Supergiant porphyry Cu deposits are failed large eruptions

Abstract Porphyry copper deposits, the principal natural source of Cu and Mo, form at convergent margins. Copper is precipitated from fluids associated with cooling magmas that have formed in the mantle and evolved at variably deep crustal levels, before raising close to the surface where they exsolve fluids and copper. Despite significant advances in the understanding of their formation, there are still underexplored aspects of the genesis of porphyry copper deposits. Here, we address the role played by magma injection rates into the shallow crust on the formation of porphyry copper deposits with different copper endowments. Using a mass balance approach, we show that supergiant porphyry Cu deposits (>10 Mt Cu) require magma volumes and magma injection rates typical of large volcanic eruptions. Because such volcanic events would destroy magmatic-hydrothermal systems or prevent their formation, the largest porphyry Cu deposits can be considered as failed large eruptions and this may be one of the causes of their rarity.