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

Summary

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 Pd₃(As,Te), stillwaterite-type Pd₈(As,Te)₃, and Pd₇(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.