滇黔交界地区峨眉山玄武岩铜矿化蚀变特征

滇黔交界地区峨眉山玄武岩铜矿化具层控特征,主要发育于上二叠统峨眉山玄武岩组第四岩性段下部.矿化主岩为玄武岩流顶部的淬碎玄武质角砾岩和玄武岩流之间的含炭沉积岩;矿石矿物主要为自然铜及其表生氧化产物黑铜矿、赤铜矿、孔雀石等;脉石矿物主要有沥青、炭质物、石英、沸石、方解石、绿帘石等,此外还有少量绿泥石、钠长石、铁阳起石、榍石、辉铜矿、硅孔雀石、铜蓝、褐铁矿等.以玄武岩为主岩的铜矿石典型矿物组合为自然铜+沥青+石英及不含沥青等有机质的自然铜+石英+绿帘石,以含炭沉积岩为主岩的铜矿石典型矿物组合为自然铜+炭质物+沸石+石英(+辉铜矿);原生铜矿化有2个期次:早期铜矿化发生于有机质流体贯入之前,晚期铜矿化发生于有机质流体贯入之后.该类铜矿化的同生火山热液特征不明显,以后生热液矿化为主.淬碎玄武质角砾岩不仅是有机流体的良好储层,也为成矿流体提供了就位空间,是铜矿化层控特征的主要控制因素.有机流体及含碳沉积岩中碳质为成矿物质以自然铜形式沉淀提供了还原条件.

Copper Mineralization Characteristics of the Emeishan BasaltDistrict in the Yunnan-Guizhou Border Area

Copper mineralization of Emeishan basalt in Yunnan-Guizhou border area shows stratabound character and occurs mainly in the lower part of the Fourth Member of Upper Permian Emeishan Basalt Formation. The host rocks are quenched-shattered amygdaloidal basalts at the tops of the basalt floods and carbonolithintercalations in the basalt floods. Copper minerals mainly include native copper and its oxides such as cuprite, tenorite and malachite together with a littlechalcocite. Gangue minerals comprise mainly bitumen, carbon matter, quartz, zeolite, calcite and epidote. The typical mineral assemblage of the basalts-hostedcopper ore is native copper + bitumen + quartz and that of the carbonoliths-hosted ore is native copper + carbon matter + zeolite + quartz (+ chalcocite). Copper ore-forming process took place probably later than Jurassic and might be divided into two stages: one was earlier than crude oil and the other was later thanbitumen. Folds provided tectonic traps for organic fluids, whereas quenched-shattered amygdaloidal basalts provided space for organic fluids and metallogenic fluids. This type of copper mineralization is somewhat different from the Keweenawbasalt copper deposits. Organic matter played an important role in copper mineralization.