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.

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 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 achieved by maximizing sulphide recovery. Producing a bulk flotation concentrate in two rougher flotation steps with relatively low selectivity and high mass pulls has been determined to provide the best results. The secondary rougher concentrate will be sent to a cleaner flotation; the concentrate obtained from the cleaner flotation will be combined with the primary rougher concentrate. The tails obtained from the cleaner flotation will be sent to a cleaner scavenger flotation train. The cleaner scavenger concentrate will be sent to the secondary grinding cyclone feed pumpbox, and the tails will be mixed with rougher tailings flow by gravity to the flotation tailings thickener. The primary rougher concentrate and the concentrate produced from the cleaner flotation will report to the concentrate thickener.

Concentrate from flotation will pass to a 11.5 ft diameter x 16.4 ft high (3.5 x 5 m) concentrate thickener de-aeration tank and then to a 148 ft diameter (45 m) concentrate thickener. Thickener overflow will be returned to the grinding and flotation areas as process water while underflow at an estimated 46% solids will be pumped to the concentrate storage tank circuit. A total of 36 hours of concentrate storage will be provided. In normal operation material will be withdrawn from this circuit and sent to the acidulation circuit. A bypass line will be provided to pump slurry directly from thickening to acidulation, where acidic solution recovered from the pressure oxidation (POX) counter-current decantation (CCD) wash circuit will be mixed with the concentrate with the aim of consuming 85% to 100% of the carbonate gangue component of the concentrate.

Acidulated feed slurry will be stored in one agitated autoclave feed storage tank adjacent to the POX area. This tank will provide the autoclave plant with a continuous feed unaffected by short-term upstream throughput variations. Each autoclave train will discharge to two flash vessels and two vent gas cyclones via parallel slurry discharge lines. The autoclave will be supplied with high-pressure oxygen gas, high-pressure cooling water, and highpressure steam.

Slurry flow from the POX circuit will be washed in a four-thickener CCD circuit. Reclaim water will be added to the last thickener in a flow direction counter to the solids in order to decrease the acidity of the pulp.

Washed slurry in the underflow from the final thickener will be pumped to the CIL solids neutralization circuit. Thickener overflow will be treated in a clarifier and used within the plant to provide acidification of the concentrate fed to the POX circuit and also to the flotation feed to assist in promotion of the sulphide mineral flotability. The remainder will report to neutralization. Clarifier sludge will be intermittently returned to the first thickener in the circuit.

A nominal tonnage of 402 st/h (365 t/h) at 35% solids will be pumped to the first of six CIL tanks. The slurry, with a retention time of four hours per tank, will flow by gravity through each of the six tanks, ultimately reporting to the cyanide destruction reactor tank.

Loaded carbon, at a nominal gold loading of 140 oz/st (4,800 g/t), will report to one of two 13.2 st (12 t) capacity carbon acid-wash vessels by gravity from the loaded carbon screen. The two acid wash vessels will process 39.6 st/d (36 t/d) of carbon. After the acid wash and neutralization processes are complete, the carbon will be pumped from the acid wash vessel to one of two strip vessels. A carbon strip will begin as soon as the carbon is transferred to the strip vessel and the transport water has completely drained out of the vessel. For ease of operation, the two strip vessels will be the same size as the two acid wash vessels. Barren solution, at a concentration of 1% NaOH and 0.1% NaCN, will be pumped through the bottom of the strip vessel. The pregnant solution will exit the strip vessel and flow through the heat exchanger before reporting to the pregnant tank.

The pregnant solution will be pumped through two parallel trains of two electrowinning cells at a nominal flow rate of 211 USgpm (48 m3/h). On exiting the cells, the solution will report to the barren solution discharge tank and is pumped to the barren tank.

Smelting fluxes will be mixed with the sludge after the retort, and the mixture will be charged to the induction smelting furnace. Doré bars will be poured from the smelting furnace and shipped off site for further refining.