Topic: Verification of a Geochemical Grade Control Programme for Placement of a Waste Rock Drainage Cover, Mount Isa, Australia
Overview:
Glencore Mount Isa Mines is nearing completion of the placement of a cover on two waste rock dumps at the Handlebar Hill Open Cut Mine in North-West Queensland. Approximately 76 million tonnes of waste rock are contained in these facilities. Rock placement in the dumps stopped following the end of open pit mining and refocussing of operations to underground mining in 2014, with geochemical site investigations and cover design commencing shortly thereafter.
Rehabilitation works have included reshaping of the waste rock dumps and placement of a cover over any potentially acid-forming (PAF) and neutral mine drainage (NMD) waste rock exposed following the reshape. The cover comprises a 1.5-metre-thick layer of non-acid forming (NAF) waste rock and locally sourced regolith. A key requirement of the cover was that only NAF, non-NMD material was used for the cover placement to limit solute release from the waste rock dumps until a final closure cover is designed and accepted by stakeholders.
This paper provides an overview of the materials screening and cover design process, reshape optimisation, cover construction including grade control, and cover geochemical verification. Project outcomes emphasise the importance of having a sound geochemical understanding of the available cover materials, their screening, and placement to achieve overall cover objectives. Rapid field-based contact tests, mineralogical logging, and onsite elemental testing allowed for quick turn-around-times and decision-making in response to evolving construction needs. The project also demonstrates the effectiveness of combining modern technology (drone surveying technology and machine-guided global positioning system) with on-the-ground geochemical verification sampling to improve project outcomes.
