VOLCANOGENIC MASSIVE SULFIDE DEPOSITS: TOWARD A NEW OCCURRENCE MODEL

The U.S. Geological Survey is preparing for a new national assessment of undiscovered mineral resources by creating updated and comprehensive mineral deposit models for a broad variety of mineral deposit types. Volcanogenic massive sulfide (VMS) deposits are very significant present and historical resources of Cu-Pb-Zn-Au-Ag, are an exploration focus in several areas, and have potentially deleterious environmental footprints. The USGS VMS deposit occurrence model provides a comprehensive review of deposit occurrence and ore genesis, and fully integrates recent advances in understanding active seafloor VMS-forming environments.

Highlights of the VMS deposit model include: the relationships between lithologic deposit classification and tectonic settings, the role of physical volcanology in controlling localization of mineralization, unique characteristics and genesis of exhalites related to seafloor hydrothermal vents, new emerging approaches to using hydrothermal alteration assemblages as vectors to mineralization, current theories of deposit formation, isotope and trace element systematics of mineralizing processes, and new observations on weathering and environmental effects of VMS deposit mining. In addition, we provide a comprehensive examination of igneous, metamorphic, and sedimentary host lithologies, hypogene and supergene mineralization, geophysical characteristics, petrology of host lithologies, isotope and trace element systematics of host rocks, and evolving theories of deposit formation.

Research on VMS deposits in the last 30 years, since the discovery of black smokers and associated sulfide chimneys on the seafloor, has been and continues to be ground-breaking and productive. VMS research is enhanced because of the huge variety of active and observable processes on the modern seafloor, which makes this field a vibrant focus of hydrothermal research. Examples of newly emerging concepts include: (1) direct observation of the role of magmatic fluids in seafloor vent fluids and using advanced fluid inclusion methods on ancient deposits, (2) understanding of exhalite deposits based on consideration of seafloor hydrothermal plumes, and (3) new awareness and understanding of hydrothermal systems hosted in ultramafic rocks.