Formation of the giant Aynak copper deposit, Afghanistan: evidence from mineralogy, lithogeochemistry and sulphur isotopes

Waizy, H., Moles, N. R., Smith, M. P. and Boyce, A. J. (2021) Formation of the giant Aynak copper deposit, Afghanistan: evidence from mineralogy, lithogeochemistry and sulphur isotopes. International Geology Review, 63(17), pp. 2104-2128. (doi: 10.1080/00206814.2020.1824129)

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Aynak is the largest known copper deposit in Afghanistan, with indicated resources of 240 Mt grading 2.3% Cu placing it in the ‘giant’ category. Host rocks are Neoproterozoic metasediments comprising dolomitic marble, carbonaceous quartz schist and quartz-biotite-dolomite schist containing garnet, scapolite and apatite. Chalcopyrite and bornite dominate the hypogene ore with lesser pyrite, pyrrhotite, cobaltite and chalcocite, and rare sphalerite, molybdenite, uraninite and barite. Sulphides occur as bedding-parallel laminae, disseminations, metamorphic segregations and crosscutting veins. Sulphide δ34S ratios range –14.5 to +17.3‰ in bedded and disseminated sulphides (n = 34). This broad range favours biogenic reduction of seawater sulphate as a major source of sulphur, although thermochemical reduction processes are not precluded. The narrower δ34S range of –6 to +12.2‰ in vein and segregation sulphides (n = 21) suggests localized redistribution and partial homogenization during metamorphism. Geochemical associations suggest that Al, P, Ca, Ti and Fe were primary sedimentary constituents whereas Cu, Mg, S, Se, As, Co and Bi were introduced subsequently. We infer that Aynak originated as a shale- and carbonate-hosted stratabound replacement deposit, resembling orebodies of the Central African Copperbelt, although underlying red-beds are absent at Aynak and mafic volcanics were the probable copper source. These giant deposits formed worldwide in the Cryogenian probably due to marine enrichment in copper, magnesium and sulphate coincident with profuse basaltic volcanism and ocean oxidation.

Item Type:Articles
Additional Information:This work was supported by the University of Brighton, a grant from the British Council, and funding in kind from the Natural Environment Research Council (NERC) approved in December 2016 by the Isotope Geosciences Facilities Steering Committee for application IP‐1681‐1116.
Glasgow Author(s) Enlighten ID:Boyce, Professor Adrian
Authors: Waizy, H., Moles, N. R., Smith, M. P., and Boyce, A. J.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:International Geology Review
Publisher:Taylor & Francis
ISSN (Online):1938-2839
Published Online:04 October 2020
Copyright Holders:Copyright © 2020 The Author(s)
First Published:First published in International Geology Review 63(17): 2104-2128
Publisher Policy:Reproduced under a Creative Commons licence

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