What is the waste material called that is left behind after the mineral is removed from ore rock?
1 Answer
Gangue is the term you are looking for.
Explanation:
In mining, gangue is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. It is thus distinct from overburden, which is the waste rock or materials overlying an ore or mineral body that are displaced during mining without being processed (Wiki).
Gangue minerals are usually closely associated with the mineral of economic interest and so both must undergo mineral processing to separate the good stuff from the economically "bad stuff". The more concentrated the mineral of value is in the overall rock, the least costly it is to extract and therefore, the most economic.
For example, say you have 10 tonnes of rock you have mined for copper that has an ore grade of 10%. This means you only get 1 tonne of copper and 9 tonnes of gangue that you have to separate and get rid of (this is only an example - in the real world, 10% copper ore would be very high grade).
As mining proceeds, the grade of ore in the mine might drop to say, 5% which then means you have 9.5 tonnes of waste gangue to 0.5 tonnes of valuable ore. At some point, the grade gets low enough that its not worth mining and the mine will be closed or suspended.
