Page 244 - Caldera Volcanism Analysis, Modelling and Response

Characterisation of Archean Subaqueous Calderas in Canada 219

CaO
Calcite
CaCO 3
Avg.
Hydrothermal
carbonates (n=71)
Syndeformation-
distal
metamorphic
carbonates (n=18)
(Lafrance, 2003)
medial
A
Ankerite Dolomite
(Ca, Fe)(CO 3 ) 2 Ferroan Ferroan (Ca, Mg)(CO 3 ) 2
ankerite Ankerite dolomite
Mg:Fe <1 Mg:Fe >4
proximal

Sideroplesite Pistomesite Breunnerite

FeO MgO
Siderite Normetal caldera Magnesite
FeCO 3 MgCO 3

Hydrothermal carbonate trends CaO
in felsic dominated sequences: Calcite
1) distal calcite - (Fe-) dolomite CaCO 3 Hydrothermal
2) medial Fe dolomite - ankerite carbonates (n=92)
3) proximal Fe ankerite - siderite - + + Ankerite
(sideroplesite) o Siderite
Kidd Creek +
hydrothermal
B carbonates (n=21)
(Schandl and Wicks,1993)
+ +
Ankerite + + + + + + + ++ + + + + + Dolomite
(Ca, Fe)(CO 3 ) 2 + + + + + + + + + + + + + + + + + + + (Ca, Mg)(CO 3 ) 2
Ferroan Ferroan
ankerite Ankerite dolomite
Mg:Fe <1 Mg:Fe >4
Proposed carbonate species trend in mafic to
ultramafic dominated sequences: Fe- dolomite
breunnerite - pistomesite -sideroplesite - siderite

Sideroplesite Pistomesite Breunnerite
FeO o o o o o o o o o o o o o o o o o o o o o o o o oo o o o o o o o o o o o o o o o o o o o o oo o o o o o o o o o o o oo o o+ + + + + + + + + MgO
Siderite Magnesite
Hunter Mine caldera
FeCO 3 MgCO 3
Figure 14 Carbonate species associated with massive sulphide deposits. (A) Normetal caldera
(modi¢ed with permission from Lafrance, 2003), and (B) Hunter Mine caldera (modi¢ed from
Chown et al., 2000, with permission from Elsevier) and carbonate analyses from Kidd Creek
(data from Schandl and Wicks,1993).