Open-pit mining is a kind of surface mining. Mining companies choose this way to get rocks and minerals out of the ground because it is the easiest and cheapest way to do it. Open-pit mining is only used if the rocks or minerals are close to the surface of the land or if a normal tunnel-type of mine isn't possible.
At first, a geologist examines and tests the land to be mined. He will also check the site for what it will do to the environment. Even before they start to mine it, the scientists know the value of the rock/minerals below the surface and how much it will cost to dig them up. Mining companies make plans to get as much out as they can for their money. The plans and the amount of money it will cost to mine the area will change over the years because prices of rock and minerals change.
Once the plan is decided, the top layers of the land are removed. After that, layer after layer is taken away until the rock or mineral is visible. This is taken out, processed when it needs it, and sold. Taking away layer after layer of land creates a gigantic, open hole [or pit] that keeps getting deeper and deeper until there is nothing left to bring out. Explosives [like dynamite] are used when the miners want to get large blocks of materials out of the earth. The picture above shows how an open pit looks.
Most of the time, when the mining company is done with it, the pit is used as a landfill. A landfill is used as a dump to get rid of our garbage. When it is filled with garbage, it is covered over with layers of dirt. After the garbage rots a long time, the land can be used again.