E. M. Spiridonov

Ferroskutterudite (Fe, Co) As3: A new mineral species from the dolomite-calcite veins of the Noril’sk ore field

Chalcogenides-sulfides, sulfoarsenides, arsenides, sulfoantimonides, and other compounds of Fe, Co, and Ni are characterized by a wide range of isomorphic substitution in the Fe‐Co‐Ni series. In some cases, these are continuous series of solid solutions: disulfides (pyrite‐vaesite‐cattierite), diarsenides (safflorite CoAs 3 ‐rammelsbergite NiAs 2 ‐lollingite FeAs 2 , and others [1‐3, 6, 8, 12, 13]), and others. With the discovery of a new mineral, ferroskutterudite, this series was supplemented by triarsenides: skutteruditeCoAs 3 ‐nickelskutterudite NiAs 3 ‐ferroskutterudite (Fe, Co)As 3 . Previously, only the skutterudite‐nickelskutterudite series was known [1‐3, 8, 10, 12‐15]. The arsenide mineralization in the Noril’sk ore field was previously assigned to hydrothermal rocks—derivatives of the ~250-Ma-old (Middle Permian‐Lower Triassic) trap complex, with Cu‐Ni sulfide mineralization [4, 5, 9]. It was established that the antimonide‐ arsenide mineralization of the Noril’sk ore field is developed among the magmatic Ni‐Cu ores and host

Metamorphic-Hydrothermal Parkerite and Associated Minerals in the Noril'sk Ore Field

In the Noril’sk ore field, parkerite is a characteristic mineral of sulfide ore that metamorphosed under conditions of zeolite and prehnite-pumpellyite facies and of arsenide-calcite veins. The mineral occurs in ores containing bornite, anhydrite, magnetite, mackinawite (3–5 wt % Ni), valleriite, calcite, ankerite, native silver, native bismuth, violarite, Te-rich bismutohauchecornite, cupropentlandite enriched in Fe, Pd-rich breithauptite (1.5–2.5 wt % Pd), galena enriched in Cu (3.8 wt % Cu), and Ni arsenides and antimonides. Parkerite occurs in those place, where the primary ores have contained pockets and veins of graphic galena and chalcopyrite aggregates with associated Pt-Pd-Au-Ag minerals. Parkerite metacrysts in galena and Fe-Cu-Ni sulfides contain 6–16 and up to 5 wt % Pb, respectively. Parkerite rims replacing PGM aggregates and galena contain 1–3 wt % Pb. In calcite veins hosted in metamorphosed sulfide ores, parkerite is associated with native silver and bismuth, maucherite, cobaltite, chalcocite, and uraninite. Parkerite from these veins contains up to 0.5 wt % Pb. Thus, the Pb and Bi contents in parkerite basically depend on those of replaced minerals. Rare bismutohauchecornite is associated with parkerite.

Solid solution fisnhesserite-naumannite (Ag,Au)2Se in ores of the volcanogenic gold deposit Ozernovskoye, Kamchatka

An abundance of tellurium and selenium in the ores of the many volcanogenic hydrothermal gold and gold‐ silver deposits (epithermal) is their peculiar feature. Among such deposits is the Ozernovskoye deposit located in the north of the Kamchatka Peninsula. Gold-bearing poor sulfide quartz, dickite‐quartz, and hydromica‐quartz veins and stockworks of the Ozernovskoye deposit occur among the secondary quartzites and argillisites and are connected with basalt‐andesite‐dacite volcanogenic bodies of Neogenic age [2]. Chalcedony-like quartz and textures of manifold brecciation are characteristic of the ores. Significant amounts of pyrite and zinc‐tennantite, copper‐ zinc tennantite‐tetrahedrite selenium-containing and poor in Te and Bi, occur in the early mineral associations (nomenclature of fahlores is given after [4]). Complex zoned zinc‐copper selenium-containing Tetetrahedrite and goldfieldite and copper and seleniumcontaining Te-tennantite, Te-tetrahedrite, and goldfieldite often enriched in Bi [7, 8] occur among the later mineral associations. Later associations contain segregations of goldfieldite, that are homogenous in composition or spotted and often arsenic-containing. The paragenesis of sylvanite AuAgTe 4 , native Te, and skippenite Bi 2 TeSe 2 is characteristic of the Ozernovskoye deposit column of ore [9]. In the parts of the deposit with the presence of abundant native tellurium, products of tellurium replacement of fahlores (arsenicum tellurantimony (Sb,As) 2 Te 3 and tellurides of copper: vulcanite and rickardite) occur [5]. The youngest and low-temperature mineralization represented by realgar and native arsenic occurs at the flanks of the Ozernovskoye orebodies.

Maucherite from metamorphic-hydrothermal assemblages of the Noril’sk ore field

In the Noril’sk ore field, maucherite, Ni11As8, occurs in magmatic pentlandite-pyrrhotite-chalcopyrite ores transformed into pyrite-millerite-chalcopyrite and millerite-bornite ores under conditions of prehnite-pumplellyite and zeolite facies of metamorphism. Maucherite spatially associated with aggregates of Pd and Pt minerals, probably, as a pseudomorph after mayakite, PdNiAs, contains up to 1.5 wt % Pd. Maucherite is relatively abundant in metamorphic-hydrothermal apophyllite-anhydrite-calcite veins hosted in metaore. In these veins, maucherite occurs as finely split and long-prismatic crystals, their intergrowths, and as a constituent of complexly zoned antimonide-sulfoarsenide-arsenide nodules. Maucherite from veins contains up to 0.6 wt % S and Sb, whereas Pd, Pt, and Au are below the detection limit of an electron microprobe.

Laurite and Ir-Osmium from Plagioclase Lherzolite of the Yoko–Dovyren Mafic–Ultramafic Pluton, Northern Baikal Region

The near-bottom part of the Yoko-Dovyren layered ultramafic-mafic intrusion host the Baikal deposit of Cu–Ni sulfide ores with Pt–Pd mineralization, whereas horizons and pockets of low sulfide ores with Pt–Pd mineralization occur at higher stratigraphic levels, including the boundary between strata of troctolite and gabbronorite, within these rocks, as well as in strata of peridotite at the lower part of the intrusion. This paper represents a new (for the Yoko-Dovyren intrusion) type of “refractory IPGE-mineralization” discovered in the lower peridotite ranging from two-pyroxene-plagioclase-bearing lherzolite. This mineralization occurs in thin intercalations of plagioclase lherzolite containing as much as 7% of alumochromite, up to 50 ppb Ru, 15 ppb Ir, and 60 ppb Pt. Crystals of cumulate alumochromite with 0.2–0.8 wt % TiO2 contain hexagonal plates of Ir-osmium up to 5 m in size. Crystals of cumulate alumochromite with 1.2–2.8 wt % TiO2 host pentagonal dodecahedrons of laurite up to 4 m in size. One of the alumochromite crystals with an inclusion of Os-poor laurite was found inside a crystal of cumulate olivine Fo86. Intergrowth of laurite and Ir-osmium enclosed in alumochromite with 1.1% TiO2 was observed in one case. Laurite from Yoko-Dovyren contains 93–66%, predominantly 92–82%, RuS2 endmember (n = 10); 3–20, predominantly 5–12%, OsS2 endmember; 4–5% IrS2 endmember; and up to 0.7% Pd and 0.5% Au. Ir-osmium is divided into two groups by composition. The first group is enriched in Os (58–73 wt %, on average 64 wt %) and Ru (3–8 wt %, on average 5 wt %), contains 24–34 wt % Ir (n = 4), up to 1.4 wt % Au, and no Pt. Compositions of the second group have 57–58 wt % Os, 27–30 wt % Ir, 1.5–5.5 wt % Ru, approximately 10 wt % Pt (n = 3), and up to 0.2 wt % Pd. The Cr# and Fe2+/(Fe2+ + Mg) values, which range within 58–69 and 61–72, respectively, are identical in alumochromite with both enclosed laurite and Ir-osmium. Alumochromite, relatively enriched in Ti, crystallized slightly later, suggesting later crystallization for hosted laurite. Occurrence of Ir-osmium seems to indicate a picritic magma undersaturated with sulfide sulfur during bulk crystallization of alumochromite Judging from the diagram from (Brennan and Andrews, 2001), intergrowths of laurite and Ir-osmium, evidence that their probable crystallization temperature did not exceed 1250°C. The presence of own minerals of Ru, Os, Ir in the rocks, containing the first ppb of these PGE shows startling degree of magmatic differentiation. In the matrix of plagioclase lherzolites, containing laurite and Ir-osmium, in association with phlogopite, pargasite, pentlandite, troilite and chalcopyrite there were found the smallest crystals of geversite, sperrilite, insizwaite, niggliite, naldrettite, zvyagintsevite, in association with serpentine and chlorite–native platinum, Pd-platinum, osarsite, irarsite, platarsite.