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Aktogai Group - Aqtogai, Aidarly, Kyzilkia |
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Kazakhstan |
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Cu Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Aktogai (Aqtogai) group of porphyry Cu-Mo-Au deposits, Aktogai, Aidarly and Kyzilkia are located in the 'Balkhash-Ili' zone of the Upper Palaeozoic Kazakh-Mongol magmatic arc, northeast of Lake Balkhash in southeastern Kazakhstan, and some 450 km NNE of Almaty (#Location: Aktogai - 46° 58' 6"N, 79° 58' 48"E; Aidarly - 46° 58' 56"N, 79° 54' 22"E).
Geology
The three main deposits of the Aktogai district are associated with stock-like granodiorite and plagiogranite porphyries intruding the extensive laccolith like Late Carboniferous Koldar Pluton and large rafts of Carboniferous volcano-sedimentary rocks within the pluton. The volcano-sedimentary rafts are composed predominantly of andesites, dacites and rhyolites, and their tuffs (Zvezdov et al., 1993; Bespaev and Miroshnichenko, 2004).
The Aktogay deposit is confined to the eastern part of the Central Aktogai raft of volcanics and the enclosing pluton. The raft is intruded by a stock like body of porphyritic granodiorite which also cross-cuts diorite, quartz-diorite and granodiorite of the Koldar pluton. The porphyritic granodiorite is in turn, cut by an elongate stock composed of ore-bearing granodiorite and plagiogranite porphyries, accompanied by a series of pipe-like bodies of explosive breccia with quartz-biotite and sericite-tourmaline matrices. The ore bearing stockwork occurs in the outer contact zone of the porphyry stock, forming a hollow, downward tapering conical body, which pinches out at depth into a series of linear west to northwest trending mineralised zones. At the surface, the orebody has an elliptical annular shape, partially opened to the west, with a maximum diameter of approximately 2500 m, and a radial width of 80 to 530 m (Zvezdov et al., 1993; Seltmann et al., 2004).
Alteration and Mineralisation
All rocks in the orebody area, with the exception of late mafic dykes, have been altered. The barren core of the cone/annulus is occupied by a siliceous zone, comprising quartz bodies surrounded by a dense stockwork of barren quartz veinlets, and a thin zone of sericite-quartz alteration. Towards its margins, the silicified core passes out into a thick zone of early potassic alteration, comprising K feldspar and biotite, that encompasses the main annular orebody. Included within this potassic zone are several linear intervals which are poorly mineralised, but intensely K feldspar altered, and flanked by a wide halo of biotite. Phyllic alteration, characterised by quartz-(carbonate)-chlorite-sericite, appears as impersistent, thin linear zones, confined to the contacts of granodiorite porphyry apophyses and to zones of fracturing along the flanks of the orebody. The periphery of the porphyry copper system is occupied by a large propylitic halo containing epidote-amphibole and albite-chlorite-prehnite (Zvezdov et al., 1993).
The mineralised system exhibits an outward zonation from bornite-chalcopyrite at the centre to chalcopyrite-pyrite to a pyritic halo on the outer margins. Cu and Mo overlap, while Pb-Zn is confined to zones of carbonatisation on the flanks of the orebody. The paragenetic sequence is as follows: i). magnetite; ii). pyrrhotite-cubanite; iii). quartz-pyrite; iv). quartz-(magnetite)-bornite-chalcopyrite; v). quartz-molybdenite-pyrite-chalcopyrite; vi). quartz-(pyrite)-bornite-chalcopyrite-chalcocite; vii). quartz-sericite-pyrite; viii). quartz-galena-sphalerite-chalcopyrite-pyrite-tennantite; ix). post ore zeolite-carbonate. Quartz is the dominant gangue mineral within the stockwork veins, although K feldspar and biotite are also found in early veins, while late veins carry chlorite, epidote, prehnite and carbonate. Fluid inclusion studies indicate that the early quartz-K feldspar veinlets were formed at between 490 and 320°C, while the late sulphide-quartz veinlets range from 320 to 180°C (Zvezdov et al., 1993, and references cited therein).
Resources published for Aktogai in the Competent Persons report by IMC Consultants to Kazakhmys plc, (2011) comprise:
Indicated+inferred resources - 1.72 Gt @ 0.34% Cu, 1.39 g/t Ag, 0.04 g/t Au, 0.01% Mo.
Reserve and resource estimates published in KAZ Minerals Annual Report 2014 were:
Proved+probable reserves - 1.516 Gt @ 0.35% Cu, 0.01% Mo,
Measured+indicated resources - 1.719 Gt @ 0.34% Cu, 1.39 g/t Ag, 0.04 g/t Au, 0.01% Mo
Inferred resource - 0.488 Gt @ 0.30% Cu, 1.39 g/t Ag, 0.04 g/t Au, 0.01% Mo.
The Aidarly deposit is located approximately 4 km to the WNW of Aktogai, and falls within the same 8 x 2 km, WNW elongated sulphidic alteration halo. It is centred on a small, north-west trending stock of ore bearing granodiorite porphyry which intrudes diorite, quartz diorite and granite phases of the Koldar pluton. The granodiorite porphyry stock has steep contacts, characterised by numerous apophyses, and is accompanied by a series of fault controlled dykes of the same composition with northeast and northwest orientations. All of these intrusives are cut by late quartz diorite and dolerite dykes. Small cylindrical breccia bodies near the granodiorite porphyry are composed of mineralised rock fragments, cemented by rock flour (Zvezdov et al., 1993).
Mineralisation is confined to the outer margins of the stock and the surrounding Koldar pluton, and closely follows the trend of the stock. At surface, the orebody outcrops as a north-west elongated annulus, surrounding a slightly mineralised granodiorite-porphyry. As at Aktogai, the orebody resembles a downward tapering, hollow, truncated cone, with a barren core occupied by poorly mineralised granodiorite porphyry and a zone of silicification. Alteration and mineral zoning is similar to that described at Aktogai. The outcropping granodiorite porphyry has been subjected to slight silicification and sericitisation. At a depth of 600 m the porphyry has a barren core of intense silicification, with scattered anhydrite in its outer margins. Towards the periphery of the porphyry system the silicification passes outward into potassic alteration of quartz-K feldspar-biotite. Higher in the system, at intermediate and near surface depths, this pattern is overlain by a zone of phyllic alteration characterised by quartz-sericite-chlorite-carbonate, with occasional tourmalinisation. The potassic zone is in turn surrounded by a wide halo of propylitic alteration (Zvezdov et al., 1993).
The orebody takes the form of a Cu-Mo stockwork concentrated in the early potassic zone and overprinted by the phyllic alteration. Although most aspects of the mineralisation and alteration are similar to that described above for Aktogai, the deposit differs in that it has a more extensive and better developed polymetallic (Pb-Zn) veinlet and vein mineralisation zone on its outer margins. These comparisons suggest that the Aidarly deposit is less deeply eroded than Aktogai (Zvezdov et al., 1993).
Resources published for Aidarly in the Competent Persons report by IMC Consultants to Kazakhmys plc (2010), comprise:
Indicated+inferred resources - 1.53 Gt @ 0.34% Cu, 1.38 g/t Ag, 0.01 g/t Au, 1.42 g/t Ag, 0.01% Mo
The small Kyzylkia deposit is 4 km to the east of Aktogai, on the opposite side to Aidarly. It appears to have been more deeply eroded than either of the other two, supporting the implication of deep erosion in the east, shallowing to the west within the Aktogay district. At Kyzylkia Cu-Mo mineralisation is associated with a small granodiorite porphyry stock intruding the granodiorites of the Koldar Pluton. Orebodies are present as a series of en echelon like zones of stringer chalcocite-bornite-chalcopyrite ore accompanied by erratic K-silicate and phyllic alteration (Zvezdov et al., 1993).
The most recent source geological information used to prepare this decription was dated: 2004.
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.
Aktogai Aidarly
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Gao, J., Qin, K., Zhou, M.-F. and Zaw, K., 2018 - Large-scale porphyry-type mineralization in the Central Asian Metallogenic Domain: Geodynamic background, magmatism, fluid activity and metallogenesis: in J. of Asian Earth Sciences Online, https://doi.org/10.1016/j.jseaes.2018.08.023.
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Li, C., Shen, P. and Pan, H., 2018 - Mineralogy of the Aktogai giant porphyry Cu deposit in Kazakhstan: Insights into the fluid composition and oxygen fugacity evolution: in Ore Geology Reviews v.95, pp. 899-916.
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Li, C., Shen, P., Pan, H. and Seitmuratova, E., 2019 - Control on the size of porphyry copper reserves in the North Balkhash-West Junggar Metallogenic Belt: in Lithos v.328-329, pp. 244-261.
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Li, C., Shen, P., Pan, H., Cao, C. and Seitmuratova, E., 2018 - Geology and ore-forming fluid evolution of the Aktogai giant porphyry Cu deposit, Kazakhstan: in J. of Asian Earth Sciences v.165, pp. 192-209, https://doi.org/10.1016/j.jseaes.2018.07.009
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Seltmann R and Porter T M, 2005 - The Porphyry Cu-Au/Mo Deposits of Central Eurasia: 1. Tectonic, Geologic & Metallogenic Setting and Significant Deposits: in Porter, T.M. (Ed), 2005 Super Porphyry Copper & Gold Deposits - A Global Perspective, PGC Publishing, Adelaide, v.2 pp. 467-512
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Seltmann, R., Dolgopolova, A. and CERCAMS team, 2012 - Porphyry Cu-Au/Mo Deposits of Central Eurasia: Geodynamics and Metallogeny: in Existing Resources, New Horizons, KazGeo 2012, Almaty, Kazakhstan, 29-31 October 2012, Conference Proceedings, 4p.
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Seltmann, R., Porter, T.M. and Pirajno, F., 2014 - Geodynamics and metallogeny of the central Eurasian porphyry and related epithermal mineral systems: A review: in J. of Asian Earth Sciences, v.79, pp. 810-841.
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Shen, P., Pan, H., Hattori, K., Cooke, D.R. and Seitmuratova, E., 2018 - Large Paleozoic and Mesozoic porphyry deposits in the Central Asian Orogenic Belt: Geodynamic settings, magmatic sources, and genetic models: in Gondwana Research v.58, pp. 161-194.
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Wan, B., Xiao, W., Windley, B.F., Gao, J., Zhang, L. and Cai, K., 2017 - Contrasting ore styles and their role in understanding the evolution of the Altaids: in Ore Geology Reviews v.80, pp. 910-922.
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Yakubchuk, A., Degtyarev, K., Maslennikov, V., Wurst, A., Stekhin, A. and Lobanov, K., 2012 - Tectonomagmatic Settings, Architecture, and Metallogeny of the Central Asian Copper Province: in Hedenquist J W, Harris M and Camus F, 2012 Geology and Genesis of Major Copper Deposits and Districts of the World - A tribute to Richard H Sillitoe, Society of Economic Geologists Special Publication 16, pp. 403-432
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Zvezdov V S, Migachev I F and Girfanov M M 1993 - Porphyry copper deposits of the CIS and the models of their formation: in Ore Geology Reviews v7 pp 511-549
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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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