Donlin Gold Receives Updated Feasibility Study
If put into production in accordance with the study, the Donlin project would be among the world’s largest low-oper-ating-cost and long-lived gold mines, averaging 1.5 million oz/y of gold in its first five years of operation at an aver-age cash cost of $409/oz and 1.1 mil-lion oz/y over its projected 27-year mine life at an average cash cost of $585/oz. The capital cost to develop the project is estimated at $6.7 billion.
Exploration upside at Donlin is believed to be excellent, with the poten-tial to expand the current open-pit resources along strike and at depth. With proven and probable gold reserves estimated at 33.8 million oz established along only 3 km of a well-established mineralized corridor in excess of 8 km long, NovaGold said it is confident that further discoveries will be made.
The study confirmed the attractive-ness of an option for power generation utilizing natural gas rather than the original diesel option. Natural gas would be delivered to site via a 500-km-long pipeline. “The change to utiliz-ing natural gas is an important modifi-cation that is believed to materially improve numerous project parameters, including lowering operating costs, improving environmental management and social infrastructure, providing flexibility for future operational modifi-cations, and facilitating potential increases in the scale of operations in this geologically prospective district,” the NovaGold announcement said. The cost to build the pipeline is included in the capital cost estimate.
The updated Donlin feasibility study is based on a conventional truck-and-shovel open-pit operation. The mine life is estimated at 27 years based on a nominal processing rate of 53,500 mt/d and a waste-to-ore strip ratio of 5.5:1. The ore will be crushed and then milled using semi-autogenous grinding and two-stage ball mills. The gold-bear-ing sulphides will be recovered by flota-tion to produce a concentrate repre-senting 17% of the mass with an aver-age gold grade of 12.7 g/mt.
The concentrate is refractory and will be treated in an autoclave prior to cyanidation. Overall gold recovery from flotation, pressure oxidation and carbon-in-leach is estimated at 89.8%. Excess acid from the autoclave circuit will be neutralized with flotation tailings and slaked lime. Tailings from the process will be impounded in a tailings storage facility that will have zero-discharge dur-ing operations, with water reclaimed for re-use in the process plant.