A CONTINUED STRUCTURAL DOCUMENTATION OF THE GE1 DRILL CORE

Abstract

Gothenburg Energy, SGU, and Gothenburg University are investigating the possibility for geothermal energy plant in the Gothenburg area. A 1 km drill core were drilled in the Högsbo area and two bachelor thesis were written by Julia Ladefoged and Anna Hynynen about the first 550 m of the core. These theses discussed the structural and petrological aspects of the rock in the core. This thesis together with Glamheden (2022) has documented the structural and petrological aspects of the last 450 m. When comparing data from Ladefoged (2021) and the data collected for this thesis, a couple of foliation sets were found. The foliation sets from this thesis point towards the southwest, west, and southeast, with some measurements pointing south. Ladefoged (2021) two sets points towards northwest and southeast and north to south. Veins have an orientation towards southwest, northeast, north, and south with a varying dip between 20 – 40°. The number of veins is slowly increasing towards the end. Fractures have a very scattered orientation but have some stronger ones towards the southwest and northeast. Fractures and veins increase with depth while the rock strength decreases. This could be because of a nearby fault zone or an increase in cross-cutting fracture sets. Two hypotheses could be drawn from this research. One includes three deformation events spanning between the Gothian orogeny and the Caledonian orogeny, and one that only contains two deformation events spanning between the Gothian orogeny and the Sweconorwegian orogeny. Fieldwork was conducted at Änggårdsbergen in Gothenburg. The result showed that the area has an orientation towards the southwest and is gently plunging and steeply inclined. Comparing the field data with the data from the core show two possible scenarios. One scenario is that the area was created during the Sweconorwegian orogeny by rotating the folds from the Gothian orogeny by 108° anti-clockwise and got a 2° change in the plunge. This would lead to a broader set of fractures. The other scenario does the same as the first but rotates the position of the fold after the Sweconorwegian orogeny by 28° clockwise and got a 1° change in the plunge during the Caledonian orogeny leading to smaller sets of fractures. Three big fracture sets could be found throughout Änggårdsbergen with clar notation of 058/55, 240/55, and 137/90. However, more data is needed to draw any final conclusions about whether it is possible and suitable to build a geothermal plant in the Högsbo area.