云南中甸地区浪都矽卡岩型铜矿床富CH4流体地球化学研究

The CH4 rich fluid geochemistry is one of the hot point in the study of ore deposit in recent years. Although CH4-rich fluid study could provide new constraints on the ore forming process, the CH4 geochemical action in hydrothermal fluid is still in the exploratory stage. The Langdu skarn copper deposit which belongs to the typical Triassic copper deposit in Sanjiang tectono-magmatic zone is located at the Zhongdian island arc belt, NW Yunnan province. It is the richest copper deposits (average grade of 6.49%) in the region. The mineralization is related to a porphyry intrusion (～216Ma), originally associated with the subduction of the Garzê-Litang oceanic crust. Recently, we have found a large number of CH4-rich fluid inclusions in the deposit, making the deposit as an ideal carrier of the CH4-rich fluid geochemistry study. This application focus on the CH4-rich inclusions from the Landgu skarn copper deposit. Based on geological investigate, the systemic sample collection and detailed petrographic observation, using microthermomety, Raman microprobe, single fluid inclusion composition and carbon, oxygen, hydrogen and sulfur isotope analysis techniques, we will explore the geochemical action of CH4 in the ore-forming element migration, enrichment and disposition, refinedly reflect the ore-forming fluid evolution, exactly build the P-T-X condition, and well reveal the mineralization mechanisms of Langdu deposit. As comprehensive comparison study with other deposits in the region could enrich and improve multi-metal metallogenic theory in the Zhongdian area. The research also provides theoretical guidance to peripheral prospecting and exploration work, and further enhance the predictive ability of new mineral deposits.

富CH4流体地球化学是近年来矿床学研究的热点问题之一，尽管富CH4流体深入探讨可以为成矿过程提供新的约束，但其研究尚处于探索阶段。浪都矽卡岩矿床是中甸地区最富的铜矿床(平均品位6.49%),最近在该矿床中发现了大量富CH4流体包裹体，使其成为富CH4流体地球化学研究的理想载体。本申请以浪都矿床中富CH4流体包裹体为研究对象，在野外地质调研、样品系统采集、详细的岩相学观察基础上，通过流体包裹体显微测温、激光拉曼、单个流体包裹体成分测试及矿物 C、H、O、S同位素分析，探索CH4在成矿元素迁移、富集、沉淀过程中的地球化学行为，阐明成矿流体的来源及成矿P-T-V条件，反演流体演化过程，揭示矿床的成矿机制。通过与区域内其它典型矿床综合对比研究，为丰富和完善中甸铜多金属矿集区成矿理论提供依据，为区内深部和外围找矿工作提供理论指导，增强发现新矿床的科学预测能力。

成矿流体性质和含矿性研究是矿床学研究的核心问题，含CH4流体在金属矿床中较为普遍，但富CH4流体并不多见，因此CH4对金属离子的富集机制及在成矿过程中的作用研究并不深入。本项目分析了与矿床关系密切的浪都侵入岩的元素地球化学、Sr-Nd同位素和年代学特征，提出了浪都侵入岩是由甘孜理塘洋消减碰撞过程中俯冲带流体交代地幔楔而形成；厘定出该矿床中主要矽卡岩矿物的化学成分，讨论了其形成环境；对成矿期石英、方解石，石榴子石、辉石显微观察厘定出四种流体包裹体，分别是水溶液包裹体(I类)、富气包裹体(II类)、单相甲烷包裹体(III类)和含子矿物包裹体(IV类)。显微测温结果表明，单相富甲烷包裹体在-117.3 ºC ~ -114.2 ºC之间均一至液相，激光拉曼光谱技术对单个包裹体进行分析显示该包裹体的主要成分为CH4，另外含有少量N2；而富气相甲烷包裹体在-87.5 ºC ~ -84.7 ºC均一至液相。该研究建立了特定压力条件下含N2富CH4流体的P-T-V关系，揭示了CH4在含S离子由氧化态向还原态转变过程的作用，分析认为在相同温度和压力条件下CH4有效增强了流体不混溶强度，促进了成矿元素有效富集。结合稳定同位素的研究，分析了CH4对成矿元素的富集机制和矿床的形成过程。