Les métaux rares, comme le niobium (Nb), le tantale (Ta), le tungstène (W) et l'étain (Sn), sont définis comme des «ressources stratégiques» ou des «matériaux critiques». Dans cette étude, nous prenons les gisements de Nb de Huangshan et de Ta de Songshugang dans le complexe de Lingshan, province de Jiangxi, en Chine du Sud, comme exemples. Les roches de ce gisement sont classées en deux catégories en fonction de la présence de micas riches en Nb et de la quantité de columbite-tantalites: granites à grain moyen avec des micas riches en Nb et sans columbite-tantalites, et granites à grain fin et pegmatites riches en columbite-tantalites. Ces columbite-tantalites sont riches en Nb et pauvres en Mn, les classant comme columbite. Ces columbites ont des zonations complexes liées à des processus répétitifs. Notre travail indique plutôt que la formation de tels minéraux est liée à des processus de mélanges multiples avec au moins deux types de magmas. Les granites à grain moyen dans la suite Huangshan sont différents des autres granites du complexe de Lingshan par la composition de leurs micas: Li-annite (granite MA) et "protolithionite" (granite MP). Ils sont caractérisés par des teneurs Nb élevées (moyenne de 144 ppm en MP et 158 ppm en MA) et des rapports Nb/Ta très élevés (moyenne 15,3 en MP et 31,2 en MA). Le niobium est principalement hébergé dans les micas, avec une teneur moyenne en Nb de 1347 ppm dans les Li annites, et 884 ppm dans le «protolithionite», concentrations encore jamais mesurées dans les micas d’origine magmatique. Avec un contenu estimé à ~80 kt Nb, les granites de Huangshan représentent un nouveau style potentiel de ressource de Nb. Le granite à albite de Songshugang est localisé dans l'ouest du complexe de Lingshan et est enrichi en Ta. Le granite de Songshugang n’affleure pas et est se trouve sous des couches de granites à feldspath K-topaze, de greisens et de pegmatite. Tous les granites et pegmatites sont fortement peralumineux. Les minéraux de columbite-tantalites, de zircons et de cassitérites sont constants pour chaque type de roches et présentent les mêmes textures bi-phasées. Les caractéristiques pétrographiques indiquent que le stade précoce de columbite et de zircon ont été formés dans un environnement strictement magmatique. Le stade postérieur de ces minéraux a été influencé par des circulations fluides à la transition magmatique-hydrothermale. Les micas montrent également une texture en deux étapes, avec une grande quantité de d’inclusions de columbite-tantalites. L'enrichissement en Rb dans les bordures (Znw-II) est le résultat d’un fractionnement magmatique, comme démontré par la diminution de la teneur en Nb (16,3-108 ppm comparé avec 109-313 ppm pour le coeur). Cependant, les teneurs faibles et invariables du Ta, W et Sn démontrent que le magma résiduel n'a eu aucune influence sur les processus post-magmatiques postérieurs, contrairement aux minéraux de columbite-tantalites. Enfin, les datations U-Pb in-situ sur zircons et columbite-tantalites démontrent que les granites de Huangshan et de Songshugang se sont mis en place vers 130 Ma durant l’épisode tardi-Yanshanien (Crétacé), au même moment que l’ensemble des roches magmatiques formant le complexe de Lingshan. Ce résultat indique que cette période géologique est d’intérêt pour la formation de ressources en Nb-Ta, définissant une nouvelle période géologique prospective pour ces ressources / Rare metals, including niobium (Nb), tantalum (Ta), tungsten (W) and tin (Sn), are defined as “strategic resources” or “critical materials”. For this work, we studied the Huangshan Nb deposit and Songshugang Ta deposit, in the Lingshan complex, Jiangxi Province, South China, as examples. The rocks from Huangshan granite are classified in two categories based on the occurrence of Nb-rich mica and the amount of columbite-tantalites minerals: medium-grained granites with Nb-rich mica and devoided of columbite-tantalites and fine-grained granites and pegmatites rich in columbite-tantalite minerals. Columbite-tantalite minerals are classified as columbite-(Fe), and characterized by complex zonings with various “go and back” processes, indicating that their formation is linked to multi-mixing processes of two different magma sources. The medium-grained granites in the Huangshan suite differed from the other granites of the Lingshan complex by their mica compositions: lithian annite (MA granite) and “protolithionite” (MP granite). They are characterized by elevated Nb contents (average 144 ppm in MP and 158 ppm in MA) and very high Nb/Ta ratios (average 15.3 in MP and 31.2 in MA). Niobium is mainly hosted in the micas, with an average Nb content of 1,347 ppm in the lithian annite, and 884 ppm in the “protolithionite”. Such contents are the highest ever reported in magmatic-related micas. With an estimated content of ~80 kt Nb, the Huangshan granites represent a new style of potential Nb resource. The Songshugang albite granite is found in the west of Lingshan complex and is specifically enriched in Ta. The major Songshugang albite granite is buried and covered by layers of K-feldspar granite, greisen and pegmatite. All the granites are strongly peraluminous. The compositions of columbite-tantalite minerals, the zircons and cassiterites are constant and display a similar two-stage texture. Petrographic features indicate that the early-stage columbite and zircon were formed in magmatic environment, whereas the later-stage of rare-element minerals were influenced by fluid fluxes at the magmatic-hydrothermal transitional stage. Micas also show a two-stage texture. The Rb-enrichment in the margin of the zinnwaldite is the result of magmatic fractionation, as also demonstrated by the decrease of Nb contents (16.3-108 ppm compare with core of 109-313 ppm). The invariable low contents of Ta, W and Sn demonstrate that the residual melt has no influence on later post-magmatic stages, contrary to the columbite minerals. Finally, in-situ U-Pb dating of zircon and columbite-tantalite by SIMS and LA-ICP-MS indicates that both Huangshan and Songshugang granites were emplaced at ca. 130 Ma during Later Yanshanian (or Cretaceous) and contemporary with the formation of the Lingshan complex. This result indicates that the Later Yanshanian is a prospective geological period for Nb-Ta deposits, and this result enlarges the time frame of rare-metal mineralization.

O Granito Desemborque, um corpo de forma, aproximadamente, circular, situado no sul do Estado de São Paulo, tem área aflorante de 50 km2 e é representado por um biotita sienogranito. O caráter peraluminoso com teores significativos de K2O e Na2O, juntamente com o baixo conteúdo de CaO, altas razões Fe/Mg, elevados valores de SiO2 e de elementos traços como Zr, Nb e Y, atestam a afinidade alcalina do granito que pode ser classificado como do tipo A. Os teores de Y refletem a presença de fases acessórias como parisita de Ce, itrofluorita e monazita. Columbita, zircão rico em háfnio e cassiterita presentes na associação de minerais acessórios do Granito Desemborque foram analisados semiquantitativamente (teores em peso) por MEV-EDS. Com isso foi possível discriminar duas fases evolutivas para a geração de alguns dos minerais de metais raros associados ao corpo; uma francamente magmática (com subfases granítica e pegmatítica) e uma fase hidrotermal. A columbita (teor médio de Nb2O5 de 66,2% e 6,5% de Ta2O5) é nitidamente gerada na fase magmática sendo que na subfase granítica ela tem presença ubíqua e caráter disseminado. O zircão, por sua vez, ocorre nas duas subfases magmática, sendo que na subfase granítica ele teria um caráter mais tardio. O teor médio das análises foi de 9,3% de HfO2, classificando-o como um zircão rico em háfnio. Na fase hidrotermal, é que se desenrolariam os processos de enriquecimento em Hf desse mineral. A cassiterita, os minerais de REE e boa parte dos minerais radioativos têm a sua formação restrita a fase hidrotermal. Dentre as classificações propostas para granitos mineralizados, o Granito Desemborque se aproxima do tipo peralcalino mineralizado a metais raros com tendência a formar depósitos ou ocorrências de Nb e ETR. Os senões seriam o fato desse corpo não ser peralcalino (ele é peraluminosso) e dos potenciais minerais de Y e ETR só terem sido registrados como inclusões minerais hospedadas nos grãos de cassiterita (ítriocolumbita) e de zircão (xenotímio). A falta de concentrações minerais econômicas de Nb-Hf-Sn associadas ao Granito Desemborque pode ser imputada ao caráter anídrico do magma (tipo-A) e a falta ou limitação do fraturamento hidráulico. A ausência de concentrações minerais econômicas em virtude da remoção erosiva da zona de cúpula não se encontra de acordo com os resultados prospectivos encontrados, pois, a presença da cromita nas amostras de leito ativo coletadas nas drenagens estabelecidas bem no cerne do corpo granítico indica a preservação de restos de pendentes de teto da rocha encaixante (ortognaisses com boudins de rochas ultrabásicas). / The Desemborque Granite, a body almost of circular shape, placed in the southernmost part of São Paulo State, has an area of ca. 50 km2. and it is represented by a sienogranite biotite. Its peraluminous features with significant contents of K2O and Na2O, together with low CaO contents, high Fe/Mg ratios, elevated values of SiO2 and trace elements as Zr, Nb and Y, assure the granite alcaline affinity that can be classified as type A. The Y numbers reflect the presence of acessory phases as parasite de Ce, yttrofluorite and monazite. Columbite, zircon rich in hafnium and cassiterite presented in the association of accessory minerals of the Granite Desemborque were semiquantitatively analysed(values in weight) by MEV-EDS. Because of this it was possible to detail the two evolutional phases for the generation of some minerals of rare metals associated to the body; one fairly magmatic (with granitic sub-phases and pegmatitic) and an hidrotermal phase. Columbite (Nb2O5 mean value 66,2% and 6,5% Ta2O5) is clearly generated in magmatic phase and in the granitric sub-phase it has ubiquitous presence and disseminated character. Zircon, in its turn, occurs in the two magmatic sub-phases, and in the granitic sub-phase it would have a later character. The mean value of the analysis was of 9,3% for HfO2, classifying it as a zircon rich in hafnium. In the hidrotermal phase, the enrichment proccesses are developed in Hf of this mineral. Cassiterite, the REE minerals and a large number of radiactive mineral have their formation restricted to the hidrotermal phase. Amongst the proposed classification for the mineralized granites, the Granite Desemborque has an peralkalkine mineralized approach to rare metals with a wide tendency to create deposits or Nb and REE occurences. The opposition could be the fact that this body is not peralkaline (it is peraluminous) and the Y and REE mineral potentials only have been recorded in the hosted mineral inclusions in the cassiterite grains (yttrocolumbite) and of zircon (xenotímio). The lack of profitable Nb-Hf-Sn mineral concentrations associated to the Granite Desemborque can be magma anhydrous character (type-A) and the lack or limitation of the hydraulic fracturing. The absence of profitable mineral concentrations because of the erosive removal of the apical zone is not in agreement with the prospective results found, once the presence of chromite in the samples of the active stream bed collected at the draining which is established exactly in the basis of the granite body indicates the preservation of remaints roof pendant the wall rocks (ortognaisses with boudins of ultrabasic rocks).

O Granito Desemborque, um corpo de forma, aproximadamente, circular, situado no sul do Estado de São Paulo, tem área aflorante de 50 km2 e é representado por um biotita sienogranito. O caráter peraluminoso com teores significativos de K2O e Na2O, juntamente com o baixo conteúdo de CaO, altas razões Fe/Mg, elevados valores de SiO2 e de elementos traços como Zr, Nb e Y, atestam a afinidade alcalina do granito que pode ser classificado como do tipo A. Os teores de Y refletem a presença de fases acessórias como parisita de Ce, itrofluorita e monazita. Columbita, zircão rico em háfnio e cassiterita presentes na associação de minerais acessórios do Granito Desemborque foram analisados semiquantitativamente (teores em peso) por MEV-EDS. Com isso foi possível discriminar duas fases evolutivas para a geração de alguns dos minerais de metais raros associados ao corpo; uma francamente magmática (com subfases granítica e pegmatítica) e uma fase hidrotermal. A columbita (teor médio de Nb2O5 de 66,2% e 6,5% de Ta2O5) é nitidamente gerada na fase magmática sendo que na subfase granítica ela tem presença ubíqua e caráter disseminado. O zircão, por sua vez, ocorre nas duas subfases magmática, sendo que na subfase granítica ele teria um caráter mais tardio. O teor médio das análises foi de 9,3% de HfO2, classificando-o como um zircão rico em háfnio. Na fase hidrotermal, é que se desenrolariam os processos de enriquecimento em Hf desse mineral. A cassiterita, os minerais de REE e boa parte dos minerais radioativos têm a sua formação restrita a fase hidrotermal. Dentre as classificações propostas para granitos mineralizados, o Granito Desemborque se aproxima do tipo peralcalino mineralizado a metais raros com tendência a formar depósitos ou ocorrências de Nb e ETR. Os senões seriam o fato desse corpo não ser peralcalino (ele é peraluminosso) e dos potenciais minerais de Y e ETR só terem sido registrados como inclusões minerais hospedadas nos grãos de cassiterita (ítriocolumbita) e de zircão (xenotímio). A falta de concentrações minerais econômicas de Nb-Hf-Sn associadas ao Granito Desemborque pode ser imputada ao caráter anídrico do magma (tipo-A) e a falta ou limitação do fraturamento hidráulico. A ausência de concentrações minerais econômicas em virtude da remoção erosiva da zona de cúpula não se encontra de acordo com os resultados prospectivos encontrados, pois, a presença da cromita nas amostras de leito ativo coletadas nas drenagens estabelecidas bem no cerne do corpo granítico indica a preservação de restos de pendentes de teto da rocha encaixante (ortognaisses com boudins de rochas ultrabásicas). / The Desemborque Granite, a body almost of circular shape, placed in the southernmost part of São Paulo State, has an area of ca. 50 km2. and it is represented by a sienogranite biotite. Its peraluminous features with significant contents of K2O and Na2O, together with low CaO contents, high Fe/Mg ratios, elevated values of SiO2 and trace elements as Zr, Nb and Y, assure the granite alcaline affinity that can be classified as type A. The Y numbers reflect the presence of acessory phases as parasite de Ce, yttrofluorite and monazite. Columbite, zircon rich in hafnium and cassiterite presented in the association of accessory minerals of the Granite Desemborque were semiquantitatively analysed(values in weight) by MEV-EDS. Because of this it was possible to detail the two evolutional phases for the generation of some minerals of rare metals associated to the body; one fairly magmatic (with granitic sub-phases and pegmatitic) and an hidrotermal phase. Columbite (Nb2O5 mean value 66,2% and 6,5% Ta2O5) is clearly generated in magmatic phase and in the granitric sub-phase it has ubiquitous presence and disseminated character. Zircon, in its turn, occurs in the two magmatic sub-phases, and in the granitic sub-phase it would have a later character. The mean value of the analysis was of 9,3% for HfO2, classifying it as a zircon rich in hafnium. In the hidrotermal phase, the enrichment proccesses are developed in Hf of this mineral. Cassiterite, the REE minerals and a large number of radiactive mineral have their formation restricted to the hidrotermal phase. Amongst the proposed classification for the mineralized granites, the Granite Desemborque has an peralkalkine mineralized approach to rare metals with a wide tendency to create deposits or Nb and REE occurences. The opposition could be the fact that this body is not peralkaline (it is peraluminous) and the Y and REE mineral potentials only have been recorded in the hosted mineral inclusions in the cassiterite grains (yttrocolumbite) and of zircon (xenotímio). The lack of profitable Nb-Hf-Sn mineral concentrations associated to the Granite Desemborque can be magma anhydrous character (type-A) and the lack or limitation of the hydraulic fracturing. The absence of profitable mineral concentrations because of the erosive removal of the apical zone is not in agreement with the prospective results found, once the presence of chromite in the samples of the active stream bed collected at the draining which is established exactly in the basis of the granite body indicates the preservation of remaints roof pendant the wall rocks (ortognaisses with boudins of ultrabasic rocks).

De två kemiskt nära besläktade metallerna niob (Nb) och tantal (Ta) räknas av Europakommissionen som kritiska råmaterial. Detta på grund av en kraftigt ökad efterfrågan och en geografiskt koncentrerad global produktion av dem. Det här arbetet utgör en del av ett större projekt som bedrivs av EuroGeoSurveys (EGS); GeoERA FRAME, som har till syfte att kartlägga förekomsten av kritiska råmaterial inom EU. Två granitpegmatitiska prov från Kolsva fältspatgruva har undersökts med avseende på deras kemi och mineralogi; dels sådana som tentativt identifierats som kolumbitmineral och dels sådana som innehåller ett samarskitliknande mineral. I arbetet har tre huvudsakliga analysmetoder använts: 1) optisk mikroskopi, 2) svepelektronmikroskopi (SEM) med energidispersiv mikrokemisk analys (EDS), samt 3) pulverröntgendiffraktionsanalys (XRD). De kemiska analyserna som genomfördes på ”kolumbit-proven” visade att de bestod av kolumbit-(Fe), med generell formel AB2O6 och med en järndominans i A-katjonposition och niobdominans i B-katjonposition. Analyserna visad även på förekomst av mineral tillhörande pyroklorsupergruppen. De samarskitartade mineralen uppvisade en partiell likhet med samarskitgruppmineral (generell formel ABO4), men med hög grad av metamiktisering, dåliga stökiometrier, låga REE-halter, samt med varierande järn- och kalciumdominans i tentativ A-katjonposition och niobdominans i B-katjonpositionen. Även aluminiumsilikater, mineral från spinellgruppen samt hematit påvisades. Uppsprickning av de metamikta och spröda samarskitartade mineralen har möjliggjort en fluidmedierad omvandling, vilket bl.a. lett till bildning av sekundär radiogen blyglans. Resultaten av undersökningarna bekräftar att Kolsvapegmatiten representerar ett lokalt niob-tantalmineraliserat system. / The two chemically related metals niobium (Nb) and tantalum (Ta) are classified by the European Commission as critical raw materials. This is due to a highly increased demand and a limited global supply situation for these metals. This work is a part of a larger project run by EuroGeoSurveys (EGS); the GeoERA FRAME, which aims to map the distribution of critical raw materials in the EU. Two granitic pegmatite samples from the Kolsva feldspar mine were studied with regards to their chemistry and mineralogy. They had been tentatively identified as consisting of a columbite mineral and a samarskite-like mineral, respectively. In the project, three main analytical methods have been used: 1) optical microscopy, 2) scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), and 3) powder X-ray diffraction analysis (XRD). The analyses performed on the “columbite samples” indicated that most of them were columbite-(Fe), general formula AB2O6, with an iron dominance in the A-cation position and niobium dominance in the B-cation position. The analyses also indicated the presence of minerals belonging to the pyrochlore supergroup. The analyses of the samarskite-like minerals yielded results showing a partial resemblance to the samarskite group minerals (general formula ABO4), but with a high degree of metamictisation, poor stoichiometries, low to very low REE contents, variable iron and calcium-dominance in a tentative A-cation position and niobium-dominance in the B-cation position. Aluminium silicates, minerals from the spinel group and hematite were also observed in this assemblage. Fracturing of the brittle, metamict samarskite-like minerals have enabled a fluid-mediated alteration, which a.o. led to the formation of secondary radiogenic galena. The study confirms that the Kolsva pegmatite represents a locally Nb-Ta mineralised system.