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WESTERN
AUSTRALIAN DIVISION West Australian Geologist (WAG) Bi-monthly newsletter of the Western
Australian Division of the Geological Society of Australia Inc. Number 494: April ̶
May 2012 (4 Mb PDF file) Monthly Meetings Time:
5.30 pm for 6.00 pm
formal start (bar open upstairs before talk) Venue: Irish Club of WA, Download a map showing the
location, or check out the venue with Google
Maps. MAY ANNUAL GENERAL MEETING Wednesday 2nd
May, 2012 Talk
title: A 3D mineralogical and geochemical model of the Salt Creek Gold
deposit Speaker: Dr Scott
Halley (Director, Mineral Mapping Pty Ltd; Winner, GSA Gibb Maitland Medal
2012) Abstract: The Salt
Creek gold deposit is located on the southern end of the Mount Monger Dome.
It was discovered in 2007(?) by Integra Mining Limited. The pre-mining resource
was X tonnes at Y g/t for Z ounces. Salt Creek is hosted in a fractionated dolerite sill. The dolerite has
a chemical composition that resembles the composition of Paringa Basalt. Gold
mineralization is related to a small displacement fault that cuts obliquely through
the sill. Gold occurs in and around extensional vein arrays and in a
laminated shear vein occupying the fault. The alteration is predominantly chloritic, with sericite and albite
being relatively minor. The chlorite is totally pervasive and somewhat
texturally destructive. Obtaining meaningful geological information from logging
the RC chips is difficult, because everything comes out as fine-grained green
rocks. Early in the life of the project, Integra Mining made a decision to use
a hyperspectral instrument to log all of the Salt
Creek drill holes. The expectation was that the hyperspectral
logging would map solid solution variations in the chlorite chemistry that
would define a zonation pattern around the gold mineralization. The outcome
was very different to the expectation. The spatial variations in chlorite
compositions mimicked the fractionation zones within the sill. Rather than
showing anything about the composition of the hydrothermal fluid, the
spectral mineralogy provided an exquisitely detailed geological model of the
deposit; a level of detail that could never have been obtained from visual logging.
It appears that low salinity, CO2-rich fluids do not
cause Fe or Mg to move around significantly within the system, so that
chlorite chemistry reflects primary rock composition rather than hydrothermal
fluid compositions. Gibb Maitland Medal Guidelines download: MS
Word doc Website maintained
by: Peter Haines |
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