Sedimentary exhalative deposit

Sedimentary exhalative deposits (SedEx deposits) are ore deposits which are interpreted to have been formed by release of ore-bearing hydrothermal fluids into a water reservoir (usually the ocean), resulting in the precipitation of stratiform ore.

SedEx deposits are the most important source of lead, zinc and barite, a major contributor of silver, copper, gold, bismuth and tungsten.

The palaeoenvironmental and palaeogeologic setting of these ore deposits sets them apart from other lead, zinc or tungsten deposits which generally do not share the same source or trap morphologies as SedEx deposits.

SedEx deposits are distinctive in that it can be shown that the ore minerals were deposited in a marine second-order basin environment, related to discharge of metal-bearing brines into the seawater. This is distinct from other Pb-Zn-Ag and other deposits which are more intimately associated with intrusive or metamorphic processes or which are trapped within a rock matrix and are not exhalative.

The process of ore genesis of SedEx mineralization is varied, depending on the type of ore which is deposited by sedimentary exhalative processes.

Alternately, SedEx deposits may be sourced from magmatic fluids from subseafloor magma chambers and hydrothermal fluids generated by the heat of a magma chamber intruding into saturated sediments. This scenario is relevant to mid-ocean ridge environments and volcanic island arcs where black smokers are formed by discharging hydrothermal fluids.

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