Distribution and dispersal of legacy sediment and contamination from historical gold mining at Hill End, New South Wales, Australia

The gold rushes in the 19th century impacted landscapes throughout the world through vegetation clearance, disturbance of soil and sediment and the release of metals (e.g. mercury and arsenic) into the environment. Legacy sediment episodically produced from anthropogenic activities such as gold mining is now stored in modern landscapes and can contain high concentrations of metals. In Australia, the little research into the environmental impacts of historical gold mining has generally focused on metal contamination and there has been limited research into long-term geomorphological changes in landscapes associated with gold mining processes such as the impact of large scale legacy sediment production. This study explored the long-term environmental impacts of historical gold mining at Hill End, New South Wales, Australia, by investigating the dispersal of legacy sediment as well as spatial patterns and temporal trends of mercury, arsenic, lead, copper and zinc contamination. Soil and sediment metal contamination was analysed using X-ray fluorescence (XRF) and a direct mercury analyser. Optically stimulated luminescence (OSL) and excess 210Pb were used to constrain temporal patterns of contamination and sedimentation. Hill End has high hillslope-channel and longitudinal connectivity and there are few places where legacysediment storage occurs within the catchment. In the uplands of Hill End, legacy sediment is stored in finely laminated sequences in tailings dams. There was no sediment stored in the steep gorges of Hill End and sediment was stored with cobbles and gravel in occasional midchannel and bank attached bars in the lower reaches of the system. The majority of samples contained little to no metal enrichment and high levels of metal contamination were mainly restricted to artificial depocentres such as tailings dams and in spoil adjacent to stamper batteries and cyanide tanks. Chemostratigraphy and sediment dating in Chappell’s Dam revealed that metal contamination peaked during the height of gold mining (c. 1871-1880). It declined shortly after the cessation of ore processing in the adjacent stamper battery, coinciding with the decline of gold mining in the region. Peak metal concentrations of mercury (44.58 mg kg⁻¹) and arsenic (221.0 mg kg⁻¹) found in Chappell’s Dam are well above ANZECC sediment quality guidelines and could pose a risk to local aquatic ecosystems. Understanding the fate of legacy sediment and metal contaminated sediment in a highly connected system such as Hill End will shed light on the larger scale impacts of historical gold mining in Australia and can be used to inform management strategies for derelict and active mines.