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Jordi Fabre
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Joined: 07 Aug 2006
Posts: 4894
Location: Barcelona
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 Posted: Aug 19, 2009 02:54 Post subject: Volcanic-associated massive sulphide (VMS) deposits |
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| mohdgeo wrote: | Volcanic-associated massive sulphide (VMS) deposits occur throughout the world and throughout the geological time column in virtually every tectonic domain that has submarine volcanic rocks as an important constituent. VMS deposits are major sources of Cu and Zn and contain significant quantities of Au, Ag, Pb, Se, Cd, Bi, Sn as well as minor amounts of other metals.
As a group, VMS deposits consist of massive accumulations of sulphide minerals (more than 60% sulphide minerals) which occur in lens-like or tabular bodies parallel to the volcanic stratigraphy or bedding.
They are usually underlain by a footwall stockwork of vein and stringer sulphide mineralization and hydrothermal alteration (Figure 1). They may occur in any rock type, but the predominant hosts are volcanic rocks and fine-grained, clay-rich sediments. The deposits consist of ubiquitous iron sulphide (pyrite, pyrrhotite) with chalcopyrite, sphalerite, and galena as the principal economic minerals. Baryte and cherty silica are common gangue accessory minerals.
Classification
VMS deposits are classified with respect to host rock type and on the basis of ore composition. The host rock classification is a useful field system as it can be relates to the geological environment which can be determined from geologic maps. The major groups are:
1.felsic volcanic hosted - 50% of deposits - eg. Buttle Lake (Westmin - Vancouver Island, B.C.), Noranda
2.mafic volcinic hosted - 30% of deposits - eg. Anyox
3.mixed volcanic/sedimentary association - 20% of deposits - eg. Windy Craggy, Tatshenshini Area, B.C.
Compositionally, VMS deposits form two broad groups:
1.Cu-Zn - eg. Noranda, Windy Craggy, Britannia (Britannia Beach, B.C.)
2.Zn-Pb-Cu - eg. Buttle Lake
Economically significant quantities of Au and Ag may occur in all the above lithological andcompositional groups. There is only a poor correlation between the ore composition types and host rock type.
Another massive sulphide category - Pb, Zn deposits -forms in a sedimentary environment
VMS deposits tend to occur in districts. Up to two dozen deposits, might be clustered in an area of a few tens, of square kilometres. Known VMS districts are good hunting grounds for new discoveries.
Deposits within a specific district tend to have similar metal ratios and a fairly narrow range in composition. In any given district, deposits will tend to range in size from less than one million tonnes to several tens of millions of tonnes, with most deposits at the small end of the range and only a few large deposits. |
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GneissWare
Joined: 07 Mar 2008
Posts: 1287
Location: California
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| Posted: Aug 19, 2009 09:52 Post subject: Re: Volcanic-associated massive sulphide (VMS) deposits |
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A very well known deposit of this type was exploited by the Flambeau Mine in Wisconsin. As most know, it produced fabulous Chalcocites, as well as about 60 other minerals. Many of these deposits were sources of minerals and ore in the past, but were not recognized as such because, until the first black smoker was seen by Alvin, no one had predicted this form of mineralization. As mohdgeo post indicates, there are lots of these deposits of all ages, and more are being found. Lets all hope they have nice mineralization and responsible mine owners who provide a conduit for specimen preservation.
| Description: |
Chalcocite.
402.0 Marker, 1000 Level (Lucky Friday Pocket)
Flambeau Mine
near Ladysmith
Rusk County, Wisconsin
United States of America
Overall Size: 4.7 cm
Collected by Casey Jones in late 1996. |
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mohdgeo
Joined: 18 Aug 2009
Posts: 8
Location: sudan
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| Posted: Aug 19, 2009 11:24 Post subject: Re: Volcanic-associated massive sulphide (VMS) deposits |
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now in Africa beg deposit of massive sulfides founded in Sudan
or than 20 million tons of volcanic massive sulfides
| Description: |
| mine in Sudan for gold and V MS HASSAI |
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geologist from sudan |
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GneissWare
Joined: 07 Mar 2008
Posts: 1287
Location: California
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| Posted: Aug 19, 2009 12:35 Post subject: Re: Volcanic-associated massive sulphide (VMS) deposits |
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| Are any crystallized specimens being found in this deposit in Sudan?
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mohdgeo
Joined: 18 Aug 2009
Posts: 8
Location: sudan
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| Posted: Aug 19, 2009 12:57 Post subject: Re: Volcanic-associated massive sulphide (VMS) deposits |
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YES
you can see some crystals of chalcopyrite and pyrite and disseminated pyrite.
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Peter Megaw
Site Admin
Joined: 13 Jan 2007
Posts: 962
Location: Tucson, Arizona
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| Posted: Aug 20, 2009 18:05 Post subject: Re: Volcanic-associated massive sulphide (VMS) deposits |
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The oxidized parts of the Jerome, Arizona produced some excellent azurites too.
Alvin was the proff of the pudding, but some pretty smart Canadian geologists had figured out what VMS's were before that.
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