A metallogenic model for the supergiant gold system in Jiaodong province:Constraints from crustal velocity structure

We investigate the role of crustal architectures playing in controlling the genesis and nature of supergiant Jiaodong orogenic gold system via seismic imaging.We deployed an NWW-SEE-trending broadband seismic linear array traversing the province to construct a shear wave velocity(V_S)transect based on ambient noise tomography.Our crustal V_S transect reveals a prominent low velocity zone(LVZ)at 12–20 km depths across the whole province and high V_S anomalies at 8–12 km depths underneath the western part that hosts most of the ore tonnage.We interpret the former as a hydrothermal alteration zone related to mineralization and the latter as a crustal component containing large amounts of mafic rocks(e.g.,amphibolites).In addition,a listric fault system and a strike-slip fault system are imaged in the western and eastern parts of the province,respectively.Combining features of crustal velocities with regional geological observations that ores are tempo-spatially associated with mafic dikes,we propose a model of gold metallogenic processes.In this model,ponding and degassing of the mafic magmas led to the formation of a hydrothermal alteration LVZ in the middle crust prior to mineralization.Later,auriferous fluid was released from this intra-crustal hydrothermal alteration zone as it was heated by upwelling asthenosphere.The ore fluid ascending along the listric fault system possibly leached extra gold from the upper-crustal amphibolites.Then,the gold-rich fluid migrated up along different fault systems,leading to the disseminated-veinlet mineralization with great gold endowment in the western listric fault system and the quartz-vein type mineralization with relatively small ore tonnage in the eastern strike-slip fault system.

Synchronous structure control of superlarge ore deposits

The control of synchronous structures on formation of superlarge stratabound ore deposits is immense. Based on studies of ore deposits in South Qinling, northern Guangdong, Langshan and other areas, three new ideas in comparison with examples of ore control of synchronous structures both in China and abroad are proposed: (i) multi order ore control of synchronous structures, which means that synchronous structures of different orders display different controls on ore deposits; (ii) synchronous structures in different stages of basin evolution display different controls on basin fluid system and ore forming system; (iii) synchronous structure accompanying hydrothermal mineralization as a preexisting weak surface in earth crust often reactivate in later tectono thermal event to be a channelway for magma or thermal fluids which superimposed on and reformed preexisting ore beds to form large or superlarge composite ore deposits.