Solution mining of salts is a technique that has been developed over the last 30 years as an alternative to conventional underground mining. The principle of solution mining involves drilling large-diameter boreholes to the bottom of the lowest carnallite layer. The solution mining concept for the extraction of carnallitite from Horizons 2, 3 and 4 is based on hot leaching in double well caverns, starting with the lowermost Horizon 4 carnallitite and developing to Horizons 3 and 2. The single wells of the double well caverns are 10m apart. Cavern diameter will be app. 50m and a safety pillar of at least 60m thickness between the caverns, resulting in a rectangular cavern area of 160x170m.
A brine solution enriched in magnesium potassium and sodium chloride is recovered from the dual well caverns and processed at the potash plant for product recovery. A portion of the magnesium and sodium chloride fractions of the brine are returned to the caverns once they are complete, to provide geotechnical support which reduces the potential for surface subsidence following mining. Excess magnesium chloride brine is discharged to the ocean.
The rate of mining, cavern shape, and preferential separation of various salts are determined by changing the positions of the inflow and outflow pipes, as well as adjusting the flow rates and the oil or rock salt blanket. This high-tech mining procedure is accomplished by geophysical measurements and other sensors to monitor cavern shape and solution concentration.
This method of solution mining salts is proven, it requires relatively low capital investment compared to conventional underground mining, and it can be applied to Carnallite deposits at depths of up to 2,000 meters (the Mengo field deposits are found at 400 to 1000 meters).