Surface mining digs up a lot of earth and rock. After the desired ore is separated, where do the earth and rock mined go?
In opencast mining it is dumped on a huge spoil heap, and if the company is environmentally conscientious or wants to avoid penalties, it is used to fill in the hole left when the mining is finished. With underground mining it is also dumped on spoil heaps, and as it is not practical to infill the mine workings, in best practice the spoil heaps are later landscaped, or at least restored to nature so they are no longer unsightly and could become a nature reserve. Some mining companies are reckless with their waste and dump it into lakes and rivers, potentially causing pollution incidents, though not all mining waste is hazardous.