Imaging Baogutu granitic intrusions in Western Junggar, NW China using an audio-frequency magnetotelluric array

Bo Yang ^1* Xiaoling Meng ² Yanjun Wu ³ Longbin Yang ⁴ Yixian Xu ^1*

• ¹ Zhejiang University, Hangzhou, China
• ² Inner Mongolia Geologic Survey and Research Institute, Hohhot, China
• ³ The Surveying and Mapping Geographic Information Center of Inner Mongolia, Hohhot, China
• ⁴ Central South Geological Survey Institute of China Metallurgical Geology Bureau, Wuhan, China

Natural-source audio-frequency magnetotelluric (AMT) data is highly sensitive to conductive anomalies associated with mineralization. To image the three-dimensional mineralized zones in the Baogutu porphyry copper belt, Western Junggar, NW China, we deployed an AMT array consisting of 176 regularly distributed sites. A parallel 3D electromagnetic data inversion scheme was employed to invert this AMT dataset. Using lab-measured electrical resistivity of rock samples, we interpret the 3D resistivity model by comparing it with borehole profiles. The most pronounced conductive anomalies in the inverted model are the east-west elongate conductive zones located at the center of the array, extending to a depth of 600 m. The inverted 3D model aligns closely with the borehole results, demonstrating that the 3D inversion of a dense AMT array can provide a high-resolution and reliable model. The electrical resistivity model shows a strong correlation with the shear wave velocity model. The positive correlation between resistivity and shear wave velocity identifies the potential mineralized areas, as supported by petrophysical and drilling data, which may assist in determining future drilling targets.