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Journal of the Geological Society; 1989; v. 146; issue.4; p. 715-720;
DOI: 10.1144/gsjgs.146.4.0715
© 1989 Geological Society of London

Article

Preliminary sulphur isotope data of diagenetic and vein sulphides in the Lower Palaeozoic strata of Ireland and southern Scotland: implications for Zn + Pb + Ba mineralization

I. K. ANDERSON1,2,4, C. J. ANDREW4, J. H. ASHTON3, A. J. BOYCE1, J. B. D. CAULFIELD1, A. E. FALLICK1 & M. J. RUSSELL2

1 Isotope Geology Unit, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G750QU, UK
2 Department of Applied Geology, University of Strathclyde, Glasgow G11XJ, UK
3 Tara Mines Ltd, Navan, Co. Meath, Ireland
4 Navan Resources plc, 3 Railway Street, Navan, Co. Meath

Genetic models for many Irish Lower Carboniferous Zn + Pb ore deposits invoke a dual supply of sulphide. The dominant source is from the bacteriogenic reduction of Lower Carboniferous seawater sulphate, but a significant, minor supply is derived from deep-seated sources. The {delta}34S range of the latter component varies among the deposits: from the lightest range of —15% to 0% at Keel, to the heaviest of –4% to +14.4% in the Navan/Tatestown area. We hypothesize that such sulphur is leached mainly from diagenetic sulphide minerals in the underlying Lower Palaeozoic sediments. 6"s of pyrite in the Silurian/Ordovician Moffat Shales (—17.1% to —0.6%), and of sphalerite and galena in Lower Palaeozoic-hosted veins at Salterstown (—8.7% to -4.5%) and Wanlockhead (—10.3% to —5.1%) are consistent with the hypothesis. Below the Navan ore deposit, Lower Palaeozoic shales containing minor diagenetic pyrite with a very wide range in {delta}34S have been found; {delta}34S is typically heavy (+16%) but extreme values up to +62% are encountered. The general enrichment in {delta}34S is in accord with the noticeably heavy isotopic composition of deep-seated sulphur in the Navan orebody and its Tatestown satellite. Our preliminary results therefore suggest that geographical variations in the {delta}34S range of Lower Palaeozoic diagenetic -write_. may have contributed to the isotopic variation in the deep-seated sulphur among the Irish deposits.