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Taldy Bulak Levoberezhny |
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Kyrgyzstan |
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Au Cu
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Super Porphyry Cu and Au
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The Taldy Bulak Levoberezhny deposit is located in northern Kyrgyzstan, approximately 120 km to the southeast of the capital, Bishkek and 12 km south of Orlovka (#Location: 42° 40' 59'N, 75° 40' 14"E).
Note: This is separate from, and not to be confused with the Tlady Bulak porphyry Cu-Au deposit 150 km to the west.
The Taldy Bulak Levoberezhny deposit is a granitoid-related mesothermal vein/stockwork associated with Devonian diorite porphyry and Carboniferous sub-alkaline diorite-monzonite porphyry dyke swarms. While it has some porphyry style characterisitcs, it has not been conclusively classified as a porphyry style deposit.
It lies within the Boordu-Taldy Bulak zone of the western Aktyuz-Boordu Metallogenic Province. The province is characterised by Baikalian and Caledonian Orogeny structures, while Palaeoproterozoic basement is intruded by Meso- to Neoproterozoic igneous rocks. The Boordu-Taldy Bulak zone comprises a 20 x 30 km diameter volcanic dome-like structure, the central point of which is occupied by the deeply eroded core of a Palaeozoic volcanic edifice. Within and peripheral to this structure, Palaeoproterozoic metamorphics and Lower Palaeozoic volcano-sedimentary rocks are overlain by Devonian, Carboniferous and Lower Permian volcanic and volcano-sedimentary complexes. Throughout the domal structure, there are abundant Middle to Late Palaeozoic mafic to felsic subvolcanic intrusions, occurring as dykes, sills and stocks controlled by deep-rooted faults, representing the root zones of the various overlying volcanic sequences of the Kipchak and Kazakh-Mongol magmatic arcs. Late Tertiary dolerite dykes cut all of the preceding rocks (Chisholm, 2003).
The Taldy Bulak Levoberezhny deposit is located on the margin of a folded and deeply eroded 2 x 4.5 km horst of Palaeoproterozoic basement, cut by sub-volcanic intrusive rocks. The principal lithologies of the basement are a greenschist, amphibolite and mafic migmatite suite overlain by felsic gneiss and mica schist. The mafic and felsic Palaeoproterozoic basement suites are separated by a tectonic contact and are intruded by a sub-volcanic complex of Devonian to Carboniferous diorite to monzonites, which are considered to be almost synchronous with, and genetically and spatially associated with the Au-Cu mineralisation. The area is structurally complex with at least five generations of faulting and large 'crush zones' of brecciated material that dip at 30 to 40° and have focussed mineralisation. These 'crush zones' are believed to be original thrusts which have been reactivated by shearing and/or by subsequent hydrothermal activity (Chisholm, 2003).
The bulk of the mineralisation occurs within a 200 to 300 m thick tabular 'melange zone' which represents one of the 'crush zones'. The 'melange' comprises highly altered rocks that dip at 35 to 40° to the southwest and can be traced for 1.2 to 1.5 km along the southwestern limb of a large antiform, before splitting into a series of horsetails down plunge. It appears to occupy the thrust contact between the Palaeoproterozoic mafic and felsic suites. The 'melange' has been altered to quartz-sericite, quartz-carbonate and quartz-tourmaline assemblages, and intruded by both Devonian diorite porphyry and Carboniferous sub-alkaline diorite-monzonite porphyry (no dating evidence provided). The porphyries have been altered to quartz-sericite. The orebody occurs as a stockwork of sulphide and quartz-tourmaline veining in a zone of sulphide rich, intense multiple brecciation. Lesser mineralisation is associated with faults and tectonic breccias (Chisholm, 2003; pers. comm. John Leishman).
The main gangue minerals within the ore are quartz (45 to 60%), muscovite-sericite (up to 55%), carbonates (up to 30%), tourmaline (up to 40%), fuchsite (1 to 5%) and other chlorites (up to 10%), with lesser barite, fluorite, apatite (0.1 to 1%), feldspar (albite, K feldspar), epidote, pyroxene, amphibole, garnet and traces of topaz. Sulphides comprise 2 to 40% of the mineralised zone, 95% of which is pyrite. Other sulphides present include chalcopyrite, galena, arsenopyrite and sphalerite. Gold is found as small grains of native gold up to 0.4 mm but generally in the 0.01 to 0.1 mm ranges, occurring along grain boundaries, interstitial fractures and to a lesser extent as lamellae within sulphide minerals. Some 46% of the gold is free, 23% occurs as coarser grains with sulphides, 21% as fine inclusions in sulphides, 4% in quartz and 6% in carbonates.
The main high grade gold orebody has the form of a tapering pipe which has been disrupted by faulting and becomes less continuous down plunge. It plunges at between 8 and 40°, steepening with depth, at an azimuth of 300°, has a long axis of 570 m and is 30 to 60 m in diameter. Seven zones of mineralisation, both within this and adjacent pipes, have been identified, two of which make up the quoted resource (Chisholm, 2003).
Malyukova (2001) describes the deposit in detail and notes that while it shares some characteristics with mesothermal Au mineralisation, it has similarities with Au-bearing tourmaline breccia pipes in the porphyry copper belt of Chile. Malyukova (2001) concludes that the deposit may be referred to as a gold-sulphide-quartz-tourmaline type of porphyry gold deposit on the basis of specific features, including i). high abundance of pyrite mainly occurring in quartz-tourmaline altered rocks, ii). veined, disseminated and stringer style mineralization, iii). extensively developed phyllic (and potassic) alteration that predates the tourmalinisation, iv). relation of ore to minor intrusions, v). great vertical extent of ore mineralization, and vi). occurrence of basic volcanics as host rocks.
At a cutoff of 1 g/t Au, the main deposit contains resources and reserves, in various grade and resource classifications, totalling 18.7 Mt at an average grade of 6.9 g/t Au, for 129 tonnes of gold (Central Asia Gold, 2005) with 4 to 5 g/t Ag and 0.2 to 0.3% Cu (Chisholm, 2003; Seltmann et al., 2004 and sources quoted therein).
Xi et al. (2021) quote Zhao et al. (2015) and Xi et al. (2018) as the source of a 'reserve' of 130 t of contained gold at an average grade of 6.9 g/t Au, which would equate to an ore tonnage of 18.8 Mt.
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.
Taldy Bulak Levoberezhny
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Selected References:
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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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Xi, W, Li, N., Xia, X., Ling, X. and Wu, Y., 2021 - Geochronological Constraint on the Evolution of the Aktyuz Terrane, Kyrgyz North Tianshan, and the Fate of the Taldybulak Levoberezhny Gold Deposit.: in Frontiers in Earth Science, Online 16p. doi: 10.3389/feart.2021.664361.
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| References in PGC Publishing Books: | |
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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), Super Porphyry Copper and Gold Deposits: A Global Perspective, v2 pp 467-512
 Abstract
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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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