The Thermomineral Waters of Vichy Basin. Geothermal Implications
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Geochemical Journal, Vol. 10, pp. 155 to 161, 1976 155 Subsuperficial changes in chemical composition of the thermomineral waters of Vichy basin. Geothermal implications GIL MICHARD, ANTON STETTLER*, CHRISTIAN FOUILLAC, GERALDOUZOUNIAN and DOMINIQUEMANDEVILLE Laboratoire de Geochimieet Cosmochimie(LA 196) UniversiteParis 7, France (Received July 23, 1976) The chemical analyses of the mineral waters issuing in the basin of Vichy St Yorre provide the means to decipher different subsuperficialmodifications superposed on the fluid originatingat great depths: (1) Increasingamounts of dissolvedCa, Sr, Mg and sometimesK, by gradual attack of shallowhost rocks. (2) Precipitation of silica and associatedaluminium. (3) Mixing with fresh surface waters. The comprehensive study of these alterations allows to shed light on the initial composition of deep water. From the silica content, the Na/K ratio and the calcite saturation, a temperature of 135°C is inferred for this water. INTRODUCTION tinguish the following geographically separated The chemistry of numerous springs issuing groups (cf. Table 1): in the thermal field of Vichy (France) has been -the group of Vichy on the right bank of Allier thoroughly investigated. The principal aim was -the group of Cusset , east of Vichy to derive the temperature of the deep seated -the group of Abrest-Bellerive , SW of Vichy, hot reservoir, using quantitative geothermo includes the hottest waters meters: silica (FOURNIER and ROWE, 1966), and -the groups of Hauterive , St Sylvestre and St sodium-potassium (WHITE, 1965; ELLIS, 1970). Priest, on the left bank of the Allier However, one had to expect the original water -the group of St Yorre , NE of the preceding composition to be considerably altered during ones on the right bank of the Allier. the penetration into subsurface sedimentary Before discharging at the surface, the thermal rocks. Presuming a variable contribution from fluids are captured in aquifers embedded in the these rocks to each individual spring of the field, series of Stampian marls. we analysed a great variety of different springs. Considering the lateral distribution of the In fact, this method yielded strong evidences springs, their temperatures and the dip of the for the chemical composition of the common marl strata, ARMAND (1933) concludes that the thermal reservoir. fracture which furnishes the springs, is situated somewhat in the west. This author adopts the SAMPLING LOCATIONS occurrence of a dislocation denoted "Macaux fault" which supplies the springs in the entire All samples reported in the present work basin. The waters issuing from the fault hence have been collected in the active thermal area follow the cracks in the series of marls to reach of the Vichy basin (France), situated in the large directly the surface or to accumulate in the Stampian graben of the Limagne. A compre shallow aquifers. We have analysed samples hensive study of the region is given by DECROS from each of the different groups, but focused (1963) and THUIZAT (1973). A very large our interest onto the hottest springs, namely number of springs are issuing and one can dis those from the groups of Vichy and Abrest * Present address: Physikalisches Institut, Universitdt Bern, Switzerland. 156 G. MICHARD et al. Table 1. List of the studied springs in the Vichy area ratio, and simultaneously the Rb and Sr con tents, the isotopic dilution technic thoroughly le Samy Basin City Spring described by BIRCK and ALLEGRE(1973, 1976) Vichy Vichy Chomel F 22 has been applied. Procedure blanks turned out du Parc F 23 to be 0.010ng for Rb and 0.035 ng for Sr, with Lucas F 24 a reproducibility of ± 20%. A mass spectro Grande Grille F 25 meter reproducibility of ± 0.00005 (2a) for Hopital F 26 the 87Sr/86Sr ratio has been inferred from peri Lardy F 27 Gdndreuse F 28 odical runs of the Sr standard NBS 987. The 3 Etoiles F 29 results are compiled in table 4. Larbaud F 30 Celestins F 31 Table 3. Chemical analyses of some Vichy springs Bellerive Boussanges F 33 (trace elements) Abrest Dome F 34 Fe Mn Sr Al Rb F Lys F 35 n° 10-5 10-6 10-5 10-6 10-6 10-3 Corndlie F 36 F 1 2.75 3.0 1.93 46 10 0.49 St Yorre Hauterive Denise F 2 F 7 3.99 3.9 1.46 46 10 0.48 St Ange F 3 F12 5.79 3.4 1.90 46 10 0.46 F22 0.38 2.8 2.02 1.8 8 0.42 St Yorre L. Armand F 7 F24 0.77 4.9 2.06 4.6 8 0.41 L. Blanquet F 8 F25 0.39 2.8 2.00 1.15 7.5 0.44 St Sylvestre Agrdable III F 1 F30 1.90 8 Berthommier Larbaud F 9 F31 0.34 2.5 1.34 5 5.5 0.30 Moina F 10 F34 0.36 0.7 1.76 0.7 8 0.48 Fderique F 11 F35 0.34 0.8 1.8 1.5 8 0.48 St Priest Jade F 12 Cusset Cusset Tracy F 4 Table 4. Rubidium and strontium data determined by Lafayette F 5 isotopic dilution of mineral watersfrom Vichy. Errors St Denis F 6 Mesdames F 32 for elemental concentration are ± 1 %. The strontium isotopic ratios are normalised to 86Sr/88Sr= 0.1194 and errors are quoted in terms of 10-5. Bellerive. Rb Sr 87Sr/86Sr n° Rb/Sr 10-5 10-5 EXPERIMENTAL TECHNICS AND RESULTS F24 0.783 1.963 0.399 0.71412 ± 7 The analyses have been performed applying F25 0.743 1.971 0.377 0.71406 ± 12 F30 0.754 1.806 0.417 0.71408 ± 4 the methods described by CAILLEAUX et al. F31 0.561 1.352 0.415 0.71402 ± 6 (1976). At least, four samples' were collected F34 0.795 1.700 0.468 0.71438 ± 4 at each spring: one sample unaltered (analyses of anions and some cations: Mg", K', Li+) DISCUSSION one sample diluted by a factor of ten with distilled water immediately after collection (ana The groups of Vichy, Bellerive and Abrest lyses of Na+, Ca", HC03 and SiO2 ) Twelve of the 14 sampled springs show one acidified to pH 2 with hydrochloric practically constant concentrations of Cl (9.47 acid (Suprapur) (trace elements, Sr isotopes) to 9.70X 10-3M/1), Na+ (79.8 to 81 X 10-3 one unaltered (isotopic analyses) M/1), Li (0.75 to 0.80 X 10-3M/1) and Rb+ The first three samples were stored in poly (7.6 to 8 x 10-IM/1). Only Lardy and Celestins ethylene bottles, the fourth in a tight glass diverge from these values: Lardy is slightly more bottle. Both pH and silica have been measured concentrated and Celestins distinctly more dilut on the field. ed. Considering the four elements mentioned Table 2 comprises the concentrations of the above, the dilution factor turns out to be 1.41 major constituents and table 3 those of trace ± 0.02. In contrast Cd" concentration is highly elements. variable from 1.00 X 10-3 M/ 1 (Genereuse) to For the determination of the Sr isotopic 4.28 X 10-3 M/ 1 (Lucas). To illustrate the n Subsuperficial changes in chemical composition 157 to O to M N 0\• O O\ \0 to to N O 00 d lq' N to to to t M Q O r+ O o M M .--I N O -1 0 0 0 0 .--1 O C> CD 0 -( CD C,-] C,4 -4 CD N' 0 M N 0\ \O N M O O d' O v'1 N 0\ N N l r, O 0\ IN M M 00 O 0\ 0\ all M M N M In . 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