关于峨眉山溢流玄武岩省资源勘查的几个问题

On mineral exploration in the Emeishan flood basalt province

通过全球资料对比表明峨眉山溢流玄武岩省具有较完整的岩浆-热液成矿系列。峨眉山玄武岩裂隙式喷发的溢流通道受地球化学边界所揭示的岩石圈不连续界面所控制。这些地段存在完整的古火山口相岩石组合,为找矿提供了重要线索。溢流通道岩浆房存在贫硫低氧逸度、贫硫高逸度和富硫3个岩浆分异趋向,构成3个岩浆成矿系列(Cu-Ni-PGE,Cu-Ag-Pd与Fe-Ti-V)。同生火山热液活动形成了从低绿片岩相、葡萄石相到沸石相(400°C至100°C)的铜成矿系列。热液组成的不同控制自然铜、氧化铜和铜硫化物的形成。反射率资料对比表明对自然铜形成起重要制约作用的沥青来自P2-T1界面地层有机质的热液裂解,并处于生油成熟期。因此和Keweenaw大陆裂谷一样,应开展铜、镍、铂钯、油气一体化的勘查。

Global correlation indicates that there occur three relatively complete magmatic-hydrothermal minerogenic series in the Emeishan flood basalt province. The outpouring conduits for fissure eruption of the Emeishan basalt was controlled by the discontinuity of the lithospheres revealed by the geochemical boundary. The preservation of a complete rock association of paleovolcanic vent facies in these districts provides an important clue to mineral exploration. There were three magmatic fractionation trends in magma chambers: sulfur-poor, low-orygen fugacity magma, sulfur-poor, high-oxygen fugacity magma and sulfur-rich magma, which produced three magmatic minerogenic series(Cu-Ni-PGE, Cu-Ag-Pd and Fe-Ti-V). Synvolcanic-hydrothermal activity gave rise to copper minerogenic series from low greenschist and prehnite to zeolite facies (from 400℃ to100℃). Hydrothermal fluids of different compositions controlled the formation of native copper, copper oxides and copper sulfides. Comparison of the vitrinite reflectance R0 indicates that bitumen that played an important role in controlling native copper precipitation was derived from hydrothermal pyrolysis of organic matter at the P2-T1 boundary and that organic matter was at the mature stage for oil genesis. Therefore, a package exploration for Cu, Ni, Pt-Pd and petroleum can be launched, as is the case with the Midcontinent Rift in Michigan, United States.