Freeport-McMoRan Copper & Gold Inc.’s Indonesian subsidiary declared a day of mourning after a cave-in at its massive Grasberg complex killed 28, prompting the mine’s closure along with a sweeping review of all Indonesia’s mining operations. The 28 deaths took place after a collapse at an underground classroom on May 14. Ten people were rescued and all of the dead have been recovered.

Memorial services have been held at PT Freeport Indonesia’s Jakarta office and its site—the world’s No. 2 copper mine—in remote West Papua. “We continue to grieve with the families even as we close this grim chapter,” Freeport Indonesia Director Rozik Soetjipto said in an emailed statement, according to Bloomberg News. “There is still much to do for us to provide the best care and support for the injured and the families of the bereaved.”

The Phoenix-based Freeport extracts 19% of its copper production and 90% of its gold output from its massive Indonesian mines, which are visible, unenhanced, from outer space.

Freeport CEO Richard Adkerson, who was on site, pledged due diligence to understand the mine’s integrity. “We had no concerns or fears about its safety, so that’s why we need to understand why this happened,” he said. “We’re undertaking a review of all of our underground activities right now. It’s our responsibility. There will be an independent review, and we will cooperate with it.”

Indonesian President Susilo Bambang Yudhoyono ordered a safety review of all mines in Indonesia—open pit and underground—while Mining Ministry Director Thamrin Sihite called the latest incident “one of the worst accidents in Indonesia.” The archipelago’s most recent comparable disaster took place when a 2009 West Sumatra coal mine blast claimed 31 lives.