Platinum-Group Elements in 

Magnetic Concentrates from the· 

Goodnews Bay District, Alaska 

By SAM ROSENBLUM, R. R. CARLSON, j. M. NISHI, and 

W. C. OVERSTREET 

Platinum-group elements (PGE) occur in magnetic 

concentrates as discrete mineral grains, as 

inclusions in magnetite, and as diffused atoms. in 

the magnetite lattice. The finer fractions ot the 

magnetic concentrates contain the greatest 

amounts of PGE 

U.S. GEOLOGICAL SURVEY BULLETIN 1660 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1986 

For sale by the 

Books and Open .. File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, CO 80225 

Library of Congress Cataloging in Publication Data 

Main entry under title: 

Platinum•group elements in magnetic concentrates from the Goodnews 

Bay district, Alaska. 

(U.S. Geological Survey Bulletin ; 1660) 

Bibliography: p. 

Supt. of Docs. No.: I 19.3:1660 

1. Platinum group. 2. Platinum ores-Alaska-Goodnews Bay Region 

(Bay). 3. Placer deposits-Alaska-Goodnews Bay Region (Bay). 4. 

Magnetite-Alaska-Goodnews Bay Region (Bay). 

I. Rosenblum, Sam. II. Series. 

QE75.89 no. 1660 557.3 s 85-600123 

[TN490.P7] [553.4'22'097984] 
CONTENTS 

Abstract 1 

Introduction 1 

Background 1 

Purpose of present study 2 

Acknowledgments 2 

Methods of study and results 2 

Semiquantitative fire-assay and emission spectrographic analyses 4 

Polished-section studies 16 

Scanning electron microscope studies 17 

Platinum-group element phases 17 

Other phases 29 

Conclusions 32 

Recommendations 33 

References cited 36 

FIGURES 

1. Index map of part of southwestern Alaska showing location of Goodnews Bay 

district 3 

2. Photograph of the Kevex screen showing the results of analysis by the X-ray 

energy-dispersive system of a PGE phase 18 

3. SEM micrograph of grains 1, 2, and 3 in polished section 69AMt14A2 19 

4. SEM micrograph of grain 1 in polished section 69AMt14A2 21 

5. SEM micrograph of grain 4 (Pt-Fe alloy, Pt) in polished section 66AMt31A6 22 

6. Graph of chondrite-normalized ratios of platinum-group elements (PGE) in three 

different groups of samples from the Goodnews Bay district 23 

7. SEM micrograph of the lower left part of figure 4 24 

8. SEM micrograph of the upper part of figure 4 25 

9. SEM micrograph of the right edge of figure 4 26 

10. SEM micrograph of grain 3 in polished section 69AMt14A2 27 

11. SEM micrograph of the upper edge of grain 1 in polished section 

69AMt14A2 28 

12. Photomicrograph of grain 2 in polished section 69AMt14A2 29 

13. Photomicrograph of the left side of figure 12 30 

14. SEM micrograph of the upper part of figure 12 31 

15. SEM micrograph of the center of figure 4 32 

16. SEM micrograph of the left edge of grain 2 33 

17. SEM micrograph of part of grain 5 in polished section 66AMt7N6 34 

18. Photomicrograph of part of grain 1 in polished section 69AMt14A2 35 

19. SEM micrograph of central part of grain 1 in polished section 69AMt14A2 36 

Ill 
TABLES 

1. Results of semiquantitative fire-assay and emission spectrographic analyses of 

platinum-group elements in 21 preliminary magnetic concentrates from the Goodnews Bay district, Alaska 6 

2. Results of semiquantitative spectrographic analyses of elements other than the 

platinum-group elements in 21 preliminary magnetic concentrates from the Goodnews Bay district, Alaska 7 

3. Results of semiquantitative fire-assay and emission spectrographic analyses of 

platinum-group elements and gold in 89 magnetic concentrates from the Goodnews 

Bay district, Alaska, including six nonmagnetic concentrates for comparison 8 

4. Results of semiquantitative spectrographic analyses of elements other than the 

platinum-group elements in 89 magnetic concentrates from the Goodnews Bay 

district, Alaska, including six nonmagnetic concentrates for comparison 12 

IV 
Platinum-Group Elements in 

Magnetic Concentrates from the 

Goodnews Bay District, Alaska 

By Sam Rosenblum, R. R. Carlson, j. M. Nishi, and W. C. Overstreet 

Abstract 

Platinum-group elements (PGE) occur in ferromagnetic concentrates from placer deposits in the 

Goodnews Bay district, Alaska, and analyses showed 

platinum values are as high as 1,100 parts per million 

(ppm) (35.37 troy ounces per ton). Scanning electron 

microscope studies showed at least seven mineral 

phases that contain the following associations of PGE: 

platinum-iron (Pt-fe) alloy, sperrylite (Pt-As), unknown A 

(lr-Fe alloy), unknown B (lr-Rh-Pt-Fe-As-S), hollingworthite (Rh-As-S), unknown C (Rh-Pd-Ni-As-S), and unknown D (Pb-Rh-Fe-lr-S). In each association, variable 

amounts of PGE and minor elements (chromium, copper, nickel), as determined by the semiquantitative X-ray 

dispersive method, made the assignment of definite 

compositions difficult. 

PGE minerals occur as discrete grains in the magnetic concentrate and as inclusions in magnetite. Furthermore, PGE apparently have diffused into magnetite 

adjacent to the borders of PGE minerals. Such PGE may 

be held in the magnetite lattice and represent a valuable 

resource lost during extractive metallurgy, but this possibility needs to be tested. 

Grain sizes of the various equant PGE-bearing inclusions in three magnetite grains ranged from less than 

1 ..,._m to about 80 ..,._m. These minerals generally formed 

irregular inclusions in magnetite hosts that were 0.2--0.4 

mm across. Discrete amoeboid grains of Pt-Fe alloy in 

two fine-grained concentrates were 25 by 55 to 40 by 

80 ..,._m in size. The average grain size for equant Pt-Fealloy inclusions was about 12 ..,._m, and the average for 

bladed lr-Fe alloy inclusions was about 1 by 12 ..,..m. 

fire-assay and emission spectrographic analyses of 

12 of 14 sized groups of magnetic concentrates showed 

that the finest grained fractions contained the greatest 

amounts of PGE, but the increase in amount was not 

always in direct relation to decreasing grain size. Five 

of the fourteen sets indicated a second, less abundant 

population of PGE in the coarse-grained fractions. 

We recommend expansion of the study of PGE in 

magnetite to include magnetite from mafic and ultramafic rocks from other parts of Alaska as well as 

geologically suitable areas in the conterminous United 

States. A study is needed to find methods for improving 

sample preparation and analytical techniques to enable 

more rapid acquisition and reliability of results of 

analyses for PGE in magnetite. Also, as the semiquantitative fire-assay and emission spectrographic analyses 

showed the presence of gold in the magnetite, a study 

is needed to determine the mode of occurrence of the 

gold. 

INTRODUCTION 

Background 

The use of detrital magnetite as a geochemical sample medium has been under investigation in the United 

States Geological Survey and in the Canadian Department 

of Energy, Mines, and Resources since the early 1960's 

(Theobald and others, 1967; Nakagawa, 1975; Raicevic 

and Cabri, 1976; Thayer and others, 1977; Overstreet and 

others, 1978; Pan and others, 1980). ·The discovery by 

Erickson and others (1966), through geochemical means, 

of economic deposits of disseminated micrometer-sized 

gold at Cortez, Nev., led Overstreet to postulate that finegrained platinum metals, in particles too small to accumulate in placers and thus not amenable to identification by 

panning, might be present in source rocks as discrete 

grains and as inclusions in magnetite. Such grains of magnetite could easily be recovered from alluvial sediments 

by panning or other methods of concentration for recovery 

of the PGE (platinum group elements) contained therein. 

The conceptual basis of genesis was that in an atr 

propriate cooling magma, myriads of centers of nucleation 

Introduction 1 
for the platinum-group metals could occur without extensive migration of the metals. The result would be large 

numbers of small grains with compositions crystallized 

from the Pt-Pd-Fe-As-S system, as summarized by Skinner and others (1976). Some of these grains, even ones 

only a few micrometers across, could serve as centers 

for the later overgrowth of magnetite; and the magnetite 

could be expected to attain sizes commonly associated 

with accessory minerals in igneous rocks. Platinum-bearing magnetite would readily accumulate in alluvial deposits with other heavy minerals. Even in rocks where 

the platinum failed to form grains large enough to be retained in placers during the erosion of the source rock, 

its presence could be detected by analysis of detrital magnetite. Thus, source rocks presently not known to contain 

platinum might be discovered through the study of detrital 

magnetite as a preferred geochemical sample medium. 

This concept was promoted by John B. Mertie, Jr., 

former platinum-commodity geologist for the U.S. 

Geological Survey, who noted that the black sand concentrates from the platinum placers in the Goodnews Bay 

district, Alaska, were commonly crushed to improve the 

recovery of the platinum metals. Because of his interest, 

and through the cooperation of the Goodnews Bay Mining 

Company, Mertie sent to the writers two suites of magnetic concentrates from the Goodnews Bay district (fig. 1). 

These magnetic concentrates provided the sample material 

on which this present laboratory investigation is based. 

Purpose of Present Study 

The association of PGE with the spinel, chromite, 

is well known in the Goodnews Bay district (Mertie, 

1969, p. 87) as well as in other areas of ultramafic rocks 

such as the Stillwater Complex, Mont. (Grimaldi and 

Schnepfe, 1969; Page and others, 1969; Page and 

Carlson, 1980), in the Tulameen River area of British 

Columbia, Canada (Cabri, 1974; Raicevic and Cabri, 

1976), and in South Africa at several PGE deposits (Gijbels and others, 1974; Vermaak and Hendriks, 1976; 

Cabri and others, 1977; Crockett, 1979). The association 

of PGE with the spinel, magnetite, has been noted by 

Page and others (1973, p. 543), Snetsinger ( 1973), 

Fominykh and Znamenskiy (1975), Volchenko and others 

(1975), Begizov and others (1975), Chyi and Crocket 

(1976), and Raicevic and Cabri (1976). Because PGE are 

in or attached to magnetite, the Goodnews Bay Mining 

Company crushed and concentrated all the magnetite concentrates during the last years of operation in order to 

recover the contained PGE (Mertie, 1976, p. 12). 

Platinum values in magnetite reported in the literature include the following: 0.12-0.47 parts per million (ppm) 

in the Tulameen River area (Raicevic and Cabri, 1976), 

244-858 parts per billion (ppb) in the Sudbury, Ontario, 

district of Canada (Chyi and Crocket, 1976), and 

2 Platinum-group Elements, Goodnews Bay District, Alaska 

0.01-0.42 ppm in the Ural platinum belt (Fominykh and 

Znamenskiy, 197 5; Volchenko and others, 197 5). These 

magnetites were all associated with mafic or ultramafic 

rocks, but platinum values from 0.016 to 0.08 ppm were 

also reported for magnetites from calcalkaline rocks ranging in composition from diorite to granite (Fominykh and 

Znamenskiy, 1975). 

In the present study, samples of magnetic concentrates from the Goodnews Bay district were examined to 

characterize the modes of occurrence of PGE in these concentrates, particularly in magnetite, and to utilize magnetic concentrates as geochemical sample media for PGE. 

To our knowledge, no similar study using chromite concentrates has been done. On the basis of the identification 

of mineral hosts and actual sites of PGE, we anticipated 

making recommendations for (1) recovery of PGE, (2) 

further investigations to characterize PGE occurrences in 

worldwide magnetic concentrates from mafic and ultramafic terranes, and (3) the use of magnetic concentrates 

as a geochemical sample medium for PGE. 

ACKNOWLEDGMENTS 

A number of people made this report possible by 

their assistance and stimulating discussions. 

We thank John B. Mertie, Jr., U.S. Geological Survey, and Charles Johnston, Treasurer, Goodnews Bay 

Mining Company, for supplying the samples of magnetic 

concentrates from the platinum placers of the Goodnews 

Bay district, Alaska. The courtesy of the Company in 

agreeing to the publication of the results of the work is 

gratefully acknowledged. 

Our appreciation is expressed to the following members of the U.S. Geological Survey for help in doing 

emission spectrographic analyses for the PGE and other 

minor elements in the magnetic concentrates: E. F. 

Cooley, J. A. Domenico, D. F. Siems, and W. D. Crim. 

In addition, N. J. Page and D. L. Rossman gave useful 

critical reviews of the draft copy, E. E. Foord performed 

some electron-microprobe analyses, and G. A Des borough 

helped in planning the search for PGE in the magnetic 

concentrates and also aided in scanning electron microscope (SEM) work. 

METHODS OF STUDY AND RESULTS 

Two suites of magnetic concentrates from the Goodnews Bay district, Alaska, were received from J. B. Mertie, Jr. , during 1972-73. They bore his field numbers, 

and they were designated in our study as the preliminary 

set of magnetic concentrates (21 fractions) and the later 

set of magnetic concentrates (89 fractions). The reader 

is referred to Mertie (1976, figs. 2, 3, and p. 35-37) 

for geologic and claim maps and sample locations. 

The preliminary set consisted of four groups of 

magnetic concentrates prepared from two commercial 
100 200 MILES 

100 200 KILOMETERS 

Figure 1. Index map of part of southwestern Alaska showing location of 

Goodnews Bay district (modified from Mertie, 1976, fig. 1). 

dredge concentrates from the Salmon River and one concentrate panned from beach sand on the shore of the 

Pacific Ocean south of Red Mountain (Mertie, 1976, fig. 

2). These magnetic concentrates had been sieved by hand 

by Mertie to as many as six sizes (making a total of 21 

fractions) before transmittal to us for study. 

The later set consisted of 20 concentrates from 

dredge cleanups, exploration drill-hole samples, and panned alluvium from the Salmon River drainage as well as 

panned concentrates from the Pacific Ocean beach. These 

samples had not been sieved or separated into magnetic 

and nonmagnetic fractions. We selected 14 of these concentrates, and using Tyler screens with mesh numbers 12 

(1.410 mm), 24 (0.70 mm), 42 (0.354 mm), 80 (0.177 

mm), and 170 (0.088 mm), we divided each concentrate 

into groups of 6 sieve fractions of decreasing grain size. 

The sixth fraction was less than 170 mesh (--0.088 mm). 

Again, not all the samples yielded six fractions. To these 

were added several nonmagnetic fractions to make the 89 

fractions sent for analysis. 

Because the sized fractions of the preliminary set 

were large, the 21 sieved fractions of magnetic concentrates were used to perfect the fire-assay and emission 

spectrographic method that was used to analyze for PGE 

and gold. Many replicate analyses and variations in technique were made on them to determine if PGE were actually present in the magnetic concentrates. When the presence of the PGE was confirmed and the analytical technique was considered satisfactory, the later set of 20 concentrates was studied using the following procedures: 

1 . Magnetic separation with hand magnet; 

2. Splitting of magnetic fractions into two parts, 

one for analyses and the other for making 

polished sections; 

3. Sieving of split for analysis into six size fractions using a Ro-Tap machine 1 to shake the 

concentrates for 10 minutes; 

4. Semiquantitative fire-assay and emission spectrographic analyses of one split of the sized 

concentrates for PGE and gold; 

5. Semiquantitative em1sswn spectrographic 

analyses of another split of each of the sized 

concentrates for 30 elements; 

6. Metallographic microscope analyses of polished 

sections of all magnetic concentrates to locate 

grains with PGE-bearing minerals. Only five 

grains with PGE minerals were recognized; 

7. Scanning electron microscope (SEM) analyses 

of selected inclusions in the magnetic grains 

done with an attached energy-dispersive spectrometer. 

1

The use of trade names is for descriptive purposes only and does 

not constitute endorsement of this product by the U.S. Geological 

Survey. 

Methods of Study and Results 3 
Preliminary scan by electron microprobe was made 

on some inclusions. 

Semiquantitative Fire-assay and Emission 

Spectrographic Analyses 

Experimentation on the 21 preliminary magnetic 

fractions using the semiquantitative fire-assay and emission spectrographic analytical technique of Cooley and 

others (1976) for platinum, palladium, rhodium, 

ruthenium, iridium, and gold produced an optimum PGE 

recovery with a fire-assay flux of 80 g PbO, 15 g Si02, 

30 g Na2C03 , 15 g Na2B4 0 7 , and 1.8 g graphite for approximately 3 g of each sample. Four to eight milligrams 

of gold wire were added to the flux to collect the PGE 

in the cupellation step. Therefore, gold was not determined by the fire-assay analyses in these initial samples. 

Three replicate analyses on each of the 21 preliminary 

fractions produced platinum values with relative standard 

deviations that ranged from 16 percent to 70 percent for 

each fraction. 

The precision and accuracy of the analyses were 

increased by investigating sampling errors due to small 

sample size and losses of PGE to the fire-assay fusion 

slag. Because samples larger than about 3 g tended to 

overload the digestive capacity of the flux, sampling errors due to small sample size were reduced by combining 

the results of replicate analyses. Losses of PGE to the 

slag during fusion were studied from both mechanical and 

chemical points of view. Microscopic examination of the 

slags found no undigested magnetite grains, even where 

the sample grain size was as great as 1. 65 mm; thus, 

mechanical losses were ruled out. However, fine grinding 

of the magnetite before fusion produced dramatic increases in recovered PGE, perhaps indicating some 

"chemical losses" during fusion of coarser grains of magnetite. Here, "chemical losses" refers to any number of 

complex chemical conditions or reactions in the fusion 

process that result in either a nonreduction of PGE to 

the metallic state or transformation of complexes of PGE 

to an overall oxidized state. Each of these conditions can 

cause subsequent loss of these elements to the silicate 

slag. Fine grinding of the samples possibly allowed for 

early exposure of PGE to reducing conditions that were 

absent later in the fusion process. 

Because grinding of a sample containing noble metals can produce significant losses of these metals to the 

grinding apparatus, a test of various grinding methods was 

applied to four splits of sample number 66AMt7N3 to 

optimize the PGE recovery. The following table summarizes results of two of these grinding methods. It points 

out some of the hazards of preparing platinum-bearing 

magnetites for analysis. 

4 Platinum-group Elements, Goodnews Bay District, Alaska 

Split Sample Average Mean Precision, 

preparation grain size recovered in percent1 

analyzed, Pt value, 

in millimeters in parts per million 

1 None 0.527 31 76 

2 Coarse grind .279 1.9 100 

with ceramic 

plates 

3 Fine grind .059 43 86 

with ceramic 

plates 

4 Fine grind .061 130 4 

with agate 

mortar and 

pestle 

1

Relative standard deviation, in percent= std. dev. x 100 percent/ 

mean recovered Pt value. Replicate analyses=3. 

The loss of platinum-group metals (PGM) to the 

ceramic grinding plates can be seen in comparing recovered platinum in the coarse-ground split to that in the 

unground split. A twenty-three-fold increase in platinum 

recovery can be seen in comparing the ceramic-plate fine 

grind to the coarse grind. The additional threefold increase 

in platinum recovery, and twentyfold increase in precision, of the fine grind on agate versus the fine grind on 

ceramic plates indicates that a fine grind or milling of 

these samples, using relatively nonporous and hard materials, would optimize PGE recovery. Re-fusion of fireassay slags from the unground and coarse-ground splits 

recovered no significant amounts of PGE; possibly the 

PGE are too strongly bound chemically to the silicate 

phase to be reduced by the standard lead-based assay. 

Further experimentation with sample preparation led 

to the use of a Bleuler eccentric mill equipped with a 

50-g grinding pot; PGE recovery from samples so ground 

was similar to recovery from agate-ground samples. Sample preparation by Bleuler milling was chosen over handgrinding in an agate mortar as a means of reducing human 

bias in preparation and because hand-grinding coarsegrained samples causes sample loss through ejection of 

grains. 

The use of these new methods of sample preparation 

and the flux described earlier to accommodate the magnetite host allowed a threefold increase in sensitivity ( detection limit) and a far greater increase in precision relative 

standard deviation (RSD) over older methods. The results 

of fire-assay and emission-spectrographic analysis are 

given in table 1. The lower limits of determination (one 

to two spectrographic report intervals above the lower 

limits of detection (Cooley and others, 1976)) for the PGE 

in parts per billion are as follows: Ru, 1~200; Rh, 1-2; 

Pd, 1; Ir, 50---100; and Pt, 2-5. Osmium is volatilized 

during the fire assay and is not reported. Of the four sam-
pies that showed greater than 50 ppm platinum, two were 

estimated at about 80 and 700 ppm. 

Semiquantitative spectrochemical analyses for 30 

elements other than the PGE were also made on the 21 

preliminary fractions. The results showing the most pertinent data are given in table 2. Not shown in table 2 are 

data for Fe, which is 50 percent or greater for all samples; 

Ba, with only 8 samples containing as much as 50 ppmthe limit of detection; Pb, with 10 samples containing 20 

ppm and 1 containing 100 ppm; Zn, with 1 sample containing 500 ppm and 3 others, 1,000 ppm; and Zr, with 

9 samples containing 20 ppm and 3 containing 30 ppm. 

Looked for but not found were Ag, As, Au, B, Bi, Cd, 

La, Mo, Nb, Sn, Sr, W, andY. 

The data in table 2 resemble trace-element compositions previously reported for magnetic concentrates from 

ultrabasic areas elsewhere in Alaska (Overstreet and 

others, 1978) except for greater amounts of chromium. 

The probable significance of these minor elements is discussed near the end of this section. 

The later set of 89 magnetite fractions was analyzed 

using 9.3 mg silver as a fire-assay collector so that gold 

could be determined along with the PGE. The results of 

the semiquantitative fire-assay and emission spectrographic analyses for PGE and gold on the 89 fractions 

are given in table 3, and the results of the semiquantitative 

spectrographic analyses for the non-PGE elements in the 

same samples are listed in table 4. 

As many as seven replicate analyses were made by 

fire-assay and emission spectrography on each size fraction in table 3, and the results are reported there as mean 

values. The weight shown for each sample in table 3 is 

the sum of the sample weights used in these replicate 

analyses. An approximate 3 g sample weight was chosen 

as an amount of magnetite that would not exceed the fusion and collection capabilities of the flux. 

The later set of 89 size fractions was prepared using 

a 15-g silica cleanup of the mill pot after each fraction. 

The cleanup silica from the mill pot was used as the 15-g 

silica flux component for one of the 3-g samples of that 

fraction. The lower platinum value reported for sample 

66AMt7N3 in table 3, compared to recovered platinum 

in earlier experimentation, probably reflected the uneven 

distribution (particulate nature) of PGE within any one 

screened fraction of magnetite. However, the magnitude 

of this variance was not sufficient to negate the trends 

of PGE distribution seen within each of the 14 groups 

of 6 screened fractions (table 3). 

Of the 14 sets of size-graded samples listed in table 

3, 12 showed a general, but erratic, increase in platinum 

values with decreasing grain size. In samples 69AMt6A 

and 69AMt14A, the greatest platinum values were in the 

second and third sieve fractions; the sixth fraction in each 

was not high. Paladium, rhodium, ruthenium, and iridium 

values were erratic; but where the platinum values were 

high, generally one or more of these PGE was correspondingly high. 

Despite these specific observed inconsistencies for 

direct increase in concentrations of the POE with decreasing grain size, the fmest particles of detrital magnetite 

strongly tended to contain the most PGE. When the values 

for the POE determined for the coarsest sieve sizes and 

the finest sieve sizes were compared in samples where 

one or both of the pair of sieve fractions contained detectable POE, the finest size magnetic fraction virtually 

always contained more POE than the coarsest sieve fraction. The following table confmns this observation. 

Number of Number of sieve pairs 

sieve pairs in which the greatest 

Element showing concentration of PGE 

element was in the finest fraction 

Pt 14 14 

Pd 13 11 

Rh 11 11 

Ru 1 1 

lr 7 7 

These relations show that the finest sieve fraction 

of the magnetic concentrate at the Goodnews Bay Mining 

district is the preferred host for POE in the magnetic concentrate. By sieving to fine size, an initial enrichment 

in POE could be made so that the amount of POE in 

the analysis was increased over that of the whole unsized 

sample, and the results of analyses offered greater contrasts for comparisons than those of the whole samples. 

Gold (table 3) followed essentially the same pattern 

as the PGE in relation to the size of the host grains of 

detrital magnetite. Except for the set represented by sample 69AMt5, where all sieve fractions were auriferous and 

were rich in PGE, the gold tended to be most abundant 

in sieve sizes smaller than 0.177 mm. No correlation 

existed between the amounts of gold and of such elements 

as copper, nickel, and zinc which suggested that the gold 

was not present in inclusions of sulfide minerals in the 

detrital magnetite. Evidently native gold was present in 

the detrital magnetite, perhaps alloyed with the POE, but 

this subject was not pursued in this investigation. In 

another study (Overstreet and others, 1978) gold was indeed found in magnetite. 

Comparison of 14 analyses that showed platinum 

values of 90 ppm or more (table 3) with analyses for 

PGE in samples free of black sand, presented by Mertie 

(1976, p. 16), showed qualitatively similar results. In both 

sets, platinum was by far the most abundant element; 

iridium was next, followed by rhodium, palladium, and 

ruthenium. When our PGE values and the values for the 

principal alloy, shown in Mertie's tables 5, 7 and 13 

Methods of Study and Results 5 
Table 1. Results of semiquantitative fire-assay and emission spectrographic analyses 

of platinum-group elements in 21 preliminary magnetic concentrates from the Goodnews Bay district, Alaska 

[Analysts: R. R. Carlson and E. F. Cooley. G, greater than value shown in parentheses; N, not detected 

at lower limit of detection shown in parentheses] 

Sample Size, Weight, Parts Eer million 

No. 1 in millimeters in grams Pt Pd Rh Ru Ir 

66AMt7Al >25 3.0 0.15 N(O.Ol) N(O.SO) N(0.25) 

66AMt7A2 25 - 20 3.0 .01 N(.Ol) N( .50) N(.25) 

66AMt7A3 20 - 15 3.0 .3 .03 N(.Ol) N(.SO) N(.25) 

66AMt7A4 15 - 10 3.0 .1 .015 N(.Ol) N(.SO) N(.25) 

66AMt7B 10 - 3.33 3.0 • 1 .os N(.01) N(.SO) N(.25) 

66AMt7C 3.33 - 2.36 3.0 .05 N(.01) N( .50) N(.25) 

66AMt7D 2.36 - 1.65 3.0 .2 .02 N(.01) N(.SO) N(.25) 

66AMt7E 1.65 - 1.17 3.0 20 .30 .20 N( .50) 

66AMt7F 1.17- .83 3.0 30 .15 .30 N(.SO) 2 

66AMt7G .83 - .59 3.0 30 .20 .so N( .50) 7 

66AMt7H .59 - .42 3.0 20 .15 .70 N(.SO) 7 

66AMt7I .42 - .29 3.0 50 .30 .so N( .50) 2 

66AMt7J .29 - • 21 3.0 G(SO) .30 .70 .so 5 

66AMt7K .21 - .15 3.0 G(SO) .30 .so 5 

66AMt7L .15 - .10 3.0 G(SO) .50 1.5 N(.SO) 3 

66AMt7M <.10 3.0 G(SO) 3 7 .70 15 

69AMt9A <.29 7.5 .3 .03 .015 N(.20) N(.10) 

69AMt9B .29 - .21 7.5 .2 .03 .015 N(.20) N(.10) 

69AMt9C .21 - • 15 7.5 .1 .02 .007 N(.20) N(.10) 

69AMt9D <.15 .5 1.5 N(.06) N(.06) N(3) N(l.S) 

72AMt1 Unsized 7.5 7 .10 .07 N(.2) .30 

1

Localities of magnetic concentrates (from Mertie, 1976, fig. 3, plot of Salmon River drainage and 

claims): 

66AMt7 series-Dredge concentrates from valley floor, Salmon River, claim 12 below Discovery 

claim. 

69AMt9 series-Pacific beach, a short distance south of the ultrabasic promontory of Red Mountain. 

72AMtl-Dredge concentrate from Fourth of July bench claim, Salmon River. 

6 Platinum-group Elements, Goodnews Bay District, Alaska 
Table 2. Results of semiquantitative spectrographic analyses of elements other than platinum-group 

elements in 21 preliminary magnetic concentrates from the Goodnews Bay district, Alaska 

[Analysts: D. F. Siems and W. D. Crim. G, greater than value shown in parentheses; L, less than the value shown in parentheses] 

Sample Size, Percent 

No. in millimeters Mg Ca Ti 

Parts per million 

Mn Co Cr Cu Ni Sc v 

66AMt 7A1 

66AMt7A2 

66AMt7A3 

66AMt 7A4 

66AMt7B 

66AMt7C 

66AMt7D 

66AMt7E 

66AMt7F 

66AMt7G 

66AMt7H 

66AMt 7I 

66AMt7J 

66AMt7K 

66AMt7L 

66AMt7M 

69AMt9A 

69AMt9B 

69AMt9C 

69AMt9D 

72AMt1 

>25 3 1.5 2 3,000 200 

25 - 20 3 .3 G(2) 3,000 300 

20 - 15 2 .3 G(2) 3,000 200 

15 - 10 2 .5 2 3,000 300 

10 - 3.33 2 .5 2 3,000 300 

3.33 - 2.36 2 .2 G(2) 5,000 300 

2.36 - 1.65 2 .2 2 5,000 200 

1. 6 5 - 1.17 1. 5 • 3 2 3. 000 300 

1.17 - 0.83 1.5 .2 2 3,000 300 

.83 - 0.59 1.5 .3 2 3,000 150 

500 

700 

700 

1,000 

1,500 

2,000 

2,000 

3,000 

5,000 

10,000 

.59 - 0.42 .2 

.42 - 0.29 1.5 .15 1.5 

.29 - 0.21 1.5 .2 1 

.21 - 0.15 1.5 .15 

.15 - 0.10 1.5 .15 

<.10 .15 1 

2,000 150 G(10,000) 

3,000 150 G(10,000) 

3,000 150 G(10,000) 

3,000 150 G(10,000) 

5,000 150 G(10,000) 

3,000 200 G(10,000) 

15 

20 

15 

15 

10 

20 

15 

15 

10 

10 

10 

10 

15 

300 50 3,000 

500 30 5,000 

500 20 5,000 

500 20 5,000 

500 20 5,000 

500 20 5,000 

500 20 5,000 

500 20 5,000 

500 20 5,000 

500 20 5,000 

500 15 3,000 

700 15 5,000 

700 10 3,000 

15 700 15 3,000 

15 1,000 20 3,000 

50 700 15 3,000 

>0.29 1.5 .15 1.5 

.29 - 0.21 1.5 .1 

.21 - 0.15 1.5 .1 1 

<.15 1.5 .2 1 

5,000 200 G(10,000) L(10) 1,000 20 3,000 

3,000 150 G(10,000) L(10) 1,000 20 2,000 

5,000 200 G(10,000) L(10) 1,000 20 3,000 

3,000 200 G(10,000) 150 700 20 3,000 

Unsized 1.5 .1 1.5 3,000 150 G(10,000) L(10) 700 20 3,000 

1

Localities of magnetic concentrates (from Mertie, 1976, fig. 3, plot of Salmon River drainage and 

claims): 

66AMt7 series-Dredge concentrates from valley floor, Salmon River, claim 12 below Discovery 

claim. 

69AMt9 series-Pacific beach, a short distance south of the ultrabasic promontory of Red Mountain. 

72AMtl-Dredge concentrate from Fourth of July bench claim, Salmon River. 

Methods of Study and Results 7 
Table 3. Results of semiquantitative fire-assay and emission spectrographic 

analyses of platinum-group elements and gold in 89 magnetic concentrates 

from the Goodnews Bay district, Alaska, including six nonmagnetic concentrates for comparison 

[Analysts: R. R. Carlson and E. F. Cooley. Sample numbers for the nonmagnetic concentrates 

are 69AMt9F, 72AMtlL, 72AMtlM, 72AMtlP, 72AMtlQ, and 72AMt2G; all nonmagnetic concentrates are unsized; N, not detected at lower limit of detection shown in parentheses] 

Sarnyle Weight, Parts per million 

No. •2 in grams Pt Pd Rh Ru Ir Au 

66AMt7N1 9.076 0.07 0.025 0.007 N(0.35) 0.60 0.012 

66AMt7N2 10.703 .45 .020 .008 N(.40) .40 .30 

66AMt7N3 10.303 50 .12 .20 N(.45) 1.1 .1 

66AMt7N4 10.811 160 .60 .60 N( .40) 2.0 0 2 

66AMt7N5 7.622 180 .40 .30 N(.60) 3.0 .4 

66AMt7N6 .908 1,100 2.0 3.5 N(l.7) 35 7.0 

66AMt9A1 .222 .45 .10 N(. 07) N(7) N(7) N(.07) 

66AMt9A2 1.380 .40 .035 .02 N(l.O) N( 1.0) .020 

66AMt9A3 11.488 .60 .017 .012 N(.13) N(.13) .010 

66AMt9A4 12.231 .30 .017 .007 N(.12) N( .12) .012 

66AMt9A5 2.423 .30 .012 .012 N(.60) N(.60) .012 

66AMt9A6 .298 14.0 .350 .08 N(5.0) N(5.0) 3.5 

66AMt30A1 12.303 .10 .020 N(.004) N(.18) N(.035) .040 

66AMt30A2 4.832 .14 .020 N(.009) N( .45) N(.09) .035 

66AMt30A3 11.988 .15 .008 N(.004) N(.19) N(.04) N(.009) 

66AMt30A4 14.876 .14 .002 N( .003) N(.15) N( .03) N( .007) 

66AMt30A5 9.836 2.0 .011 .02 N(.25) N(.045) N( .011) 

66AMt30A6 .150 8.0 N(.10) N( .30) N(lS) N(3.0) .70 

66AMt31A1 8.766 .035 .003 N(.005) N(.25) N(.OS) N( .012) 

66AMt31A2 1.019 N( .045) N(.015) N(.045) N(2.0) N( .45) N(.10) 

66AMt31A3 7.842 35 .03 .20 N(.30) 2.0 .040 

66AMt31A4 17.229 10 .04 .20 N(.13) .so .045 

66AMt31A5 16.388 50 .12 .60 N(.14) 1.6 .so 

66AMt31A6 1.101 200 .70 2.5 N(2.0) N(.10) 

66AMt32A1 .319 N(.14) N(.045) N(.14) N(7) N(l.4) N(.35) 

66AMt32N2 1.062 N( .04) N(.014) N( .04) N(2.0) N(.40) N(.10) 

66AMt32A3 6.828 17 .04 .25 N(. 35) .45 N(.015) 

66AMt32A4 11.361 14 .013 .04 N(.20) 1.7 .080 

66AMt32N5 3.748 14 .35 .06 N(.60) N(.12) .25 

66AMt32A6 .053 30 N( .30) N( .80) N(40) N(8) N(2.0) 

8 Platinum-group Elements, Goodnews Bay District, Alaska 
Table 3. Continued 

Sam~l2 Weight, 

No. ' in grams 

Parts per million 

Pt Pd Rh Ru Ir Au 

66AMt35A1 4.350 .10 • 01 N(.01) N(.SO) N(.10) N(.025) 

66AMt35A2 4.776 .30 .03 N( .009) N( .45) N( .09) N(.020) 

66AMt35A3 17.473 .035 .01 N(.003) N(.13) N(.025) N(.006) 

66AMt35A4 16.078 .02 .008 N( .003) N(.14) N( .03) N( .007) 

66AMt35A5 9.441 .035 .016 .005 N(. 2) N(.05) N(.011) 

56AMt35A6 .828 10 .07 .13 N(2.5) N( .50) N( .13) 

68AMt4A1 2.200 .30 .035 N(.02) N(l.O) N(.20) N(.050) 

68AMt4A2 5.687 .12 .005 N( .008) N(.40) N(.08) .035 

68AMt4A3 6.877 .12 .004 N(.007) N(.35) N(.06) N(.015) 

68AMt4A4 11.611 .20 .003 N(.004) N( .19) N( .04) .060 

68AMt4A5 14.588 .30 .02 N(.003) N( .15) N(.03) .080 

68AMt4A6 1.932 110 .60 1.6 1.6 19 12 

69AMt5A1 11.932 8 .045 .16 N(.19) .45 .25 

69AMt5A2 10.152 .30 .019 N( .004) N(.20) N(.045) 3.0 

69AMt5A3 11.429 40 .25 .70 .25 2.5 40 

69AMt5A4 13.671 90 2.0 .70 N(.16) 3.0 60 

69AMt5A5 15.299 120 1.3 2.0 N(.15) 12 40 

69AMt5A6 1.407 180 3.0 1.2 N(l.6) 20 80 

69AMt6A1 9.736 .03 .003 .005 N(.30) N(.15) .006 

69AMt6A2 5.356 200 .70 2.0 N(.60) 4.5 .020 

69AMt6A3 17.911 100 .19 1. 0 N(.13) 1.7 .080 

69AMt6A4 14.507 .40 .008 .006 N(.15) N(.03) N( .007) 

69AMt6A5 14.767 1.1 .017 .01 N(. 15) N(.03) N(. 007) 

69AMt6A6 13.212 15 .05 .35 N( .17) 2.0 .70 

69AMt9E2 5.427 1.5 .017 .04 N(.40) N(.08) .050 

69AMt9E3 11.600 .08 .013 .01 N(.19) N( .04) N(.009) 

69AMt9E4 11.507 .08 .015 N(.001) N(.25) N(.13) N(.001) 

69AMt9E5 9.161 6 .08 .005 N(.35) N(.16) N(.002) 

69AMt9E6 .064 180 .90 2.5 N(45) N(25) N(.25) 

Methods of Study and Results 9 
Table 3. Continued 

Sample Weight, 

No. 1 •2 in grams 

Parts per million 

Pt Pd Rh Ru Ir Au 

69AMt9F 14.070 1.9 .003 .012 N(.20) N( .11) 4.0 

69AMt14A1 14.390 .06 .009 N(.001) N(.20) N(.10) 1(.001) 

69AMt14A2 15.569 400 .19 .05 .60 30 .10 

69AMt14A3 14.837 .40 .015 N(.001) N(.25) N(.13) .004 

69AMt14A4 11.227 45 .25 .045 N(.25) 10 .60 

69AMt14A5 18.750 3.0 .04 N(.001) N(.19) .15 .80 

69AMt14A6 15.588 2.5 .06 N(.001) N(.19) .60 .045 

69AMt15A1 .312 N(.25) N(.05) N(.05) N(lO) N(5.0) N(.050) 

69AMt15A2 4.335 3.0 .02 .025 N(.70) N(.35) .003 

69AMt15A3 18.222 .11 .011 .006 N(.16) N(.08) .001 

69AMt15A4 11.161 .13 .011 .001 N(.25) N(.13) N(.001) 

69AMt15A5 10.823 .30 .017 .003 N(.30) N(.14) .006 

69AMt15A6 .116 110 1.3 1.6 N(25) N(13) 1.2 

69AMt18A1 .602 N( .12) .012 N(.025) N(5.0) N(2.5) N(.025) 

69AMt18A2 4.166 .30 .004 N(.004) N(.70) N(.35) .007 

69AMt18A3 13.483 .25 .01 .03 N(.20) N( .11) .011 

69AMt18A4 17.991 4.5 .016 .05 N( .17) .35 .025 

69AMt18A5 13.238 1.3 .025 .008 N(.25) N( .11) .060 

69AMt18A6 13.060 8 .06 .06 N(.30) N(.14) • 11 

72AMt1L 7.357 .07 .002 N(.002) N(.40) .25 .030 

72AMt1M 16.717 130 .50 1.4 .35 1.7 3.0 

72AMt1N1 11.382 .05 .012 N(.001) N(.25) N(.13) .002 

72AMt1N2 16.368 .40 .016 N(.001) N(.18) N(.09) .003 

72AMt1N3 15.483 .50 .017 .004 N(.19) N(.10) .002 

72AMt1N4 17.043 3.0 .013 .004 N(.18) N( .09) .007 

72AMt1N5 13.063 .80 .005 .005 N( .25) N(.12) .013 

72AMt1N6 6.588 16 .16 .40 N(.45) 2.5 .20 

1 0 Platinum-group Elements, Goodnews Bay District, Alaska 
Table 3. Continued 

Samyle Weight, 

No. • 2 in grams 

Parts per million 

Pt Pd Rh Ru Ir Au 

7 2AMt 1 P 7. 3 77 1.2 .02 .01 N(.40) N(.20) .004 

72AMtlQ 9.950 17 .14 .14 N( .30) 2.5 

72AMt2G 12.104 13 .08 .12 N(.25) 3.0 .40 

1

Localities of samples (from Mertie, 1976, fig. 3, plot of Salmon River drainage and claims): 

66AMt7 series-Dredge concentrates from valley floor, Salmon River, claim 12 below Discovery 

claim. 

66AMt9 series-Overburden, 20 ft (6.1 m) below ground surface, bench paystreak opposite claim 

8 above Discovery claim, Salmon River. 

66AMt30 series-Bed of Clara Creek about 100 ft (30 m) upstream from the crossing of the road 

to Platinum. 

66AMt31 serie~leanup of "Mudhog" operation, bench paystreak, east of claim 4 below Discovery 

claim, Salmon River. 

66AMt32 series-Bed of McCann Creek about 100 ft (30 m) upstream from the crossing of the 

road to Platinum. 

66AMt35 series-Bed of Smalls River about 0.25 mi (0.4 km) from the mouth of McCann Creek. 

68AMt4 series-Deep drill hole on Hannah bench claim, valley of the Salmon River; sample is 

a composite of entire section cut by drill hole. 

69AMt5 series-Dredge concentrate from valley floor, claim 11 below Discovery claim, Salmon 

River. 

69AMt6 series-Drill hole 140ft (42.7 m) deep on Alice Association bench claim, valley of Salmon 

River; sample is a composite of entire drill hole. 

69AMt9 series-Pacific beach, a short distance south of the ultrabasic promontory of Red Mountain. 

69AMtl4 series-Dredge concentrate from valley floor, claim 11 below Discovery claim; samples 

69AMtl4 and 69AMt5 were taken from different cleanups. 

69AMtl5 series-Pacific beach about 1 mi (1.6 km) north of the mouth of the Salmon River. 

69AMtl8 series-Deep drill hole on bench paystreak south of Happy Creek; sample is a composite 

of entire drill hole. 

72AMtl series-Dredge concentrate from Fourth of July bench claim, Salmon River. 

72AMt2G-Nonmagnetic fraction of composite sample from drill hole on Salmon River bench 1.5 

mi (2.4 km) downstream from Fourth of July bench claim. 

2

Sizes of sieved fractions of magnetic concentrates are shown by final numeral in each sample number 

series: 

Final 

numeral 

2 

3 

4 

5 

6 

Size 

(mm) 

> 1.410 

1.410--.707 

.707-.354 

.354-.177 

.177-.088 

<.088 

Methods of Study and Results 11 
Table 4. Results of semiquantitative spectrographic analyses of elements other than platinumgroup elements in 89 magnetic concentrates from the Goodnews Bay district, Alaska, including 

six nonmagnetic concentrates for comparison 

[Analyst: J. A. Domenico. G, greater than value shown in parentheses; L, less than the value shown in parentheses; 

N, not detected at lower limit of detection shown in parentheses, depending on sample weight; sample numbers for 

the nonmagnetic concentrates are 69AMt9F, 72AMtlL, 72AMtlM, 72AMtlP, 72AMtlQ, and 72AMt2G; all nonmagnetic 

concentrates are unsized] 

Sample 

No.1 ,2 

66AMt7Nl 

66AMt7N2 

66AMt7N3 

66AMt7N4 

66AMt7N5 

66AMt7N6 

66AMt9A3 

66AMt9A4 

66AMt9A5 

66AMt9A6 

66AMt30Al 

66AMt30A2 

66AMt30A3 

66AMt30A4 

66AMt30A5 

66AMt30A6 

66AMt31Al 

66AMt31A2 

66AMt31A3 

66AMt31A4 

66AMt31A5 

66AMt31A6 

66AMt32A2 

66AMt32A3 

66AMt32A4 

66AMt32A5 

66AMt35Al 

66AMt35A2 

66AMt35A3 

66AMt35A4 

66AMt35A5 

66AMt35A6 

Percent 

Mg Ca Ti 

1. 5 

1.5 

1.5 

5 

1.5 

.5 

1.5 

1.5 

.2 

.2 

.2 

.2 

1.5 

.1 

1( .02) 

.1 

.1 

.1 

.7 

• 7 

.3 

1( .02) 

1( .02) 

1.5 1(.02) 

G(2) 

1. 5 

1. 5 

1.5 

.7 

G(2) 

G(2) 

1. 5 

1(.02) G(2) 

1.5 1(.02) G(2) 

1.5 1(.02) G(2) 

1.5 1(,02) G(2) 

1.5 1(.02) G(2) 

1( .02) 

G(2) 

1.5 1(.02) 

.1 .7 

.1 1.5 

1.5 

1.5 .5 

1.5 .5 2 

1.5 • 7 G(2) 

.5 1. 5 

• 7 .15 .7 

Mn Ba 

200 70 

3,000 70 

3,000 70 

3,000 70 

3,000 100 

3,000 100 

5,000 70 

3,000 100 

3,000 100 

3,000 100 

3,000 70 

3,000 70 

3,000 100 

5,000 100 

5,000 100 

3,000 100 

3,000 70 

3,000 100 

3,000 100 

5,000 100 

5,000 100 

3,000 70 

3,000 70 

3,000 N(20) 

5,000 N(20) 

10,000 N(20) 

3,000 N(20) 

3,000 N(20) 

3,000 N(20) 

3,000 N(20) 

2,000 N(20) 

2,000 N(20) 

12 Platinum-group Elements, Goodnews Bay District, Alaska 

Co 

200 

300 

300 

300 

200 

150 

500 

500 

200 

200 

300 

300 

300 

300 

300 

300 

200 

300 

300 

300 

300 

200 

200 

200 

500 

700 

300 

200 

200 

200 

300 

150 

Parts per million 

Cr Cu Ni Sc v Zn 

500 100 300 15 3,000 1,500 

2,000 100 300 15 5,000 1,500 

10,000 70 300 10 2,000 1,500 

G(lO ,000) 100 500 15 3,000 5,000 

G(lO,OOO) 50 500 10 3,000 2,000 

G(lO,OOO) 500 300 N(5) 2,000 2,000 

G(lO ,000) 50 700 

G(lO ,000) 100 700 

G(lO,OOO) 70 500 

G(lO ,000) 70 300 

7,00 300 500 

1,500 200 300 

G(lO,OOO) 10 300 

G(lO ,000) 

G(lO,OOO) 

G(lO ,000) 

20 700 

10 1,000 

70 500 

1 '500 150 500 

1,000 500 300 

G(lO,OOO) 70 700 

G(lO ,000) 50 1 ,000 

G(lO,OOO) 100 1,000 

G(lO ,000) 150 700 

2,000 200 500 

G(lO ,000) 50 500 

G(lO,OOO) 

G(lO,OOO) 

20 500 

30 1,500 

1,500 100 300 

2,000 so 300 

5,000 50 300 

10,000 70 300 

5,000 70 300 

5,000 70 300 

10 3,000 5,000 

20 3,000 3,000 

15 1,500 5,000 

10 1 ,000 N(200) 

20 3,000 N(200) 

20 3,000 N(200) 

10 2,000 2,000 

15 3,000 3,000 

15 5,000 3,000 

10 3,000 2,000 

20 5,000 N(200) 

15 2,000 1,500 

15 5,000 2,000 

15 5,000 2,000 

15 s,ooo 2,000 

10 5,000 1,500 

20 7,000 N(200) 

10 3,000 N(200) 

10 3,000 N(200) 

20 3,000 N(200) 

30 3,000 N(200) 

20 5,000 N(200) 

20 5,000 N(200) 

30 5,000 N(200) 

15 5,000 N(200) 

10 3,000 N(200) 
Table 4. Continued 

Sample Percent No.1,2 Mg Ca Ti Mn Ba 

66AMt4A1 L( .05) 

66AMt4A2 N(.05) 

66AMt4A3 1.5 N(.05) 

66AMt4A4 1.5 L(.05) 

66AMt4A5 1. 5 .1 

66AMt4A6 .3 

66AMt5A1 .5 

66AMt5A2 1.5 .2 

66AMt5A3 .5 

66AMt5A4 .3 

66AMt5A5 1.5 .2 

66AMt5A6 1. 5 .5 

69AMt6A1 .5 N(.05) 

69AMt6A2 .1 

69AMt6A3 1.5 L(.05) 

69AMt6A4 1.5 .1 

69AMt6A5 1. 5 .15 

69AMt6A6 .1 

69AMt9E2 1. 5 .1 

69AMt9E3 1.5 L(.05) 

69AMt9E4 1.5 L(.05) 

69AMt9E5 1.5 L(.05) 

69AMt9F .15 

69AI-tt14Al 1.5 L(.05) 

69AMt14A2 L(.05) 

69AMt14A3 1.5 .1 

69AMt14A4 1.5 .1 

69AMt14A5 L(.05) 

69AMt14A6 1.5 L(.05) 

69AMt15A2 L(.05) 

69AMt15A3 1.5 L(.05) 

69AMt15A4 2 .1 

69AMt15A5 1. 5 .1 

69AMt15A6 1.5 .1 

1. 5 3,000 N(20) 

3,000 N(20) 

3,000 N(20) 

3,000 N(20) 

3,000 N(20) 

.7 3,000 50 

1. 5 3,000 150 

1.5 3,000 L(20) 

3,000 N(20) 

.7 3,000 N(20) 

.7 3,000 N(20) 

1.5 3,000 N(20) 

.1 G(lO,OOO) 

• 5 G(lO ,000) 

G( 10 ,000) 

30 

150 

50 

3,000 50 

• 7 3,000 L(20) 

3,000 L(20) 

1. 5 3,000 L(20) 

3,000 N(20) 

3,000 N(20) 

3,000 N(20) 

3,000 100 

1.5 3,000 L(20) 

1. 5 2,000 N(20) 

1. 5 3,000 N(20) 

3,000 N(20) 

.7 3,000 N(20) 

.7 3,000 N(20) 

.7 3,000 N(20) 

1. 5 3,000 N(20) 

1. 5 3,000 N(20) 

1. 5 5,000 N(20) 

3,000 N(20) 

Co 

300 

300 

700 

200 

300 

150 

200 

300 

300 

300 

200 

300 

300 

150 

150 

200 

150 

300 

200 

300 

300 

300 

500 

200 

200 

300 

300 

200 

300 

150 

300 

300 

300 

300 

Parts per million 

Cr Cu Ni Sc v Zn 

500 100 300 30 3,000 N(200) 

G(lO,OOO) 100 700 15 5,000 N(200) 

G(lO,OOO) 70 700 15 5,000 N(200) 

G(lO ,000) 70 700 15 3,000 N(200) 

G(lO,OOO) 100 700 15 5,000 N(200) 

G(lO ,000) 700 500 15 3,000 N(200) 

2,000 50 300 15 3,000 N(200) 

5,000 30 500 15 3,000 N(200) 

G(lO,OOO) 70 500 15 3,000 N(200) 

G(lO ,000) so 700 15 3,000 N(200) 

G(lO,OOO) 70 500 10 3,000 N(200) 

G(lO ,000) 300 700 15 3,000 N(200) 

G(lO,OOO) 1,500 2,000 N(S) 1,000 N(200) 

G(lO ,000) 1,000 7,000 N(S) 700 N(200) 

G(lO,OOO) 700 3,000 N(S) 1,500 N(200) 

G(lO ,000) 150 2,000 10 3,000 N(200) 

G(lO,OOO) 100 1,000 L(5) 3,000 N(200) 

G(lO,OOO) 200 1,500 L(S) 3,000 N(200) 

G(lO,OOO) 

G(lO ,000) 

G(lO,OOO) 

G(lO ,000) 

G(lO,OOO) 

2,000 

5,000 

G(lO ,000) 

G(lO,OOO) 

G(lO ,000) 

70 1,500 10 5,000 N(200) 

50 1,000 L(S) 3,000 N(200) 

20 1,000 L(S) 2,000 N(200) 

30 1,000 L(S) 3,000 N(200) 

20 1,500 10 2,000 N(200) 

70 700 L(S) 3,000 N(200) 

70 700 10 3,000 N(200) 

70 1,000 10 3,000 N(200) 

70 700 10 2,000 N(200) 

50 500 L(S) 2,000 N(200) 

G(lO,OOO) 150 500 L(S) 3,000 N(200) 

G(lO ,000 100 300 L(S) 2,000 N(200) 

G(lO,OOO) 70 700 15 3,000 N(200) 

G(lO,OOO) 100 700 L(S) 3,000 N(200) 

G(lO,OOO) 20 700 10 3,000 N(200) 

G( 10 ,000) 30 700 L(S) 3,000 N(200) 

Methods of Study and Results 13 
Table 4. Continued 

Sample Percent No.1,2 Mg Ca Ti Mn Ba 

69AMt18A2 1.5 L( .05) 1. 5 7,000 N(20) 

69AMt18A3 N( .OS) s,ooo N(20) 

69AMt18A4 N( .OS) s,ooo N(20) 

69AMt18AS 1.S N( .05) • 7 3,000 N(20) 

69AMt18A6 N(.OS) .7 3,000 N(20) 

72AMtlL l.S 1.5 10,000 30 

72AMt1M l.S 1.5 7,000 30 

7 2AMt1Nl l.S .2 7,000 30 

72AMt1N2 L(.OS) G(2) 3,000 N(20) 

72AMtlN3 1.S N( .OS) 3,000 N(20) 

7 2AMt 1N4 l.S N(.OS) 3,000 N(20) 

72AMt1NS N( .OS) 1.S s,ooo N(20) 

72AMt 1N6 N(. 05) 2,000 N(20) 

72AMt1P .3 1.S 10,000 N(20) 

72AMt1Q G(2) 10,000 100 

72AM2G 1.S 10,000 N(20) 

Footnote on following page. 

(1976, p. 18 and 21), were both converted to atomic percentages, they became remarkably close. The principal 

alloy was designated by the generic name platinum, 

although it contained small amounts of the five other 

PGE. These data indicated, therefore, that the principal 

alloy is the most abundant PGE phase that will be found 

and identified under a microscope. 

As expected, PGE and gold were also present in 

the nonmagnetic concentrates reported in table 3: samples 

69AMt9F, 72AMt1L, 72AMtlM, 72AMtlP, 72AMtlQ, 

and 72AMt2G. However, as this investigation was concerned with PGE in magnetic concentrates, these occurrences were merely noted; no further work was done with 

these nonmagnetic samples. 

Table 4 shows chromium was 10,000 ppm or more 

in a large majority of the analyses. Most likely chromite 

or chromiferous magnetite was in the sample. The lesser 

amounts of cobalt, nickel, vanadium, and zinc were un14 Platinum-group Elements, Goodnews Bay District, Alaska 

Parts per million 

Co Cr Cu Ni Sc v Zn 

300 G(lO ,000) 300 1,000 10 5,000 N(200) 

200 G( 10 ,000) 70 1,000 10 3,000 N(200) 

200 G(lO,OOO) 100 1,000 10 3,000 N(200) 

1SO G(lO,OOO) 70 soo L(S) 2,000 N(200) 

1SO G(lO ,000) 300 300 L(S) 3,000 N(200) 

300 G(lO ,000) 150 700 1S 2,000 N(200) 

300 G(lO,OOO) 100 700 20 1 ,soo N(200) 

300 2,000 100 300 20 s,ooo N(200) 

200 5,000 70 300 15 3,000 N(200) 

200 G(lO ,000) 70 soo 20 3,000 N(200) 

300 G(lO,OOO) 70 1,000 20 s,ooo N(200) 

300 G( 10 ,000) 100 700 20 s,ooo N(200) 

1SO G(lO,OOO) 100 soo 1S 2,000 N(200) 

300 G(lO ,000) 30 700 20 3,000 N(200) 

300 G(lO,OOO) 200 700 50 2,000 N(200) 

1SO G( 10 ,000) 70 300 so 1,000 N(200) 

doubtedly included in the magnetite lattice (Frietsch, 

1970; Overstreet and others, 1978; Pan and others, 1980). 

Copper showed no consistent relation to the PGE or gold 

in table 3 or to the other minor elements in table 4; hence, 

we presumed that the copper represented random minor 

inclusions of copper-bearing minerals such as chalcopyrite. 

When the grain size was compared to the amounts 

of the minor elements in the magnetic concentrates (table 

4), it was apparent that the chemical variation between 

the coarsest and the finest sizes of the magnetic concentrates tended to be less than the variation among samples 

from different localities. For chromium, however, this observation did not apply. Chromium tended to be strongly 

enriched in the finest sieve fraction of the 14 groups of 

sized samples; in 9 of the sets, chromium was most abundant in the finest fraction, but in 5 groups, all sieve sizes 

had reported concentrations of chromium of over 10,000 
1

Localities of samples (from Mertit[, 1976, fig. 3, plot of Salmon River drainage and claims): 

66AMt7 series-Dredge concentrates from valley floor, Salmon River, claim 12 below Discovery 

claim. 

66AMt9 series-Overburden, 20 ft (6.1 m) below ground surface, bench paystreak opposite claim 

8 above Discovery claim, Salmon River. 

66AMt30 series-Bed of Clara Creek about 100 ft (30 m) upstream from the crossing of the road 

to Platinum. 

66AMt31 series-Cleanup of "Mudhog" operation, bench paystreak, east of claim 4 below Discovery 

claim, Salmon River. 

66AMt32 series-Bed of McCann Creek about 100 ft (30 m) upstream from the crossing of the 

road to Platinum. 

66AMt35 series-Bed of Smalls River about 0.25 mi (0.4 km) from the mouth of McCann Creek. 

68AMt4 series-Deep drill hole on Hannah bench claim, valley of the Salmon River; sample is 

a composite of entire section cut by drill hole. 

69AMt5 series-Dredge concentrate from valley floor, claim 11 below Discovery claim, Salmon 

River. 

69AMt6 series-Drill hole 140ft (42.7 m) deep on Alice Association bench claim, valley of Salmon 

River; sample is a composite of entire drill hole. 

69AMt9 series-Pacific beach, a short distance south of the ultrabasic promontory of Red Mountain. 

69AMt14 series-Dredge concentrate from valley floor, claim 11 below Discovery claim; samples 

69AMt14 and 69AMt5 were taken from different cleanups. 

69AMt15 series-Pacific beach about 1 mi (1.6 km) north of the mouth of the Salmon River. 

69AMt18 series-Deep drill hole on bench paystreak south of Happy Creek; sample is a composite 

of entire drill hole. 

72AMtl series-Dredge concentrate from Fourth of July bench claim, Salmon River. 

72AMt2G-Nonmagnetic fraction of composite sample from drill hole on Salmon River bench 1.5 

mi (2.4 km) downstream from Fourth of July bench claim. 

2

Sizes of sieved fractions of magnetic concentrates are shown by final numeral in each sample number 

series: 

Final 

numeral 

2 

3 

4 

5 

6 

ppm. For those five groups, the relation of chromium to 

grain size could not be determined. For many of the trace 

elements in table 4, the range in abundance between the 

coarsest and finest sieve fractions of the magnetic concentrates was no more than three reporting units. This is within the range of accepted analytical variance; thus, the differences may have no geochemical significance. For 

example, the apparent preponderance of high values in 

the coarse fractions for calcium, magnesium, titanium, 

manganese, barium, cobalt, scandium, and vanadium 

mostly represented only one or two reporting intervals of 

difference and individually could not be regarded as constituting significant geochemical differences. Collectively, 

they might indicate a tendency for the coarse grains in 

the concentrates to be a little richer in these elements than 

the PGE-enriched finest grains. In general, the values reported for manganese, chromium, copper, nickel, and 

vanadium in these magnetic concentrates fell in the category of anomalously high values found for these elements 

Size 

(mm) 

> 1.410 

1.410-.707 

.707-.354 

.354----.177 

.177-.088 

<.088 

in other metal-rich areas in Alaska (Overstreet and others, 

1978; Pan and others, 1980). Except for the chromium, 

and possibly for nickel and vanadium, these minor elements cannot be said to be pathfinder elements for the 

PGE in magnetic fractions of panned concentrates. 

In summary, the results of the semiquantitative fireassay and emission-spectrographic analyses not only 

showed that the PGE were present in the magnetic concentrates, but also confirmed the unexpected relationship 

discovered when the preliminary analyses were done: the 

finer grained material generally contained greater proportions of PGE than the coarser fractions. In order to use 

this relationship to advantage as an aid in mineral exploration and in the recovery of PGE, with magnetite itself 

considered a source of PGE, it became necessary to know 

the actual form of the PGE in the magnetite grains. Did 

the PGE occur as inclusions in the magnetite? Were they 

present as submicroscopic discrete grains, attached somehow to the surface of the magnetite grains in each size 

Methods of Study and Results 15 
fraction? Or were the POE within the lattice of the magnetite grains? Perhaps the POE in the magnetic concentrates 

were simply present as discrete grains, similar to the other 

heavy minerals, and rather than being comminuted during 

fluvial transport, the fine grain sizes represented original 

small particles liberated by weathering and erosion from 

their host rocks. The greater amounts of PGE in the finest 

sizes would then merely reflect the greater number of tinyparticled POE. These questions required other analytical 

methods, including polished-section studies and SEM investigations, to resolve the matter of the actual location 

of the POE. 

Polished-section Studies 

Eighty-three polished sections of mounted magneticconcentrate splits were prepared and studied under the optical metallographic microscope. These magnetic splits 

represented the series samples in table 3 (where enough 

material was available), and the chemical results were 

used to guide the search for POE minerals in the several 

size fractions of each set. Those sections that showed 

brightly reflecting grains were set aside for further study 

under the SEM, which proved to be an invaluable 

mineralogical tool for this investigation. The optical 

microscope showed some of the details of the POEbearing grains at 50- to 500-times magnification, especially in oil-immersion mounts, but many of the microintergrowths present would never have been detected without the use of the SEM. Under the SEM, these grains 

were magnified as much as 5,500 times showing the 

micro-intergrowths and other details of grains originally 

located with the metallographic microscope; the instrument, with the use of an energy-dispersive spectrometer, 

also enabled the immediate semiquantitative determination 

of the composition of tiny areas of these grains. 

The chemical results shown in tables 1-4 indicate, 

in general, the types of mineral phases we could expect 

to find in the magnetic concentrates as viewed under the 

metallographic microscope. Most abundant in the 83 

polished sections examined were the oxide minerals magnetite, ilmenite, a translucent-to-transparent spinel showing low reflectivity, chromite, and hematite. In addition, 

lesser amounts of pyrite, chalcopyrite, silicate minerals 

of calcium, aluminum, iron, and magnesium (pyriboles, 

inferred from morphology and reflectivity), tramp metals 

(probably iron alloys), and one grain of gold were identified in the concentrates. 

Magnetite most often formed rounded amoeboid 

grains that showed many fractures and incipient octahedral 

cleavages. Rarely did the borders of magnetite grains 

show triangular- or diamond-shaped outlines indicating 

octahedral forms. A number of rounded chromite grains 

were mantled with magnetite overgrowths. Except for 

these two modes, magnetite was not recognized in any 

other occurrences. Magnetite grains contained inclusions 

16 Platinum-group Elements, Goodnews Bay District, Alaska 

of other minerals, such as pyrite, spinel, ilmenite, rutile, 

and hematite. Alteration to hematite along fractures and 

cleavages was common. 

The possibility that some of the magnetite was secondary, as described by Eakin (1914, p. 28) and noted 

by Overstreet and others (1978, p. 42), was indicated by 

the magnetite mantles on chromite grains, a feature that 

occurred during serpentinization. However, most of the 

magnetite was of primary origin, as indicated by the following evidence: ( 1) exsolution lamellae of ilmenite along 

crystallographic directions in magnetite grains, (2) inclusion of sulfides like pyrite, (3) source rocks that were 

magmatic in origin, and (4) all associated heavy minerals 

in the concentrates that were typical of ultrabasic magmatic provenance. Ramdohr (1969, p. 899-906) thoroughly 

discussed exsolution and magnetite and stated that this 

feature occurs especially in magmatic magnetites. 

We also found that ilmenite occurred as discrete 

equant- to lath-shaped grains and as exsolved irregular 

patches, laths, and needles in magnetite, especially along 

incipient cleavages. Its color ranged from a pale brown 

similar to magnetite to a slightly darker brown, but ilmenite was easily recognized by its strong birefringence. 

Identification of tranparent spinel minerals was tentative and was based on hardness, transparency (low reflectivity), and equant forms. The grains were observed 

typically as isotropic inclusions in magnetite and were 

only rarely present in other minerals. These spinels were 

generally clear of inclusions. 

Chromite formed octahedral-to-rounded equant 

grains that were similar in color and reflectivity to magnetite, but they showed no cleavages or irregular fractures. 

Resistance to alteration was greater for chromite than for 

magnetite. Chromite grains rarely showed inclusions of 

other minerals, but overgrowths of magnetite on chromite 

grains were noted in 20 percent of the polished sections. 

The thickness of the mantles was rarely greater than one 

tenth of the diameter of the whole grain. 

Hematite most commonly occurred as an alteration 

product of magnetite along irregular fractures and incipient cleavages, where the hematite was easily recognized 

by its white reflective color and distinctive birefringence 

under the microscope. Some magnetite grains were almost 

completely replaced by hematite. Thus, it is likely that 

this secondary hematite is one of the common detrital 

minerals in some magnetic concentrates. 

Tramp metal, where seen in polished sections of 

the magnetic concentrates, almost always appeared as 

bright white metal that showed distinctive lattice patterns 

between crossed polaroid filters. We assumed these were 

steel fragments from chipped tools. 

POE minerals seen in polished sections were few 

and scarcely discernible among the common mineral 

phases mentioned above. Because all of the POE-bearing 

aggregates were tiny and included in magnetite, the pin-
point reflectivities of these aggregates were not easily distinguishable, and all five of the POE-bearing grains found 

were overlooked during the first scan. The largest of these 

aggregates, in sample 69AMt14A2 (grain 1), measured 

only 220 by 370 J.Lm. An adjacent grain (grain 2) was 

220 by 340 J.Lm, and the third grain (grain 3) in this section was only 40 by 100 J.Lm. Single grains in samples 

66AMt7N6 and 66AMt31A6 were 25 by 55 J.Lm and 50 

by 85 J.Lm, respectively. Except in these 3 polished sections, no PGE minerals were recognized in any of the 

other 80 polished sections under the metallographic microscope. 

Under the microscope, details of the tiny POE-bearing inclusions in magnetite in sample 69AMt14A2 were 

difficult to distinguish, even at 500 times magnification. 

In grain 1 , amoeboid inclusions appeared to be homogeneous or to range slightly in reflectivity within one inclusion. In grain 2, fine needlelike forms were seen covering 

most of the grain, and a few amoeboid inclusions were 

noted, but the fine details of these PGE minerals were 

beyond the resolution of the metallographic microscope. 

Grain 3 in this polished section appeared to be homogeneous. Optical and physical properties of the seven distinctive mineral _phases that contained PGE were as follows: 

Pt-Fe: bright cream-white, soft, isotropic 

Pt-As: gray-white, soft, isotropic 

Ir-Fe: yellowish-medium gray, soft, anisotropic 

(spotty and wavy brown extinctions) 

Ir-Rh-Pt-Fe-As-S: gray-white, soft, weakly anisotropic 

Rh-As-S: gray-white, soft, isotropic 

Rh-Pd-Ni-As-S: slightly yellowish-gray-white, soft, 

weakly anisotropic 

Pb-Rh-Fe-Ir-S: cream-gray, soft, strongly anisotropic (brown tints). 

In summary, we found the following distribution of 

PGE mineral phases among three aggregates that contained PGE: 

Sample No. 

66AMt7N6 

66AMt31A6 

69AMt14A2 

PGE Mineral Phases 

Pt-Fe alloy, hollingworthite, sperrylite 

Pt-Fe alloy 

All seven mineral phases 

Scanning Electron Microscope Studies 

To try to resolve the details of PGE microminerals, 

we used a SEM to study seven different PGE minerals; 

in addition, we had limited use of an electron microprobe 

for three of these minerals. The SEM used in this investigation was the Cambridge Stereoscan 180 with magnification capability as much as 100,000 times and resolution 

capability of less than 100 angstroms when using more 

than 20 kv. The working voltage, used consistently, was 

30 kv. Polaroid photographs were made to record the images seen on the 10- by 13-cm SEM screen. Contrasts 

in gray tones were usually sufficient to distinguish between adjacent mineral phases, and a scale along the bottom of the SEM screen was used for measurement of the 

particles. An energy-dispersive spectrometer was used for 

semiquantitative determination of the composition of a 

-mineral phase under investigation. 

Semiquantitative information for elements numbered 

11 to 92 was obtained from the 13- by 15-cm screen of 

the Kevex energy-dispersive spectrometer. The screen was 

divided into 10 parts vertically, and the relative amounts 

of the several elements in a mineral phase were indicated 

by the heights of characteristic peaks (fig. 2). A tiny circle 

of light on the SEM screen could be placed around a 

spot on a grain to analyze the composition of that spot, 

and the peaks on the spectrum displayed on the Kevex 

screen grew vertically, proportional to the amount of each 

element present. 

Platinum-group Element Phases 

General comments.-The mineralogy determined 

under the SEM, like that determined from examination 

of the polished sections under the metallographic microscope, could be expected to reflect the results of chemical 

analysis. Our determinations using the SEM and the energy-dispersion X-ray fluorescence system (herein referred 

to as Kevex) were based on only a few samples of POEbearing grains, so that any semiquantitative chemistry determined by Kevex probably would not correlate with the 

spectrochemical data. The state-of-the-art techniques of 

this equipment did allow qualitative results on individual 

grains or parts of grains. However, rough quantitative results based upon similar peak heights on the Kevex screen 

were used with caution; in the following discussions, any 

implication of greater precision than semiquantitative values is not intended. 

The amplitudes of the peaks for one element differed from similar peaks for adjacent elements in the middle part of the periodic table, mainly because of absorption or enhancement effects. Lighter and heavier elements 

than the so-called transition elements did not suffer as 

much from these effects, and elements vertically separated 

in the periodic table also were less affected by these 

effects. Therefore, we feel that the semiquantitative data 

for iron (Z=26) and platinum (Z=78) indicate the amount 

of each element in the Pt-Fe alloy. As an example, if 

similar peaks for iron and platinum were of equal height, 

then we inferred that the alloy contained equal amounts 

of the two elements. If iridium (Z=77) was also present 

in this alloy, then equal heights of similar peaks for 

iridium and platinum probably indicated unequal amounts 

of each element, and the relationship to iron was impossible to assess. 

Scanning Electron Microscope Studies 17 
6 7 8 9 10 11 12 13 

Figure 2. Photograph of the Kevex screen showing the results of analysis by the X-ray energy-dispersive system 

of a PGE phase. Numbers under peaks indicate (in decreasing amounts) Fe: 6,7; Rh:4,13; S: 3; As: 1,9,11; Pt: 

2,8,10,12; Ag conductive coating on sample surface: 5. 

A difficulty recognized in analyzing a spot near the 

border of an inclusion was the probability of integrating 

energy from the underlying host mineral. The electron 

beam can penetrate a thin grain and excite the material 

below the inclusion being analyzed, thereby causing a 

false impression that the inclusion contains some of the 

elements present in the underlying host which may be 

as much as 100 tJ.m below the surface. Using an inclusion 

of Pt-Fe alloy in a magnetite host as an example, an unusually high iron peak (one was observed as great as three 

times the platinum peak) undoubtedly reflected contamination by the magnetite host below the Pt-Fe alloy being 

analyzed. Placing the analyzing spot in the center of the 

inclusion was no safeguard against this type of response, 

because the spot might be on a thin part of the inclusion. 

For purposes of this discussion, the word "phase" 

is used to denote an association of PGE and other elements that recurs and is distinctive enough in appearance 

18 Platinum-group Elements, Goodnews Bay District, Alaska 

and chemistry (within reasonable limits) to define what 

is usually called a mineral. Two associations are well 

known, and the accepted mineral names sperrylite and 

hollingworthite are assigned. Others described here are apparently new associations, and enough samples were 

tested to ascertain that they were distinctive and not mixtures of other minerals. The unnamed phases are called 

unknown A, unknown B, unknown C, and unknown D 

in the following discussion. 

The phases to be discussed are classified according 

to major PGE, in the order platinum, iridium, and 

rhodium. In each class the elements are generally in decreasing amounts based on the amplitudes of peaks measured on the Kevex screen. Iron seemed to be ever present 

in all phases, but we inferred that variable amounts usually indicated contamination from below the spot 

analyzed. Considering the penetrative capabilities of the 

SEM, we tended to discount most variable shows of iron 
300fL 

I I 

Figure 3. SEM micrograph of grains 1, 2, and 3 in polished section 69AMt14A2. Grain 1 (center) is magnetite (M) 

with amoeboid Pt-Fe alloy (Pt) inclusions. Grain 2 (right center) is magnetite largely covered by lr-Fe laths (lr), with 

inclusions of Pt-Fe alloy along lower border. Grain 3 is small aggregate (left center) of Pt-Fe alloy, sperrylite, and 

magnetite. Large grains are mostly titanomagnetite (M); small round inclusion in magnetite (upper right) is Fe-AI 

spinel (Sp). Dark areas are mounting medium. White lines at upper left and lower right are reflections from scratch 

marks. White specks on magnetite grains are mostly dust particles and some pyrite inclusions. 

and to accept those that were consistent. 

Pt-Fe alloy.-This was the most abundant phase observed, and it occurred as amoeboid grains between 5 and 

80 tJ.m across (figs. 3-5). A systematic test of 120 Pt-Fe 

alloy inclusions in grain 1 (fig. 4), using Kevex screen 

amplitudes of platinum and iron, showed the alloy generally contained 75 percent platinum and 25 percent iron. 

Several grains showed greater amounts of iron which we 

presumed were due to iron radiation from subjacent magnetite. This composition was similar to ferroplatinum 

(face-centered cubic platinum with 20-50 atomic percent 

iron) and to isoferroplatinum (primitive cubic platinum 

with composition near Pt3Fe) as defined by Cabri (1976) 

and Skinner and others (1976). However, of the several 

minor elements listed for isoferroplatinum, in our examinations of grain 1, only rhodium, nickel, and copper were 

found and that was rarely and only in minute quantities. 

A similar composition was listed as ferroplatinum by Mertie (1969, p. 12). Thirteen electron-microprobe analyses 

of Pt-Fe alloy (in weight percent) were averaged: Pt, 

87.97; Fe, 10.63; Rh, 0.63; Pd, 0.27; Os, 0.16; lr, 0.0; 

Pb, 0.44; Ni, 0.05; Cu, 0.13; As, 0.18; and S, 0.46. 

These values correspond to atomic percentages: Pt, 67; 

Fe, 28; and S, 2. All the rest were less than 1 percent. 

The formula calculated for this alloy based on platinum 

and iron only is Pt 2 .33 Fe. 

The terminology applied to platinum and Pt-Fe 

alloys has been thoroughly discussed by Cabri and Feather 

(1975). Since the composition of this phase is not well 

known, in this paper we refer to it by the general name 

Scanning Electron Microscope Studies 19 
platinum-iron alloy, or Pt-Fe alloy, as proposed by Cabri 

and Feather (1975). All of the Pt-Fe alloy inclusions in 

grain I had similar compositions, but in grain 2 (see fig. 

3, right center), the Pt-Fe alloy contained appreciable 

amounts of rhodium and arsenic, as determined by Kevex 

analysis, especially near the borders with inclusions containing these elements. In other polished sections of different samples, the Pt-Fe alloy contained small amounts 

of copper, nickel, and cobalt, but the amounts were not 

constant from place to place, even in a single grain. A 

discrete grain of Pt-Fe alloy in sample 66AMt31A6 (fig. 

5) showed a range of ratios. Based on Kevex peak heights 

at a number of spots across the grain, we found an irregular decrease in iron and copper contents from one side 

of the grain to the other (fig. 5, top to bottom). 

Previous descriptions of the magnetic properties of 

PGE alloys reveal some confusion and controversy. Mertie (1969, p. 5) pointed out that certain natural alloys 

of PGE are ferromagnetic, though the pure metals are only 

paramagnetic. Also, he indicated that the magnetic susceptibility and other physical properties of natural alloys 

of the PGE cannot be predicted by linear interpolation 

based on known proportions of their elements, and in fact, 

unexpected properties occur in such alloys. Magnetic 

properties of platinum have been cited in the literature, 

but the definitive reference by Palache and others (1944, 

p. I 07) indicates that ordinary platinum is nonmagnetic 

or slightly magnetic. Ferroplatinum with as much as 28 

percent iron is magnetic; thus it presumably may be 

Reference 

picked up by a hand magnet. In the Tulameen River area 

of British Columbia, iron-rich varieties of ferroan 

platinum (iron was 20--50 percent, according to Cabri and 

Feather, 1975, p. 117) were distinctly magnetic and were 

capable of being attracted to a hand magnet, whereas ironpoor platinum alloys were not attracted to a hand magnet 

(Raicevic and Cabri, 1976). 

Of the five grains containing PGE phases that we 

examined, three were locked with magnetite, and this 

explained their presence in the magnetic concentrate. The 

other two, in samples 66AMt7N6 and 66AMt3IA6, were 

discrete grains with major proportions of Pt-Fe alloy. Fortuitous mechanical entrapment during screening might 

have accounted for the appearance of these grains in the 

magnetic concentrate, but more likely the iron content accounted for their inclusion in the magnetic fraction. 

A number of citations on the amount of iron in PtFe alloy in platinum deposits worldwide appear in the 

literature, and platinum has been classed into four types 

based on internal structure and iron content (Cabri, 1976). 

However, because earlier references do not use this classification, when we cite these references, we refer to 

platinum with appreciable iron-content as Pt-Fe alloy. A 

summary of compositions of platinum-bearing minerals by 

Wright and Fleischer (1965, p. A6) indicated a range of 

2.6-28.0 percent iron in platinum. The advent of microprobe analyses of tiny platinum particles resulted in a 

flurry of papers which indicated averages and ranges of 

iron percentages in platinum or Pt-Fe alloys, as follows: 

Location Iron, in Percent 

Snetsinger, 1973 Goodnews Bay, Alaska 9.5 

Cabri and Hey, 197 4 Tulameen River, B.C. 5.3-12.6 

Cabri and Laflamme, 1974 Stillwater Complex, Mont. 9.3- 9.6 

Fominykh and others, 1974 Ural Mountains, USSR 6.0- 9.2 

Harris, 197 4 Papua and New Guinea 8.2-10.1 

Urashima and others, 1974 Yubdo, Ethiopia 9 -15 

Cabri and Feather, 1975 Tulameen River, B.C. 5.4- 8.8 

Stillwater Complex, Mont. 9.6 

Similkameen River, B.C. 10.8-18.5 

Talnakh, USSR 22.8 

Anglo-American Mines, S. Africa 8.86 

President Steyn Mine, S. Africa 9.5 

Western Holdings Mine, S. Africa 5.7- 9.1 

Volchenko and others, 1975 Ural Mountains, USSR 10.2 

Feather, 197 6 Witwatersrand, S. Africa 6.1-11.5 

Raicevic and Cabri, 1976 Tulameen River, B. C. 10 

Stumpf! and Tarkian, 1976 Sorashigawa, Japan 15 -25 

Vermaak and Hendriks, 1976 Merensky Reef, S. Africa 0 -30 

Cabri and Laflamme, 1981 Onverwacht, S. Africa 8.8-10.3 

Mooihoek, S. Africa 14.9-16.3 

20 Platinum-group Elements, Goodnews Bay District, Alaska 
100fL 

Figure 4. SEM micrograph of grain 1 in polished section 69AMt14A2. White amoeboid inclusions in magnetite (M) 

are Pt-Fe alloy (Pt). Other PGE phases are at lower left corner and upper right (sperrylite, 5), upper edge (unknown 

A, lr), lower right (unknown B, IRh), and upper right side (unknown C, Rh). Black areas and area with wavy reflections 

(lower right) are mounting medium. 

Previously published photographs of Pt-Fe alloys 

show generally white irregular areas for this alloy CSnetsinger, 1973; Cabri and Hey, 1974; Cabri and Feather, 

1975; Feather, 1976; Raicevic and Cabri, 1976; Stumpfl 

and Tarkian, 1976; Verrnaak and Hendriks, 1976; Cabri, 

1981). Photographs in Raicevic and Cabri (1976), Vermaak and Hendriks (1976), and Cabri (1981) show Pt-Fe 

alloy outlines that are reminiscent of Pt-Fe grains in figure 

4 and are similar in grain sizes. In Feather (1976), exsolution lamellae of Pt-Fe alloy are shown as straight rods 

and needles 5 to 20 J.Lm long, but this form was not reported by others nor was it seen in this study. 

This study has enabled us to positively confirm the 

presence of the principal alloy of Mertie (1976, p. 14) 

in our samples from the same area. He considered this 

alloy as the main carrier of PGE in the Goodnews Bay 

deposits. At first, the Pt-Fe alloy described here did not 

seem equivalent to the principal alloy of Mertie, because 

the compositions were not easily compared and the numbers seemed different. Mertie's principal alloy contained 

(in percent) Pt, about 96; lr, 2.8; Rh, 1.1; and Pd, 0.5; 

iron was not reported (Mertie, 1976, p. 18). The average 

of 13 microprobe analyses in this study showed (in percent) Pt, 87.97; lr, 0.0; Rh, 0.63; Pd, 0.27; Os, 0.16; 

Fe, 10.63; Pb, 0.44; Ni, 0.05; Cu, 0.13; As, 0.18; and 

S, 0.46= 100.92. However, if we allow the sum of 

platinum, rhodium, palladium, and osmium to equal 100 

percent, then the prorated percentages are Pt, 98.8; Rh, 

0. 7; Pd, 0. 3; and Os, 0. 2, values that are similar to those 

of Mertie's principal alloy. Likewise, if osmium and 

iridium equal to osmiridium alloy (Os:41r) are subtracted 

from the average of two analyses for platinum metals free 

Scanning Electron Microscope Studies 21 
10:2.5:0 ( 

,. 10:3:0 

10:2.4:0 

Pt 

-

10:2.5:1 \ 

' 

10fL 

Figure 5. SEM micrograph of grain 4 (Pt-Fe alloy, Pt) in polished section 66AMt31A6. The ratio platinum:iron:copper 

varies from upper to lower borders. Other grains are magnetite (M), some with minor chromium and titanium. 

Dark-gray to black areas are mounting medium. 

of gold and silver in Mertie's table 4 (1976, p. 16), then 

the prorated PGE and iron in Mertie's principal alloy are 

not too different from our average microprobe analysis 

of Pt-Fe alloy. The prorated percentages were Pt, 85.51; 

Ir, 2.82; Rh, 1.05; Pd, 0.38; Os, 0.0; Ru, 0.17; Fe, 9.45; 

Cu, 0.46; As, 0.05; and S, 0.11 = 100.00. Thus, we inferred that Mertie's principal alloy and the Pt-Fe alloy described here were similar samples. 

We tested the similarity between the PGE distribution in Mertie's principal alloy and the distribution of PGE 

in magnetic concentrates (tables 1 and 3) via chondritenormalized ratios (CNR) and discovered that the two distributions were alike. These ratios were computed by 

dividing the atomic percentages of each PGE by the 

atomic percentage of the same element in the average 

chondrite, according to estimates of abundances given by 

22 Platinum-group Elements, Goodnews Bay District, Alaska 

McBryde (1972). The ratios were then plotted as 

logarithmic ordinates versus atomic numbers (as abscissa), 

the points were connected by straight lines, and the resultant curves were visually compared (fig. 6). Unfortunately, 

this technique suffered when elements such as osmium 

and ruthenium were not reported because the CNR values 

for the reported PGE were increased proportionately. 

Thus, only eight analyses (those with four or more PGE; 

tables 1 and 3) were used to compare with three analyses 

of the principal alloy given by Mertie (1976). Despite 

the missing osmium in all analyses and the missing 

ruthenium in some analyses reported in tables 1 and 3, 

the two sets of curves are essentially similar due to similar 

atomic percentages of the PGE. We accepted this evaluation as evidence of the presence of Mertie' s principal alloy 

in the magnetic concentrates investigated in this study. 
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0 .5 

0.4 

0 .3 

0 .2 

0.1 

.09 

.08 

.07 

.06 

.05 

.04 

.03 

.02 

.01 -------- ------~--------~--------~--------~------~ 

44 

Ru 

45 

Rh 

46 

Pd 

76 

Os 

77 

lr 

78 ATOMIC NO . 

Pt ELEMENT 

Figure 6. Graph of chondrite-normalized ratios of platinum-group elements (PGE) in three different groups of samples from the Goodnews Bay district. Curve 1: PGE in eight magnetic concentrates (this report); dotted line between 

paladium and iridium indicates no data for osmium. Curve 2: PGE in three sets of the principal alloy of Mertie 

(1976, p. 18, 21) which represent 40 samples. Curve 3: PGE production from 1936 to 1972 (Mertie, 1976, p. 22). 

More conclusive proof will doubtless be attained when 

more complete chondrite-normalized ratios are computed 

from analyses of PGE that include osmium and 

ruthenium. 

CNR plots by Naldrett and others (1979) and 

Hoffman and others ( 1979) show abscissas with PGE in 

Scanning Electron Microscope Studies 23 
10fL 

Figure 7. SEM micrograph of the lower left part of figure 4 (grain 1, polished section 69AMt14A2). Most of the 

large light-gray area at lower left is sperrylite (5), several small darker gray areas at the upper end of the gray 

area and at the lower right part are unknown C (Rh), white areas are Pt-Fe alloy (Pt), and the gray host is magnetite 

(M). Dark-gray area at lower edge, and with white reflection, at left, is mounting medium. 

the order osmium, iridium, ruthenium, rhodium, 

platinum, and palladium, an order which coincides with 

decreasing melting points of the metals. We preferred an 

equal spacing of the atomic numbers of the PGE. Because 

of the differences in occurrence, the curves shown on figure 6 differ markedly from all CNR curves presented by 

Naldrett and others (1979, p. 407--408) and Hoffman and 

others ( 1979, p. 44 7) when they are transposed to a plot 

using the same abscissa as in the Naldrett and Hoffman 

articles. The ores in the Goodnews Bay district are mainly 

Pt-Fe alloys plus minor amounts of other PGE alloys, 

PGE arsenides, and PGE sulfides; the ores discussed by 

Naldrett and others ( 1979) and Hoffman and others ( 1979) 

are mainly copper and nickel sulfide mineralizations with 

minor quantities of PGE. 

24 Platinum-group Elements, Goodnews Bay District, Alaska 

Sperrylite (Pt-As).-This phase was a common one 

found in three of the five PGE-bearing grains examined. 

The sperrylite tended to be slightly darker in tone than 

the Pt-Fe alloy (figs. 7-10). Most grains tested by Kevex 

analysis showed ratios of 8 parts platinum to 10 parts 

arsenic. These elemental proportions, plus equant forms, 

indicated this probably isometric mineral of platinum and 

arsenic was sperrylite (Wright and Fleischer, 1965; Cabri, 

1972, 1976). Sperrylite was usually associated with Pt-Fe 

alloy and Rh-bearing minerals, and contained only 

platinum and arsenic except for a few border zones that 

show small amounts of chromium, sulfur, rhodium, palladium, and ever-present iron. The surface of Pt-As was 

smooth and showed no incipient cleavages; in this respect 

it was similar to Pt-Fe alloy. 
Figure 8. SEM micrograph of the upper part of figure 4 (grain 1, polished section 69AMt14A2). Most of the upper 

right light-gray area is sperrylite (5), the medium-gray area bordering the dark-gray magnetite (M) host is hollingworthite (H), the gray laths and fibers (upper left) are lr-Fe alloy (lr), and the bright grains in the lower part are Pt-Fe 

alloy (Pt). Black area at upper right is mounting medium. 

The average of four microprobe analyses of this 

phase showed 54.16 percent platinum, 41.30 percent arsenic, and small amounts of other PGE, iron, lead, nickel, 

copper, and sulfur. Element proportions ranged from 

PtAs 1•9 to PtAs2 • 1 and averaged PtAs2 .0 which is the formula for sperrylite. 

Unknown A (Jr-Fe).-This phase was found in two 

of the three POE-bearing grains in sample 69AMt14A2 

where it occurred as a local clot in grain 1 and was abundant in grain 2 (figs. 4, 11, 12, 13, and 14). The form 

was elongate and appeared to be bladed. The average 

length and width were 12 J.Lm and 1 J.Lm, respectively; 

the maximum length observed was 30 J.Lm. The blades 

appeared to be striated, a feature that may reflect cleavages, and many grains were bent like asbestos fibers (figs. 

12 and 13). The ends of the blades were most often ragged and irregular, but some were straight and at a high 

angle to the length, similar to terminations on monoclinic 

or triclinic crystals. 

A Kevex spectrometer test of 50 spots along a 

number of bent fibers showed greater iron than iridium 

in 39 spots, and greater iridium than iron in 11 spots. 

Because of the penetrating power of the electron beam, 

we felt that the iron response was too high; some of it 

might have been from the underlying magnetite host. 

However, iridium is a cubic metal (Cabri, 1972, 1976, 

1981), and the forms shown in figures 11 , 12, 13, and 

14 probably represent a noncubic alloy of iridium and 

iron. We presumed that iridium was more abundant than 

iron, but this will have to be resolved by the less powerful 

beam of the electron microprobe. 

We found no previous description of this phase in 

Scanning Electron Microscope Studies 25 
10 fL 

Figure 9. SEM micrograph of the right edge of figure 4 (grain 1, polished section 69AMt14A2). Much of the light-gray 

area in the center and right-central part is sperrylite (5), the medium-gray area in the left center and upper part 

is unknown C (Rh), the almost white areas are Pt-Fe alloy (Pt), and the dark-gray areas are magnetite (M). The 

oval area at the lower center is unknown B (IRh). The dark area along upper edge is mounting medium. 

the literature. The closest reported material, compositionally, was iridium, in which iridium was the major element 

and iron was one of the minor elements, but otherwise 

there was no resemblance between our Ir-Fe alloy and 

the iridium described (Cabri, 1976, p. 1477). Similar 

forms of PGE phases are pictured by Ramdohr ( 1969, 

p. 347, 349, 353), but iridium and iridosmium are cubic 

minerals, and the lamellar and tabular forms shown were 

probably due to exsolution along crystallographic directions in the host minerals. Exsolution lamellae that 

strongly resemble the Ir-Fe jackstraw arrangement of laths 

and rods are illustrated by Feather (1976, p. 1403), but 

the lamellae are Pt-Fe alloy. Cabri (1981 , p. 98, 106, 

112, 124, 134) showed photomicrographs and described 

characteristic euhedral laths of iridosmine, osmium, and 

26 Platinum-group Elements, Goodnews Bay District, Alaska 

rutheniridosmine that resemble the laths of unknown A, 

but iridosmine, osmium, and rutheniridosmine are all hexagonal minerals that contain osmium, a PGE that is absent 

in unknown A. We also looked for ruthenium, but we 

did not find it. Other PGE phases are known with triclinic, hexagonal, and tetragonal symmetries which could 

include bladed or fibrous forms, but none have iridium 

as a major component. 

The binary compound, Ir-Fe, is hexagonal and contains 45 atomic percent iridium, but no physical properties 

are indicated by Berlincourt and others (1981 , p. 24). A 

similar compound is indicated by Vol (1967, p. 479-480) 

with 50 atomic percent iridium; alloys with as much as 

15 atomic percent iridium are shown as ferromagnetic; 

no other physical properties are cited. 
30p. 

Figure 10. SEM micrograph of grain 3 in polished section 69AMt14A2. Most of the center is ~perrylite (5), the bright 

inclusions at lower right are Pt-Fe alloy (Pt), and the gray areas are magnetite (M). The rough dark area at upper 

and right sides that has irregular reflections is mounting medium. 

We anticipate that structural determination will be 

unusually difficult unless more of the Ir-Fe alloy is 

discovered. Microprobe analyses may determine the composition, but the grains available are too small and too 

intergrown with other phases to permit separation for Xray diffraction analysis of the crystal structure. 

Unknown B (lr-Rh-Pt-Fe-As-S).-This rare phase 

was found as a single small aggregate ( 15 by 20 J.Lm) 

near one side of grain 1 which is peppered with Pt-Fe 

alloy inclusions (figs. 4 and 9). According to amplitudes 

of peaks on the Kevex screen, the average of three spot 

analyses of this phase indicated that the relative amounts 

of the elements were Ir, 10; Rh, 7; Pt, 7; Fe, 3; As, 

7; and S, 9. Little else can be reported because so few 

data are available. One of the spot analyses showed a 

peak height for iron of eight units, probably caused by 

contamination from below. 

The closest chemical resemblance to unknown B 

that is reported in the literature is irarsite (lrAsS), in 

which iridium exceeds all other PGE (Cabri, 1976, 1981). 

However, irarsite is a cubic mineral, presumably isotropic, and arsenic generally exceeds sulfur by a factor 

of two to four (Cabri, 1981, p. 161). We found this 

aggregate to be weakly anisotropic. Thus, from chemical 

and physical evidence we inferred that it was not irarsite, 

and that it might be a new phase. 

Hollingworthite (Rh-As-S).-This minor phase was 

found in three of the five POE-bearing grains examined; 

it was mainly associated with Pt-Fe alloy (figs. 12-18). 

In most spots analyzed by Kevex, rhodium, arsenic, and 

sulfur were the only elements detected in the proportions 

Rh, 10; As, 5; and S, 7; but locally we found small 

amounts of platinum, iron, and iridium. The composition, 

equant form, and isotropic optics left no doubt that this 

Scanning Electron Microscope Studies 27 
3fL 

Figure 11. SEM micrograph of the upper edge of grain 1 in polished section 69AMt14A2. The laths and fibers are 

lr-Fe alloy (lr), the bright smooth area at lower left is Pt-Fe alloy (Pt), and the gray areas are magnetite host (M). 

phase was the mineral hollingworthite (Stumpfl and Clark, 

1965; Cabri, 1972, 197 6). Grains of hollingworthite in 

these samples were rarely more than 10 J.Lm long. They 

were irregular in form; and the surface was less bright 

than Pt-Fe, rarely smooth, and commonly microhummocky and pitted. Although areas of hollingworthite were 

similar to sperry lite in tone and reflectivity, the hollingworthite areas could be distinguished by their rough 

surfaces; however, borders of hollingworthite against sperrylite were difficult to see in places (fig. 17). In addition 

to intergrowths with Pt-Fe alloy and sperrylite, tiny hollingworthite blebs and stringers were randomly scattered 

in magnetite (fig. 18). 

Unknown C (Rh-Pd-Ni-As-S).-This rare phase was 

found in only one of the five PGE-bearing grains. It was 

associated with sperry lite and Pt-Fe alloy, but it was 

slightly darker in tone than sperrylite and appeared to have 

a rougher surface (figs. 7 and 9). The largest area was 

28 Platinum-group Elements, Goodnews Bay District, Alaska 

40 J.Lm long and as much as 15 J.Lm wide. This phase 

was similar in appearance to hollingworthite but differed 

in two important ways: the composition (according to 

amplitudes of Kevex peaks averaged for 18 spots) was 

Rh, 10; Pd, 8; Ni, 2; As, 4; and S, 2; and this phase 

was weakly, but definitely, anisotropic. The considerable 

amount of palladium and a lesser quantity of nickel added 

to the composition of hollingworthite (if such was the 

mode of formation of this material) served to distort the 

isometric symmetry to produce a nonisometric symmetry. 

Two preliminary electron-microprobe scans of this phase 

showed the following element proportions: Rh, 3, 5; Pd, 

2.4, 5; Ni, 1, 1.4; Fe, 1, 3.6; As, 3.5, 6; and S, 1, 

1. However, these are too few data to permit an attempt 

at a formula for this PGE association. 

No previous description of this phase was found in 

the literature. The composition of hollingworthite apparently includes minor amounts of palladium and nickel 
100fiFigure 12. Photomicrograph of grain 2 in polished section 69AMt14A2. The medium-gray laths and blades are lr-Fe 

alloy (lr), the white inclusions are Pt-Fe alloy (Pt), the light-gray area at lower left is hollingworthite (H), and the 

dark-gray areas are the magnetite host (M). Black areas are mounting medium. 

(Cabri, 1972, 1976), but no mention of anisotropic behavior was found (Uytenbogaart and Burke, 1971). 

Unknown D (Pb-Rh-Fe-Ir-S).-This phase occurred 

in only one of the five PGE-bearing grains and was associated with Ir-Fe alloy as many tiny interstitial blebs 

(as much as 5 J.Lm long) and selvages along the Ir-Fe 

laths and fibers (figs. 13 and 14). Pt-Fe alloy occurred 

as larger blebs and irregular patches that accompanied this 

phase as interstitial material among the Ir-Fe laths, but 

the Pt-Fe alloy was isotropic. This phase showed strong, 

but spotty, anisotropism in brown tones, and its reflectivity was less than that of Pt-Fe alloy. According to 

amplitudes of peaks on the Kevex screen, the average 

of 20 spot analyses on some of the largest blebs showed 

Pb, 10; Rh, 6; Fe, 10; Ir, 4; and S, 9. Iron amplitudes 

ranged from about 5 to 21 units of peak height, but the 

responses for the other elements were more consistent and 

therefore yielded credible semiquantitative values. 

A number of PGE-bearing phases have been known 

to contain lead, and most often lead has been associated 

with major palladium (Cabri, 1976). In one phase 

(xingzhongite), iridium, copper, and rhodium are major 

elements, lead is minor, the anion is sulfur, and the mineral is cubic. Our phase was strongly anisotropic, and 

the composition indicated by Kevex analysis was unlike 

any described in the literature. This phase will require 

more work to characterize the composition and structure, 

but because of its small size (generally less than 2 J.Lm), 

both tasks will be difficult. 

Other Phases 

Magnetite .-Magnetite was the most abundant mineral in the magnetic concentrates under study. Most grains 

Scanning Electron Microscope Studies 29 
10fL 

Figure 13. Photomicrograph of the left side of figure 12 (grain 2, polished section 69AMt14A2), enlarged to show 

(upper center) the detail of fibrous structure at the end of a lath of lr-Fe alloy (lr). White areas at bottom, left 

side, and larger interstitial areas are Pt-Fe alloy (Pt), smaller light-gray blebs are unknown D (Pb), medium-gray 

area at lower left is hollingworthite (H), and dark-gray host mineral is magnetite (M). Black areas are mounting 

medium. 

in each of the size fractions were rounded and equant 

(fig. 3); some showed slight to extensive alteration to 

hematite; many had octahedral cleavage traces with exsolved ilmenite, hematite, or spinel along these traces; 

and some showed inclusions of, or intergrowths with, 

these minerals. No intergrowths with chromite were recognized, but many chromite grains had overgrowths of 

magnetite. In a modal analysis of 120 grains in concentrate sample 69AMtl4A2, using Kevex analysis to learn 

the chemistry of each grain, we found the following percentages of minerals: magnetite, 89.2; ilmenite, 6.7; chromite, 2.5; spinel, 0.8; and Mg-Al-Ca-Fe silicate (pyroxene?), 0.8. Of 107 magnetite grains, 65 contained variable 

amounts of titianium, 8 showed aluminum, 3 had magnesium, 3 showed chromium, and 2 contained appreciable 

30 Platinum-group Elements, Goodnews Bay District, Alaska 

quantities of silicon. Of eight grains of ilmenite, six had 

considerable manganese. Some of the magnetite was 

classed as titanomagnetite (fig. 3). 

In addition to the above minor elements in magnetite, we discovered that platinum was held in the magnetite lattice near the borders with Pt-Fe alloy. To illustrate 

the platinum distribution in magnetite, we chose an area 

among three grains of Pt-Fe alloy in sample 69AMt14A2, 

grain 1 , and found we could contour the platinum values 

across several traverses using Fe-Pt ratios according to 

Kevex analyses. We allowed the most prominent peak 

(Ka 1) for iron to reach the top of the grid chart, stopped 

the accumulation of data, and estimated the height of the 

most prominent platinum peak. The results shown by contour lines in figure 19 indicate a range of ratios from 
1 OfL 

Figure 14. SEM micrograph of the upper part of figure 12 (grain 2, polished section 69AMt14A2), enlarged to show 

detail of the lr-Fe laths and blades (lr). White areas at right are Pt-Fe alloy (Pt), medium-gray areas at right edge 

are hollingworthite (H), light-gray interstitial blebs are unknown D (Pb), and dark-gray host mineral is magnetite 

(M). Dark area with irregular reflections, in upper right corner, is mounting medium. 

Fe lO:Pt 0 to Fe lO:Pt 7.5. Similarly, in grain 2-of the 

same sample, we discovered that magnetite near the borders with PGE phases contained small amounts of 

rhodium and iridium. In all such border areas of magnetite, we inferred that there was a considerable amount of 

PGE and that such magnetite grains constitute a source 

of PGE that should not be ignored. 

Ilmenite.-This mineral was fairly abundant among 

all the magnetic concentrates as discrete grains, as intergrowths with magnetite, and as inclusions and exsolution 

blebs in magnetite. However, in all our observations, we 

could find no direct association of ilmenite with PGE 

phases. 

Chromite .-This mineral was abundant as discrete 

grains, but was rarely found intergrown with magnetite. 

In some concentrates, magnetite occurred as an overgrowth on chromite grains, and the two have been partly 

altered to hematite. We recognized no association of chromite with PGE phases. 

Other minerals .-Less common minerals in the 

magnetic concentrates included pyrite, chalcopyrite, hercynite (Fe-Al spinel), and Mg-Al-Ca-Fe silicates which 

could not be identified under the metallographic and scanning electron microscopes. We did not detect any direct 

association of any of these minerals with PGE phases, 

nor did we analyze any concentrates of these minerals 

for PGE. 

Scanning Electron Microscope Studies 31 
10 fJFigure 15. SEM micrograph of the center of figure 4 (grain 1, polished section 69AMt14A2). Light- to medium-gray 

areas in upper and lower center parts are hollingworthite (H), white areas are Pt-Fe alloy (Pt), and dark-gray areas 

are magnetite host (M). 

CONCLUSIONS 

1. We found that PGE minerals occur as discrete grains 

in the magnetic concentrates, that PGE mineral 

phases form inclusions in magnetite, and that PGE 

are diffused into magnetite adjacent to the borders 

of inclusions of PGE minerals. PGE alloys appear 

to range in composition, even across a single grain, 

so that a fixed composition is not the rule and approximate ratios can only be inferred. Mineral 

phases such as sperrylite and hollingworthite may 

have fixed compositions, but with the equipment 

available we could not confirm stochiometric 

amounts of PGE and anions from grain to grain of 

each species. 

2. We do not know why the finest grained fractions in 

the screened samples contain greater amounts of 

32 Platinum-group Elements, Goodnews Bay Di~trict, Alaska 

PGE than the coarsest fractions. One explanation 

is the possible existence of two populations of PGE 

phases because of two generations of PGE deposition, but nothing in the geology of the Goodnews 

Bay mining district is suggestive of two pulses of 

PGE deposition (Mertie, 1976). The source of essentially all the PGE that have been found in the 

Salmon River and its western tributaries is the elongate ridge known as Red Mountain, which lies west 

of the headwaters of the Salmon River (Mertie, 

1976, p.- 11). There is no evidence that the ultrabasic rocks that compose Red Mountain are a composite mass of more than one episode of emplacement. Another explanation involves uneven distribution, abundances, and grain sizes of PGE minerals 

in the Red Mountain pluton, but not enough is 

known to permit a definitive statement. 
10fL 

Figure 16. SEM micrograph of the left edge of grain 2, polished section 69AMt14A2. Medium-gray area at left side 

of almost white Pt-Fe alloy (Pt) is hollingworthite (H), fibrous forms at upper right are lr-Fe alloy (lr), and dark-gray 

areas are magnetite (M). Black areas are mounting medium. 

3. We are certain that a considerable amount of PGE 

is located within the magnetite lattice especially 

near the borders with PGE mineral inclusions. Thus, 

these magnetite grains represent a resource for PGE, 

one that is easily concentrated by magnetic devices 

and easily dissolved in strong mineral acids to enable liberation of insoluble PGE. Mertie (1976, 

p. 12) has written that magnetite is known to contain small amounts of platinum metals, and that all 

iron ores in the Goodnews Bay mining area were 

crushed, milled, and concentrated to recover the 

contained platinum metals, but the impression received from Mertie's report is that only the inclusions were recovered. We presume that the PGE 

in the lattice of the magnetite might be recovered 

commercially as well, but this presumption must be 

tested empirically to learn if the benefit-cost ratio 

is favorable. 

RECOMMENDATIONS 

The study of the location of PGE in magnetic concentrates as reported here is not quite complete. The samples acquired from the Goodnews Bay mining district 

were easily available, and using the proper determinative 

tools, we located the major occurrences of PGE in the 

magnetic concentrates. Only a small amount of electronmicroprobe work needs to be done to quantify the PGE 

content of the seven PGE mineral phases described here. 

However, we envision an expanded study of PGE in magnetic concentrates to include other areas and possibly 

other host minerals. Therefore, we recommend the following: 

Recommendations 33 
3fL 

Figure 17. SEM micrograph of part of grain 5 in polished section 66AMt7N6. Rough surfaces in central area represent 

hollingworthite with minor platinum and iron (H), smooth area at right is sperrylite (5), and large smooth area 

at left is Pt-Fe alloy (Pt). Black areas are mounting medium. 

I . Further study of PGE in magnetic concentrates should 

include electron-microprobe investigations, mainly 

for the quantitative chemical analysis of tiny grains 

which occur in the Goodnews Bay area samples. 

A necessary requirement will be standards for PGE 

in the appropriate matrix in order to quantify PGE 

in magnetite. If PGE are found to be intergrown 

or associated with chromite (Mertie, 1969, p. 87), 

then similar standards for PGE in chromite will be 

required. 

2. Detrital magnetite from exploited platinum placers 

elsewhere in the world should be sieved to various 

size fractions and analyzed for PGE elements to determine if their abundances are controlled by the 

grain size of the magnetite, as we found for the 

PGE in the Goodnews Bay district. 

3. Magnetite from platinum-bearing rocks and from associated mafic and ultramafic rocks should be 

34 Platinum-group Elements, Goodnews Bay Di~trict, Alaska 

analyzed for PGE and other trace elements to determine if their abundances in the magnetite are related 

to the type of rock and to the history of crystallization of the rock. 

4. Similar studies should be made of magnetic concentrates from other areas where mafic and ultramafic 

rocks, or their eroded heavy minerals, can be sampled, including areas not now known to contain 

PGE. In the United States, such rocks are present 

in California, Oregon, and Washington on the west 

coast; in Montana and Wyoming in the mountainous 

west; in Minnesota near Lake Superior; in 

Appalachia along a discontinuous belt from 

Alabama through Vermont and including some areas 

in Maine (Larrabee, 1966, 1971; King and Beikman, 1974; Blair and others, 1977; Page and 

Tooker, 1979; Page and others, 1975); and in other 
50J-L 

Figure 18. Photomicrograph of part of grain 1 in polished section 69AMt14A2. Small, equant, medium-gray blebs 

of hollingworthite (H) are scattered in or among white inclusions of Pt-Fe alloy (Pt) in dark-gray magnetite (M). 

Medium-gray laths of lr-Fe alloy (lr) are at upper edge. Almost black areas are pits filled with mounting medium. 

areas in Alaska. Obviously, if PGE occur in sufficient quantities in magnetite and perhaps elsewhere 

in chromite (which are the common and locally 

abundant accessory minerals of mafic and ultramafic 

rocks), then these minerals represent possible 

sources of PGE. Lode deposits and placer concentrations could constitute significant resources of 

PGE as well as supply byproduct iron, chromium, 

and other metals (Page and Dohrenwend, 1973). 

5. Study should be undertaken to develop an efficient 

method of getting PGE out of magnetite and into 

a suitable medium for analysis. Because of its 

scavenging character, magnetite is a good sample 

medium for analysis of PGE, especially for tJ.msized PGE phases that could not collect in placer 

deposits. Magnetite is easily recovered by magnetic 

devices. It is easily pulverized to free the sub-tJ.msized particles of PGE and to expedite solution of 

the PGE in strong mineral acids or absorption into 

the lead button of a fire assay. Although the very 

fine grain size of some of the particles necessitates 

fine grinding, the difficulties in analyzing PGE are 

not caused by the grain size, but rather by the long 

and tedious sample preparation prior to analysis. In 

the present preparatory scheme, the sample must be 

ground to a fine powder to enable early PGE abRecommendations 35 
Figure 19. SEM micrograph of central part of grain 1 in polished section 69AMt14A2. Contour lines of platinum: iron 

ratios show that platinum has diffused into magnetite (M, dark gray) near the borders of Pt-Fe alloy (Pt, white). 

Medium-gray lens-like area at upper center is hollingworthite (H). Dark areas are pits filled with mounting medium. 

sorption into the molten-lead phase of the fire-assay 

fusion. Using the present state-of-the-art techniques 

in spectrochemical and atomic-absorption methods 

of analysis to determine the parts per billion 

amounts of PGE in these magnetites, we found that 

preconcentrations of PGE between 1 ,000 and 4,000 

times the original content are required. The fireassay technique of dissolving the magnetite with a 

lead-oxide-based fusion, collecting the PGE in molten lead and concentrating the PGE by removing 

the lead, has proven to be a reliable method, but 

it requires great care and much time to yield consistent results. Perhaps a suitable chemical dissolution 

technique can be developed, utilizing a coarser 

ground magnetite powder, a suitable reagent, or a 

combination of reagents to take all the PGE (includ36 Platinum-group Elements, Goodnews Bay District, Alaska 

ing osmium) into solution, to enable use of atomicabsorption analysis with capabilities in the parts per 

trillion range. 

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1:-r U.S. GOVERNMENT PRINTING OFFICE: 1986-773-047/46,006 REGION NO. 8