Imaging iron ore from the Quadrilátero Ferrífero (Brazil) using geophysical inversion and drill hole data

A Combined (U‐Th)/He and Cosmogenic 3He Record of Landscape Armoring by Biogeochemical Iron Cycling

“…Journal of Geophysical Research: Earth Surface 10.1002/2017JF004282 Figure 3. (a) The higher-elevation and more extensive Gandarela plateau is underlain by the thickest and most continuous canga blanket in the region (Baltazar et al, 2005a;Carlos et al, 2014). (b) Boulders of canga covered in lichen and protruding 20-50 cm from the surface reveal the mechanisms (biogeochemical dissolution and physical disaggregation) partially responsible for the very slow destruction of cangas.…”

“…These ancient weathering profiles are overlain by Fe duricrusts, which probably began armoring the landscape with the onset of weathering (Monteiro et al, ; Shuster et al, ). Depth and lateral continuity of the duricrusts vary across the region, where the highest‐elevation plateaus are capped by the deepest (up to 70 m according to Carlos et al, ) and most continuous canga blankets (e.g., Serra do Gandarela, Figure b) (Baltazar et al, ). Low‐elevation plateaus are overlain by intermittent and shallower cangas (up to 30 m) (e.g., Serra da Moeda, Figure b) (Baltazar et al, , ), whereas the narrowest and mostly discontinuous ridges are blanketed by intermittent cangas (e.g., Serra das Serrinhas, Figure b) (Baltazar et al, , ).…”

“…The interior of the QF is dissected by the das Velhas River and its tributaries, and low‐elevation convex hills dominate the surrounding “Mar de Morros” landscape. Schematic and simplified geological cross sections (Carlos et al, ; Spier et al, , , ) plotted on the topographic profile illustrate that weathering profiles as deep as 250 m are capped by continuous or intermittent cangas. The approximate location of cangas and hematite–magnetite pebbles investigated in this study is shown.…”

Three-dimensional gravity inversion using graph theory to delineate the skeleton of homogeneous sources

“…Basically, the iron formation is composed of friable and compact hematites and itabirites. Previous interpretations of the area (Carlos et al, 2011(Carlos et al, , 2014Martinez et al, 2013) suggest that the iron ore body is approximately contiguous surrounding the 200-m depth with a total mass of millions of tons. This information helps during the definition of the search limits.…”

Iridescence in Metamorphic "Rainbow" Hematite

“…Rietveld refinement is a technique for determining atomic structures by comparing the misfit between an observed powder X-ray diffraction pattern and a diffraction pattern calculated on the basis of a model crystal structure (Rietveld, 1969). Factors such as unit-cell parameters and atom positions are allowed to refine until the misfit between the observed and calculated patterns From Carlos et al (2014).…”