3-D spatial distribution of concealed ore-forming granitoid intrusion and structures determined by the CSAMT survey of Wuxu Sb-Zn-polymetallic ore district, South China

Abstract

Wuxu ore district is an important lead-zinc-antimony polymetallic ore field within the Danchi metallogenic belt of South China. Although previous geochemical studies have indicated that the deposit type is medium to low-temperature magmatic-hydrothermal, the existing metallogenic models remain controversial due to the thick covering layer and lack of exposure of granitic bodies. To address this issue, this study utilised four CSAMT parallel profiles across the Wuxu anticline to perform two-dimensional inversion, yielding high-resolution subsurface resistivity models. By comparing the resistivity anomalies along the regional strike shown by the profiles and integrating geochemical and ore deposit structural analyses, a detailed geological interpretation was conducted. A significant high-resistivity body beneath the core region of the Wuxu anticline is interpreted to be the Yanshanian period granitic intrusion. There are westward- and eastward-dipping high-conductivity belts existing within the western and eastern wings and appear to sandwich the inferred high-resistivity code of the Wuxu anticline, respectively. They may represent the deep faults extending underground and are the result of decoupling of lithological interface within the anticline and thereby rock fracturing. The high-conductivity feature may be the result of filling with high-conductivity saline fluids, and possible hydrothermal alteration. The regional compression stress during the Caledonian period and the early Yanshanian period promoted the formation of the anticline and rock fracturing of both wings of the anticline. After that, the regional extension background of the late Yanshanian period made the fault zones reactivated, becoming the site and channels for magmatic intrusion, upward transporting of hydrothermal fluid and alteration, causing lead-zinc-antimony polymetallic ore formation. The exposed ore deposits above may also corroborate this view point. In summary, our resistivity model visually depicts the spatial distribution of the granitic intrusion controlling ore formation and major structures such as anticlines, fault zones, and hydrothermal alteration zones in the 3-D space, providing new geophysical constraints for solving the controversy over the metallogenic model for Wuxu ore district.