In-situ LA-SF-ICP-MS U-Pb dating of garnet from Guanfang tungsten deposit in southeastern Yunnan Province and its geological significance

The Guanfang skam-type tungsten deposit is located in the Bozhushan tungsten polymetallic ore concentration area in southeastern Yunnan. It is situated at the junction of three major tectonic units of Yangtze block, Cathaysia block and Indosinian block. Scheelite is disseminated in garnet-pyroxene skams which are generally not in direct contact with intrusive rocks and occur in vein or lenticular forms in host rocks. The accurate determination of petrogenetic and metallogenic age is of great significance for studying the petrogenetic and metallogenic geological background, genesis and metallogenic prediction of the W-Sn deposit in southeastern Yunnan. According to the results of electron microprobe analysis, the garnets are the series of andradite-almandite solid solution. In-situ LA-SF-ICP-MS U-Pb dating of the garnet from the Guanfang deposit yielded a lower intercep Pb-26/U-238 age of 101.3 +/- 5.4Ma ( MSWD = 2.0) and 87.6 +/- 2.3Ma (MSWD = 1.5) in the Tera-Wasserburg Concordia diagram, respectively, suggesting that there may be two stages skam petrogenetic events in Early Cretaceous and Late Cretaceous in this area. The comprehensive study shows that in-situ U-Pb dating of the garnet is feasible to constrain the metallogenic age of skam-type tungsten deposit. Combined with the Late Yanshanian petrogenetic and metallogenic events, we suggest that similar to 88Ma is the main ore-forming period of W-Sn polymetallic deposits in the area, and the ore-forming process is closely related to the contemporaneous granites. similar to 101Ma may be another skam petrogenetic and metallogenic event. This new finding and understanding is of great practical significance for regional prospecting deployment.