滇西松山锡矿锡石LA-SF-ICP-MS U-Pb年代学及其对区域锡成矿作用的指示

松山锡矿位于滇西临沧花岗岩基的西北侧。矿体主要赋存于临沧黑云母二长花岗岩与松山组绢云石英片岩接触带矽卡岩以及花岗岩和围岩的裂隙中。由于缺乏精确的成矿年代学数据,在一定程度上限制了对矿床成因的认识,并制约了进一步的找矿勘查工作。本文首次利用LA-SF-ICP-MS微区原位U-Pb同位素测年技术对松山锡矿床矽卡岩型和电气石石英脉型矿石中的锡石矿物开展了 U-Pb年代学研究获得2件锡石样品的~(207) Pb/~(206)Pb-~(238) U/~(206) Pb谐和年龄分别为76.6±1.5Ma和79.6±3.6Ma,说明松山锡矿锡的成矿作用主要发生在晚白垩世,与临沧花岗岩主体侵位时间(三叠纪)明显不同。结合地质特征和前人年代学研究成果本文认为该地区存在明显的晚白垩世锡的成矿事件,研究区下一步的找矿工作应围绕岩体与围岩接触带,以及岩体和围岩中的断裂展开。

LA-SF-ICP-MS U-Pb age of cassiterite at the Songshan tin deposit and its implications for regional tin mineralization, western Yunnan

The Songshan tin deposit is located in Lancangjiang tin belt in the Sanjiang Tethys metallogenic domain, which is related to Lincang granite complex. The tin orebodies occur as skarn, veins, and greisen. The ore minerals are composed of cassiterite, pyrrhotite, chalcopyrite, arsenopyrite, and pyrite. There has no available age dating published in the area, which restricts the understanding of the genesis of the deposit. The paper reports the U-Pb isotope dating of cassiterite using the method of in-situ LA-SF-ICP-MS at the Songshan tin deposit. The results show that the ²⁰⁷Pb/²⁰⁶Pb-²³⁸U/²⁰⁶Pb concordia ages of cassiterite from the skarn ore and quartz-vein ore are 76.6±1.5Ma and 79.6±3.6Ma, respectively. These ages indicate that the Sn mineralization formed in Late Cretaceous at the Songshan tin deposit, which is quite different from the age of the Lincang granite, which emplaced in the Triassic. Combined with other published age data, it concluded that the Sn mineralization in the Late Cretaceous occured in the Songshan deposit and its adjacent areas. The next exploration target should focus on the contact zone between granite and wall rocks, as well as the faults that occur in the granite.