BRECCIAS IN SHUNGITE-BEARING ROCKS OF KARELIA AND THEIR GENESIS

Abstract

In the Lower Proterozoic formations of Karelia, USSR carbonaceous rocks are relatively widespread and are dated as Lyudikovian. The shungite-bearing rocks have an unusual chemical composition. Sharply dominant are two components, SiO2 and Cf, which together account for as much as 85 percent of them; Al2O3 reaches 5.5 percent, but the content of each of the oxides Al2O3, Fe2O3, MgO, Na2O and K2O generally does not exceed 1.5 to 2.5 percent. Diffraction analyses of the shungite-bearing rocks revealed the following minerals: quartz, plagioclase, muscovite, biotite, chlorite and apatite. Pyrite, sphalerite, chalcopyrite, pyrrhotite and rutile were identified in reflected light. White-cement breccia is most easily identified in hand specimens. It resembles 'rubble'.