Geochemistry of Famennian to Visean Metapelites from the Iberian Pyrite Belt: Implications for Provenance, Paleo-Redox C
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Original Paper
Geochemistry of Famennian to Visean Metapelites from the Iberian Pyrite Belt: Implications for Provenance, Paleo-Redox Conditions and Vectoring to Massive Sulfide Deposits Filipa Luz ,1,4 Anto´nio Mateus,1,2 Carlos Rosa,1,3 and Jorge Figueiras1,2 Received 25 November 2019; accepted 28 April 2020
Massive sulfide deposits of the Iberian Pyrite Belt (IPB) document the progression of oreforming processes in the SW Iberian Variscides, throughout uppermost Devonian to Early Carboniferous. Sulfide ores are usually hosted in volcanic-dominated or shale-dominated successions belonging to the Volcano-Sedimentary Complex (VSC; Late Famennian to Late Visean). Yet, several important orebodies at Neves-Corvo are sitting within upper sections (Famennian) of the early deposited Phyllite–Quartzite Group (PQG). Four key sectors of the Portuguese segment of IPB were revisited and 262 samples collected to characterize the geochemical features of metapelites from PQG and VSC sequences in barren and fertile settings. The selected sectors include active (Neves-Corvo and Aljustrel) and old (Lousal) mines, besides promising brownfield (Gavia˜o) and greenfield (Sesmarias) prospects, and other lithostratigraphic sections without known mineralization. The composition of PQG and VSC metapelites is similar and mainly controlled by a mixture of clayey-derived and quartz sandy-derived components largely resulting from different sources of granitic to granodiorite/quartz diorite composition. A third component of local volcaniclastic origin could be significant in many samples of upper VSC sections. Mineral transformations during diagenesis and/or hydrothermal alteration/mineralization partially overprinted the primary composition. During sedimentation/diagenesis, prevalent redox conditions were mostly confined to oxic environments, at places transiting to sub-oxic. Subsequent multistage interaction with reducing hydrothermal fluids (to which the sulfide mineralization is related) generated heterogeneous anoxic signs. Consistent increases in Fe2O3/TiO2, (Cu + Zn + Pb)/ Sc and (As + Sb)/Sc ratios to values above 10 represent a valuable footprint toward ore horizons. KEY WORDS: Alteration/mineralization indexes, Iberian Pyrite Belt, Massive sulfide deposit, Metasedimentary sequences.
1
Instituto Dom Luiz (IDL), Faculdade de Cieˆncias, Universidade de Lisboa, Campo-Grande, 1749-016 Lisbon, Portugal. 2 Dep. Geologia, Faculdade de Cieˆncias, Universidade de Lisboa, Ed. C6, Piso 4, 1749-016 Lisbon, Portugal. 3 CPR Lda Geology Consulting, Qta da Pedra Branca, Av. Casal Segulim, 1685-891 Famo˜es, Portugal. 4 To whom correspondence should be addressed; e-mail: [email protected]
INTRODUCTION Massive sulfide ores of the Iberian Pyrite Belt (IPB) are hosted in volcanic-dominated or shaledominated sequences, reflecting the progression of ore-forming processes mostly during the uppermost Devonian to Early Carboniferous (e.g., Barrie et al.
2020 International Association for Mathematical Geosciences
Luz, Mateus, Rosa, and Figueiras
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