四川省中坝晶质石墨矿床地球化学特征及成因分析

四川省中坝晶质石墨矿床位于康滇地轴中段西缘,是我国重要的晶质石墨矿床之一。通过野外地质特征调查和矿物特征梳理,结合含石墨变质岩系的地球化学特征分析可知,中坝石墨矿床主要赋存在前震旦纪会理群大田组变质岩层中。矿体呈层状、似层状和透镜状产出,主要含矿岩石为白云母石英片岩。矿石平均固定碳含量12.19%;石墨矿物多呈鳞片状,其中大鳞片石墨(>0.15 mm,或>100目)占67%,中小鳞片石墨(<0.15 mm,或<100目)占33%;含石墨变质岩系中的SiO₂含量很高,CaO和烧失量含量一般,微量元素分析表明中高场强元素变化范围较小,Ni/Co值为15.92 ~41.04 ,显示出极度贫氧-厌氧环境。∑REE含量偏高,REE的分异程度高,轻稀土较重稀土富集,Eu和Ce负异常明显。石墨的δ¹³C值分布范围为-27.64%~-28.44%之间,平均为-28.14%,表明石墨为有机碳成因。 综合推测中坝晶质石墨矿床为有机成因的区域变质型晶质石墨矿床。

Geochemical Features and Genesis Analysis of the Zhongba Scaly Graphite Deposit in Sichuan Province

The Zhongba scaly graphite deposit, one of the important graphite deposits in China, with a proved reserve of 15.55 million tons, located on the western margin of central Xikang-Yunnan axis. The study on the geological and geochemical features could be used to help define the genesis of the deposit. Through the field and microscopic observation combining with major and trace elements analysis,the graphite ore bodies are hosted in white mica quartz schist of Datian Formation, Huili Group in Pre-Sinian system in the form of layers and lens. The average grade is 12.19%. Big flake graphite (>0.15 mm) occupies 67% of the total graphite while the small to mediate ones occupies 33%. The graphite-bearing metamorphic rock is rich in SiO₂ with poor CaO and LOI. The high field strength elements vary little in the ore. Ni/Co value varies from 15.92 to 41.04 indicating oxygen poor or anaerobic environment. The total REE content is relatively high with high differentiation degree. Light REE content is higher than that of HREE with negative Eu and Ce value. The test results of graphite δ¹³C is from -27.64% to -28.44%, and the average is -28.14%, indicating the causes of graphite is the organic carbon. So, the Zhongba deposit is a regional metamorphic scaly graphite deposit of organic carbon origin.