Genesis of tin-dominant polymetallic deposits in the Dachang district, South China: Insights from cassiterite U-Pb ages and trace element compositions

摘要

The Dachang tin-dominant polymetallic district in western South China, hosts a total reserve of 110 Mt ore @ 1% Sn, 3-5% by-products of Zn, Pb, Sb, In and Cu, and 100 to 300 g/t Ag. Economic tin orebodies in the district mainly developed in Devonian limestone, black shale and siliceous rocks, as massive/stratiform and vein/ stockwork mineralization. LA-ICP-MS U-Pb dating on seven cassiterite samples from the Tongkeng-Changpo and Gaofeng Sn-Zn-Pb deposits, and the Dafulou, Huile and Kangma Sn-Zn deposits, yields weighted mean Pb-206/U-238 ages ranging from 90.3 +/- 1.8Ma to95.4 +/- 4.9 Ma. These dates are significantly younger than the Devonian ore-hosted strata, but agree well with the previously published zircon U-Pb ages of 96.6-93.9 Ma for the Longxianggai biotite granite within analytical uncertainties, showing a close temporal link between the granitic magmatism and tin mineralization.