Jökull - 01.12.1987, Side 23

Fig. 10. Geological cross section of the
Leirbotnar and hvíthólar well fields. —
Mynd 10. Jarðlagasnið af Leirbotnum
og Hvíthólum.
same perspective as the geological sections are present-
ed in Figs. 11 and 12. The alteration zones protrude to
shallow depths in most of the Suðurhlíðar wells (epi-
dote-chlorite zone at 200-300 m depth), but east of well
KJ-17 they plunge steeply and also across the Hveragil
gully from Suðurhlíðar to the Leirbotnar field. The high
temperature alteration also reaches relatively shallow
depths in well KJ-21 but is deeper in well KJ-22 farther to
the north.
At Leirbotnar where the geothermal system is divided
into an “upper” and a “lower” zone (Stefánsson 1981) the
ntain aquifers in the lower zone seem to be connected to
fissures and intrusion contacts. In the southern part of
the field the Hveragil fracture and a fracture to the west
of wells KW-1 and KG-12 feed the wells. In the northern
part wells KG-4 and KG-10 draw mainly from the con-
tact zone to a granophyre intrusion at 1900-2100 m
depth. The main aquifers in the upper zone occur at the
ntargins of the hyaloclastite formation M-2 at 400 and
800 m depth (Steingrímsson, et al. 1984a).
In the Suðurhlíðar field the main aquifers are connect-
ed to acid horizontal intrusions at the bottom of the M-2
formation at 900-1200 m depth. Deeper aquifers are
associated with contacts of vertical or subvertical frac-
tures and dykes.
In the Hvíthólar field the main upflow is apparently
connected to a nearly vertical permeability anomaly
hidden under young volcanics. The geothermal fluid
flows laterally from this anomaly (probably a dyke) into
a hyaloclastite formation at 300-700 m depth. The reser-
voir temperature is 250-260°C. The major aquifers oc-
cur at the interface of basalt and hyaloclasite formations
*n a similar way as in the upper zone of the Leirbotnar
field (Steingrímsson, etal. 1984b).
Fig. 11. The alteration zones of the Leirbotnar and
Suðurhlíðarwellfields. — Myndll. Lega ummyndunar-
belta í Leirbotnum og Suðurhlíðum.
21