Calm has returned to Tembagapura mile 74, a PT Freeport Indonesia mining area, after a mob of dozens swept through the site Sunday evening, looting ore while leaving property damage in their wake. No casualties were reported, police said; an investigation is underway to determine the cause of what appeared to be a coordinated attack.

Freeport Indonesia spokesman Karel Luntungan told The Jakarta Post some 70 people, all non-employees, vandalized assets including 13 company vehicles, a security post and concentrate tanks and stole an undetermined amount of ore concentrate. Mine security and local law enforcement restored order in two hours, according to company representatives, and several rioters were arrested.

Papua Police spokesman Sr. Commissioner I Gede Sumerta Jaya confirmed that “after entering the site, the group vandalized passing vehicles and the office, scaring the employees and sending them fleeing.”

Freeport Indonesia, which runs the Grasberg mine, one of the world’s top copper-gold sites, is a subsidiary of Phoenix-based Freeport McMoran Copper and Gold Inc.

Indonesia mining industry officials said they are close to completing their probe into a May 14 cave-in at Freeport’s Grasberg mine that killed 28 miners and injured 11 in one of the worst mining accidents in the archipelago’s recent history. The collapse, along with a separate unrelated fatality, prompted a full closure of Freeport’s site—to be followed by a three-month government investigation of all Indonesia’s underground mine sites.

After a meeting with independent investigators, Energy and Mineral Resources Minister Jero Wacik said this week that “several items still need to be completed” involving the collapse in the training tunnel at Grasberg in remote West Papua.

The stoppage also prompted a force majeure declaration, according to a statement, resulting in a company loss of 80 million copper lb and 80,000 gold oz so far; PT Freeport will book losses of 3 million lb of copper and 3,000 oz of gold daily until operations resume.