José Affonso Brod

Metal Distribution in Sediments from the Ribeira Bay, Rio de Janeiro - Brazil

Investigation of metal distribution in preserved areas is highly relevant due to the present-day lack of reliable databases against which to assess contamination. 23 samples of surface sediments from the Ribeira Bay, Rio de Janeiro State, Brazil, were analyzed by ICP/AES for Ti, Ca, Mg, Fe, Al, Sr, La, V, Y, Ni, Cu, Cr, Mn and Zn. Hg concentrations were determined by CVAAS. With respect to Al, metals were classified as strongly correlated, correlated, inversely correlated and non-correlated. Cluster analysis of the concentration data confirmed this, except for Hg. Cluster analysis of the sampling sites produced three groups, on the basis of grainsize, continental input, and marine input. Climatic and hydrodynamic factors, as well as soil characteristics, are important controls of the metal distribution in this region. The Ribeira Bay has a natural background metal content, when compared with average shales and with other impacted and non-impacted regions.

MINERAL CHEMISTRY OF KAMAFUGITES AND RELATED ROCKS FROM THE ÁGUAS EMENDADAS REGION, GOIÁS STATE

In the Aguas Emendadas Region, Goias State, Brazil, Late Cretaceous alkaline magmatism produced a series of diatreme structures of kamafugitic affinity. These occurrences consist of a central breccia body, surrounded by lavas and intruded by dykes. Compositionally, the rocks vary from kamafugites, through melaleucitites and leucitites to basanites. The results of mineral chemistry study of olivine, clinopyroxene, feldspathoids, feldspars, perovskite, opaque minerals and carbonates confirms the kamafugitic character of the studied rocks and suggests a link with carbonatite magmatism.

Variações composicionais de olivinas do complexo alcalino-carbonatítico de Salitre, MG

O complexo alcalino-carbonatitico-foscoritico de Salitre, pertencente a Provincia Ignea do Alto Paranaiba, consiste de tres intrusoes. Salitre I e composto por bebedouritos, com diques anelares de carbonatitos e foscoritos; Salitre II e III sao intrusoes menores, dominadas por bebedouritos, e localizadas a norte e a sul de Salitre I, respectivamente. Em Salitre, a olivina ocorre em bebedouritos, foscoritos e carbonatitos, e apresenta teores de forsterita entre 83 e 98%. Rochas menos evoluidas (bebedouritos) contem olivina com menores teores de forsterita do que rochas mais evoluidas (foscoritos e carbonatitos), sendo que olivinas de carbonatitos sao as mais magnesianas do conjunto. Em bebedouritos, a variacao no teor de forsterita esta relacionada a cristalizacao fracionada, enquanto nos foscoritos o teor de forsterita aumenta com a diminuicao do MgO na rocha e nos carbonatitos diminui com a diminuicao do MgO na rocha. Variacoes nas quantidades de MnO e CaO podem ocorrer nas olivinas de Salitre, e os controles de sua distribuicao ainda nao sao claros. Por vezes, sugerem variacoes localizadas na concentracao desses elementos no magma em vez de um controle cristaloquimico especifico da olivina. Discrepâncias nos teores de NiO entre olivinas da serie bebedouritica e olivinas de foscoritos e carbonatitos podem estar associadas a remocao de Ni do sistema, por cristalizacao fracionada previa de olivina rica em Ni a partir de um magma parental silicatico, ou, alternativamente, extracao de Ni por um liquido sulfetado imiscivel.