MINE TAILINGS – LEAD ISOTOPE ANALYSES FOR TRACKING INHALABLE PARTICLES IN RESIDENTIAL ENVIRONMENTS

Changes in mineral processing towards milling to finer median grain size have results in increased fractions of inhalable particles. After mineral extraction, the deposited waste fines pose a new or enhanced health hazard for residential communities living nearby to tailings storage facilities if these tailings are subject wind erosion. Up until the early 2000s, the median grain size in milled ore on the South African gold fields was ~70 µm diameter, with typically less than 5% in the less then 10 µm size range. While wind erosion of these tailings resulted in high mass loadings of total suspended particles, the PM10 inhalable fraction was minor. With the new finer milling, the average particle size has been reduced to that in some cases 50% of the waste is now in the less than 10 µm size range. This dramatically changes the dust dispersion and health implications and requires a review of dust control measures. The Witwatersrand (100 km gold mining region centered around Johannesburg) has over 200 tailings storage facilities and more than ½ a million residents living within 2 km of these facilities. This population is the target for this study of the health hazards posed by older and specifically the newer tailings storage facilities resulting from the reprocessing of existing storage facilities. Lead isotope ratios have been measured for 20 samples of source material. As the Witwatersrand gold ore contains elevated concentrations of uranium relative to average crustal rock, the resulting lead isotope distribution is unique and different from average soil and from widespread residues of Pb from the era of leaded gasoline. Results indicate that highly radiogenic lead isotope ratios (²⁰⁶Pb/²⁰⁴Pb from 40 to 200) can be used to apportion the contributions of tailings dust to the total atmospheric dust load, and thus quantify the residential exposures to tailing material.