Bureau of Mines

Report of Investigations 5377

ORES, RED MOUNTAIN DISTRICT,

LABORATORY CONCENTRATION OF CHROMITE

KENAI PENINSULA, ALASKA

BY R. R. WELLS, F. T. STERLING, E. G. ERSPAMER,

AND W. A. STICKNEY

I-United States Department of the Interior -December 1957
I

LABORATORY CONCENTRATION OF CHROMITE

ORES, RED MOUNTAIN DISTRICT,

KENAI PENINSULA, ALASKA

BY R. R. WELLS, F. T. STERLING, E. G. ERSPAMER,

AND W. A. STICKNEY

* X * * * * * * * Report of Investigations 5377

UNITED STATES DEPARTMENT OF THE INTERIOR

Fred A. Seaton, Secretary

BUREAU OF MINES

Marling J. Ankeny, Director

Work on manuscript completed April 1957. The Bureau of Mines will welcome reprinting of this paper, provided

the following footnote acknowledgment is made: "Reprinted from Bureau of Mines Report of Investigations5377."

December 1957
LABORATORY CONCENTRATION OF CHROMITE ORES,

RED MOUNTAIN DISTRICT, KENAI PENINSULA, ALASKA

by

R. R. Wells, 1/ F. T. Sterling, 2/ E. G. Erspamer, 3 /and W. A. Stickney4/

CONTENTS

Page

Summary .......... .............. ........ ......... .......... . 1

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

Marketing specifications ..................... .............. 2

The ore ......................................... ............ 3

Physical character .............. ......................... 3

General ............... ............. .................. 3

Chrome Queen ore . .......................... 3

Juneau No. 1 ore .................................... 3

Star Four ore .................................. 3

Chemical character ......................... ... 4

Laboratory mineral dressing ................................ 5

Chrome Queen sample 1 ................... ....... 5

Chrome Queen sample 2 ..................................... 6

Chrome Queen sample 3 .................................... 7

Chrome Queen sample 4 .......... .......................... 8

Chrome Queen sample 5 ............................... 8

Chrome Queen sample 6 ........................... 9

Juneau No. 1 sample .......... .......... ................ 10

Star Four sample 1 ................. ............ 10

Star Four sample 2 ..... .. .......... ................... 11

Star Four sample 3 ...................................... 11

Conclusions ........... .................................. 12

Appendix ................................................ 15

1/ Supervising metallurgist, Bureau of Mines, Region I, Juneau,

Alaska.

2/ Metallurgist, Bureau of Mines, Region I, Juneau, Alaska.

3/ Formerly metallurgist, Bureau of Mines, Region I, Juneau, Alaska.

4/ Project coordinator, Bureau of Mines, Region I, Albany, Oreg.

Report of Investigations 5377
ii

ILLUSTRATIONS

Fig. Page

1. Best recovery at 48.0-percent-Cr20 3 grade ,,,..... .......... 13

2. Chrome/iron ratio in 48.0-percent-Cr 20 3 concentrate ..... 13

TEXT TABLES

1. Chemical analysis ...................................... 4

2. Spectrographic analysis ................................. 4

3. Summary of results ........................ ............. 14

APPENDIX TABLES

A-1. Chrome Queen sample 1; table concentration ............. 15

A-2. Chrome Queen sample 1; magnetic separation ............. 15

A-3. Chrome Queen sample 1; electrostatic separation ........ 15

A-4. Chrome Queen sample 1; flotation of chromite ......... 15

A-5. Chrome Queen sample 1; combined tabling and flotation .. 16

A-6. Chrome Queen sample 2; table concentration, minus-35-

mesh ................................................. 16

A-7. Chrome Queen sample 2; table concentration, minus-48-

mesh .......... ...................... ............... 16

A-8. Chrome Queen sample 2; table concentration, minus-65-

mesh ............. ............. 17

A-9. Chrome Queen sample 2; table concentration with

middling re-treatment ........................,, ....4 17

A-10. Chrome Queen sample 3; table concentration, minus-48-

mesh .... . ......... ................... .*..*. 17

A-ll. Chrome Queen sample 3; table concentration with

middling re-treatment .............................. 17

A-12. Chrome Queen sample 4; table concentration, minus-48-

mesh ......................... ........... 18

A-13. Chrome Queen sample 4; table concentration with tailing

re-treatment ... . ................................ 18

A-14. Chrome Queen sample 4; combined tabling and flotation .. 18

A-15. Chrome Queen sample 5; table concentration, minus-65-

mesh ................. . .. ...... ........... ..... 18

A-16. Chrome Queen sample 5; table concentration with

middling re-treatment ......... ............ . 19

A-17. Chrome Queen sample 6; table concentration, minus-48-

mesh ................... ............ ... . ..... 19

A-18. Chrome Queen sample 6; table concentration, with

middling re-treatment ............... .... 19

A-19. Juneau sample 1; table concentration, minus-48-mesh .... 19

A-20. Juneau sample 1; table concentration with middling

re-treatment ................................ 20

A-21. Star Four sample 1; combined jig and table

concentration .............. .. ..................... 20
iii

APPENDIX TABLES (Con.)

Page

A-22. Star Four sample 1; table concentration, minus-48-

mesh ..... ... . ..... ..... ............... ..... . .. 20

A-23. Star Four sample 1; table concentration with middling

re-treatment ......... ................................ 20

A-24. Star Four sample 2; table concentration, minus-35-

mesh .. *.. ... ....... ........................ 21

A-25. Star Four sample 2; table concentration, minus-48-

mesh ......... ... ........ . ......... ...... .... 21

A-26. Star Four sample 2; table concentration, minus-65-

mesh ................... ............. . ..... ............ 21

A-27. Star Four sample 2; table concentration, minus-100-

mesh .................. .... ..... .......... . 21

A-28. Star Four sample 2; table concentration, with middling

re-treatment ..... ...... .... .......... ......... 21

A-29. Star Four sample 3; combined tabling and flotation ..... 22

---
1

SUMMARY

As a part of the strategic minerals program of the Bureau of Mines, nine chromite-ore samples were obtained during the period 1949-56 from mines in the vicinity

of Red Mountain, near Seldovia, Kenai Peninsula, Alaska. This report summarizes the

results of beneficiation studies of the samples at the Bureau's Juneau, Alaska, and

Albany, Oreg., laboratories.

In general, the ores were found amenable to concentration by gravity methods for

producing concentrates that assayed over 48 percent chromic oxide. Intimate association of chromite and gangue minerals, however, necessitated fine grinding and limited

the amount of chromite recoverable. Recovery of chromium in concentrate that assayed

48 percent chromic oxide or higher ranged from approximately 20 percent for low-grade

ores (10 to 12 percent Cr203) to more than 95 percent for 1 high-grade sample (42

percent Cr203).

The iron content of the chrome-bearing mineral - hence, the chrome/iron ratio

of finished concentrate - appears to vary with the grade of the ore. Concentrates

made from high-grade ores had chrome/iron ratios as high as 3.1:1; the concentrates

from low-grade ores, however, had chrome/iron ratios as low as 1.8:1.

INTRODUCTION

Almost all of the chromite consumed in the United States is obtained from foreign sources; world conditions or conditions within the supplying countries conceivably could interrupt the United States supply. Known domestic reserves of chromite

are relatively small compared with requirements, and many are offgrade. In accordance with the Government's strategic minerals policy, the Bureau of Mines continues

to search for additional domestic deposits and to determine the metallurgical characteristics of the ores.

Chromite deposits occur in a dunite intrusive in the vicinity of Red Mountain

about 10 miles southeast of Seldovia, Kenai Peninsula, Alaska. The Federal Geological Survey briefly examined the area in 1910;5 / further investigations during World

War I and World War II resulted in complete mapping and the accumulation of

5/ Grant, U. S., and Higgins, B. F., Preliminary Report on the Mineral Resources of

the Southern Part of the Kenai Peninsula: Geol. Survey Bull. 442, 1910,

pp. 168-169.
2

considerable geologic data.6 7 8 9/ The Bureau of Mines explored the chromite deposits of the district in 1941 and 1942, and again during the summer of 1944 10/

Approximately 30 chromite deposits of varying sizes and grades have been found

in the area; those deposits covered by the Star Four, Chrome Queen, Juneau No. 1,

and Juneau No. 2 claims were determined to contain significant quantities of ore.

As a result of Geological Survey and Bureau of Mines exploratory work, two deposits

have been developed and mined on a small scale. During World War II, 6,619 tons of

ore averaging 42 percent chromic oxide was mined from the Chrome Queen deposit and

delivered to the Metals Reserve Company stockpile at Jakalof Bay. Since 1954 approximately 15,000 tons of ore containing an average of approximately 46.0 percent

chromic oxide has been mined from the Star Four deposit for delivery to the General

Services Administration stockpile at Grants Pass, Oreg.

Neither the exploratory nor development work, however, included metallurgical

testing of the ores. This paper purposes to supply supplementary information concerning the amenability to beneficiation treatment of Red Mountain chromite ores.

MARKETING SPECIFICATIONS

Chromite is marketed under three classifications: Low-silica, high-iron Chemical grade; high-alumina, low-iron Refractory grade; and high-chrome, low-iron Metallurgical grade.

For the manufacture of chromium chemicals, friable material containing a minimum of 44 percent chromic oxide and a maximum of 4 percent silica usually is specified. Either "lump ore" or concentrate is acceptable to most purchasers.

Purchasers of ore intended for manufacturing chromite refractories usually require lump ore, not more than 20 percent of which shall pass a Tyler Standard 10-

mesh screen. The chemical requirements for such material usually specify a chromic

oxide content of not less than 30 percent and a combined chromic oxide plus alumina

content of at least 60 percent; material containing over 12 percent iron or over 5

to 7 percent silica seldom is acceptable.

Most purchasers of ore intended for manufacturing stainless steel and other

metallurgical uses require a minimum chromic oxide content of 48.0 percent and a

maximum sulfur and phosphorus content of 0.05 and 0.02 percent, respectively. A

chrome/iron ratio (Cr/Fe) of 3.0:1 is requested, but material with ratios as low as

2.8:1 usually is accepted at a lower price. Allowable silica content depends, to

some extent, upon the purchaser's requirements, but commonly 8 percent silica is the

maximum permitted.

6/ Mertie, J. B., Jr., Chromite Deposits in Alaska: Geol. Survey Bull. 692, 1919,

pp. 265-267.

7/ Gill, A. C., Chromite of Kenai Peninsula, Alaska: Geol. Survey Bull. 742, 1922,

52 pp.

8/ Guild, P. W., Chromite Deposits of Kenai Peninsula, Alaska: Geol. Survey Bull.

931-G, 1942, pp. 139-175.

9/ Gates, G. 0., and Unkelsbay, A. B., Report on the Chromite Deposits of Red

Mountain, Kenai Peninsula, Alaska: Geol. Survey unpublished report, 1942.

10/ Rutledge, F. A., Exploration of Red Mountain Chromite Deposits, Kenai Peninsula,

Alaska: Bureau of Mines Rept. of Investigations 3885, 1946, 26 pp.

1
3

At present the United States Government is purchasing chromite ore and concentrates at incentive prices under the Minerals Stockpile Program. For domestic chromite delivered to Grants Pass, Oreg., the General Services Administration offers

$115 per long dry ton of lump ore and $110 per long dry ton of fine ore or concentrate containing 48 percent chromic oxide and having a chrome/iron ratio of 3.0:1.

A premium of $4.00 per ton is paid for each percentage point above 48 percent chromic oxide. A penalty of $3.00 per ton is charged for each 1 percent below 48 percent chromic oxide down to and including 42 percent. A penalty is also imposed for

each 0.1 decrease in the chrome/iron ratio below 3.0:1 down to and including 2.0:1.

A bonus is paid for each 0.1 increase in the chrome/iron ratio above 3.0:1 up to

3.5:1. The specifications require further that the silica content does not exceed

10 percent.

THE ORE

Physical Character

General

The chromite deposits of the Kenai Peninsula occur in masses of ultramafic

rocks, chiefly dunite, which are intrusive into a complex series of graywackes,

slates, cherts, limestones, and interbedded volcanic rocks. The dunite consists

primarily of olivine, with small amounts of pyroxenite and serpentine with accessory

chromite grains that constitute an estimated 1 percent of the rock; chrome-rich tabular and lenticular bodies are distributed irregularly throughout the dunite. The

bands and lenses range in size from mere streaks to bodies 50 feet thick and several

hundred feet long; their chromic oxide content ranges from 5 percent to nearly. 50.

Chrome Queen Ore

Petrographic examinations of representative portions of the Chrome Queen samples revealed that essentially the ore is an altered peridotite containing chromite,

olivine, and serpentine in varying proportions; some clinopyroxene and enstatite;

relatively small amounts of quartz and feldspar; and very small amounts of limonite

and magnetite. Traces of pyrite and chalcopyrite were detected in two samples.

The chromite is partly liberated in the minus-100-, plus-200-mesh fraction. A

portion of the chromite, however, is disseminated through the olivine as inclusions

325-mesh or finer.

Juneau No. 1 Ore

Microscopic study of a portion of this ore showed that the sample essentially

contains chromite and olivine; some serpentine and clinopyroxene; small amounts of

chromium, chlorite (clinochlore), quartz, and feldspar; very small amounts of limonite and magnetite; and traces of pyrite and chalcopyrite.

The chromite is partly liberated in the minus-100-, plus-200-mesh fraction.

Because of the fine-grained nature of the material, however, part of the chromite

remains locked, even in the minus-300-mesh fraction.

Star Four Ore

These samples consist chiefly of olivine and chromite, some serpentine, relatively small amounts of associated amphibole and pyroxene, and very small amounts of
4

magnetite and chromium-bearing chlorite. Also present is a trace amount of a finegrained titanium mineral tentatively identified as anatase.

Most of the chromite is liberated in the fractions finer than 100-mesh. Because

of intimate association of chromite and gangue, however, complete liberation is not

attained, even in the minus-200-mesh fraction.

Chemical Character

Representative portions of each sample were analyzed chemically and spectrographically. Partial chemical analyses are listed in table 1. A semiquantitative

spectrographic analysis revealed the presence and approximate quantities of the

metals listed in table 2. Any other elements, if present, are in amounts lower

than the minimum detectable by the routine technique employed.

TABLE 1. - Chemical analysis

- - Assay, percent

Sample Cr203 Fe SiO 2 A1 2 03 MgO Ni S P V

C-1 ........ 42.6 10.5 11.0 7.7 13.1 0.25 1/0.01 1/0.05 1/0.05

CQ-2 ....... 35.9 9.7 16.9 5.3 27.7 .13 .04 1/ .05 1/ .05

CQ-3 ....... 33.3 9.5 16.0 5.3 27.2 .13 .04 1 .05 1/ .05

CQ-4 .......... 42.4 9.9 11.0 6.7 25.1 .40 1/ .01 1/ .05 1/ .05

CQ-5 ....... 26.2 9.0 20.8 3.9 33.4 .30 1/ .01 1/ .05

CQ-6 ....... 12.5 8.3 30.3 2.0 40.3 .30 1/ .01 1/ .05 1/ .05

J-1 ....... 34.6 9.4 16.4 5.7 26.8 .14 .02 1/ .05 1/ .05

SF- ....... 33.9 10.1 16.7 6.6 27.2 .12 .03 1/ .05 1/ .05

SF-2 ....... 27.4 9.8 21.4 6.5 30.1 .10 .02 1/ .05 1/ .05

SF-3 ....... 10.4 9.0 30.9 5.3 37.6 .16 .03 / .05 1/ .05

1/ Less than,

TABLE 2. - Spectrographic analysis

Sample Al Ca Co Cr Cu Fe Mg |Mn Ni Si Ti V

CQ-1 ........... D E E A G A C E D C E D

CQ-2 ........... C E E A F A A D D B - E

CQ-3 ........... C- E E A F A A D D B+ - E

CQ-4 ........... C E A G A A D D B E D

CQ-5 ........... D G E A G A A D D A E D

CQ-6 ........... - E A F A A D D A E E

J-1 ........... C E E A F A A D D B+ - E

SF-1 ........... D F E A F B B D D C E E

SF-2 ........... D F E A F B A D D B E D

SF-3 ........... D- - - B G A A D D B+ F E

Legend: A - more than 10 percent E - 0.01 to 0.1 percent

B - 5 to 10 percent F - 0.001 to 0.01 percent

C - 1 to 5 percent G - less than 0.001 percent

D - 0.1 to 1 percent - - not detected
5

LABORATORY MINERAL DRESSING

Petrographic examinations of the ore samples and of the concentrate from preliminary tests showed that intimate association of chromite with silicate minerals

precluded the possibility of producing concentrates by physical separation that

would meet the specifications for Chemical-grade or Refractory-grade material. The

investigation, therefore, was directed toward producing 48-percent-chromic oxide

concentrate, with as high chrome/iron ratio;as possible and with the other characteristics of Metallurgical-grade chromite,

Because the intimate chromite-gangue association prevented production of highgrade chromic oxide concentrate at coarse sizes, most of the testing was restricted

to the investigation of tabling and flotatton techniques. One sample (SF-1), however, was tested to determine the amenability of the ore to concentration by jigging

for producing coarse concentrate that would meet the minimum stockpile purchasing

specifications.

During the investigation much information was collected and compiled. For

brevity, most of the data of secondary importance have been omitted from this paper.

For example, concentration by high-intensity magnetic separation was tried on several of the samples but was generally unsatisfactory; therefore, results of only two

magnetic-separation tests are included for direct comparison with other methods of

concentration. Similarly, data from only one electrostatic separation test are

shown. Comparative figures showing the effect of degree of grind have been

minimized.

Concentration methods employed during the studies of Kenai chromite ores conformed with standard laboratory practice. Results of screen analyses of representative portions of each sample confirmed information obtained by microscopic examination and established that mineral locking precludes significant concentration by

sizing.

Chroma Queen Sample 1

A 5-ton sample of ore reported to be representative of that produced from the

Chrome Queen mine during 1942-44 was obtained by a Bureau of Mines engineer and submitted to the laboratory for beneficiation study.

Results of preliminary testing showed that this high-grade ore (42.6 percent

Cr203 ) was amenable to concentration by tabling for the production of plus-48-percent-Cr 203 concentrate, in spite of extremely intimate chromite-gangue association

that precluded production of a low-grade reject. Additional table-concentration

tests revealed that the most effective procedure consisted of roll-crushing ore to

minus-35-mesh, hydraulically sizing, and treating on a laboratory diagonal-deck

shaking table to produce concentrate, tailing, and slime. The tailing was reground

to minus-65-mesh and re-treated to produce a second concentrate, a slime product,

and a final tailing. This procedure recovered 72.4 percent of the chromium in a

concentrate assaying 51.3 percent Cr203 and having a chrome/iron ratio of 3.05:1.

Addition of the slime fractions increased the recovery to 82.5 percent; the resulting product assayed 47.5 percent Cr203 and had a chrome/iron ratio of 2.92:1

(table A-l).

Magnetic-separation treatment of sized fractions of ore, using a Wetherill-type

separator, recovered 80.3 percent of the chromium in a concentrate that assayed 48.5

percent Cr203 and had a chrome/iron ratio of 2.91:1. No low-chromium tailing was
_

6

made by this method, in spite of repeated cleanings. Operational difficulties were

caused by adherence of fine material to the delivery belt of the separator (table

A-2).

Electrostatic separation tests were conducted on this sample at the Eastern

Experiment Station of the Bureau of Mines, College Park, Md. The electrostatic separator methods of conditioning are fully described in AIME Technical Publication

2408.11/ This treatment recovered 84 percent of the chromium at 46.9-percent-Cr203

grade. An additional cleaning step probably would yield a plus-48-percent Cr203

concentrate with a recovery of 75 to 80 percent of the chromium (table A-3).

Flotation tests were conducted in accordance with a method developed at the

Salt Lake City laboratories of the Bureau of Mines.l2/ The procedure consists of

pulping deslimed sand with water to about 50 percent solids and adding an aqueous

emulsion of oleic acid until flocculation is fairly complete. The pulp is di3kted

to about 25 percent solids, and dilute hydrofluoric acid is added until the floes

free themselves of gangue. The flocculated chromite floats rapidly, and additional

collector is seldom required. The method was developed for flotation of unconsolidated beach sand; it is less applicable to treatment of consolidated ore because of

loss of chromium in the slime formed during grinding.

Flotation of CQ-1 ore ground to minus-100-mesh and deslimed recovered 85.1 percent of the chromium at 49.5 percent Cr203 grade. Combination of the slime with the

concentrate resulted in a product that contained 92.1 percent of the chromium and

assayed 48.5 percent Cr2O3 , the chrome/iron ratio was 2.91:1 (table A-4).

Several unsuccessful attempts were made to float silica from the Chrome Queen

ore with cationic reagents.

A preliminary test indicated that tabling to produce a high-grade concentrate,

followed by flotation of the table tailing, would give relatively low grade rejects

and high recovery. A sample of ore was roll-crushed to minus-35-mesh, hydraulically

sized, and tabled to produce a concentrate, slime, and tailing. The latter was

ground to pass a 65-mesh sieve and retabled to produce a second concentrate, slime,

and tailing. Chromite was floated from the table tailing in the usual manner. This

treatment recovered 95.3 percent of the chromium in a combined concentrate and slime

product that assayed 49.2 percent Cr203 and had a chrome/iron ratio of 2.96:1 (table

A-5).

Chrome Queen Sample 2

This intermediate-grade sample (35.9 percent Cr023 ) was cut from the working

face of the Chrome Queen adit by a Bureau of Mines engineer.

Ore samples were subjected to various degrees of grinding, hydraulically sized,

and treated on a laboratory shaking table (tables A-6 to A-8). Table concentration

of ore ground to minus-65-mesh and hydraulically sized recovered 74.4 percent of the

total chromium in a product that assayed 48.2 percent Cr2 03 and.had a chrome/iron

ratio of 2.80:1. Small recoveries of plus-48-percent-Cr20 3 concentrate were obtained by treatment at coarser sizes.

11/ Fraas, Foster, and Ralston, O. C., The Electrostatic Separation of Several

Industrial Minerals: AIME Tech. Publication 2408, 1948, 11 pp.

12/ Havens, Richard, Froth Flotation of Chromite With Fluoride: U. S. patent

2, 412,217, Dec. 10, 1946.
7

Several tests were run involving tabling at relatively coarse sizes, with regrinding and retabling of the middling fraction. Best results were obtained by

tabling ore ground to minus-35-mesh and hydraulically sized. The middling fraction

was reground to minus-65-mesh and 150-mesh and retabled.

This treatment gave higher recovery than other tabling procedures but had the

disadvantage of being rather complex. By this method 79.1 percent of the total

chromium was recovered in a combined product that assayed 49.0 percent Cr203 and had

a chrome/iron ratio of 2.89:1 (table A-9).

Fatty-acid flotation of chromite was not employed successfully on this ore.

Best results were obtained by treating deslimed minus-100-mesh ore; 54 percent of

the chrome was recovered at 54.4-percent-Cr203 grade. Inclusion of a cleaner tailing product lowered the grade of the combined product to 40.2 percent Cr203; total

chromium recovery was 84.8 percent. A similar test recovered 81.4 percent of the

chromium at 43.4-percent-Cr203 grade.

Chrome Queen Sample 3

The CQ-3 sample represented ore from the old stope of the Chrome Queen workings.

This material was slightly coarser grained and of slightly lower grade (33.3 percent

Cr203 ) than sample CQ-2 from the adit face.

Direct tabling of ore ground to minus-48-mesh recovered 79.5 percent of the

total chromium in a concentrate that assayed 49.1 percent Cr203 and had a chrome/iron

ratio of 2.75:1 (table A-10).

Tabling ore ground to minus-35-mesh, with regrinding and retreatment of middling, recovered 74.7 percent of the chromite in a product that assayed 51.7 percent

Cr203 and had a chrome/iron ratio of 2.95:1. Inclusion of the regrind slime product

increased the chromite recovery to 82.9 percent; the resulting combined product assayed 47.4 percent Cr203 (table A-ll). A similar test produced a concentrate assaying 51.1 percent Cr2 0 and having a chrome/iron ratio of 2.9:1. Chromium recovery

was 73.4 percent. Tabling of ore ground to minus-48-mesh, with re-treatment of middling ground to minus-150-mesh, recovered 74.6 percent of the chromiun at 48.8

percent Cr203.

A sample of ore was crushed to minus-10-mesh and screen-sized to yield closely

sized fractions. Each fraction was treated separately on a high-intensity Wetherilltype magnetic separator to produce a magnetic concentrate and tailing. Results were

poor because lack of liberation in the coarser fractions resulted in low-grade concentrate and high tailing. In the finer size ranges the tailing was high due to

mechanical inclusion of chromite in the reject.

By flotation, 65.9 percent of the total chromite was recovered in a rougher

concentrate that assayed 45.8 percent Cr 03. Cleaning raised the grade to 48.0 percent Cr20 3 , with a chromium recovery of 52.7 percent.

Tests were run using flotation to scavenge chromite from table middling products. Although flotation concentrates assaying 40 to 45 percent Cr203 were made,

the slight increase in overall recovery (approximately 2 percent) would not warrant

inclusion of the flotation treatment.
8

Chrome Queen Sample 4

This sample (42.4 percent Cr2 03 ), reported to represent hand-sorted high-grade

ore, was submitted to the laboratory by a representative of the Alaska Oil & Mineral

Co.

A series of tests was made to determine the best grind for table concentration.

Results were generally poor for ore stage-ground to minus-35-mesh; although some

high-grade concentrate was made, recovery was low, and the tailing averaged 38 to 40

percent Cr2O3 . A typical test showed a recovery of 32 percent of the total chrome

at 53.0 percent Cr2 03 grade. Tabling ore ground to minus-48-mesh recovered 75.5

percent of the total chromium in a concentrate that assayed 52.9 percent Cr2 03 and

had a chrome/iron ratio of 3.14:1. Addition of the grinding-slime product increased

the recovery to 89.3 percent; the combined product assayed 48.0 percent Cr2 03 and had

a chrome/iron ratio of 3.04:1 (table A-12). By tabling ore ground to minus-35-mesh,

with regrinding and re-treatment of the primary table tailing, 70.9 percent of the

total chromium was recovered in a combined concentrate that assayed 52.3 percent

Cr2 03 and had a chrome/iron ratio of 3.11:1. The addition of various slime fractions

permitted recoveries of 83.1 and 87.0 percent at grades of 48.0 and 46.9 percent

Cr2 03 , respectively (table A-13). In general, this method yielded results slightly

inferior to those obtained by the simpler direct tabling of ore ground to minus-48-

mesh.

Sample CQ-4 was not readily amenable to fatty-acid flotation. The best results

obtained by this method recovered 69 percent of the total chromium in a concentrate

that assayed 48.1 percent Cr203 and had a chrome/iron ratio of 3.00:1.

Of the several combined gravity-flotation techniques employed, the following

procedure yielded the best results: Ore was stage-ground to minus-35-mesh and

tabled to produce concentrate and tailing; the tailing was reground to minus-65-mesh

and retabled; the minus-65-mesh tailing was treated by flotation to produce a scavenger concentrate and finished tailing. By this treatment, 78.7 percent of the

total chromium was recovered in a combined concentrate that assayed 50.7 percent

Cr2 03 and had a chrome/iron ratio of 3.07:1. Addition of various slime products increased the recoveries to 82.5 and 89.9 percent, with resulting grades of 49.2 and

46.4 percent Cr203, respectively (table A-14).

Chrome Queen Sample 5

This intermediate-grade sample (26.2 percent Cr203 ) was submitted by the Alaska

Oil & Mineral Co. as material representative of Chrome Queen run-of-mine ore.

Samples of CQ-5 were subjected to various degrees of grinding, hydraulically

sized, and treated on a laboratory shaking table. In all tests a large amount of

chromite was retained in a middling fraction that was difficult to treat. Best results, obtained by grinding ore to minus-65-mesh before table treatment, recovered

only 36 percent of the total chromium in a concentrate that assayed 49.7 percent

Cr02 3 and had a chrome/iron ratio of 2.83. Twenty-five percent of the total chromium was contained in a middling product that assayed 37.6; repeated efforts to remove additional concentrate or tailing from this middling product were unsuccessful.

Combination of the concentrate and middling resulted in an overall recovery of 61.0

percent at a grade of 43.9 percent Cr203 (table A-15). Similar treatment of ore

ground to 48-mesh gave a recovery of only 23 percent of the chromium in a plus-48-

percent Cr203 concentrate. Treatment of minus-100-mesh ore increased the loss of

chromium as slime and did not appreciably reduce the amount of chromite contained
9

in the middling fraction; approximately 35 percent of the chromium was recovered in

a concentrate that assayed about 49 percent Cr2O3 .

A series of tests was made in which ore was ground to relatively coarse size

and tabled to produce concentrate, middling, tailing, and slime. The middling fraction was reground to a finer size and re-treated. Best results were obtained with a

primary grind of minus-48-mesh with regrind of middling to minus-100-mesh before retreatment. This method recovered 45.3 percent of the total chromium in a product

that assayed 49.1 percent Cr2O3 and had a chrome/iron ratio of 2.71:1. The final

middling product contained 13.5 percent of the total chromium at a grade of 39.9

percent Cr203. Addition of the middling to the concentrate resulted in a product

that assayed 46.6 percent Cr203 and contained 58.8 percent of the chromium in the

ore (table A-16).

Fatty-acid flotation of chromite was not employed successfully on this ore.

Best results were obtained by treatment of deslimed minus-100-mesh ore; less than

20 percent of the chromium was recovered at 48.2-percent-Cr203 grade.

Chrome Queen Sample 6

Sample CQ-6 (12.5 percent Cr203) was sorted reject from the Chrome Queen dump

submitted to the laboratory by a representative of the Alaska Oil & Mineral Co.

Good recovery of chrome as plus-48-percent Cr 2

0 3 was not made from this lowgrade sample. Best results were obtained by tabling ore roll-crushed to minsu-48-

mesh. This treatment recovered 32.2 percent of the total chromite in a concentrate

that assayed 48.1 percent Cr203 and had a chrome/iron ratio of 2.22:1 (table A-17).

Table concentration of ore crushed to minus-35-mesh recovered only 10 percent of the

chromite at plus-48-percent-Cr203 grade. Grinding finer than 48-mesh resulted in

additional loss of slime without significant reduction in tailing loss.

By tabling ore ground to minus-35-mesh, with re-treatment of middling ground to

minus-65-mesh, 20.4 percent of the total chromite was recovered in a combined concentrate that assayed 47.6 percent Cr203 and had a chrome/iron ratio of 2.34:1 (table

A-18).

In no test of this sample was a product made with a chrome/iron ratio greater

than 2.5:1. The high iron content of the concentrate is attributed to the chemical

structure of the chrome mineral. pure chromite (Fe Cr204 or FeO Cr203 ) contains 68

percent chromium sesquioxide and 32 percent iron protoxide and has a chrome/iron

ratio of 1.87:1. The iron, however, may be replaced by magnesium, and the chromium

may be replaced by aluminum or ferric iron. The latter probably has occurred in

this ore. Recent studies indicate that some chromites may show exsolution intergrowths with magnetite. In this instance the chromite may contain varying amounts of

intimately associated magnetite which would be fine grained and not liberated even

with the finest grinding. Whether or not the mechanical or chemical iron-inclusion

theory is accepted, enough testing was conducted to show that mechanical concentration of the low-grade Chrome Queen ore will not yield a concentrate with a high

chrome/iron ratio.

No encouraging results were obtained by flotation testing of this sample.
10

Juneau No. 1 Sample

This sample was obtained from trenches on the Juneau No. 1 claim; it is similar

in grade (34.6 percent Cr2 03) and mineral content to the average ore of the deposit

as determined by trenching and drilling exploration.

Results obtained by tabling ore ground to minus-35-mesh and minus-48-mesh were

almost identical. The finer grind allowed production of lower grade tailing, but

the advantage was offset by the production of additional slime. Typical results

showed a recovery of 64.3 percent of the chromite in a concentrate that assayed 52.6

percent Cr203 and had a chrome/iron ratio of 2.94:1. Addition of a middling product

increased the recovery to 84.7 percent; the combined product assayed 47.1 percent

Cr203 and had a chrome/iron ratio of 2.82:1 (table A-19).

Tabling ore ground to minus-35-mesh, with regrinding and re-treatment of middling, recovered 70.7 percent of the total chromium in a concentrate that assayed

51.2 percent Cr20 3 and had a chrome/iron ratio of 2.92:1. Addition of the minus-150-

mesh material without retabling resulted in recovery of 75.8 percent of the chromium

at 47.9-percent-Cr2 03 grade.

Flotation techniques were not as effective as tabling for concentrating Juneau

No. 1 ore. Best results obtained by flotation showed a recovery of 57.0 percent of

the chromium at 47.0-percent-Cr203 grade. Likewise, flotation was unsatisfactory as

a re-treatment method for table middlings.

Star Four Sample 1

This sample (33.9 percent Cr203) represented undersize reject from a one-halfinch slotted plate over which mine-run ore is passed for hand sorting and shipping,

It was submitted to the laboratory by the Kenai Chrome Co. to determine its amenability to simple gravity concentration with hand-sorted oversize for direct shipment.

Although optimum liberation of chromite and gangue can be effected only in the

minus-200-mesh size range, a portion of the material consists of relatively highgrade (plus-42-percent Cr203) particles.

The plus-10-mesh fraction of the sample was treated in a Harz-type jig; approximately 29 percent of the total chromite was recovered at a grade of 43.2 percent Cr203 . Tabling the minus-10-mesh material without grinding recovered an equal

amount of the chromite at 43.7-percent-Cr20 3 grade. The combined product assayed

43.4 percent Cr203 and contained 58.3 percent of the total chromite. Addition of a

jig-middling product increased the recovery to 75.0 percent but decreased the grade

to 41.2 percent Cr20 3 (table A-21).

The grade of the recovered product can be improved by grinding the ore before

treatment. Jigging the minus-1/2-inch, plus-10-mesh fraction, with tabling of the

undersize reground to pass 35-mesh, gave a 59.3-percent recovery of the total chromium in a combined concentrate that assayed 44.5 percent Cr203. Grinding all jig

reject to minus-35-mesh and combining with the reground undersize before tabling

resulted in recovery of 74.2 percent of the chromium at 44.5 percent Cr203.

Tabling ore ground to minus-48-mesh recovered 76.6 percent of the chromite in

a concentrate assaying 48.0 percent Cr203 and having a chrome/iron ratio of 2.73:1

(table A-2). A similar test of ore ground to minus-65-mesh gave a recovery of 69.8

percent of the chromite at 48.2-percent-Cr203 grade; finer grinding effected an additional loss of slime without a significant decrease of loss in the sand tailing.
11

Tabling minus-35-mesh ore, with re-treatment of middling, recovered 64.8 percent of the chromite in a concentrate that assayed 49.5 percent Cr203 and had a

chrome/iron ratio of 2.77:1. Addition of the regrind slime fraction increased the

recovery to 80 percent; the combined product assayed 45.6 percent Cr203 (table A-23).

Results of flotation treatment of this sample were inferior to those obtained

by tabling techniques. The best flotation test gave a recovery of 57.9 percent of

the chromite at approximately 45 percent Cr20 3.

Star Four Sample 2

This sample (27.4 percent Cr203 ) is reported by the Kenai Chrome Co. to be representative of ore being mined at the Star Four property for treatment in a small

concentrating plant that currently is being constructed.

A series of tabling tests run on ore stage-ground to minus-35-, 48-, 65-, and

100-mesh showed that best results could be obtained with a minus-65-mesh grind.

This treatment recovered 66.9 percent of the total chromite in a concentrate that

assayed 47.4 percent Cr203 and had a chrome/iron ratio of 2.44:1 (tables A-24 to

A-27).

Tabling ore ground to minus-35-mesh, with re-treatment of middling reground to

pass 65-mesh, recovered 61.7 percent of the chromite at a grade of 49.5 percent

Cr20 3 (table A-28).

Results of several tests indicated that this ore is not amenable to direct flotation using the fatty-acid fluoride technique commonly employed for chromite flotation. Best results showed a recovery of 29 percent of the total chromite in a product that assayed 49.5 percent Cr20 3.

Several tests were run to determine the applicability of flotation for beneficiation of table middling. Best results, obtained by tabling ore ground to minus-100-

mesh and flotation of the table middling reground to pass 200-mesh, recovered 50.6

percent of the chromite at 49.6-percent-Cr20 3 grade.

Star Four Sample 3

This low-grade material (10.4 percent Cr203) represents submarginal ore found

at the edges of the ore bodies in the Star Four mine. Extremely intimate association

of chromite and gangue limited the recovery of high-grade concentrate that could be

made from this low-grade sample.

By tabling ore ground to minus-65-mesh, only 20.8 percent of the chromite was

recovered in a concentrate that assayed 49.5 percent Cr203 and had a chrome/iron

ratio of 1.77:1. Approximately 50 percent of the chromite was recovered at 42-percent-Cr203 grade. Nearly identical results were obtained by tabling ore ground to

minus-48-mesh with two-stage re-treatment of middling at minus-100- and minus-200-

mesh. These results were superior to those obtained by treatment of coarser or

finer ore.

Tabling produced an extremely fine refractory middling that assayed about 20

percent Cr203 and contained 40 to 50 percent of the total chromite. Microscopic

examination indicated that only a small part of this product consists of locked

"true middling" grains. No method was found, however, to upgrade the material

further.
12

Tabling and flotation treatment involved grinding ore to minus-48-mesh and

tabling to produce concentrate, middling, and tailing; the middling was re-treated

after grinding to pass 100-mesh; the middling of the second tabling stage was

treated by flotation, using the standard oleic acid-hydrofluoric acid technique.

By this method, 31.8 percent of the chromite was recovered in a combined concentrate

that assayed 48.6 percent Cr203 and had a chrome/iron ratio of 1.75:1. The flotation reject products assayed over 19 percent Cr203 and contained 40.7 percent of the

total chromite in the feed (table A-29).

Although concentrates were made by gravity and flotation techniques that assayed up to 51 percent Cr203 , in no product did the chrome/ratio exceed 1.80:1.

Petrographic studies of a number of table and panned concentrates revealed no discrete iron mineral, such as magnetite. The high iron content of the concentrate,

therefore, is attributed to the chemical structure of the chrome mineral.

CONCLUSIONS

Each of the samples tested yielded concentrate that assayed at least 48 percent

Cr203 with a maximum of 8 percent SiO2 . All concentrates contained less than 0.01 P

and S. Chromium recovery ranged from 20 to 95 percent. The chrome/iron ratios of

the concentrates varied widely; concentrate from one ore (SF-3) had a chrome/iron

ratio below the 2.0:1 minimum acceptable under the Minerals Stockpile Program.

To compare the effectiveness of various treatment methods applied to the Red

Mountain ores, results have been recalculated to show the recoveries obtainable at

48.0-percent-Cr2 03 grade. These summary data are shown in table 3.

A review of the data shown in table 3 shows that, for most of the samples

treated, direct tabling of ore ground to minus-48- or minus 65-mesh yielded results

as good or better than the more complicated procedure involving tabling and re-treatment of middling. Flotation was successful on only one high-grade sample from the

Chrome Queen deposit0

A definite relationship appears to exist between the grade of ore treated and

the recovery obtainable. A similar relationship exists between the sample grade

and the average chrome/iron ratio of concentrates of 48.0-percent-Cr203 grade.

These relationships are shown graphically in figures 1 and 2.
50

13

0

U

Iz

LU

U

LU

aX

40

30

20

In

30 40 50 60 70 80 90 100

BEST RECOVERY AT 48-PERCENT Cr203 GRADE

Figure 1. - Recovery vs. head grade.

50

en

O 40

U

Iz

LU

u 30

w

aI< 20 -

0 0

LEGEND / * Chrome Queen -____

A Juneau No. 1

x Star Four -

-x 0 ..

.^ >

10

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

CHROME/IRON RATIO IN 48-PERCENT Cr203 CONCENTRATE

Figure 2. - Chrome/iron ratio vs. head grade.
Sample

CQ-1.....

CQ-2 .....

CQ-3 ....

CQ-4 .....

CQ-5 .....

CQ-6 ....

J-1 ......

SF-1 .....

SF-2....

SF-3 .....

Head

assay,

percent

42.6

35.9

33.3

42.4

26.2

12.5

34.6

33.9

27.4

10.4

14

TABLE 3. - Summary of results

Treatment

Tabling, middling re-treatment

Magnetic separation

Electrostatic separation

Flotation

Tabling plus flotation

Tabling, minus-65-mesh

Tabling, middling re-treatment

Tabling, minus-48-mesh

Tabling, middling re-treatment

Tabling, minus-48-mesh

Tabling, middling re-treatment

Flotation

Tabling plus flotation

Tabling, minus-65-mesh

Tabling, middling re-treatment

Tabling, minus-48-mesh

Tabling, middling re-treatment

Tabling, minus-48-mesh

Tabling, middling re-treatment

Tabling, minus-48-mesh

Tabling, middling re-treatment

Tabling, minus-65-mesh

Tabling, middling re-treatment

Tabling, minus-65-mesh

Tabling and flotation

Recovery

at 48.0

percent

81.0

81.6

77.0

94.0

98.0

74.6

80.4

81.0

81.2

89.2

83.1

69.1

85.5

43.5

51.5

32.3

23.0

81.6

75.5

76.6

70.0

65.0

65.0

32.2

34.0

Ave.

Ave.

Ave.

Ave.

Cr/Fe

2.93

2.90

3.01

2.91

2.92

2.94

2.78

2.85

2.82

2.72

2.88

2.80

3.04

3.07

3.00

3.04

3.04

2.79

2.69

2.74

2.22

2.37

2.30

2.84

2.88

2.86

2.73

2.73

2.73

2.43

2.44

2.44

1.78

1.77

1.78

Ave.

Ave.

Ave.

Ave.

Ave.

Ave.
15

APPENDIX

TABLE A-1. - Chrome Queen sample 1; table concentration

Weight, Assay percent Distribution,

Product percent Cr2 03 Fe SiO2 percent Cr2 03 Cr/Fe

Concentrate 1 ............... 38.2 51.0 11.4 5.3 45.6 3.06

Concentrate 2 ............... 22.1 51.8 11.6 4.8 26.8 3.05

Primary slime ............... 7.2 31.6 9.6 17.6 5.3 2.25

Secondary slime ............. 6.8 30.3 9.8 16.8 4.8 2.11

Tailing ..................... 25.7 29.2 7.8 19.8 17.5 2.56

Calculated head ........... 100.0 42.8 10.3 10.6 100.0 -

Combined conc. ............. 60.3 51.3 11.5 5.1 72.4 3.05

Conc. plus slimes .......... 74.3 47.5 11.1 7.4 82.5 2.92

TABLE A-2. - Chrome Queen sample 1; magnetic separation

Weight, Assay, percent Distribution,

product percent Cr203 Fe SiO2 percent Cr20 3 Cr/Fe

Magnetic conc. .............. 72.2 48.5 11.4 5.9 80.3 2.91

Middling .................... 3.5 40.0 - - 3.2

Nonmagnetic tailing ......... 24.3 29.5 - 16.5

Calculated head ........... 100.0 43.6 - 100.0

TABLE A-3. - Chrome Queen sample 1; electrostatic separation

Weight, Assay, percent Distribution,

Product percent Cr203 Fe Si02 percent Cr20 3 Cr/Fe

Concentrate .............. .. 77.6 46.9 10.8 7.7 84.0 2.97

Dust ........................ 10.6 35.2 - - 9.4 -

Reject ...................... 11.8 24.0 - - 6.6

Calculated head ........... 100.0 43.3 - - 100.0

TABLE A-4. - Chrome Queen sample 1; flotation of chromite

Metallurgical data

Weight, Assa percent Distribution,

Product percent Cr20 3 Fe Si02 percent Cr2O3 Cr/Fe

Concentrate ................. 75.1 49.5 11.6 6.6 85.1 2.92

Slime ....................... 7.8 39.0 9.8 15.1 7.0 2.72

Tailing ..................... 17.1 20.2 6.5 26.3 7.9

Calculated head ,........... 100.0 43.6 10.6 10.7 100.0

Cone. plus slime ............ 82.9 48.5 11.4 7.5 92.1 2.91

Operating data

Grind: 100 percent minus-100-mesh

Reagents, pounds per ton

Circuit pH Oleic acid Hydrofluoric acid

Condition ...................... 6.9 1.4 -

Rougher ........................ 3.6 - 0.4

Cleaner 1 ..................... 3.5 .2 .2

Cleaner 2 ...................... 3.5 - .2

Total ..................... 1.6 .8

-
16

TABLE A-5. - Chrome Queen sample 1; combined tabling and flotation

____Metallurgical data

Weight, Assay, percent Distribution,

Product percent Cr203 Fe Si0 2 percent Cr20 3 Cr/Fe

Table conc. 1 ............. 21.2 54.6 12.4 2.9 26.6 3.22

Table conc. 2 ............... 15.0 53.1 12.1 4.0 18.3 3.10

Flotation conc. ..... ......... 34.9 50.6 11.0 5.2 40.6 3.15

Primary slime ... ............ 8.2 33.0 10.0 16.6 6.2 2.25

Secondary slime ......... 4.9 31.7 9.6 17.6 3.6 2.25

Flotation tail .............. 15.8 12.9 5.0 31.6 4.7 -

Calculated head ........... 100.0 43.5 10.0 10.2 100.0 -

Combined conc. .............. 71.1 52.3 11.7 4.2 85.5 3.05

Conc. plus slime ........ 84.2 49.2 11.4 6.2 95.3 2.96

Operating data

Grind: 100 percent minus-65-mesh

Reagents, ounds per ton

Circuit pH Oleic acid Hydrofluoric Acid

Condition ...................... - 1.2

Rougher ..................... .. 4.0 - 0.45

Cleaner ....................... 3.8 .2 .20

Total .................... 1.4 .65

TABLE A-6. - Chrome Queen sample 2; table concentration, minus-35-mesh

Weight, Assay, percent Distribution,

Product percent Cr20 3 Fe Si02 percent Cr203 Cr/Fe

Concentrate 1 ............ 23.07 54.3 12.2 3.3 35.9 3.05

Concentrate 2 ............... 16.65 43.8 10.5 10.4 20.9 2.86

Middling .................... 17.56 37.3 9.7 15.1 18.8 2.63

Tailing ........................ 33.79 19.1 7.4 26.9 18.5 -

Slime ...................... 8.93 23.2 7.4 23.4 5.9 -

Calculated head ............ 100.00 34.9 9.4 16.3 100.0 -

Combined conc. ............. 39.72 49.9 11.5 6.3 56.8 2.97

Conc. and middling ......... 57.28 46.0 10.9 9.0 75.6 2.89

TABLE A-7. - Chrome Queen sample 2; table concentration, minus-48-mesh

Weight, Assay, percent Distribution,

Product percent Cr203 Fe SiO0 percent Cr2 03 Cr/Fe

Concentrate I ....... 5 12.5 7.... 4.3.3 1--.37 2.88

Concentrate 2 ............... 34.41 47.1 11.8 7.8 45.8 2.73

Middling ..................... 7.70 32.3 9.5 19.2 7.0 2.33

Tailing ..................... 24.09 21.0 8.0 28.1 14.3 -

Slime ....................... 21.43 24.1 8.0 22.8 14.6 -

Calculated head .......... 100.00 35.4 10.0 16.3 100.0 -

Combined conc................. 46.78 48.6 12.0 6.9 64.1 2.78

Conc. and middlin ......... 54.48 46.3 11.6 8.6 71.1 2.73
17

TABLE A-8. - Chrome Queen sample 2; table concentration, minus-65-mesh

Weight, Assay,percent Distribution,

Product percent Cr203 Fe SiO 2 percent Cr203 Cr/Fe

Concentrate 1 ............... 13.59 54.7 13.0 3.1 20.7 2.88

Concentrate 2 ......... . 41.94 46.0 11.4 8.0 53.7 2.76

Middling ................... 17.22 24.0 8.0 26.0 11.5

Tailing ..................... 14.43 13.8 6.3 32.6 5.5

Slime ....................... 12.82 24.0 7.9 24.4 8.6 -

Calculated head ........... 100.00 35.9 9.9 16.1 100.0

Combined cone. .............. 55.53 48.2 12.0 6.8 74.4 2.80

TABLE A-9. - Chrome Queen sample 2; table concentration

with middling re-treatment

Weight, Assa, percent Distribution,

product percent Cr203 Fe SiO 2 percent Cr20 3 Cr/Fe

Concentrate .................. 41.97 52.3 12.3 4.8 61.8 2.91

Middling .................... 15.33 40.0 9.7 12.9 17.3 2.82

Tailing ..................... 30.63 15.2 6.5 29.1 13.1

Primary slime ............... 1.76 20.4 6.8 22.1 1.0

Regrind slime ............... 10.31 23.4 7.3 22.6 6.8 -

Calculated head ........... 100.00 35.5 9.5 15.6 100.0

Combined conc. and middling.. 57.30 49.0 11.6 7.0 79.1 2.89

TABLE A-10. - Chrome Queen sample 3; table concentration, minus-48-mesh

Weight, Assay, percent Distribution,

Product percent Cr203 Fe SiO percent Cr2 03 Cr/Fe

Concentrate ................. 17.19 55.4 12.7 2.4 28.6 2.98

Middling ..................... 36.75 46.1 12.0 8.8 50.9 2.63

Tailing ..................... 31.40 11.9 5.5 29.5 11.2

Slime ......................... 14.66 21.1 7.1 23.4 9.3 -

Calculated head ........... 100.00 33.3 9.3 16.3 100.0 -

Conc. and middling .......... 53.94 49.1 12.3 6.8 79.5 2.75

TABLE A.-ll. - Chrome Queen sample 3; table concentration

with middling re-treatment

Weight, Assay, percent Distribution,

product percent Cr20 3 Fe Si02 percent Cr203 Cr/Fe

Concentrate .................. 42.45 53.4 12.3 4.1 66.9 2.97

Middling (minus-150) ........ 6.60 40.2 10.1 12.7 7.8 2.72

Tailing ..................... 32.26 13.2 5.6 28.5 12.6

Primary slime .............. 8.45 18.1 6.4 24.3 4.5

Regrind slime ............... 10.24 27.0 8.2 19.8 8.2 -

Calculated head ........... 100.00 33.9 9.1 15.9 100.0 -

Conc. and middling .......... 49.05 51.7 12.0 5.3 74.7 2.95

Conc.,middling, and regrind

slime ...................... 59.29 47.4 11.3 7.8 82.9 2.87
18

TABLE A-12. - Chrome Queen sample 4; table concentrationp minus-48-mesh

Weight, Assay, percent Distribution,

product percent Cr2 03 Fe SiO 2 percent Cr2 O3 Cr/Fe

Concentrate ................. 61.67 52.9 12.4 5.2 75.5 3.14

Tailing ..................... 19.65 23.6 7.3 24.1 10.7 -

Slime ....................... 18.68 31.9 8.6 18.0 13.8 -

Calculated head ........... 100.00 43.2 10.1 11.3 100.0 -

Conc. plus slime ............ 80.35 48.0 10.8 8.1 89.3 3.04

TABLE A-13. - Chrome Queen sample 4; table concentration

with tailing re-treatment

Weight, Assay, percent Distribution,

Product percent Cr2O3 Fe SiO 2 percent Cr203 Cr/Fe

primary concentrate ......... 26.28 53.1 11.5 3.9 32.4 3.16

Regrind concentrate ......... 32.15 51.6 11.5 6.1 38.5 3.07

Regrind tailing ............. 20.05 28.0 7.3 20.9 13.0 -

Primary slime ............... 5.29 31.7 7.4 18.4 3.9 -

Regrind slime ............... 16.23 32.4 7.9 17.5 12.2 -

Calculated head ........... 100.00 43.1 9.9 11.0 100.0 -

Combined concentrates ....... 58.43 52.3 11.5 5.1 70.9 3.11

Conc. plus regrind slime .... 74.66 48.0 10.7 7.8 83.1 3.07

Conc. plus total slime ...... 79.95 46.9 10.5 8.1 87.0 3.05

TABLE A-14. - Chrome Queen sample 4; combined tabling and flotation

Weight, Assay, percent Distribution,

Product percent Cr2 O3 Fe SiO 2 percent Cr0 3 Cr/Fe

Combined table conc. ......... 55.05 53.0 11.7 4.4 69.0 3.10

Flotation concentrate ....... 10.60 38.8 9.0 14.6 9.7 2.94

Flotation tailing ........... 17.96 23.7 6.3 23.9 10.1 -

Primary slime ............... 5.33 30.3 7.9 16.9 3.8 -

Secondary slime ................. 11.06 28.6 7.6 18.9 7.4 -

Calculated head ........... 100.00 42.3 9.8 11.3 100.0 -

Combined conc. ............... 65.65 50.7 11.3 6.0 78.7 3.07

Conc. plus primary slime .... 70.98 49.2 11.0 6.9 82.5 3.06

Conc. plus total slime ...... 82.04 46.4 10.6 8.5 89.9 2.99

TABLE A-15. - Chrome Queen sample 5; table concentration, minus-65-mesh

Weight, Assay, percent Distribution,

Product percent Cr2 03 Fe SiO 2 percent Cr2 03 Cr/Fe

Concentrate ................. 18.99 49.7 12.0 6.5 36.0 2.83

Middling .................... 17.44 37.6 10.4 14.2 25.0 2.47

Tailing ..................... 40.36 15.2 7.4 29.0 23.4 -

Slime ....................... 23.21 17.7 7.9 27.0 15.6

Calculated head ........... 100.00 26.2 8.9 21.7 100.0 -

Combined conc. and middling.. 36.43- 43.9 11.2 10.2 61.0 2.67
19

TABLE A-16. - Chrome Queen sample 5; table concentration

with middling re-treatment

Weight, Assay, percent -Distribution,

Product percent Cr20 3 Fe SiO2 percent Cr203 Cr/Fe

Primary concentrate ......... 4.88 53.6 13.5 0.6 9.9 2.72

Regrind concentrate ......... 19.57 48.0 12.1 6.3 35.4 2.71

Middling .................... 8.97 39.9 10.8 13.5 13.5 2.53

Primary tailing ............. 27.97 12.8 6.9 31.6 13.5

Regrind tailing ............. 19.85 18.7 7.8 27.6 14.0

Primary slime ............... 14.12 16.8 7.1 27.0 8.9

Regrind slime ............... 4.64 27.4 10.3 20.2 4.8 -

Calculated head ........... 100.00 26.5 8.9 21.5 100.0 __

Combined conc. ............... 24.45 49.1 12.4 5.2 45.3 2.71

Cone. plus middlin ......... 33.42 46.6 12.0 7.4 58.8 2.66

TABLE A-17. - Chrome Queen sample 6; table concentration, minus-48-mesh

Weight, Assay percent Distribution,

Product percent Cr2 03 Fe SiO2 percent Cr203 Cr/Fe

Concentrate ................. 8.12 48.1 14.8 7.3 32.2 2.22

Tailing ..................... 77.10 9.2 8.8 33.0 58.4

Slime .. ...................... 14.78 7.7 8.2 33.3 9.4 -

Calculated head ........... 100.00 12.1 9.2 31.0 100.0

TABLE A-18. - Chrome Queen sample 6; table concentration

with middling re-treatment

Weight, Assay, percent Distribution,

Product percent Cr2 03 Fe SiO 2 percent Cr203 Cr/Fe

Minus-35-mesh concentrate ... 1.67 53.5 14.7 3.1 7.1 2.49

Minus-65-mesh concentrate ... 3.72 45.0 13.6 9.5 13.3 2.26

Minus-35-mesh tailing ....... 46.06 5.6 7.5 35.5 20.5

Minus-65-mesh tailing ....... 29.78 19.2 9.5 26.6 45.4

Slime ....................... 18.77 9.2 8.9 32.8 13.7 -

Calculated head ........... 100.00 12.6 8.7 30.8 100.0

Combined conc. ................ 5.39 47.6 13.9 7.5 20.4 2.34

TABLE A-19. - Juneau sample 1; table concentration, minus-48-mesh

Weight, Assay, percent Distribution,

Product percent Cr203 Fe SiO 2 percent Cr203 Cr/Fe

Concentrate 1 ............... 3.37 55.3 12.8 2.6 5.4 2.95

Concentrate 2 ............... 38.90 52.4 12.2 5.2 58.9 2.94

Middling .................... 19.97 35.4 9.5 16.1 20.4 2.54

Tailing ..................... 21.21 14.9 6.1 29.3 9.1

Slime ....................... 16.55 13.0 5.9 30.1 6.2 -

Calculated head ........... 100.00 34.6 9.3 16.5 100.0 -

Combined con. .............. 42.27 52.6 12.2 5.0 64.3 2.94

Conc. plus middling ......... 62.24 47.1 11.4 8.6 84.7 2.82
20

TABLE A-20. - Juneau sample 1; table concentration

with middling re-treatment

Weight, Assay, percent Distribution,

Product percent Cr2 03 Fe SiO2 percent Cr02 3 Cr/Fe

35/65-mesh concentrate ...... 10.26 54.5 12.9 3.1 16.2 2.89

65/150-mesh concentrate ..... 9.52 55.2 12.7 2.9 15.2 2.98

Minus-150-mesh concentrate .. 6.73 51.4 12.0 5.8 10.0 2.93

Minus-150-mesh middling ..... 21.22 47.7 11.2 7.9 29.3 2.91

35/65-mesh tailing .......... 7.07 10.1 5.4 33.2 2.1 -

65/150-mesh tailing ......... 6.19 10.8 5.5 33.2 1.9 -

Minus-150-mesh tailing ...... 6.95 25.4 7.6 23.2 5.1 2.29

Total slime ................. 32.06 21.9 7.3 24.1 20.2 -

Calculated head ........... 100.00 34.6 9.3 16.4 100.0 -

Combined cone. and middling.. 47.73 51.2 12.0 5.5 70.7 2.92

Combined cone. and middling

and minus-150-mesh tailing.. 54.68 47.9 11.4 7.8 75.8 2.87

TABLE A-21. - Star Four sample 1; combined jig and table concentration

Weight, Assay, percent Distribution,

Product percent Cr203 Fe SiO2 percent Cr203 Cr/Fe

Jig concentrate ............. 22.05 43.2 11.8 10.0 29.1 2.51

Table concentrate ........... 21.94 43.7 11.5 10.6 29.2 2.60

Jig middling ................ 15.74 34.8 10.5 17.4 16.7 2.26

Jig tailing ................. 21.51 20.1 8.0 26.0 13.2 -

Table tailing ............... 17.73 20.6 7.7 25.4 11.2-

Slime ....................... 1.03 18.5 6.8 26.2 .6 -

Calculated head ........... 100.00 32.7 9.9 17.6 100.0 -

Combined conc. ............... 43.99 43.4 11.7 10.3 58.3 2.53

Combined cone. and jig

middling ................... 59.73 41.2 11.4 12.2 75.0 2.47

TABLE A-22. - Star Four sample 1; table concentration, minus-48-mesh

Weight, Assay, percent Distribution,

product percent Cr203 Fe SiO2 percent Cr203 Cr/Fe

Concentrate ................. 52.81 48.0 12.0 8.2 76.6 2.73

Tailing ..................... 32.24 13.7 6.8 31.5 13.3 -

Slime ....................... 14.95 22.4 9.0 25.7 10.1 -

Calculated head ........... 100.00 33.1 9.9 18.3 100.0 -

TABLE A-23. - Star Four sample 1; table concentration

with middling re-treatment

Weight, Assa , percent Distribution,

Product percent Cr203 Fe SiO2 percent Cr203 Cr/Fe

Concentrate ................. 42.73 49.5 12.2 6.5 64.8 2.77

Minus-35-mesh tailing ....... 11.64 7.8 5.5 34.9 2.8 -

Minus-65-mesh tailing ....... 12.76 15.0 6.6 30.2 5.9 -

Minus-150-mesh tailing ...... 6.29 17.0 7.3 29.0 3.3 -

Primary slime ............... 12.00 21.8 7.6 24.5 8.0 -

Regrind slime ................. 14.58 34.2 10.2 16.4 15.2 2.29

Calculated head ............ 100.00 32.6 9.5 17.9 100.0 -

Cone. plus regrind slime .... 57.31 45.6 11.7 9.0 80.0 2.67

s
21

TABLE A-24. - Star Four sample 2; table concentration, minus-35-mesh

Weight, Assay, percent Distribution,

Product percent Cr203 Fe SiO2 percent Cr203 Cr/Fe

Concentrate ................ 21.84 49.3 14.0 5.1 39.6 2.41

Middling .................... 25.70 30.7 10.2 19.4 29.0

Tailing ..................... 31.88 14.9 7.1 31.4 17.5

Slime ....................... 20.58 18.3 8.1 28.0 13.9 -

Calculated head ......... 100.00 27.2 9.6 21.9 100.0 -_

TABLE A-25. - Star Four sample 2; table concentration, minus-48-mesh

Weight, Assay, percent Distribution,

Product percent Cr2O3 Fe Si02 percent Cr203 Cr/Fe

Concentrate ................. 26.65 49.3 13.9 3.6 47.8 2.42

Middling .................... 24.47 30.6 10.1 19.9 27.2

Tailing ..................... 33.21 11.9 6.4 34.6 14.3

Slime ....................... 15.67 18.8 8.1 28.0 10.7 -

Calculated head ........ 100.00 27.5 9.6 21.7 100.0

TABLE A-26. - Star Four sample 2; table concentration, minus-65-mesh

Weight, Assay, percent Distribution,

Product percent Cr203 Fe SiO 2 percent Cr203 Cr/Fe

Concentrate ................. 39.11 47.4 13.3 6.2 66.9 2.44

Middling .................... 13.86 17.9 7.7 28.5 8.9

Tailing ..................... 26.28 9.6 5.9 34.9 9.1

Slime ...................... 20.75 20.2 8.2 26.9 15.1

Calculated head ........... 100.00 27.8 9.5 21.1 100.0 -

Table A-27. - Star Four sample 2; table concentration, minus-!.00-mesh

Weight, Assa percent Distribution,

Product percent Cr20 3 Fe SiO2 percent Cr203 Cr/Fe

Concentrate ................. 25.34 48.0 13.6 4.9 44.2 2.41

Middling .................... 27.78 29.3 9.8 20.9 29.6

Tailing ..................... 22.41 9.3 5.7 35.8 7.6

Slime ....................... . 24.47 20.9 8.3 25.7 18.6

Calculated head ......... 100.00 27.5 9.5 21.3 100.0

TABLE A-28. - Star Four sample 2; table concentration

with middling re-treatment

Weight, Assay percent Distribution,

Product percent Cr203 Fe SiO 2 percent Cr203 Cr/Fe

Combined conc. ............... 34.06 49.5 13.8 4.3 61.7 2.45

Minus-65-mesh middling ...... 8.81 17.6 7.5 29.0 5.7

Minus-35-mesh tailing ....... 24.26 14.2 6.9 31.5 12.6

Minus-65-mesh tailing ....... 15.87 14.3 7.0 31.6 8.3

Primary slime ............... 14.00 18.0 7.7 27.2 9.2

Secondary slime ................ 3.00 22.2 9.0 24.5 2.5

Calculated head ........ . 100.00 27.3 9.5 21.3 100.0
22

TABLE A-29. - Star Four sample 3; combined tabling and flotation

Weight, Assay, percent Distribution,

product percent Cr20 3 Fe SiO2 percent Cr02 3 Cr/Fe

Table concentrate ............ 4.58 49.8 19.7 2.5 20.2 1.73

Flotation concentrate ....... 2.80 46.7 17.9 4.4 11.6 1.79

Flotation cleaner tailing ... 7.58 19.3 11.2 24.9 13.0 -

Flotation rougher tailing ... 15.82 19.7 11.3 24.2 27.7

Table tailing ............... 37.17 3.1 6.8 36.7 10.1

Primary slime ............... 7.60 6.2 7.3 33.4 13.2

Secondary slime ............. 24.45 6.1 7.3 33.4 4.2 -

Calculated head ........... 100.00 11.2 8.9 30.3 100.0 -

Combined conc. .............. 7.38 48.6 19.0 3.2 31.8 1.75

F

INT. -.BU.OFMINESGH*. ,PA 8771