Composition and physico-chemical properties of aqueous extracts of lydites of the North Onega synclinorium in Karelia

Abstract

Relevance. The need to obtain reliable information on chemical composition of aqueous extracts of lydites. There is lack of such information, but it is so important both for understanding dispersion of elements and their impact on natural waters of a region. It is necessary to study the composition of aqueous extracts as a result of water–rock interaction to determine possible sources of water pollution with toxic elements. Mineral composition of lydites of the North Onega synclinorium contains organic carbon and mist pyrite, which may contain increased concentrations of trace elements "harmful" for drinking water. To determine the ability of such elements to pass into a dissolved state, it is necessary to study aqueous extracts of lydites. Aim. To determine trace element composition and physico-chemical properties of aqueous extracts of lydites selected from two districts of the North Onega synclinorium to assess their environmental hazard. Objects. Geological section of the shungite-lidite-dolomite complex of the Zaonezhskaya formation of the Paleoproterozoic age of the North Onega synclinorium. Samples of lidites were taken at the Tetyugino (LT) and Shunga (LSh) sites of the Medvezhyegorsk district of the Republic of Karelia. Methods. Field studies, including investigation of stratigraphic position of lydites in geological sections of the Tetyugino and Shunga sites and sampling, laboratory experiment, aqueous extraction, scanning electron microscopy, Raman spectroscopy, X-ray fluorescence analysis, Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Results. Mineralogical composition of the lydites of both sites is similar. Taking into account high content of SiO2 and negligible content of other petrogenic oxides in chemical composition of lydites, it is possible to consider them as a source for obtaining pure quartz raw materials. The structure of lydites is clot-cryptocrystalline and clot-globular. Lydite extracts environment acidity depends on the totality of the minerals extracted from it, either basic (dolomite) or acidic (pyrite oxidation products). This factor is decisive in formation of chemical composition of lydite extracts, regardless of the location of the samples within a given geological object. Many elements extracted by water from the lydite samples of two regions under consideration are characterized by varying degrees of their extraction from the massive and veined parts of the sample. The cure coefficients of chemical elements in the form of the ratio of element average concentrations in the extract and lydite solid phase show the predominant intake of Cd, Mn, Mo, Sr, Rb, Li, Ni, Co, Li from Tetyugino lydites into water. Mo, Sb and W are predominantly extracted into the solution from the Shunga lydites. Average concentrations of most elements of the extracts of the Shunga samples satisfy the requirements for drinking water and, unlike shungite, they are not sources of harmful components in water. Therefore, it is advisable to carry out work on the possibility of their use for water purification for drinking purposes.

Keywords

• Paleoproterozoic
• siliceous rocks
• lydite
• aqueous extracts
• chemical composition
• North Onegian synclinorium