辽宁弓长岭铁矿床成矿物质来源及磁铁富矿成因探讨  

Source of ore-forming material and genesis of high-grade iron ore in the Gongchangling iron deposit,Liaoning Province

作　　者：孙晓辉 汤好书 陈继宏 白鹏飞 SUN XiaoHui;TANG HaoShu;CHEN JiHong;BAI PengFei(MOE Key Laboratory of Western China's Mineral Resources and Geological Engineering,School of Earth Science and Resources,Chang'an University,Xi'an 710054,China;State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550081,China;Underground Mining Branch Company of Gongchangling Mining Company Limited of Anshan Iron and Steel Group Corporation,Liaoyang 111008,China;China ENFI Engineering Corporation,Beijing 100080,China)

机构地区：[1]长安大学地球科学与资源学院,西部矿产资源与地质工程教育部重点实验室,西安710054 [2]中国科学院地球化学研究所,矿床地球化学国家重点实验室,贵阳550081 [3]鞍钢集团矿业弓长岭有限公司井采分公司,辽阳111008 [4]中国恩菲工程技术有限公司,北京100080

出　　处：《岩石学报》2025年第1期289-303,共15页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41872085、42472109、41890833);陕西省自然科学基础研究计划项目(2022JM-152)联合资助.

摘　　要：辽宁鞍本地区是我国最大的BIF型铁矿资源基地,弓长岭铁矿床是该区最大的富铁矿床,其富铁矿成因机制备受关注。目前多认为其为热液改造条带状铁矿(贫矿)而成,但关于热液性质还存在变质热液、混合岩化热液及大气降水等不同认识。在总结前人研究成果基础上,本研究对辽宁弓长岭铁矿床二矿区条带状铁矿及富铁矿进行了系统的微量元素及Nd-Pb-S同位素分析,结果显示:条带状铁矿及富铁矿中磁铁矿的稀土配分模式一致,成矿物质来源于海水与高温热液混合。条带状铁矿中磁铁矿的ε_(Nd)(t)值变化较大(-6.9~1.5),而富铁矿中磁铁矿相应值(-7.7~-6.1)偏负且集中,指示形成富铁矿的热液流体来自地壳浅部。条带状铁矿中磁铁矿铅同位素μ值介于9.36~10.75,显示壳幔混源的特征;而富铁矿中磁铁矿的μ值(9.58~13.14)较高,指示后期壳源流体交代改造。条带状铁矿中黄铁矿的硫同位素值偏负,且分布集中(-2.08‰~-0.66‰,平均值-1.52‰),而富铁矿中黄铁矿的δ^(34)S同位素值(1.88‰~3.36‰,平均值2.39‰)明显偏重,指示富重硫同位素流体的交代作用。综合推测这种改造条带状铁矿的壳源、富重硫同位素的流体应为变质水与大气降水的混合热液流体,富铁矿为条带状铁矿在古元古代晚期经该混合热液流体改造,发生去硅存铁作用而成。The Anshan-Benxi area of the Liaoning Province is the largest BIF iron ore resource base in China.The Gongchangling deposit is the largest high-grade magnetite deposit in this area.Its genesis has been argued for a long time and is currently being considered to have relation with hydrothermal reformation.However,there are different viewpoints on the nature of hydrothermal fluids,including derived from metamorphic fluid,migmatized fluid or meteoric water.In this contribution,combined with previous studies,systematic analyses of trace element and Nd-Pb-S isotope compositions were conducted on banded(low-grade)and massive(high-grade)iron ores from the Gongchangling No.2 mining area to constrain its genesis.The features of magnetite REY patterns from banded and massive iron ores are consistent,suggesting ore-forming materials sourced from the mixture of seawater and high-temperature hydrothermal fluid.Theε_(Nd)(t)values of magnetite from massive iron ores(-7.7~-6.1)are more negative than those of banded iron ore(-6.9~1.5),indicating the hydrothermal fluid sourced from shallow crust.The lead isotopeμvalues of magnetites from banded iron ores range from 9.36 to 10.75,showing geochemical characteristics of crust-mantle material mixing.While the highμvalues of magnetites from massive iron ores(9.58~13.14)indicate reformation of crustal-derived fluid at the later stage.The sulfur isotope composition of pyrite from massive iron ores(1.88‰~3.36‰with average of 2.39‰)is heavier than that of banded iron ores(-2.08‰~-0.66‰with average of-1.52‰),suggesting metasomatism of fluid with heavy sulfur isotope.Consequently,the ore-forming fluid with heavy sulfur isotope and crustal-derived feature should be the mixture of metamorphic hydrothermal fluid and meteoric water.The massive iron ores were formed by mixing hydrothermal fluid reformation on banded iron ores in the late Paleoproterozoic,causing desilication to form high-grade iron ores.

关 键 词：弓长岭 鞍山群 条带状铁建造 磁铁富矿 Nd-Pb-S同位素 

分 类 号：P597.2[天文地球—地球化学] P611.31[天文地球—地质学] P618.31