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IC 8916 
 
 Bureau of Mines Information Circular/1983 
 
 Podiform Chromite Occurrences 
 in the Caribou Mountain and Lower 
 Kanuti River Areas, Central Alaska 
 
 Part II: Beneficiation 
 
 By D. C. Dahlin, L. L. Brown, and J. J. Kinney 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
Information Circular 8916 
 
 Podiform Chromite Occurrences 
 in the Caribou Mountain and Lower 
 Kanuti River Areas, Central Alaska 
 
 Part II: Beneficiation 
 
 By D. C. Dahlin, L. L. Brown, and J. J. Kinney 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 James G. Watt, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 
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 tf* 
 
 <V&«^ 
 
 This publication has been cataloged as follows: 
 
 Podiform chromite occurrences in the Caribou Mountain and Lower Ka- 
 nuti River areas, centra) Alaska. 
 
 (Information circular ; 8916) 
 
 Includes bibliographies. k 
 
 Supt. of Docs, no.: I 28.27:8916. 
 
 Contents: pt. 1. Reconnaissance investigations / by Jeffrey Y. 
 Foley and Mark M. McDermott— pt. 2. Beneficiation / by D. C. Dah- 
 lin, 1-. I-. Brown, and J. J. Kinney. 
 
 1. Chromite— Alaska. 2. Prospecting— Alaska. I. Foley, Jeffrey 
 Y. II. Series: Information circular (United States. Bureau of Mines) ; 
 8916. 
 
 Tfm5rW4-fW4#0rG4} 622s [553.4'643'097986] 82-600286 
 
CONTENTS 
 
 Page 
 
 Abstract 1 
 
 Introduction 2 
 
 Acknowledgments 2 
 
 Mineralogy 3 
 
 Benef iciation procedure 5 
 
 Results and discussion 7 
 
 Summary and conclusions 9 
 
 Appendix. — Metallurgical balances 10 
 
 ILLUSTRATIONS 
 
 1. General benef iciation procedure used to concentrate 11 lower Kanuti 
 
 River and Caribou Mountain samples 5 
 
 2. General procedure for the electrodynamic separation step of the benef i- 
 
 ciat ion procedure 6 
 
 TABLES 
 
 1. Head analyses of 11 chromite-bearing samples from the lower Kanuti River 
 
 and Caribou Mountain areas of central Alaska 3 
 
 2. Estimated mineral composition of 11 lower Kanuti River and Caribou Moun- 
 
 tain samples 4 
 
 3. Analyses of high-purity concentrates prepared from 100- by 200-mesh size 
 
 fractions 4 
 
 4. Summary of the calculated composite concentrates from benef iciation of 
 
 11 chromite-bearing samples from the lower Kanuti River and Caribou 
 
 Mountain areas 8 
 
 A-l. Gravity concentration and electrodynamic separation of sample A 10 
 
 A-2. Gravity concentration and electrodynamic separation of sample B 10 
 
 A-3. Gravity concentration and electrodynamic separation of sample C 11 
 
 A-4. Gravity concentration and electrodynamic separation of sample D 11 
 
 A-5. Gravity concentration and electrodynamic separation of sample E 12 
 
 A-6. Gravity concentration and electrodynamic separation of sample F 12 
 
 A-7. Gravity concentration and electrodynamic separation of sample G 13 
 
 A-8. Gravity concentration and electrodynamic separation of sample H 13 
 
 A-9. Gravity concentration and electrodynamic separation of sample I 14 
 
 A-10. Gravity concentration and electrodynamic separation of sample J 14 
 
 A-ll. Gravity concentration and electrodynamic separation of sample K. 15 
 
PODIFORM CHROMITE OCCURRENCES IN THE CARIBOU MOUNTAIN 
 AND LOWER KANUTI RIVER AREAS, CENTRAL ALASKA 
 
 Part II: Beneficiation 
 
 By D. C. Dahlin, 1 L. L. Brown, 2 and J. J. Kinney 3 
 
 ABSTRACT 
 
 The Bureau of Mines has investigated podiform chromite deposits in 
 three ultramafic bodies in the Caribou Mountain and lower Kanuti River 
 areas of central Alaska. The investigation, reported in two parts, was 
 done as part of the Bureau's mission to help insure an adequate supply 
 of minerals to meet the Nation's needs. Part I describes an extensive 
 field investigation and mineralogical studies by personnel from the Bu- 
 reau's Alaska Field Operations Center. This report, part II, describes 
 the mineralogy of 11 samples that were high-graded from surface expo- 
 sures at 10 sites and presents the results of laboratory batch benefi- 
 ciation tests designed to concentrate the chromite. 
 
 The 11 samples, peridotites and chromitites that consisted of vari- 
 able amounts of chromite or chromium-bearing spinels, olivine, and ser- 
 pentine, were beneficiated by grinding and sizing, gravity concentra- 
 tion, and electrodynamic separation. Three high-chromium chromite con- 
 centrates , two high-iron chromite concentrates , and one high-aluminum 
 chromite concentrate were produced. Three other concentrates were mar- 
 ginal, and two were submarginal. Chromium recoveries ranged from 
 54 to 92 pet. These results indicate that the areas may be significant 
 chromium resources . 
 
 Potential platinum association with the chromite was also investi- 
 gated. Analysis of these 11 samples indicates that the areas are not 
 good platinum resources. 
 
 ^Metallurgist. 
 
 ■'Group supervisor and geologist. 
 
 •^Geologist. 
 
 All authors are with the Albany Research Center, Bureau of Mines, Albany, Oreg, 
 
INTRODUCTION 
 
 The United States has no domestic pro- 
 duction or economic reserves of chromite, 
 the only commercial ore of chromium, and 
 must rely on imports and on stockpiles to 
 meet national needs. Although world re- 
 serves of chromite are adequate to meet 
 forecast world demand, sensitive politi- 
 cal and economic considerations, as well 
 as geographical location, could conceiv- 
 ably make the United States vulnerable in 
 an emergency. ^ The known large, high- 
 grade chromite deposits are in the East- 
 ern Hemisphere, and chromite imports have 
 been primarily from the Republic of South 
 Africa, the Soviet Union, the Philip- 
 pines, Finland, and Turkey. As a means 
 of meeting a potential emergency, the Bu- 
 reau of Mines is characterizing potential 
 domestic sources and developing process- 
 ing technology. 
 
 Chromium is used primarily in the met- 
 allurgical industry, but also in the 
 chemical and refractory industries. 
 There are no economical substitutes for 
 it in stainless steels and many other 
 ferrous and nonferrous alloys. Chemical 
 applications include plating, pigment 
 production, and leather tanning. Chro- 
 mite refractories are used in high- 
 temperature applications such as furnace 
 and kiln linings and as molding material 
 in foundaries. 
 
 Identified U.S. chromite resources in 
 Montana and the Pacific Coast States are 
 small, low-grade, or both. The largest 
 deposit is in the Stillwater Complex, 
 Mont., and contains a high-iron variety 
 of chromite. Laterites from northern 
 California and southwestern Oregon are a 
 large, low-grade resource that the Bureau 
 is currently investigating for chromite 
 recovery. 5 
 
 Geologists at the Bureau's Alaska Field 
 Operations Center have done reconnais- 
 sance investigations of three ultramafic 
 complexes in the Caribou Mountain- 
 Melozitna ultramafic belt in central 
 Alaska. Their study is part I of this 
 two-part investigation. 6 Geochemical 
 sampling of the three complexes , iden- 
 tified as the Caribou Mountain, upper 
 Kanuti River, and lower Kanuti River ul- 
 tramafic bodies, was used to describe the 
 occurrences of chromite and examine the 
 significance of Cr, Ni, and Co anomalies 
 reported by earlier workers. This re- 
 port, part II of the investigation, de- 
 scribes the mineralogy and benef iciation 
 of 11 chromite-bearing samples taken from 
 10 sites within the three ultramafic 
 bodies. 
 
 ACKNOWLEDGMENTS 
 
 The authors gratefully acknowledge the 
 assistance of Jeff Foley, Mark McDermott, 
 
 horning, J. L. , N. A. Matthews, and 
 E. C. Peterson. Chromium. Ch. in Min- 
 eral Facts and Problems, 1980 Edition. 
 BuMines Bull. 671, 1981, pp. 167-182. 
 
 5 Kirby, D. E., D. R. George, and C. B. 
 Daellenbach. Chromium Recovery From 
 Nickel-Cobalt Later ite and Later ite Leach 
 Residue. BuMines RI 8676, 1982, 22 pp. 
 
 and Karen Clautice, geologists, Alaska 
 Field Operations Center, Bureau of 
 Mines , in obtaining samples for this 
 investigation. 
 
 6 Foley, J. Y., and M. M. McDermott. 
 Podiform Chromite Occurrences in the 
 Caribou Mountain and Lower Kanuti River 
 Areas, Central Alaska. Part I: Recon- 
 naissance Investigations. BuMines 
 IC 8915, 1983. 
 
MINERALOGY 
 
 Each sample of chromite-bearing mate- 
 rial that was studied was high-graded 
 from surface exposures at the field site. 
 The samples were high-graded to determine 
 whether precious metals were associated 
 with the chromite. The bulk samples of 
 hard rock were collected from frost-riven 
 rubble or from discontinuous pods and 
 stringers in small outcrops and in shal- 
 low subcrops, usually along ridge crests. 
 Sample weight ranged from 10 to 350 lb, 
 and maximum rock size in each sample 
 ranged from 1 to 15 in. in the largest 
 dimension. 
 
 Representative specimens were selected 
 from each sample for petrographic exami- 
 nation. The samples ranged from hard, 
 unweathered, massive chromite to chro- 
 mite that was disseminated sparsely to 
 densely in lenses and stringers less than 
 an inch to several inches thick. Most 
 of the samples had surface alteration 
 from weathering, and most were highly 
 fractured. 
 
 All of the samples were mineralogically 
 similar. They were peridotites and chro- 
 mitites that consisted essentially of 
 variable amounts of chromite or chromium- 
 bearing spinels, olivine, and serpentine. 
 Minor constituents included magnetite, 
 chlorite, and f erromagnesian silicate 
 minerals (pyroxenes and amphiboles) . Six 
 samples contained traces of pyrite, 
 and a trace of maucherite (Ni 3 As 2 ) was 
 
 identified in sample E. Some of the oli- 
 vine was altered to serpentine, and some 
 of the serpentine and ferromagnesian sil- 
 icates were altered to chlorite. 
 
 Head analyses of the samples are shown 
 in table 1. The samples are identified 
 by the letters A through K, as they are 
 in part I. The Cr 2 03 content of the sam- 
 ples ranged from 13.2 to 47.2 pet. Plat- 
 inum was reported in the head analysis of 
 sample B at a grade of 0.039 oz/ton, but 
 the platinum analysis of the other head 
 samples was less than the minimum de- 
 tection level. The sensitivity of the 
 precious-metals analyses depends on the 
 chromium content of the sample being ana- 
 lyzed. The levels of detection are 0.01 
 oz/ton for Pt , Pd, and Ag, and 0.002 
 oz/ton for Au for a sample that contains 
 more than about 20 pet Cr 2 03. For a sam- 
 ple with less than about 20 pet Cr 2 3 , 
 the levels of detection are improved to 
 0.004 oz/ton for Pt and Pd and 0.0008 
 oz/ton for Au, and remain at 0.01 oz/ton 
 for Ag. All of the precious-metals anal- 
 yses were done by a fire assay-atomic ab- 
 sorption technique. 
 
 In one case, samples taken from the 
 same site were significantly different, 
 as can be seen by comparing the analysis 
 of sample I with that of sample J. Dif- 
 ferences could also be seen in the hand 
 specimens. The chromite in sample I was 
 
 TABLE 1. - Head analyses of 11 chromite-bearing samples from the lower 
 Kanuti River and Caribou Mountain areas of central Alaska 
 
 Sample 
 
 Chromite 
 occurrence 1 
 
 
 Analysis, 
 
 pet 
 
 
 Analysis , 
 
 oz/ton 
 
 
 
 Cr 2 3 
 
 Fe 
 
 MgO 
 
 A1 2 3 
 
 Si0 2 
 
 Pt 
 
 Pd 
 
 Au 
 
 Ag 
 
 A 
 
 3 
 
 17.0 
 
 8.5 
 
 34.5 
 
 4.1 
 
 26.8 
 
 <0.004 
 
 <0.004 
 
 <0.001 
 
 0.04 
 
 B 
 
 6 
 
 22.7 
 
 20.7 
 
 13.9 
 
 22.6 
 
 4.7 
 
 .039 
 
 .011 
 
 <.001 
 
 .10 
 
 C 
 
 7 
 
 14.8 
 
 9.3 
 
 28.1 
 
 8.4 
 
 26.0 
 
 <.004 
 
 <.004 
 
 .001 
 
 .05 
 
 D 
 
 12 
 
 31.1 
 
 12.5 
 
 22.1 
 
 7.5 
 
 14.9 
 
 <.01 
 
 <.01 
 
 <.002 
 
 .13 
 
 E 
 
 17 
 
 47.2 
 
 14.4 
 
 13.7 
 
 7.8 
 
 7.0 
 
 <.01 
 
 <.01 
 
 .003 
 
 .45 
 
 F 
 
 18 
 
 13.2 
 
 10.8 
 
 27.9 
 
 16.2 
 
 20.2 
 
 <.01 
 
 <.01 
 
 <.002 
 
 .03 
 
 G 
 
 19 
 
 44.4 
 
 18.6 
 
 12.8 
 
 7.6 
 
 7.3 
 
 <.01 
 
 <.01 
 
 <.002 
 
 .05 
 
 H 
 
 20 
 
 38.6 
 
 18.7 
 
 13.4 
 
 10.7 
 
 5.7 
 
 <.01 
 
 <.01 
 
 <.002 
 
 .05 
 
 I 
 
 21 
 
 24.8 
 
 15.8 
 
 15.6 
 
 30.5 
 
 2.8 
 
 <.01 
 
 <.01 
 
 .002 
 
 .04 
 
 J 
 
 21 
 
 15.6 
 
 9.4 
 
 27.2 
 
 8.9 
 
 25.8 
 
 <.004 
 
 <.004 
 
 <.001 
 
 .05 
 
 K 
 
 22 
 
 20.3 
 
 18.1 
 
 17.0 
 
 24.3 
 
 6.6 
 
 <.004 
 
 <.004 
 
 <.001 
 
 .05 
 
 Chromite occurrence locations are shown in part I. 
 
massive chromite, while in sample J, the 
 chromite was disseminated in thin bands. 
 
 Detailed mineralogical examinations 
 were done on table concentrates and tail- 
 ings from sized fractions. Binocular and 
 petrographic microscopy and magnetic sep- 
 aration techniques were used to determine 
 the mineral composition of the samples. 
 The composition of each sample appeared 
 to be nearly uniform from one size frac- 
 tion to the next. The 100- by 200-mesh 
 fraction was studied because it was rep- 
 resentative of the whole sample, and most 
 of the mineral components were liberated 
 in that size range. Table 2 shows the 
 mineral composition, based on weight, of 
 the samples, as calculated from the esti- 
 mated compositions of the concentrates 
 and tailings from the 100- by 200-mesh 
 fraction. 
 
 High-purity chromite concentrates were 
 prepared by carefully controlled magnetic 
 separation of table concentrates that had 
 been submitted for detailed mineralogical 
 examination. Each sample was fraction- 
 ated at several electromagnetic field 
 settings on a laboratory-model isodynamic 
 separator. The best concentrate, as de- 
 termined with a binocular microscope, was 
 submitted for chemical analysis. Table 3 
 shows the analyses of these high-purity 
 concentrates from the samples. All were 
 classified as magnesian aluminian chro- 
 mites except samples B, F, I, and K. 
 Those were identified as magnesian chro- 
 mohercynites, iron-aluminum spinels 
 (FeAl 2 4 ) that contain significant 
 amounts of chromium and magnesium substi- 
 tuted for aluminum and iron. 
 
 TABLE 2. - Estimated mineral composition of 11 lower Kanuti River 
 and Caribou Mountain samples , weight-percent 
 
 Sample 
 
 Chromite 
 
 Olivine 
 
 Serpentine 
 
 Magnetics 1 
 
 Chlorite 
 
 Fer romagnes ian 
 silicates 
 
 Sulfides 
 
 A 
 
 26 
 
 58 
 
 14 
 
 2 
 
 Trace 
 
 Trace 
 
 Trace 
 
 B 
 
 81 
 
 14 
 
 Trace 
 
 5 
 
 Trace 
 
 ND 
 
 ND 
 
 C 
 
 27 
 
 30 
 
 25 
 
 11 
 
 3 
 
 7 
 
 ND 
 
 D 
 
 60 
 
 20 
 
 16 
 
 3 
 
 Trace 
 
 Trace 
 
 ND 
 
 E 
 
 79 
 
 2 
 
 12 
 
 7 
 
 Trace 
 
 Trace 
 
 Trace 
 
 F 
 
 31 
 
 11 
 
 46 
 
 11 
 
 2 
 
 ND 
 
 Trace 
 
 G 
 
 74 
 
 Trace 
 
 19 
 
 6 
 
 Trace 
 
 ND 
 
 ND 
 
 H 
 
 74 
 
 ND 
 
 16 
 
 11 
 
 Trace 
 
 ND 
 
 Trace 
 
 I 
 
 82 
 
 Trace 
 
 5 
 
 10 
 
 3 
 
 ND 
 
 ND 
 
 J 
 
 31 
 
 23 
 
 34 
 
 s 10 
 
 Trace 
 
 2 
 
 Trace 
 
 K 
 
 62 
 
 13 
 
 15 
 
 10 
 
 Trace 
 
 ND 
 
 ND 
 
 ND Not detected. 'Minerals removable with a hand magnet. 
 
 TABLE 3. - Analyses of high-purity concentrates prepared 
 from 100- by 200-mesh size fractions 
 
 Sample 
 
 
 
 Analysis, 
 
 pet 
 
 
 
 Cr:Fe 
 
 
 Cr 2 3 
 
 Fe 
 
 MgO 
 
 A1 2 3 
 
 Si0 2 
 
 S 
 
 P 
 
 ratio 
 
 A 
 
 51.6 
 
 15.6 
 
 12.4 
 
 12.0 
 
 2.58 
 
 0.009 
 
 0.06 
 
 2.3 
 
 B 
 
 24.8 
 
 22.4 
 
 12.0 
 
 24.9 
 
 1.79 
 
 .011 
 
 .05 
 
 .8 
 
 C 
 
 38.9 
 
 15.3 
 
 14.3 
 
 20.2 
 
 3.92 
 
 .011 
 
 .17 
 
 1.7 
 
 D 
 
 49.3 
 
 15.9 
 
 13.4 
 
 12.3 
 
 2.63 
 
 .006 
 
 .14 
 
 2.1 
 
 E 
 
 53.8 
 
 15.1 
 
 11.4 
 
 9.3 
 
 3.61 
 
 .009 
 
 .05 
 
 2.4 
 
 F 
 
 31.0 
 
 16.1 
 
 17.1 
 
 27.1 
 
 2.82 
 
 .012 
 
 .05 
 
 1.3 
 
 G 
 
 52.9 
 
 20.5 
 
 10.3 
 
 8.5 
 
 1.58 
 
 .009 
 
 .12 
 
 1.8 
 
 H 
 
 45.7 
 
 20.5 
 
 10.5 
 
 13.8 
 
 1.11 
 
 .006 
 
 .06 
 
 1.5 
 
 I 
 
 27.5 
 
 16.0 
 
 14.8 
 
 33.8 
 
 .18 
 
 .004 
 
 .07 
 
 1.2 
 
 J 
 
 39.8 
 
 15.8 
 
 13.9 
 
 20.2 
 
 3.62 
 
 .009 
 
 .09 
 
 1.7 
 
 K 
 
 24.7 
 
 20.0 
 
 11.4 
 
 31.6 
 
 1.57 
 
 .006 
 
 .07 
 
 .8 
 
BENEFICIATION PROCEDURE 
 
 The benef iciation procedure that was 
 used to produce a composite chromite con- 
 centrate was essentially the same for 
 each of the 11 samples and is shown in 
 figure 1. Minor variations were adopted 
 to the procedure to suit each individual 
 sample. 
 
 The samples, as received, consisted of 
 hard, angular rock fragments from 1 to 
 15 in. in the largest dimension. Each 
 sample was crushed in a jaw crusher and 
 screened to minus 1/4 in. A head sample 
 
 and several 20-lb splits for beneficia- 
 tion tests were prepared from the minus 
 1/4-in material. 
 
 For each sample, a split was screened 
 on 48, 100, and 200 mesh. The plus 
 48-mesh fraction was ground dry in a 
 13- by 25-in rodmill and a 7- by 9-in 
 rodmill to pass 48 mesh and was sized at 
 100 and 200 mesh. Grinding was done in 
 stages to minimize production of fines. 
 Generally, the plus 48-mesh fraction from 
 a 20-lb split was first ground in the 
 
 Bulk sample 
 
 Jaw crusher 
 
 Plus 48 mesh 
 
 1 
 
 Rodmill 
 
 48 by 100 mesh 
 
 I 
 
 Sand table 
 
 Concentrate 
 
 Tai 
 
 Minus 1/4 in 
 
 1 
 
 -♦Screen 
 
 Minus 48 mesh 
 
 Screens 
 
 100 by 200 mesh 
 
 I 
 
 Slime table 
 
 ings Concentrate 
 
 Middlings 
 Dryer 
 
 Midd 
 
 Tai 
 
 Minus 200 mesh 
 
 1 
 
 Slime table 
 
 ings 
 
 Concentrate Tai 
 
 ings 
 
 ings 
 
 T 
 
 Electrodynamic separator 
 
 i r 
 
 T 
 
 Concentrate Middlings Tailings 
 
 *-Dryer 
 
 Electrodynamic separator 
 
 i i r 
 
 Concentrate Middlings Tailings 
 
 FIGURE 1. - General beneficiation procedure used to concentrate 11 lower Kanuti River and 
 Caribou Mountain samples. 
 
large mill in two stages of 5 and 3 min, 
 and then, if needed, the remaining sample 
 was ground in one to four stages of 3 min 
 each in the small mill to reduce it to 
 essentially 100 pet minus 48 mesh. The 
 size splits were chosen because mineral 
 liberation was good at 48 mesh and 
 because 200 mesh approaches the lower 
 practical limit of efficient separation 
 by gravity and electrodynamic process- 
 ing. The additional split at 100 mesh 
 gave closely sized feed for gravity 
 concentration. 
 
 The three products were passed sepa- 
 rately over a 2- by 4-ft laboratory shak- 
 ing table. The 48- by 100-mesh fraction 
 was fed to a sand deck, and the 100- by 
 200-mesh fraction and the minus 200-mesh 
 fraction were fed to a slime deck. A 
 finished high-grade table concentrate was 
 produced from each size fraction. De- 
 pending on the grade and separation char- 
 acteristics of the sample, a middlings 
 product, a tailings product, or both were 
 collected for further processing to im- 
 prove recovery. In the cases where a 
 middlings product was separated, barren 
 tailings were discarded. Only a high- 
 grade concentrate and tailings were pro- 
 duced from the minus 200-mesh fraction. 
 The minus 200-mesh concentrate contained 
 only the coarser, high-specific-gravity 
 particles of the size fraction. Several 
 of the samples had relatively high chro- 
 mite losses in the minus 200-mesh tail- 
 ings because tabling becomes less effec- 
 tive in separating very fine-sized parti- 
 cles. The water that discharged off the 
 tailings end of the table was dark brown, 
 an indication that it contained very fine 
 suspended chromite. Very fine chromite 
 settled out in the tailings discharge 
 tray. 
 
 Middlings products, and those tail- 
 ings products from tests where no mid- 
 dlings products were taken, were dried 
 and treated electrodynamically on a 
 laboratory-model high-tension separator. 
 A single layer of particles was fed onto 
 a 14-in rotor by a vibratory feeder. The 
 positions of the two electrodes were the 
 same for all of the tests. The first 
 
 electrode was oriented to give a combina- 
 tion pinning and lifting effect, and the 
 second electrode was oriented to give a 
 lifting effect. Chromite and other con- 
 ductors present were thrown from the ro- 
 tor, while the olivine, serpentine, and 
 other nonconductor gangue minerals were 
 pinned to the rotor. Rotor speed was 
 varied, and the splitters were adjusted 
 to produce good concentrate, middlings, 
 and tailings products. 
 
 The general procedure for the electro- 
 dynamic separation is shown in figure 2. 
 The dry feed was separated into a con- 
 centrate, middlings, and tailings. The 
 middlings were retreated in two or more 
 rougher steps. The concentrates from the 
 three rougher passes were combined, and a 
 cleaner step was done in which a cleaner 
 concentrate and cleaner tailings were 
 produced. The cleaner middlings were 
 combined with the cleaner concentrate. 
 The tailings from the three rougher 
 passes were combined, and a scavenger 
 step was done in which a scavenger con- 
 centrate and scavenger tailings were pro- 
 duced. The scavenger middlings were com- 
 bined with the scavenger tailings. In 
 industrial practice the scavenger concen- 
 trate, third rougher middlings, and 
 cleaner tailings would probably be com- 
 bined and recirculated to the head of the 
 electrodynamic separation circuit. 
 
 The procedure for electrodynamic sepa- 
 ration was modified to suit the samples. 
 
 Dry table middlings 
 
 I 
 First rougher electrodynamic separation 
 
 •Concentrate Middlings Tailings- 
 
 T 
 
 Second rougher electrodynamic separation 
 
 J I I 
 -Concentrate Middlings Tailings 
 
 — r~ 
 
 Thi-d rougher electrodynamic separation 
 J J —J— 
 
 -Concentrate Middlings Tailings 
 
 Cleaner electrodynamic separation Scavenger electrodynamic separation 
 I J J f— 
 
 Cleaner Cleaner Scavenger Scavenger 
 
 concentrate tailings concentrate tailings 
 
 FIGURE 2. - General procedure for the electrody- 
 namic separation step of the beneficiation procedure. 
 
Three rougher steps were impractical on 
 several middlings and tailings samples 
 that were relatively small; one or two 
 steps were sufficient. The cleaner and 
 scavenger steps were omitted on sev- 
 eral of the smaller samples. The minus 
 200-mesh table tailings were not treated 
 electrodynamically because the process is 
 not effective in that size range. 
 
 Electrodynamic separation was done pri- 
 marily to give an indication of the 
 increased recovery of chromite attain- 
 able from table middlings or tailings. 
 Optimum separation parameters were not 
 investigated. A limited number of vari- 
 ations in conditions were investigated 
 for each sample, and those that gave 
 good products, as determined visually, 
 were used. 
 
 A magnetic separation step was not in- 
 cluded in this process flowsheet , al- 
 though low-intensity wet magnetic separa- 
 tion was considered as a means to improve 
 the Cr:Fe ratio by removing magnetite. 
 The mineralogy of the samples indicated 
 that the table concentrates contained 
 2 to 15 pet magnetics as particles remov- 
 able with a hand magnet. Attempts to re- 
 move a magnetic fraction from several ta- 
 ble concentrates were ineffective with a 
 laboratory-model concurrent wet drum mag- 
 netic separator with a permanent magnet. 
 A very small percentage of the expected 
 weight of magnetics was removed. A 
 larger magnetic fraction could be removed 
 with a higher intensity magnetic field at 
 the expense of chromite recovery. 
 
 RESULTS AND DISCUSSION 
 
 The calculated composite chromite con- 
 centrates that were produced from the 
 lower Kanuti River and Caribou Mountain 
 ultramafics may be categorized in one of 
 the following groups :^ 
 
 1. High-chromium (metallurgical-grade) 
 chromite that contains a minimum of 
 46 pet Cr203 with a Cr:Fe ratio greater 
 than 2.0:1. 
 
 2. High-iron (chemical-grade) chromite 
 that contains 40 to 46 pet Cr20 3 with a 
 Cr:Fe ratio of 1.5:1 to 2.0:1. 
 
 3. High-aluminum (refractory-grade) 
 chromite that contains more than 20 pet 
 AI2O3 and more than 60 pet AI2O3 plus 
 Cr 2 3 . 
 
 4. Marginal chromite that meets either 
 the grade or Cr:Fe-ratio requirement for 
 one of the classifications above and very 
 nearly meets the other. 
 
 5. Submarginal chromite that fails to 
 meet the above classifications. 
 
 'Categories 1, 2, and 3 are from work 
 cited in footnote 4. 
 
 Table 4 summarizes the results of bene- 
 ficiation of the 11 samples using the 
 procedure in figure 1. Complete metal- 
 lurgical balances may be found in 
 tables A-l through A-ll in the appendix. 
 
 Samples A, D, and E were beneficiated 
 to produce high-chromium chromite concen- 
 trates. The best concentrate was pro- 
 duced from sample E. The grade was 53.8 
 pet Cr203 with a Cr:Fe ratio of 2.4:1, 
 and the chromium recovery was 87 pet. 
 Sample A was concentrated to 48.7 pet 
 Cr 2 3 with a Cr:Fe ratio of 2.2:1 and 
 64 pet chromium recovery. The grade of 
 the concentrate from sample D was 48.8 
 pet Cr 2 03 with chromium recovery of 81 
 pet and a Cr:Fe ratio of 2.0:1. 
 
 Four samples were beneficiated to pro- 
 duce high-iron or marginal high-iron 
 chromite concentrates. The grade of the 
 concentrate from sample G was 50.1 pet 
 0^03 , high enough to be considered a 
 high-chromium chromite, but the Cr:Fe 
 ratio was only 1.7:1; chromium recovery 
 was 89 pet. Sample H was concentrated to 
 44.7 pet Cr 2 3 with a Cr:Fe ratio of 
 1.5:1 and 87 pet chromium recovery. Con- 
 centrates from samples C and J met the 
 Cr:Fe ratio requirement, but they were 
 
TABLE 4. - Summary of the calculated composite concentrates from benef Iciation 
 of 11 chromite-bearing samples from the lower Kanuti River and Caribou 
 Mountain areas 
 
 Chromite 
 
 Wt-pct 
 
 
 
 Analysis, 
 
 pet 
 
 
 Cr recov- 
 ery, pet 
 
 Cr:Fe 
 
 classification 
 
 and sample 
 
 Cr 2 3 
 
 Fe 
 
 MgO 
 
 A1 2 3 
 
 Si0 2 
 
 S 
 
 P 
 
 ratio 
 
 High-chromium : 
 E 
 
 79.2 
 23.0 
 53.2 
 
 76.6 
 76.9 
 
 27.4 
 23.7 
 
 81.1 
 
 27.9 
 
 84.1 
 73.5 
 
 53.8 
 48.7 
 48.8 
 
 50.1 
 44.7 
 
 36.8 
 35.8 
 
 27.5 
 
 33.6 
 
 25.3 
 23.5 
 
 15.5 
 15.3 
 
 16.8 
 
 20.6 
 21.0 
 
 15.6 
 16.1 
 
 16.8 
 
 16.3 
 
 22.7 
 20.3 
 
 12.5 
 14.9 
 14.3 
 
 10.4 
 11.7 
 
 16.6 
 16.3 
 
 16.5 
 
 15.8 
 
 14.2 
 15.9 
 
 9.4 
 10.8 
 12.2 
 
 7.9 
 13.7 
 
 18.8 
 19.1 
 
 33.0 
 
 26.2 
 
 24.4 
 28.6 
 
 3.8 
 4.2 
 2.5 
 
 2.4 
 1.6 
 
 5.7 
 5.8 
 
 1.0 
 
 3.3 
 
 2.0 
 2.3 
 
 0.028 
 .020 
 .021 
 
 0.01 
 .05 
 .02 
 
 86.8 
 63.9 
 80.6 
 
 88.5 
 87.3 
 
 64.3 
 53.7 
 
 86.0 
 
 73.8 
 
 91.7 
 83.7 
 
 2.4 
 
 A 
 
 2.2 
 
 D 
 
 2.0 
 
 High-iron: 
 G 
 
 1.7 
 
 H 
 
 1.5 
 
 Marginal high- 
 iron: 
 C 
 
 1.6 
 
 J 
 
 1.5 
 
 High-aluminum: 
 I 
 
 1.1 
 
 Marginal high- 
 aluminum: F. 
 Subraarginal: 
 B 
 
 1.4 
 .8 
 
 
 .8 
 
 NOTE. — Absence of data indicates no analysis. 
 
 significantly below the grade requirement 
 of 40 pet Cr203. The metallurgical bal- 
 ances in tables A-3 and A-10 show that 
 the electrodynamic concentrates could 
 possibly be improved enough, with some 
 sacrifice in recovery, to raise the com- 
 posite grade to near 40 pet Cr 2 03» 
 
 Two samples were beneficiated to pro- 
 duce high-aluminum or marginal high- 
 aluminum chromite concentrates. The con- 
 centrate from sample I was a high- 
 aluminum product with a grade of 27.5 pet 
 Cr 2 03 and 33.0 pet Al 2 03 and a chromium 
 recovery of 86 pet. The concentrate from 
 sample F was a marginal high-aluminum 
 product with 33.6 pet Cr 2 3 and 26.2 pet 
 Al 2 03 with chromium recovery of 74 pet. 
 
 Concentrates from samples B and K had 
 Al 2 03 contents of more than 20 pet, but 
 the combination of Cr 2 03 and Al 2 03 was 
 significantly below 60 pet. The metal- 
 lurgical balances in tables A-2 and A-ll 
 show that the concentrates cannot be 
 upgraded enough to meet the marginal 
 
 high-aluminum classification. They were 
 classified as submarginal chromites. 
 
 The gravity concentration products from 
 each of the 11 samples were analyzed for 
 precious-metals content. Only the table 
 concentrates from samples B and G con- 
 tained platinum at a level above the min- 
 imum detection limit of 0.01 oz/ton. The 
 head analysis of sample B indicated the 
 presence of 0.039 oz/ton Pt. The calcu- 
 lated analysis of the composite concen- 
 trate was 0.022 oz/ton Pt , and the cal- 
 culated head was 0.021 oz/ton Pt. The 
 analyses indicate that the platinum is 
 not uniformly distributed in the rock and 
 that it may be associated with both the 
 chromium mineral and gangue. The head 
 analysis of sample G was less than 
 0.01 oz/ton Pt, and the calculated anal- 
 ysis of the composite concentrate was 
 0.01 oz/ton Pt. Examination of these 
 11 samples indicated that the chromite- 
 bearing areas of the lower Kanuti River 
 and Caribou Mountain ultramafics are not 
 significant resources for platinum. 
 
SUMMARY AND CONCLUSIONS 
 
 Eleven samples of chromite-bearing ma- 
 terials were collected from three ultra- 
 mafic bodies in the Caribou Mountain- 
 Melozitna ultramafic belt of central 
 Alaska. These samples were characterized 
 mineralogically and beneficiated to pro- 
 duce chromite concentrates. 
 
 The samples ranged from hard, unweath- 
 ered, massive chromite to chromite dis- 
 seminated in lenses and stringers. All 
 were peridotites or chromitites that con- 
 sisted essentially of variable amounts of 
 chromite or chromohercynite, olivine, and 
 serpentine. 
 
 A benef iciation process was designed to 
 treat the samples that included grinding 
 and sizing, gravity concentration, and 
 electrodynamic separation. Three high- 
 chromium (metallurgical-grade) chromite 
 concentrates, two high-iron (chemical- 
 grade) chromite concentrates, and one 
 high-aluminum (refractory-grade) chromite 
 
 concentrate were produced. Three other 
 concentrates were marginal, and two con- 
 centrates were submarginal. Recoveries 
 ranged from 54 to 92 pet ^203. 
 
 Potential platinum association with the 
 chromite was investigated. No platinum- 
 group minerals were observed in the min- 
 eralogical examinations , although in one 
 sample the calculated platinum content of 
 the gravity concentrate was 0.022 oz/ton. 
 The platinum content of the other concen- 
 trates was at or below the detection lim- 
 it of 0.01 oz/ton. 
 
 This investigation was a preliminary 
 evaluation of the chromite and platinum 
 resource potential of the lower Kanuti 
 River and Caribou Mountain ultramafic 
 bodies. Although all of the samples were 
 high-graded from surface exposures , they 
 indicate that the areas may be signifi- 
 cant chromium resources. They do not in- 
 dicate good platinum resources. 
 
10 
 
 APPENDIX. —METALLURGICAL BALANCES 
 TABLE A-l. - Gravity concentration and electrodynamic separation of sample A 
 
 Product' 
 
 Wt-pct 
 
 Cr 2 3 
 
 Fe 
 
 Analysis, pet 
 
 MgO 
 
 A1 2 3 
 
 SiO, 
 
 Cr distri- 
 bution, pet 
 
 Cr:Fe 
 ratio 
 
 48 by 100 mesh: 
 
 Table concentrate* 
 
 Table middlings 
 
 Electrodynamic separation: 
 Cleaner concentrate* .... 
 
 Cleaner tailings 
 
 3d rougher middlings.... 
 Scavenger concentrate... 
 
 Scavenger tailings 
 
 Table tailings 
 
 100 by 200 mesh: 
 
 Table concentrate* 
 
 Table middlings 
 
 Electrodynamic separation: 
 Cleaner concentrate*.... 
 
 Cleaner tailings 
 
 2d rougher middlings.... 
 Scavenger concentrate... 
 
 Scavenger tailings 
 
 Table tailings 
 
 Minus 200 mesh: 
 
 Table concentrate* 
 
 Table tailings 
 
 Composite or total 
 
 Calculated composite con- 
 
 2.7 
 32.6 
 
 12.1 
 
 .4 
 3.7 
 
 .6 
 15.8 
 11.0 
 
 3.4 
 13.6 
 
 1.9 
 
 .3 
 
 .6 
 
 .4 
 
 10.4 
 
 8.3 
 
 2.9 
 
 25.5 
 
 51.2 
 24.7 
 
 46.3 
 35.4 
 36.2 
 38.0 
 4.9 
 4.1 
 
 52.9 
 13.5 
 
 48.1 
 43.0 
 33.0 
 43.3 
 3.7 
 2.4 
 
 51.4 
 9.1 
 
 16.0 
 10.1 
 
 14.6 
 12.0 
 12.1 
 12.3 
 5.9 
 5.5 
 
 15.8 
 7.6 
 
 15.4 
 13.7 
 12.4 
 14.1 
 5.7 
 5.1 
 
 16.7 
 6.5 
 
 13.2 
 31.3 
 
 16.6 
 
 11.0 
 6.6 
 
 10.2 
 
 13.3 
 42.8 
 
 13.7 
 
 11.4 
 3.1 
 
 11.3 
 
 12.4 
 
 11.9 
 
 2.1 
 21.7 
 
 5.9 
 16.0 
 13.9 
 13.4 
 36.1 
 36.7 
 
 2.5 
 30.5 
 
 3.9 
 
 8.0 
 
 15.2 
 
 7.3 
 
 37.5 
 
 38.1 
 
 1.7 
 32.5 
 
 0.016 
 
 .022 
 
 0.16 
 
 .02 
 
 .018 
 
 .023 
 
 .01 
 
 .02 
 
 .014 
 
 .11 
 
 100.0 
 
 17.5 
 
 8.5 
 
 26.9 
 
 centrate 
 
 23.0 
 
 48.7 15.3 14.9 10.8 
 
 4.3 
 
 020 .05 
 
 7.9 
 
 32.0 
 .8 
 7.6 
 1.3 
 4.4 
 2.6 
 
 10.3 
 
 5.2 
 .7 
 1.1 
 1.0 
 2.2 
 1.1 
 
 8.5 
 13.3 
 
 100.0 
 
 63.9 
 
 2.2 
 
 2.2 
 
 2.3 
 
 2.1 
 
 2.1 
 
 2.2 
 
 Products with asterisks have been mathematically combined to give the calculated composite 
 
 concentrate. 
 
 TABLE A-2. - Gravity concentration and electrodynamic separation of sample B 
 
 Product 1 
 
 Wt-pct 
 
 Cr 2 3 
 
 Analysis, pet 
 
 Fe 
 
 MgO 
 
 A1 2 3 
 
 SiO, 
 
 Cr distri- 
 bution, pet 
 
 Cr:Fe 
 ratio 
 
 35.2 
 13.3 
 
 9.3 
 
 .2 
 1.3 
 
 .2 
 2.3 
 
 20.4 
 4.2 
 
 1.3 
 1.7 
 1.2 
 
 17.9 
 9.0 
 
 25.3 
 19.6 
 
 23*5 
 11.0 
 16.5 
 20.3 
 2.4 
 
 26.3 
 14.8 
 
 23.8 
 
 15.8 
 
 2.2 
 
 24.8 
 14.4 
 
 23.0 
 20.0 
 
 22.0 
 14.3 
 17.4 
 20.6 
 8.8 
 
 22.6 
 16.5 
 
 22.6 
 
 17.3 
 
 8.0 
 
 22.6 
 15.6 
 
 12.9 
 
 15.3 
 
 23.6 
 
 27.2 
 
 15.1 
 
 14.8 
 
 15.2 
 
 23.0 
 
 27.8 
 
 26.0 
 
 1.5 
 9.3 
 
 2.6 
 21.0 
 13.1 
 
 7.3 
 33.6 
 
 2.0 
 16.2 
 
 2.5 
 13.9 
 33.8 
 
 2.8 
 17.1 
 
 100.0 
 
 23.1 
 
 21.4 
 
 4.9 
 
 84.1 
 
 25.3 
 
 22.7 14.2 24.4 
 
 2.0 
 
 100.0 
 
 91.7 
 
 0.8 
 
 48 by 100 mesh: 
 
 Table concentrate* 
 
 Table tailings 
 
 Electrodynamic separation: 
 
 Cleaner concentrate* 
 
 Cleaner tailings 
 
 3d rougher middlings 
 
 Scavenger concentrate 
 
 Scavenger tailings 
 
 100 by 200 mesh: 
 
 Table concentrate* 
 
 Table tailings 
 
 Electrodynamic separation: 
 
 Concentrate* 
 
 Middlings 
 
 Tailings 
 
 Minus 200 mesh: 
 
 Table concentrate* 
 
 Table tailings 
 
 Composite or total 
 
 Calculated composite con- 
 
 centrate 1 
 
 Products with asterisks have been mathematically combined to give the calculated composite 
 concentrate. 
 
 38.5 
 
 9.5 
 .1 
 .9 
 .2 
 .2 
 
 23.2 
 
 1.3 
 
 1.2 
 .1 
 
 19.2 
 5.6 
 
 .8 
 
TABLE A-3. - Gravity concentration and electrodynamic separation of sample C 
 
 11 
 
 Product' 
 
 Wt-pct 
 
 Cr 2 3 
 
 Analysis, pet 
 
 Fe 
 
 MgO 
 
 A1 2 3 
 
 SiO- 
 
 Cr distri- 
 bution, pet 
 
 Cr:Fe 
 ratio 
 
 14.9 
 25.6 
 
 19.0 
 
 20.5 
 12.4 
 
 16.7 
 
 15.0 
 32.6 
 
 16.1 
 
 20.7 
 9.7 
 
 18.4 
 
 15.0 
 
 20.3 
 
 2.7 
 18.5 
 
 10.2 
 17.9 
 14.3 
 17.8 
 37.3 
 36.1 
 
 2.1 
 25.7 
 
 5.6 
 12.4 
 15.5 
 
 9.8 
 37.3 
 38.7 
 
 2.2 
 34.7 
 
 100.0 
 
 15.7 
 
 9.2 
 
 26.1 
 
 27.4 
 
 36.8 
 
 15.6 16.6 18.8 
 
 5.7 
 
 17.2 
 
 20.9 
 
 .6 
 
 9.9 
 
 .8 
 
 2.0 
 
 4.4 
 
 10.4 
 
 7.2 
 .8 
 .5 
 1.4 
 1.9 
 1.3 
 
 8.6 
 12.1 
 
 100.0 
 
 64.3 
 
 1.7 
 
 1.5 
 
 48 by 100 mesh: 
 
 Table concentrate* 
 
 Table middlings 
 
 Electrodynamic separation: 
 
 Cleaner concentrate* 
 
 Cleaner tailings 
 
 3d rougher middlings 
 
 Scavenger concentrate 
 
 Scavenger tailings 
 
 Table tailings 
 
 100 by 200 mesh: 
 
 Table concentrate* 
 
 Table middlings 
 
 Electrodynamic separation: 
 
 Cleaner concentrate* 
 
 Cleaner tailings 
 
 3d rougher middlings 
 
 Scavenger concentrate 
 
 Scavenger tailings 
 
 Table tailings 
 
 Minus 200 mesh: 
 
 Table concentrate* 
 
 Table tailings 
 
 Composite or total 
 
 Calculated composite concen- 
 
 trate 1 
 
 ^Products with asterisks have been mathematically combined to give the calculated composite 
 concentrate. 
 
 6.7 
 22.3 
 
 10.4 
 
 .4 
 
 5.3 
 
 .5 
 
 5.7 
 
 16.7 
 
 3.9 
 10.5 
 
 3.1 
 
 .4 
 
 .3 
 
 .7 
 
 6.0 
 
 8.4 
 
 3.3 
 28.2 
 
 40.3 
 23.2 
 
 31.4 
 24.1 
 29.4 
 24.1 
 5.4 
 4.2 
 
 41.8 
 16.8 
 
 36.2 
 29.4 
 26.3 
 32.3 
 5.0 
 2.4 
 
 41.1 
 6.7 
 
 16.1 
 11.8 
 
 14.4 
 11.8 
 12.0 
 11.7 
 6.2 
 5.9 
 
 16.3 
 9.8 
 
 16.2 
 13.6 
 13.1 
 14.1 
 6.3 
 4.7 
 
 17.3 
 6.6 
 
 1.8 
 
 1.5 
 
 1.6 
 
 1.6 
 
 TABLE A-4. - Gravity concentration and electrodynamic separation of sample D 
 
 Product 1 
 
 Wt-pct 
 
 Analysis, pet 
 
 Cr distri- 
 bution, pet 
 
 Cr:Fe 
 
 
 Cr 2 3 
 
 Fe 
 
 MgO 
 
 A1 2 3 
 
 Si0 2 
 
 S 
 
 P 
 
 ratio 
 
 48 by 100 mesh: 
 
 
 
 
 
 
 
 
 
 
 
 
 10.6 
 27.3 
 
 49.7 
 41.7 
 
 17.1 
 15.1 
 
 13.9 
 18.8 
 
 12.6 
 10.5 
 
 1.8 
 8.0 
 
 0.019 
 
 0.01 
 
 16.3 
 
 2.0 
 
 
 
 Electrodynamic separation: 
 
 
 
 
 
 
 
 
 
 
 
 Cleaner concentrate* .... 
 
 19.7 
 
 47.6 
 
 16.5 
 
 14.7 
 
 12.1 
 
 2.9 
 
 .020 
 
 .03 
 
 29.1 
 
 2.0 
 
 
 .3 
 
 39.5 
 
 14.8 
 
 
 
 9.0 
 
 
 
 .4 
 
 
 3d rougher middlings.... 
 
 2.6 
 
 46.6 
 
 16.0 
 
 
 
 3.9 
 
 
 
 3.8 
 
 
 Scavenger concentrate. . . 
 
 .6 
 
 42.4 
 
 15.1 
 
 
 
 6.8 
 
 
 
 .8 
 
 
 
 4.1 
 
 6.9 
 
 6.7 
 
 
 
 33.8 
 
 
 
 .9 
 
 
 
 8.5 
 
 4.2 
 
 5.7 
 
 
 
 34.8 
 
 
 
 1.1 
 
 
 100 by 200 mesh: 
 
 
 
 
 
 
 
 
 
 
 
 
 6.4 
 12.2 
 
 50.6 
 34.2 
 
 17.1 
 13.2 
 
 13.8 
 25.0 
 
 12.4 
 8.6 
 
 1.5 
 13.9 
 
 .018 
 
 .01 
 
 10.0 
 
 2.0 
 
 
 
 Electrodynamic separation: 
 
 
 
 
 
 
 
 
 
 
 
 Cleaner concentrate* .... 
 
 7.1 
 
 49.1 
 
 16.6 
 
 14.0 
 
 11.8 
 
 2.5 
 
 .024 
 
 .02 
 
 10.8 
 
 2.0 
 
 
 .4 
 
 40.0 
 
 13.6 
 
 
 
 11.7 
 
 
 
 .5 
 
 
 2d rougher middlings .... 
 
 .4 
 
 36.4 
 
 14.5 
 
 
 
 9.1 
 
 
 
 .4 
 
 
 Scavenger concentrate... 
 
 .3 
 
 44.0 
 
 15.2 
 
 
 
 5.9 
 
 
 
 .4 
 
 
 
 4.0 
 
 6.2 
 
 6.6 
 
 
 
 34.8 
 
 
 
 .8 
 
 
 
 5.1 
 
 2.3 
 
 5.1 
 
 
 
 35.7 
 
 
 
 .4 
 
 
 Minus 200 mesh: 
 
 
 
 
 
 
 
 
 
 
 
 
 9.4 
 20.5 
 
 49.3 
 15.5 
 
 16.8 
 8.5 
 
 14.5 
 
 12.3 
 
 2.9 
 26.7 
 
 .026 
 
 .01 
 
 14.4 
 9.9 
 
 2.0 
 
 
 
 
 100.0 
 
 32.2 
 
 12.7 
 
 
 
 14.6 
 
 
 
 100.0 
 
 
 Calculated composite con- 
 
 
 
 
 
 
 
 
 
 
 
 
 53.2 
 
 48.8 
 
 16.8 
 
 14.3 
 
 12.2 
 
 2.5 
 
 .021 
 
 .02 
 
 80.6 
 
 2.0 
 
 1 Products with asterisks ha 
 
 ive beer 
 
 i ma the 
 
 matica 
 
 lly combinec 
 
 to g 
 
 ive tl 
 
 le cs 
 
 ilculated con 
 
 iposite 
 
 concentrate. 
 
 
 
 
 
 
 
 
 
 
 
12 
 
 TABLE A-5. - Gravity concentration and electrodynaraic separation of sample E 
 
 Product 1 
 
 48 by 100 mesh: 
 
 Table concentrate* 
 Table tailings. . .. 
 Elect rodynamic 
 separation: 
 Cleaner con- 
 centrate*. . . . 
 Cleaner tail- 
 ings 
 
 3d rougher 
 
 middlings. . . . 
 Rougher tail- 
 ings 
 
 100 by 200 mesh: 
 Table concentrate* 
 Table tailings .... 
 Elect rodynamic 
 separation: 
 Concentrate* . . 
 
 Middlings 
 
 Tailings 
 
 Minus 200 mesh: 
 
 Table concentrate* 
 Table tailings.... 
 Composite or 
 
 total 
 
 Calculated com- 
 posite concen- 
 A 
 
 Wt-pct 
 
 Cr 2 3 
 
 Fe 
 
 Analysis, pet 
 
 MgO 
 
 A1 2 3 Si0 2 
 
 Cr distri- 
 bution, pet 
 
 Cr:Fe 
 ratio 
 
 42 
 7 
 
 1 
 
 1 
 
 16 
 3 
 
 .1 
 .8 
 
 .5 
 
 .1 
 
 .6 
 
 .6 
 
 .2 
 .5 
 
 16 
 14 
 
 .2 
 .6 
 .7 
 
 .2 
 .2 
 
 53.8 
 34.3 
 
 47.1 
 
 36.8 
 
 28.1 
 
 8.0 
 
 55.0 
 24.3 
 
 32.4 
 
 28.4 
 
 5.5 
 
 55.1 
 35.5 
 
 15.5 
 10.7 
 
 14.0 
 
 11.4 
 
 9.1 
 
 4.4 
 
 15.6 
 8.2 
 
 10.6 
 9.5 
 3.5 
 
 15.8 
 11.1 
 
 12.7 
 
 14.9 
 
 9.5 
 
 8.7 
 
 12.4 
 
 23.3 
 
 11.3 
 
 10.1 
 
 6.3 
 
 8.5 
 
 3.9 
 16.9 
 
 7.3 
 
 14.2 
 
 20.2 
 
 34.7 
 
 3.2 
 23.0 
 
 17.6 
 19.9 
 36.0 
 
 3.0 
 15.9 
 
 0.029 
 
 ,039 
 
 0.01 
 
 .02 
 
 .025 
 
 .082 
 
 .023 
 
 .02 
 
 .20 
 
 .01 
 
 46.1 
 
 4.3 
 
 .1 
 
 .9 
 
 .3 
 
 18.1 
 
 .1 
 
 1.5 
 
 .1 
 
 18.2 
 10.3 
 
 2.4 
 
 2.3 
 
 2.4 
 
 2.1 
 
 2.4 
 
 100.0 
 
 49.1 
 
 14.3 
 
 6.9 
 
 100.0 
 
 trate 
 
 79.2 
 
 53.8 15.5 12.5 9.4 
 
 3.8 
 
 .028 .01 
 
 86.8 
 
 2.4 
 
 Products with asterisks 
 composite concentrate. 
 
 have been mathematically combined to give the calculated 
 
 TABLE A-6. - Gravity concentration and elect rodynamic separation of sample F 
 
 Product 
 
 Wt-pct 
 
 Cr 2 3 
 
 Analysis, pet 
 
 Fe 
 
 MgO 
 
 A1 2 3 
 
 SiO- 
 
 Cr distri- 
 bution, pet 
 
 Cr:Fe 
 ratio 
 
 100 by 200 mesh: 
 
 Table concentrate*... 
 
 Table tailings 
 
 Electrodynamic sep- 
 aration: 
 
 Concentrate* 
 
 Middlings 
 
 Tailings 
 
 Minus 200 mesh: 
 
 Table concentrate* ... 
 
 Table tailings 
 
 Composite or total. 
 Calculated compo- 
 
 18.3 
 34.5 
 
 1.4 
 
 5.8 
 
 27.3 
 
 8.2 
 39.0 
 
 33.9 
 4.2 
 
 24.4 
 
 10.3 
 
 1.9 
 
 34.2 
 5.6 
 
 15.6 
 7.4 
 
 15.4 
 9.7 
 6.4 
 
 18.1 
 7.9 
 
 15.9 
 
 19.9 
 
 15.0 
 
 27.9 
 
 23.5 
 
 22.9 
 
 3.0 
 27.7 
 
 8.1 
 21.7 
 29.4 
 
 3.3 
 26.3 
 
 49.0 
 
 2.7 
 4.7 
 4.1 
 
 22.1 
 17.4 
 
 1.5 
 
 1.1 
 
 1.3 
 
 100.0 
 
 12.7 
 
 9.9 
 
 20.5 
 
 100.0 
 
 site concentrate 
 
 27.9 
 
 33.6 
 
 16.3 15.8 26.2 
 
 3.3 
 
 73.8 
 
 1.4 
 
 Products with asterisks have 
 composite concentrate. 
 
 been mathematically combined to give the calculated 
 
13 
 
 TABLE A-7. - Gravity concentration and electrodynamic separation of sample G 
 
 Product ' 
 
 Wt-pct 
 
 Analysis, 
 
 pet 
 
 
 
 Cr distri- 
 bution, pet 
 
 Cr:Fe 
 
 
 Cr 2 3 
 
 Fe 
 
 MgO 
 
 A1 2 3 
 
 S10 2 
 
 S 
 
 P 
 
 ratio 
 
 48 by 100 mesh: 
 
 34.4 
 6.1 
 
 2.2 
 
 .1 
 
 2.3 
 1.5 
 
 21.6 
 4.8 
 
 .8 
 1.1 
 2.9 
 
 17.6 
 15.5 
 
 49.5 
 22.7 
 
 42.8 
 31.6 
 
 18.6 
 4.3 
 
 51.0 
 17.4 
 
 41.7 
 
 32.7 
 
 3.1 
 
 51.6 
 26.2 
 
 20.4 
 12.3 
 
 19.0 
 15.0 
 
 11.0 
 6.5 
 
 20.7 
 10.6 
 
 18.3 
 
 15.5 
 
 6.9 
 
 21.1 
 13.3 
 
 10.7 
 13.3 
 
 10.2 
 14.1 
 
 9.4 
 
 7.4 
 7.8 
 
 8.3 
 7.9 
 
 8.2 
 
 2.6 
 
 21.4 
 
 7.3 
 15.8 
 
 24.3 
 34.6 
 
 2.0 
 25.4 
 
 7.7 
 14.2 
 33.4 
 
 1.7 
 19.0 
 
 0.020 
 .041 
 
 .018 
 .040 
 
 .017 
 
 0.01 
 .13 
 
 .01 
 .03 
 
 .01 
 
 39.2 
 
 2.2 
 .1 
 
 1.0 
 .1 
 
 25.4 
 
 .8 
 .8 
 .2 
 
 20.9 
 9.3 
 
 1.7 
 
 Electrodynamic separation: 
 Cleaner concentrate* .... 
 
 2d rougher middlings 
 plus scavenger concen- 
 
 1.5 
 
 100 by 200 mesh: 
 
 1.7 
 
 Electrodynamic separation: 
 
 1.6 
 
 
 
 Minus 200 mesh: 
 
 1.7 
 
 
 
 
 100.0 
 
 43.4 
 
 18.6 
 
 
 
 7.0 
 
 
 
 100.0 
 
 
 Calculated composite con- 
 
 76.6 
 
 50.1 
 
 20.6 
 
 10.4 
 
 7.9 
 
 2.4 
 
 .020 
 
 .01 
 
 88.5 
 
 1.7 
 
 Products with asterisks have been mathematically combined to give the calculated composite 
 
 concentrate. 
 
 2 2d rougher middlings, 95 pet; scavenger concentrate, 5 pet. 
 
 TABLE A-8. - Gravity concentration and electrodynamic separation of sample H 
 
 Product 1 
 
 Wt-pct 
 
 Analysis, pet 
 
 Cr distri- 
 bution, pet 
 
 Cr:Fe 
 
 
 Cr 2 3 
 
 Fe 
 
 MgO 
 
 A1 2 3 
 
 Si0 2 
 
 ratio 
 
 48 by 100 mesh: 
 
 39.8 
 5.0 
 
 1.2 
 .6 
 
 1.0 
 2.2 
 
 20.7 
 4.1 
 
 .3 
 
 .9 
 
 2.9 
 
 14.9 
 15.5 
 
 43.8 
 22.4 
 
 39.2 
 29.5 
 
 34.5 
 5.3 
 
 46.0 
 14.3 
 
 37.6 
 
 29.7 
 
 7.6 
 
 45.7 
 25.0 
 
 20.8 
 13.0 
 
 19.5 
 15.7 
 
 17.5 
 6.4 
 
 21.3 
 9.5 
 
 18.9 
 
 16.0 
 
 6.9 
 
 21.2 
 14.0 
 
 11.9 
 13.6 
 
 11.8 
 15.3 
 
 10.6 
 
 12.4 
 11.9 
 
 15.0 
 12.4 
 
 15.7 
 
 1.8 
 19.2 
 
 5.3 
 13.2 
 
 8.9 
 33.0 
 
 1.2 
 26.5 
 
 6.3 
 12.5 
 31.5 
 
 1.1 
 16.9 
 
 44.3 
 
 1.2 
 .4 
 
 .9 
 .3 
 
 24.2 
 
 .3 
 .7 
 .6 
 
 17.3 
 9.8 
 
 1.4 
 
 
 
 Electrodynamic separation: 
 
 1.4 
 
 3d rougher middlings plus 
 
 
 100 by 200 mesh: 
 
 1.5 
 
 Electrodynamic separation: 
 
 1.4 
 
 Middlings 
 
 
 
 
 Minus 200 mesh: 
 
 1.5 
 
 
 
 
 100.0 
 
 39.4 
 
 19.1 
 
 
 
 5.8 
 
 100.0 
 
 
 Calculated composite concen- 
 
 76.9 
 
 44.7 
 
 21.0 
 
 11.7 
 
 13.7 
 
 1.6 
 
 87.3 
 
 1.5 
 
 Products with asterisks have been mathematically combined to give the calculated composite 
 
 ; scavenger concentrate, 7 pet. 
 
 concentrate. 
 
 2 3d rougher middlings, 93 pet 
 
14 
 
 TABLE A-9. - Gravity concentration and electrodynamic separation of sample I 
 
 Product 1 
 
 Wt-pct 
 
 Analysis, pet 
 
 Cr distri- 
 bution, pet 
 
 Cr:Fe 
 
 Cr 2 3 
 
 Fe 
 
 MgO 
 
 A1 2 3 
 
 Si0 2 
 
 ratio 
 
 48 by 100 mesh: 
 
 47.4 
 6.4 
 
 .8 
 3.9 
 
 1.7 
 
 19.4 
 2.5 
 
 .5 
 1.0 
 1.0 
 
 13.0 
 11.3 
 
 26.7 
 17.8 
 
 24.6 
 
 22.8 
 
 2.8 
 
 29.2 
 17.1 
 
 25.7 
 
 21.9 
 
 4.2 
 
 28.1 
 21.6 
 
 16.8 
 12.3 
 
 16.0 
 
 14.9 
 
 4.1 
 
 16.7 
 11.6 
 
 16.6 
 
 14.8 
 
 5.1 
 
 17.1 
 14.6 
 
 16.5 
 17.4 
 
 16.7 
 16.3 
 
 16.1 
 
 32.5 
 31.5 
 
 34.5 
 32.9 
 
 32.5 
 
 1.0 
 11.5 
 
 3.2 
 
 5.5 
 
 28.7 
 
 1.1 
 13.5 
 
 1.9 
 
 6.4 
 
 28.5 
 
 .7 
 9.3 
 
 48.8 
 
 .8 
 
 3.4 
 
 .2 
 
 21.8 
 
 .5 
 .8 
 .2 
 
 14.1 
 9.4 
 
 1.1 
 
 Electrodynamic separation: 
 
 1.0 
 
 100 by 200 mesh: 
 
 1.2 
 
 
 
 Electrodynamic separation: 
 
 1.1 
 
 
 
 Minus 200 mesh: 
 
 1.1 
 
 Calculated composite con- 
 
 
 100.0 
 
 26.0 
 
 16.1 
 
 
 
 2.9 
 
 100.0 
 
 
 81.1 
 
 27.5 
 
 16.8 
 
 16.5 
 
 33.0 
 
 1.0 
 
 86.0 
 
 1.1 
 
 Products with asterisks have 
 site concentrate. 
 
 been ma 
 
 themati 
 
 cally 
 
 combined to give the 
 
 calculated compo- 
 
 TABLE A-10. - Gravity concentration and electrodynamic separation of sample J 
 
 Product 
 
 48 by 100 mesh: 
 
 Table concentrate* 
 
 Table middlings 
 
 Electrodynamic separation: 
 Cleaner concentrate* .... 
 
 Cleaner tailings 
 
 3d rougher middlings.... 
 Scavenger concentrate... 
 
 Scavenger tailings 
 
 Table tailings 
 
 100 by 200 mesh: 
 
 Table concentrate* 
 
 Table middlings 
 
 Electrodynamic separation: 
 Cleaner concentrate* .... 
 
 Cleaner tailings 
 
 2d rougher middlings.... 
 
 Rougher tailings 
 
 Table tailings 
 
 Minus 200 mesh: 
 
 Table concentrate* 
 
 Table tailings 
 
 Composite or total 
 
 Calculated composite con- 
 
 centrate 
 
 Wt-pct 
 
 4.9 
 21.7 
 
 11.1 
 
 .5 
 
 5.2 
 
 .8 
 
 4.1 
 
 16.4 
 
 3.8 
 13.0 
 
 2.5 
 .5 
 1.2 
 8.8 
 6.9 
 
 1.4 
 31.9 
 
 100.0 
 
 Products with asterisks have 
 site concentrate. 
 
 Cr 2 3 
 
 39.5 
 25.7 
 
 32.6 
 27.3 
 25.9 
 28.9 
 9.5' 
 5.4 
 
 39.0 
 15.5 
 
 35.8 
 
 31.3 
 
 24.6 
 
 7.8 
 
 2.1 
 
 39.9 
 9.5 
 
 15.8 
 
 23.7 35.8 16.1 16.3 
 
 Analysis, pet 
 
 Fe 
 
 16.8 
 13.0 
 
 15.2 
 13.9 
 11.8 
 14.0 
 7.4 
 6.4 
 
 17.3 
 10.2 
 
 16.6 
 
 15.0 
 
 12.9 
 
 7.5 
 
 4.9 
 
 17.3 
 7.8 
 
 9.7 
 
 MgO 
 
 14.5 
 23.0 
 
 18.1 
 
 14.0 
 32.2 
 
 16.0 
 
 15.0 
 
 A1 2 3 Si0 2 
 
 20.7 
 11.4 
 
 17.3 
 
 21.3 
 8.8 
 
 20.2 
 
 20.3 
 
 19.1 
 
 2.4 
 15.9 
 
 8.9 
 14.1 
 17.1 
 12.5 
 33.6 
 34.9 
 
 2.2 
 26.1 
 
 5.2 
 
 9.7 
 
 16.9 
 
 34.5 
 
 38.5 
 
 3.4 
 32.3 
 
 25.8 
 
 5.8 
 
 Cr distri- 
 bution, pet 
 
 12.2 
 
 22.9 
 .9 
 8.5 
 1.5 
 2.5 
 5.6 
 
 9.4 
 
 5.7 
 1.0 
 1.9 
 4.3 
 .9 
 
 3.5 
 19.2 
 
 100.0 
 
 53.7 
 
 Cr:Fe 
 ratio 
 
 1.6 
 
 1.5 
 
 1.5 
 
 1.5 
 
 1.6 
 
 1.5 
 
 been mathematically combined to give the calculated compo- 
 
15 
 
 TABLE A-ll. - Gravity concentration and electrodynamic separation of sample K 
 
 Product 1 
 
 Wt-pct 
 
 Analysis, pet 
 
 Cr 2 03 Fe MgO AI2O3 
 
 SiO- 
 
 Cr distri- 
 bution, pet 
 
 Cr:Fe 
 ratio 
 
 48 by 100 mesh: 
 
 Table concentrate* 
 
 Table tailings 
 
 Electrodynamic separa- 
 tion: 
 Cleaner concentrate*.. 
 
 Cleaner tailings 
 
 3d rougher middlings.. 
 Scavenger concentrate. 
 Scavenger tailings .... 
 100 by 200 mesh: 
 
 Table concentrate* 
 
 Table tailings 
 
 Electrodynamic separa- 
 tion: 
 Cleaner concentrate*.. 
 
 Cleaner tailings 
 
 3d rougher middlings.. 
 Scavenger concentrate. 
 Scavenger tailings .... 
 Minus 200 mesh: 
 
 Table concentrate* 
 
 Table tailings 
 
 Composite or total 
 
 Calculated composite 
 
 concentrate 
 
 39.4 
 10.5 
 
 5.8 
 .1 
 
 1.9 
 .2 
 
 2.5 
 
 16.4 
 7.4 
 
 4.0 
 .2 
 .3 
 .2 
 
 2.7 
 
 7.9 
 18.4 
 
 100.0 
 
 73.5 
 
 23.7 
 14.9 
 
 22.9 
 16.8 
 
 9.7 
 19.7 
 
 2.0 
 
 23.2 
 
 14.6 
 
 22.8 
 17.8 
 11.0 
 19.3 
 2.2 
 
 24.8 
 15.8 
 
 20.4 
 15.9 
 
 19.7 
 16.6 
 12.8 
 18.0 
 8.4 
 
 20.3 
 15.7 
 
 20.0 
 17.2 
 14.4 
 18.0 
 8.5 
 
 20.8 
 15.8 
 
 16.0 
 
 16.7 
 
 28.5 
 
 29.8 
 
 16.3 
 
 15.7 
 
 29.2 
 
 30.1 
 
 14.2 
 
 32.0 
 
 2.3 
 14.3 
 
 3.4 
 12.1 
 22.4 
 
 8.1 
 33.4 
 
 2.5 
 14.9 
 
 2.8 
 10.3 
 20.1 
 
 8.0 
 33.2 
 
 1.3 
 13.9 
 
 20.7 
 
 18.7 
 
 6.6 
 
 23.5 20.3 15.9 29.2 
 
 2.4 
 
 45.0 
 
 6.4 
 .1 
 .9 
 .2 
 .2 
 
 18.4 
 
 4.4 
 .2 
 .2 
 .2 
 .3 
 
 9.5 
 
 14.0 
 
 100.0 
 
 83.7 
 
 0.8 
 
 .8 
 
 .8 
 
 .8 
 
 Products with asterisks have been mathematically combined to give the calculated 
 
 composite concentrate. 
 
 INT.-BU.OF MINES.PGH..PA. 26786 
 


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