Mining giant PT Freeport Indonesia (PTFI) will close its open-pit mine this year and will soon fully operate an underground mine, which features a 500-kilometer tunnel the company had been building since 2015.

The company has started to produce gold and silver from Deep MLZ.

“It is not a straight [tunnel]. It has branches [and] there are mines that are spiral deeper into the ground,” PTFI vice president corporate communication Riza Pratama said as quoted by on Sunday.

He was speaking to officials from the Energy and Mineral Resources Ministry who visited the underground mine last Friday.

Riza explained that the air inside the underground mine was clean because each corner of the mine had been equipped with large fans that ensure air flow by pumping out the air from inside the mine and bringing in fresh air from outside.

At about 7 kilometers from the entrance, Riza said the walls of the 7-meter-wide and 10-m-high tunnel were made of concrete.

“This location is in safe and stable condition,” he added.

Meanwhile, light sources inside the tunnel were bright enough to support the operation of heavy equipment. The underground mine is also equipped with a mosque and church, toilets and clean water facilities.

Currently, PTFI has 7,096 permanent employees, but including contract-based workers and vendors, the figure goes up to 30,542 people. (bbn)