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AURIFEROUS MINERALIZATION OF JALES AND GRALHEIRA (NORTHERN PORTUGAL): A CONTRIBUTION TO THE UNDERSTANDING OF MINERAL PARAGENESIS

Sara Martins

Abstract

Au mineralizations of Jales and Gralheira, located in Tras-os-Montes, near Vila Pouca de Aguiar (northern Portugal), belong to the Jales Mining District, the main historic producer of gold in Portugal. Mineralizations are hosted by syn- to late-tectonic Variscan granites and by Palaeozoic metasediments ranging in age from Ediacaran to Devonian. The studies carried out consisted of the analysis of samples from drill cores (provided by the Consortium AM- Almada Mining, S.A. and EDM, Empresa de Desenvolvimento Mineiro, S.A.) and rock samples collected in the field. Characterization and macroscopic description of the samples, petrographic and metallographic study, complemented with the Scanning Electron Microscope (SEM) and Cathodoluminescence (CL) were carried out. These techniques allowed identifying for the first time, in these mineral assemblages, species such as pentlandite, xenotime-Y, monazite-Ce. This research also contributed to the better knowledge of these mineralizations, namely with respect to their mineral paragenesis, allowing to update the paragenetic table for the Gralheira deposit. Four main stages of mineralization and a remobilization stage were distinguished. The studies allowed not only to integrate the mentioned new observed minerals on the Jales/Gralheira paragenesis but also into changes on the relationship and order of deposition of some minerals.

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