Nong Bon Mines, 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.
Along the basalt plateau of Bo Rai, for a distance of 27 km, there are 23 ruby placer operations, which use mechanical methods with bulldozer stripping and hydraulic washing of the productive layer to recover gem minerals.
Ref: E.Ya. Kievlenko (2003) Geology of gems, p. 66