| dc.description.abstract | During 2021, Geogruppen got a mission by Gothenburg Energy to extract a 1000-meter
drillcore from the Högbo area in order to test the site for potential geothermal energy
production. The site was chosen because of the high amount of RA-granite in the west of the
area, which was believed to be beneficial for the potential of having deep geothermal energy.
This is because of the increased amount of radioactive decay, increasing the geothermal
gradient and allowing the borehole to be shallower and still receive the desired heat. The
following thesis aim was to continue the previous work done by Julia Ladefoged (2021) and
Anna Hynynen (2021) together with Co-student Johan Lindell (2022). Whereas this thesis’
focus is on the petrological aspects the work done by Anna Hynynen and Johan Lindell
instead concentrated on the structural properties of the sampled rocks. In addition to logging
the core, compositional measurements were done with a handheld XRF to determine the
concentrations of Potassium, Iron, Silica, Calcium, Titanium and Aluminium. The Uranium,
Thorium, and Potassium content were also measured with Mikael Tillberg's help, with a
Gamma-ray spectrometer. Other properties such as density and relatively heat production rate
were then calculated. Another aim was to do fieldwork at Änggårdsbergen in order to
correlate the petrological aspects found in the field with the ones in the core. Furthermore, the
long-term goal of this project is to evaluate the possibilities of achieving geothermal energy
for Gothenburg.
The primary lithologies found in the core between the 556- and 1001.45-meter intervals were
granitic gneiss, tonalitic gneiss, granodioritic gneiss, and biotite zones, all of which ranged
from weakly to strongly foliated. Additionally found were different amounts of accessory
minerals such as Pyrite, Fluorite, Hematite, Magnetite within the main rock types. When
correlating the core with the field results it could be seen that red stained quartz veins are
present in both the core and in field. Together with the sign of hydrothermal processes
occurring because of the presence of chlorite. Different types of intrusions with mafic
minerals such as biotite, amphiboles and chlorite are causing sudden increases in density.
The granodiorite found in field is believed to be the result of a low density of vegetation
which allowed the overlaying RA-granite to be more withered compared to other mountain
tops. Furthermore, that those samples found in field require more testing to know for certain
if they are RA-granites or not and that the potassium concentration was not enough of an
indication.
In conclusion the heat production rate can be seen as relatively low but that further
investigation is required to discussed if Geothermal energy is suitable for Gothenburg or not. | en_US |
