Jökull - 01.12.1976, Page 32

Types of Clay Minerals in HydrotKermally
Altered Basaltic Rocks, Reykjanes, Iceland
HREFNA KRISTMANNSDÓTTIR,
NATIONAL ENERGY AUTHORITY,
REYKJAVÍK, ICELAND
ABSTRACT
The clay minerals formed by hydroihermal
alteration of basaltic rocks in the geothermal
area on Reykjanes have been studied by dif-
ferential thermal analysis and infrared spectro-
scopic methods. In a previous study of the
alteration minerals by X-ray diffraction methods
several different clay minerals of chlorite/
smectite mixed-layers and swelling chlorite
types were identified. The mineral types were
supposed to have closely related structures and
the difference found between them suspected
to be merely due to the method of investiga-
tion. The results of this study confirm this
suggestion. A course of gradual transformation
is found from the triocathedral smectites form-
ed in the basaltic rocks at rock temperatures
below 200° C to the chlorite formed at rock
temperatures above 270° C. Partial chemical
analyses of the altered rocks are presented and
discussed.
H-3 I 2 3456
H —6 I 2
I
Basalt
Palagonite breccia and tuffs
ý Tuffaceous sediments
I Smectite
P Mixed-layer
Smectite /chlorite
3 Swelling chlorite 2
4 Swelling chlorite 3
5 Swelling chlorite4
6 Swelling chlorite 5
7 Chlorite I
Chlorite I, 2, 3,4,5 : numbers refer
to types listed in toble I
Fig. 1. The distribution of clay minerals with depth in three of the drillholes in the Reykjanes
area. A simplified geologic section is also shown for each drillhole.
Mynd 1. Myndin sýnir einfölduð jarðlagasnið og dreifingu leirsteinda með dýpi i þrem borhol-
um á jarðhitasvceðinu á Reykjanesi.
30 JÖKULL 26. ÁR