4 Results
4.3 Aqueous leachate data
The analysis of water-extracted constituents from powdered samples yields valuable informa-tion on the porewater composiinforma-tion of clayrocks, but requires careful interpretainforma-tion because of concurrent reactions occurring during the extraction procedure (e.g. Sacchi et al. 2000). The solutes in the extracted solution may originate from three different sources (e.g. Waber ed.
2008): a) solutes in the original porewater, b) dissolution of readily dissolvable primary mine-rals (e.g. carbonates, sulphates and sulphides) and release of cations from the exchanger, and c) constituents present in fluid inclusions.
Because of the strong dilution of porewater by the extraction method, cation exchange reactions and mineral dissolution affect the relationships between the major constituents. Thus, the cation concentration is altered and cannot be directly extrapolated to obtain the porewater composition.
This is also the case for anions which are affected by mineral dissolution reactions (e.g. bicar-bonate). The behaviour of reactive constituents can be followed by the analysis of the leachates at different solid/liquid ratios and compared to that of the conservative anions, such as chloride and bromide. These are usually not affected by dissolution reactions and can be extrapolated to in-situ conditions given their accessible pore volume – the so-called ion accessible or geo-chemical porosity – is known.
General observations
The analyses of all 126 subsamples are presented in Appendix B. For each sample, aqueous extracts of two subsamples (series a and b) were performed. As indicated in the methods section, the analytical error for major compounds is within ± 5 %, except for K, Mg and Sr at low concentrations where it is ± 10 %. The charge balance for the majority of the leachates is below 5 %, for six leachate samples it ranges between 6 and 10 % (Appendix B).
In Tab. 4-16, the averaged compositions of the two respective subsamples are shown. The standard deviation thereof reveals fairly small values, thus indicating fairly homogeneous rock material. The relative error derived from the standard deviation of the averaged composition for Na, Cl, SO4 and alkalinity is within 5 % for most samples, the maximum error is 10 % (Na, Cl, alkalinity) respectively 13 % (SO4). Ca and K display larger standard deviations with maximum relative errors of 45 % and 43 %, respectively. Mg shows similar standard deviations as Ca, except for a few samples (maximum 117 % relative error). The minor constituents Sr and F
0.25
Fraction of 'free' pore water (-)
Clay-mineral content (wt%)
show relatively small standard deviations (maximum about 30 %). Br and NO3 were often found to be below detection limit. Measured pH values show good agreement between the subsamples, with a relative error usually below 2 % (maximum 9 %).
From these observations, we deem justified to carry out the evaluation presented below with the averaged leachate compositions from the subsamples.
Considering the highest solid/liquid ratio (1:1) extract solutions, the dominant cation is Na+ whose concentrations range is 9.3 – 17.7 mmol/l, thus less than a factor of two. The other cations display distinctly lower concentrations. The anionic load is principally made up of chloride (1.5 – 5.2 mmol/l), sulphate (1.6 – 3.8 mmol/l) and bicarbonate (alkalinity 2.8 – 11.0).
A remarkable exception of the above characteristics is displayed by sample SLA 758.79 from an iron-rich oolithic horizon (Wutach Formation). These leachates show distinctly higher con-centrations in Cl (11.5 mmol/l), Na (21.2 mmol/l) and SO4 (4.7 mmol/l).
The presence of very low concentrations of low-molecular weight organic acids (acetate and formate) was observed by IC analysis. As noted in the methods section 3.4.1, no quantification was possible with the used separation column. Well-defined peaks were observed in the samples from the Wedelsandstein Formation (SLA 816.73) and the Posidonienschiefer (SLA 960.38), very small peaks in samples from the Opalinus Clay (SLA 898.31), and no peaks in sample from the Parkinsoni-Württembergica Beds.
NAGRA NAB 12-54 90 Tab. 4-16: Solute concentrations of aqueous leachates, each analysis corresponds to average of 2 subsamples (see also Appendix B). StratigraphySample IDSample IDS/LNaKCaMgSrFClBrNO3SO4Alk Labkg/lmg/lmg/lmg/lmg/lmg/lmg/lmg/lmg/lmg/lmg/lmeq/l Effinger SchichtenSLA 734.89SLA-10.1051.58.101.050.340.071.756.5<0.160.1737.61.70 SLA 734.89SLA-10.2596.711.691.350.470.103.8716.0<0.160.4492.52.44 SLA 734.89SLA-10.50159.215.722.170.720.154.7632.3<0.160.35173.52.93 SLA 734.89SLA-11.00263.522.724.291.510.315.2866.6<0.160.28342.33.32 Effinger SchichtenSLA 742.48SLA-21.00261.222.433.841.490.304.5868.80.180.28327.03.32 Effinger SchichtenSLA 750.73SLA-30.1047.78.051.220.350.081.526.2<0.160.2934.31.57 SLA 750.73SLA-30.2591.811.591.300.450.102.3115.2<0.160.3787.42.34 SLA 750.73SLA-30.50146.315.942.170.720.153.1430.7<0.160.23160.12.93 SLA 750.73SLA-31.00246.022.974.241.410.293.4063.20.190.43310.33.49 Wutach-Fm.SLA 758.79SLA-41.00487.747.7027.183.931.082.47408.80.520.33450.83.78 Variansmergel-Fm.SLA 765.31SLA-51.00224.321.322.300.730.173.4887.5<0.160.41166.34.51 Parkinsoni-Württembergica-Sch.SLA 768.62SLA-61.00231.416.461.672.340.135.57117.4<0.160.61165.43.56 Parkinsoni-Württembergica-Sch.SLA 778.70SLA-70.1060.76.270.771.580.050.8811.3<0.160.2221.32.22 SLA 778.70SLA-70.2594.09.230.540.450.051.9329.4<0.160.3750.33.15 SLA 778.70SLA-70.50151.412.490.860.480.083.1461.4<0.160.2499.03.75 SLA 778.70SLA-71.00246.216.811.730.490.154.70123.6<0.160.45191.03.39 Parkinsoni-Württembergica-Sch.SLA 787.33SLA-81.00272.417.233.020.670.204.09159.10.190.31236.42.76 Humphriesioolith-Fm.SLA 800.01SLA-91.00284.629.413.150.720.233.40143.40.180.34301.42.91 Wedelsandstein-Fm.SLA 812.11SLA-100.1064.86.230.410.490.040.9814.3<0.160.2516.62.66 SLA 812.11SLA-100.25104.98.600.500.460.052.1937.8<0.160.6244.53.32 SLA 812.11SLA-100.50161.411.110.750.260.073.4378.0<0.160.5881.53.92 SLA 812.11SLA-101.00262.214.421.630.460.145.06160.00.180.56155.33.66 Wedelsandstein-Fm.SLA 816.73SLA-111.00273.115.612.550.590.174.96184.80.221.05194.72.92 Wedelsandstein-Fm.SLA 823.53SLA-120.1068.55.810.410.320.030.8814.8<0.161.0718.22.55 SLA 823.53SLA-120.25107.87.680.600.910.052.0339.1<0.160.2341.53.35 SLA 823.53SLA-120.50162.410.130.740.330.073.3682.0<0.160.6282.43.68 SLA 823.53SLA-121.00253.514.901.700.380.144.69166.50.190.55157.63.34 OpalinustonSLA 833.08SLA-131.00288.724.663.921.140.272.74175.10.210.55154.54.99 OpalinustonSLA 844.56SLA-140.1066.25.930.680.310.050.8314.2<0.160.4121.52.40 SLA 844.56SLA-140.25118.98.420.950.250.071.6636.6<0.160.3152.53.73 SLA 844.56SLA-140.50188.211.781.680.410.122.1975.3<0.160.2398.94.73 SLA 844.56SLA-141.00307.817.483.780.960.242.39149.8<0.160.66181.86.07
91 NAGRA NA Tab. 4-16:(continued) StratigraphySample IDSample IDS/LNaKCaMgSrFClBrNO3SO4Alk Labkg/lmg/lmg/lmg/lmg/lmg/lmg/lmg/lmg/lmg/lmg/lmeq/l OpalinustonSLA 852.06SLA-151.00317.116.803.280.860.222.27155.7<0.160.72162.66.44 OpalinustonSLA 860.77SLA-160.1070.75.910.730.240.050.8615.2<0.160.8824.52.52 SLA 860.77SLA-160.25128.49.121.451.750.111.6038.7<0.160.4559.83.89 SLA 860.77SLA-160.50204.612.491.930.480.152.0880.2<0.160.99110.35.07 SLA 860.77SLA-161.00333.418.464.351.010.311.98158.60.181.06213.56.47 OpalinustonSLA 872.12SLA-171.00311.518.854.821.140.431.79154.20.180.83210.95.59 OpalinustonSLA 880.30SLA-181.00305.014.572.910.660.212.35159.50.181.00191.15.43 OpalinustonSLA 888.33SLA-191.00349.717.424.441.130.331.74162.60.180.83173.68.02 OpalinustonSLA 898.31SLA-201.00302.413.182.620.690.202.05153.60.170.27173.75.78 OpalinustonSLA 908.32SLA-211.00351.716.234.181.140.281.69145.6<0.160.28191.18.02 OpalinustonSLA 915.67SLA-220.1085.06.851.190.280.070.7814.7<0.160.5719.33.36 SLA 915.67SLA-220.25157.110.071.980.480.121.3437.4<0.161.0449.35.56 SLA 915.67SLA-220.50257.414.203.500.910.221.5376.0<0.160.2894.68.17 SLA 915.67SLA-221.00407.619.546.501.740.391.36151.5<0.160.27172.910.99 OpalinustonSLA 921.15SLA-231.00372.516.985.051.290.331.58151.8<0.160.18188.08.62 OpalinustonSLA 929.40SLA-241.00307.812.812.790.640.192.72133.3<0.160.21218.05.62 OpalinustonSLA 939.48SLA-251.00313.312.872.850.630.183.07149.3<0.160.77257.54.59 OpalinustonSLA 949.45SLA-260.1036.05.952.100.430.100.677.0<0.160.1924.31.35 SLA 949.45SLA-260.2577.78.831.780.470.101.2717.2<0.160.4560.72.19 SLA 949.45SLA-260.50126.111.662.320.610.131.7335.1<0.160.20108.92.99 SLA 949.45SLA-261.00213.915.713.900.970.201.9772.2<0.161.29208.83.82 PosidonienschieferSLA 960.38SLA-271.00323.015.754.211.110.414.23129.9<0.160.23364.43.31 Obtusus-SchichtenSLA 971.89SLA-280.1069.64.810.661.590.041.197.5<0.160.2121.12.91 SLA 971.89SLA-280.25110.66.070.551.010.042.7519.1<0.160.3456.03.78 SLA 971.89SLA-280.50162.37.950.510.200.054.3639.6<0.160.4599.44.81 SLA 971.89SLA-281.00249.311.261.220.570.095.9283.4<0.160.32201.74.54 Obtusus-SchichtenSLA 981.04SLA-290.1075.54.380.430.920.021.196.7<0.160.3318.83.06 SLA 981.04SLA-290.25115.86.230.721.050.032.8916.7<0.161.5250.44.42 SLA 981.04SLA-290.50166.87.810.560.240.044.4334.7<0.160.2793.85.59 SLA 981.04SLA-291.00255.611.371.581.130.095.7173.3<0.160.58180.85.83 Psiloceras-SchichtenSLA 987.61SLA-301.00232.013.721.010.320.065.5152.2<0.160.47161.16.43
Trends from different solid/liquid ratios
The behaviour of chloride, sulphate, alkalinity and fluoride as function of S/L ratio is depicted in Fig. 4-38. Chloride and sulphate show a linear behaviour for all samples with a high correla-tion coefficient (r2 0.99). In the case of chloride, this indicates a simple dilution relationship from the chloride porewater concentration, as is commonly noted in such formations (Pearson et al. 2003, Waber ed. 2008). In the case of sulphate, a similar dilution relationship might be deduced from the leachate data, but this is not supported by squeezing and advective displace-ment data (see below). The possible processes contributing to sulphate concentrations will be discussed in section 5.1.2. Alkalinity shows a non-linear trend, which is clearly noted above a S/L ratio of 0.25. This can be explained by the solubility control by calcite at higher S/L ratios (see section below). A similar trend is noted for fluoride.
Fig. 4-38: Concentrations of various anions for leachates as a function of S/L ratio.
See Tab. 4-16 for sample numbers.
The behaviour of the cations Na+, K+, Ca2+ and Mg2+ relative to the S/L ratio is depicted in Fig. 4-39. Sodium, the predominant cation shows for all samples a positive correlation with S/L ratio, with a slightly decreasing slope at higher S/L. It also shows a clear positive correlation with chloride (Fig. 4-40a). As illustrated in Fig. 4-39, for all samples, the curves do not pass through the origin, but have a positive intercept. Potassium follows a similar trend as Na+. Ca2+
and Mg2+ show a more variable trend for the different samples (Fig. 4-39).
0.0 0.1 0.2 0.3 0.4
0.0 0.2 0.4 0.6 0.8 1.0
fluoride (mmol/l)
solid/liquid
Fig. 4-39: Concentrations of varios cations for leachates as function of S/L ratio.
Calcium plotted against alkalinity does not exhibit a clear trend, except for two samples from the Opalinus Clay with very high alkalinity values, where a positive correlation is noted (Fig. 4-40b). For pH on the other hand, a decreasing trend with increasing alkalinity and also with increasing S/L is noted (Fig. 4-41). The explanation of this negative correlation is not straightforward and presumably the result of various simultaneously occurring reactions, such as mineral dissolution and cation exchange.
(a) (b)
Fig. 4-40: (a) Sodium vs. chloride and (b) calcium vs. alkalinity for leachates at different S/L ratio.
(a) (b)
Fig. 4-41: (a) pH vs. S/L ratio and (b) alkalinity vs. pH for leachates at different S/L ratios.
Depth profiles
The chloride concentrations from 1:1 aqueous extracts (in mg/l which is equivalent to mg/kgrock) depict a "bell-shape" curve with depth (Fig. 4-42a), thus indicating an increasing trend with depth in the Effingen Member and 'Brauner Dogger' units, whereas in the Opalinus Clay no trend with depth is observed. For the Lias unit, chloride concentrations show a decreasing trend with depth.7 A similar trend is observed for the chloride concentrations normalized to water-loss porosity (Fig. 4-42b), as calculated by eq. (3-5). Note however the distinct difference in the upper section, where the 'Brauner Dogger' samples display no trend of porewater concentrations with depth contrary to the mass-normalised profile. This difference may be explained by two opposing trends with depth for this rock unit: increase in (water-loss) porosity and increase in chloride per rock mass.
7 Note again the "outlier" of the Fe-oolithic sample from the Wutach Formation.
(a) (b)
Fig. 4-42: Chloride concentrations of 1:1 leachates as a function of depth (a) in mg/l or mg/kgrock (b) in mg/l normalised to water-loss porosity.
The sulphate depth profile for 1:1 leachates (Fig. 4-43a) shows a different behaviour compared to that of chloride. The samples for the Effingen Member display a narrow range of rather elevated concentrations (about 310 – 340 mg SO4/l). The molar SO4/Cl ratios (1.8 – 1.9) of these leachates are distinctly higher than those of the other samples. The sulphate levels of the 'Brauner Dogger' leachates depict rather large variations (about 150 – 450 mg SO4/l), which is also noted for the SO4/Cl ratios. The Opalinus Clay leachates depict concentrations ( 150 – 260 mg SO4/l) and SO4/Cl ratios which are more homogeneous than those of the 'Brauner Dogger'. The Lias leachates display concentrations of about 160 – 200 mg/l, except for the sample from the Posidonienschiefer which has 364 mg/l. There is no clear trend between sulphate contents in leachates and total sulphur contents (not shown).
(a) (b)
Fig. 4-43: (a) Sulphate concentrations of 1:1 leachates in mg/l or mg/kgrock (b) SO4/Cl molar ratio, as a function of depth.
Mineral saturation states and CO
2partial pressures
Speciation calculations for all subsamples were performed with the PHREEQC version 2 code (Parkhurst & Appelo 1999) and the Nagra/PSI database (Hummel et al. 2002). Partial pressures of CO2 and saturation indices of potentially forming minerals for all leachate waters are given in Appendix B. These parameters are also shown in Tab. 4-17 for subsamples of a series of 1:1 leachates. These are presented below.
CO2 partial pressures (pCO2) were calculated from alkalinity and pH measurements. The leachates depict pCO2 values in the range of about 10-5 – 10-3 bar (Fig. 4-44). These generally low partial pressures arise from the calcium carbonate equilibrium in a closed system (note that leachate tests were carried out in a closed N2 atmosphere). A systematic increase in pCO2 with S/L ratio is displayed. At the highest S/L ratio of 1, the pCO2 is fairly close to that representa-tive of atmospheric conditions (log(pCO2) = -3.26 ± 0.29 bar, 1), as is illustrated in Fig. 4-45.
Leachates from Opalinus Clay samples generally show slightly higher pCO2 values compared to the other ones.
The waters in all leachates are close to equilibrium with calcite and for most samples no trend with S/L ratio is manifested (Fig. 4-44). This suggests that during extract time near-to-equili-brium conditions have been reached irrespective of S/L ratio. For some Opalinus Clay samples, a trend towards slightly higher saturation index (SI) with increasing S/L ratio is noted.
However, even the samples with the highest SI (0.1 – 0.4) display only slight oversaturation.
This is an indication that CO2 degassing has induced only a minor oversaturation effect.
Tab. 4-17: Calculated pCO2 and saturation indices for leachates (only shown for series a, Appendix B).
StratigraphySample IDS/LlogSISISISISISI kg/lpCO2calcitedolomite(dis)gypsumcelestitestrontianitefluorite Effinger SchichtenSLA 734.890.10-4.26-0.35-1.45-3.68-3.15-1.03-2.21 SLA 734.890.25-3.84-0.34-1.43-3.25-2.68-0.99-1.40 SLA 734.890.50-3.72-0.18-1.13-2.88-2.32-0.85-1.22 SLA 734.891.00-3.42-0.12-1.00-2.38-1.83-0.80-0.93 Effinger SchichtenSLA 742.481.00-3.42-0.20-1.07-2.49-1.87-0.80-1.04 Effinger SchichtenSLA 750.730.10-4.46-0.20-1.23-3.66-3.13-0.89-2.09 SLA 750.730.25-4.11-0.20-1.14-3.31-2.71-0.82-1.96 SLA 750.730.50-3.84-0.05-0.90-2.88-2.38-0.77-1.55 SLA 750.731.00-3.49-0.03-0.82-2.43-1.90-0.72-1.32 Wutach-Fm.SLA 758.791.00-2.850.20-0.73-1.60-1.30-0.73-0.91 Variansmergel-Fm.SLA 765.311.00-3.27-0.23-1.23-2.92-2.35-0.89-1.55 Parkinsoni-Württembergica-Sch.SLA 768.621.00-3.55-0.33-1.03-3.08-2.47-0.95-1.27 Parkinsoni-Württembergica-Sch.SLA 778.700.10-4.68-0.06-0.07-4.14-3.60-0.74-3.00 SLA 778.700.25-4.28-0.18-0.70-3.88-3.17-0.70-2.50 SLA 778.700.50-3.91-0.26-1.35-3.50-2.87-0.85-2.01 SLA 778.701.00-3.37-0.51-1.84-2.98-2.32-1.07-1.30 Parkinsoni-Württembergica-Sch.SLA 787.331.00-3.51-0.23-1.42-2.59-2.10-0.96-1.24 Humphriesioolith-Fm.SLA 800.011.00-3.52-0.29-1.50-2.59-2.02-0.94-1.51 Wedelsandstein-Fm.SLA 812.110.10-4.34-0.43-1.00-4.52-3.91-1.04-3.21 SLA 812.110.25-4.12-0.30-0.90-4.01-3.32-0.84-2.46 SLA 812.110.50-3.80-0.31-1.37-3.62-2.95-0.86-1.96 SLA 812.111.00-3.56-0.27-1.39-3.08-2.44-0.86-1.26 Wedelsandstein-Fm.SLA 816.731.00-3.17-0.59-2.10-2.73-2.24-1.32-1.02 Wedelsandstein-Fm.SLA 823.530.10-4.35-0.43-1.09-4.47-3.88-1.05-3.25 SLA 823.530.25-4.13-0.17-0.29-3.89-3.26-0.76-2.32 SLA 823.530.50-3.84-0.37-1.54-3.65-2.94-0.89-1.94 SLA 823.531.00-3.60-0.30-1.54-3.07-2.47-0.93-1.33 OpalinustonSLA 833.081.00-3.10-0.01-0.88-2.70-2.18-0.72-1.39 OpalinustonSLA 844.560.10-3.96-0.52-1.60-4.15-3.66-1.26-3.05 SLA 844.560.25-3.73-0.28-1.41-3.71-3.12-0.91-2.38 SLA 844.560.50-3.39-0.20-1.28-3.24-2.70-0.88-1.99 SLA 844.561.00-3.130.09-0.68-2.68-2.18-0.63-1.58 OpalinustonSLA 852.061.00-3.01-0.03-0.93-2.81-2.27-0.72-1.69
Tab. 4-17: (continued)
StratigraphySample IDS/LlogSISISISISISI kg/lpCO2calcitedolomite(dis)gypsumcelestitestrontianitefluorite OpalinustonSLA 860.770.10-4.00-0.34-1.49-4.00-3.52-1.09-2.93 SLA 860.770.25-4.890.420.68-3.64-2.95-0.11-2.41 SLA 860.770.50-3.27-0.15-1.21-3.12-2.54-0.79-1.93 SLA 860.771.00-3.110.14-0.63-2.60-2.03-0.51-1.71 OpalinustonSLA 872.121.00-3.070.06-0.79-2.54-1.88-0.51-1.73 OpalinustonSLA 880.301.00-3.10-0.15-1.22-2.79-2.22-0.80-1.71 OpalinustonSLA 888.331.00-2.870.12-0.64-2.68-2.11-0.53-1.80 OpalinustonSLA 898.311.00-3.07-0.15-1.13-2.86-2.28-0.79-1.92 OpalinustonSLA 908.321.00-2.910.13-0.59-2.66-2.13-0.56-1.86 OpalinustonSLA 915.670.10-3.50-0.40-1.69-3.95-3.46-1.13-2.88 SLA 915.670.25-3.17-0.09-1.10-3.38-2.92-0.85-2.23 SLA 915.670.50-2.820.06-0.75-2.96-2.46-0.67-1.95 SLA 915.671.00-2.630.31-0.23-2.54-2.05-0.43-1.86 OpalinustonSLA 921.151.00-2.870.29-0.29-2.55-2.03-0.42-1.80 OpalinustonSLA 929.401.00-3.380.08-0.76-2.77-2.23-0.60-1.62 OpalinustonSLA 939.481.00-3.690.17-0.60-2.71-2.19-0.54-1.68 OpalinustonSLA 949.450.10-4.630.10-0.78-3.51-3.15-0.77-2.69 SLA 949.450.25-3.92-0.20-1.26-3.26-2.83-0.99-2.26 SLA 949.450.50-3.930.08-0.71-3.01-2.55-0.69-1.96 SLA 949.451.00-3.630.19-0.52-2.58-2.17-0.62-1.70 PosidonienschieferSLA 960.381.00-3.890.19-0.47-2.42-1.71-0.33-1.09 Obtusus-SchichtenSLA 971.890.10-5.080.170.53-4.17-3.72-0.61-2.75 SLA 971.890.25-4.15-3.43-0.95 SLA 971.890.50-3.49-0.55-1.78-3.67-3.03-1.13-1.81 SLA 971.891.00-3.34-0.41-1.32-3.08-2.54-1.10-1.24 Obtusus-SchichtenSLA 981.040.10-4.46-0.26-0.38-4.47-3.88-0.89-3.03 SLA 981.040.25-3.89-0.03-0.05-3.73-3.40-0.92-1.91 SLA 981.040.50-3.52-0.38-1.37-3.68-3.06-0.98-1.78 SLA 981.041.00-3.24-0.12-0.56-2.96-2.50-0.89-1.11 Psiloceras-SchichtenSLA 987.611.00-3.35-0.19-1.18-3.25-2.81-0.97-1.38
(a) (b)
Fig. 4-44: (a) logpCO2 vs. S/L ratio and (b) SI(calcite) vs. S/L ratio.
Leachates for subsamples of series a (see Appendix B).
Fig. 4-45: Calculated logpCO2 (bar) plotted for all 1:1 leachate samples.
Leachates for subsamples of series a (see Appendix B).
Leachates are slightly undersaturated with disordered dolomite, which is thought to represent the dolomitic phase forming in low temperature clay-rich sediments (Pearson et al. 2003). In general, a similar trend as for calcite is noted, with Opalinus Clay samples showing a slight increase of SI with increasing S/L ratio. For strontianite, saturation indices show slight under-saturation for all waters.
All extracts are undersaturated with respect to the sulphate phases gypsum and celestite, but show a clear positive correlation with S/L ratio. At the highest S/L ratio of 1, SI(gypsum) varies between -1.6 and -3.2. The corresponding range for celestite is -1.3 to -2.8.
-4.5 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0
734.89 742.48 750.73 758.79 765.31 768.62 778.70 787.33 800.01 812.11 816.73 823.53 833.08 844.56 852.06 860.77 872.12 880.30 888.33 898.31 908.32 915.67 921.15 929.40 939.48 949.45 960.38 971.89 981.04 987.61
log pCO2
All waters are undersaturated with regard to fluorite, but reveal increasing SI with S/L ratio. At the highest S/L ratio of 1, SI(fluorite) varies between -0.9 and -1.9.
Overall, these relationships suggest near-to-saturation for in-situ porewater with calcite and slight undersaturation with dolomite. Moreover, porewaters are clearly undersaturated with regard to gypsum, celestite and fluorite.