Epithermal Mineralization in the Okhotsk-Chukchi Volcano-Plutonic Belt

摘要

This paper considers the geochemistry and conditions of generation for the Mesozoic Au-Ag epithermal deposits in the Okhotsk-Chukchi volcanic-plutonic belt (OChVB) in Northeast Russia. We provide new data on the composition and concentrations of trace elements, including REEs, in the ores of epithermal Au-Ag deposits. The ores were found to be enriched in a wide range of trace elements. The REE distributions of these ores are dominated by light hydrophile lanthanoids of the cerium group. The Eu anomalies were found to vary between high negative to low and high positive levels. Comparative analysis over the classes of gold concentration showed a synchronous enrichment of the ores in similar sets of trace elements. A study of fluid inclusions revealed that the ore-forming solutions had hydrocarbonate potassium or hydrocarbonate sodium compositions. The fluids had high concentrations of sulfate ions for most deposits. The salinity of the fluids was frequently found to increase toward later low-temperature mineralization phases. We identified the tendency of increasing K+ percentage in the fluid from the earlier oreless quartz to productive quartz with increasing depth, as well as some decrease in the percentages of Na+, Ca++, and Cl-. The results indicate magma chambers of andesite magmas and meteoric waters as the most likely sources of the fluids that generated the epithermal Au-Ag ores in the OChVB deposits.