都龙锡锌多金属矿床LA-MC-ICPMS锡石U-Pb测年及其意义

云南都龙锡锌多金属矿床是我国最大的锡石硫化物矿床之一。缺乏精确可靠的成矿年代学判据,是该矿床成因认识存在较大分歧的重要原因之一,严重制约了地质勘探工作的深入。本文应用LA-MC-ICP-MS微区原位U-Pb同位素测年技术,对都龙矿区曼家寨矿段的锡石样品进行了研究,获得DL12-716、DL12-722、DL12-740等三件样品的206Pb/207Pb-238U/207Pb等时线年龄分别为89.2±4.1Ma(N=22,MSWD=4.5)、88.0±1.6Ma(N=24,MSWD=2.3)和87.2±3.9Ma(N=31,MSWD=14),207Pb/206Pb-238U/206Pb谐和年龄分别为96.6±3.5Ma(MSWD=8.1)、93.6±1.6Ma(MSWD=5.8)和82.0±2.5Ma(MSWD=11)。结合矿床地质特征和前人成岩-成矿年代学成果,表明都龙矿区锡成矿作用主要发生在晚白垩纪,与燕山晚期岩浆热液活动关系密切,结合地质事实,表明燕山晚期岩浆热液活动是老君山矿集区锡钨多金属成矿的关键。通过区域地质及年代学对比,表明滇东南地区晚白垩世存在大规模花岗岩成岩-锡成矿事件。

In-situ LA-MC-ICP-MS cassiterite U-Pb dating of Dulong Sn-Zn polymetallic deposit and its significance

The Dulong Sn-Zn polymetallic deposit, Yunnan Province, is one of the largest cassiterite-sulfide deposits in China. Being lack of the accurate and reliable geochronological data, the genesis of this deposit is controversial greatly, so that it is very serious to restrict the further development of the geological prospecting. This paper has reported the U-Pb isotope dating of cassiterite by the method of in-situ LA-MC-ICP-MS from the Manjiazhai section of the Dulong ore-field. The result showed that the ²⁰⁶Pb/²⁰⁷Pb-²³⁸U/²⁰⁷Pb isochron ages of cassiterite samples DL12-716, DL12-722 and DL12-740 were 89.2±4.1Ma (N=22, MSWD=4.5), 88.0±1.6Ma (N=24, MSWD=2.3) and 87.2±3.9Ma (N=31, MSWD=14) respectively, and the ²⁰⁷Pb/²⁰⁶Pb-²³⁸U/²⁰⁶Pb concordia ages of the corresponding cassiterite samples were 96.6±3.5Ma (MSWD=8.1), 93.6±1.6Ma (MSWD=5.8) and 82.0±2.5Ma (MSWD=11) separately. Combining with geology and previous petrogenetic-minerlization geochronology, indicated that the tin minealization of this deposit might mainly be in the Late Cretaceous, which related closely to the later Yanshanian magmatic hydrothermal events. Meanwhile, the basis of the geological facts revealed that the later Yanshanian magmatic hydrothermal events were the key factor of the W-Sn polymetallic deposit mineralization in the Laojunshan area. Moreover, regional geology and geochronology further suggested that there were Late Cretaceous larger-scale granitic magmatism and relative tin mineralization events in the southeastern Yunnan.