Biliran Island is constructed of Quaternary volcanoes related to active subduction along the Philippine Trench. lt is situated alongside the active Philippine Fault which directly controls the
present structural framework of the island. The interplay of volcanisrn and tectonic activity has
created favorable conditions for geothermal systems to develop. We find both active and inactive systems here. However, they are small in size and apparently short-lived. Three thermally altered ground with war springs (Panamao, Anas and Kalambis) are characterized by secondary mineral assemblages reflective of conditions hotter than present. Thus, they must be associated with dying systems. The active Volcan-Libtong system is characterized by intense fumarolic activity, hot acid springs and boiling mud pools in the hottest and central region, and near neutral pH, associated with warm and hot springs at greater distance from the center.

Our present exploration and development concepts would discard Biliran as a site of further activity. However, we anticipate that we will be encountering more of these kinds of marginal resource. Therefore, other scientific techniques (e.g. petrochemistry, radiometric dating) may have to be utilized as adjunct to our standard methods to better understand these small, less attractive resources. Biliran lsland, because of its easy accessibility and the amount of work already done in it may be a good area to conduct further studies addressing these needs.