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Rapid fluid inclusion data
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Magnetite and haematite both commonly give good decrepigrams and
decrepitation is particularly useful to investigate these opaque
minerals.
Magnetite and haematite are often considered to be
homogenous materials, but the decrepitation method reveals them to
be quite variable. These variations can be used as an exploration
tool and have also provided insight into the genesis of these
deposits.
Location map of Australian deposits
Magnetite samples show a great range of variability, which can be used to discriminate between different types of magnetite and also to discern zonation within individual magnetite bodies. Note that the carbonatite samples show unusually low decrepitation temperatures, and the auriferous magnetites sampled to date frequently have higher decrepitation temperatures, with decrepitation peaks being near 650o C.
To confirm that the decrepitation sounds measured are not merely
mechanical noises, this magnetite sample was analysed twice in
succession. The second analysis (green) gave only background
counts with a few counts from inclusions which just survived the
first analysis at the 800 C cutoff temperature. This confirms that
the counts being measured are the result of an irreversible
phenomenae, such as inclusion decrepitation, rather than thermal
expansion noises - which would be present in both analyses.