occurred uniformly in the hole, and there were some pillars of sediment remaining on the valley floor that showed where the original surface had been. The elevation of these pillars was extracted and modelled using ARCGIS, along with the elevations of the tops of surrounding scar walls, to approximate the old valley surface. The two surfaces were extracted from each other and the volume change was calculated as −5 327 642 m3. Mining of primary deposits resulted in adits being blasted along quartz reefs associated with the gold. In order to reach underground deposits, the overburden was removed, and this was often stacked locally. Processed sediment was also stacked in mullock heaps. Some of these heaps are listed in the Heritage Council of Victoria’s database. Mullock heaps that were proximal to river systems contributed sediment directly into the river system, especially during high rainfall flood events (Figure 12). Once the ore rock was extracted it was crushed. Mechanisation of this process increased over time, leading to the development of large stamp batteries. Crushing produced fairly standard sand sized clasts. These sand grains were less rounded than fluvially transported grains, and can be used a physical tracer in some environments. This was the case in the Leigh and Yarrowee Rivers where sand was deposited on the floodplain, blown up the hillsides and, ultimately, into sheep wool causing a reduction in wool value. Data on the location of mining for primary deposits is in the VICProd/VicMine database (Figure 7). This database also contains attributes relating to shaft dimensions and orientation, alongside estimates of gold production. Interpretation Hydraulic sluicing of alluvial deposits was concentrated in northeast of the state and resulted in localised higher rates of deposition on floodplains. It also contributed a broader range of sediment sizes into the river channel. This method has resulted in holes in upland landscapes that now have a very limited capacity for adjustment. Mining for primary deposits was much more targeted than mining for secondary/alluvial deposits. Mercury and cyanide were also used in processing (Rae, 2003). As a consequence, there are more likely to be higher concentrations of contaminants in the sludge derived from mining for primary deposits. Conversely, the sludge is more likely to contain sand sized grains that are less likely to adsorb contaminants than finer silts and clays. Figure 9.  Hydraulic sluicing on the Mitta Mitta (source: State Library of Victoria). Figure 10.  The impact of herringbone sluicing near Omeo apparent in photographic imagery and (left) and LiDAR (right). (source: Department of Environment, Land, Water and Planning). Feature Mining to mud 50 PREVIEW JUNE 2019