Master of Science Paul Heckmann will Friday October 24th, 2025, at 12:15 hold his Thesis Defense for the PhD degree in Science. The title of the thesis is:
« Mafic-ultramafic complexes: A role of volatiles in the formation of mafic pegmatites and massive Cu-Ni-Co sulfide deposits »
The Hamn Complex, a well-exposed Paleoproterozoic layered mafic-ultramafic intrusion in Northern Norway, provides a unique setting to study magmatic processes at multiple scales. This thesis, based on three papers, investigates the petrology and genesis of the intrusion and its associated Ni-Cu-Co sulphide mineralisation.
At the regional scale, Paper 3 integrates field mapping, geochemical analysis, and sulphide trace element and sulphur isotope data to reconstruct the intrusion’s emplacement history. The results indicate the 1.8 Ga Hamn Complex formed in a continental arc setting through multiple magma pulses that assimilated felsic crust. The sulphide mineralisation is concentrated at contacts between mafic and ultramafic rocks, particularly in chaotic zones with crustal xenoliths. Geochemical signatures, such as high δ34S values and low Se/S ratios, confirm crustal assimilation. Low PGE levels and high Cu/Pd ratios suggest early sulphide segregation or incomplete extraction.
Paper 1 explores the petrogenesis of mafic pegmatites within the intrusion. Unzoned pegmatites have coarse textures and evidence of crystallisation from H2O- and Cl-rich melt. Water and chlorine contributed to a reduced melt viscosity and enhanced crystal growth. Zoned pegmatites show grain size and compositional zoning, likely due to remobilised melt intrusion into cooler host rocks. Fast heat diffusion towards the host rock could have caused undercooling of the pegmatite-forming melt. In contrast to the unzoned pegmatites, the zoned pegmatites record crystallisation from a CO2-rich melt.
Paper 2 uses experiments to assess how H2O and Cl affect plagioclase crystallisation from mafic melts. Results show that H2O significantly delays nucleation and enhances crystal growth, contributing to pegmatitic textures. Chlorine has a weaker influence, mainly stabilising phases without promoting coarse textures.
Together, these studies highlight the complex interplay of magmatic processes and a role of volatiles in shaping the Hamn intrusion's textures and mineralisation.
1st Opponent: Professor Rune B. Larsen, NTNU
2nd Opponent: Dr. Burkhard Schmidt, Georg-August-University Göttingen, Germany
Internal member and leader of the committee: Associate profesor Carly Faber, IG, UiT, Norge
The defence and trial lecture will be streamed from these following links at Panopto:
Defence (12:15 - 16:00)
Trial Lecture (10:15 - 11:15)
The thesis is available Here