Deposit types

Kinds of ore body — patterns of mineralisation rather than rocks or places. A vein is a fracture that got filled; a porphyry deposit is alteration imposed on an intrusion.

• Epithermal vein

  Ore deposited from hot water in a fracture near the surface — where mercury, antimony and much of the world's gold and silver are found.

• Oxidised zone

  The weathered cap above a sulfide ore body, where air and water have rebuilt the ore into carbonates and oxides — and where the brightly coloured minerals come from.

• Porphyry copper deposit

  A whole intrusion shot through with copper at a fraction of a per cent — low grade, enormous, and the source of most of the world's copper and molybdenum.