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Volcanogenic massive sulfide (VMS) deposits
= VMS V olcanogenic M assive Sulfide
• - , - , - Volcanic associated volcanic hosted volcano sedimentary massive sulfides
• ( ; -Associated with volcanics mafic to felsic usually calc) ( ) alkaline and sediments siliciclastics in different
proportions
• Stratabound to stratiform tabular lenses accumulated in ( . . , , , , , , , )massive sulfides e g Py Ccp Asp Po Sp Gn sulfosalts
• : , , , , ( ), , , , , , , Polymetallic Cu Zn Pb Ag Au major Co Sn Se Mn Cd In, , , , , , ( )Bi Te Ga Ge As Sb Hg minor
• ( ) Hydrothermal origin hydrothermal fluids
• + = VMS SEDEX Massive sulfide deposits by hydrothermalfluids
• ( )Of all ages Precambrian to Phanerozoic
• Related to major ocean closing and terrane accretion events
• : (“ Modern equivalents Hydrothermal vents on seafloor Black”) Smoker
. .www whoi edu
General features
“ ” , Black smoker on seafloor submersible Alvin
General features
+ , Zn Pb– Cu
, Lydon 1984
Additional phases
•Pyrrhotite• Barite•Magnetite•Arsenopyrite•Bornite•Mackinawite• ( )Sulfosalts Tennantite etc•Tellurides• , Acanthite Argentite
Classifications I
- Host rock lithology
) - ( )6 High sulfidation bimodal felsic epithermal
Ø ( ) /Predominantly mafic volcanics tholeiitic basalts with minor sediments ultramafics
Ø - , Cu rich smallØ ( ), - Ocean ridge ophiolites back arc riftØ ( - ) Predominantly mafic volcanics tholeiitic to calc alkaline basalts
with minor felsic volcanics and subordinate sedimentsØ -Cu richØ( ) rifted primitive volcanic arcØ / ≈ , ± Mafic volcanics intrusives turbiditic sediments felsic volcanic absentØ , Sedimented oceanic rift rifted continental margin
Ø - ( ) Predominantly calc alkaline felsic volcanics rhyolite with minor mafic / volcanics felsic intrusives and subordinate sedimentsØ - , ± Highest Zn content on average bariteØ ( ) Compositionally rifted volcanic arc
) ( - )1 Mafic Cyprus type
) - ( - )2 Bimodal Mafic Noranda type
) - ( - )3 Mafic Siliciclastic Besshi type
) - ( - )4 Bimodal Felsic Kuroko type
) -5 Bimodal Siliciclastic
Ø ([ - ] > [ ] ) ≈ Volcanics calc alkaline felsic tholeiitic mafic siliciclastic rocksØ -/ - Highest Pb lowest Cu content on averageØ Greatest tonnage and largest size on averageØ( ) rifted continental arcØ - Characteristic similar to bimodal felsic group
Ø , ( , )Besides sulfides sulfosalts tetrahedrite stanniteØ (‘ ’ )Epithermal conditions hybrids of VMS and epithermal depositsØ -Shallow back arc
. ( )Galley et al 2007
, Decrease
inCu
Increasein
Pb
Primitiv eto
“”
maturesetting
Increasein
/size
ton nage
- Host rock lithology
) ( - )1 Mafic Cyprus type
) - ( - )2 Bimodal Mafic Noranda type
) - ( - )3 Mafic Siliciclastic Besshi type
) - ( - )4 Bimodal Felsic Kuroko type
) -5 Bimodal Siliciclastic
Increasein
SiO2
ofhost
rock
Classifications I
., ; , Franklin et al 1981 Large 1992
Classifications II
Base metal classification
• (- )Cu Zn
• -Zn Cu
• - -Zn Pb Cu
• - ( )Pb Zn SEDEX
World VMS( modified after
, )Franklin 1996
Classifications II
Base metal classification
• (- )Cu Zn
• -Zn Cu
• - -Zn Pb Cu
• - ( )Pb Zn SEDEX
., Galley et al 2007
World VMS( modified
after, Franklin
) 1996
Canadian VMS
Tectonic setting
., Galley et al 2007
General model
, Franklin 1993
Summary
What?
Where?
How and why?
Ø , ( ) Polymetallic stratiform deposits associated with volcanic mafic to felsic / and or siliciclastic rocks in different proportionsØ Massive sulfide lense with mineral zonation
Ø : Today Spreading ridges and arc settingsØ : Geologic record Primitive to more compositionally mature volcanic arc ( ), ( ) , , fore to back arc rifted continental arcs shallow back arcs and ( , )spreading ridges ophiolite minor
Ø ( ° ) Circulation of hot up to 400 C hydrothermal fluids within crustØ Interaction with cold seawater and cold wall rockØ - Precipitation of massive sulfides due to physico chemical processes ( . ., , , )e g ∆T ∆pH redox state