Stratigraphic Subdivision of the Yangla Copper Ore Districtu,Northwestern Yunnan

The actual measurement and lithostratigraphic subdivision for a 7.5 km geological profile across the Yangla mining area shows that the thick ocean-basin sediments in the mining area, which used to be defined as the Permian Gajinxuanshan Group, consists of highly mixed Devonian and Permian structural rocks. A series of oceanic-terrestrial transition in the Jishajiang oceanic basin, such as initial splitting, oceanic expanding, subduction and collision orogeny, resulted in widespread greenschist facies metamorphism. Lack of paleontological fossils makes it difficult to restore original sequence order. Therefore, this study, based on the previous work and discovery of conodonts,reclassified the strata into Lower Devonian massif of Tongjiangbian Group, Middle Devonian and Carboniferous massif, Permian massif, and finally discussed tectonic evolution.