By Leia Michele Toovey- Exclusive to
SedEx, or sedimentary exhalative deposits, are ore deposits
formed when hydrothermal fluids enter a water reservoir, such as
an ocean, and precipitate minerals. SedEx deposits are a
major source of minerals including copper,
- and the single most important source of
. SedEx deposits are high grade, with an average size of
approximately 70 Mt, and can host about 12 percent lead and zinc.
Depending on the deposit sub-type they also host variable amounts
of valuable by-products including copper, gold and silver.
SedEx deposits are easily distinguished from many other
deposit types by the fact that their formation is the result of
minerals being deposited through the discharge of metal-bearing
fluids into seawater. This is a strong contrast from other
deposit types that are formed as a result of some type of
intrusive or metamorphic process.
Classically, SedEx deposits are considered lead-zinc deposits,
due to the fact that lead and zinc are generally the most
prevalent mineral. As mentioned earlier, these deposits can still
host significant amounts of other minerals, particularly
copper, gold and silver. In addition, there are a
variety of other valuable SedEx deposits. For example, most
of the world's barite deposits are considered to be SedEx
deposits. The supergiant deposits of
the Zambian Copperbelt are considered to be SedEx-style
copper deposits. Some geologists consider the gold deposits of
Nevada to be formed by SedEx processes (this concept is
controversial because most gold is clearly of later epigenetic
There are variances in the manner of how SedEx deposits are
formed; however, the general process is the same. They are formed
when ore bearing fluids discharge onto a seafloor and mix with
seawater. When the two fluids mix, a variety of chemical
processes take place that result in the precipitation of minerals
on the seafloor. These deposits are lain down congruent with the
stratigraphy of the seafloor, and are fine grained and finely
laminated- characteristics of "sedimentary deposits."
Concentrated amounts of minerals can be found in "trap sites,"
which are depressed areas of the ocean floor where the
minerals may settle. Occasionally, mineralization develops
in the faults and feeder conduits that fed the mineralizing
There are a few different mechanisms that may create the
mineralizing fluids that form SedEx deposits. They may be from
magmatic fluids from sub seafloor magma chambers and
hydrothermal fluids generated by the heat of
a magma chamber intruding into saturated sediments.
Some geologists theorize that seawater convection cells play a
big part in SedEx fluid source. These sea-water convection
cells contain dissolved metals from the sediments they passed
through before being heated and forced to the surface. In the
case of these sea-water convention, the mineral types found in
the SedEx deposits are linked to the depth at which the
mineralizing fluids originated. Fluids that come from a shallow
depth are rich in
, fluids that penetrate deeper pick up lead and zinc.
Copper is picked up by fluids that reach an even greater
The Zambian Copperbelt Province
The Zambian Copperbelt Province is not distinctly composed up
of SedEx deposits; like most valuable mineral districts, the
region is composed of a variety of deposit types including SedEx,
. The Zambian Copperbelt is one of the world's greatest copper
provinces. Development of the Copperbelt commenced in the 1930s
and up to 1990 mining had produced 1122 Mt of ore grading 2.7%
Cu, producing over 25 Mt of copper metal. Total Copperbelt
reserves are estimated to be in excess of 2000 Mt. The area
witnessed a resurgence in exploration interest following the end
of socialist rule in Zambia- which in turn led to the
privatization of the Zambian copper mines.
Miners and explorers with interests in SedEx
Selwyn Resources Ltd.
Selwyn Resources Ltd. is a publicly traded, Canadian base
metals exploration and development company. The company's core
project is the world class Selwyn Project, located in eastern
Yukon. The Selwyn Project has reactivated the Howard's Pass
zinc-lead district, and since 2005 the company has invested
approximately $70M to define the Selwyn deposit as one of the
largest undeveloped zinc-lead deposit in the world.
Avannaa Resources Ltd.
Avannaa Resources is a mineral exploration company, founded in
2006 and exclusively focused on Greenland. Avannaa is targeting
sedimentary hosted copper of the Zambian copper-belt style in
Rox Resources Ltd.
Rox Resources is an Australian exploration company with
projects in the Northern Territory of Australia, including the
Myrtle zinc-lead project and the Marqua phosphate project. A
SedEx style deposit has been identified by Rox at the Myrtle
prospect, where an Inferred Mineral Resource of 43.6 million
tonnes grading 4.09% zinc and 0.95% lead has been delineated to
JORC Code standards.
Sedimentary Exhalative Deposits
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