Excelsior Mining Corp. announced the results of its updated preliminary economic assessment (PEA) on the Johnson Camp mine (JCM) heap leach, located in Cochise County, Arizona. The PEA considers the results of the drill program completed in 2022 and the implementation of sulphide leaching technology to improve recoveries. As part of the PEA, the combined report will also include a republishing of the prefeasibility study (PFS) update on the North Star deposit of the Gunnison copper project. The Gunnison project is designed as a copper in-situ recovery (ISR) mine using solvent extraction-electrowinning (SX/EW) to produce copper cathode and the Johnson Camp mine is a conventional open pit and heap leach operation.

The JCM has historically been an open pit, heap leach operation since Cyprus Minerals opened the property in the 1970s. The operation includes two open pits, a two-stage crushing-agglomerating circuit, a fully functioning SX/EW plant capable of producing 25 million lb/y of cathode copper, a complete set of pregnant leach solution (PLS) and raffinate ponds, and full infrastructure (ancillary facilities, access, power, water, and communications).

Heap leaching of sulphide copper with accelerated pyrite oxidation is proposed in this PEA. The project plans include mining oxide, sulphide, and transition material from the Burro and Copper Chief pits for 20 years and heap leaching for an additional year to produce copper cathode at a capacity up to 25 million lb/y.

To restart JCM for heap leaching, two developments need to take place simultaneously: pre-stripping and mine development, and the construction of a new heap leach pad, Pad 5. Both are considered to require between six and nine months to complete before irrigation of the new leach pad could commence. Piping of PLS and raffinate lines from Pad 5 to the JCM ponds also fits within this time frame. A PEA has been completed by M3 with respect to this planned re-opening.

The updated PEA calls for mining to take place with 100-ton haul trucks and front-end loaders. Mining is planned on 20-ft bench heights. The pit configuration is double-benched with catch benches every vertical 40 ft. Crushed and agglomerated material will be processed and placed on a newly permitted leach pad, Pad 5.

The JCM is currently covered under Aquifer Protection Permit P-100514. Excelsior has obtained a significant amendment to the existing APP to accommodate mining at JCM from the Burro Pit. A new facility, Leach Pad 5, with associated impoundments has been added to the existing APP to accommodate resumption of mining at JCM.

The full capital cost for restarting the JCM heap leaching operation including mining pre-production first fills/owner’s costs, leach pad construction, new leach pad stacking system, crusher and agglomeration refurbishment and haul road construction is approximately $58.9 million.