Uranium Mineralizations at Kiirunavaara,Northernmost Sweden

Sammanfattning: In recent years, a variably high amount of uranium (U) and radon (Rn) were found in the water and airof the Kiirunavaara mine in Kiruna, northern Sweden. The Swedish Agency for Marine and WaterManagement (Havs och vattenmyndigheten) has maximum limits for “special polluting substances” inwater that is released to natural recipients (HVMFS 2019:25), therefore, the mining company LKAB,owner and operator of the Kiirunavaara mine, decided to conduct a study to investigate the issueregarding these findings, triggering this master thesis.From LKAB’s geochemical database, 25 samples were selected, prepared and studied throughpetrographic microscopy. Fourteen samples went through more than 70h of EPMA and BSE imageanalysis and 5 of them went through MLA. All methods were performed either in Uppsala’s Universitylaboratories or in Kiruna, at LKAB´s research facility in Malmberget. The ultimate goal of this projectwas to determine the primary metal source of uranium that could cause future problems in the watertreatment processes and leakages to recipients.In order to aboard this study in Kiirunavaara, where no previous uranium related study was everconducted, the main objectives were divided into identifying the main mineral carrier(s) of uranium thatcould be the source for these U anomalies, the characterization of the rock types and mineralassemblages associated with U-bearing minerals, and last, to try to propose preliminary implications forU solubility and distribution in the rock mass and mine water. This study found uraninite, thorite and anunknown species bearing uranium in some of the samples, both hanging and foot wall, all related tohydrothermal alterations and anhydrite. The water circulation throughout the rock mass of the minecould have been the trigger and transporter of these elements that were causing the anomalies in the firstplace.