GEOCHEMISTRY OF TRACE ELEMENTS IN THE PALAEOCENE DEPOSITS OF THE YAREMCHANSKYI HORIZON (SKYBOVA ZONE, UKRAINIAN CARPATHIANS)

Abstract

During the 20th century, the main research directions of the Carpathian region geology have been associated with the search for oil deposits. Scientists studied mainly geology of the Creta-ceous and Palaeogene sediments. But geochemical features of the Palaeocene rocks remained out of sight. Some researchers have studied the geochemistry of trace elements in the Carpathians sediments for the metallogenic analysis of the region. Therefore, in our view, it is important to study the geochemical characteristics of Lower Palaeogene deposits. This will allow determining the conditions of epigenetic mineralization formation in the sedimentary rocks and the relation-ship between different phases of the rocks transformations. The object of research is multicoloured deposits of Yaremchanskyi horizon (Paleocene), which contain secondary ore mineralization. They are exposed in the riverbeds of Rybnyk, Prut, Prutets-Chymyhovskyi, Zhenets and near the Dovhe-village (Sambir district, Lviv region). We investigated the geochemical behaviour of paragenetic assemblages of elements with the use of variation, variance and correlation analyses and principal component analysis (factor analysis). We used the results of semi-quantitative spectral analysis of 99 samples from the rocks of Yaremchanskyi horizon, among them 45 samples of sandstone, 30 – limestone, 12 – aleurolite and 12 – argillite. We calculated the arithmetic average content of chemical elements (Cu, Pb, Ti, Cr, Mn, Ga, Ge, Co, Ni, Ba, Be, V, Nb, Mo, Sn, Ce, Y, Zr, Ag, La, Zn, Sc) in each type of rocks, the standard deviation, variance and coefficient of variation. For comparison, the average content of the element in the studied rocks and its average content in similar rocks of the Earth's crust, we calculated clark of concentration – the ratio of element's average value for clark of this element in the corresponding rocks of the Earth's crust. It has been found that increased concentration of some chemical elements in comparison with clark, as well as significant variance in their values is due to different forms of their occurrence in the rock composition (e. g., isomorphic admixtures in terrigenous minerals, complexes of absorp-tion in clay minerals, etc.). The differences in the formation conditions of the rocks of different composition from Yaremchanskyi horizon reveal not only in the respective average value and in variance but also in fixed in the nature the relationships between various trace elements. In the studied geochemical system, the weight of the first three factors covers 57 % of the to-tal variance (30, 16 and 11 %, respectively). This suggests that paragenetic associations of the elements have been formed mainly in conditions of maximum influence of the first factor (com-pact and stable association of Cu–Ag–Ga–Sn). The association of Co–Nb–Ge–Ti–Mo–Pb–Cr has been formed under conditions controlled by the second factor, and rare-metal association La–Y–Ce–Be–Sc – under the conditions of the third factor influence only.