Zircon U-Pb Age and Geochemical Characteristics of Granodiorite Porphyry Veins in Yushugoushan Gold Deposit,Northern Qilian Mountain,and Its Geological Significance
Yushugoushan gold deposit is located in the western part of the north Qilian orogenic belt,it is a newly discovered medium-sized gold deposit.It belongs to post-magmatic hydrothermal gold deposit.The formation of the gold deposit is closely related to the hydrothermal alteration of the granodiorite porphyry veins.In order to confirm the intrusive age,lithogenesis and magma source characteristic of the granodiorite porphyry veins,the study of LA-ICP-MS zircon U-Pb isotopic dating,Hf isotope and whole-rock geochemical were carried out.The results show that the lithology of granodiorite porphyry veins is altered granodiorite porphyry,which intrudes into the structural fracture zone in the Yingou Group strata.The LA-ICP-MS zircon U-Pb age of granodiorite porphyrys obtained is(423.5±3.5)～(422.8±3.4)Ma,indicating that the magma emplacement age is Late Silurian.The major elements of granodiorite porphyrys are characterized by low TFe2O3(1.57%～2.43%),MgO(0.91%～1.43%)contents and A/CNK values(1.10～1.29),suggesting the granodiorite porphyrys belongs to the calcalkaline and peraluminous series rock.They are relatively enriched such as Rb,Ba,Sr and light rare earth elements,and depleted Nb,Ta and Y,Yb,it is characterized by high Sr content(289×10-6～486×10-6)and Sr/Y ratio(65.1～95.3),low content of Y(4.11×10-6～5.48×10-6)and Yb(0.38×10-6～0.49×10-6),this likely indicates adakitic granite.In-situ Hf isotope analysis of zircon shows that the εHf(t)values range from 7.50 to 11.0,and Hf two-stage model age is 0.86 Ga to 0.67 Ga,suggesting that the major rock is the product of partial melting of juvenile crust derived from the Neoproterozoic depleted mantle.Combined with the regional geological background,it is preliminarily considered that the Yushugoushan granodiorite porphyry veins is formed the post collision extension stageintracontinental extension,during the Late Silurian,strong intracontinental extension induced the partial melting of the Neoproterozoic juvenile crust in the orogenic belt,and formed adakitic magma.In the process of its continuous upwelling and evolution,the Yushugoushan granodiorite porphyry dyke were formed.
North Qilian orogenic beltLate SilurianYushugoushan gold depositadakitegranodiorite porphyryzircon U-Pb age
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