The occurrence of intermediate schorl-dravite and alkali-deficient, Cr-(V)bearing tourmalines in the volcanic-sedimentary sequence of the Serra do Itaberaba Group - SP

Abstract

543spilitization, epidotization, keratophyrization and silicification. Basaltic andesites show actinolite (substituting clinopyroxene), chlorite, albite, epidote, quartz and opaques. Porphyritic types bear relic phenocrysts of magmatic hornblende. Keratophyrized dacites and rhyolites show quartz, albite, chlorite, epidote, zircon and opaques.Spinifex-textured MBVU-rocks have been referred to previously as komatiites or basaltic komatiites; this is not sustained mineralogically nor geochemically. These rocks present tremolite-actinolite, chlorite, albite, talc, epidote, carbonate and opaques. Pseudomorphosed acicular clinopyroxene spinifex textures predominate by far over those of bladed olivine, typical of (peridotitic) komatiites. SiO 2 reaching the range of intermediate rocks, low TiO 2 (0.25-0.40 wt-%), and Ti/Zr∼ 60 (50-75) relegate these rocks to siliceous magnesian basalts or low-Ti tholeiites linked to boninites, rather than komatiites with Ti/Zr > 100 (Coish 1989). These rocks may represent extrusive equivalents of the most primitive magmas, from whichAVU-andesites differentiated in infracrustal magma chambers.Differentiated magnesian basaltic flows show a spinifex-textured andesitic top and massive ultramafic cumulate base made up of pseudomorphosed euhedric medium-grained olivines and rare relic orthopyroxenes in a tremolite-chlorite intercumulus matrix with chromite as a constant magmatic intercumulus phase.The BVU consists mainly of basic Fe(-Mg) tholeiitic flows. All three volcanic units contain subordinate volcaniclastic and chemical intertrap metasediments. - ( December 14, 2001 Presented by Antonio C. Rocha-CamposSoil used to cover compacted solid waste at sanitary landfills plays an important role in attenuating contamination by interfering in leachate composition and incorporating organic and inorganic substances. In order to investigate the behavior of metallic ions associated with the soil cover of the Bandeirantes Sanitary Landfill, Municipality of São Paulo, Brazil, we propose to assess the mobility and fixation mechanisms by simulating environmental conditions of sanitary ''cells'' in vitro.The experiment will consist of glass columns, in which organic and metallic phases of an ''artificial waste'' will be placed upon a bed of soil and coarse sand layers, both supported on filter. Above this waste layer, a known mass of soil will be added and compacted keeping the proportions used in real sanitary landfill. Rain water or artificial rain will be allowed to percolate through the column at a rate based on known monthly precipitation. The control experiment will use soil only, taken from an intact soil profile near the landfill.Other experiments will also reproduce the conditions equal to those in the Bandeirantes Landfill cell, but will inject rainwater and also known concentrations of heavy metals (Zn, Cr, Pb). Soil chemistry will be analyzed as well as the chemical and physical-chemical properties of the leachates such as pH, Eh, temperature, humidity and DO. These parameters will be meas...