Mineralogical and geochemical features of pyrite nodules of sulfide turbidites from the Talgan Cu–Zn massive sulfide deposit (South Urals)

Abstract

Pyrite nodules were found in thin-layered sulfide ores localized at the flanks of the Talgan Cu‒Zn massive sulfide deposit (South Urals). The nodules consist of (1) an inner core of microgranular pyrite with inclusions of authigenic sulfides and host rock minerals, (2) an intermediate zone of anhedral and subhedral pyrite metacrystals, (3) an outer zone formed by parallel subhedral pyrite crystals and (4) dioctahedral chlorite rimming the pyrite crystals of zone 3. Each zone exhibits specific trace element association, which is identified using LA ICP-MS micromapping. The trace element content of pyrite significantly (by 13 orders of magnitude) decreases in a range of microgranular pyrite of the core an- and subhedral pyrite crystals of the intermediate zone subhedral pyrite crystals of the outer zone (average values, ppm): 131069 Zn, 241001783 Pb, 1323134 As, 10271.81 Co, 4564 Ni, 39038 Ag, 0.10.01 Au, 550.6 Te, 9.80.6 Bi. The subhedral pyrite crystals of the outer zone are enriched (ppm, up to) in Cu (8367), Sb (1627) and Mn (734) relative to microgranular pyrite of the core. The extremely high trace element contents are related to the inclusions of authigenic chalcopyrite, sphalerite, fahlore, gold and silver minerals. The host rock components of the nodules include quartz, calcite, chlorite, illite and REE minerals. The ore clasts of distal sulfide turbidites mixed with hyaloclastites, which were altered during dia- and anadiagenesis, were the source of ore material for the nodules.