Bureau of Mines

Report of Investigations 5245

LABORATORY CONCENTRATION OF VARIOUS

ALASKA COPPER ORES

BY R. R. WELLS

L United States Department of the Interior June 1956

- --
LABORATORY CONCENTRATION OF VARIOUS

ALASKA COPPER ORES

*

BY R. R. WELLS

· 0 0 0 0 0 * * * Report of Investigations 5245

UNITED STATES DEPARTMENT OF THE INTERIOR

Fred A. Seaton, Secretary

BUREAU OF MINES

Thos. H. Miller, Acting Director

Work on manuscript completed August 1955. The Bureau of Mines will welcome reprinting of this paper, provided

the following footnote acknowledgment is made: "Reprinted from Bureau of Mines Report of Investigations 5245."

June 1956
LABORATORY CONCENTRATION OF VARIOUS ALASKA

COPPER ORES

by

R. R. Wellsl-/

*

... _._____._ __._. ___.

CONTENTS

Page

Introduction and summary .....................................

Methods of concentration ......................................

Part 1 - Moth Bay ores ........................................

Ore .....................................

Physical character .................

Chemical character .................

Concentration ...........................

Part 2 - Threeman mine .......................

Ore .....................................

Physical character .................

Chemical character .................

Concentration ...........................

Part 3 - Golden Zone mine ....................

Ore .....................................

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Physical character ..................................

Chemical character ..................................

Concentration .....................

Part 4 - Maclaren River ................

Ore ...............................

Physical character .........

Chemical character ...........

Concentration .....................

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1/ Supervising metallurgist, Bureau of Mines, Region I, Alaska.

Report of Investigations 5245
I

ii

TABLES

Page

1. Chemical analysis, Moth Bay ............................... 3

2. Flotation, Moth Bay ...................................... 4

3. Chemical analysis, Threeman ............................... 5

4. Flotation, Threeman ........................................ 6

5. Chemical analysis, Golden Zone ............................ 7

6. Flotation, Golden Zone, upper level ....................... 7

7. Flotation, Golden Zone, lower level ....................... 8

8. Chemical analysis, Maclaren ................................ 9

9. Flotation, Maclaren ...................................... 9

ILLUSTRATION

1. Index map of Alaska ....................................... 2
1

INTRODUCTION AND SUMMARY

This report summarizes the results of preliminary mineral-dressing studies by

the Bureau of Mines on five samples of copper-bearing ore from various Alaska deposits. The work on each sample was not extensive enough to warrant individual publication. The results, however, indicate the possibilities and limitations of concentration of the respective ores. The information therefore may be helpful in

future development of these ore bodies.

Four of the five samples tested were submitted to the laboratory by engineers

of the Bureau of Mines as part of the examinations and survey investigations of

strategic-mineral deposits in Alaska. This program is conducted to assist development of mineral resources in the Territory and particularly to aid economic exploitation of marginal or complex ores. The fifth sample was submitted by engineers of

the Defense Minerals Exploration Administration.

A sample of ore from the Moth Bay mine, Revillagigedo Island (fig. 1, item 1),

contained 7.35 percent Zn and 1.62 percent Cu. The ore was found to be amenable to

concentration by standard selective flotation methods to produce marketable copper

and zinc concentrates with reasonably good recoveries.

A composite sample of ore from the Threeman mine, Port Fidalgo area, Alaska

(fig. 1, item 2) contained 1.65 percent Cu. Flotation of a rougher concentrate

from ore ground to minus-4 8-mesh, followed by regrinding and cleaning of the rougher

concentrate, recovered 81 percent of the total copper at 28.4 percent Cu grade.

Two samples of arsenic-bearing, low-grade copper ore were obtained from the

Golden Zone mine near Colorado Station, Alaska (fig. 1, item 3). By selective flotation of 0.97-percent Cu ore from the upper level, 82 percent of the copper was recovered in a concentrate that assayed 26.6 percent Cu; similar treatment of 0.24-

percent Cu ore from the lower level recovered 67 percent of the copper in a

concentrate that assayed 13.4 percent Cu.

Ore from the Kathleen-Margaret prospect, Maclaren River, near Paxton, Alaska

(fig. 1, item 4), contained only 1.2 percent Cu but was readily amenable to beneficiation by standard flotation procedures. Over 95 percent of the copper was recovered in a concentrate that assayed 36.7 percent Cu.

METHODS OF CONCENTRATION

During the investigations many data were obtained and compiled. For the sake

of brevity, however, data of secondary importance have been omitted or condensed;

only the tests that give the more promising results are discussed in detail.

Evaluation and concentration methods employed during the studies conformed with

standard laboratory practices. Representative portions of each sample were subjected to petrographic study and were analyzed by both chemical and semiquantitative

spectrographic methods. In no case, however, did the spectrograph reveal the
 0 0 M M M

N

/ -P

0 -/ Mites 400 U

Figure 1. - Index map of Alaska.
3

presence of significant amounts of elements other than those reported by chemical

means; therefore, the spectrographic data have been omitted from this report. Similarly, screen analyses of crushed portions of each ore showed no significant concentration of valuable mineral in a particular size fraction; consequently, the data

from these tests also have been omitted. The fine-grained nature of all the ores

tested necessitated relatively fine grinding for adequate mineral liberation. Although gravity-concentration techniques were employed in preliminary tests of some

ores, flotation concentration yielded superior results; therefore no gravity-test

data are included.

For convenience and clarity in presenting data, this report has been divided

into four sections, each of which presents the results of laboratory study of

samples from an individual property.

PART 1 - MOTH BAY ORES

Ore

The Moth Bay zinc-copper property is on Revillagigedo Island 15 miles southeast

of Ketchikan, Alaska. The material tested in the laboratory was a composite prepared from channel samples taken from the various adits of the mine during the investigation. The material was composited in weighted proportion to the footage

represented by each sample; thus the composite was considered to be representative

of the exposed ore in the mine.

Physical Character

Petrographic examination showed that the sulfides present in the ore include

pyrite, sphalerite, and chalcopyrite, with minor amounts of galena and bornite. The

gangue, classified as a mica schist, is essentially quartz, with barite, muscovite,

biotite, chlorite, limonite, magnetite, and feldspar. The microscopic study indicated that grinding to minus-65-mesh would provide satisfactory liberation.

Chemical Character

A partial analysis of a head sample prepared from the composite is shown in

table 1.

TABLE 1. - Chemical analysis, Moth Bay

Assay, percent Oz. per ton

Cu Pb Zn Fe Insol. Au Ag

1.62 0.07 .3I 1.6 .2 0.005 0.52

Concentration

A series of concentration tests was run to determine the most effective method

of treatment. Best results were obtained by grinding the ore to 95 percent minus65-mesh and applying standard flotation methods.

The ore was pulped with laboratory tap water, and the pH was adjusted with

lime. Zinc sulfate was employed as a sphalerite depressant in the copper circuit;

sodium cyanide was used to inhibit pyrite flotation. No silica depressant or slime

dispersant was required.
421

A copper concentrate was floated using sodium ethyl xanthate as the promoter.

The copper tailing was conditioned with copper sulfate. Spahlerite was floated and

cleaned once using amyl xanthate as collector.

Metallurgical results and operation data are summarized in table 2.

TABLE 2. - Flotation, Moth Bay

Metallurgical data

Assay

Weight, Percent Oz. pr ton

Product percent Cu Zn Fe Insol. Au Ag

Cu concentrate. 6.34 20.8 2.95 29.2 14.7 0.030 3.95

Zn cleaner

concentrate... 11.88 1.80 52.0 10.6 2.9 .005 .44

Zn cleaner tail 1.54 1.40 15.0 22.0 28.4 .020 1.16

Rougher tail .. 80.24 .15 .75 13.0 66.3 Tr.L/ .12

Calculated head 100.00 1.65 7.2 13.9 54.9 .005 42

Weight, Distribution ercent

Product percent Cu Zn Fe Insol. Au Ag

Cu concentrate. 6.34 78 .7 2.6 3. 4 0. 60.

Zn cleaner

concentrate... 11.88 12.8 85.8 9.1 .6 12.0 12.5

Zn cleaner tail 1.54 1.3 3.2 2.5 .8 8.0 4.3

Rougher tail .. 80.24 7.2 8.4 75.0 96.9 40.0 23.1

Calculated head 100.00 100.0 100.0 100.0 100.0 100.0 100.0

Operation data

Grind: 95 percent minus-65-mesh

Circuit pHE CaO NaCN ZnSO4 CuSO4 z-42/ Z- 5/ Pine oil

Grind .... 9.8 . 20 1. .5 - - -

Copper ... 9.8 - - - 0.1 - 0.08

Condition. - 2.0 .05 - 1.5 - 0.10 -

Zn rougher 10.9 - - - -

Zn cleaner 11.4 2.0 .05 - - - .05

Total... 12.0 .30 1.5 1.5 .1 .l~ .08 J1 f-l n /r1'..ln.H A_ _ ^ m nl a.. ._ i1/

3/

uazcuLaed ai s u.uuC ounU

Sodium ethyl xanthate.

Potassium amyl xanthate.

ce AU pe.r Ton.

By selective flotation, 78.7 percent of the copper, 40.0 percent of the gold,

and 60.1 percent of the silver were recovered in a copper rougher concentrate that

assayed 20.8 percent Cu, 2.95 percent Zn, 0.03 ounce Au, and 3.95 ounces Ag per ton.

The zinc cleaner concentrate contained 85.8 percent of the total zinc; it assayed

52.0 percent Zn and 1.8 percent Cu.

I

L
5

PART 2 - THREEMAN MINE

Ore

During the investigation of the property by engineers of the Bureau of Mines, a

series of fourteen channel samples were obtained from the Threeman mine, Port

Fidalgo area, Prince William Sound, Alaska. For laboratory study, the channel samples were composited to yield a sample comparable in grade and character to the

known ore body of the Threeman deposit and of the similar ore deposits of the Port

Fidalgo area.

Physical Character

Petrographic study showed that the Threeman ore, as represented by the composite sample tested, essentially contains chlorite, altered ferromagnesian minerals,

altered feldspar, quartz, some chalcopyrite, and small amounts of calcite, pyrite,

pyrrhotite, and epidote; also present is a very small amount of sphalerite.

Optimum liberation occurs in the minus-65-, plus-100-mesh fraction, but the

bulk of the chalcopyrite is liberated in the minus-48-, plus-65-mesh fraction.

Previous petrographic studies of ores from Prince William Sound indicate that a

portion of the mineral identified as chalcocite may be chalmersite.

Chemical Character

The partial chemical analysis shown in table 3 indicates the chemical character

of the sample of Threeman ore tested in the laboratory.

TABLE 3. - Chemical analysis, Threeman

Assae ercent Oz. er ton

Cu Fe Insol. Zn Ni Co Au Ag

1.65 15.1 49.3 1/O0.05 0.01 0.02 Tr. 0.36

1/ Less than.

Concentration

A series of flotation tests was run to determine the best grind and reagent

combination for treatment of the ore. Although good recoveries of copper were obtained by rougher flotation of ore ground to minus-48- or 65-mesh, difficulty was

experienced in cleaning the rougher concentrate. Partial oxidation of the ore

samples, as received, reduced the floatability of the copper minerals and activated

the iron sulfides; this made separation of copper and iron minerals more difficult

than if the sulfides had not been partly oxidized.

Several tests were made in which the rougher concentrate was reground before

cleaning. The metallurgical results and operation data shown in table 4 are typical

of this group of tests.

Regrinding of the flotation rougher concentrate for 12 minutes and treating the

reground product in 3 cleaning stages yielded a concentrate that assayed 28.4 percent Cu, 35.3 percent Fe, and 1.9 percent acid-insoluble matter; this concentrate

contained 81 percent of the total copper in the ore. More than 13 percent of the

total copper reported in the cleaner tailing; if this product were retreated,

recovery of copper probably would be increased slightly.
6

TABLE 4. - Flotation, Threeman

Metallurgical data

Distribution,

Weight, Assay, percent percent

Product percent Cu Co Fe Insol. Cu

Concentrate ............. 28 28. 0.01 35.3 1.9 81.1

Combined cleaner tails .. 8.08 2.5 .06 27.5 32.4 13.6

Rougher tail ............ 87.64 .09 .01 12.6 51.7 5.2

Calculated head ......... 100.00 1. .02 14.8 48.0 100.0

Operation data

Time, Reagents, pounds er ton

Circuit min. pH CaO NaCN Z-3 MIC2/

Grinding ............................

Conditioner ......................... 5 9.8 1.0 0.1 0.25 0.10

Rougher ............................. 6 9.8 - - -

Regrind ............................. 12 - 1.0 - -

Cleaner 1 ........................... 2 10.0 - - - .05

Cleaner 2 ..... ...................... 2 9.5 - - - -

Cleaner 3 ........................... 2 7.5 - - - -

Total ............................. 2.0 .1 .25 .15

1/ Potassium ethyl xanthate.

2/ Methyl isobutyl carbinol frother.

The small amount of cobalt present in the ore, which apparently is associated

with pyrrhotite, was concentrated to some extent in the cleaner tailing.

PART 3. - GOLDEN ZONE MINE

Ore

As part of the examination of the Golden Zone property near Colorado Station,

Alaska, members of the Bureau of Mines staff procured a number of trench and channel

samples. Several of the samples were composited to represent ore in the upper level

ore zone of the deposit; similarly, other samples were blended to make a sample

representative of lower level ore. The two composite samples were submitted to the

laboratory for beneficiation tests.

Physical Character

Petrographic study of the material showed that the upper level sample consists

of arsenopyrite, chalcopyrite, and relatively small amounts of sphalerite, cerussite, pyrite, a trace of smithsonite associated with sericite, quartz, a magnesianbearing calcite, and small amounts of limonite and chlorite.

The lower level sample is similar except for the lack of sphalerite and lesser

amounts of chalcopyrite. A portion of the chalcopyrite in this sample is tarnished

with an iridescent coating.

Microscopic examination showed that most of the sulfides in both samples are

unlocked in the minus-65-, plus-100-mesh fraction; grinding through 100-mesh, however, is required to provide optimum liberation.

4

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7

t

Chemical Character

Partial chemical analyses of representative portions of the two composite

samples are shown in table 5.

TABLE 5. - Chemical analysis, Golden Zone

Assay, percent Oz. Der ton

Sample Cu Pb Zn _ Fe As .Sb Insol. Au Ag

Upper ..... 0.97 1/0.05 0.32 10.4 4.1 o0.1 62.6 0.1 3.40

Lower ..... .24 1/ .05 1/.05 9.5 14.9 .1 64.0 23 1.25

1/ Less than.

Concentration

A series of preliminary tests was run to investigate the amenability of the

Golden Zone ore to concentration by gravity and flotation methods. It was determined that the most suitable treatment involved grinding essentially to minus-100-

mesh, followed by selective flotation of copper and arsenic minerals. In each test

the copper rougher concentrate was cleaned once; the cleaner tailing was returned to

the circuit before flotation of the arsenopyrite. The cleaner tailing from the

arsenopyrite flotation was added to the rougher tailing for assay. Operation data

and results are shown in tables 6 and 7.

TABLE 6. - Flotation, Golden Zone, upper level

Metallurgical data

Assay Distribution,

Weight, Percent Oz. er ton percent_

Product percent Cu As Pb Zn Au Ag Cu Au Ag

Cu concentrate.. 3.03 26.6 1.5 1.4 2.8 3.12 59.9 82.3 57.9 60.9

As concentrate.. 12.62 .85 22.6 - - .48 5.9 10.9 37.2 25.0

Tailing ........ 84.35 .08 - - .01 .5 6.8 4.9 14.1

Calculated head. 100.00 .9 .16 3.0 100.0 100.0 100.0

Operation data

Grind: 97 percent minus-l00-mesh

Time, R_ eagents pounds per ton

Circuit min. pH Na2CO NaCN M-271/ p.O/ H2S04 Z-63

Conditioner ....... 3 9.6 10.0 0.05 0.03 .04

Cu rougher ........ 3 - - - -

Cu cleaner ........ 2 9.5 - - .04 -

Conditioner ....... 2 6.7 -. 08 3.0 0.2

As rougher ........ 5 - - - - - - .1

As cleaner ........ 2 7.0 - 1.0 -

Total ........... 10.0 .05 .03 .16 4.0 .3

1/ Minerec 27.

2 Pine oil.

/ Pentasol xanthate.
8

TABLE 7. - Flotation, Golden Zone, lower level

Metallurgical data

Assay_ - Distribution,

Weight, Percent Oz. per ton percent

Product percent Cu As Pb Zn Au .A Cu Au Ag

Cu concentrate 1.28 13. 571 0.75 0.55 11.4 53.2 66.8 57.3 49.

As concentrate.. 19.52 .31 33.4 - .50 1.9 23.8 39.5 27.1

Tailing ........ 179.20 .03 - - - .01 .4 I 9.4 3.2 23.2

Calculated head. 100.00 .26 .25 1.35 100.0 100.0 100.0

Operation data

Grind: 97 percent minus-100-mesh

Time, Reagnts, pounds ton

Circuit min. pH NaPCO NaCN M-271/ P.O./ HSO4 ZConditioner ....... 3 9.7 10.0 0.05 0.03 0.0 -

Cu rougher ........ 3- - - - -

Cu cleaner ........ 2 9.3 - - - .04 -

Conditioner ....... 2 6.7 - - -. 08 4.0 0.2

As rougher ........ 5 - - - - - .1

As cleaner ........ 2 6.2 - - - - 1.0

Total ........... - 0. 1.05 .03 ,5.6 5.0 .3

/ Minerec 27.

Pine oil.

Pentasol xanthate.

Selective flotation of upper level ore (0.97 percent Cu) yielded a copper concentrate assaying 26.6 percent Cu, 1.5 percent As, 3.12 ounces Au, and 59.9 ounces

Ag per ton; the product contained 82.3 percent of the copper, 57.9 percent of the

gold, and 60.9 percent of the silver. Over 10 percent of the copper, 37 percent of

the gold, and 25 percent of the silver reported in an arsenopyrite concentrate that

assayed 0.85 percent Cu, 22.6 percent As, 0.48 ounce Au, and 5.9 ounces Ag per ton.

A similar test on upper level ore yielded a lower grade copper concentrate containing 87 percent of the copper, 71 percent of the gold, and 65 percent of the

silver. This product assayed 16.5 percent Cu, 2.24 ounces Au, and 40.75 ounces Ag

per ton but also contained approximately 5 percent As, which probably would be

objectionable.

The high-arsenic lower level ore (0.24 percent Cu) was less amenable to treatment. Best results showed copper, gold, and silver recoveries of 66.8, 57.3, and

49.7 percent, respectively, in a copper concentrate that assayed 13.4 percent Cu,

5.7 percent As, 11.4 ounces Au, and 53.2 ounces Ag per ton. The arsenopyrite concentrate contained 23.8 percent of the copper, 39.5 percent of the gold, and 27.1

percent of the silver; the product assayed 0.31 percent Cu, 33.4 percent As, 0.50

ounce Au, and 1.9 ounces Ag per ton.

Roasting and cyanidation tests on arsenopyrite concentrates produced by selective flotation of the two samples gave unsatisfactory results.
9

V

PART 4 - MACLAREN RIVER

Ore

Representatives of the DMEA field team submitted a sample of ore for evaluation

and testing from the Kathleen-Margaret prospect of the Alaska Copper Mines, Inc.,

Maclaren River, near Paxton, Alaska.

Physical Character

The material submitted to the laboratory consists chiefly of quartz and basaltic lava with a small amount of chalcopyrite and minor amounts of bornite,

chalcocite, and pyrite. The copper minerals are liberated by grinding to minus-65-

mesh.

Chemical Character

Table 8 shows a partial chemical analysis of a representative sample of the ore:

I

TABLE 8. - Chemical analysis, Maclaren

Assay, percent Oz. per ton

Cu IFel S Insol. Ni Au Ag

1.2/ 5.8 I.o 71.2 1/0.02 Tr. 0.04

1/ Less than.

Concentration

Laboratory testing indicated that, after grinding to minus-65-mesh, the Maclaren

sample was amenable to standard flotation procedures for the production of copper

concentrates of marketable grade. Typical results are shown in table 9.

TABLE 9. - Flotation, Maclaren

Metallurgical data

Distribution,

Weight, Assa percent percent

Product percent Cu Fe S Cu

Concentrate ........ 2.85 3.7 20.8 23. 95.9

Cleaner tail ....... 1.23 1.3 10.0 .89 1.5

Rougher tail ........ 95.92 .03 5.2 .06 2.6

Calculated head 100.0 1.1 . 100.0

Operation data

Grind: Stage-ground to minus-65-mesh

Time, Reagents po ds er ton

Circuit min. pH Na2CO3 Z-61/ Frother_/

Condition ............... 2 - 2.0 0.1 O.O04

Rougher ................. 3 9.5 - - -

Cleaner ................. 2 9.0 - - .04

Total ............... . 2.0 .1 .08 q- -------- ^ -- 1 1 - TM - , . . . .. -- ---- ^ ----------- L -- ^ ---

I

1/ Pentasol xanthate. 2/ Dowfroth 250.

By flotation, 95.9 percent of the total copper in the Maclaren sample was

recovered in a concentrate that assayed 36.7 percent Cu.

I NT. B U.OFMI NES. PG,. PA. 7578