SedEx Deposit.pptx

Hydrothermal Deposits Sedex

1. SedEx Deposits Sedimentary Exhalative Deposits

2. What are SedEx deposits? 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,  silver ,  gold  and  tungsten – and the single most important source of  lead  and  zinc .  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.

3. Occurrence in world

4. Mineralization types Classically, SedEx deposits are considered lead-zinc deposits, due to the fact that lead and zinc are generally the most prevalent mineral. 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 Copper belt 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 origin.)

5. Formation and processes 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 system.

6. Towards a SEDEX model

7. Formation continues 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  iron  and  manganese , fluids that penetrate deeper pick up lead and zinc. Copper is picked up by fluids that reach an even greater depth.

8. Conditions pre Requisite to form Firstly, SEDEX deposits are generally formed in fault-bounded sedimentary basins on continental crust rather than in volcanic piles on oceanic crust. For SEDEX deposits, the basin needs to accumulate several kilometres or tens of kilometres of oxygen lacking sediment , usually shells. Secondly, the heat that drives the hydrothermal system is dominantly from depth and burial rather than a felsic intrusion although there may be a deep mafic intrusion. For the same reason the metals are not derived from felsic magmas, so copper is largely missing, instead the metals are purely derived from leaching of the sediments themselves and lead, zinc and silver dominate instead. To form SEDEX deposits, you require the deep sedimentary basins so distribution is more limited than that of VMS deposits.

9. Comparison of VMS and SedEx Both types of deposits are products of submarine hot-springs VMS deposits are volcanic-hosted, dominantly copper and zinc. SEDEX deposits are dominantly sediment-hosted, they are dominantly zinc and lead they are bigger but generally less common than the VMS deposits In VMS deposits the metals are usually spatially zoned, with copper near the vent and then zinc and lead more distant to that These deposit types are major global sources of base metals, particularly zinc VMS deposits are some of the last deposits to from in terms of the upward migration of metals and mineralization drops out of the fluid either right at the surface of the seafloor or in a few tens of meters from that. So, they form at even shallower depths than shallow epi thermals. SEDEX deposits are not directly related to volcanic activity and so don’t fit in directly to this framework. However, their mode of formation is just similar. The main difference between the VMS and SEDEX deposits, it’s that VMS deposits are dominantly copper and zinc rich and associated with volcanic activity. Whereas SEDEX deposits are dominantly lead and zinc rich and rely mainly on the heat caused by the depth and burial in deep sedimentary basins to drive the hydrothermal system.

10. Characteristics and features of SedEx Deposits Sedex are dominated by Zn-Pb (with lesser Cu, But commonly Ba and Ag) Metal association and are also related to hydrothermal fluids venting onto the sea floor, but without an obvious or direct link to volcanism. Many of the large SEDEx deposits of the world are Proterozoic in age, although several examples, such as Red Dog also formed in Phanerozoic times. Although there is Generally no Spatial or temporal link between Sedex and VMS Deposits, it is widely held that they represent a continuum and are conceptually linked by the fact that they formed by the same basic processes. These processes are active and can be Studied in modern day environments as discussed below. The notion of a continuum between VMS abd SEDEX deposit types is However, contentious and readers should be Wary of over interpreting the generic link between the two deposit types.