扬子板块西缘同德鳞片状石墨矿地球化学特征及成因探讨

同德鳞片石墨矿床位于扬子板块西缘，拥有超过500×104 t鳞片石墨资源储量，是攀西地区石墨成矿带中最大、最具代表性的鳞片石墨矿床之一.研究表明：矿石中SiO2含量为55.65%~61.68%，SiO2/Al2O3比值4.59~5.42，Ni/Co比值6.23~12.88，富集Ba、Rb、Sr等大离子亲石元素和Nb、Zr、Hf、Th、U等高场强元素，ΣREE为149.13×10-6~195.37×10-6，具有弱的Ce负异常和Eu负异常，代表了缺氧的海相沉积环境.通过镜下片度测定与统计，石墨片径0.08~0.9 mm，主要分布于0.15~0.4 mm（大于100目），占比53%，属于中-大鳞片石墨.碳同位素δ13CV-PDB值介于-25.0‰~-23.5‰，表明碳质来源于有机物.碳质经过沉积并通过区域变质作用形成石墨后，岩浆岩的侵入带来的热量将使石墨进一步富集并形成大的石墨鳞片.基于前人的研究和新取得的数据，针对同德石墨矿床提出并建立了一个三阶段成因模型，即碳源沉积、区域变质作用、后期岩浆-热液改造作用.

GEOCHEMISTRY AND GENESIS OF TONGDE FLAKE GRAPHITE DEPOSIT IN THE WESTERN MARGIN OF YANGTZE PLATE

Tongde flake graphite deposit, located in the western margin of Yangtze Plate with over 500×104 t reserves, is one of the largest and most representative flake graphite deposits in the graphite metallogenic belt of Panxi area. The study shows that the SiO2 content in ores is 55.65%-61.68%, with the SiO2/Al2O3 ratio of 4.59-5.42, the Ni/Co ratio of 6.23-12.88, characterized by enrichment of LILEs (Ba, Rb and Sr) and HFSEs (Nb, Zr, Hf, Th and U), ΣREE of 149.13×10-6-195.37×10-6, and weak negative Ce and Eu anomalies, indicating an anoxic marine sedimentary environment. The microscopic size measurement of graphite shows the flake diameter is 0.08-0.9 mm, mainly ranged in 0.15-0.4 mm, averagely counting for 53%, belonging to the medium-large flake graphite. The δ13CV-PDB of carbon isotopes is -25.0‰ to -23.5‰, indicating that the carbon is derived from organic matter. After the carbon is deposited and formed into graphite by regional metamorphism, the heat from the intrusion of magmatic rocks would contribute to the further enrichment of graphite and then form large graphite flakes. Based on previous studies and newly available data, a three-stage genetic model of Tongde graphite deposit is proposed, including carbon source deposition, regional metamorphism and late magmatic-hydrothermal transformation.