Origin of the reduced, amethyst-mineralized lower tier of the Cordillera Flow, southern Paraná Volcanic Province
Abstract The structure of two superposed layers within a redox-altered basaltic flow is restricted to the Paraná Volcanic Province among large igneous provinces. World-class amethyst-geode and agate-geode deposits occur in reduced Tier 1 of the Cordillera Flow (> 100 km long). Satellite and drone...
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Sociedade Brasileira de Geologia
2025-06-01
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| Series: | Brazilian Journal of Geology |
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| Online Access: | http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2317-48892025000100306&lng=en&tlng=en |
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| author | Léo Afraneo Hartmann Leonardo Cardoso Renner |
| author_facet | Léo Afraneo Hartmann Leonardo Cardoso Renner |
| author_sort | Léo Afraneo Hartmann |
| collection | DOAJ |
| description | Abstract The structure of two superposed layers within a redox-altered basaltic flow is restricted to the Paraná Volcanic Province among large igneous provinces. World-class amethyst-geode and agate-geode deposits occur in reduced Tier 1 of the Cordillera Flow (> 100 km long). Satellite and drone-sourced imagery, several field surveys, and 11 new geochemical analyses were used in this study. The lower Tier 1 (10 m thick) consists of massive rocks without cooling joints, whereas the barren Tier 2 is massive with colonnade. The flow is identified from the stratigraphy and chemical composition (e.g., 1.3 wt.% TiO2). The presence of poikilitic microphenocrysts of magnetite (mostly plagioclase inclusions) is a distinctive feature. Tier 2 rocks are chemically similar to the original lava; Tier 1 displays a decrease in SiO2 and K2O contents and an increase in Fe2O3T. Reducing and acidic hot water formed amethyst and agate deposits in Tier 1. Curved shapes (erosional remnants with agate) were formed by silicification of the lower portion of the flow. The interaction of the Guarani Paleoaquifer with the lava flow formed the two layers: the geodes and the curved portions. Other provinces may have similar features where hot aquifer water was available below the basalt. |
| format | Article |
| id | doaj-art-dbc72502ff034a69b3cf78bede2b4b28 |
| institution | DOAJ |
| issn | 2317-4692 |
| language | English |
| publishDate | 2025-06-01 |
| publisher | Sociedade Brasileira de Geologia |
| record_format | Article |
| series | Brazilian Journal of Geology |
| spelling | doaj-art-dbc72502ff034a69b3cf78bede2b4b282025-08-20T03:19:28ZengSociedade Brasileira de GeologiaBrazilian Journal of Geology2317-46922025-06-015510.1590/2317-4889202520250007Origin of the reduced, amethyst-mineralized lower tier of the Cordillera Flow, southern Paraná Volcanic ProvinceLéo Afraneo Hartmannhttps://orcid.org/0000-0001-7863-5071Leonardo Cardoso Rennerhttps://orcid.org/0000-0002-9280-1408Abstract The structure of two superposed layers within a redox-altered basaltic flow is restricted to the Paraná Volcanic Province among large igneous provinces. World-class amethyst-geode and agate-geode deposits occur in reduced Tier 1 of the Cordillera Flow (> 100 km long). Satellite and drone-sourced imagery, several field surveys, and 11 new geochemical analyses were used in this study. The lower Tier 1 (10 m thick) consists of massive rocks without cooling joints, whereas the barren Tier 2 is massive with colonnade. The flow is identified from the stratigraphy and chemical composition (e.g., 1.3 wt.% TiO2). The presence of poikilitic microphenocrysts of magnetite (mostly plagioclase inclusions) is a distinctive feature. Tier 2 rocks are chemically similar to the original lava; Tier 1 displays a decrease in SiO2 and K2O contents and an increase in Fe2O3T. Reducing and acidic hot water formed amethyst and agate deposits in Tier 1. Curved shapes (erosional remnants with agate) were formed by silicification of the lower portion of the flow. The interaction of the Guarani Paleoaquifer with the lava flow formed the two layers: the geodes and the curved portions. Other provinces may have similar features where hot aquifer water was available below the basalt.http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2317-48892025000100306&lng=en&tlng=enReduced Tier 1Cordillera FlowParaná Volcanic ProvinceGuarani Paleoaquiferhydrothermalismamethyst-geode mineralization |
| spellingShingle | Léo Afraneo Hartmann Leonardo Cardoso Renner Origin of the reduced, amethyst-mineralized lower tier of the Cordillera Flow, southern Paraná Volcanic Province Brazilian Journal of Geology Reduced Tier 1 Cordillera Flow Paraná Volcanic Province Guarani Paleoaquifer hydrothermalism amethyst-geode mineralization |
| title | Origin of the reduced, amethyst-mineralized lower tier of the Cordillera Flow, southern Paraná Volcanic Province |
| title_full | Origin of the reduced, amethyst-mineralized lower tier of the Cordillera Flow, southern Paraná Volcanic Province |
| title_fullStr | Origin of the reduced, amethyst-mineralized lower tier of the Cordillera Flow, southern Paraná Volcanic Province |
| title_full_unstemmed | Origin of the reduced, amethyst-mineralized lower tier of the Cordillera Flow, southern Paraná Volcanic Province |
| title_short | Origin of the reduced, amethyst-mineralized lower tier of the Cordillera Flow, southern Paraná Volcanic Province |
| title_sort | origin of the reduced amethyst mineralized lower tier of the cordillera flow southern parana volcanic province |
| topic | Reduced Tier 1 Cordillera Flow Paraná Volcanic Province Guarani Paleoaquifer hydrothermalism amethyst-geode mineralization |
| url | http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2317-48892025000100306&lng=en&tlng=en |
| work_keys_str_mv | AT leoafraneohartmann originofthereducedamethystmineralizedlowertierofthecordilleraflowsouthernparanavolcanicprovince AT leonardocardosorenner originofthereducedamethystmineralizedlowertierofthecordilleraflowsouthernparanavolcanicprovince |