Open pit mines and porcelanites in Most Lignite District
THE CZECH REPUBLIC
IV. THE NORTH BOHEMIAN LIGNITE BASIN
The North Bohemian Lignite Basin (Most Lignite District) is the largest Neogene
freshwater sedimentary basin (870 km2) in the Czech Republic. The basin is situated among
Ústí nad Labem – Most – Chomutov towns. The lignite seam with thickness from 30 to 55 m
is exploited from open pit mines with depth from 160 to 210 m. The lignite mining on
outcrops of lignite seam started in 1550, but expansion of mining in open pit mines took place
after 1946 (Malkovský et al.1985). The production 76 million metric tonne of lignite (before
1991) was reduced and now is about 49 million metric tonne per year. Lignite is used as fuel
for power stations.
Fossil burning-out of lignite seams on outcrops
On the outcrops of fossil burned lignite seam there are many occurrences of
porcelanites of early Quaternary age. They originated by thermal alteration and caustic
metamorphism of clays and siltstones at temperature ranging from 890°C to 1150°C (Fediuk
1988). In colored porcelanites (Figs. 2 - 10) the variety of minerals (anhydrite, aragonite,
cristobalite, epsomite, hallysite, hematite, hyalite, calcite, quartz, limonite, magnetite, opal,
gypsum, sulphur, staffeite, wad, and feldspar) including glass occur (Bouška and Dvořák,
1997). The porcelanites were also quarried as stone aggregates for building of temporal roads
in open pit coal mines. They found utilisation as a material for production of natural pigments
and the selected parts of variegated porcelanites were polished and use as decorative stones.
Recent fires in open pit lignite mines and on the waste piles
In open pit lignite mines the lignite often underlies to self-ignition, especially in places
of historical and mine subsurface workings (Figs. 11 - 16). The spontaneous heating and/or
burning of lignite remains also occur on lignite waste piles. According to the temperature
(from hot zones near the place of burning to cold condensed zones), big variety of the
secondary minerals originated. In the North Bohemian Lignite basin the following secondary
minerals have been identified: sulphur, alunogen, mascagnite, realgar, salammoniac,
thenardite, hallotrichite, tschermigite, hematite, maghemite and wad. Sulphur, which
originates due to thermal decomposition of Fe-sulphides even contains a small amount of
native silver (Bouška and Dvořák, 1997). Some of the secondary minerals are presented in
Figs 17-22
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Open pit mines and porcelanites in Most Lignite District
Fig. 1 Places with local of porcelanite occurrences (red) and temporary mined lignite seam
(light brown) in North Bohemian Lignite Basin.
Fig. 2 (Most Lignite District, CR). Outcrop of burning out lignite seam with porcelanites.
Dobrčice (50°28´54.6´´N; 13°44´42.6´´ E). Photo by Zdenek Dvořák, 2008.
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Open pit mines and porcelanites in Most Lignite District
Fig. 3 (Most Lignite District, CR). Yellow porcelanite (with high content of TiO2. Dobrčice,
outcrop in old quarry. Polished sample. Size of sample 5 x 7 cm. Photo by Zdenek Dvořák,
2008.
Fig. 4 (Most Lignite District, CR). Speckled brown-red and blue-greyed porcelanite (with
high content of TiO2). Zelénky, outcrops in old quarry (50°36´7.5´´N; 13°47´35.2´´ E).
Polished sample. Size of sample 8 x 6 cm. Photo by Zdenek Dvořák, 2008.
Fig. 5 (Most Lignite District, CR). Speckled red and blue - greyed porcelanite (with high
content of TiO2). Zelénky, outcrops in old quarry. Polished sample. Size of sample 7 x 5 cm.
Photo by Zdenek Dvořák, 2008.
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Open pit mines and porcelanites in Most Lignite District
Fig. 6 (Most Lignite District, CR). Yellow porcelanite (for macrophoto of sample see Fig. 3).
Mineral composition: mullite, cristobalite and anatase. Thin section, optical microscopy,
paralel nicols. Photo by Jiří Ščučka, 2008.
Fig. 7 (Most Lignite District, CR). Red spotted porcelanite. (for macrophoto of sample see
Fig. 4). Mineral composition: mullite, cristobalite, hematite and anatase with glass. Thin
section, optical microscopy, paralel nicols. Photo by Jiří Ščučka, 2008.
Fig. 8 (Most Lignite District, CR). Blue-greyed porcelanite with narrow oxidative rim on
surface of contractive cracks. Mineral composition: mullite, cristobalite, hematite and anatase
with glass in a matrix. Dobrčice. Thin section, optical microscopy, paralel nicols. Photo by
Jiří Ščučka, 2008.
Fig. 9 (Most Lignite District, CR). Spotted porcelanite with low grade of thermal
transformation. Mineral composition: opal, quartz, mullite, cristobalite, hematite and glass.
Dobrčice. Thin section, optical microscopy, paralel nicols. Photo by Jiří Ščučka, 2008.
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Open pit mines and porcelanites in Most Lignite District
Fig. 10 (Most Lignite District, CR). Glass origined from lignite ash and clays in place of
burned-out lignite seam. Mineral composition: glass, mullite, cristobalite, cordierite, hematite
and anatase. Dobrčice. Thin section, optical microscopy, cross nicols. Photo by Jiří Ščučka,
2008.
Fig. 11 (Most Lignite District, CR). Spontaneous burning in actual cut in open pit mine in
places of historical mine workings in lignite seam. Open pit lignite Mine Bílina
(50°34´22.47´´N; 13°43´43.6´´ E). Photo by Karel Mach, 2008.
Fig. 12 (Most Lignite District, CR). Detail of spontaneous burning of lignite actual cut in
open pit mine in places of location of historical mine workings in lignite seam. Open pit
lignite Mine Bílina. Photo by Karel Mach, 2008.
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Open pit mines and porcelanites in Most Lignite District
Fig. 13 (Most Lignite District, CR). Detail of spontaneous lignite burning. Open pit lignite
Mine Bílina (50°34´56.0´´N; 13°43´14.4´´ E). Photo by Karel Mach, 2008.
Fig. 14 (Most Lignite District, CR). Bucket wheel excavator KU-300 and fire of lignite seam
in place of historical mine workings in lignite seam. Open pit lignite Mine Bílina. Photo by
Karel Mach, 2008.
Fig. 15 (Most Lignite District, CR). Detail of fire in old historical mine working in lignite
seam. Open pit lignite Mine Bílina. Photo by Karel Mach, 2008.
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Open pit mines and porcelanites in Most Lignite District
Fig. 16 (Most Lignite District, CR). Spontaneous combustion of rest of lignite in waste pile
and origin of native sulphur crust in condensing zone. Open pit lignite Mine Bílina. Photo by
Karel Mach, 2008.
Fig. 17 (Most Lignite District, CR). Crystals of sulphur in surrounding of place of hot gasses
output. Open pit lignite Mine Bílina. Photo: Photo by Jiří Svejkovský, 2008.
Fig. 18 (Most Lignite District, CR). Crystals of sulphur on fragment of rock in cool parts of
lignite waste pile. Open pit lignite Mine Bílina. Size: 8 cm. Photo by Jiří Svejkovský, 2008.
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Open pit mines and porcelanites in Most Lignite District
Fig. 19 (Most Lignite District, CR). Details of crystal aggregates of native sulphur on the
surface of waste pile in condensing zone. Open pit lignite Mine Bílina. Size 10 cm. Photo by
Zdenek Dvořák, 2008.
Fig. 20 (Most Lignite District, CR). Crystals of kladnoite [(C6H4(CO2)2 NH]. Sample is from
cool part surface of lignite waste pile in condensing zone. Size of crystal is 2 mm. Open pit
lignite Mine Bílina. Photo by Zdenek Dvořák, 2008.
Fig. 21 (Most Lignite District, CR). Arsenic-sulphur melt from surface condensing zone in
place of spontaneous lignite burning. Open pit coal Mine Bílina. Size of aggregate is 3 mm.
Photo by Zdenek Dvořák, 2008.
Fig. 22 (Most Lignite District, CR). Crystals of native sulphur from surface condensing zone
in place of spontaneous lignite burning. Open pit coal Mine Bílina. Size of object is 4 mm.
Photo by Zdenek Dvořák, 2008.
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