| Summary: | The Kiirunavaara iron oxide-apatite (IOA) ore deposit in the Norrbotten county of northern Sweden is well-known worldwide as it has been studied extensively throughout decades and is the largest IOA deposits known to this day. The subject of this thesis is a group of porphyry dykes (DPs) that irregularly intrude the Kiirunavaara footwall rocks and ore body to then disappear into the hanging wall rocks. The up to >10m wide dykes varies from red, green to dark colours and comprise pale glomerocrysts of feldspar often together with clinopyroxene, amphibole, and titanite, in an aphanitic groundmass. Variation in groundmass colours represent ratios of green silicates clinopyroxene and amphibole to iron oxide staining of the fine-grained feldspar matrix, resulting in sample groundmasses to be either green or red, respectively. Replacement of green silicates by biotite represent dark coloured samples. The volcanic silicate host rocks to the Kiirunavaara iron ore are extensively Na- metasomatically altered, including the DPs. Geochemical major element classifications plots show that the DPs in a range from intermediate trachyandesite to a felsic rhyolitic composition, largely overlapping both hanging wall and footwall rocks. However, in immobile trace element diagrams they plot essentially in the rhyolitic/dacite fields, again overlapping completely with the hanging wall rocks, while foot wall rocks are separated into the andesite fields. The DPs, together with the volcanic porphyries, plot as metaluminous indicating metaigneous sources, and geotectonic discrimination diagram using Ta/Yb v. Th/Yb show a dominantly active continental margin environment for the DPs. A LA-ICP-MS U-Pb zircon age determination of one sample yielded a concordia age of 1880±4 Ma (MSWD=0.79; n=26), which represent the DPs crystallization age. Results from this thesis concludes the fact that the dyke porphyries of Kiirunavaara share inseparable textural characteristics with the hanging wall rocks as well as completely overlapping each other ...
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