四川同德石墨矿床地球化学特征及原岩恢复

Geochemical characteristics and protolith recovery of Tongde graphite deposit,Sichuan Province

四川同德石墨矿床发现较早,矿床规模已达大型,但对其岩石地球化学和变质岩原岩恢复等方面的研究相对匮乏。本文通过对该矿床的全岩地球化学和碳同位素分析,探讨其地球化学特征和成岩成矿环境。分析结果表明,矿石SiO_(2)为55.65%~61.68%,SiO_(2)/Al_(2)O_(3)比值为4.59~5.42,Ni/Co平均比值8.73,富集Ba、Rb、Sr等大离子亲石元素,Nb、Zr、Hf、Th、U等高场强含量高。矿石ΣREE为149×10^(-6)~195×10^(-6),轻稀土较为富集,具有弱的Ce负异常和Eu负异常,代表了极度贫氧—厌氧的海相沉积环境,矿石的原岩主要来源于陆源碎屑物质。稳定同位素结果显示石墨矿中碳同位素δ^(13)C_(V-PDB)值为-25.0‰~-23.5‰,表明其成矿碳质来源于有机物。综合野外地质调查认识和全岩地球化学原岩恢复结果,推测同德石墨矿床含矿片岩的原岩为一套含碳质黏土质杂砂岩沉积建造。

The Tongde graphite deposit in Sichuan Province was discovered earlier and has reached a large scale.However,the studies on its rock geochemistry and proto-rock restoration of metamorphic rocks are relatively scarce.In this paper,the geochemical characteristics and diagenetic and metallogenic environment of the deposit are discussed through the analysis of whole rock geochemistry and carbon isotope.The analysis results show that SiO_(2)ranges from 55.65%to 61.68%,the ratio of SiO_(2)/Al_(2)O_(3)ranges from 4.59 to 5.42,and the average ratio of Ni/Co is 8.73.The ore is enriched with large ionic lithophile elements such as Ba,Rb and Sr,and has high field strength contents such as Nb,Zr,Hf,Th and U.TheΣREE of the ore is 149×10^(-6)~195×10^(-6),and the light rare earth is relatively enriched with weak Ce and Eu negative anomalies,which represents an extremely oxygen-poor and anaerobic Marine sedimentary environment.The primary rock of the ore is mainly derived from terrigenous detritus.The stable isotope results show that theδ^(13)C_(V-PDB) values of the graphite ore are-25.0‰~-23.5‰,which indicates that the ore-forming carbon comes from organic matter.Based on the results of field geological investiga⁃tion and whole rock geochemical protolith restoration,it is inferred that the protolith of the Tongde graphite deposit is composed of a set of carbonaceous clay sandstones.