The Nature of Tungstenite of the Bystrinskoe Porphyry-Skarn Au–Fe–Cu Deposit (Eastern Transbaikalia, Russia)

Tungstenite of unusual shapes (spheroids, rings, threads, spirals, etc.) was found in scheelite of gold-bearing quartz–carbonate–pyrite–chalcopyrite veins. It is crystallized in the veins in the final part of mineral deposition, after crystallization of sulfides, sulfosalts, and scheelite of several generations against the background of decreasing activity of sulfur. The issue concerning the type of the strong reducing agent of the W6+ → W4+reaction rarely occurring in nature is crucial for the formation of tungstenite. There are no traces of reducing agents, which could be solid or liquid hydrocarbons, in the veins. The unusual shapes of tungstenite aggregates similar to biomorphosеs may be evidence of the existence of microorganisms in the fractured anisotropic medium in scheelite at the boundary of the transition of the quartz part of the vein to the substantially carbonate part. The occurrence of the biomorphоsеs only in scheelite suggests that microorganisms have a W-dependent metabolism, which is observed in extremophiles of the Archaea domain producing a strong reducing agent H2; methanogens producing CH4 coexist in symbiosis with them.