Jökull - 01.12.1982, Page 91

Mjadmárdalur spring other components as C1 and
-Na/Cl ratio indicate the existence of sea-sediments
in the bedrocks. The geothermal water is under-
saturated with respect to the most common fluoride
containing minerals fluorite and fluorapatite. The
regional fluoride content is about 0.6 ppm in most
springs, but around 0.4 at Laugaland, Gardsá and
the Strjúgsá springs. At Y tri-Tjarnir and Y tragil the
fluoride contents are around 0.5 ppm.
In the northern part of the region there thus
occur a rough pattern with a low at Laugaland-
Gardsá with increasing contents around.
The boron concentration has been measured in
many samples. The Cl/B ratio is a convenient tool
to differentiate between aquifer systems as neither
C1 nor B participate in any important mineral/sol-
ute equilibria. Boiling or cooling of the geothermal
water should thus not change the relative concent-
rations of the elements. I’he mean Cl/B in the
northern part of the region is 23±6 (the sample
Fig. 5. a) 6 D in geothermal water in the Eyja-
fjördur region. b) ð 18 in geothermal water in the
Eyjafjördur region.
Mynd 5. a) Tvívetni, 8 D, íjarðhitavatni í Eyjafnði. b)
Súrefnisísotópahlutfall, 8 18, í jarðhitavatni í Eyjafirði.
standard deviation). No diflerence is found in
springs from the eastern and western part of the
valley. The Gardsá springs has somewhat higher
ratio of 33.
In the southern part of the region the mean Cl/B
ratio is 53±9. The Ytri-Strjúgsá spring has a Cl/B
ratio of 36, strikingly difl'erent from the other
springs in the southern region. The spring water
from Reykir in the Fnjóskadalur valley has Cl/B
ratio of 33. The springs in all the northern part of
the region could from the Cl/B ratio be fed by the
same water reservoir, except for the Gardsá spring.
The springs in the southern part appear to be fed by
several separate reservoirs.
JÖKULL 32. ÁR 87