Three diagrams showing the magmatic stages in the formation of a porphyry ore deposit. The first diagram shows emplacement and crystallization of hydrous granodioritic magma and separation of watery fluid. Consequent expansion produces fracturing and escape of fluids. At a high level, transformation of the fluid to steam gives rise to explosive fracturing. The second diagram shows rapid crystallization of the porphyritic intrusion and the escape of aqueous magmatic fluids through fracture zones. Heat from the intrusion convects hydrothermal fluids derived from the magma itself and from meteoric groundwater drawn in from surrounding rocks. The final diagram shows the distribution of sulphide mineralization typical of a porphyry copper deposit.