The Golden Chest gold mine is part of the Coeur d’Alene Mining District and is situated approximately two miles east of Murray, Idaho, US. It is a shallow underground mining operation with the potential for open-pit mining.
First ore from the mine was produced in November 2014 and delivered to the New Jersey mill for processing in mid-December. Since then, the mill processed approximately 3,500t of ore at an average gold recovery rate of approximately 94%. The first shipment of concentrate to the smelter was made in February 2015.
Golden Chest (GCLLC), a company owned jointly by Marathon Gold (52.22%) and New Jersey Mining Company (NJMC, 47.88%), is the owner of the mine. Juniper Mining is engaged as the mine operator.
Mining lease agreement
GCLLC entered a 39-month mining lease agreement with Juniper Resources in September 2013 and granted the exclusive rights to develop and mine the Skookum Shoot area of the gold mine.
Golden Chest mine history, geology and mineralisation
The historical Golden Chest gold mine was the largest producer of lode gold in the mining district during the late 1890s and 1900s. NJMC leased approximately 230 acres in the Golden Chest property, including the Golden Chest mine, from Paymaster Resources in September 2003. The company recovered 8,400t of ore grading 6.90g/t gold in a small-scale underground operation until forming a joint venture with Marathon in December 2010.
The mine is currently estimated to contain 3,900m of underground workings within 24 patented and 70 unpatented mining claims in 515ha.
The gold belt region of the Coeur d’Alene district is underlain primarily by argillites and minor quartzites of the Prichard formation. The formation, comprising of rocks of up to 3,600m thick, is the lowest exposed unit of the Belt Supergroup of Pre-Cambrian age and hosts deep-water argillite/siltite and quartzite.
Epigenetic style of gold mineralisation is found at the deposit and is mostly associated with secondary structures within or located close to major regionally extensive structures.
Gold and tungsten mineralisation is located within the Idaho fault in close proximity to Prichard formation units G and H. Unit G is a quartzitic unit hosting most of the veins while Unit H is made up of an argillite-siltite sequence of rocks. Most of the gold mineralisation occurs along 1,500m of strike length on the Idaho fault.
Golden Chest mine reserves
The global measured and indicated resources of the mine as of January 2013 were estimated at 4.63 million tonnes of ore grading 1.71g/t of gold. Contained gold is estimated to be 254,000oz.
Mining and ore processing at Golden Chest mine
The Standard cut-and-fill mining method, using a modern rubber-tyre fleet, is applied at the underground mine.
Ore from the mine is currently processed by the New Jersey mill in Silver Valley, at a rate of 360t/d. The processing infrastructure includes a flotation mill and a concentrate leach plant. The ore passes through the crushing, grinding, gravity and floatation circuits of the mill, which is supported by paste tailings disposal, concentrate leach and filtration systems.
The gravity circuit comprises a vibrating screen and a Knelson concentrator, which is used to process a portion of the recirculating load in the grinding circuit where gold particles tend to accumulate. The resultant gold concentrate is further upgraded on a Deister table and will be tested via direct smelting or intensive cyanidation to optimise gold recovery.
Small Mine Development Corporation was awarded the underground mining contract for the Golden Chest mine. Micon International was awarded a contract to prepare a technical report for the project.