Name: Tarkwa mine.

Location: The mine is located in south-western Ghana.

Controlling Company: Gold Fields.

Brief Description: Tarkwa is a large owner-operated openpit gold mine that uses well-defined selective surface mining methods to optimise the extraction of the sedimentary mineral deposits.

Four large openpits – Pepe-Atuabo, Teberebie, Akontansi and Kottraverchy – currently exploit the stacked narrow auriferous conglomerates, similar to those mined in the Witwatersrand basin of South Africa.

It is estimated that the mine’s current mineral reserves will be depleted in 2031.

Brief History: Gold Fields signed a management contract with the Ghana government to operate the Tarkwa mine in 1993 and completed a feasibility study on an openpit/heap-leach operation in 1996.

The initial Tarkwa Phase 1 development for an openpit operation mining 14.5-million tonnes a year, including 4.7-million tonnes a year of heap-leach feed ore, was completed in 1998. The Tarkwa Phase 2 expansion to increase the mining rate to 20.7-million tonnes a year and heap-leach feed ore production to 7.2-million tonnes a year was completed in 1999. All underground operations and the associated processing plant ceased production in this year. In 2000, Gold Fields acquired the northern area of Teberebie and mining production was increased to 36-million tonnes a year.

Tarkwa implemented owner mining in July 2004 and commissioned a carbon-in-leach (CIL) plant, with a nameplate capacity of 4.2-million tonnes a year in October 2004. The expanded CIL plant was commissioned in January 2009 and a design throughput of 12.3-million tonnes a year was achieved in September 2009. Conversion to owner maintenance was completed in 2010.

Gold Fields acquired the 18.9% Iamgold interest in the Tarkwa mine in 2011, and now holds 90%, with the remaining 10% being held by the Ghana government. At the end of 2013, all heap-leach operations stopped.

The CIL plant capacity was increased to 13.5-million tonnes a year in late 2014.

Products: Gold.

Geology/Mineralisation: The orebody at the Tarkwa mine comprises a succession of stacked tabular palaeoplacer units consisting of quartz pebble conglomerates (gravel beds called reefs).

The Tarkwian orebody is located within the Tarkwaian system, which is an important stratigraphic component of the Ashanti belt in south-western Ghana. The Ashanti belt is a north-easterly- trending, broadly synclinal structure comprising lower proterozoic sediments and volcanics underlain by the metavolcanics and metasediments of the Birimian system. The Tarkwaian unconformably overlies the Birimian system and is characterised by lower-intensity metamorphism and the predominance of coarse-grained, immature sedimentary units.

Reserves: Proven and probable mineral reserves as at December 31, 2015, were estimated at 211.34-million tonnes, grading 0.99 g/t gold.

Resources: Mineral resources as at December 31, 2015, were estimated at 258.79-million tonnes, grading 1.13 g/t gold.

Mining Method: Openpit.

Major Infrastructure and Equipment: Ore is processed using a conventional CIL plant, with a gyratory crusher feeding a semi- autogenous mill and ball mill. Gold is recovered from the solution by electrowinning and smelted in an induction furnace.

Life-of-mine (LoM) tailings deposition requirements are catered for in the short term by wall raise sequences at the operating tailings storage facilities (TSFs) 1, 2 and 3 and in the medium term by TSF 5, which started construction in early 2016. In the longer term, LoM tailings deposition requirements will be catered for by planned TSFs 4 and 6.

The mine has its own load-and-haul fleet of 16 excavators, which range from 120 t to 400 t. The haul fleet includes 67 dump trucks, with a payload of 146 t; eight dump trucks, with a payload of 240 t; and nine dump trucks, with a payload of 90 t. The load-and-haul fleet is supported by an ancillary fleet consisting of dozers, graders, water carts and compactors. A total of 22 owner- operated drill rigs are used for blast hole drilling. Maintenance of the fleet is undertaken by the Tarkwa mine, while maintenance of the excavators is performed by contractors.

Prospects: Further enhancements to increase the capacity of the CIL plant to 15.5-million tonnes are being considered. The plant will be fed with the old North heap-leach material or newly mined material from the pits. Gold Fields is also investigating alternative waste dumping and tailings disposal strategies, including in-pit dumping, energy and carbon-efficiency initiatives, and ongoing business and performance improvement programmes.

Contact Person: Sven Lunsche.

Contact Details:
Gold Fields,
tel +27 11 562 9763,
email media@goldfields.com, and
website https://www.goldfields.com.