Size distribution of airborne dust in Labrador iron mines.

The size distribution of the total airborne dust and its components approximates a straight line on a plot of log mass undersize against log aerodynamic size. The quartz component distribution has a reasonably constant slope, is close to the distributions found in other mines and mills, and follows the normal breakage laws. The results for the iron component suggest that the top size present is similar to that of quartz and that the slope is also similar. The slopes for total dust by weight are not as steep as for quartz and suggest a bimodal distribution consisting of a coarser mineral fraction mixed with a finer fraction from other sources, such as combustion products, that are often found. The slopes for manganese are sometimes much less than for iron or quartz and suggest that manganese is associated with a more crushable rock. The one finding of chromium suggests that it is associated mostly with very fine particles and, therefore, may have been dispersed as fume from an operation such as welding.