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Isotopic abundances of water of crystallization of gypsum from the Miocene evaporite formation, Carpathian Foredeep, Poland
Geochimiro er Cosmochimico Acra Vol. 46, pp. 293 to 296 0 Pergamon Press Ltd. 1982. Printed in U.S.A.
0016-7037/82/020293-04$03.00/O
NOTE
Isotopic abundances of water of crystallization of gypsum from the Miocene evaporite formation, Carpathian Foredeep, Poland S. H&AS Institute
of Physics,
Marie
Curie-Sklodowska
University,
20-031
Lublin,
Poland
Alberta,
Canada
T2N
and H. R. KROUSE Department
of Physics,
(Received
The University
February
of Calgary,
6, 1981; accepted
Calgary,
in revised form
September
lN4
9, 1981)
Abstract-For sulfates of Miocene evaporites in the Carpathian Foredeep, the waters of crystallization of gypsum (w.c.g.) have dD = -38 to -113% and 6’*0 = 0 to -1 IL (SMOW). The 6% and a’*0 values of the sulfates are uniform and consistent with a marine origin. It is proposed that the original w.c.g. was equilibrated with marine water. Subsequently, it re-equilibrated towards very isotopically light water (&D - -100% d’s0 - -14%) during a glacial or postglacial period and is now trending towards current waters cirdulating through the deposits (6D - -SO’%, 6” - -7’5~). The extent of reequilibration increased with decreasing crystal size.
INTRODUCTION
In these evaporite deposits, two sublayers can be easily distinguished. In most parts of the lower layer, giant and fairly transparent crystals of selenite (up to 4 m in height) occur. In contrast, the upper layer consists of compact and rather fine-crystalline gypsum which is usually laminated with thin layers of silt. Both layers of gypsum contain bitumens and silt, while the layer of giant-crystalline transparent gypsum consists of up to 95% CaS04. 2H20. In many locations (Tarnobrzeg, Jeziorko, Grzybow) the gypsum-anhydrite series are replaced by sulfur-bearing limestone containing 25-30s of native sulfur. In such places, strongly eroded sulfur-bearing gypsum occurs, which is recognized as “remaining sulfate”, which was not converted into sulfur-bearing limestone during bacterial reduction processes (Pawalowski, 1970; Ha& 1973; Czermidski and Osm&ski, 1974). At some locations, especially when gypsum appears on the surface, gypsum-karst systems developed (e.g., Skorocite). Samples were taken from several locations (Figure I ) in order to include all the types of gypsum described above (see Table 1). These samples represent gypsum and gypsum-anhydrite rocks which were deposited near the northern boundary of the evaporite facies where they either occur on the surface (Skorocice, Gacki) or are covered by less than 100 m of younger Tertiary and Quaternary layers.
THE oxygen and hydrogen isotope composition of the water of crystallization of gypsum (w.c.g.) can determine the isotopic composition of the mother brine in which the gypsum formed. The values of the isotope fractionation factors,
1000 + d w.c.g. (y=
(1)
lOOO+hbrine’
were determined to be 1.0040 and 0.980 for oxygen and hydrogen, by Gonfiantini and Fontes (1963), and Fontes and Gonfiantini (1967). These factors are not sensitive to temperature changes during gypsum deposition or the isotopic “salt effect” at saturated gypsum concentrations (Sofer and Gat, 1972). Difficulties arise in the determination of d-values of the mother brine because of the instability of gypsum. It can easily lose its water of crystallization to form anhydrite. Moreover under certain conditions, anhydrite may occur as a stable phase during salt precipitation on a basin floor. Regypsyfication usually involves water of meteoric origin. When gypsum originally precipitated in sea water, is not isolated from circulating waters, isotopic “mixing” occurs as the waters of crystallization tend towards isotopic equilibrium with the new surrounding water. For the above reasons, it is preferable to examine recent precipitates or young gypsum deposits to determine the isotopic composition of original brine (Matsubaya and Sakai, 1973; Lyon, 1978; Sofer, 1978). This report contains the first observations of the isotopic compositions of w.c.g. of Miocene evaporites in the Carpathian Foredeep, South-East Poland.
GEOLOGICAL
SETTING
OF SAMPLING
ANALYTICAL
PROCEDURES
Gypsum and gypsum-anhydrite samples were roughly crushed, loaded into L-shaped Pyrex tubes and outgassed on a vacuum line for a half hour. This pretreatment was performed below 50°C to avoid escape of the water of crystallization. The L-tube was then sealed at the top end and removed. The arm containing the sample was placed horizontally into a tube furnace and the vertical empty arm was immersed in liquid nitrogen. The furnace was slowly heated up to 400°C. Inasmuch as the water liberated in this way was contaminated by organic compounds and native sulfur, the L-tube was broken and the water transferred to another tube for purification by slow distillation under
AREA
Gypsum-anhydrite deposits occur widely within strata of Miocene age in the Carpathian Foredeep (Figure 1.) The tops of these deposits range in depth from the surface to 2000 m, and average in thickness, 20 to 45 m, (maximum, 60 m). 293
S. HAtAS
294
--
AND H. R. KROUSE
-‘-I
. Lublin
northern
- “K
boundary of gyp. -anh. facies
‘.-- - ‘----
*'1 '3 5
* Katowice
FIG. I_ The study area; sample locations shown by asterisks.
performed at the Knstitute of Physics, Marie ~uur~.Sko dowska University, Lublin, while 6D measurementti wcrc’ carried out at the Department of Physics, The 1 lniversiry of Calgary. The reproducibility (16) for the oxygen and hydrogen isotope determinations were 0.2 arid .5 per tnil. respectively.
vacuum. The oxygen isotopic composition was measured on carbon dioxide which had been equilibrated with 2-5 cc of the water sample. The hydrogen isotopic composition was determined on H, prepared using the uranium reduction method.
The extraction of waters and fi’*O measurements TABLE --.
were
1
&I80 and 6D values of the water of crystallization gypsum (w.c.g.) in the Miocene formation in the Carpathian Foredeep. (In brackets are given values for mother solutions estimated from equation Cl>). Remarks
Sample No.
Location
TS-12
Jeziorko
-3.4 (-7.3)
-66 (-471
Strongly eroded sulfur-bearing selenite, s.
TS-14
Jeziorko
-2.1 (-6.0)
-Ic: (-:>l)
Nonaltered specimen of gypsum in ;i~ sulfur deposit, s,
Gacki
-1.0 r.-4.9)
-41 C-22)
Giant-crystalline
E-9
Gacki
-6.4 C-10.3)
-i3 t
Fine-crystalline
BS-10
f-82)
3%1Oa
Gacki
BS-Il.
w.2
gypsum Isr?icnitf?! compact gypsum, G/
Giant-crystalline
-4 8
gypsum.
i;.
C-3.7)
(-291
Cacki
-0. 8 i-4* 7)
: -1.9)
BS-12
Skorocice
-0.6 (-4.5)
H-5
Horyniec
(-7.3)
No. 8, O-l
Basznia
-9.0 f-12.9)
-87 C-68)
Gypsum-anhydrite,
No. 9, 72
Basznia
-Il.0 (-14.9)
-113 C-95)
Sulfur-bearing gypsum-anhydritc a high bitumen content.
No, 10, 72
Basznia
s = prior
to distillation,
Transparent
-J8
~.;:vpsum.
Giant-crystalline gypsum, sampig: i&en out from gypsum karst area. Gypsum beneath
-3.4
-10.0
.-74
C-13.9)
C-55)
the extracted
giant-crystalline
water
Sulfur-bearing
had a strong
bitumen
i imestoner:.
sulfur-bearing distinctly
iaminati>d.
gypsum-anhydritt.
odour.
x+,i~hpi
295
NOTE
_
BASZNIA
METEORIC 6 D =
6 “OSMOW, FIG. 2. bD versus
mother
RESULTS
DISCUSSION The ‘“S/“S and ‘“O/l”0 ratios of sulphate in almost all the samples were studied previously (H&as and Mioduchowski, 1978; H&as, unpublished data). The isotopic ratios of both elements fall into narrow ranges: 6% = +23%0 and 6180 Y +13.5% (Fig. 3) implying that the evaporites were formed in a marine environment (Claypool ef al., 1980). In contrast, the w.c.g. in the same samples show large variations of 6’*0 and 6D values. The isotopic composition of water which would be equilibrated with the w.c.g. (hereafter designated e.w.c.g.) is compared with the meteoric water trend in Figure 2. Since some of the original w.c.g. was probably preserved in most specimens while the remainder was replaced by re-equilibration with the surrounding water, then waters with isotopic composition corresponding to the calculated e.w.c.g. unlikely existed physically for most specimens. However the calculated e.w.c.g. proves to be a valuable parameter for interpretation. If it is assumed that the grant-crystalline gypsum is most likely to preserve its original w.c.g., then it is surprising that the calculated e.w.c.g. are not typical of a marine basin, but rather of continental water bodies. The e.w.c.g. data points below the meteoric water trend
TREND
+ 10 (CRAIQ
LINE
i _
ISSI)
%o +
d’“0 plot for derived
The oxygen and hydrogen isotope analyses of w.c.g. samples are listed in Table 1. Using Equation (I), the 6’*0 and &D values for the mother brine were estimated. These values are plotted in Figure 2 along with the meteoric water trend line (Craig, 1961). Both isotopic compositions are expressed on the SMOW scale.
WATER
8%‘*0
24.5
I-
brines.
a
CaS04 MIOCENE
EVAPOR’TES
S. E _ POLAND 24.0 f
1i 23.5
13.0
14.0
‘3.5
5 I80
SMOW,
14.5
%o-
FIG. 3. I?‘% versus 8’“O plot for Miocene evaporites, S. E. Poland based on data from H&s and Mioduchowski (1978) and H&s (unpublished data).
S. HAEAS AND H. R. KROUSE
296
line in Figure 2 are most interesting in that a line through them is suggestive of mixing between marine water which had evaporative losses and meteoric water. It would seem tbat the introduction of meteoric water occurred subsequently to the initial hydration and the original e.w.c.g. had an isotopic composition corresponding to the circle of Figure 2. This conclusion is based on the 6’*0 values measured for sulfate in the gypsum. The fact that no data for e.w.c.g. are found close to this circle in turn implies that even the large crystalline material has not preserved its original w.c.g. The intercept of this mixing line with the meteoric line (8’“O ce -15%; SD = - 110%) would represent an e.w.c.g. with much greater depletion in the heavier isotopes than present day groundwater. This implies that the w.c.g. partially re-equilibrated along a mixing line during a cold climatic period. In the Gacki quarry, sample BS-lOa appears to have had less of its original w.c.g. replaced than all other specimens (Figure 2). In contrast, BS-100 would seem to have had most of its original w.c.g. replaced by w.c.g. equilibrated with significantly lighter meteoric water. Although these samples are close together, the former is a chip from a giant gypsum crystal while the latter was taken from a fine crystalline layer covering the former. Therefore the crystalline character of these two specimens is consistent with the isotopic composition of their e.w.c.g. A problem arises with samples BS-9 and BS-I 1 which are much closer to the meteoric line (actually slightly above it); yet both specimens are from giant gypsum crystals, In the Jeziorko mine, sample TS- 14 is an unaltered gypsum specimen and its e.w.c.g. &-values fall along the proposed mixing line. However, sample TS-12 is strongly eroded and its e.w.c.g. b-values (d’s0 - -7t, 6D - -50% are very close to the average for present day groundwaters (Trembaczowski, unpublished data, 1979). This suggests that the original w.c.g. was replaced along the e.w.c.g. trend line of Figure 2 during a glacial period and subsequently re-equilibration towards present day meteoric water occurred. The former process should have one mixing line while the latter would have many isotopic mixing lines dependent upon the minimum &values achieved during the colder climate. It is not unexpected that the minimum 6values and the subsequent approach towards the isotopic composition of present day waters circulating through the deposits should depend upon the crystalline character of the gypsum. The most negative 6”O values for e.w.c.g. were found in the Basznia mine and these correspond roughly to the 6”O intercept value described above. This suggests that during a glacial time, or shortly thereafter, essentially all of the original w.c.g. was replaced. However these data differ from all others in that they fall well above the meteoric trend line. Such isotopic shifts can arise during fractional hydration of anhydrite under a limited supply of water (Matsubaya and Sakai, 1973, Sofer, 1978). This interpretation is consistent with the current study in that the sample furthest removed from the meteoric trend line in Finure 2(10/7z) was very weakly hydrated. This shift occurs along lines with slope -5 on a 6D vs 5’*0 diagram (Matsubava and Sakai. 1973). If such a line is drawn for sample 9/7z, it is interesting that it intersects the meteoric water trend line at approximately the same point as the mixing line described above. The w.c.g. of sulfur bearing gypsum (samples TS- 12, 9,’ 72, and 10/7z) might reflect the water present at the time ”
-
_
of formation of native sulfur ore deposits since an aqueous medium is necessary for bacterial reduction. The 6% and dD values observed for these samples are consistent with carbon and oxygen isotope data on carbonates (HALAS et al. 1976) which led them to conclude that calcium carbonate was precipitated in water of continental origin. Thus, a simultaneous isotopic study of w.c.g. of strongly eroded gypsum and co-existent sulfur bearing calcium carbonate can be used to determine the isotopic composition of water present and hence the climatic conditions during ore formation. Acknowledgements-We are grateful to Dr. I. Osmolski of Geological Institute, Warsaw, for providing the samples from the Basznia mine. Funding to H. R. Krouse from the Natural Sciences and Engineering Research Council of Canada (N.S.E.R.C.) supported laboratory activities and the visit of S. Halas to The University of Calgary. We are also appreciative of comments on the manuscript by Keiko Hattori. REFERENCES Claypool G. E., Holser W. T., Kaplan 1. R., Sakai H. and Zak I. (1980) The age curves of suifur and oxygen isotopes in marine sulfate and their mutual inte~retation. Chem. Geoi. 28, 199-260, Craig H. (1961) Isotopic variations in meteortr: waters. Science 133, 1702- 1703. Czermiftski J. and OxmBlski T. ( 1974) Isotope relationships of sulfur and carbon in sulfur ore and accompanying formations and the origin of sulfur deposits in Poland (in Polish). ~wurfa~~ik Geof. 18, 334-357. Fontes J. C. and Gonfiantini R. ( 1967) Fractionment isotopique de I’hydrogene dans l’eau de crystallization du gypse. Comptes. Rend. Acad. Sci. Paris 265, 4-6. Gonfiantini R. and Fontes J. C. (1963) Oxygen isotopic fractionation in the water of crystallization of gypsum. Nature 20@,644-646. H&s S. (1973) A correlation between isotopic compositions of sulfur and carbon in native sulfur ores (in Polish). Przegiad geologiczny 21, 277279. Halas S., Slowikowska I. and Zuk W. (1976) The isotopic compositions of sulfur-bearing limestones in Tarnobrzeg mine, Proc. of National Conference on the use o_fStable Isotopes VI, Moscow (in Russian). Hahas S. and Moduchowski L. ( 1978) The isotopic composition of oxygen of calcium and strontium in sulfate minerals and aqueous sulfates from various regions of Poland. (In Polish) Annales UMCS 33AAA, I IS.1 30. Lyon G. L. (1978) The stable isotope geochemistry of gypsum, Miers Valley, Antarctia. D.S.I.R. Bulletin 220,97-” 103. Matsubaya 0. and Sakai H. (1973) Oxygen and hydrogen isotopes study on the water of crystallization of gypsum from Kuroko type mineralization. Geochem. f. 7, f 53-, 165. Pawlowski S. (1970) The geology of sulfur ores in Poland (in Polish); Geologia i surowce mineralne Polski, p. 614. Publisher: Wyd. Geol., Warsaw. Sofer Z. and Cat J. R. (1972) Activities and concentrations of oxygen- 18 in concentrated aqueous salt soiutions, analytical and geochemical implications. Earth Planet. Sci. Left. 15, 232-238. Sofer Z. (1978) Isotopic composition of hydration water in gypsum, Geochim. Cosmochim. Actn 42, 114 1 1149.
0016-7037/82/020293-04$03.00/O
NOTE
Isotopic abundances of water of crystallization of gypsum from the Miocene evaporite formation, Carpathian Foredeep, Poland S. H&AS Institute
of Physics,
Marie
Curie-Sklodowska
University,
20-031
Lublin,
Poland
Alberta,
Canada
T2N
and H. R. KROUSE Department
of Physics,
(Received
The University
February
of Calgary,
6, 1981; accepted
Calgary,
in revised form
September
lN4
9, 1981)
Abstract-For sulfates of Miocene evaporites in the Carpathian Foredeep, the waters of crystallization of gypsum (w.c.g.) have dD = -38 to -113% and 6’*0 = 0 to -1 IL (SMOW). The 6% and a’*0 values of the sulfates are uniform and consistent with a marine origin. It is proposed that the original w.c.g. was equilibrated with marine water. Subsequently, it re-equilibrated towards very isotopically light water (&D - -100% d’s0 - -14%) during a glacial or postglacial period and is now trending towards current waters cirdulating through the deposits (6D - -SO’%, 6” - -7’5~). The extent of reequilibration increased with decreasing crystal size.
INTRODUCTION
In these evaporite deposits, two sublayers can be easily distinguished. In most parts of the lower layer, giant and fairly transparent crystals of selenite (up to 4 m in height) occur. In contrast, the upper layer consists of compact and rather fine-crystalline gypsum which is usually laminated with thin layers of silt. Both layers of gypsum contain bitumens and silt, while the layer of giant-crystalline transparent gypsum consists of up to 95% CaS04. 2H20. In many locations (Tarnobrzeg, Jeziorko, Grzybow) the gypsum-anhydrite series are replaced by sulfur-bearing limestone containing 25-30s of native sulfur. In such places, strongly eroded sulfur-bearing gypsum occurs, which is recognized as “remaining sulfate”, which was not converted into sulfur-bearing limestone during bacterial reduction processes (Pawalowski, 1970; Ha& 1973; Czermidski and Osm&ski, 1974). At some locations, especially when gypsum appears on the surface, gypsum-karst systems developed (e.g., Skorocite). Samples were taken from several locations (Figure I ) in order to include all the types of gypsum described above (see Table 1). These samples represent gypsum and gypsum-anhydrite rocks which were deposited near the northern boundary of the evaporite facies where they either occur on the surface (Skorocice, Gacki) or are covered by less than 100 m of younger Tertiary and Quaternary layers.
THE oxygen and hydrogen isotope composition of the water of crystallization of gypsum (w.c.g.) can determine the isotopic composition of the mother brine in which the gypsum formed. The values of the isotope fractionation factors,
1000 + d w.c.g. (y=
(1)
lOOO+hbrine’
were determined to be 1.0040 and 0.980 for oxygen and hydrogen, by Gonfiantini and Fontes (1963), and Fontes and Gonfiantini (1967). These factors are not sensitive to temperature changes during gypsum deposition or the isotopic “salt effect” at saturated gypsum concentrations (Sofer and Gat, 1972). Difficulties arise in the determination of d-values of the mother brine because of the instability of gypsum. It can easily lose its water of crystallization to form anhydrite. Moreover under certain conditions, anhydrite may occur as a stable phase during salt precipitation on a basin floor. Regypsyfication usually involves water of meteoric origin. When gypsum originally precipitated in sea water, is not isolated from circulating waters, isotopic “mixing” occurs as the waters of crystallization tend towards isotopic equilibrium with the new surrounding water. For the above reasons, it is preferable to examine recent precipitates or young gypsum deposits to determine the isotopic composition of original brine (Matsubaya and Sakai, 1973; Lyon, 1978; Sofer, 1978). This report contains the first observations of the isotopic compositions of w.c.g. of Miocene evaporites in the Carpathian Foredeep, South-East Poland.
GEOLOGICAL
SETTING
OF SAMPLING
ANALYTICAL
PROCEDURES
Gypsum and gypsum-anhydrite samples were roughly crushed, loaded into L-shaped Pyrex tubes and outgassed on a vacuum line for a half hour. This pretreatment was performed below 50°C to avoid escape of the water of crystallization. The L-tube was then sealed at the top end and removed. The arm containing the sample was placed horizontally into a tube furnace and the vertical empty arm was immersed in liquid nitrogen. The furnace was slowly heated up to 400°C. Inasmuch as the water liberated in this way was contaminated by organic compounds and native sulfur, the L-tube was broken and the water transferred to another tube for purification by slow distillation under
AREA
Gypsum-anhydrite deposits occur widely within strata of Miocene age in the Carpathian Foredeep (Figure 1.) The tops of these deposits range in depth from the surface to 2000 m, and average in thickness, 20 to 45 m, (maximum, 60 m). 293
S. HAtAS
294
--
AND H. R. KROUSE
-‘-I
. Lublin
northern
- “K
boundary of gyp. -anh. facies
‘.-- - ‘----
*'1 '3 5
* Katowice
FIG. I_ The study area; sample locations shown by asterisks.
performed at the Knstitute of Physics, Marie ~uur~.Sko dowska University, Lublin, while 6D measurementti wcrc’ carried out at the Department of Physics, The 1 lniversiry of Calgary. The reproducibility (16) for the oxygen and hydrogen isotope determinations were 0.2 arid .5 per tnil. respectively.
vacuum. The oxygen isotopic composition was measured on carbon dioxide which had been equilibrated with 2-5 cc of the water sample. The hydrogen isotopic composition was determined on H, prepared using the uranium reduction method.
The extraction of waters and fi’*O measurements TABLE --.
were
1
&I80 and 6D values of the water of crystallization gypsum (w.c.g.) in the Miocene formation in the Carpathian Foredeep. (In brackets are given values for mother solutions estimated from equation Cl>). Remarks
Sample No.
Location
TS-12
Jeziorko
-3.4 (-7.3)
-66 (-471
Strongly eroded sulfur-bearing selenite, s.
TS-14
Jeziorko
-2.1 (-6.0)
-Ic: (-:>l)
Nonaltered specimen of gypsum in ;i~ sulfur deposit, s,
Gacki
-1.0 r.-4.9)
-41 C-22)
Giant-crystalline
E-9
Gacki
-6.4 C-10.3)
-i3 t
Fine-crystalline
BS-10
f-82)
3%1Oa
Gacki
BS-Il.
w.2
gypsum Isr?icnitf?! compact gypsum, G/
Giant-crystalline
-4 8
gypsum.
i;.
C-3.7)
(-291
Cacki
-0. 8 i-4* 7)
: -1.9)
BS-12
Skorocice
-0.6 (-4.5)
H-5
Horyniec
(-7.3)
No. 8, O-l
Basznia
-9.0 f-12.9)
-87 C-68)
Gypsum-anhydrite,
No. 9, 72
Basznia
-Il.0 (-14.9)
-113 C-95)
Sulfur-bearing gypsum-anhydritc a high bitumen content.
No, 10, 72
Basznia
s = prior
to distillation,
Transparent
-J8
~.;:vpsum.
Giant-crystalline gypsum, sampig: i&en out from gypsum karst area. Gypsum beneath
-3.4
-10.0
.-74
C-13.9)
C-55)
the extracted
giant-crystalline
water
Sulfur-bearing
had a strong
bitumen
i imestoner:.
sulfur-bearing distinctly
iaminati>d.
gypsum-anhydritt.
odour.
x+,i~hpi
295
NOTE
_
BASZNIA
METEORIC 6 D =
6 “OSMOW, FIG. 2. bD versus
mother
RESULTS
DISCUSSION The ‘“S/“S and ‘“O/l”0 ratios of sulphate in almost all the samples were studied previously (H&as and Mioduchowski, 1978; H&as, unpublished data). The isotopic ratios of both elements fall into narrow ranges: 6% = +23%0 and 6180 Y +13.5% (Fig. 3) implying that the evaporites were formed in a marine environment (Claypool ef al., 1980). In contrast, the w.c.g. in the same samples show large variations of 6’*0 and 6D values. The isotopic composition of water which would be equilibrated with the w.c.g. (hereafter designated e.w.c.g.) is compared with the meteoric water trend in Figure 2. Since some of the original w.c.g. was probably preserved in most specimens while the remainder was replaced by re-equilibration with the surrounding water, then waters with isotopic composition corresponding to the calculated e.w.c.g. unlikely existed physically for most specimens. However the calculated e.w.c.g. proves to be a valuable parameter for interpretation. If it is assumed that the grant-crystalline gypsum is most likely to preserve its original w.c.g., then it is surprising that the calculated e.w.c.g. are not typical of a marine basin, but rather of continental water bodies. The e.w.c.g. data points below the meteoric water trend
TREND
+ 10 (CRAIQ
LINE
i _
ISSI)
%o +
d’“0 plot for derived
The oxygen and hydrogen isotope analyses of w.c.g. samples are listed in Table 1. Using Equation (I), the 6’*0 and &D values for the mother brine were estimated. These values are plotted in Figure 2 along with the meteoric water trend line (Craig, 1961). Both isotopic compositions are expressed on the SMOW scale.
WATER
8%‘*0
24.5
I-
brines.
a
CaS04 MIOCENE
EVAPOR’TES
S. E _ POLAND 24.0 f
1i 23.5
13.0
14.0
‘3.5
5 I80
SMOW,
14.5
%o-
FIG. 3. I?‘% versus 8’“O plot for Miocene evaporites, S. E. Poland based on data from H&s and Mioduchowski (1978) and H&s (unpublished data).
S. HAEAS AND H. R. KROUSE
296
line in Figure 2 are most interesting in that a line through them is suggestive of mixing between marine water which had evaporative losses and meteoric water. It would seem tbat the introduction of meteoric water occurred subsequently to the initial hydration and the original e.w.c.g. had an isotopic composition corresponding to the circle of Figure 2. This conclusion is based on the 6’*0 values measured for sulfate in the gypsum. The fact that no data for e.w.c.g. are found close to this circle in turn implies that even the large crystalline material has not preserved its original w.c.g. The intercept of this mixing line with the meteoric line (8’“O ce -15%; SD = - 110%) would represent an e.w.c.g. with much greater depletion in the heavier isotopes than present day groundwater. This implies that the w.c.g. partially re-equilibrated along a mixing line during a cold climatic period. In the Gacki quarry, sample BS-lOa appears to have had less of its original w.c.g. replaced than all other specimens (Figure 2). In contrast, BS-100 would seem to have had most of its original w.c.g. replaced by w.c.g. equilibrated with significantly lighter meteoric water. Although these samples are close together, the former is a chip from a giant gypsum crystal while the latter was taken from a fine crystalline layer covering the former. Therefore the crystalline character of these two specimens is consistent with the isotopic composition of their e.w.c.g. A problem arises with samples BS-9 and BS-I 1 which are much closer to the meteoric line (actually slightly above it); yet both specimens are from giant gypsum crystals, In the Jeziorko mine, sample TS- 14 is an unaltered gypsum specimen and its e.w.c.g. &-values fall along the proposed mixing line. However, sample TS-12 is strongly eroded and its e.w.c.g. b-values (d’s0 - -7t, 6D - -50% are very close to the average for present day groundwaters (Trembaczowski, unpublished data, 1979). This suggests that the original w.c.g. was replaced along the e.w.c.g. trend line of Figure 2 during a glacial period and subsequently re-equilibration towards present day meteoric water occurred. The former process should have one mixing line while the latter would have many isotopic mixing lines dependent upon the minimum &values achieved during the colder climate. It is not unexpected that the minimum 6values and the subsequent approach towards the isotopic composition of present day waters circulating through the deposits should depend upon the crystalline character of the gypsum. The most negative 6”O values for e.w.c.g. were found in the Basznia mine and these correspond roughly to the 6”O intercept value described above. This suggests that during a glacial time, or shortly thereafter, essentially all of the original w.c.g. was replaced. However these data differ from all others in that they fall well above the meteoric trend line. Such isotopic shifts can arise during fractional hydration of anhydrite under a limited supply of water (Matsubaya and Sakai, 1973, Sofer, 1978). This interpretation is consistent with the current study in that the sample furthest removed from the meteoric trend line in Finure 2(10/7z) was very weakly hydrated. This shift occurs along lines with slope -5 on a 6D vs 5’*0 diagram (Matsubava and Sakai. 1973). If such a line is drawn for sample 9/7z, it is interesting that it intersects the meteoric water trend line at approximately the same point as the mixing line described above. The w.c.g. of sulfur bearing gypsum (samples TS- 12, 9,’ 72, and 10/7z) might reflect the water present at the time ”
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of formation of native sulfur ore deposits since an aqueous medium is necessary for bacterial reduction. The 6% and dD values observed for these samples are consistent with carbon and oxygen isotope data on carbonates (HALAS et al. 1976) which led them to conclude that calcium carbonate was precipitated in water of continental origin. Thus, a simultaneous isotopic study of w.c.g. of strongly eroded gypsum and co-existent sulfur bearing calcium carbonate can be used to determine the isotopic composition of water present and hence the climatic conditions during ore formation. Acknowledgements-We are grateful to Dr. I. Osmolski of Geological Institute, Warsaw, for providing the samples from the Basznia mine. Funding to H. R. Krouse from the Natural Sciences and Engineering Research Council of Canada (N.S.E.R.C.) supported laboratory activities and the visit of S. Halas to The University of Calgary. We are also appreciative of comments on the manuscript by Keiko Hattori. REFERENCES Claypool G. E., Holser W. T., Kaplan 1. R., Sakai H. and Zak I. (1980) The age curves of suifur and oxygen isotopes in marine sulfate and their mutual inte~retation. Chem. Geoi. 28, 199-260, Craig H. (1961) Isotopic variations in meteortr: waters. Science 133, 1702- 1703. Czermiftski J. and OxmBlski T. ( 1974) Isotope relationships of sulfur and carbon in sulfur ore and accompanying formations and the origin of sulfur deposits in Poland (in Polish). ~wurfa~~ik Geof. 18, 334-357. Fontes J. C. and Gonfiantini R. ( 1967) Fractionment isotopique de I’hydrogene dans l’eau de crystallization du gypse. Comptes. Rend. Acad. Sci. Paris 265, 4-6. Gonfiantini R. and Fontes J. C. (1963) Oxygen isotopic fractionation in the water of crystallization of gypsum. Nature 20@,644-646. H&s S. (1973) A correlation between isotopic compositions of sulfur and carbon in native sulfur ores (in Polish). Przegiad geologiczny 21, 277279. Halas S., Slowikowska I. and Zuk W. (1976) The isotopic compositions of sulfur-bearing limestones in Tarnobrzeg mine, Proc. of National Conference on the use o_fStable Isotopes VI, Moscow (in Russian). Hahas S. and Moduchowski L. ( 1978) The isotopic composition of oxygen of calcium and strontium in sulfate minerals and aqueous sulfates from various regions of Poland. (In Polish) Annales UMCS 33AAA, I IS.1 30. Lyon G. L. (1978) The stable isotope geochemistry of gypsum, Miers Valley, Antarctia. D.S.I.R. Bulletin 220,97-” 103. Matsubaya 0. and Sakai H. (1973) Oxygen and hydrogen isotopes study on the water of crystallization of gypsum from Kuroko type mineralization. Geochem. f. 7, f 53-, 165. Pawlowski S. (1970) The geology of sulfur ores in Poland (in Polish); Geologia i surowce mineralne Polski, p. 614. Publisher: Wyd. Geol., Warsaw. Sofer Z. and Cat J. R. (1972) Activities and concentrations of oxygen- 18 in concentrated aqueous salt soiutions, analytical and geochemical implications. Earth Planet. Sci. Left. 15, 232-238. Sofer Z. (1978) Isotopic composition of hydration water in gypsum, Geochim. Cosmochim. Actn 42, 114 1 1149.