Littérature scientifique sur le sujet « Burbankite »

AbstractThe Neoproterozoic Lofdal alkaline carbonatite complex consists of a swarm of carbonatite dykes and two plugs of calcite carbonatite known as the ‘Main’ and ‘Emanya’ carbonatite intrusions, with associated dykes and plugs of phonolite, syenite, rare gabbro, anorthosite and quartz-feldspar porphyry. In the unaltered Main Intrusion calcite carbonatite the principal rare-earth host is burbankite. As burbankite typically forms in a magmatic environment, close to the carbohydrothermal transition, this has considerable petrogenetic significance. Compositional and textural features of Lofdal calcite carbonatites indicate that burbankite formed syngenetically with the host calcite at the magmatic stage of carbonatite evolution. The early crystallisation of burbankite provides evidence that the carbonatitic magma was enriched in Na, Sr, Ba and light rare earth elements. In common with other carbonatites, the Lofdal burbankite was variably affected by alteration to produce a complex secondary mineral assemblage. Different stages of burbankite alteration are observed, from completely fresh blebs and hexagonal crystals through to complete pseudomorphs, consisting of carbocernaite, ancylite, cordylite, strontianite, celestine, parisite and baryte. Although most research and exploration at Lofdal has focused on xenotime-bearing carbonatite dykes and wall-rock alteration, this complex also contains a more typical calcite carbonatite enriched in light rare earth elements and their alteration products.

Abstract. In this study we report the synthesis of single crystals of burbankite, Na3Ca2La(CO3)5, at 5 GPa and 1073 K. The structural evolution, bulk modulus and thermal expansion of burbankite were studied and determined by two separate high-pressure (0–7.07(5) GPa) and high-temperature (298–746 K) in situ single-crystal X-ray diffraction experiments. The refined parameters of a second-order Birch–Murnaghan equation of state (EoS) are V0= 593.22(3) Å3 and KT0= 69.8(4) GPa. The thermal expansion coefficients of a Berman-type EoS are α0= 6.0(2) ×10-5 K−1, α1= 5.7(7) ×10-8 K−2 and V0= 591.95(8) Å3. The thermoelastic parameters determined in this study allow us to estimate the larger density of burbankite in the pressure-temperature range of 5.5–6 GPa and 1173–1273 K, with respect to the density of carbonatitic magmas at the same conditions. For this reason, we suggest that burbankite might fractionate from the magma and play a key role as an upper-mantle reservoir of light trivalent rare earth elements (REE3+).

AbstractCarbonatites from the Khibina Alkaline Massif (360–380 Ma), Kola Peninsula, Russia, contain one of the most diverse assemblages of REE minerals described thus far from carbonatites and provide an excellent opportunity to track the evolution of late-stage carbonatites and their sub-solidus (secondary) changes. Twelve rare earth minerals have been analysed in detail and compared with literature analyses. These minerals include some common to carbonatites (e.g. Ca-rare-earth fluocarbonates and ancylite-(Ce)) plus burbankite and carbocernaite and some very rare Ba,REE fluocarbonates.Overall the REE patterns change from light rare earth-enriched in the earliest carbonatites to heavy rare earth-enriched in the late carbonate-zeolite veins, an evolution which is thought to reflect the increasing ‘carbohydrothermal’ nature of the rock-forming fluid. Many of the carbonatites have been subject to sub-solidus metasomatic processes whose products include hexagonal prismatic pseudomorphs of ancylite-(Ce) or synchysite-(Ce), strontianite and baryte after burbankite and carbocernaite. The metasomatic processes cause little change in the rare earth patterns and it is thought that they took place soon after emplacement.

AbstractNatrocarbonatite lavas erupted from hornitos T37B and T49B at Oldoinyo Lengai (Tanzania) during 23–30 July, 2000 are unusual in containing sylvite and fluorite microcrysts together with fluorite-nyerereite intergrowths. The latter are relatively coarse grained and exhibit granular textures indicative of slow crystallization rates relative to those of their host subaerial lavas. Fluorite microcrysts are considered to be derived by the fragmentation of the fluorite-nyerereite clasts. Sylvite microcrysts contain inclusions of ferroan alabandite [(Mn0.67-0.71Fe0.33-0.29)S] and are poor in Na (1.9–7.7 wt.% Na; 6.1–23.4 mol.% NaCl). Intergrowth and microcrystal fluorite contains 1–3.5 wt.% Sr. Intergrowth nyerereite has a composition similar to that occurring as bona fide phenocrysts. The groundmass of lava erupted from hornito T37B contains nyerereite microphenocrysts (4–8 wt.% BaO) that are epitaxially mantled by barian nyerereite (12–20 wt.% BaO). The latter are compositionally and texturally distinct from the groundmass phase X, which is considered to be a burbankite-group mineral. The fluorite-nyerereite clasts are considered to be derived from the magma chamber underlying hornitos T37B and T49B, and thus representative of some of the products of crystallization of natrocarbonatite magma under hypabyssal conditions. The origins of the sylvite microcrysts cannot, as yet, be determined.

Abstract Drainage water quality is the significant environmental concern for the rare earth elements (REE) mining industry. REE deposits are associated with other metals and radioactive bearing minerals. REE mining and refining activities can generate significant quantities of liquid and solid wastes. Therefore, a long-term integrated approach covering the full mine-life cycle is required to mitigate possible environmental concerns. In the present study, two REE concentrates were prepared and all deposit lithologies of carbonatites and silicates sampled and investigated for their mineralogy, geochemistry, and their environmental behavior using kinetic testing. For the Montviel carbonatite (enriched in light rare earth elements, or LREE), the majority of REE-bearing minerals are associated with carbonates (i.e., monazite, kukharenkoite, burbankite, etc.), whereas the REE-bearing minerals associated with the Kipawa silicates (enriched in heavy rare earth elements, or HREE) are fluorbritholite, eudyalite, mosandrite, etc. The kinetic tests showed a neutral to alkaline pH of leachates and a low leachability of REE (carbonatites <140 μg/L; silicates <15 μg/L) with a higher mobility of HREE than LREE. The reactivity of REE carbonates are one to two orders of magnitude higher than REE silicates. For sustainable mineral development, geological and environmental data was integrated into the geometallurgical model to identify and control the environmental risks associated with mining those two deposits.

Abstract REE bearing carbonate systems at high pressure: an experimental study Carbonatites are important sources of Rare Earth Elements (REE). REE mainly reside in Ca-bearing phases carbonates, apatites, Ca-Nb oxides, Ca-silicates and in accessory phases such as monazite, burbankite, bastnäsite. At liquid phases, carbonate melts display remarkable physical properties. In particular, carbon-rich and silica-poor melts, i.e. transitional melts, are efficient metasomatizing agents of carbon between the mantle and the crust. This study focuses on two main issues: I) the effect of REE such as La and Y on the structure and melting behavior of transitional carbonate-silicate melts, which has been investigated in simple model with variable CaCO3:SiO2 ratio at 1 GPa; and II) the stability and mineral physics of REE-bearing carbonates at high pressure, in particular of La-burbankite. Few experimental works have explored phase relations, structure and the role of REE in carbonate-rich melts. The typical unquenchable nature of carbon-rich melts makes for a difficult, determination of the structure of carbon-rich glasses. Wyllie and Jones (1986) synthesized a REE-bearing carbonatite glass in a series of experiments performed in the system CaO–CaF2–BaSO4–CO2–H2O–La(OH)3 using a composition similar to carbonatites ore deposits in Mountain Pass (California). At 0.1 GPa the investigated carbonatite composition starts to melt at temperatures as low as 550°C. As today, there are no data available regarding melting behavior, structural properties of melts, and the stability of REE-bearing phases in model system of hydrous carbon-rich low silica. Furthermore, although in alkali free systems a complete miscibility between silicate and carbonate liquids is expected, the compositional threshold at which carbonate-silicate liquids might form a glass, i.e. are quenchable, is still scarcely explored in simple model systems. In this study, I investigated i) how viable is the quenching of a carbon-rich melt as a function of the bulk SiO2:CaCO3 ratio, ii) the structure of these glasses, iii) and the role of REE in the molecular structure(La, Y). I also determined the CO2 solubility in transitional melts by micro-Raman spectroscopy. Single stage and end-loaded piston cylinder experiments have been performed at 1 GPa in two model systems: CaO–SiO2–La2O3–H2O–CO2 in the range 700–1250°C, and CaO–SiO2–Y2O3–H2O–CO2 in the range 1200–1250°C. The starting materials were prepared as a powder mixture of La2(CO3)3 or La2O3 or Y2O3 and amorphous SiO2 and CaCO3 with approximately 5-10 wt.% of H2O. Different bulk compositions with different SiO2:CaCO3 ratio have been considered. Run products were characterized by backscattered electrons images (BSE), X-ray diffractometry, micro-Raman spectroscopy, nuclear magnetic resonance (NMR) of selected experiments, and chemically analyzed by electron microprobe. At subsolidus conditions (T < 1000°C), all bulk compositions in CaO–SiO2–La2O3–H2O–CO2 system contain calcite and quartz coexisting with a Ca-La silicate phase with an apatite-type structure of general formula between La3Ca2(Si3O12)OH and La4Ca(Si3O12)O. Liquidus conditions have been observed in runs on bulk compositions with SiO2:CaCO3 = 0.28 1.4 at T >1150°C for both investigated systems. Homogeneous quenched glasses have been retrieved for composition with up to SiO2:CaCO3=0.28 ratio, whereas at lower ratio (0.12) dendritic textures are visible. Deconvolution of Raman spectra of glasses reveal a CO2 content up to 20.40% in the CaO–SiO2–La2O3–CO2–H2O system and up to 10.80% in the CaO–SiO2–Y2O3–CO2–H2O system classifying the melts as carbonate-silicate transitional melt. While studiyng the behavior of Ca-rich carbonatitic hydrous glasses with REE, we also investigated the influence on the REE distribution of an alkaline carbonate, burbankite [(Na,Ca)3(Sr,Ba,Ce,REE)3(CO3)5], at upper mantle conditions. Recently, the alkaline-carbonate system has been observed at High Pressure and High Temperature (HP-HT) by Shatzky et al., (2016); they found a new class of Ca-rich alkaline-alkaline earth carbonates and burbankite with the latter being abundantely presents in carbonatites that constitutes important ore concentrations of strategic metals, including Nb and REE elements on Earth’s surface. A La rich burbankite [Na3Ca2La(CO3)5] was synthesized at 5 GPa and 1000°C, to scope out the possibility that REE can enter the structure of this carbonate also at upper mantle conditions. Furthermore, the elastic properties of the synthesized La-burbankite have been determined by in-situ HP and HT single crystal X-ray diffraction measurements at synchrotron facilities using a diamond-anvil cell for HP experiments and a quartz-glass capillary for the HT experiments. The determination of these thermoelastic parameters allowed to calculate the possible density of this phase at upper mantle conditions, that is ca. 3.2 g/cm3 at 5.5–6.0 GPa and 900–1000°C. Results suggest that potentially the La-burbankite could fractionate at HP and HT from a carbonatitic melt, because the latter has a lower density (ca. 2.1-3.1 g/cm3) and may constitute a REEs reservoir at upper mantle conditions.