Three-dimensional audio-frequency magnetotelluric imaging of Zhuxi copper-tungsten polymetallic deposits, South China

Abstract

The Zhuxi copper-tungsten polymetallic deposit is a typically skarn-type deposit and the largest tungsten ore to date in the world, located in the northeastern of the Jiangnan Orogenic Belt. Previous exploration activity has revealed that tungsten ore is typically formed in the contacting zone between the Carboniferous limestone in Neoproterozoic formation and the Mesozoic granitic intrusions and shown as low resistivity. This characteristic strongly requires a three-dimensional resistivity model to locate the metal mineralization zones for next exploration. We here present the results from an irregular audio-frequency magenetotelluric array consisted of 47 sites deployed around Zhuxi area. Only 37 sites with quality data were used to invert the 3-D resistivity distribution by the latest parallel ModEM system. There are three main low resistivity anomalies related to metal mineralization in our imaged area: 1) the northeast anomaly is the expression of the Zhuxi copper-tungsten polymetallic deposit proved by recent drilling program; 2) the southeast anomaly may be an indicative of metal mineralization with the metallogenic structure very similar to Zhuxi deposit, where the Carboniferous limestone discretely distributes in Neoproterozoic formation that has been considered the best wall rocks to form tungsten ore deposit as long as the Mesozoic granitic magmas touched; 3) the southwest anomaly distributes along the Zhuxi-Taqian Fault with large extension and could be linked to copper dominated deposit. We suggest that the next drilling demonstration can be conducted to the southeast and southwest anomalies.