Property Geology
Mesozoic tectonostratigraphy in the vicinity of the Relief Canyon mine consists chiefly of a metamorphosed footwall mafic volcanic package (Smelser Pass Member of the Augusta Mountain Formation); a metamorphosed, foliated, and highly deformed carbonate-dominant package with intercalations of conglomerate and mafic volcanic rocks (Deformed Limestone Unit); a tectonically thickened, thick-bedded to massive limestone unit (Cane Spring Formation); and a tectonically thickened package of siliciclastic rocks of the Late Triassic Grass Valley Formation.

A southerly dipping, fault-bounded package of schistose intermediate to mafic metavolcanic rocks, including lenses or boudins of mafic meta-tuff breccia, forms the footwall to gold mineralization at the Relief Canyon mine.

Overlying the basal metavolcanic unit is a deformed and metamorphosed carbonate package consisting of limy ductile tectonites and calcareous mudstones to silty limestones intercalated with stretched-pebble conglomerate and mafic metavolcanic and intrusive rocks.

Mineralization
Gold mineralization at the Relief Canyon mine is primarily found in three zones that are structurally controlled and characterized by distinctive host rocks. From structurally lowest to highest, the zones are the Jasperoid Zone, the Lower Zone, and the Main Zone. The Main Zone hosts the bulk of the current and historical gold resources at Relief Canyon, while the Lower and Jasperoid zones are newly discovered mineral zones encountered below the Main Zone in the North Target area (see Figure 5.1 for location of the North Target area) during the recent Pershing Gold drill programs. Figure 7.3 shows a diagrammatic lithostructural section of the Relief Canyon mine area along with the mineral zone locations.

The Jasperoid Zone gold mineralization is hosted within the Deformed Limestone package in a sequence of limey ductile tectonites with local stretched and boudinaged quartz veins, stretched-quartz-pebble conglomerate/sandstone, folded and foliated limestone, and altered gabbro, all of which have been replaced by dark-colored quartz. Silicification is also found in a set of sheeted, N30-35°E-striking, steep fractures that may be extensional in origin. In addition, auriferous fluids were localized by brecciation along contacts between lithologies of contrasting competency, such as between the stretched-pebble conglomerate and carbonate units, or less commonly, between pale green schistose volcanic and carbonate horizons. Locally, collapse breccia is also a site of gold deposition in the Jasperoid Zone.

Lower Zone gold mineralization displays a strong spatial association with gabbro sills and/or transposed dikes (i.e., dikes in which progressive ductile deformation has transposed originally discordant contacts into contacts subparallel to foliation, giving the dikes a sill-like appearance). Mineralization is hosted in, or is proximal to, complex tectonic breccias that show multiple generations of structural reactivation and/or shearing, decalcification, locally superimposed carbonate-dissolution collapse breccia, and the presence of illite and/or kaolinite, sulfides iron-oxides and fluorite.

The tectonic breccia was generated by multiple (minimum of two) episodes of movement in the North Target area. The latest movement was likely normal-fault offset in response to Tertiary extension. The principal clasts in the tectonic breccia comprise dark grey foliated limestone, jasperoid, and quartz. Finegrained gouge material is chiefly composed of quartz flour and kaolinite.

DEPOSIT TYPE
Gold and silver mineralization at Relief Canyon is believed to be largely epithermal in origin, but the deposit also exhibits similarities to Carlin-type deposits (Fifarek et al, 2015) and to orogenic vein deposits.

Gold-bearing jasperoid breccias as well as a suite of trace elements associated with the precious metal mineralization, such as mercury, antimony, and arsenic, are two of the more important similarities between the mineralization at Relief Canyon and Carlin-type gold deposits. Another characteristic of a Carlin-type system is the preferential weathering of the jasperoid material. The jasperoid breccias at Relief Canyon are brittle and highly fractured, which enhances permeability. In many places, they are weathered and oxidized to great depths, whereas surrounding rocks are generally oxidized to shallower depths. A single crystal of euhedral pyrite with a later overgrowth of pyrite has been described in a petrographic study of material from the Jasperoid Zone. Similar arsenic-rich pyrite overgrowths are typical of Carlin-type deposits. It has yet to be determined if the overgrowth in the Jasperoid Zone is arsenic-rich.

There is evidence at Relief Canyon for gold-bearing mineralization of three different styles representing possibly three different ages. The quartz-illite±fluorite±kaolinite alteration associated with gold occurs in all three mineralized zones – Jasperoid Zone, Lower Zone, and Main Zone – and is the most important type of alteration. This assemblage is believed to have formed by weakly acidic hydrothermal fluids. Illite from the quartz-illite±fluorite±kaolinite alteration assemblage has been dated with 40Ar/39Ar methods at 23.51+0.11 Ma (Fifarek et al, 2015). Low-sulfidation quartz-calciteadularia veins with associated gold are hosted by gabbro and constitute a relatively small volume of the mineral resource. This assemblage typically forms from slightly alkaline solutions. Adularia from this assemblage has been dated at 14.92+0.05 Ma with 40Ar/39Ar methods (Fifarek et al, 2015). The presence of orogenic vein mineralization is indicated by the alteration mineral assemblage of quartzcarbonate-tourmaline-leucoxene, in which some gold-mineralized intervals are associated with low amounts of arsenic, but with anomalous molybdenum and tungsten

The Relief Canyon deposit has been mined in the past by open pit methods, followed by heap leaching. This Feasibility Study considers mining by open pit methods. To determine potentially minable material, a number of pit optimization runs were completed utilizing pit slope parameters developed by Golder and Associates. The property is currently permitted to mine inside a permit boundary down to an elevation of 5,080 feet. These limitations were used to constrain the pit design for design Phase 1.

Pit Design
Three main pit phases were designed utilizing the pit optimization results as templates for the design. All of the pit phases were split into at least two scheduling pit phases. A total of seven scheduling pit phases were used to develop the production schedule.

The Phase 1 pit extends slightly beyond the southern permit boundary on previously disturbed ground and finalizes the southeast portion of the pit. The final pit is designed based on the $1,300 per ounce gold, base-case optimized pit, and includes an internal ramp system. It should be noted that the final pit contains about 20 percent more waste than the optimized pit. The resulting ultimate pit design is approximately 14 percent larger than the optimized pit due to inclusion of the ramp system and requirements for mining room between pit phase designs. It may be possible to improve on this design, but it is important to consider all pit phases when redesigning the final pit. Some of the additional waste included in the final design is due to the permit boundary size, which causes access issues between the pit phases requiring additional waste to be mined to maintain working space between the pit phases. If the boundary on the east and south could be expanded by 200 feet, design issues and stripping may be reduced.

The base case mine plan assumes contract mining based on proposals from mining contractors. The base case also assumes that the contractor will load the crusher using a front end loader, and the crushed material will be transported by conveyor to the leach pad.

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Ore will be mined by standard open-pit mining methods and processed at an average rate of 16,700 tons per day. Mined ore will be single-stage crushed to approximately 80% passing 3 inches in size, belt agglomerated using cement, conveyor stacked onto the heap-leach pad in 20-foot lifts and processed in a conventional heap-leach recovery circuit. Stacked ore will be leached with a dilute cyanide solution, and the resulting pregnant solution will be processed in an adsorption, desorption and recovery plant (“ADR”) for the recovery of precious metals from solution. The gold will be stripped from the loaded carbon using a pressurized desoption process, followed by electrowinning to produce a precipitate sludge. Gold and silver sludge from the ADR plant will be treated in a mercury retort and smelted to produce doré bars.

Process Description
Ore for the Relief Canyon project will be delivered to the ROM stockpile using 100 ton haul trucks. ROM ore will be reclaimed and crushed to a P80 of 3.0 inches in a single-stage crushing circuit at an average rate of 16,700 tons per day. Crushed ore will be stockpiled and reclaimed using vibrating pan feeders before being transferred to the conveyor stacking system by an overland conveyor. Cement is to be added ahead of the conveyor stacking system at an average rate of 8 lbs per ton of ore for pH control and permeability, and belt agglomerated by the conveyor stacking system. The process solution for agglomeration will be barren solution and directly dosed on the conveyor transfer points after the cement addition.

The conveyor stacking system includes mobile grasshopper conveyors which feed a radial stacking system. The leach pad will be stacked in 20-foot lifts. Drip tubes will be used to irrigate the ore with a low concentration sodium cyanide solution to leach gold and silver values with a 60-day leach cycle. Pregnant solution from the heap will flow by gravity to a pregnant solution tank where it will be pumped to a carbon in column (“CIC”) adsorption circuit. Gold and silver will be loaded onto activated carbon and will periodically be stripped from the carbon using a modified Zadra pressure-strip circuit, electrowon and smelted to produce the final doré product. A mercury retort will be utilized to remove mercury prior to smelting.

The conveyor stacking system includes mobile grasshopper conveyors which feed a radial stacking system. The leach pad will be stacked in 20-foot lifts. Drip tubes will be used to irrigate the ore with a low concentration sodium cyanide solution to leach gold and silver values with a 60-day leach cycle. Pregnant solution from the heap will flow by gravity to a pregnant solution tank where it will be pumped to a carbon in column (“CIC”) adsorption circuit. Gold and silver will be loaded onto activated carbon and will periodically be stripped from the carbon using a modified Zadra pressure-strip circuit, electrowon and smelted to produce the final doré product. A mercury retort will be utilized to remove mercury prior to smelting.

The existing solution ponds, Operating Pond East (OPE) and Operating Pond West (OPW), will be used to contain process solution in the event of a large storm event or other upset conditions that cannot be managed during normal operations with Pad 5, 6, 7 (pre-production leach pad). An additional contingency pond will be constructed with Pad 8 (Years 3+ leach pad) to account for the added heap-leach pad expansion. Solution collected in the process solution ponds will be returned to the system as makeup solution.

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