Shaft Sinking to the Potash Level in a Sedimentary Basin – Scissors Creek Case Study


Arnfinn Prugger, Independent (Retired Geophysicist)

The Rocanville potash mine (owned and operated by Nutrien Inc.) in southeast Saskatchewan, Canada has been in continuous production since 1971.  Devonian potash, formed approximately 380 Mybp, is mined in a sedimentary basin environment at approximately 1000m depth below surface in this area of Saskatchewan.  In 2007 it was announced that the Rocanville mine would be expanded to increase production from 3.0Mtpa to approximately 6.0Mtpa of finished potash products, requiring an increase in hoisting capability from approximately 9.0Mtpa to over 18.0Mtpa.  The Rocanville potash mine has historically been accessed through two shafts: a production and ventilation exhaust shaft, and a service and ventilation fresh-air shaft.  A very important part of the Rocanville expansion involved construction of the new service shaft (6m diameter, 1143m deep) for fresh-air ventilation and access, 15km from the existing surface plant.  Once this third shaft was completed in 2015, the historical service shaft was converted to a second exhaust and production shaft.  Three shafts are now available for mine access, ventilation and ore hoisting at Rocanville.  The construction of the new Scissors Creek shaft at the Rocanville mine, the first potash shaft successfully completed in Saskatchewan since 1979, is summarized here.  Shaft construction in the Saskatchewan sedimentary basin involves sinking through five different rock-types: glacial tills, shales, sandstones, carbonates and salts.  The first four rock-types are all water-bearing, and the salts will dissolve in water.  This results in five different sinking challenges and requires five different shaft lining designs.  The upper 580m of rock (till – shale – sands) was frozen before sinking, and grouting methods were used for water control through deeper carbonate levels.  Challenges that were faced and overcome during shaft sinking are reviewed, and ideas that future operators working in sedimentary basin environments might consider in order to avoid these difficulties are discussed.
Keywords: sedimentary basin shaft sinking freezing grouting