When the potash to be extracted is at a depth of 1000 m or deeper and/or the potash it is located in sedimentary rock then solution mining provides a cost effective, efficient and safe way to extract the resource. Added benefits of solution mining include: lower up-front capital cost, no underground workforce, relatively lower volumes of waste salt, and more limited subsidence. Conventional mining involves extracting a lot of rock material to access the mineral resource resulting in large underground caverns and this excess waste material must also be stored on surface. With solution mining, a brine is heated and injected into the deposit to dissolves the potash. The potash-rich brine is then pumped out of the cavern to the surface where the water is evaporated.
Solution mining involves dissolution of the potash with water. Wells are drilled into the potash-bearing area (sylvinite bed) and water, later brine, is pumped down the wells to dissolve the potassium chloride (KCl) (potash product) and sodium chloride (NaCl) (waste salt) that is in the sylvinite bed. Brine is returned to the surface and is conveyed to the process plant through pipelines and separated by mechanical evaporation and crystallization. No underground workers are required, as the sylvinite is accessed by drill pads and production well from the surface.
Potash processing will include the following:
- injection and solution recovery;
- evaporation and crystallization;
- product drying and screening;
- product compaction; and,
- product storage and shipping.
Mineral resources and potash grades have been determined for the project through an explorations program that included both drillholes (with core samples) and an advanced 3D seismic survey to determine the continuity of the deposit between drillholes. Sufficient resources have been delineated to extend the mine life to 65-100 years.
Mining is planned to start from the northwest section of the mine boundary and then migrate to the east.
Upon completion of the primary production phase, the injection fluid will be changed from fresh water to brine-saturated in waste salt and the potash will be more selectively dissolved, thus more waste salt will be left underground. During secondary mining, potassium on the walls and on the roof of the cavern will be mined. Salt waste within the cavern remains essentially in-place. Secondary mining can be conducted as a continuous or an intermittent batch operation.
Secondary mining production is not possible until primary mining has been completed in the first 35 caverns, which will be available for secondary recovery after 4.2 years after start-up. A pillar of unmined material is required between caverns to maintain isolation of the caverns and to support the overlying strata (limit potential for subsidence). The cavern dimensions and pillar sizes have been selected to control cavern closure during mining. The pillar dimension has been set at 80 m, the cavern radius at 75 m, and the spacing between the wells is 80 m. These caverns dimensions are based on stress analysis and site-specific data. The cavern dimensions are similar to other Saskatchewan potash solution mines.
The well field pipelines will be installed below ground with a nominal depth of cover of 2.4 m. Leak detection, monitoring, cathodic protection, and appropriate pipeline isolation will be provided.