AN ASSESSMENT OF THE GEOTHERMAL ... - Orkustofnun

Report 5 17 Akbar
380 m (Wardell Armstrong, 1991) and 52°C at a
depth of 440 m (IMC, 1998). A high
temperature gradient with an average 48.7°C/km
was reported in the coal mine, whereas in the
deeper part of the Gondwana basin the thermal
anomaly was recorded as high as 116.9°C/km
(CMC, 1994), as shown in Figure 15. High
temperatures are associated with faulting;
spontaneous combustion and traversing of an
igneous dyke through the coal seams caused the
high heat flow in the region (Kabir, 2008). The
southern part of the coal basin is characterized
by higher heat flow than the north. Overlying
the Lower Dupi Tila formation above the coal
seam is clay which acts as a seal to trap heat in
the underground chamber. When miners open
the southern colliery to extract coal faces high
underground temperature, an inrush of water
flooding and spontaneous combustion prevents
mining operations. The northern part of the
basin is comparatively colder and lacks the
Lower Dupi Tila clay unit on top of the
FIGURE 13: Anomalous geothermal gradient
at the Madhyapara hard rock mine area
Gondwana coal. The overlying Upper Dupi Tila Sandstone is a highly porous and permeable water
bearing formation constituting the main aquifer system of the area. The low geothermal gradient is
possibly caused by the downward vertical movement of cool meteoric water. Some stratigraphic
dissimilarity also exists north and south of the basin.
FIGURE 14: W-E cross-section of Barapukuria coal
mine area (after Islam and Shinjo, 2009)
Thakurgaon high-temperature area
The Thakurgaon high-temperature area, located
northwest of Barapukuria belongs to the Tista flood
FIGURE 15: Anomalous geothermal
gradient at the Barapukuria coal basin
plain and constitutes the Bangladesh part of the Himalayan Foredeep region. The depth of the
crystalline Achaean basement further north to the fan complex was found at a depth of 2500 m at
Shalbonhat 1 well (BSPD, 1988). The basement occurs only at 150 m depth at Phulbari coal basin to
the southeast (GSB, 1990). Neogene Siwalik sediments and recent alluvium directly overlie the
basement in most of the northwest part of the stable shelf (Rabbani et al., 2000). Although the surface
of the Tista alluvial fan appears smooth and undisturbed, the fan is deposited in a tectonic transition
zone subject to complex strong forces driven by the collision of the Indian plate with the Eurasian
plate to the north. In response to past tectonic events, a series of well-defined deep seated basement