I'm working on an artice in which the goal is to propose an exploration key for a deposit.
In geologic perspective, the mine is in the limestone and lime_ dolomite stone.
The type of this deposit is SEDEX. the questions are :
1. Are there any SEDEX deposits in which the hydrothermal solution put the mineral on joints and fractures of limestone and lime_ dolomite stones, around the world?
2. Are the faults proposing to be exploration keys for recognition of this type of deposit?
Hi there,
to me, this doesn't actually sound very much like SEDEX at all but much more like MVT (Mississippi-Valley-Type) which commonly occurs in calcareous rocks far away from any igneous activity as both replacement and space-filling bodies. If fissures are present, minerals will of course be precipitated in them. What makes you think it is SEDEX? Are there any massive sulphide bodies which have obviously been deposited by exhalative processes? Is there any evidence of discharge of solutions onto the sea-floor or of sub-sea-floor processes? SEDEX is commonly associated to more siliceous sedimentary rocks. If there is confusion about the big types of sediment hosted sulphide deposits, I recommend Robb (2005) Introduction to ore-forming processes. An excellent introductory text.
The key of SEDEX (sedimentary exhalative) deposits is barite!. MVT deposits don't usually have much barite, and regarding the sulfides textures, are rather different.
Most SEDEX have very large barite accummulations that cover Pb-Zn sulfides above the redox boundary, and as pointed out above by Max, these hydrothermal solutions are expelled from sub-sea extensional faults (i.e., opening basins, continental margins...). The faults are the counduits for fluid expulsion (i.e., the feeder), and these might be shown in potential geopphysical data, as well as the barite accummulations due to the large specific gravity of Ba.
You should expect precipitation of metal cations along the faults-fractures network but most of the ore can actually be spread over the seafloor at the time of exhalation-sedimentation. If your're lucky to find an undisturbed non-deformed sedex deposit, good for your!. In many cases, subsequent deformation remobilises the ores and accumulates them along fault zones or the hinges of folds (same for VMS deposits for instance).
Have a look to this link by Goodfellow from the Geological Survey of Canada:
unalmed.edu.co/rrodriguez/VMS/SEDEX.doc
Another nice reference is the special volume of Economic Geology devoted to the Red Dog Pb-Zn-Ba-Ag deposit of the Brooks Range (Arctic Alaska ).
http://econgeol.geoscienceworld.org/content/99/7.toc
OR this one:
http://econgeol.geoscienceworld.org/content/105/3/593.full
Pablo
Dear colleague,
first and foremost your deposit is a carbonate-hosted mineral deposit. You might call it MVT if you like. What is the element association and mineral assemblage, respectively, like? It is decisive to see what the ore traps look like, terms like fractures, faults are not very distinctive and make us speculate too much. In DILL, H.G. (2010) The “chessboard” classification scheme of mineral deposits: Mineralogy and geology from aluminum to zirconium.- Earth Science Reviews, 100: 1-420. There are several color images of carbonate-hosted Pb-Zn-Cu ore types and cross sections. Which of them comes next to yours. Then I can give you some further information. Currently, it seems to be too much of a matter of conjecture.
Excluding barite from MVT or carbonate-hosted deposits is not correct. You find in the cave-in-rock-type a Ba-F-Pb-Zn-(Ag) mineral assemblage, in the Irish type a Ba-Pb-Zn-As-, in the Silesian-type (Ba)-Pb-Zn-(As)- and in the Tunisian-type a Pb-Zn-(Sr-Ba) (celestobarite) mineral assemblage. Some of the largest concentrations of barite are found in calcareous host rocks. It is correct that SEDEX (Rammelsberg, Meggen) have large barite lenses associated with the sulfides. Even VMS deposits have barite- see e.g., Kuroko.
I hope that for the moment it will help you and I am looking forward to your constraints on the ore-type.
Best regards
Harald G. Dill
not all SEDEX districts have barite. In Selwyn Basin, those in the MacMillan Pass district do have barite. However, there is no barite in the (larger, tonnage-wise) Howards Pass district.
Jan: this paper does not give a useful explanation, but discusses a stratified Devonian ocean as a prerequisite for SEDEX (and possibly HEBS) deposition
Article Photic-zone euxinia and anoxic events in a Middle-Late Devon...
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