岩浆-热液系统中铁的富集机制探讨  

Enrichment mechanism of iron in magmatic-hydrothermal system

作　　者：张招崇[1] 侯通[1] 李厚民[2] 李建威[1] 张作衡[2] 宋谢炎[3] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]中国地质科学院矿产资源研究所,北京100037 [3]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550002

出　　处：《岩石学报》2014年第5期1189-1204,共16页Acta Petrologica Sinica

基　　金：国家“973”计划项目(2012CB416800);国家自然科学基金项目(40925006);国土资源部公益性行业科研专项(200911007-25)联合资助

摘　　要：与岩浆-热液系统有关的铁矿类型有岩浆型钒钛磁铁矿床、玢岩铁矿、矽卡岩型铁矿和海相火山岩型铁矿,与这些铁矿有关的岩浆岩从基性-超基性、中性到中酸性岩均有,其中岩浆型钒钛磁铁矿床与基性-超基性深成侵入岩有关,形成于岩浆阶段,主要与分离结晶作用有关,但是厚大的富铁矿石的形成则可归结于原始的富铁钛苦橄质岩浆、分离结晶作用、多期次的岩浆补充以及流动分异等联合过程。钒钛磁铁矿石产于岩体下部还是上部与母岩浆的氧逸度有关:高的氧逸度导致磁铁矿早期结晶而使得其堆积于岩体的下部,相反,低氧逸度则导致低品位的浸染状矿石产于岩体的上部。虽然野外一些证据表明,元古宙斜长岩中的磷铁矿石可能是不混溶作用形成的,但是目前尚无实验证据。某些玢岩铁矿的一些磷灰石-磁铁矿石可能与闪长质岩浆同化混染了地壳中的磷导致的不混溶作用有关。除此之外,其他各类与岩浆作用有关的铁矿床均与岩浆后期的岩浆-热液作用有关。这些不同类型铁矿床的蚀变和矿化过程具有相似性,反映了它们形成过程具有相似的物理化学条件。成矿实验以及流体包裹体研究表明,岩浆-流体转换过程中出溶流体的数量以及成分受多种因素控制,其中岩浆分离结晶作用以及碳酸盐地层和膏盐层的混染可导致出溶的流体中Cl浓度的升高。早期高氧逸度环境可以使得硫以SO42-形式存在,抑制硫与铁的结合形成黄铁矿,有利于铁在早期以Cl的络合物发生迁移。大型富铁矿的形成需要一个长期稳定的流体对流循环系统,而岩浆的多期侵位或岩浆房以及在相对封闭的环境中(需要一个不透水层)一个有利于流体循环的断裂/裂隙系统是形成一个长期稳定的流体对流循环系统的必要条件。但是由于不同地质环境,流体中铁的卸载方式和位置会有明显差别,由此�The magmatic-hydrothermal system-related iron deposits include magmatic V-Ti magnetite deposits, apatite-magnetite deposits, iron skarn deposits and submarine volcanic-hosted iron deposits. The ore-related igneous rocks have a wide spectrum, ranging from basic-ultrabasic, intermediate to intermediate-felsie rocks. The magmatic V-Ti magnetite deposit are associated with basic- ultrabasic plutonic intrusions. These deposits are formed during the magma evolution, particularly fractional crystallization. We proposed that the thick stratiform Fe-Ti magnetite ore layers can be attributed to intergration of Ti-rich ferropicritic magma, fractional crystallization, frequent magma replenishment coupling with the sorting of magma flowing. However, whether the V-Ti magnetite ores ccur in the lower or upper part of the layering intrusion depends on the intitialfo2 of the parent magmas. The elevatedfo2 could lead to an early crystallization phase of magnetites, accumulating at the base of the magma chamber, whereas low-grade disseminated ores occur at the upper part due to low oxygen fugacity. Although field observations support the genesis of immiscible apatite-magnetite magmas for the Proterozoic anorthositc complex, there are no such experiments for this viewpoint so far as now. Some apatite-magnetite deposits may be linked to immiscibhty, which could be caused by addition of crustal P by contamination. Except for the above iron deposits, other magmatism-related iron deposits are formed by post-magma-hydrothermal processes. These iron deposits exhibit similar alteration and mineralization patterns, reflecting the similar physico-chemical conditions. The previous studies on experiments and fluid inclusions show that the amounts and compositions of exsolution of fluids from melt are controlled by many factors during the magma- fluid transition. The frational crystallization and assimilations of carbonate rocks and evaporites could lead to elevated C1 concentration of exsoluted fluids. In an oxidized fluid, more of the sulphur

关 键 词：岩浆演化 不混溶 热液 流体出溶 铁的富集 

分 类 号：P611.11[天文地球—矿床学] P618.31[天文地球—地质学]