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[en] New geochronological data (Rb/Sr, Pb/Pb) for the Amparo and Pinhal Complexes, southern State of Minas Gerais and adjacent areas of the State of Sao Paulo are presented and discussed with respect to other lithostratigraphic complexes which there occur. Among the different complexes considered, 4 are composed mainly by rock belonging to typical infrastructure associations. They are the Barcelona, the Guaxupe, the Amparo and the Pinhal complexes. The Barbacena Complex is a typical gray gneiss complex and geochronological data by different methods confirm its Archean age. The Guaxupe Complex is composed mainly by different types of charnockitic rocks and an Archean age is assumed on geotectonic basis due to its neighboring association with the gray gneiss/greenstone belt, a though confirming geochronological data are still missing, a normal feature in this type of mobile belts which generally show a complex, polycyling evolution. Geochronological data by different methods on diverse rock types indicates that the Amparo and Pinhal complexes are respectively of Lower an Upper proterozoic age. Geochronological, geological and petrographic data reveal that both complexes are composed mainly by 3 basic rock associations: a-mainly derived magmatic rocks including mafic/ultramafic ones as well as calc-alkaline, subalcaline and even alkaline granitoids; b-orthogneisses, migmatites and crustal granites derived by metamorphic processes acting on older, pre-existing rocks; corthogneisses and migmatites resulting from metamorphic processes acting on magmatic rocks intruded during the same tecto-metamorphic cycle during which its transformation took place. The results suggest a polycyclic evolution by successive tecto-metamorphic events which affected the older rocks of the considered are either by the reworking of enclosing rocks around pericratonic continental main magmatic arcs or by the remobilisation of older basement rocks during continental collisions. (author)
[pt]A intrincada geologia da regiao Sul do Estado de Minas Gerais e areas adjacentes do Estado de Sao Paulo tem despertado no decorrer dos ultimos decenios o empenho de numerosos pesquisadores no sentido do desenvolvimento de um modelo geotectonico que permitisse a integracao das diversas associacoes petrotectonicas magmaticas, migmatiticas, metamorficas e (meta) sedimentares sucessivamente discriminadas atraves de trabalhos de campo e estudos petrograficos/petrologicos/tectonicos/estratigraficos cada vez mais detalhados. Uma das linhas de abordagem importante para a compreensao das relacoes entre as diversas associacoes petrotectonicas e sua evolucao, base para a elaboracao de modelos geotectonicos, e a das determinacoes geocronologicas. Entretanto, os dados disponiveis para a regiao considerada sao ainda muito escassos e frequentemente envolvem isocronas de referencia. No presente trabalho os autores apresentam novos dados referentes aos Complexos Amparo e Pinhal e da Faixa de Cisalhamento Ductil Varginha (Artur, 1988). As datacoes referem-se tanto a migmatitos, granitoides, charnockitoides, ortognaisses quanto blastomilonitos e envolvem tantos dados Rb-Sr quanto Pb-Pb. A localizacao das amostras datadas esta contida na Figura 1
PurposeA surplus cost potential (SCP) indicator has been developed as a measure of resource scarcity in the life cycle impact assessment (LCIA) context. To date, quality SCP estimates for other minerals than fossils are either not yet available or suffer methodological and data limitations. This paper overcomes these limitations and demonstrate how SCP estimates for metals can be calculated without the utilisation of ore grade function and by collecting primary economic and geological data.
MethodsData were collected in line with the geographical distribution, mine type, deposit type and production volumes and total production costs in order to construct cost-cumulative availability curves for platinum group metals (PGMs) and lithium. These curves capture the total amount of known mineral resources that can be recovered profitably at various prices from different types of mineral deposits under current conditions (this is, current technology, prevailing labour and other input prices). They served as a basis for modelling the marginal cost increase, a necessary parameter for estimating the SCP indicator. Surplus costs were calculated for different scenario projections for future mineral production considering future market dynamics, recyclability rates, demand-side technological developments and economic growth and by applying declining social discount rate.
Results and discussionSurplus costs were calculated for three mineral production scenarios, ranging from (US$2014/kg) 6545–8354 for platinum, 3583–4573 for palladium, 8281–10,569 for rhodium, 513–655 for ruthenium, 3201–4086 for iridium and 1.70–5.80 for lithium. Compared with the current production costs, the results indicate that problematic price increases of lithium are unlikely if the latest technological trends in the automotive sector will continue up to 2070. Surplus costs for PGMs are approximately one-third of the current production costs in all scenarios; hence, a threat of their price increases by 2070 will largely depend on the discovery of new deposits and the ability of new technologies to push these costs down over time. This also applies to lithium if the increasing electrification of road transport will continue up to 2070.
ConclusionsThis study provides useful insight into the availability of PGMs and lithium up to 2070. It proves that if time and resources permit, reliable surplus cost estimates can be calculated, at least in the short-run, based on the construction of one’s own curves with the level of quality comparable to expert-driven consulting services. Modelling and incorporating unknown deposits and potential future mineral production costs into these curves is the subject of future work.
[en] In order to investigate the time dependence on behaviors of Tc, Mn, Sr and Cs in two soils (Andosol and Gray lowland soil) under two different water contents, corresponding to upland and paddy field condition, a radiotracer experiment was carried out. At 1, 3, 7, 14, 30, 60 and 180 days, three soil fractions, (a) water soluble and ion exchangeable, (b) specifically adsorption, and (c) organically bound fractions, were determined by selective extraction methods with 0.05M calcium chloride (CA), 0.5M acetic acid and 0.1M sodium pyrophosphate, respectively. The results showed that the relative amount (Qra) of CA extractable Cs decreased rapidly to almost zero within a few days after being freshly introduced to the soil samples. The Qra of CA extractable Sr in all the samples was almost the same during 6-month. For Mn, the Qra of CA-Mn in Gray lowland soils decreased throughout the experiment, but the soil redox conditions did not affect on the change. The Qra of CA-Mn in Andosol was much lower than that in Gray lowland soils. Interestingly, for Tc, the Qras of CA-Tc was lower in the anaerobic condition than in the aerobic conditions in both soils. Due to the reduce of the amounts of water soluble and exchangeable forms of these elements in soils, the amounts of these elements entering the food chain probably decrease gradually with time. (author)
[en] Distribution coefficients (Ksub(d)) were measured for cesium and strontium in 16 samples of Canadian unconsolidated geological materials. The samples were collected to cover a wide range of grain size, clay-mineral composition, cation exchange capacity and carbonate mineral content. Distribution coefficients ranged between 102 and 2.0 x 104 ml/g for cesium and between 2.5 and 102 ml/g for strontium, indicating that most unconsolidated geological materials have a substantial ability to retard the migration of cesium, while strontium could generally be expected to be somewhat more mobile. The measured K values were not significantly correlated with the measured soil properties, but appeared to be significantly affected by the background concentration of stable isotopes of the respective radionuclides
[en] Calculation of electron impact total and ionization cross sections for Sr, Y, Ru, Pd, and Ag atoms were performed using spherical complex optical potential and complex scattering potential-ionization contribution methods. The complex optical potential model is formulated from the target parameters and the atomic charge density. The spherical charge densities are in turn derived from the Roothaan-Hartree-Fock wavefunctions defining the atomic orbital of the target. In the present study cross sections are computed in the energy range from ionization threshold to 2000 eV. The results obtained are compared with other theories and measurements wherever available and were found to be quite consistent and uniform. In general, present data show an overall reasonable agreement with other results. Dependence of total cross sections on the number of target electrons and peak of ionization cross section on target parameters were also found to be consistent with previous observations. (author)
[en] Quasicrystal-forming ability is considered from the viewpoint of Pettifor maps, where a single phenomenological coordinate, the Mendeleev number, captures the bonding characteristics of elements in forming intermetallics. By considering the largest sized atom as the most important constituent, it is shown that most known ternary and quaternary quasicrystals can be treated as pseudo-binary intermetallics. This also results in a classification of quasicrystals into four structural classes based on the nature of the bond orbital - s, p, d or f - of the large atom with four associated related crystal structures. A colour scheme is introduced to indicate preferences for two types of sites. We propose a new classification of quasicrystals as centred on Li, Mg, Al, Ga, Ca, Sc, Y, Ti, Zr, Hf and rare earth elements, as they are the largest atoms in the constituent quasicrystals in contrast to the conventional classification based on majority species
[en] Density functional theory is used to study the electronic and atomic structure of small clusters of Na, Mg, Al und Pb. We study the quantity EN-1-EN, which has relevance to the processes of cluster growth and evaporation (EN is the total energy of the cluster with N atoms). By comparing the results of the jellium model with those of a more realistic model (although still simple) we are able to appreciate 'structural' effects beyond the 'electronic-shell effects' which form the essence of the predictions of the jellium model. The calculations predict formation of atomic shells and appreciable reconstruction as the cluster grows. (orig.)
[en] Most of us think of barium and rubidium as simple metals. At normal pressures, both metals have a ''body-centred cubic'' crystal structure and their electronic properties are reasonably well described by the so-called nearly free electron model. When pressure is applied, the crystal lattice changes from the body-centred cubic structure in which the atoms are rather loosely packed to a more closely packed structure. It therefore comes as a surprise to learn that as the pressure is increased beyond 12 Gpa, these close-packed structures become unstable. We know that barium returns to the hexagonal close-packed structure above 45 Gpa, while rubidium forms a fairly close-packed tetragonal phase above 20 Gpa. However, the crystal structures of barium and rubidium at intermediate pressures were unknown until recently. Now a team of physicists from Edinburgh University in the UK, and also a collaboration between researchers from the Max Planck Institute for Solid State Physics in Stuttgart, Germany, and the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, have found that both materials have similar crystal structures with quite unexpected properties (R J Nelmes et al. 1999 Phys. Rev Lett. 83 4081; U Schwarz et al. 1999 Phys. Rev Lett. 83 4085). In this article the author describes the unexpected richness of the structures of these materials. (UK)