Lydites in the North Onega Synclinorium, Karelia: Trace Element Composition and Possible Genesis

We studied the geochemistry of Paleoproterozoic siliceous rocks (lydites) from the North Onega synclinorium (Karelia). The study objects are represented by 16 lydite samples taken from one stratigraphic level in the geological sections of two sites–Tetyugino and Shunga. Their structural characteristics and mineral composition were studied using a scanning electron microscope equipped with an energy-dispersion microanalyzer. The trace element composition was determined by the inductively coupled plasma mass spectrometry (ICP-MS). The contents of most trace elements are below the Clarke concentrations. The Tetyugino lydites contain mainly biophile elements (P, Co, Cu, Mo, V, Ba), while the Shunga lydites are dominated by lithophile elements (Li, Rb, Cs). The trace element composition of lydites indicates that their formation took place on the periphery of the hydrothermal system, whereas the Tetyugino site was closer to the hydrothermal discharge zone than the Shunga site. The chemical peculiarities of the lydites allow us to consider them as a raw material for very pure quartz.