Diagram from ITAM Gold by the Minerals Council of Australia. Gold in Porphyry Deposits Gold and copper are found in ore bodies associated with porphry. The term is from a Greek word for purple dye and was first applied to a purple-red rock with phenocrysts of alkali feldspar that was quarried in Egypt. Diagram from ITAM Copper by the Minerals Council of Australia. This type of deposit forms beneath stratovolcanoes and is associated with subduction zones .
Erosion strips off overlying rocks to expose the mineralization.
This requires large amounts of rock to be mined, often in open pits. Gold in Epithermal Deposits Epithermal refers to mineral deposits that form in association with hot waters. The deposits form within 1 km of the surface and water temperatures are about 50-200 degrees C. Shallow bodies of magma supply heat. The rising hot water carries dissolved gold and other elements. The water boils about 300 m below the surface and hydrogen sulfide gas escapes.