Distinguishing and characterising point-source mining dust and diffuse-source dust deposits in a semi-arid district of eastern Australia

The routine monitoring of dust deposition around mines does not typically distinguish between allochthonous and locally-sourced dust. In this paper, contemporary aeolian dust deposition within a semi-arid part of eastern Australia is examined to determine the contribution of an open-pit gold mine to local dust dynamics. Over a 2.5 year period, monthly deposited dust samples were obtained from 12 sites located around the Cowal Gold Mine (CGM), and analysed for inorganic and organic proportions and granulometric properties. Although there was considerable variation in deposition between the gauges and sampling periods, there was a moderate and statistically significant seasonal trend, with mineral dust deposition lowest in winter. Imprinted over this seasonal pattern was a distinct spatial pattern of dust deposition, with gauges downwind of the CGM receiving significantly more dust than those gauges upwind (20 t/km2/yr). This effect was most pronounced adjacent to the mine (dust deposition of 60 t/km2/yr), where coarse-grained particles comprised a large proportion of the deposited dust, and diminished with distance east of the mine. Such a spatial trend is typical of a point source of dust. Average dust deposition at gauges located 8 km downwind of the mine was only slightly greater than that of gauges upwind of the mine. The ‘background’ dust populations captured at the upwind locations were dominated by fine particles, with modal particle diameters of 3–5 and 13–16 μm common. The macro-organic component of dust deposits also tended to vary seasonally, but the spatial distribution of this material was quite erratic.