Geology and Geochemistry of the Dashuigou Tellurium Deposit,Western Sichuan,China |
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| Abstract: | The Dashuigou tellurium deposit, located on the western margin of the Yangtze platform, is unique. The deposit is hosted by Triassic metabasalt 50 to 80 meters thick. The orebodies occur as a group of NNE-striking parallel veins. Mineralization developed in three stages: Stage I— pyrrhotite-pyrite, Stage II—tetradymite, and Stage III—chalcopyrite-pyrite. Stage II is the principal tellurium mineralization stage and the tellurium-bearing minerals are mainly tetradymite, tsumoite, tellurbismuth, joseite, calaverite, stuetzite, and native tellurium. The general ore grade of the tellurium in Stage II ranges from 0.2 to 5 wt%, and it reaches 15 to 25 wt% for the massive ores. The dominant gangue minerals are calcite and dolomite, with minor biotite, muscovite, albite, quartz, and chlorite. Fluid-inclusion studies of calcite, dolomite, and quartz from Stages I, II, and III yield homogenization temperatures of 356° to 260° C (mean = 320° C), 295° to 198° C (mean = 240°), and 235° to 152° C (mean = 170° C), respectively. Salinities of primary fluid inclusions in all three stages are 1.5 to 5.8 wt% NaCl equivalent, 9 to 15.2 wt% NaCl equivalent, and 2.8 to 3.0 wt% NaCl equivalent, respectively. Isotopic studies show that δ34 values of sulfides range from -2.2 to +2.8 per mil. δ13C values of calcites and dolomites in the ore veins range from -5.3 to -7.42 per mil, and δ18O values range from +10.9 to +13.1 per mil, which are quite different from the δ13C values of+1.0 to +2.8 per mil and δ18O values of +16.8 to +28.5 per mil for the calcites from the Triassic carbonates in the deposit. The δD and δ18O values of muscovite and quartz were measured to be -61 to -54 per mil and +9.9 to +13.0 per mil, respectively. Values of δ18Owater computed from fluid-inclusion trapping temperatures are +3.9 and +7 per mil. A date of 93 Ma was obtained through measurement of muscovite from the No. 12 ore vein. Sulfur-, oxygen-, carbon-, and hydrogenisotope data indicate that the ore-forming substances of the Dashuigou tellurium deposit were derived from deep-seated sources, and the mineralizations probably are associated with Late Mesozoic alkaline or alkaline granitic magmatism. The estimated sulfur fugacities (fs2) are 10?16.7 for Stage I and 10?14 to 1015.5 for Stage II, whereas the tellurium fugacities (fTe2) are 10?15 to 10?14 and 10?11.2 to 10?10.5, respectively. |
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