Manganese Oxides in Iron Ore Province Soils, Brazil and Their Relations with Trace Elements.

The mineralogy of manganese (Mn) oxides is highly variable and complex, since the number of minerals is large and the knowledge of their structures imprecise. In view of the scarcity of specific papers on Mn oxides in Brazilian soils and their unusually high contents in some soils of one of the Iron Ore Province (IOP) of Minas Gerais State, this study aimed to characterize the chemistry and mineralogy of these oxides in the soils of this region, stratifying them according to the parent material and their relations with trace elements (TE). The study was conducted in a representative area of the IOP, in an area of environmental protection of Belo Horizonte city (APA Sul RMBH), with 1,625.32 km². Soils with high Mn contents of three distinct parent materials were sampled and characterized: itabirites, ferruginous dolomites and serpentinites, as well as some soils derived from other parent materials within the IOP. Some IOP soils have extraordinarily high Mn contents in the fine earth fraction, mainly soils derived from the ferruginous dolomites of the Gandarela Formation (Mn until 69 g kg ^-1). Diverse manganese oxides were identified by x-ray diffraction (XRD) and high-resolution imaging and electron diffraction (TEM) without concentration pretreatments especially: todorokite, lithiophorite and pyrolusite with Ni and Cr associated in the soils clay fraction. The influence of the parent material on the chemistry and mineralogy of Mn oxides was stronger than the weathering degree of Mn-rich soils.