Evolution and preservation of volcanogenic sulphides at Avoca, Southeast Ireland

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Authors:McArdle, Peadar
Author Affiliations:Primary:
Geological Survey of Ireland, Dublin, Ireland
Volume Title:Transactions - Institution of Mining and Metallurgy. Section B: Applied Earth Science
Source:Transactions - Institution of Mining and Metallurgy. Section B: Applied Earth Science, Vol.102, p.149-163. Publisher: Institution of Mining and Metallurgy, London, United Kingdom. ISSN: 0371-7453
Publication Date:1993
Note:In English. 72 refs.; illus. incl. sects., 2 tables, geol. sketch maps
Summary:This is an Ordovician volcanogenic Cu deposit hosted by the Avoca volcanic formation, the lowest (Castlehoward) and highest (Tigroney) members of which are characterized by tuffs and felsites with a dominantly sericitic mineralogy. The central (Kilcashel) member consists of chloritic tuffs; the bulk of the mineralization occurs near its top. The Avoca deposit contains banded sulphides, a few m thick, that consist mainly of pyrite with varied amounts of chalcopyrite, galena and sphalerite. More extensive zones of disseminated and vein-type sulphides occur in concordant zones < or = 30 m wide. Characterized by pyrite and chalcopyrite, as well as sporadic galena and sphalerite, the mineralization shows very different metal ratios between the two sides of the Great fault in the Avoca river valley, which is interpreted as the location of the original feeder zone. Immobile element geochemistry indicates that host rocks range from peralkaline rhyolites to dacite with only a small proportion of more basic lithologies. All three members had a similar range of primary compositions. The Kilcashel member is interpreted as a semi-conformable footwall alteration zone of regional extent. It seems that the rocks developed as pyroclastic flows of turbiditic origin. The evidence suggests that the precursors of the late- stage faults were active during sedimentation. Faulting was most active during deposition of the Tigroney members, the rapid deposition of which led to the preservation of sulphides. [R.E.S.]
Subjects:Copper ores; Gold ores; Lead ores; Metal ores; Mineral deposits, genesis; Sulfides; Volcanism; Zinc ores; Europe; Ireland; Western Europe; Avoca; Southeastern Ireland
Abstract Numbers:94M/4204
Record ID:1994022849
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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