DENISON MINES CORP.

Surface Access Borehole Resource Extraction (SABRE) Mining Program

The SABRE program is focused on developing a viable alternate mining method combining surface drilling and borehole mining technology. Benefits of the method may include a reduced time to production, reduced or deferred capital costs, as well as minimized safety and environmental risks.

Hydraulic borehole mining is a technique used to extract materials through a small access borehole, typically less than one-half of a metre in diameter, resulting in a very small disturbance to the surface. A mining tool containing a high-pressure water jet nozzle is lowered through the access borehole in the overburden and sandstone to the mineralized horizon. The high-pressure water jet is used to cut or erode the mineral-bearing ore and to create a cavity up to four metres in diameter. The cuttings are transported to surface in a slurry form and sent through a series of screens and settling ponds to separate the ore from the jetting water. Jetting water is filtered further and re-used in the process. Each mined out cavity is backfilled after completion with a cemented mixture in the mineralized horizon.

Between 2007 and 2012, approximately 2,100 tonnes of ore was recovered through various SABRE test mining programs, a portion of which has been fed to the mill between 2007 and 2014. After the completion of several significant milestones in 2012 and 2013, a decision was made in late 2013 to suspend the SABRE program in 2014 in response to the low uranium price environment. In 2015, SABRE activities were limited to patent applications and upgrading down-hole sonar capabilities with the objective of improving surveying of cavity dimensions and mining performance. In 2016, an expanded program was evaluated for SABRE including the re-tooling of the program to allow for larger volumes and jetting pressures designed to increase the production rate. In addition, the purchase, installation and testing of a new solid / liquid separation system was completed to assess the improvement in recovery of small uranium particles from the production slurry created during the SABRE mining process.

In 2017 and 2018, development of the re-tooled SABRE program continued with engineering of larger diameter mining pipes, procurement of high-pressure pumps and a tendering process to contract drilling equipment and labour for a further mining test. In addition, in 2018 four access holes were drilled and cased from surface to just above the McClean North orebody elevation. At the time, it was expected that these access holes would be used in 2020 as part of planned mining tests using the re-tooled equipment. In 2019, engineering and procurement activities for the re-tooled mining equipment continued and various equipment acceptance testing activities were completed. Due in part to COVID-19 pandemic related operational disruptions, work at SABRE in 2020 focused on further de-risking various elements of the SABRE equipment and the SABRE mining process.

In 2021, the MLJV completed the SABRE test mining program at McClean North, using the access holes drilled in 2018. The SABRE field test ran safely from May to September 2021 with four cavities mined and the recovery of approximately 1,500 tonnes of high-value ore ranging in grade from 4% to 11% U 3 O 8. The program was concluded successfully with no safety, environmental or radiological incidents. Importantly, key operating objectives associated with the test program – including targets for cavity diameter, rates of recovery, and mine production rates – were all achieved during the field test.

The majority of the ore recovered from the 2021 test mining program was processed at the McClean Lake mill in late 2021. Denison’s share of production was 40,000 pounds of U 3 O 8.

In January 2024, Denison and Orano Canada announced that the MLJV has approved a restart of uranium mining operations using the joint venture’s patented SABRE mining method. Mining is planned to commence at the McClean North deposit in 2025, with 2024 activities expected to focus on preparations necessary to ready the existing SABRE mining site and equipment for continuous commercial operations, as well as the installation of pilot holes for the first mining cavities planned for excavation.