Goldstrike Complex.
The Goldstrike deposits are Carlin style deposits. Carlin deposits comprise stratabound disseminated gold mineralization hosted by Silurian-Devonian carbonate rocks that have been metamorphosed to varying extents. The deposits are hydrothermal in origin and are usually structurally controlled. The carbonate host rocks are part of an autochthonous miogeoclinal carbonate sequence exposed as tectonic windows beneath the Roberts Mountains allochthon.

Cortez.
The Cortez deposits are “Carlin” style sedimentary rock-hosted and porphyry/epithermal deposits. Deposits are localized at contacts between contrasting lithologies, metamorphosed to varying extents. They can also be discordant or breccia-related. The deposits are hydrothermal in origin, are usually structurally controlled and at Cortez are hosted in Lower Plate carbonate strata exposed by two erosional windows through allochthonous Upper Plate siliclastic units; the windows are on either side of Crescent Valley.

Mineralization consists primarily of submicron to micrometre-sized gold particles, very fine sulphide grains, and gold in solid solution in pyrite. Gold is disseminated throughout the host rock matrix in zones of silicified and decarbonatized, argillized, silty calcareous rocks and associated jasperoids. Gold may occur around limonite pseudomorphs of authigenic pyrite and arsenopyrite. Major ore minerals include native gold, pyrite, arsenopyrite, stibnite, realgar, orpiment, cinnabar, fluorite, barite, and rare thallium minerals. Gangue minerals typically comprise fine-grained quartz, barite, clay minerals, carbonaceous matter, and late-stage calcite veins.

In the Cortez district, the favoured host rocks for gold mineralization are the Wenban Limestone, followed by the Horse Canyon and Roberts Mountain formations. Mineralization reflects an interplay between structural and lithological ore controls in which hydrothermal solutions from intrusives moved to favourable porous decalcified limestone. Mineralized host rocks are predominantly characterized as oxides, along with sulphidic and carbonaceous refractory material. Carbon content in the deposits is highly variable and occurs generally in the Wenban and Roberts Mountain Formations.

Supergene alteration extends up to 656 ft depth resulting in oxide ores which overlie the refractory sulphides. Alteration has liberated gold by the destruction of pyrite and resulted in the formation of oxide and secondary sulphate minerals which include goethite, hematite, jarosite, scorodite, alunite, and gypsum.

Goldstrike Complex.
Conventional open pit and underground mining consisting of the Betze-Post open pit and the Meikle and Rodeo underground mines.

Meikle is a high-grade ore body which is mined by transverse longhole stoping, underhand drift and fill mining methods. Rodeo is a trackless operation, using two different underground mining methods: long-hole open stoping and drift-and-fill.

Cortez.
The Cortez Hills underground mine is accessed by twin declines portaled in the old Cortez Gold F canyon pit. The Pipeline and South Pipeline deposits are mined by conventional open-pit methods.

Cortez Hills pit dimensions: 2km long x 1km wide x 400m deep and Typical bench height 15m.

The underground mining method is underhand cut and fill with a cemented rock fill. Ore is drilled with two boom jumbos, blasted on a round by round basis, loaded into haul trucks, and hauled to surface. Parallel 5m wide by 5.5m high and 3 km declines with crosscuts at every 150m.

Historically, Cortez ore was processed in a 1,800 stpd CIL plant called Mill No. 1, as crushed ore on heap leach pads, and refractory ore was pre-oxidized in a circulating fluid bed roaster. The crushing and leaching circuits were built in 1969; the roasting circuit was completed in 1990. The Mill No. 1 processing facilities were placed on care and maintenance in 1999.

Ore from Cortez can either be processed on site in the oxide processing facilities or transported to the Goldstrike operation for refractory ore treatment.

OXIDE ORE MILLING
Mill No. 2, or the Pipeline mill, was commissioned in 1997 to process oxide ore from the Pipeline open pit mine. The treatment plant currently includes crushing, SAG mill, ball mill, grind thickener, carbon-in-column (CIC) circuit for the grind thickener overflow solution, CIL circuit, tailings counter-current-decantation (CCD) wash thickener circuit, carbon stripping and reactivation circuits, and a refinery to produce gold doré. Plant throughput is up to 16,000 stpd. depending on the hardness of the ore being processed. The plant is permitted for an
annual average of 15,000 stpd.

Electro-winning takes place in six EW cells. After loading with gold, the stainless steel cathodes are washed with high pressure water. The gold sludge from the EW cells is dewatered in a filer press. The stripped cathodes are returned to the EW cells. The filter cake is dried, melted in an induction furnace, and poured into doré bars. The stripped carbon is transferred from the elution column over a screen and into the reactivation furnace feed tanks. Carbon reactivation is accomplished in two propane-fired kiln-type furnaces.

OXIDE ORE HEAP LEACHING
Low-grade oxide material is leached as ROM ore on three prepared double-lined leach pads. Pregnant solution from the leach pads is fed to CIC columns for gold recovery. The loaded carbon from the heap leach operation is transported to the mill for gold recovery in the carbon elution and EW circuits and the refinery. The carbon is also acid washed and regenerated at the mill. Make-up solutions come from the mill or mine dewatering wells to account for evaporative losses and ore saturation requirements.

Area 28 heap leach circuit has a water balance that is interlinked with the Pipeline mill circuit since it uses the tailings pond under-drain solution as leach solution and excess pad effluent is processed in the mill CIC circuit. Area 28 is at maximum capacity for ore stacking and is no longer an operating leach pad. The Area 30 heap leach circuit is independent of the Pipeline mill. Ore delivery to the pad recommenced in 2013. An expansion of seven million square feet is planned for 2019 with ore deliveries extending through 2031. Area 34 heap leach is a third pad that was designed to treat CHOP ore. The first cells were placed under leach during March 2011 and ore deliveries are scheduled to continue through June 2019 based on the current LOM plan.

REFRACTORY ORE TREATMENT
Ores that have an CNAA/FA ratio of less than 50% are transported to Goldstrike for processing in the roaster. Haulage of refractory ore to Goldstrike is currently limited by permit to 1.8 million stpa. At Goldstrike, the ore will be processed in the roaster followed by a CIL circuit. Goldstrike also has the opportunity to process refractory ore using the TCM process, which includes pressure oxidation (POX) followed by resin-in-leach (RIL) with calcium thio-sulphate (CaTS), however, this option is not contemplated for Cortez ore at this time.

Fluid bed roasters were constructed at Goldstrike in 1999 to treat carbonaceous refractory ores that could not be treated effectively by the POX circuit that existed at Goldstrike at that time. The roasters process double refractory (i.e., sulphide refractory and total organic carbon refractory) feed with a moderate carbonate content to help fix the sulphur dioxide that is generated by the oxidation reactions. Minimum sulphide sulphur levels are required to maintain sufficient bed temperatures. When the ore does not contain the minimum required sulphide sulphur content, sulphur prills are used as a supplement to provide the energy necessary to operate the roasters.

The roasters use oxygen to oxidize organic carbon and sulphide sulphur prior to processing the neutralized slurry in a conventional CIL circuit. There are two circuits, each include crushing and dry grinding followed by a two stage roaster, a calcine quenching tank, and dust and gas handling operations. The quenched gas goes to the gas cleaning stage, which is common to both roaster circuits, and the calcine is processed in common neutralization and CIL circuits. The loaded carbon is sent to the main refinery for elution, regeneration, and production of the gold doré.