Palladium and gold minerals from the Baronskoe-Kluevsky ore deposit (Volkovsky complex, Central Urals, Russia)

Drill cores from the newly discovered Baronskoe-Kluevsky Pd-Au deposit (Volkovsky massif, Central Urals) have been investigated by reflected-light and electron microscopy, and the ore minerals were analyzed by electron microprobe. The most abundant Platinum-group mineral (PGM) is vysotskite, ideally PdS, characterized by an unusual Pt,Ni-poor composition. Palladium also occurs in kotulskite (PdTe), stillwaterite (Pd8As3 and unknown Pd-As-Te compounds with vincentite-type Pd-3(As,Te), stillwaterite-type Pd-8(As,Te)(3), and Pd-7(As,Te)(2) stoichiometries. The main carrier of Au is Pd-rich electrum, approaching the composition Au75Ag15Pd10, with minor Fe, Cu, Ni and Pt. The precious minerals are closely associated with minute blebs of chalcopyrite + magnetite disseminated throughout serpentinized olivine-apatite host rock. Paragenetic relationships among the ore minerals define a succession of crystallization events in the order: 1) Cu-Pd sulfides + electrum, 2) replacement by Pd-Te-As and late Pd-As PGM, 3) final replacement by magnetite. The paragenesis is tentatively related with cooling of a fluid phase in the late-to post-magmatic stage.