Geology and geochemistry of gossans and ironstones in carbonate and alumino-silicate environments in northeastern Algeria
Identifieur interne : 001205 ( Main/Exploration ); précédent : 001204; suivant : 001206Geology and geochemistry of gossans and ironstones in carbonate and alumino-silicate environments in northeastern Algeria
Auteurs : Eric Hanssen [Belgique, Mali] ; Mohammed Bourezg [Algérie]Source :
- Journal of Geochemical Exploration [ 0375-6742 ] ; 1990.
Abstract
Nine gossans and ironstones, overlying known mineralization in carbonate and alumino-silicate environments in northeastern Algeria were investigated in order to develop criteria to distinguish between them. Texture, mineralogy and chemical composition were determined. In the highly reactive carbonate environment, boxwork development and element retention are excellent, even above pyrite-rich ores. The secondary mineral assemblage is varied, especially in the presence of As and Sb. It involves most elements of the primary paragenesis. In the moderately reactive alumino-silicate environment, element retention is much lower with Zn, and to a lesser extent Cu being mobile during weathering. Boxworks and secondary minerals are common above pyrite-poor mineralization. High pyrite contents, leading to low pH on oxidation and fine grain size inhibit boxwork development over polymetallic volcanic-hosted deposits. Two extreme types of weathering behaviour can be defined: 1. (1) At low pH (pyrite-rich ores) most elements, even As and Sb, are mobilized. Complex sulfates of the alunite-jarosite family become stable and may highly contribute to gossan geochemistry. 2. (2) Near-neutral to slightly alkaline conditions occur over pyrite-poor mineralizations. High chal-copyrite contents lower the pH into the solubility field of Cu2+. Correlations are induced by coprecipitation with goethite and secondary mineral formation. Factor scores, separately calculated for the two environments, allow satisfactory discrimination of gossans from above PbZn and Cu mineralization from barren gossans and ironstones. Gossan assessment taking into account wallrock reactivity, enhances successful identification based on chemical analysis.
Url:
DOI: 10.1016/0375-6742(90)90117-S
Affiliations:
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Texture, mineralogy and chemical composition were determined. In the highly reactive carbonate environment, boxwork development and element retention are excellent, even above pyrite-rich ores. The secondary mineral assemblage is varied, especially in the presence of As and Sb. It involves most elements of the primary paragenesis. In the moderately reactive alumino-silicate environment, element retention is much lower with Zn, and to a lesser extent Cu being mobile during weathering. Boxworks and secondary minerals are common above pyrite-poor mineralization. High pyrite contents, leading to low pH on oxidation and fine grain size inhibit boxwork development over polymetallic volcanic-hosted deposits. Two extreme types of weathering behaviour can be defined: 1. (1) At low pH (pyrite-rich ores) most elements, even As and Sb, are mobilized. Complex sulfates of the alunite-jarosite family become stable and may highly contribute to gossan geochemistry. 2. (2) Near-neutral to slightly alkaline conditions occur over pyrite-poor mineralizations. High chal-copyrite contents lower the pH into the solubility field of Cu2+. Correlations are induced by coprecipitation with goethite and secondary mineral formation. Factor scores, separately calculated for the two environments, allow satisfactory discrimination of gossans from above PbZn and Cu mineralization from barren gossans and ironstones. Gossan assessment taking into account wallrock reactivity, enhances successful identification based on chemical analysis.</div></front></TEI><affiliations><list><country><li>Algérie</li><li>Belgique</li><li>Mali</li></country></list><tree><country name="Belgique"><noRegion><name sortKey="Hanssen, Eric" sort="Hanssen, Eric" uniqKey="Hanssen E" first="Eric" last="Hanssen">Eric Hanssen</name></noRegion></country><country name="Mali"><noRegion><name sortKey="Hanssen, Eric" sort="Hanssen, Eric" uniqKey="Hanssen E" first="Eric" last="Hanssen">Eric Hanssen</name></noRegion></country><country name="Algérie"><noRegion><name sortKey="Bourezg, Mohammed" sort="Bourezg, Mohammed" uniqKey="Bourezg M" first="Mohammed" last="Bourezg">Mohammed Bourezg</name></noRegion></country></tree></affiliations></record>Pour manipuler ce document sous Unix (Dilib)
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