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Geochemistry, mineralogy, Cu, Zn and Fe isotopic composition of Gossans found in Cyprus-type VMS systems from the Troodos ophiolite

The Troodos ophiolite hosts significant Volcanogenic Massive Sulfide (VMS) systems, well-known as Cyprus-type sulfide deposits. They are mafic type VMS deposits, mainly enriched in copper and zinc and they have been deposited from seawater derived-hydrothermal fluids. Along the Troodos ophiolite, the VMS system is covered by thick, Fe- rich altered caps, known as gossans, which are likely due to weathering of the VMS under oxidizing conditions. However, the conditions for their formation remain largely debated, suggesting either a submarine weathering origin or mineralization weathering on land. Gossans represent a valuable part of the Troodos ophiolite, presenting not only significant amount of extractible copper and zinc, but also, gold and silver. The studied gossans present as mineral assemblage: goethite, jarosite, hematite, alunite, silica, clays, anatase and siderite. Magnetite, ilmenite and gypsum occur as accessory phases. In this study, we show combined data of Cu, Zn and Fe isotopes from three different mines of the Troodos ophiolite (West Apliki, Skouriotissa and Agrokipia), which indicate δ65Cu values varying from -3.55 ±0.01‰ to -0.05 ±0.02‰ and δ66Zn values ranging from -1.24 ±0.02‰ to +0.34 ±0.05‰. In addition, δ56Fe values vary from -0.65 ±0.07‰ to +0.80 ±0.02‰. We aim to investigate the debated origin of the Troodos ophiolite gossans influenced by physicochemical conditions, fluid composition, hypogene ore (e.g., pyrites) and examine the supergene weathering process in VMS systems, based on the redox-sensitive behavior of Cu and Fe, as well as the pH-sensitive behavior of Zn in supergene-weathering environments.


Nina Zaronikola1, Vinciane Debaille1, Sophie Decrée2, Ryan Mathur3, Christodoulos Hadjigeorgiou4
1Laboratoire G-Time, Universite Libre de Bruxelles, Brussels, Belgium; 2Royal Belgian Institute of Natural Sciences, B-1000, Brussels, Belgium; 3Juniata College, 1700 Moore Street, Huntingdon, Pennsylvania 16652, USA; 4Geological Survey Department, 1 Lefkonos Street, 2064 Strovolos, Lefkosia, Cyprus
GeoKarlsruhe 2021