West Africa region - Regional overview

Gold Fields holds a 90% attributable portion of the Mineral Resources and Mineral Reserves for Tarkwa and Damang, with the remaining 10% held by the Ghanaian Government as a free carried interest.

The West Africa region's Mineral Resource base has decreased from 15.1Moz to 14.8Moz (2%) net of depletion. The total Mineral Reserve has decreased from 7.8Moz to 7.6Moz (2%), net of mined depletion.

The West Africa region operations are located in the southern area of western Ghana, 300km by road west of the capital of Accra and approximately 90km north of the port city of Takoradi. The ore bodies are located in the West African Craton, near the southern end of the Tarkwa Basin. They occupy a significant portion of the stratigraphy of the Ashanti Belt, which hosts the important Birimian and Tarkwaian geological series.

Damang, which is located 25km north-north-east of the Tarkwa gold mine, exploits predominantly fresh hydrothermal mineralisation and limited oxides, in addition to palaeoplacer mineralisation similar to that of the Tarkwa gold mine. The hydrothermal mineralisation occurs at the culmination of a regional anticline and is associated with dominantly east-dipping thrust faults and sub-horizontal quartz veins.

The ore body at Tarkwa consists of a succession of stacked tabular palaeoplacer units consisting of quartz pebble conglomerates (gravel beds called reefs) that are very similar to those mined in the Witwatersrand Basin in South Africa. Tarkwa is currently mining multiple narrow reef horizons from four open pits.

GENSER Energy, an independent power producing company, was contracted through a power purchase agreement with Gold Fields Ghana to build and operate power plants on the mines' premises and supply power to both mines. The plants were commissioned in Q4 2016 at the Damang and Tarkwa sites. Damang's power plant is operating at full capacity and solely supplying power to the mine with Tarkwa's power plant expected to reach full capacity by the end of Q1 2018.

Regional geology

The ore bodies are 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 striking, broadly synclinal structure made up of lower Proterozoic sediments and volcanics underlain by the metavolcanics and metasediments of the Birimian System. The Tarkwaian unconformably overlies the Birimian, and is characterised by lower-intensity metamorphism and the predominance of coarse-grained, immature sedimentary units.

Exploration drilling and expenditure

At Damang, exploration is dominated by extensional drilling of the current resource pits to identify expansion opportunities and improve their life through a better understanding of geological structures and mineralisation controls.

At Tarkwa, brownfields or on-lease exploration is primarily focused on targeting near surface hydrothermal deposits that could provide open pit opportunities to supplement existing mill feed with comparatively higher-grade ore sources.

The region maintains rigorous QA/QC protocols on all its exploration programmes. It draws on industry leading practice for data acquisition and utilises accredited laboratories that are regularly reviewed both internally and externally. Analytical QA/QC is maintained and monitored through the submission of blanks, certified reference material and duplicates, plus umpire laboratory checks.

  December 2017     December 2016  
Exploration drilling Metres
Damang 35,265   5.66      20,065   1.67   
Tarkwa 36,324   5.37      10,495   1.47   
Total West Africa operations 71,589   11.03      30,560   3.14   

Exclusive of grade control drilling.