Greinar (Vísindafélag Íslendinga) - 01.01.1976, Síða 176

Progressive alteration
172
E
<r
V>
o O O
o ^ i
— c <
I
E -
— o
.tz o
í 'i
Zone I Smectite - zeolite zone 1 I
Zone IL Mixed-layer clay minerals (prehnite) zone 1 1 1 1 i i í ! : ! ! :
ZoneIE Chlorite - epidote zone 1 i i 1 i i
Fig. 4: The figure shows the three main alteration zones formed hy progressive
alteration in Icelandic high-temperature geothermal areas. The distribution of the
main alteration minerals within the zones is also shown.
the dominant alteration minerals. Also shown in the table is the
distribution of common alteration minerals within the zones.
The uppermost zone is characterized by smectites and zeolites.
In the high temperature areas no regular sequence can be seen
in the occurrence of zeolite species. The most common zeolites
are mordenite and heulandite. Analcime is normally scattered
throughout the zeolite-smectite zone and traces of wairakite are
found in most areas. Laumontite is common in most areas and
stilbite is usually found in varying concentrations.
In the second or intermediate zone the zeolites disappear and
clay minerals of mixed-layer types, swelling chlorite and vermi-
culite minerals become abundant. Prehnite appears in this zone.
The third zone is characterized by the appearance of chlorite
and epidote, and the disappearance of the smectite and mixed layer
minerals.