Metallogenesis, Ore-controlling Factors And Prospecting Direction Of The Liubagou-Hadamengou Gold Deposit, Inner Mongolia

The Liubagou-Hadamengou gold field, located in middle north margin of NorthChina Platform, is the largest one in the Wulashan area characterizing by widespreadK-feldspathization. For a long time, most studies on this ore field were focused on theHadamengou ore deposit. However, some disputes still exist in diagenetic-metallogenic chronology, ore-forming materials and ore genesis, and the researcheson alkaline-metasomatic alteration, characteristics of ore-forming fluids andgeochemistry of magmatic rock is weak in this deposit. As for the nearby Liubagoudeposit, even no research has been carried out. Therefore, the peripheral and deepprospecting work of this area has been restricted to some extent. In this paper, basedon the detailed research on the Liubagou deposit and comparative studies on theLiubagou and Hadamengou deposits, the understandings about this ore field werefurther deepened on the aspects of metallogenic background, geological features ofore deposit, ore-controlling factors and ore genesis. Furthermore, the prospectingdirection was pointed out in this area.The ore field are hosted by Late Archaean metamorphic rocks of WulashanGroup, and controlled by faults. Ore bodies occur as nearly EW-trending vein, withore types of quartz vein, quartz-K-feldspar vein and potassic-silicified altered rock.Wall rock alterations are dominated by K-feldspathization and silicification adjacentto ore veins, and gradually transited to epidotization, chloritization, carbonatization,and weak sericitization away from ore bodies. Mineralization process is divided intofour stages, including K-feldspar-quartz stage, quartz-pyrite-sericite-epidote/chloritestage, quartz-gold-polymetallic sulphides stage and carbonate stage.Element geochemistry, fluid inclusion and isotope studies indicate that theore-forming fluids were dominated by magmatic water, though some meteoric waterwas added during later mineralization stage. The ore-forming fluids of mainmineralizing stage belonged to the NaCl-H₂O-CO₂system of medium-hightemperature (200³50℃), medium-low / medium-high salinity (5⁴5 % NaCl eq.)and medium density (0.88⁰.96 g/cm3) generally. Boiling may have caused the precipitation of gold and other metals. Mineralization occurred in Middle Triassic(218 Ma), this age is consistent with the metallogenic epoch of the Xishadegaimolybdenum deposit (225 Ma). Metallogenic materials mainly derived from silicon-,alkali-rich Indosinian granite represented by Xishadegai (245 Ma) and Shadegai (231Ma) rock mass, and partly from Late Archaean metamorphic rocks of WulashanGroup. Hence, the Liubagou-Hadamengou ore field shows features of magmatichydrothermal (medium to high temperature) alkaline-related gold deposits.Primary halo results of the Liubagou deposit show that, the ore-formingassemblage is Au, Mo, Ag, Pb and Ba. The head halo is As, Sb, Hg and Ba, the rearhalo is W, Mo, Pb and Bi, as well as Cu, Zn and Ag generally occur in the middlesection of ore body. Thus, axial zoning sequence is basically positive. Meanwhile,coexistence of head and rear halos, as well as reverse zoning feature of As, Sb and Bishow the characteristics of multistage superimposed mineralization. In terms ofdenudation, it gradually declines from western to eastern part of num. 313 veins. Theore bodies of the Liubagou gold deposit are less denudated than the ones of theHadamengou gold deposit. Combined with features of geochemical parameters andintensity of anomaly, the western and eastern parts of num. 313 veins have a good oreprospecting potential. The understandings mentioned above are supported by resultsof studies on genetic mineralogy, fluid inclusion, as well as H-O and S isotopes andverified by drilling project.Comprehensive studies suggest that the ore deposit is controlled by the factorssuch as strata, structures, magmas, wall rock alteration, geophysics, geochemistry,mineralogy etc. Based on this, prospecting criteria is confirmed andtectonism-magmatism-mineralizaiton is discussed. Meanwhile, genetic andexploration models are established.