Geochemistry of Platinum-Group Elements (PGE) in Cerro Matoso and Planeta Rica Ni-Laterite deposits, Northern Colombia

Abstract

Platinum-group elements (PGE) are included among the so-called critical metals, and are essential metals for the technological industry. However, there are very few deposits in the world from which these metals can be extracted. The present work investigates three Ni-laterite profiles (hydrous Mg silicate type) formed over the ultramafic rocks of Cerro Matoso and Planeta Rica in Colombia. The main goal is to determine their PGE concentration and distribution, as well as to identify the carrier phases of these noble metals. The highest PGE contents in Cerro Matoso and Planeta Rica are concentrated in the limonite horizon (141–272 ppb), showing a strong decrease towards the saprolite and the underlying serpentinized peridotite (parent rock; < 50 ppb). The highest concentrations correspond to Pt>Ru>Pd and the lowest to Rh<Os<Ir. Such distribution indicates that PGE are mobilized in different proportions by the laterization processes. The high affinity between PGE and Fe favors the formation of PGE-Fe mineral alloys such as the Pt-Ir-Fe-Ni minerals hosted by Fe-oxyhydroxide found in the limonite–saprolite transition zone in Planeta Rica. In addition, in the same zone, nanoparticles of Pt (< 1 µm) were found within framboidal pyrite. Both types of platinum group minerals (PGM) are secondary in origin. In the case of Pt-Ir-Fe-Ni alloys, this interpretation is supported by their morphology and chemical composition, which is comparable with PGE-Fe-Ni alloys found in laterites of Dominican Republic. In the case of Pt nanoparticle, textural relations suggest the neoformation of PGM adhered to the porous edges of altered pyrite. Cerro Matoso and Planeta Rica should be considered as unconventional PGE deposits, if adequate recovery processes can be applied for their recovery as by-products during Ni (+Co) production.

Distribution and Mobility of Platinum‐Group Elements in the Late Cretaceous Ni‐Laterite in the Northern Oman Mountains

“…Previous studies on the mobility of PGE during lateritization processes revealed that acidic conditions (pH < 6 and Eh > 0.4) could lead to the dissolution of PGE‐bearing minerals, especially PPGE phases, and then they would undergo subsequent transportation in solution and accumulation in the oxidized Fe‐rich laterite profiles (Plimer & Williams, 1988; Talovina & Lazarenkov, 2001). The PGE are accumulated as PGE‐rich alloys, which co‐precipitate with Fe and Mn oxides under such acidic conditions (Bowles, Gize, & Cowden, 1994; Bowles, Gize, Vaughan, & Norris, 1994; Ndjigui & Bilong, 2010; Salpéteur et al., 1995; Tobόn et al., 2020). Complex Pt‐Ir‐Fe‐Ni alloys were recently found as inclusions and packed nanoparticles within pore spaces of Fe oxides and oxyhydroxides of the Loma Peguera Ni‐laterite deposit in the Dominican Republic (Aiglsperger et al., 2015, 2017) and in the Planeta Rica Ni‐laterite profiles of Northern Colombia (Tobόn et al., 2020).…”

“…The PGE are accumulated as PGE‐rich alloys, which co‐precipitate with Fe and Mn oxides under such acidic conditions (Bowles, Gize, & Cowden, 1994; Bowles, Gize, Vaughan, & Norris, 1994; Ndjigui & Bilong, 2010; Salpéteur et al., 1995; Tobόn et al., 2020). Complex Pt‐Ir‐Fe‐Ni alloys were recently found as inclusions and packed nanoparticles within pore spaces of Fe oxides and oxyhydroxides of the Loma Peguera Ni‐laterite deposit in the Dominican Republic (Aiglsperger et al., 2015, 2017) and in the Planeta Rica Ni‐laterite profiles of Northern Colombia (Tobόn et al., 2020). These observations are in good agreement with the previous studies, which indicated that the high contents of Pt, Pd, and Ru, as well as the transition metals such as Ni, Co, Cu, and Zn, in laterite profiles, are essentially hosted by secondary minerals like Fe‐oxy‐hydroxides or smectite clay minerals (Ndjigui & Bilong, 2010; Oberthür & Melcher, 2005).…”

“…Laterite profiles produced by pervasive chemical weathering of mafic/ultramafic rocks are known to be important sources of metals such as nickel (Ni), cobalt (Co), and iron (Fe) and are collectively known as Ni‐laterite deposits (Butt & Cluzel, 2013; Evans, 1993; Freyssinet et al., 2005; Golightly, 2010; Reich & Vasconcelos, 2015; R. Thorne et al., 2012, R. L. Thorne et al., 2012). Supergene enrichment processes are also important for residual and secondary enrichment of PGE and gold in these mineral deposits (Aiglsperger et al., 2015, 2016, 2017; Gray et al., 1996; Rivera et al., 2018; Tobόn et al., 2020; Traoré et al., 2008; Varajão et al., 2000). There is consensus that three main processes control the concentration and distribution of PGE in terrestrial rocks.…”

The formation of alluvial platinum-group minerals: present knowledge and the way ahead

“…The laterite profile at Yubdo is similar to other tropical lateritic occurrences, but it has been well exposed by the mining activity. The pit of the Ni mine at Cerro Matoso, Colombia, is also the result of mining activity (Tobón et al, 2020), and it shows a comparable profile with a cover of allochthonous soil over in situ red laterite with saprolite beneath (Fig. 8a,b).…”

“…PGM occurrences northern Colombia (after Tobón et al , 2020); (a) laterite overlying saprolite at the Cerro Matoso pit; (b) the laterite profile; (c) PGE in a drill hole at Planeta Rica; (d) PGM near the saprolite–laterite boundary from the same drill core.…”