Cloudbreak mine water conveyance infrastructure

Abstract

Cloudbreak is an iron ore mine located in the Pilbara region of Western Australia. The mine extends 40 km east-west, 5 km north-south and has excavations up to 70 m depth. It is home to one of Australia's largest and most complex Managed Aquifer Recharge (MAR) operations. It also adjoins the new Christmas Creek mine, currently under development to the east, of similar scale and characteristics. The two mines form a single water managed entity. Ninety percent of the ore body is below the water table, the ore body itself containing the main aquifer of brackish water. The mine is bounded to the south by the Fortescue Marsh – an internally draining, periodically flooded wetland of national significance. The marsh and the ore body are underlain by hyper saline conditions in an irregular pattern trending more saline towards the marsh and with depth. MAR is the chosen method of dewatering operation to preserve the fresh and brackish water source, manage the quality of the remaining unexcavated ore body, safeguard groundwater levels at the marsh, and maintain balance to local ecology by zero surface discharge. Through an evolution of review and optimisation, a mix of infrastructure components have been installed and commissioned alongside ongoing mine expansion, within a very dynamic operational environment. The scheme currently includes 200 abstraction bores (60 operational at any time), ten in-pit sumps, 200 km of pipeline, six major transfer or settlement ponds, 100 brackish injection bores (50 operational, others for standby or future use) and 20 saline injection bores (currently operating five at a time on a trial basis). These numbers are due to be significantly augmented as dewatering license limits increase and the mine progressively develops. Hydraulic network modelling software is applied for system design and optimisation. The system is operated using a mix of manual and automatic controls, with regular monitoring for compliance and optimising system performance. This paper focuses on how the self contained MAR system has been designed, developed and operated successfully, though many challenges remain.