The Donlin mineralization model is a high-level, reduced intrusion-related vein system. The Lewis–ACMA part of the district is a low sulphidation, reduced intrusion related, epizonal system with both vein and disseminated mineral zones.

The Donlin gold deposits lie in the central Kuskokwim basin of southwestern Alaska, which contains a back-arc continental margin basin fill assemblage of the Upper Cretaceous Kuskokwim Group, and Late Cretaceous volcano-plutonic complexes. The Project area is underlain by a 5 mile (8.5 km) long x 1.5 mile (2.5 km) wide granite porphyry dike and sill swarm hosted by lithic sandstone, siltstone, and shale of the
Kuskokwim Group.

The deposits are hosted primarily in igneous rocks and are associated with an extensive Upper Cretaceous gold–arsenic–antimony–mercury hydrothermal system. The northeast, elongated, roughly 5,000 ft (1.5 km) wide x 10,000 ft (3 km) long cluster of gold deposits has an aggregate vertical range that exceeds 3,100 ft (945 m). These areas consist of the ACMA and 400 Zone, Aurora and Akivik mineralized areas (grouped as ACMA) and the Lewis, South Lewis, Vortex, Rochelieu and Queen mineralized areas (grouped as Lewis).

Gold occurs primarily in sulphide and quartz–carbonate–sulphide vein networks in igneous rocks and, to a much lesser extent, in sedimentary rocks. Broad disseminated sulphide zones formed in igneous rocks where vein zones are closely spaced. Submicroscopic gold, contained primarily in arsenopyrite and secondarily in pyrite and marcasite, is associated with illite–kaolinite–carbonate–graphite-altered host rocks.

Southeast-dipping north-northeast-oriented fracture zones are the primary control on gold-bearing vein distribution within the north-northeast mineralized corridors. Composite vein zones or mineralized corridors range up to 30 meters in width and extend for hundreds of meters along strike. Intrusive rocks and to a lesser extent competent massive greywacke are the most favored host rocks, and act as a secondary control on the mineralization. Gold distribution in the deposit closely mimics the intrusive rocks, which contain about 74% of the mineral resource identified in the Donlin Gold FS. Structural zones in competent sedimentary units account for the remaining 26%.

Gold occurs primarily in sulphide and quartz–carbonate–sulphide vein networks in igneous rocks and, to a much lesser extent, in sedimentary rocks. Broad disseminated sulphide zones formed in igneous rocks where vein zones are closely spaced. Submicroscopic gold, contained primarily in arsenopyrite and secondarily in pyrite and marcasite, is associated with illite–kaolinite–carbonate–graphite-altered host rocks.

Two pits are planned, one at Lewis (nine phases), the other at ACMA (six phases); the pits will partly coalesce toward the end of the mine life. The pits have similar mineralization characteristics, with ore-grade gold hosted in both intrusive and sedimentary rock units. The grade of the gold mineralization in ACMA is higher than in the Lewis area, and because of the higher grades, the ACMA pit will be the first developed.

The mine is proposed to be a year-round, conventional “truck and shovel” operation using both bulk and selective mining methods on 12 m and 6 m benches, respectively. Ramps in final walls have a design width of 131 ft (40 m) and a gradient of 10%. A nominal minimum mining width of 492 ft (150 m) was used for phase design. The mine plan assumes the ACMA pit will be backfilled.

Mining will use a conventional truck-and-shovel fleet. Large electric hydraulic shovels mining the full 40 ft (12 m) benches will be the primary loading equipment in zones of waste and steeply-dipping ore. The same primary shovels will be used on the 20 ft (6m) split benches, thereby avoiding the need for a mixed fleet of hydraulic shovels. All shovels will be equipped with GPS positioning to allow real-time updates of the digging face and delineation of the ore–waste contacts. Large front-end loaders (FELs) will be used as a backup to the shovels and to work on less-productive faces and muckpile cleanup. Large 400 st (360 t) capacity haul trucks will be used for transporting both ore and waste out of the pit. All trucks will be equipped with a GPS dispatch system for tracking ore and waste from the mine face to the designated stockpiles or dumps. The mine and fleet design is appropriate for the Mineral Reserves defined.

The operation would have a projected average mining rate 422,000 stpd (383,000 t/d), or 154 Mstpy (140 Mtpy), and an average process plant production rate of 59,000 stpd (53,500 t/d).

Run-of-mine ore would be delivered by mine haul trucks to the feed hopper of a 60 x 89 inch (152 x 226 cm) direct-dump gyratory crusher. The crusher would be driven by an 800 hp (600 kW) motor, be set at 6 inches (15 cm), and have a nominal throughput capacity of approximately 3,780 stph (3,430 t/h). When the hopper is full, ore would be dumped on a bypass stockpile for rehandle to the crusher at a later time.

The crusher would discharge through a surge bin to a variable-speed drive apron feeder, which in turn would discharge to a 54 inch (1.4 m) wide conveyor that would transport the ore to a coarse ore stockpile near the process plant. Baghouses would control potential fugitive dust emissions at all transfer points.

A reclaim tunnel and reclaim feeder chamber containing four feeders (two apron-type and two belt-type) would be installed underneath the coarse ore stockpile to deliver the coarse ore to the SAG mill feed conveyor. The nominal feed rate to the SAG mill would be achieved with three feeders operating.

The grinding equipment includes a SAG mill, a pebble crusher, hydrocyclones, and a primary ball mill for slurry that is recirculated as required to reduce feed to the flotation circuit to the correct size.

The SAG mill feed conveyor would feed ore to the SAG mill at an average rate of about 2,642 stph (2,397 t/h). The mill would be 38 ft diameter x 26.5 ft long (11.6 x 8.1 m), powered by a 26,800 hp (20 MW) electric motor sufficient to accommodate fluctuations in ore type and to maintain tonnage. Recycled solution water from within the process or from the TSF, along with copper sulfate, would be added to the feed end for slurry density control and to activate the sulfide minerals prior to flotation. Discharge from the mill would pass to vibrating screens from which oversize would be conveyed to the pebble crusher and then back to the SAG mill; the undersize would report to the SAG/ball mill discharge pump box.

The oversized material (pebbles) conveyed to the pebble crusher building would be further reduced in size by two cone crushers before the material was conveyed back to the SAG mill. Two surge bins and a bypass bin would be provided. Slurry from the SAG/ball mill discharge pump box would be pumped through a bank of hydrocyclones for sizing. Cyclone underflow (oversized material) would pass to a 24,000 hp (18 MW) ball mill measuring 26 ft diameter x 45.5 ft long (7.9 x 13.9 m) for further size reduction. Ball mill discharge would flow back into the SAG/ball mill discharge sump where it would be combined with the SAG mill product and be resized. Cyclone overflow would advance to the flotation circuit at 35% solids with an average particle size of 80% passing 300 mesh (50 µm).

The process is based on conventional technology. The concentrator, pressure oxidation, and cyanidation facilities will be at the forefront of technology for large, modern gold processing plants.

Mine haul trucks (with capacities to 380 st (345t)) will dump run-of-mine (ROM) open pit ore directly into dump hoppers ahead of a 60" x 89" gyratory crusher.

The overall grinding configuration will consist of an open-circuit SAG mill followed by the “mill-chemical-float-mill-chemical-float” (MCF2) circuit. The MCF2 circuit will entail a primary ball mill followed by primary rougher flotation; the tailings produced from primary flotation will be sent to a secondary ball mill, followed by a secondary rougher flotation. The two individual ball mills will operate in a closed circuit with their respective classification cyclones.

Donlin ore contains a mixture of intrusive and sedimentary rock containing sulphide mineralization. The optimum gold recovery will be a ........