【作者】 朱志敏；

【导师】 郑荣才；

【作者基本信息】 成都理工大学 ， 矿物学、岩石学、矿床学， 2011， 博士

【摘要】 四川会理拉拉铜矿床位于扬子地台西缘康滇铜矿带中段,是四川省最大的铜矿床,也是我国西南重要的铜矿产地。该矿床赋存于古元古界河口群落凼组浅变质火山沉积岩系中,是近年来新确认的一个典型的铁氧化铜金矿床(IOCG)。本文以四川会理拉拉IOCG矿床为研究对象,结合区域地质、矿区地质和矿床地质研究,通过野外地质调查和室内分析测试,在矿化和蚀变研究基础上,应用电子探针、元素地球化学、铂族元素地球化学、锆石年代学、Re-Os同位素地球化学、硫同位素地球化学等手段,对矿区矿石、赋矿的变质火山岩、辉绿辉长岩、成矿物质来源、成矿时代等问题进行了系统研究,确定了热液成矿时代和成矿金属来源,探讨了矿床成因。通过以上研究,论文主要取得了以下认识和进展:(1)拉拉铜矿金属矿物以磁铁矿、黄铁矿和黄铜矿为主,磁铁矿的含量大于黄铁矿,黄铜矿是主要的含铜矿物,脉石矿物出现大量碳酸盐矿物、萤石和磷灰石;除Fe、Cu矿化外,还伴生有Au、Ag、REE、Mo、Co、P和F矿化,其中Au、Co、Mo矿化达中型规模;矿石具有自形-半自形-它形晶粒结构、交代残余结构、包含结构和枝状结构,矿石构造包括浸染状构造、脉状-网脉状构造和角砾状构造,与典型的热液矿床矿石组构特征一致;成矿作用包括磁铁矿-磷灰石阶段(成矿温度310-442℃)、黄铜矿-黄铁矿阶段(成矿温度200-270℃)和辉钼矿阶段;矿石中磁铁矿的Ti含量低,介于0.06～0.21%之间(平均0.128%),表明该矿床属于IOCG矿床。(2)矿区河口群落凼组赋矿的变质火山岩形成于古元古界晚期,其锆石LA-MC-ICP-MS U-Pb年龄为1667±11Ma。火山岩为一套以安山岩、玄武岩为主的中-基性岩,结合元素地球化学特征,表明其形成于大陆岛弧的弧后拉张环境。(3)矿区辉绿辉长岩的锆石U-Pb年龄为1062±31 Ma,为成矿后侵入,与成矿关系不大,仅在局部改造或破坏矿体。(4)黄铜矿的Re-Os同位素地球化学研究表明,成矿年龄为1262±19Ma,成矿金属主要来自于河口群变质火山岩,成矿的硫主要来自海水硫酸盐还原,但不排除岩浆硫的贡献。(5)总之,矿床的形成经历了以下阶段:古元古(大约1670Ma)的火山成矿作用,海底火山喷发带来了大量的成矿金属(如PGE、LREE、Cu、Au等),这些成矿物质在一定的物理化学反应下沉淀下来,预富集于河口群火山沉积岩系;中元古(大约1260Ma)的热液成矿作用,此阶段扬子与华夏板块碰撞开始,此时拉拉矿区所在的扬子西南缘为被动大陆边缘,盆地卤水沿断裂下渗淋滤河口群火山岩中的成矿金属形成氧化的富金属的热液而上升,与海水混合而沉淀黄铜矿、黄铁矿等硫化物;新元古(1000~850Ma)的变质热液改造,此阶段扬子与华夏板块碰撞完成,此时拉拉矿区所在的扬子西南缘为陆-陆碰撞造山带,构造作用将中元古形成的矿床抬升到近地表,同时,该期运动形成的变质热液可能沉淀了大量的辉钼矿,从而在矿区叠加了一起钼成矿作用。更多还原

【Abstract】 Lala copper deposit is located in the mid-west of Kangdian copper belt, tectonicly on the western margin of Yangtze Block, and is important Cu-Au producing area in South-West China. This deposit is hosted by Paleoproterozoic greenschist metamorphosed volcanic-sedimentary sequences of Luodang Formation of Hekou Group and is a typical Iron Oxide copper-gold (IOCG) deposit in China. Based on study on regional geology, mining area geology and ore deposit geology, the electron microprobe, element geochemistry (including major elements, trace elements, REEs and PGEs), LA-MC-ICP-MS U-Pb zircon geochronology and Re-Os isotope geochemistry were applied to study the nature of the host rocks, ores and intrusive rocks, the sources of ore-forming metals, and mineralization age. Finally, the ore genesis is demonstrated. In conclusion, main understandings and progresses are as following:(1) Sichuan Lala copper deposit is one of important large deposits in SW China not only for Cu but also for considerable economic Au-Mo-Co-REE-Fe. Ore minerals are mainly composed of hydrothermal magnetite, chalcopyrite and molybdenite. The wall-rock alterations include biotitization, silicification, carbonatation, albitization, potash feldspathization, apatitation, actinolitation and fluoritation. The ores have euhedral-subhedral-allotriomorphic crystalline grained texture, metasomatic relict texture, poikilitic texture, and dendritic texture, and have disseminated, banded, vein-stockwork and breccia structure. Copper is mainly in chalcopyrite, Cobalt is mainly in pyrite and marcasite, molybdenum is mainly in molybdenite and gold is mainly in chalcopyrite, pyrite and pilsenite as native or silver-bering native gold. The main mineralization stages include magnetite-apatite stage, chalcopyrite-pyrite stage and molybdenite stage. The content of Ti in magnetite is low, the content of S is low in ore with a little Pb-Zn sulfide minerals. So these evidences show that Lala copper deposit is a typical Iron Oxide-Cu-Au (IOCG) deposit.(2) A weighted mean LA-MC-ICP-MS 206Pb/207Pb age of 1667±11Ma for a tuffaceous schist unit confirms the Paleoproterozoic formation age of the host rock of Hekou group. These volcanic rocks mainly consist of andesites and basalts. Combination with element geochemistry, it suggests that these volcanic rocks were formed in continental back-arc environment.(3) The diabase-gabbro intrusions formed later than mineralization age, so these intrusive rocks show no genetic relation to Cu-Au mineralization and only modified or destroyed the orebodies locally.(4) The Re-Os isotope data of chalcopyrite yield a isochron age of 1262±19Ma as direct Cu-Au mineralization age. The high initial 187Os/188Os ratio of the chalcopyrite may suggest a crustal-dominated source with pre-enriched Re and Os. In addition, the sources of sulfur mainly derived from sulfate reduction of seawater but not exclude from magma.(5) In conclusion, the Lala deposit experienced three stages as following: the first is Paleoproterozoic (ca. 1670Ma) volcanogenic mineralization stage. In this stage, the ore-forming metals (e.g., PGE, LREE, Cu and Au) were brought about from submarine volcanic eruption and precipitated and pre-enriched in volcanic-sedimentary sequences of Luodang Formation of Hekou Group under suitable physicochemical conditions. The second is mesoproterozoic (ca. 1260Ma) hydrothermal mineralization stage and is intial stage of collision between Yangtze and Cathaysia in South China Block. In this stage, the basin brine infiltrated along with the faults and leached ore-forming metals in volcanic rocks of Hekou Group to form metal-bearing hydrothermal fluid. This fluid ascended for its higher temperature and lower density, and mixed with seawater to precipitate sulfide such as the chalcopyrite and pyrite. The third is Neoproterozoic (ca. 1000~850Ma) metamorphic hydrothermal alteration of concluding stage of collision between Yangtze and Cathaysia Block. In this stage, the orebodies were tectonicly uplifted and molybdenite might precipitate.更多还原