Stable isotope (C-O) analysis was applied to smithsonites and cerussites from Zn(Pb) nonsulphide ores from Britain and Ireland, to determine the nature of the fluids responsible for the precipitation of secondary carbonates, and any relationship with palaeoclimatic conditions. The carbon isotope compositions of the Irish smithsonites show a major contribution of organic carbon whereas those of both Zn- and Pb-carbonates in the UK deposits indicate contribution of organic carbon and host rock carbonates. δ18OVSMOW values for cerussite from both areas are about 13‰ lower than those of smithsonites, UK smithsonites δ18OVSMOW values are more variable than cerussites and the Irish smithsonites have unusually high values. Isoscape maps indicate that δ18O values for both carbonates are higher in the west and decrease toward the east. This trend correlates with a general decrease in the oxygen isotope compositions of rainwater moving eastward, and suggests that oxidation of sulphides occurred at temperatures of about 15 to 20°C, under climatic conditions warmer than today.