Temporal growth of epitaxial layers in the CaCO3-REECO3OH system during mineral replacement processes
- 1Department of Geology. School of Natural Sciences. Trinity College Dublin, Dublin, Ireland.
- 2National High Magnetic Field Laboratory, Florida State University, Tallahassee FL USA
Mineral replacement reactions are essential for the understanding of the genesis and chemistry of REE-bearing carbonatite deposits. Many of these reactions involve interaction of Ca-Mg and REE carbonate phases, leading to the formation of minerals with complex compositions and structures.
This study explores the oriented surface precipitation of REE carbonates during the interaction of individual and multiple REE-bearing aqueous solutions with calcite and aragonite (CaCO3) at low hydrothermal conditions (25-220 °C). This mineral-fluid interaction is translated into a temperature-dependent solvent-mediated surface precipitation and subsequent pseudomorphic mineral replacement of the CaCO3 seeds by newly formed REE carbonates. This complex replacement sequence includes the crystallisation of metastable kozoite (orthorhombic REECO3OH) via the formation of individual spindle-shaped crystals following a transient non-random orientation on the surface of the host grains, gradually covering their full surfaces.
Our experiments show that the likelihood of formation of the oriented overgrowth and its stability are controlled by structural constraints which in turn depend on four factors: temperature, ionic radii and ionic potential of the REE in the system, and dissolution rate of the host CaCO3 minerals. Also, we demonstrate that REE elements can be rapidly immobilized as REE hydroxicarbonates, even at low hydrothermal conditions. An explanation of the epitaxial overgrowth’s configuration and the atomic arrangement of the structures of the CaCO3 polymorphs and REE-kozoite will be discussed.
[1] Szucs AM et al. Reaction Pathways toward the Formation of Bastnäsite: Replacement of Calcite by Rare Earth Carbonates. Crystal Growth & Design, 2021;21(1):512–527.
[2] Szucs AM et al. Targeted Crystallization of Rare Earth Carbonate Polymorphs at Hydrothermal Conditions via Mineral Replacement Reactions. Global Challenges. 2022;2200085.
How to cite: Rodriguez-Blanco, J., Szucs, A. M., Rateau, R., Maddin, M., and Terribili, L.: Temporal growth of epitaxial layers in the CaCO3-REECO3OH system during mineral replacement processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4776, https://doi.org/10.5194/egusphere-egu24-4776, 2024.
