辽宁鞍本地区沉积变质型富铁矿的成因:Fe、Si、O、S同位素证据  

The Genesis of Gongchangling High-Grade-Iron Ores,Anshan-Benxi Area,Liaoning Province,NE China:Evidence from Fe-Si-O-S Isotopes

作　　者：李延河[1] 张增杰[1] 侯可军[1] 段超[1] 万德芳[1] 胡古月[1] 

机构地区：[1]中国地质科学院矿产资源研究所,国土资源部成矿作用与资源评价重点实验室,北京100037

出　　处：《地质学报》2014年第12期2351-2372,共22页Acta Geologica Sinica

基　　金：国家"973"项目(编号2012CB416801);国土资源部公益性行业科研专项项目(编号201111002-06;201211074)资助的成果

摘　　要：辽宁鞍本地区是我国最重要的鞍山式沉积变质型(BIF)铁矿矿集区,弓长岭铁矿是我国唯一的由鞍山式贫铁矿经后期热液改造形成的大型磁铁富矿。本文在前人工作基础上,对比研究了鞍本地区贫铁矿、富铁矿和蚀变围岩的铁、硅、氧、硫同位素组成特征和空间变化规律,结合磁铁富矿的地质特征,对成矿流体的性质、来源、成矿作用和富矿成矿机制提出了新的认识。指出鞍本地区富铁矿的成矿作用与辽东地区古元古代造山运动结束后(1.85Ga)地壳抬升引发的非造山岩浆侵入和热液活动有关,成矿溶液由大气降水演化形成,而非变质热液或混合岩化热液;成矿溶液淋滤了辽河群蒸发盐地层中富13 C碳酸盐、富34 S石膏、CH4等成矿物质,成矿溶液具偏酸性弱还原特征;铁质活化再富集是鞍本地区富铁矿形成的重要机制,成矿溶液与贫铁矿及围岩反应使铁质以Fe2+形式活化迁移。温度降低、氧逸度升高或与大气降水混合是溶液中Fe2+氧化形成磁铁矿沉淀的主要原因;在Fe2+被氧化形成磁铁矿的同时,成矿溶液中的CH4被氧化形成石墨,与磁铁矿一起沉淀下来,形成含石墨磁铁富矿;溶液中SO42-被还原形成富34S黄铁矿。Anshan-Benxi area is one of the most important banded iron formation （BIF） type iron ore clusters in China.The Gongchangling iron deposit is the only one large scale high-grade-iron ores in China,which is formed from low-grade BIFs by the alteration of later hydrothermal fluid,but its genesis is still controversial.In this paper,based on the previous studies,the new understandings on the ore-forming fluid properties and sources,mineralization,and the rich ore mineralization mechanism have been put forward,with the comparative study of the Fe,Si,O and S isotopes characteristics,spatial variations and geological characteristics of poor BIF ores,rich ores,alterated rocks and wall rocks in Anshan-Benxi area.The rich ore mineralization was associated with the hydrothermal activity caused by the crustal uplift and non orogenic magmatic intrusion after the Paleoproterozoic orogeny in Liaodong area （1.85 Ga）.The oreforming fluid was formed by the meteoric water evolution or massive meteoric water was added during itself evolution.The ore-forming fluid at first is acidic and weak reductive,which leached the carbonate rich in ^13C,the gypsum rich in ^34S and CH4from the evaporate formation of the Liaohe Group.The iron activation and re enrichment is an important mechanism of the rich iron ore genesis in Anshan-Benxi area.The reaction of ore-forming fluid with poor BIF ore and wall rocks improved the iron activation and migration.The temperature decreasing and oxygen fugacity increasing or mixture with the meteoric water,which lead the magnetite precipitation with the Fe^2＋ oxidation.While the Fe^2＋ oxidation,the CH4was also oxidized into graphite which precipitation with magnetite and formed the graphite-magnetite rich ore.And the SO4^2-was reduced and the pyrite rich in 34S has been formed.

关 键 词：弓长岭富铁矿 铁硅氧硫同位素 铁质活化再富集 辽河群蒸发盐 

分 类 号：P618.31[天文地球—矿床学] P597[天文地球—地质学]