| 西藏邦铺斑岩钼铜矿床岩浆-热液流体演化: 流体包裹体研究 |
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| 引用本文：罗茂澄,毛景文,王立强,冷秋锋,陈伟.2012.西藏邦铺斑岩钼铜矿床岩浆-热液流体演化: 流体包裹体研究[J].地球学报,33(4):471-484. |
| DOI：10.3975/cagsb.2012.04.08 |
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| 基金项目:国家973项目(编号: 2011CB403100);中国地质调查局青藏高原专项(编号: 1212010012005) |
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| 中文摘要:邦铺矿床产于西藏冈底斯成矿带东段, 是一个与二长花岗斑岩-闪长(玢)岩侵入体有关的斑岩型钼铜矿床。在前人的研究基础上, 本文依据矿物组合、脉体穿切关系的不同, 划分了3个成矿阶段: 成矿前阶段、主成矿阶段以及成矿后阶段。根据气液充填度的不同以及是否含有子矿物, 流体包裹体可分为5类: B15、B20H、B35、B60和B80。成矿流体从早到晚具有规律性演化特征: 成矿前阶段发育B20H、B35、B60和B80包裹体, 均一温度(243～421℃)变化范围较大, 盐度集中在1.4～15.4 wt%和34.3~48.3 wt%, 密度为0.62~1.25 g?cm-3; 主成矿阶段发育典型的沸腾包裹体组合(B20H与B60、B80共存), 均一温度为240～423℃, 盐度集中在1.7~16.5 wt%和32.2~47.5 wt%, 密度为0.55~1.12 g?cm-3; 成矿后阶段发育B15、B35包裹体, 均一温度(119~301℃)和盐度(0.9~9.7 wt%)较低, 密度为0.59~0.92 g?cm-3。成矿压力分别为~120 Mpa、 34~85 Mpa、20~58 Mpa。激光拉曼探针分析结果表明液相成分主要为H2O, 气相成分含CO2。流体包裹体研究结果表明, 在＞5 km的古深度, 岩浆房发生出溶。在约2 km的古深度岩浆流体曾发生减压沸腾和不混溶作用, 主成矿阶段的压力波动可能是邦铺矿床Mo、Cu在此阶段沉淀的原因。随着裂隙进一步扩大, 流体氧逸度不断提高, 该阶段也有少量Mo矿化的产生。 |
| 中文关键词:地球化学 流体包裹体 岩浆-热液流体 邦铺斑岩钼铜矿 冈底斯 西藏 |
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| Fluid Inclusion Evidence for Magmatic-Hydrothermal Evolution in the Bangpu Porphyry Molybdenum-Copper Deposit, Tibet |
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| Abstract:The Bangpu Mo (Cu) deposit, located in the east section of Gangdise, Tibet, is a porphyry metallogenic system, and monzogranite and diorite (porphyrite) intrusions contributed to the mineralization. According to the vein types and crosscutting relationships, the mineralization at Bangpu can be divided into three stages: Pre-mineralization stage, main-mineralization stage and post-mineralization stage. Fluid inclusions at Bangpu can be classified into types B15, B20H, B35, B60 and B80. Ore-forming fluids evolved regularly from pre-mineralization stage to post-mineralization stage. B20H, B35, B60 and B80 inclusions dominated the pre-mineralization stage with wide range of homogenization temperatures (243–421℃), salinities are 1.4–15.4 wt% and 34.3–48.3 wt%, and densities are 0.62–1.25 g?cm-3. Typical boiling inclusion assemblages of the main-mineralization stage are characterized by the coexistence of B20H, B60 and B80 inclusions with homogenization temperatures of 240–423℃, salinities of 1.7–16.5 wt% and 32.2–47.5 wt%, and densities of 0.55–1.12 g?cm-3. In the post-mineralization stage, fluid inclusions are mainly B15 and B20H types with narrow range of homogenization temperatures (119–301℃), salinities (0.9–9.7 wt%) and densities of 0.59–0.92 g?cm-3. Trapping pressures differ from the pre-mineralization stage to the post-mineralization stage, being respectively ~120 Mpa, 34–85 Mpa and 20–58 Mpa. Using Laser Raman spectroscopic analysis, the authors identified H2O contents in liquid and CO2 amounts in vapors. With Fluid inclusions microthermometry the authors studied the revolution history of fluid inclusions and linked this history to ore formation at Bangpu, Tibet. It is likely that the exsolution of magma chambers occurred at plaeodepths of ＞5 km. Transition from lithostatic to hydrostatic pressure at paleodepths of ~2 km once caused the initiation of boiling and immiscibility, and pressure fluctuations were probably the main driving force for Mo (Cu) sulfide deposition during the main-mineralization stage. At shallower depths the oxygen fugacity of magma-derived fluid increased and caused slight Mo precipitation. |
| keywords:geochemistry fluid inclusion magmatic-hydrothermal fluid Bangpu porphyry Mo (Cu) deposit Gangdise Tibet |
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