Magnetotelluric signatures for deep copper exploration in North Xinjiang, China: Revealing controls of deposit type and sulfide content on geophysical responses

Abstract

Discriminating deep-seated orebodies across diverse copper deposit types remains a challenge in exploration geophysics, largely due to highly variable sulfide mineralization styles and complex host-rock settings. To address this, we conducted an integrated geological–geophysical study that combines deposit geological models with high-frequency audio magnetotelluric (AMT) surveys using the Stratagem EH4 system. Three representative copper deposits in North Xinjiang, China, were examined: the Ashele deposit (volcanogenic massive sulfide, VMS-type, high-grade massive sulfides), the Hongguleleng deposit (Manto-type, moderate-grade vein-style sulfides), and the Baogutu deposit (porphyry-type, low-grade disseminated sulfides).

Geological cross-sections and laboratory measurements of rock electrical properties were integrated to constrain two-dimensional (2D) inversions of the AMT data. The results reveal distinct resistivity signatures for three deposit types: very low resistivity anomalies (10–100 Ω·m) characterize VMS mineralization, moderate resistivity anomalies (100–300 Ω·m) correspond to Manto-type vein systems, and relatively higher yet significant resistivity anomalies (100–1000 Ω·m) are associated with disseminated porphyry mineralization. Furthermore, a series of concealed resistivity anomalies were delineated adjacent to and beneath known orebodies at all three deposits, identifying promising targets for deep exploration. Based on these findings, we propose three resistivity structural patterns: a “lens-over-feeder” geometry for VMS deposits, a “stratabound conductive slab” for Manto-type deposits, and a “conductive ring” structure for porphyry systems. This integrated geology–geophysics approach provides a practical framework for enhancing the detection and targeting of concealed copper mineralization in North Xinjiang and other similar terrains worldwide.