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The geology, petrography and mineralogy composition of coal from the Nováky deposit
zdroj: Acta montanistica slovaca 2002, autori: Zlatica Machajová, František Verbich, Ivana Sýkorová 
pridané: 18.11.2004

Mineralogy characterisation

The coal deposit of Nováky, owing to a varying rock composition of the surrounding mountains and intensive volcanic activities before, during and after the coal deposit settling, has one of the richest parageneses of minerals. Mineral additions are present both in the concentrated form as inorganic slices in the coal and in the form of mineral additions directly in the coal mass. The bond of minerals in the coal deposit has the following forms:

• primary bond in original plants,
• bond to the mineral additons in the coal,
• clastic and chemogenous minerals from the sedimentation period,
• minerals arising during diagenesis - coalification,
• minerals arising from hydrotherms penetrating the deposit,
• minerals arising in the deposit that was already formed, during the circulation of water after tectonic faults,
• secondary minerals arising from the decomposition of certain minerals formed by the above - mentioned processes,
• bond to freely bound water in the coal in the sediments.

Minerals identified in Nováky coal (minerály identifikované v Nováckom uhlí)

Syngenetic mineral additions consist mainly of clayey and tufagenic material that forms a part of the layer structure; besides the macroscopically evident syngenetic mineral additions.

The postgenetic mineral additions consist mainly of pyrite, marcasite, sporadically melnikovite and various modifications of silica that occur mainly as the fracture filling or they incrust the structural components of coal. Pyrite inclusions occuring in the coal of Nováky are of various kinds and they can be divided into three groups:

• relatively coarse inclusions of compact grained pyrite. They occur in the form of continuous interlayers, lentils, concretions and fracture filling. Their thickness is usually from x mm to 3 - 5 cm.

• fine inclusions of the porous or tabular structure form fine interlayers, plates and veinlets that are dispersed in the whole coal mass non-uniformly.

• microscopis inclusions that are distributed in the coal mass non-uniformly. The usual shape of the microscopic parts is spherical and they have a diameter from 25 to 40 µm.

Various modifications of silica form an another postgenetic mineral addition that is not a carrier of an increased content of harmful secondary elements from the chemical point of view, despite of the fact that it is often a significant component of the coal ash matters. It is mainly present as a clastic product of the sedimentation mode. Besides the crystalline form of SiO2, its amorphous form - opal - is present relatively often. It forms the filling of fractures and contraction cracks in coal. It was formed in the diagenetic stage of the feldspar carbonisation.

Orpiment makes a major contribution to the high content of arsenic in coal. It is the question of an anomalous increase of realgar and orpiment that form fine deposit on the layer surfaces and they also occur in connection with various modifications of silica, especially the colloform one that sporadically fills tectonicaly damaged parts of a layer. The accurate genetic classification of these minerals is not unambiguous because from the viewpoint of their occurrence, realgar and orpiment occur as the filling of damaged zones, they can be classified among epigenetic mineral additions, but they also occur on the layer surfaces and their syngenetic origin also cannot be excluded.

As regards calcite, besides its occurrence in ash matters, the occurrence of calcified organic residues - microboxes - is also usual.

Magnetite and limonite also occurs, but rarely.

Gypsum and anhydrite are minerals that are very close each other, both genetically and by development. In the coal deposit of Nováky they occur in two generations. The older generation is formed by free crystals and their fragments, coatings, filling of cavities with druse-like development. The second generation is formed by so-called "secondary" gypsum that forms microscopic "bloom" on fragments of coal, claystone.

Acta montanistica slovaca 2002, autori: Zlatica Machajová, František Verbich, Ivana Sýkorová