Perković, I., Martinuš, M., Tešović, B.C. et al. (7 more authors) (2024) Tracing the evolution of the world's first mined bauxite from palaeotopography to pyritization: insights from Minjera deposits, Istria, Croatia. Geologia Croatica, 77 (2). pp. 159-178. ISSN 1330-030X
Abstract
The Minjera bauxites are the first analysed and mined bauxites in the world. They are a group of pyritised bauxites situated in northern Istria, developed during the subaerial exposure phase which marked a major part of the Late Cretaceous and Palaeocene in northern Istria. In this study, the morphology, petrography, mineralogy, geochemistry as well as stable sulphur isotopes of the D-1 and D-15 deposits from Minjera were studied, as well as the evolution of their bedrock and cover. This study found that those two deposits differ in morphology, mineralogy and geochemistry as a consequence of their different palaeotopographical positions, with the D-1 deposit located at a higher position at the time of its formation compared to D-15, which led to the higher degree of leaching and desilicification in the D-1 deposit. The pyritisation in the studied deposits was a multi-phase process, which began with the deposition of framboidal pyrite and micrometre-sized anhedral pyrite, over which colloform pyrite was precipitated. This indicates that the solutions were initially supersaturated with iron sulphide, saturation of which subsequently changed, as finally euhedral, dendritic and acicular pyrite were deposited, indicating undersaturated conditions. The final stage was marked by deposition of pyrite veins. This formational sequence of pyrites is also supported by stable sulphur isotopes, as the δ34S values exhibit a wide range from -40.86 to 2.32 ‰, where lower values indicate an open system with an unrestricted sulphate supply in which supersaturated conditions could have been achieved, while the higher values indicate a change towards a closed system with limited sulphate supply. The organic matter necessary for microbial sulphate reduction was derived from the marshy environment established atop of the bauxite. The initial flooding started in the Palaeocene, with the first part of the sequence being deposited under lacustrine conditions, which changed towards fully marine with the deposition of Foraminiferal limestones.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © The Authors. This is an open access article under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits unrestricted use, distribution and reproduction in any medium, provided the original work is properly cited. |
Keywords: | Minjera, Istrian Palaeogene bauxites, Pyritisation in karst bauxites, Iron sulphide morphology in karst bauxites, Stable sulphur isotopes in karst bauxites |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Earth Surface Science Institute (ESSI) (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 25 Jul 2024 10:20 |
Last Modified: | 25 Jul 2024 10:20 |
Status: | Published |
Publisher: | Hrvatski geološki institut |
Identification Number: | 10.4154/gc.2024.12 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:215147 |