Argyle's ore reserves were slashed 45% to 16 million tonnes at the end of 2017 versus a year earlier, or 38.5 million recoverable carats of diamonds, the company said in a statement.
Image credit: Rio Tinto
The decrease includes almost 5 million tonnes of ore that depleted during the year. It comprises a further 3 million tonnes due to reduced production outlook resulting from operational challenges in 2017, it said.
Rio Tinto also cut its price expectation for the mine for 2020 and 2021, resulting in a higher “economic shut-point” — the minimum volume it must produce per quarter for operations to be worthwhile. This, combined with adjustments to its estimates of future mining grades, shaved just over 5 million tonnes off its reserves.
The available reserves will enable Argyle operations to continue until 2020. The company could increase the estimate and extend the life span beyond that, depending on how the mine performs, it added.