Geologically the flat lying nature, regionally extensive and often thin undulating mineralised zones make this ore body suitable for the use of surface mining equipment. With a view to minimising stripping costs and maximising ore recovery, a great advantage of the deposit is that most of the ore is near surface with secondary ore types lying at surface and above 15 metres. It is intended to utilise a mining contractor to mine the waste material above the ore horizons using conventional mining techniques. Two companies, Wirtgen and Vermeer have been approached to provide costs based on testwork of samples.
Vermeer (left) and Wirtgen (right) surface miners
During the technical study a series of optimisations and schedules were conducted on the 2012 resource model. Quotations for a bulk prestrip, mining with surface miners and truck haulage to the ROM were received from several mining contractors. Vermeer and Wirtgen also evaluated productivity and costs from the testwork undertaken on various lithologies expected during the operations.
The proportion of material to be mined is approximately;
- 64% mudstone and carbonaceous mudstone,
- 14% siltstone and fine sandstone,
- 12% sandstone and arkosic sandstone and
- 5% conglomerate and breccia and
- 5% surficial material.
These rock types have variable Cerchar abrasiveness (CAI) from slightly abrasive to very abrasive with an overall average of 2.0 (medium abrasiveness) and hardness’s (UCS) which average from 10 to 55Mpa. Occasional (<1%) very high UCS values of >100Mpa have been observed from thin sandstone units. With this range of UCS values surface mining costs are low with high productivity.
Haulage distances from the pits to the ROM vary from 1.3 to 8.3km and a study is to be undertaken to see if a central conveying system may offer benefits over truck haulage. The in-pit resources were scheduled using the Minemax Scheduler and produced a 16 year mine life and an 18 year process life with:
- Total process feed of 156,599,369 tonnes at a grade of 191ppm U3O8,
- Of which 102,821,163 is direct feed to the leach pads,
- 53,778,206 tonnes is reclaimed from stockpiles in the latter years of the Project,
- The Indicated resources amount to 29,257,991 tonnes averaging 209 ppm U3O8 while the Inferred resources total 73,563,172 averaging 164 ppm U3O8
- The proportion of Indicated to Inferred in the direct feed to process is currently 28.5% to 71.5%.
A-Cap plans to conduct a surface miner trial on site once the Letlhakane mining licence has been obtained.