Geological, fluid inclusion and stable isotope studies of Mo mineralization, Galway Granite, Ireland

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Authors:Gallagher, V.; Feely, M.; Högelsberger, H.; Jenkin, G. R. T.; Fallick, A. E.
Author Affiliations:Primary:
Geol. Surv. Ireland, Dublin, Ireland
Volume Title:Mineralium Deposita
Source:Mineralium Deposita, 27(4), p.314-325. Publisher: Springer-Verlag, Berlin, Federal Republic of Germany. ISSN: 0026-4598
Publication Date:1992
Note:In English. 2 p. refs.; illus. incl. 2 tables, geol. sketch map
Summary:Mo mineralization within the Galway granite at Mace Head and Murvey, Connemara, W Ireland, has many features of classic porphyry Mo deposits including a chemically evolved I-type granite host, associated K- and Sr-rich alteration, quartz vein- (Mace Head) and granite-hosted (Murvey) molybdenite, chalcopyrite, pyrite and magnetite mineralization, and a gangue assemblage which includes quartz, muscovite and K-feldspar. Dilute aqueous fluid inclusions in quartz veins probably record the influx of meteoric water during prolonged post-mineralization granite-fluid interaction; CO2-bearing inclusions in the most richly mineralized vein (Mace Head) are interpreted to represent a H2O-CO2 fluid, weakly enriched in Mo, produced in a magma chamber by decompression-activated unmixing from a dense Mo- bearing NaCl-H2O-CO2 fluid of probable magmatic origin. S isotope values (approx 0 per mille at Murvey and 3-4 per mille at Mace Head) provide strong support for the proposed magmatic origin for the mineralization. delta18O and deltaD data for granites, veins and fluid inclusions indicate the involvement at some stage of a meteoric fluid with deltaD >= -30 per mille . The mineralization is interpreted as having been produced by highly-fractionated granite magma; meteoric water interaction postdates the main mineralizing event. The differences between the Mace Head and Murvey mineralizations reflect the trapping of migrating mineralizing fluid in structural traps at Mace Head and precipitation of mineralization in the granite itself at Murvey. [R.E.S.]
Subjects:Carbon; Chalcopyrite; Copper ores; Fluid inclusions; Framework silicates; Geologic thermometry; Granites; Host rocks; Hydrogen; I-type granites; Igneous rocks; Inclusions; Isotopes; Magnetite; Metal ores; Mineralization; Molybdenite; Molybdenum ores; Oxides; Oxygen; Plutonic rocks; Porphyry copper; Pyrite; Quartz; Silica minerals; Silicates; Stable isotopes; Sulfides; Sulfur; Veins; Connemara; Europe; Galway Granite; Galway Ireland; Ireland; Western Europe
Abstract Numbers:93M/1873
Record ID:1993028782
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe
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