Electrical Resistivity Structure and Ore-Controlling Factors in the Heyuanbei Area, Xiangshan Region, China: Implications for Polymetallic Mineralization

Abstract:The Heyuanbei area, located in the western part of the Xiangshan region of China,is a promising area for deep exploration of polymetallic deposits.However, there is still a lack of sufficient understanding and reliable constraints regarding the spatial distribution of deep ore-controlling factors and the favorable zones for deep polymetallic mineralization.Therefore, identifying the spatial distribution of these deep ore-controlling factors is essential for advancing breakthroughs in deep exploration efforts.This study employs an 8-km-long audio-magnetotelluric (AMT) profile.After segmenting the data and applying impedance tensor rotations using the phase tensor analysis, a nonlinear conjugate gradient method was used for 2D inversion considering topographic effects. As a result, a refined electrical structure model of the study area was developed.Based on regional geology, drilling, and gravity and magnetic data, the following conclusions were drawn:(1)The red basin in the study area shows a two-layer electrical structure, with a low-resistivity red layer overlying a high-resistivity metamorphic basement. The volcanic basin, on the other hand, shows a three-layer electrical structure, consisting of a high-resistivity Ehuling Formation, a medium-low resistivity Daguding Formation volcanic layer, and a high-resistivity metamorphic basement.(2)The main ore-controlling faults in the Heyuanbei area are the He-Xiao faults and Ku-Xiao faults. The composite variation zones between these faults and the interfaces of the volcanic rock formation and the upper boundary of the metamorphic basement provide favorable spaces for the mineralizing hydrothermal fluids, controlling the deposition of polymetallic ores. The thickening of volcanic rocks at depth represents a promising segment for future breakthroughs in polymetallic exploration.(3)In the early stages of the western Xiangshan region, polymetallic-rich hydrothermal fluids mixed with downward-seeping atmospheric precipitation at depth, resulting in metasomatic exchange and precipitation, which formed polymetallic mineralization.Under continued extensional and tectonic stretching, later mineralizing hydrothermal fluids ascended, migrated along deep faults, and underwent differentiation and evolution, ultimately resulting in a vertically distributed polymetallic mineralization pattern.Key words:Heyuanbei area；Audio frequency magnetotelluric sounding；Electrical structure；Ore-controlling factors；Acknowledgments: This research was supported by Phase I of the Northwest Region Magnetotelluric Subnetwork(2024ZD1000201),the China Geological Survey for Regional Geophysical Survey in Beishan and Adjacent Areas (Grant No. DD20230254),the National Natural Science Foundation of China(42130811,41864004,41674077)