Caledonian ore-forming event in the Laojunshan mining district, SE Yunnan Province, China: In situ LA-MC-ICP-MS U-Pb dating on cassiterite

摘要

The Laojunshan mining district is an important part of the SE Yunnan W-Sn polymetallic mineral belt. Previous geochronologic data have shown that the main metallogenic stages in this area are Indosinian and Yanshanian in age. In this paper, we present a new dating result that differs from those published previously by using the in situ LA-MC-ICP-MS geochronologic method on a cassiterite sample from the giant Xinzhai tin deposit. Analyses of this sample yielded a U-Pb Tera Wasserburg age of 419.1 +/- 6.7 Ma. This new date identifies a Caledonian metallogenic event at the Xinzhai tin deposit and this age is also consistent with Caledonian magmatic and tectonic activity previously recognized in the Laojunshan mining district. Therefore, not only Yanshanian and Indosinian metallogenic stages but also a Caledonian mineralization event must have occurred in the study area. This new result may play an important role in ore prospecting and metallogenic study in the Laojunshan mining district and, more importantly, in all of SE Yunnan.