is most intensely concentrated in marbles of the Chuksin-Kuchin graben-syncline, to the north and south of which the Chuksin
and Kuchin ruby placer deposits were explored.
The Kuchin site is in the axial part of the graben-syncline within a sequence of marbles, about 200 m thick. Primary ruby occurs as disseminated crystals and lenses oriented conformable with the bedding, as well as in cleavage cracks. Mineralization is controlled by tectonic fracture zones in marbles and is confined to fiels of dikes and veins of leucocratic granites, aplites and pegmatites.
Ref: E. Ya. Kievlenko, Geology of gems, 2003, p. 50