The Monte Rosa Gold District (NW Italian Alps) comprises hundreds of late Alpine, epigenetic, gold-bearing quartz veins. We report a lead isotope study on an important one of these veins, Fenilia (Brusson, Val d'Ayas), which reveals a complex isotope geochemistry of petrographically cogenetic vein minerals. Petrographic observations allow to distinguish a quartz-dominated main-stage and a quartz-poor final-stage mineral assemblage. Most of the free gold crystallized in the beginning of the final stage, whereas sulphides were deposited during its waning. Three distinct lead isotope fields result for the paragenetic sequence of vein minerals. The variable lead isotope signature (15.517 < ²⁰⁷Pb/²⁰⁴Pb < 15.623) trapped in final-stage free gold, and minor quartz can be interpreted as a variable mixture between a primitive MORB-type and a radiogenic Pb component. It differs distinctly from the radiogenic lead signature of the main-stage mineral assemblage (²⁰⁷Pb/²⁰⁴Pb > 15.706), as well as from the uniform radiogenic lead (15.649 < ²⁰⁷Pb/ ²⁰⁴Pb < 15.691) characteristic of the waning final stage. We favour a model where the deeply circulating final-stage fluid, the ultimate source of which remains obscure, acquired lead and thus possibly its gold in Piemonte metaophiolitic rocks beneath the Monte Rosa nappe. During ascent, the primitive gold-bearing fluid was variably contaminated by an evolved crustal lead (15.706 < ²⁰⁷Pb/²⁰⁴Pb < 15.743) compatible with derivation from Monte Rosa nappe rocks. During deposition of final-stage minerals the Pb isotope composition of the fluid changed to a constant signature becoming again dominated by a radiogenic lead source. Thus within an assemblage defined as cogenetic on petrographic grounds the Pb isotopic signature is not necessarily uniform and source modelling based on lead isotopes of associated minerals may be inappropriate. It remains open at present, whether the inferred Piemonte metaophiolite gold source is confined to the Fenilia vein in Val d'Ayas only, or whether it might be more widespread in the Monte Rosa Gold District.