Copper mining. The main stages. - SchoolScience.co.uk
They occur in both sedimentary and igneous rocks. The outer 10km of the crust contains 33g of copper for every tonne of rock. This is not enough to make it commercially viable to extract the rock. Copper mines are only set up where there is more than 5kg of copper per tonne of rock (0.5% by mass). Ideally, the figure should be closer to 2%.