Coupling Relationship Between Large-scale Mineralization And Major Geological Event In The Yangshan Gold Ore Belt,Gansu Province

Yangshan gold ore belt is situated in the Kangma segment of the Mianlue tectonic belt which belongs to the southern margin of the Western Qinling orogenic belt.Sandwiched among the Bikou block,Qinling microplate and Songpan-Ganzi orogenic belt,it is one of the most important Au-Sb metallogenic belts in West China.Due to the opening and closing of the Mianlue ocean,this region experienced complicated multi-stage orogenesis,including Paleozoic-Early Triassic plate breaking up?D₁-C₁?and subduction?C₂-T₁?,Middle to Late Triassic oblique shear and collision between North China and Yangtze Cratons,Late Triassic to Early-Middle Yanshanian transient extension after the collision and Late Yanshanian to Cenozoic intracontinental orogeny?after J₂?.As the most representative deposit in the metallogenic belt,Yangshan gold deposit is famous for its large scale of gold resources,complex geological features and special deposit type.The deposit is the integrative product of multi-stage deformations and metamorphisms and magmatic events in different geological environments,which mainly occurred during transient extension after regional collisional orogenesis?210¹90Ma?and intracontinental orogenesis?144¹26Ma?.There exists a complicatedcoupling relationship between regional important geological events and metallogenesis.The Devonian thick clastic sedimentary formation and Precambrian basement-derived magma provided material source for the mineralization.The first stage mineralization is closely associated with the regional nappe and ductile,ductile-brittle shear metamorphism and deformation events,which occurred during the collision-extension orogenic stage after the plate suturing.It formed a large number of ore bodies.They are widely distributed and are featured by middle-low grade,uneven scale,complex occurrence and micro-disseminated gold.The second stage mineralization has close relationship with the regional brittle tectonic activities and concealed magmatic activities during the intracontinental orogeny.It formed a relatively small number of quartz-sulfide vein orebodies.Limitedly distributed,they have steady occurrence and are characterized by tailing-out and dilation and high grade?grain gold is commonly visible?.The enrichment regularity of gold mineralization in Yangshan deposit is the epitome of the metallogenic regularity of the whole metallogenic belt.The orebodies are controlled by the integration of nappe structure,ductile?-brittle?shear structure and special lithologic combination and are characterized by piecewise enrichment,clustering occurrence,lithology boundary restraining and superimposition.The two-stage mineralization not only superimposed to form large-scale and high-grade ore bodies,but also formed relatively independent ore bodies in independently favorable space.Metallogenic model has been established in light of the study of the coupling relationship between mineralization and geological events.Based on metallogenic regularity and comprehensive information analysis,14 metallogenic prediction areas are determined in the Yangshan gold belt.According to resource potential evaluation,more than ten prospecting targets have been proposed,indicating the great prospecting potential in Yangshan gold ore belt.