Platinum, palladium, and rhodium analyses of ultramafic and mafic rocks from the Stillwater Complex, Montana
<p>Analyses by a combination fire- assay-solution-optical-emission spectrographic method of 137 rocks from the Stillwater Complex, Mont., indicate that…
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GEOLOGICAL SURVEY CIRCULAR 624 Platinum, Palladium, and Rhodium Analyses of Ultramafic and Mafic Rocks from the Stillwater Complex Montana
Platinum, Palladium, and Rhodium Analyses of Ultramafic and Mafic Rocks from the Stillwater Complex Montana By Norman J Page, Leonard B. Riley, and Joseph Haffty G E 0 L 0 G I C A L 5 U R V E Y C I R C U L A R Washington 1969
United States Department of the Interior WALTER J. HICKEL, Secretary Geological Survey William T. Pecora, Director Free on application to the U.S. Geological Survey, Washington, D.C. 20242
Abstract Introduction Acknowledgments Sampling and analytical methods CONTENTS Page Pt, Pd, and Rh assay data Conclusions References cited ILLUSTRATION Figure 1. Platinum, palladium, and rhodium ratios for each specimen from the Stillwater Page Page Complex, ~ont TABLES Page Table 1. Subdivisions and terminology used for the Stillwater Complex, ~ont 2. Platinum, palladium, and rhodium analyses of rocks from the Stillwater Complex, ~ont 3. Arithmetic averages of Pt, Pd, and Rh_,in parts per billionJfor zones, members, and rock types of the Stillwater Complex, ~ont
Platinum, Palladium, and Rhodium Analyses of Ultramafic and Mafic Rocks from the Stillwater Complex, Montana By Norman J Page, leonard B. Riley, and Joseph Haffty ABSTRACT An a 1 y s e s by a combination fire- assa~solution-optical· emission spectrographic method of 137 rocks from the Stillwater Complex, Mont., indicate that platinum, palladium, and rhodium are preferentially concentrated in chromitite zones. The A chromitite zone (21 samples) has an average of 988.9 ppb (pans per billion, w-9) Pt, 2290.2 ppb Pd, and 245.9 ppb Rh and reaches a maximum (to date) of 8,000 ppb Pt, 11,000 ppb Pd, and 1,700 ppb Rh. INTRODUCTION The occurrence of minor amounts of platinum -group metals in the Basal, Banded, and Upper zones of the Stillwater Complex was first documented by Howland (1933) and Howland, Peoples, and Sampson (1936). As part of the Heavy Metals program of the U.S. Geological Survey, a study of the distribution of the platinumgroup metals within the complex resulted in the discovery of platinum-bearing minerals in the Peridotite member of the Ultramafic zone (Page and Jackson, 1967). Some of the platinum-group metals occur as the minerals laurite, cooperite, and a platinum-iron alloy which are included within cumulus olivine and c h r om i t e of the G and H c h r o m i t it e zones. The platinum-bearing minerals are associated with ironnickel-copper sulfide minerals and are concentrated in chromite relative to olivine. Recently, Grimaldi and Schnepfe ( 1969) have proposed that most of the rhodium and some of the platinum are in chromite either as solid solution or as small inclusions. In order to survey the other petrologic environments within the complex, large bulk rock samples were collected for Pt, Pd, and Rh assays. The results from 137 samples are given in this report (table 2). Samples have been located relative to coordinate systems used on the maps of the complex which appear in the following reports: Peoples and Howland (1940), Howland, Garrels, and Jones (1949), Jackson, Howland, Peoples, and Jones (1954), Peoples, Howland, Jones, and Flint (1954), Howland (1955), and Jones, Peoples, and Howland (1960). Designation of geographical areas follows the usage of these reports. Stratigraphic terminology is shown in table 1 and follows that of Hess (1960), Jones, Peoples, and Howland (1960), and Jackson (1961); cumulus terminology is from Jackson (1967). Table 1.--Subdivisions and terminology used for the Stillwater Complex, Mont. Zone Member Upper zone Banded zone Bronzitite member Ultramafic zone about 15 cyPeridotite member clic units,each of which normally has Basal zone a chromitite zone, labelled A through Hornfels K from the base upward. ACKNOWLEDGMENTS The contribution of samples taken previous to 1968 by E. D. Jackson is warmly acknowledged. SAMPLING AND ANALYTICAL METHODS Ten to 40 pounds of rock was collected from surface outcrops as hand-specimen samples (a single large block), as chip samples (chips at specified intervals perpendicular to the foliation over the outcrop extent), and as channel samples. The specimens were crushed to a size fine enough to pass through a 50-mesh screen and then split and put in paper containers. One-quart splits of screened material were then submitted for analysis. The combination method of analysis of Haffty and Riley ( 1968) was used to obtain the v a 1 u e s of the platinum-group metals reported in this paper. In this method, fire-assay techniques are used to collect the Pt-Pd-Rh of the sample into a gold bead; this bead is
Rh EXPLANATION
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Norite and sulfides
Hornfels 3 samples 2 samples o -3 samples 18 samples Figure 1.--Platinum, palladium, and rhodium ratios for each specimen from the Stillwater complex, Mont. d i s so 1 v e d in aqua regia, and an optical-emission spectrographic analysis is made of this solution. As shown by Haffty and Riley, samples of certain types of materials and especially samples rich in chromite are more difficult to fire assay than routine gold ores. Several expedients have been used to overcome these difficulties, such as varying the flux composition, reducing the amount of sample taken (as from 15 g (gram) to 3 g), or increasing the amount of flux. Fine grinding helped on some of the chromitites. Another helpful variation for many chrome-rich samples was the addition of a small amount of molten flux to the main charge a few minutes before pouring, so that it could act as a "wash." PT, PD, AND RH ASSAY DATA Table 2 lists the results of the fire-assay-emissionspectrographic analyses of the rocks from the com2 plex as values in parts per billion (10-9). Included are coordinate locations of the sam p 1 e s, brief rock descriptions, and sample-collection types. The analyses are grouped in geographic areas from east to west in the complex and are listed, as closely as possible, within the groups in stratigraphic order from the base of the complex upward. Figure 1 is a plot of Pt, Pd, and Rh ratios for all the samples; rock types and zones are designated by symbols. Examination of figure 1 and table 2 shows that the Pt, Pd, and Rh ratios for the three main zones vary widely and that a s i n g 1 e value or range of values is probably not representative of a particular zone, whereas the total amount of platinum metals tends to correlate well with rock type and zone. The amount of platinum metals seems to correlate with stratigraphic position, the larger amounts being found at low stratigraphic positions. The general order of concentration of platinum metals, from the
most enriched rocks to the least enriched rocks, is (1) chromitites, (2) other Ultramafic zone rocks, (3) Basal zone norites and massive sulfide pods, (4) hornfels, and (5) Banded and Upper zone rocks. Table 3 gives the arithmetic averages for Pt, Pd, and Rh. Average mill concentrates and tailings are included because they represent combined samples of the G and H chromitite zones. The sum of the averages of Pt, Pd, and Rh tends to decrease from the A chromitite zone to the G chromitite zone and tends to increase from the G chromitite zone to the J chromitite zone. From the A to the G zone, there is an increase in the Rh/ (Rh+Pt+Pd) ratio, whereas from the G to the J zone the Rh/(Rh+Pt+Pd) ratio remains fairly constant. Examination of the other samples analyzed shows no definite trends of Pt, Pd, and Rh ratios with stratigraphic position or rock type. Comparison of the geographic areas in which Pt, Pd, and Rh are more enriched in chromitites to the lateral variations in the thicknesses of chromitite zones and the Peridotite member (Jackson, 1963, fig. 3) indicates that the enriched areas are on the edges of basinlike structures. If the Rh/ (Rh+Pt+Pd) ratios are compared with the Fe+3; (Fe+3 + Fe+2) ratio in chromite from the chromitite zones (Jackson, 1963, fig. 6), then it appears that low Rh/ (Rh+Pt+Pd) ratios cor r e 1 at e with low values of oxidation ratios. Tentatively, low Fe+3 concentrations in the chromite, which probably reflect low p a r t i a 1 pressures of oxygen in the differentiating magma, tend to favor the concentration of Pt and Pd with respect to Rh. This is to be expected if Pt and Pd occur as platinum -metal-iron alloys which require low partial pressures of oxygen for their formation. Each sample was an a 1 y zed by a semiquantitative spectrographic method (R. H. Heidel, analyst). The following list of 54 elements were looked for: Al, Ag, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Fe, Ga, Ge, Hf, In, Ir, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, Os, P, Pb, Pd, Pt, Re, Rh, Ru, Sb, Sc, Si, Sn, Sr, Ta, Te, Th, Ti, Tl, U, V, W, Y, Yb, Zn, Zr. Preliminary examination of the spectrographic results suggests that only V has a correlation with the sum of Pt, Pd, and Rh, as determined by the quantitative fire-assayspectrographic method; that is, increased V is associated with increases in the platinum metals. It is possible that V may be a favorable geochemical tracer for these metals within the Stillwater Complex. CONCLUSIONS The A chromitite zone of the Stillwater Complex is enriched in Pt, Pd, and Rh, has an average platinummetal content of 3.5 ppm (parts per million) along the strike (Jackson, 1963, 1968), and ranges in thickness from a few inches to a couple of feet. Samples of the A chromitite zone taken in the eastern end of the West Fork area to Crescent Creek (a linear distance of about 1 1/2 miles) have an arithmetic average of 4.6 ppm platinum metals; this zone has not been sampled from Crescent Creek west to the B o u 1 de r River. This average value is comparable with averages of 8.6ppm platinum metals from the Merensky Reef, 3.4 to 5.1 ppm from the Great Dyke, and 0.86 ppm from Sudbury (Allen, 1960). More systematic reconnaissance and geochemical exploration is necessary to define more promising targets within the lower chromitite zones than has been reported here. The present data only suggest zones of economic interest. REFERENCES CITED Allen, C. C., 1960, The platinum metals: CanadaMineral Resources Division, Department of mines and technical surveys: Mineral Rept. 3, 68 p. Grimaldi, F. S., and Schnepfe, M. M., 1969, Mode of occurrence of Pt, Pd, and Rh in chromitite: U.S. Geol. Survey Prof. Paper 650-C. (Inpress). Haffty, Joseph, and Riley, L. B., 1968, Determination of palladium, platinum, and rhodium in g eo 1 o g i c materials by fire-assay and em i s s ion spectrography: Talanta, v. 15, p. 111-117. Hess, H. H., 1960, The Stillwater Igneous Complex, Montana, a quantitative mineralogical study: Geol. Soc. America Mem. 80, 230 p. Howland, A. L., 1933, Sulphides and metamorphic rocks at the base of the S t i 11 water Complex, Montana: Princeton Univ., unpub. Ph.D. thesis, 76 p. 1955, Chromite deposits in the central part of ---rile Stillwater Complex, Montana: U.S. Geol. Survey Bull. 1015-D, p. D99-0121. Howland, A. L., Garrels, R. M., and Jones, W. R., 1949, Chromite deposits of the Boulder River area, Sweetgrass County, Montana: U.S. Geol. Survey Bull. 948-C, p. C63-C82. Howland, A. L., Peoples, J. W., and Sampson, Edward, 1936, The Stillwater igneous com p 1 ex and associated occurrences of nickel and platinum metals: Montana Bur. Mines Misc. Contr. 7, 15 p. Jackson, E. D., 1961, Primary texture and mineral associations in the Ultramafic zone of the Stillwater Complex, Montana: U.S. Geol Survey Prof. Paper 358, 106 p. 1963, Stratigraphic and lateral variation of chro- ---rTihe composition in the Stillwater Com p 1 ex: Mineral. Soc. Am. Spec. Paper 1, p. 46-54. 1967, Ultramafic cumulates in the S t i 11 water, -creat Dyke, and Bushveld intrusions, in Wylie, P. J., ed., Ultramafic rocks: New York, John Wiley & Sons, Inc., p. 20-38. 1968, The chromite deposits of the S t i 11 water -complex, Montana, in Ridge, J. D., ed., Ore deposits of the United States 1933-1965: New York, Am. Inst. Mining, Metall., and Petroleum Engineers, p. 1496-1510. Jackson, E. D., Howland, A. L., Peoples, J. W., and Jones, W. R., 1954, Geologic maps and sections of the eastern part of the Stillwater complex, in Stillwater County, Montana: U.S. Geol. Survey open-file rept.
Jones, W. R., Peoples, J. W., and Howland, A. L., 1960, Igneous and tectonic structures of the S t i 11 water Complex, Montana: U.S. Geol. Survey Bull. 1071-H, p. H281-H335. Page, N. J, and Jackson, E. D., 1967, Preliminary report on sulfide and platinum-group minerals in the chromitites of the Stillwater Complex, Montana: U.S. Geol. Survey Prof. Paper 575-D, p. Dl23Dl26. Peoples, J. W., and Howland, A. L., 1940, Chromite deposits of the eastern part of the Stillwater complex, Stillwater County, Montana: U.S. Geol. Survey Bull. 922-N, p. N371-N416. Peoples, J. W., How land, A. L., Jones, W. R., and Flint, Delos, 1954, Geologic map, sections, and map of underground workings of the Mountain View Lake area, Stillwater County, Montana: U.S. Geol. Survey open-file rept.
TABLES 2 and 3
Table 2.--Platinum, palladium, and rhodium analyses of rocks from the Stillwater Complex, Mont. [Analysts: Joseph Haffty, W. D. Goss, and 0. M. Parker. Samples were analyzed by a combination fire-assay-optical-emission spectrographic method. System: ACM, based on SE corner of NEl/4 sec. 21, T. 55 S., R. 15 E., as 50,000 N.-50,000 E. (Peoples and others, 1954). BM, based on section corner common to sees. 25, 36 of R. 15 E. and sees. 30, 31 of R. 16 E., T. 5 S., as 120,000 N.-120,000 E. (Jackson and others, 1954). NB, based on SE corner of NEl/4 sec. 21, T. 55 S., R. 15 E., as 50,000 N.-50,000 E. (Jackson and others, 1954). MS, Montana (South) rectangular coordinate system, Mount Douglas and Mount Wood 15-minute quadrangles. WF, based on Wl at east end of West Fork base line assumed as 20,000 N.-20,000 E. (Howland, 1955). GM, based on Flat north end of Boulder River base line assumed as 20,000 N.-20,000 E. (Howland and others, 1949). Rock type: Cr, chromite; ol, olivine; br, bronzite or orthopyroxene; cpx, clinopyroxene; pc, plagioclase. Sample type: H, hand-specimen samples; CH-10',1.5', chip sample; first number is the width of outcrop, second number, the chip interval; C-10', channel sample for distance specified, width and depth of channel varies to yield enough rock for analysis; var., varying interval. Limits of determination: <10 ppb Pt, ppb Pd, ppb Rh. tr indicates element is present but below limits of determination and too low to assign a value, all values based on a 15g sample weight] Coordinates Northerly Easterly System Rock Sample Parts per billion type type Pt Pd Rh BASAL ZONE BENBOW AREA 119,245 117,880 BM Chill norite H
119,245 117,880 BM Hornfels H tr
117,645 121,017 BM Gossan <10
117,595 121,036 BM Norite, sulfjde, hornfels H tr
117,512 121,162 BM Diabase dike H <10
119,433 117,645 BM Gossan H
121,413 116,470 BM Gossan in norite H <10
119,704 117,965 BM Br cumulate H <10 tr
NYE LIP AREA 48,000 54,395 NB Norite H "10
47,740 54,570 NB Chill nori te H
MOUNTAIN VIEW AREA 47,822 44,193 ACM Quartz monzonite H <10
47,817 44,190 ACM Hornfels H <lO
47,842 44,115 ACM Massive sulfides CH-40 1 ,4 1 <10 tr "A" tunnel mine dump Massive sulfides H "A" tunnel mine dump Nor~te with sulfides H tr <-5 47,886 43,919 ACM Nori te CH-30 1 ,2 1 <10
47,892 43,815 ACM Hornfels CH-20 I ,1 I
48,040 43,622 ACM Nori te <10
509,780 1,898,130 MS Norite and hornfels CH-50 1 ,5 1 <10
47,060 49,409 ACM Norite H
42,755 49,409 ACM Norite H tr
Table 2. -Platinum, palladium, and rhodium analyses of rocks from the Stillwater Complex, Mont.-Continued Coordinates Rock Sample Parts per billion Northerly Easterly System type type Pt Pd Rh BASAL ZONE-Continued BLUEBIRD PEAK AREA 505,020 ~1,880,380 MS Hornfels H <10
WEST FORK AREA 21,070 15,500 WF Hornfels H
GISH AREA 542,300 1,814,440 MS Hornfels H tr 542,440 1,814,450 MS Norite H tr
ULTRAMAFIC ZONE BENBOH AREA Peridotite Member 119,582 118,615 BM Chromitite, A zone 120,485 117,663 BM Chromitite, B zone H 117,665 121,260 BM Chromitite, B zone H 117,755 121,450 BM 01-br cumulate, B zone CH-20' ,1 I <10 tr
120,387 118,025 BM Chromitite, c zone C-2' 118,443 121,485 BM Chromi ti te, E zone C-4' 119,020 121,340 BM Chromitite, G zone Benbow mill site Chromite concentrate H Benbow tailings pond Mi 11 tailings H 121,734 118,967 BM Chromitite, H zone H 119,427 121,525 BM Gabbro-pegmatite, CPI-9' ,1' J zone 119,410 121,520 BM Chromitite~ J zone CH-2' 119,450 121,545 BM 01-br cumulate, J zone CH-20' ,0 .5' <10 119,695 121,597 BM Chromitite, K zone C-3" <10
119, no 121,586 BM 01 cumulate, K zone CH-8 1 ,0.5 1 <10
119,830 121,580 BM Br cumulate, K zone CH-20 1 ,1 I <10 tr Bronzitite Member -500,000 -1,995,000 MS Br cumulate CH-1700' ,60 1 123,203 120,408 BM Br-cr cumulate C-2.5' NYE LIP AREA Peridotite Member 48,736 55,612 NB Chromitite, A zone H
Table 2.--Platinum, palladium, and Phodium analyses of Pocks fPom the StillwateP Complex, Mont.--Continued Coordinates Northerly Easterly System 49,014 48,588 48,722 48,792 49,063 48,236 48,236 48,172 49,200 48,124 49,823 49,838 49,878 50,235 50,236 50,240 50,314 50,527 55,555 53,205 53,295 53,338 57,030 39,578 39,578 39,538 42,925 42,890 40,801 40,785 40,720 40,428 40,222 40,418 40,406 40,214 Mouat chrome stockpile Mouat Mill Tailings pond 512,540 512,700 512,760 505,140 1,896,540 1,896,700 1,896,900 1,887,650 NB NB NB NB NB ACM ACM ACM ACM ACM ACM ACM ACM ACM ACM ACM ACM ACM MS MS MS MS Rock type Sample type ULTRAMAFIC ZONE--Continued NYE LIP AREA--Continued Peridotite Member--Continued Chromitite, B zone Chromitite, G zone Chromitite, H zone Chromitite, I(?) zone Chromitite, K zone MOUNTAIN VIEW AREA Peridotite Member Gossan H Sulfide box work H Chromitite, A zone 01 cumulate~ H serpentinite Chromitite, A zone 01 cumulate H 01-br cumulate H Br cumulate H Gabbro pegmatite, G zone H Chromitite, G zone Chromitite, G zone 01 cumulate, G zone CH-30 1 ,2 Chromitite, H zone Chromite concentrate Mill tailings Bronzitite Member Br cumulate Br cumulate Br cumulate INITIAL AREA Peridotite Member Chromitite, A zone CH CH CH-220 I ,3 I CH-205 I' 5 I CH-190 1 ,3 1 Parts per billion Pt Pd Rh <10 tr tr <10 <10 <10
tr
tr
Table 2.--Ptatinum, pattadium, and rhodium anatyses of rocks from the Stittwater Comptex, Mont.--Continued Coordinates Parts per billion Northerly Easterly System Rock type Sample type Pt Pd
506,ll0 505,940 21,284 20,415 21,286 21,773 21,285 21,285 20,480 21,284 21,284 21,284 21,284 21,284 21,850 21,284 21,323 21,320 21,633 21,776 dl,979 22,439 22,439 22,439 21,738 1,883,120 1,880,980 17,684 15,350 17,686 14,288 17,684 17,684 15,350 17,684 17,684 17,685 17,685 17,685 14,388 17,684 15,665 15,670 14,776 14,720 15,228 14,745 14,745 14,745 15,938 MS MS WF WF WF WF WF WF WF WF WF WF WF WF WF WF WF WF WF WF WF WF WF WF WF ULTRAMAFIC ZONE-Continued
INITIAL AREA--Continued Peridotite Member--Continued Chromitite, B zone H BLUEBIRD PEAK AREA Peridotite Member Chromitite, B zone H WEST FORK AREA Peridotite Member 01 cumulate CH-10' ,0.6' 11 Chromite, A zone, lower H llOO Chromitite, A zone, lower H Chromite, A zone, lower H Chromitite, A zone, lower C-1' 01 cumulate CH-10' ,0.6' 98 Chromitite, A zone, lower H llO Chromitite, A zone,upper C-0.75' Chromitite, A zone, upper C-0.75' Chromitite, A zone, upper C-9" 01-cr cumulate, A zone upper C- 4" llOO Chromitite, A zone, upper C- 1" Chromitite, A zone, upper H 01 cumulate CH-10' ,0.6' 18 Chrom:i t i te, A zone, upper H Ol clLwulai;e H <10 Chromitite, A zone, lower C-3' Chromitite, A zone, upper C-l' Br cumulate H <10 01 cumulate H <10 Chromitite, G zone C-0.92' 01 cumulate H Chromitite, G zone H nooo
tr llO
Table 2.--Platinum~ palladium~ and rhodium analyses of rocks from the Stillwater Complex~ Mont.--Continued Coordinates Parts per billion Northerly Easterly System Rock type Sample type Pt Pd Rh 21,737 21,802 21,882 22,432 506,460 506,78C 511,260 526,520 524,130 16,958 l7 ,109 17,078 16,595 17,380 16,705 17,200 16,918 499,080 501,540 501,280 501,760 15,937 16,000 16,026 15,803 1,865,740 1,865,970 WF WF WF WF MS MS 1,857, 850 MS 1,839,100 1,838,180 21,635 21,710 21,688 22,378 21,782 22,375 22,058 22,675 1,923,880 1,925,570 1,925,870 1,926,950 MS MS GM GM GM GM GM GM GM GM MS MS MS MS ULTRAMAFIC ZONE--Continued WEST FORK AREA--Continued Peridotite Member--Continued Chromitite, G zone Chromitite, H(?) zone Chromitite, I(?) zone Bronzitite Member Br cumulate CRESCENT CREEK AREA Peridotite Member H C-0.13' C-0.67' H <10 Chromitite, A zone Chromitite, B(?)zone C-2" IRON MOUNTAIN AREA Peridotite Member Chromitite, A(?)B(?) CHROME MOUNTAIN AREA Peridotite Member Chromitite, G zone Mafic dike GISH MEMBER Peridotite Member 01-br cumulate Intrusive dunite Br cumulate Br cumulate Chromltite, G zone Chromitite, G zone 01 cumulate Chromitite, H(?) zone BANDED AND UPPER ZOJ':W BENBOW AREA Br-pc cumulate Br-pc cumulate Pc cumulate Pc cumulate with sulfides CH-L5' ,var. C-0.75' C-1. 67' H <10 H <10 H <10 H <10 H <10 C-16' C-5' H H H H <10 H <10 C-7' <10
tr
tr
tr
Table 2.--Platinum, palladium, and rhodium analyses of rocks from the Stillwater Complex, Mont.--Continued Coordinates Rock Sample Parts per billion Northerly Easterly System type type Pt Pd Rh BANDED AND U~PE~ZONE--Continued BENBOW AREA--Continued 501,840 l. 927,020 MS Pc cumulate with sulfide~ H <10
501,720 1,926,900 MS Pc-cpx cumulate H <10
MOUNTAIN VIEW AREA 512,840 1,897,020 MS Pc-br cumulate H
512,000 1,899,400 MS Pc-br cumulate CH- 45 1 ,2'
512,000 1,899,580 MS Pc-br cumulate H tr
513,260 1,899,890 MS Pc cumulate CH-10'1] <10
513,550 1,900,000 MS Pc cumulate CH-7', l' 513,560 1,900,000 MS Pc-br-cpx cumulate H <10
513,830 1,900,480 MS Pc-br-cpx cumulate CH-60'5' <10
514,510 1,900,940 MS Pc-br-cpx cumulate CH-8' ,0.5' <10 tr
514,510 1,900,940 MS Pc-br-cpx cumulate H <10
514,550 1,900,990 MS Pc-ol cumulate CH-15' ,0.5' <10 tr
514,540 1,900,990 MS Pc-ol cumulate H <10
514,550 1,900,990 MS Pc-ol cumulate, altered H <10
514,560 1,900,990 MS Pc-ol cumulate H <10
514,560 1,900,990 MS Pc-ol cumulate H <10
514,590 1,901,030 MS Pc cumulate CH-84',1' <10
514,590 1,901,030 MS Pc cumulate H <10
514,590 1,901,030 MS Pc cumulate with sulfides C-30" <10
514,600 l ,901,030 MS Pc cumulate, shear zone H <10
514,750 1,901,020 MS Pc-br-cpx cumulate CH-40',3' <10
514,600 1,901,980 MS Pc-br-cpx cumulate H <10
PICKET PIN PEAK AREA 531,200 1,859,800 MS Pc cumulate with sulfides CH-15' ,0.5' <10
GISH AREA 541,260 1,820,920 MS Br-pc cumulate H <10
Table 3.--APithmetic avePages of Pt, Pd, and Rh, in paPts peP billion, fop zones, membePs, and Pock types of the StillwateP Complex, Mont. Number of Zone or rock type samples Basal zone Ultramafic zone Peridotite member A chromitite B chromitite C chromitite E chromitite G chromitite H chromitite Mil1 concentrates Mill tailings 1 chromitite J chromitite K chromitite Average chromitite-- Other cumulus rocks Bronzitite member Banded and Upper zone Arithmetic average Pt Pd Rh 2,290.2 Sum of averages Pt+Pd+Rh 1,050.1 3,525.0 1,546.3 Range of l:(Pt+Pd+Rh) 4-20 '700 4-20 '700 227-20,700 41-20,700 GPO 87 5·9 41