Mineralogical and Geochemical Features of Pyrite Nodules from Sulfide Turbidites in the Talgan Cu-Zn Massive Sulfide Deposit (Southern 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) which consists of (1) an inner core (microgranular pyrite with inclusions of gangue minerals and authigenic sulfides), (2) an intermediate zone (anhedral and subhedral pyrite metacrystals), (3) an outer zone (parallel-columnar subhedral pyrite crystals), and (4) the dioctahedral chlorite rim overgrowing on pyrite crystalls of the outer zone. Each zone is characterized by a specific assemblage of trace elements revealed by the LA-ICP-MS micromapping. The content of trace elements in the pyrite significantly (by 1–3 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 value, ppm): Zn from 13 106 to 9, Pb from 24 100 to 1783, As from 1323 to 134, Co from 1027 to 1.81, Ni from 456 to 4, Ag from 390 to 38, Au from 0.1 to 0.01, Te from 55 to 0.6, and Bi from 9.8 to 0.6. The subhedral pyrite crystals of the outer zone is enriched in Cu (up to 8367 ppm), Sb (up to 1627 ppm), and Mn (734 ppm), relative to microgranular pyrite of the nodule core. Anomalously high contents of trace elements are related to the presence of authigenic inclusions of chalcopyrite, sphalerite, fahlores, and Au–Ag minerals in the pyrite. Gangue components in 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.