The NE-SW Tertiary magmatic belt of central Kalimantan is related to two separate periods of subduction; during the Eocene-Oligocene and Late Oligocene-Miocene. The younger magmatic belt is superimposed upon the earlier belt. This magmatic belt is characterized chiefly by Late Oligocene-Miocene volcanic products, among which limited exposures of the Eocene volcanics have also been mapped by previous investigators. This calc-alkaline magmatic belt has become known as the 'gold belt' of Central West Kalimantan on account of a number of discoveries of Neogene epithermal gold mineralization. This mineralization is found in central to proximal volcanic settings and occurred at relatively shallow depths. The earliest known subduction-related magmatism took place in the Eocene-Early Oligocene with the emplacement of calc-alkaline silicic pyroclastics, followed by a period of continental collision. Subsequent subduction-related magmatism continued from Late Oligocene-Pleistocene, during which time the magma evolved from calc-alkaline to potassic calc-alkaline. Plio-Pleistocene magmatism resulted in the formation of basalt flows. The present available K-Ar ages of the Cenozoic volcanics range from 51 to 1 Ma.