Rio Tinto has reduced its mineral resources estimate for the Argyle diamond mine in Western Australia.
The miner said in a statement that estimated mineral resources - the volume of material that can be extracted for economic purposes - fell last year.
The miner cut its estimate by 66 percent to 15 million tonnes in 2016.
It said this was due to an “ongoing review of potential mine-life extension options and restricts reported resources to that component of the known mineralization which may be developed, mined and processed within the current operational mine life".
Rio Tinto pointed out that current mining plans will continue as scheduled. Production at the Argyle mine is due to continue until 2021.