Ore Deposits and Weathering

ORE DEPOSITS AND WEATHERING

Rock weathering can concentrate certain minerals in soil that was oxidized from weatherized rocks. This is cool because you can find clusters of metals, regoliths or laterites, soils that have had this happen. Aluminum oxides and nickel oxides can become concentrated, but only if other metals have been washed away. Bauxite is found in tropical areas and is high in aluminum. This is where most of the aluminum in the world comes from. Nickel laterite can be found in the same types of environments.

Weathering can remove the sulfur from sulfur mines. Many metals are in the ground as metal sulfides. If you wash the sulfur out, you get the metals out of the ground in more usable ways. This means that nature does most of the work in making these usable. Iron pyrite is essentially iron sulfide. If you expose it to light and water, the sulfide part goes away and you get rust plus a sulfate. The water left behind is more acidic so it more readily leaches metals out of the rock.

Weathered pyrite by itself is not useful economically but if you weather it, you get gossans, which are orange or red-stained rocks on exposed rock surfaces. Gossans aren't useful either but they can herald spots where more valuable mineral ores are located. Acidic streams are also clues to the presence of something potentially valuable.

Gold and copper are mined when the sulfides are stripped away in weathered rocky areas. Silver, zinc, and lead are cheaper to refine when they come out of the ground as sulfides rather than oxides. Now you see how complicated it can be to find these natural resources and why geology can help you do this more efficiently.