Exploration guidelines for Volcanogenic Massive Sulphide deposits by Dr Thomas Monecke
G01, School of Earth Sciences, UCD, Belfield, Dublin 4
The next UCD School of Earth Sciences seminar will be presented by Dr Thomas Monecke from Colorado School of Mines on 'Exploration guidelines for VMS deposits'.
Volcanogenic massive sulphide deposits (VMS) are stratiform or stratabound accumulations of base metal sulphides that formed in submarine settings on or immediately below the seafloor by precipitation from 250–350°C, dominantly seawater-derived hydrothermal liquids. Based on the study of VMS deposits hosted in ancient volcanic successions and their modern seafloor analogues, processes involved in the formation of these deposits are well understood. It has been shown that VMS deposits form mostly in zones of rapid, but short-lived extension within intra-oceanic, transitional, and continental margin arcs. Many of the large VMS camps worldwide are hosted by bimodal volcanic successions. Extension results in crustal thinning and mantle depressurization, with mantle-derived mafic magmas being injected in the thinned crust. Ponding of mafic magmas causes partial melting of the crust, generating felsic melts. In many VMS camps, evidence for synchronous mafic and felsic volcanism is recorded by compositional shifts within the stratigraphic interval hosting the deposits and the occurrence of magma mingling and mixing textures in shallow intrusions and lavas. In many cases, VMS deposits occur in clusters along discrete stratigraphic intervals. While hydrothermal fluid flow is a universal process of heat transfer within the crust, the presence of such favourable stratigraphic intervals suggests that deposit formation is tied to particular processes in the regional tectonic and basin evolution. At the local scale, VMS deposits typically occur at topographic highs, marking the location of volcanic vents. Careful volcanic facies analysis has shown that VMS deposits always occur within vent-proximal volcanic facies associations. In many cases, a particular style of felsic volcanic centres is recognized as being particularly favourable. The location of volcanic centres hosting VMS deposits is controlled by syn-volcanic faults, which also form conduits for the hydrothermal fluid flow. Hydrothermal alteration halos associated with these structures represent important vectors to ore. In volcanic successions dominated by volcanoclastic rocks, massive sulphides are commonly formed by sub seafloor replacement, while mound-style deposits formed on the ancient seafloor are more common in flow-dominated volcanic successions. In combination with geophysical and geochemical methods, these key elements of the VMS model can be used to guide exploration for massive sulphides in ancient volcanic successions.
Thomas Monecke is an economic geologist who specializes in the formation of base and precious metal deposits in modern and ancient volcanic arcs. He has more than 25 years experience in geological research and mineral exploration and has authored or co-authored approximately 80 journal papers, book chapters, government publications, and field guides during that period. Thomas graduated from the University of Freiberg, Germany, with a M.Sc. in 1996. He obtained his Ph.D. from the same university with his doctoral thesis focusing on the anatomy of a volcanic-hosted massive sulphide deposit in northern Australia. Between 2002 and 2008, Thomas conducted post-doctoral research at the Institute of Marine Sciences in Kiel, Germany, the University of Ottawa, and the Geological Survey of Canada on modern and ancient gold-rich volcanic-hydrothermal systems. In 2006, Thomas received the Waldemar Lindgren Award of the Society of Economic Geologists. He joined the Colorado School of Mines in 2008 where he teaches economic geology. Thomas runs a large research group and supervises graduate student working on hydrothermal ore deposits around the world.
The presentation will begin at 4pm in G01 of the School of Earth Sciences.
All welcome to attend.