Bo Waen, Trat Province, Thailand
Rubies are recovered near the town of Trat, 45 km east of Chanthaburi.Black spinel, magnetite, ilmenite and zircon are common among other minerals in the heavy fraction. The gem-bearing alluvium occurs near the surface or is buried under a sequence of sandy-clay and red-brown clay deposits at depths of a few meters to 10 m.
Ref: E.Ya. Kievlenko (2003) Geology of gems, p. 66