Freeport-McMoRan has temporarily halted work at its Grasberg mine in Indonesia after four workers died in a vehicle collision at the site.
The workers were killed when their vehicle collided with a haulage truck at the mine, and a further five staff were injured in the accident.
Freeport's Indonesian unit PT Freeport Indonesia said in a statement: "PTFI is closely working with mine inspector from the Ministry of Energy and Mineral Resources in the investigation into the incident and full operation of the Grasberg Mine will only resume upon completion of internal socialisation of the accidents to all employees of Grasberg mine as part of safety procedure.
"As of now, activities will focus on the maintenance of the open pit mine."
This marks the second fatal accident this month, as another mine worker was killed when a boulder fell on top of him.
In May last year, the Indonesian Government had ordered the company to cease operations at the Grasberg mine after 28 mine workers were killed when an underground tunnel collapsed.
Freeport Indonesia spokesperson Daisy Primayanti said: "Safety is a priority at PTFI and we will be cooperating fully with the Ministry's officials to determine the cause of the incident.
"The entire PTFI family extends its most heartfelt condolences and prayers to the families of our late employees."
The latest incident comes after PT Freeport Indonesia agreed to pay export taxes and high royalties to the government in August, which imposed a ban on exports of copper concentrate for eight months.
In 2013, the Grasberg mine produced 885 million pounds of copper and 1.1 million ounces of gold.
Image: A collision at the Grasberg open pit mine has claimed the lives of four workers. Photo: courtesy of Alfindra Primaldhi.