关键词: CSAMT, 金矿体, 地球物理信息, 深部找矿, 仓上金矿, 三山岛—仓上断裂

Abstract:

There are abundant gold resources in Jiaodong area, which are mainly controlled by Sanshandao-Cangshang fault, Jiaojia fault and Zhaoping fault.Three major gold metallogenic belts were formed in the area, where several large and super-large gold deposits have been found. Jiaodong area has provided a large amount of gold reserves, and it’s an significant gold concentration area and gold industrial base in China.The main research area in this paper is Cangshang gold deposit,which located in southwest of Sanshandao-Cangshang fault that adjacent to the Bohai Bay.It is one of the large open-air gold deposit in China. Since Cangshang gold deposit closure in 2005,Shandong Gold Group,many geological exploration agencies and scientific research institutes have conducted a lot of prospecting work around the mine,but no new progress has been made in prospecting.In order to find out the spatial distribution of the fault and rock mass in the depth and periphery of the mining area,and search for deep gold resources, geophysical exploration method was used to conduct deep exploration in the area,and the conventional electrical and magnetic exploration was compared with CSAMT (Controlled Source Audio-Frequency Magnetotellurics).The conventional electric and magnetic exploration is difficult to meet the needs of exploration because the the depth of conventional electric and magnetic exploration is relatively shallow,and the results are reflected on the plane.CSAMT was choose to conduct deep profile exploration in the area.Field construction was carried out in the northern part of the mining area, and two CSAMT sounding sections were arranged along the vertical direction of the Cangshang fault,numbered L4000 and L4300. The length of L4000 section was 1 440 m,and L4300 section was 1 160 m,line distance was 300 m,point distance was 40 m and azimuth angle was 120°.The emission dipole sources AB were arranged in parallel lines in the northeast.The dipole distance of AB was 1.2 km, the receiving dipole distance of MN was 40 m,the receiving and transmitting distance was 5 km, and the detection depth was 1 km.The frequency acquisition range was 1～7 680 Hz,with a total of 40 frequency points.In order to ensure the quality of data acquisition and reduce human interference,a 21 KAV high-power generator was used for power supply.The low frequency current (1 Hz) was not less than 18 A,the high frequency current (7 680 Hz) was not less than 5 A,and the current at intermediate frequency was decreasing.Data processing and inversion were carried out by using software CMTPro and CSAMT-SW V3.0.The data processing included data preprocessing,trip point removal,near-field source correction,static correction and two-dimensional joint inversion.Finally,a map was drawn and the inversion results were compared and analyzed comprehensively with previous geophysical prospecting data and geological profile 331.The inversion results of CSAMT showed that the resistivity characteristics of strata and rock mass were basically consistent with those of conventional electrical methods, and the inferred fault F1 was consistent with Sanshandao-Cangshang fault,indicating that this method has good application effect in this area.In order to verify the low-resistance abnormal zone (F1 fault),a verification borehole was deployed at the corresponding surface location.Through the verification of drilling project,fault mud,weak sericitization granite cataclastic rocks,cataclastic granite rocks and sericitization granite cataclastic rocks were found at the depth of 776.25 ～829.70 m,corresponding to the low-resistance abnormal zone (F1 fault).Gold orebodies were found in sericitization granitic cataclastic rocks,the highest grade is 7.30×10^-6 after assay.In summary，good prospecting results are achieved while applying to the field geological exploration work，and will provide valuable geophysical information basis for further geological prospecting.

Key words: CSAMT, gold orebody, geophysical information, deep prospecting, Cangshang gold deposit, Sanshandao-Cangshang fault