Mineralogy and geochemistry of sulfide ores in ocean-floor hydrothermal fields associated with serpentinite protrusions

Abstract

The aim of this paper is to analyze and compare the mineralogy and geochemistry of copper–zinc sulfide ores from the Logachev-2 and Rainbow hydrothermal fields of the Mid-Atlantic Ridge (MAR), confined to serpentinite protrusions. It was found that the Zn(Fe) and Cu, Fe(Zn) sulfides had been deposited in black smokers pipes almost simultaneously from intermittently flowing, nonequilibrium H2S-low solutions of different temperatures. The Pb isotope composition confirmed that the source of lead had been the deep oceanic crust. The ores of the Rainbow Field contain 20-fold more Co than the ores restricted to the basalts and show a high ratio of Co/Ni = 46. The Rainbow ore is enriched in heavy 34S isotope (δ34Sav = 10o/oo) because of the constant flow of cold sea water into the subsurface zone of the hydrothermal system. The ore of the Logachev-2 field is 8 times higher in gold compared to the other MAR regions. The sulfide ores of the Rainbow and Logachev-2 fields have no analogues among the MAR ore occurrences in terms of the enrichment in useful components (Zn, Cd, Co, and Au).