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Caracterização petrográfica e geoquímica das fácies graníticas contíguas ao sistema filoniano W-Sn de Mata da Rainha (Fundão); implicações metalogenéticas
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Resumo(s)
This work focused on the analysis of the spatial distribution and petrographic, mineralogical and geochemical characterisation of the granitic facies and lode structures forming the NE domain of the Orca pluton (Central Iberian Zone, Portugal). The possible relationship between the textural and mineralogical variations observed and the magmatic-hydrothermal mineralising systems of Mata da Rainha was also investigated. Four granitic facies were distinguished. The internal facies, core (FN) and rim (FB), are two-mica, porphyroid granites containing pseudomorphs of muscovite and quartz, probably replacing magmatic cordierite. The proximal rim facies (FBP), distinct from the rim facies, is characterised by a greater amount of muscovite and tourmaline. The most altered facies is a ‘pseudogreisen’, comprising abundant muscovite and quartz. The pluton’s rim is cut by aplitic and microgranitic veins, which formation is assigned to early to late stages of melt segregation. The main granite mass, enriched in fluxing elements and with a significant metasedimentary component, was emplaced at ca. 310 Ma (syn- to late-D3 of the Variscan Cycle), crystallising at around 800ºC under reducing conditions. The magmatic evolution, outlined by significant differentiation, led to the FN FB FBP sequence, culminating with intense hydrothermal alteration processes, such as muscovitisation, tourmalinisation and silicification (450-250ºC, between 298-280 Ma). These processes obliterated the primary features of the proximal border and ‘greisen-like’ facies, also generating quartz, tourmaline and perhaps cassiterite lodes, possibly carrying some mineralisation of interest. The late stages of the (magmatic-)hydrothermal events led to the formation of numerous quartz vein arrays, some of them exploited in the old W(-Sn) mine of Mata da Rainha. The importance of structural control in the Orca pluton emplacement, cooling and alteration was also highlighted, which should have promoted the local increase of permeability, focusing the fluid circulation and favouring the lode’s development.
Descrição
Tese de Mestrado, Geologia (Geodinâmica e Recursos Geológicos), 2025, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
W-Sn Lode mineralization Orca batholith Magmatic differentiation Hydrothermal alteration