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Author(s): Barkov, AY; Bindi, L; Tamura, N; Martin, RF; Ma, C; Winkler, B; Shvedov, GI; Morgenroth, W | Abstract: Fleetite, Cu2RhIrSb2, a new species of platinum-group mineral (PGM), was discovered intergrown with an Os–Ir–Ru alloy in the Miass Placer Zone (Au–PGE), southern Urals, Russia. A single grain 50 lm across was found. Osmium, ruthenium, and iridium are the main associated minerals; also present are Pt–Fe alloys, laurite, Sb-rich irarsite, Rh-rich tolovkite, kashinite, anduoite, ferronickelplatinum, heazlewoodite, PGE-bearing pentlandite and digenite, as well as micrometric inclusions of forsterite (Fo93.7), chromite–magnesiochromite, and Mg-rich edenite. In reflected light, fleetite is light gray; it is opaque, isotropic, non-pleochroic, and non-bireflectant. We report reflectance values measured in air. A mean of seven point-analyses (wavelength-dispersive spectrometry) gave Cu 13.93, Ni 8.60, Fe 0.10, Ir 28.07, Rh 7.91, Ru 1.96, Sb 39.28, total 99.85 wt.%, corresponding to (Cu1.41Ni0.58Fe0.01)R2.00(Rh0.49Ni0.36Ru0.12)R0.97Ir0.95Sb2.08 on the basis of six atoms per formula unit, taking into account the structural results. The calculated density is 10.83 g/cm3. Single-crystal X-ray studies show that fleetite is cubic, space group Fd3m (#227), a = 11.6682(8) A, V = 1588.59(19) A3, and Z = 16. A least-squares refinement of X-ray powder-diffraction data gave a = 11.6575(5) A and V = 1584.22(19) A3. The strongest five reflections in the powder pattern [d in A(I)(hkl)] are: 6.70(75)(111), 4.13(100)(220), 3.52(30)(311), 2.380(50)(422), 2.064(40)(440). Results of synchrotron micro-Laue diffraction experiments are consistent [a ¼ 11.66(2) A]. The crystal structure of fleetite was solved and refined to R ¼ 0.0340 based upon 153 reflections with Fo . 4r(Fo). It is isotypic with Pd11Bi2Se2 and best described as intermetallic, with all metal atoms in 12-fold coordination. Fleetite and other late exotic phases were formed by reaction of the associated alloy phases with a fluid phase enriched in Sb, As, and S in circulation in the cooling ophiolite source-rock. The mineral is named after Michael E. Fleet (1938–2017) in recognition of his significant contributions to the Earth Sciences.

We describe a potentially new species of a platinum cupride–stannide mineral (PCSM) of composition Pt(Cu0.67Sn0.33). It occurs in a placer deposit in the River Bolshoy Khailyk, southern Krasnoyarskiy kray, Russia. A synthetic equivalent of PCSM was obtained and characterized. The PCSM occurs as anhedral or subhedral grains up to 15 μm × 30 μm in association with various platinum-group minerals, Rh–Co-rich pentlandite and magnetite, all hosted by a placer grain of Cu–Au–Pt alloy. Synchrotron micro-Laue diffraction studies indicate that the PCSM mineral is tetragonal and belongs to the inferred space-group P4/mmm (#123). Its unit-cell parameters are a = 2.838 (3) Å, c = 3.650 (4) Å, and V = 29.40 (10) Å3, and Z = 1. The c:a ratio calculated from the unit-cell parameters is 1.286. These characteristics are in good agreement with those obtained for specimens of synthetic Pt(Cu0.67Sn0.33). A review on related minerals and unnamed phases is provided to outline compositional variations and extents of solid solutions in the relevant systems PtNi–PtFe–PtCu, PdCu–PdHg–PdAu, PdHg–PtHg, and AuCu–PtCu. The PCSM-bearing mineralization appears to be related genetically with an ophiolitic source-rock of the Aktovrakskiy complex of the western Sayans. The unnamed phase likely crystallized from microvolumes of a highly fractionated melt rich in Cu and Sn.

We describe the new species ognitite, NiBiTe, and a Co-rich variety of maucherite, hitherto unreported; both were discovered in the Ognit ultramafic complex of Neoproterozoic age in Eastern Sayans, Russia. The mean composition of ognitite (n = 7) is: Ni 17.05, Fe 0.07, Cu 0.14, Pd 0.14, Te 32.53, Bi 49.64, total 99.57 wt.%, corresponding to: (Ni1.11Cu0.008Fe0.005Pd0.005)Σ1.13Bi0.90Te0.97 (Σ atoms = 3 apfu). Ognitite is trigonal, space group P3m1 [R1 = 0.0276 for 81 reflections with Fo > 4σ(Fo)]. The unit-cell parameters derived from the single-crystal X-ray diffraction data are: a = 3.928(1) Å, c = 5.385(1) Å and V = 71.95(4) Å3, with Z = 1. The c:a ratio is 1.37. The powder X-ray diffraction data obtained on the same fragment used for the single-crystal study are: a = 3.9332(4) Å, c = 5.3920(6) Å and V = 72.24(1) Å3. Ognitite exhibits the brucite-type structure with edge-sharing NiTe3Bi3 octahedra forming sheets parallel to (0001). It is related to melonite, but is distinct compositionally by the extreme Bi-enrichment (melonite and its synthetic analogue contain At more than 9 wt.% Co, or ~2 apfu Co, the core of Co-rich maucherite [(Ni,Co)11As8] in a zoned crystal, which is surrounded by Co-depleted orcelite, far surpasses the norm (≤1 and up to 3.9 wt.% Co). The unit-cell parameters of the Co-rich maucherite are: a = 6.85(2) and c = 21.83(5) Å, which are based on results of synchrotron micro-Laue diffraction.The host rock consists of serpentine, clinochlore (Mg# 95–97) and skeletal chromite. We favour the metastable crystallisation of fluid-saturated globules of a sulfide–arsenide melt to explain the anomalous compositions of ore minerals at Ognit. These anomalies seem consistent with rapid cooling in a fluid-enriched system, possibly related to late-stage degassing of the magma, as reflected in a prominent metasomatic aureole at the contact with the enclosing gneissic rocks.

Highly atypical mineralization involving Pd-Pt, Au-Ag, REE, Y, Zr, U, Th, and Cl-F-enriched minerals is found in zones with base metal sulfides (BMS, ~5 vol.% to 20 vol.%) in the eastern portion of the Oktyabrsky deposit in the Norilsk complex (Russia). The overall variations in Mg# index, 100 Mg/(Mg + Fe2+ + Mn), in host-rock minerals are 79.8 → 74.1 in olivine, 77.7 → 65.3 in orthopyroxene, 79.9 → 9.2 in clinopyroxene, and An79.0&nbsp, → An3.7. The span of clinopyroxene and plagioclase compositions reflects their protracted crystallization from early magmatic to late interstitial associations. The magnesian chromite (Mg# 43.9) trends towards Cr-bearing magnetite with progressive buildups in oxygen fugacity, ilmenite varies from early Mg-rich to late Mn-rich variants. The main BMS are chalcopyrite, pyrrhotite, troilite, and Co-bearing pentlandite, with less abundant cubanite (or isocubanite), rare bornite, Co-bearing pyrite, Cd-bearing sphalerite (or wurtzite), altaite, members of the galena-clausthalite series and nickeline. A full series of Au-Ag alloy compositions is found with minor hessite, acanthite and argentopentlandite. The uncommon assemblage includes monazite-(Ce), thorite-coffinite, thorianite, uraninite, zirconolite, baddeleyite, zircon, bastnäsite-(La), and an unnamed metamict Y-dominant zirconolite-related mineral. About 20 species of PGM (platinum group minerals) were analyzed, including Pd-Pt tellurides, bismuthotellurides, bismuthides and stannides, Pd antimonides and plumbides, a Pd-Ag telluride, a Pt arsenide, a Pd-Ni arsenide, and unnamed Pd stannide-arsenide, Pd germanide-arsenide and Pt-Cu arseno-oxysulfide. The atypical assemblages are associated with Cl-rich annite with up to 7.54 wt.% Cl, Cl-rich hastingsite with up 4.06 wt.% Cl, ferro-hornblende (2.53 wt.% Cl), chlorapatite (&gt, 6 wt.% Cl) and extensive solid solutions of chlorapatite, fluorapatite and hydroxylapatite, Cl-bearing members of the chlorite group (chamosite, up to 0.96 wt.% Cl), and a Cl-bearing serpentine (up to 0.79 wt.% Cl). A decoupling of Cl and F in the geochemically evolved system is evident. The complex assemblages formed late from Cl-enriched fluids under subsolidus conditions of crystallization following extensive magmatic differentiation in the ore-bearing sequences.

We describe occurrences of palladoan melonite in intimate intergrowths with cobaltite-gersdorffite from the Neoproterozoic dunite-wehrlite-gabbro complexes of Kingash and Kuskanak, Eastern Sayans, Russia. The observed compositional trends of melonite are consistent with the overallvariations examined on the basis of numerous literature sources. The levels of Bi in NiTe2are normally limited to ≤0.25 Bi atoms per formula unit (apfu), under natural conditions. Greater levels (≤0.5 Bi apfu) are associated with the (Pd + Pt) enrichment in the palladoanvarieties. The telluride–sulfarsenide intergrowths probably formed at Kingash and Kuskanak late in the crystallization history of the ore zones, from microdroplets of residual melt rich in semimetals (Te, Bi, As) and noble metals (Pd and Ag), below the solidus of the enclosing gabbroicrocks and within a narrow range of temperatures (500–550°C). On the basis of our observations made on specimens of melonite and synthetic Ni(Te,Bi)2–x(x = 0.6), we infer that the limit of incorporation of Bi into a melonitetype phase is ≤0.5 Bi apfu.

We examine overall compositional ranges and substitutions of elements in intermetallic compounds of Pd, Pt, Cu, and Sn (cabriite, taimyrite, “stannopalladinite”, and tatyanaite), on the basis of (1) new results based on electron microprobe analyses of these stannides from Noril9sk (Krasnoyarskiy kray, Russia) and Lukkulaisvaara (northern Karelia, Russia), and (2) data published in the literature on natural and synthetic stannides. These results are consistent with the existence of a single and extensive field of solid solutions of the stannides of Pd-Pt-Cu, related to cabriite–taimyrite and tatyanaite, with generalized formulae (Pd,Pt) 2+ x Cu 1– x (Sn,Sb) – (Pt,Pd) 2+ x Cu 1– x (Sn,Sb), where 0 x 2+ x (Fe,Cu) 1– x (Sb,Sn). No miscibility gap is evident. An unlimited substitution of Pt-for-Pd appears to exist; in addition, Pd partly substitutes for Cu, whereas there is no evidence for the existence of a Pt-for-Cu substitution in these solid solutions. The stannides of Pd-Pt-Cu were likely deposited relatively late in the crystallization history of mineral associations, at low temperatures, likely as a result of a significant drop in temperature and increase in activity of Cu and Sn in a fractionated sulfide melt or a fluid phase. An atypical combination of relatively low levels of fugacities of O 2 and S 2 could account for the appearance of these rare compounds instead of common oxide or sulfide minerals, and could explain the observed scarcity of phases of the Pd-Pt-Cu stannides in nature.

We describe assemblages of platinum-group minerals (PGM) and associated PGE&ndash, Au phases found in alluvium along the River Bolshoy Khailyk, in the western Sayans, Russia. The river drains the Aktovrakskiy ophiolitic complex, part of the Kurtushibinskiy belt, as does the Zolotaya River ~15 km away, the site of other placer deposits. Three groups of alloy minerals are described: (1) Os&ndash, Ir&ndash, Ru compositions, which predominate, (2) Pt&ndash, Fe compositions of a Pt3Fe stoichiometry, and (3) Pt&ndash, Au&ndash, Cu alloys, which likely crystallized in the sequence from Au&ndash, (Cu)-bearing platinum, Pt(Au,Cu), Pt(Cu,Au), and PtAuCu2, to PtAu4Cu5. The general trends of crystallization of PGM appear to be: [Os&ndash, Ru alloys] &rarr, Pt3Fe-type alloy (with inclusions of Ru-dominant alloy formed by exsolution or via replacement of the host Pt&ndash, Fe phase) &rarr, Pt&ndash, Cu alloys. We infer that Rh and Co mutually substitute for Fe, not Ni, and are incorporated into the pentlandite structure via a coupled mechanism of substitution: [Rh3+ + Co3+ + □ &rarr, 3Fe2+]. Many of the Os&ndash, Ru and Pt&ndash, Fe grains have porous, fractured or altered rims that contain secondary PGE sulfide, arsenide, sulfarsenide, sulfoantimonide, gold, Pt&ndash, Ni-rich alloys, and rarer phases like Cu-rich bowieite and a Se-rich sulfarsenide of Pt. The accompanying pyroxene, chromian spinel and serpentine are highly magnesian, consistent with a primitive ultramafic source-rock. Whereas the alloy phases indicate a highly reducing environment, late assemblages indicate an oxygenated local environment leading to Fe-bearing Ru&ndash, Os oxide (zoned) and seleniferous accessory phases.

Microcrystals of platinum-group element (PGE)-bearing cobaltite occur in the Gulcari A deposit of vanadiferous titanomagnetite in the lower zone of the Rio Jacaré mafic-ultramafic layered intrusion, Brazil. Aggregates of cobaltite and sperrylite are cluster-like and developed generally along the boundary of Fe-Ti oxide grains with deuteric silicates. Our observations of cryptic zoning, compositional variability and interelement correlations are based on 37 analytical points (wavelength-dispersion spectrometry mode) of cobaltite, and indicate that Ir and Rh behave uniformly with Ni and antipathetically with Co which, in turn, correlates directly with S content. Iridium, Rh and Ni apparently substitute for Co in the As-enriched grain core, and the substitution mechanism invokes solid solution with a cattierite-type molecule: (Ni + Ir + Rh) + (AsS) = Co + (S2). The PGE-bearing cobaltite probably crystallized as a primary phase at 500 to 300°C, from microvolumes of a late fluid phase. The observed enrichment in S and decrease in the As:S ratio at the cobaltite grain margins is a reflection of the increase in sulfur fugacity (fS2) with decrease in temperature of crystallization.

New results (compositional data and reflectance values) are reported for some rare sulfides enriched in K, Tl and Pb, which are related to djerfisherite, thalfenisite, bartonite, a “Cl-bearing bartonite”, or chlorbartonite, and also for shadlunite, from the Noril'sk and Salmagorsky complexes, Russia. Our observations and comparisons with relevant data in the literature imply that: (1) bartonite is probably a S-dominant (or Cl-free) analogue of djerfisherite; and a “Cl-bearing bartonite” and chlorbartonite are probably compositional variants of the djerfisherite–bartonite series. (2) The most probable formulae of bartonite and djerfisherite are (K,Me2+)6(Fe,Cu,Ni)25–xS26(S,Cl) and (K,Me2+)6(Fe,Cu,Ni)25–xS26(Cl,S), where 0 ≤ x ≤ 5, respectively. (3) Two independent substitution mechanisms probably operate in the natural series. A coupled substitution [Me2+ + S2– ↔ K+ + Cl–] is reflected by an observed deficit in K, accompanied by the incorporation of Me2+(Pb, Fe, or Ni) in the K site. Another mechanism is inferred to be [2Fe3+ + 〈 ↔ 3Fe2+], which assumes the existence of vacancy-type defects at the Me site. Thus, the second mechanism could possibly control the existing variations of Σ(Fe, Cu, Ni) in the range of ∼21 to 25 a.p.f.u., documented in djerfisherite- and bartonite-type minerals. The minerals analysed from Noril'sk, which are free of Cl and related to bartonite and to a Tl-dominant analogue of bartonite (unnamed species), probably crystallized from microvolumes of late fluid rich in K and Tl, under conditions of relatively low oxygen fugacity in the environment. Uniform contentss of Fe and Cu, observed in coexisting phases of normal (Cl-bearing) djerfisherite and bartonite (or Cl-free analogue of djerfisherite) at Salmagorsky imply that they reached equilibrium with regard to the distribution of these elements during crystallization. These phases probably formed as a result of fluctuations in the ratios of sulfur and chlorine fugacity in a fluid at a postmagmatic hydrothermal stage.

Tetra-auricupride, ideally AuCu, represents the only species showing the coexistence of Au with an elevated level of Pt, as in the case of a detrital grain studied structurally for the first time, from an ophiolite-associated placer at Bolshoy Khailyk, western Sayans, Russia. We infer that tetra-auricupride can incorporate as much as ~30 mol. % of a &ldquo, PtCu&rdquo, component, apparently without significant modification of the unit cell. The unit-cell parameters of platiniferous tetra-auricupride are: a 2.790(1) &Aring, c 3.641(4) &Aring, with c/a = 1.305, which are close to those reported for ordered AuCu(I) in the system Au&ndash, Cu, and close also to the cell parameters of tetraferroplatinum (PtFe), which both appear to crystallize in the same space group, P4/mmm. These intermetallic compounds and natural alloys are thus isostructural. The closeness of their structures presumably allows Pt to replace Au atoms so readily. The high extent of Cu + Au enrichment is considered to be a reflection of geochemical evolution and buildup in levels of the incompatible Cu and Au with subordinate Pt in a remaining volume of melt at low levels of fO2 and fS2 in the system.

Compositional variations of major and minor elements were examined in Pt–Fe alloys from various geological settings and types of deposits, both lode and placer occurrences. They included representatives of layered intrusions, Alaskan-Uralian-(Aldan)-type and alkaline gabbroic complexes, ophiolitic chromitites, and numerous placers from Canada, USA, Russia, and other localities worldwide. Pt–Fe alloy grains in detrital occurrences are notably larger in size, and these are considered to be the result of a special conditions during crystallization such as temperature, pressure, geochemistry or time. In addition, the number of available statistical observations is much greater for the placer occurrences, since they represent the end-product of, in some cases, the weathering of many millions of tonnes of sparsely mineralized bedrock. Typically, platinum-group elements (PGE) present in admixtures (Ir, Rh, and Pd) and minor Cu, Ni are incorporated into a compositional series (Pt, PGE)2–3(Fe, Cu, Ni) in the lode occurrences. Relative Cu enrichment in alloys poor in Pt implies crystallization from relatively fractionated melts at a lower temperature. In contrast to the lode deposits, the distribution of Ir, Rh, and Pd is fairly chaotic in placer Pt–Fe grains. There is no relationship between levels of Ir, Rh, and Pd with the ratio Σ(Pt + PGE):(Fe + Cu + Ni). The compositional series (Pt, PGE)2–3(Fe, Cu, Ni) is not as common in the placer occurrences; nevertheless, minor Cu and Ni show their maximums in members of this series in the placer grains. Global-scale datasets yield a bimodal pattern of distribution in the Pt–Fe diagram, which is likely a reflection of the miscibility gap between the ordered Pt3Fe structure (isoferroplatinum) and the disordered structure of native or ferroan platinum. In the plot Pt versus Fe, there is a linear boundary due to ideal Pt ↔ Fe substitution. Two solid solution series are based on the Ir-for-Pt and Pd-for-Pt substitutions. The incorporation of Ir is not restricted to Pt3Fe–Ir3Fe substitution (isoferroplatinum and chengdeite, plus their disordered modifications). Besides, Ir0 appears to replace Pt0 in the disordered variants of (Pt–Ir)–Fe alloys. There is a good potential for the discovery of a new species with a Pd-dominant composition, (Pd, Pt)3Fe, most likely in association with the alkaline mafic-ultramafic or gabbroic complexes, or the mafic units of layered intrusions. The “field of complicated substitutions” is recognized as a likely reflection of the crystallochemical differences of Pd and Ir, extending along the Ir-Pd axis of the Ir–Pd–Rh diagram. The inferred solid solution extends approximately along the line Ir–(Pd:Rh = 2:3). Minor Pd presumably enters the solid solution via a coupled substitution in combination with the Rh. An Ir-enrichment trend in Pt–Fe alloys typically occurs in the Alaskan-type complexes. The large size of the Pt–Fe nuggets associated with some of these complexes is considered to be related to an ultramafic-mafic pegmatite facies, whereas significant Pd-enrichment is characteristic of gabbroic source-rocks (e.g., Coldwell Complex), resulting in a markedly different trend for the Pt versus Fe (wt.%). However, based on our examination of a large dataset of Pt–Fe alloys from numerous origins, we conclude that they exhibit compositional overlaps that are too large to be useful as reliable index-minerals.

We report results of multiple electron-microprobe analyses of nine grains of alloy minerals, 2–5 mm in size, rich in the platinum-group elements (PGE), from a unique, very old collection (~1890s) of placer material from Trinity Co., California. Osmium, iridium, ruthenium, and rutheniridosmine are the principal alloy species poor in Fe (typically

We report results of detailed electron-microprobe analyses (EMP) of fourteen grains of Pt–Fe alloy, ca. 0.4 to 1 mm, principally droplet-shaped or roundish, from Florence Creek, Yukon. We also describe new occurrences of Pt–(Pd)–Fe alloy from Arch Creek (up to 11 wt.% Pd) and Canadian Creek, Yukon. An extensive compositional series is observed at Florence, in which values of ∑PGE/(Fe + Cu + Ni) vary from 2.2 to 5.4. Minor Ir and Os display a contrasting behavior in this series. The observed levels of Ir are generally greater than those of Os. The Ir correlates negatively with Pt (the correlation coefficient, R, is −0.81; 140 EMP point-analyses); in contrast, the correlation between Os and Pt is slightly positive (R = 0.64). Probably, at a higher temperature of crystallization, Ir readily replaces Pt in the structure of a Pt–Fe alloy. As a result, Ir did not attain its maximum, and the observed inclusions of exsolution-induced Ir-dominant alloy, hosted by the Pt–Fe alloy, are moderately enriched in Ir (52–54 at.%). An inclusion of erlichmanite (4.2 wt.% Rh) and a partial rim of Au–Ag alloy (Au 0.80 Ag 0.18 ) were observed. Droplet-like inclusions of highly aluminous silicate minerals, hosted by grains of Pt–Fe alloy, are rich in Na, K and in Cl (up to 2 wt.%). Veinlets and micrograins of an Os-rich alloy (86–92 wt.% Os) are intimately associated with micrograins of nearly pure albite, Ab 97.8 An 1.7 Or 0.5 , and with an intermediate member of the chamosite–clinochlore series. The observed association chamosite + albite + native osmium, infilling a cavity in a host grain of Pt–Fe alloy, was likely deposited from a late Na–H 2 O–(Cl)-bearing fluid phase at a postmagmatic–hydrothermal stage, at a temperature less than 700°C. The Os and Na were possibly mobilized and transported as Na–(Os)-rich complexes related to the sodium hydroxy- or oxo-osmates. The precipitation of the metallic Os phase could be related to a change in physicochemical conditions, e.g., in fluid pressure or redox potential, leading to instability of these Na–(Os)-rich hydroxy- or oxo-osmate complexes. We suggest that a mineralized zone rich in chromite–magnesiochromite and hosted by an Alaskan–Uralian-type complex is the likely provenance for grains of Pt–Fe alloy recovered in Florence Creek.

An extensive, nearly continuous and hitherto unreported solid-solution series is observed in Sr-Na-REE titanates in a fenitized megaxenolith, Khibina alkaline complex, Kola Peninsula, Russia. These titanate minerals, related to crichtonite, landauite and davidite-(Ce,La), may represent potentially new members of the crichtonite group. They display compositional zoning, and are associated with diverse oxide minerals, albite and alkali feldspar. Our compositions (EMP) suggest that the “large cations” (Sr, Na, K, and the rare-earth elements, REE), along with minor Ca, occupy fully the A ( M 0 ) site in their structure; in contrast, Ca enters dominantly the B ( M 1 ) site, probably via a coupled substitution of the type [(Ca 2+ +Ti 4+ ) = (Zr 4+ +Fe 2+ )]. The extensive Na + -for-Sr 2+ substitution observed at the A site is coupled with a Ti 4+ -for-Fe 2+ substitution at the C ( M 3 - M 4 - M 5 ) site. The tetrahedral T ( M 2 ) site is dominated by Fe. Among the REE, only the light REE are present in substantial amounts (up to 7.37 wt.% REE 2 O 3 ); they are positively intercorrelated, indicating an ordered distribution at the A site. The incorporation of the REE 3+ , which probably replace Sr 2+ and K + , is controlled by a corresponding decrease in Zr 4+ (and by relative increase in divalent Mn) at the B site in order to maintain charge balance. The observed presence of up to 1.87 wt.% Cr 2 O 3 in the Sr-Na-REE titanate minerals at Khibina indicates that rocks of mafic affinity were the protolith for the mineralized megaxenolith. The high Na contents of these minerals are clearly related to the geochemical environment ( i.e. , Na-metasomatism). The contrasting association of Cr and Nb (up to 1.06 wt.% Nb 2 O 5 ) in these minerals undoubtedly involves derivation from two different sources. We suggest that the Ti-(Fe)-Nb-REE oxide mineralization formed in the megaxenolith as a result of interaction of a pre-existing mafic rock(s), probably Proterozoic rocks of the Imandra-Varzuga Supergroup, with metasomatizing oxidizing fluids of alkaline affinity.

A shell-like polycrystalline grain (ca. 1 mm) of W-(Mo)-bearing Os-Ir alloy (11.4–18.6 wt% W; up to 1.5% Mo) is present in a very old collection (probably the 1890s) of tiny nuggets from Trinity Co., California. An extensive compositional series [(Os0.43–0.80Ir0.28–0.05) W0.12–0.18], and inverse Ir-Os correlation, are observed; the mean composition [Os0.676W0.153Ir0.124Fe0.021Mo0.015Ru0.011; Σatoms = 1], based on results of 50 electron-microprobe analyses, displays a ratio (Os + Ir):W of 5:1. The observed variations and element correlations suggest that (W + Mo) contents are controlled by Ir, and incorporated via the following substitution scheme: [(W + Mo) + Ir] ↔ Os. The X-ray diffraction data indicate that the W-rich alloy has a hexagonal close-packed structure, related to that of osmium and allargentum, with a = 2.7297(4) A, c = 4.3377(6) A, and V = 27.99(1) A3 ; the c:a ratio is 1.59. The probable space-group is P63/mmc, and Z = 2; the calculated density is 21.86(1) g/cm 3 . The W-rich alloy is associated with an Os-Ru-Ir alloy rich in Fe (7.0–9.7 wt%), which exhibits atomic Fe ↔ [Os + Ru] and Ir ↔ [Os + Ru] mechanisms of substitution. We suggest that these W-(Mo)- and Fe-rich alloys formed by metasomatic alteration of a primary Os-Ir-Ru alloy, associated with mineralized ultramafi c-mafi c rocks of ophiolite affi nity. A fl uid phase may well have remobilized and transported W, Mo, and Fe. The W-rich alloy likely crystallized from a reducing fl uid under conditions of low fugacities of O2 and S2, thus promoting the observed siderophile behavior of W and Mo. These unusual W-(Mo)- and Fe-rich alloy grains were likely derived, as a placer material, from the Trinity ophiolite complex of northern California.

Various platinum-group minerals (PGM), phases rich in the platinum-group elements (PGE), and unusual species occur in the Kirakkajuppura area, Penikat layered complex, Finland. The PGM are intimately associated with actinolite and clinochlore. The base-metal sulfides [chalcopyrite, millerite, bornite, chalcocite, ferroan chalcocite(?), digenite or roxbyite: Cu9S5] are in minor or trace amounts. The observed PGM and rare species are: vysotskite–braggite series [PdS–(Pt,Pd)S], zvyagintsevite [Pd3Pb], a zvyagintsevite-like phase [(Pd,Pt)3(Pb,Cu)], unnamed Pd–Pb oxide [Pd7PbO8 or Pd3.5Pb0.5O4], various Cu–Fe–PGE thiospinels (large grains and unusual micro-aggregates), laflammeite [Pd3Pb2S2], laurite–erlichmanite series [(Ru,Os,Ir)(S,As)2 –(Os,Ru,Ir)(S,As)2], irarsite–hollingworthite series [(Ir,Rh,Ru)As1− x S1+ x – (Rh,Ir,Ru)As1− x S1+ x ; x ≤ 0.2], konderite-like Pb–(Pd)-rich sulfides and a Fe-dominant analogue of konderite [(Cu,Ni,Fe)3+ x (Fe,Pb)(Rh,Ir,Pd)8− x S16; x < 0.5], unnamed Rh1− x (Ni,Fe,Cu)2+ x S3 (0 ≤ x ≤ 0.1), a Pd–Pt–Cu alloy [Pt-rich, Cu-rich palladium: Pd89.42–91.22Pt5.94–6.16Cu2.62–4.64], skaergaardite–hongshiite [(Pd0.92 Pt0.10)∑ 1.02Cu0.98], keithconnite [Pd20(Te,Bi)7], plumbian keithconnite [Pd20(Te6Pb)], unnamed Pd5(As,Te,Sn,Pb)2, Pd-rich, Cu-rich gold [Au76.1–81.1Pd13.7–16.0Cu6.1–6.3Ag1.2–3.4], Zn-rich copper (natural?), unnamed Pb4O(VO4)2, and an undefined Pb-rich iron silicate (hydrous?). In addition, unnamed (Th,Ca)(V5+,Si,P)O4 and associated baddeleyite, barite, and a phosphatian huttonite or thorite occur in a pegmatitic gabbro from Kirakkajuppura. The Kirakkajuppura PGE mineralization probably formed by efficient hydrothermal remobilization and transport of PGE from their “primary” zones [Pd–Pt zones associated with the low-sulfide SJ reef and Ru–Os-mineralized chromitite zones], resulting in the local deposition of the extremely S-poor, PGE-rich assemblage, which is intimately associated with hydrous silicates and is located near the northern end of the Penikat complex.

Platinum-group minerals (PGM) from a selected suite of gold- and platinum-group-element (PGE) placer deposits in British Columbia have been analyzed using the electron-microprobe (EMP). The PGM placer grains ( n = 70, 0.1–1.5 mm in size) principally comprise various Pt–Fe–(Cu) alloys: “Pt 3 Fe”-type alloys [Fe-rich platinum (formerly, ferroan platinum: Bayliss et al. 2005) or isoferroplatinum], Fe-rich Pt with an atomic ∑PGE:(Fe + Cu + Ni) ratio of 3.6–5.6, “(Pt,Ir) 2 Fe”-type alloy, members of the tulameenite–tetraferroplatinum solid-solution series extending from Pt 2 Fe(Cu,Ni) toward PGE 1+ x (Fe,Cu,Ni) 1− x , less common Ir-dominant Ir–Os–(Ru–Pt) alloys, subordinate Os-dominant alloys, and minor Ru-rich alloys and rutheniridosmine, the latter with an atomic Ir:Os:Ru proportion close to 1:1:1. Trace amounts of PGE sulfides and sulfarsenides: cooperite PtS, Ni-rich cuproiridsite (Cu,Ni,Fe)(Ir,Rh,Pt) 2 S 4 , unusual sperrylite-type [(Pt,Rh,Fe)(As,S) 2− x ] and platarsite-type [PtAs 1− x S 1+ x , or unnamed Pt(S,As) 2− x ] phases, and unnamed (Ir,Rh,Pt)S (?) crystallized at a late stage in low-S environments. Some PGM grains contain micro-inclusions of diopside, augite, ferro-edenite, a potassian sodic-calcic amphibole (richterite?), talc, clinochlore and euhedral quartz. High values of mg# [100Mg/(Mg + Fe)] of the ferromagnesian minerals in these inclusions suggest highly magnesian source-rocks. Textural and compositional data, in particular the zoned intergrowths of Pt–Fe–(Cu) alloy grains, which broadly resemble the zoned Pt–Pd–Cu stannides from the Noril’sk complex, indicate the following sequence of crystallization: (Pt,Ir,Rh) 3 Fe → (Pt,Ir,Rh) 1+ x (Fe,Cu) 1− x or Pt 2 Fe(Cu,Ni). The zoned Pt–Fe–Cu alloys likely formed by fractional crystallization of primary solid-solutions under closed-system conditions as a result of increase in the activity of Cu in the residual liquid after an early-stage (magmatic) crystallization of the Cu-poor core. The Cu-rich Pt–Fe alloys formed around these core zones and at their peripheries during a significant drop in temperature at a late stage of crystallization of the composite alloy grains. The compositions of micro-inclusions and exsolution lamellae of Os- and Ir-dominant alloys in Pt–Fe alloys imply uniform temperatures of equilibration within the range 750–800°C. The compositions of Cu-rich Pt–Fe alloys, PGE sulfides and sulfarsenides, and exsolution lamellae of Os- and Ir-dominant alloys, observed in intimate association with Pt–Fe alloys, are likely related to the crystallization of the coexisting Pt–Fe alloys. Narrow zones of Pt–Fe alloys richer in Pt and poor in Fe, observed at the boundary of placer Pt–Fe alloy grains, provide evidence for a removal of Fe and corresponding addition of Pt as a result of interaction with a low-temperature fluid. The terrane affinities, compositions and associations of the placer PGM examined appear consistent with two types of potential source-rocks, associated with Alaskan-type intrusions and the Atlin ophiolite complex. The preservation of faceted morphologies on many of the placer PGM grains implies a relatively short distance of transport from their source.

L'oulankaite, stannosulfotellurure complexe de metaux de base et de metaux precieux provenant du gisement de Nadezhda, complexe stratiforme de Lukkulaisvaara, dans le nord de la Karelie, secteur nord-ouest de laRussie, fait preuve d'une variation importante en composition. A la localite type, cette espece unique parmi les mineraux du groupe du platine (MGP) est associee a plusieurs sulfures de metaux de base et de MGP dans des lentilles de gabbronorite a grains grossiers, voire pegmatitiques, montrant les effets d'une alteration hydrothermale, le tout a l'interieur d'un filon-couche de microgabbronorite. Nos documentons des covariations en teneurs de (Pd + Pt) et de (Cu + Fe + Ag) dans l'oulankaite a faible teneur en Ag (

Nous avons decouvert une association inhabituelle de mineraux du groupe du platine (MGP) dans un niveau de chromitite du gisement du Mont Bol'shaya Varaka, complexe stratiforme d'Imandra, peninsule de Kola, en Russie. Les MGP se presentent generalement en micro-aggregats ou en chaines, et en grains isoles de taille infime au contact avec la chromite le long des grains. Les MGP sont inclus dans la magnesiohornblende, l'edenite, le talc ou la phlogopite, et peuvent meme recouper les silicates hydrates qui les renferment. Parmi les MGP se trouvent sperrylite, laurite-erlichmanite, Cu 2 (Ni,Co)Pt 3 S 8 sans nom, hollingworthite, pyrite riche en elements du groupe du platine (Ru 10.96, Os 0.98, et Ir 0.54%, poids), platarsite nickelifere (?), (Pt 0 . 7 1 Ni 0 . 2 6 Co 0 . 0 5 ) Σ 1 . 0 2 As 1 . 1 0 S 0 . 8 8 . daomanite, et cooperite. La concentration de Rh et S dans la sperrylite varie de 1.0 et 0.8 a 6.6 et 4.9% (poids), respectivement, et la composition la plus enrichie en Rh et S est (Pt 0 . 7 8 Rh 0 . 2 0 Ir 0 . 0 3 ) Σ 1 . 0 1 (As 1 . 5 3 S 0 . 4 7 ) Σ 2 . 0 0 . Les correlations Pt-Rh (coefficient de correlation R = -0.99), Pt-As (R = 0.98), Pt-S (R = -0.99), Rh-As (R = -0.97), Rh-S (R = 0.97), et As-S (R = -1.00) sont importantes et semblent indiquer l'existence d'une solution solide entre PtAs 2 et Rh 1 - x S 2 ("Rh 2 S 5 ") structuralement affiliee a la pyrite. La plupart des MGP se sont formes au cours d'une alteration deuterique a un stade postmagmatique hydrothermal de la cristallisation de la chromitite. La majorite des grains de laurite-erlichmanite demontrent un lien textural etroit avec les silicates hydrates et font partie de l'evenement d'alteration hydrothermale a Imandra.

Laflammeite, Pd 3 Pb 2 S 2 , is a new parkerite-type sulfide discovered in the Penikat layered complex, Finland. It occurs in altered pyroxenite in the Kirakkajuppura deposit in association with actinolite and clinochlore, accessory chromite, various platinum-group minerals [vysotskite, zvyagintsevite, cuprorhodsite – (ferrorhodsite) – malanite, laurite – erlichmanite, irarsite, keithconnite, unusual Pb–(Pd)-rich thiospinels of Cu, Fe, Rh and Ir, unnamed Pd 9 PbO 10 and Rh(Ni,Fe,Cu) 2 S 3 ], Pd-rich gold, and minor base-metal sulfides (chalcopyrite, bornite and millerite). Laflammeite occurs as individual subhedral to euhedral crystals up to 0.3 mm in size, and in intergrowths with Pt–Ni-poor vysotskite. Laflammeite is opaque and cream-colored with a brownish tint in reflected light in air. The anisotropy is weak, from brownish gray to grayish brown. The bireflectance is weak; pleochroism was not observed. Reflectance percentages in air (and in oil) are, for R 1 and R 2 , 45.3, 46.2 (31.55, 32.45) at 470 nm, 46.5, 47.55 (32.6, 33.75) at 546 nm, 47.7, 48.8 (33.9, 35.05) at 589 nm, and 49.6, 50.0 (36.0, 36.3) at 650 nm. Fine twins are present. Microhardness values VHN 50 are 156 and 185; the average is 171 kg/mm 2 . Cleavage is {010}, perfect. The average results of 26 wavelength-dispersion electron-microprobe analyses are Pd 39.16, Ir 1.08, Pb 52.01, S 7.90, total 100.15 wt.%, corresponding to (Pd 2.96 Ir 0.05 ) ∑3.01 Pb 2.02 S 1.98 (basis: 7 atoms per formula unit). The powder pattern was indexed on a monoclinic cell with a 11.521(11), b 8.294(10), c 8.321(6) A, β 134.38(5)°, V 568.3(6) A 3 . The space group is probably C 2/ m , with Z = 4. D calc is 9.41 g/cm 3 . The strongest lines in the pattern [ d in A(I)( hkl )] are: 5.953(6)(001), 4.144(10)(020), 2.917(9)(220), 2.413(8)(022), 2.365(7)(422) and 2.082(5)(040). Laflammeite likely crystallized from a hydrothermal fluid or a late-stage liquid in an environment poor in overall sulfur and rich in the PGE , Pb and volatiles.

Menshikovite, ideally Pd3Ni2As3, is a new mineral species found in two localities in Russia. It occurs in a pod of coarsegrained, entirely altered gabbronorite rich in sulfides (up to 30 vol.%), hosted by a microgabbronorite, in the Vostok deposit, Lukkulaisvaara intrusion, in Karelia. There, menshikovite (up to 0.2 mm) is associated with chalcopyrite, pentlandite, calcic amphibole (mostly actinolite), clinochlore, merenskyite, kotulskite, sobolevskite, michenerite, hollingworthite, hessite, and a Re-rich sulfide. Menshikovite (up to 0.1 mm) also occurs in mineralized quartz–feldspar sandstones, which are metasomatically altered and recrystallized. They are located at the lower (exo)-contact of the Chiney intrusion in Siberia, and contain amphibo le(s), mica(s), chlorite, disseminated or massive sulfides (mostly chalcopyrite), Pd-rich maucherite, nickeline, sperrylite, mertieite -II or stibiopalladinite (or both), isomertieite, majakite, and michenerite. We also report a third occurrence of menshikovite from th e Oktyabr’ deposit, Noril’sk complex, in Siberia. In reflected light, menshikovite is pink and opaque. A cleavage is not observed. There is no evidence of bireflectance. The anisotropy is weak, from light gray to brownish gray. Reflectance percentages in air (and in oil) are, for R 1 and R2, at 470 nm 48.4, 50.2 (38.45, 39.3), at 546 nm 51.2, 53.2 (41.0, 41.8), at 589 nm 53.2, 55.3 (42.3, 43.3), and at 650 nm 56.6, 58.7 (46.6, 47.8). Fine twins are present. The average value of microhardness VHN 40, 50, 65 is 517.1 kg/ mm 2 ; it has Mohs hardness of ~5 and is brittle. The average of two sets of multiple wavelength-dispersion electron-microprobe analyses of menshikovite from Lukkulaisvaara gave Pd 48.18, Pt 0.07, Ni 17.77, Fe 0.07, As 33.91, the total is 100.0 wt.% (not normalized), corresponding to Pd2.99(Ni2.00Fe0.01)2.01As2.99 (basis: atoms = 8). Compositions of menshikovite from Chiney vary from Pd3.00(Ni1.98Co0.01)1.99As2.99 to Pd3.15(Ni1.97Co0.01)1.98As2.86. A solid-solution series probably exists between menshikovite and majakite [i.e., (Pd,Ni)2As of the -Pd2As type]. The powder pattern of menshikovite from Lukkulaisvaara was indexed on a hexagonal cell with a 8.406(4), c 6.740(4) A, and V 412.4(6) A 3 . The strongest eight lines in this pattern [ d in A (I)(hkl)] are 2.626(10)(112), 2.477(10)(202), 2.429(8)(300), 2.283(7)(301), 2.150(6)(103), 1.978(7)(113), 1.818(7)(400) and 1.757(6)(401). Menshikovite formed in volatile-rich environments relatively late in the crystallization history of the layered complexes. The name honors Yurii P. Men’shikov, of the Kola Science Center, Apatity, Russia.

An unusual phase rich in Cl (78.4 wt.% Pb, 19.2% Cl) and close in composition to penfieldite [Pb 2Cl3(OH)] was found as a ~5 m inclusion in chalcopyrite, in a spatial association with platinum-group minerals, in a sulfide-poor ( ≤5 vol.% of base-metal sulfides) enstatite orthocumulate of the Merensky Reef, Bushveld layered complex, South Africa. This seems to be the first reported occurrence of a Pb–Cl–(OH) compound in mafic-ultramafic rocks. The associated platinum-group minerals are members of the braggite series, cooperite (which forms large intergrowths with braggite: up to 0.5 mm in the longest dimension), member s of the rustenburgite–atokite and merenskyite–moncheite series, zoned laurite, and an unknown stannosulfide of Pt, the likely chemical formula of which is PtSnS. The stannosulfide probably formed at a hydrothermal stage from microvolumes of a latestage fluid or liquid. The Cl-rich phase precipitated from a late-stage solution rich in Cl, or formed as a result of replaceme nt of a precursor mineral (probably galena) by an aqueous hydrochloric solution at a very low temperature, at the final stage of hydrothermal alteration.

Rare Pd–Ag tellurides, telargpalite and the phase Pd 6AgTe4 occur in pods

We report on the existence of a newly recognized extensive solid-solution series between taimyrite and tatyanaite, its Pt-dominant analogue. Copper probably occupies a separate site. Substitution involving Pd and Cu also is important, such that taimyrite–tatyanaite forms a solid-solution series with cabriite, which is structurally closely related to taimyrite and tatyanaite. These platinum-group minerals ( PGM ) occur in base-metal sulfide ( BMS ) ores in the Oktyabr’sky deposit, Noril’sk complex, Siberia, Russia. The taimyrite–tatyanaite is present as single grains and aggregates, associated with a heterogeneous Ag–Au alloy, and also as zoned intergrowths of Pt–Pd–Cu stannides. These intergrowths commonly, but not necessarily, occur within chalcopyrite and typically display the following sequence of crystallization, based on textural and compositional data: atokite–rustenburgite → tatyanaite → Pt-rich taimyrite → taimyrite poorer in Pt → late-stage Ag–Au alloys. Subsolidus re-equilibration of the atokite–rustenburgite core with the Cu-rich host is considered unlikely to produce the peripheral zones of the Cu-rich PGM around this core. These zoned PGM probably formed from a trapped liquid rich in noble metals, Cu, and Sn. Decrease in temperature and increase in activity of Cu in the remaining liquid seem to have been the main factors to control the order of crystallization of the PGM in the zoned intergrowths.

Thiospinels of Cu-(Fe) and platinum-group elements (PGE) are relatively abundant in the Kirakkajuppura PGE deposit of the Penikat layered complex, Finland. In actinolite-clinochlore rock that is nearly base-metal sulfide-free and relatively poor in chromite, the thiospinels occur as subhedral or anhedral grains (up to 0.4 mm). They are members of the cuprorhodsite-ferrorhodsite and cuprorhodsite-malanite series, relatively poor in cuproiridsite, and display considerable grain-to-grain variations in Cu, Fe, Pt, and Rh. Strong negative Fe-Cu, Pt(+Ir)-Fe, Rh-Cu, and Rh-Pt and strong positive Pt(+Ir)-Cu and Rh-Fe correlations in these thiospinels are indicative of a coupled substitution: Fe-for-Cu substitution in the tetrahedral (A) sites causes an excess in formal positive charge, which is compensated by Rh-for-(Pt+Ir) substitution in the octahedral (B) sites. Probable valence states in the Fe-free and Fe-rich end-members of the solid-solution series at Penikat are Cu+[Rh3+(Pt,Ir)4+]S2−4 and (Fe3+0.5Cu+0.5)Rh3+2 S2−4, and these suggest the heterovalent substitution scheme AFe3+ + 2 BRh3+→ ACu+ + 2 BPt4+(+2 Ir4+) to incorporate Fe in the ferrorhodsite-rich end member.

The new mineral species edgarite, FeNb3S6, was discovered in a feldspar-rich fenite, in a fenitized xenolith enclosed by nepheline syenite of the Khibina alkaline complex, Kola Peninsula, northwestern Russia. It occurs as platy inclusions (up to 0.15 mm) in Ti-(V)-rich pyrrhotite and ferroan alabandite, and as dark gray aggregates of platy grains located on the surface of the pyrrhotite. The associated minerals include Ti-(V)-rich marcasite, Mn-Fe-rich wurtzite-2H, corundum, nearly end member phlogopite, rutile, monazite-(Ce), and a graphite-like material. Edgarite is soft (VHN5;10= 135–205 kg/mm2), distinctly bireflectant, and has a strong anisotropy. Its reflectance in air (and in oil) (R1 and R2 in percent, respectively) is: 470 nm: 28.1, 40.2 (13.0, 24.2), 546 nm: 27.4, 39.3 (12.3, 22.7), 589 nm: 27.0, 38.5 (12.2, 21.7), and 650 nm: 27.0, 36.9 (12.4, 20.3). The composition is Nb 52.87, Fe 10.12, V 0.36, Mn 0.10, Ti 0.04, S 35.86, sum 99.35 wt%, which corresponds to (Fe0.96V0.04Mn0.01)Σ1.01Nb3.03S5.95 (basis: Σ atoms=10). By analogy with synthetic FeNb3S6, the X-ray powder pattern of edgarite was indexed on a hexagonal cell, a=5.771(1), c=12.190(6) A, and V=351.6(3) A3, Dcalc is 4.99 g/cm3. The space group is most probably P6322, with Z=2. The strongest lines of the pattern [d in A (I, hkl)] are: 6.11 (8, 002), 3.04 (6, 004), 2.88 (5, 110), 2.606 (8, 112), 2.096 (10, 114), 1.665 (8, 300), 1.524 (6, 008), 1.126 (7, 322), and 1.027 (6, 414). Edgarite appears to have formed at a very late or final stage of metasomatism, after the main event of fenitization, from a highly reduced, subalkaline S-C-H-rich fluid, which may have remobilized Nb as a result of destabilization of oxide minerals. These reducing conditions promoted the chalcophile behavior of lithophile elements (Nb, Ti, V and Mn) on a local scale in the fenite.

Sorosite, ideally Cu(Sn,Sb), is a new mineral species from the Baimka gold-platinumgroup mineral placer deposit, Chukotka, Russian Far East. It occurs as large subhedral to euhedral crystals (0.1‐0.4 mm in length), hexagonal in cross section, minute crystals (# 15 mm, also hexagonal), and anhedral grains. Sorosite forms inclusions in Sb-bearing native tin, is often intergrown with stistaite (Sn 1.12-1.13Sb0.87-0.88) and occurs with herzenbergite (SnS), native lead, and trace cassiterite. Sorosite is brittle with a microhardness VHN 40;50 5 443.7 kg/mm 2 (n 5 3). No cleavage is observed. In reflected light, the large crystals are nearly white with a pinkish tint, whereas the microcrystals show a pronounced pinkish tint. Bireflectance is variable. The average of nine electron microprobe analyses gave Cu 35.33, Fe 1.18, Sn 58.18, and Sb 4.77, sum 99.46 wt%, corresponding to (Cu1.00Fe0.04)S1.04 (Sn0.89Sb0.07)S0.96. The powder pattern is close to those of natural Cu(Sn,Sb) and synthetic h-Cu6Sn5; it was indexed for a hexagonal cell, with a 5 4.217(4) A ˚, c 5 5.120(6) A ˚, and V 5 78.85 A ˚ 3