Deep Electric Structure And The Distribution Of Minerals In Motianling And Its Adjacent Areas

Motianling is located in the adjacent area of Sichuan,Gansu and Shanxi provinces, lies to the northwestern margin of Yangtze block, northeast of Songpan-Ganzi tectonic belt and south of West Qinling tectonic belt. There are abundant polymetallic minerals in research area, but the main concentration of mining is in the surface or shallow ground, concealed mineral resources exploration was in a low-level. Proven reserves of mineral can no longer meet the needs of social and economic development. The main reason is that research on the deep structures and metallogenetic materials origin lack. Magnetotelluric sounding(MT) is an effective method to explore the crust-mantle electrical structure using the natural electromagnetic field as its source, and provide geophysics evidence for the origin and migration of deep material.This paper is based on the project of Longmenshan deep geological survey, use two MT profiles that across Motianling area from north Yuzhong to south Jiange and west Songpan to east Hanzhong. Remote reference and Rhoplus methods had been used to reduce noise and improve data quality. Through selecting appropriate inverse method can get deep electric structure distribution of the study area.This paper introduced the stratum, the distribution of igneous rocks, major fault, tectonic evolution and the distribution of minerals in the study area, analyzed the relationship between typical mineral age and magmatic rocks and summed up the discipline of the distribution. Then interpreted the inversion profiles of MT across Motianling. Based on the deep electric structure and combined with related geological information, obtained the relationship between deep electric structure and magmatic rocks distribution, inferred the deep origin and migration channel of magmatic rocks, analyzed the source and transport of polymetallic minerals, and provided foundation for seeking concealed minerals and prospecting perspective.Yuzhong-Jiange MT profile revealed the deep electric structure of Motianling from north to south. Motianling belt reveals the structure of high resistance in crust and low resistance in mantle. In the top of mantle exists an obvious low resistance chamber structure which is considered to be a partial melting magma chamber. Under this magma chamber is a low resistance column that connects with asthenosphere under the lithosphere and forms mantle column for migration up and gathering of magma. Both north and south ends of the magma chamber are upwarp, connect to the upper low resistance conductive channel to compose reversed strike-slip flower structure. The magma upwells along Mianlue suture zone in the north and Longmenshan tectonic belt in the south respectively. The upwelling in the north is stronger than south. Songpan-Hanzhong MT profile revealed the deep electric structure of Motianling from west to east. This profile shows that Motianling has a similar electric structure of high resistance in crust and low resistance in mantle with the previous profile. It indicates the corresponding magma chamber migration situation on east-west. Magma emplaced westward to surface near the Liujiaping and Xuebaoding.There are some other new cognitions and discussions in research: through compared north part of Longmenshan electric structure with south part, it can be indicated that heterogeneity existed in the different horizontal parts of Longmenshan. The central zone of west Qinling has a low resistance belt that connects crust to mantle. Combined with other related research, it can be speculated that a large crust-mantle low resistance channel of magma exists in the central zone of west Qinling. This magma channel has corresponding characteristic with widespread large granites along this zone.According to the geological tectonic background and the feature of Au-polymetallic deposit, we can discover that small-scale, hypabyssal, medium-acid stocks, branchs especially dykes of Indosinian granite on top of the magma upwelling have close relationships to Au-polymetallic deposit, which are the most important promising structures and marks of prospecting, and further put forward favorable metallogenic belt for research area, provide direction for concealed exploration and further prospecting.