Characteristics of Triassic epithermal Au mineralization at the Q prospect, Chatree mining area, Central Thailand

摘要

The Chatree deposit is located in the Loei-Phetchabun-Nakhon Nayok volcanic belt that extends from Laos in the north through central and eastern Thailand into Cambodia. Gold-bearing quartz veins at the Q prospect of the Chatree deposit are hosted within polymictic andesitic breccia and volcanic sedimentary breccia. The orebodies of the Chatree deposit consist of veins, veinlets and stockwork. Gold-bearing quartz veins are composed mainly of quartz, calcite and illite with small amounts of adularia, chlorite and sulfide minerals. The gold-bearing quartz veins were divided into five stages based on the cross-cutting relationship and mineral assemblage. Intense gold mineralization occurred in Stages I and IV. The mineral assemblage of Stages I and IV is characterized by quartz-calcite-illite-laumontite-adularia-chlorite-sulfide minerals and electrum. Quartz textures of Stages I and IV are also characterized by microcrystalline and flamboyant textures, respectively. Coexistence of laumontite, illite and chlorite in the gold-bearing quartz vein of Stage IV suggests that the gold-bearing quartz veins were formed at approximately 200°C. The flamboyant and brecciated textures of the gold-bearing quartz vein of Stage IV suggest that gold precipitated with silica minerals from a hydrothermal solution that was supersaturated by boiling. The δ~(18)O values of quartz in Stages I to V range from +10.4 to +11.6‰ except for the δ~(18)O value of quartz in Stage IV (+15.0‰). The increase in δ~(18)O values of quartz at Stage IV is explained by boiling. P_(H2o) is estimated to be 16 bars at 200°C. The f_(co2) value is estimated to be 1 bar based on the presence of calcite in the mineral assemblage of Stage IV. The total pressure of the hydrothermal solution is approximately 20 bars at 200°C, suggesting that the gold-bearing quartz veins of the Q prospect formed about 200 m below the paleosurface.