Jökull - 01.12.1982, Page 93

Fig. 7. 6 18 against depth in samples from drill-
holes in Eyjafjördur.
Mynd 7. Súrefnisísotópahlutfall (b 18) í vatnssýnum úr
borholum í Eyjafirði.
water and pumped water give 8 18 of about -f- 13 in
the Laugaland drillholes and about H- 14 in the two
other areas. The results strongly suggest that the
Laugaland area is fed by two reservoirs and the one
feeding the deep aquifer also feeds the two other
areas to the north and west of Laugaland. The
reservoirs are geochemically very similar and their
recharge areas are close to each other.
CONCLUSION
The recharge area of the geothermal water in the
northern Eyjafjördur region appears from study of
stable isotopes to be the North western part of the
glacier Vatnajökull. Geothermal water in one
spring area in southern Eyjafjördur (Hólsgerdi) has
a defmitely diíferent origin and is probably older
than ten thousand years. The other springs in
southern Eyjafjördur are fed by water of similar
stable isotopic composition as the springs in the
northern part of the region. In a few of the colder
springs mixing with local groundwater, is reflected
by the stable isotope values.
On basis of a detailed study of 8 18 measure-
ments of water samples from drillholes there appear
to be two separate reservoirs feeding the geothermal
areas in the northern Eyjafjördur region. The upp-
er> main aquifers in the Laugaland area are fed by
one reservoir and the Ytri-Tjarnir and western
Eyjaíjördur areas (Grísará) by another. The slugg-
'sh yielding deep aquifers in the Laugaland area
appear to be fed by the same reservoir as Ytri—
Tjamir and western Eyjafjördur. No significant dif-
ference in dissolved solids has been detected bet-
ween those two reservoirs. Two springs in the
northern Eyjafjördur show characteristic difference
from mean values ofCl and Cl/B. Samples from all
other springs are chemically very similar.
In southern Eyjafjördur the chemistry of the wat-
ers is much more varying than in the northern part
of the region. The springs are fed by at least three
different reservoirs and one of them is chemically
similar, and could be the same, as the one feeding
the springs in the northern part of the Eyjafjördur
region.
The chemical geothermometer found to be most
useful in the Eyjafjördur waters is the Na-K geo-
thermometer based on thermodynamic data from
Helgeson (1969). The empirical Na-K and Na-K-Ca
geothermometers showed poor fit with measured
deep temperature. The chalcedony geothermomet-
er gives consistently too low deep temperatures.
REFERENCES
Amason, B. 1976: Groundwater systems in Iceland
traced by deuterium. Soc. Sci. Islandica, Occa-
sional publ. 42, 236 pp.
Amórsson, S., E. Gunnlaugsson and H. Svavarsson 1982:
The chemistry of geothermal waters in Iceland.
III. Chemical geothermometry in geothermal
investigations, Geochim. Cosmochim. Acta. in
press.
Björnsson, A., K. Stemundsson, S. Einarsson, F. Thorar-
insson, S. Amórsson, H. Kristmannsdóttir, A. Guð-
mundsson, B. Steingrímsson and P. Thorsteinsson
1978: A mimeographed report on the status of
research in the Eyjafjördur region, OS-7827, 139
pp.
Björnsson, A., 1981: Exploration of low-temperature
geothermal fields for district heating in Akur-
eyri, North Iceland. Geothermal Resources
Council Transactions, 5: 495-498.
Dansgaard, W. 1964: Stableisotopes in precipitation.
Tellus 16: 436-468.
Ellis, A.J. and W.A.J. Mahon 1977: Chemistry and
geothermal systems. Academic Press, N.Y., 392
pp.
Fournier, R.O. and A.H. Truesdell 1973: An empirical
Na-K-Ca geothermometer for natural waters.
Geochim. etCosmochim. Acta, 37: 1255-1275.
Kristmannsdóttir, H. and J. Tómasson 1978: Zeolite
zones in geothermal areas in Iceland. Natural
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