Review on the Compositional Variation of Eudialyte-Group Minerals in the Ilímaussaq Complex (South Greenland)

Abstract

We review the compositional variation of eudialyte-group minerals (EGM) from the Ilímaussaq complex in South Greenland. Investigated samples cover all major rock units and associated pegmatites and aplites. The whole data set (>3000 analyses from >250 samples) exhibits variable XMn (0.1–0.5), REE (0.2–1.7 apfu), Nb (0.1–0.4), and Cl contents (0.4–1.6 apfu). Most EGM compositions are Na-rich (13–15 apfu), while deviations to Na-rich but also to Na-poor compositions occur because of a combination of primary features (peralkalinity, water activity) and secondary alteration. During magma evolution, REE contents in EGM cores generally increase and reach their highest contents in the most evolved rock units of the complex. This points to the moderate compatibility of REE in EGM and a bulk D (cEGM/cmelt) value of <1 during magma differentiation. Chlorine contents in EGM cores continuously decrease, and are lowest at the rims of individual crystals, suggesting a continuous decrease of Cl activity in the magmas by large-scale EGM and sodalite extraction during the orthomagmatic stage and water enrichment during the late-magmatic stage. The overall variations of XMn across stratigraphy are only minor and likely influenced by the co-crystallization of sodic pyroxene and amphibole (c.f. aegirine, arfvedsonite) and local phase proportions. Similarly, Nb and Ti contents are influenced by co-crystallizing aenigmatite, rinkite, and others. Their presence buffers Ti and Nb contents to rather constant and low values, while their absence may cause variable enrichment on a local scale. Very low Sr contents (<0.1 apfu) in magmatic EGM from Ilímaussaq are related to the basaltic nature of the parental magmas of the complex, as large-scale plagioclase fractionation occurred prior to the formation of the Ilímaussaq magmas, effectively removing Sr from the system. This is in line with very strong negative Eu anomalies in EGM from Ilímaussaq. Consistently, Sr contents in EGM from alkaline complexes, for which foiditic parental magmas are assumed, are much higher and, in such cases, negative Eu anomalies are generally absent.

The role of local heteropolyhedral substitutions in the stoichiometry, topological characteristics and ion-migration paths in the eudialyte-related structures: a quantitative analysis

“…Eudialyte-group minerals (EGMs) are of significant scientific and industrial interest as important concentrators of rare and strategic elements [mainly, Zr and rare earth elements (REE)] in agpaitic alkaline rocks (Marks et al, 2020;Mikhailova et al, 2020;Kogarko & Nielsen, 2020;Atanasova et al, 2020;Kogarko, 2020;Schilling et al, 2011;Kogarko et al, 2010;Sheard et al, 2012) and are considered as potential source of these elements (Binnemans & Jones, 2017;Chanturiya et al, 2020;Balinski et al, 2020Balinski et al, , 2019aZhang et al, 2020). The general crystal chemical formula of EGMs is [N(1) 3 N(2) 3 N(3) 3 N(4) 3 N(5) 3 ]{M(1) 6 M(2) 3 M(3)M(4)Z 3 [Si 9 -O 27-3x (OH) 3x ] 2 (Si 3 O 9 ) 2 Ø 0-6 }X(1)X( 2), where M(1) = VI Ca, VI Mn 2+ , VI REE, VI Na, VI Fe 2+ ; M(2) = IV,V Fe 2+ , V,VI Fe 3+ , V,VI Mn 2+ , V,VI Na, IV,V Zr; M(3) and M(4) = IV Si, VI Nb, VI Ti, 5) are extraframework cations (Na, H 3 O + , K, Sr, Ln, Y Ba, Mn 2+ , Ca) or H 2 O; X(1) and X(2) are extra-framework water molecules, halide (Cl À , F À ) and chalcogenide (S 2À ) anions, and anionic groups (CO 3 2À , SO 4 2À…”

Assimilation and extensive metasomatism of agpaitic rocks from the transitional layered kakortokite, Ilímaussaq Intrusion, South Greenland

“…Perhaps the ongoing precipitation of eudialyte up through the kakortokite sequence drained the melt so much of chlorine that reaction with and assimilation of naujaite was possible at the transition from kakortokite to lujavrite. The decrease of chlorine in the melt through the kakortokite sequence is reflected in the decreasing chlorine content in eudialyte (Borst et al, 2018; Marks et al, 2020; Pfaff et al, 2008).…”

“…Some of the lujavrites have been referred to as younger separate intrusive phases (Ratschbacher et al, 2015; Sørensen et al, 2006). Marks et al (2020) assigned the Transitional Layered Kakortokite to this intermediate sequence.…”

Zr-Rich Eudialyte from the Lovozero Peralkaline Massif, Kola Peninsula, Russia

“…According to the literature data, the Zr-content in EGM from most deposits does not exceed 3 apfu. The ZrO2 and REE2O3 content vary in the range (wt.%): 11.40-12.07; 2.00-3.30 for North Qôroq centre, South Greenland; 10.35-11.48; 0.39-10.15 for Mont Saint-Hilaire, Quebec, Canada; 9.85-10.82; 0.15-0.52 for Gardiner complex, East Greenland; 10.90-11.20, 1.15-12.12 for Ilímaussaq, Southern Greenland; 0.15-5.00 (ZrO2) for Tanbreez, South Greenland [7,[26][27][28]. Meanwhile, most of the EGM samples (70%) from the rocks of the Lovozero massif are hyperzirconium, i.e., their Zr content exceeds 3 apfu [3].…”