Petrology and Ore Deposits Volcanic Hosted Massive Sulfide Deposits

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Petrology and Ore DepositsVolcanic Hosted
Massive Sulfide Deposits
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References/Links

• Web sites
• http//esa.www5.50megs.com/mindep/depfile/ma_sulp.
  htmclass

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Volcanic-associated Massive Sulfide (VMS) Deposits

• These are an important group of hydrothermal
  deposits that form on the sea-floor often
  referred to as VMS (volcanic-associated massive
  sulfide)
• They are typically conformable bedded in their
  upper sections and epigenetic (stockwork) or
  stratabound in their lower parts
• Deposits of this type have observed forming as
  hydrothermal vents (black smokers) on the
  sea-floor at spreading centres

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VMS Deposits

• Usually small 0.1-10 Mt but occasionally can be
  very big rich eg Rio Tinto, Spain 500Mt _at_ 1.6
  Cu, 2 Zn, 1 Pb, 67 g/t Ag, 1 g/t Au Rosebury,
  Tasmania 19 Mt
• Mineralogy usually consists of gt90 iron sulfide,
  mostly pyrite with some pyrrhotite. Chalcopyrite,
  sphalerite galena may be important constituents
  depending on deposit class along with bornite,
  chalcocite, arsenopyrite, magnetite
• Most VMS deps are zoned. Galena and sphalerite
  being more abundant in the upper half whereas
  chalcopyrite increases toward the
  footwall-staockwork zone

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VMS-associated Wallrock Alteration

• Usually confined to the footwall-stockwork zone
• Chloritization and sericitization are the 2 most
  common forms
• Pipe shaped alteration usually containing the Cu
  minzn
• Diameter of alteration increases upward

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VHMS Lifeforms
http//www.nature.com/cgi-taf/DynaPage.taf?file/n
ature/journal/v405/n6787/full/405676a0_fs.html
Figure 2 Remnant cores and bands containing
filaments. a, Silica-rich colloform cores
containing filaments, surrounded by replacive
pyrite (gold). Combined transmitted and reflected
light (TL and RL) photographic montage. b, Thin
banded layer containing filaments within
paragenetically early chert (TL and RL). c,
Detail of a showing the partial replacement of
quartz-rich colloform structures displaying
fine-scale lamination (TL and RL). Scale bar is
1 mm for a, b and 0.1 mm for c.
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VMS Environment

• Cyprus-type Cu - Assoc with basalts at spreading
  centres
• Kuroko-type - assoc with intermediate-acid volc
  rocks in island-arc environ termed
  (Cu-Pb-Zn-Ag-Au). Occur with lg amounts of qtz,
  barite and gypsum eg Woodlawn NSW, Hellyer Tas.
• Besshi within plate back-arc rifting

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VMS Classification
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Black Smokers
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VMS Formation
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VMS Fluid Circulation
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Stages of VMS Develop-ment Zoning
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Spreading Centres (Cyprus-type VMS)
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Tectonic Settings