The role of structural reactivation for gold mineralization in northeastern Hunan Province, South China

Gold ore deposits in northeastern Hunan Province are hosted within E-W- to ESE-WNW-trending fracture zones in Neoproterozoic meta-sediments of the Jiangnan Orogen. These rocks have been subjected to multiple tectonic deformations, and the nature of structural control on gold mineralization remains poorly understood. It is unclear when the ore-controlling structures were initially formed and why they are favorable for early Cretaceous gold mineralization. We present a systematic structural analysis to establish a structural evolution model and analyze the structural conditions favorable for gold mineralization. Five deformation events (D1 to D5) were identified based on crosscutting and/or overprinting relationships of structural elements. It is established that ore-hosting structures were initially formed during early Paleozoic (D2), and gold mineralization took place during early Cretaceous (late D4). The reactivation of D2 structures during the late D4 tectonic event, when the stress regime transformed from compression to tension, is critical for gold mineralization. It created a structural network linking mineralizing fluids to structural-chemical traps in Neoproterozoic rocks, where fluid-rock reactions and fluid mixing resulted in gold mineralization. This case study provides a typical example of how structural reactivation played a critical role in mineralization, and emphasizes the significance of structural analysis for mineral exploration.