Water problems in Saskatchewan potash mining — what can be learned from them?

CIM Bulletin, Vol. 84, No. 945, 1991

Fritz F. Prugger, AMINSA, El Escorial, Spain, and Arnfinn F. Prugger, Department of Geological Sciences, University of Saskatchewan

The Saskatchewan potash beds are overlain by a number of water-bearing formations. There are water zones in the footwall as well. These aquifers created difficulties during the construction of shafts to the potash beds at 1000 m depth, and they pose a continuous threat to the safe and efficient operation of potash mines in the province. The first shafts to be sunk in Saskatchewan encountered major problems during shaft sinking. Of the 17 potash shafts started in the province, five had major water inflows during shaft sinking or after production startup, and one was abandoned because of water problems. The biggest obstacle encountered during shaft sinking was a poorly consolidated sand-shale-clay-siltstone unit commonly called the Blairmore Formation, which occurs at a depth of about 500 m. The initial problems with shaft sinking were overcome in the 1960s by using European methods of freezing and the installation of cast-iron tubbings or a double-steel lining through waterbearing horizons. From the start of production in the early 1960s, operators have been aware of the ever-present hazard of potential water inflows into mine openings from permeable units in both the hanging wall (carbonates of the Dawson Bay Formation which occur 15 m to 50 m above the mining level) and the footwall (carbonates of the Winnipegosis Formation which occur 50 m to 150 m below). This awareness has been reflected in conservative over-all extraction rates and mining layouts specific to local conditions. In spite of this consciousness, a number of water problems have occurred in operating mines. These have resulted in everything from simple increases in expenditure to the shut-down of one mine in 1987. In this paper a history of water problems in the Saskatchewan potash industry is given, followed by a summary of measures that are now commonly used to avoid these problems. A description of each inflow event is given, and the attempt is made to analyze the causes of each occurrence. Based on what was learned from each event, suggestions are made to prevent future water inflows into potash mines.

Mots Clés: Potash mining, Underground mining, Water-bearing formations, Saskatchewan potash industry.