Characterization and paragenesis of nordite-group minerals from the Ilímaussaq alkaline complex, South Greenland

• Main Author: Gulbransen, Emil Holtung
• Format: Master Thesis
• Language: English
• Published: 2020
• Subjects: Barium; REE; Igdlutalik; nordite; mineral; Ilímaussaq; Taseq; Greenland; Kola Peninsula; greenlandic; kola peninsula
• Online Access: http://hdl.handle.net/10852/79599; http://urn.nb.no/URN:NBN:no-82788

This thesis uses chemical and X-ray data to explore the composition and crystal-structure of nordite-group minerals from the two localities Igdlutalik Island and Taseq slope in Ilímaussaq Alkaline Complex in South Greenland. The nordite-group is a complex rare-earth silicate with the general formula of A2BXYZT6O17 and consists of five approved species all of which have first been described from the alkaline complexes of the Kola Peninsula, Russia. From the Ilímaussaq Alkaline Complex, nordite-(Ce) has been described from a trachytic dyke on the island of Igdlutalik, and I suggest how nordite could have formed in this low alkaline system. The Igdlutalik nordite forms 20 µm - 100 µm euhedral crystals sparsely distributed in an aegirine and albite matrix. The mineral is homogeneous with the ideal formula of Na3SrCeZnSi6O17. The crystal structure was refinement in Pcca to R1 = 0.0158, with a unit cell of a = 14.3891(2), b = 5.1799(1), c = 19.7554(2) Å and V = 1472.44(3) Å3. At a new occurrence on the Taseq nordite is associated with ussingite, i.e. highly agpaitic conditions, as it is the case from most of the Kola occurrences. The Taseq nordite forms concentric circles growing from a chemical distinct Nd-rich core, forming clusters up to 5 mm in the ussingite matrix. The Taseq nordite is heterogeneous and displays sector zoning. The different zones are either Ba or Sr dominated, which has not previously been described in nordites. The ideal formula is Na3BaCeZnSi6O17. The crystal structure was refinement in Pcca to R1 = 0.0246, with a unit cell of a = 14.5596(4), b = 5.2213(1), c = 19.8270(4) and V = 1507.25(3) Å3. Overall, the X-site in the structure is dominated by Ba, which reflected in the chemical analysis. This means that the Taseq nordite is a new mineral to the world and the Ba-equivalent to nordite-(Ce) with the ideal formula of Na3BaCeZnSi6O17. Since the nordite-group already have a prefix and suffix determined by the Z-site and Y-site, respectively, a new root name is required. Illoq is the Greenlandic word for cousin and would describe the Ba-bearing nordites chemical relation to the other group members. Therefore, the new mineral from Taseq is suggested to be named illoqite-(Ce).