Abstract:

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.

Key words: Emeishan basalt, mantle plume, native copper, fluid inclusion, Layimu