The islands of Samar and Leyte lie in the eastern periphery of the Visayan Region. They are located within the immediate vicinity of the Philippine rift zone and the Philippine deep, two major structures greatly influencing the geology of the archipelago.

Morphologically, the plateau like landscape of Samar, a result of a series of gradual vertical diastrophisms, is relatively less deformed than any of the other areas in its immediate tectonic vicinity. Leyte, on the other hand, is greatly influenced by the Philippine rift zone. Sogod and
Cabalian Bays, adjoining Panaon Island, are graben structures caught between marginal faults. Volcanism appears to have broken out along, and to have been controlled by the rift-zone.

The lithologic units present in Sumar fall under two (2) broad classifications: a suite of igneous rocks of Cretaceous-Paleogene age, forming the island’s nucleus, and the sedimentary sequence of Miocene-Pleistocene age surrounding this nucleus. Similarly, the rock units found in Leyte consist of a schist body and an igneous complex with serpentinized facies intruded by gabbroic dikes of Cretaceous age, the sedimentary sequence of Miocene-Pleistocene age, and the Quarternary volcanics.

Promising mineral prospects have been identifed and their economic viability was studied. Among these are the massive sulfide: and the bauxite deposits of Samar, the gold prospects and the rock asphalt deposits of Leyte. To date, the massive sulfides and the bauxite: have been extensively studied.

The massive sulfides of Central Samar are related to volcanism in a shallow-in-land basin. Colloidal ore tex tures, and the presence of foraminifera and radiolaria in the associated ferruginous mudstone attest to this. It is believed that the sulfide: were partially eroded and, subsequently, deposited in an adjacent basin, together with coal measures.