than 8,000 years of global mine production. Porphyry deposits represent an important resource of copper; however, they are also important sources of gold and molybdenum – with porphyry deposits being the dominant source of the latter. In general, porphyry deposits are characterized by low grades of ore mineralization, a porphyritic intrusive complex that is surrounded by a vein stockwork and hydrothermal breccias. Porphyry deposits are formed in arc-related settings and are associated with subduction zone magmas. Porphyry deposits are clustered in discrete mineral provinces, which implies that there is some form of geodynamic control or crustal influence affecting the location of porphyry formation. Porphyry deposits tend to occur in linear, orogen-parallel belts (such as the Andes in South America). There also appear to be discrete time periods in which porphyry deposit formation was concentrated or preferred. For copper-molybdenum porphyry deposits, formation is broadly concentrated in three time periods: Palaeocene-Eocene, Eocene-Oligocene, and middle Miocene-Pliocene. For both porphyry and epithermal gold deposits, they are generally from the time period ranging from the middle Miocene to the Recent period, however notable exceptions are known. Most large-scale porphyry deposits have an age of less than 20 million years, however there are notable exceptions, such as the 438 million-year-old Cadia-Ridgeway deposit in New South Wales. This relatively young age reflects the preservation potential of this type of deposit; as they are typically located in zones of highly active tectonic and geological processes, such as deformation, uplift, and erosion. It may be however, that the skewed distribution towards most deposits being less than 20 million years is at least partially an artifact of exploration methodology and model assumptions, as large examples are known in areas which were previously left only partially or under-explored partly due to their perceived older host rock ages, but which were then later found to contain large, world-class examples of much older porphyry copper deposits. Magmas and mantle processes In general, the majority of large porphyry deposits are associated with calc-alkaline intrusions, although some of the largest gold-rich deposits are associated with high-K calc-alkaline magma compositions. Numerous world-class porphyry copper-gold deposits are hosted by high-K or shoshonitic intrusions, such as Bingham copper-gold mine in USA, Grasberg copper-gold mine in Indonesia, Northparkes copper-gold mine in Australia, Oyu Tolgoi copper-gold mine in Mongolia and Peschanka copper-gold prospect in Russia. The magmas responsible for porphyry formation are conventionally thought to be generated by the partial