The study by A&B Mylec found that the 895 million tonne Mmamantswe project could yield two product streams: 200Mt of export-grade thermal coal and 100-150Mt of domestic power coal capable of supporting a 300-megawatt domestic power station.
Aviva chief executive Lindsay Reed said the results were “considerably above our expectations and were very positive for the project in the current energy fuel market”
With virtually no change to the 10Mtpa run-of-mine mine plan prepared by SRK Consulting, Mmamantswe could produce 3Mtpa of export thermal coal and 1-1.5Mtpa of domestic power coal with sufficient reserves for over 60 years, he said.
“The company retains the flexibility to lift production, thereby bringing forward the project’s cash flows.”
Two-stage processing of the Mmamantswe deposit is a viable option to deliver both export-grade 20-22 megajoule per kilogram and domestic-grade 13.5-16.5 gigajoule per tonne thermal products.
The whole-of-plant yield is enhanced by the two-stage washing process compared to the previous single-stage base-case scenario with recoveries lifted to 46%.
“The preferred process option combines coal from zones A, C and D in a single-feed stream for processing, greatly reducing the complexity of the plant resulting in lower capital, operating and maintenance costs,” Aviva said.
The conclusions assume that coal from Zone B is discarded as waste but notes that in-pit scalping of Zone B coal could deliver additional feed tonnes at an overall yield of greater than 30% and recommends further evaluation of this option.
If Zone B is discarded as waste, the effective strip ratio of the deposit would only increase from 1 bank cubic metre of waste per tonne of coal to 1.5bcm/t.
The A&B Mylec study was based on the 20-year preliminary mine layout prepared by SRK Consulting as part of the Mmamantswe scoping study completed in 2009.