TWO GOLD-BEARING SEQUENCES AND THEIR SEDIMENTARY ENVIRONMENTS IN SOUTHWESTERN GUIZHOU AND ITS ADJACENT AREAS

The strata in which the micrograined-disseminated gold deposits are hosted in southwestern Guizhou, northwestern Guangxi and southeastern Yunnan can be divided into two sequences: the Longtoushan and Laizishan sequences on the basis of the regional geologic settings. The main goldbearing horizons of the Longtoushan sequence are confined dominantly to the Upper Permian strata and the lower part of the Lower Triassic strata, whereas those of the Laizishan sequence mainly to the lower and middle parts of the Middle Triassic strata. The host rocks consist chiefly of terrigenous lutite and siliceous rocks. The sedimentary environments of the above-mentioned sequences include tidal flat-lagoon and lower slope. Taking the emergence, development and disappearance of the palaeo-Tethys as the background, the formation of the sequences is interpreted to be closely related to divergent tectonic settings.