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

Feely, Martin; Costanzo, Alessandra; Gaynor, Sean P.; Selby, David; McNulty, Emma

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.

Citation

Feely, M., Costanzo, A., Gaynor, S. P., Selby, D., & McNulty, E. (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, Article 105267. https://doi.org/10.1016/j.lithos.2019.105267

• Journal Article Type: Article
• Acceptance Date: Oct 28, 2019
• Online Publication Date: Nov 9, 2019
• Publication Date: Feb 28, 2020
• Deposit Date: Nov 15, 2019
• Publicly Available Date: Nov 9, 2020
• Journal: Lithos
• Print ISSN: 0024-4937
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 354-355
• Article Number: 105267
• DOI: https://doi.org/10.1016/j.lithos.2019.105267