川滇黔接壤区拉一木玄武岩铜矿流体包裹体

扬子地台西南缘形成的大面积自然铜矿化是峨眉地幔柱成矿系统的重要组成部分。以四川省昭觉县拉一木玄武岩铜矿流体包裹体为研究对象，通过与自然铜矿共生的石英和方解石中各类型包裹体测定，将该自然铜矿成矿过程划分为两个阶段，其中早阶段成矿流体具有中-低温、高盐度的盆地热卤水与有机流体的混合作用特征，流体组成为H₂O，含少量甲烷、烃类及沥青，液态烃以荧光性强的芳烃为主，包裹体均一温度140~306 ℃，w(NaCl)值分布在3%~10%、11%~14%、21%~24%三个区间，平均盐度为8.6%；晚阶段流体表现为低温低盐度特征，均一温度80~190 ℃，w(NaCl)值0.2%~8%，平均值4.8%，表明流体是由地表下渗的大气降水经水岩反应后转变而成。研究区自然铜矿流体包裹体与滇东北昭通地区玄武岩铜矿流体包裹体特征基本一致。无机物与有机物反应、地幔流体促成不同类型流体与其混合以及缺硫条件和有机质的还原作用是导致本区自然铜沉淀富集成矿的主要机制。

Fluid Inclusions of Layimu Basalt Native Copper Deposit in the Sichuan-Yunnan-Guizhou Border Area,China

A large area of native copper mineralization, which formed in the southwestern margin of the Yangtze platform, is an important part of the Emei mantle plume metallogenic system. We studied the fluid inclusions of Layimu basalt native copper deposit in the Zhaojue County, Sichuan Province. According to the determination of inclusions composition in quartz and calcite, the ore forming fluid is divided into two stages as follows. Early stage ore-forming fluids have mixed characteristics of basinal saline fluid and organic fluid with medium-low temperature and high salinity. The fluid is composed of water, a small amount of methane, hydrocarbon and asphalt. Liquid hydrocarbon is an aromatic hydrocarbon, with strong fluorescence. The homogenization temperature range of early-stage fluid inclusions is 140-306 ℃, with three salinity content values of 3%-10%，11%-14%，21%-24%, and average salinity content of 8.6%. The late-stage fluids are of low temperature and low salinity characteristics, and the homogenization temperature range of these fluid inclusions is 80-190 ℃, with salinity content of 0.2%-8%, and average salinity content of 4.8%. These data suggest that the late-stage fluid is formed by the atmospheric precipitation infiltration and water-rock reaction. The features of fluid inclusion of Layimu basalt native copper deposit are consonant with those of the Zhaotong area, northeast of Yunnan. The main mechanism of the enriched precipitation of native copper mineralization in this area is as the following: reaction of inorganic and organic substances, mixture of mantle fluids and other different types of fluid, lackness of sulfur conditions or organic reduction.