Session 5 Epigenetic gold systems - Extra Materials - Springer

dition to CO 2 may contain up to 10 % N 2 . The early event
of grey quartz crystallization corresponds to auriferous
arsenopyrite and pyrite precipitation.
The second generation of quartz of white colour that
forms veinlets and rock matrix seems to be related to pyrite
and base-metals sulphides precipitation also associated
with crystallization of carbonates of various compositions
(mainly ankerite). This quartz crystallized within
the temperature ranges from 273 to 244 ° C with the salinity
of fluids of 8.5 to 6.4 wt % NaCl equivalent and at
pressure of 0.7 kb. The contents of salts in comparison to
the inclusion solution composition in grey quartz are characterized
here by higher NaCl contents up to 85% and
lower content of KCl, CaCl 2 and AlCl 3 (Fig. 2). In the sample
richest in gold (>60 ppm Au) FeCl 3 appears in the amount
up to 5% of total salts. Furthermore, in two-phase aqueous
fluid inclusions beside CO 2 methane appears commonly
(up to 10% CH 4 ). The third generation of quartz
crystallized from 200 to 180 0 C with salinity of fluids about
4.5 of wt % NaCl equivalent and pressure at 0.7 kb. The
salts in inclusion fluids are dominated by NaCl (92-97 %
of total salts) and low contents of CaCl 2 (3-7 % of total
salts). The lowest crystallization temperatures from 165
to 154 ° C are measured in quartz veinlets of the next generation.
Fluid inclusions in that quartz homogenized into
the liquid phase and are characterized by presence of NaCl
dissolved in water, exclusively. The data in Fig. 1 shows a
clear linear trend, due to hypothetical dilution by formation
waters?
5 Sulphur isotope in sulphides from Klecza
The sulphur isotope compositions (δ 34 S CDT) have been
determined in several pure sulphide samples from the
Klecza area. Contents of sulphur δ 34 S CDT in mediumand
fine-grained arsenopyrite from Klecza range from
+2.25 to +7.88 ‰ δ 34 S and in coarse-grained pyrite they
are from –1.62 to –1.49 ‰ δ 34 S. The values of the sulphur
isotope compositions of the considered sulphides reflect
a sulphur contribution from the host rocks beside the
magmatic input of sulphur into mineralizing fluids during
precipitation of the sulphides. However, there is no
direct evidence of magmatism in the surrounding area.
Especially, samples of massive arsenopyrite aggregates
hosted by a quartz vein in chlorite-sericite schists have
heavier sulphur isotope compositions (up to 7.88 ‰) that
indicate for sulphur contribution from the host rocks.
6 Discussion and conclusions
Chapter 5-9 · Fluid inclusion study of quartz veins from the orogenic Klecza gold deposit in the Kaczawa Mountains (SW Poland)
Primary fluid inclusions in different generations of auriferous
quartz from rock samples from the Klecza gold
deposit revealed the presence of moderate to low saline
two-phase aqueous fluids with CO 2 , N 2 and CH 4 . Reported
crystallization temperatures for the refractory sulphide-
bearing grey quartz ranges from 340 to 284 ° C with the
salinity of fluids of 12.3 to 9.2 wt% NaCl equivalent and
pressure of 0.9 kb. The white quartz associated with nonrefractory
gold, base metal sulphides, and carbonates crystallized
at temperatures range from 273-244 ° C with the
salinity of fluids of 8.5 to 6.4 wt % NaCl equivalent and at
pressure of 0.7 kb. The features of fluid inclusions in goldbearing
quartz were considered by Kozlowski and Metz
(1989). They are: temperatures 250-350 ° C, pressure 0.4-1
kbar, abundance of CO2 , especially hetero-genisation
(splitting of the one phase medium into two- or morephase
medium) of aqueous and carbon dioxide fluids
(Popivnyak 1975), methane in the ore-forming fluids
(Kalyuzhnyi et al. 1975) and presence of other than sodium
cations in fluids, especially high contents of K and
occurrence of Al, Ca, and Fe in gold-precipitating solutions,
and strong domination of Na in pre- and post-ore
fluids.
These features were recognized in fluid inclusions in
quartz of the studied deposit. The changes of the oreforming
solution like separation of carbon dioxide and
aqueous fluids, replacement of sodium by potassium and
other ions and presence of methane influencing the oxygen
fugacity may cause the instability of the gold-transporting
chloride, carbonate or bisulphide complexes, leading
to precipitation of native gold. Gold mineralization
zones are hosted in quartz ± sericite ± graphitic schists.
Common presence of organic matter and graphite has
been recognized in the studied samples from Klecza. Contents
of TOC (Total Organic Carbon) range from traces
up to 18.7 %. Graphitic schists horizons are common in
the Pilchowice unit and formed during recrystallization
and redistribution of carbon in metamorphosed black
argillites. Carbon present in the country rocks reacted
with water from fluids to produce carbon dioxide and
methane according to reaction: 2C + 2H2O = CO2 + CH4 .
In this study methane was always measured in fluid inclusions
(up to 10 %) in the most auriferous samples. Presence
of methane causes reduction of the oxygen fugacity
and destabilizes gold complex inducing gold precipitation
(Cox et al. 1991). Graphitic schists with their reducing
character, acted as preferential site for gold precipitation.
The correlation between gold and sulphur as well as
common occurrence of gold inclusions in pyrite and arsenopyrite
of the first ore stage mineralization suggest
that gold was transported as reduced bisulphide complexes
[Au (HS) - 2 ] during this stage of ore precipitation. However,
the composition of fluid inclusions indicates also
for chloride complexes as gold transporting during next
stages of Au precipitation.
The role of nitrogen in the fluids is not obvious. It may
come either from the decomposing organic matter or from
dissolved potassium feldspars or micas, where it may be
present in form of ammonia ions. In any of the abovelisted
cases it may migrate into the system together with
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