Alteration and mineral assemblages throughout the deposit are represented by widespread argillic alteration, generally abundant alunite, and the presence of minor amounts of base metals, all of which indicate the ore deposits to belong to the high sulfidation (acids sulfate) class of epithermal mineral deposits.

The Isabella mineralization is entirely oxidized, very siliceous, contains numerous vugs in former feldspar and pumice sites (vuggy-silica textures), and typically lacks any evidence of cross-cutting veinlets. Narrow, structurally controlled zones of silica-pyrite, as well as the more pervasive silica replacement bodies, generally grade outward into silica-kaolinite with local alunite envelopes, which in turn grade into pervasive illite-montmorillonite zones. The iron oxide minerals goethite, jarosite, and hematite are present in the siliceous groundmass. Gold occurs as very small (<10 microns) liberated particles in cavities and along fracture surfaces. Rare secondary minerals include barite, cinnabar, and corodite. A nearhorizontal zone of pervasive argillic and advanced-argillic alteration occurs above the Isabella deposit in the upper, poorly to moderately welded rhyolitic ash-flow tuff of the Guild Mine Member. Within this altered zone, alunite occurs as pseudomorphs after potassium feldspar phenocrysts and as replacements of pumice fragments.

The Pearl deposit is hosted by the lower, densely welded portion of the Guild Mine Member and, to a lesser extent, by Cretaceous granite. Mineralization is largely controlled by the northwest-striking, northeast-dipping contact zone between the granitic basement and the overlying Tertiary volcanic units. This contact may be partially or entirely faulted; this report assumes the contact is marked by the fault. Strong silicification accompanies gold mineralization and is associated with fracture fillings and replacement of the welded tuff. The mineralization is usually associated with strong brecciation. Multiple stages of fracturing and brecciation with associated silicification have been observed in drill core.

Sulfide minerals at Pearl commonly exceed ten percent (by volume) and are composed primarily of crystalline grains and aggregates of pyrite, colloform banded “melnikovite”-type pyrite, and bladed marcasite (or pyrite after marcasite) in dark microcrystalline quartz. This quartz has replaced both the volcanic and intrusive host rocks. In the granite, alteration has resulted in the complete leaching of feldspars and ferromagnesian silicates, and pyrite and marcasite have filled the voids left by the silicate dissolution. Rare sulfide minerals observed in thin and polished sections include arsenopyrite, pyrrhotite, galena, sphalerite, chalcocite, chalcopyrite, polybasite, and pyrargyrite. Other minerals include very minor magnetite, zircon, monazite, and rutile. Native gold has not been observed in the sulfide mineralization.

The oxidation boundary is depressed over and immediately around the Pearl deposit, with oxide mineralization extending to more than 150m (500ft) below the surface. Goethite, jarosite, and manganese oxide are common, and barite and chlorargyrite occur rarely in the siliceous groundmass. Gold within the oxide mineralization occurs both as locked and liberated particles, as well as electrum. Particles range in size from 2 to 34 microns, averaging 14 microns. The liberated particles occur as small wire-like grains in cavities, while the locked gold is encapsulated by silica or goethite.

The Civit Cat mineralization, which is relatively minor and poorly defined by drilling, lies to the northeast of Pearl and is associated with the northwest-striking, southwest-dipping Civit Cat fault. The control on mineralization by the Pearl and Civit Cat faults, which have similar strikes but opposing dips, results in northwest-trending, roughly lens-shaped zones of mineralization that flank both sides of a graben-like structural trough.

The Isabella Pearl mine design consists of one pit accessing the Isabella, Pearl and Civit Cat deposits. Open pit mining will be by conventional diesel-powered equipment, utilizing a combination of blasthole drills, wheel loaders, and 91-tonne (100-short ton) trucks to handle ore and waste. Support equipment composed of graders, track dozers, and water trucks will aid in the mining. ROM Ore will be hauled directly to the leach pad. Higher-grade ore will be hauled to the crushing area and crushed before being placed on the leach pad. Waste rock will be stored in the waste rock facility designed in close proximity to the pit to reduce haulage costs.

The final pit was designed using 6 m (20 ft) benches, a bench face angle of 68° and an inter-ramp slope of 49.7° between a triple bench-catch of 8 m (26 ft). Haul roads were designed to 14 m (46 ft) widths for one-way traffic and 24 m (79 ft) widths for two-way traffic. These widths included an external safety berm in compliance with Mine Safety and Health Administration (MSHA) regulations. The final location of the ramps was optimized in order to reduce the overall pit slopes in areas where the pit slope was required to be less than 50°.

All ore and waste will be hauled utilizing a 91-tonne (100-short ton) truck fleet. The mine pits will generate an estimated total of 16.0 million tonnes (17.6 million short tons) of waste rock. Preproduction and 1st year waste rock will be end-dumped on natural ground first from near the crest elevation of the Pearl pit, falling southward toward a natural swale. The dump face is expected to advance at the estimated 40° angle of repose of the material. Starting in year 2 of production, the Pearl dump will be built from the south toe upward, with the outer slopes concurrently graded to 3(Horizontal):1(Vertical). The outer faces of the graded waste will be contoured, compacted, overlain with growth medium and re-vegetated as soon as it is practical. Contouring and re-vegetation of the top of the dump will occur during postproduction reclamation.

Low-grade ROM ore, which will not be crushed, will be placed on the heap leach pad with only lime addition on pad areas protected by a minimum of four feet of cover over the leach pad liner and collector piping system. Most of such material will be placed in interior portions of the leach heap to minimize the difficulty of re-grading for reclamation.

Higher-grade oxidized ore will be hauled to a crusher pad stockpile to then be fed to the crusher by a front-end loader. Ore may be delivered to the heap by either haulage trucks or a stacker conveyor system.

A production schedule was developed to mine up to 600,000 tonnes (661,400 short tons) of material per month from the 2-phase pit over a 4-year mine life. The Pearl zone is mined in 2 phases (Pearl Phase 1 & 2) in order to balance the high strip ratio of the upper benches and maintain and adequate cash flow balance. A 4-month preproduction period is planned while the ADR processing facility is commissioned.

Over the life of the mine, ore will be delivered from the open pit, some of which will be placed directly on the heap leach pad by truck as ROM, with the majority being trucked to the crusher and then transported to the heap leach pad via an overland conveyor and stacked onto the heap leach pad by a radial stacker.

The most economically effective process has been identified as conventional heap leaching of ROM and crushed ore followed by and absorption/desorption recovery plant (ADR) and refining to produce doré bars. The processing facilities accommodate a leachable reserve of approximately 2.7 million tonnes (3.0 million short tons) of ore at a grade of 2.22 g/t Au (0.065 opst Au) and 13 g/t Ag (0.38 opst Ag). The design of the crushing circuit is nominal 250 tonne (276 short ton) per hour and the ADR plant to treat 1,600 gpm.

The lower grade ROM ore, above 0.38 g/t Au and below 0.61 g/t Au, will be trucked from the open pit to the heap leach pad. On route to the heap, the mine trucks will pass under the lime silo and receive the appropriate amount of lime addition, before dumping on the heap.

The Isabella Pearl higher-grade ore above the 0.61 g/t Au cutoff will be crushed to P80 5/8”. This will be accomplished with a two-stage portable crushing plant with a 250 tonne (276 short ton) per hour capacity.

The leach pad area covers about 114,000 m2 (1.5 million ft2 ) and will provide containment for 3.1 million tonnes (3.4 million short tons) of ore. The leach pad is a modified valley fill with a double liner system. A berm ranging from 1 to 5 m (3.3 to 16.4 ft) will be constructed along the sides and downstream (south) edge of the pad.

Pregnant solution trickling through the heap will be collected by 20 cm (8 in) HDPE piping resting on the upper geomembrane, the solution will flow by gravity to solid HDPE outlet pipes resting in HDPE doublelined ditches in notches through the perimeter berm and will enter shunt valve boxes located between the heap leach pad and the ponds.
Pregnant solution will be conveyed via the closed circuit pregnant solution pipeline to the pregnant tank at the ADR plant. The pregnant solution will be pumped from the pregnant tank to a feed box in the carbon-in-column (CIC) circuit where it is contacted with activated carbon for extraction of the gold via carbon adsorption. The CIC circuit will consist of five columns. Solution from the last column overflows to the barren tank where liquid sodium cyanide, fresh water and anti-scalent will be added on an as needed basis prior to the solution returning to the heap leach pad for additional leaching of the ore.

The pregnant strip solution will be electrolyzed at the on-site facility and the cathode sludge will be dried, blended with fluxes, and melted to produce doré bullion for shipment to a refiner.

The plant will consist of five 2 m (7 ft) diameter vertical adsorption towers in series with a carbon screen on the barren discharge; a 2.7 tonne (3 short ton) carbon-stripping plant with a carbon conditioning and sizing screen; and barren and pregnant solution tanks. Electro-winning will be done in a 150-ft3 electrolytic cell. Smelting will be done in a T-200 melt furnace. The strip heater and the furnace will be propane fired.