Stratigraphic Section and Geochronological Studies of the Shoushan Basin, Fujian Province, South China, and Its Implications for the Mineralization of Shoushan Stone

As one of the most famous craft-carving stones in China, Shoushan stone commonly consists of clay minerals, including the kaolinite, pyrophyllite, or illite group, which is the product of hydrothermal alteration. In Fujian Province, the Xiaoxi Formation of the Early Cretaceous is a critical formation containing pyrophyllite deposits (including Shoushan stone). Here, we carry out a geological field investigation of a typical section in the Shoushan basin of southeastern China to identify lithology and volcanic sequences of the Xiaoxi Formation. The section included four lithofacies: eruption facies, flood lava facies, sedimentary facies, and volcanic channel facies. The petrogenesis of these lithofacies demonstrates the evolution of volcanism, which is critical for understanding the formation of the Shoushan-stone-associated hydrothermal system. For the geochronological study, the samples of unaltered rhyolitic tuff are collected from the layers topping and bottoming a pyrophyllite orebody. The zircon U-Pb dating results constrain the age of pyrophyllite alteration during the episodic eruption. Shoushan stone is formed in an epithermal hydrothermal environment, so we suggest that high-quality Shoushan stone is formed by the hydrothermal alterations in the interval time of the volcanic episode (135–131 Ma) and after volcanic activity (<131 Ma). Furthermore, the Shoushan basin’s stratigraphic section suggests that there have been large-scale hydrothermal systems in the volcanic basin during the Early Cretaceous volcanism. The stratigraphic correlation and geochemical results indicate that the Mesozoic basins in the Fu’an-Yongtai volcanic eruption belt have the potential for pyrophyllite deposit exploration.