磁铁矿危机与铜金热液成矿
Magnetite Crisis and Copper Gold Mineralization

孙卫东 ¹ 李贺 ¹ 凌明星 ² 丁兴 ² 李聪颖 ¹

文摘	磁铁矿结晶造成氧化性岩浆中的硫酸根被还原为硫酸氢根,进而将铜、金等元素以硫酸氢根络合物的形式萃取到流体相中,形成成矿热液,这一现象称之为磁铁矿危机。这一过程是斑岩型和浅成低温热液型铜金矿床成矿的关键因素之一。对于斑岩型矿床,由于成矿体系是处于封闭、半封闭环境,硫酸根的还原过程主要发生在热液中,反应过程中释放出大量的氢离子,使成矿热液的pH值降低,硫酸根氧化还原电位升高,在成矿的后期,往往出现镜铁矿蚀变,氧逸度达到磁铁矿-赤铁矿氧化还原缓冲线附近。对于浅成低温热液型矿床,硫酸根的还原主要发生在岩浆中,反应不释放氢离子,因此体系的氧逸度趋于下降且变化较小。岩体的成矿潜力主要受控于初始铜金含量,而铜金含量则主要受控于氧逸度和源区岩石的性质。年轻的俯冲洋壳发生部分熔融,形成具有高初始铜金含量的氧化性岩浆,是形成斑岩型铜金矿床最重要的地质过程。高硫型浅成低温热液型矿床深部有斑岩型铜金矿床的几率较大。
其他语种文摘	Magnetite crisis refers to the abrupt decrease of Cu,Au contents in convergent magin magmas induced by magnetite. The crystalization of magnetite in oxidized magmas causes sulfate reduction,forming hydrosulfide complexes that scavenge Cu and Au into hydrous phase,resulting in ore-forming fluids. This is one of the key processes that control porphyry and epithermal Cu,Au mineralizations. For porphyry deposits,the mineralization occurs in closed or semi-closed systems. Sulfate reduction occurs mainly in hydrothermal fluids,releasing large amount of H~+,lowering the pH values and thus elevates the oxidiation potential of sulfate,reaching the magnetite-hematite oxygen fugacity buffer. Consequently,there is usually speculerite alteration at the late stage of porphyry mineralizations. For epithermal deposits,sulfate reduction occurs mainly in the magmas without releasing H~+. Therefore,the oxygen fugacity tends to drop but does not change much. The initial Cu,Au contents,which are the main factors and essential to the mineralization potential of magmas,are controlled by oxygen fugacity and characteristics of source rocks. Subduction of young oceanic crust forms oxidized adakitic magmas with high initial Cu,Au contents,which are favorable for Cu,Au porphyry deposits. High sulfur epithermal deposits are more likely to be associated with porphyry Cu,Au deposits underneath.
来源	矿物岩石地球化学通报 ,2015,34(5):895-901 【核心库】
DOI	10.3969/j.issn.1007-2802.2015.05.002
关键词	板块俯冲 ; 氧逸度 ; 磁铁矿 ; 斑岩型铜金矿床 ; 浅成低温热液型矿床
地址	1. 中国科学院广州地球化学研究所, 中国科学院矿物学与成矿学重点实验室, 广州, 510640 2. 同位素地球化学国家重点实验室, 同位素地球化学国家重点实验室, 广州, 510640
语种	中文
文献类型	研究性论文
ISSN	1007-2802
学科	地质学
基金	国家自然科学基金项目
文献收藏号	CSCD:5581865