Trace elements distribution in stream sediments of an abandoned U mining site in the Eastern Carpathians, Romania, with particular focus on REEs

Abstract

Trace elements distribution, including rare earth elements (REEs), in stream sediments of an abandoned U mining site in the Eastern Carpathians, Romania, were of high concern of interest in the present work. A total number of 40 riverbed sediments samples collected from the Bistricioara River and local tributaries (Primatar, Bradul, Prisacani, Barasau, Grintiesul Mare and Valea Seaca) were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) and energy dispersive X-ray fluorescence spectrometry (XRF). All REEs including La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu were identified and quantified in the present work using ICP-MS technique. For other 24 elements (Ti, V, Cr, Co, Zn, Li, Be, Rb, Sr, Y, Sc, Zr, Nb, Sb, Ba, Ta, W, Pb, U, Ni, Cu, Mo, As, Th) similar information was obtained either by ICP-MS or XRF techniques. The impact and the relevance of the obtained data base might be significant at a local scale of about 50 km2.Enrichments of some trace elements of interest in comparison to the upper continental crust allowed discrimination between various mineralization processes specific for the investigated areas. Uranium mineralization and Paltin-type (Pb, Zn) mineralization seems to be specific for the NW area of the investigated region. Negative anomaly characteristic for the upper crustal rocks was identified for Eu and Ce elements. Evidences were obtained also for the existence of ultramafic rocks (Ni, Cr, Co and V) in the investigated riverbed sediments. The observation was also confirmed by the binary plots analysis of Th/Cr vs. Th/Co and Cr/V vs. Y/Ni pairs. From the investigated tributaries to Bistricioara River, Barasau seems to exert the highest influence on the abundances of REEss in the entire area. Most probably some chemical parameters such as the pH of the water streams influence leaching and depletions of some chemical constituents in various minerals specific for the region.The existence of magnetite, garnets, pyrite and sillimanite minerals was confirmed by SEM-EDAX and XRF analysis, as well by optical microscopy. Principal Component Analysis runs confirmed the association of some chemical elements in the riverbed sediments in close connection with the minerals from which they originate.The present work reports for the first time upon the authors knowledge clear scientific evidence and chemical information concerning the geology and geochemistry, i.e. transition metals, high field strength elements, alkali and alkaline earth elements, rare earth elements (REEs) and others, in stream sediments crossing the Tulghes-Grinties mining area (Eastern Carpathians, Romania). For the analysed REEs this is the first study reporting consistent information on the concentrations of the entire array of both light REEs (six elements) and heavy REEs (ten elements) in Bistricioara Basin stream sediments. Relevant scientific data related to geochemical characteristics of ultramafic rocks existent in the investigated area were also generated. Moreover, data reported in the present work might be considered as a reference geochemical database relevant for the investigated area, which can be used as a trustworthy input for a systematic national geochemical atlas.