Name: Fosterville mine.
Location: The Fosterville mine is located 20 km from the City of Bendigo in the state of Victoria, Australia.
Mine Owner/s: Kirkland Lake Gold.
Brief History: Gold was first discovered in the Fosterville area in 1894, with mining activity continuing until 1903. Mining in this era was confined to the near-surface oxide material. Aside from a minor tailings retreatment in the 1930s, activity resumed in 1988 with a further tailings retreatment programme conducted by Bendigo Gold Associates, which ceased in 1989. Mining restarted in 1991 when Brunswick Mining and then Perseverance Corporation started heap-leaching operations from shallow oxide openpits. From 1988 to the cessation of oxide mining in 2001, 240 000 oz of gold were produced.
A feasibility study into a sulphide mining operation was completed by Perseverance in 2003, and openpit mining started in early 2004. Commercial production began in April 2005 and underground development in March 2006. In October 2007, Perseverance announced that it had entered into an agreement with Northgate Minerals Corporation to acquire the company, with full control passing to Northgate in February 2008.
Northgate entered into a merger agreement with AuRico Gold in August 2011, who assumed control of Northgate in October 2011. In March 2012, AuRico and Crocodile Gold Corporation jointly announced that Crocodile Gold would acquire the Fosterville and Stawell gold mines. Crocodile Gold’s acquisition of Fosterville was concluded in May 2012. In July 2015, Newmarket Gold merged with Crocodile Gold to form Newmarket Gold Inc.
Kirkland Lake Gold Inc merged with Newmarket in November 2016 to form a new midtier gold company, which was renamed Kirkland Lake Gold. The company has since rapidly increased the output of the Fosterville operation based on its exploration success, particular the development of the high-grade Eagle and Swan mineralised zones. Gold production has increased year-on-year, facilitated by increasing grade profiles at depth, with the mine producing 1.77-million ounces since the construction of the sulphide plant in April 2005.
Brief Description: The Fosterville mine is a high-grade, low-cost underground gold mine and the largest gold producer in the state of Victoria.
Primary Metals: Gold.
Secondary Metals: None stated.
Geology/Mineralisation: The Fosterville goldfield is located within the Bendigo structural zone in the Lachlan fold belt. The deposit is hosted by an interbedded turbidite sequence of sandstones, siltstones and shales. This sequence has been metamorphosed to subgreenschist facies and folded into a set of upright, open to closed folds.
Mineralisation at Fosterville is controlled by late brittle faulting. These late brittle faults are generally steeply west-dipping reverse faults, with a series of moderately west-dipping reverse splay faults formed in the footwall of the main fault. There are also moderately east-dipping faults, which have become the more significant footwall to the anticlinal offsets along the west-dipping faults. Primary gold mineralisation occurs as disseminated arsenopyrite and pyrite forming as a selvage to veins in a quartz–carbonate veinlet stockwork. The mineralisation is structurally controlled, with high-grade zones localised by the geometric relationship between bedding and faulting. Mineralised shoots are typically 4 m to 15 m thick, 50 m to 150 m up or down dip and 300 m to 1 500 m down plunge, with average grades of 5.10 g/t gold, with individual assays up to 60 g/t gold.
Primary gold also occurs as visible gold at Fosterville, where it variably overprints sulphide mineralisation, and is found as disseminated fine specks (>1 mm) of gold within host quartz veins. The visible gold is spatially associated with antimony mineralisation in the form of stibnite, which occurs with quartz and varies from replacement and infill of earlier quartz-carbonate stockwork veins to massive stibnite-only veins of up to 0.5 m wide. The stibnite-quartz event occurs in favourable structural locations such as the Phoenix, Eagle and lower Phoenix structures.
The occurrence of visible gold is becoming increasingly significant at depth and is observed more frequently below an estimated 800 m, down-plunge within the lower Phoenix and Harrier gold systems.
Reserves: Total proven and probable reserves as at December 31, 2018, were estimated at 2.72-million tonnes grading 31 g/t gold. Proven carbon-in-leach residues were estimated at 683 000 t grading 7.6 g/t gold.
Resources: Total measured and indicated resources as at December 31, 2018, were estimated at 14.8-million tonnes grading 4.4 g/t gold. Inferred resources were estimated at 10.3-million tonnes grading 5.5 g/t gold.
Mining Method: All areas are extracted using open stoping techniques, with the application of cemented rock fill where applicable and practical. Selection of the specific mining method within the open stoping regime is based upon previous experience at the Fosterville mine and expectations of ore zone geometry and geotechnical conditions.
Major Infrastructure and Equipment: Underground mining is conducted using a conventional fleet, including jumbos, production drills, loaders, trucks and ancillary equipment.
Opencut mining, when required, is conducted using a conventional fleet including excavators and trucks, with the mining fleet and workforce being on contract.
The process plant has a nominal capacity of 830 000 t/y and incorporates:
- single stage crushing with a primary jaw crusher;
- open stockpile with reclaim tunnel;
- semiautogenous grinding (sag) mill;
- a gravity gold recovery circuit;
- flotation circuit;
- flotation concentrate regrind mill;
- a gravity gold recovery circuit;
- de-sliming hydrocyclones;
- bio-oxidation circuit;
- a three stage CCD circuit;
- a liquor neutralisation circuit;
- a limestone grinding facility comprising a single wet ball mill operated in closed circuit with hydrocyclones;
- a carbon-in-leach (CIL) circuit;
- a heated leach circuit; and
- pressure Zadra elution circuit and electrowinning.
Prospects: Kirkland continues to develop the Fosterville mine and increase production from the Swan zone, with stope production advancing on multiple levels.
Contact Details:
Kirkland Lake Gold
Tel +1 416 840 7884
Email info@klgold.com
Website https://www.klgold.com