Unaltered hausmannite ores from Långban, Sweden, contain two rhombohedral carbonate phases, namely calcite and a carbonate with a disordered calcite structure; the latter with the approximate composition Ca0.4Ba0.4(Pb, Mg)0.2CO3 and cell dimensions (hexagonal setting)a = 5.12 and c = 18.12A;. The carbonate phases were emplaced together with the ore minerals before the metamorphic events, which in their turn preceded the late vein and vug forming period in Långban. It appears likely that such carbonates are much more common than was previously realized, and that they were the source of most of the Pb, Ba and Ca present in the native lead-pyrochroite veins.