Research On The Geological Characteristicsand Ore Controlling Structures Of The Daqiao Gold Deposit In Gansu Province

The Daqiao Gold Deposit is located in the taphrogenic trough of the middle of West Qinling,which isbetween the two major dislocations:Minxian-Dangchang-Liangdang and Zhouqu-Chengxian-Huixian.The gold orebodies exist in the lower lithologic section?Ta-1?of the lower part of Triassic system,andits main lithology is silicified breccia.The ore bodies are in stratiform,stratoid,lenticular and saddle shaped.The ore minerals are pyrite,marcasite and arsenopyrite,the main gangue mineral is quartz,and the major wall rock alterations are silicification,pyritization and ferritization.On the basic research of regional and mining geologic characteristics,this paper focused on major and trace elements,macro-and micro-structure of the Daqiao Gold Deposit rocks?ores?,and achieved following 5 main creative results:?1?Combining the analysis of geology feature,major and trace elements of silicified breccias,we suggested that its distribution was determined by NE-directional faults.The fracture was the migration channel of ore-forming hydrothermal fluid.Silicified breccia had obvious characteristics of siliceous cementation.Magmatic hydrothermal fluids provided SiO₂,and silicified breccia was formed from broken breccia by silicification cementation.?2?Major and trace elements characteristics of the rocks?ores?indicated that stratum was the main source of gold and had the characteristics of gold enrichment.At the same time,there was material exchange between surrounding rock and magma,which provided SiO₂ and etc.?3?The Daqiao Gold Deposit was strictly controlled by structure,while fault was ore-passing structure and the decollement area of the fold was ore-hosting structure.Folds could be divided into two periods.The first period was the formation of regional anticline folds,whose core was Carboniferous limestones,and secondary folds in axial NE direction.The second stage was the recumbent fold caused by bending.Among them,the fold of second period was mainly ore-hosting structure.?4?The main stress of the Daqiao Gold Deposit was NE-SW compressive stress,and intraregional structures experienced tectonic deformation from ductile to ductile-brittle to brittle.?5?The Daqiao Gold Deposit was part of sedimentary-reformation type.Stratigraphic gold was the major source of ore-forming materials of the deposit.Before Permian,the terrigenous clastics formed by weathering and denudation made initial enrichment of gold.Triassic orogeny and magmatism caused the activation and migration of gold in stratum,and then it deposited in favorable position of structure to form the gold deposit.