Investigating critical metals Ge and Ga in complex sulphide mineral assemblages using LIBS mapping

editorial reviewedLIBS mapping is a powerful tool for visualizing chemical heterogeneity of geological materials [1, 2 and references therein]. Fast data acquisition, minimal sample preparation, multi-elemental detection and high dynamic range are key advantages of LIBS compared to other techniques. In this contribution we show that LIBS maps can provide geologists and engineers with a wealth of information including identification, characterization and quantitation of the different mineral phases, and detection of trace-elements together with their distribution within their host minerals [e.g., 3]. Several ore samples from Kipushi mine, DRC, were selected from the university collection. These ores are known for their mineral complexity and economic value as they contain critical metals such as Ge and Ga. Analyzing colocalisation of major elements in the extracted LIBS maps allowed the reconstruction of the mineralogy. Detected minerals include chalcopyrite [CuFeS2], bornite [Cu5FeS4], chalcocite [Cu2S], sphalerite [ZnS], galena [PbS], tennantite-(Zn) [Cu6(Cu4Zn2)As4S12S], germanite [Cu13Fe2Ge2S16], renierite [(Cu1+,Zn)11Fe4(Ge4+,As5+)2S16], tungstenite [WS2], betekhtinite [Pb2(Cu,Fe)22-24S15] and a series of non-sulphide gangue minerals. SEM-EDS analyses are planned to check this LIBS-derived mineralogy. Relative abundance and grain size of the different minerals can be easily evaluated by image analysis of the LIBS maps. These minerals are preferential hosts for trace-elements Ga and Ag, with Ga being preferentially enriched in chalcopyrite and, to a lesser extent, in renierite, and Ag occurring within bornite and tennantite, with some migration in fractures affecting other sulphides

Cartographie de luminescence induite par plasma en parallèle (ou pas) avec la spectroscopie de plasma induit par laser

editorial reviewedLa luminescence induite par plasma (Plasma-Induced Luminescence, PIL) est une nouvelle technique de luminescence qui utilise les radiations d’un plasma induit par laser comme source d’excitation[1]. Plusieurs dispositifs expérimentaux peuvent être utilisés pour enregistrer la PIL, en utilisant le plasma généré directement à la surface de l’échantillon[1,2], ou indirectement, c’est-à-dire dans l’atmosphère[3,4]. La seconde méthode est complètement non-destructive mais ne permet pas l’analyse conjointe de la composition élémentaire par spectroscopie de plasma induit par laser (LIBS). Nous avons comparé les deux méthodes appliquées, entre autres, à la calcite (CaCO3), en utilisant un dispositif classique pour la PIL combinée à la LIBS (Figure a), et un autre pour la PIL «indirecte» (Figure b). L’emploi d’une caméra couleur synchronisée permet d’enregistrer des images PIL qui peuvent être assemblées afin d‘obtenir très rapidement une cartographie de luminescence de la surface d’un échantillon. En effet, la taille du plasma, qui détermine l’étendue de la zone excitée, est plus grande que le pas de déplacement généralement fixé lors de l’acquisition des cartographies LIBS. Il est dès lors possible d’augmenter la longueur du pas et de diminuer ainsi le temps analytique. Pour les échantillons testés, les deux méthodes fournissent des résultats similaires entre eux et similaires aussi à ceux obtenus par cathodoluminescence, ce qui laisse à penser que les électrons sont ici la source principale d’excitation. Cependant, uniquement les centres de luminescence à longue durée de vie ne sont accessibles car un délai de l’ordre de quelques millisecondes doit être appliqué entre le tir laser et le début de l’enregistrement afin de garantir que le brouillard formé par le plasma refroidit soit complètement dissipé. Références 1. M. Gaft, L. Nagli, Y. Groisman, Optical Materials. 368-375, 34 (2011) 2. M. Gaft, Y. Raichlin, F. Pelascini, G. Panzer, V. Motto-Ros, Spectrochimica Acta Part B. 12-19, 151 (2019) 3. E. Clavé, M. Gaft, V. Motto-Ros, C. Fabre, O. Forni, O. Beyssac, S. Maurice, R.C. Wiens, B. Bousquet, Spectrochimica Acta Part B. 106111, 177 (2021) 4. S. Veltri, M. Barberio, C. Liberatore, M. Sciscio, A. Laramée, L. Palumbo, F. Legaré, P. Antici, App. Phys. Lett. 021114, 110 (2017

LIBS profiles of sedimentary sections: a new tool for paleoclimatic and paleoenvironmental reconstructions?

peer reviewedReconstructing climates and/or environments of the past requires analysis of sedimentary sections based on profiles of various geological data (geochemistry, sedimentology, mineralogy, paleontology, ...). LIBS analysis can be carried out with a fast acquisition rate on minimally-prepared samples, allowing measurement of large geological sample sets such as sedimentary sections. Here we show preliminary results obtained from a field and a core section to illustrate the potential of LIBS for paleoclimatic and paleoenvironmental studies. The studied field section consisted in 6 m thick Devonian siliciclastics with varying carbonate content used as a reference for cyclostratigraphy (New York State, USA [1]). 300 samples were analyzed manually in less than two days and the results showed very good match with the XRF measurements previously used for astrochronology, including productivity (Ca) and detrital (Ti, Al, etc.) proxies. Therefore, astronomically-forced climatic cycles could be analyzed based on LIBS data as it is reliably done with XRF. The studied core section, which consists of 150 m of Ypresian to Bartonian formations (Le Tillet borehole, France) was more challenging for LIBS measurement as it consists of both soft siliciclastic sediments and consolidated carbonate rocks [2]. Therefore, the 157 selected samples were powdered and fixed onto double-sided adhesive and automatically analyzed with the LIBS within about 1 hour. The obtained data, still under interpretation, showed that some elemental ratios such as Cs/k and Li/k exhibit interesting correlations with mineralogical and environmental data (Fig. 1)