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Mineralium Deposita

, Volume 27, Issue 4, pp 314–325 | Cite as

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

  • V. Gallagher
  • M. Feely
  • H. Högelsberger
  • G. R. T. Jenkin
  • A. E. Fallick
Article

Abstract

Mo mineralization within the Galway Granite at Mace Head and Murvey, Connemara, western Ireland, has many features of classic porphyry Mo deposits including a chemically evolved I-type granite host, associated K- and Si-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. Most fluid inclusions in quartz veins homogenize in the range 100–350°C and have a salinity of 1–13 eq. wt.% NaCl. They display Th-salinity covariation consistent with a hypothesis of dilution of magmatic water by influx of meteoric water. CO2-bearing inclusions in an intensely mineralized vein at Mace Head provide an estimated minimum trapping temperature and pressure for the mineralizing fluid of 355°C and 1.2 kb and 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. δ34S values of most sulphides range from c. 0‰ at Murvey to 3–4‰ at Mace Head and are consistent with a magmatic origin. Most quartz vein samples have δ18O of 9–10.3‰ and were precipitated from a hydrothermal fluid with δ18O of 4.6–6.7‰. Some have δ18O of 6–7‰ and reflect introduction of meteoric water along vein margins. Quartz-muscovite oxygen isotope geothermometry combined with fluid inclusion data indicate precipitation of mineralized veins in the temperature range 360–450°C and between 1 and 2 kb. Whole rock granite samples display a clear δ18O-δD trend towards the composition of Connemara meteoric waters. The mineralization is interpreted as having been produced by highlyfractionated granite magma; meteoric water interaction postdates the main mineralizing event. The differences between the Mace Head and Murvey mineralizations reflect trapping of migrating mineralizing fluid in structural traps at Mace Head and precipitation of mineralization in the granite itself at Murvey.

Keywords

Fluid Inclusion Meteoric Water Quartz Vein Structural Trap Mineralizing Fluid 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. Bigeleisen J., Perlman M. L., Prosser H. C. (1952) Conversion of hydrogenic materials to hydrogen for isotopic analysis. Geochim. Cosmochim. Acta 27: 43–52Google Scholar
  2. Bowers T. S., Helgeson H. C. (1983) Calculation of the thermodynamic and geochemical consequences of non-ideal mixing in the system H2O-CO2-NaCl on phase relations in geologic systems: equation of state for H2O-CO2-NaCl fluids at high pressures and temperatures. Geochim. Cosmochim. Acta 45: 225–228Google Scholar
  3. Brigham R. H., O'Neil J. R. (1985) Genesis and evolution of water in a two-mica pluton: a hydrogen isotope study. Chem. Geol. 49: 159–177Google Scholar
  4. Brown P. E. (1989) FLINCOR: a microcomputer program for the reduction and investigation of fluid inclusion data. Am. Mineral. 74: 1390–1393Google Scholar
  5. Chiba H., Chacko T., Clayton R. N., Goldsmith J. R. (1989) Oxygen isotope fractionation involving diopside, forsterite, magnetite and calcite: application to geothermometry. Geochim. Cosmochim. Acta 53: 2985–2995Google Scholar
  6. Clayton R. N., Mayeda T. (1963) The use of bromine pentafluoride in the extraction of oxygen from oxides and silicates for isotopic analysis. Geochim. Cosmochim. Acta 27: 43–52Google Scholar
  7. Coats J. S., Wilson J. R. (1971) The eastern end of the Galway Granite. Min. Mag. 38: 138–151Google Scholar
  8. Collins P. L. F. (1979) Gas hydrates in CO2-bearing fluid inclusions and the use of freezing data for estimation of salinity. Econ. Geol. 74: 1435–1444Google Scholar
  9. Derham J. M. (1986) Structural control of sulphide mineralization at Mace Head, Co. Galway. In: Andrew C. J., Crowe R. W. A., Finlay S., Pennell W. M., Pyne J. F. (eds) Geology and genesis of mineral deposits in Ireland. Irish Assoc. Econ. Geol., pp. 187–193Google Scholar
  10. Derham J. M., Feely M. (1988) A K-feldspar breccia from the Mo-Cu stockwork deposit in the Galway Granite, west of Ireland. J. Geol. Soc. London 145: 661–667Google Scholar
  11. Ellis R. A., Coats J. S., Haslam H. W., Michie U. McL., Fortey N. J., Johnson C. E., Parker M. E. (1977) Investigation of disseminated copper mineralization near Kilmelford, Argyllshire, Scotland. Inst. Geol. Sci. Mineral Reconnaissance Prog. Report No. 9Google Scholar
  12. Feely M., Högelsberger H. (1991) Preliminary fluid inclusion studies of the Mace Head Mo-Cu deposit in the Galway Granite. Irish J Earth Sci. 11: 1–10Google Scholar
  13. Feely M., Madden J. S. (1988) Trace element variation in the leucogranites within the main Galway Granite, Connemara, Ireland. Min. Mag. 52: 139–146Google Scholar
  14. Gallagher M. J., Michie U. McL., Smith R. T., Haynes L. (1971) New evidence of uranium and other mineralization in Scotland. Trans. Inst. Min. Metall. 80: B150–173Google Scholar
  15. Hall W. E., Friedman I., Nash T. J. (1974) Fluid inclusion and light stable isotope study of the Climax molybdenum deposits, Colorado. Econ. Geol. 69: 884–901Google Scholar
  16. Harmon R. S., Clayburn J. A. P., Stephens W. E. (1984) Chemical and isotopic systematics of the Caledonian intrusions of Scotland and northern England: a guide to magma source region and magma-crust interaction. Phil. Trans. Roy. Soc. London A310: 709–742Google Scholar
  17. Harris M., Kay E. A., Widnall M. A., Jones E. M., Steele G. B. (1983) Geology and mineralization of the Lagalochan intrusive complex, western Argyll, Scotland. Trans. Inst. Min. Metall. 97: B15–21Google Scholar
  18. Jenkin G. R. T., Fallick A. E., Leake B. E. (1992) A stable isotope study of retrograde alteration in S.W. Connemara, Ireland. Contrib. Min. Pet. 110: 269–288Google Scholar
  19. Kennan P. S., McArdle P, Gallagher V., Morris J. H., O'Connor P. G., O'Keeffe W. G., Reynolds N., Steed G. M. (1988) A study of the contribution of isotope geology in the development of exploration strategy: Commission of the European Community Report EUR 11628, 103 pp.Google Scholar
  20. Lawrence G. (1975) The use of Rb/Sr ratios as a guide to mineralization in the Galway Granite, Ireland: Proc. Geochem. Expl. (Vancouver), Developments in economic geology, Spec. Pub. No. 2, Elsevier, Amsterdam New York, pp. 353–370Google Scholar
  21. Leake B. E. (1974) The crystallization history and mechanism of emplacement of the western part of the Galway Granite, western Ireland. Min. Mag. 39: 498–513Google Scholar
  22. Leake B. E. (1978) Granite emplacement: the granites of Ireland and their origin. In: Bowes B. R., Leake B. E. (eds) Crustal evolution in NW Britain and adjacent regions. Geol. J. Spec. Issue No. 10: 221–248Google Scholar
  23. Leake B. E. (1989) The metagabbros, orthogneisses and paragneisses of the Connemara complex, western Ireland. J. Geol. Soc. London 146: 575–596Google Scholar
  24. Leake B. E. (1990) Granite magmas: their source, initiation and consequences of emplacement. J. Geol. Soc. London 147: 579–589Google Scholar
  25. Laouar R., Boyce A. J., Fallick A. E., Leake B. E. (1990) A sulphur isotope study on selected Caledonian granites of Britain and Ireland. Geol. J. 25: 359–369Google Scholar
  26. Madden J. S. (1987). Gamma-ray spectrometric studies of the main Galway Granite, Connemara, west of Ireland. Unpub. Ph. D. Thesis, National Univ. of IrelandGoogle Scholar
  27. Matsuhisa Y, Goldsmith J. R., Clayton R. N. (1979) Oxygen isotope fractionation in the system quartz-albite-anorthite-water. Geochim. Cosmochim. Acta 43: 1131–1140Google Scholar
  28. Max M. D., Talbot V. (1986) Molybdenum concentrations in the western end of the Galway Granite and their structural setting: In: Andrew C. J., Crowe R. W. A., Finlay S., Pennell W. M., Pyne J. F. (eds) Geology and genesis of mineral deposits in Ireland. Irish Assoc. Econ. Geol., pp. 177–185Google Scholar
  29. Max M. D., Long C. B., Geoghegan M. A. (1978) The Galway Granite. Geol. Surv. Ireland Bull. 2: 223–233Google Scholar
  30. Max M. D., Ryan P. D., Inamdar D. D. (1983) A magnetic deep structural geology interpretation of Ireland. Tectonics 2: 431–451Google Scholar
  31. McKie D., Burke K. (1955) The geology of the islands of south Connemara. Geol. Mag. 92: 487–498Google Scholar
  32. Murphy T. (1952) Measurements of gravity in Ireland: gravity survey of central Ireland. Dublin Inst. Advanced Studies, Geophysics Memoir, Vol. 2, 31 pp.Google Scholar
  33. Nabelek P. I., O'Neil J. R., Papike J. J. (1983) Vapour phase exsolution as a controlling factor in hydrogen isotope variation in granitic rocks: the Notch Peak granite stock, Utah. Earth Planet. Sci. Letts. 66: 137–150Google Scholar
  34. Ohmoto H., Rye R. O. (1979) Isotopes of sulfur and carbon: In: Barnes H. L. (ed) Geochemistry of hydrothermal ore deposits, 2nd edn. Wiley, New York, pp. 509–567Google Scholar
  35. O'Neil, Taylor H. P. (1969) Oxygen isotope equilibrium between muscovite and water. J. Geophys. Res. 74: 6012–6022Google Scholar
  36. Pidgeon R. T. (1969) Zircon U-Pb ages from the Galway Granite and the Dalradian, Connemara, Ireland. Scot. J. Geol. 5: 375–392Google Scholar
  37. Plant J. A. (1986) Models for granites and their mineralizing systems in British and Irish Caledonides. In: Andrew C. J., Crowe R. W. A., Finlay S., Pennell W. M., Pyne J. F. (eds) Geology and genesis of mineral deposits in Ireland, Irish Assoc. Econ. Geol., pp. 121–156Google Scholar
  38. Rankin A. H., Alderton D. H. M. (1985) Fluids in granites from Southeast England. In: High heat production (HHP) granites, hydrothermal circulation and ore genesis, Instn. Min. Metall., pp. 287–299Google Scholar
  39. Rice C. M., Harmon R. S., Shepherd T. J. (1985) Central City, Colorado: the upper part of an alkaline porphyry molybdenum system. Econ. Geol., 81: 1769–1796Google Scholar
  40. Robinson B. W., Kusakabe M. (1975) Quantitative preparation of SO2 for 34S/32S analysis from sulphides by combustion with cuprous oxide. Anal. Chem. 47: 1179–1181Google Scholar
  41. Ryan P. D., Feely M. (1983) The Main Galway Granite. In: Archer J. B., Ryan P. D. (eds) Geological guide to the Caledonides of western Ireland. Geol. Surv. Ireland Guide SeriesGoogle Scholar
  42. Schwartz M. O. (1989) Determining phase volumes of mixed CO2-H2O inclusions using microthermometric measurements. Mineral. Deposita 24: 43–47Google Scholar
  43. Spooner E. T. C. (1981) Fluid inclusion studies of hydrothermal ore deposits. In: Hollister L. S., Crawford M. L. (eds) Short course in fluid inclusions: application to petrology, Vol. 6. Mineralogical Association of Canada, pp. 209–240Google Scholar
  44. Talbot V., Max M. D. (1984) Application of various geochemical exploration techniques to Cu and Mo mineralization in the Galway Granite, Ireland. Trans. Instn. Min. Metall. 93B: 109–113Google Scholar
  45. Vukalovich M. P., Altunin V. V. (1968) Thermophysical properties of carbon dioxide. Collets, LondonGoogle Scholar
  46. Wallace S. R., MacKenzie W. B., Blair R. G., Muncaster N. K. (1978) Geology of the Urad and Henderson molybdenite deposits, Clear Creek County, Colorado, with a section on a comparison of these deposits with those at Climax, Colorado. Econ. Geol. 73: 325–368Google Scholar
  47. Westra G., Keith S. B. (1981) Classification and genesis of stock-work molybdenum deposits. Econ. Geol. 76: 844–873Google Scholar
  48. White W. H., Bookstrom A. A., Kamilli R. J., Ganster M. W., Smith R. P., Ranta D. E., Steininger R. C. (1981) Character and origin of Climax-type molybdenum deposits. Econ. Geol. (75th Anniversary Volume) 270–316Google Scholar
  49. Williams D. M., Armstrong H. A., Harper D. A. T. (1988). The age of the South Connemara Group, Ireland, and its relationship to the Southern Uplands Zone of Scotland and Ireland. Scottish J. Geol. 23: 279–287Google Scholar
  50. Wright P. C. (1964) The petrology, chemistry and structure of the Galway Granite of the Carna area, Co. Galway. Proc. Roy. Irish Acad. 63B: 239–264Google Scholar

Copyright information

© Springer-Verlag 1992

Authors and Affiliations

  • V. Gallagher
    • 1
    • 2
  • M. Feely
    • 3
  • H. Högelsberger
    • 3
  • G. R. T. Jenkin
    • 4
  • A. E. Fallick
    • 4
  1. 1.Geological Survey of IrelandDublin
  2. 2.Geology DepartmentUniversity CollegeCork
  3. 3.Geology DepartmentUniversity CollegeGalwayIreland
  4. 4.SURRC, East KilbrideGlasgowScotland

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