Fortescue Metals Group (FMG)’s Solomon Hub has a large Channel Iron Deposit (CID) that makes up most of the resource of the mine. This CID is in hydrogeological terms a palaeochannel and the ore body is the primary aquifer, hosted within low permeability bedrock. The dewatering approach using standard industry practice is to install multiple vertical production bores in the centre of the channel. This approach results in a large amount of in-pit infrastructure, which results in added complexity in the mine design with the need to allow for infrastructure corridors. The traditional approach also means that there are significant people movements in the mining area and the in-pit infrastructure is susceptible to damage by mining activities, such as blasting. Horizontal directional dewatering (HDD) is a valuable tool that borrows on technology developed in the oil and gas industry to enable dewatering infrastructure to be removed from the active pit area.
FMG has successfully constructed and developed a 1 km horizontal dewatering bore at the Solomon deposit. This success is the result of several years of evaluation work involving conceptualisation, modelling and mine planning. Critical elements of the work have included quantifying vertical permeability, assessing potential head losses due to turbulent flow, constructing a bore with suitable materials and sufficient open area and ultimately establishing the standoff distance to minimise disturbance. The resulting production bore is the first know application of HDD technology in Australian mining and should ultimately form an integral component of the mine dewatering scheme.
Gaining the approval by senior management within FMG to undertake the trial completion of an HDD dewatering bore highlights the potential significance and application of the technology. Whilst every potential application will ultimately need to assess the specific hydrogeological setting and constraints, the inclusion of Horizontal dewatering represents another valuable option in open pit mine water management.