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A comparison of two methods to assess diamond potential using major and trace element analysis of diamond heavy mineral concentrate (peridotitic and eclogitic garnets)


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Lear, G R(Gregory Richard) 1993 , 'A comparison of two methods to assess diamond potential using major and trace element analysis of diamond heavy mineral concentrate (peridotitic and eclogitic garnets)', Unspecified thesis, University of Tasmania.

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Thirty garnets from each of nine kimberlite pipes from southern Africa
and Yakutia were analysed for major element as well as for trace element
concentrations using electron and proton probes. The concentrates came
from a mix of barren and diamondiferous kimberlites as well as from both
on-craton and off-craton localities. The major element approach (using
plots of CaO vs Cr203 and Na20 vs Ti02) was used to predict the diamond
potential of the source(s) from which the garnets were derived.
Histograms of TiO2 were used to separate high and low temperature
garnet populations. The major element method correctly predicted the
diamond potential of the source of five out of nine (56%) of the
concentrates from the geochemistry of the eclogitic garnets contained
within them.
The same garnets were analysed for trace element levels of nickel and
the nickel concentration in each garnet grain was used to calculate its
temperature of crystalisation by use of the garnet-nickel geothermometer.
This temperature was then related to diamond potential by interpreting it
in terms of the graphite and diamond stability fields. The two sets of
predictions were then compared.
The garnet-nickel geothermometer gave an accurate assessment of the
diamond potential for six of eight pipes studied (75%). The two inaccurate
predictions derived from the interpretative process not taking into
consideration the shallowness of the lithosphere for one source (Nouzee) -
giving a steeper than ."ideal" geotherm- and to the presence of a lowtemperature
suite of concentrate garnets in the Roberts Victor sample.
The analyses failed to confirm the presence of a single G10 garnet in one
hundred and twenty seven peridotitic garnets examined from eight of the
heavy mineral concentrates, even though seven of these came from
diamondiferous kimberlites, five of which were of economic grade. This
indicates that, in those areas where soil sampling recovers quite small
numbers of (peridotitic) garnets, it may not be possible to adequately
assess diamond potential using the presence or absence of G10 garnets.

Item Type: Thesis - Unspecified
Authors/Creators:Lear, G R(Gregory Richard)
Keywords: Ores, Mineralogy, Determinative, Diamond deposits
Copyright Holders: The Author
Additional Information:

Thesis (M.Econ.Geol.)--University of Tasmania, 1994. Includes bibliographical references

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