Research On Electrical Structure Of Lu-zong Volcanic Basin And Technology Of Deep Mine Prospecting

Lujiang-Zongyang volcanic basin is located in the Middle-lower Yangtze metallogenic belt of eastern China。It is a large ore-concentrated areas mainly of iron, sulfur (copper), including the main metallogenic types of porphyrite iron deposits,porphyry copper deposits and strata-bound and hydrothermal superimposed deformation type,and so on.The contents of the dissertation specifically include as follow:the first part, five magnetotelluric sounding profiles were arranged covering the volcanic basin and tectonic units in neighboring area. After the collection of field data, data processing and2D inversion, the basement structure of volcanic basin, internal structure, interface of lithology, volcanic apparatus, the spatial distribution of subvolcanic rock and syenite mass were analysised and researched combining with the geological data; the secend part, we selected the Shaxi porphyry copper deposit which is located in the northwestern margin of basin,within Tanlu fault zone as test deposit, carried out the deep prospecting experiment using the comprehensive electromagnetic method of AMT, CSAMT and TEM method.The application effects and the consistency of each method had been studied and compared, the detection ability of three method to deep porphyry copper deposits has been evaluated and the3D resistivity model of the quartz diorite porphyry body has been built.The five magnetotelluric sounding profiles(sum to500sounding points) covered the eastern margin of the Dabie orogenic belt, the Lujiang-Zongyang volcanic basin, Kongcheng red sedimentary basin, Tan-Lu fault zone and Yangtze fault depression. As the decomposition of the magnetotelluric impedance tensor show the underground electrical structure of Lujiang-Zongyang volcanic basin is approximately a two-dimensional structure, but the deep structure of basin has the three-dimensional characteristics, the electrical axis is nearly east-north direction indicating the main structure of research area is E-N direction. After the data processing (including the remote reference processing, power spectrum selecting and static shift correction) and the2D NLGG inversion of five profiles, the2D electric structure images about10km depths are obtained. The results show that the Lujiang-Zongyang volcanic basin has the characteristic of high resistivity and the thickness of ca.6km, the abnormality of low resistivity in the depths of-8km to-10km may be caused by the hydrothermal activity, fluid and water-rock interaction, the deformation bottom layer from Triassic to Sinian occurs as dense and compact masses with middle-high resistivity value. Kongcheng red sedimentary basin has the characteristic of low resistivity, the bottom layer shows the high resistivity and superimposition,dip direction is southeast, may be the result of extrusion and overthrusting.Within the depths of10km, the Yangtze fault depression can be divided into two electrical layer, top layer is the high conductivity layer, the deep layer is low conductivity layer. A Triassic thrust fault, in NW direction may be in the deep of the Yangtze fault depression. Deposit position have perfect correspondence to the deep high resistance body or fault zone.The deep high resistance body may be the subvolcanic rock and syenite,which formed by the magmatic hydrothermal fluids.The geophysical and geological model for Shaxi porphyry copper deposit was established according to the geological data and exploration profiles. In order to compare the detection ability of AMT and CSAMT in theoretically, the numerical simulations were proceeded. Based on the acquisition parameter experiment and analysis influence of selection parameter for data acquisition, the detection experiment of three method were arranged in known geological exploration profiles.The test results show that the ore body has the characteristic of high resistivity in the resistivity section of AMT,CSAMT and TEM. There are obvious differences of electric structure in different AMT resistivity section, the high resistance anomaly takes the shape of kupola or columnar, may be related to the attitude of stratum and high resistivity. The electrical structure of CSAMT profiles have better consistency, can clearly reflect the host space and ore-controlling structure. The ability of TEM to distinguish between surrounding rock and the rock mass is poor, but more sensitive to low resistance body. All the analysis shows that the AMT method can be used in the regional exploration to delineated the favorable mineralized section, then the fine detection by CSAMT method can be used.At last, based on the AMT data, using3D block Kriging interpolation method to constructed a3D interpolation of the resistivity value in the depth of-1000m, finally a3D resistivity model had been constructed to display the distribution and the shape of deep quartz diorite porphyry, which provides a reference for ore prospecting of Shaxi porphyry copper deposit and its surroundings.