The Donlin mineralization model is a high-level, reduced intrusion-related vein system. The ACMA (ACMA is named after the American Creek magnetic anomaly)-Lewis part of the district is a low sulphidation, reduced intrusion related, epizonal system with both vein and disseminated mineral zones.

The Donlin 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 8.5 km long x 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 1.5 km wide x 3 km long cluster of gold deposits has an aggregate vertical range that exceeds 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. Sub-microscopic gold, contained prim ........

The preferred development is for a 53,500 t/d process facility with on-site power; and a mine capacity of 440 kt/d with an elevated cut-off policy applied in the initial part of the mine life.

There is sufficient area within the Project to host an open pit mining operation, including the proposed open pits, mine and plant infrastructure, waste rock and tailings storage facilities.

Lewis Pit - Northeast Wall (Design Sector I-219)
Given the monoclinal dip of the sedimentary rocks in this area of the pit, where the bedding dips at an average of 43°, a standard 65° to 70° bench face would undercut bedding and likely result in instability. As a result, a footwall mining configuration has been recommended and will achieve the maximum slope angle in this area.

Stability analyses to assess standard potential footwall instability modes indicate that a 48 m high unbenched slope will be stable against buckling, bi-linear slab, and ploughing failures. To practically dewater this area and maintain adequate protection against rock and ice fall, a rockfall catchment berm should be placed every 48 m vertically. The berm will need to be a minimum of 8 m wide, increasing to 13 m wide at every second bench to accommodate water wells, horizontal drain hole collection systems, a rockfall catchment ditch / net, and a roadway with a 5 m wide running surface for service vehicles. This results in a 38° inter-ramp slope angle for this wall.

ACMA Pit ........

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