Volcanic successions associated with ore deposits: facies characteristics and ore-host relationships

Four important ore deposits are commonly hosted in volcanic successions: volcanic-hosted massive sulfide (VHMS) deposits, komatiite-hosted nickel sulfide deposits, epithermal gold silver deposits, and kimberlite-hosted diamonds. There are different reasons why these ore deposit types occur in volcanic successions. The occurrence of VHMS deposits and komatiite-hosted nickel sulfide deposits in volcanic rocks reflects the strong genetic connection between the volcanism and the ore-forming processes. Such a connection may also link epithermal gold silver deposits with contemporaneous volcanism, both being products of high heat flow and extension. However, the connection does not always exist for epithermal gold silver deposits because some of these deposits are significantly younger than the host volcanic succession, or the host succession is not volcanic. In the case of kimberlite-hosted diamonds, kimberlite magmas serve as the medium for transporting diamonds from the mantle to the Earth's surface; the diamonds are not generated by the host kimberlite magmas nor by the processes that produced those magmas. A fifth important ore deposit type, porphyry copper gold molybdenum deposits, typically occurs in volcanic arcs and may be hosted by volcanic successions. However, the magmatic-hydrothermal processes that produce these deposits operate exclusively subsurface, and venting of either the fluids or the magmas reduces the metal potential of the system (Pasteris, 1996). Hence, in general, there is no systematic relationship between porphyry deposits and volcanism even in cases where the host succession is volcanic or partly volcanic.