The Hasbrouck deposit is a low-sulfidation, epithermal gold–silver deposit located in the western portion of the Divide Mining District. Host rocks are primarily tuffs and sediments of the Siebert Formation with limited mineralization within the underlying Fraction Tuff. Gold and silver mineralization consists principally of 0.1in to 1.0in wide, discontinuous silica-pyrite veinlets, sheeted veinlets and stockworks, all closely associated with larger, but erratic bodies of hydrothermal breccia. Sulfide minerals have been largely oxidized. Mineralization is accompanied by strong pervasive silicification, with associated adularia and pyrite, and has a known extent of 2,800ft east–west by 2,400ft north–south, with a maximum depth of 900ft. Mineralization is open at depth and to a limited extent to the northwest and east.

Gold occurs as electrum, as inclusions in pyrite and in goethite derived from the partial to complete oxidation of pyrite, and within siliceous gangue minerals (Graney, 1985; Hazen, 1989). Silver occurs in the native state and in argentite (Wittkopp, 1982). Silver is also intimately associated with iron oxides derived from the oxidation of silver-rich sulfide minerals that occurred as inclusions in pyrite (Wittkopp, 1982).

Hasbrouck mineralization is primarily characterized as structurally-controlled, with secondary lithologic control. West-northwest and northeast fault orientations localize higher-grade mineralization (+0.05 oz Au/ton) with lower grade material occurring as halos and straddling the clastic and tuffaceous package contact within the Siebert Formation. North-south faults appear to be late-stage or offset mineralization. Mineralization remains open at depth along the intersection of the cross-cutting structural fabrics. However, deeper drilling into the Fraction Tuff has yet to intersect significant mineralization.

Brecciated veins associated with northwest structures are dark gray to brick-red in color, and 0.05–20 inches in width. The breccia fragments are monolithic, and float in the silica matrix. Outcropping veins have the appearance of jasperoid, and strike parallel to the northwesterlytrending structural fabric. This vein type has been encountered in core holes. Banded quartz veins range from 0.05inches to as much as several inches in width. These veins parallel local structural trends, and consist of cream–white to tan to brown colored parallel bands from <0.05– 0.5 inches in width. Veins have been noted in outcrop to undulate, and follow the outer trace of large blocks of fractured rock. A vein swarm trending northeast was noted to dip both to the east and west, but not to offset each other. Stockwork quartz–sulfide veins are typically up to 0.5inch in width. Silica occurs as gray or clear quartz selvages, with a center line of sulfides (typically oxidized). Occasionally, oxidized sulfides form selvages about the veins. Rare euhedral pyrite has been noted in some veins. Veins cross cut each other, and form a crude orthogonal set. Native gold in the form of small grains was noted in one vein along the center oxidized sulfide line.

The Three Hills deposit, located in the Tonopah Mining District, is a low-sulfidation, epithermal gold deposit, and occurs in a zone of pervasive silicification within the outcropping Siebert Formation immediately above and along the contact with the underlying Fraction Tuff. Mineralization occurs in discontinuous, irregular 0.05in to 0.5in-wide veinlets, vein stockworks, and erratic breccia veins of chalcedony and quartz. Oxidation has destroyed sulfide minerals within the deposit. The currently drill-defined extent of mineralization is approximately 1,000ft east–west by 2,700ft north–south with a maximum depth of 500ft. Mineralization remains open at depth, down-dip to the east along the Siebert/Fraction Tuff contact.

Gold mineralization at Three Hills is commonly associated with areas of higher permeability lithologies, rock unit contacts, and structural features. Previous authors have described the mineralization as “disseminated” though examination of outcrops and drill core shows the higher gold grades associated with discontinuous, irregular 0.05- to 0.5inch-wide veinlets, vein stockworks, and erratic breccia veins of chalcedony and quartz. Lower gold grades in the top of the south hill are found in zones of grey to brown chalcedony, and hydrothermal breccia veins and pipes.

The Hasbrouck project PFS includes mining at both the Three Hills Mine and the Hasbrouck Mine. These are planned as open-pit, truck and loader operations. Access roads were included in the pit and waste rock storage area designs, which were considered suitable for the type of equipment used. Waste rock storage areas were designed to contain the rock waste associated with the reserves. One main waste rock storage areas was identified for Three Hills and 2 additional waste rock storage areas were designed for Hasbrouck. Safety berms were designed between the designed pits and dumps and US Highway 50 to contain any material that may try and roll off of the mining site.

Three Hills production schedules have been completed based on a 15,000tpd production requirement for the ROM heap-leach pad. In total, 504,000 cubic yards (702,000 tons) of waste rock is scheduled for construction purposes.

Hasbrouck Mine production schedules were completed based on a 17,500tpd production requirement. Mining at Hasbrouck was assumed to start during the second year of production for the project. Little pre-stripping is required as ore is located near the surface, though waste rock is mined early to provide construction fill material.

It is anticipated that the contractor will have between 60 and 80 operators and staff involved with the operation. It has been assumed that the contractor will work 12 hour shifts, 2 shifts per day, 7 days per week. Other mine personnel will be maintained by the owner for general activities, including mine supervision, engineering, surveying, geology, and ore control.

All mining is anticipated to be above the water table, so no dewatering wells will be required. Storm water that enters the pit will be handled by allowing for sumps in the pit as needed. Any excess water that doesn’t naturally infiltrate into the ground will be placed in water trucks using a portable pump and then used for dust control on haul roads.

The Hasbrouck heap-leach project includes two separate facilities to be located 5 miles apart. The Three Hills Mine will be constructed first, followed by the Hasbrouck Mine. The Three Hills Mine will be a ROM heap-leach operation with carbon-column adsorption and support infrastructure facilities. Loaded carbon produced at the Three Hills Mine will be processed offsite by “toll stripping”. If necessary, loaded carbon will be processed by “ashing”. The Hasbrouck Mine will be a crushed ore, heap-leach operation with mining, a full recovery plant and associated infrastructure.

Three Hills Process Description Summary

The Three Hills Mine will be a 15,000 ton per day ROM heap-leach operation. Processing at Three Hills will be by conventional heap-leaching of ROM ore stacked on a single use pad. Gold will be leached from the mineralized material with dilute cyanide solution and recovered from the solution in a carbon adsorption circuit. Loaded carbon will be processed offsite by “toll stripping” where the carbon is stripped of metal in a desorption- recovery plant and returned for re-use along with the doré product. In the event that there is insufficient capacity or other circumstances that prevent the processing of loaded carbon by toll stripping, carbon will be processed by “ashing” (carbon is smelted directly) to produce doré bars.
All process equipment has been sized for 5.475 million tons per year. Doré bars will be exported from the Three Hills property to a third party for refining and sale.

Summary of Hasbrouck Mine Process Description

The Hasbrouck Mine will include a 17,500 ton per day heap-leach operation. Processing at Hasbrouck will be by conventional heap leaching of crushed ore stacked on a single use pad. Gold and silver will be leached with a dilute cyanide solution and recovered from the solution using a carbon adsorption-desorption-recovery process to produce doré bars.

ROM ore will be delivered, and direct dumped to the greatest extent possible, by haul trucks from the mine to a primary crusher’s dump hopper. Haul trucks will deliver ore to an ROM stockpile either for blending or when the dump hopper is full or inaccessible due to other traffic. A front-end loader will deliver ore from the ROM stockpile to the dump hopper either for blending or to supplement haul truck availability.

The crushed ore will be agglomerated with cement prior to cyanide leaching. The crushed ore will be conveyed from the crushed ore stockpile to the agglomeration area by an overland conveyor, which will discharge onto the pug mill feed conveyor. Cement will be added to the pug mill feed conveyor from a 100 ton silo with a screw feeder at a nominal rate of 5 lb per ton of crushed ore. The crushed ore and cement will then be fed to the pug mill for blending. Barren solution will be added in the pug mill to adjust the crushed ore’s moisture content to between 7 and 13%. The pug mill will discharge onto the pug mill discharge conveyor, which in turn will discharge onto an overland conveyor, which feeds the stacking system. This overland conveyor will be adjusted as necessary to accommodate stacking.

The grasshopper and ramp conveyors will transport the crushed ore from the overland conveyor on the heap to the stacking conveyors. The stacking conveyors will allow the radial stacker to place crushed ore in 30ft lifts with minimal downtime. The radial stacker and horizontal feed conveyor together will be capable of moving while slewing and stacking ore in an arc. The radial stacker will be able to retreat approximately the length of a grasshopper conveyor.

The ore will be leached using a dilute solution of sodium cyanide applied by a system of drip emitters, which will reduce evaporation and minimize make-up water requirements. Leach solution will be applied to the crushed ore heap at a nominal application rate of 0.0025 gpm/ft2.

The dilute sodium cyanide leach solution will percolate through the ore on the heap, dissolving gold and silver, and drain by gravity to a pregnant solution tank, which will store the solution prior to further processing. Submersible pumps in the pregnant tank will pump solution to the head tank of the carbon columns. The solution will flow by gravity through the carbon in columns, and returning to a barren tank.

The adsorption facility at the Hasbrouck Mine will consist of a single train of 5 up-flow, opentop CICs. The columns will be capable of holding 7 tons of carbon each, providing a CIC process inventory of 35 tons of carbon.

Loaded carbon from the adsorption circuit will be advanced to an acid wash vessel. In this vessel, hydrochloric acid will be circulated through the carbon to remove calcium carbonate scale before being moved to the desorption cycle. The acid wash vessel is a fiberglass reinforced plastic lined, carbon steel vessel designed to contain 3.0 tons of carbon.

The carbon will be advanced to the elution vessel after acid washing. The elution vessel is designed to process up to three tons of carbon in a modified Zadra-type desorption cycle, typically requiring 12 to 16 hours per cycle.

Pregnant eluent will flow to two electrowinning cells that will be operated in parallel. Stripped gold from the desorption cycle will be removed from the pregnant eluent by electro-plating onto stainless steel cathodes. Periodically, the stainless steel cathodes will be removed from the electrowinning cell and washed with a high pressure spray to remove the gold sludge. The resulting sludge will be filtered in a plate and frame type filter press. The filter cake will then be processed in an electric mercury retort to remove mercury from the sludge. The mercury will be recovered in a water trap collector and periodically drained from the trap into air-tight vessels and shipped off-site for disposal.

After removal of the majority of mercury by retorting, the gold sludge will be treated in an electric induction smelting furnace. The gold sludge will be mixed with fluxes, typically a combination of borax, niter, soda ash and silica sand, and smelted. The soda ash and niter oxidize impurities and allow them to collect into the slag phase while the bullion settles to the bottom of the crucible. Fluorspar may also be used to modify the slag viscosity. The slag and impurities will be poured off into a slag mold and the molten bullion will then be poured into a series of cascading molds.

The bullion, or doré, will be quenched and cooled in a water bath. Doré bars will be cleaned of slag and loose metal particles, labeled and weighed. Doré will then be shipped to an off-site refiner for further processing and sale as fine gold.

Slag will be crushed and inspected to remove visible beads of bullion that can be immediately remelted or recycled to the pour. The remaining slag will be re-smelted to settle and recover any unrecovered bullion. The resulting barren slag will be shipped offsite for disposal.