Magmatism And Au-Cu-Fe Polymetallic Mineralization System In The Tulasu Volcanic Belt, Xinjiang, NW China

The Tulasu volcanic belt is located in the western of the Boluokenu metallogenic belt in Chinese western Tianshan.It is well endowed with epithermal Au and Pb-Zn deposits,including the Jingxi-yelmend Au high-sulfidation type deposit,the Axi and Tawuerbieke Au low-sulfidation type deposits,and the Tabei Pb-Zn hydrothermal vein-type deposit.Recently,the Kexiaxi Cu-Au porphyry deposit and Kuokuqueke Fe-Cu skarn-type deposit were found in the Tulasu volcanic belt.In this paper,based on the detailed studies on the Dahalajunshanzu volcanic rocks?DVRs?and the different types of deposits from the Tulasu volcanic belt,the epithermal-porphyry-skarn ore system were set up in the Tulasu area,providing a theoretical basis for further prospecting area.According to the LA-ICP-MS zircon dating,the age of the DVRs in the Tulasu basin range from 367 to 377 Ma,suggesting that they erupted in the Late Devonian,rather than the Early Carboniferous as accepted previously.Geochemically,most of the andesite show a remarkable affinity with the Cenozoic sanukites in the Setouchi Volcanic Belt of SW Japan,and formed via partial melting of subducting sediments and subsequent interaction of melt-mantle.The felsic volcanic rocks were produced by the fractional crystallization of the early andesitic magma.Geochemical characteristics of these Late Devonian volcanic rocks are similar to those of arc volcanic rocks,indicating that they could form in a continental arc setting produced by the North Tianshan Oceanic plate southward subduction under the Yili-Central Tianshan plate.Fluid inclusions studies show that the quartz in the main mineralization stage of the porphyry deposit contain H₂O-rich and halite-bearing three-phase inclusions,and the ore-forming fluids are characterized by medium-low temperature with medium-high salinity.For the high-sulfidation deposit,the fluid inclusions are only composed of H₂O-rich inclusions with medium-low temperature and low salinity.For the low-sulfidation and hydrothermal vein-type deposits,the ore-forming fluids are characterized by a H₂O-NaCl system with low temperature and salinity.The fluid boiling could take place during the main mineralization stage in the different types of deposits,causing the ore precipitation.However,the fluid-rock reaction or the sulfidization may play a role in the Tawuerbieke deposit.Isotope studies indicate that the ore-forming fluids of the porphyry and high-sulfidation deposits were dominated by magmatic water,and some meteoric water was involved in which during later mineralization stage.The ore-forming fluids of the low-sulfidation deposits were mainly derived from the circled meteoric water.Metallogenic materials of different types of deposits were all mainly derived from the Late Devonian to Early Carboniferous volcanic and intermediate to acidic intrusive rocks in the Tulasu area.The timing of mineralization of these deposits is the late Devonian to the early Carboniferous,coincident with that of the magmatic rocks.This suggests that these different types of deposits are under the same epithermal-porphyry-skarn Au-Cu-Fe-Pb-Zn polymetallic metallogenic system,and produced by the same tectonic-magmatic-hydrothermal mineralization process in the continental arc setting.The deposits in the Tulasu volcanic belt have suffered different degrees of erosion after the Au-Cu-Fe polymetallic mineralization,indicating that the major porphyry Cu-Au deposits may have been developed beneath or adjacent to the epithermal gold deposits,especially the Jingxi-Yelmend and Tawuerbieke gold deposits.