论扬子准地台西缘前震旦纪基底及其成矿作用

THE PRESINIAN BASEMENT ON THE WESTERN MARGIN OF THE YANGTZE PARAPLATFORM AND ITS MINERALIZATION

运用近代变质地质学的观点,总结了扬子准地台西缘前震旦纪基底不同时代的变质岩系、形成的构造环境、演化历史与成矿作用。康滇克拉通代表晚太古代的花岗岩-绿岩地体,其中以变质成矿作用为主。元古代活动带代表克拉通分裂后出现的裂谷槽盆,其中以火山、沉积成矿作用为主,还有与花岗岩有关的热液成矿作用。于中元古代在克拉通边缘基性—超基性岩浆的活动,伴随岩浆成矿作用。因多期成矿作用,本区成为黑色与有色金属矿床的重要成矿区域。

The Presinian basement on the southwest margin of the Yangtze paraplatform consists of three metamorphic rock series of different ages. Being products of different tectonic events and environments, they differ markedly in original rock sequences, metamorphism, tectonic style and characteristics of granitoids and deposits.The late Archean Kangdian craton mainly comprises the Kangding and Julin Groups with a metamorphic age of nearly 2500 Ma. They are supracrustal rocks dominated by mafic volcanics enclosed in trondhjemites. The craton is believed to represent a granite-greenstone terrane of Late Archean age. Economic deposits include graphite and kyanite deposits of metamorphic origin, muscovite deposits in pegmatites and gold quartz veins in gneissic granites, banded hornblende-magnetite mineralization, copper and zinc mineralizations related to felsic volcanics. Large V-Ti bearing magnetite deposits were also formed in the mafic-ultramafic stratiform intrusions emplaced on the margins of the craton during the middle Proterozoic. Copper and nickel deposits are found in several ultramafic intrusions.Extending north-south, the Proterozoic mobile belt mainly comprises the early Proterozoic Hekou and middle Proterozoic Huili and Kunyang Groups, and they are thought to be accumulations in a Proterozoic rift or aulacogen. During the early Proterozoic, the rift was characterized by intense volcanism and. presence of iron deposits of voclanic-magmatic type, iron-copper deposits of exhalative-sedimentary type. The Mid-late Proterozoic of the rift mainly witnessed sedimentary mineralization and formation of stratiform copper deposits of sedimentary type and of iron deposits of submarine sedimentary type in several horizons. In the wake of the emplacement of the Jinningian and Chengjiangian granites in the late Proterozoic, skarn tin and tin-iron deposits were formed.