O carbonatito Fazenda Varela é um ferrocarbonatito que possui altos teores de ETR (>1%), que são elementos considerados estratégicos por muitos países devido à importância econômica. Este carbonatito faz parte do distrito alcalino de Lages (SC), que possui idade entre 63 e 81 ± 8 Ma. A rocha ocorre na forma de veios que intrudem os sedimentos da Formação Rio Bonito (Bacia do Paraná), formando brechas metassomatizadas. A mineralogia magmática do carbonatito é composta principalmente por ankerita e ferrodolomita, além de pirita, ortoclásio e quartzo. O ferrocarbonatito foi afetado por eventos tardi a pós-magmáticos, que gerou domínios hidrotermais, onde se depositaram barita, apatita, quartzo, calcita, ferrodolomita e parisita-(Ce). A parisita-(Ce) é o principal mineral de ETR e não possui fluorita associada, diferentemente dos outros depósitos de fluorcarbonatos do mundo. A parisita-(Ce) é tardia, depositada em meio aos domínios hidrotermais e intersticial a todos os minerais. Nas imagens ao MEV é possível identificar que este mineral forma policristais fibrorradiados bem desenvolvidos com crescimento sintaxial entre parisita-(Ce) e synchysita-(Ce). Este crescimento pode ser identificado nestas imagens pelas bandas brancas e cinza, com proporções de Ca e ETR diferentes em cada banda. A composição média do policristal de parisita-(Ce) apresenta excesso de Ca e deficiência de ETR e de F em relação a uma composição ideal, devido ao crescimento sintaxial. O padrão de ETR da parisita-(Ce) é semelhante ao das amostras de carbonatito. Este mineral se formou em meio com baixa atividade de F e altas atividades de Ca e CO3, a partir de um fluido hidrotermal ascendente, que interagiu intensamente com o carbonatito, ocasionando a partição preferencial dos ETRL provavelmente na forma de complexos clorados. Sua cristalização pode ter ocorrido pelo aumento na atividade de HCO3- pela dissolução do carbonato primário ou pela elevação do pH pelo aporte de água da rocha encaixante quartzo-feldspática. / The Fazenda Varela carbonatite is a ferrocarbonatite which has high contents of REE (> 1%), that are considered by many countries as strategic elements due to its economic importance. This carbonatite is part of the Lages alkaline district (SC) witch age is between 63 and 81 ± 8 Ma. The rock occurs as veins cutting the sediments of the Rio Bonito Formation (Paraná Basin) forming a metasomatized breccia. The magmatic mineralogy of the carbonatite is composed mainly by ankerite and ferrodolomite, together pyrite, orthoclase and quartz. The ferrocarbonatite was affected by late to post-magmatic events that generated hydrothermal areas where barite, apatite, quartz, calcite, ferrodolomite and parisite-(Ce) were deposited. The parisite-(Ce) is the main REE mineral, and without associated fluorite, different to others fluorcarbonates deposits of the world. The parisite-(Ce) is a late mineral, and was deposited in hydrothermal areas among all minerals. With the SEM images was possible identify that this mineral form well developed fibroradiated polycrystals with sintaxial growth between parisite-(Ce) and synchysite-(Ce). This growth can be identified in SEM images by their gray and white bands, with different Ca and REE ratios in each band. The average composition of the parisite-(Ce) polycrystal presents excess of Ca and deficiency of REE and F in relation to an ideal composition, due to their sintaxial growth. The pattern of the REE parisita-(Ce) is similar to those from the carbonatite samples. This mineral was formed in an environment with low F activity and high activities of Ca and CO3, from a rising hydrothermal fluid, which interacted strongly with carbonatite, resulting in the preferential partitioning of LREE, probably as chlorinated complexes. The parisite-(Ce) crystallization may have occurred by increasing HCO3 activity by primary carbonate dissolution or by the pH rising do to the contribution of water from the quartz-feldspar host rock.

O carbonatito Fazenda Varela é um ferrocarbonatito que possui altos teores de ETR (>1%), que são elementos considerados estratégicos por muitos países devido à importância econômica. Este carbonatito faz parte do distrito alcalino de Lages (SC), que possui idade entre 63 e 81 ± 8 Ma. A rocha ocorre na forma de veios que intrudem os sedimentos da Formação Rio Bonito (Bacia do Paraná), formando brechas metassomatizadas. A mineralogia magmática do carbonatito é composta principalmente por ankerita e ferrodolomita, além de pirita, ortoclásio e quartzo. O ferrocarbonatito foi afetado por eventos tardi a pós-magmáticos, que gerou domínios hidrotermais, onde se depositaram barita, apatita, quartzo, calcita, ferrodolomita e parisita-(Ce). A parisita-(Ce) é o principal mineral de ETR e não possui fluorita associada, diferentemente dos outros depósitos de fluorcarbonatos do mundo. A parisita-(Ce) é tardia, depositada em meio aos domínios hidrotermais e intersticial a todos os minerais. Nas imagens ao MEV é possível identificar que este mineral forma policristais fibrorradiados bem desenvolvidos com crescimento sintaxial entre parisita-(Ce) e synchysita-(Ce). Este crescimento pode ser identificado nestas imagens pelas bandas brancas e cinza, com proporções de Ca e ETR diferentes em cada banda. A composição média do policristal de parisita-(Ce) apresenta excesso de Ca e deficiência de ETR e de F em relação a uma composição ideal, devido ao crescimento sintaxial. O padrão de ETR da parisita-(Ce) é semelhante ao das amostras de carbonatito. Este mineral se formou em meio com baixa atividade de F e altas atividades de Ca e CO3, a partir de um fluido hidrotermal ascendente, que interagiu intensamente com o carbonatito, ocasionando a partição preferencial dos ETRL provavelmente na forma de complexos clorados. Sua cristalização pode ter ocorrido pelo aumento na atividade de HCO3- pela dissolução do carbonato primário ou pela elevação do pH pelo aporte de água da rocha encaixante quartzo-feldspática. / The Fazenda Varela carbonatite is a ferrocarbonatite which has high contents of REE (> 1%), that are considered by many countries as strategic elements due to its economic importance. This carbonatite is part of the Lages alkaline district (SC) witch age is between 63 and 81 ± 8 Ma. The rock occurs as veins cutting the sediments of the Rio Bonito Formation (Paraná Basin) forming a metasomatized breccia. The magmatic mineralogy of the carbonatite is composed mainly by ankerite and ferrodolomite, together pyrite, orthoclase and quartz. The ferrocarbonatite was affected by late to post-magmatic events that generated hydrothermal areas where barite, apatite, quartz, calcite, ferrodolomite and parisite-(Ce) were deposited. The parisite-(Ce) is the main REE mineral, and without associated fluorite, different to others fluorcarbonates deposits of the world. The parisite-(Ce) is a late mineral, and was deposited in hydrothermal areas among all minerals. With the SEM images was possible identify that this mineral form well developed fibroradiated polycrystals with sintaxial growth between parisite-(Ce) and synchysite-(Ce). This growth can be identified in SEM images by their gray and white bands, with different Ca and REE ratios in each band. The average composition of the parisite-(Ce) polycrystal presents excess of Ca and deficiency of REE and F in relation to an ideal composition, due to their sintaxial growth. The pattern of the REE parisita-(Ce) is similar to those from the carbonatite samples. This mineral was formed in an environment with low F activity and high activities of Ca and CO3, from a rising hydrothermal fluid, which interacted strongly with carbonatite, resulting in the preferential partitioning of LREE, probably as chlorinated complexes. The parisite-(Ce) crystallization may have occurred by increasing HCO3 activity by primary carbonate dissolution or by the pH rising do to the contribution of water from the quartz-feldspar host rock.

O carbonatito Fazenda Varela é um ferrocarbonatito que possui altos teores de ETR (>1%), que são elementos considerados estratégicos por muitos países devido à importância econômica. Este carbonatito faz parte do distrito alcalino de Lages (SC), que possui idade entre 63 e 81 ± 8 Ma. A rocha ocorre na forma de veios que intrudem os sedimentos da Formação Rio Bonito (Bacia do Paraná), formando brechas metassomatizadas. A mineralogia magmática do carbonatito é composta principalmente por ankerita e ferrodolomita, além de pirita, ortoclásio e quartzo. O ferrocarbonatito foi afetado por eventos tardi a pós-magmáticos, que gerou domínios hidrotermais, onde se depositaram barita, apatita, quartzo, calcita, ferrodolomita e parisita-(Ce). A parisita-(Ce) é o principal mineral de ETR e não possui fluorita associada, diferentemente dos outros depósitos de fluorcarbonatos do mundo. A parisita-(Ce) é tardia, depositada em meio aos domínios hidrotermais e intersticial a todos os minerais. Nas imagens ao MEV é possível identificar que este mineral forma policristais fibrorradiados bem desenvolvidos com crescimento sintaxial entre parisita-(Ce) e synchysita-(Ce). Este crescimento pode ser identificado nestas imagens pelas bandas brancas e cinza, com proporções de Ca e ETR diferentes em cada banda. A composição média do policristal de parisita-(Ce) apresenta excesso de Ca e deficiência de ETR e de F em relação a uma composição ideal, devido ao crescimento sintaxial. O padrão de ETR da parisita-(Ce) é semelhante ao das amostras de carbonatito. Este mineral se formou em meio com baixa atividade de F e altas atividades de Ca e CO3, a partir de um fluido hidrotermal ascendente, que interagiu intensamente com o carbonatito, ocasionando a partição preferencial dos ETRL provavelmente na forma de complexos clorados. Sua cristalização pode ter ocorrido pelo aumento na atividade de HCO3- pela dissolução do carbonato primário ou pela elevação do pH pelo aporte de água da rocha encaixante quartzo-feldspática. / The Fazenda Varela carbonatite is a ferrocarbonatite which has high contents of REE (> 1%), that are considered by many countries as strategic elements due to its economic importance. This carbonatite is part of the Lages alkaline district (SC) witch age is between 63 and 81 ± 8 Ma. The rock occurs as veins cutting the sediments of the Rio Bonito Formation (Paraná Basin) forming a metasomatized breccia. The magmatic mineralogy of the carbonatite is composed mainly by ankerite and ferrodolomite, together pyrite, orthoclase and quartz. The ferrocarbonatite was affected by late to post-magmatic events that generated hydrothermal areas where barite, apatite, quartz, calcite, ferrodolomite and parisite-(Ce) were deposited. The parisite-(Ce) is the main REE mineral, and without associated fluorite, different to others fluorcarbonates deposits of the world. The parisite-(Ce) is a late mineral, and was deposited in hydrothermal areas among all minerals. With the SEM images was possible identify that this mineral form well developed fibroradiated polycrystals with sintaxial growth between parisite-(Ce) and synchysite-(Ce). This growth can be identified in SEM images by their gray and white bands, with different Ca and REE ratios in each band. The average composition of the parisite-(Ce) polycrystal presents excess of Ca and deficiency of REE and F in relation to an ideal composition, due to their sintaxial growth. The pattern of the REE parisita-(Ce) is similar to those from the carbonatite samples. This mineral was formed in an environment with low F activity and high activities of Ca and CO3, from a rising hydrothermal fluid, which interacted strongly with carbonatite, resulting in the preferential partitioning of LREE, probably as chlorinated complexes. The parisite-(Ce) crystallization may have occurred by increasing HCO3 activity by primary carbonate dissolution or by the pH rising do to the contribution of water from the quartz-feldspar host rock.

Rare earth elements (REE) are considered as critical and non-substitutable metals for electronics and green technology. A greater diversity of supply is needed and the REE occur in a wide range of REE- and REE-bearing minerals within different ore deposit types. The beneficiation processes for REE ores can vary widely based on their mineralogy and texture. It is, therefore, essential to understand the mineralogical characteristics when designing processing routes. Little research was carried out on this topic until the last few years, apart from bastnäsite, monazite, and xenotime, and most REE minerals in deposits currently under exploration are poorly understood in terms of processing characteristics. This geometallurgical study brings together the results of process mineralogy and minerals processing to recover synchysite-(Ce) and apatite from the carbonatite at Songwe Hill, Malawi. This deposit is unusual because it is a potential carbonatite source of both LREE and HREE. Results from previous flowsheet development studies on this deposit suggest that flotation is the most promising processing route and therefore this study concentrated on testing this hypothesis. It sought to understand the mineralogy better in order to predict processing response and carried out a series of flotation experiments to improve the processing efficiency. It also investigated the fundamental magnetic properties of the rare earth fluorcarbonate minerals (including synchysite) and established for the first time that there is a systematic variation in their properties that can be applied to minerals processing. Eight samples of REE carbonatite drill core, crushed to 1700 μm, and a composite sample ground to 53 μm and 38 μm were used throughout this research. Automated mineralogy (QEMSCAN®) was applied to determine the mineralogical characteristics of the ore deposit. This utilised a novel species identification protocol (SIP) for REE minerals in carbonatites, which was validated by electron microscopy (SEM-EDS), and electron probe microanalysis (EPMA). The principal REE minerals at Songwe are the REE fluorcarbonates, synchysite-(Ce) and also parisite-(Ce). These are challenging minerals for automated mineralogical techniques owing to their chemical similarity and common occurrence either as bladed (needle-like) crystals, which is the main textural type at Songwe Hill, or as syntaxial intergrowths. However, using the SIP developed in this study, the QEMSCAN® can distinguish between these minerals based on the Ca content and can also recognise syntaxial intergrowths on a scale of about > 20 μm. The Songwe Hill carbonatite hosts about 6 wt% to 10 wt% of REE- and REE-bearing minerals. Apatite hosts the more valuable HREE in addition to P2O5, followed by synchysite-(Ce)/parisite-(Ce) (mainly synchysite-(Ce)), and minor florencite-(Ce), which host the LREE. These minerals are commonly associated with the predominant gangue minerals, ankerite and calcite, and, to a lesser extent Fe- Ox/CO3 and K-feldspar, strontianite and baryte. Fundamental magnetic properties of pure REE fluorcarbonate single crystal minerals using a vibrating sample magnetometer (VSM) were determined. The magnetic susceptibility is highly dependent on the mineral composition. It is positive (paramagnetic) for bastnäsite-(Ce) and gradually decreases as the amount of Ca increases in parisite-(Ce), becoming negative (diamagnetic) for the Ca-rich member of the series, röntgenite. Synchysite-(Ce) in this deposit was experimentally determined by magnetic separation and behaved as a diamagnetic mineral. This can be explained by the layered structure common to the REE fluorcarbonate series minerals. Selected laboratory scale mineral processing experiments including magnetic separation and froth flotation were performed. Pre-concentration tests by magnetic separation showed a recovery of 84% for P2O5, 80% for Y2O3, and 76% for Ce2O3 in the non-magnetic product, with gangue minerals rejection of about 49% for ankerite and 48% for Fe-Ox/CO3 to the magnetic product. Apatite and synchysite-(Ce) loss to the magnetic product is mainly the result of their association with the paramagnetic minerals i.e. ankerite and Fe-Ox/CO3 as indicated by automated mineralogy. A spectrophotometer was utilised to measure the solubility of the organic chemical reagents including fatty acids and lignin sulphonate in different alkaline solutions and to determine the appropriate operating parameters for bench flotation tests. The results indicated that the solubility of fatty acids increased with increasing the pH value from 8.5 to 10.5, while the opposite was observed for lignin sulphonate. 35 bench-scale froth flotation tests under a wide range of chemical and operating conditions including pH modifiers and dosages, soluble and insoluble collectors, depressants, temperature, and conditioning time were performed. The results demonstrated that fatty acids and lignin sulphonate are sensitive to changes in pH, conditioning time, and temperature. These factors significantly affected flotation efficiency. A recovery of 86% for P2O5 and 74% for both of Y2O3 and Ce2O3 with TREO upgrading from 1.6 wt% to 3.8 wt% at a mass pull of 31% were achieved under a constant pulp pH of 9.5, elevated temperature, and long conditioning time. This study suggests that combining magnetic separation and froth flotation techniques to pre-concentrate and upgrade the REE- and REE-bearing minerals, should be considered further to minimise the cost of the chemical reagents used in froth flotation and gangue leaching.