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Lobanov K.V.,Orsu Metals Corporation | Gaskov I.V.,RAS Institute of Geology and Mineralogy
Russian Geology and Geophysics | Year: 2012

The Karchiga copper massive sulfide deposit is located in the Kurchum block of high-grade metamorphosed rocks. This block is part of the Irtysh shear zone, which belongs to the largest transregional fault in Central Asia. The deposit is associated with the gneiss-amphibolite middle unit of the metamorphic complex, which is distinct in the geochemical fields. The mineralization is spatially and paragenetically related to the amphibolite beds, which are ore-bearing together with terrigenous rocks.The deposit contains two spatially isolated lodes, in which all the discovered commercial reserves concentrate. They conformably overlie the host rocks and are tabular or ribbonlike. The mineralization has a close spatial relationship with Mg-rich anthophyllite-containing rocks. The sulfide ores are disseminated or massive and comprise pyrite, chalcopyrite, pyrrhotite, sphalerite, and magnetite. The ore is of Zn-Cu composition, in which Cu dominates considerably over Zn (average contents 2 and 0.4%, respectively; Cu/(Cu + Zn) = 0.83). The ores are rich in Co (up to 0.16%, averaging 0.02%), poor in Au and Ag (0.3 and 7.2 ppm, respectively), and almost free of Pb and Ba.All the rocks and ores experienced epidote-amphibolitic metamorphism. Meanwhile, the ores experienced a recrystallization and partial regeneration, but the initial shape of the lodes remained unchanged.The essentially chalcopyritic ores, the volcaniclastic ore-bearing rocks, and the spatial and genetic relationship of the mineralization with undifferentiated mafic and siliciclastic rocks suggest that this deposit belongs to the Besshi type, formed in a back-arc environment, near large rises.The studies show that Besshi-type Cu-Zn massive sulfide deposits differ from most of the polymetallic (Kuroko-type) deposits in Rudny Altai in the composition of volcanics and geodynamic settings, but belong to the same evolutionary series in this VMS province. Both types of deposits might have formed in the Paleozoic, during the main peak of VMS generation in the Earth's history. © 2011.

Lobanov K.,Orsu Metals Corporation | Yakubchuk A.,Orsu Metals Corporation | Creaser R.A.,University of Alberta
Economic Geology | Year: 2014

For the first time in the Rudny Altai, we propose to distinguish Besshi- and Kuroko-type deposits, previously considered as members of a single massive sulfide-polymetallic group. The ores of the two deposit types differ in mineral composition, with pyrite-pyrrhotite-chalcopyrite ± sphalerite mineralization in the Besshi-type deposits versus pyrite-sphalerite-galena- chalcopyrite-gold mineralization in the Kuroko-type deposits. The Besshi-type deposits are restricted to the Irtysh terrane and associated with deformed and metamorphosed (greenschist to mid-amphibolite facies) mafic-siliciclastic rock sequences. This contrasts with the well-preserved Kuroko-type deposits, hosted in bimodal volcanic sequences in the Devonian-Carboniferous Rudny Altai magmatic arc. Our U-Pb, 40Ar/39Ar, and Re-Os isotope dating of sulfides and host rocks of the Besshi-type deposits suggests that they were probably formed during the early Paleozoic in a back-arc rift setting. They were then metamorphosed during Devonian times within the accretionary wedge in front of the Rudny Altai arc, synchronously with formation of the Kuroko-type deposits. © 2013 Society of Economic Geologists, Inc.

Yakubchuk A.,Orsu Metals Corporation | Stein H.,Colorado State University | Wilde A.,Paladin Energy
Ore Geology Reviews | Year: 2014

The pilot study with Re-Os dating of sulfides from Sukhoi Log and Olympiada gold deposits revealed early Paleozoic ages of the auriferous sulfides from the two largest orogenic gold systems in the Neoproterozoic orogens of the Baikalides framing the Siberian craton. The age-dating results indicate that gold mineralization is therefore epigenetic. The formation of the dated orogenic gold deposits is synchronous with some regional metamorphic events in the Baikalides, at least in case of the Sukhoi Log deposit. The metamorphic events occurred in the rear parts of the early Paleozoic magmatic arcs, where coeval subduction-related magmatism produced porphyry copper-(molybdenum) mineralization. © 2013 Elsevier B.V.

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