ISSN 10757015, Geology of Ore Deposits, 2015, Vol. 57, No. 5, pp. 402–432. © Pleiades Publishing, Ltd., 2015. Original Russian Text © E.M. Spiridonov, E.A. Kulagov, A.A. Serova, I.M. Kulikova, N.N. Korotaeva, E.V. Sereda, I.N. Tushentsova, S.N. Belyakov, N.N. Zhukov, 2015, published in Geologiya Rudnykh Mestorozhdenii, 2015, Vol. 57, No. 5, pp. 445–476.

Genetic Pd, Pt, Au, Ag, and Rh Mineralogy in Noril’sk Sulfide Ores E. M. Spiridonova, E. A. Kulagovb, †, A. A. Serovaa, I. M. Kulikovac, N. N. Korotaevaa, E. V. Seredad, I. N. Tushentsovad, S. N. Belyakovb, and N. N. Zhukova a

Moscow State University, Moscow, 119991 Russia Noril’sk Mining and Metallurgical Combine, Gvardeiskaya pl. 2, Noril’sk, 663310 Russia c Institute of Mineralogy, Geochemistry, and Crystal Chemistry of Rare Elements, ul. Veresaeva 15, Moscow, 121357 Russia Noril’skgeologiya OOO, Promzona 1, Noril’sk, 663300 Russia b

Received January 26, 2014

Abstract—The undeformed orebearing intrusions of the Noril’sk ore field (NOF) cut through volcanic rocks of the Late Permian–Early Triassic trap association folded in brachysynclines. Due to the nonuniform load on the roof of intrusive bodies, most sulfide melts were squeezed, up to the tops of orebearing intrusions; readily fusible Ni–Fe–Cu sulfide melts were almost completely squeezed. In our opinion, not only one but two stages of mineralization developed at the Noril’sk deposits: (i) syntrap magmatic and (ii) epigenetic post trap metamorphic–hydrothermal. All platinumgroup minerals (PGM) and minerals of gold are metaso matic in the Noril’sk ores. They replaced sulfide solid solutions and exsolution structures. All types of PGM and Au minerals occur in the ores, varying in composition from pyrrhotite to chalcopyrite, talnakhite, moo ihoekite, and rich in galena; they are localized in the inner and outer contact zones and differ only in the quantitative proportions of ore minerals. The aureoles of PGM and Au–Ag minerals are wider than the con tours of sulfide bodies and coincide with halos of fluid impact on orebodies and adjacent host rocks. The pneumatolytic PGM and Au–Ag minerals are correlated in abundance with the dimensions of sulfide bodies. Their amounts are maximal in veins of late fusible ore composed of eutectic PbSss and iss intergrowths, as well as at their contacts. The Pd and Pt contents in eutectic sulfide ores of NOF are the world’s highest. In the process of noblemetal mineral formation, the fluids supply Pd, Pt, Au, As, Sb, Sn, Bi, and a part of Te, whereas Fe, Ni, Cu, Pb, Ag, Rh, a part of Te and Pd are leached from the replaced sulfide minerals. The pneu matolytic PGM of the early stage comprises Pd and Pt intermetallic compounds enriched in Au along with Pd–Pt–Fe–Ni–Cu–Sn–Pb(As) and (Pd,Pt,Au)(Sn,Sb,Bi,Te,As) solid solutions. Pneumatolytic PGM and Au minerals of the middle stage are products of solidphase transformation and recrystallization of early PGM in combination with the newly formed mineral species Sbpaolovite–insizwaite–geversite–maslovite, niggliite, tetraferroplatinum, rustenburgite–atokite–zvyagintsevite, moncheite, majakite, plumbopalla dinite, polarite in association with altaite. The late minerals of the middle stage include stannopalladinite, tatianaite–taimyrite, Ag–Pd–Pt tetraauricupride, and cuproauride. PGM and Au–Ag minerals of the late stage are represented by sobolevskite–sudburyite–kotulskite, maslovite–michenerite, lowSb paolovite, hes site, cabriite, Au–Ag minerals with fineness of 870–003, froodite, Sbfree insizwaite, Bifree geversite, and Sbfree niggliite. Electrum and küstelite in PGM aggregates are not zoned. Crystals of Au–Ag minerals that grow over PGM minerals are smoothly zoned. Their zoning may be direct (crystal margins are enriched in Ag), inverse, oscillatory, and complex. Despite favorable annealing conditions, exsolution structures are not identified in Au–Ag minerals from the Noril’sk ores. Sperrylite—the latest of pneumatolytic PGM—occurs as metacrysts up to 14 cm in size. Sperrylite, which replaces highSb minerals, contains up to 11 wt % Sb. Pneumatolytic noblemetal minerals originated under the effect of the fluids released during crystallization of sulfide melts in an extremely reductive setting and at extremely low fS2; temperature drops from ~450 to ~350°C. Metamorphic–hydrothermal Ag mineralization (native silver, Hgsilver, sulfides and selenides, chalcopyrite–lenaite solid solutions, argentopentlandite), Pd mineralization (vysotskite, palladoarsenide, vincentite, Sbfree Agpaolovite, malyshevite, native palladium), and Pt mineralization (kharaelakhite, coo perite, native platinum) develop in those parts of orebodies that are affected by lowgrade metamorphism. DOI: 10.1134/S1075701515050062 †

INTRODUCTION Platinum group elements (PGE) are readily dis solved in metallic sulfide melts that are close in prop erties. For this reason, PGE behavior in low and Corresponding author [email protected] † Deceased.

E.M.

Spiridonov.

Email:

highsulfide mafic–ultramafic magmatic systems is radically distinct. Highsulfide mantlederived mag matic systems, e.g., Noril’sk, are richer by orders of magnitude in PGE than the same crustal systems, e.g., Sudbury. At elevated temperatures, PGE are typically chalcophile elements, which have a striking affinity to S, As, Te, Sb, Bi, and Sn. The standard trend of noble metals in hightemperature endogenic processes is as

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follows: Ru (+S) → Os (+S) → Ir (+S) → Rh (+S) → Pt + Au + Ag (±S, As) → Pd + Au + Ag (+S, As, Sb, Bi, Te, Sn, Pb) → Au + Pd + Ag (±S, As, Sb, Bi, Te, Sn, Pb). The deposits of the Noril’sk ore field, which con tain most of the world’s Pd reserves and make an appreciable contribution to Pt reserves, are remarkable phenomena of the East Siberian Platform. These depos its were studied by V.K. Kotulsky, M.N. Godlevsky, N.S. Zontov, V.A. Maslov, V.V. Zolotukhin, E.A. Kulagov, V.K. Stepanov, D.M. Turovtsev, A.D. Genkin, V.V. Ryabov, V.A. Lyul’ko, Yu.N. Amosov, O.N. Simonov, A.D. Nal drett, A.A. Filimonova, S.F. Sluzhenikin, T.L. Evstigne eva, V.V. Distler, G.A. Mitenkov, V.M. Isoitko, N.A. Krivolutskaya, A.V. Tarasov, A.M. Karpenkov, V.A. Kovalenker, the authors of this paper, and other geologists. Despite numerous publications concerned with Rh–Ag–Au–Pt–Pd mineralization of the NOF (Zvy agintsev, 1940; Iskyul, 1940; Maslenitsky et al., 1947; Mikheev et al., 1961; Genkin and Zvyagintsev, 1962; Genkin et al., 1966, 1974, 1981, 1985; Genkin, 1968; Zhuravlev et al., 1968; Kulagov, 1968; Evstigneeva et al., 1975, 1990; Begizov and Sluzhenikin, 1976; Begizov, 1977; Kulagov et al., 1978; Kovalenker et al., 1979a; Evstigneeva, 1980; Begizov et al., 1981; Evstigneeva and Genkin, 1983; 1990; Sluzhenikin et al., 1994; Izoitko, 1997; Mitenkov et al., 1997; Dis tler et al., 1999; Barkov et al., 2000a, 200b; Spiridonov et al., 2003–2013, 2014; Naldrett, 2004; Spiridonov, 2004; Vymazalová et al., 2009; Spiridonov, 2010; Kriv olutskaya et al., 2011; Sluzhenikin and Mokhov, 2015, and others), we are only beginning to understand the formation history of noblemetal minerals in Noril’sk ores, which is not simple. Most geologists have regarded and do regard PGM as products of mag matic–latemagmatic crystallization; however, A.D. Genkin and T.L. Evstigneeva had already estab lished that a part of PGM are typical metacrysts, i.e., products of solidphase replacements. Our observa tions have shown that all PGM hosted in Noril’sk ores are metasomatic in origin and replace not only high temperature sulfide solid solutions, but also the prod ucts of their annealing and breakdown. A.D. Genkin and O.E. Zvyagintsev established that some PGM, e.g., vysotskite, are associated with hydrothermal minerals, e.g., actinolite, and probably originated with the involvement of matter of replaced sulfides, e.g., Pd from pentlandite. Later on, T.L. Evstigneeva revealed the parageneses of some PGM with minerals of a “ser pentinite stage.” It was assumed that hydrothermal alteration is a derivative of trap formation. In our opinion, not only one but two mineralization stages developed at the Noril’sk deposits: (i) syntrap mag matic to pneumatolytic and (ii) epigenetic posttrap metamorphic–hydrothermal. GEOLOGY OF ORE DEPOSITS

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MATERIALS AND METHODS We have studied many hundreds of samples col lected representing massive, disseminated (drop stones, etc.), amygdaloid (mandelstein), and impreg nated ores to lowsulfide varieties from the under ground works of all operating mines and open pits in the NOF, a series of prospect and exploration bore holes within a depth interval from the surface (Moro zov Mine) to –1600 m. Many tens of samples from collections gathered by the geological exploration departments of the Oktyabrsky, Taimyr, Komsomol sky, Mayak (Majak), and Zapolyarny mines. The pur poseful search for noblemetal minerals in ore was carried out by sawing large hand specimens. Rocks hosting sulfide and lowsulfide ore lodes and products of lowgrade metamorphism were examined thor oughly. Comparative data on metavolcanic rocks of trap association have been obtained for the Noril’sk region at a distance up to 200 m from the NOF. The analysis of Pb isotopes in galena, altaite, and intermetallic Pd compounds from eight samples of sulfide ores and six samples of galena from carbonate veins was carried out by V.N. Golubev at the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences (IGEM RAS) using the technique described by Chernyshev et al. (2004). This work is based on the results of study of 2–10 μm3sized samples of definite Pb minerals. Isotopic analysis was performed on a Neptune Thermo Finnigan (Germany) MCICPMS spectrometer. Preparations recovered from polished sections were dissolved in concentrated HNO3; the solution was dried, and a dry residue was converted to a 3% HNO3 solution containing ~20 ng/L Tl. The Pb content in H2O and HNO3 reagents did not exceed 10 pg/mL. Calibration of amplifiers was conducted at the onset of each measurement session. All analyses were carried out in a static regime. The isotopic analysis comprised recording 30 mass spectra. Correction of measured 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios for mass discrimination was realized by normal ization to 205Tl/203Tl. Correction for interference of 204Hg+ and 204Pb+ mass lines was conducted by 202Hg+ intensity, which was recorded simultaneously with Pb isotopes. The contribution of 204Hg+ to total error of 208Pb/204Pb, 206Pb/204Pb, and 207Pb/204Pb measurements is less than 0.001. The complete 2σ uncertainties of measurements are as follows: 0.024 for 208Pb/204Pb, 0.022 for 207Pb/204Pb and 206Pb/204Pb, 0.004 for 207Pb/206Pb, and 0.010 for 208Pb/206Pb. The thermobarogeochemical study of fluid inclu sions was carried out by V.Yu. Prokof’ev on a Linkam THMSG600 heating stage within a temperature range from –196 to +600°С, accuracy ±1.5–2°C at the IGEM RAS. The Rb/Sr isotopic age of apophyllite was deter mined by V.N. Golubev at the IGEM RAS.

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The chemical compositions of ore minerals were determined by I.M. Kulikova at the Institute of Min eralogy, Geochemistry, and Crystal Chemistry of Rare Elements (IMGRE) using a CamebaxMicrobeam electron microprobe operating at an accelerating volt age of 20 kV, a current strength of 30 nA, and an expo sition of 10–16 s for each line; standards are as follows: pure metals, including Pt, Bi (Mα), Pd, Au, Sb (Lα), and Ni (Kα); synthetic PbTe (PbMα, TeLα), HgS (HgMβ), GaAs (AsLα), SnO2 (Sn), Ag2Te (Ag), FeS2 (FeKα), Cu3VS4 (Cu). Detection limits (wt %) were 0.07 Pb, 0.05 Pt, Bi, and 0.03 Pd, Rh, Sn, Au, Ag. Concentrations were calculated using the SetZaf pro gram with standard ZAFcorrection. Microprobe analyses were performed in target areas using high quality electron photomicrographs taken by N.N. Korotaeva and maps of chemicalelement dis tribution (JSM6480LV SEM, the Department of Petrology, Moscow State University); 2770 complete analyses of PGM and Au–Ag minerals have been obtained. GEOLOGY OF ORE FIELD The Noril’sk ore field is situated in a zone of mar ginal dislocations in the northwestern corner of the ancient East Siberian Platform. The thickness of the Earth’s crust is 42–48 km, including 34–40 km of deformed Archean and Proterozoic crystalline schists and amphibolites (platform basement) and 8–18 km of slightly deformed and metamorphosed Riphean– Vendian–Phanerozoic sequences (plate cover) (Simo nov et al., 1994). The platform basement is broken by numerous faults. The Noril’sk ore cluster in the south west of NOF and the Talnakh ore cluster in the north east of NOF (20 km apart) are accommodated in plate cover composed of Riphean terrigenous sequences (~2.5 km), variegated anhydrite–carbonate–terrige nous sequences from Upper Riphean to Carbonifer ous in age (5.5–9.0 km), Carboniferous–Permian coalbearing Tunguska Series (~0.5 km), and Upper Permian–Lower Triassic plateau basalts (up to 4 km) (Simonov et al., 1994). The anhydrite sequences con tain halite and lessfrequent sylvite lenses, brine lenses, and spots of naphtides. The Upper Permian–Lower Triassic traps occur not only on the East Siberian Platform but also fill a series of large rifts in the West Siberian epiCale donian–epiHercynian plate. The trap association was formed under conditions of extension and con comitant volcanic activity, which periodically alter nated with compression and related intrusions. Volca nic rocks of the trap association vary from alkali oliv ine basalt to dominating tholeiitic basalt. Basic intrusions vary from barren tholeiitic gabbrodolerite to orebearing picritic and olivine gabbrodolerite enriched in potassium (Godlevsky, 1959; Genesis …, 1981, Lightfoot et al., 1993; Walker et al., 1994). Igne

ous rocks of the trap association are related to mantle magma sources (Fig. 1). In the Noril’sk region, the plate cover is deformed with the formation of the Noril’sk, Vologochan, and Kharaekakh lowangle brachysynclines and steeper anticlines complicated by variously oriented folds (Simonov et al., 1994). The total thickness of volcanic sequences is ~1 km in core of the Noril’sk Brachysyn cline and ~3.5 km in the core of the Kharaekakh Brachysyncline. The dislocations are represented by steeply dipping normal and normal–strikeslip faults and less often by inclined reverse faults, reverse–strike slip, and under and overthrust faults with up to hun dreds of meters in offset. The plate cover of the East Siberian Platform was apparently folded due to the opening of large rifts in the West Siberian Plate. AGE OF TRAP ASSOCIATION AND NORIL’SK DEPOSITS This is not a customary case where the problem of age can be reliably solved. The giant Late Permian– Early Triassic trap association primarily composed of continental tholeiites develops in the northwestern and central parts of the East Siberian Platform. Isoto pic Ar/Ar, U–Pb, and Rb–Sr ages of plateau basalts are 251 ± 3 Ma (Naldrett, 2004). Judging by paleo magnetic data on plateau basalts of the trap associa tion, basaltic eruptions lasted for no longer than 1.7 Ma (Pavlov et al., 2011). The U–Pb isotopic dat ings of baddeleyite and zircon from orebearing intru sions are 251.2 ± 0.3 Ma (Kamo et al., 1996). The Ar/Ar age of plagioclase, biotite–phlogopite, and amphibole from orebearing intrusive rocks and Re– Os dating of sulfide ore from the Noril’sk ore field are 250 ± (1–2) Ma (Wooden et al., 1992; Walker et al., 1994; Naldrett, 2004). According to Yu.M. Sheinman, the younger (Early Triassic) Maimecha–Kotui association of ultramafic– alkaline igneous rocks, alkali lamprophyres, and car bonatites with Ir–Os specialization occurring in the north of the East Siberian Craton corresponds to pale omagnetic polarity the next after trap association (Pavlov et al., 2011). Its isotopic age is about 250 Ma, younger than the trap age by 1 Ma (Arndt et al., 1998). The Noril’sk orebearing intrusions and sulfide lodes are intersected by alkali lamprophyre dikes (phlogo pite minette) of the Maimecha–Kotui association. Such relationships have been observed in the under ground workings of the Zapolyarny and Oktyabrsky Mines. Thus, the duration of the active life of the Noril’sk ore–magmatic system does not exceed 1 Ma. OREBEARING INTRUSIONS AND RELATED ORE DEPOSITS The ore deposits in the Noril’sk ore field are genet ically related to intrusions. The undeformed orebear ing intrusions of the NOF cut through the volcanic GEOLOGY OF ORE DEPOSITS

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Fig. 1. 206Pb/204Pb versus 207Pb/204Pb for rocks and ores of trap association in Noril’sk district. Evolution lines of Pb isotopic composition in various reservoirs are given after Doe and Zartman (1979). (1) Basalts of trap association, after Lightfoot et al. (1993) and Czamanske et al. (1994); (2) gabbrodolerite of Noril’sk intrusions, after Czamanske et al. (1994); (3) magmatic sulfide ore of Noril’sk ore cluster, after Wooden et al. (1992) and Spiridonov et al. (2010); (4) gabbrodolerite of Talnakh and Kharaelakh intrusions, after Czamanske et al. (1994); (5) magmatic sulfide ore of Talnakh ore cluster, after Wooden et al. (1992) and Spiri donov et al. (2010); (6) magmatic PbSss of Talnakh ore cluster; (7, 8) pneumatolytic galena and altaite from magmatic sulfide ore of Talnakh ore cluster: (9) palladium intermetallic compounds: zvyagintsevite and Pbatokite of Noril’sk ore district; (10) palla dium intermetallic compounds of Talnakh ore district; (11) galena from epigenetic posttrap metamorphic–hydrothermal ars enide–carbonate veins; (12) galena from arsenide–carbonate veins in association with uraninite. (6–12) after Spiridonov et al. (2010).

rocks of trap association folded into brachysynclines. The injection of mantlederived sulfidebearing basic melts along the steeply dipping Noril’sk–Kharaelakh 1

Fault apparently took place in the process of folding. The deposits are related to the Noril’sk I and II, Upper Talnakh, and Taimyr (Kharaelakh) intrusions of oliv ine and picritic gabbrodolerites, gabbronoritic doler ite, gabbroanorthosite, plagiolherzolite, troctolite, and gabbrodiorite (Kotulsky, 1946; Godlevsky, 1959; Natorkhin et al., 1977; Genezis …, 1981; Zolotukhin, 1988; Distler et al. 1999; Turovtsev, 2002). The Noril’sk intrusions make up the Noril’sk ore cluster (Medvezhy Creek, Ugol’ny Creek, Zapolyarny mines) and the Talnakh (Taimyr–Talnakh) ore clusters (Mayak (Majak), Komsomolsky, Oktyabrsky, Taimyr, Skal’ny mines). The orebearing intrusions are extended ribbon and troughlike bodies cutting the country rocks at angles of 4°–10°. Noril’sk intrusions were emplaced into the Noril’sk Brachysyncline from the from plat form boundary in the southwest to the northeast. The Talnakh and Taimyr intrusions were emplaced into the Kharaelakh Brachysyncline from platform boundary in the northeast to the southwest. Orebearing intru 1 This fault was first mapped by Yu.M. Sheinmann in 1942.

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sions of the Noril’sk type are distinguished by the abundance of moderately magnesian olivine and Cr spinel. Magma of barren intrusions was depleted in fluids (Sobolev, 1936). The hightemperature magma of orebearing intrusions was saturated with fluids; this is emphasized by wide zonal aureoles of the rocks transformed into hornfels (Turovtsev, 2002). Contact hornfels are not enriched in PGE and Au. Thus, the fluids of magmatic studies were depleted in noble met als, which were dissolved in sulfide melts. In the course of magmatic crystallization, water and halogens accu mulated and saturated sulfide melts together with potassium, which also enriches orebearing magma. Coal of the Tunguska Series is metamorphosed to graphite under the effect of orebearing intrusions (Godlevsky, 1959; Turovtsev, 2002). Coal of the Tun guska Series contains 25–38% volatile components. The intensely graphitized coal (as far as 300 m from intrusive contact) retains 4–10% volatile components. Contact metamorphism was accompanied by the release of an enormous volume of hightemperature reduced gases (CH4, H2, CO), which actively inter acted with anhydrite of Paleozoic sedimentary sequences to form H2S, SO2, and COS enriched in 34S. Approaching the cooling and contracting hot intru sions and country rocks, these gases intensely inter

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fels underlying the intrusions. The main lodes of mas sive ore are localized beneath the Kharaelakh–Taimyr intrusion, including the world’s largest Main Kharaelakh Lode 3000 × 1000 m in area and 5–75 m in thickness. The more fusible Ni–Fe–Cu sulfide melts were squeezed out into the top of intrusions almost completely or partly and then up to 800 m beyond the intrusions.

300 µm

Fig. 2. Amygdaloid ore from Medvezhy Creek. Minicast ing of sulfide melt in gas cavity of trap basalt. Reaction fay alite (light gray) and highTi biotite (black) at contact with basalt and among mss and iss (white) as products of Fe– Cu–Ni sulfide melt crystallization. Image in reflected electrons.

acted with Febearing minerals. As a result, fine sul fide disseminations as well as secondary sulfide melt were formed in rocks (Zolotukhin, 1988). This par tially explains the great amount of sulfide melts in NOF and the quasianhydrite type of sulfur isotopic composition enriched in 34S typical of sideronite and massive ores (Godlevsky and Grinenko, 1963); the lowered contents of noble metals therein as compared with dropstone ore; and the elevated contents of radiogenic (crustal) osmium in sideronite and massive ores. The data on geochemistry of volatile Re give evi dence that the intrusion–sulfide lode system is closed (Walker et al., 1994). SULFIDE ORE LODES Magmatic sulfides occur as disseminations in intrusions; lodes, veins, and impregnations in contact zones of orebearing intrusions, including minicast ings in gas hollows of plateau basalt (Fig. 2); and veins within and off the orebearing intrusions. The dissem inated, sideronitic, and massive sulfide ores are mostly localized in apical parts of intrusions. Sulfide drops of magmatic “rain” (fragments of primary sulfide melts) are a widespread type of ore. A certain portion of this rain is stuck in bottom intrusive rocks enriched in oli vine and Crspinel; however, most of the sulfide rain trickled down into depressions of the intrusion bot tom. Due to the cooling and contraction of intrusive bodies, a certain mass of sulfide melt has been squeezed out beyond their limits frequently into horn

The crystal fractionation trend of sulfide melt com bines monosulfide solid solution Mss1 (Т ~ 1100°C) → Mss2 → intermediate solid solution Iss1 → Iss2 to Iss5 (Т ~ 750°C) and is characterized by gain of Cu and loss of Fe. This results in the zonal structure of sulfide bodies from small drops to giant lodes. The hightem perature mss of large lodes is not quite monosulfide and is enriched in sulfur. Therefore the minerals of the chalcopyrite group depleted in sulfur (talnakhite, mooihoekite, putoranite) rather than standard chal copyrite are predominant as late products of fraction ation; iss as a lighter product of fractionation is concen trated at the roof of sulfide bodies. Ni and Co are distrib uted in approximately equal amounts in mss and iss. Noble metals are quite another matter. The refrac tory PGE (Ru, Os, Ir, and especially Rh) accumulate in mss, whereas the easily melted Pt and Pd, as well as Au and Ag accumulate in iss. These features were already established by Vogt (1927). ORES AS EUTECTIC INTERGROWTHS Schlieren, pockets, and veins of graphic eutectic iss intergrowths and solid solution based on PbSss as products of crystallization of fusible (600–510°C) sul fide Ni–Fe–Cu–Pb melts are a remarkable feature of the NOF deposits. The abundant potassium and coherent lead in the Noril’sk ore–magmatic systems are the cause of their occurrence. Several generations of crosscutting veins of eutectic sulfide (Fig. 3a) ore are observed in various parts of massive sulfide lodes, as well as in host intrusive rocks and hornfels. The con tacts of these bodies are distinct but not sharp. Length of veins along the strike and down the dip is a few meters and occasionally reaches 10–15 m; thickness is 1–50 cm and sporadically larger. These bodies are concentrated at the upper selvage of large sulfide lodes. The NWtrending pockets and veins are espe cially abundant at the upper selvage in center of the Main Kharaelakh Lode. Judging by the cleavage of galena, the crystal size of iss and PbSss in eutectic intergrowths varies from fractions of a millimeter to 120 mm. Based on Se distribution in coexisting chal copyrite and galena of eutectic intergrowths (Betke– Barton geotermometer, 1971), their formation tem perature is 507°С (Kovalenker et al., 1979b). GEOLOGY OF ORE DEPOSITS

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Fig. 3. (a) eutectic ores of two generations. Graphic intergrowths of iss and PbSss as products of crystallization of readily fusible Pb–Cu–Fe–Ni sulfide melt from vein at roof of Main Kharaelakh Lode. Image in reflected electrons; (b) PGE and Au contents in eutectic ores (graphic PbSss–iss intergrowths in Talnakh ore cluster, after Spiridonov (2010) and in ore of UG2 Unit and Mer ensky Reef in Bushveld (Naldrett, 2004).

SOLIDPHASE TRANSFORMATION OF SULFIDE MINERALS Diverse solidphase transformations of sulfide solid solutions occur after crystallization of sulfide melts: (1) phase transformations of cubic iss into tetragonal chalcopyrite, orthorhombic cubanite, etc. and exsolu tion with segregation of pentlandite, cubanite, etc. take place throughout; (2) locally developed partial or complete recrystallization of exsolution structures, twins of polymorph transformations, etc.; (3) local partial redeposition of ore matter with formation of pyrrhotite, cubanite, or chalcopyrite veinlets. Twins of polymorph transition and exsolution lamellae are cor related in dimensions with sulfide bodies: in minicast ings, they are micrometersized and up to 25 cm in the center of the Main Kharaelakh Lode (cubanite–chal copyrite). The highAg pentlandite contains exsolu tion lamellae of argentopentlandite. In the course of cooling, the iss eutectic ore is transformed into chal copyrite or/and talnakhite, mooihoekite, putoranite ± cubanite and pentlandite. Being cooled, PbSss is con verted into galena matrix with numerous altaite PbTe lamellae. Judging by the composition of Tebearing galena and Sbearing altaite, PBSss breaks down from a temperature of 490–470°C (Spiridonov, 2010) to 420–415°С (Kovalenker et al., 1979b). COMPOSITION OF PRIMARY SULFIDE ORE The primary ore is composed of products of solid phase transformations of mss and iss and magnetite GEOLOGY OF ORE DEPOSITS

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(Godlevsky, 1959; Kulagov, 1968; Genkin et al., 1981). According to the data of the geological exploration departments at the Zapolyarny, Mayak (Majak), Komsomolsky, Oktyabrsky, and Taimyr mines, the substantially pyrrhotite ore contains a few gpt Pd and Pt, up to 0.5 gpt Os, up to 2 gpt Ru, and up to 20 gpt Rh. The substantially cupriferous chalcopyrite, talna khite, mooihoekite, and putoranite ores contain from a few tens to 100 gpt Pd and Pt, hundredths of gpt Os and Ir, up to 0.5 gpt Ru and up to 5 gpt Rh. The Rh content in chalcopyrite–pyrrhotite ore is commonly 5–10 times higher than in pentlandite–chalcopyrite ore (Kulagov, 1968). An average proportion of noble metals in ores is Pd : Pt : Ag : Au ~40 : 15 : 40 : 1 (Nal drett, 2004). The sulfide ores composed of PbSss–iss inter growths are extremely rich in Pd, Pt, Ag, and Au: 1204 (25–5296), 537 (5–6119), 1217 (169–2985), and 17 (up to 88) gpt, respectively. These ores contain 3.8 gpt Rh, 0.14 gpt Ru, and traces of Os and Ir, on average (Spiridonov, 2010). These are the world’s richest Pd and Pt deposits per sulfide mass unit (Fig. 3b). AUREOLES OF FLUID IMPACT AROUND SULFIDE BODIES The sulfides melts are very rich in volatile compo nents. Aureoles of fluid impact develop around each body of magmatic sulfides from minicastings to giant lodes. The size of these aureoles correlates with the dimensions of sulfide bodies: up to 4 mm near mini

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SPIRIDONOV et al. Apatite(CaCl) 0% 100%

25%

1

Pneumatolytic trends

75%

50%

75%

Mines: Skalisty Mayak (Majak) Oktyabrsky

50%

2

100% 0% 25% Apatite(CaF)

25%

50%

75%

0% 100% Apatite(CaOH)

Fig. 4. Composition of apatite from Noril’sk sulfide ore and its evolution. Numbers in figure: 1, first generation, trend toward chlorapatite; 2, second generation, trend toward fluorapatite.

castings, up to 12 mm around drops, and up to 15 m and larger above the Kharaelakh lode. The aureoles of fluid impact are composed of highTi biotite and phl ogopite with appreciable F and Cl contents, chlorapatite, hydroxylchlorfluorapatite, and fluorapatite (Fig. 4), hastingsite, anhydrite, titanomagnetite, ilmenite with baddeleyite lamellae, and alkaline Clbearing sulfides (djerfisherite, bartonite) (Godlevsky, 1959; Genkin et al., 1981; Distler et al., 1999; Spiridonov, 2010). The newly formed highTi biotite above the Kharaelakh ore lode occupies up to 30 vol % of horn fels and up to 20 vol % of nearcontact gabbrodolerite. Five meters above roof of the Kharaelakh lode, a par gasite pocket with sperrylite crystals 8 mm long was observed in underground works of the Oktyabrsky Mine. According to the geological exploration depart ment of the Komsomolsky Mine, any rock type at a distance up to 15 m from the upper contact of the Kharaelakh sulfide lode contains 1.5–2.0 times more PGE and Au than similar rocks located at the same level separately, which is evidence for the fluid impact of the crystallizing sulfide melt. Judging by the sub stantially hydroxyl composition of biotite and amphiboles in aureoles of fluid impact, aqueous vapor first dominates in fluid (Zhu and Sverjensky, 1991). Owing to abundant potassium, almost the entire mass of aqueous vapor is fixed in hydroxylbiotite. A certain part of aqueous vapor is linked to hastingsite and amphiboles close in composition. Further, judging by the composition of pneumatolytic apatite, chlorine and then fluorine become among the leading compo nents of fluid (Zhu and Sverjensky, 1991), see Fig. 4, along with the reduced gases carbon monoxide,

hydrocarbons, and probably fullerenes. This is a cause of extremely reductive setting during formation of pneumatolytic PGM with abundant bismuthides, stannides, plumbides, and cuprides. LEAD ISOTOPIC COMPOSITION Judging by the lead isotopic composition (Fig. 1), all rocks of trap association in the Noril’sk region had a single mantle source. As is evident from geochemis try, the mantlederived melts were appreciably con taminated with continental crustal material (Wooden et al., 1992; Lightfoot et al., 1993; Czamanske et al., 1994; Naldrett, 2004). The Pb isotopic compositions of orebearing intrusions and sulfide ores from the Noril’sk and Talnakh clusters are markedly different: in the Talnakh cluster it is much more radiogenic (Spiridonov et al., 2010). The range of Pb isotopic compositions of magmatic PbSss, pneumatolytic galena and altaite from the Talnakh cluster is extremely narrow. The Pb isotopic composition of plumbopalladinite and polarite from this cluster is almost the same. The Pb isotopic compositions of zvy agintsevite and Pbatokite from the Noril’sk cluster significantly differ from that of the Talnakh minerals and fall in the field of Noril’sk ores. This is evidence for the genetic links of sulfide ores to specific intru sions, for distinct mantle sources in the Noril’sk and the Talnakh ore clusters, and for a higher degree of mantlederived magma contamination in the Talnakh ore cluster, and this, probably, ensures the giant scope of mineralization (Spiridonov, 2010). GEOLOGY OF ORE DEPOSITS

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iss PbSss

PGM

1000 µm

(a)

(b)

500 µm

Alt

PbSss

100 µm

(c)

(d)

Fig. 5. (a, b) pneumatolytic PGM of early stage: (a) pocket of metacrysts (intergrowths) of tetraferroplatinum and atokite (light) in magmatic magnetite–pentlandite–chalcopyrite–cubanite ore. Zapolyarny Mine; (b) metasomatic PGM in eutectic PbSss– iss ore. Oktyabrsky Mine; (c) metasomatic altaite (Alt) with PGM microinclusions (“cabbage” at margin of PbSss grain (white) in eutectic ore. Taimyr Mine; (a–c) images in reflected electrons; (d) closeup of Fig. 5c, Xray map of tellurium.

PNEUMATOLYTIC Rh–Ag–Au–Pt–Pd MINERALIZATION The substantial portion of Pd, Pt, Au, and Ag in ores of the NOF is represented by their proper miner als; a part is dispersed in sulfides, e.g., Pd and Ag in pentlandite; Rh is mostly dispersed in pyrrhotite (Kulagov, 1968). All types of PGM and Au–Ag minerals in sulfide ores are metasomatic phases replacing sulfide solid solutions and products of their exsolution (Fig. 5). Sil icate aggregates along contacts with sulfide bodies are frequently metasomatic as well. PGM and Au miner als commonly occur in the areas where exsolution structures of iss and PbSss are recrystallized. These minerals are approximately identical in all varieties of magmatic sulfide ores, from pyrrhotite to chalcopy GEOLOGY OF ORE DEPOSITS

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rite, talnakhite, mooihoekite; massive, impregnated, and disseminated; inner and outer contact zones. Only the quantitative proportions of PGM and Au minerals are variable (Mitenkov et al., 1997; Spiri donov, 2010). The aureoles of PGM and Au minerals are somewhat wider than the contours of sulfide bodies and coincide with aureoles of fluid impact around the sulfide bodies. Early Pneumatolytic PGM The early pneumatolytic Pd–Pt intermetallic com pounds are solid solutions with extensive replacement of Pt–Pd–Au and Sn–Sb–Bi–Pb–Te–As, probably cubic, which contain from 0.5 to 3–8 wt % Au. Lamel lar exsolution structures are characteristic. The inter growths of tetraferroplatinum Pt2Fe(Fe,Ni,Cu) with

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At At Tfp Rsb

Tfp Mjk 100 µm

(a)

Pol Pbpd

(c)

Snpd

30 µm

20 µm

(b)

Pd3Pb 100 Atokite 10 Rustenburgite 90 Zvyagintsevite 20 80 30 70 40 60 50 50 60 40 70 30 80 20 90 10 100 Pt3Sn Pd3Sn 100 90 80 70 60 50 40 30 20 10 (d)

Fig. 6. Products of transformation of earlystage PGM (Pd–Pt–Fe–Ni–Cu–Sn–Pb (As): (a) tetraferroplatinum (Tfp) with small exsolution bodies of Ptatokite (At). Komsomolsky Mine; (b) zonal rutenburgite–atokite (At–Rsb) crystal intergrown with tetraferroplatinum (Tfp) and majakite (Mjk). Small zvyagintsevite grains (light) occur along atokite boundary. Mayak (Majak) Mine; (c) transformation of sliced aggregate of plumbopalladinite (Pbpd) and stannopalladinite (Snpd) into subgraphic inter growths of polarite (Pol) with stannopalladinite and plumbopalladinite surrounded by majakite (Mjk). Zapolyarny Mine. (a–c) are images in reflected electrons; (d) compositions of rustenburgite–atokite–zvyagintsevite.

lamellae of Au–Pt–Pb atokite (Pd,Pt,Au)3(Sn,Pb) and Au–Pt–Pb atokite with tetraferroplatinum lamel lae (Spiridonov et al., 2004) are widespread, as well as PGM metacrysts consisting of exsolution structure assemblages with an approximately equiatomic bulk composition (Pd,Pt,Au)(Sn,Sb, Bi,Te). Pneumatolytic PGM and Au Minerals of Middle Stage Pneumatolytic Pd–Pt intermetallic compounds of the middle stage are products of exsolution, reworking of early PGM, and newly formed phases. They are accompanied by altaite and minerals of copper gold group, which are enriched in Pt and Pd, including the solid solutions tetraauricupride AuCu–hongshiite

PtCu, cuproauride AuCu–skaergaardite PdCu, auri cupride with characteristic exsolution structures, and other solidphase transformations. Some PGM of a middle stage contain up to 5 wt % Au in solid solution. In the case of the transformation of the probably early cubic hightemperature Pd–Pt–Fe–Ni–Cu– Sn–Pb(Au) solid solutions, they are converted into intergrowths of Aubearing tetraferroplatinum with exsolution lamellae of Au–Pb–Pt atokite and atokite with tetraferroplatinum lamellae. Later on, aggregates of zonal rustenburgite Pt3Sn–atokite Pd3Sn and tetra ferroplatinum without exsolution structures in associ ation with zvyagintsevite, stannopaladinite, and Au– Cu minerals ultimately originate (Figs. 6a, 6b) (Spiri GEOLOGY OF ORE DEPOSITS

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Table 1. Chemical compositions (wt %) of tetraferroplatinum from exsolution structures of early solid solutions with ato kite. Magmatic sulfide ore from Medvezhy Creek Component Pt Pd Rh Au Fe Ni Cu Total Pt Pd Rh Au Total Fe Ni Cu Total

1

2

74.47 2.56 0.12 0.22 17.97 2.80 2.32 100.46

3

4

74.73 76.06 74.52 76.08 2.42 1.11 1.07 1.02 0.16 0.11 0.09 0.23 0.15 0.40 0.74 0.29 17.21 17.45 17.70 16.85 3.57 2.93 2.61 1.94 2.06 2.38 2.47 3.46 100.30 100.44 99.20 99.87 Formula units calculated on the basis of 4 atoms 1.895 1.94 1.92 1.97 0.11 0.045 0.05 0.05 0.01 0.005 – 0.01 0.005 0.01 0.02 0.01 2.02 2.00 1.99 2.04 1.52 1.56 1.59 1.52 0.30 0.25 0.22 0.17 0.16 0.19 0.20 0.27 1.98 2.00 2.01 1.96

1.87 0.12 0.005 0.005 2.00 1.58 0.23 0.18 2.00

donov et al., 2003, 2004). Judging by the oval shape, the early sliced intergrowths of plumbopalladinite and stannopalladinite, apparently replacing PbSss, are gradually transformed into subgraphic intergrowths of polarite Pd2PbBi–Pd2Pb2 and stannopalladinite in association with plumbopalladinite Pd3Pb2 (Fig. 6c). Majakite with relics of replaced pentlandite, tetrafer roplatinum, zvyagintsevite, and later Pt–Pd tetraauri cupride are associated with them. The detailed char acterization of the above minerals and their composi

6

7

76.57 0.80 0.28 0.30 18.01 2.61 2.33 100.90

76.95 0.42 0.20 0.54 17.40 3.18 1.86 100.55

1.94 0.035 0.015 0.01 2.00 1.60 0.22 0.18 2.00

(b)

Pt2FeFe 100 10 90 20 80 30 70 40 60 50 50 60 40 70 30 80 20 90 10 100

Pt2FeCu

100 90 80 70 60 50 40 30 20 10

Pt2FeNi

Pt2FeFe 100 10 90 20 80 30 70 40 60 50 50 60 40 70 30 80 20 90 10 100 100 90 80 70 60 50 40 30 20 10

Fig. 7. Compositions of tetraferroplatinum from (a) Talnakh and (b) Noril’sk ore clusters. GEOLOGY OF ORE DEPOSITS

1.97 0.02 0.01 0.015 2.015 1.565 0.275 0.145 1.985

tions is published by Spiridonov et al. (2003, 2004, 2011). The chemical compositions of the Noril’sk tet raferroplatinum and Au–Pb–Pt atokite are given in Tables 1 and 2, of the Talnakh rustenburgite and atok ite, in Table 3, and of zvyagintevite in Table 4. The composition of the Noril’sk Au–Pb–Pt atokite appar ently corresponds to the initial stage of the transfor mation and breakdown of a hightemperature Pd– Pt–Fe–Ni–Cu–Sn–Pb(Au) solid solution. The com positions of minerals that are products of transformation

(а)

Pt2FeNi

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Pt2FeCu

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Table 2. Chemical compositions (wt %) of Au–Pt–Pb atokite from exsolution structures of early solid solutions with tet raferroplatinum. Magmatic sulfide ore from Zapolyarny Mine Component

8

9

Pd Pt Au Cu Ni Fe Sn Bi Pb Total

42.12 30.36 0.96 0.50 0.07 0.03 19.42 0.15 4.68 98.29

Pt Pd Au Cu Ni Fe Total Sn Bi Pb Total

0.84 2.10 0.03 0.04 0.01 – 3.01 0.87 – 0.12 0.99

10

11

12

13

52.41 58.43 59.50 60.96 61.43 17.12 9.07 9.00 5.88 3.85 1.76 2.62 2.24 2.48 2.67 0.87 0.54 0.73 0.44 0.76 0.08 0.07 0.11 0.09 0.07 0.15 0.04 0.04 0.07 0.09 19.84 15.74 17.95 17.08 16.61 0.10 0.31 0.30 0.24 0.28 7.63 14.10 11.11 12.70 13.86 99.96 100.92 100.98 99.94 99.62 Formula units calculated on the basis of 4 atoms 0.435 0.225 0.22 0.145 0.095 2.43 2.675 2.67 2.755 2.77 0.045 0.065 0.055 0.06 0.065 0.07 0.04 0.055 0.035 0.06 0.005 0.005 0.01 0.01 0.005 0.01 – – 0.005 0.01 2.995 3.01 3.01 3.01 3.005 0.825 0.65 0.725 0.69 0.67 – 0.01 0.01 0.005 0.005 0.18 0.33 0.255 0.295 0.32 1.005 0.99 0.99 0.99 0.995

14

15

60.37 2.97 2.96 0.94 0.09 0.06 14.47 0.19 16.60 98.65

59.53 2.89 3.00 0.54 0.06 0.03 11.91 0.22 20.69 98.87

0.075 2.775 0.075 0.07 0.01 0.005 3.01 0.595 0.005 0.39 0.99

0.075 2.80 0.075 0.04 0.005 – 2.995 0.50 0.005 0.50 1.005

16 61.39 2.99 2.94 0.54 0.06 0.03 12.74 0.24 19.67 100.60 0.075 2.82 0.075 0.03 0.01 – 3.005 0.525 0.005 0.465 0.995

Rh, Ag, Sb, and As have not been detected.

Table 3. Chemical compositions (wt %) of rustenburgite (nos. 17–20) and atokite (nos. 21–26) in zonal crystals from re crystallized early solid solutions. Magmatic sulfide ore from Oktyabrsky Mine Compo nent Pt Pd Rh Au Cu Ni Fe Sn Pb Bi Sb As Total Pt Pd Rh Cu Ni Fe Total Sn Pb (Bi) Sb As Total

17

18

19

20

21

22

23

24

25

26

65.38 12.82 0.06 bdl 1.09 0.18 0.07 18.31 trace amounts 0.36 0.12 0.04 98.50

58.90 19.89 0.11 bdl 0.46 0.11 0.05 17.70 bdl

53.76 23.71 bdl bdl 0.44 0.10 bdl 18.42 0.08

50.85 27.54 bdl 0.06 0.39 0.14 0.05 19.24 0.17

49.20 28.82 0.06 bdl 0.52 0.10 bdl 21.01 bdl

41.07 35.39 bdl bdl 0.52 0.05 0.03 21.65 bdl

36.40 40.02 bdl bdl 0.45 0.03 0.01 22.52 0.24

27.47 46.63 0.08 bdl 0.34 bdl 0.01 23.22 bdl

16.15 55.09 bdl bdl 0.37 0.08 0.15 19.84 7.63

8.44 63.96 bdl bdl 0.06 0.00 0.06 25.26 bdl

bdl 2.02 0.07 99.31

bdl bdl bdl bdl bdl 1.59 1.89 bdl 0.17 bdl 0.03 bdl 0.03 0.06 bdl 98.13 100.33 99.74 98.94 99.67 Formula units calculated on the basis of 4 atoms 1.63 1.47 1.42 1.14 0.98 1.32 1.46 1.52 1.805 1.97 – – – – – 0.04 0.035 0.05 0.045 0.04 0.01 0.015 0.01 0.005 – – 0.005 – – – 3.00 2.985 3.00 2.995 2.99 0.92 0.92 1.00 0.99 1.00 – 0.005 – – 0.01 0.08 0.09 – 0.01 – – – – 0.005 – 1.00 1.015 1.00 1.005 1.01

bdl bdl 0.01 97.76

0.10 bdl bdl 99.41

bdl 0.08 0.04 97.90

0.72 2.24 0.005 0.03 – – 2.995 1.005 – – – 1.005

0.41 2.54 – 0.03 0.01 0.01 3.00 0.82 0.18 – – 1.00

2.11 0.76 – 0.11 0.02 0.01 3.01 0.97 (0.01) 0.01 – 0.99

1.81 1.12 0.005 0.05 0.01 0.005 3.00 0.895 – 0.10 0.005 1.00

0.20 2.79 – – – 0.005 2.995 0.995 – 0.01 – 1.005

Te has not been detected. Here and hereafter: bld is below detection limit. GEOLOGY OF ORE DEPOSITS

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Table 4. Chemical compositions (wt %) of zvyagintsevite. Magmatic sulfide ore from Mayak (Majak) Mine Component

27

Pd Pt Au Cu Fe Ni Pb Sn Bi Te As Total

61.24 bdl bdl 0.21 0.16 0.04 39.97 0.10 bdl bdl bdl 101.72

Pd Pt Au Cu Fe Ni Total Pb Sn Bi Te Total

2.96 – – 0.02 0.02 – 3.00 0.99 0.01 – – 1.00

28

29

30

31

61.06 61.24 62.14 62.49 0.06 bdl 0.45 bdl 0.10 bdl bdl bdl 0.15 0.10 0.34 0.22 0.08 0.04 0.06 0.02 bdl 0.03 0.10 0.09 39.06 38.77 38.66 36.91 0.25 0.45 1.08 1.06 0.37 0.51 0.32 1.47 0.08 0.08 0.07 0.61 bdl 0.06 0.01 0.03 101.21 101.28 103.23 102.90 Formula units calculated on the basis of 4 atoms 2.98 2.98 2.94 2.97 – – 0.01 – – – – – 0.01 0.01 0.03 0.02 0.01 – 0.01 – – – 0.01 0.01 3.00 2.99 3.00 3.00 0.98 0.98 0.94 0.90 0.01 0.02 0.05 0.04 0.01 0.01 0.01 0.04 – – – 0.02 1.00 1.01 1.00 0.99

32

33

61.18 0.53 0.32 0.77 0.21 0.01 36.06 2.09 1.11 0.42 bdl 102.70

58.70 0.45 bdl 0.68 0.19 0.08 33.66 1.32 2.77 0.76 bdl 98.61

2.89 0.01 0.01 0.06 0.02 – 2.99 0.87 0.09 0.03 0.02 1.01

2.90 0.01 – 0.05 0.02 0.01 2.99 0.85 0.06 0.07 0.03 1.01

Sb has not been detected.

of early intermetallic compounds, e.g., the Pdrusten burgite–atokite–Pbatokite–Snzvyagintsevite continu ous series, are shown in Fig. 6d and tetraferroplatinum in Fig. 7. The Talnakh tetraferroplatinum is richer in Ni and poorer in Cu (Fig. 7a) than the Noril’sk coun terpart (Fig. 7b). The early, probably cubic intermetallic compounds of equiatomic (Pd,Pt,Au)(Sn,Sb,Bi,Te,As) composi tion (Fig. 8a) are transformed into aggregates of shee tlike twins of polymorphic transition consisting of Sb paolovite and close phases (matrix). Thereby, each sheet of Sbpaolovite is distinguished by its special pattern of exsolution structure and specific orientation of Te–Sb insizwaite and Te–Bi geversite lamellae (Figs. 8b, 9a). Small particles of niggliite–Sbniggli ite–Snstumpflite exsolution are localized between sheets (Figs. 8b, 9a–9c). Judging by exsolution pat terns (Figs. 9a, 9b), the exsolution of hightempera ture PGE solid solutions is a twostage process. After ward, further segregation of paolovite, platinum dichalcogenides, and niggliite take place locally. The compositions of insizwaite and geversite lamellae and small particles of niggliite exsolution are given in Fig. 10. The structures of collecting recrystallization of these GEOLOGY OF ORE DEPOSITS

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minerals are widespread; Sbniggliite is abundant among them. The newly formed products of pentlandite replace ment are rather widespread. These are majakite PdNiAs, less frequent menshikovite Pd3Ni2As3 (Barkov et al., 2000a), and associated palarstanide Pd3(As,Sn) (subordinate). The composition of majakite is pub lished by Spiridonov et al. (2004, 2011). Aggregates of Sbpaolovite Pd2(Sn,Sb) or Sb paolovite and phase Pd4SnSb, sporadic naldrettite Pd2Sb (Fig. 9d) or stibiopalladinite cemented with Bi geversite and Sbinsizwaite are widespread among newly formed PGM of the middle stage. Sbpaolovite Pd2(Sn,Sb), which is the most abundant Pd mineral of eutectic ores (Figs. 11a, 11b), contains up to 9 wt % Sb, up to 15 wt %, up to 5 wt % Au, and traces of Ag. The Sbpaolovite sheets vary from fractions of a micrometer to 2 mm; sheet aggregates are up to 22 × 20 × 6 mm in dimensions, commonly less than 3 mm. The mineral is distinguished by distinct birefringence and bright anisotropy in color. Phase Pd4SnSb hexag onal (from lauegrams for three samples), in contrast to orthorhombic paolovite and naldrettite, occurs as

414

SPIRIDONOV et al. (a)

(b)

300 µm

100 µm

Fig. 8. (a) pneumatolytic PGM of early stage: metacryst (cuboctahedron) of equiatomic (Pd,Pt,Au)(Sn,Sb,BiTe,As) intermetal lic compound; (b) products of transformation of equiatomic intermetallic compound into aggregate of tabular twins of polymor phic transition, each with its special exsolution pattern; matrix is Sbpaolovite, lamellae are insizwaite–geversite (white). Okty abrsky Mine. Images in reflected electrons.

Ng

20 µm

(a)

5 µm

(b) (d) Number of analyses

Naldrettite, orthorhombic

Phase Pd4SnSb, hexagonal

Paolovite, orthorhombic

150

100

Ng

132

50

92 28

(c)

20 µm

16

25

46 26

6

100 95 90 85 60 55 50 45 40 35 15 10 0 Pd2Sn Pd2Sb

Fig. 9. (a–c) pneumatolytic PGM of middle stage; products of transformation of equiatomic intermetallic compound into aggre gate of tabular twins of polymorphic transition, each with its at least twostage exsolution pattern: paolovite and less frequent phase Pd4SnSb, sporadic naldrettite (matrix), insizwaite–geversite (white, lamellae of two generations), niggliite (Ng). Images in reflected electrons; (d) compositions of paolovite, phase Pd4SnSb, and naldrettite. Oktyabrsky Mine. GEOLOGY OF ORE DEPOSITS

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GENETIC Pd, Pt, Au, Ag, AND Rh MINERALOGY (а) PtBi2 100 10 90 20 80 30 70 40 60 50 50 60 40 70 30 80 20 90 10 100 PtTe2 PtSb2 100 90 80 70 60 50 40 30 20 10

(b) PtBi2 100 10 90 20 80 30 70 40 60 50 50 60 40 70 30 80 20 90 10 100 PtTe2 PtSb2 100 90 80 70 60 50 40 30 20 10

(c)

60

70 Number of analyses

Number of analyses

(d)

80

50 40 n = 220 30

56

20 10

415

37

37 33

5 18

16 8

0 100 PtSn

95

90

85

7

50 40

75 PdSn

n = 220 71

30 58 20 10

3

80

60

27

35

27

2 0 100 90 80 70 60 50 40 30 20 10 0 PtSn PtSb niggliite stumpflite

Fig. 10. Compositions of pneumatolytic PGM of middle stage as products of exsolution of equiatomic intermetallic compounds: (a) insizwaite, (b) geversite, (c, d) niggliite, to stumpflite. Oktyabrsky Mine.

sheetlike segregations similar in morphology to paolo vite. Parallel intergrowths of Sbpaolovite sheets and phase Pd4SnSb with alternation of the nextnearest sheets are frequent. The gap in composition between them is appreciable (Fig. 9). Stibiopalladinite Pd5Sb2 is represented by sheetlike crystals resembling paolovite, which are associated with geversite and Sbinsizwaite. The average chemical composition of Talnakh stibiopal ladinite is as follows, wt %: 65.75 Pd, 0.95 Pt, 0.98 Cu, 24.74 Sb, 5.75 Sn, 0.36 Bi, and 0.10 Pb; the total is 98.63 wt %. The formula is (Pd4.86Pt0.04Cu0.12)5.02 (Sb1.59Sn0.38Bi0.01)1.98. The gain of tellurium is characteristic of the middle stage. In some large samples of eutectic ores, entire strips of PbSss and galena are replaced with altaite PbTe. Moncheite Pt(Te,Bi)2 sheets up to 20 × 20 × 3 mm in size are formed. These sheets are overgrown by zonal crystals of maslovite PtBiTe, geversite TeBi, and insizwaite TeSb (Fig. 12a). Similar crystals develop GEOLOGY OF ORE DEPOSITS

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nearby in altaite matrix. The compositions of these minerals are shown in Fig. 12b. The stannopalladinite (Pd,Pt)5CuSn2 rims of replacement around Sbpaolovite are widespread in PGM aggregates of eutectic ore (Fig. 13). The chemi cal composition of the Talnakh stannopalladinite is given in Table 5; the composition of the same mineral from the Talnakh ore cluster was published by Spiri donov et al. (2003, 2004). The lowPt stannopalladinite is enriched in Pb and vice versa. Our data corroborate a variant of the stannopalladinite formula proposed by Evstigneeva (1980). Taimyrite (Pd,Pt)9Cu3Sn4 and tati anaite (Pt,Pd)9Cu3Sn4) are among late minerals of the given stage (Barkov et al., 2000) and occur as rims replacing margins of large rustenburgite–atokite grains and as complete pseudomorphs after small grains (Figs. 14a–14c). Taimyrite1 and tatianaite1 are characterized by tabular exsolution structures; taimyrite2 and tatianaite2 are devoid of exsolution structures. Our data corroborate a variant of taimyrite

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(b) Gev Gev

Plv

Plv

Au–Ag

Ins

Ins 100 µm

100 µm

Fig. 11. Pneumatolytic PGM of middle stage: (a, b) newly formed metasomatic Sbpaolovite (Plv) (intergrowths of tabular crys tals with insizwaite (Ins) and geversite (Gev)); late electrum and küstelite (Au–Ag). Images in reflected electrons. Oktyabrsky Mine.

(b)

(a) Msl

Ins

Gev Alt Mon 10 µm

PtSb2 geversite 100 geversite 10 insizwaite 90 20 maslovite 80 30 moncheite 70 PtSbTe 40 60 50 50 60 40 70 30 80 20 90 10 100 PtTe2 PtBi2 insizwaite 100 90 80 70 60 50 40 30 20 10

Fig. 12. Pneumatolytic PGM of middle stage: (a) zonal insizwaite (Ins)–maslovite (Msl)–geversite (Gev) crystals in altaite (Alt) matrix grown over moncheite (Mon) sheet. Image in reflected electrons; (b) compositions of Pt chalcogenides in this sample. Oktyabrsky Mine.

formula proposed by Evstigneeva (1980). The Talnakh Pdtatianaite and Pttaimyrite make up a continuous series (Fig. 14d). The variations of the Pt : Pd ratio in tatianaite–taimyrite are close to those in the replaced rustenburgite–atokite. Minerals of copper gold group, namely tetraauricupride AuCu and auricupride AuCu3, are among the latest pneumatolytic noblemetal min erals of the middle stage; they contain substantial Pd and Pt amounts and frequently enriched in Ag. These minerals are characterized by finelatticed exsolution structures and twins of polymorphic transitions. The chemical composition of Ptauricupride is given in Table 6; the composition of Pt–Pd tetraauricupride is

published by Spiridonov et al. (2003, 2004) and Spiri donov (2010). Late Pneumatolytic PGM and Au–Ag Minerals Pd minerals in association with minerals of the Au–Ag series, altaite, and hessite are predominant late pneumatolytic PGM and Au–Ag minerals. They grow over early PGM and Au–Ag minerals, corrode them or make up separate intergrowths. Fine and oscilla toryzoned maslovite PtBiTe–michenerite PdBiTe (Fig. 15b) crystals make up a continuous series and develop in association with froodite and altaite (Table 7; GEOLOGY OF ORE DEPOSITS

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417

Alt Snpd

Ins Plv

Gev Ins

20 µm

Fig. 13. Pneumatolytic PGM of middle stage: reaction rim of stannopalladinite (Snpd) around Sbpaolovite (Plv) with insizwaite (Ins) inclusions. On the left, intergrowth of insizwaite, geversite (Gev), and altaite (Alt). Image in reflected electrons. Taimyr Mine.

Fig. 15b). The parageneses Tesobolevskite + altaite + Sbfree paolovite + maslovite + michenerite + hessite (Figs. 16a, 16b) and Tesobolevskite + altaite + Bifree geversite + Sbfree insizwaite are characteristic. Sb free paolovite is a typical mineral of the late pneuma tolytic mineralization. In composition, precisely this variety of paolovite corresponds to its holotype, dis covered and studied by T.L. Evstigneeva (Genkin et al., 1974). Sobolevskite PdBi (Evstigneeva et al., 1975) is one of the most abundant late pneumatolytic min eral intergrowths with tabular hessite. This is com monly Tesobolevskite, a member of the continuous sobolevskite–kotulskite series (Fig. 16c). Less fre quently, it is Sbsobolevskite, a member of the contin uous sobolevskite–sudburyite series. Sudburyite PdSb is widespread enough in small amounts as a late pneu matolytic PGM. The minerals are commonly enriched in Bi and makes up continuous series with Sbsobolevskite (Table 8). Small grains of kotulskite PdTe is frequent in association with hessite and maslo vite. The majority of kotulskite crystals are enriched in Bi and Pb (Table 9). Cabriite Pd2CuSn (Evstigneeva and Genkin, 1983) occurs as separated grains, inter growths with küstelite and Ausilver, as well as rims up to 7 mm wide replacing margins of paolovite grains. When cabriite replaces paolovite, only copper in reduced form is gained. The process develops in the medium of copper sulfides (chalcopyrite, cubanite, talnakhite, mooihoekite). The Talnakh cabriite is close to the theoretical composition, and some crystals are enriched in Pt and Sb (Table 10). Polyarite Pd2BiPb frequently occurs in association with sobo GEOLOGY OF ORE DEPOSITS

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levskite and hessite; the composition of the mineral varies from Pb to Bienriched varieties (Fig. 16d). Hessite Ag2Te is an abundant mineral in association with late pneumatolytic PGM. The intergrowths of flattened hessite and sobolevskite crystals are typical. Froodite PdBi2 is a characteristic late mineral, which occurs as metasomatic segregations in galena and less frequently in Fe–Cu–Ni sulfides; the size of these seg regations varies from submicrometric to 0.5 mm. Frood ite also intergrows with zonal gold grains. The chemical composition of froodite is close to theoretical (Spiri donov, 2010). Genkinite (Pt,Pd)4(Sb,Bi)3 is a rare min eral. Minerals of the Au–Ag series (Aggold, electrum, küstelite, Ausilver) are constantly associated with late pneumatolytic PGM. They occur as veinlets along the cleavage of deformed paolovite with inclusions of Pt dichalcogenides (minerals of the Middle stage) (Fig. 17a). Homogeneous electrum and küstelite segregations occur within PGM aggregates (Figs. 17b, 17d). The later zonal Au–Ag minerals intergrown with froodite and altaite overgrow PGM aggregates (Figs. 17c, 17d, 18c). Direct zoning with gradual drop of Au content from core to rim (Fig. 17c), inverse zoning (Fig. 17d), and oscillatory zoning (Figs. 18a, 18b), as well as complex and very complex zoning (Fig. 18c) are distinguished in gold grains. No Pt and Pd are detected in minerals of the Au–Ag series, i.e., the affinity of Pt and Pd to Au is much lower than their affinity to As, Sb, Bi, Te, Sn, and Pb. The fineness of Au–Ag minerals continu ously varies from 870 to 3; electrum and küstelite are predominant (Fig. 18d). Native gold occurs in areas

418

SPIRIDONOV et al.

Table 5. Chemical compositions (wt %) of stannopalladinite from magmatic sulfide ores of Noril'sk ore cluster (Medvezhy Creek Mine, nos. 36, 37, 39, 40, 42) and Talnakh ore cluster (Mayak (Majak) Mine, nos. 34, 35, 38, 41) Compo nent

34

35

Pd Pt Rh Au Ag Cu Ni Fe Sn Pb Sb Bi As Te Total

48.44 17.36 bdl bdl bdl 7.10 bdl 0.02 22.14 3.14 1.04 0.51 0.19 bdl 99.94

49.00 16.48 bdl 0.24 bdl 7.02 0.02 0.01 23.55 1.94 1.16 bdl 0.15 bdl 99.57

Pd Pt Rh Au Ag Total Cu Ni Fe Total Sn Pb Sb Bi As Total

4.18 0.82 – – – 5.00 1.03 – – 1.03 1.71 0.14 0.08 0.02 0.02 1.97

36

37

38

39

40

41

52.96 58.15 53.61 58.45 59.22 9.01 6.08 4.88 3.72 2.90 bdl 0.06 bdl bdl bdl 0.59 0.51 bdl 0.14 0.50 bdl bdl 5.43 bdl bdl 6.97 7.17 7.39 6.88 7.28 0.13 0.06 bdl 0.10 0.01 0.05 0.10 bdl 0.26 0.08 21.93 25.01 25.60 22.43 20.18 4.53 1.61 1.80 5.60 7.88 1.52 0.70 0.71 1.29 2.45 0.92 0.47 0.06 0.78 0.85 0.09 0.13 0.10 0.04 0.03 0.06 bdl bdl bdl bdl 98.76 100.05 99.58 99.69 101.38 Formula units calculated on the basis of 8 atoms 4.21 4.51 4.73 4.34 4.81 4.825 0.77 0.415 0.27 0.215 0.165 0.13 – – 0.005 – – – 0.01 0.025 0.02 0.015 0.005 0.02 – – – 0.435 – – 4.99 4.95 5.025 5.005 4.98 4.975 1.01 0.99 0.975 1.00 0.945 0.995 – 0.02 0.01 – 0.015 – – 0.01 0.015 – 0.04 0.01 1.01 1.02 1.00 1.00 1.00 1.005 1.81 1.67 1.825 1.86 1.655 1.475 0.085 0.195 0.065 0.08 0.235 0.33 0.085 0.115 0.05 0.05 0.095 0.175 – 0.04 0.02 – 0.035 0.04 0.02 0.01 0.015 0.01 – – 2.00 2.03 1.975 1.995 2.02 2.02

42

61.44 2.08 bdl bdl bdl 7.39 bdl 0.03 28.09 bdl bdl bdl 0.03 bdl 99.06 4.90 0.09 – – – 4.99 0.99 – – 0.99 2.02 – – – – 2.02

60.19 1.71 bdl bdl bdl 7.26 0.01 bdl 14.91 11.60 5.21 0.58 0.10 bdl 101.57 4.925 0.075 – 0.015 – 5.015 0.995 – – 0.995 1.095 0.485 0.375 0.025 0.01 1.99

Table 6. Chemical compositions (wt %) and formula units of Pt and Pdbearing auricupride. Magmatic sulfide ore from Mayak (Majak) Mine Component

43

44

45

46

43

44

45

46

Au Ag Pt Pd Cu

31.76 0.24 18.05 0.20 49.21

29.13 0.48 16.95 2.16 50.10

35.16 1.37 9.04 3.72 50.44

36.14 2.38 7.58 3.26 52.06

0.625 0.01 0.36 0.005 3.00

0.565 0.015 0.33 0.08 3.01

0.67 0.05 0.17 0.13 2.98

0.67 0.08 0.14 0.12 2.99

Total

99.46

98.82

99.73

101.42

4

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Tat–Tm Tat Rsb–At

Gn

Rsb–At Tm

Au–Ag

100 µm

(a)

30 µm

(b)

Gn

N

Au–Ag

(d)

40 30

Tat 20

n = 201

10

Tm 10 µm

(c)

0 100 90 Pt9Cu3Sb4

80

70

60

50

40

30

20 10 0 Pd9Cu3Sb4

Fig. 14. Pneumatolytic PGM of middle stage: (a, b) reaction rims and (c) pseudomorphs of Pdtatianaite–taimyrite (Tat–Tm) around and after zonal rustenburgite–atokite (Rsb–At). Tatianaite–taimyrite solid solution partly underwent breakdown; lamellae are variable in composition: taimyrite (black–gray), Pttaimyrite (gray), Pdtatianaite (light gray), and tatianaite (whitish gray). Galena (Gn), küstelite (Au–Ag). Images in reflected electrons. (d) Compositional variations of tatianaite–taimyrite. Oktyabrsky Mine.

containing hessite and maslovite. It is supposed that the zoning of Au–Ag minerals in the Noril’sk ores is caused, to a certain degree, by the variable activity of Te in fluids. At the given parameters of ore formation, Te binds Ag (in hessite) and is not linked with Au. Exsolution patterns in the Au–Ag series. The ques tion on the possible or impossible exsolution of native gold, especially in varieties enriched in silver, is under animated discussion in the literature. Noril’sk ore is a crucial object for the solution of this problem. Abun dant gold grains enriched in Ag and giant lodes of mas sive sulfide ore as products of sulfide melt crystalliza tion ensure a favorable regime of annealing and exso GEOLOGY OF ORE DEPOSITS

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lution. Exsolution structures are abundant in sulfide solid solutions containing PGM and Au–Cu inclu sions. The exsolution lamellae in chalcopyrite and cubanite reach decimeters in size! At the same time, smooth direct, inverse, and oscillatory compositional zoning is identified in minerals of Au–Ag series, whereas exsolution structures are not observed even at magnifications up to 35000 times. These data on nat ural Au–Ag minerals are consistent with experimental results on synthetic phases of the Au–Ag system, which do not reveal attributes of exsolution (Dowdell et al., 1943; White et al., 1957).

420

SPIRIDONOV et al. (a)

(b)

(Pt, Pd)Te2 100 10 90 20 80 30 70 60

Msl

Mch Alt

PtBiTe maslovite 50 40 30

40 50

PdBiTe michenerite 60 70 80

20 Fro 10 µm

90

10 PtBi2

100 90 80 70 60 50 40 30 20 10

100 PdBi2

Fig. 15. Pneumatolytic PGM of middle stage: (a) fine and oscillatory zoned maslovite–michenerite (Msl–Mch) crystal in froodite (Fro) within altaite (Alt) matrix. Image in reflected electrons; (b) compositions of zonal maslovite–michenerite crystals. Komsomolsky Mine.

The Latest Pneumatolytic PGM Sperrylite PtAs2, the latest pneumatolytic PGM, occurs as isometric and flattened metacrysts varying from submicrometric to 14 cm in size. Sperrylite is locally widespread in pyrrhotite, cubanite, chalcopy rite, and galenarich eutectic ores. This mineral is dis tributed extremely nonuniformly in the iss–PbSss and halos near them. The maximum amount of sperrylite develops in mooihoekite aggregates at contacts with eutectic ore veins near the roof of the giant Kharaelakh sulfide lode. Precisely in these localities, sperrylite segregations up to 150 cm across were observed by E.A. Kulagov in the 1970s. In the 1990s, S.N. Belyakov observed sperrylite intergrowths up to 30 × 20 × 20 cm in size, which consisted of tens of crystals up to 4 cm in length and numerous small crystals up to 1 cm long. The boundaries of sperrylite metacrysts crosscut all other pneumatolytic PGM and Au–Ag minerals (Figs. 19a–19c). The large sperrylite crystals are close to the theoretical chemical composition of this min eral, contain 0.02–0.30 wt % Rh as a microadmixture, and are almost sulfurfree (Spiridonov, 2010). The small sperrylite crystals that replace highSb minerals contain up to 11 wt % Sb (Fig. 19d). Sperrylite hosted in pyrrhotite ore enriched in Rh contains microinclu sions of hollingworthite RhAsS. Thus, the assemblage of pneumatolytic noble metal minerals from the Noril’sk ores is almost devoid of sulfides. These are intermetallic compounds of Pd and Pt with Fe, Ni, Cu, Sn, Pb, and Bi; their tellu rides, arsenides, and antimonides; minerals of the Cu gold group, Au–Ag series, and hessite (Genkin, 1968; Kulagov, 1968; Begizov, 1977; Genkin et al., 1981; Distler et al., 1999; Barkov et al., 2000; Spiridonov, 2010).

FORMATION CONDITIONS OF PNEUMATOLYTIC PGM IN NORIL’SK ORE Inasmuch as PGM replaces products of PbSss exsolution, the upper temperature limit of their for mation is below 490–470°С (temperature of PbSss breakdown). Judging by association of many PGM with tetraauricupride and cuproauride, their forma tion temperature is below 390–385°С; this is the upper stability limit of synthetic analogs of tetraauricupride and cuproauride (Okamoto et al., 1987). It cannot be ruled out that noble metals are transported as chloride or fluorine complexes. It is also possible that noble metals are migrated in form of carbonyls, which are stable at elevated temperatures (Belozersky, 1958) or/and as fullerides. This is supported by the occur rence of cohenite (iron carbide) in sulfide ore (Genkin et al., 1981). COMPARISON OF PGM FROM THE BUSHVELD DEPOSITS, WORLD’S LARGEST, AND NORIL’SK DEPOSITS The Pt and Pd monosulfides (cooperate, braggite, vysotskite) are the main primary minerals in ores of the giant lowsulfide PGE–Cu–Ni deposits of Bush veld (Naldrett, 2004). In ores of the giant sulfide PGE–Ni–Cu deposits of Noril’sk, the main primary Pd and Pt minerals are intermetallic compounds: paolovite, atokite, tetraferroplatinum, sperrylite, insizwaite, geversite, niggliite, moncheite, taimyrite, froodite, and sobolevskite. What is the cause of this paradox? It is apparently the PGM crystallization conditions. GEOLOGY OF ORE DEPOSITS

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Table 7. Chemical compositions (wt %) of maslovite (nos. 47–51) and michenerite (nos. 52–56). Zonal crystals in mag matic sulfide ore from Oktyabrsky Mine. Compo nent

47

Pt Pd Rh Au Cu Ni Fe Bi Te Sb Sn Pb As Total

36.76 0.67 0.13 bdl 0.01 bdl bdl 38.71 24.01 0.18 bdl bdl bdl 100.47

Pt Pd Rh Au Cu Ni Fe Total Bi Te Sb Sn Pb Total

0.99 0.03 0.01 – – – – 1.03 0.97 0.99 0.01 – – 1.97

48 35.88 0.60 0.05 bdl bdl bdl bdl 39.39 23.98 0.09 bdl bdl bdl 99.99 0.975 0.03 – – – – – 1.005 0.995 0.995 0.005 – – 1.995

49

50

51

52

53

31.84 23.17 20.00 17.92 12.30 3.40 7.70 10.21 11.65 15.24 bdl 0.10 bdl 0.06 bdl 0.10 bdl bdl bdl bdl bdl bdl bdl bdl 0.01 0.01 bdl 0.14 bdl bdl 0.07 bdl 0.02 bdl bdl 41.04 47.88 45.40 45.13 46.01 25.07 17.42 20.56 23.16 24.54 0.39 1.02 2.45 0.72 0.16 bdl 0.08 0.23 bdl bdl 0.14 0.94 1.11 0.70 bdl bdl 0.03 bdl bdl bdl 102.06 98.34 100.12 99.34 98.26 Formula units calculated on the basis of 3 atoms 0.825 0.62 0.51 0.455 0.305 0.16 0.38 0.47 0.54 0.695 – 0.005 – – – – – – – – – – – – – – – 0.01 – – 0.01 – – – – 0.995 1.005 0.99 0.995 1.00 0.99 1.20 1.07 1.065 1.065 0.99 0.72 0.80 0.89 0.93 0.02 0.05 0.10 0.03 0.005 – – 0.01 – – 0.005 0.025 0.03 0.02 – 2.005 1.995 2.01 2.005 2.00

In Bushveld, Pt and Pd monosulfides are products of silicate melt crystallization at Т ≈ 1000–700°С with participation of fluids characterized by moderate fS2 (Naldrett, 2004); Pt and Pd intermetallic compounds and minerals close to them in composition (isoferro platinum, sperrylite, stannides, bismuthides, and tel lurides) are products of fluid reworking of Pt and Pd monosulfides. In Noril’sk, the formation of noblemetal minerals was a twostage process: (1) entrapment of noble met als during crystallization of hightemperature sulfide solid solutions (mss, iss, and PbSss and (2) their fluidal reworking and crystallization of noblemetal interme tallic compouns in highly reductive setting, at extremely low fS2 value, and gradual decrease in tem perature from ~450 to ~350°C (Spiridonov, 2004). GEOLOGY OF ORE DEPOSITS

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54 7.27 18.75 bdl 0.14 0.05 0.04 0.05 46.42 27.21 0.04 0.18 0.15 bdl 100.30 0.17 0.81 – 0.005 0.005 0.005 0.005 1.00 1.015 0.975 – 0.005 0.005 2.00

55 3.57 21.72 bdl bdl 0.03 bdl 0.01 44.64 29.06 0.01 bdl 0.13 bdl 99.17 0.08 0.92 – – – – – 1.00 0.97 1.03 – – – 2.00

56 0.54 23.15 0.06 0.20 0.07 0.21 bdl 45.63 28.72 0.81 0.13 0.10 0.02 99.64 0.01 0.96 – 0.005 0.005 0.02 – 1.00 0.97 0.995 0.03 – – 2.00

EPIGENETIC METAMORPHIC– HYDROTHERMAL MINERALIZATION The East Siberian Platform, covered by a 4km sequence of plateau basalts and enriched in numerous gabbrodolerite intrusions, underwent posttrap sub sidence. The derivatives of trap association and sub trap sequences were affected by epigenetic lowgrade metamorphism under conditions of zeolite facies fol lowed by metamorphism of the highertemperature prehnite–pumpellyite and then again zeolite facies, developing a loop of metamorphism (Perchuk and Aranovich, 1981). The Rb–Sr age of metamorphism (apophyllite, metabasalts) is 232 Ma and 122 Ma (onset and final of metamorphism) (Spiridonov and Gritsenko, 2009). The Pb isotopic composition of galena from metamorphic–hydrothermal carbonate

422

SPIRIDONOV et al.

Table 8. Chemical compositions (wt %) of sudburyite (nos. 57–63) and Sbsobolevskite (64–66) from magmatic sulfide ores of Talnakh ore cluster. Oktyabrsky and Komsomolsky Mines Compo nent Pd Pt Rh Au Cu Ni Fe Bi Sb As Sn Pb Te Total

57

58

43.32 bdl bdl bdl 0.15 0.08 0.03 8.37 44.25 0.12 0.51 0.22 0.19 97.24

39.44 5.80 bdl 0.07 0.13 0.07 bdl 12.30 41.20 bdl 0.57 bdl 0.20 99.78

Pd Pt Au (Rh) Cu Ni Total Bi Sb As Sn Pb Te Total

0.99 – – 0.005 – 0.995 0.105 0.88 0.005 0.01 – 0.005 1.005

0.92 0.07 – 0.005 – 0.995 0.15 0.84 – 0.01 – 0.005 1.005

59

60

61

62

63

40.92 41.35 40.68 40.87 39.20 bdl bdl bdl bdl bdl bdl bdl bdl 0.13 bdl bdl bdl 0.05 bdl 0.37 bdl bdl bdl bdl 0.06 bdl 0.09 0.02 0.20 0.09 bdl bdl bdl 0.01 bdl 27.86 27.48 32.02 29.96 34.45 29.83 27.67 26.48 25.06 21.48 0.17 0.02 bdl 0.07 0.16 1.01 2.84 0.85 3.61 2.44 bdl 0.76 bdl 0.36 0.34 0.53 0.27 0.47 0.61 0.75 100.32 100.48 100.57 100.88 99.34 Formula units calculated on the basis of 2 atoms 0.99 0.995 1.00 0.99 0.99 – – – – – – – – (0.005) 0.005 – – – – – – 0.005 – 0.01 0.005 0.99 1.00 1.00 1.005 1.00 0.34 0.34 0.40 0.37 0.44 0.63 0.58 0.57 0.53 0.47 0.01 – – – 0.005 0.02 0.06 0.02 0.08 0.06 – 0.01 – 0.005 0.005 0.01 0.005 0.01 0.01 0.02 1.01 1.00 1.00 0.995 1.00

64

65

38.56 bdl bdl bdl bdl bdl bdl 37.39 16.91 bdl 0.43 0.17 6.67 100.13

66

31.41 7.72 bdl bdl bdl 0.01 bdl 48.75 9.90 bdl 0.92 0.58 1.24 100.53

28.10 4.69 bdl bdl 1.39 0.99 bdl 56.75 4.35 bdl 1.22 0.51 1.92 99.92

0.88 0.12 – – – 1.00 0.70 0.24 – 0.02 0.03 0.03 1.00

0.80 0.07 – 0.07 0.05 0.99 0.82 0.10 – 0.03 0.01 0.05 1.01

0.985 – – – – 0.985 0.485 0.375 – 0.01 – 0.145 1.015

Table 9. Chemical compositions (wt %) of Pb and Bibearing kotulskite from magmatic sulfide ore from Medvezhy Creek Mine Component Pd Pt Au Cu Ni Fe Te Bi Pb Sn As Total Pd Pt Cu Fe Total Te Bi Pb Sn As Total

67 37.19 0.30 0.15 0.51 0.01 0.83 26.78 24.02 9.74 0.08 0.11 99.72 0.935 0.005 0.02 0.04 1.00 0.56 0.305 0.13 – 0.005 1.00

68 69 70 71 72 36.83 38.03 38.78 36.48 37.84 1.03 0.60 0.78 bdl 0.34 bdl bdl 0.32 bdl bdl 0.20 0.26 0.31 0.55 0.14 bdl 0.01 0.01 bdl 0.01 0.01 0.03 0.06 0.85 0.04 24.01 24.34 24.30 23.51 20.47 19.15 18.75 18.33 25.12 25.96 17.35 17.95 14.22 12.36 13.95 bdl 0.04 1.57 bdl bdl 0.06 bdl 1.75 0.05 0.34 98.64 100.01 100.43 98.92 99.09 Formula units calculated on the basis of 2 atoms 0.96 0.98 0.97 0.94 0.99 0.02 0.01 0.01 – 0.005 0.01 0.01 0.01 0.025 0.01 – – – 0.04 – 0.99 1.00 0.99 1.005 1.005 0.53 0.52 0.51 0.505 0.45 0.25 0.24 0.23 0.33 0.345 0.23 0.24 0.18 0.16 0.185 – – 0.03 – – – – 0.06 – 0.015 1.01 1.00 1.01 0.995 0.995

73 37.10 0.46 bdl 0.23 bdl 0.05 19.19 26.28 17.19 bdl 0.09 100.59

74 37.21 0.35 bdl 0.24 0.01 0.08 18.78 26.22 17.18 bdl 0.05 100.12

0.975 0.005 0.01 – 0.99 0.42 0.35 0.235 – 0.005 1.01

0.98 0.005 0.01 – 1.00 0.415 0.35 0.235 – – 1.00

Rh and Sb have not been detected. GEOLOGY OF ORE DEPOSITS

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GENETIC Pd, Pt, Au, Ag, AND Rh MINERALOGY

423

Au–Ag Hes Alt Sob Plv Msl Sob

(a)

Hes

100 µm

Mch

100 µm

Msl (b)

PdTe kotulskite 100 10 90 20 80 30 70 40 60 50 50 60 40 70 30 80 20 90 10 100 PdBi PdPd sobolevskite 100 90 80 70 60 50 40 30 20 10

16

Number of analyses

(c)

(d)

n = 52

12

8

14 13

11

9

4 5

0 100 90 80 70 60 50 40 30 20 10 0 Pd2Bi2 Pd2BiPb Pd2Pb2

Fig. 16. Pneumatolytic PGM of middle stage: (a) metasomatic intergrowth of Tesobolevskite (Sob, matrix) with inclusions of Sbfree paolovite (Plv), Pdmaslovite (Msl), Ptmichenerite (Mch) with altaite (Alt), hessite (Hes), electrum, and küstelite (Au– Ag) rim; (b) metasomatic intergrowth of Tesobolevskite (Sob), hessite (Hes), and maslovite (Msl). Images in reflected electrons; (c) composition of sobolevskite–kotulskite; (d) compositional variations of polarite. Oktyabrsky Mine.

veins is markedly distinct from that of magmatic sul fide ore and is close to the crustal value (Fig. 1). The model Pb/Pb age of galena from arsenide–carbonate veins is 144 Ma; galena in carbonate veins containing silver minerals and uraninite is dated at 110 Ma. The metamorphosed rocks and ores are not foli ated. Metamorphism variable in grade is accompanied by hydraulic fracturing. Numerous fractures are filled with mineral matter mobilized from adjacent rocks. Thus, we encounter fluiddominating metamorphism of subsidence (Fyfe et al., 1978; Spiridonov et al., 2000). In metavolcanic rocks of the first stage formed under conditions of zeolite facies (ZF), all pores are filled with celadonite, albite, epidote, corrensite, cal cite, chlorite, titanite, zeolite, quartz, iddingsite, and lizardite; agate amygdules are filled with finefibrous stranded chalcedony. Metabasalts host occurrences of copper–zeolite mineralization, Iceland spar, and GEOLOGY OF ORE DEPOSITS

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datolite. Metavolcanic and metagabbroic rocks of the second stage formed under conditions of prehnite– pumpellyite facies (PPF): prehnite, albite, chlorite, epidote, pumpellyite, quartz, titanite, actinolite, cum mingtonite (pseudomorphs after iddingsite), serpen tine, hydrogarnets, and datolite are tyypical; these rocks also contain metaagate (metaquartzite). Metavolcanics and metagabbroic rocks of the third stage formed under conditions of ZF are composed of celadonite, albite, epidote, corrensite, calcite, chlo rite, titanite, and julgoldite. Numerous cavities and fractures are filled with zeolite, okenite, apophyllite, and quartz; agate amygdules are filled with fine fibrous stranded chalcedony. Each sample of the Noril’sk ore contains meta morphic–hydrothermal magnetite and mackinawite veinlets. The following minerals occur as veinlets and pockets (from early to late): millerite + chalcopyrite +

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Au–Ag Plv

Plv Gev Au–Ag 300 µm

(а)

30 µm

(b) Plv

Gn

Fro

Fro Au–Ag 30 µm

30 µm

Fig. 17. Pneumatolytic Au–Ag minerals: (a) electrum (Au–Ag) veinlets along cleavage of paolovite (Plv) with exsolution struc tures of insizwaite, geversite, and niggliite; exsolution structures are recrystallized; (b) pocket of homogeneous küstelite within PGM intergrowth (matrix is paolovite, lamellae are geversite); (c) gold–electrum– küstelite–Aubearing silver crystal with smooth direct zoning intergrown with froodite (Fro) in galena (Gn), Fe–Cu sulfides are black; (d) pocket of electrum (Au–Ag) intergrown with PGM: paolovite (Plv) with geversite lamellae and froodite (Fro) ingrowths. Aggregate of Au–Ag minerals with inverse zoning has been grown over PGM: küstelite (dark gray) is in center of crystals, electrum and further Agbearing gold (light gray) are around. Images in reflected electrons. Oktyabrsky Mine.

pyrite (ZF); anhydrite + chalcopyrite + pyrrhotite + stilpnomelane (ZF–PPF); bornite + magnetite + anhydrite (PPF); chalcocite + heazlewoodite (ZF); valleriite + Nipyrite (ZF); fiveelement U–Ag–Bi– Co–Ni mineralization; Fe–Ni–Co arsenides and antimonides, native silver, arsenic, and bismuth; Ag, Bi, Pb, Mn. and Cd; uraninite (ZF); marcasite + quartz + calcite + hisingerite + tochilinite (lowtem perature ZF) (Iskyul, 1940; Godlevsky and Shum skaya, 1960; Zolotukhin et al., 1967; Kulagov et al., 1969; Ryabov and Zolotukhin, 1977; Spiridonov, 2004; Spiridonov and Gritsenko, 2009; Spiridonov et al., 2012–2013, 2014). The regenerative metamor phic–hydrothermal Ag, Pd, Sn, and Pt mineralization develops in sulfide ore lodes and nearby. This mineral ization originates under the effect of moderately and

lowsaline carbon dioxide–chloride fluids with vari able but generally elevated oxygen fugacity and alka linity. These are NaCl–MgCl2 solutions with salinity of 15 to 0.4 wt % NaCl equiv (approximately two thirds of fluid inclusions) and NaCl–CaCl2 (±NaHCO3) solutions with salinity of 23 to 6.5 wt % NaCl equiv (one third of inclusions) at a temperature from 270°C (commonly 250–216 to 140–120°С, occasionally 90°С and pressure of 1.2 to 0.3 kbar (Spiridonov and Gritsenko, 2009). Metamorphic–Hydrothermal Palladium Mineralization In metamorphosed and brecciated magmatic sul fide ores in the Norilsk ore field with abundant parker ite, hisingerite, and quartz veinlets and pockets, an GEOLOGY OF ORE DEPOSITS

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GENETIC Pd, Pt, Au, Ag, AND Rh MINERALOGY

PbSss

425

Fro

Fro

iss iss (a)

50 µm

30 µm

(b) iss Number of analyses 200 Fro

(d)

150 n = 1425 100

Au–Ag

0 PGM (c)

30 µm

850 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50

50

Fineness, ‰

Fig. 18. Pneumatolytic Au–Ag minerals: (a, b) metasomatic gold grains with smooth oscillatory zoning from Agbearing gold to Aubearing silver and froodite (Fro) at contact with PbSss and iss; (c) froodite (Fro) and complexly zoned gold grains have been grown over PGM (exsolution structures: Sbpaolovite is matrix; insizwaite, geversite, and niggliite are small exsolution bodies). Images in reflected electrons. Oktyabrsky Mine; (d) variable fineness of Au–Ag minerals in massive and disseminated sulfide and lowsulfide ores of Talnakh ore cluster.

appreciable amount of pneumatolytic Sbpaolovite (the most abundant Pd mineral) is replaced with Sb free paolovite (Fig. 20a). Magnetite and mackinawite flasers with regenerated paolovite, which is depleted in Sb but enriched in Ag, locally develop in the same ore (Fig. 20b). As follows from the results of hundreds of analyses, pneumatolytic paolovite contains 2–9 wt % Sb, up to 15 wt % Pt, up to 5 wt % Au, and Ag traces; more than 6 mole fractions of Pd2Sb end member. The metamorphic–hydrothermal paolovite transformed and regenerated contains <2.2 wt % Sb, <2.4 wt % Pt, Au traces, up to 9.9 wt % Ag, and less than 4 mole frac GEOLOGY OF ORE DEPOSITS

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tions of Pd2Sb end member (Spiridonov et al., 2014). The products of endogenic oxidation of paolovite: cas siterite (Fig. 20c), Snbearing hydrogrossular, as well as malyshevite CuPdBiS3, sobolevskite, froodite, Pd breithauptite (up to 4 wt % Pd), and vysotskite are contained in metamorphosed ores. Holotype of vysotskite PdS is identified in the Noril’sk ore con taining actinolite and decomposed pentlandite (Gen kin and Zvyagintsev, 1962). According to our observa tions, vysotskite develops only in the lowgrade meta morphosed sulfide ore in association with millerite, chalcopyrite, galena, chlorites, ilvaite, prehnite, bab

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SPIRIDONOV et al. Alt

Sulf

Fro Spy Spy

Plv 2 mm

(a)

20 µm

GevIns (b)

PtAs2 Spy

Tfp

90

10

At Rsb

(c)

50 µm

80 PtSb2

20 Pt(Sn, Te)2

Fig. 19. Metacrysts of the latest pneumatolytic PGM (sperrylite, Spy): (a) large metacryst at contact of customary sulfide ore (Sulf) and eutectic ore with numerous PGM pockets. Oktyabrsky Mine; (b) cubic metacryst in aggregate of paolovite (Plv), Pt dichalcogenides (Gev–Ins), froodite (Fro), and altaite (Alt). Taimyrsky Mine; (c) flattened sperrylite crystal (Spy) at contact of rustenburgite–atokite (Rsb–At) and tetraferroplatinum (Tfp). Mayak (Majak) Mine. (a–c) Images in reflected electrons; (d) compositional variations of small sperrylite crystals replacing Sbpaolovite, geversite, and Sbpalladinite.

ingtonite (Fig. 20d), and pumpellyite. The average chemical composition of vysotskite (n = 17) is as fol lows, wt %: 65.65 Pd, 0.12 Pt, 0.01 Rh, 8.25 Ni, 0.95 Fe, 0.32 Cu, 0.03 Co, 25.03 S, 0.03 As; 100.39 in total. Formula is (Pd0.79Ni0.18Fe0.02Cu0.01)1S1. The meta morphic–hydrothermal vysotskite differs from the mag matic mineral (Cabri et al., 1978; Naldrett, 2004) in its extremely low Pt contents and enrichment in Ni and Fe. Palladoarsenide Pd2S is contained in metamor phosed ore of the Talnakh cluster as reticulate veinlets that replace majakite (Fig. 21a) at the extension of cal cite veinlets with chlorite, magnetite, and serpentine within the sulfide matrix (Spiridonov et al., 2011). The average chemical composition of palladoarsenide (n = 4) is as follows, wt %: 68.67 Pd, 1.03 Pt, 0.13 Au, 1.49 Cu, 1.35 Ni, Fe 0.34, 26.10 As, 0.17 Pb, 0.03 Te, 0.03 Sn, 0.02 Bi; 99.36 in total. Formula is (Pd1.84Pt0.02Cu0.07Ni0.06Fe0.02)2.01As0.99.

2PdNiAs → Pd2As + 2Nisol + Assol. Carbonate veins with Ni arsenides occur near the areas with palladoarsenide mineralization. Vincentite Pd3As develops in metamorphosed ore of the Noril’sk cluster as a product of replacement of pneumatolytic majakite and is associated with millerite, chlorite, and prehnite (Fig. 21b). The average chemical composi tion of vincentite (n = 11) is as follows, wt %: 77.27 Pd, 1.35 Pt, 0.03 Rh, 0.19 Ag, 0.22 Cu, 0.12 Ni, 0.44 Fe, 16.89 As; 0.28 Sb; 0.13 Bi, 0.22 Pb, 0.16 Te; 99.70 in total. The formula is (Pd2.91Pt0.03Fe0.03Ag0.01Ni0.01Cu0.01)3 (As0.90Sn0.08Sb0.01Te0.005Pb0.005)1. Native Pd as films on native platinum surrounding sperrylite crystals was observed by A.I. Ponomarenko (oral communication, 1999). Thus, a metamorphic trend of dearsenization has been outlined: majakite PdNiS → palladoarsenide Pd2As → vincentite Pd3As → native palladium. GEOLOGY OF ORE DEPOSITS

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GENETIC Pd, Pt, Au, Ag, AND Rh MINERALOGY

427

Table 10. Chemical compositions (wt %) of cabriite from magmatic sulfide ore of Oktyabrsky Mine Compo nent

75

76

77

78

79

80

81

82

83

Pd

53.84

51.30

50.23

45.82

38.26

30.61

44.56

52.04

52.98

Pt

bdl

2.52

4.98

9.44

19.19

30.72

11.31

0.97

0.29

Cu

14.95

15.42

14.96

14.92

14.15

14.02

15.01

15.44

15.79

Ni

bdl

bdl

bdl

0.01

bdl

0.02

0.02

bdl

bdl

Fe

0.11

0.14

0.02

bdl

0.01

0.03

0.02

0.04

bdl

Sn

29.42

28.45

28.71

27.46

25.43

24.32

25.07

25.42

21.16

Sb

bdl

bdl

bdl

0.74

1.61

1.60

3.19

4.01

8.98

Bi

0.10

bdl

bdl

bdl

bdl

0.17

bdl

0.19

0.23

Pb

bdl

0.13

bdl

0.21

bdl

bdl

bdl

bdl

bdl

As

0.01

0.09

bdl

bdl

0.06

bdl

bdl

bdl

bdl

99.43

98.05

98.90

98.63

98.71

101.49

99.18

98.11

99.43

Total

Formula units calculated on the basis of 4 atoms Pd

2.04

1.965

1.94

1.81

1.58

1.30

1.76

1.98

1.99

Pt

–

0.055

0.10

0.20

0.43

0.71

0.25

0.02

0.01

Total

2.04

2.02

2.04

2.01

2.01

2.01

2.01

2.00

2.00

Cu

0.95

0.99

0.97

0.99

0.98

1.00

0.99

0.99

0.99

Fe

0.01

0.01

–

–

–

–

–

–

–

Total

0.96

1.00

0.97

0.99

0.98

1.00

0.99

0.99

0.99

Sn

1.00

0.975

0.99

0.97

0.95

0.93

0.89

0.87

0.71

Sb

–

–

–

0.03

0.06

0.06

0.11

0.14

0.30

As

–

0.005

–

–

–

–

–

–

–

1.00

0.98

0.99

1.00

1.01

0.99

1.00

1.01

1.01

Total

Te, Au, and Rh have not been detected.

Metamorphic–Hydrothermal Platinum Mineralization The pentladitelike kharaelakhite (Pt,Cu,Pb,Fe,Ni)9S8) discovered and studied by T.L. Evstigneeva (Genkin et al., 1985) develops locally in metamorphosed sul fide ore in association with bornite and millerite. Kharaelakhite occurs as separate segregations and rims around vysotskite grains. In turn, cooperite PtS rims kharaelakhite itself and less frequently rims plat inum as a product of replacement and dearsenization of sperrylite (Evstigneeva et al., 1990). At most deposits, Pt and Pd monosulfides (cooper ite and vysotskite) are products of late magmatic crys tallization (Cabri et al., 1978; Naldrett, 2004). In the Noril’sk ores, they are epigenetic hydrothermal min GEOLOGY OF ORE DEPOSITS

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erals associated with millerite, ilvaite, chlorite, actin olite, and prehnite. Judging by experimental results (Evstigneeva and Tarkian, 1996), cooperite and vysotskite also can crystallize from hydrothermal solu tions at a temperature of ~200°C. Metamorphic–Hydrothermal Silver Mineralization The silver mineralization is a component of five element type mineralization in the Noril’sk ore field (Spiridonov and Gritsenko, 2009; Spiridonov et al., 2012–2013). Native silver with <0.01 wt % Au, as well as less abundant metasomatic argentopentlandite and chalcopyrite–lenaite solid solutions AgFeS2 variable

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Plv2 Qtz Plv

Hsn Plv1

20 µm

(a)

300 µm

(b)

Plv

Chl

Cp

Bbg

Mlr Cst

Vsk (c)

Sob

10 µm

(d)

10 µm

Fig. 20. PGM of lowgrade metamorphosed ores: (a) Sbfree Agpaolovite (Plv) replacing pneumatolytic Sbpaolovite in brec ciated ore with hisingerite (Hsn) veinlets and small quartz (Qtz) metacrysts; (b) flasers of regenerated Sbfree paolovite (Plv2) with magnetite and mackinawite near pocket of pneumatolytic Sbpaolovite (Plv1); (c) cassiterite (Cst) metacrysts with relict lamellae of insizwaite (white): product of endogenic oxidation of paolovite; newly formed sobolevskite (Sob); (d) newly formed vysotskite (Vsk) intergrown with millerite (Mlr), chalcopyrite (Cp), chlorite (Chl), prehnite, and babingtonite (Bbg). (a–c) Okty abrsky Mine, (d) Medvezhy Creek Mine. Images in reflected electrons.

in composition occur in metamorphosed sulfide ore in association with carbonates, bornite, magnetite, Ni pyrite, anhydrite, chalcocite, chlorite, and serpentine. Native silver grains reach 13 mm in size. Carbonate and anhydrite–carbonate veins of fiveelement miner alization contain silver, Hgsilver with 1–11 wt % Hg, argentite, acanthite, pyrargyrite, mckinstryite, argen topyrite, naumannite, aguilarite in association with Ni–Co–Fe arsenides and sulfoarsenides, breithaup tite, ulmannite, native arsenic, chalcocite, galena, würtzite, clausthalite, and uraninite (Kulagov et al., 1978; Sluzhenikin et al., 1994; Spiridonov and Grit senko, 2009; Spiridonov et al., 2007, 2013, 2014).

CONCLUSIONS All noblemetal minerals in the Noril’sk sulfide and lowsulfide ores are products of metasomatic replacement and solidphase transformations of sul fide solid solutions. The aureoles of noblemetal min erals are somewhat wider than contours of sulfide ores and coincide with halos of fluid impact on sulfide bod ies and the adjacent host rocks. When pneumatolytic PGM, Au–Cu–Ag, and Au–Ag minerals are formed, fluids transfer Pd, Pt, Au, Te, Sn, As, Sb, and Bi, whereas Fe, Ni, Pb, Cu, Ag, Rh, and partly Te and Pd are recovered from the replaced sulfide minerals. The pneumatolytic noblemetal minerals comprise inter GEOLOGY OF ORE DEPOSITS

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429

Pd2As Mjk Chl

Prh

Mjk

Mlr AuCu (a)

Tfp 20 µm

(b)

10 µm

Fig. 21. PGM of lowgrade metamorphosed ores: (a) palladoarsenide (Pd2As) replacing majakite (Mjk), where majakite is cross cut by magnetite, mackinawite, chlorite, serpentine, and calcite veinlets; tetraferroplatinum (Tfp), Pt–Pdtetraauricupride (AuCu). Mayak (Majak) Mine; (b) newly formed vincentite (white) in association with millerite (Mlr), chlorite (Chl), and pre hnite (Prh). Medvezhy Creek Mine. Images in reflected electrons.

metallic compounds, including stannides, bismuth ides, plumbides, cuprides, and close to them ars enides, antimonides, and telllurides. Hollingworthite, sporadic crystals of which are incorporated into sper rylite metacrysts hosted in pyrrhotite ore, is a single exception. The isomorphic capacity of pneumatolytic PGM decreases from early minerals to late Sbfree paolovite, Sbfree insizwaite, and Bifree geversite. Paolovite Pd2(Sn,Sb), atokite (Pd,Pt)3Sn, and sobo levskite Pd(Bi,Pb) are the most abundant Pd minerals. The most abundant platinum minerals are tetraferro platinum Pt2Fe(Fe,Ni,Cu), rustenburgite (Pt,Pd)3Sn, and insizwaite–geversite (Pt(Sb,Bi)2. The early pneu matolytic PGM are characterized by appreciable Au admixture, exsolution structures, and twins of poly morphic transitions. Au–Cu–Ag minerals (middle stage, with substantial Pd and Pt admixtures) and Au– Ag minerals (late stage, without Pd and Pt admixtures) are associated with pneumatolytic PGM of the middle and late stages. The formation of noblemetal miner als was a twostage process: (1) entrapment of noble metals during crystallization of hightemperature mss, iss, and PbSss sulfide solid solutions and (2) fluid reworking of them and crystallization of intermetallic noblemetal compounds in sharply reductive setting and at extremely low fS2 at gradual drop of tempera ture from ~450 to ≈350°С. Despite the favorable con ditions for annealing of the Noril’sk ore, no exsolution structures in minerals of the gold–silver series are identified. The Ag, Pd, Pt sulfides, native Pt and Pd, and Ptbearing breithauptite are known among metamor phic–hydrothermal noblemetal minerals. Metamor phic–hydrothermal PGM and Ag minerals substan GEOLOGY OF ORE DEPOSITS

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tially differ from pneumatolytic PGM, Ag, and Au– Ag minerals. A metamorphic dearsenization trend has been established: majakite PdNiAs → palladoarsenide Pd2As → vincentite Pd3As → native palladium Pd. Metamorphism of Noril’sk sulfide ore resulted in the appreciable mobilization of Ag, to a lesser degree, of Pd, and still less of Pt. No Au mobilization has been established. ACKNOWLEDGMENTS We are grateful to M.A. Yudovskaya and anony mous reviewers for critical comments. This study was supported by the Russian Foundation for Basic Research (project no. 130500839). REFERENCES Arndt, N., Chauvel, C., Czamanske, G., and Fedorenko, V., Two mantle sources, two plumbing systems: tholeiitic and alkaline magmatism of the Maymecha river basin, Siberian flood volcanic province, Contrib. Mineral. Petrol., 1998, vol. 133, pp. 297–313. Barkov, A.Y., Laajoki, K., Gervilla, F., and Makovicky, E., Menshikovite Pd–Ni arsenide and synthetic equivalent, Mineral. Mag., 2000a, vol. 64, pp. 847–851. Barkov, A.Y., Martin, R.F., Poirier, G., and Yakovlev, Y.N., The taimyrite–tatyanaite series and zoning in intermetallic compound of Pt, Pd, Cu, and Sn from Noril’sk, Siberia, Russia, Can. Mineral., 2000b, vol. 38, pp. 599–609. Begizov, V.D. and Sluzhenikin, S.F., Palladium Arsenide Assemblages in the outercontact rocks of the Talnakh Intru sion, Tr. TsNIGRI, 1976, no. 122, pp. 93–97.

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Translated by V. Popov

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