The Moonlight copper deposit is classified as a porphyry copper deposit with associated gold, silver and molybdenum credits.

Oriented core and inspection of the bedrock in drilling sumps and shallow prospect workings showed that copper mineralization was contained on fractures with a wide variety of orientations. Strong copper mineralization was commonly observed on veinlets trending N20-35W and dipping 15-35 SW. In addition to the mineralization in shallow dipping fractures, copper is contained on NS steep
to moderately E dipping, N60-75E steeply N dipping, N70-85W steeply south dipping veinlets.

Both Sheffield and Placer have recognized that there at least two styles or stages of mineralization at the Moonlight deposit. The paragenetically earlier style is characterized by disseminated copper minerals located interstitial to quartz, feldspar, chlorite and especially disseminated rosettes of tourmaline. This mineralization usually consists of fine grained chalcopyrite but zones of disseminated bornite are also common. High in the system disseminated hypogene chalcocite has also been occasionally observed. Bornite has been observed to rim chalcopyrite grains in some places. Placer characterized this mineralization as late stage magmatic or pneumatolytic. A metasomatic origin should not be precluded. This style of mineralization shows some association with potassium feldspar and a very strong association with tourmaline and sometimes chlorite abundance.

The second transgressive stage of mineralization is characterized by veinlets or stockwork breccias which often have a gangue of tourmaline and lesser quartz with strong hematite. Strong copper mineralization was commonly observed on veinlets trending N20-35W and dipping 15 -35 SW. The overall orientation of the Moonlight deposit appears to be parallel to these gently southwest dipping fractures and indicates a good exploration target underneath the metavolcanics to the southwest. In addition to the mineralization in shallow dipping fractures, copper is contained on N-S steep to moderately E dipping, N60-75E steeply N dipping, N70-85W steeply south dipping veinlets. Although fracture hosted mineralization is widespread and often high grade at Moonlight, drilling to date has not revealed extensive vein- like structures similar to those mined at the Superior and Engels mines.

The Engels deposit is characterized as a shear zone-hosted, structurally-controlled, tabular breccia body(s) hosted within mafic units of the Lights Creek Stock as well as the metavolcanic rock into which the stock was intruded. Copper and silver mineralization at Engels appears to be associated with late-stage differentiates of the more felsic units of the Lights Creek Stock.

The steeply northward plunging, tabular Engels copper ore body is contained in a vertical shear zone that ranges from 25-125 ft in width. The ore principally consisted of bornite and chalcopyrite hosted in a hornblende gabbro body. Younger quartz diorite and quartz monzonite bodies are associated with the gabbro and likely played an important role in the placement of the copper mineralization.

The Superior and Sulfide Ridge deposits are classified as a porphyry copper deposits with associated silver and, to a lesser extent gold.

The Superior mine is thought to have formed at a higher temperature than the Moonlight deposit. The previously mined deposit consists of a stockwork of seven parallel, northeasterly striking, and easterly dipping (550-800) vein zones. The veins principally consist of chalcopyrite and some bornite, along with associated magnetite and pyrite and are 8-20 ft thick. Magnetite is more prevalent at the Superior Mine than at the Moonlight deposit while specularite, common at Moonlight is non-existent at Superior. The Superior mine exhibits some porphyry like attributes and similarities to Moonlight in that they are both found within an intrusive body in close proximity to an older metavolcanic sequence. Its copper mineralization is contained in stockwork vein system hosted in a similar quartz monzonite body to the host of the Moonlight deposit. Mineralization historically was mined from steeply dipping, thick chalcopyrite rich veins, steeply dipping controls to the mineralization at Moonlight are only now being considered important.

All mining for the Moonlight deposit will be conducted utilizing conventional open pit mining methods with drill and blast, followed by load and haul with large diesel truck and shovel equipment.

The pit was designed to have varying haul road widths. A majority of the pit has a doublelane road, which is 100 ft (30.5 m) wide. This is based on the industry standard for the running width of a haul road to be a minimum of 3.5 times the width of the largest equipment, which in this case is a Komatsu 830 E haul truck. This does not include additional allocation for a drainage ditch and safety berm.

The depths of the pit were transitioned to a single-lane road to achieve a steeper pit slope and minimize the excavation and removal of uneconomical material. The singlelane road dimensions are 72 ft (22 m) wide.

The overall ramp gradient is 8% for both double lane and single lane roads.

Material will be drilled and blasted and then loaded with a hydraulic shovel into a fleet of haul trucks. This material will then be hauled from the open pit location to the primary crusher, where it will be end dumped into the crushing pocket. Waste will also be drilled and blasted, but will be loaded via one of two wheeled loaders. This waste will then be hauled to the WRMF and end dumped. From here a tracked dozer will push the dumped piles and shape the management facility as required.

Based on the selected bench height and the production schedule, a 10-inch diameter production drill was selected with a smaller drill rig to be used for pre-splitting. The blast design concept anticipates use of ammonium nitrate fuel oil (ANFO) as the main explosive for the blast holes (90%) with 10% by emulsion.

Primary loading is planned to be performed by a diesel hydraulic front shovel (Komatsu PC4000) with support from two-wheeled loaders (Komatsu WA1200) that will typically be allocated to loading waste. The shovel has a 29 cu yd capacity while the wheeled loaders have a 26 cu yd capacity.

The smaller excavator will also be utilized for pushback areas that don’t meet the minimum mining width, allowing for further flexibility and selectivity.

Komatsu 830E trucks were selected for the mining operation, which have a 240 st (218 t) capacity.

The 60,000 st/d processing plant will utilize three stages of crushing (gyratory, cone and HPGR crushing), ball mill grinding, and conventional flotation to produce a high-grade copper concentrate with associated precious metal credits. The processing plant will operate in two 12 h shifts per day, 365 d/a. The primary crushing plant availability will be 70%. Secondary crushing, tertiary crushing, grinding, and flotation plant availability will be 92%.

The process plant will consist of the following unit operations and facilities:

• run-of-mine (ROM) mineralized material receiving
• primary (gyratory) crushing
• crushed mineralized material stockpile and reclaim
• secondary crushing (cone crushers)
• tertiary crushing (HPGR crushers)
• ball mill grinding circuit incorporating with hydro-cyclones for classification
• copper rougher and scavenger flotation
• copper concentrate regrinding
• copper cleaner flotation
• copper concentrate thickening, filtration, and dispatch
• tailings disposal to a tailings pond.

The mill feed will be crushed by one 63” x 89” or equivalent gyratory crusher to 80% passing approximately 6”. Crushed material will be fed into a stockpile of 55,000-ton live capacity and then be further crushed by three cone crushers (each with an installed power of 1,000 hp, two in operation and one standby) followed by two high pressure grinding rolls (HPGR, each with an installed power of 7,500 hp). The product from the HPGR circuit will be further ground to 80% passing 110 micron by two ball mills (each with an installed power of 25,000 hp). The slurry from the hydrocyclones will feed one bank of rougher flotation cells, each with 10,500 ft3 volume. The rougher concentrate will be reground to 80% passing approximately 50 micron prior to three stages of cleaner flotation by conventional flotation cells. The flotation concentrate will be thickened and filtered and sent to the concentrate stockpile for subsequent shipping to the smelter. The tailings produced will be impounded in a tailings management facility (TMF) located at south of the processing plant.