Elements Geochemistry of the Neoproterozoic Xiajiang Group in Jinping County, Guizhou Province, and Its Impact on the Gold Deposits

Low-degree metamorphic clastic rocks of the Neoproterozoic Xiajiang Group in southeastern Guizhou Province host numerous quartz vein type gold deposits and prospects. But the origin of the deposits of this kind, especially gold source, has long been a research issue. Therefore, gold-bearing possibility and element geochemical characteristics of formation rocks in the Xiajiang Group have also received extensive concern. This paper conducted a systematic analysis of the trace elements and rare earth elements. Comparative study indicates that the Xiajiang Group is characterized by enrichment in As, Ba, Zr and Ti and depletion in Cr, Rb, Sr, Ta and Sc, and element association shows obvious similarity and inheritance from Fanzhao Formation to Pinglue Formation. In Addition, tuffaceous sequence in the Fanzhao and Pinglue formations has a high content of gold, and horizons which contain high contents of gold have a low REE content. Gold in the sequences has a close relation with crustal elements such as Ag, Hg and As. Therefore, gold migration and enrichment may have been closely related to hydrothermal activities and regional metamorphism. The trace element characteristics of country rocks, sequences and ore, and consistency and inheritance of REE compositions suggest that ore-forming material was derived mainly from sequences. Part of gold-bearing quartz veins in the Pingqiu gold deposit exhibit different geochemical features, indicating that it was more close to lower upper or upper mantle and some of the deep fluids were likely involved into mineralization.