He-Ar-H-O isotopic signatures in AuAg bearing ore fluids of the Sunshin epithermal gold-silver ore deposits, South Korea

Abstract

Helium ( 3He/ 4He), argon ( 40Ar/ 36Ar) and oxygen ( 18O/ 16O) isotopic ratios in fluid inclusions trapped in quartz and pyrite from the Sunshin epithermal gold-silver ore deposits in South Korea were analyzed to investigate the magmatic contribution to ore forming fluids. Mantle helium with high 3He/ 4He ratios (up to 3He/ 4He~9R A, where R A=1.4×10 -6 for air) were identified from fluid inclusions in auriferous quartz veins, which are characterized as low sulfidation (adularia-sericite) type. The ratios provide direct evidence of links between low sulfidation ore fluids in epithermal gold deposits and magma from a mantle source. Interestingly, the oxygen and hydrogen isotopic compositions of the ore fluids (δ 18O=-1.9 to -6.6‰, δD=-82 to -100‰), calculated from ore quartz, indicate that meteoric waters were predominant during precipitation of the AuAg ore. Microthermometric measurements for fluid inclusions indicate relatively low temperatures (≤300°C) for the formation of the low sulfidation epithermal ore deposits. © 2012 Elsevier B.V.