Yang, D & Binks, F 2022, 'Developing a systematic model to rehabilitate key domains of gold mines for environmental sustainability', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: Proceedings of the 15th International Conference on Mine Closure
, Australian Centre for Geomechanics, Perth, pp. 973-986, https://doi.org/10.36487/ACG_repo/2215_71
The primary focus of the Mine Rehabilitation Model is to eliminate the acid metalliferous drainage (AMD) released from waste rock dumps (WRDs), reinstate natural biodiversity and ecosystems, ensure a sustainable post-mining land use and ultimately lease relinquishment. The overall strategy is aligned with industry-recognised guidelines, standards with applicable government regulations, integration design methods and innovative technologies, establishing an optimum performance platform for sustainable rehabilitation management.
Cosmo Howley Project Area (CHPA) is located 130 km southeast of Darwin, between Adelaide River and Pine Creek. The nearest township is Adelaide River, 50 km to the northwest. The CHPA is operated by Agnico Eagle NT Mining Operations (NTMO).
The most significant environmental risk at the CHPA is represented by the WRDs, which are the key source of AMD, impacting on the local creeks and groundwater quality. The issue is unlikely to abate in the foreseeable future unless the AMD source is removed. The ineffective design of the WRDs, limited geochemical characterisation and the highly seasonal tropical rainfall patterns at CHPA compounds the problem with respect to the formulation of a cost-effective, permanent rehabilitation strategy. Longer term, and as part of this mine rehabilitation strategy, NTMO propose to control AMD via oxidation control. This will be achieved by rehandling of waste rock from Howley and Mottrams WRD and placement in-pit in the Cosmo Pit, below the recovery watertable level, which will provide an effective barrier to significant oxygen diffusion.
Other environmental risk areas include large dams within the CHPA that store the residue of heavy metal contaminated soil. NTMO adopted biological treatment to ameliorate the acid sulphate soil within these receptors. Naturally occurring biological micro-organisms and plants able to withstand high concentrations of heavy metals can be useful in eradicating hazardous contaminants. This is a process known as bioremediation and is an eco-friendly and efficient method of reclaiming environments contaminated with heavy metals.
Biological treatment can be combined with physical processes, such as anionic clay precipitation. The clay binds to metals and other contaminants, which make the toxic metal inactive. Biological treatment can then add nutrient to the soil to promote vegetation growth. A trial treatment investigation was implemented at CHPA to define the best possible physical and biological options for capping to ensure safe remediation of the site as well as potential cropping opportunities for the site after remediation.
Keywords: acid metalliferous drainage mitigation, wet cap, biological soil amelioration
ANZECC 2000, Australian and New Zealand Guidelines for Fresh and Marine Water Quality, viewed 20 July 2022,
Lorax Environmental Services Ltd. June 2021, Predictive Modelling of Pit Lake Water Quality and Water Balance for the Cosmo Pit, Cosmo-Howley Project Area, Darwin, Australia, Lorax Project No. A589-1.