Applied Mineral Exploration
Discussion and research relevant to mineral
exploration. Decrepitation data of gold deposits in the Kalgoorlie area, Western Australia
In 1994 an extensive suite of samples was collected from several gold deposits in and near to Kalgoorlie
Summary
It is well known that Au mineralization is frequently associated
with CO2 rich fluids. Such
fluids produce distinctive decrepitation graphs with significant
decrepitation at low temperatures, below 300 C, particularly
for epithermal type deposits, such as those in the Kalgoorlie
region of West Australia. This extensive decrepitation study aimed
to document the distribution of such CO2 rich fluid
systems and their relationship to gold mineralization..
Many of the samples in the study show evidence of CO2
rich fluids, particularly at the Mt Pleasant and Kalgoorlie
superpit areas. In fact samples from these two areas (and the
Victory mine at Kambalda) had the most intense low temperature
decrepitation of all the samples in my entire database of more
then 5000 samples. However there are also areas in which CO2
rich fluids are absence despite known mineralization, such as the
Bayley's mine at Coolgardie.
It is also notable that close groups of samples ( those with the
same sample number with alphabetic suffixes, collected within a
radius of a few metres maximum) can show great variation in
low-temperature decrepitation intensity and thus CO2
content. It is clear that quartz veins are quite inhomogeneous,
which is not apparent in hand specimen and can only be determined
by study of their fluid inclusion populations.
Although low-temperature decrepitation, indicating the presence
of CO2 rich fluids, can be used as a guide to
gold mineralization , each deposit and region needs to be assessed
individually to confirm the relationship and the degree of local
heterogeneity within the quartz veins.
This data is grouped into seperate areas
Discussion of the Kalgoorlie and Coolgardie areas follows
below.
Brief sample descriptions
of the Kalgoorlie area samples are here.
Brief sample descriptions
of the Coolgardie area samples are here.
Discussion of the Victory mine, near Kambalda
(point 3 on this map) is here
Discussion of the Southern Cross area is here
Discussion of the Londonderry pegmatite (non-gold)
is here
In all cases same-numbered samples with alphabetic suffixes were
collected from the same location within a few metres and show the
local variability of the data.
Regional location map
Samples were collected from locations 1,2,3,4 & 5
(numbers inside black circles) on the following map of the
kalgoorlie region
Kanowna Belle
At Kanowna Belle low temperature decrepitation occurs in the ore
zone, but some 20m away (sample 1504) there is only weak
low-temperature decrepitation, perhaps reflecting distance from
mineralization.
Sample 1504 is some distance from the main ore zone and shows only weak low-temperature decrepitation
Mt Pleasant
The 3 pink shaded deposits were sampled in this study.
Sample 1505 has some of the most intense low temperature
decrepitation ever observed. However this quartz was waste rock on
the coreshed floor and it is uncertain if it was gold mineralized.
Sample 1508 of breccia contained feldspar which caused the high
counts above 600 C. Quartz does not decrepitate above the alpha
beta transition temperature of 573 C.
Kalgoorlie Superpit
Samples from the Kalgoorlie superpit ore zone often show very
intense low-temperature decrepitation due to CO2 rich
fluid inclusions.
Coolgardie
The 3 mines shaded pink were sampled in this study. The
Londonderry pegmatite was also sampled and is reported upon separately here.
Unmineralized granite hosted quartz veins
Note the lack of low-temperature decrepitation on these
unmineralized quartz samples.
Bayley's mine
Only a few of the samples from Bayley's mine show low-temperature
decrepitation. Such decrepitation cannot be assumed to be
necessary for gold mineralization on a regional scale.
King's Cross mine
Samples from the King's Cross mine show no low temperature
decrepitation.
Three Mile Hill mine
The three mile hill mine is only about 3 Km from Bayley's and King's Cross mines, but has very different fluid inclusion character with intense low-temperature decrepitation.
