The general objective of this research is to advance our understanding of the chemical processes controlling trace element distribution and mobility in tropical surficial environments. Specifically, an integrated field and laboratory study is proposed to examine the hypothesis that adsorption processes and vegetative uptake are dominant chemical controls in humid, lateritic terrains. This research will involve close cooperation between Brazilian and American researchers. The field site is in an undeveloped region of Brazil containing Cu, Mo and Au mineralization. The field sampling strategy is designed to determine the distribution and dispersion of these elements in the soils, waters and vegetation of the area. The mineralogy of lateritic terrains is dominated by Fe and Al oxides, kaolinite and quartz which makes adsorption processes, in principle, less difficult to assess than in soils containing a more complex mineralogy. To this end laboratory studies will determine parameters necessary to model adsorption processes including ambient pH, pHzpc, and surface area in addition to conducting adsorption experiments, investigating trace element phase associations using selective dissolution analyses and modeling these results with available adsorption models. Lateritic soils occupy large areas in tropical and sub-tropical regions and our study will increase our understanding in several areas related to the use of these terrains including soil fertility, pollution episodes, weathering regimes and rates, and geochemical exploration.
