TN 295 .U4 *"()* 'o> '^O v ; >°*+ \/ %^-*y v^v' ^v^v v* : ^v"' v^v 'Ao' S* % n - • ©finis * ax ^* o^/J&aF * V «>•, • *0f ^y A* "** ,1> ^ ^ o; ^>* A K # °v^"-V » ^ -ov^ :^»^*- ^o^ r-^iK: -ov* A* \^.^A o^ r o»o, -^o A % • ^ ** •j$M/ih\ ^ > •fife'- ^ *+ *. \x\\vi_«///>^ * - » tsx/fn m\\\\ — ■■ wwv" — ^/x^y — \ x A V ^ * A. % ^ "^ ' A v ' *% ♦^T» A j* A" 0" 0, *q ^oV" i • o, c> * ^. ^ % \a° ' V <>i* r •iWA\ ^ .^ /tfte*. ♦*..*♦ .v&Ma;-. V,^ /<»'•. ^^ .-is«.-. %. t ^ /J IC 9023 Bureau of Mines Information Circular/1985 Bulk Mineralogy and Geochemistry of Selected Alaskan Chromian Spinel Samples By William S. Roberts UNITED STATES DEPARTMENT OF THE INTERIOR CD C 3J m > C Tgi 4f/NES 75TH A^ ZiU^ M fa<%w>j' u ^ \ nformation Circular) 9023 r\ Bulk Mineralogy and Geochemistry of Selected Alaskan Chromian Spinel Samples By William S. Roberts UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary BUREAU OF MINES Robert C. Horton, Director -^5 U4 c\0& Library of Congress Cataloging in Publication Data: Roberts, William S Bulk mineralogy and geochemistry of selected Alaskan chromian spinel samples. (Information circular / United States Department of the Interior, Bureau of Mines ; 9023). Bibliography: p. 9. Supt. of Docs, no.: I 28.27:9023. 1. Spinel— Alaska— Composition. 2. Chromite — Alaska— Composi- tion. I. Title. II. Series: Information circular (United States. Bu- reau of Mines) ; 9023. TN295.U4 TQE39LS681 622s T549\ 5261 84-600362 CONTENTS Page Abstract 1 Introduction 2 ^- Acknowledgments 2 Samples 2 2, and NiO, have lower average amounts of FeO and Cr 2 03, and exhibit greater dispersion in values. Considerable mineralogical variability of chromian spinel exists be- tween and within individual Alaskan chromite-bearing ultramafic com- plexes. Of 34 samples analyzed, 25 samples are magnesiochromite, 5 are chromite, 3 are spinel, and 1 is hercynite. As a group the inte- rior Alaska samples have a smaller average unit cell dimension than the Chugach group of samples. The chemical and mineralogical differences between the two groups of samples can be attributed to different genetic histories and may have implications for locating chromian spinel deposits amenable to standard benef iciating techniques. Physical scientist, Alaska Field Operations Center, Bureau of Mines, Juneau, AK. INTRODUCTION This report summarizes mineralogical and geochemical work done on samples col- lected during field investigations of Alaskan chromite occurrences. Field work assessing chromite deposits, as part of a critical and strategic minerals program, began in 1981 by the Bureau of Mines Alaska Field Operation Center (AFOC), and several deposits have recently been de- scribed (_6-_7> 11) .2 Benef iciation stud- ies of chromian spinel samples have been done by the Bureau's Albany Research Cen- ter (ALRC) (3-A)- The purpose of this study is to charac- terize and compare the geochemical deter- minations for 34 purified chromian spinel samples. The samples, plus 18 other chromian spinel samples , were analyzed by X-ray diffraction. Chromite mineralogy is sufficiently complex to require a com- bination of X-ray diffraction, X-ray fluorescence, and chemical analyses for characterization. Previous studies have focused on the description of chromian spinel occur- rences and standard benef iciation tests of bulk samples. Mineralogical deter- minations have generally been restricted to the identification of gangue and trace minerals associated with chromian spinel. This report provides information on the mineralogy of Alaskan chromian spinel samples and reports trace and major oxide chemical signatures of samples collected statewide. ACKNOWLEDGMENTS K. Broadhead, metallurgical engi- metallurgist, Albany neer, Reno Research Center, provided provided splits of the FeO determinations, and D. Dahlin, samples. Research Center, chromian spinel SAMPLES Fifty-two samples were collected by Bu- reau personnel. The samples represent splits taken from grab or bulk samples that were high-graded in the field for mineralogical and benef iciation tests. The results of this study represent reconnaissance-type information since a few samples from each occurrence do not constitute a thorough characterization for any single deposit, area, or region. The samples were obtained from widely scattered ultramafic occurrences across the State; however, all chromian spinel occurrences in Alaska are not represented in this report (fig. 1). For comparative purposes the samples are lumped into two logical groups that are based on geo- graphic location or extension of geo- graphic or geologic features. The two groups include the interior Alaska and Chugach groups. General localities and grouping of the samples are indicated in appendix C. PROCEDURES The procedures used for this study are not standard concentration techniques. High-purity chromian spinel samples are required for mineralogical characteriza- tion using molecular proportion plots, so modified laboratory techniques were used. ^Underlined numbers in parentheses re- fer to items in the list of references preceding the appendixes. Two different sources for samples resulted in slight variations in the concentration procedures. Samples ar- chived at AFOC were prepared in the man- ner outlined in figure 2. Samples re- ceived from ALRC were table concentrates of minus 28-plus 65-mesh sized fraction, so crushing and hand picking were not required. Borrow FIGURE 1. - Locations of ultramafic rocks hosting chromian spinel occurrences characterized in this report. A, Avan Hills; 5, Caribou Mountain, Kanuti River; C, Yuki River; D, Mount Hurst; E, Tonsina- Bernard, Sheep Hill; F, Wolverine Complex, Eklutna; G, Claim Point, Red Mountain; H, Miners Bay, Grant Lagoon, Halibut Bay; /, Red Bluff Bay. The samples were run through a labora- tory model isodynamic magnetic separator to remove all magnetite, and a hydroflu- oric acid (HF) bath effectively removed unwanted silicate minerals. The HF bath altered the magnesium silicates to chon- drodite, a relatively low density, frag- ile f luorohydroxide which could be washed out by agitation and wet screening. There is no evidence the HF bath altered the chemistry or mineralogy of the chro- mian spinels. High-purity chromian spinel concen- trates free of magnetite and silicates were analyzed by energy-dispersive X-ray fluorescence spectrometry (XRF), with the exception of FeO, which was analyzed by wet chemical methods. Ferric oxide (Fe 2 03) was calculated from total Fe. The analytical precision is less than a few percent relative error, while errors in accuracy may range as high as ±20% in the case of Mg or trace elements because of low counting rates. Comparison of Fe and Cr determinations by ALRC and AFOC during this study generally indicates a relative error in accuracy of ±5% to 10% or less. National Bureau of Standards NBS103A was the primary reference stan- dard used in the XRF determinations. Chromite sample Crush to minus 1/4 inch Hand sort Grind Screen (minus 20 plus 100 mesh) Magnetic separation HF acid bath Wash, agitate, wet-screen (minus 100 mesh) Regrind to minus 300 mesh (nominal) X-ray fluorescence and chemical analysis Diffraction analysis FIGURE 2. - Schematic diagram of sample preparation procedures. Samples received from Albany were con- centrated using tabing methods, and splits consisted of minus 28- plus 65-mesh fractions. These samples were treated beginning with the magnetic separator. After analysis by XRF the samples were analyzed by X-ray diffraction using two modes: a scanning speed of 1/4° two-theta per minute from 31° to 37° two-theta, and a scanning speed of 2° (8 0831) , MgAljOa ' (8.119) FeAljO, Cr /Cr .Al 1 I (Pleonaste) - Spinel Hercynite i - i i (Mitchellite) 1 l l (Piconie) i - Mognesiochromite Chromite 1 l i ' MgCr 2 4 0.2 4 6 (8.333) Fe 2 */Fe ! * + Mg** (8 360) FIGURE 3. - Nomenclature of chromium-bearing spi- nels based on molecular proportion plot of divalent and trivalent cations. Note: Changes along horizontal axis reflect different proportions of divalent cations (Fe, Mg), and changes on the vertical axis represent differ- ent proportions of trivalent cations (Cr, Al). Unit cell dimensions, in angstroms, are indicated in parentheses and are for end member minerals only. two-theta per minute from 2 to 62° two- theta. Measured precision of d-spacings in the former mode is ±0.0005 A. An in- ternal standard (NaCl) was used to stan- dardize the d-spacing measurements using a full-width-half -maximum technique of marking peak centroids. The (113) d-spacing, the strongest spi- nel reflection, was used to calculate unit cell dimensions. Since multiple re- flections from different crystallographic planes were not used to calculate the unit cell dimensions, the values reported must be considered provisional. NOMENCLATURE AND MINERALOGY Mineral nomenclature is adapted from Palache ( 10 ) and conforms to terminology used by the Joint Committee Powder Diffraction Society ( 1) . Chromite from podiform and stratiform ultramafics is mineralogically part of the spinel group, which consists of the magnetite, spi- nel, and chromite series. Spinel-group minerals may be represented by the gener- al formula AB 2 X 4 , which may be expressed as R 2+ R 3+ (13) . Extensive ionic sub- stitution of divalent cations (Fe, Mg, and Ti) and trivalent cations (Cr, Al, Fe , and Mn) makes characterization by X- ray diffraction difficult since crystal lattice dimensions are variably affected by substitution at the octahedral and tetrahedral positions. Although there are natural limits on ionic substitution, characterization is best achieved by com- bining X-ray diffraction and quantitative chemistry. Low-titanium chromium-bearing spinels consist of six idealized end members: chromite (FeCr 2 4 ), magnesiochromite (MgCr 2 04), hercynite (FeAl 2 C>4), spinel (MgAl 2 04), magnesioferrite (MgFe 2 4 ), and magnetite (Fe304) ( 9) . A multi component prism described by Haggerty (8) best characterizes chromium spinels, but for this study only the base of the prism is used. Figure 3 outlines, on a molecu- lar proportion plot, the fields repre- sented by four of the end-member minerals listed above. Magnesioferrite and mag- netite are not represented on the plot, although there is an appreciable ferrian (Fe+ 3 ) component represented by the analyses. RESULTS The results of the chromian spinel chemical analyses are presented after a brief discussion of X-ray diffraction re- sults. Diffraction data for 52 samples are listed in appendix A, along with chemical results for 34 samples. Molecu- lar proportions of the principal spinel cations are listed in appendix B, and mineral terms and general localities are tabulated in appendix C. X-RAY DIFFRACTION High-resolution X-ray diffraction in- dicates that average d-spacings of the (113) reflection vary from 2.4835 to 2.5260 A. These measurements indicate unit cell dimensions of 8.237 to 8.378, respectively. Figure 4 represents a plot of calculated cell dimensions with sum- mary envelopes of the Chugach and inte- rior Alaska groups of samples. There is a clear difference in average cell dimen- sions, with the Chugach group averaging 8.312 A and the interior Alaska group averaging 8.279 A. The disparity in unit cell dimensions is apparently due to a difference in average amounts of Al, Mg, Fe, and Cr. Eleven samples have multiple (113) re- flections ("doublet"), indicating more than one spinel mineral is present. Nine of the 11 samples with doublets are from the Chugach group of samples. Dahlin (3) and Bliss (2) describe zoned chromian spinel minerals , which are the probable cause for the doublets. X-RAY FLUORESCENCE Plots comparing molecular proportions of Fe 2+ /Fe 2+ + Mg 2+ and Cr 3+ /Cr 3+ + Al 3+ concentrations are presented in figure 5. The plots define R 2+ and R 3+ cation proportions and the mineralogy of the high-purity bulk chromian spinel splits. Fe +3 is not represented on the plot even though the chemical analyses indicate an appreciable ferrian component. Mineral terms for 34 samples are based mainly on molecular proportions. Analy- sis by X-ray diffraction was used to check purity of the samples and to con- firm the presence of a spinel. A total of 25 samples are characterized as mag- nesiochromite, 5 are chromite, 3 are spi- nel, and 1 is hercynite. ® / . i -- — 1 : * \ 1 . • • 1 ® ./ / Chugacti G -Interior Alaska Group Eklutna, Wolverine Red Mountoir LOCALITY FIGURE 4. - Unit cell dimensions of chromian spinel based on (113) reflection. Note: Envelopes are used to diagrammatically illustrate differences between the interior Alaska and Chugach groups of samples. The range of cell dimensions shows the variation in chro- mian spinel compositions within a related area or complex. Avon Kanuti, Caribou Yuki River Mount Hurst Eklutno, Wolverine Red Mountain, Claim Point Kodiak Tonsino Southeast FIGURE 5. - Molecular proportion plot of purified chromian spinel samples. Note: Refer to figu,re 3 for mineral nomenclature. The concentrations of major oxides in the chromian spinel samples exhibit con- siderable variability (table 1). This variability exists not only between regions , but between samples taken with- in the same ultramafic complex. This emphasizes the importance of understand- ing the chemistry and mineralogy of chromian spinel occurrences since the benef iciating procedures and market de- pend heavily on ore chemistry. Systematic chemical and unit cell dif- ferences exist between the Chugach and interior Alaska samples when the groups, rather than specific samples, are com- pared. Compared with the Chugach group of samples , the interior Alaska group TABLE 1. - Range of oxide concentrations in chromian spinel samples, weight percent Oxide 1 Minimum value Maximum value Mean value Al oO t. 4.5 7.0 25.8 4.2 17.7 26.7 59.8 15.6 22.0 11.4 13.9 Cr oO 7 49.5 Fe oO * 8.2 14.5 1 0xide cally by from tot s based on X-ray fluorescence analyses except FeO which was determined chemi- the Bureau of Mines, Reno Research Center. The Fe 2 03 values were calculated al iron. samples have higher average amounts of A1 2 3 , Fe 2 3 , Ti0 2 , and NiO and exhibit greater dispersion in values (table 2). Figures 6, 7, and 8 graphically summarize the differences between the two groups when Ni , Zn, and Ti concentrations are compared to Cr content. The significance of the chemical differences between the groups can be attributed to different genetic histories. TABLE 2. - Statistical comparison of oxides and lattice data for the interior Alaska and Chugach group of samples Statistical parameter Interior Alaska group N Mean wt % SD, 2 wt % N Chugach group Mean wt % SD, 2 wt % MgO . . , A1 2 3< FeO... Fe 2 3< Cr 2 3 . Si0 2 .. P 2 5 .. Ti0 2 .< NiO... ZnO , d-spacing, Unit cell, 17 17 17 17 17 17 17 17 17 17 27 27 11.2 17.4 12.7 9.5 46.4 0.27 0.12 0.50 0.10 0.11 2.4965 8.279 2.1 8.9 4.3 4.1 11.6 0.19 0.04 0.22 0.04 0.10 0.0075 0.024 17 17 22 17 17 17 17 17 17 17 27 27 11.5 10.4 15.8 6.9 52.5 0.27 0.11 0.30 0.06 0.09 2.5060 8.312 3.9 3.8 4.0 3.5 6.1 0.21 0.04 0.15 0.03 0.09 0.0081 0.027 In = N = number of observations. 2 SD = standard deviation. tn ^_^^ 40 o\ .1 nterior Alaska Group i --" * ffi A \. \ 4 \ (o #\ • N 35 \ X D \ V X \ D O \ \ \ o\ 30 \ \ * o • \ \ \ 25 Chugach Group' \ * \ \ \ \ \ 20 \ \ • oj \ ___ o y 15 600 800 Ni, ppm Avon Kanuti, Coribou Yuki River Mount Hurst Eklutno, Wolverine ,000 1,200 Red Mountain, Claim Point Kodiak Tonsino Southeast 1,400 1,600 FIGURE 6- - Trace Ni versus Cr. Note: Envelopes are usedto diagrammatical ly illustrate differences between the interior Alaska and Chugach groups of samples. 4b 40 „ l \ • \ \ ^hugoch Group 35 X °° v\ _3 o\ .10 \ \-Q - — \o « \ \ \ \ . i n 2b \ \ \ . ^Interior Alaska Group 20 \ \ v9_ ^ 15 500 1,000 Zn, ppm KEY 1,500 ■ Avon A Red Mounto Claim Point o Kanuti, Caribou * Kadiok Yuki River D Tonsino 9 Mount Hurst Eklutno, Wolver X Southeast FIGURE 7. - Trace Zn versus Cr. Note: Envelopes are usedto diagrammatica I ly illustrate differences between the interior Alaska and Chugach groups of samples. 45 40 - 35 _ 30 20 15 - 10 -(*"" — — ^i\ aV a ^> /^a® ® v^ ^Interior Alaska Group \x X D \ v j / ° \ - / ^ # o \ Chugach Group . \ \ \ a« \ \ ffi \ \ N \ \ . N - — — — ____ o^ i i i i 1,000 2,000 3,000 4,000 5, Ti , PPm • Avan KEY A Red Mountain, Claim Point o Kanuti, Caribou * Kodiak «* Yuki River D Tonsina © Mount Hurst X Southeast 5,000 6,000 7,000 Eklutna, Wolverine FIGURE 8. - Trace Ti versus Cr. Note: Envelopes are used to diagrammatically illustrate differ- ences between the interior Alaska and Chugach groups of samples. CONCLUSIONS The following conclusions are based on X-ray diffraction, X-ray fluorescence, and chemical analyses of 34 high-purity chromian spinel samples: 1. Samples that are grouped by region or geologic extension have systematic chemical differences when average values are compared. The interior Alaska group of samples, when compared to the Chugach group of samples , have higher average amounts of AI2O3, Fe 2 03, Ti0 2 , and NiO, exhibit greater dispersion in values, have lower average amounts of FeO and Cr 2 03, and have similar average MgO concentrations . 2. Considerable mineralogical varia- bility exists between and within indi- vidual Alaskan chromian spinel-bearing ultramafic complexes. Of 34 chromian spinel samples analyzed, 25 consist of ferroan or aluminian magnesiochromite, 5 are aluminian or magnesian chromite, 3 are chromian spinel, and 1 is chromian hercynite. The Chugach sample group has a larger average unit cell dimension when compared to the interior Alaska group of samples and has a higher incidence of doublet (113) diffraction reflections, indicating the presence of more than one spinel phase. 3. The chemical and mineralogical dif- ferences between the groups may be a sig- nificant factor in the location of chro- mian spinel deposits amenable to standard beneficiating techniques. REFERENCES 1. Berry, L. G. (ed.). Selected Pow- der Diffraction Data for Minerals. Joint Committee on Powder Diffraction Stan- dards, Swarthmore, PA, 1974, 833 pp. Caribou Mountain and Lower Kanuti River Areas, Central Alaska. Part 1. Recon- naissance Investigations. BuMines IC 8915, 1983, 27 pp. 2. Bliss, N. W. , and W. H. MacLean. The Paragenesis of Zoned Chromite From Central Manitoba. Geochim. et Cosmochim. Acta, v. 39, 1975, pp. 973-990. 3. Dahlin, D. C. , L. L. Brown, and J. J. Kinney. Podiform Chromite Occur- rences in the Caribou Mountain and Lower Kanuti River Areas, Central Alaska. Part 2: Beneficiation. BuMines IC 8916, 1983, 15 pp. 4. Dahlin, D. C. , D. E. Kirby, and L. L. Brown. Low-Grade Chromite Deposits Along the Border Ranges Fault , Southern Alaska. 2. Beneficiation. BuMines IC 8991, 1984. 5. Deer, W. A., R. A. Howie, and J. Zussman. An Introduction to the Rock- Forming Minerals. Longman Group Limited, 1966, pp. 424-433. 6. Foley, J. Y. , and J. C. Barker. Low-Grade Chromite Deposits Along the Border Ranges Fault, Southern Alaska. 1. Field Investigations and Descriptions of Chromite Deposits. BuMines IC 8990, 1984. 7. Foley, J. Y. , and M. M. McDermott. Podiform Chromite Occurrences in the 8. Haggerty, S. E. Opaque Mineral Oxides in Terrestrial Igneous Rocks. Sec. in Oxide Minerals. Mineralogical Society of America Short Course Notes, v. 3, Nov. 1976, pp. 101-150. 9. MacGregor, I. D. , and C. H. Smith. The Use of Chrome Spinels in Petrographic Studies of Ultramafic Intrusions. Can. Mineral., 1962, pp. 403-412. 10. Palache, C. , H. Berman, and C. Frondel. The System of Mineralogy of J. D. Dana and E. S. Dana. Wiley, v. 1, 7th ed. , 1944, pp. 687-712. 11. Roberts, W. S. Economic Potential for Chromium, Platinum, and Palladium in the Mount Hurst Ultramafics, West-Central Area, Alaska. BuMines OFR 22-84, 1984, 52 pp. 12. Stevens, R. E. Composition of Some Chromites of the Western Hemisphere. Am. Mineral., v. 29, Nos. 1-2, 1944, pp. 1-34. 13. Thayer, T. P. Principal Features and Origin of Podiform Chromite Deposits, and Some Observations on the Guleman- Soridag District, Turkey. Econ. Geol. , v. 59, 1964, pp. 1497-1524. 10 APPENDIX A. —ANALYTICAL RESULTS Sample No 1 2 3 4 5 6 7 8 9 10 Analysis, wt %: MgO NA NA Na NA NA NA NA NA NA NA 2.5010 8.295 9.8 11.5 15.0 2.5 58.7 0.06 0.15 0.56 0.09 0.05 2.5015 8.297 9.3 26.7 15.0 7.5 38.3 0.63 0.08 0.76 0.12 0.08 2.4845 8.240 NA NA NA NA NA NA NA NA NA NA 2.4970 8.282 NA NA NA NA NA NA NA NA NA NA 2.5025 8.300 NA NA NA NA NA NA NA NA NA NA 2.4970 8.282 NA NA NA NA NA NA NA NA NA NA 2.4985 8.287 8.1 29.8 18.0 14.3 27.4 0.24 0.10 0.89 0.09 0.14 2.4870 8.248 NA NA NA NA NA NA NA NA NA NA 2.4875 8.250 NA A1 2 3 FeO NA NA Fe 2 3 Si0 2 NA NA NA P 9 0s NA Ti0 2 NA NiO NA ZnO NA d-spacing. . .A. . Unit cell. . .A. . 2.4950 8.275 11 12 13 14 15 16 17 18 19 20 Analysis, wt %: MgO NA NA NA NA NA NA NA NA NA NA 2.5065 8.313 NA NA NA NA NA NA NA NA NA NA 2.5005 8.293 11.0 15.2 9.3 7.7 54.2 0.16 0.12 0.50 0.12 0.05 2.5040 8.305 12.3 11.7 14.0 6.3 52.7 0.12 0.19 0.45 0.08 0.10 2.5005 8.293 11.3 22.9 15.0 5.6 43.1 0.11 0.07 0.53 0.11 0.07 2.4890 8.255 11.4 31.9 17.0 13.4 25.8 0.30 0.09 1.05 0.13 0.09 2.4835 8.237 11.7 8.5 17.0 3.5 53.9 0.19 0.07 0.22 0.03 0.47 2.5045 8.306 9.9 34.6 12.0 11.1 28.2 0.12 0.08 0.48 0.18 0.112 2.4775 8.217 8.6 15.0 15.0 14.1 46.1 0.17 0.19 0.32 0.17 0.14 2.5045 8.306 12.9 FeO 12.9 13.0 Si0 2 9.2 49.8 0.09 P 9 Or 0.20 Ti0 2 0.45 NiO 0.10 ZnO 0.06 d-spacing. . . A. . Unit cell. . .A. . 2.5015 8.296 21 22 23 24 25 26 27 28 29 30 Analysis, wt %: MgO 11.7 8.5 4.2 15.6 58.2 0.23 0.17 0.39 0.07 0.05 2.4925 8.267 11.6 7.8 6.8 9.6 59.5 0.39 0.10 0.30 0.12 0.04 2.4975 8.283 16.4 16.7 14.0 7.4 43.6 0.22 0.12 0.44 0.08 0.10 2.4990 8.288 NA NA NA NA NA NA NA NA NA NA 2.5000 8.291 13.4 10.1 9.1 6.5 57.4 0.53 0.11 0.31 0.07 0.06 2.4990 8.288 8.4 22.4 16.0 15.2 36.0 0.64 0.09 0.44 0.08 0.12 2.4945 8.273 12.0 9.8 4.6 12.3 56.4 0.45 0.09 0.32 0.08 0.06 2.4960 8.278 13.5 3.6 14.0 3.6 59.8 0.24 0.14 0.03 0.02 0.08 2.5120 8.331 NA NA 20.0 NA NA NA NA NA NA NA 2.4955 8.277 NA FeO NA 19.0 Si0 2 NA NA NA P 9 Or NA Ti0 2 NA NiO NA ZnO NA d-spacing. . .A. . Unit cell. . .A. . 2.4970 8.282 See explanatory notes at end of table. 11 31 32 33 34 35 36 37 38 39 40 Analysis, wt %: MgO 14.6 17.7 NA 17.5 10.0 11.0 9.1 6.6 10.7 4.5 A1 2 3 11.8 7.2 NA 7.6 8.2 9.9 9.1 7.0 9.8 15.5 FeO 11.0 8.5 10.0 16.0 13.0 16.0 13.0 16.0 22.0 21.0 Fe 2 3 5.8 7.4 NA 1.9 6.2 4.5 7.6 4.9 0.0 9.2 Cr 2 3 54.6 53.6 NA 51.6 58.8 57.1 57.8 59.7 60.3 46.9 Si0 2 .20 .28 NA .49 .01 .18 .19 NA .08 .70 P2O5 .08 .10 NA .11 .21 .10 .07 .04 .11 .08 Ti0 2 .44 .30 NA .29 .24 .28 .29 .27 .31 .38 NiO .09 .09 NA .09 .04 .06 .07 .03 .05 .03 ZnO .04 .05 NA .05 .05 .05 .04 .05 .04 .14 d-spacing. . .A. . 2.5020 2.5045 2.5025 2.5040 2.5050 2.5065 2.5070 2.5100 2.5065 2.5030 Unit cell. . .A. . 8.298 8.306 8.300 8.305 8.308 8.313 8.315 8.325 8.313 8.302 Sample No 41 42 43 44 45 46 47 48 49 50 Analysis, wt %: MgO 8.7 NA NA NA 15.3 13.2 NA 11.2 10.3 NA A1 2 3 10.3 NA NA NA 11.8 17.6 NA 11.3 18.1 NA FeO 19.0 NA NA NA 13.0 13.0 15.0 17.0 18.0 20.0 Fe 2 3 9.6 NA NA NA 5.4 7.2 NA 8.2 14.0 NA Cr 2 3 49.2 NA NA NA 51.7 46.7 NA 48.2 38.1 NA Si0 2 .46 NA NA NA .47 .15 NA .08 .21 NA p 2 o 5 .11 NA NA NA .13 .12 NA .14 .14 NA Ti0 2 .36 NA NA NA .27 .25 NA .23 .75 NA NiO .10 NA NA NA .09 .08 NA .04 .09 NA ZnO .09 NA NA NA .05 .08 NA .10 .23 NA d-spacing. . .A. . 2.5120 2.5155 2.5255 2.5260 2.4995 2.4915 2.5090 2.5045 2.4985 2.5005 Unit cell... A. . 8.331 8.343 8.375 8.380 8.290 8.263 8.321 8.306 8.286 8.293 Sample No 51 52 Analysis, wt %: MgO 15.7 6.2 A1 2 3 9.4 8.3 FeO 11.0 22.0 Fe 2 3 8.7 12.8 Cr 2 3 49.4 48.2 Si0 2 .66 .15 P2O5 .08 .15 Ti0 2 .22 .14 NiO .09 .03 ZnO .06 .38 d-spacing. . .A. . 2.5075 2.5095 Unit cell... A.. 8.316 8.323 NA Not analyzed. 'All analyses by X-ray flu- orescence except FeO which was done by Reno Research Center using wet chemical methods. X-ray fluorescence and X-ray diffraction results by Alaska Field Operations Center, Juneau, AK. 12 APPENDIX B. —NUMBER OF CATIONS PER 32 OXYGENS 2 3 8 13 14 15 16 17 18 19 Cation: Fe 2 + 3.70 4.30 0.49 12.00 3.51 0.88 0.46 0.77 3.80 4.20 1.34 7.19 7.47 0.78 0.47 0.49 4.44 3.56 2.55 5.13 8.32 0.80 0.55 0.38 2.57 5.43 1.39 10.30 4.31 0.73 0.32 0.71 3.12 4.88 1.26 11.07 3.67 1.00 0.39 0.75 3.42 4.58 1.03 8.35 6.62 0.90 0.43 0.56 3.65 4.35 2.37 4.79 8.84 0.92 0.45 0.35 3.59 4.41 0.76 12.34 2.90 1.15 0.45 0.81 3.24 4.76 1.87 4.99 9.14 0.69 0.41 0.35 3.96 Mg 2 + 4.04 Fe 3 + 2.62 Cr 3 + 9.00 Al 3 + 4.37 R0/R 2 O 3 2 0.78 Molecular ratio: 3 Cr 3+ /Cr 3+ Al 3+ 0.49 0.67 20 21 22 23 25 26 27 28 31 32 Cation: Fe 2 + 2.89 5.11 1.80 10.24 3.96 0.98 0.36 0.72 1.34 6.65 6.65 3.67 5.68 1.48 0.17 0.82 1.98 6.02 1.82 11.86 2.32 0.72 0.25 0.84 2.59 5.41 1.49 9.23 5.27 1.21 0.32 0.64 2.21 5.79 1.26 11.68 3.06 0.89 0.27 0.79 4.13 3.87 2.76 6.87 6.37 0.78 0.52 0.52 1.42 6.58 2.26 10.91 2.83 0.66 0.17 0.79 2.94 5.06 0.80 13.95 1.25 1.17 0.37 0.92 2.38 5.62 1.14 11.24 3.62 1.01 0.30 0.76 1.70 Mg 2 + 6.30 Fe 3 + 1.58 Cr 3 + 12.01 Al 3 + 2.41 RO/R 2 3 2 1.19 Molecular ratio: 3 Cr 3+/ Cr 3+ A1 3+ 0.21 0.83 34 35 36 37 38 39 40 41 45 46 Cation: Fe 2 + 2.71 5.29 0.45 12.75 2.80 1.54 0.34 0.82 3.37 4.63 1.23 12.23 2.54 0.85 0.42 0.83 3.60 4.40 0.90 12.00 3.10 0.99 0.45 0.79 3.56 4.44 1.47 11.76 2.76 0.77 0.33 0.81 4.61 3.39 1.00 12.77 2.23 0.79 0.58 0.85 4.29 3.71 0.00 12.88 3.12 1.16 0.53 0.81 5.79 2.21 1.78 9.53 4.69 0.78 0.72 0.67 4.41 3.59 1.98 10.68 3.33 0.99 0.55 0.76 2.58 5.42 1.10 11.11 3.78 1.14 0.32 0.75 2.85 Mg 2 + 5.15 Fe 3 + 1.37 Cr 3 + 9.36 Al 3 + 5.26 RO/R 2 3 2 0.97 Molecular ratio: 3 Cr 3+ /Cr 3+ Al 3+ 0.35 0.64 48 49 51 52 Cation: Fe 2 + 3.68 4.32 1.71 10.58 3.70 1.07 0.46 0.74 3.96 4.04 2.72 7.77 5.51 0.98 0.50 0.58 2.26 5.74 1.85 11.02 3.13 1.15 0.28 0.78 5.33 2.67 2.68 10.50 2.72 0.96 0.66 0.80 Mg 2 + Fe 3 + Cr 3+ Al 3 + RO/R 2 3 2 Molecular ratio: 3 Cr 3+ /Cr 3+ Al 3 + Stevens (12). Unit cell contains 8 R 2+ cations, 16 R 3+ cations, and 32 oxygen atoms. Ratio based on molecular proportions calcu- lated from data in appendix A. 3 Molecular ratios are calculated from data in appendix A and are plotted on figure 5. Fe 2+ / Fe 2 + r 2 + + Mg z represent values along the x-axis, and Cr 3+ /Cr 3+ + Al 3+ represent values along the y-axls. 13 APPENDIX C— MINERAL TERMS AND SAMPLE KEY Sample Field Locality Mineral terms LOCALITIES IN INTERIOR ALASKA 1 , 2 , 3 , 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19.. 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 58 49 50 51 52 ND Insuffici WB20438. WB16537, WB16538. WB20435. WB20436. WB20437. WB16539. WB16540. WB16541. WB20825. WB20826. WB20827. WB16768. PT16641. PT16637. PB15787. PT16635. PT16638. PT16639. PT16636. KW20780. KW20782. KW20779. KW19476. KW19477. KW19868. KW19881. Avan Hills, ...do , .do, . . .do. . . .do, ...dc lo, . . .do , . . .do, . . .do, ...dc lo . . .do. . . .do . . .do Caribou Mountain. . . .do. . . .do Kanuti River . . .do . . .do , . . .do Yuki River . . .do . . .do. Mount Hurst , . . .do. . . .do ...do ND. Magnesiochromite, aluminian. Spinel, chromian. ND. ND. ND. ND. Hercynite, chromian. ND. ND. ND. ND. Magnesiochromite, aluminian. Do. Do. Spinel, chromian. Magnesiochromite, ferroan. Spinel, chromian. Magnesiochromite, aluminian. Do. Magnesiochromite, ferrian. Magnesiochromite, aluminian. Do. ND. Magnesiochromite, aluminian. Chromite, aluminian. Magnesiochromite, aluminian. LOCALITIES ALONG EXTENSION OF CHUGACH MOUNTAINS CM20261. CM20268. CM19277. CM18624. CM19649. CM11168. CM19641. CM17679. CM19680, CM17675. CM17670, CM17670. CM19312. CM19322. CM19326, CM19371. CM19373. CM20488. CM20497. CM18678. CM20467, CM20466, CM20443. 1S153... 2S430... Grant Lagoon Halibut Bay . . .do . . .do . . .do • . .do. Miners Bay Claim Point . . .do. Red Mtd-Kenai . . .do . . .do. Eklutna Wolverine Complex. ...do . . .do. . . .do ..< Tons ina-Bernar d . . . .do , ...do Sheep Hill.... . . .do Dust Mountain. Red Bluff Bay. . . .do Magnesiochromite, ferroan. ND. ND. Magnesiochromite, aluminian. Do. ND. Magnesiochromite, ferroan. Do. Do. Do. Chromite, magnesian. Do. Do. Do. ND. ND. ND. Magnesiochromite, aluminian. Do. ND. Magnesiochromite, ferroan. Do. ND. Magnesiochromite, aluminian. Do. ent data to designate mineral term (no chemical data). #11. S. 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