Vasilinovskoe platinum-palladium occurrence – a new type of mineralization in the ophiolites of the Polar Urals. Report 1. Geological position and mineralogy

A detailed description of the new noble metal (Pt-Au-Pd) Vasilinovskoe occurrence discovered near the Kharp town of the Yamalo–Nenets Autonomous Okrug is given. It is associated with amphibolized gabbroids and clinopyroxenites. Mineralization zones with an apparent thickness from 0.5 to 50 m (sulfides 1–3 vol.%, occasionally more) are developed in these rocks. In areas with scattered or finely nested sulfide inclusions, feldspar-quartz and epidote veinlets are often present. The first expedition to study the platinum-bearing area of the Rai-Iz mountains was organized by Professor A.N. Zavaritsky 100 years ago, in 1925 (A.G. Betekhtin was the head of the рrospecting party), but the expected placer platinum deposits were not found. Communication 1 includes general geological and detailed mineralogical characteristics of the ore occurrence and brief information on the bulk geochemistry of rocks and ores of the object. The mineralized gabbro-amphibolite ore macrocomponents, which are often found in bulk samples, can be noted (wt.%) V up to 0.2, Co up to 0.06 and Ni up to 0.02. According to assay data, in bulk 0.5–1 kg samples with sulfide inclusions, the Pd content reaches 1.4 g/t, Au – 0.8 g/t, and Pt – 0.2 g/t. The PGE minerals are represented by abundant impregnation of micron–sized palladium minerals: tellurides (merenskiite, temagamite, kotulskite, sopcheite), antimonides (stibiopalladinite, sadberite), arsenoantimonides (arsenic stibiopalladinite, isomertiite), as well as other noble metal compounds – moncheite, native osmium and others. In addition, the magnetite–chalcopyrite–pyrite assemblage contains microinclusions of native silver, bismuth and tin. In the later polysulfide–feldspar–carbonate–quartz assemblage, Au and Ag tellurides, native gold (including Hg-bearing), Se-containing argentite, and greenockite are found. In the zones of sulfide impregnation of the Podgornensky site (1.5 km to the south), occurring in the diorites of the Sob’ complex and closely associated with quartz veins, the amount of sulfides is higher, the copper profile is enhanced, and concentrations of Co, Ni, and especially Ti, V, Pd and Pt are falling. According to the LA-ICP-MS analyses of pyrite, chalcopyrite, pyrrhotite of the Vasilinovskoe occurrence, the profiling trace element for them is cobalt – up to 1.2 wt.% Co in pyrite of the early assemblage. The Ni impurity is also high (400-800 ppm, up to 0.2 wt.%) in the early pyrite and decreases to 16–90 ppm in the late pyrite. The impurity of Se, on the contrary, increases in pyrite of the late assemblage (up to 207 ppm). Chalcopyrite commonly contains As and Se (~100–300 ppm). In contrast to the Vasilinovskoe occurrence, at the Podgornensky site, an admixture of Mo (up to microinclusions of molybdenum), Te (up to 35 ppm), noticeable impurities Tl (up to 25 ppm) and Re (0.3 ppm) are present in pyrite. Impurities are often found in chalcopyrite: Ag up to 65 ppm, Sn up to 65 ppm, Cd up to 35 ppm and Bi up to 11 ppm. Significant impurities of Co and Ni (up to 0.n wt%) are typical here only for minor pyrrhotite. According to the mineral composition and geochemical spectrum of Pt-Au-Pd-Co ±Ni-Cu-V-Ti, the low-sulfide platinoid mineralization of the Vasilinovskoe occurrence contrasts quite strongly with the zones of low-sulfide mineralization (+chalcedony quartz) with the specialization Fe-Cu-Au-Ag (±W, Bi, Sn, Mo, Re) of the Podgornensky site, which probably belong to the skarn-porphyry gold-bearing system. The conclusion is made about the prospects of expanding the contours of Pd mineralization to the west and east, where the halos of Cu, Co and Ni, as well as magnetic anomalies, occur in the rocks of the basite-ultrabasite association.