Genesis of the sediment-hosted Fe-Cu-Zn(-Au) sulfide deposits in Escanaba Trough, Gorda Ridge, NE Pacific, with emphasis on the solubility and deposition of gold

摘要

Massive sulfide deposits in the Escanaba Trough, Southern Gorda Ridge, represent one of the few known occurrences of modern seafloor sediment-hosted deposits. Semi-continuous exposures of massive sulfides extend for hundreds of meters along the flanks of uplifted sediment hills which are, in turn, related to intrusive centers at depth. The mineralogy of massive sulfides is dominated by pyrrhotite, isocubanite, and sphalerite with minor to trace amounts of pyrite-marcasite, galena, Fe-Co sulfarsenides and arsenides, Bi-minerals, tetrahedrite, several gold-bearing minerals, and native gold. The occurrence and chemistry of mineral phases at Escanaba Trough and a comparison with other sediment-hosted deposits indicate that gold was deposited from low fS_2-fO_2 fluids at temperatures between 275-330℃. Scavenging of gold from hydrothermal fluid by liquid Bi possibly contributed to the enrichment of Au in pyrrhotite-rich samples.