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.

The gold mineralization is associated with silicification, argillization, and sulphide mineralization with little or no oxide mineralization remaining. In sulphide ore, the gold is intimately associated with very fine-grained pyrite and marcasite and is refractory. Over time, the pyrite oxidized, freeing the gold and making its extraction relatively easy, as in the historic Post Oxide deposit. Associated sulphide minerals include arsenopyrite, realgar, orpiment, and stibnite. Gangue minerals include quartz, calcite, and barite. Realgar and orpiment are generally low in abundance; however, these minerals are locally common in stockwork veinlets, fracture fillings, and breccia matrices.

OPEN PIT
The Betze-Post deposit, the largest on the Carlin Trend, is divided into sub-deposits which, from east to west, are the Deep Post, Post, Betze, West Betze, and Screamer. Other zones within the pit are North Betze, West Barrel, and North Screamer.

Five generations of pyrite mineralization have been recognized at the Betze-Post open pit. Early stages of diagenetic pyrite, and coarse-grained pyrite in the metamorphic aureole of the Goldstrike diorite, are barren. Early hydrothermal, very fine-grained pyrite and marcasite grains of the third generation are coated by a 25 µm thick rind and cut by micro-veinlets of arsenic and gold bearing pyrite of the fourth generation. Barren, late hydrothermal coarsegrained pyrite and marcasite is accompanied by barite and stibnite. Sulphides make up approximately 5% by weight of the ore, locally up to 20%.

The gold bearing arsenian pyrite may be subdivided into coarse grained sulphides at ±200 µm diameter and fined grained at 10 µm to 20 µm, with the latter carrying proportionately much more gold. Gold at 0.05 µm to 0.1 µm is occluded in the iron sulphides. Approximately 10% to 20% of the gold is free, 20% to 30% is held in the fine-grained pyrite/marcasite, a few percent is contained in coarse pyrite, and the balance is in very fine pyrite associated with clay.

UNDERGROUND
Gold mineralization in the underground mine is subdivided into East Banshee, West Banshee, Meikle, South Meikle, (East) Griffin, Extension, West Griffin, Rodeo, Barrel, West Rodeo, and North Post deposits and sub-deposits. The sulphide mineralization is associated with silicification and argillization, and there is little or no oxide mineralization. In sulphide mineralization, the gold is intimately associated with very fine-grained pyrite and marcasite. Associated sulphide minerals include arsenopyrite, realgar, orpiment, and stibnite. Gangue minerals include quartz, calcite, and barite. Realgar and orpiment are generally low in abundance; however, these minerals are locally common in stockwork veinlets, fracture fillings, and breccia matrices.

The orientation of the mineralization is different in each zone. East Banshee, Meikle, MeikleEast, Extension, Rodeo, North Post, and East-Griffin are characterized by steep and shallow angle east-dipping mineralization. South Griffin, West Banshee, and part of Lower Rodeo are more moderately west dipping. South Meikle, West Griffin, and Barrel mineralization are relatively flat lying.

The Goldstrike Mine consists of operating open pit and underground mines.

The Betze-Post open pit is a truck and shovel operation. With completion of the 3rd NW phase targeted for March 2019, the open pit has three remaining phases (4th NW, West Barrel, and 5th NW). The ultimate pit will measure approximately two miles east to west, 1.5 miles north to south, and have an average depth of approximately 1,300 ft.

Underground mine production comes from the Rodeo, Meikle, North Post, and Banshee areas.

The underground mine consists of 11 separate production areas stretching over a length of 12,000 ft, and a vertical distance from approximately 600 ft to 2,000 ft below surface. At the southern end of the underground zones, the pit workings cut the underground zones.

Two main mining methods are used underground at the Goldstrike Mine, both of which rely on cemented backfill for support.

In relatively good to fair ground conditions, where longhole stoping methods are used, the wall and back instability is reduced by mining smaller, longhole sections and filling before mining the next section. In poor ground, the underhand drift and fill method provides a backfill roof for subsequent lifts in the mining cycle.

Transverse longhole stopes are designed at various heights ranging from 35 ft to 100 ft, based on the existing and planned sill development levels used in the active mining areas. Stope widths are designed at 20 ft to 25 ft, based on the ground conditions. In secondary stopes, the width is dictated by the actual dimensions of the adjacent primary stopes. Development of the secondary sills may be reduced to 13 ft leaving a rock “skin” to account for poor quality backfill in the adjacent stopes. The overall stope length is based on the transverse dimension of the ore, however, individual stopes can be limited to 45 ft. Transverse longhole stopes are designed with at least 60° hanging walls and with subvertical footwalls.

Longitudinal stopes are utilized in areas of the mine where the geometry and ground conditions allow. The stopes are accessed from a footwall drive and then driven parallel to the strike of ore. If the strike length of the ore is greater than 60 ft, the development is driven to the end and the stope is mined in a retreat fashion in sections no longer than 60 ft. Each section is mined and filled before the next section is mined. If ground conditions are poor, the longhole stope section length can be reduced.

Goldstrike process facilities provide the capability to treat single refractory ore (sulphidic) and double refractory ore (sulphidic and carbonaceous) through roasting or pressure oxidation.

ACID/ALKALINE POX CIRCUIT
The autoclave circuit receives a blended feed via a rubber-tired loader from ore stockpiles located adjacent to the primary crusher.

CRUSHING AND GRINDING CIRCUIT
The grinding circuit was constructed in two phases to accommodate increases in Goldstrike production rate over time. The total installed grinding circuit capacity is in the order of 17,500 stpd (dry).

The Phase I grinding circuit is fed by a 50 in. by 60 in. jaw crusher which in turn discharges to a primary crushed ore stockpile. Ore is withdrawn from the stockpile by reclaim feeders and fed to a 22 ft diameter SAG mill operating in closed circuit with a pebble crusher. The SAG mill discharge is pumped to secondary ball mills in closed circuit with a bank of six 20 in. diameter cyclones. There are two ball mills operating, one 12.5 ft diameter by 14 ft long and the other 12.5 ft diameter by 18 ft long. The overflow from the cyclones feed a tertiary 16 ft diameter by 23.5 ft long ball mill operating in closed circuit with a bank of six 30 in. diameter cyclones.
Cyclone overflow feeds dewatering with one 100 ft diameter thickener and one 125 ft diameter thickener providing an ability to operate the grinding circuits separately on Alkaline or Acid POX feed blends. A third 100 ft diameter thickener is used to recycle grinding circuit process solution make-up water.

The Phase II grinding circuit is fed by a 42 in. by 65 in. gyratory crusher followed by a crushed ore stockpile. Ore is withdrawn from the stockpile and fed to a 24 ft diameter SAG mill operating in closed circuit with a pebble crusher. SAG mill discharge screen undersize is pumped along with ball mill discharge to a bank of twelve 20 in. diameter cyclones. The underflow from the cyclopak returns to a 16.5 ft diameter by 30.5 ft long ball mill.

ROASTER OPERATION
Fluid bed roasters were constructed at site in 1999 to treat double refractory carbonaceous ores that could not be processed in the existing POX circuit due to elevated organic carbon content.

CRUSHING
Ore is reclaimed from one of the roaster stockpiles and goes through two stages of open circuit
crushing including a gyratory crusher, scalping screen and cone crusher for screen oversize.
The screen undersize and the cone crusher product are combined in a coarse ore stockpile.

DRY GRINDING
Ore is reclaimed from the coarse ore stockpile by apron feeders and conveyed to one of the
two parallel dry grinding circuits. The ore is heated with natural gas and progresses toward
the centre of the mill as it is being dried and ground where it is transported with air through
screens, a static cyclone classifier and a dynamic classifier for size separation. Oversize is
returned to the second stage of the grinding mill for further size reduction while undersize
material is transferred to bag houses for further processing. Target grinding circuit product
size to roasting is 80% passing 74 µm.

Goldstrike process facilities provide the capability to treat single refractory ore (sulphidic) and double refractory ore (sulphidic and carbonaceous) through roasting or pressure oxidation. The roaster circuit accommodates Goldstrike open-pit and underground ore as well as Cortez Hills Open Pit (CHOP) and Cortez Hills Underground (CHUG) ore. A blended feed to the roaster is required to control the circuit heat balance. Pressure oxidation also receives a blended feed from stockpiles and operates as either alkaline or acid POX dependent upon feed carbonate/sulphide ratios. Pressure oxidation is followed by CaTS leaching, also referred to as the Thiosulphate Leach Conversion (TLC) with an RIL adsorption circuit for gold recovery. Respective facilities include:

1. An autoclave circuit consisting of:
• Primary crushing
• Two parallel SAG Mill-Ball Mill grinding circuits with pebble crushing
• Five parallel autoclaves capable of alkaline or acid POX
• Two para ........