Genetic environment of the intrusion-related Yuryang Au-Te deposit in the Cheonan metallogenic province, Korea

The Yuryang gold deposit, comprising a Te-bearing Au-Ag vein mineralization, is located in the Cheonan area of the Republic of Korea. The deposit is hosted in Precambrian gneiss and closely related to pegmatite. The mineralized veins display massive quartz textures, with weak alteration adjacent to the veins. The ore mineralization is simple, with a low Ag/Au ratio of 1.5:1, due to the paucity of Ag-phases. Ore mineralization took place in two different mineral assemblages with paragenetic time; early Fe-sulfide mineralization and late Fe-sulfide and Au-Te mineralization. The early Fe-sulfide mineralization (pyrite + sphalerite) occurred typically along the vein margins, and the subsequent Au-Te mineralization is characterized by fracture fillings of galena, sphalerite, pyrrhotite, Te-bearing minerals (petzite, altaite, hessite and Bi-Te mineral) and electrum. Fluid inclusions characteristi cally contain CO₂ and can be classified into four types (Ia, Ib, IIa and IIb) according to the phase behavior. The pressure corrected temperatures (≥500°C) indicate that the deposit was formed at a distinctively high temperature from fluids with moderate to low salinity (<12 wt% equiv. NaCl) and CH₄ (1 ∼ 22 mole %). The sphalerite geobarometry yield an estimated pressure about 3.5 ∼ 2.1 kbar. The dominant ore-deposition mechanisms were CO₂ effervescence and concomitant H₂S volatilization, which triggered sulfidatlion and gold mineralization. The measured and calculated isotopic compositions of fluids (δ¹⁸ O_H2O = 10.3 to 12.4 ‰; δD_H2O = -52 to -77 ‰) may indicate that the gold deposition originated from S-type magmatic waters. The physicochemical conditions observed in the Yuryang gold dep osit indicate that the Jurassic gold deposits in the Cheonan area, including the Yuryang gold deposit are compatible with deposition of the intrusion-related Au-Te veins from deeply sourced fluids generated by the late Jurassic Daebo magmatism.