Stratigraphic characteristics of the Cambrian Qingxudong Formation in relation to lead-zinc mineralization in western Hunan-eastern Guizhou area

In the western Hunan-eastern Guizhou area,the Cambrian strata are well developed and characterized by sedimentary succession from black shale to carbonate rocks.Vertically,the limestone segment and dolomitite segment constitute the Qingxudong Formation made up of an upward-shoaling succession of sedimentary facies and demonstrates a growth process of the ramp carbonate platform.Horizontally,the principal lithofacies palaeogeographic units in the study area have been recognized,which include carbonate tidal flat,subtidal facies of restricted platform,platform marginal bioherm(or bank) facies and shallow ramp—deep ramp facies as well as shelf-basin facies in southward succession.All these data suggest that the formation of the lead-zinc deposits was controlled by stratigraphy,lithologic character and lithofacies-palaeogeographic framework and related to turbidite and tempestite.The host rocks(reservoir beds) were micrite mounds(mud mounds) formed by CO2-bearing hydrothermal solution and bio-process.The assemblage made up of turbidite and micrite mounds(algal bioherm) and rudstone was a well developed succession favorable for the formation of lead-zinc deposits.