西昆仑赞坎铁矿床地质特征、形成时代及高品位矿石的成因  被引量:6

Geological characteristics, formation age and high-grade ore genesis of Zankan banded iron deposit in the West Kunlun Mountains

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作  者:李智泉[1,2] 张连昌[2] 薛春纪[1] 郑梦天 朱明田[2] 董连慧[3] 冯京[3] 

机构地区:[1]地质过程与矿产资源国家重点实验室,中国地质大学地球科学与资源学院,北京100083 [2]中国科学院矿产资源研究重点实验室,中国科学院地质与地球物理研究所,北京100029 [3]新疆地质矿产勘查开发局,乌鲁木齐830000

出  处:《岩石学报》2018年第2期427-446,共20页Acta Petrologica Sinica

基  金:本文受国家自然科学基金项目(41372100)、国家“305”科技支撑计划项目(2015BAB05BOO)和新疆地矿局科研项目(XGMB2012011)联合资助.致谢感谢新疆地矿局第二地质大队石玉君、郝延海、王海军高级工程师,中国科学院地质与地球物理研究所代堰锫、李红中、王长乐、黄华等博士和黄柯、南景博硕士生的指导和帮助.感谢赵太平研究员和李厚民研究员评阅此文,并提出了宝贵的修改意见.

摘  要:新疆赞坎铁矿床位于西昆仑塔什库尔干地块西段,是近年新发现的一个大型沉积变质型磁铁矿床。赋矿岩系布伦阔勒群主要由黑云母石英片岩、斜长角闪片岩、变粒岩、硅质岩及磁铁石英岩等组成。目前探明工业矿体4条,单个矿体长度大于2.5km,矿体厚10~70m;局部见高品位铁矿段(mFe>50%),长度达900m,厚度40m左右。矿石类型主要为2种,一种为原生的条纹-条带状磁铁矿(为主);另一种为热液改造形成的块状(高品位铁矿石)及浸染状磁铁矿。矿石稀土元素配分(PAAS)表明,原生条纹-条带状铁矿石Ce和Y元素异常不明显(~1.15、~0.94),Eu具正异常(~1.69),Y/Ho平均值为25,稀土配分模式与沉积变质型铁矿相似。而受改造的矿石中,浸染状矿石具有较高的稀土总量,明显富集轻稀土,La和Ce显示正异常(~1.46、~1.17),Y显示负异常(=0.66~0.72),Eu表现为强烈的正异常(~4.37),稀土配分模式明显不同于原生条纹-条带状铁矿石。矿体围岩斜长角闪片岩(变沉积岩)中的碎屑锆石U-Pb年龄为591±1Ma,结合前人对矿区内侵入体的年代学研究(霏细斑岩,533Ma),大致反映沉积铁矿的形成时代为新元古代至早寒武世。电子探针显示,条带状磁铁矿中的TiO_2、AL_2O_3、MgO、MnO含量较低,标型组分含量与沉积变质型磁铁矿颇为接近,在磁铁矿单矿物成因图解中,条带状磁铁矿整体显示磁铁矿为沉积变质型铁矿;浸染状矿石和块状矿石的组成与典型沉积变质型铁矿的偏离反映了后期岩浆-构造热事件对条带状铁矿石的改造;上述结果显示赞坎铁矿整体属于沉积变质型铁矿(BIF)。调查发现赞坎高品位铁矿体与早寒武世侵入的霏细斑岩联系密切,高品位矿石及其围岩发育一定程度的矽卡岩化,如阳起石化、碳酸盐化和黄铁矿化。本文推测高品位铁矿石的成因可能为霏细斑岩的岩浆热液溶解并运移早期沉积变质铁矿中的含铁物质,在构The large-scale Zankan magnetite-rich Fe deposit (belt) in the Taxkorgan ancient landmasses (West Kunlun Mountains), Xinjiang, northwestern China, contains 4 proven Fe commercial ore bodies with more than 2.5km long and 10~70 meters thick. High-grade ore bodies (mFe〉50%) are 900 meters long and 40 meters thick. The deposit is hosted in the previously defined Paleoproterozoic Bulunkuole Group, a suite of sedimentary rocks experience greenshist-facies metamorphism. The Fe orebodies are interlayered with plagioclase-amphibole schist, biotite-quartz schist, granulite and siliceous rocks. Most Fe ores display metasomatic textures with banded, disseminated or massive structures. Based on geology and geochemical analyses we recognized primary ores and reformed ores. Primary ores are mostly banded. Reformed ores are massive (high-grade ore) and disseminated structures. Ce and Y elements had no clear anomaly (Ce/Ce*=0.92~1.15, Y/Y*=0.86~0.94) but positive Eu anomaly (Eu/Eu*=1.29~1.69). The REE pattern in accord with sedimentary metamorphic iron; Reformed ores are mainly disseminated ores and massive ores. Disseminated ores are enriched in REE and enriched in LREE. La and Ce have positive anomaly (La/La*=1.12~1.46, Ce/Ce*=1.03~1.17). Y has no clear anomaly but strong positive anomaly in Eu (Y/Y*=0.66~0.72, Eu/Eu*=3.16~4.37). The U-Pb analyses on the detrital zircons from plagioclase-amphibole schist (metasediments) yielded a youngest age of 591±1Ma, coupled with the previous geochronological study to the intrusions in Zankan, further suggested that the depositional age of the Zankan deposit is from 591Ma to 533Ma. Electron microprobe analysis shows the composition such as TiO2, Al2O3, MgO, MnO of magnetite is very few. Magnetite typomorphic studies indicate the Zankan deposit is attached to metamorphism sedimentary iron deposit (BIF) but influenced by the magmatic activation. The phenomenon of skarnization, antinolitization, carbonatization and pyritization in high-g

关 键 词:沉积变质铁矿 热液改造 锆石U-PB定年 西昆仑 赞坎铁矿 高品位铁矿成因 

分 类 号:P597.3[天文地球—地球化学] P618.31[天文地球—地质学]

 

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