Me. Barley et al., Hydrothermal origin for the 2 billion year old Mount Tom Price giant iron ore deposit, Hamersley Province, Western Australia, MIN DEPOSIT, 34(8), 1999, pp. 784-789
Giant iron-ore deposits, such as those in the Hamersley Province of northwe
stern Australia, may contain more than a billion tonnes of almost pure iron
oxides and are the world's major source of iron. It is generally accepted
that these deposits result from supergene oxidation of host banded iron for
mation (BIF), accompanied by leaching of silicate and carbonate minerals. N
ew textural evidence however, shows that formation of iron ore at one of th
ose deposits, Mount Tom Price, involved initial high temperature crystallis
ation of magnetite siderite-iron silicate assemblages. This was followed by
development of hematite- and ferroan dolomite-bearing assemblages with sub
sequent oxidation of magnetite, leaching of carbonates and silicates and cr
ystallisation of further hematite. Preliminary fluid inclusion studies indi
cate both low and high salinity aqueous fluids as well as complex salt-rich
inclusions with the range of fluid types most likely reflecting interactio
n of hydrothermal brines with descending meteoric fluids. Initial hematite
crystallisation occurred at about 250 degrees C and high fluid pressures an
d continued as temperatures decreased. Although the largely hydrothermal or
igin for mineralisation at Mount Tom Price is in conflict with previously p
roposed supergene models, it remains consistent with interpretations that t
he biosphere contained significant oxygen at the time of mineralisation.