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《Mineral Deposits》 2004-01
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Oxygen and Carbon Isotopic Geochemistry of Baiyangping Silver-Copper Polymetalli c Ore Concentration Area in Lanping Basin of Yunnan Province and Its Significance

Liu Jiajun 1,2 , He Mingqin 2, Li Zhiming 2,3 , Liu Yuping 2, Li Cha oyang 2, Zhang Qian 2, Yang Weiguang 4 and Yang Aiping 4(1 China University of Geosciences, Beijing 100083, China; 2 Institute of Geoche mistry, Chinese Academy of Sciences, Guiyang 550002, Guizhou, China; 3 Graduate School, Chinese Academy of Sciences, Beijing 100039, China; 4 No.3 Geological Party, Yunnan Bureau of Geology and Mineral Resources, Dali 671000, Yunnan, China)  
The Baiyangping silver_copper polymetallic ore concentration area in the norther n Lanping basin of western Yunnan can be divided into two ore zones. The eastern ore zone consists of Dongzhiyan, Yanzidong, Huishan, Heishan, Xinchangshan and Huachangshan ore blocks, whereas the western ore zone is composed of Baiyangping , Fulongchang and Wudichang ore blocks. They exist mainly in limestone and dolo mite of Upper Triassic Sanhedong Formation, sandstone and fine_grained sandstone of Lower Cretaceous Jingxing Formation, and sandstone of Eocene Baoxiangsi Form ation. The orebodies mostly occur in veined, network and lenticular forms. Ore m inerals are dominated by tetrahedrite, galena, chalcopyrite, sphalerite, calcite , siderite, barite and celestine. Ore fabrics are characterized by crystallizati on and replacement textures and veined, network, brecciated and disseminated str uctures. Wall rock alterations are mostly silicification, calcitization and bari tization. Two stages of mineralization can be recognized in the ore concentratio n area.Oxygen and carbon isotopic analyses of the Baiyangping silver_copper polymetalli c ore concentration area show that the δ 13 C values range from -8.3‰ to +2.7‰ in hydrothermal minerals such as calcite, siderite and strontianite, whos e variation is relatively limited. Nevertheless, the δ 18 O values range fr om -2.5‰ to +24.3 ‰, which are highly variable and include very low values (±0‰) rarely seen in nature. Based on the simulation of the water_rock exchang e reaction, the authors have reached the following conclusions: At the early sta ge, the ore_forming fluids have the δ 18 O value of +7‰ and the δ 13 C value of -7‰, which are similar to those of magmatic water. They belong to ho t brine, and the CO 2 is derived from deeper sources. The HCO - 3 is mainly i n the form of dissoluble carbon. The formation temperatures of calcite and other hydrothermal minerals are 300~160℃. The amount of the hydrothermal fluids in the mineralization and alteration systems is relatively small. At the late stage , however, the ore_forming fluids are characterized by the δ 18 O value of -12.5‰, the δ 13 C value of -2.5‰ and the dissoluble carbon of H 2CO 3 . The ore_forming fluid is derived from meteoric water . The calcite and othe r hydrothermal minerals are formed under the conditions of low temperature and t he existence of large amounts of hydrothermal fluids in the mineralization and a lteration systems. In addition, the increase of δ 13 C value is possibly re lated to the decrease of temperature, the dissolution of carbonates, or the deca rbonation of carbonates.
【Fund】: 国家重点基础发展规划 (编号 :G1 9990 4 32 0 8);; 中国科学院与中国科学院知识创新工程(编号 :KZCX 2_1 0 1 )资助项目
【CateGory Index】: P618.52
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