Abstract:

Lamuyouta Sb (Au) deposit is located in the eastern section of Sb-Au metallogenic belt, south Tibet. The ore body mainly distributes at the contact between the strata of the Middle Jurassic Zhala Formation and diabase (allgovite) veins. The results show that the dominant fluid inclusion types in quartz are the gas-liquid two-phase inclusions with rich liquid. Those fluid inclusions are generally smaller. All of them are texturally complex, display elongated, rounded, oval-shaped and irregularshaped inclusions. The fluid inclusions in calcite are contrarily bigger. Similarly, all of them are also the gas-liquid two-phase inclusions with rich liquid. However, the texture is rather simple where the negative crystal and irregular shape dominate. The inclusion micro-thermometry results reveal that the homogenization temperatures vary from 150 to 344 ℃ while the salinities and the densities change from 0.53% to 9.61% and 0.55 to 0.93 g/cm³, respectively. The metallogenic pressure is deemed from 39 to 83 MPa, which reflect that the metallogenic process was under midlow temperature conditions and the ore-forming fluid is of low salinity and low density. The homogeneous temperature and salinity of the fluid inclusions decreased as the ore deposits formed gradually from early to late phases. H-O isotopic studies shows the δD_V-SMOW of ore bearing quartz veins is from -137 ‰ to -163 ‰ while δ¹⁸O_H2O changes from 9.42‰ to 14.58‰; the δD_V-SMOW of ore bearing calcite veins is from -148 ‰ to -151 ‰ while δ¹⁸O_H2O changes from -9.83‰ to -17.02‰ and the ore-forming fluids are considered to be sourced from the precipitation. The ore-forming material derives from water-rock interaction and mixing of fluids.

Key words: fluid source, fluid characteristic, inclusion, Sb(Au)deposit, Lamuyouta, Tibet