Table 1 Comparison of previous models (① and ②) and our proposed model (③).
Formation mechanismPrecusorReaction fluid/liquidFe-oxide mineralizationFe
state
① Chan et al.
model
Goethite precipitation by redox-oxic
reaction
NoneBuoyant, reducing fluid due to
hydrocarbon
Precipitation of goethite (not clear for crust
formation)
Fe2+
② Loope et al.
model
Siderite formation and microbial
oxidation
Siderite
(not found)
Reducing groundwater with methane
dissolved
Internal Fe source (siderite)Fe2+
③ Our proposed
model
Calcite-acid reaction by pH
buffering
Calcite
(found)
Penetration of CO2-charged
acidic groundwater
Inward precipitation of goethite by Fe-rich
acidic water from outside
Fe3+