Applied Mineral Exploration
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Rapid fluid inclusion data
for exploration (decrepitation) |
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The Au deposits in Nevada are young and in contrast with typical
archaen deposits they lack any significant CO2 in
their
fluid inclusions. The samples from these 3 deposits, as well as
jasperoid
style deposits in Nevada, all lack any significant low temperature CO2
decrepitation peak.
There are numerous jasperoid outcrops in eastern Nevada, most of
which are simply surficial silicification, but some of them are gold
mineralized
and formed from hydrothermal fluids. Decrepitation can be used as a
screening
procedure to discriminate between these two types of jasperoid.
The Cranovitch and Jaydee pits are small gold deposits in the Robinson district. The Purple vein deposit, in the Carlin district, was an exploration prospect when this drillcore was sampled in 1990. See the adjacent figure for some surface results at Purple Vein. An example of typical background jasperoid from near the Easy Junior mine shows the contrast between the mineralized and barren jasperoids.
Within known deposits, most but not all samples decrepitate. Two
samples from the Purple Vein deposit show the range of decrepitation
which
can occur, sometimes over quite small distances. Some 50 samples of
background
jasperoids were collected in eastern Nevada and almost all of these had
no decrepitation. The North Easy ridge sample is one of the few from
outside
of a known mine which did decrepitate. Samples from close to but not
actually
within mines also show no decrepitation activity indicating that there
is almost no detectable anomalous aureole outside of the mineralized
zone
itself. Although decrepitation does seem capable of discriminating
between
potentially mineralized and barren jasperoids, a high sampling density
is required to compensate for the lack of aureoles around the
mineralized
zones.
