MICROMINERALOGY OF MINE WASTES IN RELATION TO LEAD BIOAVAILABILITY, BUTTE, MONTANA

Electron microprobe analysis of soil and waste rock mineralogy helps explain the low blood Pb levels observed in young children living in Butte, MT. The sulfide/sulfate assemblage consists primarily of galena, anglesite, and lead jarosite, while the oxide/phosphate assemblage was principally manganese lead oxide, lead phosphate solid-solution series, and lead oxide. Modeled paragenetic sequences initiated using galena and lead oxide demonstrated that both primary phases weather to less soluble anglesite and pyromorphite end members, respectively. If these soils were ingested, Pb solubility would be constrained by alteration and encapsulation of the Pb-bearing minerals, which limits the available Pb-bearing surface area. This premise is supported by the results of the Butte-Silver Bow environmental health Pb study, which indicate that no statistical relation exists between blood-Pb levels and the presence of individual Pb-bearing phases.