By Michael Schwartz
Forty years of potash production, each yielding around three to four million tonnes will be Vale’s reward if its application to mine the Kronau project in Saskatchewan is successful. Kronau, which lies roughly 30 kilometres southeast of the province’s capital Regina, will be Vale’s first potash project in Canada, subject to full approval.
Saskatchewan’s potash deposits are the remnants of a large shallow inland sea — one portion of the Western Canadian Sedimentary Basin that once extended from southwest Manitoba to northeast British Columbia. It has been globally estimated that 40 per cent of the world’s total potash deposits lies within Saskatchewan.
Forming part of the Prairie Evaporite Formation located between 1,600 metres and 1,750 metres underground, Kronau’s potash deposit – to be mined by solution mining techniques – spans roughly 50,000 ha. The potash is contained within several mineral beds comprising the top 55-metre thickness of the total Prairie Evaporite Formation. The potash beds are a mixture of potash (Sylvite: KCl) and salt (Halite: NaCl), with minor amounts of other minerals and clays.
As of mid-August, the go-ahead for final feasibility (construction planning) has been authorized. In a year’s time, this stage will be completed; its conclusions, combined with market conditions and the opinions of potential partners, will produce the final decision as to whether or not to proceed. If the decision is made to proceed, processing plant production will begin in 2019.
“Mega projects in the mining industry are a major investment,” says Matthew Wood, senior project leader in Regina. “Successful completion depends on a multitude of internal and external factors. However, Vale is in a unique position with production in South America and existing port, logistics and distribution infrastructure in Brazil. Vale is confident in the long-term fundamentals of potash, and this project has the potential to become an integral part of Vale’s fertilizers strategy.
“The main challenge for us is timing,” adds Wood. “This is not uncommon for mega mining projects of this size and scope.”
Supporting the core mining operations will be conventional water, power and transport infrastructure, as well as a dedicated combined heat and power plant for processing. By the time operations do commence, around 2,000 people will have been employed during construction, and 350 will be permanently engaged during actual processing.
While final construction and drilling activities depend on authorization and would not start until 2016, involvement of local communities has been essential since 2011. Vale has welcomed feedback from aboriginal communities, rural municipalities and the general public as soon as the project proposal was released to the province. Community updates and feedback opportunities on the project are planned for the life of the mine
Up to 60,000 m3 of water will be needed for the project daily, although Vale is committed to reducing water usage via recycling and other methods. For example, brine will be diverted to a reclaim pond and kept until it can be reused in the mine or processing plant. The pond will be designed to provide protection against storm events to further ensure that the brine does not spill over into surrounding soils.
Tailings at Kronau will comprise the salt remaining from the solution mining. It will be retained in a tailings management area enclosed by a dyke above ground and, when the mine closes, the tailings will be dissolved and restored to the ground. The process is currently used by existing potash mines throughout Saskatchewan.
The tailings area will be monitored for subsidence, slope stability, groundwater chemistry and hydraulic head. Additionally, downhole geophysical electromagnetic surveys, terrain conductivity surveys, and air-quality monitoring will also be completed. Simultaneously, when mining is underway, Vale will leave pillars between the mine caverns to increase stability during solution mining and subsidence.
One key area for power conservation comes in the form of a cooling pond: an alternative processing method would see hot brine being transferred into the external pond during the winter months. As the brine cooled, helped by Saskatchewan winter temperatures, potash would be processed with less energy, assisting both the environment and the bottom line of the project.
The potash will be put in storage and eventually loaded onto railcars destined for Vancouver. It will then be shipped to Asian and Brazilian markets for distribution.by