火山成因块状硫化物矿床研究进展

摘要

The VMS (Volcanogenic Massive Sulfide) deposits can be classified into four types,i.e.Kuroko-type,Cyprustype,Besshi-type and Sullivan-type,in respect to their tectonic settings and host lithology.There are commonly two major styles of footwall alteration associated with VMS deposits:footwall alteration pipes which occur immediately below the massive sulfides; and semiconformable or strata-bound footwall alteration which can be regionally extensive.As with footwall alteration,hanging-wall zone alterations vary from pipe shapes to semiconformable zones.There are two alternative sources which have been suggested for the metals in VMS deposits:leaching from the ore-bearing volcanic rocks and related basement rocks by heated seawater above a magmatic intrusion or a volcanic magma chamber; and direct input of a magmatic volatile phase from the magma chamber.The fluids involved are derived dominantly from seawater penetrating downward through the basement rocks.Fluid inclusion and stable isotope studies suggest that abundant magmatic fluid component may have been incorporated into the circulating fluid system.VMS deposits are characterized by well developed metal zonation patterns defined by a typical sequence from Fe to Fe-Cu to Cu-Pb-Zn to Pb-Zn-Ba in an upward and lateral sense and this zonation reflects the evolution of fluids and the growth mechanism of the massive sulfide mound with time.The four-stage model with the change of the fluid temperature through time can interpret the classic massive sulfide mound-type deposit well.%火山成因块状硫化物(VMS)矿床可形成于太古宙至现代各个地质时期.现代海底热液成矿作用是赋存于海相火山岩系中的古代VMS矿床成矿作用的再现.VMS矿床可形成于多种构造环境,但均与拉张背景有关.按照构造环境和容矿岩系将VMS矿床分为黑矿型、塞浦路斯型、别子型和沙利文型.VMS矿床的热液蚀变由下盘蚀变带和上盘蚀变带两个结构单元组成.下盘蚀变一般有两种类型:(1)不整合的蚀变岩筒,直接产在块状硫化物带的下方；(2)半整合或层控的上盘蚀变带,并可以在区域范围内展布.与下盘蚀变类似,上盘蚀变也具有蚀变岩筒和半整合的蚀变带两种类型.成矿金属主要有两种可能的来源:(1)在岩浆侵入体和浅位岩浆房之上被加热的循环海水对含矿火山岩系及下伏基底物质的淋滤；(2)深部岩浆房挥发分通过释气作用直接释放.下渗的海水是成矿流体的主要来源,同时流体包裹体和稳定同位素资料显示岩浆流体对成矿流体系统亦有较大贡献.VMS矿床具有明显的金属分带现象,其金属序列组合从下至上依次为Fe→Fe-Cu→Cu-Pb-Zn→Pb-Zn-Ba,这种金属分带的演化反应了流体的演化和块状硫化物丘的生长机制.根据成矿流体温度变化而不断演化的4阶段成矿模式可以很好的解释经典丘堆式矿床的形成过程.