Characterization and origin of clays in the Bou Arhous (Morocco) non-sulfide Zn ore deposit

Abstract : Supergene non-sulfide Zn deposits offer high mineralogical diversity including clay minerals that can incorporate significant amounts of Zn like sauconite. Although clayey material is commonly observed in such ore deposits, its nature and origin have been rarely studied, especially in carbonate-hosting environments. However the role of clay minerals is essential for mineral processing because they usually have a negative impact on zinc recovery. In this work, we focus on the Bou Arhous Zn-Pb ore deposit in Eastern High Atlas, Morocco. This deposit is located in an anticline formed by Lower Jurassic limestone and marl, with Upper Triassic shale in the core of the anticline. Zn-rich clayey material fills karstic cavities and two types of clay rich deposits have been identified field: 1) white to ochre granular clay (kaolinite/smectite (K/S) irregular mixed layers, smectite and illite) and 2) red smooth clay (kaolinite, chlorite, illite). The white to ochre granular clays are closely associated with supergene willemite (zinc silicate), one of the main Zn bearing mineral phases of the Bou Arhous deposit. The red smooth clays fill karst-related cavities cutting across the non-sulfide mineralized bodies. The red smooth clays present evidence of stratification that reflects internal sedimentation processes during karst evolution. Bulk chemical analyses reveal that the Zn content is highly variable in all clayey samples and even can reach several percent. This enrichment may be due to fine inclusions of zinc silicate or carbonate in the clayey material, or to the occurrence of Zn clay minerals (i.e. sauconite). The mineralogy of clays and associated minerals in bulk powders and separated <2μm oriented fractions from the two types of clay deposits and from surrounding Triassic to Lower Jurassic rocks has been investigated. X-ray diffraction (XRD) analyses complemented by Scanning Electron Microscope (SEM) observations, have allowed us to identify the nature of the clay minerals and to characterize the textural relationships between clays and other zinc-bearing minerals like willemite. In a few samples with high zinc content (5%), bulk XRD analyses do not reveal the occurrence of zinc sulphides, carbonates or silicates, suggesting that zinc is associated with clay minerals. Preliminary XRD results indicate that white and ochre clays are composed of kaolinite/smectite (K/S) irregular mixed layers with up to 20% of smectite in some samples; smectite, illite and chlorite are also present. On the other hand, the red clays contain kaolinite, chlorite, illite, and illite/smectite mixed layers (goethite is commonly present in these samples). SEM observations demonstrated that willemite crystals are partially dissolved and are surrounded by authigenic clay minerals. Microprobe analyses and cation-exchange capacity on clay mineral fractions are currently performed to highlight the localization of zinc within the structure of clay minerals, and to provide crucial information on Zn recovery potential of the studied deposit. All these new results will enable characterizing Zn speciation in these supergene deposits to check the following hypotheses for clay origin: 1) interactions between Zn-rich solution due to supergene oxidation and residual clays originated from dissolution of limestone-dominated host rocks, 2) secondary alteration of Zn minerals like willemite into clay minerals, and 3) reaction between detrital clays and Zn-rich solutions.
Complete list of metadatas

https://hal-insu.archives-ouvertes.fr/insu-01143105
Contributor : Nathalie Pothier <>
Submitted on : Thursday, April 16, 2015 - 4:38:27 PM
Last modification on : Friday, May 10, 2019 - 1:54:16 PM

Identifiers

  • HAL Id : insu-01143105, version 1

Citation

Flavien Choulet, Martine Buatier, Luc Barbanson, Régis Guégan, A. Ennaciri. Characterization and origin of clays in the Bou Arhous (Morocco) non-sulfide Zn ore deposit. International Mineralogical Association IMA 2014, Sep 2014, Johannesburg, South Africa. pp.EG5 - NONSULPHIDE ZN-PB ORES, 2014. ⟨insu-01143105⟩

Share

Metrics

Record views

274