The shaft at the  valkenberg coalmine was part of the  Oranje Nassau Mine 1 which was originally sunk in 1899  and finally closed in 1974 .

During this time, the mine produced  31.978.000 tonnes of coal and the pit head was in Heerlen. Originally there were 2 shafts  but a third was constructed.

 

A. THE ORIGIN OF COAL

The geological history of the Earth is divided into several epochs. One of these is called the Carboniferous. The Carboniferous is an epoch in the Geological record, which lasted from 359,2 ± 2,5 tot 299,0 ± 0,8 millon years ago. The Carboniferous is part of the  Paleozoïc. It is precede by the Devonian epoch, and followed by the Permian.

During the Carboniferous, the formation of the supercontinent Pangea came to an end. The drift of the continents towards each other had started already much earlier. The sealevel was relatively high, and large parts of modern Europe were covered by swamps and marshes. In these swamps the plant remains were stored  which form nowadays  a large part of the coal deposits on Earth. Many new species of insects, amphibious creatures, and seed bearing plants appeared.

The Carboniferous in the Netherlands, Belgium, Great Brittain, Germany, and Central Europe was formed in an area that lay approximately at the equator, with warm seas, mangrove's areas, and riverdeltas. The high concentration of CO2 made extensive vegetation on the land possible. In the marshes first peat formed, which later became coal and natural gas.  In the total system of the Carboniferous, coal deposits form only a limited part. Large parts of the the Carboniferous basins are filles with deltaic deposits and shallow marine limestones.

 

The South-Limburg coal is of Carboniferous age. It has an Upper Carboniferous (Westphalien) age.

The same coal seams which were mined in South Limburg, are present at larger depths (3 - 4 km and more) in the northern part of the Netherlands. Because of the heat at that depth, the coal degassed, and the methane was trapped in the porous sandstones of the Permian Rotliegend. Sealed by the salt layers of the Zechstein formations above the Rotliegend, the gas has been conserved for millions of years: the Slochteren field (Groningen, The Netherlands) is one of the largest gas fields in the world.

It is generally accepted that coal is formed from plant remains. In the roof, but also in the floor of the coal seams, plant fossils are found.

In the era in which the coal was formed, South Limburg, which was subject to continuous slow subsidence, was at or just above sealevel. As a result of the continuous influx of fresh water by rivers, a fresh water marsh was formed.
On the wet plains, a lush vegetation developed, also under influence of the (tropical) climate of that time. 

Trees and plants died and sank into the swamp. New plants grew and died again. In the end, a thick layer of plant remains formed, which disappeared under the water level. The thickness of the layer depended on the time plant life could sustain itself. Layers of plant remains have been found varying in thickness from a few meters tot 60 meters and more. . 

If as a result of subsidence the forest ended below water level, than the plant life ended. Clastic material, carried by the rivers, was deposited on top of the plant remains. This layer of sand, clay or silt, became thicker when deposition continued for a longer time.

If because of decreasing subsidence, or by fast upheaval, the plain came again above waterlevel , than things could repeat themselves. In this way, several layers of plant remains, sand, silt or clay ended up above one another.

 

If the layers of plant remains had remained at the surface, coal could never have been formed. The plant remains would have rotted away. In the Carboniferous, this did not happen.

 

The plant remains, which accumulated in the swamp, hundreds of millions of years ago, gradually sank away, and were covered with sediment. In this way they were cut off from air. After a long time, as a result of increasing pressure and temperature, coal seams separated by layers of shale and sandstone were formed. This proces is called Coalification . See also below at E.

For a coal seam of approximately 2 meters thickness, a layer of plant remains with a thickness of 40 meters was required.

 

B. POSITION OF THE COAL SEAMS

In the foregoing we have seen that the layers of plant remains, from which coal was formed , have originated on a vast plain, at or just above sealevel. From this we can conclude that the coals seams originally will have had a horizontal position.

Orogenic forces later have caused large tensions in the Earth's crust. As a result, the coal seams and the sediments in between have been folded and faulted. In the South-East of South Limburg, this tectonic effects were more intense than in the North-West.

After the deformation of the coal-seams, again the crust became active. Now a general tension occured, and cracks (faults) were formed. Along these faults, large slabs of the Earth's crust have subsided, or were uplifted: a Graben structure was developed.

The wear of rocks by weather, wind and water (erosion) also did its work, and large part of the covering sediments was removed. Erosion was in the South-East of Limburg stronger than in the North-West.
In the higher uplifted South-East, erosion has removed more than in the lower North-West.
In later epochs, again deposition of sediments has occurred on top of the Carboniferous rocks. These rocks are called the overburden.

The final result of erosion is that in the South-Limburg Area in the south-east there are less coal seams than in the North-west, and that the overburden is also less thick than in the North-West.

At the site of the Domaniale Mine, the thickness of the overburden is approximately 40 meters, but at the site of the Maurits mine this is about 300 meters.

 

Between Sittard and Roermond, there is a graben system (Roergraben). The depth of the surface of the Carboniferous varies between 1000 and 2500 meters. Between Roermond and Belfeld, the Carboniferous rises again closer to the surface, due to the Peelhorst. North of Venlo the Carboniferous is found again at greater depths. The Horst and Graben structure is a part of the Rhine-Graben, a major feature in the Geology of Western Europe. The Rhine Graben extends from southern Germany to the Doggersbank shallows in the Northsea.

The most important faults in South-Limburg are:

• The Feldbiss Fault.
• The Heerlerheide Fault.
• The Benzenrade Fault.

In the landscape the faults are, however, not very clearly discernable, even for the trained eye. Apart from the fact that in general they do not penetrate to the surface, the intense urban habitation generally obscures the faults from view. Even where there is no urbanisation, localisation of the faults is difficult, although sometimes, like in a part of the Brunsummerheide, between Brunssum and Nieuwenhagen (Landgraaf) a fault can be traced for a little while, if one knows what to look for. Often zones of strongly water-containing soil indicate traces of the fault system. In the area mentioned above, it is the Feldbiss Fault. Below a geological profile through South Limburg is given.

 

D. NUMBERING AND NOMENCLATURE OF THE COAL SEAMS.

Miners used a nomenclature that was valid for all South Limburg mines, or a numbering depending om how the coal seams were found when drilling the shaft. The numbering was then of course only valid for that mine.

In the first case names like:Furth, Merl, Steinknipp, Finefrau, Grauweck, Senteweck, etc. were used. In the second case there might be a numbering like: layer I, layer II, etc.

Coal seams which are found above layer I, but because of their dip were noyt discovered when drilling the shaft, were often discovered later, when drilling tunnels, and were indicated with a capital letter. For example": layer A, layer B B. etc.

E. TYPES OF COAL

The layer of plant remains which was locked off from air, has become coal, after a long time under increasing temperature and pressure. Plant are composed mainly of the elements:
carbon - hydrogen - oxygen - nitrogen. . The process which is called coalificationpeat changes vialignite, and coal into anthracite