Deutsch (27.2 MB) - Nagra

showed that the water from the upper part of the
Permian (1'116.5 m) is a saline Na-CI-(S04)-water
with mineralisation of around 36 gIl. The sample
from the lower part of the Permian (1'408.3 m) is an
Na-Ca-CI water with mineralisation of 98 gIl.
It is assumed that both samples from the Permian
are saturated with calcite. The model calculations
also showed a slight undersaturation for dolomite.
The sample from the upper part of the Permian is in
equililbrium with gypsum and anhydrite while the
water from the lower part is undersaturated with
respect to these two minerals. The water from the
upper part of the Permian is in equilibrium with
quartz. The same has to be assumed for the water
from the lower part of the Permian. In a regional
comparison, the Permian waters proved to have a
significantly higher mineralisation than all other
known waters from the Buntsandstein,· Permian or
Crystalline in the investigated area.
It can be concluded from the 8 2 H- and 8 1S _ values
and from noble gas analyses that the Permian waters
originate from a period with a warmer climate. It can
not be excluded that they still contain some old seawater.
As yet, no positive statements can be made
with regard to age.
Water-flow in the Crystalline of Weiach is restricted
to a few zones with increased permeability. Only two
groundwater samples could be taken. Analyses showed
that the waters (from 2'218.1 m and 2'267.0 m)
are relatively highly mineralised Na-CI waters (7 gIl).
Model calculations show saturation with calcite and
quartz but the waters are clearly undersaturated with
respect to dolomite, gypsum, anhydrite and chalcedony.
Of all the Crystalline waters in Nagra's investigation
area, there is no direct equivalent of the Weiach Crystalline
waters. The results of isotope measurements
(8 2 H-, 8 1S O- and 8 34 S-measurements in dissolved
sulphate) point to independent development within
the crystalline rock. It is not yet possible to make any
defmite statements about the age of the waters.
The Water-Flow Systems in the Weiach Crystalline
The Crystalline in the Weiach borehole generally has
a very low permeability. The permeability of the solid
unfractured rock is in the order of lx10- 1 2m/s, or
even lower. The effective overall transmissivity of the
Crystalline drilled through (T = 1x10-sm2/s) is basically
determined by zones of increased hydraulic
permeability (transmissivities up to T = 4x10-9m2/s).
These zones of increased permeability are irregular
networks with some open fractures which are associated
with the aplite dykes and their surrounding
rock. Water-flow therefore basically occurs in a single
system type which, at least for the present, cannot
be further differentiated.
Six water-bearing zones were found over a section of
around 460 m in the Crystalline of the Weiach borehole.
There is very little information on their threedimensional
orientation and extent. The same is true
of the aplite dykes with which they are apparently
associated. In the drilling profile, the apparent
thickness of the water-bearing aplite dykes can be up
to several meters. Based on the frequency of their
occurrence, it can be assumed that they form a more
or less interconnected irregular network of waterbearing
zones in. otherwise low-permeability crystalline
rocks.
To date, there have been no detailed investigations
of the porosity distribution in the immediate vicinity
of fractures. Individual measurements of aplite
samples gave open porosities between 1.26 and 1.41
Vol.-%, which is comparable with the open porosities
of fresh unaltered gneiss (1.05-1.72 Vol.-%).
Gneisses which have been hydrothermally altered
and subjected to cataclasis may have higher open
porosities, with an increase primarily in the open
microporosity. With the data available, it is not clear
whether the water-bearing zones tend to be associated
more with areas which have undergone cataclasis
or those which have not been altered.