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After the ECROFI 22 conference (2013) the Cukuralan Au mine was
visited. The opportunity was taken to collect samples for
baro-acoustic decrepitation analysis to compare the fluid
inclusion assemblages from this deposit with that of many other
gold deposits shown elsewhere on this website.
There are too few sample locations in this brief study to draw broad conclusions. However it is clear that baro-acoustic decrepitation can be applied to this type of deposit, although the mixed quartz and feldspar samples make interpretation difficult. There are several distinctly different decrepitation signatures which could assist in identifying different hydrothermal phases, most notably the barren quartz veins which seem to be a late stage overprint of the system. None of the samples had low temperature decrepitation which indicates that CO2 was absent or only a minor constituent of the hydrothermal fluid system.
The following geological information is from the ECROFI 22 field
trip guide, 2013 by Huseyin Ozturk & Zeynep Cansu.
The Çukuralan Au deposit is in the Bergama (İzmir) region
of western Turkey. The deposit is a low sulphidation epithermal
deposit (similar to the Ovacık-Au deposit (40 km southeast of
Çukuralan) occurring within the porphyritic dykes that cut
the local metamorphic sequence known as Karakaya Complex. The gold
grade varies between 0.5 and 50g/T, with mining from an open pit.
Mineralisation at Cukuralan is related to porphyry dykes which
were formed at the same time as the tectonics which caused ductile
deformation. It is uncertain if the gold is derived by leaching of
the regional Permian aged metamorphics during later Miocene aged
magmatic events. It is thought that the mineralisation is related
to the intrusion of porphyry dykes. The gold deposition is
primarily lithologically controlled by reducing host rocks, but
deposition also occurs without lithological control. Quartz, and
calcite occur as gangue minerals. The mineralisation is
structurally controlled and occurs along 2 different fault systems
oriented NE-SW (younger) and NW-SE (older).
Samples were collected from the unoxidized ore zone and also from
the adjacent oxidized ore zone. At each sample location multiple
sub-samples were collected within a few metres radius and these
were analysed individually. Samples from the same location are
plotted together on the following graphs. The samples were mostly
of porphyry rather than quartz. An additional sample from a barren
quartz vein in the footwall was collected from about 30 metres
away. During sample preparation 2 samples (2219C and 2219D) were
treated with dilute HCl to dissolve carbonates which were present.
Only sub-sample 2219D was predominantly of quartz and the other
sub-samples were of porphyry and also contained feldspar. This
mineral mixture has probably caused a complex decrepitation
pattern and contributes to the unusually high decrepitation at 600
C on sub-samples 2219A, 2219B and 2219D. The lack of decrepitation
below 350 C indicates that there was little or no CO2
in the hydrothermal fluids.
This quartz sample has similar character to the quartz sub-sample
2219D (above) from within the unoxidized ore zone. It suggests
that the quartz veining may be a late stage barren overprint and
that the gold mineralisation is part of a separate event, possibly
more closely associated with the porphyry. There is no evidence of
CO2 in this fluids in this sample.
