金属矿床的卤素元素异常及其形成机理——以粤西茶洞银金矿床为例

HALOGEN ANORMALY AND ITS FORMING MECHANISM IN THE METAL ORE DEPOSITS: AS EXAMPLIFIED BY CHADONG Ag-Au DEPOSIT IN WESTERN GUANGDONG PROVINCE

金属矿床中卤素元素参与了金属元素的活化、迁移到沉淀成矿的全过程。然而 ,除F能作为萤石和云母类矿物的组成部分有时富集于矿石中外 ,Cl、Br、I很难在矿石中富集。在成矿过程中尤其在成矿的后期 ,它们能在矿体上部形成范围较广的卤素扩散晕。在茶洞矿床 ,这种上部扩散晕范围可达 2 0 0m。其中以I扩散范围最大 ,Br扩散晕在距矿体 5 0m～ 130m的范围内最明显 ,Cl扩散晕在距矿体 30m～ 110m范围内最明显。卤素元素的这种变化特点 ,一方面可用来解释成矿热液的演化过程 ,另一方面可用来作为勘查深部隐伏矿体的地球化学标志。成矿流体中卤素元素与金属元素的配合物随着成矿条件的改变而不断被破坏 ,金属元素作为硫化物等矿物的组成部分沉淀下来 ,随着热液蚀变的发生和进行 ,部分卤素元素被带入蚀变带 ,大部分仍残留在流体相 ,在成矿的后期 ,和残余热液一道 ,以排泄和渗透等方式 。

Halogen may participate in the whole processe of activation, migration and mineralization of ore\|forming metals. However, only F can be usually fixed in the ore as the component of fluoride and mica, Cl, Br and I are difficult to fix in the ore. In the post\|stage of mineralization, they may form a halogen halo in the wall rocks in the upper part of the orebody. Such the halo extends over a distance of 200m from the buried orebody to the surface in the Chadong Ag\|Au deposit. The iodine halo has the largest scope, Br halo is located over a distance of 50m to 100m and Cl halo, 30～110m away from the buried orebody. These characteristics of halogen halo can be used not only to explain the ore\|forming fluid evolution, but also to prospect buried orebody as an effective geochemical indicator. The compounds of metal with halogen in the ore\|forming fluid are decomposed owing to the variation of ore\|forming conditions. Metallic elements are deposited as the components of sulfide minerals, some halogens diffuse onto the alteration belt, but a greater part of halogen is retained in fluid. In the post\|stage mineralization, halogen elements together with the remaining fluid difused upward and then a large scope of halogen anormaly was formed in the upper wall rocks of the orebody or on the way the remaining fluid flows through.