The early Cretaceous anorogenic Erongo Granite of Namibia is known to host abundant boron mineralization in rounded, quartz-tourmaline clusters and in NYF-type miarolitic, pegmatitic cavities. Rock and mineral samples were taken from the bulk granite, tourmaline nests, and miarolitic cavities and analyzed using a variety of modern analytical techniques. Geochemical and mineralogical data suggest substantial input from the metasedimentary rocks of the Damara orogen was important in the genesis of the Erongo Granite magma. The geochemical signature of the Damara orogen is most evident in the tourmaline clusters and miarolitic cavities, where fractional crystallization accumulated volatile and incompatible elements enough to exsolve a second fluid phase and induce drastic textural and mineralogical changes. As a result, the geochemical character of the pegmatitic cavities is far removed from that of classic NYF-type systems, where boron mineralization is usually not observed.

Subvolcanically emplaced granitic, miarolitic pegmatites associated with the White Mountain Igneous Province (WMIP), New Hampshire, were sampled and analyzed using modern analytical techniques including X-ray fluorescence, electron microprobe, scanning electron microscopy, and direct-coupled plasma spectrophotometry. Analytical results suggest that all the sampled miarolitic pegmatites from this study are petrogenetically related to the same intrusive suite, the WMIP. Based on the geochemical data, all the samples formed in an anorogenic tectonic setting and are rift-related. They are classified as NYF-type and plot in the “within plate granite” field on tectonic discrimination diagrams. The majority of the samples are peraluminous, A1-type granites. The trace element abundances on the spider diagram and chondrite-normalized diagram, which include a pronounced negative Eu anomaly and REE enrichments, are consistent with these miarolitic pegmatites resulting from a strongly fractionated granitic parental melts, but less fractionated than the classic NYF-systems such as South Platte (Simmons et al. 1987) and the Wausau Syenite Complex (Meyers et al. 1984).

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.