Controls on REE mineralization in the Tioueine ring complex (Western Hoggar, Algeria): examination of magmatic vs hydrothermal processes

Le résumé fourni par la source

The Hoggar is a rare metal endowed province within the Tuareg shield with variably mineralized post Pan-African granitoid complexes. The investigated Tioueine Ring Complex is among them, with two major units: a weakly evolved calc-alkaline central unit containing monzogranite and granodiorite, and a highly evolved alkali feldspar granite-dominated major outer unit that hosts magmatic to magmatic-hydrothermal LREE-dominant mineralization. The Tioueine Ring Complex is a mantle-derived A 1 -type granitoid complex that crystallized at ca. 600 Ma during a post-orogenic to anorogenic episode of the Pan-African orogeny. Its parental magmatic system is characterized by high concentrations of alkali elements, with moderate total REE 2 O 3 (TREE 2 O 3 ) contents up to 0.2 wt%; allanite is the major REE-rich mineral, with limited proportions of apatite, xenotime, and rare monazite. Primary mineralization resulted from low degrees of partial melting of an enriched mantle source that produced reduced ferroan REE-rich magma following advective mantle heat input. The derivative melt may have experienced crustal assimilation and crystal fractionation that caused further enrichment in HFSE and REE before reaching the solidus. A late- to post-magmatic-hydrothermal event allowed limited secondary enrichment of REE by causing allanite breakdown to form REE-fluorocarbonate minerals. Fluid—rock interaction likely resulted from magmatic-hydrothermal F- and CO 2 -rich aqueous fluids and late meteoric hydrothermal fluids that circulated through ring faults. The Tioueine Ring Complex exhibits elevated REE concentrations that warrant follow-up sampling and drilling to assess its economic viability. However, despite REE enrichment in A-type granites globally, the role of F-rich fluids in remobilizing REE from magmatic allanite to form hydrothermal REE-fluorocarbonates remains poorly constrained. The Tioueine Ring Complex offers a case study to elucidate this process.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.