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Kokpatas |
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Uzbekistan |
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Au
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Super Porphyry Cu and Au
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The Kokpatas ore field is located approximately 80 km NNW of Zarafshan and 95 km NW of the giant Muruntau gold deposit (see separate record) in the central Kyzylkum region of western Uzbekistan. It contains Au, Ag and Sb mineralisation. Individual prospects include Kvartsevoe, Zapadno-Kokpatasskoe, Sulphidnoe and Vostochno-Kokpatasskoe (#Location: 42° 15' 42"N, 63° 53' 30"E).
The deposit is found within the overthrust terrane of the South Tien Shan tectonic province, to the south of the main magmatic zone of the Carboniferous Beltau-Kurama Magmatic Belt. Highly schistose, mafic to intermediate volcanic and volcaniclastic rocks of this magmatic belt are thrust over Devono-Carboniferous platform carbonates. The host rocks are mid-Carboniferous micro-granular limestones, flinty slate formations and volcano-sedimentary formations composed of tuff-breccia, quartz-tuff siltstone, sandstone, siltstone and argillite.
The gold deposits of the field are individually small, but numerous, distributed over a NW-SE elongated area of ~8 x 5 km. Gold mineralisation occurs in veins in association with the pyrite and arsenopyrite. The ore comprises a quartz-pyrite-arsenopyrite association and antimonite with a gangue of quartz, ankerite, dolomite, calcite and sericite. The alteration minerals include quartz, sericite, fuchsite, chlorite and Mg-Fe carbonates (Berger, et al., 1994).
Within the ore field, the structurally overlying volcanic sequence hosts stratabound pyrite lenses, underlain by structurally controlled stockwork-like vein zones.
According to Dunin-Barkovskaya et al. (2005), disseminated sulphide orebodies are layer- and lens-shaped, with dips that are gentle, and seldomly steep. Sulphides (arsenopyrite, pyrite) comprise up to 10% of the ore. Gold is finely dispersed with a grain size of up to 0.2 µm, and is partly of gold 'invisible'. The maximum concentration of invisible gold in pyrite and arsenopyrite is as much as 0.11 and 1.3%, respectively. Three mineral assemblages have been distinguished: i). gold-pyrite- arsenopyrite (the main economic assemblage); ii). quartz-ankerite-gold-fahlore; and iii). quartz-silver-stibnite. Fahlore is the tetrahedrite-tennantite solid solution. In the first assemblage, gold occurs in pyrite and arsenopyrite, and is either very fine (0.2 to 5 µm) or 'invisible' (<0.2 µm). In the second association, the gold is up to tens of µm is associated with tetrahedrite. The primary ores are difficult to concentrate. However, an oxide zone is widely developed and mined, comprising Fe-hydroxides containing 83 to 91% native gold and, 9 to 17% silver.
Based on Soviet era testing patterns and reserve classifications, the reserves/resources comprise 120 t of Au in class C1, with a further 150 t in class C2. The average grade is 4 g/t Au. The mineralisation was discovered in 1963, with exploration since 1969, and commencement of open pit exploitation at a rate of 1 Mt of ore per annum in 1986.
The most recent source geological information used to prepare this decription was dated: 2002.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Kokpatas
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Selected References:
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Dunin-Barkovskaya, E.A., Aripov, U.K., Tsoy, L.A. and Kim, M.A., 2005 - Mineralogical features and ore-forming conditions of goldbearing deposits of Uzbekistan: in IGCP Project 486, 2005 Field Workshop, Kiten, Bulgaria, 14-19 September 2005 Geochemistry, Mineralogy and Petrology, Bulgarian Academy of Sciences, v.43, pp. 69-74.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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