Browsing by Author "Tepsell, Johanna"

The geology of the Eastern Lapland Archean domain (the sudy area of this study) is vaguely known due to high metamorphism and poorly exposed lithologic assemblages. Three new U-Pb age determinations from key locations aim for more profound understanding of the geochronology of the area. Cu-Fe-S stable isotope data for copper sulfides from the Eastern Lapland Archean domain are presented for the first time. The stable isotope analytical method for Cu-Fe-S isotopes is refined and its applicability as a proxy for magmatic Ni-Cu-PGE sulfide deposits is evaluated. It has been suggested that, within an individual mineralized intrusion, negative correlation of δ34S and δ65Cu might be a useful indicator of the economic potential of Ni-Cu-PGE sulfide deposits. Combined S and Fe isotope systematics have also been used to fingerprint for the origin of sulfur. Three new samples were dated using the LA-ICP-MS method on zircon. Most of the Pultoselkä granite data are concordant and yield an age of 2795 ± 6 Ma. The data from the Kontioselkä pegmatite are mostly discordant and define maximum age for the pegmatite at 1766 ± 36 Ma. The Janesselkä gabbro yields an minimum age of 2425 ± 17 Ma, consistent with the 2,4–2,5 Ga age group of mafic magmatism observed widely across the Fennoscandian shield. The established U-Pb data imply distinct metamorphic effects during the Svecofennian and Caledonian orogenies. 28 stable isotope (Cu-Fe-S) data sets were measured from dissolved samples utilizing MC ICP-MS. A micro drilling method was used to extract sulfide cores for the solution work. Collectively the δ65Cu values of analysed sulfides (n = 28) range from -4,65 to 0,29‰, δ56Fe values from -0,21 to 1,44‰, and δ34S values from -1,38 to 11,77‰. Isotope values from magmatic sulfides (n = 7, 2σ) have a restricted range and distinct mean δ65Cu value of -0,99 ± 0,21‰, mean δ56Fe value of 0,16 ± 0,23‰, and mean δ34S value of 2,08 ± 0,3‰, consistent with chondritic compositions. The variation of isotopic values reflects the composition of the sulfide. Overall, they reflect varying crystallization histories and subsequent modification of the samples examined.