Rare earth element fractionation in heterogenite (CoOOH): implication for cobalt oxidized ore in the Katanga Copperbelt (Democratic Republic of Congo)

Abstract

Heterogenite (CoOOH) is the most abundant cobalt oxide mineral in the Katanga Copperbelt, which hosts around half of the world's known reserves of mineable cobalt. Heterogenite formed by the oxidation of Co-sulfides and accumulated as residual deposits during a Pliocene weathering event. Bulk analysis samples of oxidized cobalt ore samples containing with variable heterogenite concentration display two rare earth element (REE) patterns: (i) Type 1 is enriched in middle REE, with a negative cerium anomaly and a relatively low REE content; (ii) Type 2 is variably enriched in light REE (LREE), without a cerium anomaly and *Revised Manuscript with No Changes Marked Click here to view linked References with higher REE content. However, in situ LA-ICP-MS reveals that the Type patterns are due to the mixing of heterogenite with a LREE-rich mineral. Weathering processes leading to heterogenite formation mainly consist of water-rock interactions at high Co activity, in the near-surface environment. These result in the formation of a lateritic deposit. Heterogenite precipitates at near-neutral pH conditions together with manganese oxides. REE are mainly fractionated between these Co-and Mn-oxide minerals. In the deeper part of the oxidized profile, cobalt activity decreases and the heterogenite stability field shifts to alkaline pH conditions due to the dissolution of dolostone in the bedrock. In such an alkaline environment, REE speciation is mainly driven by carbonate complexation/precipitation. This environment would be favorable for the formation of REErich carbonate which is intimately associated with heterogenite (LREE-rich Type 2 patterns). The combined whole-rock and in situ geochemical analyses presented here clearly help (1) to distinguish the REE signature of the Co oxidized ore (mineral paragenesis comprizing heterogenite) and of heterogenite itself, and subsequently (2) to highlight two different chemical environments for the formation of heterogenite in supergene ores. This study therefore improves the understanding of REE behaviour and metal mobility in nearsurface environments, and more particularly in environments where the supergene ores form. In the future, the approach developped here can be applied to other Co-Ni-Mn lateritic deposits such as those in New-Caledonia and Cameroon.

Critical elements in non-sulfide Zn deposits: a reanalysis of the Kabwe Zn-Pb ores (central Zambia)

“…Although a late Eocene-Oligocene age has been produced for the Kabwe descloizite (∼20-37 Ma; N.J. Evans, unpubl., in Boni et al, 2007), by analogy with other supergene deposits occurring in this region (e.g. supergene Cu-Co and manganese deposits in the Katanga region; Dewaele et al, 2006;Decrée et al, 2010;Decrée et al, 2015;De Putter et al, 2015) and, more in general, in the southern African craton (Pack et al, 2000;Boni et al, 2007;Gutzmer et al, 2012;Arfèet al, 2017, Smithsonite 1 smithsonite replacing the host rock −6.2 9.1 21.5 S109 and references therein), the ∼300-500 m deep (Kamona and Friedrich, 2007) supergene alteration profile at Kabwe could have formed during a period longer than the single descloizite age, possibly starting in the Late Cretaceous-early Eocene and extending until the Mio-Pliocene. In this timeframe, a tropical-humid climate persisted in the region and laterite profiles developed in the Katanga region (Giresse, 2005).…”

Mobility of copper and cobalt in metalliferous ecosystems: Results of a lysimeter study in the Lubumbashi Region (Democratic Republic of Congo)

“…This situation may be explained by the controlled conditions of the experiment in favour of higher reactions between rocks, soil water and soil compounds. The presence of Cu and Co as stable compounds such as malachite and heterogenite as suggested by Decrée et al (2015 and Pourret et al (2016) could also explain this low Cu and Co mobility (Fig. 6).…”

“…The mineralogical composition of samples was further determined by optical microscopy, scanning electron microscopy (SEM) and energy dispersion spectrometry (EDS). Samples were examined under a Leica DRM-XP polarizing microscope in transmitted and reflected light and subsequently studied under a Hitachi S3400 SEM equipped with a ThermoNORAN NSS Ultradry EDS (Pourret et al, 2016) and further refined using previous studies from literature (Fay and Barton, 2012;Schuh et al, 2012;Decrée et al, 2015;Mambwe et al, 2017).…”

Zinc Presence during Mineral Formation Affects the Sorptive Reactivity of Manganese Oxide

“…Manganese oxides (MnO x ), especially layered phyllomanganates, are important metal oxides in terrestrial and oceanic environments [1][2][3]. Because of the high surface area, negative surface charge, vacancy sites, and high oxidative potential, phyllomanganates have a strong tendency to interact with and strongly influence the fate and transport of trace metals, such as Ni [4][5][6][7][8], Co [6,[8][9][10][11][12][13], Pb [7,[14][15][16][17][18], Cu [6,19,20], Zn [4,7,17,[21][22][23], and Cd [24,25]. Phyllomanganates can interact with metals in different ways (e.g., sorption, coprecipitation, incorporation), which in turn can affect the property and reactivity of the host mineral phases.…”