| dc.description.abstract | This study investigates the RA-granite (also known as Kärra Granite), which form a northsouth
trending intrusive body traversing Gothenburg. The spatial distribution of the
radioactive elements K, U and Th in RA-granite was measured in southern Gothenburg
(Änggårdsbergen and Sahlgrenska University Hospital), Sweden. The 1311 Ma old intrusive
RA-granite has high concentrations of U and Th. It is the dominating bedrock of
Änggårdsbergen, Sahlgrenska University Hospital and parts of Medicinareberget. The area
has been deformed during two major orogenies but the RA-granite has only been affected by
the last orogeny, the Sweconorweigan orogeny. This study investigates concentrations in the
areas mentioned above, with focus on Sahlgrenska University Hospital/Medicinareberget
where an enrichment in Th and K has been found in previous studies, the so called
Sahlgrenska anomaly. The aims of the report were to, via field studies, chemical and optical
analysis, map the spatial distribution of K, U and Th – and to investigate in which minerals U
and Th reside. The main focuses of the report were to discuss the possible extension of the
Sahlgrenska anomaly, evidence of possible hydrothermal and tectonic events in this area. The
spatial distribution of Th shows a local enrichment surrounding the Sahlgrenska anomaly and
an increase of concentrations from east to west. Uranium has lower concentrations
surrounding the anomaly. Potassium is enriched surrounding the Sahlgrenska anomaly but
have normal granite values throughout the field area. The study has shown new normal values
for the radioactive elements in RA-granite, 3.5-5 % K, 7-18 ppm U and 30-70 ppm Th. The
U/Th ratios indicates a hydrothermal event both in parts of Änggårdsbergen but also
surrounding the Sahlgrenska anomaly. The radioactive elements U and Th were found in
accessory minerals zircon and titanite, both primary but also possibly secondary titanite. No
biotite was found, but instead we found the typically hydrothermal mineral chlorite, so all
biotite could have been chloritized. Allanite was found in previous studies but not in this
study. The U/Th ratios indicates a hydrothermal event both in parts of Änggårdsbergen but
also surrounding the Sahlgrenska anomaly. The conclusion of the report was that we now
have normal values for the RA-granite, that hydrothermal events have taken place at the
Sahlgrenska anomaly and tectonic implications were seen in the microscopy studies. | sv |
