Gold Polymetallic Metallogenic Systems, In Damaoqi Area, Inner Mongolia

Located on the western section of the northern margin of North China Plate, theDamaoqi areas, in Inner Mongolia, is a very important metallogenic belt which compriseslots of gold polymetallic ore deposits. Based on the theory of the metallogenic system, thispaper analyzed the depostional mechanism, summarized the composition and evolution ofthe metallogenic system, and then denoting the favourable prospecting criteria in this area.The main achievements are listed as follows:The tectonic location of the Damaoqi area is unique as it straddles both the edge ofthe North China Craton and Central Asia Orogenic Belt. Geochemical data revealed thatthe Damaoqi area is characterized by the high gold backgroud content. Recently, plenty ofgold deposits were found, which verified this area to be also a gold Ore Cluster Area. Thedistribution of the element enrichment and gold deposits are jointly controlled by the LateArchean granitic-greenstone belt, clastic sedimentary and volcanic rocks of the Jianshanand Bilute formation in Proterozoic rift system, and stata of the Early Paleozoic volcanicarcs. The E-W trending faults, including the ancient block margin faults, synsedimentaryrift margin faults, ductile shear zones, and the intersection of NE trending faults providethe most favorable spaces for mineral deposition.Fluid inclusion investigation showed that the hydrothermal fluids from most of thegold deposits having homogenazation temperature varied from100to440℃, averaging159.3-326.6℃, and the average depositional depth is0.79km. It is therefore could beclassified as epithermal medium-low temperature gold deposit. H-O isotopic compostionsshow that the multi-episode metallogenic hydrothermal fluids are of multi-source. Sulfurisotopic result show that the sulfur of the sulfide minerals were originated mainly from themagmatic or volcanic rocks. Pb isotopic data of gold deposit from the rift systemsuggested that the lead of the ore minerals mainly sorced from the mantle.Geochemical characteristics of magma rocks (veins) associated with goldmineralization suggest that Saiwusu granodiorite belong to K calc-alkaline series, is ofI-type granites, which yielded a La-ICP-MS zircon U-Pb age of241.5±1.0Ma. AlageObo diorite belong to the calc-alkaline series, yielded a La-ICP-MS zircon U-Pb age of419.9±1.1Ma. a set of zircon grains of Alage Obo quartz porphyry sample yielded aLa-ICP-MS zircon U-Pb ages of141.9±3.0Ma. Combined with results of previousresearch, six phase of Paleozoic-Mesozoic magmatism in the Damaoqi areas: the EarlyPaleozoic (452~420Ma), Early Permian (290~287Ma), Middle Permian (281~268Ma),Early-Middle Triassic (260-242Ma) and Late Triassic（224Ma）, Early Cretaceous (142 Ma), implacate that six epoch of hydrothermal mineralization may be related withmagmatic activity.The gold polymetallic metallogenic systems in the area consists of three sub-systems:the ancient block, rift system and accretion zone, and metallogenic models of them havebeen established preliminarily. The area has undergone the evolution and superposition ofthe five sub-branch systems: the passive continental margin rift-hydrothermal sediment-Au metallogenic system in Proterozoic, the active continental marginsubduction–sediment/orogeny-Au metallogenic system in Early Paleozoic, the activecontinental margin collision-orogeny-Au metallogenic system in Late Permian-Triassic,the tectonic regimes transformation-hydrothermal superposition-Au metallogenic systemin Yanshan era and the supergene changes-Au metallogenic system in Cenozoic era.Among them, the Late Permian-Early Triassic, is an importent metallogenic epoch ofepithermal hydrothermal superposition on this area.The experience of geological prospecting on the area was summarized, andexploration proposals based on metallogenic system theory were proposed.