LA-ICP-MS Zircon U-Pb Isotopic Dating of Lamprophyre Located Zhuxi Copper-Tungsten Mine of Jiangxi Province and Its Geological Significance
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摘要:
江西朱溪超大型矽卡岩铜钨矿的重大找矿突破，确定了“南钨北铜”格局被打破，建立了“南钨北扩”的新格局，成矿相关岩浆岩的时代及构造属性的研究是分析“南钨北扩”科学问题的关键。朱溪铜钨矿区分布数条煌斑岩脉，在时空上与铜钨矿床有关。本文在详细野外调查、岩心编录和岩矿鉴定的基础上，利用激光剥蚀-电感耦合等离子体质谱技术（LA-ICP-MS）对朱溪铜钨矿区的煌斑岩进行锆石U-Pb法同位素精确测年，获得两组岩浆锆石年龄：其中一组锆石的206Pb/238U加权平均年龄为（856 ± 10）Ma（MSWD=0.22），另一组锆石的206Pb/238U加权平均年龄为（160.3 ± 2.1）Ma（MSWD=0.17）。分析研究认为：第一组年龄（856±10）Ma代表了新元古代早期华南古洋壳俯冲消减及杨子陆块与华夏陆块碰撞的岩浆作用；第二组年龄（160.3 ± 2.1）Ma代表了晚侏罗世早期岩浆侵位事件，是在早侏罗世古太平洋板块向欧亚板块之下俯冲消减的背景下，导致早期岩石发生重熔，在燕山期侵位成岩，与朱溪所在的塔前—赋春成矿带内的成矿作用时间接近。本工作对煌斑岩同位素年代学的研究，为研究朱溪铜钨矿的成矿作用提供了理论依据。
Abstract:Accompanied by the crucial breakthrough of prospecting for skarn-type Cu-W deposit in Zhuxi of Jiangxi Province, the previously established model of ore distribution was incorrect in that the W and Cu deposits distribution was in the south and north regions respectively. A new model is presented, indicating that the south W deposit might occur in the north region. To verify the new hypothesis, the crystallizing ages and tectonic attributes of ore-related igneous rocks become a critical issue. Furthermore, there are several lamprophyre veins in the study area that might have some temporal and spatial relationships to the Cu-W deposit. Consequently, after extensive field surveying, core logging recording and thin section observation, the veins were dated accurately by zircon U-Pb isotopic method of LA-ICP-MS. Two groups of 206Pb/238U weighted ages of crystallization were yielded, one being (856 ± 10) Ma (MSWD=0.22), and the other is (160.3 ± 2.1) Ma (MSWD=0.17). Considering overall proofs, it is suggested here that the former group of age might represents a magmatism event during the period of subduction for South China ancient oceanic crust in early Neoproterozoic and of collision between the Yangtze and the Cathaysia continental blocks, while the latter one might indicate a magma intrusion event in the early period of Late Jurassic, which produced re-melting of previous rocks triggered by subduction from the Pacific to the Eura-asia plates in Early Jurassic, in accordance with the metallogenic age of the Taqian-Fuchun metallogenic belt in Zhuxi area. The lamprophyre geochronological study in the paper provides a sound theory basis for the metallogenesis of Zhuxi Cu-W deposits.
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Key words:
- Zhuxi of Jiangxi Province /
- copper-tungsten mine /
- Lamprophyre /
- zircon U-Pb dating
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