New lead isotope determination from five Proterozoic sulfide deposits,Skellefte district,Sweden

Lead isotope analyses of 25 sulfide samples (galenas, iron sulfides, and sulfosalts) from five different mines of the Skellefte district, northern Sweden, demonstrate that the Pb-isotopic composition of galenas and other sulfides rich in lead varies between individual deposits within the district. This contrasts with many other base-metal districts, where ore lead is isotopically homogeneous on a regional basis. Although all of the Skellefte leads are depleted in ²⁰⁷Pb relative to average global lead evolution models, thus suggesting a large mantle-derived component in their sources, the Nasliden deposit lying at the contact of the host volcanic rocks and the overlying metasediments contains a significant component of crustal lead. It is concluded that while the Pb-isotope data are consistent with a volcanic exhalative origin of the ores of the Skellefte district, they also demonstrate that older crustal lead was incorporated into the sulfides during their emplacement and the subsequent period of magmatic and metamorphic activity which followed their deposition.