THE KARCHIGA COOPPER MASSIVE SULFIDE DEPOSIT IN THE HIGH-GRADE METAMORPHOSED ROCKS OF THE KURCHUM BLOCK: GEOLOGIC STRUCTURE, FORMATION, AND METAMORPHISM ( Rudny Altai )
K.V. Lobanova and I.V. Gas'kovb
aOrsu Metals Corporation, 1 Red Place, W1K 6PL London, United Kingdom
bV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Chalcopyrite deposit, Irtysh crumpled zone, Kurchum block, Rudny Altai
Pages: 77-91
Abstract
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 ore lodes, in which all the discovered commercial reserves concentrate. They conformably overlie the host rocks and are tabular and ribbon-like. 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-amphibolite metamorphism. Meanwhile, the ores experienced recrystallization and partial regeneration, but the initial shape of the accumulations remained unchanged.
The essentially chalcopyritic ores, the volcanosedimentary ore-bearing rocks, and the spatial and genetic relationship of the mineralization with undifferentiated basaltoids suggest that this deposit belongs to the Besshi type, formed in a back-arc environment, near large uplifts.
The studies show that Besshi-type chalcopyrite deposits differ from most of the complex (Kuroko-type) deposits in Rudny Altai in the composition of volcanic rocks and geodynamic settings but belong to the same evolutionary series in this pyrite-bearing province. Both types of deposits might have formed in the Middle-Late Paleozoic, during the longest peak of pyritization in the Earth's history.
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