The Hamersley province of northwest Australia is one of the world's
premier iron ore regions with high-grade martite-microplaty hematite
iron ore deposits mostly hosted within banded iron formation (BIF)
sequences of the Brockman Iron Formations of the Hamersley Group. These
high-grade iron ores contain between 60 and 68 wt percent Fe, and formed
by the multistage interaction of hydrothermal fluids with the host BIF
formation.
The oxygen isotope compositions of magnetite and hematite from BIF,
hydrothermal alteration assemblages, and high-grade iron Ore were
analyzed from the Mount Tom Price, Paraburdoo, and Charmar iron ore
deposits. The delta(18)O values of magnetite and hematite from
hydrothermal alteration assemblages and high-grade iron ore range from
-9.0 to -2.9 per mil, a depletion of 5 to 15 per mil relative to the
host BIF. The delta(18)O values are spatially controlled by faults
within the deposits, a response to higher fluid flux and larger
influence the isotopic compositions by the hydrothermal fluids. The
oxygen isotope composition of hydrothermal fluids (delta(18)O(fluid))
indicates that the decrease in the (18)O content of iron oxides was due
to the interaction of both basinal brines and meteoric fluids with the
original BIF. Late-stage talc-bearing ore at the Mount Tom Price deposit
formed in the presence of a pulse of delta(18)O-enriched basinal brine,
indicating that hydrothermal fluids may have repeatedly interacted with
the BIFs during the Paleoproterozoic.