Trace elements contained in rocks, especially those classified as potentially toxic elements (PTEs), can be largely harmful. Knowledge of the geochemical composition of waste is of great importance due to the potential possibility of contamination with these elements in the environment. The paper presents the geochemical characteristics of the sedimentary rocks from the Carboniferous coal-bearing series of the USCB. The present study used data for 120 samples from borehole WSx representing Zaleskie layers and Orzeskie layers within the Mudstone Series (Westphalian A, B). Major oxide concentrations (Al2O3, SiO2, Fe2O3, P2O5, K2O, MgO, CaO, Na2O, K2O, MnO, TiO2, Cr2O3, Ba) were obtained using an X-ray fluorescence spectrometry. The concentration of potentially toxic elements (Be, Sc, V, Cr, Co, Ni, Cu, Zn, As, Rb, Sr, Zr, Mo, Cd, Sn, Sb, Ba, W, Tl, Pb, Bi, Th, and U) was analyzed using inductively-coupled plasma mass spectrometry. As there are no relevant standards for the content of toxic elements in post-mining waste stored in dumps, the concentrations of elements were compared to their share in the Upper Continental Crust. Most elements, such as B, Sc, V, Cr, Ni, Cu, Zn, As, Sb, W, Tl, Pb, Bi, Th, and U had higher mean concentrations than those of the Upper Continental Crust (UC). Concentrations of the analyzed toxic elements in the studied samples did not exceed permissible values for soils, therefore they are not a potential threat to the environment. The results of the Pearson correlation analysis showed differing relationships among the analyzed toxic elements in the studied samples.

The geochemistry of sedimentary rocks is increasingly being used in palaeoenvironmental studies, in the identification of marine versus continental stratigraphy and in chemostratigraphic correlation. The selection of an appropriate research methodology, particularly in terms of sample digestion, can have a significant impact on the accuracy of the results obtained. Depending on the type of rock being studied and the aim of the analysis, a suitable mixture of acids should be used. The most commonly used sample digestion methods are based on a mixture of four acids (multi-acid), aqua regia and inverse aqua regia. As opposed to multi-acid whole-rock digestion, the use of aqua regia and inverse aqua regia result in only the partial digestion of sedimentary rocks. Geochemical analyses using these two different methods were carried out on Carboniferous sedimentary rocks from the Lublin Coal Basin from Poland.The elemental concentrations obtained showed essentially different results for some of the elements. A comparison of the elemental concentrations allowed the distinction of three groups of elements:

 - those that showed small differences between the results from the preparation methods (Co, Mn, Bi, Cu, Zn and Fe),

- those where the elemental concentrations were 20–50% lower using aqua regia digestion (i.e. Ni, P, Pb, Mg, Cd, Th, Mo, Sr),

 - elemental concentrations that were significantly lower (by up to 80%) following aqua regia digestion (U, Cr, Ba, Na, V, Al, Rb, K, Zr).

The S-7 borehole log from the Sumina area (USCB Poland) revealed the presence of three basaltic veins

originating from a basalt dyke. Coal interlayers in the rocks surrounding the basaltic veins have been coked to

form natural coke. Photometric measurements revealed that the optical properties of the studied natural coke

samples are characteristic of semi-graphite (Rmax > 9%). The natural coke matrix of all of the analyzed samples

has a biaxial negative optical character. Vitrinite in the examined natural coke samples is characterized by a

lower optical anisotropy than that of the natural matrix and it has a biaxial positive optical character. Vitrinite

in almost all samples taken at locations more distant from the intrusion has a biaxial positive optical character.

A reversal of the changes of the true maximum vitrinite reflectance and bireflectance with changing distance

from the second basaltic vein has been observed. The temperature regime that acted upon the dispersed organic

matter located in the immediate vicinity of the intrusion, estimated on the basis of the selected experimental

data, is suggested to be higher than 750 °C.