Controls on prolate and oblate geode geometries in the Veia Alta basalt flow, largest world producer of amethyst, Paraná volcanic province, Brazil

Autor:	Léo Afraneo Hartmann, J. T. N. Medeiros, Sérgio Benjamin Baggio, Lucas Machado Antunes
Rok vydání:	2015
Předmět:	Basalt geography geography.geographical_feature_category Geochemistry Geology Prolate spheroid Amethyst engineering.material Hydrothermal circulation Geode Volcano Geochemistry and Petrology Oblate spheroid engineering Economic Geology Loss on ignition
Zdroj:	Ore Geology Reviews. 66:243-251
ISSN:	0169-1368
DOI:	10.1016/j.oregeorev.2014.11.005
Popis:	Variable intensity of hydrothermal alteration of the Veia Alta basalt flow, Ametista do Sul, Brazil, exerted the fundamental control on the shape and size of the amethyst geodes. The loss on ignition (LOI) of the host basalt is used as a proxy for intensity of alteration and has direct relationship with the height of the geodes (up to 150 cm in the three study mines) and with the prolaticity of geodes. All rocks with LOI > 5 wt.% host prolate geodes and all oblate geodes are hosted in rocks with LOI 2 , K 2 O and Rb. The hydrothermal origin of the geodic cavities is thus established and their shapes explained by the empirical observation of the results from a previous numerical simulation experiment.
Databáze:	OpenAIRE
Externí odkaz:	https://explore.openaire.eu/search/publication?articleId=doi_________::d0ba5133e4b8a099f9fc7663101ad09c https://doi.org/10.1016/j.oregeorev.2014.11.005 Zobrazit plný text záznamu Full Text from ScienceDirect