摘要
根据地壳丰度/水圈丰度比值,金在表生条件下是一种活动性元素.原生矿或含金岩石中的金粒通常太细小,在水流搬运分选过程中不能富集成矿.砂金矿形成的一个必要前期步骤是在风化壳中,在地下水氧化-还原界面附近,通过电化学作用形成粗金粒.
Almost all gold grains occurred in gold veins or Au-rich rocks are too small to be concentratedin detrital sediments by running water sorting. In this paper the author suggests a two-stage genetic model for the origin of placer gold. At the first stage coarse gold grains were formed in theweathering zone, probably by an electrochemical process took place at the interface between theoxidizingreducing waters. In general, in the vinicity of such enviromment a sulfide body, carbonaceous rock or other electron conductor (commonlybeing gold bearing or rich in itself) duringweathering, will set up an oxidation-rc duction potential gradient and cause a natural current flowingthrough the conductor, from its lower end to the top end by passing outside medium. This currentplays an important role in migratiaon, precipitation and accumulation of the gold. Coarse gold in large quantity are thus supplied to form gold placers. At the second stage, the hypergene coarse goldwould be sorted and concentrated during denudation and transportation to form placer deposits ofgold in the same way like other heavy minerals.The validity of the above suggested genetic model of placer gold is related to the mobility ofgold under the supergenetic condition. For this reason, comparative analyses were made on gold abundance in continental crust to that in fresh water, and gold abundance in the whole earth crust tothat in ocean water. The estimated values show that the gold in a hypergene environment has alarger mobility than some other elements (such as As, Mo, Hg, Pb, Zn, Cu, etc.). They are quitedifferent from the values estimated by using Perelman's coefficient of aqueous migration. It isbelieved that the Perelmen's results is suitable only to account for the origin of coarse gold. Butthe geochcmical behaviour of gold under a hypergene condition is chiefly determined by an overwhelming majority of gold grains of very small size occurred in Au-bearing rocks or deposits.
出处
《地质与勘探》
CAS
CSCD
北大核心
1989年第2期1-6,共6页
Geology and Exploration
