The gold mineralization at Mesquite Mine was deposited in an epithermal setting, within 500 to 1,000 ft of the surface. The majority of the economically attractive mineralization is found in the biotite gneiss and hornblende-biotite gneiss, while the mafic gneiss and intrusive rocks are generally less mineralized. Gold mineralization is found both disseminated and vein hosted within these units. The majority of the veining is controlled by faults and fault junctions, which have moderate to steep dips.

The gold mineralization dominantly occurs in two types:

- pods of mineralization limited in lateral and vertical extent at fault intersections

- trends of mineralization along faults.

The principal types of mineralization defined at Mesquite are as follows:
• Early epidote - quartz veinlets overprinted by chlorite veinlets;
• Two-stage siliceous matrix breccia (SMBX) developed along faults planes with quartzadularia matrix ± pyrite;
• Quartz ± adularia ± pyrite ± electrum veinlets with sericite halos;
• Ankerite ± Dolomite ± pyrite veinlets;
• Bleached zones on fault planes with green sericite ± pyrite;

Gold occurs at Mesquite as both submicron disseminated and coarse gold. All documented gold occurrences are native gold, and classification has been based on silver content and grain size. A silver-free native gold is the most common type in the oxidized zone. It occurs in particles less than five microns, although clusters up to 100 µ are common in fault zones. Gold grains are subhedral to anhedral in shape, with anhedral morphology predominating. In general, the grains are characterized by irregular, ragged boundaries and equant to elongate shape. Gold within the oxide portion of the deposit is commonly associated with goethite pseudomorphs after pyrite and mica minerals. Later stage gold, less than five microns, is found along the cleavages of the micas.

A second type of gold is the silver-bearing (5% to 20%) coarse (10 µ to 600 µ) gold. Its average size is 30 µm to 50 µm and it is typically found in the unoxidized zone, and only occasionally in the oxidized zone. Grains have octahedral morphology, with cuspate to sharp boundaries. Gold specimens are usually bright yellow electrum, with minor inclusions of galena and pyrite. Silver-bearing gold is associated with quartz-adularia pyrite veins containing arsenopyrite, magnetite, and chalcopyrite.

Visible gold has been identified throughout Mesquite. Small flakes, less than 50 µm, of free “flour” gold have been found within the oxidized gouge and clay fault zones. The flour gold is thought to be a result of remobilization during oxidation and is supergene in nature. Gold is typically associated with titanium oxides (rutile) and hematite. These zones are limited in extent (one inch to three feet wide, with three feet to 50 ft of strike length), but can be extremely high grade. Selective sampling indicates typical gold values of 1.0 opt to 2.0 opt Au, with a high of 35.9 opt Au recorded in Big Chief.

Coarse-grained hypogene gold has also been noted with more frequency and larger size in the unoxidized portion of the deposits. Recent test work on non-oxidized ore indicates that 65% to 78% of the gold is liberated free milling gold, 13% is associated with refractory sulphide minerals, and the remainder is associated with iron oxides and carbonates. Grain size ranges from 10 µm to 600 µm, with no textural indications of re-mobilization. Coarse gold generally occurs as electrum within quartz veins (occluded and void fill), while the refractory portion is found within overgrowth rims of arsenopyrite, chalcopyrite, and pyrite.

Mining is performed using a conventional ruck/shovel open pit mining method. Operations include drilling, blasting, loading, and hauling. Run-of-mine ore is hauled directly to the leach pad to the south for processing. Waste mining uses the same equipment fleet used to produce ore.

The Mesquite Mine is an operating open pit mine with ore processing by heap leaching using a carbon-in-column (CIC) circuit to recover gold.

The processing facilities include the following operations:
• Heap leaching
• Carbon adsorption
• Desorption and gold recovery
• Reagents and utilities
• Water services.

Originally the ore was crushed, however since the operation was re-started in 2007, on run-ofmine (ROM) ore is leached. ROM ore, with lime added for pH control, is trucked to the heap leach pad. The ore is stacked to a height of 20 ft. The ultimate pad height has been increased from 200 ft to 300 ft.

Dilute sodium cyanide solution is pumped from either the barren or the intermediate solution ponds and distributed to the surface of the leach pad with drip emitters. The solution then percolates through the pad extracting the gold. The gold bearing pregnant solution is collected in a series of flume boxes, with the option to direct solution to the intermediate pond, the barren solution tank, or the pregnant solution tank. Low-grade solution in the intermediate pond is pumped back to areas of the leach pad that contain fresh ore in order to increase the solution grade prior to processing. The higher grade solution that is collected from areas that are newly under leach is directed to the pregnant solution tank.

From the pregnant solution tank, the gold bearing solution is pumped to the adsorption plant, which includes six ton carbon-in-columns (CIC), where the gold is recovered from the solution by adsorption onto activated carbon.

The activated carbon is advanced counter current to the solution flow in the CIC circuit. Loaded carbon from the first column of the CIC circuit is transported to the desorption circuit located at the existing gold plant via trailer.

At the gold plant, the activated carbon is washed with a dilute hydrochloric acid solution for removal of inorganic contaminants and stripped in a traditional pressure Anglo American Research Lab (AARL) strip circuit. Electrowinning cells are used to recover gold from the strip solution. The sludge recovered from the electrowinning circuit is mixed with fluxes and melted in an induction furnace to produce doré gold bars. After stripping, the carbon is thermally regenerated in a carbon reactivation kiln for removal of organic contaminants. Following stripping and regeneration, the carbon is loaded into a trailer and returned to the CIC columns for re-use.