川南攀西地区茅坪石墨矿地球化学特征及成矿时代

    Geochemical Characteristics and MetallogenicAge of the Maoping Graphite Deposit in the Panxi Area, Southern Sichuan

    • 摘要: 这是一篇地球科学领域的论文。茅坪石墨矿是近年新发现的超大型晶质石墨矿床,位于上扬子古陆西缘的康滇断隆带中北段,成矿物质来源及其成矿时代研究较为薄弱。矿体赋存于中元古界天宝山组浅变质岩中,本文主要开展了矿石主量、微量及稀土元素地球化学特征研究。结果表明含矿岩层原岩为副变质岩,一套含碳质石英粉砂岩,沉积于缺氧环境。微量元素特征指示矿体原岩由近海陆源碎屑物沉积形成,矿石稀土含量(ΣREE)平均为158 g/t,δ Ce值平均为0.63,呈弱负异常,δ Eu值平均为0.69,呈负异常,具滨海潮坪相沉积特征。石墨矿体δ13C值为-28.35‰~-29.08‰,平均为-28.59‰,表明成矿碳质主要为有机碳。昔街角闪二长闪长岩锆石的LA-MC-ICP-MS 锆石U-Pb 年龄为(823.4±3.6) Ma,晚于天宝山组火山岩形成时代(954 Ma),代表了石墨矿受叠加变质时间。综上,该矿床成因类型为沉积-变质型,其变质作用可能包括晋宁期区域动力变质作用并叠加了接触变质。

       

      Abstract: This is an article in the field of earth sciences. The newly discovered Maoping graphite deposit is a super-large crystalline graphite deposit that is located in the middle-northern section of the Kang-Dian fault-uplift belt on the western margin of the Upper Yangtze paleo-continent, and the research on the source of mineralization and its mineralization age is relatively weak. The orebodies occur in the epimetamorphic rocks of Mesoproterozoic Tianbaoshan Formation. In this paper, the geochemical characteristics of major ores, trace amounts and rare earth elements were mainly studied. The results show that the original rock of the ore-bearing rock layer is parametamorphic rock, a set of carbonaceous quartz-bearing siltstone, which is deposited in an oxygen-deficient environment. The characteristics of trace elements indicate that the original rock of the ore body is formed by the deposition of offshore terrigenous clasts. The ores show sedimentary characteristics of coastal tidal flat facies, with an average ΣREE of 158 g/t, average δ Ce value of 0.63 (weak negative anomaly), and an average δ Eu value of 0.69 (negative abnormaly). The graphite ore body has a δ13C value of -28.35‰~-29.08‰, with an average of -28.59‰, indicating that the mineralized carbon is dominated by organic carbon. The LA-MC-ICP-MS Zircon U-Pb of amphibole zircon from Xijie hornblende diorite Zircon is (823.4±3.6) Ma, which is later than the formation era of volcanic rocks of the Tianbaoshan Formation (954 Ma), representing the time of superposition metamorphism of graphite. In summary,the genetic type of the ore deposit is sedimentary- metamorphism and its metamorphism may include the regional dynamic metamorphism of Jinning period that is superimposed by contact metamorphism.

       

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