| 云南白秧坪银铜多金属矿集区碳氧同位素组成及其意义 |
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| 引用本文：.2004.Oxygen and Carbon Isotopic Geochemistry of Baiyangping Silver_Copper Polymetallic Ore Concentration Area in Lanping Basin of Yunnan Province and Its Significance[J].Mineral Deposits,23(1):1~10 |
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| 基金项目:国家重点基础发展规划(编号: G1999043208)和中国科学院与中国科学院知识创新工程(编号 ：KZCX2_101) |
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| 中文摘要:为探讨兰坪盆地内白秧坪银铜多金属矿集区水_岩反应的可能性，对矿集区的热液矿物、蚀变岩石和原岩的碳、氧同位素组成进行了分析。分析结果显示，热液成矿阶段形成的方解石、菱铁矿、菱锶矿的δ13CPDB值为-8.3‰～+2.7‰，相对变化较小；而δ18OSMOW值为-2.5‰～+24.3‰，变化较大，且出现了自然界中少见的极低值(±0‰)。水岩交换模拟反应显示，在成矿早阶段，成矿流体的δ13C和δ18O值分别为-7‰和+7‰，与岩浆水组成特征相似，它是一种具有深源CO2的热卤水。在此流体中，可溶性碳以HCO-3为主，方解石等热液矿物的形成温度为300～160℃，水岩交换比值较小(0～0.4)。在成矿晚阶段，成矿流体的δ13C和δ18O值分别为-2.5‰和-12.5‰，可溶性碳以H2CO3为主，方解石等形成温度为250～150℃，水岩交换比值稍大(0.2～0.6)，显示出晚阶段成矿流体具有大气降水的特征。δ13C值的增加，很可能与降温作用和灰岩的溶解或去碳酸盐化作用有关。 |
| 中文关键词:地球化学 热液碳酸盐 碳氧同位素组成 水-岩反应 银铜多金属矿集区 白秧坪 滇西 |
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| Oxygen and Carbon Isotopic Geochemistry of Baiyangping Silver_Copper Polymetallic Ore Concentration Area in Lanping Basin of Yunnan Province and Its Significance |
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| Abstract: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 δ13C 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 δ18O 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 δ18O value of +7‰ and the δ13C value of -7‰, which are similar to those of magmatic water. They belong to ho t brine, and the CO2 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 δ18O value of -12.5‰, the δ13C value of -2.5‰ and the dissoluble carbon of H2CO3 . 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 δ13C value is possibly re lated to the decrease of temperature, the dissolution of carbonates, or the deca rbonation of carbonates. |
| keywords:geochemistry, oxygen and carbon isotopic composition, rock and water reaction, silver_copper polymetallic ore concentration area, Baiyangping, western Yunnan |
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