LOCATION LENGEFELD

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The deposit Lengefeld contains exclusively dolomitic marble. It is lithostratigraphically classified into the Raschau Formation as part of the Keilberg Group. This corresponds to an age of 530-540 million years.

Simplified geological map of Lengefeld

Simplified geological map of Lengefeld

In the deeper footwall of the carbonaceous metasediments biotite-paragneis has been proven that belongs to the Proterozoic Niederschlag Group ("Gneisses of Marienberg"). The Lower Cambrian, about 530-540 million years old Raschau Formation of the Keilberg Group forms the host rock suite of the marble deposit. In contrast to other areas, the basis of the formation in Lengefeld consists of feldspar-bearing muscovite schist with thin intercalated lenses of amphibolites.

Garnet-bearing muscovite schists occur as wall rock of the dolomitic marble horizon (thickness 50-90 m). The hanging wall is formed by folded quartzitic muscovite schists with intercalated quartzite schists.

The carbonate body is of marine-sedimentary origin. The dolomitisation of the primary limestone was caused by magnesium-rich pore water during diagenesis of the sediments.

The Lengefeld deposit is part of the Middle European Variscides. The carbonaceous sediments belong to the oceanic crust of the Saxothuringian suture zone, which was subducted beneath parts of the continental crust of the Bohemian Mass. Increasing pressure and temperature caused greenschist- to almandine-amphibolite-facies metamorphism and deformation leading to the recrystallization of limestone to marble.

Simplified geological cross-section (N-S) of the marble deposit Lengefeld (click on the picture for enlargement)

Simplified geological cross-section (N-S) of the marble deposit Lengefeld (click on the picture for enlargement)

Simplified geological cross-section (W-E) of the marble deposit Lengefeld (click on the picture for enlargement)

Simplified geological cross-section (W-E) of the marble deposit Lengefeld (click on the picture for enlargement)

Finally, during the Variscan orogeny 320 million years ago, magnesium-rich fluids were responsible for magnesium-metasomatism. These metasomatic processes proceeded uncontrolled throughout the whole marble body due to the previous brittle tectonic deformation.

The metamorphic transformation from diagenetic dolomite to dolomitic marble resulted in grain boundary sliding and dynamic recrystallisation with contemporaneous homogenisation of grain sizes.

The originally compact marble body was subdivided into several blocks by tectonic processes during and after the Variscan orogeny. Five of these blocks are known to date (Old Block, New Block, Deep Block, Lößnitz Block, White Kiln Block).

PETROPHYSICAL PARAMETERS OF THE MARBLE

Gross Density: 2.85 g/cm3

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

Frost Resistance: 0,13 % mass loss

Compressive Strength: 105.0 N/mm2

Bending Tensile Strength: 11.0 N/mm2

Abrasion Resistance: 19 cm3/50 cm2

Polishing Value: 42 SRT-units

pH-Value in Aqueous Suspension: 8.5

The dolomitic marble of Lengefeld is characterised by a high frost resistance, low water absorption capability and a high abrasion resistance. The compressive strength amounts to 105 N/mm². Additionally, the marble is free of heavy metals resulting in a high-purity and pigment-poor raw material.