Goldstrike mineralization is best described to be in the class of sedimentary rock-hosted Carlinstyle deposits. The Carlin-style class of gold deposits are not unique to the eastern Great Basin. They are characterized by concentrations of very finely disseminated gold in silty, carbonaceous, and calcareous rocks. The gold is present as micron-size to sub-micron-size disseminated grains, often internal to iron-sulphide minerals (arsenical pyrite is most common) or with carbonaceous material in the host rock. Free particulate gold, and particularly visible free gold, is not a common characteristic of these deposits; significant placer alluvial concentrations of gold are therefore not commonly associated with eroded Carlin-style gold deposits.

All Carlin-style deposits in the Great Basin have some general characteristics in common, although there is a wide spectrum of variants. Anomalous concentrations of arsenic, antimony, and mercury are typically associated with the gold mineralization; thallium, tungsten, and molybdenum may also be present in trace amounts. Alteration of the gold-bearing host rocks of Carlin-type deposits is typically manifested by decalcification, often with the addition of silica, fine-grained disseminated sulphide minerals, remobilization and/or the addition of carbon, and late-stage barite and/or calcite veining. Small amounts of white clays (illite) can also be present. Decalcification of the host produces volume loss, with incipient collapse brecciation that enhances the pathways of the mineralizing fluids. Due to the lack of free particulate gold, Carlin-style deposits generally do not have a coarse-gold assay problem common in many other types of gold deposits.

Deposit configurations and shapes are quite variable. Carlin-type deposits are typically at least somewhat stratiform in nature, with mineralization localized within specific favourable stratigraphic units. Fault and solution breccias can also be primary hosts to mineralization.

Most of the gold discovered at Goldstrike can be characterized as finely-disseminated “micron gold”, incorporated in the lattice of arsenical pyrite grains, in association with strong pervasive silicification. Very little of the mineralization at Goldstrike is preserved in this form, as most of the pyrite has been oxidized to iron oxides including hematite, goethite and limonite. As discussed above, gold is paragenetically late with respect to silicification, such that most of it is concentrated along fractures. Gold is geochemically correlated with arsenic, silver, antimony, thallium and mercury, although oxidation tends to disperse elements such as arsenic, making the correlation less strong.

Faults associated with gold mineralization typically have large zones of calcite veining or calcite vein breccias developed along them. These calcite zones can be up to 15.2 m wide in places. It is assumed that these calcite veins are late with respect to Carlin-style mineralization, and barren, although early reports of gold production state that coarse gold was associated with the calcite veins. These same fault zones are in places intruded by thin basaltic dikes and sills that locally host coarse gold along their margins and internal steep sheers.

Extensive mineralization is also found in favourable Paleozoic carbonate, sandstone and shale units, particularly where they are in proximity to the basal Claron Formation unconformity or large faults. In general, the Paleozoic rock units at the unconformity young east to west in the Main Zone Covington Pit area, with the Redwall Limestone in contact with the Claron Formation in the eastern Main and Hamburg pit areas and the Queantoweap Sandstone in contact with the Claron Formation north of the Covington Pit. The Callville Limestone is in contact with the Claron Formation in the Moosehead pit area and probably at Beavertail. In general, the upper portion of the Callville Limestone is the most favourable unit to host mineralization, while the Redwall, Scotty Wash, Chainman and the middle sandy member of the Pakoon Dolomite also host mineralization. The Queantoweap Sandstone and the upper and lower dolostone members of the Pakoon Dolomite tend to be barren of mineralization. As well, the basal Claron Formation adjacent to these units tends to be less well endowed with gold mineralization than when it is adjacent to more favourable Paleozoic units. This generalization can be extended to locations in the southeast part of the property where the Claron Formation is in contact with the Grapevine Wash Conglomerate. It is possible that the relative lack of calcite associated with these formations may be a factor in the lack of gold mineralization, or lack of a permeability/porosity contrast.

The style of disseminated mineralization at Goldstrike is similar to other sediment-hosted gold deposits in the Great Basin, where elemental gold is located within the lattice of arsenical rims on pyrite grains. Mineralization drilled and mined to date is oxidized, and thus the original presence of arsenical pyrite is inferred from the presence of scorodite with iron oxides and by the elevated arsenic content of mineralized rocks. Few other minerals have been noted in association with gold. These include very local occurrences of orpiment, realgar, stibnite and stibiconite.

The PEA Study utilizes open pit mining with mine planning based on economic pit shells generated by mine planning software. Mine production is planned at 22,500 tonnes per day or 8.2 million tonnes per year of leach feed (mineralized) material. With an average waste to leach feed material strip ratio of 1.2 to 1, the average mining rate is approximately 50,000 tonnes per day of leach feed and waste material. The open pit mining at Goldstrike was designed utilizing an owner-operated, conventional mine fleet of front end loaders and trucks.

The project consists of a ROM heap leach with a carbon plant for solution recovery and on-site smelting of gold and silver into doré bars.

ROM material will be transported directly from the open pits to the heap and dumped by mine haul trucks. Before stacking on the heap, lime will be added to the trucks at a rate of 1.2 kg lime per tonne in a dedicated staging area along the mine haul road.

Material will be stacked in 9-meter high lifts. Stacking will be assisted by a low-pressure track dozer to push and spread material in preparation for leaching. Dozer ripping to facilitate improved percolation will also be performed after each lift has been stacked to the determined height.

The annual tonnage of ROM material stacked is approximately 8.1 million tonnes.

After each leach cell has been stacked and dozer ripped, the irrigation system will be installed. Dripline emitters will be used to apply a dilute cyanide solution, at an average application rate of 10 L/hr/m2. A minimum primary leach cycle of 120 days has been selected, based on a review of the selected leach curves.

Barren leach solution pH will be maintained at a minimum value of 10 and will be controlled by the lime addition to the haul trucks. Barren solution will be delivered from a barren tank located at the recovery plant, by high-flow high-head pumps at the design flow rate of 1700 m3/h. This solution will be carried by a steel pipeline to the base of the heap and then to a network of sub- headers and risers to the top of the heap where it is finally applied to the material by drip emitters.

Solution passing through the heap will dissolve the contained metals and then collect in a network of perforated solution collection pipes, which feed to a common discharge point at the base of the heap. The solution will then be carried by gravity to a pregnant solution tank. Excess solution from the heap will overflow from the pregnant tank to a lined process pond. Pregnant solution is pumped from the pregnant tank to the adsorption carbon column circuit at the recovery plant.

The carbon adsorption circuit consists of a series of gravity-fed cascade-style columns. Pregnant solution runs through the columns to load the soluble gold onto the carbon. Barren solution exiting the columns is directed to the barren tank where make up cyanide is added and the solution returned to the heap for further leaching. Overflow from the barren tank is directed to a barren/event pond designed by others.

Two storage ponds are assumed for the management of solutions, the process pond and barren/event pond. The process pond will collect overflow from the pregnant solution tank and is sized to also contain 24 hours of pregnant solution working volume. Overflow from the process pond will report to the barren/event pond via an HDPE-lined channel. The barren/event pond will collect overflow from the barren solution tank during process upsets, and is expected to be sized to handle storm water collection from a severe storm event plus 24 hours of solution storage, in the event of pregnant or barren pump failure or site power loss. Pond sizing and design is by others.

Solutions collected in these ponds will be pumped back to the corresponding barren or pregnant solution tanks using submersible pond pumps for distribution either to the recovery plant or to the heap.

Loaded carbon from the carbon adsorption circuit will be passed over a carbon dewatering screen, where process solution and any carbon fines in the undersize are transferred to a carbon fines tank, and the oversize loaded carbon is directed to the acid wash circuit. The loaded carbon will be acid washed in a dilute hydrochloric acid solution to remove calcium and other contaminants as required. The acid wash circuit sizing will allow for acid washing after every strip, which is expected for optimum performance of the carbon.

Loaded, acid-washed carbon will then be pumped to the elution circuit where it will be batch stripped in a 6-tonne pressure stripping vessel, in a modified Zadra circuit. The loaded carbon is eluted using a sodium hydroxide solution rate of about two bed volumes per hour at a temperature of 275-300°F. The eluted pregnant solution will report to the electrowinning cells.

Eluted carbon will be passed over a sizing screen and then reactivated as necessary using a carbon regeneration kiln. The kiln will have capacity to regenerate at minimum a third of the total carbon stripped. Regenerated carbon will be again screened to remove fine carbon from the circuit, as required.

Solution from the strip vessel will be pumped through electrowinning cells where gold and silver will be precipitated on stainless steel cathodes. The eluted barren solution from electrowinning will then be recycled back to a barren eluant solution storage tank. Solution from the eluted barren tank will be pumped back to the strip vessel to be reused for loaded carbon stripping.

When sufficiently loaded, the electrowinning cells will be shut down, and the gold and silver sludge will be removed from the cathodes. The sludge will then be pumped to a filter press for dewatering. The de-watered sludge will be blended with fluxes and then smelted in a diesel-fired crucible furnace to yield doré. The doré will be shipped off site for final processing and sale.