With conventional mining techniques unsuitable for potash extraction in this location, Allana Potash Corp decided to use solution mining – a process whereby fresh groundwater is pumped through pipelines into solution wells, dissolving the potash and pumping the brine up into open evaporation ponds.
Solution mining requires a sustainable supply of relatively fresh water. Although one of the hottest areas on Earth - with no rainfall for most of the year - the Danakil Depression has a surprising amount of water, supplied by the nearby Ethiopian Highlands and stored in aquifers beside the salt flats.
Fugro used geophysical techniques (including TEM) to a depth of 400 metres to identify aquifers, water depth and the fresh water/salt water interface. A geological structural analysis identified tectonic elements that transport water to the lowlands, and satellite-supported climate data confirmed the water balance.
Over thirty holes were drilled at groundwater monitoring points in the most promising locations. Five pumping wells were constructed at one well field, initially for pump testing and later as water supply wells. Samples from all wells were analysed to determine groundwater quality and the level of recharging. An 82-day step-drawdown pumping stress test verified the water recharging levels.
The project presented many operational challenges. Danakil has temperatures between 40 and 50 degrees Celsius, which impacted on both staff and equipment. Despite stretching the manufacturer’s technical specifications to the limit, the multi-purpose drilling rig performed well, thanks to its hydraulic oil cooler.
The high mineralisation of the groundwater meant that the drilling fluid had to be replaced frequently. Borehole materials could not be stored on site, and many materials, including the drilling rig, container workshop, drill pipes and quartz filter gravel had to be shipped to Djibouti and transported 800 kilometres by road to the project site.
Our pump tests and water analysis confirmed there was suitable water in the area for solution mining of potash salts. We also helped establish that the groundwater recharge from the alluvial fans was sufficient to cover at least 3 million cubic metres annually, from one alluvial fan for mining operations over the next 20 to 25 years.