滇西南与花岗岩有关的锡矿床时空分布与成矿作用

滇西锡矿带与全球著名的东南亚锡矿带具有相似的成矿地质背景,其成矿规律与资源潜力一直是研究热点。本文在前人已有研究的基础上,探讨了滇西南锡矿时空分布规律与成矿作用。滇西南锡矿主要分布在腾冲地体、保山地体与昌宁-孟连造山带。已有的年代学数据显示腾冲地体发育三期锡成矿事件,分别为125～120Ma,75～68 Ma,52～47 Ma。本文在保山地体识别出晚新生代(约32～24 Ma)和晚白垩世(约75 Ma)两期锡成矿作用,进一步厘定了昌宁-孟连造山带东部三叠纪临沧花岗岩体中锡成矿时代为三叠纪(约235～220 Ma)。提出滇西南与三叠纪花岗岩有关的锡成矿作用发生于古特提斯洋闭合后碰撞环境,与早白垩世花岗岩有关的锡矿形成于中特提斯洋闭合后碰撞环境,与晚白垩世—古近纪花岗岩有关的锡成矿作用与新特提斯洋俯冲和板片回撤有关,而保山地体晚新生代锡矿则可能与新生代隐伏的新生代花岗岩有关,其侵位可能与走滑断裂活动诱发的软流圈上涌和地壳熔融有关。滇西南含锡花岗岩多为复式花岗岩体中晚阶段的高分异花岗岩(如二云母花岗岩或白云母花岗岩)。保山地体三叠纪花岗岩中的锡矿成矿时代显著晚于赋矿围岩,应注重加强成矿期花岗...

Temporal and spatial distribution of granite- associated tin deposits and ore- forming process in southwest Yunnan, China

Southwest Yunnan in China experienced geological evolution similar to the world- famous Southeast Asian tin belt, so the potential of tin mineralization has always been a research hotspot. Based on previous research, this study investigates the temporal and spatial distribution patterns and ore- forming processes of Sn deposits in southwest Yunnan. The tin deposits in southwest Yunnan are mainly distributed in the Tengchong terrane, Baoshan terrane, and Changning- Menglian orogenic belt. Literature geochronological data show that three periods of tin mineralization occurred in the Tengchong terrane, i.e., 125~120 Ma, 75~68 Ma, and 52~47 Ma, respectively. Our recent geochronological data identify two periods of tin mineralization in the Baoshan terrane, including Late Cenozoic (about 32~24 Ma) and Late Cretaceous (~75 Ma), and Triassic (about 235~220 Ma) tin mineralization in the Changning- Menglian orogenic belt. We propose that the Triassic tin mineralization is related to the collision after the closure of the Paleo- Tethys Ocean, the Early Cretaceous tin mineralization is related to the collision after the closure of the Meso- Tethys Ocean, the Late Cretaceous to Paleogene tin mineralization is related to the subduction of the Neo- Tethys Ocean and the subsequent slab rollback, and the Late Cenozoic tin mineralization is related to strike- slip fault activity. Generally, the tin deposits in southwest Yunnan are closely related to the late phase of the composite granite pluton, including fine- grained biotite granite, two- mica granite, or muscovite granite, which are highly differentiated and have low magmatic oxidation states. These characteristics are also shown in the Southeast Asian tin belt. Our research shows that the tin mineralization is significantly later than the emplacement of the ore- bearing Triassic granites in the Baoshan terrane and highlights the need for increased exploration and evaluation of the Late Cretaceous and Cenozoic granites and associated Sn deposits.