses by Matthey-Bishop, Inc.] 

Trace Trace 

.03 .03 

.09 .09 

.11 .ll 

Trace 

.04 

---- 

8.33 

.40 

Trace 

.04 

A,, B,, recomputed free of gold and silver. 
ECONOMIC GEOLOGY 17 

of 20 granules of the principal alloy, choosing under 

high magnification those with uniformly smooth surfaces devoid of cracks, cavities, or external signs of 

adhering intergrowths. These eight granules were 

separately dissolved in aqua regia, and after decanting, 

the residues were dried and studied in order to establish 

approximately the proportion of osmiridium in the 

sample and to identify the included minerals. The eight 

solutes were then combined and analyzed. The weighted 

mean values of the resulting fractions were found to be 

those shown below: 

(Percent) 

Soluble platinum group metals ........................ 85.34 

Soluble base metals _ - - _ _ - - _ - - - - -- - - - - - - - - - - - - - - - - - - - - 10.98 

Insoluble platinum group metals ___--_---------------- 1.15 

Insoluble base minerals --_ _---------- ------ ----- --- -- 2.53 

The insoluble metals and minerals proved to be of great 

interest, as they included osmiridium and 11 mineral 

species. The components identified microscopically are 

listed below: 

Osmiridium. Irregular grains up to 0.3 mm in size 

with some brilliant hexagonal plates, both separate 

and as complex growths. A few grains were 

attached to crystals of enstatite; a few grains occur 

in tiny veinlets. 

Enstatite. In grains up to 0.7 mm in size. 

Chromite. Several brilliant octahedra and a lesser 

number of complete or nearly complete crystals 

with somewhat dull facets and fragments. 

Rutile. One good crystal and some fragments. 

Tremolite. One group of transparent colorless acicular crystals. 

Epidote. One perfect brilliant dark-greenish-black 

crystal, 0.12 mm long and 0.055 mm thick. Verified 

by interfacial angles. 

Spinel. Several brilliant flattened crystals, blue or 

green by transmitted light. One opaque reddishbrown octahedron, slightly modified by the cube. 

Sphene. One tan-colored perfect crystal. 

Diamond. A perfect dodecahedron with curved faces, 

dark reddish black, and 0.081 mm in size. Also a 

transparent pale straw-colored octahedron 

0.093 mm in size, modified by the cube. 

Tourmaline. One singly terminated brilliant darkgreen crystal. 

Topaz. Straw-colored fragments. 

Corundum. One dark-blue crystal found in a different 

sample. 

The five platinum minerals that have been identified, 

the two types of osmiridium intergrown with the 

principal alloy, and the 11 minerals that occur as 

inclusions clearly show the complexity of these 

platinum alloys. 

SPECIAL CHEMICAL INVESTIGATIONS 

A fundamental problem in chemical investigations is 

the composition of the two alloys. In 1943 John 

Cochrane made an attempt to solve this problem. His 

method was based upon the premise that the principal 

alloy consisted solely of the four cubic metals, platinum, 

iridium, rhodium, and palladium, all of which could be 

dissolved in hot aqua regia. On the other hand, he 

believed that platinum, iridium, and rhodium, when 

alloyed with the hexagonal metals osmium and 

ruthenium, constituted a completely insoluble mixture. 

If true, this would have provided an elegant method for 

separating the two alloys and for determining their 

compositions. It was necessary merely to dissolve the 

placer metals and to analyze separately the solute and 

the insoluble residue. This is not literally true, but it is 

sufficiently close to the truth that its application, as 

proposed and utilized, yielded very valuable information. 

The Goodnews Bay Mining Co. dredge, working 

upstream in the valley floor of the Salmon River in 1943, 

was operated on the upper (northern) end of claim 6B, 

throughout the length of claim 5B, and on the lower 

(southern) end of claim 4B, at a mean distance of about 

6,000 feet downstream from the mouth of Platinum 

Creek (fig. 4). Samples were taken of the 24 cleanups 

made within this stretch, of which the soluble and 

insoluble fractions were analyzed separately. During 

the same period, a dragline excavator was working on 

the upper (northern) end of the bench pay streak, 

opposite the mouth of Dowry Creek and east of claim 9A. 

The 15 cleanups of this operation were similarly 

sampled and analyzed. Thus 78 superior analyses were 

made, which, recomputed free of gold and impurities, 

are shown in tables 5,6,7, and 8. The symbols S and I, 

shown in tables 5 and 7, refer to the weights of the 

metals recovered in the soluble and insoluble fractions. 

The operating sites of the dredge and dragline 

excavator were fortunately located. The metals recovered by the dredge were derived dominantly from the 

valley of Platinum Creek, with a smaller increment 

from the upper valley of the Salmon River upstream 

from the mouth of Platinum Creek. Hence this product 

represents mainly the platinum metals that came from 

bedrock at the southern end of the Red Mountain ridge. 

The metals recovered by the dragline excavator came 

almost entirely from the valleys of Dowry and Clara 

Creeks, or their ancestral predecessors, and therefore 

represented the platinum metals eroded from the 

northern end of the Red Mountain ridge. These two 

factors lend the greatest significance to these two sets of 

chemical analyses. 

The Cochrane hypothesis implies that the principal 
18 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

TABLE 5.-Principal alloy, in percent, for dredge cleanups of 1943 

Cleanup No. 

S ratio 

Pt IT Rh I '* (soluble: 

insoluble) 

Mean ----___- 95.68 

TABLE 6.4smiridium alloy, in percent, for dredge cleanups of 1943 

Cleanup No. Pt Ir 0s Ru Rh 

Mean ---__--- 

alloy is composed of the four cubic platinum metals, 

with no osmium or ruthenium. It also implies that no 

platinum, iridium, or rhodium, which form a part of the 

osmiridium, can be dissolved by aqua regia, even on the 

TABLE 7.-Principal alloy, in percent, for dragline excavator 

cleanups of 1943 

Cleanup No. 

Insoluble) 

Mean -__--__- 95.56 2.87 1.09 .48 12.29 

TABLE 8.4smiridium alloy, in percent, for dragline excavator 

cleanups of 1943 

Cleanup No. Pt Ir 0s Ru Rh 

Mean -------- 11.21 66.15 17.54 1.23 3.87 

surficial faces of the placer grains. It is probable, 

however, that very small amounts of osmium and 

ruthenium may constitute a part of the principal alloy, 

occuring in complex phase relations. And it is unlikely 

that the cubic metals of the osmiridium are entirely 

unaffected by aqua regia, though undoubtedly most of 

them are immune to chemical solution. These aberrant 

factors cannot be exactly evaluated; nevertheless, the 

working hypothesis on which these analyses were made 

has yielded valuable information that could not 

otherwise have been obtained. 

The overall tenors of platinum are known to increase 

and those of iridium to decrease moving upstream in the 

valley of the Salmon River. These facts are shown in 

table 22 and in figure 11. The 25 analyses of the output 

from the dredge, even though they represent little more 

than a claim length, tend to show this same relation. 
ECONOMIC GEOLOGY 19 

The most significant result of this analytical work, 

however, is that the principal alloy and the osmiridium, 

for the outputs of both the dredge and the dragline 

excavator, tend toward two constant compositions that 

depart little from the mean values of the contained 

metals. This will be evident from a comparison of tables 

5 and 6 with tables 7 and 8. Therefore the only 

reasonable explanation for the differences in the bulk 

compositions of the platinum metals in the placers is 

that these represent different ratios of two alloys of 

nearly constant composition. This interpretation is 

corroborated by the S:I ratios in tables 5 and 7, which in 

turn, explains the changes in the composition of the 

platinum metals from south to north on the Red 

Mountain ridge, as discussed later on a quantitative 

basis. 

Another specialized chemical investigation of these 

platinum metals was undertaken to learn whether the 

compositions of the two alloys might vary with 

granularity. For this purpose the Goodnews Bay Mining 

Co. provided the writer with a sample of 365.5 grams of 

the platinum metals recovered in 1945 from the 

northeastern part of Discovery claim, about opposite the 

mouth of Platinum Creek. This sample was screened 

into 14 fractions, ranging in size from grains larger than 

3.96 mm to grains smaller than 0.06 mm in diameter; 

these fractions were weighed by John Cochrane (at that 

time Chief Chemist of Matthey-Bishop, Inc.). The 

largest fraction, No. VIII, weighing 90.9455 grams and 

consisting of grains 0.50-0.35 mm in diameter, was 

later divided magetically and electromagnetically into 

seven subfractions. Subfraction VIII-a, which was 

ferromagnetic, was separated by the use of a 2% inch 

Dings alnico horseshoe magnet. Subfractions VIII-b to 

VIII-f were separated by the use of a large electromagnet, using currents of 0.042,0.084,0.126,0.167, and 1.2 

amperes. Subfraction VIII-g was the residue not held by 

the electromagnet. Fraction VIII was therefore not 

analyzed directly; its composition was computed indirectly from its seven subfractions. Unlike commercial 

analyses, the parts of each fraction and subfraction that 

were soluble and insoluble in aqua regia were analyzed 

separately in order to secure all the data that were 

possibly obtainable. Thus 40 superior analyses were 

made by C. J. Johnson, a chemist employed by 

Matthey-Bishop, Inc.; the cost was born jointly by the 

Goodnews Bay Mining Co. and Matthey-Bishop, Inc. 

The results of this work are shown in table 9. As the gold 

and impurities have very little significance in the 

conclusions drawn from these analyses, they were 

eliminated by a recomputation of the platinum metals 

alone, as show in table 10. 

A recomputation of table 9 from percentages to grams 

reveals that the greatest volume of platinum, rhodium, 

and palladium and also of the metals of the solute (S) 

occurs in fraction VIII, in grains or aggregates with a 

mean diameter of 0.42 mm; the corresponding weights 

are 67.0996,1.0913,0.3092, and 68.7475 grams. On the 

other hand, the volumetric maxima for iridium, 

osmium, and ruthenium and those for the metals 

insoluble in aqua regia (I) occur in fraction IX, in grains 

or aggregates with a mean diameter of 0.30 mm; the 

weights are respectively 11.2955, 2.3614, 0.1653, and 

14.1764 grams. As platinum, rhodium, and palladium 

represent approximately the principal alloy and 

iridium, osmium, and ruthenium constitute a major 

part of the osmiridium, it follows that the grains and 

aggregates of the principal alloy are appreciably larger 

than those of the osmiridium. Another feature of 

interest is that most of the gold occurs in fraction VII, 

with a mean diameter of 0.60 mm. Hence the grains of 

gold are larger than the grains or aggregates of the 

platinum metals, although this is not necessarily true 

throughout both pay streaks. 

Recomputed values (table 10) show marked but 

irregular variations in the composition of the platinum 

metals with regard to granularity, notably in fractions 

11,111, XII, XIII, and XIV. These aberrations are related 

to the parameter K = S1Z and indicate clearly that these 

fractions contain abnormal additions of osmiridium. 

Such increments are too large to be regarded as 

haphazard, but the reason for their existence is 

unknown. It is apparent, however, from the contents of 

metals in the other fractions that no distinct correlation 

exists between composition and granularity other than 

in the discrepancies caused by irregular increments of 

osmiridium. 

The magnetic subfractions of fraction VIII, given in 

table 9 as percentages, have been recomputed to grams 

in order to clarify certain relations and are shown in 

table 11. 

This recomputation shows that only 4.3 percent ofthe 

platinum and 4.1 percent of the palladium are in the 

ferromagnetic subfraction VIII-a. The largest volumes 

of platinum and palladium are in subfractions VIII-c 

and VIII-d, which have a fairly strong paramagnetism 

commensurate with the magnetic susceptibilities of 

these two metals. Obviously, therefore, the ferromagnetism of fraction VIII-a results from a large number of 

inclusions of magnetite. Subfractions VIII-d, VIII-e, 

VIII-f, and VIII-g show decreasing paramagnetism 

owing to the progressive elimination of the principal 

alloy by magnetic action. Subfraction VIII-g is accepted 

as the most probable composition of the osmiridium 

contained in the screened sample shown in table 10. The 

reasons for this interpretation are the low paramagnetism, the high content of iridium, the low content of 

platinum, and the total absence of palladium. The 
20 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

TABLE 9.-Analyses, in percent except as indicated, of screened 

[Analyst, C. J. Johnson, 

Weight Screen size, S Total metals and impurities 

(g) (mm) Au Pt Ir 0s Ru Rh Pd Impurities 

Sieved fraction 

V _______-__________ 22.3650 1.39>S> .99 3.64 75.48 7.27 1.27 .11 1.22 .40 10.61 

VI -_-___________-_ 29.7026 .99>S> .70 2.62 76.58 7.53 1.29 .10 1.22 .35 10.31 

VII ---_------------ 77.3894 .70>S> .50 1.69 77.13 7.79 1.40 .10 1.23 .34 10.32 

VIII ________________ 90.9455 .50>S> .35 1.29 73.78 10.91 1.81 .16 1.20 .34 10.51 

IX -__-__--___-____ 78.7142 .35>S> .25 1.01 70.21 14.35 3.00 .21 1.24 .31 9.67 

X _____-__-_______-_ 35.1331 .25>S> .18 1.05 69.88 14.14 3.01 .21 1.21 .33 10.17 

XI -_-__________-__ 13.3072 .18>S> .12 1.70 70.37 12.12 2.34 .17 1.07 .36 11.87 

XI1 -_-________-_--_ 1.8053 .12>S> .09 3.22 64.35 8.94 2.58 .17 .95 .40 19.39 

XI11 --__-_--_-__-_-- .4056 .09>S> .06 3.90 65.29 5.30 3.01 .26 1.12 .42 20.70 

XIV __-~___~_______- .I415 .06>S 4.15 62.09 3.52 4.88 .39 1.65 .44 22.88 

Total _____--_ 365.5335 Weighted mean __-__- 1.57 73.40 10.86 2.06 .16 1.22 .34 10.39 

Magnetic subfraction 

VIII-a __-____-__-___ 3.5106 Alnico magnet 0.00 82.11 1.71 0.29 0.04 0.89 0.36 14.60 

VIII-b _____________- 9.3850 Mgt.-.042 ampere .OO 82.70 2.99 .56 .05 1.04 .40 12.26 

VIII-c - __- _-_ _ __ __- _ 24.3440 ,042 -.084 ampere .OO 83.22 3.91 .59 .04 .99 .36 10.89 

VIII-d __________-__ 22.7669 ,084 -.I26 ampere .OO 81.75 5.33 .86 .07 1.14 .37 10.48 

VIII-e _____________ 12.4085 ,126-,167 ampere .OO 79.03 7.94 1.33 .ll 1.35 .36 9.88 

VIII-f __-___-______ 10.4004 .I67 -1.2 amperes .12 66.07 19.14 3.74 .28 1.59 .38 8.68 

VIII-g -__-__________ 8.1301 Residue 14.27 11.12 54.69 8.45 .88 1.65 .OO 8.94 -- 

Total ___-_-__ 90.9455 Weighted mean _-____ 1.29 73.78 10.91 1.81 .16 1.20 .34 10.51 

TABLE 10.Screened sample of platrnum metals, recomputed free of 

gold and rmpurities, Dzscovery clarm, Salmon River 

No We~ght Screen slze, S Pt Ir 0s Ru Rh Pd (grams) (mm) (percent) 

Sieved fraction 

TotalL321.8364 Weighted mean -. 83.37 12.33 2.34 .18 1.39 .39 

Magnetic subfraction 

VIII-a ...... 2.9981 Alnicomagnet 96.15 2.00 0.34 0.05 1.04 0.42 VIII-b 8.2344 Mgt.-,042 ampere 94.23 3.41 .64 .06 1.18 .48 VIII-c ------ 21.6929 ,042-,084 ampere 93.39 4.39 .66 .05 1.11 .40 

VIII-d ----.. 20.3809 ,084-,126 ampere 91.32 5.96 .96 .08 1.27 .41 

VIII-e ...... 11.1825 ,126-,167 ampere 87.69 8.81 1.48 .12 1.50 .40 

VIII-f 9.4852 ,167 -1.2 amperes 72.44 20.99 4.10 .31 1.74 .42 

VIII-e 6.2431 Resldue 14.48 71.22 11.00 1.15 2.15 .OO 

Total .. 80.2169 Weighted mean ... 83.64 12.38 2.05 .18 1.37 .38 

metallic content of subfraction VIII-g and of its soluble 

and insoluble parts, recomputed to grams, are presented 

in table 12. This table shows clearly that parts of the 

TABLE 11.-Magnetic subfractions, in grams, of fraction VIII 

TABLE 12.4hemical data, in ,grams, of subfraction VIII-g 

Pt Ir 0s Ru Rh 

Weight of subfraction VIII-g .......... 0.9041 4.4464 0.6870 0.0715 0.1341 Weight of soluble part ................ ,2105 ,0130 ......... ,0022 

Weight of insoluble part .............. ,6933 4.4335 ,6873 ,0716 ,1323 

platinum, iridium, and rhodium are dissolved by aqua 

regia, the dissolved parts constituting, respectively, 

23.3,0.3, and 1.6 percent, supporting the interpretation 

that the soluble part of any sample represents only 

approximately the composition of the principal alloy. It 

follows that certain percentages of platinum, iridium, 

and rhodium derived by partial solution of the 

osmiridium must be subtracted from the soluble part of 

any sample in order to obtain the composition of the 

principal alloy. Thereafter the metallic content may be 

recomputed to total 100 percent. 

Theoretically, the composition of the principal alloy 
ECONOMIC GEOLOGY 21 

sample ofplatinum metals, Discovery claim, Salmon River 

Matthey-Bishop, Inc.] 

Soluble (S) and insoluble (I) Soluble Insoluble 

S I Dross, Dross, (SII) Pt Ir Rh Pd F't Ir 0s Ru Rh K 

Sieved fraction 

Magnetic subfraction 

84.61 0.79 12.78 1.82 107.101 96.81 1.95 0.82 0.42 25.32 7.59 36.71 5.06 25.32 

85.67 2.07 10.75 1.51 41.386 96.17 2.37 .99 .47 14.98 46.38 27.05 2.41 9.18 

86.05 3.06 10.35 .54 28.121 96.36 2.28 .94 .42 9.80 63.73 19.28 1.31 5.88 

84.80 4.72 9.91 .57 17.966 95.86 2.63 1.07 .44 9.75 65.68 18.22 1.48 4.87 

82.52 7.60 9.32 .56 10.858 94.85 3.49 1.22 .44 10.00 66.58 17.50 1.45 4.47 

67.48 23.72 7.75 .93 2.845 93.79 4.45 1.20 .56 11.72 68.04 15.77 1.18 3.29 

2.77 74.02 .54 8.40 .037 93.50 5.78 .72 .OO 11.52 73.67 11.42 1.19 2.20 

may be obtained by subtracting the weights of the 

metals of the osmiridium from those of the entire 

sample, after both have been recomputed to grams. For 

fraction VIII shown in table 10, this is impracticable 

because parts of the osmiridium are in subfractions 

VIII-a to VIII-f, inclusive, and these increments cannot 

be ascertained from the available chemical data. The 

best that can be done is to assume certain factors, which 

are first multiplied into the metals of subfraction 

VIII-g; thereafter, these products are subtracted from 

the corresponding values of fraction VIII, thus yielding 

several compositions, any one of which may closely 

represent the principal alloy. The factors that have been 

selected for this purpose are 1.6, 1.7, 1.8, and 1.9, and 

the resulting possible compositions of the principal 

alloy are labeled respectively A, B, C, and D in table 13. 

The stated factors were chosen because they yield 

values for platinum and iridium of the correct order of 

TABLE 13.4omputation of principal alloy, fraction VIII 

Possible composition, in percent 

(computation factor) . 

VIII VIII-g A B C D (grams) (grams) 1.6 1.7 1.8 1.9 

Platinum ....--------. 67.0996 0.9041 93.49 94.20 94.92 95.96 Iridium -..-----.----.-. 9.9222 4.4464 4.00 3.40 2.78 2.16 Osmium -.. .. .. .. ...... 1.6461 ,6810 .78 .68 .59 .50 Ruthenium .. ,1455 ,0115 .04 .03 .02 .01 Rhodium -..--..---.-. 1.0913 ,1341 1.25 1.24 1.23 1.22 Palladium ..- .- --.--... ,3092 .. .. -- .44 .45 .46 .46 

I magnitude, after the decrements of platinum, iridium, 

and rhodium, dissolved from the osmiridium, have been 

subtracted from the values of the fraction VIII. From 

these possible compositions, it follows that small 

contents of osmium and ruthenium constitute an 

integral part of the principal alloy. 

The parameter K = S/I was obtained originally from 

the weights of the soluble and insoluble parts of each of 

the fractions and subfractions that resulted from 

screening or magnetic separation. It may also be 

obtained from the percentages of the total, soluble, and 

insoluble parts of any one of the six platinum metals by 

the following method. 

Let W be the weight of any fraction or subfraction and 

A andB be the weights of its soluble and insoluble parts. 

It is obvious thatA = KWIK + 1 and B = WIK + 1. Now 

let Xt represent the percentage of a specified platinum 

metal in one of the fractions or subfractions shown in 

table 10 andX, andXil the corresponding percentages of 

the soluble and insoluble parts of this metal shown in 

table 9. The following identities then apply: 

WXt = weight of the specified metal in the given 

sample, 

KW -. 

K+1 Xs = weight of soluble fraction, same 

W metal, and 

-. 

K +,I Xi = weight of insoluble fraction, same 

metal. 
22 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

Thus, 

KW wxt = - . W Xs + - Xi. K+l K+l 

Eliminating W, we have 

KXs + - Xi xt = --- 

K+l K+1' 

whence 

Xt - Xi K= 

Xs - xt 

PLATINUM PLACERS 

ANALYTICAL DATA 

The volume, distribution, composition, and grain 

sizes of the precious metals found as placer deposits in 

the Goodnews Bay district are of great significance in 

determining the character and occurrence of these 

metals in their bedrock sources. Similar data on the 

platinum lodes are critical to an understanding of the 

mineralization and the discovery of new workable 

deposits. As few such data have been published, the 

economic geology of the platinum metals is therefore 

less well understood than that of many other metalliferous ores. The Goodnews deposits are unique in that the 

owners have made available for publication all the 

pertinent analytic and related data on these placers. 

The data made available include 710 screen analyses 

of the cleanups for the period 1938-70, except for the 

years 194CL41, which are missing, and 995 superior 

chemical analyses of the platinum metals, including 

duplicates by different analysts. Matthey-Bishop, Inc. 

made 871 of these analyses; the remainder were made 

by other concerns. To these should be added the 59 

double analyses (soluble and insoluble fractions) recorded under special chemical investigation~, 20 by 

Matthey-Bishop, Inc. and 39 by John Cochrane. A great 

deal of collateral information has been acquired from 

conferences with the owners and employees of the 

company. 

The numerical data are too numerous to permit their 

complete tabulation or charting, but it is feasible to 

represent them collectively by claims, in order 

downstream. On the bench of the Salmon River, 

however, this scheme was somewhat modified, as the 

dimensions and orientation of the bench claims differ 

from those of the valley floor. Hence a system of 

consecutive "units" was devised whose longitudinal or 

north-south limits correspond approximately with the 

claim lengths of the valley floor. These two collective 

modes of presentation are more for genetic 

interpretations, as minor variations and errors tend to 

cancel one another. 

The tabulations presented are arithmetic means of 

the screen and chemical analyses. The original data for 

granularity are in ounces and fractions thereof, but the 

chemical analyses are in percentages. Accurate mean 

values cannot be obtained by averaging percentages 

arithmetically or 'by any method other than by 

weighting. But weighting is not possible for the 

analytical data, as the weights of the individual 

shipments are not known. However, the weights of the 

cleanups taken at regular intervals are not very 

aberrant, and the character of the metals does not 

change greatly from claim to claim. And as the weights 

of the shipments to the refiner, where the analyses are 

made, are of the same order of magnitude, weighting of 

the analyses is not so urgently needed. For these 

reasons, it is believed that the mean values obtained 

from unweighted tabulations are not greatly in error. 

Annual production data for the years 193672 have 

been made available by the Goodnews Bay Mining Co. 

These data, though presented as percentages, are based 

upon actual weights of the six platinum metals, gold, 

and impurities and are therefore accurate. This 

information, computed into a form suitable for publication, is presented in three forms of table 14. 

TABLE 14.-Percentages of platinum metals, gold, and impurities, 

Goodnews Bay district 

[Based on data from Goodnews Bay Min~ng Co.] 

Year ~t rr os RU ~h PCI AU Impur- ities 

1936 ................ 68.39 12.72 3.24 0.24 1.46 0.23 0.45 13.27 

1937 ................ 64.95 17.29 3.29 .29 1.85 .25 1.08 11.01 1938 ................ 72.19 1.24 2.24 .17 .99 29 1.69 11.19 

1939 ................ 71.54 12.26 2.57 .20 1.16 .31 1.63 10.33 1940 ................ 71.77 12.34 2.56 .19 1.16 .32 1.80 9.86 1941 ................ 72.44 11.05 2.22 .20 1.14 .31 2.01 10.63 

1942 ................ 72.50 10.37 2.14 .16 1.31 .36 2.73 10.43 

1943 ................ 74.68 9.39 1.75 .13 1.21 .36 2.19 10.29 1944 74.67 9.65 1.82 .14 1.21 .37 2 13 10.01 1945 . 73.09 10.30 2.07 .16 1.31 34 2.16 10.57 

1946 ................ 76.24 7.61 1.42 .10 1.12 .39 2.91 10.21 1947 ................ 77.25 5.83 .94 .07 1.01 .3a 3.73 10.79 

1948 ................ 77.47 6.20 1.01 .08 1.04 .39 2.83 10.98 1949 ................ 7.8 7.07 1.22 .lo 1.14 .38 2.54 10.69 1950 . 75.46 9.13 1.59 .14 1.23 .35 1.64 10.46 1951 75.26 9.33 1.76 .14 1.28 .35 1.43 10.45 

1952 ................ 73.23 11.10 2.15 .18 1.30 .33 1.32 10.39 i9~3 . 71.57 12.19 2.45 .19 1.21 .31 1.46 10.62 

1954 ................ 73.31 10.91 2.02 .17 1.19 .34 1.37 10.69 

1955 ................ 74.39 9.83 1.76 .16 1.31 .38 1.69 1048 1956 76.19 8.27 1.10 .10 1.16 .37 1.57 11.24 1957 ................ 75.39 8.26 1.42 1.12 .38 1.70 11.62 1958 ................ 75.03 7.96 1.25 .ll .98 .33 1.70 12.64 1959 ................ 75.22 7.88 1.40 .ii .95 .32 1.98 12.14 

1960 ................ 75.64 7.85 1.34 .ll .89 .36 1.54 12.27 1961 76.19 7.42 1.28 .lo .96 .37 1.68 12.00 

1962 76.16 7.22 1.25 .10 .96 .37 1.82 12.12 1963 ................ 71.83 10.18 1.93 .i5 .98 .33 2.52 12.08 

1964 ................ 69.42 11.92 2.38 .19 1.00 .29 3.11 11.69 1965 ................ 69.80 12.26 2.41 .19 1.01 .29 3.34 11.60 

1966 . 67.62 12.89 2.56 .19 1.04 .28 3.85 11.57 1967 ................ 67.51 12.60 2.59 .la .98 .27 4.17 11.70 

1968 ................ 66.14 13.55 2.72 .19 1.09 .33 4.26 11.72 1969 .. 67.47 12.63 2.35 .19 1.19 .32 4.02 11.83 

1970 . 68.41 10.94 2.06 .17 1.10 .35 4.90 12.07 

1911 ................ 71.41 9.38 1.71 .14 1.09 .36 3.76 12.15 

1972 ................ 68.26 13.87 2.53 .23 1.21 .33 1.60 11.97 

Wi",EA . 73,27 ,15 ,34 2,17 

WzEB 82.25 11.32 2.15 .I7 1.30 .38 2.43 .--- WzbEdC . 84,30 11,60 2,21 ,la ,39 ---- ---- 

i: k~~~~tT~,"~~,"f9$~~ii~puriti

C. R"cOmputed free Of and impurities. 
ECONOMIC GEOLOGY 23 

SIEVE AND CHEMICAL ANALYSES 

Sieve analyses are available only of the precious 

metals recovered from the placers of the Salmon River. 

Of these, 308 represent cleanups from the valley floor, 

and 402 represent cleanups from the bench pay streak. 

Most of these were screened through sieves of sizes 12, 

14, 20, 28, 35, and 48, yielding mean sizes of > 1.40, 

1.28, 1.00, 0.71, 0.50,0.36, and < 0.30 mm respectively; 

a few cleanups were run through 6 and 8 mesh screens. 

Numerous cleanups were screened through a 100-mesh 

sieve with an aperture of 0.15 mm. In such cases the 

mean sizes smaller than 0.030 mm are 0.22 and 

< 0.15 mm. In this paper, the grain sizes are tabulated 

and charted in three sizes: grains of 0.83 mm diameter 

and larger, grains smaller than 0.83 mm and larger 

than 0.42 mm, and grains smaller than 0.42 mm, 

designated respectively as coarse, medium, and fine 

grains. The total range in sizes extends from < 0.15 mm 

to nuggets, of which the largest found weighed about 4 

troy ounces (124.4 grams). 

The mean values of 816 platinum analyses of samples 

from the valley of the Salmon River have been charted 

by claims and units for the years 1937-70. Of these, 404 

represent platinum metals from the pay streak of the 

valley floor, and 412 platinum metals from the bench 

pay streak. Also tabulated are 26 analyses of samples of 

minus 100-mesh grain size (< 0.15 mm diameter), 9 

from the valley floor and 17 from the bench. These 26 

analyses cannot be consistently assigned to particular 

claims or units, as most of them represent accumulations of ultrafines later submitted separately for 

analysis. Weighted by the number of claims from which 

they were recovered, they must be added to the totals in 

order to obtain mean compositions. 

LOCALITIES OF PLACER DEPOSITS 

Platinum lodes have not been located in the Goodnews Bay district even though the bedrock source of all 

platinum placers is known to be the ultrabasic rocks of 

Red Mountain ridge by discovery of platinum placers in 

all the western headwater tributaries of the Salmon 

River that drain this ridge. No other tributaries of this 

river contain platinum metals. The streams draining 

the eastern slopes of Red Mountain are the fluvial 

conduits that have discharged all the platinum metals 

found in the valley of the Salmon River, as the valley 

floor of this river contains no bedrock that could be a 

source of these metals. For this reason, the placers of 

these headwater tributaries are described first, and 

their characteristics will yield a better understanding of 

both the placers of the Salmon River and their bedrock 

sources. 

Two major paystreaks have been discovered and 

mined in the valley of the Salmon River. One of these, 

located on the valley floor, extends from the mouth of 

Clara Creek downstream for approximately 6 miles. 

Contributory pay streaks lie in the valleys of Platinum 

Creek and its tributaries and in Dowry and Clara 

Creeks. A small tributary between Squirrel and Dowry 

Creeks, known as First Chance Creek, contains some 

platinum in its valley but has no workable pay streak. 

The valley of McCann Creek, a tributary of the Smalls 

River, is also platiniferous but has no pay streak. 

A second major pay streak, called the bench pay 

streak, lies in a depression along the eastern side of the 

valley of the Salmon River and has been mined from a 

point opposite the mouth of Dowry Creek downstream 

for about 4.4 miles. The lower or southeastern extension 

of this pay streak has not been mined, owing to the 

thickness of its overburden, but prospecting by drilling 

indicates that it may extend 4 miles farther 

downstream. Remnants of still higher and older fluvial 

deposits with small amounts of platinum are known to 

be present between Snow Gulch and Happy Creek. 

TRIBUTARIES OF SALMON RIVER 

PLATINUM CREEK 

Platinum Creek is a western tributary of the Salmon 

River having an air-line length of about 2 miles; it 

receives three tributaries from the north, in order 

downstream Fox Gulch, Dry Gulch, and Squirrel Creek. 

All are platiniferous, but Platinum Creek above the 

mouth of Fox Gulch is essentially barren of platinum 

metals. The valley of Platinum Creek may best be 

described in three units: upper Platinum Creek above 

the mouth of Squirrel Creek, Squirrel Creek, and the 

lower valley of Platinum Creek below the mouth of 

Squirrel Creek. 

Fox GULCH AND UPPER PLATINUM CREEK 

Fox Gulch heads in the ultrabasic rocks of Red 

Mountain; its pay streak has a length of about 2,600 feet 

extending downstream on Platinum Creek for another 

stretch of 3,300 feet. The early mining on Fox Gulch was 

done in 1927 to 1934, but the whole pay streak of Fox 

Gulch was reworked by a dragline excavator in 1937 

and 1938; a small area at the head of the creek was 

worked in 1941. That part of the upper valley of 

Platinum Creek above the mouth of Dry Gulch was 

mined in 1938, but about 1,600 feet of the pay streak 

below the mouth of Dry Gulch was not worked at that 

time, as this stretch was then considered to be marginal 

ground. Dragline mining of this stretch began in 1968 at 

the mouth of Squirrel Creek and was continued 

upstream to the limit of workable ground. 

The average width of the pay streak on Fox Gulch was 

about 75 feet, but variations in width and depth to 

bedrock have not been recorded. Downstream the pay 
24 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

ultrabasic rock, whereas the bedrock of the valley floor 

of upper Platinum Creek is mainly altered graywacke 

and sheared argillite alternating with lavas and tuffs of 

andesitic character. 

The tenor in platinum metals was highest on Fox 

Gulch; the average tenor is not known. In one cleanup 

on Platinum Creek, however, a short distance below the 

mouth of Fox Gulch, a tenor of 0.03 ounce of platinum 

metals per cubic yard was recorded. Downstream on 

Platinum Creek, the tenors diminished, and in the early 

days of mining, the stretch from Dry Gulch to Squirrel 

Creek was not considered workable. 

The platinum metals occur mainly on the surface and 

in the crevices of bedrock but are also present in the 

lower 3-4 feet of the overlying gravels. The higher 

gravels and other sediments contain little platinum. No 

record has been kept of the granularity of the precious 

metals; but those recovered from Fox Gulch and the 

upper valley of Platinum Creek are known to have been 

fairly fine grained, and nuggets were uncommon. Prior 

to 1937, the largest nugget found weighed only a 

quarter of an ounce; larger ones were later recovered 

from other areas. Some nuggets were found to be 

intergrown with chromite. 

streak became wider, ranging from 100 feet to as much 

as 200 feet at the mouth of Dry Gulch. The gravels of Fox 

Gulch, made up primarily of ultrabasic rokks, are large 

and subangular, averaging 8-12 inches in diameter, 

and include boulders as much as 3 feet in diameter. The 

character and depth of the overburden on Fox Gulch 

have not been recorded, but in the upper valley of 

'latinurn Creek' the consists of 

mately 12 feet of subrounded to subangular gravels 

overlain by 3 feet of CO~~UV~U~ and turf mixed locally 

with sand and eluvial material. These gravels, a 

mixture of ultrabasic intrusive rocks and sedimentary 

rocks, have an average diameter of 5-6 inches but 

include cobbles and boulders of larger size. The bedrock 

in the upper valley of Fox Gulch is predominantly 

Twenty-six analyses are available of the product 

recovered from the head of Fox Gulch to the mouth of 

Squirrel Creek. The exact sequence of the cleanups 

represented by these analyses has not been recorded, 

but six are known to represent the platinum metals 

recovered from the upper valley of Fox Gulch. The mean 

values of these 6 analyses and of 26 analyses from the 

area, together with two others showing maximum and 

minimum values of iridium, are shown in table 15. A 

significant characteristic of the values shown by table 

15 is that the content of platinum increases 

downstream, whereas reciprocally the tenors of iridium, 

osmium, and ruthenium diminish downstream. 

Sample E represents a bulk mixture of intergrowths 

of the principal alloy with osmiridium in a ratio not 

TABLE 15.-Ana1~ses, in percent, of precious metals, Fox Gulch 

and upper Platinum Creek 

~t Ir os RU ~h ~d AU 

A ...-.-..-._... 50.56 39.14 7.74 0.71 1.62 0.14 0.09 

B ...-.---.-_-.. 50.61 39.18 7.74 .71 1.62 .14 ---- 

:::IIIIIII:III z:::: ;::?: :::? .47 1.82 .23 .37 .48 1.83 .23 ..-- 

::::IIIIII:III $:::: ::::: :::: .84 2.29 .20 --.- 

.22 2.09 .31 .. 

A. Mean value of six analyses of the product from the upper valley of fox Gulch, recomputed free of impurities. B. Same as A, recomputed free of gold and impurities. 

C. Mean value of 26 analyses ofthe product from Fox Gulch and from Platinum Creek above the mouth of Squirrel Creek, recomputed free of impurities. D. same as C, recomputed free of gold and impurities. E. Analysls from extreme head of Fox Gulch showing the minlmum content of platinum and the ~mpurities. maximum content of ~ridium, osmium, and ruthenium, recomputedfree ofgold and 

F. Analysis from Platinum Creek, a short distance ahove the mouth of Squirrel Creek, 

showing maximum content of platinum and minimum content of iridium, osmium, and 

ruthenium, recomputed free of gold and impurities. 

accurately determinable. This analysis shows a higher 

content of iridium, osmium, and ruthenium than any 

other sample within the Goodnews Bay district; the 

1r:Os ratio is about 5:1, similar to that found by 

Cochrane for the more commonplace, or type B, 

osmiridium. But the content of platinum is about three 

times as great as that of pure osmiridium found 

elsewhere in the world. A rough calculation indicates 

that the ratio of the principal alloy to osmiridium in 

sample E is about 1:l; the same ratio for sample F is 

approximately 3: 1. 

The percentages of gold from Fox Gulch and the upper 

valley of Platinum Creek increase generally but not 

linearly downstream. The content of gold of the first 10 

analyses range from a trace of 0.20 percent with a mean 

value of 0.05 percent. The next five analyses 

downstream show a range of 0.17-0.42 percent with a 

mean value of 0.30 percent. And the last 11 analyses, 

extending to the mouth of Squirrel Creek, show a range 

of 0.44-1.05 percent with a mean value of 0.65 percent. 

The content of gold is not related genetically to that of 

the platinum metals, as the gold is not of local origin but 

instead is an alien constituent introduced by glaciation. 

Squirrel Creek, the principal tributary of Platinum 

Creek, has a length of approximately 1.6 miles. Heading 

in the Red Mountain ridge, about 1 mile from the head of 

Fox Gulch, this stream flows southeastward for about 

0.7 mile, then turns southward and flows to Platinum 

Creek. This change in course is at the contact between 

the ultrabasic rocks of Red Mountain and the adjacent 

sedimentary rocks. The upper valley of Squirrel Creek 

is a narrow gulch; the lower valley, which contains the 

workable pay streak, is broad and open. 

The gravels are similar to those of Platinum Creek, 

ranging from cobbles and boulders in the upper valley to 

smaller gravels in the pay streak, diminishing in size 
ECONOMIC GEOLOGY 25 

A. Mean value of 22 analyses, recom uted free of impurities. B. Same as A, recom~uted free of eoPd and im~urities. 

downstream. The petrographic character of the gravels 

in the lower valley is largely like that of the underlying 

bedrock, consisting of sedimentary rocks alternating 

with andesitic lavas and tuffs, but at the igneous 

contact, perknitic rocks appear, followed upstream by 

other ultrabasic gravels. The average thickness of the 

overburden in the pay streak of Squirrel Creek is about 

13 feet; in the most westerly mining cut near Tupper 

Gulch, a small tributary from the west that joins 

Squirrel Creek close to the junction of claims 1B and 2B 

(below Discovery), the thickness is about 20 feet. 

The pay streak of Squirrel Creek has been worked for 

a distance of 3,900 feet, from the bend of the creek 

southward to Platinum Creek. About 2,600 feet was 

worked by small-scale mining methods; the entire pay 

streak was later reworked by a dragline excavator. In 

the first span of 2,600 feet, the pay streak ranged in 

width from 150 to 500 feet, being narrowest in the 

medial part of claim 3B and widest in the vicinity of 

Tupper Gulch. Originally the pay streak was worked in 

as many as four parallel cuts; the most westerly cut, 

near Tupper Gulch, was of lowest grade. Some of the 

placer deposits of Squirrel Creek were of high grade, 

approaching 0.1 ounce of platinum metals per cubic 

yard; the average tenor for the whole pay streak is 

reported to have been about 0.03 ounce to the cubic ~ard. 

The platinum metals recovered from the valley of 

Squirrel Creek were generally of coarser grain than 

those on Platinum Creek. The largest nugget known to 

have been found in this pay streak weighed 1.5 troy 

ounces (46.7 grams). The record of the composition of 

these metals is fairly complete but unfortunately is not 

such that the changes in composition may be traced 

sequentially downstream. Twenty-two analyses have 

been made of these platinum metals, presented in 

table 16. 

The product of Squirrel Creek differs from that of Fox 

Gulch and upper Platinum Creek mainly in the content 

of iridium, the mean tenors being, respectively, 15.76 

and 28.11 percent. This suggests that the platinum 

lodes at the head of Squirrel Creek were lower in 

osmiridium than those at the head of Fox Gulch. A 

similarity is that the highest tenors in iridium, osmium, 

and ruthenium were found in the upper part of the pay 

streak, diminishing downstream. A possible explanaTABLE 16.-Analyses, in percent, of precious metals, Squirrel Creek 

Pt Ir 0s Ru Rh Pd Au 

C. Analysis of from upper &d of pays tkak showing minimum content ofplatinum and maximum contents of iridium and osmium. recomnuted free of gold and irnnnntieq 

tion of this anomaly is that the upper horizons in the 

lodes may have had lower tenors in osmiridium, and as 

these were first eroded, they were washed farther 

downstream. 

The tenors in gold on Squirrel Creek, like those of the 

platinum metals, cannot be arranged sequentially 

downstream. They appear, however, to show a considerable variation, as the minimum and maximum values 

are 0.12 and 1.40 percent; the mean value is 0.55 

percent, about 50 percent greater than that on Fox 

Gulch and the upper Platinum Creek. As elsewhere in 

this district, gold is an alien mineral introduced by 

glaciation and is therefore unrelated to the distribution 

of the platinum metals. 

LOWER PLATINUM CREEK 

TWO pay streaks were present on Platinum Creek for 

a short distance below the mouth of Squirrel Creek. One 

on the north side of the valley was the continuation of 

the pay streak of Squirrel Creek and the other was the 

downstream extension of the pay streak of upper 

Platinum Creek. The former was mined as far as it 

persisted, but the main pay streak appeared to be on the 

south side of the valley. The main pay streak at the 

mouth of Squirrel Creek had a width of about 120 feet 

but widened downstream, attaining a width of 400 feet 

at the confluence with the Salmon River. 

The placers in the lower valley of Platinum Creek 

were not mined sequentially; it is therefore not possible 

to arrange the available analyses downstream or even 

to state the sites of the cleanups that showed the largest 

and smallest tenors in platinum, or reciprocally the 

smallest and largest tenors in iridium, osmium, and 

ruthenium. As might be expected, some of the richest 

deposits were found at or just below the mouth of 

Squirrel Creek, where the pay streak of upper Platinum 

Creek joined that of Squirrel Creek. 

The platinum metals of lower Platinum Creek clearly 

were derived from two different types of lodes; it is 

therefore of interest to examine the metals downstream 

from the mouth of Squirrel Creek. In relation to the 

tenors of the platinum metals in the valley of the 

Salmon River, a general mean of the metals in the 

entire valley of Platinum Creek proves to be significant. 

The analyses of precious metals in the lower valley of 

Platinum Creek, and in the entire valley of PlatiIlum 

Creek and its tributaries, are shown in table 17. 

The mean values of the platinum metals from the 

. - D Analysis ofproduct from lower end of ay streak show Lg max~rnum"cont~n~ ofilatlnum and mtnlmum contenb of lrldtum ancfosmlurn, recomputed free of gold and trnpurlt~e, 

lower valley of Platinum creek, when compared with 

the mean values from the two headwater tributaries, 

are highly significant. Such a comparison shows that 

the platinum metals in the lower valley of Platinum 

Creek are more closely related to the product of Squirrel 

Creek than to that derived from Fox Gulch and the 
26 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

TABLE 17.-Analyses, in percent, of precious metals, valley of 

Platinum Creek 

A. Mean value of 38 analyses of the products from the mouth of Squirrel Creek to the confluence with the Salmon River, recomputed free of impurities. B. Same as A, recomputed free of gold and impuritles. C. Analysis showing minimum content of platinum and maximum contents of iridium, 

osmium, and ruthenium recomputed free of gold and impurities. D. Analysis showing maxiAum content of platinum and minimum contents of iridium, 

osmium, and ruthenium, recomputed free of gold and impuritles. E. Mean value of 86 analyses of all the platinum metals recovered from the valley of Platinum Creek and its tributaries, recomputed free of impurities. F. Same as E, recomputed free of gold and impurities. 

upper valley of Platinum Creek. Without the actual 

weights of the cleanups, no quantitative apportionment 

can be given, but the tabulated percentages suggest 

that as much as 80 percent of the platinum metals in the 

lower valley of Platinum Creek may have issued from 

the valley of Squirrel Creek. This suggests that bedrock 

lodes are more likely to be discovered at the head of 

Squirrel Creek than at the head of Fox Gulch. Any 

statement concerning platinum lodes of commercial 

value, however, must be qualified by two conditions: 

first, the original lodes may or may not have been 

entirely eroded and, second, any remaining lodes may 

be either of high or low grade. Only exploratory drilling 

will resolve these alternatives. 

The content of gold in the lower valley of Platinum 

Creek is approximately the same as in the valley of 

Squirrel Creek. This similarity supports the inference 

that most of the precious metals entered the lower 

valley of Platinum Creek from Squirrel Creek rather 

than from Fox Gulch and the upper valley of Platinum 

Creek. It should be emphasized that all the gold in the 

valley of Platinum Creek was derived from the 

morainal material left by the older (Nebraskan) glacier 

with no additional increments from outwash deposits of 

Kansan or Illinoian age. This constitutes a fundamental 

difference between the valley of Platinum Creek and 

the valley of the Salmon River. 

Several gulches northeast of Squirrel Creek are 

tributary to the Salmon River, which named from south 

to north are Last Chance, Boulder, Dowry, and Clara 

Creeks. Platinum metals occur on Last Chance Creek, 

but no workable ground has been found; mining has 

been done on Boulder and Dowry Creeks. No data are 

available on the widths and depths of the pay streaks on 

these two streams or on the nature of the alluvial cover. 

One analysis has been made of the platinum metals 

recovered from Boulder Creek, and five analyses have 

been made of the product of Dowry Creek. The mean 

values of these analyses are presented in table 18. 

The platinum metals of Boulder Creek are similar to 

those of Squirrel Creek, whereas the metals of Dowry 

Creek closely approach those of Clara Creek. The 

decrease northward in iridium, osmium, and ruthenium 

and the corresponding increase in platinum are notable 

features of this product. The tenor of gold from Boulder 

Creek is the same as the mean tenor from Squirrel 

Creek, but the mean value of gold from Dowry Creek is 

much greater, veering toward the still larger values on 

Clara Creek. 

TABLE 18.-Analyses, in percent, of precious metals, Boulder 

and Dowry Creeks 

- -- 

A. Boulder Creek, recomputed free of impurities. B. Same as A, recomputed free of old and impurities. 

C. Dowry Creek, mean of five anafyses, recomputed free of impurities. D. Same as C, recomputed free of gold and impurities. 

Clara Creek, about 2 miles long, enters the Salmon 

River from the west about 3% air miles upstream from 

the mouth of Platinum Creek. The valley is not well 

marked; its headwaters and its watershed consist of a 

straight shallow gulch without tributaries, incised in 

the northeastern side of Red Mountain. The total area of 

the watershed is estimated to be about 1% square miles. 

Seven placer claims have been staked on Clara Creek. 

The actual extent of the mining done by the early 

operators and by the Clara Creek Mining Co. is not 

known; the company mined on Discovery claim and on 

claims lA, 2A, and 3A, defining a pay streak with a 

length of at least 1 mile. The overburden on Clara Creek 

is 10-12 feet deep; the upper 2 or 3 feet consists of turf, 

peat, and dark-colored mossy material mixed with sand. 

The underlying gravel is subangular and of small size, 

averaging perhaps 3-4 inches in diameter, though some 

large cobbles are present. The gravel consists both of 

rocks of local origin and other material derived from 

glaciofluvial deposits on the divide between the Salmon 

and the Smalls Rivers. Along the north side of the pay 

streak at the west end of claim 3A, mining operations 

uncovered large boulders as much as 3 or 4 feet in 

diameter in the upper horizons of the gravels. These 

boulders are interpreted as glacial erratics that were 

deposited at higher altitudes on the northeast slope of 

Red Mountain and migrated slowly downhill into the 

valley of Clara Creek. As the extent of the older 

glaciation is indeterminate, such boulders are considered to be a part of the Illinoian outwash deposits. 
ECONOMIC GEOLOGY 27 

Bedrock exposed by mining in 1937 consisted of 

metamorphosed rocks of several types that included 

sheared chert, quartzites derived from chert and 

graywacke, tuffaceous rocks, and chloritic siliceous 

schist; some of these are greatly decomposed by 

weathering. The cleavage and schistosity of these rocks 

appear to be local phenomena induced by stresses 

incident to the intrusion of the ultrabasic massif of Red 

Mountain. Mining operations revealed a bedrock floor 

with an asymmetrical profile, rising steeply to the south 

and gradually to the north. 

The pay streak of Clara Creek was worked in two 

operations, one on the north side of the stream, one on 

the south side. The total width is estimated to have been 

200-250 feet. The pay streak was found to extend from 

the contact between the ultrabasic rocks and the 

metamorphosed sedimentary rocks downstream almost 

to the Salmon River, but the records are vague. Early 

mining showed a tenor of as much as 0.08 ounce of 

platinum metals to the cubic yard, but the overall tenor, 

as determined by dragline mining, was closer to 0.02 

ounce per cubic yard. 

The platinum metals on Clara Creek are rather fine 

grained, although nuggets have been recovered, the 

largest 2 troy ounces (62.2 grams). Most of the precious 

metals were found in the gravels close to bedrock, but at 

some places 3-4 feet of fractured bedrock had to be 

excavated in order to obtain a high recovery. It was 

found unwise to strip off more than 2-3 feet of the 

overburden, as the upper horizons of gravel were in 

some degree platiniferous. 

Six analyses are available of the platinum metals 

recovered from the placers of Clara Creek. Three of 

these were made by Matthey-Bishop, Inc., one by D. C. 

Griffith & Co., one by the Wildberg Bros. Smelting and 

Refining Co., and one by K. J. Murata of the U.S. 

Geological Survey. The results of this analytical work 

are not altogether consistent, but the mean values, as 

shown in table 19, are believed to represent closely the 

true proportions of the precious metals. 

The mean content of gold is greater for Clara Creek 

than for any of the other western headwater tributaries 

of Platinum Creek; in fact, it is of the same order of 

magnitude as the mean content for the pay streak of the 

valley floor of the Salmon River. From this, it is inferred 

that a considerable volume of outwash deposits, 

TABLE 19--Mean analyses, in percent, ofprecious metals, Clara Creek 

Pt Ir 0s Ru Rh Pd Au 

A. Mean values of six analyses recomputed free of impurities. B. Mean values of six analyses: recomputed free of gold and impurities. 

deposited originally at the head of the Salmon River, 

was reworked to yield this increment in gold. 

A small stream known as McCann Creek heads 

against Clara Creek and flows northward to the Smalls 

River. Its valley contains some platinum metals but has 

not yielded a workable pay streak. No complete 

analyses are available, but John Cochrane analyzed 

eight hand-picked grains and found that on treatment . with aqua regia the soluble part contained 95.5 percent 

platinum, 2.8 percent iridium, 1.2 percent rhodium, and 

0.5 percent palladium. These figures are very close to 

the mean values shown as the composition of the 

principal alloy in table 7. The ratio K = SIZ was found to 

be 7.42, which is a little larger than the mean value of 

5.34 in table 7, but of the same order of magnitude. No 

analysis was made of the insoluble fraction. It therefore 

appears that the platinum metals of McCann Creek are 

comparable with those at the head of the bench pay 

streak, which correlate with the metals of Clara Creek. 

A comparison of the platinum metals from the 

streams that drain the eastern slope of the Red 

Mountain ridge is shown by the mean analyses from six 

areas, named from south to north (table 20). These 

values are charted and analyzed in the discussion of 

platinum lodes. 

SALMON RIVER 

Most of the platinum metals of the Goodnews Bay 

district have been recovered from two pay streaks in the 

valley of the Salmon River, although this stream does 

not erode any area of platiniferous rocks. One of these 

pay streaks is in the present valley floor; the other, 

called the bench pay streak, occupies a depression along 

the east wall of the valley. Most of these platinum 

metals have been derived from the western headwater 

tributaries of the Salmon River; a small part has come 

from the eluvial deposits along the eastern and 

southern flanks of the Red Mountain ridge. The volumes 

of platinum metals so far recovered from these two pay 

TABLE 20--Comparison of platinum metals, in percent, from 

streams on east flank of Red Mountain ridge 

R Ir 0s Ru Rh Pd 

A. Fox Gulch and the valley of Platinum Creek above the mouth of Squirrel Creek 

B. Valley of Squirrel Creek. 

C. Lower valley of Platinum Creek. D. Valley of Boulder Creek. E. Valley of Dowry Creek. F. Valley of Clara Creek. 
28 PLATINUM DEPOSITS OF THE GI )DNEWS BAY DISTRICT, ALASKA 

streaks, as gauged by mining data, are nearly equal, but 

as the southern end of the bench pay streak has not yet 

been worked, its total content of platinum metals must 

considerably exceed that of the pay streak of the valley 

floor. Moreover, the total volume of platinum metals 

recovered and recoverable from these two pay streaks is 

probably 10 times as great as that recovered from the 

headwater tributaries. And finally, these two pay 

streaks were deposited at widely different times. All 

these facts indicate a very long period of erosion and a 

considerable vertical iange in the original platiniferous 

lodes of Red Mountain. Gold, which constitutes only 

about 2.4 percent of the output, is an alien metal derived 

from a moraine that once occupied the valley of the 

Salmon River and from glaciofluvial deposits that now 

form the divide between the head of the Salmon River 

and the Smalls River. These and other data to be 

presented point to a complex history of the placers, 

involving their accumulation throughout the Pleistocene epoch. 

The bedrock floor of the Salmon River is characterized 

by one or more V-shaped incisions indicative of 

incomplete stream rejuvenation. Drilling has shown 

that the main incision begins at claim 8A and deepens 

downstream, attaining a depth of 15 feet in the wide 

valley floor of Discovery claim. Above and below the 

mouth of Snow Gulch, there are two such incisions, 

showing a lateral migration of the rejuvenated stream. 

The main incision extends a short distance up the 

valleys of Platinum and Medicine Creeks. This configuration persists downstream and attains a depth of 50 

feet on claim 15B. This incision was caused by a regional 

lowering of the base level of erosion which did not 

persist long enough for the river to carve a new and 

widened valley floor. There appears to be no additional 

concentration of platinum metals in this elongate 

trench. The chronology of the erosional features in 

relation to the gravels of the valley floor is uncertain; 

the absence of enrichment in precious metals suggests 

that the trench may have predated the deposition of the 

main gravel covering. 

The bedrock of the valley floor consists of a mixture of 

unweathered sedimentary and igneous rocks. The 

sedimentary rocks include highly indurated 

graywacke, siliceous argillite, and chert, together with 

dikes and sills of intrusive rocks, mainly of andesitic 

character, and siliceous tuffs. Bedrock is exposed in the 

valley floor at only two places, both along the east wall. 

One such exposure is on claim 14B; the other is on a 

bench claim just east of claim 15B. These outcrops are 

actually surficial protuberances of the bedrock reef that 

separates the two pay streaks. 

The pay streaks of the valley floor starts at the mouth 

of Clara Creek and continues without interruption 

downstream for an airline distance of about 6 miles, 

extending to the lower part of claim 15B. At the lower 

end of claim 6A where dredging ended, the average 

diameter of the gravels is 6-8 inches, with some cobbles 

and occasional boulders as large as 2 feet in diameter. 

All these gravels are essentially unweathered and are 

nearly as firm as the underlying bedrock. Unlike the 

bench pay streak, clay is generally absent except on 

claim 4B and for a few claim lengths downstream, 

where the two pay streaks are laterally contiguous and 

have bedrock floors at nearly the same altitude. The 

thickness of the gravels increases gradually 

downstream, ranging from 30 feet on claim 5A, to 75 

feet at the lower end of claim 15B, exclusive of the 

bedrock trench. The precious metals may extend 

downward into bedrock for several feet; to insure a high 

recovery, the dredge excavated at least 3 feet ofbedrock. 

The width of the pay streak is variable. At the mouth 

of Clara Creek, the width is 250 feet; on the lower end of 

claim 6A, 300 feet; on Discovery claim, at the mouth of 

Platinum Creek, 1,000 feet; on claim 3B, 800 feet; on 

claim 6B, 400 feet; and on claim 15B, 600 feet. The 

overall gradient of bedrock over the distance mined is 

41.2 feet to the mile, or 13.5 feet less than that of the 

bench pay streak. On the lower end of claim 6A the 

altitude of bedrock is 50 feet lower than on the adjacent 

bench pay streak; at a point on the upper end of claim 

7B, the bedrock of the two pay streaks, though 

separated from one another by a rock barrier, has the 

same altitude. A bedrock reef everywhere separates the 

channels of the two pay streaks, except on claim 4B, 

where for a short distance the two pay streaks are 

contiguous, although the altitude of the bench channel 

is 5 feet higher than the bedrock of the stream channel. 

Where the Salmon River discharges into Kuskokwim 

Bay, the bedrock of the main valley floor (not in the 

incision) is at .least 100 feet below sea level. The 

complexity of the geomorphic history is indicated by the 

fact that the bedrock of the bench channel, projected to 

Chagvan Bay, is about 250 feet below sea level. 

The pay streak of the valley floor has been dredged in 

two cuts from the lower end of claim 6A to the lower end 

of claim 15B. A third cut from claim 10B to claim 5B was 

completed in 1972. Thereafter the dredge moved 

eastward onto the bench pay streak and began to mine 

marginal ground and to rework old tailings. The 

uppermost 5 claims in the valley floor from 6A to 10A 

have not yet been mined but will probably be worked by 

a large dragline excavator. 

Dredging and dragline mining of the pay streak of the 

valley floor has yielded 404 cleanups through 1972. The 

available record includes 308 sieve analyses for the 
ECONOMIC GEOLOGY 29 

periods 1938-39 and 1942-72; a record of the sieving 

analyses for the period 1940-41 is lacking, although the 

production records are available. The mean granularity 

of the platinum metals for the stated intervals is shown 

by claims in table 21. The sizes of the grains and the 

relative magnitudes of the production for each claim up 

to 1972, with the elimination of ordinates, in order to 

conform with the practice of the U.S. Geological Survey 

not to reveal the production of individual properties, are 

charted in figure 10. 

Curve 3 of figure 10, which illustrates the distribution 

of the smallest grains, clearly shows that the granularity diminishes progressively, though not linearly, 

downstream; the reverse is necessarily true for curves 1 

TABLE 21.-Percentage of mean sizes (S) of platinum grains by claims, 

pay streak of valley floor, Salmon River 

Number Claim of S>0.83 mm 0.83 mm>S>0.42 mm 0.42 mm>S analyses 

5~ ................ lo 21.89 41.69 36.42 4A . 14 20.31 41.11 38.58 3~ ................ 13 18.41 43.52 38.07 

2A ................ 13 24.23 42.25 33.52 IA ................ 18 27.52 36.65 35,83 

D ................ 26 25.33 53.79 20.88 IB ................ 19 25.94 43.55 

2B ................ 10 26.57 42.35 31.08 3~ .. 15 22.13 46.69 31.18 

4B ................ 16 13.98 49.73 36.29 5~ ................ 12 16.19 31.91 51.90 6B ................ 7 11.51 28.91 59.58 7B .................... ...... -----. ...... 

8B ................ 19 7.23 26.40 66.37 9~ ................ 21 5.61 24.31 70.08 

10B ................ 22 7.41 24.03 68.56 11~ .. 16 3.82 13.43 82.75 

12B ................ 16 3.99 15.60 80.41 13B ................ 15 5.43 16.04 78.53 

14B ................ 16 3.34 14.12 82.54 15B ................ 10 2.41 10.39 87.20 

d-~ ZE! 

k.2 

<no 

2:5 LL 

90 

2 - 

- 

- 

- 

I- 80 - Z 

70 - 

- 

- 

- 

- 

5A 3A 1A 18 38 58 76 98 118 138 158 

4A 2A D 28 48 68 88 108 128 148 

CLAIM 

FIGURE 10.-Mean size (S) of platinum grains by claims (curves 1,2, 

and 3) and production curve for pay streak of valley floor, Salmon 

River. D, Discovery claim; A, claim above Discovery; B, claim below 

Discovery. 

and 2. In fact, the percentage of grains larger than 

0.83 mm diminishes nearly to zero on claim 15B. A 

diminution of grain size less than 0.42 mm shows in 

curve 3 on Discovery claim, and a corresponding 

increase in grain size is shown by curve 2. This relation 

undoubtedly has resulted from the addition of a large 

volume of coarser metals from the valley of Platinum 

Creek. 

Noticeable irregularities appear in the three granularity curves on claim 4B and on claim 11B. From the 

upper end of the pay streak of the valley floor 

downstream to claim 7B, the bedrock of the valley floor 

is lower than that of the bench pay streak; the valley 

floor could have been enriched from the bench where 

tributary streams, such as Medicine Creek, Snow 

Gulch, and Anita Creek, entered from the east. Such 

enrichments could account for the irregularities on 

claim 4B, but the variations on claim 11B have resulted 

from another cause, probably that some enrichment has 

occurred from an ancient pay streak high on the east 

wall of the Salmon Valley that antedated the formation 

of the bench pay streak. An enrichment of this kind 

cannot be related to specific tributaries, as the courses of 

such streams, must have changed greatly since the early 

development of the main valley. 

The composition of the platinum metals in the pay 

streak of the valley floor is established by 404 analyses 

representing that number of shipments to the refiner. 

The 22d or final listing shows the mean value of 9 

additional analyses whose granularity was less than 

0.15 mm. These samples were anlayzed separately, and 

because they accumulated from one cleanup to another, 

they cannot be assigned to individual claims. The 404 

analyses have been averaged claim by claim, starting at 

claim 5A and extending downstream to claim 15B; the 

resulting values are presented in table 22. 

TABLE 22.--Percentage of mean values of platinum analyses by claims, 

pay streak of valley floor, Salmon River 

Number Claim of Pt Ir 0s Ru Rh Pd 

analyses 

A .................. 8 90.20 6.82 1.25 0.08 1.20 0.45 4A .................... 9 90.43 6.67 1.19 .08 1.18 .45 3A 9 90.49 6.61 1.18 .08 1.19 .45 2A .................... 11 89.48 7.37 1.35 .09 1.24 .47 1A ................... 25 86.81 9.53 1.82 .13 1.28 .43 D 48 84.31 11.65 2.32 .18 1.18 .36 1B .. 29 83.84 11.78 2.39 .19 1.43 .37 2B 25 83 74 11.92 2.39 .19 1.37 .39 3B .................... 34 83.91 11.86 2.37 .17 1.30 .39 4B 39 82.62 12.94 2.48 .19 1.38 .39 5B .................... 26 82.12 13.25 2.65 .20 1.40 .38 6B 25 81.84 13.53 2.68 .22 1.37 .36 7B .................... 25 81.16 13.83 2.89 .24 1.47 .41 8B .................... 15 81.32 13.96 2.94 .23 1.20 .35 9B 13 80.56 14.62 2.99 .24 1.24 .35 10B .................... 15 80.63 14.62 2.86 .23 1.31 .35 11B 13 79.67 15.32 3.04 .24 1.35 .38 12B .................... 11 77.47 15.35 3.22 .24 1.37 .35 13B 9 79.90 15.18 3.13 .24 1.18 .37 14~ . 8 79.53 15.37 3.25 .24 1.27 .34 

.................... 

15B 79.26 15.57 3.34 .24 .33 

.............. fines 72,18 20,88 4,79 ,33 ,41 

Weightedmeans .................. 83.07 12.52 2.51 .I9 1.32 .39 
30 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

omitted, as these two scarce elements have little 

significance. The outstanding feature of these curves is 

the reciprocal relation between the curves for platinum 

and those that represent iridium and osmium plus 

ruthenium, a reflection of the dominance of platinum in 

the principal alloy and the prevalence of iridium, 

osmium, and ruthenium in the osmiridium. The 

magnitude of platinum compared with the other metals 

indicates the dominance of the principal alloy in the 

placer product. This feature is corroborated by the 

examination of polished sections of nuggets and grains 

under the microscope, where the areas of osmiridium 

are seen to be smaller and less common than those of the 

principal alloy. 

Examination of the curves of the pay streak of the 

valley floor shows that at claim 3A platinum shows a 

sharp decrease downstream to Discovery claim, and the 

decline continues more slowly downstream to claim 

15B. Conversely, the amount of iridium suddenly 

begins to increase at claim 3A and continues to increase 

to Discovery claim, where the variation curve changes 

to a slow but progressive increase that continues 

downstream to claim 15B. The curve of osmium plus 

ruthenium with flattened flexures behaves concordantly with the curve of iridium, suggesting that most 

of the iridium is contained in osmiridium. 

Several factors enter into the distribution of the 

platinum metals in the pay streak of the valley floor. 

First, the metals above the mouth of Platinum Creek 

are notably different from those entering the Salmon 

Valley from Platinum Creek in that the 1r:Pt ratio in 

those above the mouth is lower. Moreover, fewer 

platinum metals originated in the vaIley of Salmon 

River above the mouth of Platinum Creek. As a result, 

the 1r:Pt ratio was appreciably raised by the metals 

from Platinum Creek. A second factor is the tendency of 

the coarser heavy metals not to migrate far downstream 

from their original sites of deposition unless rejuvenation or some other activating erosional process has 

taken place. The V-shaped incision in the valley floor of 

the Salmon River indicates an incipient rejuvenation 

which, however, never became effective in the upper 

valley. Hence the decrement of the 1r:Pt ratio that 

resulted from the addition of metals from the upper 

valley was relatively slight and was gradually overcome by the higher 1r:Pt ratio of the metals that issued 

from the mouth of Platinum Creek. The 1r:Pt ratio, 

0.134 on Discovery claim, gradually increased to 0.196 

on claim 15B, approaching the limiting value of 0.218 

for the lower valley of Platinum Creek. A third factor 

Two sources of error arise in this compilation. All 

mining in the valley floor has been done by dredging, 

but all cleanups did not have the same weights; 

moreoever, a part of one cleanup was added occasionally 

to the next. But the analyses are sequential, and as the 

composition varies little from one cleanup to the next, 

this discrepancy is largely cancelled by the mean 

analyses. 

A more significant source of error arises from the fact 

that percentages cannot be averaged, arithmetically or 

otherwise, except by weighting. The percentages in the 

analyses cannot be weighted. The weights of the 

shipments vary considerably and are not known to the 

writer, though ordinarily they are of the same order of 

magnitude, ranging from 300 to 400 troy ources. 

However, the composition of the platinum metals differs 

little from one cleanup to the next and does not differ 

greatly from the terminal part of one claim to the initial 

part of the next. For these reasons, it is believed that the 

arithmetical means of the analyses are not greatly in 

error as representative of consecutive claims. 

The mean analyses of the platinum metals for the 

valley floor and for the bench pay streak are charted in 

figure 11. This is feasible as there is no interference 

between the two sets of curves. Three curves are charted 

for each pay streak: one for platinum, one for iridium, 

and one for osmium plus ruthenium, the two hexagonal 

elements. The curves for rhodium and palladium are 

UNIT 

1 3 5 7 9 11 13 1517 

2 4 6 8 10 12 14 1618 

FIGURE 11.-Mean analyses of four platinum metals by claims and 

units, pay streaks of valley floor and bench, Salmon River. D, 

Discovery claim; A, Claim above Discovery; B, Claim below 

Discovery. 

95 

tU 

1: a 

Wa 

g 80- 

79 

may have been a "chulitna" or backhand drainage in the 

lower valley of Platinum Creek inherited from an 

earlier physiographic cycle, as later described, when the 

northern end of the bench channel drained toward the 

- , , , , , , , , , , , , , , , , , , , , , , - - - - - - - 

bench p\ati+*' 

[[: 

- "la ti - - ""m, 

Y floor 1 - 1 - - 

I 

I 

- 

9A 7A 5A 3A 1A 18 38 58 78 98 118 138 158 

8A 6A 4A 2A 28 48 68 8B 10B 12B 14B 

CLAIM 
ECONOMIC GEOLOGY 31 

Smalls River. This would explain why the marked 

change in the composition of the platinum metals began 

on claim 3A instead of on Discovery claim. 

The bench pay streak begins on the lower end of a 

left-limit bench claim opposite claim 10A and has been 

worked downstream to the upper end of the Olson bench 

claim, opposite claim 10B, an air distance of 4.4 miles. 

The ancient channel occupied by this pay streak 

continues downstream to, or nearly to, Chagvan Bay, an 

additional 4% miles. Drilling shows that this channel, 

about 1 mile from Chagvan Bay, splits into two 

distributary channels. The downstream limit of a 

commercial pay streak has not yet been firmly 

established, but intensive drilling had proven by 1969 

that it extended as far south as Happy Creek. As this 

area is south of the Alaskan zone of permafrost, nearly 

all the overburden is unfrozen; drilling in the lower end 

of the bench pay streak, however, has revealed a 

number of frozen strata, some as thick as 20 feet. 

The bedrock gradient of the bench channel over the 

distance mined is 54.7 feet per mile, or 13.5 feet greater 

than the gradient of bedrock on the valley floor of the 

Salmon River. At its upper end, the bedrock floor of the 

bench pay streak is about 80 feet higher than the 

corresponding bedrock of the valley floor. On claim 4B, 

where the two pay streaks are contiguous for a short 

distance, the bedrock of the bench channel is only 5 feet 

higher than that of the valley floor; opposite claim 7B, 

about 3,000 feet below the mouth of Anita Creek, the 

two channels have the same altitude, though separated 

by a bedrock reef. About 4.8 miles from Chagvan Bay, 

the bedrock of the bench channel is at sea level; and at 

Happy Creek, drilling has shown that the bedrock of the 

bench channel is 50 feet below sea level. At a point 

seven-eighths of a mile from Chagvan Bay, the bedrock 

lies 200 feet below sea level. 

Still farther southwest, near the northern limit of the 

peninsula between Kuskokwim and Chagvan Bays, 

eight holes were drilled by the Goodnews Bay Mining 

Co. within an area of about 1 square mile. The depths of 

seven of these holes ranged from 68 to 110 feet; the 

eighth, located at lat. 58"48'27" N. and long. 161'44'24" 

W., was drilled to a depth of 252% feet and reached 

bedrock at 244 feet. Although these holes are in line 

with the bench pay streak, no platinum metals were 

found. The depth to bedrock is an index of the oceanic 

level during one of the glaciations even though it does 

not necessarily correlate with the formation of the 

bench pay streak; nor is the minimum depth of-244 feet 

indicative of the minimum base level of erosion in this 

area during the Pleistocene Epoch. 

The thickness of the alluvium that overlies bedrock 

on the bench pay streak increases downstream from a 

thickness of only 10 feet at the northern limit of the pay 

streak to 45 feet east of Discovery claim and to 125 feet 

at the lower end of the Olson bench claim. With these 

thicknesses of overburden, it was possible to mine the 

upper end of the pay streak with a dragline excavator; 

from Medicine Creek downstream, all mining except 

some marginal strips was done by dredging. Unlike the 

operation on the valley floor, the mining of the bench 

pay streak was accomplished by a single, but very 

sinuous, traverse of the dredge moving both laterally 

and longitudinally. 

The width of the bench pay streak was found to be 

variable, increasing generally but not linearly 

downstream. Opposite the mouth of Dowry Creek, the 

width of the pay streak was 200 feet; opposite Discovery 

claim, it widened to as much as 1,200 feet; on the Olson 

bench claim, it was 550 feet; and by drilling it has been 

established on the Alice Association claim to be between 

750 and 800 feet. A characteristic feature of the bench 

pay streak is that the bedrock floor is nearly flat from 

side to side. This indicates a fairly constant base level of 

erosion for a long period of time, enabling the ancient 

stream that occupied this channel to carve away the 

lateral spurs, expanding the valley floor to its present 

shape and width. 

The alluvium of the bench pay streak is about 80 

percent clay and 20 percent gravel, reworked from the 

ancient moraine that occupied this channel. The gravel 

is erratically distributed vertically and occurs as 

lenticular beds inlaid in clay, generally ranging in 

thickness from 6 inches to 3 feet. Locally, particularly at 

the lower end of the pay streak, thick beds ofgravel have 

been uncovered or located by drilling. On the lower end 

of the Olson bench claim in a drill hole 122 feet deep, 

gravel formed the upper 30 feet of the section, and on the 

Hannah bench claim, in a drill hole 135 feet deep, gravel 

constituted the upper 72 feet of the section; these 

superficial gravels are not platinum bearing. The 

gravels of the beds intercalated with the clay are 

typically subrounded to subangular, ranging generally 

in size between 2 and 3 inches in diameter, although 

some cobbles are present; the nonsiliceous types are 

greatly altered by weathering. Many of the gravels are 

so fractured and broken that sharp edges show along the 

faces of the siliceous types. 

The precious metals are recovered from the lower 68 

feet of clay and gravel and from the upper 3-4 feet of 

altered bedrock. The country rock is generally fractured, and the nonsiliceous varieties are so greatly 

altered that it is difficult in drilling at some localities to 

identify bedrock when it is reached, as it has disintegrated to mud. Bedrock is characterized by fractured 

grains of quartz and chert, and in order to obtain a 
32 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

complete recovery of the precious metals, drilling and 

mining are extended downward for about 7 feet into 

what is regarded as bedrock. It seems probable that the 

infiltration of the platinum metals into bedrock 

occurred at an early stage in the erosional history of the 

area, possibly beginning during the Pliocene Epoch and 

that the deep alteration of bedrock was a feature of 

much later date. Otherwise the bedrock, altered to clay, 

would have acted as a false bedrock, preventing the 

ingress of the platinum metals. 

A feature of special interest is the incipient lithification of the clay in the overburden. Induration has 

progressed so far that the clay does not disintegrate 

entirely in the trommel screen of the dredge and this has 

caused appreciable losses of the precious metals. The 

magnitude of such losses was gauged in 1966 by the use 

of an experimental rig called a "mud hog," built and 

operated on the bench pay streak at a site opposite claim 

4B to rework the bench tailings. To obtain a complete 

recovery of the precious metals, it was necessary to 

pulverize not only the clay but also the intermixed and 

adhering gravels before sluicing, as the two were 

inseparable. This was an expensive operation, designed 

solely to appraise the losses incurred in dredging; yet 

this crude pilot plant showed a profit for the duration of 

the operation. A part of this indurated clay has 

evidently slaked under weathering, as the dredge is now 

successfully reworking the tailings on the Fourth of 

July bench and adjacent ground. 

Exploratory drilling of the bench pay streak has now 

progressed into that part of the valley south of Happy 

Creek where a change has been observed in the 

character of the overburden. Clay and gravels of the 

type described still constitute the lower section of the 

alluvium, but at some sites the upper part consists of 

thick beds of cleaned, little weathered gravels similar to 

those in the bluffs along the lower Salmon River and 

those facing Kuskokwim Bay; in one line of drill holes 

south of Happy Creek, such gravels constitute the upper 

115 feet of the section. It is evident that these are 

outwash gravels derived from an old Kinegnak glacier 

of Illinoian age that overrode the spur east of Happy 

Creek and followed a westerly course to the sea. That 

this glacier did not erode and obliterate the bench pay 

streak as it did the pay streak of the valley floor is 

doubtless due to the much greater depth of the older pay 

streak. 

The granularity of the platinum metals on the bench 

pay streak is established by 402 sieve analyses from the 

same number of cleanups for the period 1942-69. The 

mean values of these analyses arranged by units that 

correspond roughly to the position of the creek claims 

are shown in table 23 and are charted in figure 12. The 

granularity curves of the platinum metals in the pay 

TABLE 23.-Percentage of sizes (S) of platinum grains by units, bench 

pay streak, Salmon River 

Unit 

Number of I S>0.83 mm 0.83 mm>S>0.42 mm 0.42 mm>S analyses 

UNIT 

17 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 18 

CI ' """ h " '""lJ 

1111111'11'1111111' 

9A 7A 5A 3A 1A 18 38 58 78 98 

8A 6A 4A 2A D 28 48 68 88 

CLAIM 

FIGURE 12.-Mean size (S) of platinum grains by units (curves 1, 2, 

and 3) and production curve for bench pay streak, Salmon River. D, 

Discovery claim; A, Claim above Discovery; B, Claim below 

Discovery. 

streak are complicated by the fact that the upper course 

of the ancient channel was northward to the Smalls 

River and later, by stream capture, was diverted 

southward. This led to a complex distribution of the 

precious metals that is evident in both the sieve 

analyses and the chemical analyses. 

Curve 1 of the coarsest grains shows a maximum, and 

i curve 3 of the finest grains a minimum in the zone of 

unit 7, corresponding to claim 2A. This relation leads to 

two inferences: first, that relatively coarser metals 

issued from the valley of Platinum Creek than from 

farther upstream and, second, that during the early 

development of the bench pay streak, the course of the 
ECONOMIC GEOLOGY 33 

lower stretch of Platinum Creek was northeastward to a 

stream that drained into the Smalls River. Otherwise, 

the cited maximum and minimum would have shown 

opposite the mouth of Platinum Creek as they do in the 

pay streak of the valley floor. Curves 2 and 3 show a 

reverse relation at unit 9 opposite Discovery claim; a 

possible explanation is that this part of the curve 

represents a development subsequent to the stream 

piracy described. Finally, at unit 11, opposite claim 3B, 

another maximum for curve 1 and a minimum for curve 

3 reappear. These flexures are believed to be the result 

of enrichment of the bench pay streak from an older 

channel high on the eastern valley wall, now represented by fragmentary remnants of alluvial deposits 

that are not commercially workable. 

The mean granularity of the platinum metals in the 

two pay streaks is shown by the means of eight sieved 

fractions that represent the entire production from both 

pay streaks through 1969. No seiving records are 

available for the years prior to 1938, and none are 

available for the years 1940-41, but the record is 

otherwise complete, covering 710 cleanups. Thirtythree sieving records from the lower valley of Platinum 

Creek have been added to those of the valley floor of the 

Salmon River, making a total of 743 samples. These 

mean values are tabulated in table 24. 

Although it is not always possible to assign all 

cleanups to specified claims, the sums are known from 

the actual weights of the sieved fractions; the totals are 

therefore actually weighted mean values, which should 

have a high degree of dependability. 

The mean granularities of the platinum metals in the 

bench pay streak and in the pay streak ofthe valley floor 

are respectively 0.528 and 0.553, (table 24). The mean 

granularity of the metals from the bench is 4.5 percent 

less than that of the metals from the valley floor. This 

seems to be a small difference, but considering the 

volume of the available data, it is highly significant. 

Moreover, there is a striking difference in the size 

distribution of the platinum metals in the two pay 

streaks: The most plentiful metals recovered from the 

TABLE 24.-Mean granularity of platinum metals in two pay streaks, 

valley of Salmon River 

S~eve slzes Mean 'lzes Valley floor Bench E"t"e out- 

(mm) put (percent) (percent) 

Total .............................. 100.00 100.00 100.00 

Weighted mean size .................. 0.553 0.528 0.539 

bench pay streak have a mean diameter of 0.36 mm, 

whereas the mean diameter for the valley floor is 

0.50 mm. The most prevalent grains in the bench pay 

streak, in the range 0.42-0.30 mm, are about twice as 

plentiful as the grains of the same size in the pay streak 

of the valley floor. This does not obtain for grains 

smaller than 0.30 mm, as might be expected, because 

large amounts of fine-grained platinum metals were 

lost by retention in the semi-indurated clay of the bench 

pay streak. 

The production curve for the bench pay streak (fig. 12) 

differs materially from that of the valley floor. There is a 

marked increment in the curve as a result of the high 

output from the valley of Platinum Creek, but the 

maximum point is at unit 8 opposite claim 1 above 

Discovery, rather than at Discovery claim. This 

increment, starting at unit 6 opposite claim 3A, is 

further evidence that the lower course of Platinum 

Creek was northeastward in the initial stage of the 

development of the bench channel. Two minor maxima 

are recognizable in the production curve of the bench 

pay streak at units 13 and 15. A possible explanation of 

these increments is enrichment from a more ancient 

platiniferous deposit high on the east wall of the valley, 

now represented only by eroded remnants. 

The composition of the platinum metals in the bench 

pay streak is established by 412 superior analyses. 

These have been arranged by units, starting at unit 1, 

opposite claim 9A, and extending downstream to unit 18 

opposite claim 10B, as shown in table 25. The final 

listing shows the mean value of 17 additional samples 

having a granularity smaller than 0.15 mm that cannot 

be referred to individual claims. 

The composition of the platinum metals in the two 

pay streaks are charted in figure 11. The bench curve of 

platinum metals shows a minimum value 4or platinum 

and a maximum value for iridium on unit 9 opposite 

TABLE 25.-Percentage of mean values of platinum analyses by units, 

bench pay streak, Salmon River 

Number Unlt of Pt Ir 0s Ru Rh Pd analyses 

-100 fines .............. 17 78.71 15.28 3.89 .27 1.39 .46 Weighted means .................. 86.00 10.15 1.97 .15 1.32 .41 
34 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

Discovery claim, owing to the contribution of metals 

high in iridium from the valley of Platinum Creek, but 

these changes begin on unit 7 opposite claim 2A. The 

higher content of iridium upstream from unit 9 

constitutes further proof that in an early stage in the 

development of the bench pay streak, the lower course of 

Platinum Creek was northeastward to a stream that 

discharged into the Smalls River. 

The composition of the platinum metals shows 

diagnostic differences downstream from unit 9 as the 

tenor in platinum increases and that of iridium 

decreases. This is exactly the reverse of the relation that 

prevails in the pay streak of the valley floor. It is clear 

that there was an influx of high-iridium metals into 

both pay streaks from the valley of Platinum Creek at 

the same time that low-iridium metals were being 

added from the upper Salmon valley above the mouth of 

Platinum Creek. This anomaly can be explained by one 

of two factors, possibly by both: (1) The low-iridium 

metals of the upper valley may have migrated farther 

downstream, owing to the higher gradient of the bench 

channel, thus cancelling in some measure the output 

from Platinum Creek; (2) more low-iridium metals were 

introduced into the upper Salmon valley when the 

bench pay streak originated than at a later time when 

the pay streak of the valley floor was being formed. A 

possible corollary of the second explanation is that the 

low-iridium metals occurred mainly at higher horizons 

in the original lodes. 

The occurrence of gold may be tabulated in two ways 

that have quite different meanings. The amount of gold 

recovered from each claim can be shown as a percentage 

of the total gold recovered from the pay streak, or the 

amount may' be stated as a percentage of the precious 

metals recovered from each claim. Both these distributions, listed respectively as A and B, are shown in table 

26. The distribution A, charted as figure 13, should have 

a greater genetic significance. 

Tabulation A displays a number of anomalous 

features. One of these is the maxima shown for 

Discovery claim and claims 3B, 4B, and 7B. Oddly these 

, maxima correlate closely with the maxima for the 

production of platinum metals, as shown in figure 10. It 

will be remembered that gold is scarce in the valley of 

Platinum Creek and its tributaries, and therefore the 

maximum on Discovery claim cannot be a result of 

enrichment from that source. Moreover, a genetic 

relation between gold and the platinum metals is not 

believed to exist. The only reasonable explanation for 

the three cited maxima is that they represent enrichment in gold from eastern tributaries of the Salmon 

River, such as Medicine Creek and Snow Gulch or 

streams antecedent to these, that were eroding outwash 

deposits in their headwaters. It will be remembered that 

the two pay streaks were at the same bedrock level on 

and adjacent to claim 4B, and so enrichment from the 

TABLE 26.-Distribution, in percent, of gold by claims and units in two 

pay streaks, valley of Salmon River 

Pay streak of the valley ROOT Bench pay streak 

Claim A B Unit A B 

Mean ........... 2.84 Mean .................. 152 Total ........ 100.00 Total ........ 100.00 

A. Total gold recovered from pay streak. B. Gold in precious metals. 

UNIT 17 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 18 

CLAIM 

FIGURE 13.-Gold production by claims and units for two pay streaks, Salmon River. D, Discovery claim; A, Claim above Discovery; B, 

Claim below Discovery. 
ECONOMIC GEOLOGY 35 

bench pay streak, both in gold and the platinum metals, 

could have occurred at that site. Either or both such 

enrichments are suggested as a reason for the maxima 

in gold on claims 3B and 4B, but only lateral stream 

enrichment could obtain for claim 7B. 

A second anomaly is the high value in gold at the 

south end of the pay streak of the valley floor, as 

compared with that at the north end. Ordinarily the 

precious metals become progressively finer grained and 

scarcer downstream from their real or proximate 

source. No data are available on the granularity of the 

gold, but contrary to the usual distribution, it becomes 

more plentiful downstream. The uppermost (northern) 

four claims contain 11.67 percent of the gold, whereas 

the lowermost (southern) four claims contain 14.35 

percent of the gold. The physiographic history of the 

Salmon River is long and complex and is imperfectly 

understood; only such events for which there are cogent 

proofs are chronicled. But the cited anomaly suggests a 

startling and unprovable hypothesis involving a reversal in the flow of this river at some time in the remote 

past. If the reversal occurred, it must have occurred as a 

result of an ice dam of Kansan age in the valley of the 

Kinegnak River at an early stage in the development of 

the pay streak, possibly during the Yarmouth interglacial stage. Thus the Salmon River could have eroded 

outwash deposits at the southern end of its valley. This 

course of events is proposed as a remote possibility for 

which no evidence can be offered. 

The distribution of gold in the bench pay streak is 

likewise anomalous. The overall content of gold is about 

46 percent less than that in the pay streak of the valley 

floor. This is understandable, for the gold of the bench 

pay streak was concentrated from unsorted moraine, 

whereas the gold in the valley floor was derived from 

outwash deposits and was already partly concentrated 

before these deposits were formed and subsequently 

eroded. But there are pronounced maxima in the 

content of gold in units 8 and 9, opposite creek claim 1A 

and Discovery claim, and to a much smaller degree on 

unit 13, opposite creek claim 4B. The explanation for 

these maxima must be enrichment from west-flowing 

tributaries of the Salmon River that were eroding 

outwash deposits. Tabulation B, however, shows a 

content of gold that is sensibly constant throughout the 

length of the pay streak. The bench pay streak, like the 

pay streak of the valley floor, was richest in platinum 

metals in its median zone and leaner at both ends; no 

explanation can be offered for why the gold should be 

similarly distributed. 

The accessory minerals of the country rock are 

released from their bedrock sources by weathering and 

after stream transportation are concentrated in alluvial 

deposits; the character, distribution, and amounts of 

these minerals constitute significant data that bear 

upon their origins and upon the physiographic processes 

whereby they were concentrated. A large volume of 

accessory or semiheavy minerals is recovered with the 

platinum metals; these consist mainly of magnetite but 

include considerable amounts of ilmenite and chromite 

and smaller amounts of other rock-forming minerals. 

Forty samples of such alluvial concentrates were 

collected within the Goodnews Bay district, and the 

locations of these are given herewith. 

Localities of samples of alluvial concentrates 

[Astertsk indicates sample is in table 271 

1. 66A-Mtl* Concentrates from two pans of fractured and decomposed bedrock at a 

site on bench pay streak east of the 

lower end of claim 2A, Salmon 

River. 

2. 66A-Mt4 Concentrates from two pans of decomposed bedrock at a site on bench pay 

streak east of the upper end of claim 

2A, Salmon River. 

3. 66A-Mt6" Concentrates from three pans of an 

alluvial red clay in the overburden 

overlying bedrock at a site on bench 

pay streak east of the upper end of 

claim lA, Salmon River. 

4. 66A-Mt7 Concentrates from dredge cleanup in 

pay streak ofvalley floor, claim 12A. 

5. 66A-Mt8 Concentrates from one and one-half 

pans of stream gravels of Dowry 

Creek about 100 feet upstream from 

the automobile road to Platinum. 

6. 66A-Mt9" Concentrates from one pan of the 

overburden about 60 feet thick, 

about 20 feet below the surface, at a 

site on bench pay streak east of the 

center of claim 8A, Salmon River. 

7. 66A-Mt10 Concentrates from two pans of stream 

gravels at the upper end of the pay 

streak on Squirrel Creek. 

8. 66A-Mt28 Concentrates from two pans of stream 

gravels of Squirrel Creek about 

halfway between the upper end of 

the pay streak and the junction with 

Platinum Creek. 

9. 66A-Mt29" Concentrates from one pan of the sand 

and gravel at the site of the "mud 

hog" operation on the bench pay 

streak east of claim 4B, Salmon 

River. 

10. 66A-Mt30 Concentrates from one and one-half 
36 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

pans of stream gravels of Clara 

Creek about 100 feet upstream from 

the automobile road to Platinum. 

11. 66A-Mt31 Concentrates from a cleanup of the 

"mud hog" at a site on bench pay 

streak east of claim 4B, Salmon 

River. 

12. 66A-Mt32 Concentrates from one pan of stream 

gravels of McCann Creek, a tributary of the Smalls River, about 100 

feet upstream from the automobile 

road to Platinum. 

13. 66A-Mt33 Concentrates from one pan of stream 

gravels on Fox Gulch about 150 

yards above its confluence with 

Platinum Creek. 

14. 66A-Mt34 Concentrates from three-quarters pan 

of gravels from Platinum Creek 

about 150 yards above junction with 

Fox Gulch. 

15. 66A-Mt35* Concentrates from one pan of stream 

gravels sampled about one-quarter 

mile upstream from the mouth of 

McCann Creek on the Smalls River. 

16. 66A-Mt36 Concentrates from one pan of stream 

gravels sampled about 1,000 feet 

east of the eastern limit of the bench 

pay streak on Medicine Creek, an 

eastern tributary of the Salmon 

River. 

17. 66A-Mt37 Concentrates from one-half pan of 

fractured shaly bedrock about 6 feet 

below its upper surface at a site near 

the northern limit of the bench pay 

streak and about 400 feet east of this 

pay streak, valley of the Salmon 

River. 

18. 66A-Mt38* Concentrates from three-fourths pan 

of yellowish gravelly material at 

east side of northern limit of bench 

pay streak, valley of Salmon River. 

19. 66A-Mt39 Concentrates from one-third pan of 

grayish gravels a short distance 

west of sample 66A-Mt38 at northern limit of the bench pay streak, 

Salmon River. 

20. 66A-Mt40* Concentrates from two pans of outwash gravel at a bluff 30 feet high 

alaiag the east side of the valley of 

the Salmon River about 400 yards 

upstream from the mouth of Happy 

Creek. 

21. 66A-Mt41* Concentrates from two pans of gravel 

at base of a drill hole with a depth of 

192 feet along the north side of the 

road to Platinum about 1.6 miles 

from Kuskokwim Bay, between 

Seattle Creek and the Smalls River. 

Concentrates from one pan of yellow 

mud from a drill hole at a depth of 60 

feet in an alluvial section of 122 feet 

in a line of drill holes in the southern 

half of the Olson bench claim, valley 

of the Salmon River. 

Concentrates from one pan of gravel 

from a drill hole at a depth of 25 feet 

in an uppermost stratum of gravel 

30 feet thick in a second line of drill 

holes in the southern half of the 

Olson bench claim, valley of the 

Salmon River. 

Concentrates from one pan of gravel 

from a drill hole at a depth of 60 feet 

in an uppermost stratum of gravel 

72 feet thick in a third line of drill 

holes in the southern end of the 

Olson bench claim, valley of the 

Salmon River. 

Concentrates of several pans from an 

entire drill hole on the Hannah 

bench claim, valley of the Salmon 

River. 

Concentrates from one pan of bedrock 

at the bottom of drill hole 26, line 1 

N., at a depth of 130 feet on Alice 

Association bench claim, valley of 

the Salmon River. 

Concentrates from jigs, dredge 

cleanup, and pay streak of valley 

floor, claim 11B. 

Concentrates of several pans from an 

entire drill hole with a depth of 140 

feet, hole 20 line 1 N., on Alice 

Association bench claim, valley of 

the Salmon River. 

Concentrates from three-fourths pan 

of mud and angular fragments of 

bedrock taken about 4 feet above 

bedrock in hole 28, line 1 N., which 

had a depth of 136 feet, on Alice 

Association bench claim, valley of 

the Salmon River 

Concentrates from cleanup of dragline 

excavator from site on Platinum 

Creek just above the mouth of 

Squirrel Creek. 

Concentrates from an unknown 

number of pans recovered from 
ECONOMIC GEOLOGY 37 

Pacific beach a short distance south 

of the narrow stretch of beach 

caused by the promontory of Red 

Mountain. Sample submitted by 

Edward Olson. 

32. 69A-MtlO* Concentrates from one and one-fourth 

pans of outwash gravel at approximately the same site but not the 

same stratum as sample 66A-Mt40. 

33. 69A-Mtll* Concentrates from one and one-half 

pans of morainal or outwash gravel 

taken from a gravel pit on the east 

side of the road to Platinum about 

2,000 feet south of the divide between the Salmon River and the 

Smalls River. 

34. 69A-Mt14" Concentrates from dredge cleanup in 

pay streak of valley floor claim 11B 

(below Discovery). 

35. 69A-Mt15* Concentrates from one pan recovered 

from Pacific beach about 1 mile 

north of the mouth of the Salmon 

River. Sample submitted by Joseph 

F. Fisher. 

36. 69A-Mt16* Concentrates from two pans of outwash gravels at a sea cliff facing 

Kuskokwim Bay about 1% miles 

north of the mouth of the Salmon 

River; submitted by Joseph F. 

Fisher. 

37. 69A-Mt17* Concentrates from one pan of outwash 

gravels at a sea cliff facing Kuskokwim Bay about 2% miles north ofthe 

mouth of the Salmon River; submitted by Joseph F. Fisher. 

38. 69A-Mt18* Concentrates of several pans from an 

entire drill hole on the bench pay 

streak south of Happy Creek; panned and submitted by Joseph F. 

Fisher. 

39. 72A-Mtl Concentrates from dredge cleanup in 

bench pay streak on Fourth of July 

bench; submitted by Joseph F. 

Fisher. 

40. 72A-Mt2 Concentrates from an entire drill hole, 

no. 27 line 15, a short distance 

downstream from Happy Creek; 

submitted by Joseph F. Fisher. 

Of the samples listed, 14 were taken from surficial 

stream gravels, 5 from suficial outwash deposits, 6 

from the cleanups of mechanical excavators, 9 from drill 

holes, 4 from bedrock, and 2 from beach sands. It should 

be stressed that regardless of the methods of recovery, 

the percentages of accessory minerals in alluvial 

deposits can seldom be ascertained, as the requisite data 

are seldom available. The samples panned from 

suficial gravels are inherently low in the heavier 

accessory minerals that lie close to bedrock. If a sample 

is taken from the cleanup of a dredge or dragline 

excavator, neither the total weight of the concentrates 

nor the volume of the mined ground is generally known 

to the sampler. And unless a drill hole is cased from top 

to bottom, and this is seldom done, the total volume is 

not accurately known. Moreover, the actual ratios of the 

accessory minerals to one another is indeterminate, as 

the sampling of surficial deposits necessarily yields 

more minerals of low than of high density; in a dredge or 

dragline excavator, where sluices or jigs are used, most 

of the lighter accessory minerals are eliminated. 

Samples from hardrock or residual deposits comprise 

both accessory minerals of alluvial origin, introduced 

into crevices of the bedrock, and those indigenous to the 

hardrock. Finally, an important factor is the skill of the 

sampler in the art of panning. A miner in search of the 

precious metals can clean a pan of gravels in a few 

minutes. If a high recovery of accessory minerals is 

desired, the job may take a skilled panner 30 minutes or 

more. If much plastic or semi-indurated clay is present, 

a much longer time will be needed. Despite these 

obvious shortcomings, alluvial concentrates have cogent values that depend partly upon the methods of 

recovery and partly upon the uses for the resulting data. 

The following magnetic methods have been used in 

separating the accessory minerals. The concentrates 

are spread evenly and thinly on a large sheet of paper so 

that the various minerals do not overlap. Magnetite is 

removed without the inclusion of other minerals by 

passing a small alnico horseshoe magnet over the 

concentrates at a distance of %-'/z inch. It is necessary to 

lift the magnetite in a single operation because grains of 

magnetite placed in a strong magnetic field often 

become miniature magnets that can adhere in clumps, 

enclosing other nonferromagnetic minerals. Hence the 

separation of magnetite, either in bulk or in multiple 

operations, is not feasible. 

The principal accessory minerals, other than magnetite, are ilmenite, chromite, and olivine; other minerals 

are present in smaller amounts. Approximate separations into three additional fractions are made by using 

two other alnico horseshoe magnets of increasingly 

higher gauss, utilizing the same technique as for 

magnetite except that the separates are obtained by 

contact. Because the magnetic susceptibility and 

density of ilmenite are only slightly greater than for 

chromite, the first of the three fractions is made up of 

ilmenite, chromite, and a small part of the olivine. The 

second fraction consists of olivine and other minerals of 

similar magnetic susceptibility, including epidote and 
38 PLATINUM DEPOSITS OF THE Q )DNEWS BAY DISTRICT. ALASKA 

garnet, if present. The third fraction includes the 

remaining minerals that are so weakly paramagnetic or 

diamagnetic that they are not held by the strongest 

alnico magnet. This degree of separation and the 

weights of the fractions usually suffice for the recognition of the various minerals and for an approximate 

determination of their abundance. For special purposes, 

some of these fractions are sieved into 14 sizes. 

The samples taken from stream gravels are mainly of 

local interest, as they represent the minerals derived 

from the Red Mountain ridge, excepting those from 

Medicine Creek and the Smalls River. The dredge 

concentrates, excepting 72AMt-1 from the bench pay 

streak, represent the pay streak of the valley floor of the 

Salmon River; sample 69AMt-8 is from the closely 

related pay streak of Platinum Creek. The three dredge 

samples from the Salmon River and the dragline sample 

from Platinum Creek consist mainly of minerals of local 

origin from which most of the lighter accessory minerals 

have been eliminated. The samples of the bench 

deposits, including 72AMt-1, consist largely of minerals from reworked morainal deposits and therefore 

contain a higher proportion of alien minerals. Some of 

the finer grained minerals, both local and alien, have 

penetrated deeply into cracks and crevices of the 

shattered bedrock of the bench. For these reasons, the 

bench concentrates are of special interest. 

Magnetite, owing to its abundance, ease of separation, and lack of alteration, is perhaps genetically the 

most useful mineral in this collection. Under tropical or 

subtropical conditions, magnetite alters readily to other 

minerals. In the southern United States, notably in 

Florida, the alluvial concentrates contain little or no 

magnetite, and even ilmenite is partly or wholly altered 

to arizonite or to leucoxene. Under the arctic and 

subarctic conditions that must have prevailed in Alaska 

during the Pleistocene glaciations and interglaciations, 

magnetite appears to have been practically immune to 

surficial alteration. 

The mean percentages of the iron ores and other 

minerals of the concentrates for 23 samples, given in 

table 27, show the ratios of magnetite to ilmenite 

(including small amounts of chromite and olivine) to be 

highly variable. Probably the most significant ratio is 

that shown by the dredge and dragline concentrates, 

about 7.51, and this may be taken as the mean 

abundance of these two minerals in the pay streak of the 

TABLE 27.-Mean mineral content, in percent, of alluvial concentrates 

Type of deposit Magnetite Ilmenite Other 

Stream gravel ... ...-------- .......-------. .. . .. 53.4 35.1 11.5 

Dredge and dragline sample ...----...... 87.3 11.7 1.0 Bench pay streak deposit .-.---.---.....---------.. 66.6 29.5 3.9 Decom osed bench bedrock ......... 48.7 47.9 3.4 la cia rout wash deposit .....-.------..... 37.9 49.0 13.1 Beach sand - -.....------.--......----------- 75.5 21.1 3.4 

valley floor of the Salmon River. One sample of this 

group, taken from a dragline cleanup on Platinum 

Creek just above the mouth of Squirrel Creek, showed a 

ratio of 7.9:l. In contrast, the mean ratio of magnetite to 

ilmenite from upper Platinum, Squirrel, Dowry, Clara, 

and McCann Creeks was only 2:l. The cause of this 

discrepancy is uncertain, but it may result from an 

abnormally high content of chromite. 

The least magnetic fraction contains small amounts 

of minerals with densities greater than 3.3, mainly 

zircon, corundum, rutile, garnet, pyrite, and cinnabar, 

as well as any precious metals of the concentrates. Most 

of the minerals of this fraction have densities less than 

3.3; they include quartz, feldspars, chert, serpentine, 

chlorite, pyroxene and amphibole, dolomite, tourmaline, apatite, and sphene, approximately in the order 

named. Of the heavier constituents, all but zircon, 

rutile, and garnet are regarded as largely of local origin; 

zircon, more common than the other two, is considered 

to be a critical index of alien origin. It is essentially 

absent in the concentrates of the stream valleys and is 

most prevalent in the outwash deposits, though present 

in concentrates of the bench pay streak, the Smalls 

River, and in smaller amounts in the dredge concentrates of the Salmon River. Of the lighter minerals, only 

tourmaline and sphene are considered to be of foreign 

origin. 

Cinnabar in very small amounts was first recognized 

in the concentrates from the bench, but small amounts 

were later found in the dredge concentrates from the 

valley floor. Cinnabar was first thought to be an alien 

mineral, particularly as deposits of this mineral are 

present in the Kuskokwim valley and in the vicinity of 

the Tikchik Lakes. As it seemed doubtful that a mineral 

as soft as cinnabar could have survived glacial transport 

from these places, it was concluded that the cinnabar of 

the Goodnews placers was of local origin, derived either 

from the perknitic rocks of Susie Mountain or from late 

hydrothermal veinlets in the dunite. Collateral evidence is the presence of cinnabar in the platinum 

placers of the Ural Mountains, as recorded by Duparc 

and Tikonowitch (1920), and in the placers of the 

Goenoeng-Lawack district of Borneo, as recorded by 

Mertie (1969, p. 74). Of interest mineralogically is the 

presence of minute amounts of native mercury in some 

of the dredge concantrates, though this element is not 

utilized in the recovery of the precious metals. Native 

mercury has also been identified in primitive alluvial 

deposits in the Kuskokwim valley in the vicinity of the 

cinnabar deposits. 

The platinum metals of this area have been shown to 

be closely associated with chromite, but it is known from 

the work done on numerous samples by W. C. 

Overstreet and associates of the U.S. Geological Survey 
ECONOMIC GEOLOGY 39 

that the magnetite also contains small quantities of 

these metals. The tenor of platinum metals in the 

magnetite has been found to be a fifth or less of that 

present in the chromite. Another peculiarity of this 

magnetite is that practically all samples submitted for 

spectrographic analysis showed about 1 percent 

chronium. Inasmuch as ferric iron makes up 48.24 

percent of the molecule of magnetite, this increment 

constitutes an ionic replacement of about 2 percent 

chromium. It is possible that a part of this tenor in 

chromium represents an inhomogeneity, that is, an 

inclusion of chromite. The magnetite also contains 

about 0.3 percent manganese and smaller amounts of 

vanadium, zinc, nickel, and cobalt, in the order named. 

Traces of 18 other base elements have been identified. 

PLATINUM LODES 

All the platinum metals of the Goodnews Bay district 

have been derived from a mass of dunite, partly altered 

to serpentinite, that forms the ridge west of the upper 

valley of the Salmon River. All the headwater 

tributaries of the Salmon River flowing eastward from 

this ridge have fluvial deposits that are platinum 

bearing, and McCann Creek, draining northeastward to 

the Smalls River, also carries platinum metals. No 

other tributaries of the Salmon River are platinum 

bearing. The virtual absence of platinum metals in the 

streams draining westward from the Red Mountain 

ridge is believed to have resulted from their removal by 

glacial scouring, although it is possible that the bedrock 

sources of the platinum metals may have been localized 

in the eastern flank of the ridge. 

No workable lodes have yet been found in the dunite 

of the Red Mountain ridge. Two possible explanations 

are offered for the absence or paucity of lodes at or near 

the present surface. One is that all or most of the lodes 

have been almost or entirely eroded. An experiment 

bearing upon this interpretation has been made by the 

Goodnews Bay Mining Co. In 1965, a portable washing 

plant, with an adequate supply of water in drums, was 

transported to the top of the Red Mountain ridge near 

the head of Squirrel Creek, and the residual material at 

that site was sampled and sluiced. Some grains of 

platinum and traces of gold were recovered. The results 

suggest, but do not constitute, definite proof that the 

platinum was of residual origin; in fact, the presence of 

gold, which is believed to be derived from an ancient 

morainal deposit, suggests that the platinum was not 

derived from bedrock near the present surface and that 

both metals were of ancient origin. 

A second and more probable explanation is that most 

of the platinum metals were widely and sparsely 

distributed in the dunite and that the detrital metals 

have accumulated very slowly over a very long period of 

time, that is, since the beginning of the Pliocene Epoch, 

when the dunite is believed to have been first bared to 

erosion. This explanation renders unlikely the discovery of any large volume of workable ore; it does not 

preclude the possibility of finding small local concentrations of high-grade ore similar to those found in the 

dunites of the Ural Mountains. 

The crest of the Red Mountain ridge, throughout its 

length, is characterized by a fairly flat surface. It is 

possible that along this crest platinum metals have 

accumulated residually over a long period of time and 

have remained undisturbed except where transected by 

headwater fluvial gulches. The experimental prospecting of residual materials atop the ridge by the Goodnews 

Bay Mining Co. suggests this possibility. Such deposits, 

if they exist, have not been concentrated by stream 

action and therefore cannot be high-grade ores. But if 

some method could be devised to move these residual 

deposits into the lower valleys where sluice water is 

available, they might qualify as low-grade but workable 

ores. 

The original lodes, even if their exact sites have not 

been determined, have some interesting aspects that 

have been gleaned from the distribution of the platinum 

metals in the derived placers. The metals found in the 

valleys that drain the Red Mountain ridge show 

unmistakably that the composition of the lodes, and 

particularly the ratio of the major to the minor alloy, is 

variable. A very small part of these variations may 

result from the presence of certain platinum minerals, 

including cooperite and minerals intergrown with the 

alloys, such as laurite, sperrylite, mertieite, and other 

species as yet unnamed. Also the two alloys may vary 

somewhat in their compositions. But the principal 

variations in composition are dependent almost entirely 

upon the proportions of the two alloys. 

A striking variation in the composition of the lodes 

has been recognized in the platinum metals recovered 

from the placers of the western headwater tributaries of 

the Salmon River. Mining on these streams has shown 

that the content of platinum increases from Platinum 

Creek northward and, conversely, that the contents of 

iridium, osmium, ruthenium, and rhodium decrease in 

the same direction. The magnitude of these changes is 

presented in table 20 and is also charted in figure 14, 

where the abscissas are taken as the air distances from 

Fox Gulch to the heads of Squirrel Creek, Boulder 

Creek, Dowry Creek, and Clara Creek, that is, 1.1, 1.6, 

2.55, and 2.9 miles, respectively. 

Platinum and iridium, owing to their larger volumes, 

are genetically the two most significant elements. For 

the same reason, variations in composition introduced 

by different analysts are much less likely to show. 

Neither the platinum nor the iridium curves are linear, 
40 PLATINUM DEPOSITS OF THE GOODNEWS BAY DISTRICT, ALASKA 

SOUTH NORTH 

Osmium and ruthenium 

Rhodium I I 

0 I - 

0 1 2 3 

DISTANCE FROM PLATINUM CREEK, IN AIRLINE MILES 

FIGURE 14.-Variation in composition of platinum metals from 

streams that drain Red Mountain ridge. 

although they appear to have almost a reciprocal 

relation. The content of platinum increases about 43 

percent and the content of iridium decreases about 78 

percent from the upper valley of Platinum Creek to 

Clara Creek. The content of osmium plus ruthenium 

decreases about 82 percent, with a curve that is almost 

linear. From this result, it is inferred that osmiridium 

also increases linearly from south to north. Therefore if 

a curve for the principal alloy could be charted, it would 

be expected to be nearly linear. Rhodium decreases 

about 38 percent from south to north, thus suggesting 

that it is more closely related to osmiridium than to the 

principal alloy; that is, the osmiridium should contain 

more rhodium (by weight) than the principal alloy. This 

conclusion is confirmed in table 13. No inferences can be 

drawn from the percentages of palladium, as the 

analyses from Dowry and Clara Creeks are not regarded 

as dependable in every respect. 

Another possible variation in the platinum metals 

with distance is the granularity or sizes of the metallic 

grains in the lodes. Such a variation cannot be 

substantiated, as no sieving analyses were made of the 

products recovered from the western headwater 

tributaries of the Salmon River. If such a variation 

exists, it would have to be recognized in the metals 

recovered from the two pay streaks of the Salmon River 

above the mouth of Platinum Creek. Unfortunately, 

this is not possible, as the platinum metals in the upper 

stretches of the two pay streaks have been considerably 

intermixed by geologic processes heretofore described; 

this condition is further complicated by the fact that the 

metals of the two pay streaks were derived from lodes 

that existed at different erosional levels on Red 

Mountain. Only two facts are definitely known. First, 

the mean granularity of the metals in the bench pay 

streak is smaller than that in the pay streak of the 

valley floor. And second, the metals that issued from the 

valley of Platinum Creek, as heretofore shown, were 

coarser grained than those from the valley of the 

Salmon River upstream from the mouth of Platinum 

Creek. The favored interpretation is that the metals 

deposited in the bench pay streak were derived from the 

lodes that were first barred to erosion and that these 

higher horizons in the lode system yielded platinum 

metals of smaller granularity. On the other hand, it 

seems possible that within the lower horizons of the lode 

system, which yielded the metals in the pay streak of 

the valley floor, the granularity decreased from south to 

north. The curves of figures 10 and 12 will not serve to 

validate these interpretations owing to obvious intermixing of metals of the two pay streaks, but two curves 

of these figures show at least that the percentage of 

grains smaller than 0.42 mm in the bench pay streak is 

much larger than the corresponding percentage for the 

pay streak of the valley floor. 

The original size of the lode system and the tenor of 

the lodes in platinum metals are problems that have no 

explicit solutions, yet it may be of some value to venture 

certain approximations. The ultrabasic rocks that 

constitute the Red Mountain ridge were probably 

barred to erosion at the beginning of the Pliocene Epoch, 

about 5 million years ago. The shape of the original 

mass of dunite is unknown, but the contacts suggest 

that it may have had the general form of a triaxial 

ellipsoid, with a major axis trending N. 20" E., a median 

axis tilted slightly westward, and a near-vertical minor 

axis plunging steeply S. 70" E. This intrusive body may 

either have been emplaced in this position or it may 

subsequently have been tilted from some earlier 

position. For maximum simplicity in computation, the 

ellipsoid is considered to be vertically emplaced. The 

present surficial contact with the adjacent country rock 

is arbitrarily interpreted as an ellipse that delimits the 

base of an eroded segment of the ellipsoid. 

The rate of denudation for the United States has been 

estimated by Dole and Stabler (1909) to be 1 inch in 730 

years, or approximately 0.0001 foot per year. This 

estimate, though made many years ago, was carefully 

prepared and is believed still to be of the right order of 

magnitude. On this basis, the altitude of the Red 

Mountain ridge may have been lowered about 500 feet 
SELECTED REFERENCES 41 

since the dunite was first barred to erosion at the 

beginning of the Pliocene Epoch. Assuming that half 

the intrusive mass has been removed by erosion, the 

present outcrop may be used to obtain the dimensions of 

two semiaxes of the ellipsoid. The length of the 

intrusive, including a small part'north of the Smalls 

River, is 6 miles, whence the major semiaxis is 3 miles. 

By mechanical integration, the surficial area was found 

to be 7.3 square miles. The area of an ellipse isA =n-ab, 

whence the average median semiaxis is found to be 

b = -=-- A 7'3 - 0.775 mile. 

n-a 3%- 

From this, the dimensions are 

a = major semiaxis = 3.0 miles, 

b = median semiaxis = 0.775 mile, and 

c = minor semiaxis = 500 feet = 0.0947 mile. 

The volume of half of a triaxial ellipsoid is given by 

2 V = - n-abc. 3 

Substituting the values given for a, b, and c, we obtain 

V = 2.0944abc = 0.461 cubic mile and 

V = (0.461) = (1,760)3 cubic yards. 

The platinum metals contained in the eroded half of the 

ellipsoid are estimated to have amounted to one million 

troy ounces. This includes metals mined, metals lost in 

mining, metals not yet mined, and metals permanently 

lost by erosion. This estimate may in fact be low, but it 

seems as large as warranted by the facts now at hand. 

The derived mean tenor is therefore 1,000,000/(0.461) x 

(1,760)3=0.00040 troy ounce, or about 0.19 grain per 

cubic yard. The tenor of the Nishniy-Tagil dunite of the 

Ural Mountains was computed by Duparc and 

Tikonowitch (1920) to be 0.13 grain per cubic yard. 

Another check depends upon two analyses made by 

E. T. Erickson, U.S. Geological Survey. The first 

analysis, made of a composite sample of dunite taken at 

regular intervals from the south to the north end of the 

Red Mountain ridge, showed a tenor of 0.27 percent of 

Cr203 or 0.4 percent chromite. The second analysis, 

made of a random sample of chromite pebbles taken 

from a cleanup on Fox Gulch, where this mineral is 

unusually abundant, showed a tenor of 0.05 troy ounce 

of platinum metals per ton of chromite. Combining 

these two analyses and taking the density of dunite as 

3.3, it is found that a cubic yard of dunite contains 0.27 

grain ofplatinum metals. These two tenors, that is, 0.19 

and 0.27 grains platinum metals per cubic yard of 

dunite, may therefore be taken as the limiting values. It 

is conceded that the tenors to be expected in prospecting 

may be higher than these, as the tenors in the 

uppermost horizons of the dunite must have been much 

lower than the mean value. But even if the mean tenor 

were as great as 1 grain per cubic yard, the platinum 

metals contained would have a value of only about 47 

cents per cubic yard or about 17 cents per ton with the 

value of platinum at $225 an ounce (as of April 1974). 

Many years ago The Alaska-Juneau Co., by handling 

very large tonnages, was able to mine hardrock with a 

tenor of a dollar per ton in gold, but that would no longer 

be possible. 

The prospecting for lodes requires that these results 

be carefully scrutinized. There is no evidence that the 

platinum metals were distributed uniformly within the 

dunite, in either a horizontal or a vertical sense; ample 

proof has been given that the ratios of the two alloys 

differ from south to north. The richness of the placers in 

the valleys of Squirrel Creek and Fox Gulch, as 

compared with those of Clara Creek, indicates an 

uneven horizontal distribution, and this is corroborated 

by the paucity of platinum metals in the intervening 

streams. And metals with the high density of the 

platinum group are not likely to have been distributed 

uniformly in a vertical sense. The importance of such a 

vertical concentration cannot be appraised but is a 

factor to consider. If all the known facts are considered, 

the area at or near the heads of Squirrel Creek and Fox 

Gulch appears to be the best site for prospecting for 

lodes. It should be kept in mind that the dunite of the 

Red Mountain ridge is strikingly similar to that of the 

Nishniy-Tagil area of the Ural Mountains, where small 

bodies of platinum-bearing chromite were found, 

ranging in length from 1 to 400 feet. The highest grade 

of such aggregates was the "Krutoy Log lode," a mass of 

chromite 2 metres in length that yielded 965 ounces of 

platinum metals. In conclusion, it may be said that the 

dunite of Red Mountain is not a favorable site for the 

discovery of any large body of low-grade but workable 

ores of the platinum metals. It is possible that some 

small concentrations of high-grade ore may be located. 

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Survey Water Supply Paper 234, p. 78-93. 

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Ford, L. A., 1964, Platinum alloy permanent magnets: Platinum 

Metals Rev., v. 8, no. 3, p. 8Z90. 
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Goodnews quadrangle, Alaska; U.S. Geol. Survey Misc. Geol. Inv. 

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Johnson, Matthey and Co., Ltd., 1972, Physical properties of the 

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Leonard, B. F., Desborough, G. A., and Page, N. J, 1969, Ore 

microscopy and chemical composition of laurite: Am. 

Mineralogist, v. 54, p. 133C1346. 

MacNeil, F. S., Mertie, J. B., Jr., and Pilsbry, H. A,, 1943, Marine 

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