By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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Kalar-Stanovoy Metallogenic Belt ofAu in Shear Zone and Quartz Vein Deposits(Belt KS) (Russia, Aldan-Stanovoy Shield)This latitudinal Paleoproterozoic Kalar-Stanovoy metallogenic belt extends for 300 km along the Kalar tectonic melange zone and ranges up to 100 km wide. The isotopic age of the belt is about 2,000 Ma. The Kalar tectonic melange zone separates the West Aldan granite-greenstone terrane from the Tynda tonalite, trondhjemite, gneiss terrane to the south. The zone consists of extensive, major thrust and strike-slip faults and companion folds, and contains a large number of tectonic slabs that differ in composition, age, and metamorphic grade. Examples of tectonic slabs are granulites in the Khani-Kurul’ta, Zverev, and Iengra blocks, orthogneiss (tonalite and trondhjemite), anorthosite, granite, and Archean and Paleoproterozoic greenstone belts. The metallogenic belt contains numerous Au occurrences, as at Pravokabaktanskoe and Namarskoe, and deposits, as at Ledyanoe and Skalistoe, that are related to diaphthorite formed in Archean and Paleoproterozoic rocks. Also occurring are Ti-magnetite and apatite occurrences and deposits in mafic and ultramafic rock. Ledyanoe Au in Shear Zone and Quartz Vein DepositThis deposit (Glukhovsky and others, 1993; Koshelev and Chechyotkin, 1996; Moiseenko and Eirish, 1996) occurs in shear zone and quartz vein and mineralized zones in blastomylonite that cut retrograded Paleoproterozoic gabbro and anorthosite, leucocratic anorthosite and rare melanocratic anorthosite, charnockite, and pegmatoid granitoid. The veins vary from 0.2 to 0.5 to 4 m thick and are 2 km long. The deposit occurs in an area with dimensions 6 by 3 km. The veins are concordant with blastomylonite, and dip both steeply south and north. Wallrock blastomylonite is cut by quartz and carbonate veinlets that comprise 15 to 30% rock volume. The veins consist of white saccharoidal cavernous quartz and sulfides (pyrite, and rare chalcopyrite, galena, sphalerite, pyrrhotine) that comprise 5% rock volume. Grade ranges from 11.7-30 g/t Au. Origin andTectonic Controls forKalar-Stanovoy Metallogenic BeltThe belt interpreted as forming during the collision between Tynda and West Aldan terranes in Aldan-Stanovoy region and during subsequent collapse of orogenic belt. The cause of collision was amalgamation of terranes during the formation of the North Asia Craton. Au deposits occur shear zones that cut metamorphosed mafic and ultramafic and plutonic rock.. REFERENCES: Fedorovskiy, 1972; Beryozkin, 1977Koshelev and Chechyotkin, 1996; Moiseenko and Eirish, 1996;; Bushmin and others, 1983; Dook and others, 1986; Rudnik, 1989; Jahn and others, 1990; Kovach and others, 1995b; Parfenov and others, 1999, 2001. Amga-Stanovoy Metallogenic Belt ofAu in Shear Zone and Quartz Vein Deposits(Belt AS) (Russia, Aldan-Stanovoy Shield)This Paleoproterozoic metallogenic belt is related to Amga tectonic melange zone and has an isotopic age of about 2000 Ma. The belt is 600 km long and 75 km wide and consists of tectonically juxtaposed blocks and sheets of Archean and Paleoproterozoic rock complexes with varying degrees of metamorphism. The Au deposits occur mainly in zones with blastomylonite and diaphthorite formed in mafic and ultramafic rock. Some zones consist of actinolite-plagioclase schist with carbonate minerals and biotite Au grade ranges up to 1.0 to 2.0 g/t. Zones of blastomylonite developed in granitoid contain concordant quartz veins with low sulfide deposit with grades that range up to 10 g/t Au (Popov and others, 1999). Large Au deposits are not known. Origin and Tectonic Controls forAmga-Stanovoy Metallogenic BeltThe belt is interpreted as forming during the collision of the West-Aldan and Tynda composite terranes and the Central Aldan superterrane in the Aldan-Stanovoy region and during subsequent collapse of orogenic belt. The reason for collision is unclear. The Au deposits occur in shear zones that cut metamorphosed mafic, ultramafic, and other plutonic rocks. REFERENCES: Parfenov and others, 1999, 2001; Popov and others, 1999. Upper Aldan Metallogenic Belt ofPiezoquartz Deposits(Belt UA) (Russia, Aldan-Stanovoy Shield)This Late Paleoproterozoic metallogenic belt is hosted in the Nimnyr granulite-orthogneiss terrane in the Central Aldan superterrane. The piezoquartz deposits occur in quartzite in high-alumina gneiss and mafic schist. Two rock crystal districts occur: the Upper Aldan (Perekatnoye deposit) and Upper Timpton (Bugarykta deposit). Perekatnoye Piezoquartz DepositThis deposit (Dorofeev and others, 1979) consists of piezoquartz quartzite in high-alumina gneiss and mafic schist. The rock crystal deposits tend to occur at rupture intersections, and in fold flexures and periclines. They form single veins that range from 0.5 to 2 m thick and 20 to 30 m long, and veins that range from 1 to 30 m thick with an average of 5 to 15 m, and lengths of a few tens of meters to 400 m, with an average of 100 to 200 m. Most important are pipe veins and stockworks that are a few tens of meters across. The veins consist of rock crystal or smoky quartz, clay in voids, K-feldspar, and rare crystals of hematite, chlorite, sericite, tourmaline, albite, epidote, and adularia. Rock crystals occur on void walls or in lower parts of the voids in clay. The voids occur in quartz veins, at contacts of veins and the host rocks, or in adjacent host rocks that are altered to sericitie, chlorite, and epidote. The deposits cut Paleoproterozoic metadiabase dikes, and rock crystal clasts occur in Vendian conglomerate. The veins have K-Ar isotopic ages of 1830 to 1750 Ma. The deposit is large. Origin and Tectonic Controls forUpper-Aldan Metallogenic BeltThe belt is interpreted as forming during a post-collisional tectonic event, possibly in a rift. Deposits occur in Late Archean and Paleoproterozoic piezoquartzite associated with high-alumina gneiss and mafic schist metamorphosed to granulite facies. REFERENCES: Arkhipov, 1979; Parfenov and others, 1999, 2001. |