滇东南官房钨矿床石榴子石原位LA-SF-ICP-MS U-Pb定年及地质意义

官房矽卡岩型钨矿床位于滇东南薄竹山W多金属矿集区，大地构造上处于扬子地块、华夏地块、印支地块三大构造单元的接合部位。白钨矿呈浸染状赋存于石榴子石-辉石矽卡岩中。矽卡岩一般不直接与岩体接触，呈脉状或透镜状产于围岩中。精确的成岩成矿年龄的测定对于研究滇东南W-Sn矿床成岩成矿地质背景、矿床成因、成矿预测均具有重要意义。根据电子探针分析结果，石榴子石属钙铁榴石-钙铝榴石固溶体系列。石榴子石原位LA-SF-ICP-MS U-Pb年代学研究获得T-W图下交点年龄分别为101.3±5.4Ma（MSWD=2.0）、87.6±2.3Ma（MSWD=1.5），暗示该区可能存在早白垩世和晚白垩世两期矽卡岩成岩事件。综合研究表明，石榴子石原位U-Pb定年对于限定矽卡岩型W矿床的成矿时代是可行的。结合区域燕山晚期成岩成矿事件，认为~88Ma为该区W-Sn多金属矿主要成矿期，成矿作用与同期花岗岩密切相关；~101Ma可能为另外一期矽卡岩成岩事件，这一认识和发现对于区域找矿部署有很强的实践意义。

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 skarn-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 skarns 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 ²⁰⁶Pb/²³⁸U 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 skarn 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 skarn-type tungsten deposit. Combined with the Late Yanshanian petrogenetic and metallogenic events, we suggest that ~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. ~101Ma may be another skarn petrogenetic and metallogenic event. This new finding and understanding is of great practical significance for regional prospecting deployment.