康滇地轴元古代重大地质事件与拉拉IOCG矿床成矿响应

The Main Geological Events of the Kangdian Proterozoic Eon and Response from to the La-La IOCG Deposit

有关IOCG最新研究成果建议,将IOCG矿床限定于资源量大于1 Mt的大型/超大型矿床。对世界上已知的大型/超大型IOCG矿床的成矿背景和成矿作用进行分析对比,发现前寒纪大型/超大型IOCG矿床均位于前寒纪超大陆的边缘、形成于非造山期,与壳幔相互作用有关,与板底垫托、地幔柱等相关的重大地质事件关系密切。通过对康滇地轴元古代地质体岩石/矿物的同位素年龄数据分析研究,同时对拉拉IOCG矿床成矿特征及同位素测龄分析,认为扬子地台西缘康滇地轴存在早元古代早期(2 486～1 884 Ma BP)古陆壳,是Kenorland超大陆的一部分。在中元古代发育了康滇陆缘裂谷(1 725～1 466 Ma BP),与Columbia超大陆非造山期同时。新元古代的晋宁运动使该裂谷产物变质,及形成康定杂岩,成为康滇地轴的上层结晶基底(1 100～721 Ma BP)。其是Rodinia超大陆的拼贴与裂解事件的响应。拉拉矿床具有2期成矿作用。第一期火山喷发成矿期(1 712～1 680 Ma BP),是康滇裂谷事件的产物。第二期变质热液成矿期主成矿阶段(1 000～900Ma BP),是Rodinia超大陆的拼贴作用的响应。康滇地轴元代地层中具有形成IOCG矿床的巨大潜力。

Precambrian deposits are the dominant members of the IOCG group in terms of both copper and gold resources.These giant IOCG deposits are located in intracratonic settings within about 100 km of the margins of Archean or Paleoproterozoic cratons or other lithospheric boundaries.Their tectonic setting at formation was most likely anorogenic,with magmatism and associated hydrothermal activity driven by mantle underplating and/or plumes.Based on a review of isotopic dating data from the Kangdian Proterozoic rocks/minerals,three major geological events are suggested： the formation of the Kangdian basement of the Yangtze craton,2486-1884 Ma,which would be as a part of Kenorland supercontinent;the Kangdian Continental Rifting located along the west margin of Yangtz craton,1725-1466 Ma,which happened during the anorogenic period of Columbia supercontinent;metamorphism-magmatism events（1100-721 Ma） were the response to assembling and rifting of Rodinia supercontinent.The La-La IOCG deposit is hosted by the Kangdian basement of the western margin of Yangtze craton.The host rocks of the deposits are Proterozoic metamorphic rocks,Hekou Group,the protolith of which was the products of the Kangdian Rifting during 1712-1680 Ma,which contributed Stage I meneralization of the Lala IOCG deposit： Iron-P-REE.StageII（1000-900 Ma）,with chalcopyrite（I） ＋ magnetite（II） ＋ molybdenite＋purple fluorite ＋ ankerite ± pyrite ± cobaltite ± quartz ±biotite（II） ± garnet（II） ± sericite,and StageIII（~850 Ma）,with dolomite/calcite＋chalcopyrite±quartz,followed assembling of Rodinia supercontinent.