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

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 ~ 9RA, where RA = 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 (δ18O = − 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.