敦煌地块大水峡北晶质石墨矿床地球化学特征及成因意义  

Geochemical characteristics and genetic implications of the Dashuixiabei crystalline graphite deposit in the Dunhuang Block

作　　者：宋宏 汤庆艳 苏天宝 刘聪 黎卓明 鲍坚 赵吉昌 李立武 SONG Hong;TANG QingYan;SU TianBao;LIU Cong;LI ZhuoMing;BAO Jian;ZHAO JiChang;LI LiWu(School of Earth Sciences and Key Laboratory of Mineral Resources in Western China(Gansu Province),MNR Key Laboratory of Strategic Mineral Resources of the Upper Yellow River,Lanzhou University,Lanzhou 730000,China;Northwest Institute of Eco-Environment and Resources,Chinese Academy of Sciences,Lanzhou 730000,China;University of Chinese Academy of Sciences,Beijing 100049,China;National Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization,Baotou Research Institute of Rare Earths,Baotou 014030,China;Fourth Institute of Geological and Mineral Exploration of Gansu Provincial Bureau of Geology and Mineral Resources,Jiuquan 735000,China)

机构地区：[1]兰州大学地质科学与矿产资源学院,甘肃省西部矿产资源重点实验室,自然资源部黄河上游战略性矿产资源重点实验室,兰州730000 [2]中国科学院西北生态环境资源研究院,兰州730000 [3]中国科学院大学,北京100049 [4]包头稀土研究院,白云鄂博稀土资源研究与综合利用全国重点实验室,包头014030 [5]甘肃省地质矿产勘查开发局第四地质矿产勘查院,酒泉735000

出　　处：《岩石学报》2023年第9期2679-2696,共18页Acta Petrologica Sinica

基　　金：第二次青藏高原综合科学考察研究(2019QZKK0704);国家自然科学基金项目(U2244204、41872073、41472070);甘肃省重点人才项目(2023);甘肃省科技计划项目(21JR7RA498);中央高校基本科研业务费专项资金(lzujbky-2021-ct07);自然资源部黄河上游战略性矿产资源重点实验室开放课题(YSMRKF202201);甘肃省自然资源厅科技创新项目重点攻关项目(202201)联合资助.

摘　　要：大水峡北晶质石墨矿床位于阿尔金大断裂北侧的敦煌地块,是新近发现的大型晶质石墨矿床。石墨矿体主要赋存于二云石英片岩中,晶质石墨具有典型的条状或鳞片状构造。目前该矿床的研究仅限于基础地质方面,其成因尚不清楚。本文对大水峡北晶质石墨矿床开展了岩石学和地球化学的研究,结果表明,本次分析的大水峡北晶质石墨矿床样品总体呈高硅、低碱、贫钙的特点。其中,含石墨矿样品V/Cr=8.00~11.14,U/Th=0.45~1.13,指示其形成于缺氧的还原环境;而矿体围岩Ni/Co比值为1.44~17.61,指示其形成于富氧的氧化环境。所有分析样品的Eu负异常明显,δEu=0.60~1.00;∑REE含量偏高,具有轻稀土相对富集的特征。此外,二云石英片岩型晶质石墨矿石的原岩以砂质岩和杂砂岩为主,围岩二云石英片岩的原岩为页岩和粘土岩。样品除斜长角闪岩外全为副变质岩,这些副变质岩的古沉积环境为干燥气候条件下富氧的海陆交互相环境,其古水体介质主要为盐度较高的半咸水环境。石墨矿石δ13 C=-22.4‰~-22.3‰,围岩大理岩δ13 C=-6.3‰~-2.4‰,表明成矿碳质来源主要为有机碳,并混入部分无机碳。大水峡北晶质石墨样品拉曼谱峰相似,拉曼谱峰特征显示石墨的结晶程度较高,结晶温度为565℃。构造活动和热事件是研究区石墨矿床形成的重要因素,初步认为大水峡北晶质石墨矿床属于区域变质型石墨矿床。The Dashuixiabei crystalline graphite deposit is located in the Dunhuang Block to the northern part of the Altyn Fault.Graphite ore bodies mainly occur in two-mica-quartz schist with typical strip or flake graphite.At present,the study of this deposit is limited to its basic geology,however,its genesis is unclear.In this paper,we present the petrological and geochemical data of the Dashuixiabei crystalline graphite deposit to reveal its genetic nature.Geochemically,the studied samples from the graphite deposit have high silicon and low alkali and calcium contents;their V/Cr and U/Th ratios vary within the ranges of 8.00~11.14 and 0.45~1.13,respectively,indicating that they are formed in an anoxic and reducing environment.The Ni/Co ratios of the country rocks vary from 1.44 to 17.61,indicating an oxygen-rich environment.The samples show obvious negative Eu anomalies(0.60~1.00)and relative enrichment of light rare earth elements,with high contents of rare earth elements.The protoliths of the crystalline graphite-bearing two-mica quartz schist are mainly sandstones and graywackes,while the protoliths of the country rocks,including the two-mica quartz schists(from shales and claystones)and amphibolites.The samples are all para-metamorphic rocks except the amphibolites,which are formed at an oxygen-rich marine-land interaction environment under dry climate conditions,and the identified paleo salinity type of paleo-water body was brackish with relatively high salinity.Theδ13 C V-PDB values of the graphite ore samples range from-22.4‰to-22.3‰,while those of the marbles range from-6.3‰to-2.4‰.These data suggest that the ore-forming carbon is mainly originated from organic carbon,with some inorganic carbon mixed in.The Raman peaks of crystalline graphite samples are similar,showing that the crystallization degree of graphite is high,and the calculated crystallization temperature is 565℃.Tectonic activity and thermal events are important factors in the formation of this graphite deposit,and it is preliminarily c

关 键 词：大水峡北 晶质石墨 敦煌地块 碳同位素 原岩恢复 区域变质型石墨矿床 

分 类 号：P595[天文地球—地球化学] P611[天文地球—地质学] P619.252