Elsevier

Ore Geology Reviews

Volume 125, October 2020, 103665
Ore Geology Reviews

Contribution to the origin of Mn-U-Be-HREE-enrichment in phosphorite, near Bükkszentkereszt, NE Hungary

https://doi.org/10.1016/j.oregeorev.2020.103665Get rights and content
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Highlights

  • U-Be-Mn-REE indications in phosphorite were investigated.

  • Biosignatures were studied by high resolution microscopy, FTIR and Raman spectroscopy.

  • The FeOB (Fe oxidizing bacteria) are filamentous, necklace-like vermiform structures and coccoid-like forms.

  • The biomats are composed of ferrihydrite, pyrite, organic matter and phosphorite.

  • Fossil mineralized microbial mediation is proposed as origin of element enrichment.

Abstract

Strongly deformed phosphorite layers enriched with U-Be-Mn-REE occur in a weathered Triassic metarhyolite tuff near the town of Bükkszentkereszt, NE Hungary. The phosphorite is massive or earthy, has an especially fine-grained texture, and forms inhomogeneous bands with different Mn-oxide contents.

High-resolution optical rock microscopy investigations helped to distinguish mineralized biosignatures, filamentous, vermiform structures, and coccoid-like aggregates. These microstructures encompass almost the whole phosphorite. Based on in situ FTIR and Raman spectroscopy, the phosphorites contain ferrihydrite and pyrite, and also different types of embedded organic matter. These structures can be interpreted as series of Fe-rich biomats, forming microbialites. On a larger scale, these microstructures can play a role in shaping the stratiform structure by evolving stromatolite-like bands.

Results presented here propose a new interpretation of the origin of the P-Mn-U-Be-HREE-enrichment. The Bükkszentkereszt occurrence claim a mineralized microbially mediated deposit, and our results support this scenario based on the mineralized microbial structures, the embedded minerals, and the presence of organic matter.

Keywords

Beryllium
Hydrothermal
Microbial
Phosphorite
Raman spectroscopy
Uranium

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