青海省格尔木市妥拉海河超大型石墨矿床地球化学特征及其成因探讨

Geochemical Characteristics and Genesis of Tuolahaihe Super-Large Graphite Deposit in Golmud, Qinghai Province

妥拉海河石墨矿床是在青海省发现的首个超大型大鳞片晶质石墨矿。该矿床位于柴达木盆地南缘、东昆仑中段,矿体呈层状、似层状赋存于下元古界金水口岩群下岩组的片麻岩、钙质片麻岩、石英片岩和大理岩中,属于典型的片麻岩型石墨矿床。为探讨其矿床成因,本文对含矿地层开展了详细的岩相学、全岩地球化学和同位素地球化学研究。研究结果表明:含矿的石墨片麻岩、石墨石英片岩稀土元素总量为82.95×10^(-6)~154.86×10^(-6),轻稀土富集,具有明显的Eu负异常和Ce弱负异常,显示了原岩形成于大陆边缘浅海缺氧沉积环境。赋矿的变质岩原岩为富含有机质的砂质岩、杂砂岩和钙硅酸盐岩,物质来源主要是陆源碎屑,少量为浅海的碳酸盐岩。矿石中石墨片麻岩和大理岩的δ^(13)C同位素组成指示石墨的碳质来源于生物有机碳,而大理岩的碳质来源为无机碳。妥拉海河石墨矿床是形成于古元古代的区域变质型矿床。

Tuolahaihe graphite deposit is the first super-large scale crystalline graphite deposit discovered in Qinghai Province,which is located in the southern margin of Qaidam basin and the middle part of East Kunlun.The ore bodies appear in bedded and near bedded within gneiss,calcareous gneiss,quartz schist and marble of the Lower Proterozoic Jinshuikou Group,which belong to a typical gneiss graphite deposit.In order to discuss ore genesis,detailed petrography,whole-rock geochemistry and isotope geochemistry studies have been carried out on the ore-bearing strata.The results show thatΣREE in graphite gneiss and graphite quartz schist containing graphite is 82.95×10^(-6)-154.86×10^(-6),enriched in light rare earth elements,with obvious Eu negative anomaly and weak Ce negative anomaly,showing the protoliths formed in anoxic depositional environment of the shallow sea at the continental margin.The protoliths of ore-hosting metamorphic rocks are organic-rich sandy rocks,greywacke and calcium silicate rocks,and the material sources are mainly terrigenous debris and a small amount of them are shallow marine carbonate rocks.Theδ^(13)C isotopic composition of graphite gneiss and marble indicating that the carbon in graphite comes from bioorganic carbon,while and carbon of marble is inorganic carbon.Tuolahaihe graphite deposit is a regional metamorphic graphite deposit that formed in Paleoproterozoic.