70 km NW of Ho Chi Minh city.
Placer deposits of sapphire
, transparent yellowish-brown zircon
rest on the slopes and near the bases of volcanic cones.
The placer deposits are closely related to Quaternary (Holocene) trachybasalts, which contain nodules of olivinites. They rest on tholeiitic Neogene-Pleistocene basalt.
Ref: E.Ya. Kievlenko (2003) Geology of gems, p. 67