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Erdenet, Erdenetiin Ovoo
Main commodities: Cu Mo

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The Erdenet porphyry Cu-Mo deposit is located some 250 km WNW of Ulaanbaatar, the capital of Mongolia (#Location: 49° 01' 21"N, 104° 07' 54"E).

It lies within the Orkhon-Selenge volcano-sedimentary trough of the Northern Mongolian magmatic belt which is characterised by late Palaeozoic to Mesozoic calc-alkaline volcanism.

This belt, which was developed on an active continental margin is believed to have formed as a consequence of the collision of the Siberian craton with the Mongolian-North China block to the south and subduction of oceanic crust from the intervening Mongol-Okhotsk basin.

The geodynamic evolution of the trough involves an early intra-continental stage, comprising rifting of a shallow continental shelf, accompanied by the emplacement of sub-aerial Permian mafic and felsic, and Triassic mafic volcanic rocks. The Permian volcanics are predominantly alkali-rich trachyandesites, occurring as interlayered flows and pyroclastics of the Khanui Group, overlying a Vendian (late Neoproterozoic) to early Cambrian basement with Palaeozoic (Devonian) granitoid intrusions, and Carboniferous sedimentary rocks.

Plutons, ranging in composition from diorite to granodiorite, quartz syenite and leucogranite intrude the Permian volcanic succession and exhibit similar compositional trends as the host volcanics, suggesting the intrusions are related to, and possibly coeval with, the volcanic rocks. These include the 290 to 260 Ma granites, granodiorites and gabbro-norites of the late Permian Selenge Complex which intrude the Precambrian and early Palaeozoic basement, and are in turn cut by the upper Permian to Mesozoic ore bearing porphyries of the Erdenet Complex.

Early Mesozoic porphyritic subvolcanic and hypabyssal intrusions of the Erdenet Complex, which are genetically associated with the early trachyandesite volcanics, are related to a continental collisional setting. These include syn-mineral granodiorite-porphyry intrusions which form shallow bodies, occurring as elongated dykes or small, shallow stocks. These porphyries vary from quartz diorite through granodiorite to granite in composition. They are characterised by porphyritic textures (up to 40% phenocrysts) with plagioclase phenocrysts set in a fine-grained groundmass of K feldspar, and are found in the core of the hydrothermal systems, where they are associated with high-grade ore.

The Erdenet Complex includes the following ore-related stages:  i). the main syn-mineral phase, dominantly diorite porphyry and microdiorite, with lesser dacite and dacite autobreccia (~250 Ma), ii). granodiorite porphyry (approx 230 Ma) and iii). plagiogranite and granodiorite porphyries, iv). rare dykes of leucocratic porphyries and rhyodacites, and v). diorite porphyries, andesites and granodiorite porphyries.

The Triassic Mogod Formation trachyte, trachyandesite and basaltic-trachyandesite flows that directly overlie the Permian sequence, and post-mineralisation syenite porphyry dykes, and intrude both the Selenge and Erdenet complexes, are of upper Triassic to lower Jurassic age (182±6 and 177±6 Ma). Samples of hypogene mineralisation have been dated as lowermost Jurassic (207±2 Ma) (Gerel and Munkhtsengel, 2005, and references cited therein).

Three principal alteration zonations are developed within the upper part of Erdenet deposit (Kominek et al., 1977, Khasin et al., 1977), from the core to the periphery, namely: i) sericitic (quartz-sericite) and late siliceous, ii) intermediate argillic (chlorite-sericite), and iii) propylitic (chlorite and epidote-chlorite).

The paragenesis of mineralisation at Erdenet is suggested to comprise (Gavrilova et al., 1990) i) pre-ore quartz-sericite; followed by the ore stages of ii) quartz-chalcopyrite-pyrite; iii) quartz-pyrite-molybdenitechalcopyrite; iv) quartz-chalcopyrite-tennantite; v) quartz-pyrite-galena-sphalerite; vi) over-printing bornite-chalcocite-covellite; and vii) post-ore gypsum-calcite with pyrite. The first two ore stages are dominated by vein stockworks, while the succeeding three phases are localised by dykes and associated fracturing. All of these phases however, overprint, and largely obliterate, an earlier weak potassic alteration with associated chalcopyrite. The early potassic phase occurs as secondary biotite and magnetite, followed by pink feldspar veining, and is only encountered as remnants in the less fractured, deeper, central sections of the deposit.

The dominant hypogene stage is characterised by chalcopyrite, bornite, covellite and minor chalcocite. An upper oxide zone, composed of Cu carbonates, oxides, phosphates and sulphates, native Cu and ferrimolybdite overlies a 30 to 300 m thick supergene enrichment chalcocite blanket.

The deposit, which covers an area of 2 x 1 km, has produced some 1.5 Mt of copper, largely from the chalcocite blanket which contains bornite-covellite-chalcocite (where secondary chalcocite replaces hypogene pyrite, chalcopyrite and bornite-covellite assemblages in stockworks and sheeted veins) with an average grade of 0.75% Cu within a zone of sericitic alteration.   This secondary enrichment overlies 0.4% Cu hypogene mineralisation which persists to depths of 560 m within a broader halo of K feldspar altered Erdenet Complex porphyries.   The deeper hypogene assemblage includes chalcopyrite, bornite, molybdenite and pyrite within quartz veinlets with muscovite halos and as disseminations within the host porphyries in the following paragenetic order:  a). magnetite,  b). quartz-pyrite,  c). quartz-molybdenite  d). chalcopyrite-pyrite-quartz,  e). pyrite,  f). pyrrhotite-chalcopyrite ±cubanite,  g). hypogene chalcocite-bornite and  h). galena-sphalerite-tennantite.

While potassic alteration is widespread within the complex, the mineralisation appears to be largely associated with late sericitisation.

The deposit, which has been exploited since 1977, has been estimated to have contained a total of 9.2 Mt of copper and 0.27 Mt of molybdenum in 'reserves' and historic production, with a remaining geological resource of 1.78 Gt @ 0.62% Cu, 0.025% Mo (Gerel and Munkhtsengel, 2005, and references cited therein).

This summary draws from and directly quotes sections of Gerel and Munkhtsengel (2005) published in Porter (Ed.), Super Porphyry Copper and Gold Deposits: A Global Perspective, v2.

The most recent source geological information used to prepare this decription was dated: 2006.    
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.

  References & Additional Information
   Selected References:
Berzina, A.N., Berzina, A.P. and Gimon, V.O.,  2016 - Paleozoic-Mesozoic Porphyry Cu(Mo) and Mo(Cu) Deposits within the Southern Margin of the Siberian Craton: Geochemistry, Geochronology, and Petrogenesis (a Review): in    Minerals   v.6,  doi:10.3390/min6040125
Berzina, A.N., Sotnikov, V.I., Economou-Eliopoulos, M. and Eliopoulos, D.G.,  2005 - Distribution of rhenium in molybdenite from porphyry Cu-Mo and Mo-Cu deposits of Russia (Siberia) and Mongolia : in    Ore Geology Reviews   v.26 pp. 91-113.
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.
Gerel O and Munkhtsengel B,  2005 - Erdenetiin Ovoo Porphyry Copper-Molybdenum Deposit in Northern Mongolia: in Porter, T.M. (Ed), 2005 Super Porphyry Copper & Gold Deposits - A Global Perspective, PGC Publishing, Adelaide,   v.2 pp. 525-543
Kavalieris, I., Khashgerel, B.-E., Morgan, L.E., Undrakhtamir, A. and Borohul, A.,  2017 - Characteristics and 40Ar/39Ar Geochronology of the Erdenet Cu-Mo Deposit, Mongolia: in    Econ. Geol.   v.112, pp. 1033-1053.
Kim, Y., Lee, I., Oyungerel, S., Jargal, L. and Tsedenbal, T.,  2019 - Cu and S isotopic signatures of the Erdenetiin Ovoo porphyry Cu-Mo deposit, northern Mongolia: Implications for their origin and mineral exploration: in    Ore Geology Reviews   v.104, pp. 656-669
Lamb M A, Cox D  1998 - New 40Ar/39Ar age data and implications for Porphyry Copper deposits of Mongolia: in    Econ. Geol.   v93 pp 524-529
Monecke, T., Reynolds, T.J., Gonchig, T. and Batbayar, N.,  2024 - Evolution of the magmatic-hydrothermal system at the Erdenetiin Ovoo porphyry Cu-Mo deposit, Mongolia: constraints on the relative timing of alteration and mineralization: in    Mineralium Deposita   v.59, pp. 907-929.
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
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.
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.
Sotnikov V I, Berzina A N, Economou-Eliopoulos M and Eliopoulos D G  2001 - Palladium, platinum and gold distribution in porphyry Cu±Mo deposits of Russia and Mongolia : in    Ore Geology Reviews   v18 pp 95-111
Watanabe Y, Stein H J  2000 - Re-Os ages for the Erdenet and Tsagaan Suvarga porphyry Cu-Mo deposits, Mongolia and tectonic implications: in    Econ. Geol.   v95 pp 1537-1542
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

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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