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Trace Element Geochemistry of Alluvial TiO2 Polymorphs as a Proxy for Sn and W Deposits

Publication . Gaspar, Miguel; Grácio, Nuno; Salgueiro, Rute; Costa, Mafalda

ABSTRACT: The Segura mining field, the easternmost segment of the Gois-Panasqueira-Segura tin-tungsten metallogenic belt (north-central Portugal), includes Sn-W quartz veins and Li-Sn aplite-pegmatites, which are believed to be genetically related to Variscan Granites. Sediment geochemistry indicates granite-related Ti-enrichments, locally disturbed by mineralization, suggesting magmatic and metamorphic/metasomatic titaniferous phases. Therefore, Segura alluvial samples and the geochemistry of their TiO2 polymorphs (rutile, anatase, and brookite) were investigated, and their potential as exploration tools for Sn and W deposits was evaluated. The heavy-mineral assemblages proved to be good proxies for bedrock geology, and TiO2 polymorph abundances were found to be suitable indicators of magmatic and/or metasomatic hydrothermal processes. The trace element geochemistry of Segura's alluvial rutile, anatase, and brookite is highly variable, implying multiple sources and a diversity of mineral-forming processes. The main compositional differences between TiO2 polymorphs are related to intrinsic (structural) factors, and to the P-T-X extrinsic parameters of their forming environments. Anomalous enrichments, up to 9% Nb, 6% Sn and W, 3% Fe, 2% Ta, and 1% V in rutile, and up to 1.8% Fe, 1.7% Ta, 1.2% Nb, 1.1% W 0.5% Sn and V in anatase, were registered. Brookite usually has low trace element content (<0.5%), except for Fe (similar to 1%). HFSE-rich and granitophile-rich rutile is most likely magmatic, forming in extremely differentiated melts, with Sn and W contents enabling the discrimination between Sn-dominant and W-dominant systems. Trace element geochemical distribution maps show pronounced negative Sn (rutile+anatase) and W (rutile) anomalies linked to hydrothermal cassiterite precipitation, as opposed to their hydrothermal alteration halos and to W-dominant cassiterite-free mineralized areas, where primary hydrothermal rutile shows enrichments similar to magmatic rutile. This contribution recognizes that trace element geochemistry of alluvial TiO2 polymorphs can be a robust, cost- and time-effective, exploration tool for Sn(W) and W(Sn) ore deposit systems.

2022-10Journal article

Open access

Alluvial Sn and W minerals mapping for mineral resources exploration and research in Segura mining region (Portugal)

Publication . Salgueiro, Rute; Grácio, Nuno; Gaspar, Miguel; de Oliveira, Daniel Pipa Soares

SUMÁRIO: Com base em amostras aluvionares em arquivo no LNEG, foi possível conceber mapas de concentração de grãos de cassiterite, volframite e scheelite, para a região mineira de Segura (Castelo Branco) enquadrada na Faixa metalogenética estanho-tungstanífera de Góis-Segura. O padrão de distribuição da concentração de grãos destes minerais de minério de Sn e W, materializa-se em halos concêntricos distintos, em torno do endo/exo-contacto do granito de Segura; estes padrões podem ser correlacionados com distintos eventos metalogenéticos que ocorreram na região, sob controlo estrutural, litológico ou magmático-hidrotermal e em fases distintas, possivelmente com maior sobreposição na parte oeste da mesma. Deste modo, o mapeamento da cassiterite, volframite e scheelite, à escala regional, provou ser útil para ser aplicado à investigação e prospeção de recursos minerais, podendo contribuir para traçar vetores neste tipo de mineralizações de Sn e W.

2023-07Conference object

Open access