Elemental Geochemistry and Significance of Prospecting for Yangshan Super-Large Gold Deposit, Gansu Province

The Yangshan gold deposit recently found in south Gansu province is a supper-large finegrained,disseminated type deposit in China.Four ore segments found by now in the deposit all occurred in the Devonian low grade metamorphic sandstone and limestone.The ore occurrences are structu rally controlled by the Anchanghe-Guanyinba fault zone and orebodies usually exist in the secondary shear zones and faults of the folds in the Anchanghe-Guanyinba fault zone.The orebodies in lenticular or veinlike forms are spatially related to a plagioclase granite.Pyrite and arsenopy rite are the main metallic minerals,and native gold can usually be seen in pyrite,arsenopy rite and clay minera ls as micrograined inclusions (2～3 μm).Trace elements analyses from samples from vertical and transverse sections of the deposit showst ronglyen riched Au,Hg,As,Bi and Sb in the ore and a positive correlation among the elements.This indicates that the Au,Hg,As,Bi and Sbtogether represents amajor element association for the deposit.Moreover,the analyses suggest that oreforming materials was derived from magmatic rocks and Au-Hg-As-W-Sbcan betreated as an indicator for prospecting.We argue,by the ratios of some indica to relements that the ore deposit has been only eroded to amiddle-upper level,and the denudation,fromeast to west,becomes stronger.Therefore,a much richer deposit could be seen at depth of the deposit.