Abstract: In vein material from the abandoned copper mine at Dhurode, County Cork, Republic of Ireland, the sulphosalt meneghinite is partly replaced by later minerals, notably a symplectite of galena and bournonite. Mineral analyses and proportions indicate that the bulk Pb/Sb ratio in the symplectite is almost identical to that of the meneghinite. It is inferred that Pb and Sb were the relatively immobile elements whose short-range segregation controlled the scale of symplectite intergrowth, during a diffusive replacement reaction in which Cu and S were added from the vein-forming fluid. This is the second sulphosalt-bearing symplectite for which immobile elements have been identified. In both cases, the inferred replacement reaction causes a volume increase, approximately 15% in the present example.