By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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Kema Metallogenic Belt ofAg-Au Epithermal Vein,Porphyry Cu-Mo (±Au, Ag),Porphyry Cu (±Au), andPorphyry Mo (±W, Sn, Bi) Deposits(Belt Kem) (Russia, Far East)This early Tertiary metallogenic belt is related to veins in the East Sikhote-Alin volcanic-plutonic belt that intrudes and overlies the Kema island arc terrane. The Ag epithermal vein deposits, as at Tayoznoe, occur in Early Cretaceous clastic and volcaniclastic rocks and in overlying Late Cretaceous and Paleogene, subalkalic, postaccretionary volcanic rock. Rare Pb-Zn polymetallic vein deposits occur, but are not economic. The epithermal vein deposits generally occur mostly in, or neai Danian (early Paleocene) and Paleocene volcanic rock; however, a few occur in granodiorite plutons. Porphyry Cu-Mo (±Au, Ag) deposits in the metallogenic belt occur mainly in the northern part of the belt. These deposits generally consist of disseminations and veinlets in, and near intrusive rocks and coeval volcanic rock that often contain anomalous Pb, Zn, W, Au, and Ag in addition to Cu and Mo. The porphyry Cu-Mo deposits occur in Late Cretaceous to Paleogene granitic and diorite intrusions. A porphyry Cu (±Au) deposit also occurs in the southern part of the belt. The major Au-Ag epithermal vein deposits are at Burmatovskoe, Glinyanoe, Salyut, Sukhoe, Tayozhnoe, Verkhnezolotoe, and Yagodnoe. Porphyry Cu (±Au) deposits are at Nesterovskoe and Nochnoe, a porphyry Cu-Mo (±Au, Ag) deposits is at Sukhoi Creek, and a porphyry Mo (±W, Bi) deposit is at Moinskoe. Glinyanoe Ag-Au Epithermal Vein DepositThis deposit (A.N. Rodionov, written commun., 1986) consists of adularia-quartz, sericite-chlorite-quartz, and carbonate and chlorite-quartz veins and zones that contain pyrite, arsenopyrite, galena, sphalerite, chalcopyrite, argentite, acanthite, Ag-tellurides, and native gold and silver. The veins and zones occur in altered, silicified volcanic rock that overlie Late Cretaceous (Santonian) felsic volcanic rock. The deposit as occurring in four stages: (1) gold-pyrite-quartz; (2) quartz-hydromica and quartz-carbonate; (3) gold-silver; and (4) quartz-chlorite-adularia with Ag-sulfosalts. The age of the deposit is interpreted as Late Cretaceous to Paleogene. The deposit is small with an average grades of 8.3 g/t Au, and 122 g/t Ag. Sukhoi Creek Porphyry Cu-Mo (±Au, Ag) DepositThis deposit (Petrachenko and others, 1988) consists of stockworks that are several hundred m across, and in altered zones. Polymetallic ore is dominant. The ore minerals are chalcopyrite, molybdenite, sphalerite, galena, cassiterite, scheelite, and pyrite; with significant Au and Ag. The deposit occurs in Early Cretaceous sedimentary rock that is overlain by Late Cretaceous volcanic rock and crosscut by deposit-hosting granitic intrusions with a K-Ar isotopic age of 73 Ma. The deposit is related to several granodiorite and granite stocks that are intensely hydrothermally altered. Quartz-sericite alteration, and medium-temperature epidote-prehnite-chlorite propylitic alteration occur at the core and grade into micaceous-chlorite-carbonate propylite at the periphery. Granite is locally altered to quartz-muscovite greisen with tourmaline and sphene, and in a few places into a peculiar garnet-phlogopite rock with apatite. Host siltstone and sandstone are altered to orthoclase-actinolite-chlorite hornfels and the felsic extrusive rocks are altered to quartz and phyllite. The deposit is small and grades up to 0.2% Cu and 0.01% Mo. Tayozhnoe 1 Ag-Au Epithermal Vein MineThis mine (A.N. Rodionov and others, written commun., 1976; Ratkin and others, 1991) consists of steeply-dipping quartz veins that occur along northwest to north-south fractures that intrude Early Cretaceous sandstone. The veins vary from 100 to 500 m long and 0.5 to 2 m thick, and also occur laterally beneath a contact between sandstone and an overlying 50 to m-thick section of Late Cretaceous felsic volcanic rock. The ore minerals occur in veins, and in metasomatic zones along the sub-horizontal contact, and between veins and overlying volcanic rock. The major Ag minerals are Ag sulfosalts and sulfides. Pyrite and arsenopyrite are rare and formed before Ag minerals. In the upper part of veins, Ag occurs in tetrahedrite, freibergite, stephanite, pyrargyrite, and polybasite. At middle depths, Ag occurs mainly in acanthite and stephanite, along with arsenopyrite and allargentum. Acanthite is dominant at depth. The deposit is medium size with an average grade of 50-2000 g/t Ag and 1 g/t Au. Mined since 1980's. Verkhnezolotoe Porphyry Cu (±Au) DepositThis deposit (Orlovsky and others, 1988) occurs at the northwest margin of a caldera that contains dikes of calc-alkaline andesite porphyry that is interpreted as tongues of a dome-like subvolcanic intrusion. A stockwork occurs in a circular aureole of hydrothermally altered rock with a surface exten of 200 m2 over the intrusive dome. Successive alterations are: (1) quartz-biotite-actinolite with pyroxene and epidote; (2) quartz-biotite-actinolite; (3) quartz-biotite-sericite and local chlorite; and (4) quartz-hydromica with carbonate. The stockwork contains the first three alterations and consists of a thick network of quartz-epidote-actinolite veinlets and lenses up to 2 to 3 cm thick with chalcopyrite, bornite, and pyrite. The stockwork is related to a diorite stock. The stockwork boundary coincides with the aureole of the biotite alteration. An intensely-fractured breccia of mineralized siliceous siltstone was encountered by drill holes that extend to 100 m depth. The ore minerals in the breccia zones are chalcopyrite and bornite. Molybdenite and pyrite, and rare pyrrhotite, cubanite, arsenopyrite, galena, and sphalerite also occur. Carbonate and chalcopyrite veinlets also occur. The richest ore is associated with Sn, Cu, and local W tungsten minerals. A zone of oxidized ore up to 20-30 m thick caps the deposit. The deposit is small with an average grade of 3 g/t Au, 86 g/t Ag, 0.35-2.27% Cu, 0.69% Pb, 0.26% Sn. Origin and Tectonic Controls for Kema Metallogenic BeltThe belt is interpreted as forming during generation of granitoids along a continental-margin arc related to subduction of ancestral Pacific Ocean Plate. The granitoids hosting the belt are part of the Late Cretaceous and early Tertiary East Sikhote-Alin volcanic-plutonic belt. This belt consists chiefly of five major units: (1) Early Cenomanian rhyolite and dacite; (2) Cenomanian basalt and andesite; (3) thick Turonian to Santonian ignimbrite sequences; (4) Maastrichtian basalt and andesitc; and (5) Maastrichtian to Danian (early Paleocene) rhyolite. The East Sikhote-Alin belt also contains coeval, mainly intermediate-composition granitoid plutons that in the frontal (eastern) part of the belt are predominantly Early Cretaceous magnetite-series granitoids. The East-Sikhote-Alin belt is correlative with the Okhotsk-Chukotka volcanic-plutonic belt on strike to the north in the Russian Northeast, and is tectonically linked to the Aniva, Hidaka, and Nabilsky accretionary wedge and subduction-zone terranes. REFERENCES: S.M. Rodionov and others, written commun., 1976, 1986; Orlovsky and others, 1988; Petrachenko and others, 1988; Khomich and others, 1989; Nokleberg and others, 1994, 1997, 1998, 2000, 2003; Pakhomova and others, 1997. |