Geothermal mapping project was initiated with the intention to produce a detailed and complete data base of the geothermal resources of Sri Lanka. Although Sri Lanka is not situated on an active geothermal area, i.e. closer to an active plate boundary, there are clear indications of low-enthalpy activities as evidenced by the presence of thermal springs. Generally, all of the known thermal springs are located at a close proximity to the Highland-Vijayan (H/V) lithological boundary. This has led to the hypothesis that H/V boundary could be playing a role in the formation of geothermal resources.
A detailed geophysical survey was conducted using state-of-the-art techniques such as Magnetotelluric (MT) to investigate the deep structures and possible heat sources. Although the underlying structures, fractures and the possible hydrological pathways were identified, no heat source has so far identified. Further observations revealed the association of dolerite dikes with the thermal springs. Since the dolerite dykes are relatively very young (less than 150 MY), the origin of the thermal springs may have some relationship with the intrusion of dolerite dykes. In addition to MT, some other geophysical techniques such as Time-Domain Electromagnetics (TDEM), magnetic methods and resistivity techniques are employed during this research project.
Preliminary results indicate that the water-bearing fractures run deep into the earth, connecting with major, large scale fracture systems, which may run through the heat-bearing intrusive bodies such as dolerite dyke. A schematic diagram of the proposed model is shown in figure 01.
Prof. Deepal Subasinghe
Mr. S. Opatha