Elemental and mineralogical constraints on environmental contamination from slag at Gulf Creek copper mine

The environment downstream of Gulf Creek, a legacy copper mine in southeastern Australia, has been impacted by leachate and the stream channel is lined with algae coated in powder blue precipitates rich in copper (Cu) and zinc (Zn). The workings have been rehabilitated, with slag rich in Cu and Zn distributed over soil surfaces to control erosion. Slag, a waste from metallurgical processing, was commonly left on site at old mines and was rarely prioritised for later remediation as it was assumed to be relatively inert. This study assesses the potential contribution that leaching of this slag has on downstream metal contamination, via an understanding of macro- and micro-scale elemental composition and mineralogy. The slag is composed of up to 2.0 wt% Cu and 1.4 wt% Zn, with Cu present in copper sulfide and native copper prills from 4 mm to <0.1 µm diameter, hosted in a glass phase. Leaching of up to 54 mg L⁻¹ Cu and 33 mg L⁻¹ Zn occurred after 60 days, reducing leachate pH from 6.1 to <4.