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.
SedEx References (free):
- Geologic Criteria for the Assessment of Sedimentary Exhalative (Sedex) Zn-Pb-Ag Deposits
(2009) Emsbo, Poul, U.S. Geological Survey Open-File Report 2009−1209, 21 p.
- 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.
- The Importance of Oxidized Brines for the Formation of Australian Proterozoic Stratiform Sediment-Hosted Pb-Zn (Sedex) Deposits
(2000) Cooke, D., Bull, S. Large, R., and McGoldrick, P., Bulletin of the Society of Economic Geologists, Economic Geology, Vol. 95, No. 1, January-February 2000, provided courtesy of the Memorial University of Newfoundland and Labrador, 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.
- Sediment-Hosted Copper Deposits of the World: Deposit Models and Database
(2003 - revised June 2007) Cox, D.P., Lindsey, D.A., Singer, D.A., and Diggles, M.F., U.S. Geological Survey Open-File Report 2003-107, 53 p.
- Sediment-Hosted Zinc-Lead Deposits of the World−Database and Grade and Tonnage Models
(2009) Singer, D.A., Berger, V.I., and Moring, B.C., U.S. Geological Survey Open-File Report 2009−1252, 67 p.
- Descriptive Models, Grade-Tonnage Relations, and Databases for the Assessment of Sediment-Hosted Copper Deposits—With Emphasis on Deposits in the Central African Copperbelt, Democratic Republic of the Congo and Zambia
(2013) Taylor, C.D., Causey, J.D., Denning, P.D., Hammarstrom, J.M., Hayes, T.S., Horton, J.D., Kirschbaum, M.J., Parks, H.L., Wilson, A.B., Wintzer, N.E., and Zientek, M.L., U.S. Geological Survey Scientific Investigations Report 2010−5090–J, 154 p. and data files.