☆ 4.7 Article

Petrographic and geochemical features of the B3 bauxite horizon (Cenomanian-Turonian) in the Parnassos-Ghiona area: A contribution towards the genesis of the Greek karst bauxites

ORE GEOLOGY REVIEWS (2022)

Journal

ORE GEOLOGY REVIEWS

Volume 143, Issue -, Pages -

Publisher

ELSEVIER

DOI: 10.1016/j.oregeorev.2022.104759

Keywords

Bauxite; Greece; Parnassos-Ghiona; Diaspore; Pyrite; REEs

Funding

Am-biente e delle Risorse, Universit`a Federico II
Rocks Research Laboratory, Depart-ment of Geology University of Patras
Laboratory of Electron Microscopy and Microanalysis, Faculty of Natural Sciences, University of Patras
EU Erasmus + Placement project
Universit`a degli Studi di Napoli Federico II
European Union
Marie Skodowska-Curie Individual Fellow-ship [751,103]
Universit`a di Napoli Federico II

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Abstract

The karst bauxites of the Parnassos-Ghiona Unit in Greece are hosted within carbonate rocks from the Upper Jurassic to Late Cretaceous. This study focuses on the characteristics of the B3 horizon, including prevailing oolitic texture and major mineral components such as diaspore, boehmite, hematite, and goethite. Minor phases like kaolinite, rutile, and anatase are also present. The three-stage genesis of the bauxite is reflected in complex correlations between major, minor, and trace elements. Detrital minerals like chromite and serpentine indicate the presence of mafic parental rocks, likely originating from nearby ophiolite suites.

The karst bauxites of the Parnassos-Ghiona Unit (Greece) are hosted within Upper Jurassic to Late Cretaceous carbonate rocks. Three bauxite horizons are intercalated within shallow water limestones. They are named B1, B2 and B3 from bottom to top. In this study we present the characteristics of the B3 horizon (CenomanianTuronian) sampled in Agia Anna, Variani and Shila 1 underground mines. The bauxite ore has a prevailing oolitic texture. Diaspore, boehmite, hematite and goethite are the major mineral components of the analyzed samples. Kaolinite, rutile and anatase are common minor phases. Pyrite occurs in a small number of samples. Ilmenite, rutile, chromite, zircon, baddeleyite and serpentine are common detrital minerals. Authigenic minor minerals are mostly represented by REE-phosphates, barite, and gypsum. The presence of pyrite and diaspore suggests that after a first stage of additional in situ weathering and bauxitization, the deposits were affected by early diagenetic reducing conditions (allowing the formation of pyrite) and significant diagenesis, resulting in diaspore formation. This three-stages genesis is reflected in complex correlations between major, minor and trace elements. The occurrence of detrital chromite and serpentine in the bauxite reflects mafic parental rocks. The mafic component likely originated from the ophiolite suites exposed in the vicinity of the Parnassos-Ghiona bauxites.

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Activation mechanism of diasporic bauxite calcined with sodium carbonate

Yue Sun, Aifang Pan, Yuzhao Ma, Jie Chang, Kuimeng Li, Shentao Hu

Summary: This study investigates the thermal behavior, phase transformations, and bonding changes of aluminum-bearing minerals in diasporic bauxite using thermogravimetric analysis, X-ray diffraction, and Fourier transform infrared spectroscopy. The results demonstrate that under specific conditions, diasporic bauxite can be transformed into a series of sodium aluminosilicates, some of which exhibit good dissolution performance.

MINERALS ENGINEERING (2022)