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- Insights into rare earth elements and other critical raw materials from Castelo Branco massif alluvial deposits (Portugal)Publication . Salgueiro, Rute; Silva, Teresa; Martín-Méndez, I.; de Oliveira, Daniel Pipa Soares; Batista, Maria Joao; Inverno, CarlosABSTRACT: Actual and future demands for critical raw materials and strategic raw materials (CRM/SRM) justify the global search for their potential sources and the exploration approaches to reach them. This study discloses the characterization of rare earth elements (REE) and other CRM-bearing alluvial heavy minerals samples sourced from the late- to post-tectonic Variscan Castelo Branco Massif (Portugal). It also contributes to an understanding of REE, Th, and U anomalies from local and correspondent stream sediments identified in past geochemical surveys. The alluvial samples were subjected to semiquantitative analysis of their minerals under a binocular microscope and to chemical analysis through portable X-ray fluorescence. A varied mineralogical association and a geochemical fingerprint compatible with their main granitic source was identified, revealing several minerals that carry CRM, in which REE and titanium minerals stood out. The titanium minerals have the higher average abundance (54%), being ilmenite-dominant (50%), as supported by the relatively higher Ti content of these samples (up to 28.88%). The REE minerals occur as accessories and have a summing average of 12%, in which monazite is the most abundant (4.97%). Geochemical data support alluvial monazite as the mineral with the highest REE and Th concentrations, as described in the literature on its granitic source. In addition, the magnetic fraction of samples (∼85%) that includes monazite and xenotime presents LREE anomalous contents (up to 4,557 mg/kg) in relation to their granitic source, NASC, and even to ΣREE anomalous values revealed by local stream sediments. The Th (up to 1,969 mg/kg) and U (up to 244 mg/kg) contents follow the same trend. Nevertheless, the nonmagnetic mineral fraction that includes apatite and zircon reaches higher U contents (up to 448 mg/kg). This study indicates that the SRM Ti (ilmenite) and LREE (monazite) have the potential to form placer deposits sourced from Castelo Branco granitic rocks in a wider area, which is supported by the regional Ti placers exploited in the past. The occurrence of other accessory elements/minerals with industrial applicability associated with those placers may also represent future added value.
- New Contributions to Mineralogical and Geochemical Knowledge of Old Preguiça Mine, Beja, PortugalPublication . Silva, Teresa; Morais, Igor; Mesquita Soares, Sofia; Rodrigues, Ivo; de Oliveira, Daniel Pipa Soares; Mirao, JoseABSTRACT: Abandoned mining areas provide valuable opportunities to investigate ore-forming processes, supergene mineral transformations, and the geochemical behaviour of metals. In this sense, the old Preguiça mine (Beja, Portugal), exploited for Fe–Zn–Pb, was studied providing new mineralogical and geochemical data aimed at improving the understanding of the secondary mineral assemblages of this deposit. A total of 70 samples collected from three accessible underground levels (first, second and third) and mine waste, complemented by 16 samples from a deeper level (fourth) previously collected, were analysed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and a portable X-ray fluorescence (pXRF) equipment. Mineralogical phases are dominated by a wide range of secondary oxides, carbonates, arsenates, vanadates, silicates, phosphates and sulphates, but remnants of primary sulphides were also found. The following minerals can be emphasised: goethite, hematite, calcite, dolomite, descloizite, willemite, mimetite, cerussite, smithsonite and fraipontite. The presence of massicot in the Preguiça mine, is described for the first time. Bulk geochemical analyses show high concentrations of Fe, Ca, Zn and Pb, consistent with the observed mineralogy. The presence of vanadium- and arsenic-bearing minerals highlights the occurrence of critical raw materials, supporting the importance of reassessing other abandoned mining areas in the context of sustainable resource management and strategic raw-material planning.