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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 156–110 Ma, 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 CO 2 -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. [ABSTRACT FROM AUTHOR]

Abstract: The Qian''echong Mo deposit in Guangshan county, Henan Province, China, is a giant porphyry Mo deposit formed in Early Cretaceous in the Dabie Shan. Mo mineralization is associated with the Qian''echong granite porphyry, mainly presenting as numerous veinlets in the altered wallrocks, with potassic, phyllic, argillic and propylitic alteration developed. The hydrothermal ore-forming process can be divided into four stages: quartz+potassic feldspar+magnetite stage 1, quartz+molybdenite stage 2, quartz+carbonate+polymetal sulfide stage 3 and quartz+carbonate+fluorite stage 4. Fluid inclusions (FIs) can be distinguished between pure carbonic, carbonic, aqueous and solid-bearing types, but only the stage 1 quartz contains all the four types of FIs. The stage 2 quartz has three of the four types of FIs, with exception of PC-type. The stage 3 minerals are developed with the aqueous FIs with or without daughter minerals, but short of any kinds of CO2-bearing FIs. In stage 4 minerals, only the W-type FIs can be observed. The FIs in minerals of stages 1, 2 and 3 are mainly homogenized at temperatures of 260−400°C, 200−340°C and 160−300°C, with salinities of 2.00−11.58wt.% NaCl.eqv, 1.06−10.98wt.% NaCl.eqv and 0.53−9.47wt.% NaCl.eqv, respectively. The estimated minimum trapping pressures are up to 100MPa in stage 1 and to 62MPa in stage 2, respectively, corresponding to an initial mineralization depth of no less than 4km. The quartz separates from veinlets yield δ18O values of 7.1−10.2‰, corresponding to δ18OH2O values of −1.4−5.7‰, and the δDH2O values of fluid inclusions of −55−−72‰, suggesting that the ore-fluids evolved from magmatic to meteoric in sources. Therefore, the initial fluids forming the Qian''echong deposit, compared to those forming the porphyry systems in volcanic arcs, are characterized by relatively high temperature, high salinity, high fO2, CO2-rich, and NaCl-poor, considering that no halite has been observed in S-type FIs. We suggest that the “CO2-rich fluid” is a distinctive feature of porphyry systems developed in continental collision regime. [Copyright &y& Elsevier]

The Tianmugou molybdenum (Mo) deposit is a newly discovered porphyry deposit in the Dabie Shan of eastern China. The Mo-mineralization is spatially and genetically related to the Tianmushan granite batholith, and mainly occurs as thin molybdenite-bearing pegmatite dykes and numerous hydrothermal veins, with the development of potassic alteration, silicification, sericitization, propylitization, and fluoritization. The Tianmushan batholith is composed of outermost fine-grained K-feldspar granite (Phase 1), medium-grained K-feldspar granite (Phase 2), coarse-grained biotite monzogranite (Phase 3), porphyritic granite (Phase 4), and innermost fine-grained K-feldspar granite (Phase 5). Zircon crystals from the biotite monzogranite yield a weighted average 206 Pb/ 238 U age of 123.0 ± 0.8 Ma, but those from the porphyritic granite do not yield a good age because of their high contents of Th, U and Pb. Seven molybdenite samples from the ores yield individual Re–Os isotopic ages of 120.5 ± 1.7 Ma to 122.5 ± 1.9 Ma, which are slightly younger than the U–Pb age for the biotite monzogranite. These ages constrain the ore-forming magmatic-hydrothermal activity at the Tianmugou Mo deposit that took place during the post-collisional tectonism subsequent to the collision between the Yangtze and North China continents, consistent with the 142–111-Ma regional Mo mineralization event in Dabie Shan. The biotite monzogranite and porphyritic granite have high contents of SiO 2 , K 2 O and Al 2 O 3 , and low contents of TiO 2 , MgO and CaO, showing a metaluminous to peraluminous high-K calc-alkaline affinity, with significant depletion in Eu, Ba, Sr, P and Ti, and enrichment in Rb, Th, U, Nb, Ta, Hf and Y. The rocks have high initial 87 Sr/ 86 Sr ratios of 0.73546–0.89204, and negative εNd( t ) values of − 11.6 to − 11.0, with T DM2 (Nd) of 1.81–1.86 Ga. Their ( 206 Pb/ 204 Pb)t, ( 207 Pb/ 204 Pb)t and ( 208 Pb/ 204 Pb)t are 17.337–17.554, 15.450–15.465 and 37.992–38.147, respectively. The Sr-Nd-Pb isotopic signatures indicate that the causative granitic intrusions for the Tianmugou deposit mainly originated from partial melting of the Qinling Group during Early Cretaceous post-collisional tectonic extension. The Tianmugou Mo deposit belongs to a collisional- or Dabie-type porphyry Mo system. [ABSTRACT FROM AUTHOR]