RI 8553

Bureau of Mines Report of Investigations/1981

Beneficiation of Potential Platinum

Resources From Southeastern Alaska

By D. C. Dahlin, A. R. Rule, and L. L. Brown

UNITED STATES DEPARTMENT OF THE INTERIOR
Report of Investigations 8553

Beneficiation of Potential Platinum

Resources From Southeastern Alaska

By D. C. Dahlin, A. R. Rule, and L. L. Brown

UNITED STATES DEPARTMENT OF THE INTERIOR

James G. Watt, Secretary

BUREAU OF MINES
This publication has been cataloged as follows:

Dahlin, D. C. (David Clifford), 1951-

Beneficiation of potential platinum resources from southeastern Alaska.

(Report of investigations / United States Department of the Interior, Bureau of Mines ; 8553)

Bibliography: p. 14.

Supt. of Docs. no.: I 28.23:8553.

1. Ore-dressing. 2. Platinum ores-Alaska. I. Rule, A. R.

(Albert R.). II. Brown, L. L. (Lawrence L.), 1928- . III. Title.

IV. Series: Report of investigations (United States. Bureau of

Mines) ; 8553.

TN23.U43 [TN538.P53] 622s [622'.3424] 81-607026 AACR2
CONTENTS

Page

Abstract ..................................... .........................

1

Introduction .... ..................... ..................................... 1

Acknowledgments........................................................... 3

Material preparation and test procedures ................................ 3

Salt Chuck sulfide...................................................... 4

Location ..................................................................... 4

Petrography t n .................................. ................... 4

Beneficiation ...................................................... 7

Snettisham titaniferous magnetite ....................................... 8

Location.................. ......................................... 8

Petrography........................................................ 8

Beneficiation...................................................... 8

Union Bay chromite ...................................................... 10

Location ........................................................... 10

Petrography ........................................................ 10

Beneficiation...................................................... 10

Yakobi Island sulfide................................................... 11

Location ........................................................... 11

Petrography ........................................................ 11

Beneficiation ...................................................... 11

Conclusions ............................................................. 13

References .............................................................. 14

ILLUSTRATIONS

1. Locations of the four sample sites in southeastern Alaska ........... 2

2. Electron microprobe element displays of Salt Chuck sulfide

concentrate................................................. 6

TABLES

1. Head analyses of four potential platinum resources from southeastern

Alaska ............................................................ 5

2. Sulfide flotation and magnetic separation of Salt Chuck sulfide ..... 7

3. Conditions and reagents for Salt Chuck sulfide flotation ........... 7

4. Magnetic separation and sulfide flotation of Snettisham titaniferous

magnetite .......... ....... .......................... 9

5. Conditions and reagents for sulfide flotation of Snettisham titaniferous magnetite ................................................... 9

6. Tabling and magnetic separation of Union Bay chromite ............... 11

7. Bulk flotation and magnetic separation of Yakobi Island sulfide ..... 12

8. Conditions and reagents for bulk flotation of Yakobi Island sulfide. 12
BENEFICIATION OF POTENTIAL PLATINUM RESOURCES

FROM SOUTHEASTERN ALASKA

by

D. C. Dahlin, 1 A. R. Rule, 1 and L. L. Brown 2

ABSTRACT

The Bureau of Mines conducted laboratory batch beneficiation tests on

samples from four potential platinum resources in southeastern Alaska to concentrate platinum and other precious metals. This investigation was done as

part of the mission of the Bureau to insure an adequate supply of minerals to

meet the Nation's needs. Petrographic studies and beneficiation methods

including gravity concentration, froth flotation, and magnetic separation were

used to determine mineral association and to attempt to concentrate the platinum values with a primary mineral value such as chromite, copper sulfide, or

magnetite. A high-graded sample from the Salt Chuck copper sulfide deposit

yielded the best platinum-group metal concentrate; the maximum grade attained

was 0.04 oz Pt and 1.5 oz Pd per ton of high-grade copper sulfide concentrate.

The other samples yielded low-grade primary mineral concentrates with low

platinum-group values, and/or the platinum-group metals did not concentrate

with the primary mineral value.

INTRODUCTION

The platinum-group metals (platinum, palladium, rhodium, iridium, ruthenium, and osmium) have chemical and physical properties that are critically

important in many industrial applications. The United States produces less

than 1 pet of the platinum-group metals it consumes annually. Approximately

10 pet is refined from scrap and, consequently, the United States must import

nearly 90 pct of its annual consumption. Nearly all of the world production

comes from two countries, the Republic of South Africa and the U.S.S.R., and

the dependence of the United States on foreign sources has strategic as well

as economic implications. Although the United States has small reserves of

platinum-group metals, its resources are large (5);3 most, however, are poorly

explored or otherwise defined.

1

Metallurgist.

2Geologist.

All authors are with the Albany Research Center, Bureau of Mines, Albany,

Oreg.

3Underlined numbers in parentheses refer to items in the list of references at

the end of this report.
2

The United States consumed an estimated 2.5 million troy ounces of

platinum-group metals in 1979 (8). The automotive industry used the largest

portion of the total, 40 pet, for catalysts in emission control devices. The

electrical industry used 18 pet of the total consumption, and the chemical

industry used 15 pet. Other significant users include the petroleum, dental

and medical, glassware, and jewelry industries. The metals are used as chemical reaction catalysts; electrical contacts; medical and dental instruments,

alloys, and drugs; laboratory and process equipment; and galvanic systems for

corrosion protection. Potential use of platinum-group metals in solar power

and fuel cell technologies could significantly increase domestic consumption.

U.S. production of platinum-group metals, all as a byproduct of copper

mining, was estimated at 10,000 troy ounces in 1979 (8). This represents less

than 0.2 pet of the estimated world production. The Republic of South Africa

and the U.S.S.R. together accounted for 95 pet of world production, with

Canada supplying most of the remainder. The United States imported nearly

90 pct of its annual consumption or platinum-group

metals. This dependence on

foreign sources creates a

poor strategic position for

this critical industrial

metal and an adverse affect

on the national balance of

payments.

As part of its mission

to insure an adequate supply

of minerals to meet the

Nation's needs, the Bureau

of Mines has conducted

research to identify potential platinum resources in

the United States. Although

U.S. production is unlikely

to ever meet U.S. demand,

the need and desirability

of exploring for and evaluating potential platinumgroup metals resources is

evident. The Bureau of

Mines is currently investigating platinum-group metals

resources in the Stillwater

Complex, Montana; the Duluth

Gabbro, Minnesota; and the

basic igneous rocks of the

Pacific Northwest and

Alaska. This report describes the potential of

four sites in southeastern

Alaska, shown in figure 1,

FIGURE 1. - Locations of the four sample sites in southeastern Alaska.
3

as platinum-group metals resources that may be recovered as byproducts with

other valuable minerals.

Alaska has long been considered a resource for platinum-group metals (2,

6). Both placer and lode deposits have been identified. The mafic and ultramafic complexes in southern and southeastern Alaska have been studied as

potential lode-type platinum deposits (1).

Samples from four mafic-ultramafic areas reported to contain platinumgroup metals were obtained for petrographic and beneficiation tests. The samples were as follows:

1. Pyroxenite that contains copper sulfide from Salt Chuck.

2. Pyroxenite that contains titaniferous magnetite from Snettisham.

3. Dunite that contains chromite from Union Bay.

4. Pyroxenite that contains copper and nickel sulfides from Yakobi

Island.

The Bureau of Mines has published reports of earlier work at Salt Chuck

(4), Snettisham (7), and Yakobi Island (3). These reports describe comprehensive drilling and sampling programs and some beneficiation studies. Determination of platinum content and association in the materials was not considered

in the reports on Snettisham and Yakobi Island, and it was not an important

part of the Salt Chuck report. The present study examines the samples as

potential platinum resources by determining platinum and palladium content,

and by determining whether the platinum and other precious metals concentrate

with the primary mineral values in the sample, such as sulfides, magnetite,

or chromite. The precious metals content of the four samples in this investigation is very low, so their economic recovery would be as a byproduct of

concentrating a primary mineral value. No attempts were made to recover the

precious metals beyond producing the concentrates.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the assistance of Tom Pittman, Supervisory Mining Engineer, Alaska Field Operations Center, Bureau of Mines, and

Vance Thornsberry, Project Manager, Inspiration Development Co., in obtaining

samples for this investigation.

MATERIAL PREPARATION AND TEST PROCEDURES

The investigation was similar for each sample. Representative hand specimens were selected from as-received materials, and head samples and splits

for beneficiation tests were prepared from the materials after they had been

crushed to approximately minus 1/4-inch. Petrographic examination was done

on hand specimens and beneficiation products to determine mineral identification and associations. Preliminary beneficiation tests were performed on 1-

or 2-kg samples to develop effective procedures to concentrate the primary
4

mineral values, with which the platinum-group metals were associated. Largescale batch tests using 10- or 20-kg samples were then performed to provide

beneficiation products for precious metals analyses. Products were sent to

the Bureau's Reno Research Center for determination of platinum, palladium,

gold, and silver. Analyses were done by a fire assay-atomic absorption technique with a minimum level of detection of 0.001 oz/ton. Weight distributions

of the beneficiation products and the small amounts of the precious metals

present were such that very small changes in analyses caused large changes in

distributions. Therefore, distribution data for the precious metals were not

included in the metallurgical balances in this report.

SALT CHUCK SULFIDE

Location

Salt Chuck is a shallow, saltwater inlet located at the head of Kasaan

Bay on Prince of Wales Island, about 45 miles northwest of Ketchikan. A mine

and a mill operated at this location intermittently from 1905 to 1941; the

mill is now in ruins.

Platinum-group metals were reported to be associated with bornite, so

sampling was done by high-grading for bornite. The intent was to determine

platinum occurrence, not to determine average grade of the deposit. Waste

rock and blast debris were selected from the waste dumps to the north and

northeast of the glory hole, from the eastern flank of the deposit and from

the mill waste dump. No attempt was made to segregate the samples.

Petrography

Petrographic examination of representative hand specimens showed the samples were medium-grained, sulfide-enriched pyroxenites. The rocks consisted

essentially of pyroxene wtih some amphibole, chlorite, and bornite; a small

amount of magnetite; very small amounts of feldspar, epidote, and malachite

(as copper stain); and traces of pyrite and chalcopyrite. The bornite was

randomly distributed in small to relatively large masses and showed some

alteration to covellite. Head analyses of the sample are shown in table 1.

Electron microprobe examination was done on polished surfaces prepared

from selected high-sulfide specimens. No platinum was found, but many very

small grains of a palladium-tellurium mineral containing variable amounts of

mercury were observed. These grains were included in and interfaced with

sulfide minerals and, to a minor extent, also in the silicate gangue minerals.

Minor amounts of silver and selenium were observed in the sulfide and palladium minerals.
Salt Chuck

sulfidel

5

TABLE 1. - Head analyses of four potential platinum resources

from southeastern Alaska

Constituent

Snett

titani

magne ! -v

PEF

A1203 ...... 9.19 7.92 0.34 6.76

CaO........ 1.14 14.4 .41 8.13

Co......... .01 .01 .01 .01

Cr203 ...... .10 .09 1.13 .10

Cu ........ 2.36 .04 .01 .21

Fe ........ 10.3 17.0 8.30 7.46

MgO........ 9.64 10.4 25.8 11.5

Ni......... .01 .01 .14 .32

S......... 1.03 .27 .004 1.31

SiO 2 ....... 41.5 36.5 41.1 50.0

TiO 2. . . . .. . 1.08 2.92 .45 .48

OUNCE PER TON

Ag ......... 0.6 0.2 20.011 0.1

Au......... .2 2.006 2.003 2.003

Pd......... .13 2.002 2.003 2.001

Pt ......... 2.004 2.001 2.002 2.001

1 Sample contained 2.4 ppm Hg.

2Average calculated head analysis determined from individual

tests. The element was not detected in the head sample.

Electron microprobe examination was also conducted on polished surfaces

prepared from sulfide flotation concentrates. Figure 2 shows an electron

backscatter image and microprobe X-ray scans for platinum, palladium, tellurium, and copper for a portion of the concentrate. Scans were also made for

iron, aluminum, silicon, mercury, and sulfur but are not shown. The bright

areas in each micrograph show the element concentrations. A platinum grain

approximately 15 pm by 5 pm is seen at the interface between a copper sulfide

and an iron-aluminum silicate. It is also associated with a palladiumtellurium grain that, in this instance, contains almost no mercury.

Electron microprobe quantitative analyses were made on a region of bornite and telluride association. The telluride contained 36.5 pct Pd, 38.7 pct

Te, 22.8 pet Hg, 1.6 pct Cu, 0.2 pct Fe, and 0.1 pet S. The bornite contained

64.0 pet Cu, 11.3 pct Fe, 24/6 pct S, and less than 0.1 pct Te. Palladium and

mercury were not detected in the bornite.
6

Specimen I Im OArM Platinum

T - | | . ' .

Palladium I ellurium

-^ . -. . . ^ >. '2 .. . * - *

Copper

FIGURE 2. - Electron microprobe element displays of Salt Chuck sulfide concentrate. The

grads are 10 micrometers square.
7

Product

Flotation cleaner concentrate

Flotation cleaner tailings...

Nonmagnetic rougher tailings.

Magnetic cleaner tailings....

Magnetic cleaner concentrate.

Composite/totals........

Flotation cleaner concentrate

Flotation cleaner tailings...

Nonmagnetic rougher tailings.

Magnetic cleaner tailings....

Magnetic cleaner concentrate.

Composite/totals .......

Weight,

pet

5.6

.3

85.6

.9

7.6

100.0

Weight,

pct

5.6

.3

85.6

.9

7.6

Analyses. oct

Cu

43.8

3.37

.19

.26

.09

2.64

Distri

Cu

93.1

.4

6.2

.1

.2

100.0

Beneficiation

Beneficiation tests were designed to concentrate the sulfide minerals and

associated platinum-group minerals. Also, magnetic separation was investigated to

determine whether platinum-group metals concentrated in the magnetic fraction.

Small-scale exploratory tests were done, and the following procedure was

designed for large-scale batch tests. A 10-kg sample was ground in a rodmill for

20 minutes at 50 pet solids. Grab samples indicated that the ground material was

essentially minus 65 mesh, but a complete size analysis of the grind was not done.

The ground pulp was conditioned with potassium amyl xanthate and a frother for sulfide flotation. In flotation, a rougher step and one or two cleaner steps were done

to produce a high-grade copper sulfide concentrate. The rougher tailings and sometimes the first cleaner tailings from flotation were treated in a concurrent wet

drum magnetic separator with a field intensity of 500 to 1,100 gauss. A final magnetic concentrate was produced from a rougher and a cleaner magnetic separation step.

Results from a typical test using this procedure are shown in table 2, and

table 3 shows the conditions and reagents used in the flotation step. The sulfide

flotation cleaner concentrate analyzed 43.8 pet Cu with recovery of 93 pet of the

copper and contained, per ton, 0.036 oz Pt, 1.5 oz Pd, 1.1 oz Au, and 6.4 oz Ag.

The magnetic cleaner concentrate analyzed 61.4 pet Fe with recovery of 43 pet of

the total iron and contained, per ton, 0.003 oz Pt, 0.013 oz Pd, 0.005 oz Au, and

0.035 oz Ag.

TABLE 2. - Sulfide flotation and magnetic separation of Salt Chuck sulfide

Fe

9.5

11.4

6.5

7.4

61.4

S

20.0

1.30

.04

.06

.01

1.16

j--- --/--

Pt

0.036

NA

.003

.003

.003

.005

- '" "`

Pd

1.5

NA

.032

.024

.013

.113

Arnlrc r. It I-nn

Au

1.1

NA

.006

.038

.005

.067

, jl -/ Ll

Ag

6.4

NA

.021

.044

.035

10.9 .379

- -

.bution. - - -pct

Fe

4.9

.3

51.2

.6

43.0

100.0

S

96.6

.3

2.9

.1

.1

100.0 100.0 - _ -- Zn~-1 - - - - -_ _I ___- 7_ .. * INA IUL ainayzea; insurllicenL sample ror analysis.

TABLE 3. - Conditions and reagents for Salt Chuck sulfide flotation

Operation Conditions Reagents, lb/ton

Time, min pH1 I of flotation feed

Conditioning ......... 2.5 9.6 0.1 potassium amyl xanthate,

0.05 frother.

Rougher flotation.... 6 ND None.

Cleaner flotation.... 6 9.0 None.

ND Not determined. 1Natural pH = 9.5.
8

The data in table 2 show the platinum and palladium to be present in the

flotation concentrate in approximately a 1:40 ratio. In the flotation concentrates from other tests, the platinum to palladium ratio ranged from 1:1 to

1:80. In this series of tests, the platinum content in the sulfide flotation

cleaner concentrate ranged from 0.020 to 0.051 oz/ton, and the palladium content ranged from 0.046 to 1.6 oz/ton.

SNETTISHAM TITANIFEROUS MAGNETITE

Location

The Snettisham Peninsula is located on the south side of Port Snettisham

and west of Gilbert Bay, about 30 miles southeast of Juneau. A titaniferous

magnetite deposit extends along the northern shoreline. The composite sample

for this study was collected in the area of an old mill site on the western

end of the deposit. Representative material was taken from two small pits and

from outcrops along the beach between the pits.

Petrography

Hand specimens from the deposit were medium- to coarse-grained pyroxenites consisting essentially of pyroxene with some magnetite and amphibole,

small amounts of ilmenite, and small veins and random concentrations of pyrite

with associated chalcopyrite and pyrrhotite. Smaller amounts of chlorite,

epidote, actinolite, quartz, and calcite occurred in veins and alteration

halos. Random feldspar and apatite crystals also were observed. Magnetite

and ilmenite grains were intergrown with the ferromagnesian silicates. Head

analyses of the sample are shown in table 1.

Sulfide mineralization occurred in at least two stages. One accompanied

the epidote alteration stage, and one accompanied the chlorite alteration

stage. Some sulfide mineralization appeared to be random and may be primary.

A scanning electron microscope was used to examine polished surfaces prepared from magnetic and nonmagnetic sulfide concentrate products. No platinumgroup metals or minerals were observed during microscopic examination.

Beneficiation

Beneficiation tests were designed for magnetic concentration of the magnetite and flotation of the sulfide minerals. Chemical analyses of beneficiation products indicated that the platinum and palladium concentrate with the

sulfides.

For each large-scale batch beneficiation test a 10-kg sample was ground

in a rodmill for 20 minutes at 50 pet solids. The ground pulp was treated in

a concurrent wet drum magnetic separator with a field intensity of 500 to

1,100 gauss. The rougher magnetic concentrate was sized at 200 mesh, and

the oversize fraction was stage-ground to about 85 pet minus 200 mesh. The

rougher concentrate was then treated in two cleaner magnetic steps to produce

the second cleaner magnetic concentrate. The second cleaner magnetic step was
Product

Second cleaner magnetic

concentrate..............

Second cleaner nonmagnetic

tailings.................

Nonmagnetic flotation

products:

Sulfide concentrate.....

Flotation tailings......

Composite/totals.....

Second cleaner magnetic

concentrate..............

Second cleaner nonmagnetic

tailings.................

Nonmagnetic flotation

products:

Sulfide concentrate.....

Flotation tailings......

Composite/totals.....

Weight,

pct

15.7

.6

.7

83.0

100.0

Weight,

pet

15.7

.6

.7

83.0

Analyses. pct

63.2

13.6

31.9

8.2

9

Fe

58.2

.5

1.3

40.0

100.0

TiO 2

done primarily to improve the grade of the magnetic concentrate and the second

cleaner nonmagnetic tailings were considered, at the time of the tests, to be low in

sulfides. Subsequent chemical analyses indicated that they, too, should have been

included in the sulfide flotation feed. The rougher and first cleaner tailings from

magnetic separation were conditioned with potassium amyl xanthate and a frother, and

a single flotation step was done to produce a sulfide concentrate.

Results of a test using the above scheme are shown in table 4, and table 5

shows the conditions and reagents used in the sulfide flotation step. Platinum did

not concentrate with the primary mineral value, magnetite, but it concentrated with

the sulfide fraction. The sulfide concentrate contained 2.32 pet Cu, 31.9 pct Fe,

and 33.5 pet S with recovery of 62 pet of the copper, and it contained, per ton,

0.02 oz Pt, 0.03 oz Pd, and 0.03 oz Au. The second cleaner magnetic concentrate

contained 63.2 pet Fe and 3.77 pet TiO 2 with recovery of 58 pet of the total iron.

Platinum and palladium were not detected in the magnetic concentrate.

TABLE 4. - Magnetic separation and sulfide flotation of Snettisham

titaniferous magnetite

Fe

3.77

6.85

1.60

2.49

TiO 2

0.01

.04

2.32

.01

Cu S

0.08

.35

Annlv--,-.Q n7.fnn v.|cz z J ark

ND

ND

0.02

ND

<.01

Pd

ND

ND

Au

0.01

.01

.03

Trace

<.01

33.5

.03

.27

0.03

ND

<.01

NA

ND

Ag

0.01

ND

17.0 2.71

-stribul

.03

:ion. D,

<.01

D- t

D-. --

21.8

1.5

.4

76.3

100.0

Cu

6.1

.8

61.6

31.5

100.0

S

4.8

.7

85.4

9.1

100.0 100.0 -----

ND Not detected.

NA Not analyzed.

TABLE 5. - Conditions and reagents for sulfide flotation

of Snettisham titaniferous magnetite

Reagents, lb/ton

of flotation feed

otassium amyl xanthate,

frother.

ND Not determined. 1Natural pH = 7.1.
10

UNION BAY CHROMITE

Location

Union Bay is located on the northwest end of Cleveland Peninsula, about

35 miles north-northwest of Ketchikan. About 5 miles east of the bay, a large

dunite outcrop is exposed on a mountain at an elevation of 2,535 feet. The

dunite occurs as uniform, large masses cut occasionally by thin dikes of

peridotite up to about 6 inches thick. Random samples were taken from the

surface over an area approximately 100 yards by 30 yards near the middle of

the exposure.

Petrography

The samples were medium-grained dunite consisting essentially of olivene

with a small amount of associated chromite. Some of the samples were cut by

small dikes or veins of enstatite. No sulfides were observed. Chromite was

randomly distributed in the dunite as small euhedral crystals and in larger

masses of crystals. In some cases the chromite masses stood out in relief as

the result of erosion of the surrounding highly fractured olivene. Head analyses of the sample are shown in table 1.

Some of the chromite has an atypical response to magnetic separation; it

is much more magnetic than is normal for chromite. Chemical analyses showed

that it contains considerable chromium, yet it can be concentrated by a hand

magnet. The analyses indicated that this chromite contains an excess of iron

when compared with analyses of other chromites, and some of this iron may be

present as magnetite or maghemite. However, optical and microprobe examination of polished surfaces of high-grade sections of the sample showed no

zoning or compositional variations to explain the anomalous magnetic

susceptibility.

Beneficiation

Gravity concentration and magnetic separation techniques were applied to

produce chromite concentrates. From the results of exploratory tests, the

following procedure was designed for large-scale batch tests. A 10- or 20-kg

sample was ground for 20 minutes in a rodmill at 50 pet solids. Grab samples

indicated that the ground material was minus 100 mesh. The ground slurry was

pumped to a slime deck on a shaking table. A wide cut was made on the first

pass to provide good recovery. The rougher concentrate was then retabled, and

a narrower cut was made to improve concentrate grade. The cleaner table concentrate was treated in a concurrent wet drum magnetic separator with a field

intensity of 500 to 1,100 gauss to separate a magnetic fraction from a nonmagnetic fraction.

Results from a typical test are shown in table 6. The platinum concentrated in the magnetic fraction of the cleaner table concentrate at a grade of

0.032 oz/ton Pt. The concentrates do not meet any chromite specifications.

The magnetic cleaner table concentrate analyzed 29.4 pet Cr203 and 40.1 pct Fe

with recovery of 5 pet of the chromium. The nonmagnetic cleaner table concentrate analyzed 39.6 pet Cr203 and 27.0 pet Fe with recovery of 42 pct of the

chromium.
11

TABLE 6. - Tabling and magnetic separation of Union Bay chromite

Weight, Analyses, Analyses, oz/ton Distribu- Cr/Fe

Product pct pct tion, pet ratio

Cr20 3 Fe Pt Pd Au Ag Cr20 3 Fe

Magnetic cleaner table

concentrate.......... 0.2 29.4 40.1 0.032 0.001 <0.003 0.039 4.9 1.0 0.50

Nonmagnetic cleaner

table concentrate.... 1.3 39.6 27.0 .002 .006 <.002 .016 42.3 4.3 1.00

Cleaner table tailings 6.0 3.0 9.0 .003 .001 <.001 .011 14.8 6.7

Rougher table tailings 92.5 .5 7.7 .003 .001 <.001 .033 38.0 88.0

Composite/totals. 100.0 1.2 8.1 .003 .001 <.001 .031 100.0 100.0__

YAKOBI ISLAND SULFIDE

Location

Yakobi Island is located approximately 75 miles west of Juneau and 75 miles

north of Sitka. The Bohemia Basin, the area from which the sample was taken, lies

on the east side of the island, about midway between the north and south ends. The

sample was taken from an existing adit. A layer of oxidized material was removed

from the adit wall prior to sampling freshly exposed surfaces.

Petrography

The sample, as received, was already crushed to approximately minus 1/4-inch,

so hand specimens were not available for rock characterization. The sample, probably a peridotite, consisted essentially of pyroxene with small amounts of pyrrhotite, pentlandite, chalcopyrite, and quartz, and traces of bornite and nickeliferous

pyrite. Head analyses of the sample are shown in table 1.

Spectroscopic examination of products from magnetic separation of a sulfide

flotation concentrate revealed a relatively high nickel content in the nonmagnetic

fraction. Subsequent examination with a scanning electron microscope showed that

the sulfide mineral is nickeliferous pyrite that contains about 17 pet Ni. Platinum

group minerals were not detected in the microscopic examination.

Beneficiation

Beneficiation tests including sulfide flotation and magnetic separation were

designed to concentrate the copper and nickel sulfides. A series of small batch

flotation tests was done to determine conditions for good flotation. Reagent

schemes in acid, alkaline, and neutral circuits were tested. The general procedure

was to grind the sample to minus 100 mesh in a rodmill, condition the pulp at about

40 pet solids, and make a rougher and one or two cleaner sulfide floats.

Best results occurred when lead acetate was used as an activator in an alkaline

circuit, and potassium hexyl xanthate was used as the sulfide collector. This

scheme was used in large-scale batch flotation tests.

In one test, a 10-kg sample was ground in a rodmill for 30 minutes at 50 pet

solids. Size analysis of a grab sample of the ground material showed it to be about

90 pct minus 200 mesh, but sizing of a representative sample was not done. Conditioning and flotation were done as described above. The flotation concentrate and
Product

Nonmagnetic second cleaner

flotation concentrate......

Nonmagnetic second cleaner

flotation tailings.........

Nonmagnetic first cleaner

flotation tailings.........

Nonmagnetic rougher flotation tailings..............

Magnetic flotation products1

Magnetic rougher flotation

tailings...................

Composite/totals.......

Nonmagnetic second cleaner

flotation concentrate......

Nonmagnetic second cleaner

flotation tailings.........

Nonmagnetic first cleaner

flotation tailings.........

Nonmagnetic rougher flotation tailings..............

Magnetic flotation products1

Magnetic rougher flotation

tailings...................

Composite/totals......

Weight,

pct

4.6

.5

2.8

90.5

.5

1.1

100.0

Weight,

pct

Analyses. ....Dct

Cu

3.78

.80

.23

.04

.58

Cu

3.19

2.08

.37

.11

1.95

-

12

three flotation tailings fractions were treated separately in a concurrent wet drum magnetic separator with a field intensity of 500 to 1,100 gauss. The magnetic concentrates

from the first and second cleaner flotation tailings and the second cleaner flotation concentrate were combined as one product (magnetic flotation products) for chemical analyses.

The results of the test described above are shown in table 7, and the conditions and

reagents used in the flotation step are shown in table 8. The nonmagnetic second cleaner

flotation concentrate contained, per ton, 0.005 oz Pt, 0.008 oz Pd, 0.04 oz Au, and 0.1 oz

Ag, and it analyzed 3.78 pct Cu, 3.19 pet Ni, and 0.09 pet Co with recoveries of 78 pet of

the copper, 52 pct of the nickel, and 28 pet of the cobalt.

TABLE 7. - Bulk flotation and magnetic separation of Yakobi Island sulfide

.06 .76

Ni

.22 .29

Distril

Fe

15.9

10.6

4.9

2.6

47.4

29.7

Co

0.09

.06

.02

.01

.04

S

13.3

6.2

.9

.1

34.4

17.8

-

3.8

>ution

4.6

.5

2.8

90.5

.5

1.1

Pt

0.005

ND

ND

ND

.006

Pd

0.008

-- - - ,- · -

ND

ND

ND

ND

ND

Au

0.04

.01

ND

ND

ND

ND

ND

.03 ND ND ND

Ag

0.1

.1

.1

Analyses. oz/ton

-- I

77.7

1.8

2.7

16.1

1.3

.4

100.0

.01 1.1 <.001 <.001 <.01 1<.1

pct

Ni Fe

51.6

3.5

3.5

35.1

3.5

2.8

100.0

19.0

1.4

3.6

61.3

6.2

8.5

100.0

CO

28.1

2.1

4.1

62.3

1.3

2.1

100.0

S

54.3

2.7

2.2

8.1

15.3

17.4

100.0 100.0

ND Not detected. 1

The products were magnetic second cleaner flotation concentrate,

70.8 pet; magnetic second cleaner flotation tailings, 18.8 pet;

and magnetic first cleaner flotation tailings, 10.4 pet.

TABLE 8. -Conditions and reagents for bulk flotation of Yakobi Island sulfide

Operation Conditions Reagents, lb/ton of flotation feed

Time, min pH 1

Conditioning.............. 3 9.5 1.2 CaO.

Do...................... 3 8.9 0.5 Pb(C 2H 30 2)2.

Do ...................... 2 8.7 0.1 potassium hexyl xanthate, 0.05

frother.

Rougher flotation......... 7 ND None.

First cleaner flotation... 10 8.2 None.

Second cleaner flotation.. 8 8.0 None.

ND Not determined. 1

Natural pH = 7.1.
13

CONCLUSIONS

Four samples of mafic-ultramafic deposits from southeastern Alaska were

examined as potential platinum resources. Beneficiation schemes including

gravity concentration, magnetic separation, and froth flotation were used to

concentrate platinum-group minerals with a primary mineral value.

The Salt Chuck sulfide sample yielded a high-grade copper sulfide concentrate with 0.04 oz/ton Pt and 1.5 oz/ton Pd. Gold and silver also concentrated with the sulfide.

Although the primary mineral value of the Snettisham deposit is magnetite, platinum concentrated with the small sulfide fraction. A low-grade

iron-copper sulfide concentrate was produced that contained 0.02 oz/ton Pt.

Platinum concentrated with the magnetic fraction of a table concentrate

from the Union Bay chromite sample. The grade was 0.03 oz/ton of concentrate.

Neither the magnetic fraction nor the nonmagnetic fraction of the table

concentrate met any chromite specifications.

The Yakobi Island sulfide sample was beneficiated to a low-grade coppernickel sulfide concentrate that contained 0.005 oz/ton Pt.
14

REFERENCES

1. Clark, A. L., and W. R. Greenwood. Geochemistry and Distribution of

Platinum-Group Metals in Mafic to Ultramafic Complexes of Southern

and Southeastern Alaska. U.S. Geol. Survey Prof. Paper 800-C, 1972,

pp. C157-C160.

2. Cobb, Edward H. Occurrences of Platinum-Group Metals in Alaska.

U.S. Geol. Survey Miner. Inv. Res. Map MR-64, 1:2,500,000. 1975.

3. East, J. H., Jr., W. M. Traver, Jr., R. S. Sanford, and W. S. Wright.

Yakobi Island Nickel Deposit, Sitka Mining District, Alaska.

BuMines RI 4182, 1948, 28 pp.

4. Holt, S. P., J. G. Shepard, R. L. Thorne, A. W. Tolonen, and E. L. Fosse.

Investigation of the Salt Chuck Copper Mine, Kasaan Peninsula, Prince of

Wales Island, Southeastern Alaska. BuMines RI 4358, 1948, 16 pp.

5. Jolly, James H. Platinum-Group Metals. BuMines Mineral Commodity Profiles, 1978, 23 pp.

6. Mertie, J. B., Jr. Platinum Deposits of Alaska. U.S. Geol. Survey Open

File Report 297, 1968, 65 pp.

7. Thorne, R. L., and R. R. Wells. Studies of the Snettisham Magnetite

Deposit, Southeastern Alaska. BuMines RI 5195, 1956, 41 pp.

8. U.S. Bureau of Mines. Platinum-Group Metals. Mineral Commodity Summaries

1980, pp. 118-119.

INT.-BU.OF MINES,PGH.,PA. 254 1
Product

Nonmagnetic second cleaner

flotation concentrate......

Nonmagnetic second cleaner

flotation tailings.........

Nonmagnetic first cleaner

flotation tailings.........

Nonmagnetic rougher flotation tailings..............

Magnetic flotation products 1

Magnetic rougher flotation

tailings...................

Composite/totals.......

Nonmagnetic second cleaner

flotation concentrate......

Nonmagnetic second cleaner

flotation tailings.........

Nonmagnetic first cleaner

flotation tailings.........

Nonmagnetic rougher flotation tailings..............

Magnetic flotation products1

Magnetic rougher flotation

tailings...................

Composite/totals......

Weight,

pet

4.6

.5

2.8

90.5

.5

1.1

100.0

Weight,

pct

4.6

.5

2.8

90.5

.5

1.1

3.78

.80

.23

.04

.58

.06

Cu

Cu

3.19

2.08

.37

.11

1.95

Ni

Bureau of Mines

Report of Investigations 8553

BENEFICIATION OF POTENTIAL PLATINUM RESOURCES

FROM SOUTHEASTERN ALASKA

by

D. C. Dahlin, A. R. Rule, and L. L. Brown

ERRATA

Corrected table 7 below should be used instead of the one that appears on

page 12.

TABLE 7. - Bulk flotation and magnetic separation of Yakobi Island sulfide

J

.76

.22 .29

Distril

----- F

Fe

15.9

10.6

4.9

2.6

47.4

I Co

0.09

.06

.02

.01

.04

Analyses. nct

S

13.3

6.2

.9

.1

34.4

17.8

77.7

1.8

2.7

16.1

1.3

.4

100.0

Pt

0.005

ND

ND

ND

.006

ND

ND

ND

ND

ND

. vL s USA

Pd

0.008

.-

Au

0.04

.01

ND

ND

ND

29.7 .03 ND ND ND

mAg

0.1

.1

.1

ND

ND

Analyses. oz/ton

3.8 A.

I .011 1.1 <.001 <.001 <.01 <.1 » -- 4 .+

Ni Fe

51.6

3.5

3.5

35.1

3.5

2.8

100.0

19.0

1.4

3.6

61.3

6.2

8.5

100.0

Co

V-L

28.1

2.1

4.1

62.3

1.3

2.1

100.0

S

54.3

2.7

2.2

8.1

15.3

17.4

100.0 100.0

ND Not detected. 1

The products were magnetic second cleaner flotation concentrate,

70.8 pct; magnetic second cleaner flotation tailings, 18.8 pet;

and magnetic first cleaner flotation tailings, 10.4 pct.