Les chromitites podiformes et les mineraux de Fe-Cu-Ni-Co associes a l'ophiolite de Bou Azzer-El Graara (Anti-Atlas Central, Maroc)  [Podiform chromitites and Fe-Cu-Ni-Co minerals associated with the Bou Azzer-El Graara Ophiolite (central Anti-Atlas, Morocco)]

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Alternate Title:Podiform chromitites and Fe-Cu-Ni-Co minerals associated with the Bou Azzer-El Graara Ophiolite (central Anti-Atlas, Morocco)
Authors:Wafik, Amina; Saquaque, Ali; El Boukhari, Abdelmajid
Author Affiliations:Primary:
Université Cadi Ayyad, Département des Sciences de la Terre, Marrakech, Morocco
Other:
Reminex (ONA), Morocco
Volume Title:Ofioliti
Source:Ofioliti, 26(2B), p.467-478. Publisher: Pitagora Editrice, Bologna, Italy. ISSN: 0391-2612
Publication Date:2001
Note:In French with English summary. 56 refs.; illus., incl. 2 tables, geol. sketch maps
Summary:The presence of chromitites pods within tectonites renders particularly interesting the Proterozoic ophiolite of Bou Azzer The chromitites are some centimeters to over than ten meters thick and twenty to thirty meters wide, and they spread several dozen of meters in length. They are either concordant (N110 to N130E dominant direction) or discordant (about 30°) on the primary magmatic structures (S0) of harzburgites. Their study reveals primary inclusions of metallic phases in the crystals of chromite. The analysis of these phases with the electronic microprobe (Camebax, laboratory of Petrology, Paris VI, France) and with the MEB (Reminex laboratory, Mine of Guemassa, ONA, Morocco), give the following compositions for the metal sulfides and alloys: - Pyrite FeS2 slightly impoverished in Fe; - Chalcopyrite CuFeS2 enriched in S (55.20% atomic); - Galena PbS; - Arsenopyrite FeAsS, enriched in S (40.61% atomic); - Millerite NiS, to cobaltiferous pentlandite Ni3(Co,Fe)2 S5 slightly enriched in sulfur, to Ni3(Co,Fe)2-x S5+x; - CoAsS2 (structure analogue to that of skutterudite CoAs3); - (Co,Fe)(As,S) glaucodot; - alloys range from Fe0.9Cu0.1 to Cu-Fe-Ni-As more complex compounds with or without S. All these minerals contain some hundreds ppm of Pt and/or Pd as trace elements. In the serpentine minerals, at the border of chromite crystals, other secondary alloys of Fe-Cu-Sn-Co-As-Ag and S occur. These compounds vary from Fe6(Ni,Cu,Ag)4-x(Sn,S,As)x to Fe9(Ni,Cu,Ag)1-x (Sn,S,As)x, and are often associated with interstitial serpentine. The enrichment in Ag and Sn of these alloys is secondary, and it could be contemporary to the serpentinization events related to the hydrothermal circulations.
Sections:Economic minerals and ore deposits; Geochemistry
Subsections:Metallic deposits: specific
Subjects:Chemical composition; Chemical ratios; Chromite ores; Chromitite; Gabbros; Geochemistry; Igneous rocks; Inclusions; Major elements; Metal ores; Metallogeny; Metals; Mineral assemblages; Mineral composition; Mineral deposits, genesis; Mineral exploration; Neoproterozoic; Ophiolite; Pan-African Orogeny; Petrography; Plutonic rocks; Podiform deposits; Precambrian; Proterozoic; Sulfides; Trace elements; Ultramafics; Upper Precambrian; Africa; Anti-Atlas; Atlas Mountains; Bou Azzer; Moroccan Atlas Mountains; Morocco; North Africa; West African Shield; Bou Azzer Ophiolite; El Graara Ophiolite
Coordinates:N303500 N303500 W0064500 W0064500
Abstract Numbers:06M/4742
Record ID:2006051283
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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