Gold and palladium minerals (including empirical PdCuBiSe3) from the former Roter Bar mine, St. Andreasberg, Harz Mountains, Germany: a result of low-temperature, oxidising fluid overprint

摘要

At Roter Bar, a former underground mine in the polymetallic deposits of St. Andreasberg in the middle-Harz vein district, Germany, native gold and palladium minerals occur very locally in clausthalite hematite pockets of few millimetres across in carbonate veinlets. The native gold is a Au-Ag intermetallic compound and the palladium minerals are characterised as [Pd-8(Sb,As)(3)] and empirical PdCuBiSe3 with some S. The latter coexists with bohdanowiczite (AgBiSe2), a mineral that is stable below 120 degrees C. The geological setting of Roter Bar, underneath a post-Variscan unconformity, and its hematite selenide gold association suggest that oxidising hydrotheimal brines of low temperature were instrumental to the Au-Pd mineralisation. The Roter Bar Au-Pd mineralisation can be explained by Permo-Triassic, red-bed-derived brines in the context of post-Vaiiscan, unconformity-related fluid overprint.