Trace elements abundance ratios of Riphean fine-grained terrigenous rocks of the Uchur- Maya region and Yenisei ridge
Abundance ratios (Кк) of a wide range of trace elements (Li, Be, B, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, In, Sb, Cs, Ba, REE, Hf, Ta, Hg, Tl, Pb, Bi, Th, and U) of fine-grained terrigenous rocks (argillites, metapelites) of the Riphean reference sections of the Uchur-Maya region and Yenisei ridge are examined. It is established that clay shales and argillites of the Uchur and the Aimchan Group of the Riphean hypostratotype are moderately (2.5 < Кк < 5) and intensively (Кк > 5) Li-, B- and Zn-specialized, whereas analogous assemblages of the Lakhanda and the Ui Group display no distinct geochemical specialization, though being markedly enriched in HREE. Metapelites of basal formations of the Yenisei ridge Riphean sedimentation groups are distinctly and intensively B-specialized, and weakly Li-, Rb-, Be-, Nb-, Ta-, Th-, Ge,- and Cd-specialized. Besides, metapelites of the Lopatino and the Kordinsky Formation are moderately Cuspecialized; of Potoskui Formation, Bi-, Sb-, Hg- and V-specialized; and of Lopatino Formation, Hg- and Csspecialized. Metapelites of the Kordinsky Formation (Lower Riphean, central zone of the Yenisei ridge) as compared with metapelites of the eastern, near-platform zone are geochemically specialized in a much greater number of elements (Li, Be, Sc, V, Cr, Co, Ni, Zn, Ga, As, Rb, Y, Zr, Nb, Sb, Ag, In, Hf, Hg, etc.), and argillites of the ore-bearing (Pb, Zn) Gorevsky Formation are distinguished by elevated concentrations of a number of ore elements (Pb, Cd, As, Sb, and Bi). Increased Кк of rare lithophyle and some ore elements in the metapelites of the Yenisei ridge is conditioned by a high sialic content - geochemical differentiation of the Early Precambrian blocks of the Siberian cratons western margin, which were washed out in the Riphean, and riftogenic and intraplate magmatism synchronous with sedimentation. On the contrary, the fine-grained and terrigenous rocks of the Riphean lower strata of the Uchur-Maya region are compositionally close to immature substratums of the Late Archean or their Early Proterozoic analogs.