The paper presents the results of petrographic and geochemical studies of the cement of Neoarchaean polymictic conglomerates in the molassoid complex in the Lake Pitkilampi area of the Koikary domain (central part of the Vedlozero-Segozero greenstone belt). The composition of the cement of the conglomerates was found to vary across the profile, being represented by an alternation of mafic, lithite graywacke and graywacke sandstones. The geochemical characteristics of the matrix are similar to that of the komatiites and komatiitic tuffs underlying the molassoid complex. It has an admixture of an acidic (dacite) terrigenous component, which indicates a polymodal source of the primary material. Petrogenetic ratios (La/Y, Sc/Cr, Ti/Zr, and La/Sc) in the cement of the conglomerates demonstrate a geodynamic association of the primary rocks with convergent ocean – island arc systems.