From Fresh Itabirites and Carbonates to Weathered Iron Ore: Mineral Composition, Density and Porosity of Different Fresh and Altered Rocks from the Quadrilátero Ferrífero, Brazil
The weathering of Paleoproterozoic itabirites (metamorphic-banded iron formations) and dolomites from the Cauê and Gandarela Formations in the Quadrilátero Ferrífero (QF), Brazil, produces supergene iron ore with different mineralogical, chemical, and physical properties. In this work, we present a...
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MDPI AG
2020-12-01
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| Series: | Minerals |
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| Online Access: | https://www.mdpi.com/2075-163X/11/1/29 |
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| author | Diniz Ribeiro Israel Moraes Rogerio Kwitko-Ribeiro Deivid Braga Carlos Spier Pedro Santos |
| author_facet | Diniz Ribeiro Israel Moraes Rogerio Kwitko-Ribeiro Deivid Braga Carlos Spier Pedro Santos |
| author_sort | Diniz Ribeiro |
| collection | DOAJ |
| description | The weathering of Paleoproterozoic itabirites (metamorphic-banded iron formations) and dolomites from the Cauê and Gandarela Formations in the Quadrilátero Ferrífero (QF), Brazil, produces supergene iron ore with different mineralogical, chemical, and physical properties. In this work, we present a methodology to assess the changes in chemical and physical features of those rocks during weathering, via quantitative analyses of mineral assemblages. These mineral assemblages were calculated from chemical analyses of fresh and weathered samples collected from drill holes drilled in different iron ore deposits in the QF. In general, the number of mineral species found in fresh or/and weathered itabirite is restricted, which helps the quantification of the mass and volumes of minerals by normative calculation in a large dataset of drilling and channel samples. The calculation of the bulk density takes into consideration, besides the mineral phases, the voids and free water in the altered rock matrix. This study shows that the estimated porosity in supergene ore varies from 0% to 20%, for compact materials, and from 15% to 55% for friable rocks, indicating an important process of rock matrix dissolution during the weathering of itabirites. In this process, MgO, CaO, and FeO are leached out from carbonates, talc, and amphiboles. Magnetite is oxidized to hematite, releasing Fe<sup>2+</sup>, which is oxidized and precipitates as Fe-hydroxide. There is a concentration of Fe<sub>2</sub>O<sub>3</sub>, MnO, Al<sub>2</sub>O<sub>3</sub>, and SiO<sub>2</sub> in the supergene ore (saprolite) by residual enrichment or recrystallization of hematite, goethite, quartz, manganese oxides, and kaolinite. A calculation of weathering effects on the original protoliths allowed for the establishment of a correlation between different types of fresh itabirites and their corresponding weathered materials. The calculation was carried out in several steps, to account for changes in porosity and masses and has taken into consideration differences in the mineralogical composition of the protolith. Within the weathered zones, a strong link is observed between the existence of collapse on the topographic surface and the presence of supergene ore underneath. The partial to total dissolution of quartz and carbonates from the protolith itabirite results in very porous materials and leads to gravitational collapses. |
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| spelling | doaj.art-0541c9c989ea4e7d88b821e96b3fef1c2023-11-21T02:53:00ZengMDPI AGMinerals2075-163X2020-12-011112910.3390/min11010029From Fresh Itabirites and Carbonates to Weathered Iron Ore: Mineral Composition, Density and Porosity of Different Fresh and Altered Rocks from the Quadrilátero Ferrífero, BrazilDiniz Ribeiro0Israel Moraes1Rogerio Kwitko-Ribeiro2Deivid Braga3Carlos Spier4Pedro Santos5Vale S.A., Iron Resource Management, Escritório de Águas Claras, Nova Lima, MG 34.006-200, BrazilVale S.A., Iron Resource Management, Escritório de Águas Claras, Nova Lima, MG 34.006-200, BrazilVale S.A., Mineral Technology, Centro de Desenvolvimento Mineral, Santa Luzia, MG 33.040-900, BrazilVale S.A., Iron Resource Management, Escritório de Águas Claras, Nova Lima, MG 34.006-200, BrazilSchool of Earth and Environmental Sciences, The University of Queensland, Saint Lucia, QLD 4072, AustraliaIndependent Consultant, Itabira, MG 35.900-360, BrazilThe weathering of Paleoproterozoic itabirites (metamorphic-banded iron formations) and dolomites from the Cauê and Gandarela Formations in the Quadrilátero Ferrífero (QF), Brazil, produces supergene iron ore with different mineralogical, chemical, and physical properties. In this work, we present a methodology to assess the changes in chemical and physical features of those rocks during weathering, via quantitative analyses of mineral assemblages. These mineral assemblages were calculated from chemical analyses of fresh and weathered samples collected from drill holes drilled in different iron ore deposits in the QF. In general, the number of mineral species found in fresh or/and weathered itabirite is restricted, which helps the quantification of the mass and volumes of minerals by normative calculation in a large dataset of drilling and channel samples. The calculation of the bulk density takes into consideration, besides the mineral phases, the voids and free water in the altered rock matrix. This study shows that the estimated porosity in supergene ore varies from 0% to 20%, for compact materials, and from 15% to 55% for friable rocks, indicating an important process of rock matrix dissolution during the weathering of itabirites. In this process, MgO, CaO, and FeO are leached out from carbonates, talc, and amphiboles. Magnetite is oxidized to hematite, releasing Fe<sup>2+</sup>, which is oxidized and precipitates as Fe-hydroxide. There is a concentration of Fe<sub>2</sub>O<sub>3</sub>, MnO, Al<sub>2</sub>O<sub>3</sub>, and SiO<sub>2</sub> in the supergene ore (saprolite) by residual enrichment or recrystallization of hematite, goethite, quartz, manganese oxides, and kaolinite. A calculation of weathering effects on the original protoliths allowed for the establishment of a correlation between different types of fresh itabirites and their corresponding weathered materials. The calculation was carried out in several steps, to account for changes in porosity and masses and has taken into consideration differences in the mineralogical composition of the protolith. Within the weathered zones, a strong link is observed between the existence of collapse on the topographic surface and the presence of supergene ore underneath. The partial to total dissolution of quartz and carbonates from the protolith itabirite results in very porous materials and leads to gravitational collapses.https://www.mdpi.com/2075-163X/11/1/29itabiriteweatheringnormative mineral calculationsiron oreQuadrilátero Ferríferodensity |
| spellingShingle | Diniz Ribeiro Israel Moraes Rogerio Kwitko-Ribeiro Deivid Braga Carlos Spier Pedro Santos From Fresh Itabirites and Carbonates to Weathered Iron Ore: Mineral Composition, Density and Porosity of Different Fresh and Altered Rocks from the Quadrilátero Ferrífero, Brazil Minerals itabirite weathering normative mineral calculations iron ore Quadrilátero Ferrífero density |
| title | From Fresh Itabirites and Carbonates to Weathered Iron Ore: Mineral Composition, Density and Porosity of Different Fresh and Altered Rocks from the Quadrilátero Ferrífero, Brazil |
| title_full | From Fresh Itabirites and Carbonates to Weathered Iron Ore: Mineral Composition, Density and Porosity of Different Fresh and Altered Rocks from the Quadrilátero Ferrífero, Brazil |
| title_fullStr | From Fresh Itabirites and Carbonates to Weathered Iron Ore: Mineral Composition, Density and Porosity of Different Fresh and Altered Rocks from the Quadrilátero Ferrífero, Brazil |
| title_full_unstemmed | From Fresh Itabirites and Carbonates to Weathered Iron Ore: Mineral Composition, Density and Porosity of Different Fresh and Altered Rocks from the Quadrilátero Ferrífero, Brazil |
| title_short | From Fresh Itabirites and Carbonates to Weathered Iron Ore: Mineral Composition, Density and Porosity of Different Fresh and Altered Rocks from the Quadrilátero Ferrífero, Brazil |
| title_sort | from fresh itabirites and carbonates to weathered iron ore mineral composition density and porosity of different fresh and altered rocks from the quadrilatero ferrifero brazil |
| topic | itabirite weathering normative mineral calculations iron ore Quadrilátero Ferrífero density |
| url | https://www.mdpi.com/2075-163X/11/1/29 |
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