Study On The Relationship Between Metallogenic Mechanism And Electrical Structure Of Porphyry Copper Deposit In Central Gangdise

The Gangdese metallogenic belt is an important metallogenic area located in the Lhasa terrane between the Indus-Yarlung Zangbo suture and the Bangonghu-Nujiang suture.There are a large number of porphyry copper deposits related to the Eurasian and Indian continental collision and compression.The metallogenic regularity of these deposits has attracted more and more attention of scholars.The magnetotelluric sounding can obtain the deep electrical structure characteristics,structural characteristics and material state.In this paper,using the magnetotelluric sounding data collected from 87 ° E-91 ° E and 29 ° N-30 ° N in the central Gangdese region,through data processing and inversion calculation,the three-dimensional electrical structure model and deep material state of this region were obtained.The relationship between the electrical structure and the metallogenic model and metallogenic regularity of the porphyry copper deposit in the central Gangdise is also discussed.Based on the three-dimensional inversion results,the main electrical characteristics of the study area are analyzed: the southern Lhasa terrane can be roughly divided into two layers,the resistivity layer of about 20 km thick and the conductivity layer of about 20-30 km thick.The resistivity cover in the upper crust may represent widely distributed gangdese granite base and volcanic clastic rock,which may be formed by the accumulation of the southern Lhasa terrane after multiple periods of magmatic activity;The conductivity of the middle and lower crust may be the result of partial melting and saline fluids.It may be the fracture and delamination of the northwardly subducting Indian plate,which caused the upwelling of the asthenosphere hot material,leading to large-scale local melting of the middle and lower crust.In addition,the lateral distribution of high-resistance bodies in the upper crust is uneven,and there is a phenomenon of being "eroded" by conductors in the middle and lower crust.There are some electrical gradient bands or high-conductivity bands,which may be fracture zones formed by the high-conductors in the middle and lower crust,and may be a manifestation of the transition from the brittle layer of the upper crust to the plastic layer of the middle crust.Based on the electrical structure model of the Lhasa-Gangdese block,it provides new deep geophysical constraints on the mineralization dynamics of the porphyry copper deposits in the region,the sites of mineral enrichment and exchange,and the material migration channels.(1)Under the porphyry copper ore concentration area,there are extensive high-conductivity layers in the middle and lower crust.Combined with other data,it is inferred that it has high water content and partial melting percentage,and it is inferred that it is a place where ore-bearing magma gathers and stores,melts,contaminates,and homogenizes.Not only that,it restricts the layer to have a lower effective viscosity and rheological strength,so the ore-bearing magma is able to migrate upward along the deep and large faults and emplace to the shallow crust.This provides constraints for mineralization power and mineral enrichment and extraction sites;(2)The large-scale porphyry copper deposits exposed on the surface are mostly connected with the high-conductivity layers of the middle and lower crust through nearly upright high-conductivity belts,which are inferred to be channels for the upward migration of magma rich in minerals and fluids.(3)To image the subducting Indian lithosphere,which is located on the southern side of the Yarlung Zangbo suture zone,which exhibits high resistance.It is because of its dehydration or tearing and rewinding that part of the lower crust of the Gangdise-Lhasa block melts,which remelts the remaining metal in the deep part of the pre-existing crust.This provides constraints for mineralization power and material sources.