Recent studies carried out by the authors of this paper reveal that ultramafic rocks of the NËm Bót Complex (in the south of Hµ Giang) suffered strongly the hydrothermal alteration. The association of altered ultramafic rocks consist of serpentinite, serpentinite-talc-carbonate and carbonate-talc rocks. Carbonate in those rocks is mainly of breunnerite.The carbonate-talc and serpentinite-talc-carbonate rocks can be used not only as an unbaked material, but also as a kind of magnesite ores.