Rare Earth Element Deposits of Alkaline Igneous Rocks

Abstract

Alkaline igneous complexes host deposits of rare earth elements (REE), which represent one of the most economically important resources of heavy REE and Yttrium (Y). The hosts are differentiated rocks ranging from nepheline syenites and trachytes to peralkaline granites. These complexes usually occur in continental within-plate tectonic settings associated with rifts, faults, or hotspot magmatism. The REE mineralization is found in layered alkaline complexes, granitic stocks, and late-stages dikes and rarely trachytic volcanic and volcaniclastic deposits. The bulk of REE is present in accessory minerals, which can reach percentage levels in mineralized zones. The mineralization contains various REE-bearing minerals that can display complex replacement textures. Main REE minerals present in these deposits are bastnäsite, eudialyte, loparite, gittinsite, xenotime, monazite, zircon, and fergusonite. The parent magmas of alkaline igneous complexes are derived from partial melts of mantle sources. Protracted fractional crystallization of the magma led to an enrichment in REE, particularly in the late stages of magma evolution. The primary magmatic mineralization is commonly overprinted (remobilized and enriched) by late magmatic to hydrothermal fluids. Elevated abundances of U and Th in the deposits make a gamma-ray (radiometric) survey an important exploration tool, but also represent a significant environmental challenge for exploitation.

Evidence for Nb-Ta Occurrences in the Syn-Tectonic Pan-African Mayo Salah Leucogranite (Northern Cameroon): Constraints from Nb-Ta Oxide Mineralogy, Geochemistry and U-Pb LA-ICP-MS Geochronology on Columbite and Monazite

“…Rare-element deposits (Li, Be, Ta, Nb, Sn, W, and REE) are commonly found in magmatic rocks: peralkaline to pegmatitic peraluminous granites, carbonatites, and alkaline igneous rocks [1][2][3][4][5]. Enrichment of these lithophile elements may be directly linked to magmatic processes, as evidenced for the Beauvoir granite (French Massif Central [6][7][8]), Yichun granite of China [9,10], Czeck Podlesí granite [11,12]; or, magmatic-hydrothermal processes (e.g., [13][14][15].…”

Rare Earth Elements in Planetary Crusts: Insights from Chemically Evolved Igneous Suites on Earth and the Moon

“…Ore deposits associated with chemically evolved igneous rock suites have been the intense focus of research over the past several decades [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Magmatic-associated mineral deposits are mineralogically and chemically diverse, occur in a range of geological settings, and have long been the target of the mineral industry.…”

Introduction to a Resources Special Issue on Criticality of the Rare Earth Elements: Current and Future Sources and Recycling

“…This REE mineralization is located within layered alkaline complexes, granitic stocks, and late-stages dikes, as well as more rarely within trachytic volcanic and volcaniclastic deposits. Dostal [16] indicates that the majority of alkaline igneous rock-related REE mineralization is present as accessory minerals such as bastnäsite, eudialyte, loparite, gittinsite, xenotime, monazite, zircon, and fergusonite. These minerals are concentrated during the later stages of magmatic evolution, a process that generates the REE enrichments associated with this type of magmatism.…”

“…These minerals are concentrated during the later stages of magmatic evolution, a process that generates the REE enrichments associated with this type of magmatism. In addition, this primary REE mineralization is often remobilized and potentially enriched by late-stage magmatic-hydrothermal fluid activity [16].…”

“…Dostal [16] provides an overview of the REE deposits genetically linked with this type of magmatism, where REE mineralization is associated with differentiated rocks that range in composition from nepheline syenites and trachytes to peralkaline granites. The alkaline igneous units associated with these REE enrichments are located in continental within-plate tectonic settings.…”