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Northeastern Section - 48th Annual Meeting (18–20 March 2013)

Paper No. 3
Presentation Time: 8:55 AM

SPATIAL DISTRIBUTION OF ARSENIC IN GOLD BEARING QUARTZ VEINS FROM A HIGH ARSENIC GROUNDWATER REGION IN THE CALEDONIDES OF WESTERN IRELAND


GILLIGAN, Martin1, FEELY, Martin1, HENRY, Tiernan1, HIGGINS, Timothy2, ZHANG, Chaosheng3, TIMMINS, Éadaoin4, ROLLINSON, Gavyn K.5 and MORRISON, Liam6, (1)Earth and Ocean Sciences, School of Natural Sciences, National University of Ireland, Galway, University Road, Galway, Ireland, (2)School of Chemistry, National University of Ireland, Galway, University Road, Galway, Ireland, (3)School of Geography and Archaeology, National University of Ireland, Galway, University Road, Galway, Ireland, (4)National Centre for Biomedical Engineering Science, National University of Ireland, Galway, University Road, Galway, Ireland, (5)Cambourne School of Mines, School of Engineering, Mathematics and Physical Sciences, University of Exeter, Cornwall Campus, Penryn, Cornwall, TR10 9EZ, United Kingdom, (6)Ryan Institute, National University of Ireland, Galway, University Road, Galway, Ireland, m.gilligan5@nuigalway.ie

This study focuses on the mineral alteration of the primary arsenic phase evident in a region of naturally elevated groundwater arsenic levels with concentrations ranging from 5 to 188 µg L-1.

Arsenopyrite, niccolite, pyrite and chalcopyrite are all reported in the Croagh Patrick area of western Ireland and are hosted by a suite of gold bearing quartz veins. The veins transect Silurian sedimentary rocks that are in close proximity to the Cambro-Ordovician Clew Bay and Deer Park complexes in the north. The late Caledonian Corvock Granite occurs to the south.

A series of elemental maps generated using scanning electron microscopy combined with energy dispersive spectroscopy and mineral distribution maps using QEMSCAN® reveal the spatial distribution of arsenic and As-bearing phases in the quartz veins. These distribution maps highlight intense alteration of arsenopyrite and the formation of secondary arsenic, calcium and iron-bearing phases in microfractures. These secondary Ca, Fe arsenates suggest the presence of Yukonite and Arseniosiderite. The hydrothermal alteration of the primary arsenopyrite and fracture generation are considered to be synchronous. Results also indicate a spatial relationship between calcium and the alteration rims surrounding unaltered islands of arsenopyrite. These mineralogical relationships and textures indicate that the microfractures containing the secondary arsenates are the conduits along which arsenic is released into the groundwater.

Cross-Atlantic geological correlations with high arsenic groundwater provinces along the Appalachian-Caledonian belt will also be discussed.

Session No. 3

T7. Naturally Occurring Contaminants in Groundwater Used for Water Supply in the Northeastern United States
Monday, 18 March 2013: 8:00 AM-12:00 PM
Reagan Room (Omni Mount Washington Resort)
Geological Society of America Abstracts with Programs. Vol. 45, No. 1, p.46
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