Bacteria were responsible for the magnitude of the world-class hydrothermal base metal sulfide orebody at Navan, Ireland

Sulphur and lead isotope analyses of mine concentrates from the Navan Zn-Pb deposit, each sample representing a million tonnes of ore, show very limited variation, with mean delta (super 34) S - 13.6 + or - 20/00 (n = 20) and galena concentrate mean (super 206) Pb/ (super 204) Pb = 18.19 + or - 0.03 (n = 3). Calculations suggest that > or = 90% of the Navan sulphides were derived through the bacteriogenic reduction of Mississippian sea-water sulphate, whereas metals were acquired from a local, orogenic crustal source beneath the orebody. It appears that enhanced bacterial activity was fundamental to ore deposits at Navan.