Gold Fields



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Mineral Resources and Mineral Reserves Supplement

Regional overview

West Africa Region Salient Points

Mineral Resources


Mineral Reserves


* 90% attributable to Gold Fields
# Excludes Asanko gold mine

west africa region

Operational Profile

    Damang   Tarkwa   Asanko JV
Mining method   Open pit   Open pit   Open pit
Infrastructure   Two open pits and one Carbon in Leach (CIL) gold plant with a current capacity of 4.3Mtpa   Four open pits and one CIL gold plant with a current capacity of 13.5Mtpa   Three open pits and one CIL gold plant with current capacity of 5.4Mtpa
Mineralisation style   Hydrothermal (orogenic) and palaeoplacer   Palaeoplacer   Hydrothermal shear hosted
Mineralisation characteristics  
  • Hydrothermal mineralisation hosted within structural shears and fault zones
  • Confined to well-defined prospective structural belts
  • Mineralisation within pods with short-range predictability
  • Exploration and resource definition programmes required to further define controls on mineralisation and continuity
  • Palaeoplacer characteristics are the same as for Tarkwa
  • Mineralisation hosted within sedimentary conglomerates of the Tarkwaian Group
  • Laterally continuous with mid- to long-range predictability
  • Clear patterns of mineralisation governed by sedimentary characteristics
  • Exploration programmes ongoing to test near-mine palaeoplacer potential
  • Deposits are typically hydrothermal shear hosted in style and situated within the Kumasi basin within the Asankrangwa Gold Belt
  • Mineralisation is structurally hosted along several regional NE trending shears and within sandstone, siltstone and shale sedimentary packages
  • Most deposits have intrusive tonalitic-porphyritic granite dyke associations
  • Exploration programmes are ongoing to identify strike and depth extensions to existing ore bodies, and to profile new opportunities along these well-defined structural pathways

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. A 50:50 interest in the Asanko JV is also held, covering 90% of the Mineral Resources and Mineral Reserves attributable to the JV, with the remaining 10% held by the Ghanaian government as a free carried interest. The West Africa region’s Mineral Resource base has increased from 14.8Moz to 16Moz (7.5%), net of depletion. The total Mineral Reserve has decreased from 7.6Moz to 7.4Moz (-3%), net of mined depletion.

The Tarkwa and Damang 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.

The Asanko concessions are located in the Amansie West District of the Ashanti region of Ghana, approximately 250km NW of the capital Accra, and about 50km to 80km SW of the regional capital of Kumasi. The mine exploits a number of hydrothermal ore bodies, which are similar in mineralisation style typically occurring in sub-vertical shear zones and shallow dipping quartz vein arrays frequently in proximity to granitic intrusions.

Damang, which is located 25km NNE of Tarkwa, 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.

Regional geology

The Damang and Tarkwa ore bodies are located within the Tarkwaian System, which is an important gold mineralised stratigraphic component of the Ashanti Belt in south-western Ghana. The Ashanti Belt is a NE striking, broadly synclinal structure made up of lower Proterozoic sediments and volcanics underlain by the metavolcanics and metasediments of the Birimian System. The Tarkwaian unconformity overlies the Birimian and is characterised by lower-intensity metamorphism and the predominance of coarse-grained, immature sedimentary units.

Asanko deposits are located in the Asankrangwa Belt hosted within the Kumasi Basin sediment. The belt is located east of the Ashanti Belt which hosts the Tarkwa and Damang mines. The geology of Asankrangwa comprises strongly deformed Birimian metasediments, with minor granitic intrusions and mafic igneous rocks. The lithological units are cut by deep NW dipping primary and sedimentary structures. It is this geological and structural architecture that has been important in the localisation of gold mineralisation. Gold mineralisation is linked to at least two separate deformation events and fluid emplacement, with certain similarities to the gold deposits of the Ashanti Greenstone Belts.

Exploration drilling and expenditure

At Damang, the 2018 drilling programme focused on Resource conversion and increasing confidence in the area to the north of the current mining at Amoanda Pit, as well as the upgrade of Inferred material at Damang pit cut-back (DPCB). Work is ongoing on the Amoanda geological and evaluation models. The anticipated revisions to the Amoanda model will include drill hole data returned by the drilling programme undertaken during 2018,as well as data collated from grade control drilling and in-pit mapping.

At Tarkwa, on-lease drilling continued in 2018 under the accelerated exploration programme targeting near-surface hydrothermal deposits as potential open pit opportunities and extensions to existing palaeoplacer ore bodies. A total of 48.4km of drilling was completed over 31 target areas in both Tarkwa North and Tarkwa South. A total of 29 predominantly hydrothermal targets were downgraded and one target was upgraded to development stage by completing resource definition drilling. A total of 26.1km of drilling was completed on initial and advanced targets while 22.3km of drilling were used for palaeoplacer and hydrothermal resource conversion in three areas (Kobada, Akontansi-underlap north extension, and Pepe West). In addition, a total of 2,571m of mechanised auger drilling were completed over two brownfield targets in Tarkwa North. A ground geophysical survey (ground magnetics) was conducted over a number of targets in Tarkwa South.

In 2019, the team will focus on investigating the near-mine palaeoplacer potential in four main areas. Work in Akontansi-underlap north extension is planned to investigate reef extensions along a 500m strike-length. A 2.2km strike-length potential of the Pepe West trend will also be tested. Two drill fences will be completed in the Teberebie area as part of a programme designed to investigate ‘shallow’ underground palaeoplacer mining potential.

The region maintains rigorous quality assurance and quality control (QA/ QC) protocols on all its exploration programmes. It draws on industryleading 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 2018     December 2017  
Exploration drilling Metres
  US$M     Metres
Damang 33,857   5.45     35,265   5.66  
Tarkwa 48,429   9.00     36,324   5.37  
Total West Africa operations 82,286   14.45     71,589   11.03  
Exclusive of grade control drilling and Asanko JV drilling

Mineral Resources and Mineral Reserves

Mineral Resources

The Mineral Resources declared are classified as Measured, Indicated or Inferred, as described in the SAMREC Code. Mineral Resource categories are assigned with consideration given to geological complexity, grade variance, drill hole intersection spacing, and proximity of mining development. The following factors apply to the Mineral Resources reported:

  • Cut-off grades are calculated for the individual deposits
  • The application of realistic modifying factors to ensure a reasonable prospect of eventual economic extraction
  • Use of an appropriate in situ economic cut-off grade with tonnages and grades based on the relevant resource block models, including estimates of any material below the cut-off grade required to be mined to extract the complete economic portion of the Mineral Resource
  • Open pit Mineral Resources comprise the material above the nominated cut-off grade within a diluted optimised pit shell and constrained to an optimised minimum mining width
Mineral Reserves

The Mineral Reserve estimates are based on appropriately detailed and engineered life-of-mine (LoM) plans. All design and scheduling work is undertaken to a suitable level of detail by experienced engineers using appropriate mine planning software. The planning process incorporates realistic modifying factors and the use of appropriate cut-off grades, geotechnical criteria, mining fleet productivities, processing capacities and other techno-economic investigations.

No Mineral Resource or Mineral Reserve will be reported by Gold Fields for Asanko as at 31 December 2018. Although all resource models have been updated with the latest drilling, work is still in progress to complete a trade-off study to optimise extraction, transport and costs at Esaase and finalise the associated PFS. The intention is to complete a fully integrated LoM plan, inclusive of the Esaase open pit, which is expected to be completed in H2 2019.


    Mineral Resources         Mineral Reserves  
    December 2018   Dec 
        December 2018   Dec 
Measured, Indicated and Inferred   Tonnes 
    Proved and Probable   Tonnes  (Mt)   Grade  (g/t)   Gold 
Damang   85.1  2.21    6.06    6.12      Damang   28.9    1.74    1.62    1.73   
Tarkwa – open pits   213.2  1.30    8.89    7.58      Tarkwa – open pits   121.4    1.20    4.69    4.83   
Tarkwa – surface stocks   73.1  0.46    1.09    1.07      Tarkwa – surface stocks   73.1    0.46    1.09    1.07   
Total West Africa   371.4  1.34    16.04    14.78      Total West Africa   223.4    1.03    7.39    7.63   
Mineral Resources are inclusive of Mineral Reserves. All tonnes (t) relate to metric units. Rounding-off of figures may result in minor computational discrepancies, where this happens it is not deemed significant. In West Africa (Damang and Tarkwa) the Mineral Resources and Mineral Reserves were determined using a gold price of US$1,400/oz and US$1,200/oz, respectively
1 Managed, unless otherwise stated
2 Excludes Asanko gold mine, pending completion of PFS