The largest cobalt ore reserves are located in DRC, the Democratic Republic of Congo. Most of cobalt is observed as black cobaltic oxide minerals: heterogenite [HCoO2] and asbolane [(Ni,Co)2-xMn(O,OH)4.nH2O] which are hardly differentiable since they exhibit similar macroscopic habit and textures. These minerals are frequently observed in similar environment (oxidized horizon of ore deposits) and they are commonly poorly-crystallized limiting their study with XRD. Their chemical composition is also not very well-constrained since they exhibit significant chemical substitutions with cations as Cu, Co, Ni, Mn. Our observations on a set of heterogenite and asbolane samples from DRC combined with samples from other localities shows that each phase, even under an amorphous form, can be readily distinguished by Raman microspectrometry. This technique is therefore attractive during ore deposit characterization campaigns or during the follow-up extraction operations where it is important to distinguish the main constituting Co-phase(s). The main advantage of this technique is its speed since no sample preparation is required during the collection Raman spectra that usually last few tens of seconds. The method provides information at a mum-scale and several points are thus required to fully characterize ore batches composed of different mineralogical phases. Our petrographical observations show also that asbolane and heterogenite mineralogical phases can coexist at a mum-scale as two distinct phases into 'heterogenite' ore. The distinction between heterogenite and asbolane from our sample set can also be conducted on a chemical base showing that heterogenite represents the richer Co-phase with variable Cu concentrations. By contrast, only Mn traces are usually observed in heterogenite minerals from DRC except in few samples, but always in lower concentration than in asbolane. The latter shows variable Mn/(Mn+Co) ratio between 0.85 and 0.3 and the decrease of this value is related to enrichment into Cu.
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The middle Eocene Subathu Group of Kalakot area (northwest Himalaya, India) is well known for its diverse mammalian fauna, especially of raoellid artiodactyls, which are presently represented by four genera: Indohyus, Khirtharia, Kunmunella, and Metkatius. Our recent work on artiodactyls from the Kalakot area recovered several new taxa in addition to earlier known raoellids. The first new taxon is characterized by its small size, higher and more conical lower molar cusps than in Khirtharia and Metkatius; protoconid and metaconid closely appressed; crista obliqua meets at trigonid notch, presence of an hypolophid and a welldeveloped labial cingulid; bunodont upper molars, subrectangular M1-M2, and subtriangular M3, large metaconule (pseudohypocone) and small well distinct paraconule; cristae well distinct, small metastyle on M3 (absent in the four other raoellid genera), slightly inflated anterior and posterior cingulae. The second new taxon is the smallest of all known Raoellidae; it has bunodont lower molars with tiny paraconid in m1-2 (paraconid is absent in all other raoellids) and crista obliqua meeting the labial base of protoconid; m3 with an hypolophid and well-individualized hypoconulid centrally placed and higher than entoconid; M2 subrectangular, protocone higher than metacone, para and metastyle less distinct than in Indohyus and Kunmunella, ectoloph distinct. Besides these two new taxa, Khirtharia dayi known from Pakistan is reported for the first time from India on the basis of its morphology and size of m3. A new species of Metkatius is characterized on the basis of m1-2, which differ from those of M. kashmirensis by the metaconid higher than the protoconid and by being more than 20% larger. Outside the Indian sub-continent, raoellid artiodactyls are also known from the middle Eocene Pondaung Formation of Myanmar and Shanghuang fissure filling of Jiangsu, China. The predominance of the family Raoellidae in Kalakot provides new information about their phylogenetic position and allow to discuss their origin, evolution, and dispersals. This work is partly funded by project BR/121/A3/PALEURAFRICA from the Belgian Science Policy Office.
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RBINS Staff Publications 2019
