Cambrian mercury mineralization event in South China: Insights from U-Pb dating of hydrothermal dolomite in the large Chatian Hg district

The genesis of many giant mercury (Hg) deposits/belts is widely debated largely because of a lack of reliable ore-forming age constraints. The LA-ICP-MS/MS dolomite U-Pb were employed to date the large Chatian Hg district in Xiangxi-Qiandong Hg belt of South China. The mineralization of this district can be divided into three stages: an initial Pyrite-Quartz stage before mercury deposition, a main Cinnabar-Sphalerite-Dolomite (Dol I) stage, and a subsequent Dolomite vein (Dol II) stage after ore formation. Three Dol I samples from the Chashula and Touponao Hg deposits were chosen for U-Pb dating, yielding ages of 509.8 ± 7.4 Ma, 509.4 ± 4.7 Ma and 507.4 ± 4.0 Ma respectively, indicating the mineralization occurred in the Cambrian Miaolingian, concurrent with or shortly after the deposition of the host-rock. These ages correspond with the emplacement periods of two Large Igneous Provinces (LIP) (the Pinghe silicic SLIP and the Kalkarindji LIP) in northeastern Gondwana, as well as the mantle-derived rocks in the study region. Combined with previous mercury isotopic data, our study proposes that the large-scale Hg mineralization in the area most likely resulted from the mantle-derived fluids, which would have directly contributed a significant amount of Hg for ore formation. Furthermore, the close timeframe between the Cambrian Series 2-Miaolingian trilobite extinction events and Hg mineralization in South China, may suggests a potential direct connection between the widespread mercury release and mineralization and the Cambrian Series 2-Miaolingian trilobite crisis in the region.