Metallogenic Characteristics And Ore System Of The Nailenggele Polymetallic Orefield In Western Tianshan, Xinjiang, NW China

The polymetallic ore field of Nailenggele deposited in the northern edge ofKazakhstan-Yining plate active continental margin, is located in the area of thenorthern-central Boluohuoluo metallogenic belts of Western Tianshan in Xinjiang. Inthis paper, based on metallogenetical geological characteristics, mineralization-relatedinstructions geochemical characteristics, geochemical analysis on mineral depositsand metallogenic chronology study of the Lailisigao’er Mo,3571Cu and QixingPb-Zn-Au-Ag polymetallic deposits in the polymetallic ore field of Nailenggele, themain alteration and mineralization types are clarified, the formation process andgenetic types of mineralization-related instructions are revealed, the evolution processof ore-forming fluids and migration precipitation mechanism of ore-forming materialsare found out, deposit formation era is set up, and the genetic relationship betweendifferent mineral deposits are discussed. The main achievements and understandingsobtained are as follows:(1) Rock geochemical characteristics showed that SiO2content in the granitediorite porphyry body ranged narrow (68.65%~74.02%), total alkali content washigher(6.05%~6.90%), and A/CNK=0.86~1.04, with the features of rich potassium,high alkaline and quasi aluminum. Therefore, granite diorite porphyry belongs to highpotassium-calcium alkaline series, with the characteristics of type I evolution ofgranitic rocks, and forms in the continental arc environment. Appearance of dioriticdark inclusions suggests that it mixxed the deep mantle source materials, whichprovides the ore-forming metallic elements.(2) Fluid inclusions microthermometry and gas-liquid phase compositionanalysis showed that ore-forming fluid was a kind of H2O-NaCl system with themiddle-high temperature and the middle-low salinity during the early stage ofLailisigao’er Mo deposit. Metallogenic temperature originally ranged from290~370℃to200~325℃, then ranged from200~325℃to154~186℃. Mo elements in thefluid mainly existed in the form of KHMoO4or H2MoO4. During quartz-sulfide stage,Mo elements in the fluid experienced fluid boiling, thus temperature decreasing and reduced sulfur increasing were the major causes of leading to Mo elements precipitate;Metallogenic temperature of Qixing Pb-Zn-Au-Ag polymetallic deposit ranged from150~230℃to140~180℃, then ranged from140~180℃to120~140℃. Pb and Znelements mainly existed in the form of sulfur-hydride complex in ore-forming fluids.In tensile fractures, pressure and temperature decreasing and reduced sulfur increasingwere the major causes of leading to Pb and Zn elements precipitate. FromLailisigao’er Mo deposit to Qixing Pb-Zn-Au-Ag polymetallic deposit, ore-formingfluids had the characteristics of continuous evolution.(3) Carbon, hydrogen and oxygen isotopes showed that ore-forming fluids hadthe characteristics of magmatic water mixture with meteoric water. From Lailisigao’erMo deposit to Qixing Pb-Zn-Au-Ag polymetallic deposit, meteoric water content inore-forming fluids showed a trend of increasing. Sulfur, lead and strontium isotopesshowed that ore-forming materials had the characteristics of deep source, which wasconsistent with Lailisigao’er granite diorite porphyry.(4) In this paper, molybdenite Re-Os age-dating of the quartz-molybdenite veinsin Lailisigao’er Mo deposit showed mineralization took place in365.6±7.4Ma,paragenetic hornblende Ar-Ar age-dating of the quartz-molybdenite veins showedmineralization occurred in365.6±4.2Ma, which was consistent with molybdenite age.Sphalerite Rb-Sr age-dating of the quartz-sulfide veins in Qixing Pb-Zn-Au-Agpolymetallic deposit showed mineralization come up362.2±4.9Ma, so three age datawithin the error range is consistent. The zircon SHRIMP U-Pb of granite dioriteporphyry in Lailisigao’er Mo deposit aged362±12Ma, and Rb-Sr of whole rock aged350±15Ma (Li Huaqin etc.,2006), therefore all the results indicate thattectonic-magmatic-hydrothermal mineralization in the polymetallic ore field ofNailenggeler occurred in the late devonian to early carboniferous epoch.（5）Integrated the work and in the era of regional tectonic evolution, diagenesismineralization, the research of ore deposit geochemistry, etc, and compared with thetypical porphyry metallogenic system, the author think that Lailisigao’er porphyrymolybdenum deposit,3571copper deposit and Qixing Pb-Zn-Au-Ag polymetallicdeposit in the Nailenggeler polymetallic ore field is under the same porphyry metallogenic system, and is formed in the early devonian to the late carboniferousbeneath the strong regional tectonic-magmatic-hydrothermal mineralization process.