河南舞阳经山寺铁矿床C-O-Si同位素成矿物质来源示踪  

Carbon, oxygen and silicon isotope composition tracing for the ore-forming material source of the Jingshansi iron deposit in Wuyang, Henan Province

作　　者：刘清泉 黄自力 张智慧 李国平 谢克家 

机构地区：[1]河南省有色金属地质勘查总院,河南郑州450052 [2]河南省有色金属矿产探测工程技术研究中心,河南郑州450016 [3]河南省有色金属地质矿产局第四地质大队,河南郑州450016

出　　处：《中国地质》2015年第6期1919-1930,共12页Geology in China

基　　金：中国地质调查局河南省舞阳新蔡铁矿整装勘查区关键基础地质研究(12120114035101);河南省国土资源地质矿产科技攻关项目(2010-61-4);国土资源公益性行业科研专项(20111107-2)联合资助

摘　　要：河南经山寺铁矿位于华北板块南缘,矿体形态为似层状、透镜状,铁建造以条带状铁矿石为主,含有少量的块状矿石,其顶底板围岩及矿体夹层主要为太华群铁山庙组大理岩。为探讨矿床成矿物质来源,对铁矿床进行碳、氧、硅同位素特征进行分析和研究,研究结果表明,矿化样品方解石的碳、氧同位素组成为δ13CV-PDB=-5.2‰^-1.4‰,δ18OV-SMOW=8.5‰~16.9‰,围岩大理岩样品方解石的碳、氧同位素组成为δ13CV-PDB=-1.0‰~1.6‰,δ18OV-SMOW=20.3‰~23.4‰,说明在成矿流体与围岩发生了水-岩反应,且流体与围岩发生了同位素交换,碳同位素组成主要由海相沉积碳酸盐岩经溶解作用提供的,且受中低温蚀变作用的影响,δ18OH2O组成值变化范围较大,指示热液体系可能为岩浆水和海水的混合热液。石英辉石磁铁矿矿石中石英的硅同位素组成为δ30SiNBS-28=-1.9‰^-0.4‰,围岩浅粒岩中硅同位素组成为δ30SiNBS-28=0‰,表明条带状铁建造中硅质来源于火山喷气作用,在变质成矿作用过程中硅同位素发生了动力学分馏作用,条带状铁建造中硅质沉淀造成δ30Si显示负值,综合分析认为,经山寺铁矿应属前寒武纪海底火山-沉积环境中热水化学沉积产物。The Jingshansi iron deposit in Henan Province is located in the southeastern part of the North China Craton. The orebodies occur in nearly bedded and lenticular forms, and the iron ores are predominantly banded, with minor massive ones. Taihua Group Tieshanmiao Formation marbles are developed as main wall rocks and interlayers among the orebodies. Geochemical studies of carbon, oxygen and silicon isotopes of the ore deposit were carried out to investigate the ore-forming fluid nature and its potential sources. The results show that δ^13V- PDBvalues of ore-forming calcite range from-5.2‰ to-1.4‰, δ^18V- SMOWvalues range from8.5‰ to 16.9‰, δ^13V-PDBvalues of carbonate host rocks calcite range from-1.0‰ to 1.6‰, and δ^18V-SMOWvalues range from 20.3‰to 23.4‰, the C and O isotope evolution indicates that drastic water-rock interaction took place at the ore-forming stage, and isotope exchange took place between ore-forming fluids and carbonate host rocks. The carbon isotope components were mainly provided by the marine carbonate rocks through dissolution, influenced by middle-low temperature alteration. The characteristics ofδ^18H hydrothermal solution is the mixture of magmatic water and seawater. The 2Oindicate that theδ^30iNBS- 28 values of iron ore quartz range from-1.9‰ to-0.4‰, and the δ^30i value of leptite quartz is 0‰, which indicates that the silicon isotope were derived from volcanic exhalation. The Si isotope fractionation took place in the ore-forming process. A comprehensive analysis shows that the Jingshansi iron deposit was formed in a submarine volcanic eruptions-sedimentary environment in Precambrian.

关 键 词：条带状铁建造 碳同位素 氧同位素 硅同位素 经山寺铁矿 

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