a range of elemental compositions within 90 seconds. The samples were then removed, sieved and re-analysed using XRF and acid digestion. Source sediment was taken from spoil heaps at the top of the catchment. Arsenic was found to be a good indicator of mined sediment, most likely associated with the primary source of the gold. Manganese and a higher organic content appear to be good indicators of the contact sediment in the pre-sludge floodplain. An attempt was made to use multispectral satellite imagery to identify sludge extents, following the method of Kotsonis and Joyce (2003), which was used in Bendigo. This was not successful, and we found that we could not repeat the process in the same location or elsewhere. In the Hodgsons Creek system transects were hand cored across the floodplain looking for a change in colour, sediment size and chemical composition. These cores have been combined with data from prospecting carried out under exploration licenses. (Figure 19). This has allowed an estimate of the deposited sludge volume to be made of 2.5–3.5 million m3. This means that Hodgson Creek may contain most of the eroded sediment from the upper catchment (Figure. 20). Inference Whilst our analyses of the chemical composition of sludge is still ongoing, it is clear there is a downstream reduction of sludge volume and concentration as expected. The incision of the sludge with the cessation of mining meant that there was a secondary pulse of sludge that had the potential to move further down the river system, however, this may have been limited in places by increased regulation. The depth and appearance of sludge when exposed in an incised riverbank is fairly obvious, especially proximal to mining where it is particularly thick. Further down the system and out onto the floodplain it becomes more difficult to identify visually, and this is where the geochemistry has been extremely useful. Sampling does, however, need to take into account the likely sedimentation processes that have occurred both in-channel Figure 20.  A 2 m section of sludge above the previous floodplain contact (left) and holes showing where sample were taken for geochemical analyses. Figure 19.  Depths of sludge (m) across the Hodgson Creek floodplain, shown against a prospector estimate of sludge extent (red outline). Feature Mining to mud 55 PREVIEW JUNE 2019