Geochemical characteristics of the giant Nibao Carlin-type gold deposit (Guizhou, China) and their geological implications

摘要

A large gold orebody controlled by Fault F1 was newly discovered in the giant Nibao Carlin-type gold deposit from southwestern Guizhou, China. Ore or rock samples were collected and studied to reveal the relationship among various orebodies which distributed in Fault F1 and its upper and lower plates, and to figure out the possible origin of ore-forming material. Tuff or tufaceous material was considered to be basic volcanic rocks in terms of their characteristic values of Al2O3/TiO2. Positive correlation was found between Au and As, and the correlation coefficient is particularly high within the fault fracture zone of the F1. Analysis shows that As can be regarded as a preferentially indicative element in gold prospection, while minerals of hydrothermal origin such as pyrite and arsenopyrite can be used as mineralogical indicative for gold prospection. Geochemical characteristics of trace elements and rare earth elements (REE) show that mantle source materials might have been involved in gold mineralization of different ore bodies. Large-scale Emei mantle plume eruption in the Early Permian resulted in thick volcanic sedimentary rock positioned between the karst unconformity surface at the top of the Maokou Formation and the bottom of the Longtan Formation. The Yanshanian tectonic activities played a significant role in driving gold-rich fluids to pressure-release spaces such as fault fracture zone and structure-controlling alteration zone (abbreviated to Sbt, according to Chinese). Those fluids reacted with ore-hosting rocks through water-rock interactions and resulted in the formation of gold-rich arsenian pyrite and arsenopyrite. Gold mineralization might have resulted from reactions between Fe-poor and gold-rich ore-forming fluids and tuffs which was relatively rich in iron, during which Fault F1 was considered to be the key to the formation of this giant gold orebody.