Prolonged Mesozoic intracontinental gold mineralization in the South China Block controlled by lithosphere architecture and evolving Paleo-Pacific Plate subduction

Abstract

The diverse types of Mesozoic intracontinental gold mineralization in the South China Block (SCB) are genetically linked to prolonged oceanic plate subduction. These gold deposits, with estimated resources greater than 2000 tonnes, comprise four gold provinces: Hainan Island, Wuyi-Yunkai Belt, Jiangnan Orogen, and Youjiang Basin. In these provinces, Paleo-Pacific Plate subduction, crustal thickness and composition, structural reactivation, and fluid-wall rock reactions collectively controlled the distribution and diverse features of the Mesozoic intracontinental gold mineralization.Three stages can be identified in the metallogenic evolution of the SCB. (1) Formation of orogenic gold deposits gradually younging from the coast (Hainan) to the hinterland (Youjiang Basin and Jiangnan Orogen) related to flat-slab subduction of the Paleo-Pacific Plate and clockwise rotation of the SCB between 245 and 200 Ma. (2) Formation of intrusion-related Au-(Sb-W) deposits in the western Jiangnan Orogen in a continental extensional setting in the wake of flat-slab subduction between 210 and 195 Ma prior to the early to middle Jurassic hiatus (190–170 Ma) of high-angle subduction and stagnant slab. (3) Between 170 and 90 Ma, intermittent formation of intrusion-related gold deposits in the coastal region (∼160 Ma, ∼100 Ma) and hinterland (∼160 Ma, 140–130 Ma), and the formation of Carlin-type gold deposits in the Youjiang Basin (∼140 Ma) during episodic extension caused by slab foundering and changes in subduction angle. After 90 Ma, regional differential crustal thinning and denudation determined the extent of uplift and exposure of various types of ore deposits.In stage 1, the quartz vein-type and disseminated orogenic gold deposits hosted in Precambrian rocks, and with a subcrustal source, are related to the reactivation of crust-scale NE-trending faults. In contrast, disseminated orogenic gold deposits hosted in Phanerozoic rocks and influenced by fluid-rock reactions relate to landward propagation of a fold-thrust system. In stage 2, intrusion-related Au-(Sb-W) deposits only formed in intracontinental Precambrian rocks and were controlled mainly by shallow, brittle, and extensional NW-trending structures. Highly fractionated late-stage S-type granite (used sensu lato throughout) complexes controlled the distribution of intrusion-related gold-(polymetallic) deposits in stages 2 and 3. In stage 3, stratabound and disseminated Carlin-type gold deposits are restricted to platform facies carbonate sequences, and intrusion-related gold deposits are structurally related to the reactivation of NE-trending faults. Both are interpreted to have a magmatic-hydrothermal source.The crustal architecture of the four gold provinces exhibits marked differences in crustal thickness, contrasts in rheology, abundance of deep faults, and intensity of mantle-crust interaction. Those gold provinces in the central-southeastern SCB are the result of the reactivation of a paleo-orogen, in contrast to those hosted by deformation systems in shallow crust in the western SCB during the Mesozoic. The Carlin-type and intrusion-related gold deposits are located in regions with more mafic and felsic components, respectively, as indicated by seismic Vp/Vs ratios. However, the spatial distribution of orogenic gold deposits is poorly correlated with that of Vp/Vs ratios, suggesting a subcrustal source.