US EPA

1439334 

Journal Article 

Premineral hydrothermal alteration of host rocks at the Schlema uranium deposit, Erzgebirge, Germany: II. A computer modeling 

Barsukov, VL; Sokolova, NT; Knyazeva, SN; Shvarov, YV 

2000 

Yes 

Geochemistry International
ISSN: 0016-7029 

38 

7 

652-675 

WOS:000088597200003 

The study of actual premineral alteration of ""productive""
rocks [1], which host the pitchblende-bearing veins at the Schlema deposit, Erzgebirge, Germany,
served as a groundwork for the elaboration of computer models reproducing the interaction between
hydrothermal solutions and host rocks at the uranium-ore stage. The first set of models was aimed
at the computation and analysis of interaction (mainly at 200 degrees C and 2 kbar) of the water
phase with granites of the Aue dome and Ordovician light phyllites of its outer contact zone. The
equilibration of the water phase with rocks in the near-contact zone predetermined the
composition and properties (pH, Eh, I) of solutions, as well as their saturation with uranium.
Such solutions ascended along thousands of steep fractures into the so-called ""productive
sequence"" where the major mass of veined uranium ore was deposited in open fissures. The second
set of models dealt with interaction of ascending solutions with acid and basic rocks of the
""productive sequence."" A series of models describes the mass exchange between ascending
solutions and rocks of the ""productive sequence"" under isothermic conditions; another series of
models takes into account the cooling of the solution and pressure drop from P-T conditions of
the near-granite region to 150 degrees C and 1000 bar within the ""productive sequence"".
Finally, the third series of models (so-called ""layered"" models) mimics the intercalation of
acid and basic rocks within the ""productive sequence."" The above models reproduce the main
specific feature of premineral alteration of ""productive rocks,"" i.e., the vigorous mass
exchange between solutions and basic rocks and almost absolute inertness of solutions with
respect to major components at contact with acid rocks. The near-vein alteration haloes in basic
rocks best fitting the natural prototypes and containing the typical assemblage of secondary
minerals (adular, albite, mica, chlorite, quartz, hematite, etc.) were obtained in models which
took into account the T and P drop of the ascending hydrothermal solutions and their intensive
interaction with wall rocks.