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Tynagh |
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Ireland |
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Zn Pb Cu Ag
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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Tynagh - is stratabound sulphide body hosted by lower Carboniferous carbonates, in the central plain of Ireland.
The hypogene ore is hosted by a wedge shaped body of massive micritic and locally crinoidal limestones of the Waulsortian Limestone that have been downthrown more than 600 m by a major ENE trending normal fault to juxtaposed on the northern side of an inlier of Devonian fluviatile sediments. Further north the host lithology interfingers with a sedimentary iron formation composed essentially of finely banded hematite and chert with intercalated graded crinoidal limestone and a few thin tuffaceous beds.
Prior to mining, the hypogene ore was overlain in part by a residual mass of metal rich rubble and sulphide-oxide mud. These may have formed during the Tertiary in a karstic depression covering an area of 50x600 m with a maximum depth of 75 m that followed the North Tynagh Fault, the primary ore controlling structure. It has been suggested that as the depression deepened the sidewalls became steeper and decalcified boulders and fragments collapsed into the karst infill black muds resulting in a mixture of detrital and supergene sulphides, smithsonite and hemimorphite. Some of the supergene sulphides replace fossil wood. Decomposition of primary and secondary sulphides resulted in the development of the smithsonite, cerussite and Cu carbonates within the karstic black muds as well as in the carbonate wall rocks.
The primary orebody was composed of two sulphide lenses separated by a barren dolomitised zone. The ore is interpreted to have been emplaced in four stages, as follows:
(1). Possible syn-sedimentary or syn-diagenetic clots, colloform and granular pyrite in the micrite,
(2). Rapid geopetal precipitation of microcrystalline sulphides, mainly sphalerite within a high level dilatant fracture system in response to activity on the fault zone,
(3). Subsequent veining and replacement of the host and earlier ore textures by an assemblage dominated by tennant ite, galena and barite,
(4). Precipitation of calcite in post ore fractures and cavities and dolomitisation of Waulsortian Limestone.
The original resource/reserve has been variously quoted as:
13.6 Mt @ 4.5% Zn, 4.9% Pb, 0.4% Cu, 50 g/t Ag, or
9.4 Mt @ 3.2% Zn, 3.0% Pb, 0.3% Cu, 31 g/t Ag.
The non-sulphide zinc mineralisation is estimated to have totalled:
1.2 Mt @ 4.66% Zn (associated with secondary Pb and Cu ores).
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1996.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Boast A M, Coleman M L, Halls C 1981 - Textural and stable isotope evidence for the genesis of the Tynagh base metal deposit, Ireland: in Econ. Geol. v76 pp 27-55
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Boni M, Large D 2003 - Nonsulfide zinc mineralization in Europe: an overview: in Econ. Geol. v98 pp 715-729
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Clifford J A, Ryan P, Kucha H 1986 - A review of the geological setting of the Tynagh orebody, Co. Galway: in Andrew C J, Crowe R W A, Finlay S, Pennell W M, Pyne J F (Ed.s) 1986 Geology and Genesis of Mineral Deposits in Ireland Irish Association for Economic Geology, Dublin pp 419-439
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Hitzman M W 1995 - Mineralisation in the Irish Zn-Pb-(Ba-Ag) Orefield: in Anderson K, Ashton J, Earls G, Hitzman M, Tear S (Eds.), Irish Carbonate Hosted Zn-Pb Deposits SEG Guidebook Series, Littleton, Colorado, USA v21 pp 25-61
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Hitzman M W 1995 - Geological setting of the Irish Zn-Pb-(Ba-Ag) Orefield: in Anderson K, Ashton J, Earls G, Hitzman M, Tear S (Eds.), Irish Carbonate Hosted Zn-Pb Deposits SEG Guidebook Series, Littleton, Colorado, USA v21 pp 3-23
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LeHuray A P, Caulfield J B D, Rye D M, Dixon P R 1987 - Basement controls on sediment-hosted Zn-Pb deposits: a Pb isotope study of Carboniferous mineralization in central Ireland: in Econ. Geol. v82 pp 1695-1709
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Phillips W E A, Sevastopulo G D 1986 - The stratigraphy and structural setting of Irish mineral deposits: 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 Association for Economic Geology, Dublin pp 1-30, xvi
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Wilkinson J J 2003 - On diagenesis, dolomitisation and mineralisation in the Irish Zn-Pb orefield: in Mineralium Deposita v38 pp 968-983
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Wilkinson JJ, 2010 - A Review of Fluid Inclusion Constraints on Mineralization in the Irish Ore Field and Implications for the Genesis of Sediment-Hosted Zn-Pb Deposits : in Econ. Geol. v105 pp. 417-442
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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