Newmont is developing the Long Canyon gold mine, a high-grade oxide deposit, in Nevada, US. The open-pit deposit is the only significant discovery made in Nevada in the last decade and is expected to create 300 to 400 construction jobs and approximately 260 operational jobs.
The environmental impact statement (EIS) for the project was released in early 2015 and the Bureau of Land Management (BLM) granted the Record of Decision in April 2015. Commercial production at the project is anticipated to begin in the first half of 2017.
The project is proposed to be developed in two stages, with the first phase including the development of an open pit mine and a heap leach operation. The first phase operation is expected to have a mine life of eight years and is forecasted to produce approximately 100,000 to 150,000 ounces of gold a year.
Long Canyon gold mine geology and mineralisation
Newmont acquired the Long Canyon project as part of its acquisition of Fronteer Gold in 2012. The mine is located approximately 100 miles from Newmont’s existing infrastructure facility at Carlin and four miles south of the Oasis/Montello exit (Exit 378) off Interstate 80, Nevada.
The project area covers both private land, owned or controlled by Newmont, and public lands administered by BLM.
The mine is a part of the northern Pequop Mountains, an uplifted block of regionally east-dipping carbonate and siliclastic rocks. Most of the mineral is contained within the carbonate rocks of Cambrian-Ordovician age, especially the limestone of the Ordovician Pogonip group and the limestone and dolomite of the upper Cambrian Notch Peak Formation.
Gold mineralisation occurs mainly within the limestone along dolomite margins. Haematitic matrix of collapse breccias contains most of the high-grade mineralisation, in addition to the adjacent zones of strata-bound mineralisation characterised by strong decalcification. All of the mineralised zones discovered to date are oxidised.
Long Canyon gold mine reserves
As of 31 December 2014, the Long Canyon gold mine is estimated to contain probable ore reserves of 18.4 million tonnes grading 2.29 grams per tonne (g/t). Contained gold is estimated to be 1.23 million ounces (Moz).
Mining and processing of ore at Long Canyon
Conventional open-pit mining method involving drilling and blasting will be applied at the Long Canyon mine. Ore from the mine is proposed to be transported in off-highway trucks to either an on-site mill, which is under construction, or processed it at its existing Gold Quarry surface mine near Carlin, Nevada.
At its on-site mill, Newmont proposes to feed higher grade ore directly from haul trucks into a crushing facility. After crushing, the ore will be conveyed to the mill for grinding, processing and gold recovery. Metal recovery will involve carbon-in-column (CIC) and tank cyanidation and carbon-in-pulp (CIP) recovery.
The loaded carbon will be transported to Newmont’s carbon stripping and refining facility at Carlin for final processing, resulting in the production of gold doré bars. The resulting tailings are proposed to be delivered to a synthetically lined tailings storage facility (TSF) using a dual-containment pipeline.
Newmont also proposes to process lower-grade “run-of-mine” oxide ore at a fully-lined heap leach facility. Lime will be added to ore material in a silo to maintain an elevated pH level. At the heap leach facility, ore material will be placed in lifts and a dozer will be used to facilitate percolation of the process solution.
A weak cyanide solution will then be applied to the surface of the stacked ore, which will penetrate through the stacked ore and dissolve the gold contained in the ore. The dissolved solution will then flow to the pregnant solution tank, where the solution will be pumped into a carbon-in-column (CIC) recovery system to adsorb the precious metals onto carbon.
The barren solution from the CIC columns will be recycled back to the heap leach facility. The loaded carbon (carbon-containing gold) will be consolidated and transported offsite to one of its existing refineries in Nevada for final processing.
Infrastructure facilities at Long Canyon gold mine
Three alternatives are being considered to source power for the Long Canyon mine. The alternatives are to purchase electricity from Wells Rural Electric Company (WREC), on-site generation, or off-site generation of electricity.
A water well supply system, including potable water and water for mining and ore processing, is proposed for the project.