By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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Luliangshan Metallogenic Belt ofBanded Iron Formation (BIF, Superior Fe) andAu in Shear Zone and Quartz Vein Deposits(Belt LL) (North China)This Early Paleoproterozoic metallogenic belt is hosted in the Hutuo rift basin and occurs in the Luliangshan Mountains in the Northeast Shanxi Province. The belt is over 200 km long, varies 40 to 60 km wide, and is hosted in the Hutuo Group overlap assemblage in the Archean Liaoning-Hebei-Shanxi terrane. BIF deposits are related to metamorphic clastic rocks and marble, whereas shear zone Au deposits are hosted in metamorphosed clastic rocks of the Hutuo Group. Metallogenic belt is a composite that includes several mineral deposit types. The significant deposits are at Yuanjiachun (BIF) and Hulishan (shear zone Au). Yuanjiachun Banded Iron Formation (BIF, Superior Fe) DepositThis deposit (Zhang, Qiusheng, and others, 1984a, b) consists of bedded and stratiform Fe deposits that are concordant to host rocks that consist of clastic rock, mudstone, carbonate rocks and minor volcanic rock that are metamorphosed to greenschist facies. The Fe beds strike north-south for several to more than ten kilometers, and are 300 m thick. Ore minerals are mainly oxides and consist of specularite, hematite, magnetite, quartz, cummingtonite, and stilpnomelane. Deposit minerals occur in silicate and carbonate rocks with laminated and stripped structures. Host rocks are part of the Paleoproterozoic Luliang Group. Original sedimentary environment interpreted as a second-order basin in a rift zone along a craton margin. The deposit is similar to Superior Lake Fe deposits. The deposit is large with reserves of 895 million tonnes grading 32.37% Fe. Hulishan Au in Shear Zone and Quartz Vein DepositThis deposit (Chang, Xiangyang, and Tian, Rongqing, 1998) occurs in an intensely deformed zone that consists of isoclinial folds developed in metamorphosed volcanic and sedimentary rock of the Wutai Group and metamorphosed conglomerate of the Hutuo Group. Deposit occurs in bands, veinlets, disseminations and stockworks. Bands consist of quartz, sericite, limonite, and sulphide minerals. Gold occurs along schistosity as disseminations and streaks. Disseminations, veinlets, and stockworks contain mainly pyrite, chalcopyrite, and pyrrhotite. Ore minerals are Au, pyrite, chalcopyrite, pyrrhotite, magnetite, and native lead, and minor galena and bornite. Gangue minerals are quartz, sericite, chlorite, calcite, siderite, and Fe-dolomite, and minor apatite, tourmaline, corundum, amphibole, and fluorite. Gold mostly occurs in quartz and limonite or between the two minerals. Au fineness is high (Au+Ag greater than 98%). Proximal alteration consists of silica, sericite, chlorite, carbonate, and pyrite alterations. Deposit is interpreted as forming in the late stage of evolution of an Archean greenstone belt that has a Pb-Pb isotopic age of 2230±130 Ma. Deposit interpreted as forming during shearing and deformation. The deposit is medium size. Origin and Tectonic Controls forLuliangshan Metallogenic BeltThe BIF iron and shear zone Au deposits are interpreted as forming in the Paleoproterozoic Hutuo rift or foreland basin (Zhai Mingguo and others, 2000) that was superposed on the Archean Sino-Korean Craton. The Paleoproterozoic overlap assemblage of the Archean Liaoning-Hebei-Shanxi terrane consists of the following geological units from the bottom to the top: (1) metaconglomerate, quartzite, feldspar quartzite, phyllite, and dolomite; (2) phyllite, dolomite, sandy slate and quartzite intercalated with metabasalt; (3) metaconglomerate, phyllite, plagioclase quartzite, and quartzite. A U-Pb zircon isotopic age for metabasalt is 2,366 Ma. Both the strata and the deposits are regionally metamorphosed, folded, and sheared to greenschist facies (Zhang Qiusheng and others, 1984). REFERENCES: Zhang Qiusheng and others, 1984; Zhai Mingguo and others, 2000. Oryudong-Gapyeong Metallogenic Belt ofMetamorphic Graphite Deposits(Belt OM) (South Korea)This Late Paleoproterozoic and Early Mesoproterozoic metallogenic belt is hosted in the Gyeonggi migmatitic gneiss terrane. Isotopic ages for the terrane range from 1800 to 1400 Ma. The deposits occur in an Archean and Proterozoic metamorphic complex that consists of biotite schist, some chlorite schist, injection gneiss, and marble. Injection gneiss is intercalated with banded structure of 10 to 15 m width. Crystalline graphite is mainly hosted in biotite schist. The major deposits are at Oryudong and Gapyeong. Oryu-dong Metamorphic Graphite DepositThis deposit (Lee, 1960) occurs in Proterozoic schist and consists of graphite lenses that generally occur parallel to the host-rock. Weathered ore is higher in grade and can be distinguished from the non-weathered ore by appearence and chemical analysis. The deposit is hosted mainly in Proterozoic granitic gneiss and schist. Crystalline graphite occurs in lenses that parallel schistocity. Strike and dip are variable; however, general strike is northeast with dips to southwest or northeast. The deposits were formed contemporaneously with granitic gneiss and schist. Carbon was derived from organic matter. The graphite is variable grade and crystallinity. Average grades of outcrop samples are: 14.55% F.C:, 80.41% ash, 1.14% VM, and 1.11% H2O. Average grade of drill core is 14.51% F.C., 80.86% ash, 4.92% VM, and 0.21% H2O. Grade ranges up to high. The deposit is small with reserves of 2,592 tonnes ore. Origin and Tectonic Controls forOryudong-Gapyeong Metallogenic BeltThis belt is hosted in Paleoproterozoic metamorphic complex composed of biotite schist, lesser chlorite schist, injection gneiss and marble. Injection gneiss intercalated with banded structure of 10 to 15 m thick. Crystalline graphite mostly associated with biotite schist. The belt is interpreted as forming during metamorphism of marine sedimentary rocks. REFERENCES: Lee, 1960; Cho, Moon, Lee, and Lee, 1977; Duk Hwan Hwang, this study |