The CuMo deposit is a porphyry type deposit and has been classified as a porphyry copper molybdenum deposit (Klein, 2004; Spanski, 2004), or as a porphyry molybdenum-copper (low fluorine type) deposit (Mutchler et al, 1999).

The CuMo deposit is primarily of economic interest for its Mo content but contains significant values of Cu and Ag. Low-grade zones of copper enrichment typically form above and partially overlap with molybdenum shells in porphyry molybdenum deposits (Carten et al, 1993). The CuMo deposit is classified as a porphyry Mo-Cu deposit (Mo greater than 0.04% and Cu being potentially economically significant).

The CuMo deposit is typical of large, dispersed, low-grade molybdenum ± copper deposits. These systems are associated with hybrid magmas typified by fluorine-poor, differentiated monzogranite igneous complexes, characteristic of continental arc terranes. Due to their larger size, the total contained potentially economic molybdenum in these types of deposits can be equivalent to or exceed that of high-grade molybdenum deposits such as Henderson or Climax (Carten et al, 1993).

Molybdenum mineralization was discovered at CuMo in 1963. The only other molybdenum showing in Boise County is the Little Falls molybdenum prospect, which is situated just to the northeast of CuMo.

Mineralization on the property occurs in veins and veinlets developed within various intrusive bodies. Molybdenite occurs within quartz veins, veinlets and vein stockworks. Individual veinlets vary in size from tiny fractures to veinlets five centimeters in width, with an overall thickness averaging 0.3-0.4 cm. Pyrite and/or chalcopyrite are commonly associated with molybdenite although molybdenite can occur alone without other metallic mineralization.

Chalcopyrite occurs in quartz-pyrite + molybdenite veinlets, in magnetite + pyrite as well as in pyritebiotite + quartz + magnetite veins with secondary biotite halos. Scheelite is common on the property and closely parallels the distribution of molybdenite (Baker, 1983).

The CuMo project is envisaged to be developed using open pit mining techniques. The scale of the deposit is such that ultra-class mining equipment (e.g. 400-ton trucks) has been considered for the purposes of this PEA. As well, to improve the head grade of the flotation mill feed, the author has considered the implementation of mineral sorting for the project. Specifically, the author envisions a multi-stage bulk sorting process accompanied by a final particle-sorting stage to upgrade the mil feed. The result of the mineral sorting strategies is a reduction of waste fed to the mill, thereby improving feed head grade. There is however added cost, but this is all taken into consideration in determining the potential mineable resource for the project.

Pit wall slopes used in the PEA were given for ground elevation intervals and became shallower with pit depth i.e. the upper interval was 45°, the next 40°, and the north south and west walls had a lower interval of 35°.

At an ultimate depth of over 600 m, the conceptual design walls are significantly higher than most operating mines in North America. The precedent for cases is very limited but the pits that are of those heights have all encountered slope stability problems in some areas of the mine. The plot suggests that these proposed overall slope angles (OSA) fall around FoS of equity and may not be achievable.

Pit Slope Recommendations

For the PEA pit design, the author recommends the following pit wall design criteria:
- maximum bench height of 50 ft
- bench width of 26 ft
- inter-ramp wall angles of 42°
- geotechnical berm of 65 ft every seven benches.

To allow for geotechnical berms and a spiral ramp to reach the pit bottom, derived an overall slope angle to be used in pit shell definition of 37°.

The CuMo processing facilities and associated service facilities will process ROM (run-of-mine) feed delivered to the primary crusher, to produce separate copper and molybdenum concentrates, waste rocks, and tailings. The proposed process encompasses crushing the ROM feed, bulk sorting, particle sorting, grinding, bulk rougher and cleaner flotation, regrinding, molybdenum separation and dewatering of copper and molybdenum concentrates. Molybdenum concentrates will be further processed downstream in a roaster to produce a saleable molybdenum trioxide product.

The process plant design is based on a flow sheet with unit operations that are well proven in the sulfide flotation industry, incorporating the following unit process operations. Where considered practical, unit operations are sized to maximize the economies of scale possible with large equipment. The sorting system consists of the following unit processes. Mine sort feed (300 kstpd) from the open pit is crushed usin ........