Vasilinovskoe Platinum‒Palladium Occurrence As a New Type of Ophiolite Mineralization in the Polar Urals. Report 1. Geological Position and Mineralogy

The new noble metal (Pt‒Au‒Pd) Vasilinovskoe occurrence discovered near the Kharp town, Yamalo-Nenets autonomous okrug is described in detail. It is associated with amphibolized gabbroids and clinopyroxenites. Mineralization zones with an apparent thickness of 0.5‒50 m (1‒3 vol %, sometimes more, of sulfides) are developed in these rocks. The areas with scattered or finely nested sulfide inclusions often contain feldspar–quartz and epidote veinlets. Report 1 includes the general geological and detailed mineralogical characteristics of the ore occurrence and brief information on the bulk geochemistry of the rocks and ores of the object. The ore macrocomponents often found in bulk samples of mineralized gabbro-amphibolites, along with Cu (up to 0.06 wt %), are V (up to 0.2 wt %), Co, and Ni (up to 0.02 wt %). According to the assay data, in bulk (0.5‒1 kg) samples with sulfide inclusions, the Pd content attains 1.4 g/t; the Au content, 0.8 g/t; and the Pt content, 0.2 g/t. The platinum group elements are represented in them by abundant impregnation of micron-sized palladium minerals: tellurides (merenskiite, temagamite, kotulskite, and sopcheite), antimonides (stibiopalladinite and sadberite), and arsenoantimonides (arsenic stibiopalladinite and isomertiite), as well as other noble-metal compounds: moncheite, native osmium, and some others. In addition, the magnetite–chalcopyrite–pyrite assemblage contains native silver, bismuth, and tin microinclusions. In the later polysulfide–feldspar–carbonate–quartz assemblage, Au and Ag tellurides, native gold (including Hg-bearing), Se-containing argentite, and greenockite are encountered. In the sulfide impregnation zones of the Podgornensky site (1.5 km to the south) occurring in the Sob' complex diorites and closely associated with quartz veins, the amount of sulfides is higher, the copper mineralization profile is enhanced, and the concentrations of Co, Ni, and, especially, Ti, V, Pd, and Pt decrease. According to the LA-ICP-MS analyses of pyrite, chalcopyrite, and pyrrhotite of the Vasilinovskoe occurrence, the profiling trace element for them is cobalt (up to 1.2 wt % 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 Se impurity, on the contrary, increases up to 207 ppm in pyrite of the late assemblage. Chalcopyrite commonly contains As and Se (100–300 ppm). In contrast to the Vasilinovskoe occurrence, at the Podgornensky site, admixtures of Mo (up to microinclusions) and Te (up to 35 ppm) and noticeable impurities of Tl (up to 25 ppm) and Re (0.3 ppm) are contained in pyrite. The impurities are often found in chalcopyrite: up to 65 ppm of Ag, 65 ppm of Sn, 35 ppm of Cd, and 11 ppm of Bi. Significant Co and Ni impurities (up to 0.n wt %) are typical here only of minor pyrrhotite. According to the mineral composition and geochemical spectrum Pt‒Au‒Pd‒Co ± Ni‒Cu‒V‒Ti, the low-sulfide platinoid mineralization of the Vasilinovskoe occurrence contrasts quite strongly with the low-sulfide mineralization zones (+chalcedony quartz) with the Fe‒Cu‒Au‒Ag (±W, Bi, Sn, Mo, Re) specialization of the Podgornensky site, which probably belong to the skarn-porphyry gold-bearing system. The conclusion is made about the prospects of expanding the Pd mineralization contours to the west and east, where the Cu, Co, and Ni halos, as well as magnetic anomalies, occur in the rocks of the basite‒ultrabasite assemblage.