Maksovites and tuff siltstones in the northwestern Maksovo deposit (Ludicovian superhorizon of the Paleoproterozoic Onega synclinorial structure, Karelia) are believed to have been subjected to alkaline-Fe-Mg alteration. They are confined to a multiple ridge-like fold and a brecciation zone. Metasomatic rocks are poorly-defined (broken unaltered rocks persist). Derived in a reducing environment, they are accompanied by an increase in Na, P, Ti and K and the formation of anthraxolite and various sulphide, sulfoarsenide and selenide (Fe-Ni-Co, base metal, Mo and Pb) streaks. Concentrations of some elements in streaky zones increase 2-100 times. ∑REE, U and Th rise less markedly (radioactivity increases but does not exceed allowable values for maksovites). Alkaline-Fe-Mg alterations are similar to those in Padma-type metasomatic rocks.
Keywords: alkaline-Fe-Mg metasomatic rocks, ore mineralization, geochemistry, maksovites, tuff siltstone, deposit Maksovo, Onega synclinorium, Karelia