By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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South Verkhoyansk Metallogenic Belt ofAu in Shear Zone and Quartz Vein,Polymetallic Pb-Zn ± Cu (±Ag, Au) Vein,Stockwork, Granitoid-Related Au Vein,Cu (±Fe, Au, Ag, Mo) SkarnW-Mo-Be Greisen, Stockwork, and QuartzVein, and Au-Ag Epithermal Vein Deposits(Belt SV) (Russia, Verkhoyansk-Kolyma Region)This Aptian to Late Cretaceous metallogenic belt is related to veins related to granitoids in the South Verkhoyansk granite belt that intrude the Verkhoyansk fold and thrust belt in the North Asian Craton Margin. The metallogenic belt occurs in the central part of the South Verkhoyansk synclinorium, is bounded to the west by the Minorsk-Kiderikinsk fault and to the east by the Yudoma fault. The belt extends longitudinally for about 300 km from the Yudoma River in the south to the East Khandyga River in the north. The belt is hosted in Late Carboniferous to Middle Jurassic clastic rock that are deformed into folds with gentle crests and smoothly undulating hinges. In the northern part of the belt are northeast-striking strike-slip faults (Suntar system) with horizontal displacements of up to 10 km and vertical displacements ranging up to 1 km. Related magmatic rocks consist of large polyphase plutons (Tarbagannakh, Uemlyakh, and others), and stocks, dikes, and subvolcanic bodies. The belt contains Au in shear zone and quartz vein and crush zones (Nezhdaninka deposit), Au REE deposits that occur in, and above the apices of granitoid plutons (Levo-Dybinsk district), and polymetallic Pb-Zn ± Cu (±Ag, Au) vein and stockwork deposits (Upper-Menkeche deposit). The major deposits are at Nezhdaninka, Upper-Menkeche, and Levo-Dybinsk. Nezhdaninka Au in Shear Zone and Quartz Vein DepositThis deposit (Gamyanin and others, 1985; Gamyanin and others, written commun., 1990; Benevolsky and others, 1992) consists of disseminated gold that occurs in: (1) steeply-dipping shear zones up to 40 m thick and 5.4 km long; (2) related tension-gash quartz veins that range up to 200 m long and 1.2 m thick; and (3) quartz lenses in shear zones. The vein minerals are quartz, carbonate, arsenopyrite, galena, sphalerite, scheelite, sericite, albite, chalcopyrite, tetrahedrite, Pb and Cu sulfosalts, stibnite, and gold. Wallrocks display silica, sulfide, and sericite alteration. Quartz Ag polymetallic deposits cross-cut and post-date feathered quartz-veins. The deposit occurs along a major fault that cuts the core of a doubly-plunging anticline in Late Carboniferous to Early Permian sandstone and shale. The deposit extends extends more than 1,000 m vertically, and is explored by boreholes and seven levels of adits. The deposit is large with proven reserves of 475 tonnes Au, and estimated resources of more than 500 tonnes Au. The average minimum grade is 5 g/t Au, with up to 6,748 g/t Au, and up to 8,300 g/t Ag. Upper Menkeche Polymetallic Pb-Zn ± Cu (±Ag, Au) Vein and Stockwork DepositThis deposit (V. Korostolev, written commun., 1963; Indolev and Nevoisa, 1974) consists of abundant Ag polymetallic sulfide lenses and veins that occur in a linear, steeply-dipping northeast-trending fault zone in Late Permian sandstone, siltstone, and shale. The fault zone is about 10 km long and 1 km wide. The sulfide bodies occur mostly parallel to the fault zone, dip steeply, range from hundred of meters to 3.5 km long, and from 1 to 10 m (average 3 m) thick. The main ore minerals are galena, sphalerite, pyrrhotite, arsenopyrite, and pyrite. Lesser ore minerals are cassiterite, chalcopyrite, magnetite, owyheeite, pyargyrite, tetrahedrite, diaphorite, boulangerite, native silver, and gold. Gangue minerals are quartz, siderite, ankerite, and calcite. Three sulfide assemblages and stages of deposit formation are: (1) sphalerite-quartz-siderite; (2) sulphoantimonite-galena; and (3) sulfide-carbonate. Regional metamorphism occurred between stages 2 and 3. The fault zone occurs along the dome of a plunging brachyform anticline. Part of deposit occurs within the contact metamorphic aureole of a Late Cretaceous granitoid intrusion that forms stocks and numerous dikes of granite-porphyry and granodiorite-porphyry. Lamprophyre and diabase dikes are widespread. The deposit is medium size with an average grade of 2.7-11% Pb, 3.9-7.0% Zn, 138-332 g/t Ag. Origin and Tectonic Controls for South Verkhoyansk Metallogenic BeltThe belt is interpreted as forming during accretion of the Okhotsk terrane to the North Asian Craton and resultant deformation of the southern Verkhoyansk fold and thrust belt. The belt occurs in the Minorsk-Kiderikinsk zone of highly deformed Late Carboniferous and Permian rock in the western South Verkhoyansk synclinorium. Au quartz veins are relatively older than large granitic plutons that intrude the South Verkhoyansk synclinorium which have 40Ar-39Ar isotopic ages of 120 to 123 Ma. REFERENCES: Indolev and Nevoisa, 1974; Gamyanin and others, 1985; Bortnikov and others, 1998; Parfenov and others, 2001; Nokleberg and others, 2003. Upper Uydoma Metallogenic Belt ofCassiterite-Sulfide-Silicate Vein andStockwork, Polymetallic Pb-Zn±Cu(±Ag, Au) Vein and Stockwork, Sn-WGreisen, Stockwork, and Quartz Vein, andPorphyry Mo (±W, Sn, Bi) Deposits(Belt UY) (Russia, Verkhoyansk-Kolyma Region)This Late Cretaceous metallogenic belt is related to veins and replacements that are part of the Okhotsk-Chukotka volcanic-plutonic belt that intrudes and overlies the Verkhoyansk fold and thrust belt in theNorth Asian Craton Margin. The metallogenic belt occurs along the western margin of the Okhotsk-Chukotka volcanic-plutonic belt on the eastern limb of the South-Verkhoyansk synclinorium, extends for 200 km, and ranges up to 60 km wide. The igneous rocks cut Permian and Triassic clastic rock that is deformed into folds that trend north to northeast. Typical are small fields of Late Cretaceous, Late Cretaceous horizontal, volcanic and subvolcanic bodies of rhyolite and dacite. The Late Cretaceous igneous and deposits are controlled by longitudinal, northwest-, and northeast-striking faults. Pb, Zn, Sn, Ag, Au, W, and Sb deposits is are widespread and most prevalent are low-sulfide cassiterite-silicate and argentiferous Sn polymetallic deposits (galena-pyrrhotite-sphalerite). The major deposits are at Khoron, Khaardakh, Kutinskoye, and Djatonskoye. Khoron Cassiterite-Sulfide-Silicate Vein and Stockwork DepositThis deposit (Andriyanov and others, 1984) occurs on the northeastern side of the metallogenic belt at the intersection of the Khoron and the Pravonitkansk faults. The deposit is hosted in Permian sandstone and siltstone that are simply folded. The sedimentary rock are intruded by pre-ore dikes and a granodiorite porphyry stock. The deposit occurs in crush zones and veins that range up to 100 m long from 1 m to 1.5 m wide. The vertical span is 500 m. The principal minerals are quartz, tourmaline, and muscovite, and local chlorite and pyrrhotite. Accessory minerals are actinolite, axinite, galena, Fe disulfide, sphalerite, cassiterite, chalcopyrite, stannite, and Bi minerals. Minor minerals are stibinite, Ag minerals, teallite, native Bi and gold. Deposit formed in five phases: quartz-tourmaline, cassiterite-quartz with arsenopyrite, greisen, quartz-sulfide, and quartz-carbonate. Most cassiterite formed in the second phase. The deposit is large with an average grade of 1.17% Sn. Origin and Tectonic Controls for Upper Udoma Metallogenic BeltThe belt is interpreted as forming during generation of granitoids along an active continental margin arc consisting of the Albian to Late Cretaceous Okhotsk-Chukotka volcanic-plutonic belt. Late Cretaceous magmatism and deposits of the belt are controlled by longitudinal, northwest, and northeast faults. REFERENCES: Andrianov and others, 1984; Flerov, 1984; Parfenov and others, 2001; Nokleberg and others, 2003. |