Perth: Rio Tinto has lowered its estimate of the mineral resources available at its Argyle diamond mine in Australia, as the company reconsiders its plans to extend the project.

Estimated mineral resources fell 66 percent to 15 million tonnes in 2016, compared with the previous year, the miner said in a statement last week. Mineral resources are the quantity of material in a mine that has reasonable prospects for being extracted economically.

Previous estimates had taken into account the possibility of prolonging the mine’s planned lifespan, the company explained.

“As mine-life extension options are under ongoing review, the reported mineral resources have now been restricted to those parts of the mineralization which can be potentially developed, mined and processed during the existing mine life defined by the current underground operation,” the company said.

The reduction in resources does not affect the current plan for the mine, which would see production continue until 2021, the company added.