The in-situ leach - or ISL - technique recovers minerals from ore in the ground by dissolving them in situ, using a mining solution injected into the orebody. The solution is then pumped to the surface, where the minerals are recovered from the uranium-bearing solution. More than half of the world's uranium production is now produced by ISL, but the technique - which requires a geologically suitable orebody - has not so far been used in Canada. It is sometimes referred to as in-situ recovery, or ISR.
Midwest Main is one of two high-grade unconformity-hosted uranium deposits at the Midwest joint venture, co-owned by Denison (25.17%) and Orano Canada Inc (74.83%).
Denison's inaugural programme involved drilling ten small diameter boreholes within the Midwest Main deposit, primarily to evaluate site-specific conditions for ISL mining. A series of tests were successfully performed on each borehole, the company said, creating an extensive database of geological, hydrogeological, geotechnical, and metallurgical data and validating certain key assumptions in the previously completed internal conceptual mining study evaluating the potential use of ISL mining at Midwest, released in April 2023.
Denison President and CEO David Cates said the joint venture had been able to assemble a strong team to carry out the test programme, thanks to Orano's significant global expertise in ISL mining and Denison's industry leadership in the advancement of the technique in the Athabasca Basin region: Denison is looking to use ISL at the Phoenix deposit at the Wheeler River project, and completed a first ISL field test programme on the Tthe Heldeth Túé uranium deposit at Waterbury Lake last year.
"The programme achieved its planned objectives, and the results provide preliminary validation that the Midwest Main deposit possesses the characteristics necessary for an ISR operation," Cates said. "Accordingly, further evaluation is warranted and, building on the Concept Study and incorporating the data acquired in the test programme, we are proceeding with a Preliminary Economic Assessment for ISR mining."
Midwest is about 25 kilometres by road from the McClean Lake Operation, owned by Denison-Orano Canada.
