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 δ34S 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 δ34S have been found; δ34S is typically heavy (+16%) but extreme values up to +62% are encountered. The general enrichment in δ34S 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 δ34S range of Lower Palaeozoic diagenetic -write_. may have contributed to the isotopic variation in the deep-seated sulphur among the Irish deposits.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.