Abstract
Panasqueira is a world-class W-Sn-Cu lode-type deposit located in Portugal. It consists of a dense swarm of subhorizontal quartz lodes criss-crossed by several ENE–WSW and N–S fault zones, bordering Late Variscan granite and hosted in Late Ediacaran—Early Cambrian metasediments. The relative abundance and compositional variation (assessed with EPMA) of the main silicates, oxides and phosphates forming the quartz lodes and their margins were examined, aiming to explore: (i) mineral and geochemical zonation at the mine scale; and (ii) some conclusions on the chemical nature of prevalent fluid inflows and T-conditions of mineral deposition. Quartz lodes nearby or far from the known greisen-granite cupola display significant differences, reflecting multiple fluid influxes of somewhat distinct composition related to various opening and closing events extending for several My, ranging from an early “oxide–silicate stage” (OSS) to a “main sulfide stage” (MSS), and further on to a post-ore carbonate stage (POCS); however, a rejuvenation event occurred after MSS. The onset of OSS was placed at ca. 299 ± 5 Ma and the rejuvenation event at ca. 292 Ma. The OSS was confined to ≈500 ≤ T ≤ 320 °C, following rutile and tourmaline growth under ≈640 ≤ T ≤ 540 °C (depending on aSiO2). The rejuvenation event (≈440–450 °C) preceded a late chlorite growth (≈250–270 °C) and the progression towards POCS.
Highlights
Granite-related deposits represent a natural source of various ore minerals, incorporating a large suite of metals necessary for an increasing number of industrial and technological applications [1,2,3].Threats regarding possible shortages of some raw materials in the future, along with the need to diversify the suppliers, have been instrumental to fostering a renewed interest in deepening the current knowledge on these deposits and the processes involved in their formation
Together these results indicate that fluids driven to quartz lodes in this event should have provided a revitalization of the ore system, renewing the availability of a large number of chemical constituents that are not present during the previous deposition of sulfides
Four different geological trends can be observed on the basis of mineral assemblages forming the lode borders and the relative abundances of wolframite and cassiterite
Summary
Granite-related deposits represent a natural source of various ore minerals, incorporating a large suite of metals necessary for an increasing number of industrial and technological applications [1,2,3]. The present work intends to address some key issues related to the chemical nature of prevalent fluid inflows and temperature conditions of mineral deposition, as recorded by the compositional variation of the main silicates, oxides and phosphates forming the quartz lodes of the Panasqueira mine. To this end, a large mineral database will be reported and discussed, documenting a systematic survey of 215 samples representing all the accessible mine sectors and underground mining levels. The obtained results contribute to an exploratory mapping of particular mineralogical and geochemical features, which may help assess possible compositional zonings at the deposit scale, providing clues about the superposition of ore-forming processes possibly controlled by distinct sources and structures
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