Potash, also known as potassium chloride, is one of the main fertiliser ingredients of which deposits are found all over the world. In the Danakil Depression in northern Ethiopia, vast salt flats lie above extremely rich potash deposits, up to 800 metres below ground. Here Fugro has been involved in the exploration phase of a potash mining project run by Canadian mining company Allana Potash Corp, now acquired by Israel Chemicals Limited (ICL) .
Our client is very satisfied with the results. Not only did we find suitable water, but we also provided every piece of information required to help make a solid investment decision.
Fugro combined several areas of expertise and, as part of a bankable feasibility study, conducted groundwater research in preparation for solution mining of potash salts. Established capabilities in hydrogeology, geology, geophysics, satellite imaging, drilling and mapping as well as expertise in data management and logistics proved invaluable.
Insurmountable problems with conventional mining techniques made it necessary to seek alternative methods. Since potash is water-soluble, solution mining was the best option.
Solution mining techniques are energy and water intensive: fresh groundwater is pumped through pipelines into solution wells, dissolving the potash, and the resulting brine is pumped up into open evaporation ponds. The water evaporates to leave crystallised salts that can easily be harvested. It is a simple, clean and natural technique.
The primary preconditions for solution mining include a stable and sustainable supply of relatively fresh water. Although the Danakil Depression is one of the hottest areas on Earth, with no rainfall for most of the year, it has a surprising amount of water. It is supplied by the nearby Ethiopian Highlands, which rise up to 3,000 metres. Water flows to the Danakil desert via canyons, wadis and fault structures into alluvial fans and is stored in aquifers beside the salt flats.
Fugro applied geophysical techniques with transient electromagnetics (TEM) up to a depth of 400 metres to identify aquifers, water depth and the fresh water/salt water interface. A geological structural analysis based on satellite images identified tectonic elements that transport water from the Highlands to the lowlands. The water balance was determined with the help of satellite supported climate data.
At the most promising locations, more than thirty drill holes were sunk at groundwater monitoring points. In addition, five pumping wells were constructed at one well field; these were used initially for pump testing and later as water supply wells. Samples were taken from all wells and analysed to determine the quality of the groundwater and the level of recharging. Finally, an 82-day step-drawdown pumping stress test was conducted to verify water recharging levels.
With Danakil temperatures between 40 and 50 degrees Celsius, this presented a major challenge for both the staff working on this project and the equipment used. Most of the drilling work utilised a multi-purpose drilling rig which performed well (thanks to its hydraulic oil cooler) despite the manufacturer’s technical specifications being stretched to their limits.
Other challenges included the need to replace the drilling fluid frequently because of the high mineralisation of the groundwater, and the storage and transportation of borehole materials which could not be stored on site. Many of the necessary materials had to be imported: the drilling rig, a fully-functioning workshop in a container, drill pipes and quartz filter gravel were shipped to Djibouti and then transported 800 kilometres by road to the project site.
Fugro’s pump tests and water analysis showed that there is suitable water in the area for solution mining of potash salts. It has also been established that the groundwater recharge from the alluvial fans is sufficient to cover at least 3 million cubic metres yearly from one alluvial fan for mining operations over the next 20 to 25 years.
With potash not the only commodity suitable for solution mining, Fugro is also set to support other mining companies seeking new opportunities and to apply its expertise to global mining for other bulk materials such as lignite, coal and iron ore.
In 2015 the world consumed 36 million tonnes of potash.