Currently viewing: Regional overview / Next: Damang gold mine
|*||90% attributable to Gold Fields|
|#||Excludes Asanko gold mine|
|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|
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.
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.
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|
|Total West Africa operations||82,286||14.45||71,589||11.03|
|Exclusive of grade control drilling and Asanko JV drilling|
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:
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.
WEST AFRICA REGION SUMMARY OF THE MINERAL RESOURCE AND MINERAL RESERVE ESTIMATES1, 2
|Mineral Resources||Mineral Reserves|
|Measured, Indicated and Inferred||Tonnes
|Proved and Probable||Tonnes (Mt)||Grade (g/t)||Gold
|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|