The structurally‐controlled polyphase Au mineralization in the southern Youjiang Basin: Insights from magnetotelluric imaging

Abstract

The Youjiang Basin, located on the southwestern margin of the Yangtze Craton, hosts significant Upper Triassic and Lower Cretaceous gold (Au) deposits. Isotope studies suggest that the polyphase Au mineralization in the Youjiang Basin is derived from Indosinian and Yanshanian magmatic events, but the structural plumbing system beneath the basin remains poorly understood. We collected 32 magnetotelluric (MT) stations extending from the southern margin of the Youjiang Basin which hosts the Zhesang, Badu, and Jinya Au deposits at the western margin of the Jiangnan Orogenic (JNO) belt. The full impedance tensor of MT data is utilized to generate a high-precision lithospheric resistivity model by three-dimensional (3-D) inversion. Importantly, our MT data reveals several crustal conductors (<30 Ω·m) underlying major structures in the northwestern part of the study area. These crustal conductive anomalies spatially overlap with high-magnetic anomalies and polymetallic Au-Sn deposits. We interpret these anomalies as solid conductive materials such as graphite and/or sulfides related to the structurally controlled Mesozoic Au mineralization. Additionally, we interpret these conductive anomalies beneath the known Au deposits as the conduits of magmas and solidified paleo-magma chambers that were emplaced along deep-seated northwestern faults and likely documenting the genetic relationship between Au mineralization and Mesozoic magmatism. The synthesis of the electrical resistivity structure and metallogenic considerations is presented in a schematic sketch model illustrating that the deep-seated northwest-trending structures likely acted as a plumbing system controlling both the migration and emplacement of magmas and related oxidizing fluids that subsequently precipitated the polyphase Au deposits.