MODES OF OCCURRENCE OF THE PLATINUM-GROUP ELEMENTS AND THEIR ORIGIN IN THE SUKHOI-LOG GOLD DEPOSIT (RUSSIA)

A platinum group element (PGE) mineralization was discovered and studi ed in the unique Sukhoi Log stratabound gold deposit. The PGE minerali zation is also stratabound and localized in both gold ores and the ove rlying metasedimentary rocks. Platinum dominates in ores among the oth er PGE, which have much lower concentrations. The modes of PGE occurre nce are first established for deposits of this type. Native platinum a nd Pt-Fe-Cu solid solutions are the major platinum-bearing phases. Pal ladium tellurobismuthide was identified; rhodium was also found as a m ineral phase. The PGE-bearing minerals are accompanied by a large numb er of native metals and metal solid solutions, such as native iron, ch romium, tin, lead, nickel, tungsten, titanium, Fe-Cr-W and Ni-Sn-Sb so lid solutions, and other phases. This paper contains new data on gold ore mineralogy and phase composition of organic matter. Based on the a nalysis of mineral assemblages as well as thermobarometric and isotope data, we concluded that PGE mineralization and associated native meta ls and metal solid solutions formed earlier than the gold ores. The re duced metal forms, including PGE, originated during hydrogen-induced r eduction coupled with oxidation of hydrocarbons. The classification of the Sukhoi Log as a platinum-gold deposit is the main result of our s tudy. The PGE behavior and formation of PGE-bearing phases in ores fol low the general laws of migration and concentration of these elements in endogenous processes.