The Wharf Operation deposits are considered Tertiary epithermal replacement mineralization, both intrusive-hosted and sediment-hosted (Coeur internal report, 2014). Depth of mineralization at the Wharf Operation (~1.5 km; Paterson and Giebink, 1989) is considered deeper than normal for epithermal deposits, but low temperature of mineralization are consistent with epithermal-type deposits (Paterson, 1990), although these temperatures may represent late stage of fluorite mineralization.

The main trends of mineralization at Wharf parallel the strike of a major joint sets that Shapiro and Gries (1970) measured in upper and lower Deadwood Fm. outcrops. At Golden Reward, the mineralized trends strike north-south. Mineralized trends at Golden Reward may reflect more of an influence from basement structure, as the later faults in the Golden Reward graben area may have been reactivated along faults or moved along existing foliation planes, and mineralization occurred along the same trend as the faulting.

Gold or gold-bearing minerals may be disseminated in porphyry, or may be confined to fractures (Paterson and Giebink, 1989; Paterson, 1990). Highly fractured porphyry is known to be the most mineralized, and preliminary work shows a correlation of fractured porphyry with gold, in contrast to unfractured and unmineralized rocks within mineralized zones. This, however, may be due again to gold-bearing sulfides occurring as the primary economic mineral. Porphyry near fractures is usually the most oxidized, grading outwards into gray, blocky porphyry with very small (< 0.25 mm) grains of disseminated sulfides. Atomic absorption (AA) assaying is limited in determining gold encapsulated in sulfides, but assays of fractured samples that are oxidized will readily measure gold formerly in sulfides. Additional fire assays may help to better understand this association.

Visible native gold observed at Wharf has been only seen twice during current mining activities; one occurrence was found within a fluorite vein. Because fluorite is considered a late-stage mineral (e.g., Paterson et al., 1989), the fluorite-gold occurrence may indicate a later, minor mineralizing event, distinct from earlier, goldbearing sulfide mineralization. Thin sections of very high-grade (1.173 and 0.615 oz/ton Au) samples from the Annie Creek mine analyzed by Schurer and Fuchs (1991) show native gold associated with hematite, goethite, jarosite which forms from oxidation of iron sulfides, and arseniosiderite which forms from oxidation of
arsenopyrite; quartz was also associated with gold. A thin section from the lowestgrade sample in this study (0.195 oz/ton Au) showed no native gold, but abundant sulfides, which was assumed to indicate lattice or submicron gold. The discussion suggests that oxidation of arsenic-bearing sulfides may have remobilized gold in an arsenic complex and deposited it as native gold in higher-grade samples (Schurer and Fuchs, 1991).

The Wharf Operation is currently a conventional truck and loader heap leach gold mine. The Wharf Operation consists of five heap leach pads, which are all load/offload pads. The entire planned mining disturbance falls within the current permitted area.

Wharf leases nearly all of the earth moving equipment used at the mine. The current earth moving equipment under lease through local equipment dealers includes: (14) 777 trucks, (1) D-10 and (2) D-9 dozers, (4) 993 front end loaders, (2) 16M motor graders, and (2) DM 45 hammer drills. Relationships with local dealers span over 15 years, and the earthmoving equipment is under contract through 2017.

A single crushing circuit is used to process ore before being transferred to the leach pads. This crushing circuit has undergone numerous modifications over its history in order to accommodate operational conditions and optimize performance.

There are currently five on/off heap leach pads used for the leaching cycle; the newest pad (pad #5) was constructed in 2008. In 2013, Wharf received certification by the International Cyanide Management Institute (ICMI) in recognition of being compliant with the ICMI cyanide code for adhering to the best industry practices for storage, handling, and use of cyanide.

In the gold leaching process, barren (non-metal bearing) process solution is pumped to the active leach pads and applied at the rate of 0.004 gpm/sq ft. Barren solution sodium cyanide concentrations are maintained around 0.20 to 0.25 pound/ton of solution (maximum Weak Acid Dissociable (WAD) cyanide value of 50 ppm). The barren solution dissolves metals as it filters through the crushed ore. The pregnant (metal bearing) solution is collected on high density polyethylene (HDPE) liner under the pad. The solution is directed through a series of pipes into the pregnant sump. From the sump, the solution is pumped to the first tank of a series of carbon-in-column (CIC) tanks. There are three CIC circuits to process precious metal solutions. Activated coconut shell carbon is used to concentrate the metals. Once the precious metals have been adsorbed on to the carbon, the pregnant carbon is transferred to the strip circuit. The barren solution has additional sodium cyanide added to it and is pumped back to the pads. A safety screen is used to prevent fine carbon loss.

Gold and silver are stripped (removed) from the loaded carbon using a heated sodium hydroxide and sodium cyanide solution. This process upgrades the solution gold grade to prepare for the next step. The pregnant strip solution is then passed through a series of electrowinning cells. The precious metals plate on the cathode in the cells, forming a sludge. The metal sludge is washed off the cathode, processed through a filter press, dried in a retort, and shipped to a commercial refinery for further processing. Alternatively, the refinery has the capability to smelt the sludge, using a furnace to make doré. Liquid mercury is collected from the retort process and is sold to a third party, or stored. The barren carbon is placed back into the carbon tanks to continue treating additional pregnant solutions.

If the pregnant leach solution does not have a high enough metal content, it can be cycled through the enrichment process. The low-grade pregnant solution is routed through the enrichment sump, additional sodium cyanide is added to the solution and it is pumped back up to the pad. In the event of a water balance upset or power bumps, the four process ponds (Pregnant, Barren, Overflow, and Contingency) are used to collect either the excess or drain down solution. Prior to releasing any excess process solution to the water treatment facility, the solutions are passed through a set of four CIC columns that are used to collect metal in solution.

Once the leach cycle is complete, pad neutralization and denitrification cycles can begin. The bulk of the process solution is routed over to other active pads. The drain down solution from the pad is then directed to the neutralization pond/carbon column system. Hydrogen peroxide is added to the solution to neutralize the cyanide in the solution. The neutralized solution is pumped through the carbon circuit for metal removal and back onto the pad that is being rinsed. Rinsing continues until the metal content and sodium cyanide levels are reduced to the point the bacteria in the CWTP can process the solution.

Post-neutralization water is pumped through the CWTP and then cycled up to the pad being denitrified. Denitrification rinse continues until the permitted criteria are met. When the material meets the criteria for off-loading, the state and Coeur both sample the solutions and verify those results through third party analysis. When the material is approved for removal from the pad, the spent ore is trucked to a spent ore storage area.

Carbon fines are collected and shipped off site for precious metals removal. Spent environmental carbon for either cyanide or mercury collection is sent off site for disposal.