扬子地块西南缘中生代大面积低温成矿年代学和动力学

Both large-scale Mesozoic W-Sn Mineralization in Nanling Range and large-area epithermal mineralization in southwestern Yangtze Massif are relatively unique throughout the world. In recent years, the metallogenic timing and its dynamics background of Mesozoic W-Sn mineralization in the Nangling Range have been well-constrained. However, due to the lack of minerals suitable for those conventional radiometric dating methods, the metallogenic epoch of epithermal deposits in this region is poorly constrained, which seriously hampered the understandings for dynamic model of large-area epithermal mineralization. A few clues reveal that, there probably exist some associations on their formation timing and dynamic mechanism between large-area epithermal mineralization in southwestern Yangtze Massif and large-scale W-Sn mineralization in Nanling Range..In this research program, we take some important deposits in large-scale epithermal domain as the studying objectives; utilize some radiometric dating methods newly developed in recent years, and carry out systematic researches on the geochronology and dynamics of these epithermal deposits. We attempt to precisely determine mineralization timing and epoch of these epithermal deposits, and reveal the intrinsic connections between epithermal mineralization in this region and major geological events in South China, and try to demonstrate the possible correlations between large-area epithermal mineralization in southwestern Yangtze Massif and large-scale W-Sn mineralization in Nanling Range. Achievements attained in this program will enrich the theory of large-area epithermal mineralization, and expand the theoretical system between continental dynamics and metallogeny, and provide some important guidance for regional prospecting in South China.

华南南岭地区中生代与花岗岩有关的钨锡大规模成矿和扬子地块西南缘中生代金、锑、铅、锌等大面积低温成矿在全球均很具特色。南岭钨锡矿的成矿时代和动力学背景已得到较好确定,但由于低温矿床中缺少适合传统放射性同位素定年的矿物，其年代学研究十分薄弱。这制约了对大面积低温成矿动力学模型的合理总结。已有少量线索表明，扬子地块西南缘大面积低温成矿与其东侧南岭钨锡成矿带的大规模成矿在时代和动力学机制上可能具某种联系。本项目拟以大面积低温成矿域的主要矿床为对象，选择近年发展起来的被认为可精确确定低温矿床成矿时代的方法，深入开展低温成矿年代学和动力学研究，以精确确定大面积低温成矿的时代和期次，揭示各期次低温成矿作用与主要地质事件的内在联系，论证扬子地块西南缘大面积低温成矿与南岭钨锡大规模成矿可能存在的关系。研究成果对丰富大面积低温成矿理论、充实大陆动力学与成矿关系的理论体系、指导区域找矿勘查工作均具有重要意义。

大面积低温成矿是全球很具特色的重要成矿事件。扬子地块西南缘50 万km2的广大范围内，金、锑、汞、砷、铅、锌等低温热液矿床广泛发育，构成华南低温成矿域。虽然以往对其研究取得重大进展，但因低温矿床矿物颗粒细且常缺适合定年的矿物，给矿床成因和年代学研究带来巨大难度。因此，大面积低温成矿究竟与什么地质事件有关，以往远未形成清晰认识。得益于一些适合定年的微细矿物的发现和微区原位分析技术的进步，本项目在成矿年代学、成矿流体成因、成矿动力学等方面取得重要进展。研究发现，大面积低温成矿发生在200-230Ma和140-160Ma；印支地块与华南陆块在印支期的碰撞后伸展作用，驱动盆地流体循环并浸取地层中的铅、锌以及岩浆—雨水混合流体循环并浸取地层中的金、锑、汞、砷，形成了低温成矿域的主体格架(200-230Ma) ；右江、湘中矿集区的深部可能存在与花岗岩有关的W-Sn矿化。研究成果发展了大面积低温成矿理论，对指导找矿勘查具有重要意义。