XIE Peng1,2, SU Wen-chao1*, ZHAO Hai1,2, SHEN Neng-ping1, DONG Wen-dou1,2, CAI Jia-li1, WEI Liu-bing3
(1. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;
2. University of Chinese Academy of Sciences, Beijing 100049, China;
3. Nanguo Mining Company, Nandan 547200, China)
Abstract: Dachang district, Guangxi Province, China, has one of the largest tin-polymetallic ore field in the word. Kangma deposit is located at the eastern part of Dachang ore field and the orebodies mainly occur as veins hosted in Devonian black shale. Petrography, microthermometry, and laser Raman spectroscopy, combined with scanning electron microscope cathodoluminescence (SEM-CL) analyses of fluid inclusions were used to characterize the chemical evolution of ore fluids in Kangma deposit. Results show that quartz associated with the main ore stage of cassiterite-sulfides veins only contains two-phase, CO2 vapor-rich and daughter-bearing fluid inclusion assemblages. The vapor-rich fluid inclusion assemblage yield homogenization temperatures of 304－392 °C and salinities of 3%－8% NaCl equiv. The daughter- bearing inclusion assemblages have similar range of homogenization temperatures of 314－420 °C, but high salinities of 36%－48% NaCl equiv., whereas the fluid inclusions in calcite associated with the late ore stage of carbonate-sulfosalt veins are only two-phase, liquid-rich aqueous fluid inclusions, with low homogenization temperatures of 108－197 °C and medium salinities of 6%－12% NaCl equiv. The coexistence, similar homogenization temperature, contrasting salinity of vapor-rich and daughter-bearing fluid inclusion assemblages in the main ore stage of cassiterite-sulfides indicate that boiling and redox of ore fluids are key process for deposition of cassiterite and sulfides. The late ore fluids may be sourced from cooling and contraction of vapor phase of the main stage to liquid that deposited carbonates and sulfosalts in the late ore stage.
Keywords: Fluid inclusion; ore fluid evolution; Kangma tin-polymetallic deposit; Dachang ore field
