LOCATION HAMMERUNTERWIESENTHAL

LOCATIONGEOLOGYMININGCHRONICLE

The deposit Hammerunterwiesenthal has a lithostratigraphic age of approximately 525 million years. The rocks of the Obermittweida Formation (two-mica schists and gneisses, amphibolites/eclogites, metagreywackes) and the Raschau Formation (garnet mica schists) as part of the Keilberg Group are the host lithologies of six marble occurrences known so far. These are from west to east: Schlösselweg Block, Böhme's Block, Schreiter's Block, Schmiedel's Block, Päßler's Block, Bachberg Block.

The carbonate complex formed in the Lower Cambrian in a marine environment with thin subvolcanic intercalations. During the Saxothuringian tectogenesis, almandine-amphibolite facies metamorphism overprinted the originally calcitic and syn- to post-sedimentarily dolomitised limestone body and transformed it into marble. Additionally, calcium-metasomatism during the Variscan orogeny, 400-320 million years ago, caused the formation of magnesium-calcite now dominating the marble composition. The orogeny is further responsible for intensive folding of the deposit.

Schematic and simplified geological cross-section through the marble deposit Hammerunterwiesenthal

Schematic and simplified geological cross-section through the marble deposit Hammerunterwiesenthal

The dominant isoclinal folds are characterised by NW-SE trending and shallowly SE or NW dipping fold axes. Variscan- and Alpine-influenced brittle tectonic deformation faulted the folds perpendicular to the fold axes. Today these faults are karstified near the surface.

In Oligocene, about 30 million years ago, the last great geological event was the development of a maar with a diameter of 2,000 m E-W and 1,400 m N-S. This volcanic structure extends into the central part of Böhme's Block. The beginning of the maar formation is marked by deposition of 30.5 million years old tuffs and tuffites, whereas the end is characterised by the emplacement of a large phonolite body 28.4 million years ago.

PETROPHYSICAL PARAMETERS OF THE MARBLE

Gross Density: 2.72 g/cm3

Water Absorption:
0.38 wt.-% for 25 freeze-thaw cycles

Frost Resistance: 0,13 % mass loss

Compressive Strength: 95.0 N/mm2

Bending Tensile Strength: 11.0 N/mm2

Abrasion Resistance: 17 cm3/50 cm2

pH-Value in Aqueous Suspension: 8.0

Contrasting previous assumptions, the different marble layers are not of the same lithostratigraphic position. Whereas Schlösselweg, Böhme's, Schmiedel's and Schreiter's Block mainly consist of magnesium-calcite or alternating calcite and dolomite horizons, the marble of Päßler's and the Bachberg Block are composed of pure calcite. With respect to the depositional conditions it is suggested that they predate the other marble blocks.

Three-dimensionally outcropping narrow fault within the marble of Päßler's Block. This is an important site referring to the history of the geologic investigation of Saxony.

Three-dimensionally outcropping narrow fault within the marble of Päßler's Block. This is an important site referring to the history of the geologic investigation of Saxony.