By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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Kyllakh Metallogenic Belt ofCarbonate-Hosted Pb-Zn(Mississippi Valley type) Deposits(Belt KY) (Russia, Southern Verkhoyansk fold and thrust belt)This Vendian metallogenic belt is hosted in carbonate sedimentary rock. The belt extends longitudinally for 400 km along the North Asian Craton boundary in the southern Verkhoyansk fold and thrust belt. The belt is hosted primarily in thick Riphean through Cambrian carbonate and clastic rock. Several stratigraphic horizons of stratiform Pb-Zn and Cu deposits are recognized. The main deposits (from bottom to top) are in the: (1) middle Riphean Bik and Muskel Formations (Cu, Pb-Zn); (2) late Riphean Lakhanda Formation (Pb-Zn); (3) late Riphean Uy Formation (Cu, Pb-Zn); (4) Vendian Sardana formation (Pb-Zn); (5) Early Cambrian Pestrotsvetnaya Formation (Cu); and (6) Middle Cambrian Ust’-Maya Formation (Cu). The major horizon is the Vendian Sardana Formation that contains about 40 Pb-Zn deposits and occurrences that occur in a transition zone from the western, near-platform facies to the eastern, basin facies area. The Sardana Formation is subdivided into a lower barren sandstohe, mudstone, and carbonate unit, and an upper productive limestone and dolomite unit. Commercial deposits occur in the area of facial thinning out of saccharoidal dolomite. The major deposits are at Sardana, Urui, and Pereval'noe. Sardana Carbonate-Hosted Pb-Zn (Mississippi Valley type) DepositThis deposit (Ruchkin and others, 1977; Kuznetsov, 1979; Kutyrev and others, 1989; Davydov and others, 1990) consists of disseminated, banded, massive, brecciated, and stringers of ore minerals in and adjacent to a dolomite bioherm that ranges from 30 to 80 m thick and is hosted in the Neoproterozoic (Late Vendian) Yudom Formation. Lensoid deposits are concordant with dolomite in the Upper Sardana subformation that contains three members (from bottom to top): (1) light-grey fine-grained dolosparite (17 to 30 m thick); (2) dark-grey bituminous limestone and dolosparite (5 to 29 m thick); and (3) layered limestone and massive saccharoidal dolosparite (31 to 87 m thick). Several ore horizons occur, and the central area on the western limb of the Kurung anticline is the most productive. In this area, three Pb-Zn sulfides deposits extend for 150 to 1300 m and range from 9 to 70 m thick. The largest part of the deposit occurs in the third member and ranges up to 50 m thick. Galena and sphalerite are predominant and occur in masses, veinlets, and disseminations. Main ore minerals are sphalerite, galena, and pyrite, with subordinate chalcopyrite, marcasite, and arsenopyrite. Oxidized ore minerals are smithsonite, cerussite, anglesite, goethite, hydrogoethite, and aragonite. The deposit is the largest deposit in the Sardana Formation and occurs in the Selenda syncline that is complicated by the Kurung anticline and longitudinal thrusts. Low grade disseminations occur in Neoproterozoic (Upper Vendian) dolomite for many kilometers in both limbs and in the axis of a north-south-trending syncline that is 3 km wide and more than 10 km long. Deposit intruded by sparce diabase and dolerite dikes. Average combined Pb+Zn grade is 6%, with a maximum of 50%. The deposit is large with reserves of more than 1.0 million tonnes combined Pb+Zn. Drilling indicates additional sulfide bodies occur at a depth of 200 to 300 m. Origin and Tectonoc Controls forKyllakh Metallogenic BeltThe belt is interpreted as forming along the passive margin of the North Asian Craton. Economic deposits occur in areas of facial thinning out of dolomite REFERENCES: Arkhipov, 1979; Davydov and others, 1990; Davydov, 1992; Parfenov and others, 1999, 2001. Angara-Pit Metallogenic Belt ofSedimentary Siderite Fe andVolcanogenic-Sedimentary Fe Deposits(Belt AP) (Yenisei Ridge, North-AsianCraton Margin, Russia)This Upper Riphean metallogenic belt is hosted in the North Asian Craton Margin (East Angara fold and thrust belt) and occurs in the southeastern part of Yenisei Ridge. The belt forms a band along the east wing of the Central anticlinorium from Angara River to the south to the Gorbilok River to the north, and is up to 100 km long. The belt contains three large chlorite-hematite deposits at Nizhne-Angarskoye, Ishimbinskoye, and Udorongovskoye, and numerous smaller occurrences. The deposits occur in clastic sedimentary rock of the late Riphean Nizhneangarsk. Each deposit consists of several (about 7 to 36) ore layers that vary from 2 to 16 m thick (ranging up to 30 m), have a total thickness of up to 50 m, and are 0.3 to 14 km long. All deposits exhibit similar geological structure, mineral composition, and quality of ore minerals. Ore layers and lenses hosted in clastic and clastic-chemogenous sedimentary rocks, mainly hematite gritstone and conglomerate, hematite sandstone, and sandy hematite-chlorite siltstone. Host rocks and deposits are metamorphosed to phyllite (Matrosov and Shaposhnikov, 1988). The major deposit is at Nizhne-Angarskoye. Nizhne-Angarskoye Sedimentary Siderite Fe DepositThis deposit (Yudin, 1968; Brovkov and others, 1985; Orlov, 1998) consists of layered hematite hosted in late Riphean argillite, siltsone, and sandstone. Fe horizon is 45 to 180 m thick and occurs in 36 separate deposits that range up to 29 m thick, extend up to 15 km along strike, and range to 650 m depth. Fe layers are intercalated with sedimentary rocks ranging up to 2 to 15 m thick. Ore layers consist of hematite, sandy-hematite, argillaceous chlorite hematite gritstone, hematite-siderite. Main ore minerals are hydrogoethite, hematite, and goethite with lesser siderite, magnetite, and pyrite. Gangue minerals are quartz, leptochlorite, clays, and sericite. Deposit contains 0.03% S and 0.08% P. The deposit is large with reserves of 1,200,000,000 tonnes grading 40.4% Fe. Origin and Tectonic Controls for Angara-Pit Metallogenic BeltThe belt is interpreted as forming during a preorogenic stage of the Yenisei pericratonal subsidence in a back-arc (interland) sedimentary basin. Lithological-facial control of distribution of sedimentary hematite ores occurred. The paleodelta setting of formation of Fe ores is indicated by structural, mineralogical, and geochemical features of host rocks (Yudin, 1968). A possible source of clastic ore minerals was residual Fe-rich weathering crust (Brovkov and others, 1985). REFERENCES: Yudin, 1968; Brovkov and others, 1985; Matrosov and Shaposhnikov, 1988. |