新疆备战火山岩型铁矿床大哈拉军山组碳酸盐岩中铁矿体的发现及成因意义  

Discovery of iron orebodies in the Dahalajunshan Formation carbonate rocks in the Beizhan volcanic-hosted iron deposit,Xinjiang and its genetic significance

作　　者：潘鸿迪[1,2] 申萍 李昌昊[3,4] 冯浩轩 马华东[2] 武阳 郭新成 张建收[5] PAN HongDi;SHEN Ping;LI ChangHao;FENG HaoXuan;MA HuaDong;WU Yang;GUO XinCheng;ZHANG JianShou(School of Earth Science and Resources,Chang'an University,Xi'an 710054,China;Xinjiang Natural Resources and the Ecological Environment Research Center,Urumqi 830000,China;Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;No.11 Geological Party,Xinjiang Bureau of Geology and Mineral Resources,Changji 831100,China)

机构地区：[1]长安大学地球科学与资源学院,西安710054 [2]新疆自然资源与生态环境研究中心,乌鲁木齐830000 [3]中国科学院地质与地球物理研究所,中国科学院矿产资源研究重点实验室,北京100029 [4]中国科学院大学地球与行星科学学院,北京100049 [5]新疆地质矿产开发局第十一地质大队,昌吉831100

出　　处：《岩石学报》2022年第10期3104-3124,共21页Acta Petrologica Sinica

基　　金：国家重点研发计划项目(2018YFC0604004);中国科学院国际伙伴计划项目(132A11KYSB20190070);上海合作组织国际科技合作计划项目(2020E01043)联合资助。

摘　　要：新疆西天山备战铁矿床出露下石炭统大哈拉军山组海相火山喷发-沉积碎屑岩夹碳酸盐岩建造,前人认为矿区铁矿体赋存在中-基性火山岩中,主要为岩浆-热液成因。本文作者对矿区进行了剖面测量和钻孔岩芯编录,发现在碳酸盐岩地层中也发育有铁矿体,该矿体由纹层状、浸染状、条带状和块状矿石组成,前三种矿石组成贫矿体,呈层状分布于碳酸盐岩中;块状矿石组成富矿体,呈脉状产出于不同围岩界面及裂隙中。对矿区的碳酸盐岩进行了岩相学、地球化学和同位素分析,认为区内碳酸盐岩包括灰岩、硅质灰岩、白云岩、钙质白云岩和大理岩等,含矿岩石主要是白云岩。碳酸盐岩的碳同位素δ^(13)C_(V-PDB)值(3.0‰~5.2‰)变化小,而氧同位素δ^(18)O_(V-PDB)值(-21.7‰~-12.3‰)变化大,与成岩作用及热液活动有关;灰岩和硅质灰岩的U/Th(<0.5)、Ni/Co(2.99~7.59)和V/Cr(1.37~2.32)比值相对较低,δCe(0.85~1.02)异常不明显,硅质灰岩中含有较高的SiO_(2)(>15%)和Al_(2)O_(3)(>3%),其中还有硅质岩夹层,指示其沉积环境为受陆源碎屑混染作用影响的酸性、氧化环境。白云岩的U/Th(>0.5)、Ni/Co(6.01~-18.36)、V/Cr(2.06~5.38)比值适中,δCe(0.83~0.98)具有负异常,岩石含有硫化物和有机质,很少有陆源碎屑混染,指示白云岩沉积环境为碱性、还原环境,利于Fe^(2+)的溶解及铁胶体沉淀成矿。矿相学和矿物化学研究表明,碳酸盐岩中的纹层状和浸染状矿石的磁铁矿分别是铁胶体后期转化和黄铁矿被交代的产物,磁铁矿具有富镁低硅的特点,为沉积成因;而条带状和块状矿石中的磁铁矿是重结晶作用和热液交代及充填作用所致,磁铁矿具有富钙和铝的特点,为热液成因。因此,备战铁矿床的碳酸盐岩中发育的铁矿体为沉积成因,有后期热液成矿作用的叠加,可归为沉积-热液叠加成因。The Beizhan Fe deposit,located in the western Tianshan,Xinjiang,outcrops a series of marine volcanic-sedimentary clastic rocks with carbonate rock interlayers of the Lower Carboniferous Dahalajunshan Formation.Previous studies believe that the Fe orebodies at the deposit are hosted in volcanic rocks and dominantly of magmatic-hydrothermal genesis.In this paper,based on profile measurement and drill core logging,we found that some Fe orebodies,consisting of lamellar,disseminated,banded and massive ores,also occur in the carbonate rocks.Among them,the low-grade orebodies composed of the first three ores are distributed in carbonate rocks in layers;the high-grade orebody composed of massive ore occurs as veins in interfaces of the different country rocks and fractures.Petrographic,geochemistry,and isotope analysis results of the carbonate rocks at Beizhan show that the carbonate rocks include limestone,siliceous limestone,dolomite,calcareous dolomite,and marble,and that the dolomite is the main host rock.Carbon isotopes(δ^(13)C_(V-PDB))of carbonate rocks show a narrow range(3.0‰~5.2‰),but theirδ^(18)O_(V-PDB)values show a variable range(-21.7‰~-12.3‰)which are related to diagenesis and hydrothermal activities.The limestone and siliceous limestone have low ratios of U/Th(<0.5),Ni/Co(2.99~7.59),and V/Cr(1.37~2.32)without obviousδCe(0.85~1.02)anomalies,and the siliceous limestone with siliceous intercalation contain high SiO_(2)(>15%)and Al_(2)O_(3)(>3%)contents,indicating that they were precipitated in an acidic and oxidizing environment with terrigenous materials input.The dolomites,which contain sulfides and organic matter,have moderate U/Th(>0.5),Ni/Co(6.01~18.36)and V/Cr(2.06~5.38)ratios and negativeδCe(0.83~0.98)anomalies,indicating an alkaline and reducing environment with rare terrigenous materials input.This environment is conducive to the dissolution of Fe^(2+)and the precipitation of Fe colloids,which results in mineralization.Mineralogical and mineral chemical studies show that magnetites of lam

关 键 词：含矿白云岩 沉积环境 沉积成因铁矿 火山岩型铁矿 LA-ICP-MS 备战铁矿床 

分 类 号：P588.245[天文地球—岩石学] P618.31[天文地球—地质学]