Spatial coupling relationship between metamorphic core complex and gold deposits: Constraints from geophysical electromagnetics

Abstract

The evolution of metamorphic core complexes is closely related to gold formation. Due to the thick cover and orebodies’ lying depth, exploration regularities, and metallogenic prediction have faced challenges. Therefore, new data were obtained through controlled-source audio magnetotelluric (MT) and broadband MT methods to predict the ore-bearing properties at depth and decipher the spatial coupling relationship, respectively. The results of broadband MT surveys allow us to identify the thick cover (apparent resistivity of 3,000 Ω m), the strongly deformed metamorphic rock (apparent resistivity of 18,000 Ω m), and two low-angle detachment faults (apparent resistivity from 5,000 to 8,000 Ω m). The fault-dip value on the left side is roughly 30°, while on the other side, the values significantly change from 30° to 75°, although they are in the same structure. Moreover, the controllable source audio MT method provides more detailed examinations of the right side fault. The proved ore-bearing gold orebodies were all located in the transition zone where the inclination angle changes from steep to gentle or gentle to steep. The discovery of this mineralization pattern allows us to evaluate the mining prospecting potential and predict the deep-seated metallogenic location. Based on the geotectonic environment and the geophysical profiles, we conclude that the coeval exhumation of the metamorphic core complex with non-symmetrical northwest-southeast shear senses may have resulted from a decratonization event during the retreat of the Paleo-Pacific Plate.

Keywords

• north china craton
• metamorphic core complex
• ductile shear zone
• gold deposit
• geophysical method