Its decommissioning , Caldas ' mine pit .
Which is approximately 180 meters ( 590 feet ) deep and contains a diameter of about 1,200 meters ( 3,937 feet ) , has turned into a giant lake of acid water .
Since its decommissioning , Caldas ' mine pit , which is approximately 180 meters ( 590 feet ) deep and contains a diameter of about 1,200 meters ( 3,937 feet ) , has turned into a giant lake of acid water .