The collision-type porphyry Mo deposits in Dabie Shan, China

Abstract

The Dabie Shan in central East China is a collisional orogenic belt suturing the North China and Yangtze blocks. It was formed by Jurassic-Early Cretaceous continental collision, following the Triassic closure of the northernmost paleo-Tethyan Ocean. In the area, at least ten porphyry Mo systems have been discovered, including two giant ones, with a total reserve of >3 Mt Mo metal. The porphyry-type Mo mineralization mainly occurred during 156–110Ma, in the post-collisional extension setting. The location of Mo deposit is controlled by NW- and NNE-trending faults, mostly in the south of the Gui-Mei Fault suturing the North China and Yangtze blocks. Mo mineralization is generally associated with the Yanshanian high-K calc-alkaline metaluminous-peraluminous granitic intrusions, with orebodies being located in the intrusions and/or host-rocks. The hydrothermal ore-forming process generally includes four stages, with the initial ore-forming fluids being featured by high temperature, high salinity and CO2-rich. Geochemical signatures indicate that the ore-causative magmatism in the Dabie Shan mainly originated from either the northern or southern Dabie complex, but mixed with the Precambrian rocks of the North China block, except for the Tianmugou porphyry system which shares more similar geological and geochemical characteristics with the porphyry Mo deposits in eastern Qinling Orogen. We also develop a scissor-style intracontinental subduction model to interpret the differences in spatial distribution, geneses, and geochemical and geological characteristics between the Mo deposits in Dabie Shan and Qinling Orogen. In our model, the basement of the North China Block southwardly underthrusted beneath the Dabie Shan, possibly along the Gui-Mei Fault; whilst the basement of the Yangtze Block northwardly underthrusted beneath the Qinling Orogen; and the inferred Minggang-Xinyang fault zone served as a dextral strike-slip fault zone in the North China Block, but acted as a sinistral transpressional fault zone within the orogenic area. Compared to the subduction- or Endako- and rift- or Climax-types of porphyry Mo deposits, the porphyry Mo deposits in the Dabie Shan are unique because of their crustal source for the magma and ore-forming materials, and as such are assigned to the Dabie- or collision-type. Hence we develop a new global tectonic model for porphyry Mo deposits of three types, showing their genetic tectonic settings.