Mineralogical and Geochemical Factors Influencing the Final Disposal of HLW in the Stassfurt Halite
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MINERALOGICAL AND GEOCHEMICAL FACTORS INFLUENCING THE FINAL DISPOSAL OF HLW IN THE STASSFURT HALITE HERMANN GIES Gesellschaft fdr Strahlen- und Umweltforschung mbH Mfnchen, lagerung, D-3300 Braunschweig, FRG
Institut fdr Tief-
STRATIGRAPHY AND MINERALOGY As the thickest and primarily monomineralic saline horizon in the Federal
(Na2)
is
Stalfurt-Halite
investigation of the Zechstein-2-Series,
Republic of Germany,
being emphasized for the final disposal of HLW. This horizon is especially since it
particular importance,
is
formation in northern Germany (Fig. 1). Bunt sondstein BruitsandteinThickness Grenzonhydrit Tonbrockensolz
,4
CI -
Sceesoiz c•;
Ci
Pegmatitort
f i
Aller-
~rit
Roter Salzton Torvnittel-Zooe Foz Redel 6- Sclooodensolz A klrritorlet-Zone
Mr
1 60-80
Halite
so-6o
(No 4)
1.5 15 -. 0 15 -40 4-6 15 -60
Leine-
30-6o
Halite (No l
WA Floe Rornoiibeg Hi uptHol hyr it
0
2-4/ 3D-60
GeoserSalzte
5 -15
Floz Stalfurl t
Sleinsolz a-5
C
6-/0
Stafflurt Halite
-0
(lNo2)
Geoo NNl
Fig.
1.
of
the base of the whole saline
Stratigraphy of the "Germanischer Zechstein"
'
460
The thicker chloride parts of the oldest precipitation sequence,
The overlying Na2, 'Stakfurt',
the Werra
were deposited only on the border seas of the Zechstein ocean.
Series (Zl),
which is
overlain again by the carnallitic potash seam
consists of a deep sequence of 8-20 cm thick halite banks which
are separated by sulfate layers of only a few millimeters thickness. sulfate is
chiefly anhydrite (CaSO 4)
called 'Hauptsalz' regions,
in the thickest parts of Na2,
the stratigraphically higher
('Main Salt'), whilst in
2H2 0) and finally kieserite (MgSO 4 * H20)
polyhalite (K 2 MgCa 2(So4)4
are increasingly admixed.
This
the so-
to a general Mg-increase when
This corresponds
approaching the overlying potash seam. The general stratigraphic structure and the resulting stratigraphic are based in part on mineralogy and petrography
and
which are subject to certain local and regional changes.
division
on textural differences The characteristic
features and the stratigraphic development as mentioned above are,
however,
generally present. For an exact description of the facies of the most variable uppermost Na2-horizon,
extensive sampling was carried out at the Asse,
the
results of which may principally be regarded as an example for larger parts of the depositional area. Thus,
samples from drill
cores,
channel samples
from stopes and average running samples of 1.5 m are investigated mineralogically and geochemically.
The mineralogical analysis of a larger number of individual
samples had already shownI that only four minerals halite and, in
very small amounts (4
1,0%),
irregular quantities of carnallite are first
(halite, anhydrite, poly-
kieserite can occur).
Minor and
detected at the base of the
potash seam. Microscopic investigations 2 carried out on a larger number of samples showed that the sulfate layers generally consist of up to > 90 vol. % of anhydrite. quantities.
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