Miners today face many challenges, from low commodity prices to the exhaustion of accessible high-quality ore bodies and high development costs.1 However, by drawing on the oil and gas industry’s process of hydraulic fracturing, miners may have new ways to tackle those problems through the technique of “frack mining.”
The frack mining concept combines the mining industry’s practice of in-situ leaching with the oil and gas industry’s hydraulic fracturing process. In-situ leaching is a well-established process that involves the drilling of vertical wells to pump leaching solution into an ore body. Once the solution is impregnated with the mineral, it is pumped out via a recovery well. Hydraulic fracturing—used frequently in the US, Russia and China—involves the drilling of horizontal directional wells, which are then injected with pressurized chemicals to create small fissures in the rock, freeing the oil or gas for extraction.
With frack mining, one directional borehole could be drilled from a central well and guided to the top of an ore vein, with another being drilled into the base of the ore vein. The ore body would be pressurized, causing fissures. An in-situ leaching solution could then be pumped into the top borehole; gravity would carry the solution down through the fissures, picking up targeted minerals along the way. The saturated solution would drain into the lower borehole and pool in a common extraction well, where it could be pumped to the surface. With this technique, the solution does not have to erode a path to the recovery well, as it does with in-situ leaching. That path is provided by the fissures.
This approach offers potentially lower costs compared to in-situ leaching. For example, to cover a surface area of approximately 3,800 square meters, a typical in-situ leaching operation would require three extraction wells and 13 inlet wells (16 wells in total), with a submersible pump in each of the extraction wells for transporting the solution to the surface (assuming a distance of 20 meters from inlet well to extraction well).
Meanwhile, a frack mining operation would require just one inlet well and one outlet well (two wells total) to cover a similar area. Only one submersible pump would be needed to drain the outlet well. The inlet and outlet wells would be located as a central “hub” with “spokes” of 12 horizontal 35 meter-long lines, each with upper and lower wells, emanating out from them. That would mean 24 horizontally drilled sections in total.
In these two scenarios, the in-situ leaching operation would require total drilling of 3,200 meters; the frack mining approach would require just 1,240 meters (assuming a well depth of 200 meters.) If drilling costs were $80 per meter, the total cost of drilling would be $256,000 and $99,200, respectively.
Other cost benefits are also likely. For example:
Experiments have not yet been done to determine maximum spoke length, but increasing that length would enable production of a larger surface area than the above example—further improving the cost advantage over in-situ leaching.
Frack mining is likely to require a smaller footprint than in-situ leaching, which could lead to relatively lower mine development and closure costs.
With the hub-and-spoke pattern, operation could begin after the completion of just one set of upper and lower horizontal spokes, with additional spokes coming online as they are completed. This arrangement could enable miners to start generating cash sooner to cover initial capital costs, with future expansion becoming an operational cost. This would improve project economics and allow miners to increase production when required by the market.
Beyond lower costs, frack mining could also mean higher production rates. The fissuring process would increase the surface area between the ore and leaching solution, thus increasing the amount of ore being picked up by the solution.
Frack mining could be valuable in operations that currently use in-situ leaching, such as uranium, copper and potash mining. It could also enable miners to cost-effectively extract lower-grade ores in traditional, less-remote locations. And, as environmentally safer dissolving solutions are developed, the process could be expanded to other minerals, such as gold.2
Overall, the approach is a potentially promising hybrid application of existing and well-known technologies3—and an opportunity that warrants consideration as miners look for innovative solutions to today’s industry challenges.
1“Mining report: Multitude of mining industry challenges need innovative solutions,” Business Vancouver, March 17, 2014. Retrieved July 15, 2015 from https://www.biv.com/article/2014/3/mining-report-multitude-of-mining-industry-challen/
2“Cyanide Leaching of Gold,” Mine Engineer.com, (n.d.) Retrieved July 16, 2015 from http://www.mine-engineer.com/mining/minproc/cyanide_leach.htm
3Vladimir Ugorets and Dmitry Yermakov. “In-Situ Leaching or In-Situ Recovery,” SRK Consulting, (n.d.) Retrieved July 16, 2015 from http://www.srk.com/en/newsletter/metallurgy-mineral-processing/situ-leaching-or-situ-recovery