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Durham University

Department of Earth Sciences

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Publication details for Prof. Dave Selby

Feely, Martin, Costanzo, Alessandra, Gaynor, Sean P., Selby, David & McNulty, Emma (2020). A review of molybdenite, and fluorite mineralization in Caledonian granite basement, western Ireland, incorporating new field and fluid inclusion studies, and Re-Os and U-Pb geochronology. Lithos 354-355: 105267.

Author(s) from Durham

Abstract

The recent discovery of late-magmatic quartz vein hosted molybdenite, and exceptional gem quality vein fluorite, in the Caledonian Galway Granite Complex (GGC), has prompted a review of these contrasting styles of mineralisation in the late-Caledonian granite basement, Connemara, western Ireland. Existing published U-Pb and Re-Os chronometry and fluid inclusion microthermometry are combined with new: a) geological field observations, b) U-Pb zircon and Re-Os molybdenite geochronometry and c) fluid inclusion microthermometry to generate a new pressure-temperature-time model (P-T-t) of mineralization for the GGC. Re-Os chronometry molybdenite indicates that granite related molybdenite mineralisation extended from 423 to 380Ma overlapping with the GGC emplacement history determined by U-Pb zircon chronometry. The P-T-t model reflects initial granite emplacement and Mo-mineralisation at ∼423Ma followed by lower P and T granite emplacement and related quartz vein hosted Mo-mineralisation at ∼410Ma (Carna pluton), ∼400Ma (Kilkieran pluton) and at ∼380Ma (Costelloe Murvey granite). The gem quality fluorite veins in the GGC represent late-Triassic hydrothermal mineralisation. These veins form part of a regional N Atlantic-European Triassic-Jurassic hydrothermal mineralisation province. Vein emplacement was triggered by the rifting of the N Atlantic facilitating crustal thinning and subsidence of continental crust and initiating hydrothermal activity at the margins of Mesozoic basins.