Burbankite, a (Sr,REE,Na,Ca)-carbonate in fluid inclusions from carbonatite-derived fluids: Identification and characterization using Laser Raman spectroscopy, SEM-EDX, and synchrotron micro-XRF analysis

Burbankite, ideally (Na, Ca) 3 (Sr, REE, Ba) 3 (CO 3 ) 5 , is rare REE carbonate mineral that until now had been encountered only at a few localities including highly alkaline silicate rocks, carbonatites, and lacustrine sediments. It was identified as an abundant solid phase in fluid inclusions that represent fluids derived from the Kalkfeld carbonatite complex (Namibia). Burbankite occurs in association with other solids including nahcolite, halite, sylvite, rouvilleite (?), fluorite, calcite, cryolite, base metal sulfides, and phosphates. The carbonatite-derived fluids were trapped in quartzite country rocks close to the carbonatite contact. The optical and geochemical identification of burbankite has been confirmed by confocal Laser Raman spectrometry. The burbankite crystals show a Raman shift at 1078 cm (super -1) , which is significantly displaced relative to peaks for other common carbonates and is much broader. The elemental composition of burbankite was determined by a combination of SEM-EDX on opened inclusions and synchrotron-XRF analysis on unopened wafers. The SEM-EDX analyses of the burbankite crystals yielded a compositional range (in wt%) of Na 2 O 10.6-17.5, CaO 3.6-17.4, SrO 12.0-26.7, BaO 2.5-5.5, La 2 O 3 3.5-7.0, Ce 2 O 3 4.7-9.0, Nd 2 O 3 0.9-2.1, and CO 2 (calc.) 29.8-35.2. The Na/Ca ratios are between 1.0 and 4.3, which is high in comparison with rock-forming burbankite occurrences, and clearly distinguishes the burbankite crystals from carbocernaite. Synchrotron micro-XRF spectra yielded REE patterns decreasing from La to Yb over 2.5 orders of magnitude with small negative Eu anomaly [(Eu/Eu (super *) ) cn = 0.5-1.0] in some cases. The Y/Ho ratios range from 1 to 5, and Th/U ratios are between 1 and 10. The fluids trapped are interpreted to represent a highly evolved but pristine, alkali-rich, hydrous, carbonate melt, which had not lost alkalis to the country rocks by fenitization processes. The common occurrence of burbankite crystals in the fluid inclusions shows the high capability of carbonate melts and fluids to transport high-field-strength and large-ion-lithophile elements

Provenance of the Vazante Group: New U-Pb, Sm-Nd, Lu-Hf isotopic data and implications for the tectonic evolution of the Neoproterozoic Brasilia Belt

The Vazante Group show varied U-Pb provenance patterns along the basin. Zircon ages range from 936 to 3409Ma, but Paleo- and Mesoproterozoic terrains constitute the main sources of the original sediments. The youngest population (~930Ma) establishes the maximum depositional age of the group. Sm-Nd T DM data show the predominance of Paleoproterozoic ages (1.90-2.08Ga) and also indicate some input from younger sources in rocks of the Lapa Formation (1.67 to 2.0Ga) in the upper part of the group, whereas rocks of the Serra do Garrote Formation present the oldest model ages (2.03 to 2.76Ga). Hf isotopic compositions of the detrital zircons indicate that they were derived mainly from recycled Paleoproterozoic crust with a minor Mesoproteroic juvenile component. Terranes within the São Francisco Craton represent the main sources of detrital sediments of this group and reinforce the interpretation that it may be a passive margin sequence developed along the western margin of the original continent. However, the origin of Mesoproterozoic grains remains uncertain. Slightly younger Sm-Nd model ages in the Lapa Formation, however, are not entirely consistent with derivation solely from the craton and may indicate contribution from younger sources, such as the Neoproterozoic Goiás Magmatic Arc

Biocultural diversity, pollinators and their socio-cultural values.

Pollinators, pollination and nature's benefits to people; Pollinators, pollination and good quality of life; Impacts, management and mitigation options; Method