The Gunnison Project (North Star) lies on the eastern edge of the Little Dragoon Mountains.

The North Star copper deposit is a classic copper skarn (Einaudi et al, 1980 and Meinert et al, 2005). Skarn deposits range in size from a few million to 500 million tonnes and are globally significant, particularly in the American Cordillera. They can be stand- alone copper skarns, which are generally small, or can be associated with porphyry copper deposits and tend to be very large. The North Star deposit is large, at the upper end of the range of size for skarn deposits, and is likely associated with a mineralized porphyry copper system that has not been discovered.

Copper skarns generally form in calcareous shales, dolomites and limestones peripheral or adjacent to the mineralized porphyry. Copper mineralizing hydrothermal fluids are focused along structurally complex and fractured rocks and convert the calcareous shales and limestones to andradite rich garnet assemblages near the intrusive body, and to pyroxene and wollastonite rich assemblages at areas more distal to the stock. Retrograde hydrothermal fluids produce actinolite-tremolite-talc-silica-epidote-chlorite assemblages that overprint earlier garnet and pyroxene. The mineralization is typically pyrite -chalcopyrite-magnetite proximal to the mineralizing porphyry and chalcopyrite-bornite more distally from the body. The copper-gold porphyry and skarn model by Sillitoe (1989) is being used as a conceptual exploration model for the North Star deposit.

Copper sulfide mineralization has formed preferentially in the proximal (higher metamorphic grade) skarn facies, particularly along stratigraphic units such as the Abrigo and Martin Formations near the contact with the quartz monzonite and within structurally complex zones. Primary mineralization occurs as stringers and veinlets of chalcopyrite and bornite. Primary (unoxidized) mineralization remains “open” (undetermined limits) at depth and to the north, south, and east.

Oxidation of the mineralization occurs to a depth of approximately 1,600 feet, resulting in the formation of dominantly chrysocolla and tenorite with minor copper oxides and secondary chalcocite. The bulk of the copper oxide mineralization occurs as chrysocolla, which has formed as coatings on rock fractures and as vein fill. The remainder of the oxide mineralization occurs as replacement patches and disseminations.

Excelsior proposes to use the In-Situ Recovery (ISR) method to extract copper from oxide mineralization located within the North Star deposit. ISR was chosen based on the fractured nature of the host rock, the presence of water saturated joints and fractures within the ore body, copper mineralization that preferentially occurs along fracture surfaces, the ability to operate in the vicinity of Interstate 10, and to avoid the challenges of open pit mining in an area with alluvium overburden thickness ranging from approximately 300 feet to 800 feet.

In the ISR process, a low pH raffinate solution (“lixiviant”) is injected into the ore body via a series of injection wells. As the lixiviant migrates through the joints and fractures within the mineralized bedrock, copper is dissolved. This pregnant leach solution (PLS) is recovered by a series of recovery wells that surround each respective injection well.

The PLS is pumped to the surface where the copper is stripped from the solution using the solvent extraction/electrowinning (SX-EW) process. The SX-EW process begins with the SX plant extracting and concentrating the dissolved copper from the PLS, after which the EW plant reduces the concentrated copper to copper cathode. Once the copper is recovered by SX, the barren solution is re-acidified with sulfuric acid to create new lixiviant which is pumped back to the well field and re-injected. The total volume of lixiviant injected and PLS extracted will remain effectively equal throughout ISR operations.

After ISR in a production block is complete, as determined by degradation of the PLS grade below the economic cutoff, the bedrock within the completed production block will be rinsed in compliance with appropriate permit conditions.

Economic recovery of acid soluble copper using ISR requires certain hydrogeological conditions be present within an ore body, such as: (1) a saturated ore body; (2) sufficient hydraulic conductivity within the fractured bedrock; (3) hydraulic connection between the injection and recovery wells so lixiviant can circulate through the mineralized bedrock; and (4) lixiviant/mineral contact and adequate lixiviant retention time. These conditions allow for lixiviant to be circulated through the ore body, with sufficient contact and retention time with acid soluble copper in the ore body to meet the required PLS grade. Site characterization efforts described in this chapter have focused on gathering data to assess these hydrogeological conditions.

The Gunnison Project uses solvent extraction (SX) and electrowinning (EW) to recover copper from an in situ recovery (ISR) wellfield. The Gunnison Project is planned for development in three stages. Stage 1 uses the existing JCM plant to recover 25 million pounds per annum (MM lbs/yr) of copper cathode from the Gunnison wellfield. Stage 2 envisages construction of a 50 MM lbs/yr SX-EW plant in the Gunnison Project area south of I-10 that will be independent of the JCM plant. Stage 3 development expands the Gunnison plant to double the capacity to 100 MM lbs/yr, resulting in an aggregate capacity of 125 MM lbs/yr of copper cathode. The SX-EW facilities are designed to recover copper from pregnant leach solution (PLS) to produce cathode-quality copper with 99.99% purity.

Raffinate from the SX-EW plant is acidified and pumped to the ISR wellfield through a network of process piping to a series of injection wells that are each surrounded by four extraction wells. The extraction ........