Research On Speed Characteristics Of Jinchuan Mining Area Based On Ambient Noise Tomography

As an important resource for national development,metal minerals have always played an important role.The Jinchuan copper-nickel sulfide deposit has the third largest nickel resource in the world.Since the deposit was mined,many experts and scholars at home and abroad have studied it.Many geophysical methods have been applied to the mining of the deposit,and great progress has been made.At the same time,the combination of geophysical methods,geochemistry and geological data to study underground deposits reduces the ambiguity of geophysics.In recent years,with the continuous exploitation of mineral resources,it is urgent to conduct research on deep concealed deposits to maintain stable development.The research on the mining area is currently mainly concentrated in the shallow part of the underground,usually about 500-1000 m,while the research on the deep structure of the mining area is rarely carried out.Based on the the predecessors' geological understanding of the Jinchuan mining area and its surrounding areas and the application of geophysical methods to the mining area,we give a new understanding from the perspective of ambient noise tomography.From mid-July 2019 to mid-August 2019,with the Jinchuan mining area as the center,65 short-period intensive stations were deployed,and a one-month measurement was carried out,through data preprocessing and direct inversion of surface wave dispersion based on ray tracing.The three-dimensional shear wave velocity structure at the depth of 5.4 km underground in the Jinchuan mining area and the surrounding area is obtained.We got the following knowledge:(1)The velocity distribution in the Jinchuan mining area and its surroundings shows that the Jinchuan copper-nickel sulfide deposit is characterized by relatively high velocity in the shallow part of the underground,and low velocity in the deep part.Differentiation leads to the separation of magma components,which is the main reason for the difference in formation rate.(2)Compared with the surrounding underground medium,the Jinchuan mining area exhibits an obvious low-velocity anomaly in the deep underground.It is speculated that this may be the residual low-velocity material after the upwelling of magma,which can be used as a basis for deep prospecting.(3)As a large regional fault,the F1 fault does cause the difference in speed on both sides of the fault,which is mainly reflected in the deep part of the ground,but it is not obvious in the shallow part of the Jinchuan mining area.The depth profile results show that the boundary between the low-velocity body and the high-speed body in the shallow underground on the south side of the F1 fault is higher than the boundary line on the north side of the fault,indicating that the F1 fault has undergone strong thrusting nappe during the tectonic evolution process,leading to the Jinchuan rock The body is further uplifted,and deep prospecting should be carried out around the hanging wall of the fracture.Compared with the surrounding media,the F1 fault has a significantly lower velocity.It is speculated that the F1 fault is a channel for magma upwelling in the later stage of mineralization.This study reveals the underground structure of the Jinchuan mining area and its surroundings,which provides a basis for later prospecting.