Geochimica d Cosmochimica Ado Vol. 53, pp. 1765-1175 0016-7037/89/$3.00+ 03 cowright 8 1989 Pogamon Pres plc.Printed in U.S.A.

The of in groundwater at Stripa*

P. FRITZ’,~, J-CH. FONTE!?, S. K. FRAPE’, D. LOUVAT*,J-L. MICHELOT*and W. BALDERER~ ‘Department of Earth Sciences University of Waterloo, Waterloo, Canada, N2L 3Gl ‘Laboratoire de Hydrologie et de Gtochimie Isotopique, Universitt de Paris&d, F-9 1405 Orsay, France ‘Department of Engineering-Geology, ETH Ziirich, CH-8093 Ziirich, Switzerland

(Received March 4, 1981; accepted in revisedform May 21, 1988)

Ah&r&-The carbon isotopic composition of the total dissolved inorganic carbon in groundwater associated with a granitic pluton at Stripa (Sweden) reflects both inorganic and organic carbon sources. Following the uptake of -dioxide, dissolution dominates the geochemical evolution of shallow groundwater. Calcite saturation is reached at a depth of about 100 m. In deeper waters geochemical release of Ca and increasing pH cause calcite precipitation. Radiocarbon contents suggest carbon (and water ?) ages in excess of 20 000 years for waters at 300-400 m depth. In deep groundwaters with enhanced salinities organic carbon is added to the dissolved inorganic carbon either through bacterial activity (e.g. sulphate reducing bacteria) or the oxidation of organic compounds such as . The lowest radiocarbon contents were measured at the 3UO-400 meter levels and not in the deepest fluids. The distribution of “C in the deep groundwaters suggests the existence of well-defined flowsystems with limited active hydraulic interaction. Isotope analyses on fracture calcites substantiate the complex geochemical history of the pluton. _

INTRODUCI’ION despite a very limited knowledge of their geology and history; d) surface boreholes into the granite which served for hydro- RADIOCARBONDATING of groundwater was initially seen as geological observations and tracer tests; e) all boreholes drilled an essential element of all hydrogeological and hydrochemical from mine levels and which yielded enough water for carbon investigations at Stripa. Limits were primarily expected be- isotope analyses. cause of the sample size required for conventional carbon- 14 analyses and the very low alkalinities of these waters. Only EXPERIMENTAL PROCEDURES recently, first attempts have been made to utilise tandem Samples for 13Cand 14C measurements were collected either by accelerator mass-spectrometry (TAMS) to determine both precipitation of the total dissolved inorganic carbon (TIC) with “C and 14C contents on samples which are up to 100 times BaC12. 2 Hz0 or were shipped in aqueous form to the laboratory and extracted by acidification with phosphoric acid. Methods used are smaller than those required for gas or liquid scintillation indicated in Table 1. counting (MURPHY, 1987). Precipitation with BaC12- 2 Hz0 is a standard procedure which in The interpretation of 14C data obtained on inorganic or most cases produces very reproducible results for both “C and ‘% organic carbon compounds in groundwater systems, usually determinations. However, the low inorganic carbon contents of the deep Stripa water (< 10 mg 1-l) provided a challenge for conventional require a detailed understanding of the carbon geochemistry. 14C counting which requires >l g carbon. A number of different Stable carbon isotope data contribute significantly to the dis- sampling procedures had to be used for both ‘% and 13Canalyses. cussion. a) For samples with carbonate alkalinities above about 10 mg I-‘, This manuscript discusses the 14C and 13C data obtained up to six 60 liter bottles were tilled in series to minimize air contam- on aqueous carbonate from groundwater at Stripa (Sweden) ination, and precipitation was done with Fresh, decarbonated reagents. as well as results of fracture calcite analyses on samples col- After settling and decanting, the Ba- was washed with de- lected from cores from the Stripa granitic pluton. However, gassed, distilled water before filtration and shipment or was shipped a detailed discussion of the isotopic composition of fracture to the laboratories in heavy wall plastic bottles with tight caps. Both gave reproducible results although the washed and Iiltered samples minerals, their chemistry and mineralogy, will be presented appear to be more reliable because the lowest 14Ccontents were mea- elsewhere (hAPE ti al., 1989); organic carbon analyses will sured on such samples. be discussed in detail by E. MURPHY (1987). b) All samples collected in the above manner were also analyzed Sampling locations for groundwater samples include: a) a for 13C.Results obtained were compared to “C measurements made tailings pond which served as discharge for the mining/ex- on samples shipped as water in glass or heavy wall plastic bottles. To prevent biological activities the samples were poisoned with HgCI. cavation operation; b) watertable wells which were installed Gas extraction was done in the laboratory by acidification with con- within hydrogeological programmes to obtain a regional pic- centrated H3P04 and purification by cryogenic distillation. With very ture of the groundwat$r table at Stripa; c) private water supply few exceptions 6°C values obtained by the two methods agree Wells in the general region of Stripa (see also FRITZ et al., within +I%. c) For alkalinities below about 10 mg I-’ and flow rates of less 1979) which were sampled to obtain geochemical data as than 5 l/hour (most deep boreholes) a flow-through stripping system well as information on the average isotopic composition of was constructed (Fig. 1). Mean residence times of the water was ad- groundwater and its aqueous carbon and sulphur compounds, justed through float controls to 3-5 hours. was lib- erated by controlled H3P04 acidification, tlushed with purified N2 or He and trapped in 5 N NaOH solution. The float controls nermitted continuous operation for up to four weeks with very little supervision. l This paper is published as part of a series reporting results of the Nevertheless, the long sampling times may permit minor air contam- International Stripa Project. ination and the lowest 14Cvalues measured are, therefore, considered t Present address: GSF-Institut fIir Hydrologic, D8042 Neuherber& to be most reliable. The carbonate was precipitated as BaC4 before F.R.G. shipment. 1765 1166 P. Fritz et al.

TABLE 1 The carbon isotopic conposition of aqueous inorganic rarbon I” strip” groundwaters

Lacation/Boreholr ‘al- pmc

Tailing pond 77.-09-12 23 2 Watertable wells WT-2 79 -OS-06,18 -23.2 wl-3 79-05-0, -21.8 Private wells PW 1 77-09-27 -15.2 79-05-18 --14.0 PW 2 77.-10.24/27 -15.0 53.8”’ 71-10.24/27 -15.2 -14.9 54.1” PW 3 79-05-16 -13.4 PW 4 79.05-17/24 -13.7 -14.1 52.1” PW 5 77-lo-06,13 -19.1 -18.1 89.3b’ 79-05-15 -22.3 SBH-3 79-05-22/28 -15.6 -15.2 62.8=’ “3 77-09-09/21 -15.8 2.5b’ 78.06-08,12 -16.8 -15.7 3 4”’ 16-11m20/24 -16.8 3.5” 79-05-02/10 -16.2 -16.3 6.4=’ 79.11.11/12 -15.9 -16.9 2.8=’ 79.11.20,22 -16.0 -15.8 3.3”’ 64-03 -15.9(-16.7)*’ 86-05 -16.8 RI O-30 78.08.09/26 -16.2 4.5” 78mll-17/24 -17.1 -19.” 6 6“ 79.06-02,08 -16.4 17 7 7 0” 79-05-09 -16.1 R9 O-30 79-05-22 15.5 N-l 252-300 84-02-14 (Fl7.3) 151-251 -15.9(-17.1) 120-150 (-13.0) 10-119 1~14.0) 83 -23.1+2.4 3.95t3.03” -18.7’3.2 16.06+0.33” E-1 open hole 84-02-14 (-17.6) V-1 IO-550 84-02-14 (-23.4) 430-505 85-03 -21.0 430-505 86-05 -24.6 “-2 6-50 77.09-09/20 -16.1 -15.5 6.Ob’“’ 8-40 78.06-08/12 -16.6 -15.7 2.1” 78-l-16/20 -16.5 2.0” 79-09-11/13 -15.9 -16.9 2.81’ below 50 71-09-06/14 -18.3 -16.9 below 280 77.09-14/20 -18.6 -17.8 below 380 18-06-12/24 -18.7 -17 5 13.6” 332-259 79-01&31/02-20 -17.6 ll.l_’ 79-02~20,03-16 -18.7 10.6”

400-428 78 ~11-20 -16.9 78-l-22/12-20 19.4_’ -13.3 400-428 79-04-06,27 -13.3 7.8” 79.05-07/11 -14.0 ~13 6 5.w 79-05-18/21 -14.4 O-428 77-lo-24,26 -16.1 -16.9 5.1”’ -18.5 4.7”’ 424-499 83-11-28 -35.6+7.8 14.67+0.75=’ 362-423 84-02-15 (-16.9) 424-490 84-02-16 t-28.31 500-561 84-02-15 i-30.8) 562-822 84-02-15 (-19.6) 390-402 86-05 -16.5 402-410 86-05 -18.0 490-498 86-05 -23.3 560-556 86-05 -25.9 559-822 86-05 -16.1

a) The ‘=C. TIC () values refer to samples collected and acid extracted specifically for ‘V analyses. (sample size 1 1). whereas the “=C - B&O. values were obtained on barium carbonate precipitated for ‘*c analyses (large volumes).

b) ‘=C-BaCO, and ‘*C analyses done at Inter”. Atom. Energy Agency. Vienna. Austria.

Cl 13C-BaC0, and ‘&C analyses done at Univ. of Waterloo. Waterloo. Canada.

dl Results in brackets refer to data obtained on samples shipped in plastic bottles. Ail other TIC samples were collected in glass bottles and analysed by UW or UPS.

e) Analyses done by accelerator measurements by the University of Bern on barium- carbonate precipitated at Stripa.

f) Analyses done by accelerator n~easurenent by the University of Bern 0” acid- extracted CO. prepared at University of Paris Sud.

‘V and ‘=C analyses were gl “C samples were collected with flow through stripper. done on B&O,, precipitated from NaOH sOlUtio”. The ‘OC TIC samples are considered to be more reliable. Analyses by University of Waterloo.

h) ‘*C samples collected as B&U, precipitate fron several 60 litre jugs; unless noted analyses by University of Waterloo. Stripa groundwater: C isotopes 1767

GAS OUTFLOW a strong indication that the carbon geochemistry of different SAMPLE WATER INFLOW groundwaters is dissimilar. Furthermore, all 13C-TIC values PRESSURE - RELIEF VALVE GAS OUTFLOW are below - 1Ok, which suggests that biogenic carbon or or- ganic carbon compounds are important in these systems.

Carbon-13 The carbon isotopic composition of the aqueous carbon is a direct reflection of the geochemical history of a ground- water. This evolution begins in the recharge environment and continues in the subsurface where mineral-water inter- action will dominate. Bacterial processes can further modify the isotopic composition of the aqueous carbon. d13Cvalues as high as +20% can be generated if methane production occurs or very negative values are found where organic com- POROUS STAINLESS STRlPPEO WATER pounds are mineralized and added to the inorganic aqueous STEEL q lSC OUTFLOW carbonate (TIC). -‘qrdy0-f4NG SEALS Geochemically least evolved is water collected from wa- C+-FREE NS or H. GAS ter-table wells in which the carbon geochemistry is largely

FIG. 1. Carbonate stripper used to extract carbon dioxide by acid- determined by the pCOz of the soil zone. In the shallow ification with a countercurrent of purified Nr and NaOH absorption. groundwater environment, the lowest 13Ccontents are found The residence time of a sample volume in the column was in the in water-table well WT2 which has a b13C = -23.2?60 PDB order of 3 hours. The system was built with J. F. Barker, University of Waterloo. and pH = 5.1. Assuming open system equilibration the soil- CO2 would be close to -23.0% (relevant Fractionation factors are summarized by FRIEDMANand O’NEIL, 1977). Chemical d) To overcome the problems associated with this large volume data agree with this interpretation since the field alkalinity sampling, TAMS dating was attempted. For sample preparation two (2.9 ppm HCOr) corresponds to contents expected in high 2 litre samples were collected and shipped to UPS for acid extraction. pCOz, + low pH water. Furthermore, the water is saturated An additional similar sized sample was collected as BaCOs in the mine and all three samples were analyzed by TAMS through the with atmospheric oxygen. The water in this well is thought University of Bern (Target preparation at the University of Bern, to represent most closely the initial recharge condition for accelerator measurements at ETH Zurich). The results are encour- presently forming groundwaters in this area. a8ing, although contamination problems on acid extracted samples Calcite dissolution probably occurs already in the shallow prepared in the laboratory appear to persist. Similar problems were groundwaters at Stripa, yet only deeper waters in private wells encountered by E. Mutu+tv ( 1987)on samples of Strips groundwater. (- 100 m) are saturated with respect to calcite (FRITZ et al. All but the three TAMS 14Canalyses were done by liquid scintil- 1979). This is in agreement with observations made at other lation counting on benzene prepared from carbon dioxide. Results Swedish test sites (LARSONand TULLBORG, 1984; TULLBORG are expressed as percent modem carbon (pmC) which is defined as and LARSON,1986). Calcite saturation is most likely achieved 95% of activity of an oxalic acid standard distributed by the National Bureau of Standards (Gaithersburg, MD). by open system uptake of soil-CO2 which is followed by dis- Carbon-13 analyses were done by mass-spectrometry on carbon solution of calcite. Calcite occurs locally in the overburden dioxide prepared vin acid extraction or reaction of BaCOs with phos- but is also abundant on fracture surfaces of the Stripa granitic phoric acid; comparisons on sequentially coIlected samples am shown rock. Model calculations on waters from private wells, as- in Table 1. Results are expressed as permille differences (L% values) from the PDB standard. Analytical precision is better than ItO. 15% suming a pure carbonate system (FONTES and GARNIER, and overall reproducibility on repeat samples collected at the same 1977, 1979; REARDONand FRITZ, 1978), show that for the time is better than about kO.5560. above conditions the dissolving calcite has 6’3C-values be- Fracture calcites were collected from borehole samples and fracture tween about -5 and -8%. surfaces exposed in the excavation. Isotope analyses (“C and ‘*O) In these calculations it is also assumed that the dissolving were done on carbon dioxide produced by reaction with 100% phos- phoric acid at 50°C. Results are expressed as d-values with respect calcites are free of “‘C and that the measured 14C activities to the PDB standard for “C and PDB or SMOW for ‘*O. The con- reflect dilution effects (see below). version from &PDB to I-SMOW is given by: The importance of closed system calcite dissolution is also 6’sOss,o,., = 1.030866’80pt,B + 30.86. (1) seen in the 13Ccontents of the total dissolved inorganic carbon (TIC) in water from private wells (depth

RESIDUAL FRACTION exist in these fracture systems. This does not exclude similar 0.8 0.6 0.4 0.2 geochemical evolutionary paths but excludes direct compar- ison of many samples. Borehole N 1 is remarkable because it shows a larger spread -:,;:::,:;::\ towards negative 613C values. MICHELOT et al. (1984) and FONTESet al. (1989) point out that sulphate reduction may be actively proceeding in this borehole, as the aqueous sul- phate concentrations are very low. Thus, the low G”3C-values could be due to sulphate reducing bacteria. However, water with higher salinities enters this borehole within a small sec- tion and as saline waters are found in the deep groundwater at Stripa it appears possible that some fractures intercepted by N 1 were supplied by a system that resembles or is identical to the one providing the saline water dishing at depth. As will be seen below, some of the deep, saline waters are

I . * * . & I I I characterized by very low 8°C contents possibly associated 50 6.0 7.0 6 0 90 with sulphate reduction. PH The changing 13Ccontents are emphasized in Fig. 3. To a 0.8 0.6 0.4 0.2 0 depth of about 800 m the GL3C-valuesof most TIC samples are close to values seen in M3, Rl and the top of V2. This f is followed by a sharp drop in ‘% which has its minimum FE. 2. Carbon isotope effectsduring closed system calcite pmcip at about 900 m below ground surface (borehde intervals are itation. The equilibrium fractionation effect between halite and indicated in Table 1). At this depth b”C-values as low as aqueous carbon in the Rayleigh curve was assumed to be 1.0025 -35%0 were observed. Below this zone more “typical” values (WIGLEY, 1976). return. Figure 3 shows a trendline based on V 1 and V2 data. This low 13C zone closely coincides with the high salinity Chemical analyses suggest that in the 300 m level mine water, It is unlikely that Rayleigh effects account for the shift waters up to 50% and in the deeper, saline waters 90% or because the carbonate contents of these waters do not differ more of the initial TIC is “removed” (FRITZ et ai., 1979; substantially from other mine waters. Therefore, these low NORDSTROMet al., 1985). Where calcite precipitation occurs 613Cvalues are seen as an indication that at least these waters under closed system conditions in a finite reservoir this re- received “organic” (not necessarily biogenic) carbon. The moval could cause some isotopic depletion in the residual aqueous carbonate. At the high pH values of the Stripa groundwaters the fractionation effects are between 2 and 3% S =C %. PO8- TIC O-3o -25 _ -20 -15 and, as shown in Fig. 2, r3C depletions in the TIC by -Z&O / I.,", or more may have to be expected (WIGLEY, 1976). ##/ The b13C values of the waters from the 300-400 m depth 100 0 interval (boreholes M3, RI and the top of V2) group in a rather narrow range of - 15.5 to - 17.6’50. These values are close to or slightly lower than those seen in most private wells and could be explained by a minor isotope effect associated with the precipi~tion of calcite. (Note, the isotope fraction- ation between calcite and dissolved carbonate or bicarbonate ion is experimentally not well defined; SALOMONSand MOOK, 1986) summarize data from various sources which could in- dicate that the TIC-calcite fractionation might be somewhat smaller than indicated by the data shown in Fig. 2 and used by WIG~EY (1976) or DEINESet al. (1974). The recharge con- ditions of the deep waters in terms of vegetation cover and NO,, could then be similar to those existing today in the area. Should calcite formation not play a significant role (es- pecially if smaller isotope effects were valid) then the 613C- values would have to reflect lower i3C contents in the recharge environment. Calcite pupation and changing recharge conditions are, .-- however, not the only explanations for the 6r3C values ob- FIG. 3. The G’3C-valuesof Total Dissolved Inorganic carbon (TIC) served in different mine waters. Chemical and ‘eO/2H data versus depth below ground surface for Stripa groundwater. The discussed in this volume strongly suggest that the different trendline is based on data from boreholes VI and V2. Similar data waters collected in the Stripa boreholes are not directly were obtained by E. MURPHY (pm. commun., 1986). Vertical bars evolved from one another but that independent flow systems indicate sampling intervals. Stripa groundwater: C isotopes 1769 source of this carbon is not yet known but it is important to with A, and A0 being the measured and initial 14Cactivities, note that the deep waters of V 1 contain relatively high counts X the decay constant (1.209 X 10e4 a-‘) and t the time in of anaerobic bacteria, including denitrifiers and sulphate re- years. ducing bacteria (CHRISTOIZIet al., 1985). Within any repository it is essential to arrive at an under- Minor amounts of methane are present in the deep standing of the age and geochemical history of waters en- groundwaters of Stripa and a sample analysed within the countered. Thus, radiocarbon dating plays a crucial role de- Swedish Deep Gas Project gave a 613C value of -3OL. spite the fact that numerous studies focussed on the large (SWEDISHSTATEPOWERBOARD, 1985). The“bacterialoxi- uncertainties associated with the transformation of measured dation” of such gas could account for the low 6°C values of 14Cactivities into “water ages”. the TIC. Note, that the word “age” is used in these discussions, Another process which could generate such isotopically although it does not describe the “age” of a single water mass. light carbon could be the bacterial reduction of sulphate based At best one can consider “mean residence times” of a on a organic carbon (DGC) food source. As already men- groundwater. However, even this term may be misleading tioned sulphate reduction does occur in parts of the granitic because it is quite likely that many of the waters collected in pluton (see FONTES et al., 1989) and sulphate reducing bac- this study represent mixtures of two or more components. teria have been identified. Furthermore, dissolved organic For example, a saline old component may have been added matter and other “nutrients” appears to be present in suffi- to less saline, younger groundwater and the radiocarbon data cient quantities to sustain a variety of bacterial processes would reflect the “average” of the two carbon sources, where (CHRISTOFIet al., 1985). The TIC would then receive iso- AB_C = QeBA%-Ar + Q,mcA%x’ topically light carbon via bacterial respiration, whereby the (3) isotopic composition is determined by isotope effects which QBm + Qcmc occur during the bacterial metabolism. Experimental data and Q describes the proportion of mixing, m the carbonate obtained by W. STICHLER (pers.commun., July 1987) doc- alkalinity, A the initial 14Cactivities and t the mean residence ument that bacterial matter and thus respiration CO* can be time of components B and C respectively (see FONTES, 1983, significantly depleted over the carbon source. 1985, for details). Where bacterial activities lead to methane production, Since at Stripa the shallow, young groundwater carry con- carbon dioxide will be co-produced and will be strongly en- siderably more carbon than the deep water (typically > 100 riched in “C. No evidence for such activities are presently mg/L vs. < 15 mg/L respectively) the admixture of minor found but may have occurred locally and is inferred from amounts of young carbon (water) to the deep waters could 13Cdata on fracture calcites on which 613C values as high as mask the radiocarbon contents of the deep waters. However, +15’% have been measured (FRITZ et al., 1979, see also mass balance calculations are at best tenuous because end- below). member compositions are poorly defined especially for very Based on the data available it is concluded that the carbon young waters, which can show considerable chemical and in the aqueous carbonate of the Stripa groundwaters is isotopic variations and because exponential decays can hardly strongly influenced by the presence of biogeniclorganic car- be averaged. bon with the possible participation of active bacterial systems. Thus, it is suggested that absolute age determinations based A strictly inorganic evolution of the groundwater chemistry on 14C are not possible for the Stripa groundwaters and, in- would only be supported by the stable carbon isotope data stead, such analyses should only be used to assess the relative if Rayleigh effects during calcite precipitation were very ef- “age” of the different aqueous geochemical systems in the fective in one specific fracture system only. Chemical data Stripa granite. Similar observations are probably necessary provide no support for this interpretation. for other tools such as 39Arbecause the subsurface production of radionuclides within the crystalline rock of the Stripa plu- Carbon-14 ton are significant. The concentration of carbon-14 in the dissolved carbon Carbon uptake in the recharge environment is usually fol- (organic or inorganic) in a groundwater is determined by a) lowed by geochemical reactions in which the carbon-budget the geochemical history of a water and b) the radioactive of a groundwater is affected by carbonate mineral dissolution decay of 14C. If the first is understood, the second can be and/or precipitation. The dissolving carbonate is usually 14C- used to date the aqueous carbon and thus indirectly the water. free (an activity of x0.3 pmC was measured on a sample The basic concept underlying the carbon- 14 dating requires from the 300 m levels) and will dilute the existing 14C res- that water inliltrating through vegetated soil becomes charged ervoir. This necessitates an adjustment of A0 in the decay with soil-CO2 before it is incorporated into a groundwater equation. Where a simple two component mixing system exists “C contents will reflect this mixing and can be used IWXVO~~.Because this soil-CO2 has a partial pressure generally much higher than the atmospheric CO*, it dominates the to quantify the 14Cdilution. The mixing model by INGERSON carbon isotope contents of infiltrating water. Its 14Cactivity and PEARSON(1964), modified through the introduction of an isotope effect between soil-CO1 and TIC to obtain from is very closeto the 14Cactivity of the . If no other carbon were added, and only decay altered the 14Ccontents changing 13C contents a correction factor (q) for the decay of the dissolved carbonate, this residual activity would be a equation, is still the most simple and most applicable: function of time only where G’3C-TIC - 6°C-CARB (4) A, = A&’ (2) ’ = G’3C-SGIL + e - G13C-CARB 1770 P. Fritz et al. and not exclude some open system dissolution where calcite is present in near surface environments. A, = q“&)e--“I (5) where 613C-TIC is the measured 613C value of the sample, These conclusions are not unreasonable. The low pH im- G”C-CARB is the value for the dissolving rock-carbonate (or plies a pCOz of > lo-* atm which is not abnormal for soils any other secondary carbon source), G’3C-SOIL is the isotopic in these environments (unpublished data from the Kenora composition of the soil-CO2 and e is the pH dependent iso- Lakes Experimental Watersheds, Kenora, Ontario, Canada), topic difference between soil-CO~ and inorganic carbon (TIC) and/or the presence of organic acids. Under moss covers, under open system equilibrium conditions. This latter value pCG2 values can reach values in excess of 10-l atm and will be close to OL for recharge environments with pH close organic acids are present in abundance. The initial 14C ac- to 5-such as found at Stripa-but increases to values as tivities will be above 100 pmC for very young waters and at high as 10% as the pH in the recharge area rises and the about 100 pmC for the somewhat older, shallow systems. system remains open to equilibration with soil-C02. Where The surface environment in the immediate vicinity of the recharge conditions cannot be estimated, the term “e” is usu- Stripa mine appears to be free of carbonate. Therefore, very ally neglected. shallow groundwater are undersaturated with respect to cal- In cases where the geochemical evolution of a groundwater cite. However, calcite is present on deeper fractures and dis- can be described by simple inorganic reactions (chemical and solution does most likely occur under closed system condi- isotopic) geochemical/isotope models can be developed to tions. TULLBORGand LARSON(1986) observed for the Klip- evaluate the required correction factors (WIGLEY, 1975; peras site in southern Sweden that calcite dissolution proceeds REARDON and FRITZ, 1978; WIGLEY et al., 1978; FONTES to a depth of about 100 m; below it calcite saturation is and GARNIER, 1979). These models are applicable to the reached. The situation is similar in Stripa groundwater from shallow groundwaters sampled at Stripa. Figure 4 shows the 300-400 m mine levels (FRITZ et al., 1979; NORDSTROM graphically the dilution of initial activities for two wells (PW et al., 1989). 2 and PW 5) on the basis of chemical and isotope analyses, The uptake of calcite carbon influences both ‘“C and 14C using a model calculation in which the measured carbon iso- contents of the Stripa groundwaters. The calculated 14C di- topic composition can be compared with a theoretical com- lution factor “q” derived from these shallow samples, by position calculated for assumed atmospheric 14C activities comparing measured and calculated initial activities lies be- (to reflect pre- and postbomb situations) and different 6”C- tween 0.7 and 0.5. This value is considerably smaller than values for rock carbonate. Different evolutionary paths result was estimated (GEYH, 1972) for groundwaters in crystalline and since decay cannot have affected the 14Cactivities of the rocks. Figure 5 is a comparison of 613Cvalues and 14Cactiv- TIC, intercept at age zero represents a possible solution ities and shows both the increase in 13C and dilution of ra- (REARDONand FRITZ, 1978). diocarbon, It suggests that shallow groundwaters follow an The principal conclusions of these calculations are “evolutionary trend” which leads to G’3C-values between about - 12 and - 15%0.The somewhat lower 6’3C-values seen -soil CO2 with a 6°C = -23%0 has equilibrated with the in the 300 m level boreholes are possibly explained by calcite infiltration water at pH -5. precipitation and associated Rayleigh effects (see above). -the 14C activity of the soil COZ was between 100 and The removal of calcium carbonate from solution has little 130 pmc, and effect on the 14Cactivities because the 14Cisotope effects are -14C-free rock carbonate with an average 613Cvalue below only about 2.3 times those known for 13C (SALIEGEand -5%0 dissolved under closed system conditions. This does FONTES, 1984). Thus a 2%0 decrease in 13C activity corre- sponds to a 4.6?& or about 0.5 percent decrease in 14Cactivity. Therefore, the lower 14C contents seen in the mine waters must be explained either by decay or additional dilution of the 14Cpool. It is difficult to find any specific process which could ac- count for the low 14C activities measured in boreholes M3, Rl and the top of V2 (see Fig. 5). No evidence exists that the addition of biogenic or organic carbon plays a role in the waters of these boreholes. CHRISTOP~et al., (1985) note that water in M3 contains enough oxygen to support aerobic bac- teria. Furthermore, the narrow range of 613C values argues against active biological processes. These would be much more “dispersive”. YEARS 1 IO-’ I However, NERETNIEK~(198 1) showed that diffusive loss 2 -2 -4 -6 -0 -10 - 12 of radiocarbon into water within micropores of the rock ma- FUTURE HISTORY trix can become very significant, depending on fracture spat- FIG. 4. Evolutionary paths of total dissolvedinorganic carbon (TIC) ing and width. For example, for a 2 m fracture spacing and in shallow groundwater at Stripa. The matchpoint between measured a fracture opening of 0.1 mm the ratio of measured to actual C13Cof the TIC and the calculated 613Cvalues at time “0” defines water ages can become as high as 100. However, the most potential input conditions for initial “C activities (Ao) and/or calcite composition. important fracture systems at Stripa appear to have larger Stripa groundwater: C isotopes 1771

PW4 sampling was done within a short time interval. This qualifter is important because tritium data clearly indicate that modem PWE o&b surface waters have arrived at M3 and possibly V 1 (see MOSER ef al., 1988), i.e. flow systems are changing or evolving. 2 + -17 -----____).f Furthermore, 13Cdata strongly suggest that organic carbon M3 ,RI.VZ ,G’, \ has affected the inorganic carbonate of these deep waters (see bz I a -19 4 9’*NI : i vi-’ ~ PW5 Fig, 3). The origin of this carbon is yet unknown (E. MURPHY, 1987). If it has a surface origin and represents a dissolved load acquired during recharge, then its oxidation and incor- poration into the TIC will have no effect on “‘C in the TIC, if its addition is balanced by carbonate dissolution. Where carbonate di~lution is not important, the oxidation of such carbon under closed system conditions would simply reverse some of the original dilution described above for shallow CARBON - 14 pmc groundwaters. Should, however, old carbon be oxidized, then FIG.5. Comparison of ‘“C activities and G13C-vahresof Stripa this would enhance the dilution effects. groundwater. The approximate evolutionary trends seen in young Attempts to quantify potential organic carbon contribu- groundwater is indicated. tions and their influence on radiocarbon in the TIC are futile at this point. However, also in the deep waters 14Cactivities as low as 5 pmC were measured. This could be an indication openings and smaller spacing and, therefore, it is felt that that the deep waters are also rather old because such low these waters are little aBeted by this process, although further values do not readily support the argument that these waters evaluations are warranted. are very young and at best a few hundred years old-as might Similarly, no evidence exists that isotope exchange between be argued on the basis of the observation that the hydraulic aqueous carbonate and fracture carbonates is of any impor- sink generated by the mine during several hundred years of tance, for the bulk of the latter is not in isotopic equilibrium operation should have disturbed flow regimes. Mixing of dif- with the TIC, although equilibration on a small scale can not ferent waters within sampling intervals and possibly some of be excluded. It is remarkable, however, that borehole M3 the fracture systems will further complicate the interaction received water with up to 11 TU (tritium units) following of these data. heater experiments (see MOSER etal., 1989) but did not show any significant change in its i4C contents (Table 1). Since Fracture calcite these tritium contents indicate a significant inflow of recent water, a measurable change in “C-contents should have been Calcite was collected from cores retrieved in a number of expected. Nothing is yet known about the origin of the recent boreholes and all isotope &ta obtained are listed in Table 2. water (component) in this borehole, but the carbon data may Figure 7 compares the measured S”O- and G”C-values and well indicate that a loss of 14C from the aqueous carbonate distin~ishes between samples from different boreholes and reservoir does occur. Calculated ages would then be too high. mineralogical associations. In the absence of any identifiable process of 14C dilution Calcite is an important and almost ubiquitous fracture and as no other inorganic carbon source is known, it can be mineral throughout the Stripa pluton. It occurs in a wide argued that only dilution occurring during carbonate uptake variety of mineralogical associations which, because of their (until calcite saturation is reached) has to be taken into ac- complexity, must be the subject of a later, more detailed pub- count to evahrate the “q” factor for the 300-400 m level boreholes. The values would be comparable to those deter- mined for the shallow ~oundwater. Applying this correction to the measured 14Cactivities, the TIC of the water entering these boreholes would have a mean residence time between 23,000 and 25,000 years. At present it is impossible to assess how realistic those “ages” are in terms of mean residence P --,--- z- times of the water. - 400’. 410 LEVEL In Fig. 6 the measured 14C activities are plotted against + i depth and the impression arises that the deeper and more 0 eoo- saline waters possibly have slightly higher 14Cactivities than % those encounters at the 300-400 m levels. However, Fig. 6 Boo- f f and Table 1 also emphasize the variation in radiocarbon ) contents obtained for samples from the same borehole and 1000 i depth interval. I 2 6 10 20 40 60 en As indicated above, the most serious problem in this study “C pmc was the collection of uncontaminated samples and, therefore, FIG. 6. Radiocarbon concentration in the dissolved inorganic car- it is assumed that samples with the lowest 14C activities for bon (TIC) in Stripa groundwater versussampling depths. Measure- any sampling interval are probably most reliable-if repeat ment errors are indicated as horizontal bars I772 P. Fritz et al

Table 2 Isotopic values for fracture tilling calcites. Stripa. Sweden

Rorehole Depth 1.1 6’JC PDB 61-2 PDB Type af Mineral (per mill (per mill Calcite Association Borehale Depth (m) 6’*C PDB 6,-o PDB Type of Mineral .__.-- (per mill (per nil) CalCite Association -. - .-____ _.. N1 4 81 -7.78 -14.2a P 16 30 4.23 -23 01 M SBH-l 106.43 10.70 II 10 26 00 -3.47 -14.11 M 107.85 --7.00 50.71 -4.95 -22.07 M-P 124 03 4 50 58.50 -4 18 -16.07 P-M 132.31 9.00 58 50 -4 21 -16.13 P-M 152.90 ~lO.lO 74.60 -21.26 -13.99 M 152.80 12 40 11 50 85.50 -7.03 ~18 81 FM 174.67 -6 80 160.70 3.80 -14 6” n 178.35 13 2” -9.50 161.00 -0 38 -15.06 M 189.95 -1, 3 161.00 -0.42 -16.05 M 206.63 Il.6 190.95 -19.04 -16.79 P 247.11 -6.3 10.3 190.95 -18.62 16.94 P 218.4 -4.1 -23.7 190 95 -6,07 -23 62 M 276.4 -3.9 190.95 -8.86 -17.14 M 306 7 -15.2 193.90 -26.85 -19 32 P 306.2 ~3 8 -21 7 212.70 -13 93 11 70 P 218.21 ~10.37 -12.22 P SBH-2 9.4 -1.4 218.21 -10.07 -11 a4 P 79.43 -13.5 256.31 -13 45 --I2 97 P-F 92.43 6.5 259 35 0 08 -10.58 P 99.43 -11.1 -12.7 259.35 0.26 -11 04 P 103.82 15.3 272.04 -20.70 -19.50 M 104.27 13 0 272.04 -15.60 -14.90 M 272.04 -18.60 -18.5” M 0V2 BHHl 9 54 -9.6 -9.6 272.08 -15.22 -17 33 M BHH3 6.64 -9 7 -9.8 286.00 -4 65 -IO 66 F BHH6 1.64 -6 4 -15.8 286.00 -4.64 -10 5a P 286.00 -1.47 -15.23 P-M 286 00 -11.78 -14.69 P Type of Calcite Associations (donlnant minerals) 266.00 -11.85 -14.51 P 2R6.21 -6.62 -IO 38 P M - massive (usually closed, 1 - dark chlorite, epidote 289.30 3.97 -16 14 P P - platy (usually open) 2 - fluorite 293.45 -14.35 -16.61 M 3 no ass0c1at10n 293.45 -14.35 -16.61 M 293.45 -3.40 -13.78 M 293.45 -II a6 -17.29 M lication (FRAPE et al., 1989). A summary will be presented “1 42 90 10.22 -12.70 P 71 00 -21.81 -20.80 M here. 435 73 -16.20 16 72 P The complex geochemical environment which character- 435.73 -25 37 -18.56 P 473.90 -12.61 -13.33 P izes the Stripa pluton is, however, clearly reflected in the very 473.90 -10.14 -12.90 P wide range of b”C-values between -42.7 and + 15.3%, which 473 90 10.23 12 43 P 493.00 -8.40 -20.90 P 496.00 -16.20 17 40 P

Vl 495.70 -35.70 -13.40 P TOTAL INORGANIC 496.00 -16.80 -19.30 P CARBONATE 497.00 -14.30 -17 40 P 503.20 -12.71 -1a.40 P 503.20 --12.58 -18.37 P

“2 8.77 -11.74 10.27 P 19.30 -3 28 -15.30 P 31.50 -11.32 -12.22 P 31.70 -6.48 -12.38 P 59.37 -4.45 -23.37 M 59.31 -4.52 -22.80 M 144.75 -13.11 -15.23 P 150.31 11 82 -11.95 P 157.14 -4.46 -15.82 P 157.14 -4.64 -16 03 P 157.74 -4.19 -18.28 P 157.74 -3.94 -17.61 P 317.63 -11.11 -17.96 P 317.63 -9.89 -20.83 P 317 63 -9.52 -20.22 P _yJt I 1 I t I I / ,b _I 318 61 -14.51 -17.28 P -50 -40 -30 -20 -10 0 328.22 -10.08 -17.30 P 8 13C %. PDB 328 60 -7.57 16.39 P 355.33 a 75 -11.49 I’ NO ASScmAT,ONS FuJoRITE EPIWTE FL”ORlTE 355.33 6.90 -12.09 P N, CORE 0 G . 355.33 2.09 -11.63 M 409.30 -4.60 -24.44 M “, CORE a d . 4*1.,1 2.03 -12 37 F “2 CORE 0 4 a 411.20 0.82 -13.07 P 416.06 -30.07 -12.32 P FIG. 416.10 -26.65 --13.21 P 7. The oxygen and carbon stable isotope compositions of 416.10 -38.06 -13.84 P fracture calcites from the Stripa granite. Filled symbols denote the 418.00 -42.76 -12 75 P earliest generation(s) of magmatkjhydrothermal or&in, half-tilled 418.00 -42.69 -13.06 P 540.85 -9 30 -20.02 P-M symbols are for hydrothermal calcites ass&a&d with ftuorite an4 540. a5 -9.06 -20.08 P-M open symbols indicate calcites with no or minor mineral BssociBtiolls. 566.85 -4.49 -23.00 P Also shown is the range of 6% values for calcites in isotopic e&- 565.90 -4.90 -25.18 M librium with present day groundwater. The “Total Inorganic Car- 569.90 -2.91 -11.55 M 696.26 -2.72 -16.84 P bona*” data refer to measurements of 6% in TIC. Stripa groundwater: C isotopes 1773 is very unusual for similar geological settings in Sweden (e.g. sulphate reduction has occurred-as substantiated by isotope TULLBORG and LARSON, 1982, 1983, or LARSONand TULL analyses on sulphate (see FONTES et al., 1989)-or where BORG, 1984). organic carbon was added to the inorganic aqueous carbon The earliestcalcite generation at Stripa is most likely rep- pool (TIC) through other processes, the very positive 613C- resented by massive fillings found in almost always closed values of the fine-crystalline calcites most likely reflect a re- fractures. The calcite is often prismatic and under the mi- ducing regime in which methane producing bacteria were croscope shows a wavy, stressed appearance. It is usually as- present. As sulphate reduction usually precedes methane sociated with dark chlorite, quartz, micas and epidote. The production in a reduction sequence and as sulphate is present PC-values fall into a range between -25 and -3960, with in all waters collected in this study, it is unlikely that methane the bulk of 613C values between about -10 and -3%. The production is an active process. latter range is especially typical of many hydrothermal car- The available data base is not large enough to make defin- bonates in crystalline or sedimentary rocks (e.g. FRITZ,1976; itive statements about the vertical or horizontal distribution KERRICH et al., 1986). Their b’*O-values are typically lower of the different calcite generations in the Stripa granite. This than - 15% (see Fig. 7) and assuming the participation of is emphasized by the data obtained from the horizontal bore- magmatic/hydrothermal fluids with 6%-values between 0.0 hole Nl where 6’80-values vary between about -10.4 and and +5.0%0 (typical for ore forming fluids in the Canadian -23.6% and the G”C-values spread between +4 and -26.8%~. Shield, e.g. KERRICH et al., 1986) their temperature of for- Uranium-thorium dating of three fracture calcite samples mation would exceed about 300°C. was attempted by MILTON (1987). In all three cases the sam- The second major group of calcites identified in Fig. 7 ples were platy calcites with no apparent mineral association belongs to a “hydrothermal” generation where fluorite and (see Table 2). The samples were chosen in an attempt to epidote are the principal associated minerals. The veins can analyse only the youngest generation and selection was based be several cm thick. They are most often closed although not on PO values as well as apparent paragenetic position within infrequently these veins are found in association with a very the crystallization sequence of fracture minerals (Fig. 7). prominent open fracture zone(s). The calcite is massive to Sample No. 259.35 is a very thin platy calcite which is “granular” and usually pure white. Its 6’*0 varies between associated with dirt or clay minerals. It has a 613C= +O.OSL - 14 and - 19.5%0,but has a much wider range in G”C-values and a Al80 = -10.6%. Its uranium-thorium age is about than the dark chlorite-associated calcites varying between 95,000 years. The other two samples (Nl 275.09 (613C about 0.0 and -2lb. The oxygen isotopic composition in- = -5.22% and 6180 = -11.27%) and Nl 286.00 (613C dicates a lower temperature of deposition (especially if the = - 1.47% and 6180 = - 15.23%)) are both very thick con- fluid also had lower “0 contents), whereas the “C can be tinueous platy calcites with no visible mineralogical associ- seen as an indication for an increasingly heterogeneous geo- ation. Their ages are 209,000 f 60,000 years and >350,000 chemical environment in the pluton. years, respectively. The remaining calcites indicated in Fig. 7 are almost always platy or “sugary” (fine-crystalline) calcites from open frac- CONCLUSIONS tures, i.e. they are the carbonates which would most likely influence or depend on the present-day fluids in the granite. The stable carbon isotopic compositions of shallow ground- They typically occur on the bare host rock surface without waters indicate that the geochemical evolution of ground- any other readily visible mineral association. It is noteworthy waters to a depth of at least 100 m is strongly influenced by that the fracture surfaces do not show any significant degree the dissolution of calcite which occurs as fracture mineral on of weathering when examined under SEM. fissures of the Stripa granite. This carbon uptake results in a This last group of open fracture calcites can be subdivided dilution of the radiocarbon pool acquired as dissolved in- into a group of platy calcites with 6i3C-values above about organic carbon (TIC) in the soils of the recharge zone. Di- -10960 and fine-crystalline calcites with very negative 613C- lution factors as low as q = 0.5 were calculated. values. The latter group is best exemplified by the samples Below a depth of approximately 100 m groundwater is collected in borehole V2 between intervals 4 16 and 4 18 m. saturated with respect to calcite. Because of silicate weathering This interval coincides with top of the zone of low G’3C-values the pH of the water approaches 10 and the total dissolved of the TIC in borehole V2. Unfortunately no samples were load increases. As Ca*+ becomes a dominant ion, and because obtained within the area of maximum “C depletion as iden- of the high pH values, calcite supersaturation is achieved and tified in Fig. 3. Nevertheless, the data appear to reflect a close the mineral does precipitate. Isotope data on fracture calcite “genetic” association of calcite and TIC where calcite pre- shows that indeed a “potentially modem” calcite generation cipitation or recrystallization could occur under present-day can be recognized on the basis of stable isotope and miner- conditions. Support for this interpretation is provided by the alogical data. MILTON (1987) used uranium/thorium isotope oxygen isotopic composition of these calcites, since their PO- data to argue that indeed active precipitation may have oc- values agree with values expected for calcites precipitated curred during the past 100,000 years or so. under equilibrium conditions from the local groundwater. Removal of calcite has no measurable effect on the r4C The platy calcite found on open fractures yield d”O-values activities of the dissolved inorganic carbon and thus radio- which overlap with those seen in the fine-crystalline subgroup. carbon dating. Similarly, no evidence exists that diffusive loss Thus, this group also has potentially a “modern” origin. of radiocarbon into micropore-water in the granite or isotope However, whereas the low r3C contents of the platy calcites exchange with fracture calcites played any significant role. (and the associated TIC) reflect conditions under which either Therefore, indications are that TIC of the waters entering 1114 P. Fritz et al.

short boreholes at the 300 m mine level and the top of bore- initially undertaken within the LBLKBS program by the University hole V2 has a mean residence time (“age”) which, in terms of Waterloo (VW) and the International Atomic Energy Agency (IAEA) in Vienna. J. F. Barker, J. Gale, and D. Reimer (all VW) of model calculations, could exceed 20,000 years. participated during this phase. Subsequent analyses were done by The geochemical history of the deeper groundwater and, UW, the Universite de Paris-Sud (UPS) and the University of Arizona therefore, the interpretation of radiocarbon data is substan- (AR). M. Andree, University of Bern and W. Woellli, ETH Zurich, tially more complex. The most important observation is that were responsible for the preparation and analyses of the TAMS sam- ples. organic carbon is most likely added to some of the more saline waters which occur at a depth between about 850 and 950 m below ground surface. This addition is a possible in- Editorial handling: H. P. Schwartz dication for active bacterial processes, an interpretation also supported by sulphur isotope data (see FONTES et al., 1989) and bacteriological analyses (CHRISTOFI et al., 1985). Low REFERENCES G’3C-values seen in the TIC are also recognized in fracture CHRISTOFIN., WEST J. M. and PHILIP J. C. (1985) The geomicro- calcites collected at these depths. biology of European mines relevant to radioactive waste-disposal. The source of the organic carbon is as yet unknown but British Geol. Surv. Rept. FLPU 85-1, 2 lp. should it originate in the soil zone of recharge environments DE~NESP., LANGMUIRE. T. and HARMON R. S. ( 1974). Stable carbon isotope ratios and the existence of a gas phase in the evolution of then 14Cdating of the organic carbon would be of value and carbonate groundwaters. Geochim. Cosmochim. Acta 38, 1147- provide information about groundwater age. If it is old car- 1154. bon, such as methane, which migrated into these systems FONTESJ-C&. (1983) Dating of Groundwater. In Guidebook to Nu- from the outside then the initial radiocarbon pool of the clear Techniques in Geology. IAEA, Vienna, Tech. Rept. Series groundwater would be diluted and appropriate corrections No. 91. FONTESJ-C&. (1985). Some considerations on groundwater dating would have to be applied before age calculations can be un- using environmental isotopes. Proc. IAH 18th Congr. “Hydrology dertaken; true ages would be younger than apparent ones. in the Service of Man, ” Cambridge. 1, I 18- 156. The 14C concentrations of TIC in the deep groundwaters FONTES,J-CH. and GARNIERJ. M. (1977) Determination of initial appears to be somewhat higher than the values measured at 14Cactivity of the total dissolved carbon: Age estimation of waters in confined aquifers. Proc. Water Rocks Interact. Strasbourg, Aug., the 300-400 m levels. It is not impossible that this reflects 1977, 1.363-1.376. relative age distributions, especially if the presence of tritium FONTESJ-CH. and GARNIERJ. M. (1979) Determination of the initial in Vl will be confirmed. It must be mentioned, however, activity of the total dissolved carbon. A review of the existing models that the lowest tritium values are found in the zone of saline and a new approach. Water Resour. Rex 12, 399-4 13. groundwater with very low 6’3C-values and that mixing in FONTESJ-CH., FRI~ P., LOUVATD. and MICHELOTJ-L. (1989) Aqueous sulphates from the Stripa groundwater system. Geochim. boreholes and between fracture systems can explain the ob- Cosmochim. Acta 53. 1783-1789 (this issue). served data. Nevertheless, the TIC of all deep groundwater FRAPES. K., FRITZ P., &BSON I.L., IVANOVI&HM. and KAMINEMI has low 14C contents and it appears safe to assume that the D. C. (1989) Geochemistry and isotopic composition of fracture deep water samples contain at least a potentially old com- calcites in the Stripa granite (Sweden). Can. I. Earth Sci. (sub- mitted). ponent of groundwater. FRIEDMANI. and O’NEILLJ. R. (1977) Compilation of stable isotope It is important to note that the distribution of chemical fractionation factors ofgeochemical interest. In Data oJGeochem- constituents, stable isotope concentrations in the water and istry (ed. M. FLEISCHER);U.S. Geol. Surv. Prof: Pap. 440-m 6°C-values in the TIC document that different flow regimes p. 12. exist within this granite and that the hydraulic interaction FRITZ P. (1976) Oxygen and carbon isotopes in ore deposits in sed- imentary rocks. In Handbook on Strata-bound and Strati-form between different fracture systems is very limited, at least Ore Deposits (ed. K. WOLF), Chap. 7, pp. 19 I-2 17. Elsevier, Am- under “natural” flow conditions. sterdam. The isotopic composition of fracture calcites substantiates FRITZ P., BARKERJ. F. and GALE J. E. (1979) Geochemistry and the existence of several calcite generations which encompass isotope hydrology of groundwaters in the Stripa granite. Results and preliminary interpretation. Lawrence Berkeley Lab.. Tech. very early hydrothermal, magmatic generation as well as po- Rept. SAC-12, LBL-8285, 105~. tentially modem calcites which may have formed from pres- GEYM M. A. (1972) On the determination of initial ‘% content in ent-day type groundwater. The complex geochemical envi- groundwater. Proc. 8th Intl. Conf Radiocarb. Dating, Wellington, ronment which characterizes the Stripa granite is reflected in New Zealand 1, D58-D69. the very large spread of 6’3C-values. Of special significance INGERSONE. and PEARSONF. J. (1964) Estimation of age and rate of motion of groundwater by the 14Cmethod. In Recent Researches are very low 6i3C-values (< -4OL) because they may reflect in the Fields of Hydrosphere, Atmosphere and Nuclear Geochem- biologically active systems at depths approaching 1000 m istry, pp. 263-283. Maruzen, Tokyo. below ground surface. KERRICH R., STRONGD. F., ANDREWS A. J. and OWSIACKIL. (1986) The silver deposits at Cobalt and Gowganda, Ontario. III. Hydro- thermal regimes and source reservoirs-evidence from H, 0, C Acknowledgements-The geochemical portion of the Stripa project and Sr isotopes and fluid inclusions. Can. J. Earth Sci. 23, 15 19- was initiated in collaboration with J. F. Barker (UW). His contri- 1550. butions were essential to the study. The support of the Lawrence LARSONS. A. and TULLB~RGE. -L. (1984) Stable isotopes Of &sure- Berkeley Laboratories and its director P. Witherspoon as well as the filling calcite from Finnsjon, Uppland, Sweden. Lithos I?, 117- assistance of J. E. Gale (Memorial U., Canada) during the initial 126. phase and of the SKB stakthroughout the project are al& gratefully MICHEL,OTJ-L., BENTLEYH. W., BR~S~AUDI., ELMORE D. and acknowledged. The sampling had the assistance of D. Lindstrom FONTESJ-CH. (1984) Progress in environmental isotope studies (SGAB), the mine staff at Stripa and R. Drimmie (VW). Their help (%, Ys, ‘*O) at the Stripa site. In Isotope Hydrology 1983, IAEA was essential and we thank them for it. The analytical work was Vienna, pp. 207-229. Stripa groundwater: C isotopes 1775

MILTON G. M. (1987) ~~hy~lo~~ inferences from fracture du fm~onnement isotopique “C/‘3C. J. Appl. Radiat. Isot. 35, calcite analyses. Appl. Geochem. 2,33-36. 55-62. MOWERI-I., WOLFM., FRln P., FONTESJ-CH., FL,ORKOWSKIT. and SALOMONSW. and MOOK W. G. (1986) Isotope geochemistry of PAYNEB. R. ( 1989). Deuterium, oxygen- 18 and tritium in Stripa carbonates in the weathering. In Handbook of Environmental Iso- groundwater. Geochim. Cosmochim. Acta 53, 1757-l 763 (this is- tope Geochemistry (eds. P. FRITZ and J-CH. FONTES),Vo12, pp. sue). 239-269. Elsevier, Amsterdam. MURPHYE. M. (1987) Carbon-14 rn~u~rnen~ and ch~~tion SWEDISHSTATE POWERBOARD ( 1985) Deep gas, Swedish premises. of in groundwater. Ph.D. thesis, Univ. Gaf Project G2, No. 3, 9lp. TULLBORGE. L. and LARSONS. A. (1982) Fissure fillings from of Arizona, 18%. Finnsjon and Studsvik, Sweden. Identification, chemistry and dat- NERETNIEKSI. (198 1) Age dating of groundwater in fissured rock: ing, SKBF/KBS Stockholm. Tech. Rept. 82-20, 76~. In8uence of watervolume in micropores. Water Resow. Rex 17, TULLBORGE. L. and S.A. (1983) Fissure filling from Gidea, 42 l-422. LARSON Central Sweden. SKBF/KBS St~kholm, Tech. Rept. 83-74. NORDSTROMD. IL, ANDREWSJ. N., CARLSSONH., FONTESJ-C%., TULLBORCE. -L. and LARSONS. A. (1986) The effect of recharge FRITZ P., MOSERH. and OWN T. (1985) Hydrogeological and water on fissure filling material-an isotopic investigation from hydrogeochemical investigations in boreholes-Final Report of Khpperas, southern Sweden. Proc. Symp. WRI 5 Water Rock In- Phase 1 geochemical investigations of Stripa groundwaters. Stripa teract., Island, Aug., 1986, pp. 587-590. Project, SKB Stockholm, Tech. Rept., 1985-86. WIGLEY T. M. L. (1975) Carbon-14 dating of groundwater from NORDSTROMD. K., BALLJ. W., DONAHUER. J. and WHITTEMORE closed and open systems. Water Resow. Res. 11, 324-328. D. ( 1989) Groundwater chemistry and water-rock interactions of WIGLEYT. M. L. (1976) Effect of mineral p~pi~tion on isotopic Stripa. Geochim. Cosmochim. Acta 53, 1727- 1740 (this issue). composition and Y dating ofgroundwater. Nature 263,2 19-22 1. REARDONE. J. and FRITZ P. (1978) Computer modelling of ground- WIGLEYT. M. L., PL.UMMERL. N. and PEARSONF. J. (1978) Mass- water “C and ‘“C isotope compositions. J. Hydrol. 36, 2 10-224. transfer and carbon isotope evolution in natural water systems. SALIEGEJ. F. and FONT= J-CH. (1984) Determination experimental Geochim. Cosmochim. Acta 42, 11 l7- 1139.