Jökull - 01.12.1976, Page 38

TABLE2
Chemical analyses of hydrothermally altered basaltic rocks (drill cuttings)
in the geothermal area on Reykjanes
TAFLA 2
Efnasamsetning nokkurra sýna af myndbreyltu bergi úr borholum frá jarðhitasvœöinu
á Reylijanesi
1 2 3 4 5 6 7 8
sío2 46.78 48.24 48.91 49.29 44.02 48.39 48.26 47.07
tío2 0.90 2.03 1.55 1.75 1.45 1.65 1.35 1.14
Al203 13.01 10.93 11.09 11.24 13.13 10.96 9.86 15.66
Fe203* 8.03 13.31 11.59 12.46 9.43 12.44 12.25 11.52
MnO 0.15 0.21 0.20 0.20 0.14 0.19 0.18 0.18
MgO 7.80 8.77 8.06 7.71 9.60 7.59 8.38 9.36
CaO 9.85 11.18 12.85 11.46 9.15 9.95 13.55 12.65
Na20 2.88 2.36 2.05 2.07 2.22 1.85 1.41 1.81
k2o 0.47 0.22 0.11 0.17 1.36 0.84 0.17 0.11
p2o5 0.07 0.20 0.16 0.18 — 0.16 0.08
Ignition
Loss 9.29 2.08 1.65 1.84 9.43 4.01 2.52
Total 99.23 99.53 98.22 98.37 99.93 98.03 98.01 99.5
*) Total iron
1
2
3
4
5
6
7
8
from drillhole no. 8, 306 m palagonite breccia
„ „ „ 8, 712 m
„ „ „ 8, 1300 m basalt
„ „ „ 8, 1754 m „
„ „ „ 3, 392 m tuffaceous sediment
„ „ „ 3, 466 m palagonite breccia
„ „ „ 3, 1128 m basalt
fresh basalt in the area (K. Grönvold, pers. comm.).
The variation of main elements in the rocks
by depth is shown in Fig. 5. The chemical ana-
lyses used are from rock samples from three
clrillholes sunk in the area, named H-3, H-6
ancl H-8. Drillhole H-3 is located in the area
of active visible surface alteration ancl H-8 is
on the northern edge of the geothermal area.
H-6 is cold, but in an area showing signs of
former geothermal alteration. This drillhole is
much shallower than the two others and of
clay minerals only smectites are found. The
variation pattern of this drillhole will there-
fore not be discussed in detail here. Concent-
rating on the two others a slight increase of
MgO is indicated in the uppermost 400 m of
drillholes 3 and 8. This enrichment is not very
significant and in only one sample the MgO
content exceeds the maximum content found
in recent basalts from the area (Grönvold, pers.
comm.). For the other main elements the varia-
tion with depth is within the limits found for
the composition of recent basalts in the area
(Grönvold, pers. comm.). The alteration thus
does not involve significant changes in total
chemistry and no large scale transportation of
the niain elements has happened. As 50—80%
of the rocks have recrystallized to clay minerals
they must contain considerable Mg and Fe.
36 JÖKULL 26. ÁR