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Volcanic activity, magma-sediment-water interaction, hydrothermal alteration and vein mineralisation in south County Waterford

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dc.contributor.advisor Moore, Kathryn
dc.contributor.advisor Feely, Martin
dc.contributor.author Breheny, Catherine
dc.date.accessioned 2011-10-28T13:56:29Z
dc.date.available 2011-10-28T13:56:29Z
dc.date.issued 2010-11-05
dc.identifier.uri http://hdl.handle.net/10379/2243
dc.description.abstract The Ordovician volcanic sequence of the south Waterford coast is used to investigate magma-sediment-water interaction and its role in hydrothermal systems. Field investigations and rock textures analysis have shown that relatively constant composition intrusions were emplaced in rapidly consolidating host sediments. Early intrusions into water-laden sediments generated peperite clasts, with morphology determined primarily by magma:sediment ratio. Hydrothermal alteration (chlorite + epidote + sericite ± pumpellyite) of the volcanic rocks is more pronounced within the more permeable and glassy sequences, such as peperite, hyaloclastite and pillow rims. The chemistry of chlorite (Fe# = 0.35-0.63), its distribution, and its association with epidote, pumpellyite, pyrite and Fe-oxides have been used to determine that an iron-rich hydrothermal fluid interacted with magnesium-rich seawater in varying ratios and that fluid convection was promoted in the permeable sequence. Later intrusions show no evidence of interaction with unconsolidated sediment and/or water and as a result the dominant alteration assemblage is representative of later diagenesis. Chlorite geothermometry shows that alteration occurred between 300°C and 400°C and, adjacent to peperitic intrusions, Na, K, Si and some REE are locally mobile within fluidised sediment. Sulphide-bearing veins were formed at lower temperatures (200°C to 350°C) as a result of mixing between a high temperature, low salinity fluid and a lower temperature, high salinity (possibly meteoric) fluid. The overall drop in temperature of the hydrothermal fluid may have contributed to the precipitation of base metals. Extensive volcanic activity within the seafloor generated an elevated geothermal gradient that drove a hydrothermal convection system and formed veins with base metals sourced from early volcanic and volcano-sedimentary products. en_US
dc.subject Iapetus closure en_US
dc.subject Peperite en_US
dc.subject Chlorite geothermometry en_US
dc.subject Fluid inclusion en_US
dc.subject Southeast volcanic belt en_US
dc.subject Earth and Ocean Sciences en_US
dc.title Volcanic activity, magma-sediment-water interaction, hydrothermal alteration and vein mineralisation in south County Waterford en_US
dc.type Thesis en_US
dc.contributor.funder Science Faculty, NUI Galway en_US
dc.local.note Volcanic rocks in south Waterford were formed as a result of magma extrusion onto an ancient seafloor. Heat transfer from magma to the surrounding environment produced a metal-rich hydrothermal fluid. Circulation of the hydrothermal fluid was coeval with alteration of the volcanic host rocks and formation of metal rich veins. en_US
dc.local.final Yes en_US

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