By Sergey M. Rodionov1, Alexander A. Obolenskiy2
|
|  Yüklə 2.21 Mb.
|
Sergeevka-Taukha Metallogenic Belt ofGranitoid-related Au Vein, Boron (datolite)Skarn, Zn-Pb (±Ag, Cu) Skarn,Polymetallic Pb-Zn Cu (Ag, Au) Vein andStockwork, Polymetallic (Pb, Zn±Cu, Ba,Ag, Au) Volcanic-Hosted Metasomatite,Au-Ag Epithermal Vein, and Porphyry Cu (±Au)Deposits(Belt Ser) (Russia, Far East)This Late Cretaceous and early Tertiary metallogenic belt is related to veins and granitoids related to East Sikhote-Alin volcanic-plutonic belt that overlies and intrudes Sergeevka, Samarka, and Taukha terranes. The belt includes several deposit types. Progress Granitoid-Related Au Vein DepositThis deposit (A.N. Rodionov, written commun., 1991) consists of sulfide-poor veins and small veinlets that contain pyrite, arsenopyrite, quartz, and Au. In addition the deposit contains poorly mineralized fracture zones, mylonite zones, and zones of metasomatically-altered carbonate and chlorite-sericite rock. The deposit occurs in, or near a Late Cretaceous granitoid pluton and dikes that intrude Cambrian granitic and gabbro rocks of Sergeevka complex. The deposit is also the source for local placer Au mines. The deposit is medium size with an average grade 5.89 g/t Au. Askold Granitoid-Related Au Vein DepositThis deposit (M.I. Efimova and others, written commun., 1971; Efimova and others, 1978) consists of a Au-quartz vein stockwork in a Mesozoic granite that is altered to greisen and that intrudes Paleozoic volcanic and sedimentary rock. A K-Ar muscovite age for alteration associated with the vein is 83.2 Ma. The deposit is prospected to depths of more than 100 m. The deposit is medium size with an average grade of 5.9 to 7.6 g/t Au. Dalnegorsk Boron (datolite) Skarn MineThis major, world-class boron mine (Ratkin, 1991; Ratkin and Watson, 1993; P. Layer, V. Ivanov, and T. Bundtzen, written commun., 1994) occurs in a thick skarn formed in a large, upturned olistolith of bedded Triassic limestone that is enclosed in Early Cretaceous clastic sedimentary rock. The skarn extends to a depth of approximately 1 km, where it is intrude off by a granitic intrusion. The skarn formed in two stages, with a second-stage skarn over-printing an earlier skarn. The two stages of skarn formation are separated in time by intrusion of intermediate-composition magmatic bodies (with an approximate K-Ar isotopic age of 70 Ma). The first stage skarn consists of grossular-wollastonite skarn, is concentrically zoned, and consists of finely-banded aggregates with numerous finely crystalline datolite and druse-like accumulations of danburite crystals in paleohydrothermal cavities. The second stage skarn consists predominantly of long, radiated hedenbergite and andradite with coarsely-crystalline datolite, danburite, quartz, axinite, and calcite. An Ar-Ar isotopic age for orthoclase in the second stage skarn assemblage is 57 Ma. The silicate mineralogy of the first-stage skarn is similar to Zn-Pb (±Ag, Cu) skarn deposits in the belt. B isotopic studies indicate a magmatic source for boron. The Dalnegorsk open-pit mine at the deposit is explored to a depth of 1 km. The deposit is very large and had been mined from 1970's to present. The deposit produces over 90% all borate in Russia. Nikolaevskoe Zn-Pb (±Ag, Cu) Skarn MineThis mine (Garbuzov and others, 1987; V.V. Ratkin in Nokleberg and others, 1997) is hosted in a giant olistolith of Triassic limestone that is part of an Early Cretaceous accretionary complex. The skarn occurs along the contacts of limestone with hosting siltstone and sandstone, and with overlying felsic volcanic rock of a Late Cretaceous to Paleogene post-accretionary sequence. Small skarn bodies also occur in limestone blocks in the volcanic rock that were faulted from the underlying basement. The ore minerals are dominantly galena and sphalerite that replace an older hedenbergite skarn near the surface, and, at depth, replace a garnet-hedenbergite skarn. Subordinate ore minerals are chalcopyrite, arsenopyrite, pyrite, pyrrhotite, fluorite, and Ag-sulfosalts. The K-Ar age of deposits ranges between 60 and 80 Ma. Average grades are 62 g/t Ag, 1.5 to 8.7% Pb, and, 1.36 to 10.5% Zn. The deposit has been mined from 1970's to present. Partizanskoe Zn-Pb (±Ag, Cu) Skarn MineThis mine (Ratkin and others, 1991) consists of numerous, small, steeply-dipping skarn bodies that occur at the contact of a Triassic limestone olistolith surrounded by Early Cretaceous clastic rock. The deposits merge and form a single skarn body about 400 m below the surface, and pinch out at a depth of approximately 600 m. The skarn assemblages are vertically zoned and higher temperature assemblages occur deeper. Massive, densely disseminated Ag-Pb-Zn sulfides (with a Pb/Zn ratio of about 1.0) occur above a quartz-calcite aggregate in the upper part of the deposit. Massive, densely-disseminated Pb-Zn sulfides (with a Pb/Zn ratio of about 0.8) are associated with Mn hedenbergite skarn and occur in the middle part of the deposit. Disseminated Zn sulfides (with a Pb/Zn ratio of about 0.5) occur in ilvaite-garnet-hedenbergite skarn in the lower part of the deposit. Galena and sphalerite are the dominant ore minerals; chalcopyrite and arsenopyrite are common; and minor magnetite, pyrrhotite, and marcasite also occur. Silver-bearing minerals are Ag-and Sb-sulfosalts in the upper part of the deposit and galena in the lower part. Galena contains Ag as a solid solution of matildite. The age of deposits is bracketed between 60 and 80 Ma by basalt dikes that intrude the deposit at the contact of olistolith, and by the lower part of the overlying volcanic strata that are intruded by deposit. The deposit consists of four or more related ore bodies that occur along an about 5 km strike length, including the Soviet 2, Partizansk East, Partizansk West, and Svetliyotvod bodies. The underground workings have a total length of about 11 km. The deposit is medium size and average grades are 67.6 g/t Ag, 1.5 to 3% Pb, and 0.6 to 4 Zn%. The deposit has been mined from the 1950's to present. Krasnogorskoye Polymetallic (Pb, Zn±Cu, Ba, Ag, Au)Volcanic-Hosted Metasomatite DepositThis deposit (Ratkin and others, 1990) consists of steeply-dipping quartz-sulfide veins that range up to several hundred m long along strike and from 0.2 to 1.5 m thick. The veins intrude Late Cretaceous tuff. Sphalerite, cassiterite, and galena are the dominant ore minerals and the margins of veins contain pyrite-marcasite-pyrrhotite with lesser Sb-Ag-sulfosalts. In the deeper level of the deposit, galena contains up to several percent Ag and Bi in matildite. The volcanic rock adjacent to the polymetallic veins is altered to quartz and chlorite. In the core of the veins, chlorite, Mn calcite, rhodochrosite, rhodonite, and spessartine occur with quartz gangue. The veins occur near a Late Cretaceous and Paleocene volcanic vent. The vent breccia also contains disseminated sphalerite, galena, and cassiterite. The veins formed immediately after deposits of the vent breccia that has an approximate K-Ar isotopic age of 65 Ma. The deposit is medium size and average grades are 62 g/t Ag, 5% Pb, 0.26% Sn, and 6.77% Zn. Origin and Tectonic Controls for Sergeevka-Taukha Metallogenic BeltThe belt is interpreted as forming during generation of granitoids along the East-Sikhote-Aline continental-margin arc related to subduction of ancestral Pacific Ocean Plate. This belt is hosted in, or near igneous rocks that intrude the Taukha accretionary-wedge terrane that contains a complex assemblage of abundant Paleozoic and early Mesozoic oceanic rocks and lesser Jurassic and Early Cretaceous turbidite deposits. REFERENCES: M.I. Efimova and others, written commun., 1971; Efimova and others, 1978; Garbuzov and others, 1987; Ratkin and others, 1990, 1991; Ratkin, 1991; Ratkin and Watson, 1993; Ishihara and others, 1997; Vasilenko and Valuy, 1998; S.M. Rodionov, written commun., 1991; Nokleberg and others, 2003. |