Police were called to the site, 130km from Port Hedland, at 6:30am WST yesterday morning after a man, believed to be in his 40s, was found dead.
A 30-year-old man is currently in custody and is assisting with the investigation.
Homicide Squad detectives from Perth were travelling to the mine site yesterday to continue with the investigation with local police and detectives.
Pilbara called a trading halt yesterday morning, citing an incident that needed investigating.
The company said the death was unrelated to mining operations.
The company is cooperating with the investigation and said it could not provide any further details.
Operations have been temporarily suspended to facilitate the investigation.
Pilbara managing director Ken Brinsden said he was extremely shocked and saddened by the events.
"At this difficult time our focus is on ensuring that our people are cared for and supported, while we continue to support the police investigation that is currently underway," he said.
"On behalf of Pilbara Minerals, I would like to express our sincere condolences to the affected people and their families."
Pilbara resumed trading this morning, rising 0.6% to A32.7c.