Colombian coal deposits range in age from Maestrichtian-Paleocene in the Sabana de Bogotá and Boyacá basins to middle Oligocene in the Amagá-Titiribí basin in Antioquia. On the basis of age alone, these coal beds should be of lignitic rank, but because of the intense Andean tectonism (especially during Pliocene time) the rank has been increased to bituminous coal with high to medium volatile-matter content. In some areas, as a result of thermometa-morphic action by the intrusion of porphyritic andesite, the coal beds have been transformed to meta-anthracite. Chemical analyses of the best known coal deposits show a large range in rank.

The main basins studied are Amagá-Titiribí (middle Oligo-cene), Santander (Paleocene-Oligocene), Valle del Cauca (Eocene), Cerrejón and Jagua de Ibirico (Paleocene), and Boyacá-Sabana de Bogotá (Maestrichtian-Paleocene).

Evaluations made in Colombia in 1968 were 5 billion metric tons of exploitable coal, of which 5 percent is measured coal, 15 percent is indicated coal, and 80 percent is inferred coal. There are some basins yet to be explored and evaluated; when this is accomplished, total coal resources in Columbia may be as much as 10 billion metric tons.