Complex mineralogical-geochemical sequences and weathering events in the supergene ore of the Cu–Co Luiswishi deposit (Katanga, D.R. Congo)

Laurent Fontaine, Thierry De Putter, Alain Bernard, Sophie Decrée, Jacques Cailteux, Johan Wouters, Johan Yans

Research output: Contribution to journalArticle

Abstract

The Luiswishi Cu–Co ore deposit (Haut-Katanga, D.R. Congo) belongs to the Katanga Copperbelt (KCB), a world-class Cu–Co district. The primary orebodies in the KCB consist of sulphide ore hosted in Neoproterozoic fine-grained siliciclastic and carbonate sedimentary rocks. The secondary weathered ores are still poorly documented, though most of them are strongly enriched in both copper and cobalt with regard to the primary sulphide ores. Combined mineralogical (transmitted and reflected light microscopy, XRD, SEM-EDX) and geochemical investigations (FUS-MS and FUS-ICP) on both host rocks and ore minerals allow identifying and characterizing three distinct zones in the studied profile, at Luiswishi, from base to top: the protore, which contains sulphides and massive dolomite; the cementation zone where oxides and sulphides coexist, and the saprolite, comprised of oxidized ores only. The mixed oxidized-sulphide zone occurs down to about 100 m in depth. At Luiswishi, the formation of the oxidized ores proceeded as follows: (1) oxidation of the primary sulphides (mainly chalcopyrite, carrollite and pyrite); (2) rapid neutralization of the released acidity by carbonate minerals (mainly dolomite) and Mg-chlorite in the host rock; and (3) concomitant precipitation of a wide range of oxidized mineral phases: goethite, malachite, heterogenite, pseudomalachite, amorphous copper silicate compound. Complex geometries and recurring mineralogical successions within heterogenite – malachite, or malachite – copper silicate – malachite aggregates are highlighted in the weathering profile. Mineralogical transformations in the weathered profile result in an overall selective leaching of the LREE and a concomitant residual enrichment in HREE. The leached LREE accumulate in the cementation zone, where both secondary chalcocite-type sulphides and residual and replacement goethite form, by oxidation within the rims and cracks in chalcopyrite. Deriving from a specific protore, the oxidized S.D.1b (formerly “Black Ore Mineralized Zone” or B.O.M.Z.) shows a specific geochemical response to weathering, with enrichment in both LREE and HREE and positive Ce-anomaly in the saprolite.

Original languageEnglish
Article number103674
JournalJournal of African Earth Sciences
Volume161
DOIs
Publication statusPublished - Jan 2020

Fingerprint

weathering
sulfide
malachite
saprolite
copper
cementation
goethite
chalcopyrite
host rock
dolomite
silicate
oxidation
weathering profile
ore mineral
mineral
neutralization
ore
carbonate rock
cobalt
ore deposit

Keywords

  • Heterogenite
  • Katanga copperbelt
  • Luiswishi
  • Malachite
  • Supergene ore
  • Weathering

Cite this

@article{3e73b8a32b824010b7c17f315e5b4d4c,
title = "Complex mineralogical-geochemical sequences and weathering events in the supergene ore of the Cu–Co Luiswishi deposit (Katanga, D.R. Congo)",
abstract = "The Luiswishi Cu–Co ore deposit (Haut-Katanga, D.R. Congo) belongs to the Katanga Copperbelt (KCB), a world-class Cu–Co district. The primary orebodies in the KCB consist of sulphide ore hosted in Neoproterozoic fine-grained siliciclastic and carbonate sedimentary rocks. The secondary weathered ores are still poorly documented, though most of them are strongly enriched in both copper and cobalt with regard to the primary sulphide ores. Combined mineralogical (transmitted and reflected light microscopy, XRD, SEM-EDX) and geochemical investigations (FUS-MS and FUS-ICP) on both host rocks and ore minerals allow identifying and characterizing three distinct zones in the studied profile, at Luiswishi, from base to top: the protore, which contains sulphides and massive dolomite; the cementation zone where oxides and sulphides coexist, and the saprolite, comprised of oxidized ores only. The mixed oxidized-sulphide zone occurs down to about 100 m in depth. At Luiswishi, the formation of the oxidized ores proceeded as follows: (1) oxidation of the primary sulphides (mainly chalcopyrite, carrollite and pyrite); (2) rapid neutralization of the released acidity by carbonate minerals (mainly dolomite) and Mg-chlorite in the host rock; and (3) concomitant precipitation of a wide range of oxidized mineral phases: goethite, malachite, heterogenite, pseudomalachite, amorphous copper silicate compound. Complex geometries and recurring mineralogical successions within heterogenite – malachite, or malachite – copper silicate – malachite aggregates are highlighted in the weathering profile. Mineralogical transformations in the weathered profile result in an overall selective leaching of the LREE and a concomitant residual enrichment in HREE. The leached LREE accumulate in the cementation zone, where both secondary chalcocite-type sulphides and residual and replacement goethite form, by oxidation within the rims and cracks in chalcopyrite. Deriving from a specific protore, the oxidized S.D.1b (formerly “Black Ore Mineralized Zone” or B.O.M.Z.) shows a specific geochemical response to weathering, with enrichment in both LREE and HREE and positive Ce-anomaly in the saprolite.",
keywords = "Heterogenite, Katanga copperbelt, Luiswishi, Malachite, Supergene ore, Weathering",
author = "Laurent Fontaine and {De Putter}, Thierry and Alain Bernard and Sophie Decr{\'e}e and Jacques Cailteux and Johan Wouters and Johan Yans",
year = "2020",
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Complex mineralogical-geochemical sequences and weathering events in the supergene ore of the Cu–Co Luiswishi deposit (Katanga, D.R. Congo). / Fontaine, Laurent; De Putter, Thierry; Bernard, Alain; Decrée, Sophie; Cailteux, Jacques; Wouters, Johan; Yans, Johan.

In: Journal of African Earth Sciences, Vol. 161, 103674, 01.2020.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Complex mineralogical-geochemical sequences and weathering events in the supergene ore of the Cu–Co Luiswishi deposit (Katanga, D.R. Congo)

AU - Fontaine, Laurent

AU - De Putter, Thierry

AU - Bernard, Alain

AU - Decrée, Sophie

AU - Cailteux, Jacques

AU - Wouters, Johan

AU - Yans, Johan

PY - 2020/1

Y1 - 2020/1

N2 - The Luiswishi Cu–Co ore deposit (Haut-Katanga, D.R. Congo) belongs to the Katanga Copperbelt (KCB), a world-class Cu–Co district. The primary orebodies in the KCB consist of sulphide ore hosted in Neoproterozoic fine-grained siliciclastic and carbonate sedimentary rocks. The secondary weathered ores are still poorly documented, though most of them are strongly enriched in both copper and cobalt with regard to the primary sulphide ores. Combined mineralogical (transmitted and reflected light microscopy, XRD, SEM-EDX) and geochemical investigations (FUS-MS and FUS-ICP) on both host rocks and ore minerals allow identifying and characterizing three distinct zones in the studied profile, at Luiswishi, from base to top: the protore, which contains sulphides and massive dolomite; the cementation zone where oxides and sulphides coexist, and the saprolite, comprised of oxidized ores only. The mixed oxidized-sulphide zone occurs down to about 100 m in depth. At Luiswishi, the formation of the oxidized ores proceeded as follows: (1) oxidation of the primary sulphides (mainly chalcopyrite, carrollite and pyrite); (2) rapid neutralization of the released acidity by carbonate minerals (mainly dolomite) and Mg-chlorite in the host rock; and (3) concomitant precipitation of a wide range of oxidized mineral phases: goethite, malachite, heterogenite, pseudomalachite, amorphous copper silicate compound. Complex geometries and recurring mineralogical successions within heterogenite – malachite, or malachite – copper silicate – malachite aggregates are highlighted in the weathering profile. Mineralogical transformations in the weathered profile result in an overall selective leaching of the LREE and a concomitant residual enrichment in HREE. The leached LREE accumulate in the cementation zone, where both secondary chalcocite-type sulphides and residual and replacement goethite form, by oxidation within the rims and cracks in chalcopyrite. Deriving from a specific protore, the oxidized S.D.1b (formerly “Black Ore Mineralized Zone” or B.O.M.Z.) shows a specific geochemical response to weathering, with enrichment in both LREE and HREE and positive Ce-anomaly in the saprolite.

AB - The Luiswishi Cu–Co ore deposit (Haut-Katanga, D.R. Congo) belongs to the Katanga Copperbelt (KCB), a world-class Cu–Co district. The primary orebodies in the KCB consist of sulphide ore hosted in Neoproterozoic fine-grained siliciclastic and carbonate sedimentary rocks. The secondary weathered ores are still poorly documented, though most of them are strongly enriched in both copper and cobalt with regard to the primary sulphide ores. Combined mineralogical (transmitted and reflected light microscopy, XRD, SEM-EDX) and geochemical investigations (FUS-MS and FUS-ICP) on both host rocks and ore minerals allow identifying and characterizing three distinct zones in the studied profile, at Luiswishi, from base to top: the protore, which contains sulphides and massive dolomite; the cementation zone where oxides and sulphides coexist, and the saprolite, comprised of oxidized ores only. The mixed oxidized-sulphide zone occurs down to about 100 m in depth. At Luiswishi, the formation of the oxidized ores proceeded as follows: (1) oxidation of the primary sulphides (mainly chalcopyrite, carrollite and pyrite); (2) rapid neutralization of the released acidity by carbonate minerals (mainly dolomite) and Mg-chlorite in the host rock; and (3) concomitant precipitation of a wide range of oxidized mineral phases: goethite, malachite, heterogenite, pseudomalachite, amorphous copper silicate compound. Complex geometries and recurring mineralogical successions within heterogenite – malachite, or malachite – copper silicate – malachite aggregates are highlighted in the weathering profile. Mineralogical transformations in the weathered profile result in an overall selective leaching of the LREE and a concomitant residual enrichment in HREE. The leached LREE accumulate in the cementation zone, where both secondary chalcocite-type sulphides and residual and replacement goethite form, by oxidation within the rims and cracks in chalcopyrite. Deriving from a specific protore, the oxidized S.D.1b (formerly “Black Ore Mineralized Zone” or B.O.M.Z.) shows a specific geochemical response to weathering, with enrichment in both LREE and HREE and positive Ce-anomaly in the saprolite.

KW - Heterogenite

KW - Katanga copperbelt

KW - Luiswishi

KW - Malachite

KW - Supergene ore

KW - Weathering

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U2 - 10.1016/j.jafrearsci.2019.103674

DO - 10.1016/j.jafrearsci.2019.103674

M3 - Article

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JO - Journal of African Earth Sciences

JF - Journal of African Earth Sciences

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