Maria do Carmo Lima e Cunha

Biogeochemistry of REE elements and tetrad effect in the soil-plant system: a study on volcanic rock covers in southernmost Brazil

This paper deals with the distribution of REE in rock, soil and plant in an area of monzonitic rocks from southernmost Brazil. The REE patterns in Schinus lensticifolius show a negative-Ce anomaly and a prominent tetrad effect, characterized as W-type that are not present in rock and soil samples. The REE patterns in the soils and rocks sampled are very similar and there is no fractionation of REE during the processes of soil formation. The W-type patterns are interpreted as indicating that REE were absorved by S. lentiscifolius as simple ions rather than as complex ions, or, alternatively, that the transport of REE in the plant metabolic processes was as free ions. The recognition of tetrads, either, M- or W-type patterns, is an additional tool for understanding the biogeochemistry of REE and can contribute to the study of monitoring processes of contaminated environment or to mineral prospecting.

Absorção e fracionamento dos elementos terras raras por vegetais: estudo comparativo em plantas ocorrentes em diferentes contextos geológicos

This work investigates the behavior of REE in some plant species in relation to the concentration levels of these elements in the substratum, independent of the metabolic and physiological specificities of each type of plant and of the nature of the geochemical environment. REE concentrations of leaf ashes determined by ICP-MS e ICP-3500 techniques had been compared with the concentrations of the soil or rock samples of different geologic contexts such as carbonatitic, syenitic and ultramafic environments. In the syenitic environment the REE patterns in leaf ash are similar to those of the whole rock, reproducing the LREE enrichment. In the ultramafic environment the leaf ash contents are higher than those of soils, with REE patterns displaying the W-type tetrad effect. In the lateritic covering of the carbonatite leaf ash patterns have lower REE contents and lack positive Ce anomalies. The results show that the diverse species reflect the REE patterns of the substratum with some variations, such as the tetrad effect, resulting from the fractionation of the elements of the series by the plants.

Evaluation of biological absorption coefficient of trace elements in plants from the pitinga mine district, amazonian region

Specimens of Ampelozizyphus amazonicus and Adiantum sp., together with adjacent soils, were sampled in the Pitinga Mine District, Amazonian region, in order to investigate the distribution of some trace elements in plants and soils, and their relation to the presence of mineral deposits. The Pitinga Mine contains large deposits of tin, with high concentrations of niobium and zirconium, hosted by the Madeira Granite, which is intrusive into a volcanic sequence named the Iricoume group, all of them with Paleoproterozoic age. Our results point to the potential use, for both plants, of the Biological Absorption Coefficient (BAC) as an indicator of mineral deposits when the elements involved in this process have moderate to high mobility in the supergene environment. The high BAC for gold indicates that this element can be used as an indicator of gold deposits. The presence of sulfide deposits is indicated by high BAC for Cu, Zn and Pb, whereas tin deposits are indicated by increasing BAC for Y and Sn. This suggests that the BAC of some trace elements in both plants is a good indicator of geochemical enrichment associated with mineral deposits. The importance of biogeochemistry for mineral exploration is confirmed for areas with thick vegetal cover.

Quantificação da dinâmica dos remanescentes florestais no município de Jaquirana, RS, em imagens de satélite

Techniques of remote sensing and geoprocessing were used to evaluate the dynamics of the vegetal cover, more specifically in Mixed Ombrophile Forest (Araucaria Forest) and Forestry classes in the Jaquirana, northeastern Rio Grande do Sul, from 2002 to 2007. The results showed a significant increase of forestry in detriment to natural forest covering in this short time period. The loss of the natural wood belonging to Mixed Ombrophile Forest was of 5,643.37 ha in a five-year period of time. On the other hand, the forestry area which was 921.10 ha in 2002, increased to 4,814.37 ha in 2007. It was also observed that large areas along the banks of the rivers Antas, Tainhas, and Camisas are now occupied by Pinus sp. crops.

Exemplos de efeito tétrade nos lantanídeos em sistemas naturais

Padroes irregulares de elementos terras raras causados pelo denominado efeito tetrade sao revisados e discutidos neste trabalho, incluindo sua conceituacao e subdivisao em tipos M e W, quantificacao e mecanismos que os geram em sistemas magmaticos-hidrotermais e biologicos. Padroes do tipo M sao mais frequentes em sistemas magmatico-hidrotermais altamente diferenciados, onde a supersaturacao em volateis e altas atividades de F sao reconhecidas. Padroes do tipo M e W sao reportados em plantas e interpretados como resultantes da absorcao de complexos na rizosfera (tipo W), da absorcao de ions livres pelo vegetal (tipo M), ou de variacoes do pH e composicao mineralogica dos solos. Exemplos de efeitos tetrades em plantas, solos, minerais e rochas sao discutidos em diferentes contextos geologicos na regiao da Mina de Pitinga na Amazonia e no extremo sul do Brasil.