Studies Of The Intrusion-related Fe-Cu-Mo Polymetallic System In The Boluokenu Metallogenic Belt,Western Tianshan,Xinjiang

The Boluokenu metallogenic belt,located in the north margin of the Western Tianshan,Xinjiang,has a set of Fe-Cu-Mo polymetallic metallogenic system that associated with intermediate to acidic intrusive rocks.The system comprises the Halegati-Muzuke Fe-Cu-Pb-Zn and the Kekesala-Aimusidaiyi Fe-Cu skarn deposits,the Lailisigaoer-3571Cu-Mo porphyry deposit,and the Qixing Ag-Pb-Zn hydrothermal vein-type deposit.The field investigation indicate that the Fe-Cu-Mo polymetallic mineralization is genetically related to monzonitic granite,granodiorite and granodiorite porphyry.Geochemically,these rocks are peraluminous to weakly peraluminous,and show calc-alkaline to high K calc-alkaline affinity,i.e,alkalis-rich,high SiO2 and K2O contents with high K2O/Na2O ratios.They are characterized by a pronounced enrichment of Rb,Th and light REE and a deficit of Ta,Nb,Ba,Sr,P,Ti and high REE with significantly negative Eu and slightly positive Ce anomalies.These features resemble those of subduction-related I-type granite.Zircon U-Pb dating yielded an age of 386-363 Ma for the Husite intrusion,376-365 Ma for the Dawabulake intrusion,and³12 Ma for the Nailenggele intrusion.Fluid inclusion studies show that fluid inclusions in the main mineralization stage of the porphyry and skarn deposits are mainly liquid-rich,halite-bearing,and CO₂-bearing three-phase inclusions.The ore-forming fluids are characterized by medium to high temperature and salinity with intermediate density.Fluid immiscibility or boiling may have played an important role during ore precipitation.For the hydrothermal vein-type deposits and the late mineralization stage of the skarn deposits,the fluid inclusions are mainly liquid-rich inclusions with lower temperature,salinity,and density than the main mineralization stage of the porphyry and skarn deposits,and the role of fluid immiscibility in the mineralization is unconspicuous.Measured sulfur isotope composition indicate that the ore-forming sulfur was derived mainly from a magmatic source.The lead isotope data of the ores indicating a crust–mantle mixed source of lead with major magmatic component.The source of carbon of the ore-forming fluids was derived from a mixture of magmatic and marine carbonate.For the two skarn deposits,the fluids in the skarn-stage show isotopic signature consistent with a magmatic source,and evolved into a magmatic–meteoric mixed source in the quartz-sulfide stage.The ore-forming fluids of the Lalisigaoer-3571 Cu-Mo and Qixing Ag-Pb-Zn deposits are both originated from a mixing of magmatic and meteoric water.The mineralization age of the Halegati-Muzuke deposit is³66 Ma,which is consistent with the emplacement age of the Dawabulake intrusion.The age of the Kekesala-Aimusidaiyi deposit is²88 Ma,which is significantly later than the emplacement age of the Husite intrusion.The discrepancy between the mineralization and intrusion ages in the Kekesala-Aimusidaiyi deposit can be ascribed to the followings:1)the dated emplacement age represent the age of an early phase of the Husite composite intrusion;or 2)the dated mineralization age?²88 Ma?represent a late superimposed Mo mineralization event.The study area has suffered intense erosion after the Fe-Cu-Mo polymetallic mineralization,and there is a great potential for ore prospecting at the depth of the 3571 Cu deposit.