Classification and Key Characteristics of VMS Deposits

Summary• Cu-rich deposits form in primitive, basalt-dominant oceanic arcbackarcsystems: deep water• Zn-rich deposits form in epicontinental, felsic and sedimentdominantoceanic backarc systems• Subvolcanic intrusions are more common, and are commonlymafic or composite• High-T reaction (ep-ab-act-qtz) zones are metal depleted withsilicified caps (or carbonate in shallow-water systems): Theseprovide good indictors of potentially productive regions• Alteration pipes occupy synvolcanic faults: usually verticallyextensive, Mg-metasomatized, Na ± Ca depleted and Cu-rich• Cu-rich VMS typically form as mounds on the paleo-seafloor;extensive metal redistribution may result in Cu-rich core, Au ±Ba cap (post PC)• Zn-rich VMS form sub-seafloor, some metal redistribution,copper in limited stringer zones, Au-rich (cap), oxidized distalexhalite• Laterally extensive “exhalite” (chert or pelite) containsanomalous metals and conserved elements, useful as vectorsto ore