Google is too dumb to let me put the list of news in this column and falsely claims that all my pages are self-duplicates.
Google's so-called "Artificial Intelligence" is an abuse of the concept of intelligence!
The Woods Point gold deposit, Victoria, Australia
A selection of quartz samples from the Morning Star mine and environs were
analysed by baro-acoustic decrepitation as part of a project carried out by Caitlyn Hoggart and supervised by
Reid Keays of Monash University.
The decrepitation data showed that the auriferous hydrothermal fluids
which formed the deposit typically contained very high quantities of CO2. Decrepitation is a rapid and simple method to estimate the CO2 contents of the ore forming fluids
and this method would be useful in exploring for extensions to the
existing deposits or in finding new deposits in this region by
identifying quartz formed from these CO2 rich, potentially auriferous fluids..
Geology and Location:
The Woods Point mine is located 120 km NE of
Melbourne and has produced some 900,000 oz of gold. It occurs in a dyke
swarm hosted within Devonian sandstones
and shales. The dyke rocks are of granophyre, peridotite, diorite and
gabbro and the gold occurs within quartz and quartz/carbonate
within the dykes. For a thorough overview of the geology see: Nature of
gold mineralisation in the Walhalla Goldfield, southeast Australia by
M.A. Hough, F.P. Bierlein, L. Ailleres & S. McKnight,Aust. Jnl. of Earth Sciences, 2010, V57, pp 969-992.
Simplified geology map of central Victoria showing major faults and the
extent of Palaeozoic metasedimentary and metavolcanic rocks. (After
F.P. Bierlein, D.C. Arne, D.A.Foster & P. Reynolds, Mineralium
Deposita V36, p741-767, 2001.)
Geological map of the eastern Melbourne Zone, showing the distribution
of individual dykes within the Woods Point dyke swarm and principal
geological and structural features. (After Phillips & Hughes, 1996;
Bierlein et al 2001.)
34 quartz samples from the Woods Point region were analysed by
baro-acoustic decrepitation to determine the relationship between
decrepitation response and known mineralisation as well as to examine
the variability of the results within and between different types of
The graph below shows the results from 9 samples collected in the
Morning Star adit. All of these samples show a low temperature CO2
decrepitation peak ranging in intensity from substantial to extreme.
The Morning Star mine was the largest in the Woods point area and
confirms the strong relationship between Au mineralisation and CO2 rich fluids. The decrepitation data from all the samples shows that CO2 rich fluids were common throughout this area. The complete set of results is shown here.
To compare the histograms of the samples, de-convolution was carried
out to resolve them into individual skewed gaussian component
populations. From 3 to 8 component populations were found depending on
the sample. The result of a typical deconvolution, in this case of
sample 511 from the Morning Star adit, is shown in the graph below. In
this graph the original data is shown in black, and the mathematically
derived sum of individual populations is shown in red. These two graphs
are in good agreement. The 5 individual gaussian component populations
are also shown as gaussian_2 to gaussian_6. The parameters of the
component populations are recorded during the de-convolution and can be
used in semi-quantitative comparisons between the samples. This is much
more precise than merely trying to visually compare the decrepigrams in
a suite of samples. The curve fitting results of selected samples is
Using the data from the curve fitting, the graph below shows the central temperature of the low temperature CO2
peak together with the height of that peak. The height of this peak
(red squares) is an approximate estimator for the quantity of CO2
present in the fluid that formed the quartz sample concerned. this
graph includes some additional results from replicate analyses and
duplicate de-convolution calculations. Many, although not all, samples
show high levels of CO2. A compilation plot of all the fit data is shown here.
Gold analyses were provided by Caitlyn for all except 2 samples. It is
not clear how these Au analyses were obtained and it seems that they
are estimated values based on nearby samples rather than direct
analyses of the exact samples which were sent for decrepitation
analysis. Nor is it known what analytical technique was used to measure
the Au. Despite this uncertainty, the data plotted below show an
interesting correlation between the Au analysis and the height of the
low-temperature (CO2 - caused) decrepitation peak. All of the samples (with 1 exception) which contain 10ppm or more of Au show high CO2 peak heights. Many additional samples with low Au contents also show high CO2
peak heights. This is to be expected as the fluid characteristics of a
hydrothermal system provide a much larger anomaly halo around
mineralization than does the mineralization itself. This provides a
bigger and more homogeneous exploration target than trying to use Au
analyses as a geochemical exploration method. The Au analyses are also
prone to erratic variations due to inhomogeneous distribution and the
nugget effect during sampling and analysis. In addition, the use of Au
estimates rather than direct analyses on the same sample would
introduce further variation.
All of the samples, except for the "cleaning quartz" for which there is
no Au analysis, were collected from mineralized quartz occurrences or
actual working mines. Unfortunately, there are no confirmed
unmineralised samples in the sample suite to provide a comparison
between mineralised and barren quartz. It is suspected that barren
samples would show low or no CO2 peak as is the case with the cleaning quartz, which is presumed to have no measurable Au content.
The quartz samples from the Woods Point mineralization occurrences have
low temperature decrepitation peaks which are caused by the presence of
substantial amounts of CO2 in the fluids which deposited the quartz vein and gold mineralisation. Samples with high gold contents also have high CO2 decrepitation peaks and it is clear that the presence of CO2
rich fluids would be an effective exploration method to explore for
extensions of the known deposits or to explore for additional new
deposits in the region. Because the distribution of CO2 rich fluids is wider and more homogeneous than the distribution of Au itself, it is advantageous to use CO2 analyses in exploration because of the larger and more consistent target size of CO2 anomalies.