Oulankaite, a Pd-rich stannosulphotelluride, and associated platinum-group minerals from the Dzhaltul microgabbroic intrusion, Krasnoyarskiy kray, Russia

摘要

A new occurrence of oulankaite, Pd-5(Cu,Fe)(4)SnTe2S2, and platinum-group minerals (PGM; telargpalite, tulameenite, kotulskite-sobolevskite, merenskyite, moncheite, michenerite, froodite, atokite-rustenburgite, zvyagintsevite, sperrylite, palarstanide, and Pd2AgSn?) are reported from the Dzhaltul microgabbroic intrusion in the Siberian Platform, Krasnoyarskiy kray, Russia. The development of submicrometric grains of PGM (generally <= 5 mu m), located principally at boundaries of grains of base-metal sulphides (BMS; cubanite, chalcopyrite, troilite, pentlandite), in association with a low-sulphide fine-grained mineralization, is consistent with their precipitation at a postmagmatic stage of crystallization, after the associated BMS; some of the observed PGM may have formed via exsolution from the BMS. The following similarities exist between the presently reported (at Dzhaltul) and the type occurrences of oulankaite (at Lukkulaisvaara): (1) a close geochemical association of Pd and Ag, reflected in relative abundance and intergrowth relationships of oulankaite with Ag-based minerals, such as telargpalite; (2) a spatial association with microgranular rocks, i.e., a microgabbronorite of the sill-like body at Lukkulaisvaara and a mineralized dolerite in the Dzhaltul intrusion. Thus, a special regime of relatively rapid cooling or a rapid loss of a volatile phase may have been important to stabilize oulankaite, having one of most complex compositions among all known species of PGM.