The corundum 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.
On the Chuksin site, the corundum-bearing strata of marbles is limited by faults, which control hydrothermal alteration and contain pink topaz
. Granite pegmatites with columbite
are widespread west of the site.
In the northern part of the Chuksin area, fine-grained quartz sand with staurolite, kyanite and irregularly distributed grains of corundum
prevail in the formation. The corundum is red of different tints, some of which are transparent. The heavy fraction of pan concentrates contains monazite, small (up to 3 mm) crystals of pink topaz
Ref: E. Ya. Kievlenko, Geology of gems, 2003, p. 50, 62