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Extreme enrichment of selenium in the Apliki Cyprus-type VMS deposit, Troodos, Cyprus

Martin, Andrew J., McDonald, Iain, MacLeod, Christopher J., Prichard, Hazel M. and McFall, Katie 2018. Extreme enrichment of selenium in the Apliki Cyprus-type VMS deposit, Troodos, Cyprus. Mineralogical Magazine 82 (SI3) , pp. 697-724. 10.1180/mgm.2018.81

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Abstract

The Troodos ophiolite Cyprus hosts the type locality for Cyprus-type, mafic volcanogenic massive sulphide (VMS) deposits. Regional soil geochemical data for Troodos are highly variable with the Solea graben, one of three regional graben structures on Cyprus, showing enrichment in Te and Se. Of the three VMS sampled within the Solea graben, Apliki exhibits the most significant enrichment in Se. Samples from the South Apliki Breccia Zone; a zone of hematite-rich breccia containing euhedral pyrite and chalcopyrite, contain up to 4953 and 3956 ppm Se in pyrite and chalcopyrite respectively. Four paragenetic stages are identified at Apliki and different generations of pyrite are distinguishable using trace element chemistry analysed via LA-ICP-MS. Results indicate stage I pyrite formed under reduced conditions at high temperatures >280 ˚C and contains 182 ppm (n=22 σ=253) Se. Late stage III pyrite which is euhedral and overprints chalcopyrite and hematite is enriched in Se (averaging 1862 ppm; n=23 σ=1394). Sulphide dissolution and hematite formation displaced large amounts of Se as hematite cannot accommodate high concentrations of Se in its crystal structure. The mechanisms proposed to explain the pronounced change in redox are twofold. Fault movement leading to localised seawater ingress coupled with a decreasing magmatic flux that generated locally oxidising conditions and promoted sulphide dissolution. Se/S ratios of 9280 indicate a probable magmatic component for late stage III pyrite which is suggested as a mechanism explaining the transition from oxidising back to reduced conditions. This study highlights the significance of changes in redox which promote sulphide dissolution, mobilisation and enrichment of Se.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Publisher: Mineralogical Society
ISSN: 0026-461X
Funders: NERC
Date of First Compliant Deposit: 30 April 2018
Date of Acceptance: 15 April 2018
Last Modified: 28 Apr 2019 12:36
URI: http://orca.cf.ac.uk/id/eprint/111070

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