Rit (Vísindafélag Íslendinga) - 01.06.1976, Page 151

The Reykjanes brine contains much more Cl- and Na+ than ex-
pected when simple mixing of the two water types is assumed. This
is, however, not an unacceptable fact. The ground below the Reykja-
nes area has been found to contain numerous sedimentary layers in
the uppermost 1700 m. More sedimentary layers might also exist at
greater depths. We also know that deep thermal water which flows
through sediments can aquire large amount of salt. A part of the
dissolved salts in the Reykjanes brine could have been obtained in
such a way.
15. 10 Reykjavík and Mosfellssveit.
The two low-temperature areas Reykjavík and Mosfellssveit are
situated some 10 km north of the volcanic Reykjanes rift zone (see
Fig. 31). A geological description of these areas is given by several
authors (Sigvaldason 1963, Thorsteinsson et al. 1970 and Tómasson
et al. 1974).
Since the two areas are obviously hydrothermally related they
will be discussed under the same section. On the basis of tempera-
ture, chemistry and isotopic composition of the water the Reykjavík
area may be subdivided into at least three hydrothermal systems,
Laugarnes, Elliðaár and Seltjarnarnes, which all seem to exist also
in the Mosfellssveit area.
Numerous wells have been drilled in both of these areas, ranging
in depth from 50 to 2200 m. The location of all the wells from which
samples have been collected for deuterium analysis is shown in Fig.
37, together with the mean ðD-values obtained for each well.
15. 10.1 Laugarnes.
The wells in the Laugarnes area (see Fig. 37, samples No. 88-92)
all seem to give the same deuterium content, the mean 8D = — 65 %0.
They also all have similar Cl“ concentration, mean CL ~ 30 mg/1,
and the silicate content, Si02 — 180 mg/1, is the value expected
when the water has reacted with igneous rocks at a temperature less
than 150°C.
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