Pétrologie du gisement latéritique manganésifère d'Azul (Brésil)
Identifieur interne : 004F10 ( Main/Exploration ); précédent : 004F09; suivant : 004F11Pétrologie du gisement latéritique manganésifère d'Azul (Brésil)
Auteurs : A. Beauvais [France] ; A. Melfi [Brésil] ; D. Nahon [France] ; J. Trescases [France]Source :
- Mineralium Deposita [ 0026-4598 ] ; 1987-04-01.
Abstract
Abstract: At Azul (state of Para, Brazil) the lateritic weathering of organic shales with rhodochrosite and phyllosilicates (mainly muscovite) has led to one of the largest maganese deposits of Brazil (45 Mt of reserves with 42.65% Mn). The oxidation of the rhodochrosite-rich levels produces ore that typically breaks into plates preserving the original bedding of the rock. This oxidation corresponds to a sequence of transformation (rhodochrosite → cryptomelane → nsutite → pyrolusite) by pseudomorphic replacement of the initial textures. At the top of this platy ore layer the late weathering of the micas releases potassium, and the nsutite and pyrolusite plasmas undergo a true retromorphic evolution toward cryptomelane, which is subsequently epigenized by lithiophorite. The geochemical balance computation at each stage and the modeling of this evolution show that acid and reducing conditions of the superficial layer favor the recycling of the Mn to the bottom of the profiles. Cryptomelane and lithiophorite constitute the more stable forms of manganese in the superficial layers of the lateritic profiles.
Url:
DOI: 10.1007/BF00204689
Affiliations:
- Brésil, France
- Poitou-Charentes, Provence-Alpes-Côte d'Azur, État de São Paulo
- Marseille Cédex 13, Poitiers, São Paulo
- Université de Poitiers, Université de São Paulo
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Deposita</title><idno type="ISSN">0026-4598</idno><idno type="eISSN">1432-1866</idno><imprint><publisher>Springer-Verlag</publisher><pubPlace>Berlin/Heidelberg</pubPlace><date type="published" when="1987-04-01">1987-04-01</date><biblScope unit="volume">22</biblScope><biblScope unit="issue">2</biblScope><biblScope unit="page" from="124">124</biblScope><biblScope unit="page" to="134">134</biblScope></imprint><idno type="ISSN">0026-4598</idno></series><idno type="istex">C7E4D93225BF8B084D17EAD07CF015F028D1C75D</idno><idno type="DOI">10.1007/BF00204689</idno><idno type="ArticleID">Art6</idno><idno type="ArticleID">BF00204689</idno></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0026-4598</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass><langUsage><language ident="fr">fr</language></langUsage></profileDesc></teiHeader><front><div type="abstract" xml:lang="en">Abstract: At Azul (state of Para, Brazil) the lateritic weathering of organic shales with rhodochrosite and phyllosilicates (mainly muscovite) has led to one of the largest maganese deposits of Brazil (45 Mt of reserves with 42.65% Mn). The oxidation of the rhodochrosite-rich levels produces ore that typically breaks into plates preserving the original bedding of the rock. This oxidation corresponds to a sequence of transformation (rhodochrosite → cryptomelane → nsutite → pyrolusite) by pseudomorphic replacement of the initial textures. At the top of this platy ore layer the late weathering of the micas releases potassium, and the nsutite and pyrolusite plasmas undergo a true retromorphic evolution toward cryptomelane, which is subsequently epigenized by lithiophorite. The geochemical balance computation at each stage and the modeling of this evolution show that acid and reducing conditions of the superficial layer favor the recycling of the Mn to the bottom of the profiles. Cryptomelane and lithiophorite constitute the more stable forms of manganese in the superficial layers of the lateritic profiles.</div></front></TEI><affiliations><list><country><li>Brésil</li><li>France</li></country><region><li>Poitou-Charentes</li><li>Provence-Alpes-Côte d'Azur</li><li>État de São Paulo</li></region><settlement><li>Marseille Cédex 13</li><li>Poitiers</li><li>São Paulo</li></settlement><orgName><li>Université de Poitiers</li><li>Université de São Paulo</li></orgName></list><tree><country name="France"><region name="Poitou-Charentes"><name sortKey="Beauvais, A" sort="Beauvais, A" uniqKey="Beauvais A" first="A." last="Beauvais">A. Beauvais</name></region><name sortKey="Nahon, D" sort="Nahon, D" uniqKey="Nahon D" first="D." last="Nahon">D. Nahon</name><name sortKey="Trescases, J" sort="Trescases, J" uniqKey="Trescases J" first="J." last="Trescases">J. Trescases</name></country><country name="Brésil"><region name="État de São Paulo"><name sortKey="Melfi, A" sort="Melfi, A" uniqKey="Melfi A" first="A." last="Melfi">A. Melfi</name></region></country></tree></affiliations></record>Pour manipuler ce document sous Unix (Dilib)
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