The company said the worker died following a “serious incident” on site.
“The company will provide all the necessary support for the employee's family and colleagues during this difficult time,” a Rio spokesman said.
Police were informed of the accident just after midday yesterday and have travelled to site to investigate.
An inspector from the Resources Safety division of the WA Department of Mines, Industry Regulation and Safety is travelling to site today to begin an investigation.
This is the first mining fatality in Western Australia in almost a year. The last mining fatality was on July 28, 2016.