The following is from "Sedimentary Exhalative (SEDEX) Deposits" by W. Goodfellow and J. Lydon, 2007 in Mineral Deposits of Canada:

SedEx deposits are typically tabular bodies composed predominantly of Zn, Pb, and Ag bound in sphalerite and galena that occur interbedded with iron sulphides and basinal sedimentary rocks, and that were deposited on the seafloor in associated sub-sea floor vent complexes from hydrothermal fluids vented into mostly reduced sedimentary basins in continental rifts.

Sub-types of SedEx deposits include Broken Hill type and those that formed below but near the sea floor (e.g. Irish-type deposits). The Irish type of SedEx deposits is hosted predominantly by carbonate rocks and these deposits, either individually or collectively, may show characteristics of both seafloor deposition and epigenetic features typical of Mississippi Valley-type (MVT) deposits.

It is generally recognized that, especially at the deposit scale, no matter the criteria used to define a SedEx deposit, there is a continuum of characteristics between SedEx and VMS deposits on the one hand (Besshi deposits), and SedEx and MVT deposit on the other hand. Both SedEx and MVT deposits occur within marine platforms of thick sedimentary basins and are thought to result from the migration of basinal metalliferous saline fluids, whereas VMS deposits occur in submarine volcanic-sedimentary sequences and are formed from convective hydrothermal fluids driven by, and/or magmatic fluids from, a sub-volcanic magma body.

The video on VMS and SedEx has been provided by Andrew Jackson of Sprott Global Resource Investments Ltd.

Download (Sedex-deposits.ppt)

SedEx References (free):


  • SEDEX - Sedimentary Exhalative Deposits
    (1991) MacIntyre, D.G., in Ore Deposits, Tectonics and Metallogeny in the Canadian Cordillera, Paper 1991-4, provided courtesy of the British Columbia Geological Survey, British Columbia, Canada.
  • Sediment-Hosted Stratabound Copper Deposit Model
    (2010) Hayes, T.S., Cox, D.P., Piatak, N.M. II, and Seal, R.R., Chapter M of Mineral Deposit Models for Resource Assessment: U.S. Geological Survey Scientific Investigations Report 2010–5070–M, 147 p.