HALOGEN ANORMALY AND ITS FORMING MECHANISM IN THE METAL ORE DEPOSITS: AS EXAMPLIFIED BY CHADONG Ag-Au DEPOSIT IN WESTERN GUANGDONG PROVINCE
Zhang Qian\ Shao Shuxun\ Pan Jiayong (Lab. of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002)
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.