The Goldstrike deposits are all Carlin type deposits, with fine to very finely disseminated gold and arsenic bearing pyrite. The host rocks are generally sedimentary, mostly calcareous formations, frequently altered and decalcified. There is hydrothermal alteration and there are collapse structures which generated the breccias that host the deposits. The alteration and folding and faulting have led to poor rock quality in the deposits in generally and locally very poor ground conditions in the vicinity of the major faults.

The Rodeo deposit is located approximately 4,500 ft south of the Meikle underground mine and 3,600 ft north of the Betze-Post open pit.

Economic grade mineralization occurs in two zones in the Rodeo area, the Upper and Lower zones. The combined dimensions of the two zones have a strike length of 2,300 ft. The zones extend from the elevation of 3,500 ft to 4,700 ft, with a true thickness of 100 ft to 200 ft.

The Upper Zone consists of four subzones: The Upper North, Middle, Upper South, and West subzones. The Upper Zone lies within a stratigraphic and structural antiform that has a shallow plunge to the north-northeast. Mineralization is hosted in the Upper Mud, Soft Sediment Deformation, and Planar units of the Popovich Formation as well as Jurassic lamprophyre dikes. The morphology of the mineralized zone is dictated, in order of significance, by the proximity to favorable feeder structures, receptive lithologies, and structural preparation.

The Lower Zone occurs in the Wispy Unit of the Popovich Formation. The Wispy Unit in Rodeo is characterized by laminated limestone, debris flow horizons, and local collapse breccia zones associated with structural intersections and discontinuous lamprophyre dikes. The morphology of the zone is strongly influenced by the proximity of through-going northwest striking faults, north-northeast striking feeder faults, and favourable lithology.


BARREL: The Barrel mineralized zone is a tabular body located 200 ft northwest to approximately 1,000 ft west-northwest of the Rodeo deposit, between the 3,900 ft and 4,200 ft elevation. It has a strike length of 1,600 ft along a N30ºW orientation and varies in thickness from 30 ft to 50 ft. It is hosted mainly in the Planar unit of the Popovich Formation, with minor values within the overlying Sediment Deformation unit, as well as in the underlying Wispy unit at the south end of the zone. The zone is bounded by a series of low and high angle east dipping structures and is also partly controlled by west dipping lamprophyre dikes.

NORTH POST: The North Post deposit is located between the southern end of the Rodeo deposit and the northeast final wall of the Betze-Post Pit, between the 3,100 ft and 4,600 ft elevation. North Post mineralization can be subdivided in three zones: the Upper Zone, Main Zone, and Lower Zone. The Main Zone is partially split by a property boundary with Newmont (Figure 7-6). Upper Zone gold mineralization is hosted in the Popovich Formation limestone along west dipping lamprophyre filled faults. The Main Zone is hosted primarily in the Roberts Mountains limestone, footwall to the Post Fault, between interpreted moderate east dipping reverse faults at intersections with Dormant Fault splays. The Lower Zone or Deep North Post Zone is hosted in the Roberts Mountains Formation limestone, footwall to the Post Fault, between interpreted moderate east dipping reverse faults and between splays of the Dormant Fault.

Goldstrike underground operations use two mining methods for extraction: long hole open stoping and underhand drift & fill, 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.

Rodeo is a trackless operation, using two different underground mining methods: long-hole open stoping and drift-and-fill.

The paste fill plant was commissioned at Rodeo in 2013. The method utilizes tailings from the Roaster facility mixed with cement. This method replaced backfill from the Rodeo cemented rock fill plant in 2013 when the open pit mined through the plant’s aggregate delivery raise. Paste fill is cheaper and more efficient than the cemented rock fill and offers another way to dispose of Roaster tailings.

The underhand drift and fill method is utilized in areas of fair to poor ground conditions regardless of the width of the zone. The underhand drifts are nominally designed as 4.6 metres (15 ft) wide by 4.6 metres (15 ft) high. The minimum width is 4.6 metres (15 ft) (one drift). The primary drift is driven with increased ground support to hold the ground open, then backfilled with a high strength cemented rock fill at the Meikle mine, paste fill at the Rodeo and North Post mine. Where the ore width exceeds the nominal drift width, subsequent drifts are developed (parallel or at oblique angles to the primary drift) and then backfilled. This process continues until the entire ore shape at a given elevation has been excavated and filled. Successive lifts are taken beneath the primary workings, utilizing the backfill as an engineered back. This method can provide a consistent production rate from a mining area given a sufficient number of headings to complete the full mining cycle.

Transverse longhole stopes are designed at various heights ranging from 10.7 m (35 ft) to 30.5 m (100 ft), based on the existing and planned sill development levels used in the active mining areas. Stope widths are designed at 6.1 to 7.6 metres (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 4.0 metres (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 13.7 metres (45 ft). Transverse longhole stopes are designed with at least 60° hanging walls and with subvertical footwalls.

Transverse longhole stoping is used where the mineralized zone has a significant width. Footwall drifts are driven parallel to the strike of the ore to provide access for stoping. Mining with transverse stopes requires a primary, secondary, and sometimes tertiary extraction to completely mine out the area.

Longitudinal stopes are utilized in areas of the mine where the geometry and ground conditions allow. The stopes are accessed from a footwall drive driven parallel to the strike of ore. If the strike length of the ore is greater than 18.3 metres (60 ft), the development is driven to the end and the stope is mined in a retreat fashion in sections no longer than 18.3 metres (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.

Overhand drift and fill, back stoping, and benching are all used to a much lesser extent, based on ground conditions and the geometry of the ore zones.

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 ........