P-T-X evolution of the fluids associated with Sn-Li mineralization from Pedra Alta (Argemela, Portugal)

• Type: Article in International Scientific Journal
• Date: 2025

Authors

Yakovenko, A (Author) Other; Guedes, A (Author) FCUP; Noronha, F (Author) Other; da Silva, ID (Author) Other; Mateus, A (Author) Other

Journal

Title: Journal Of Iberian Geology

ISSN: 1698-6180

Publisher: Springer Nature

Indexing

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Other information

Authenticus ID: P-018-HYA

DOI: 10.1007/s41513-025-00289-7

Abstract (EN): A comprehensive inspection of the accessible exposures at the Pedra Alta (Argemela, Portugal) old mining site shows that the main Sn-Li carriers (such as cassiterite, stannite and amblygonite-montebrasite) are subvertical, ENE-WSW to E-W trending quartz veins. The local preservation of an early group of quartz-phosphate lodes, affected by boudinage and folding, documents the superposition of diachronic mineralizing events. Both sets are systematically cut by a dense array of low dipping planar joints, interpreted as a late feature of strain accommodation during the Variscan D-3 regional phase of deformation (ca. 320-305 Ma). These observations suggest that the key period for the quartz vein network and mineralization formation at Pedra Alta might have occurred after the climax of D-3, i.e. around 310 Ma. Thicker quartz veins preserve evidence of multiple opening and minor branching, supporting the inference of a relatively long-lasting evolution. This is consistent with the progression of three main stages of mineral growth, which are dominated by amblygonite, quartz-cassiterite I and quartz-cassiterite II +/- stannite +/- chalcopyrite. The study of fluid inclusions (FIs) in amblygonite, quartz and cassiterite shows that the ore-forming fluids involved in the Pedra-Alta Sn-Li system are aqueous, with low salinity (< 6.0 wt.% NaCl equiv.) and low volatile content (usually < 7 mol%). Fluids displaying a CO2-dominant volatile phase are associated with amblygonite and quartz deposition, and fluids in cassiterite show a volatile component varying from CO2-dominated to CH4-dominated compositions. This FI record conceivably traces the participation of fluids compositionally buffered by the metasedimentary rocks hosting the quartz lodes throughout the ore-forming events, which is consistent with information provided by delta O-18 and delta D values obtained for quartz and cassiterite. Deposition of amblygonite and cassiterite has occurred under distinct P-T conditions, clearly higher for the formation of the former mineral phase. Fluid inclusions preserved in the different bands of zoned cassiterite indicate two main crystallization stages for this oxide, the first occurring at ca. 400 degrees C and 110 MPa from low salinity CO2-dominated fluids and the second at lower temperature (ca. 300 degrees C) from CH4-enriched fluids.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 20