辽河群富铁表壳岩系磁铁矿微量元素组成对古元古代铁矿成因的制约——以周家地区为例  

Trace element geochemistry of the magnetite from the iron-rich supracrustal rocks of the Liaohe Group:Constraints on the genesis of Paleoproterozoic iron ores,a case study from the Zhoujia area

作　　者：王伟[1] 李勇[2] 樊金虎[2] 马双 贾督 WANG Wei;LI Yong;FAN JinHu;MA Shuang;JIA Du(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;The Fifth Geological Brigade Co.Ltd of the Liaoning Province,Dashiqiao 115110,China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]辽宁省第五地质大队有限责任公司,大石桥115110

出　　处：《岩石学报》2024年第10期3103-3113,共11页Acta Petrologica Sinica

基　　金：国家重点研发计划项目(2022YFC2903502);国家自然科学基金委重点支持项目(92062214)联合资助

摘　　要：铁矿石是工业发展不可缺少的矿产资源,多数铁矿石赋存于前寒武纪条带状铁建造(BIF)中。古元古代是苏必利尔型BIF形成的重要时期,但它们在华北克拉通并不发育。在胶-辽-吉构造带的辽河群中存在一系列形成于2.2~2.1Ga的富铁表壳岩系及具有经济价值的块状和层状铁矿石。揭示这些富铁岩石中磁铁矿的成因,并与苏必利尔型BIF进行对比,对探索华北元古宙铁矿找寻方向有重要意义。本文对辽宁周家地区辽河群中的块状和层状铁矿石、共生浸染状和脉状矿化变粒岩及弱矿化磁铁变粒岩开展的岩相学和磁铁矿微量元素研究表明,区域存在三类地球化学特征不同的磁铁矿。第一类磁铁矿来自块状矿石和浸染状矿化变粒岩,它们的Mg、Mn含量较高,Ti、V和Co含量低;第二类磁铁矿赋存于层状矿石和弱矿化磁铁变粒岩中,它们的Mg、Mn含量较低而Ti、V和Co含量稍高;第三类磁铁矿仅产出于脉状矿化变粒岩中,它们的Cr-Ni-V-Ti-Mn体系与前两类磁铁矿均不相同。元素含量及变化趋势的相似性表明,块状和层状矿石的形成分别是浸染状矿化变粒岩和弱矿化磁铁变粒岩中磁铁矿进一步生长富集的结果,而脉状矿化变粒岩中铁镁组分含量高是导致第三类磁铁矿具有最高Cr、Mn含量的主要因素。在Cr-Ni、Ti-Ni/Cr和V-Ti图解中,本文研究的磁铁矿多数具有低温热液成因的元素地球化学特征。弱矿化磁铁变粒岩中磁铁矿的Ti和Ni含量具负相关性,表明它们经历了由高温到低温条件的变化过程。虽然都是变质-热液作用的产物,但本文研究的辽河群三类磁铁矿与西澳古元古代Hamersley苏必利尔型BIF中的磁铁矿在元素组成上存在明显差异,表明它们的形成条件在温度、氧逸度和体系成分等方面与典型苏必利尔型BIF中的磁铁矿不同。Iron ore is a kind of indispensable mineral resources for industrial development,and most iron ores occurred within the Precambrian Banded Iron Formation(BIF).The Paleoproterozoic was an important period for the formation of Superior type BIFs,however,this type BIFs are rare in the North China Craton.There are iron-rich supracrustal sequences with economically valuable massive and layered iron ores developed in the 2.2~2.1Ga Liaohe Group,which is extending along the Jiao-Liao-Ji belt.Studies on the genesis of the magnetite from the Liaohe iron-rich supracrustal sequences will provide new clues for the prospecting of Proterozoic iron deposits in the North China Craton.In this paper,studies on petrography and trace element geochemistry of the magnetite from the massive and layered iron ores,the infected and vein mineralized fine-grained gneiss and the weakly mineralized magnetite fine-grained gneiss exposed in the Zhoujia area were carried out to reveal their genesis,from which three types of magnetite are recognized in the regional supracrustal sequences.The first type magnetite came from the massive iron ore and infected mineralized fine-grained gneiss,which exhibited relatively higher Mg and Mn and lower Ti,V and Co contents.The second type magnetite is derived from the layered iron ore and weakly mineralized magnetite fine-grained gneiss.Contrast to the first type,they show lower Mg and Mn and higher Ti,V and Co contents.The third type magnetite is only from the vein mineralized fine-grained gneiss with Cr-Ni-V-Ti-Mn systematics unrelated to the other magnetite types.The similarities of trace element contents and their varying trends indicated that the formation of massive and layered iron ore is attributed to the continuous growth and enrichment of the magnetite from the infected mineralized and magnetite fine-grained gneiss,respectively.On the Cr-Ni,Ti-Ni/Cr and V-Ti diagrams,most of the studied magnetites are characterized by hydrothermal fluid originated geochemical affinities.Negative correlations between

关 键 词：磁铁矿 地球化学 古元古代 BIF 辽河群 

分 类 号：P578.46[天文地球—矿物学] P618.31[天文地球—地质学]