Study On Geological Characteristics And Metallogenesis Of Biliyagu Pb-Zn Deposit In Da Hinggan Mts., Inner Mongolia

Biliyagu Pb-Zn deposit is situated in Deerbuer County, Hulunbeier City, InnerMongolia Province. It is also located geotectonically in the Eurguna Block and Xing’anBlock which is in Xiaoyinuogaigou-Moerdaoga mineralized concentrate district lying atthe middle part of Deerbugan ore belt. And this region has a good geological condition ofmineralization and is rich in mineral resources including several middle-large scale Pb-Zndeposit.Most of the exposed strata in this area are Middle Jurassic Tamulangou Formation,Upper Jurassic Manketouebo Formation and Quaternary deposition. Among them,Manketouebo Formation is composed of intermediate-acid volcanic rocks whosefractionation of LREE and HREE is not that strong, and is geologically formed in thetransitional environment of subduction to syn-collision.As the ore district is regionally located in the middle of Deerbugan Fault, itsNW-striking secondary faults are ore-control structures which constrain the attitudes,planar and spatial distribution rules and so on. Along in the NW-striking extensional faults,the ore bodies are mainly occurred in dacite and tuff breccia of Tamulangou Formation. Sofar, it has been found17industrial ore bodies and55low-grade ore bodies with themineralization height in between305.00～1035.00m. These ore bodies show lenticularand vein-shape with enlargement and systolic characteristics, reflecting the segmentationenrichment of the ore bodies. Vertically, some large industrial ore bodies were usuallyformed in the section where turns steep suddenly.Metallic minerals in Biliyagu Pb-Zn deposit are mainly pyrite, chalcopyrite, galena,sphalerite, limonite and malachite, and gangue mineral are mainly quartz, chlorite, calcite, sericite and so on. Major textures of ores are metasomatic texture, exsolution texture andgranular texture. And the major structure is vein structure, disseminated structure andmassive structure. The country rock alterations are mainly silicatization, chloritization,carbonatation and sericitization, which is typical low to moderate assemblage.Silicatization is closely related to the mineralization. The mineralization can be dividedinto two periods: the hydrothermal period and the supergene period, and the hydrothermalperiod can be divided into quartz-pyrite stage, quartz-polymetallic sulfide stage andcarbonate stage.The major types of fluid inclusions in Biliyagu Pb-Zn deposit are aqueous two-phaseinclusions and CO2-bearing three-phase inclusions. The ore-forming fluids arecharacterized by meso-low temperature, low salinity and low density with a certainamount of CO2. The forming pressure ranges from32～46MPa suggesting a shallowforming depth of3.20～5.39km. The homogenization temperature of ore-forming fluidskeeps between160～200℃, of inclusions in quartz is between120～280℃, of inclusionsin sphalerite is140～180℃, and of inclusions in barite has a large range of102～378℃.The peak value of fluid salinity is1～8%. And because lots of volatile components suchas CO2and H2O escaped from fluids, the salinity of residual fluids rose rapidly anddaughter-minerals bearing polyphase inclusions can be seen occasionally. Combining withrelevant information, it can be concluded that the initial fluid of Biliyagu Pb-Zn deposit ismixed hydrotherm of magmatic water and meteoric water, and as temperature decreasedrapidly, meteoric water became dominant, implying one of ore-forming mechanism is themixture of different fluids.According to the tectonic background, geological characteristics and themineralizing condition of Biliyagu Pb-Zn deposit, we conclude that the deposits is thetype of mesothermal hydrothermal vein deposit controlled by faults structure, whichformed under the extensional environment during late Yanshanian epoch.