Regional Geological Background,Ore-Forming Characters and Metallogeny of Songxi Silver Deposit,East Guangdong
The Songxi silver deposit is located in the north segment of the late Paleozoic Meixian-Huiyang depression zone in the East Guangdong,at the margin of the late Jurassic terrestrial volcanogenic basins. There are two large scale silver polymetallic deposits as well as many ore spots in the east Guangdong,which is a metallogenic province of nonferrous metals and silver. A study on the metallogeny of the deposit from regional geology is helpful for the recognition of metallogenic characters and ore exploration in the area. The regional metallogenic geological background shows that tectonic and magmatic activities in the east Guangdong are most intense in late Jurassic. Many terrestrial volcanic eruption basins are distributed along an deep fault zone. The rock-forming substances of the volcanic rocks were originated from the lower crust. The geological exploration has shown that the vein orebodies controlled by faults occur between the lower and the middle Jurassic. The textures and structures of the ores as well as the alteration zoning indicate that it is a typical hydrothermal deposit. The Pb isotopic composition is of mixture lead of both the crust and the mantle,showing that the ore-forming substances should be originated from deep magma. The S isotopic compositions of the ores,H-O isotopes of the ore-forming vein quartz and the C isotopic compositions of the vein calcite indicate that the ore-forming fluid is mainly originated from magma. Based on the mineralization and alteration characters,origins of the ore-forming substances and ore-forming fluid,combined with the regional metallogenic geological background,the magmatic distribution and magmatic composition,it is proposed in the paper that the deposit is closely related with the late Jurassic terrestrial facies volcanism,belonging to the terrestrial facies volcanogenic post-magmatic hydrothermal deposit.