163-G 4.1

Provenance and transport of Sn (Nb-Ta) and REE from the pre-Andean crustal basement: primary mineralization and secondary enrichment processes

This project will investigate the primary source rocks for Sn (and Nb-Ta) and rare earth elements (REE) in the pre-Andean basement rocks (granites, pegmatites, metamorphic complexes) and the enrichment/mobilization processes related to chemical (hydrothermal alteration or weathering) and mechanical processes (ductile or brittle deformation in fractures and ductile shear zones). The investigation will focus on selected field occurrences of Palaeozoic granites, pegmatites, and their highly deformed metamorphic equivalents of the pre-Andean crustal basement, especially of the Salta Province. For the REE minerals especially (carbonates, phosphates, fluor-carbonates, oxides), there is substantial redistribution related to solubility-reprecipitation processes in the deep crust (e.g. lode deposits in shear zones) as well as surface adsorption in weathered exposures (e.g. heavy REE enrichment in clays: Longnan-type deposits). Because tin minerals and coltan (Nb-Ta ore) from pegmatite fields are commonly mined in alluvium (placers), it is critically important to understand how secondary processes (alteration, chemical and mechanical weathering) affect the criteria used for provenance identification. Therefore, the major aim of the project will be to analyse the origin and enrichment processes of the rare elements in primary (magmatic) as well as in secondary (fluid- and structurally controlled) environments. Emphasis will fall on studies in Salta province, because of the geological situation, including rare element pegmatites, and the direct links with project [G 2.2] working on the reactivation of fault zones and project [G 3.5], which addresses the role of basement composition for metal enrichment in near-surface volcano-tectonic complexes. Close collaboration with project [G 4.2] and the Argentine metallogenesis projects will extend the scope of investigation to places best suited to study the relevant processes (e.g., shear zones, alteration/weathering profiles, etc.). The research will combine modern techniques of mineralogical, microstructural and (isotope) geochemical analysis with field campaigns to examine key localities best suited to study the chemical and mechanical alteration of primary mineralization. The relevance of this study is in the field of mineral exploration primarily, i.e., for orogenic structurally-controlled REE deposits, and also for the growing field of provenance certification to control conflict ores.