Jansen Potash Project, Saskatchewan, Canada
The Jansen project is a proposed underground potash development project located in east-central Saskatchewan, approximately 140km east of Saskatoon.
Owned by BHP Billiton, the mine will be one of the world's largest potash mines, producing eight million tons of marketable potash annually at full capacity.
The project has advanced to the feasibility study in February 2011 and is scheduled to begin first production in 2015. Development of the mine to full capacity will be carried out over three phases, at an estimated cost of over $12bn. The mine will operate for an estimated life of more than 50 years.
The mine contains 3,250 million dry tons of indicated resources graded at 25.4% potassium oxide. Inferred resources have been estimated to be 120 million dry tons grading at 26.7% potassium oxide.
Geology and mineralisation
The Jansen resource lies within the locally extensive and consistent Prairie Evaporite formation, which forms part of the Elk Point basin. The regional geology is classified into three stratigraphic segments.
The deposit is hosted at a depth of 900m to 1,000m. The main potash bearing zone plunges gently from the north-east to the south-west. It is underlain by a sequence of limestone, dolomites and anhydrites that host reef mound sequences known as Winnipegosis. Overlying the zone are the Mannville formation, the Davidson Evaporite and Hubbart Salt formations, the Dawson Bay formation as well as collapse structures.
Also known as the Blairmore formation, the Mannville formation comprises a sequence of clean sandstone interbedded with shales. The Dawson Bay formation hosts two halite beds, the uppermost Hubbart salt and the Davidson Evaporite. The two halite beds are separated by an anhydrite bed within the Davidson Evaporite.
A 4m-thick soft shale formation forms the lower most unit of the Dawson bay formation. It includes approximately 30m of limestone. Collapse structures in the deposit area are found in localised areas where the original geological layering has been considerably or completely destroyed. Ranging in size from a few hundred metres to tens of kilometres, these structures extend from the surface till the Prairie Evaporite horizons.
In the main potash bearing zone, the lowermost lower salt unit is overlain by another unit of three-potash bearing units known as the Esterhazy Member, Belle Plaine Member and the Patience Lake Member, and one marker bed known as White Bear Marker Bed.
Sylvinite-hosted beds within these members contain a combination of sylvite, halite, trace amounts of carnallite and water-insoluble minerals including clay, anhydrite and dolomite. Together this mixture composes the sylvinite rock.
Mining and processing
Mining will involve the long room and pillar method. The potash-bearing members will be accessed through a production and service shaft that will be sunk 1km from the surface. BHP Billiton has initiated drilling for the ground freezing process, required to sink the shaft.
Several rooms will be cut into the potash-bearing zones, leaving several pillars to hold the mine roof. As mining proceeds, a grid-type pattern of rooms and pillars will be created. The ore will be mined using large borers. Through conveyors, the mined ore will be brought to the production shaft that will hoist it to the surface. Approximately 24 million tons of ore will be hoisted to the surface at peak capacity.
During processing, the ore will be crushed to separate the potassium chloride and sodium chloride crystals. The final saleable product will be produced following the stages of scrubbing, conditioning, flotation and de-brining.
The tailings including salt and clay will be stored and managed on surface separately. Surplus brine from the Tailings Management Area will be returned to a geological unit named Deadwood formation which is hosted 1km below surface. Approximately one million cubic metres of water be will used by the process plant annually.
The contract to construct two mine shafts at the Jansen Potash project was awarded to DMC Mining in December 2010. The five-year contract is valued at $400m.