还原性流体与斑岩型矿床成矿机制探讨  

An Interpretation of the Role of Reduced Fluid in Porphyry Metallogenesis

作　　者：徐文刚[1] 张德会[1] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083

出　　处：《地质学报》2012年第3期495-502,共8页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号40573033;40173021)资助的成果

摘　　要：目前已经广泛认同斑岩型Cu-Mo-Au矿床是在氧化性相对较高的含矿流体作用下形成的。但是随着研究的深入,逐渐发现了一系列具备还原性特征的斑岩型矿床,这些矿床往往不发育表征高氧逸度的原生磁铁矿和硫酸盐矿物。本文针对目前发现的与还原性I型花岗岩相关的斑岩矿床进行了综合分析,发现此类矿床的成矿流体中普遍含有CH4等还原性流体成分,并且伴生有CO2。结合相关资料分析认为还原性流体中所含有的CH4可能来自邻近的S型花岗岩的混染作用,但也不排除是经地球排气作用从地幔进入到地壳的可能性。结合典型还原性斑岩型矿床研究,给出了一个化学模型,认为CH4和SO2属于岩浆系统自生成分,在特定化学物理阶段发生反应,形成H2S和CO2,从而抑制了硫酸盐矿物的形成。反应所生成的H2S可以与Mo结合形成辉钼矿矿化,而Cu-Au由于在氧逸度较低的环境下具备更高的活性,易于富集在气相流体中,所以可以迁移到某一距斑岩系统较远的有利部位沉淀成矿,从而形成以Mo矿化为核心区,外围Cu-Au矿化的模式。It is widely accepted that porphyry type deposits form from some oxidized ore fluids.But recently,some typical ilmenite-bearing,reduced I-type granite related porphyry Cu-Mo-Au deposits with relatively reduced ore-forming fluids are found,in which primary hematite,magnetite and sulfate minerals are absent.The ore-forming fluids of these deposits always contain abundant CH4 associated with CO2.According to related research results,the CH4 is proposed to be derived from the contamination of S-type granite into I-type one,but it is also possible that CH4 comes from the degassing process of the Earth.A chemical model is set in order to interpreting the role of reduced fluids in porphyry metallogenesis.According to the model,H2S and CO2 are derived from the reaction between CH4 and SO2 both of which come from one evolved igneous system,which will cause the precipitation of the molybdenite and cogenetic calcite.While the Cu and Au will be transported by the reacted fluids under reducing conditions and deposit in some cites far away from the granite system,the process will form a cogenetic subclass porphyry Cu-Au deposits.

关 键 词：还原性流体 流体包裹体 I型花岗岩 斑岩型矿床 成矿机制 

分 类 号：P618.41[天文地球—矿床学]