The Au-Bearing Mineralogy Of Dachang Gold Deposit In Qinghai Province And Its Significances

Dachang gold deposit located in Maduo County,Qinghai Province tectonicly in the northern Bayankala orogenic belts.It is a giant gold deposit discovered in Qinghai recent years.The main ore-bearing stratum is Changmahe formation segment of early Triassic,the main lithology are sandstone with interleies of slate and phyllite.The main structure is Gande-Maduo regional deep fault.The ore bodies controlled by structure relatively strong,the morphology mainly are veins,lenses or veins-like.Quartz veins and altered rock are the mainly ore types.Main sulphide in the ores are pyrite,arsenopyrite,which are also major gold-bearing minerals.In this paper,we put main gold-bearing mineral pyrite and arsenopyrite as the research object,using X-ray diffraction phase analysis,microscopic identification under microscope,scanning electron microscopy,electron microprobe analysis and the whole rock analysis,and so on,in order to understanding the gold occurrenceObserved under the microscope,ore structure are fragmentation structure,variable mud structure,brecciated structure,blastopsammitic structure,micro lepidoblastic structure,plate-like structure,massive structure,veinlets disseminated structure,phyllitic structure and so on.The Au content is low in the main hosted rocks but high in significantly.The Au element has a strong correlation with As,Ag,Sb and other element.In particular with As.X-ray diffraction phase analysis showed that the main gangue minerals are quartz feldspar and clay minerals,and secondly also contains dolomite,siderite and other minerals are arsenopyrite and pyrite.Magnetite,galena,chalcopyrite,ilmenite and other minerals in ore have to been awalys by scanning electron microscopy of spectroscopy to observe the interaction with other minerals.Test pyrite and arsenopyrite by electron probe,zonal pyrite core and annulus elements were different significantly,in which the core part is characterized by low As high S,the opposite edge zone different.The EPMA element distribution maps showed that both the coarse-grained euhedral pyrite arsenopyrite,pyrite and fine-grained euhedral pyrite,brightness Au elements are low,showed blurring edgeThe gold in Dachang gold deposit mainly exists by the form of "invisible gold".including natural nanoscale gold particles and solid solution.Due to isomorphous substitution the S of pyrite and arsenopyrite,crystal texture has been changed,making the ability of accommodate gold enhanced,It is the main mechanism for the enrichment of mine.