The XRF data is generally consistent with previous historical surveys of laterites and indicates metal concentrations of an average of 33.8 wt.% for Fe, 0.576 wt.% for Mn, 0.330 wt.% for Ni, 1.07 wt.% for Cr, and 0.161 wt.% for Co. TEM-EDS mapping on selected sample material indicates oxyhydroxide mineral particles are uniformly intergrown and create a bird's nest texture. These individual crystallites of oxyhydroxide minerals observed have an average length of approximately 500 nanometers and width of approximately 50 nanometers. Also, the TEM-EDS data shows Fe was the most dominant element found, with minor amounts of Mn, Cr, Ni, and Al, and is consistent with XRF data and HR-ICP-MS data. The preliminary XRD data is complex and for laterite shows diffraction consistent with goethite-diaspore solid solution, and multiple types of pyroxene including ferroan enstatite, and probable clinopyroxene. In addition, the bedrock samples are dominated by serpentine while exhibiting a minor amount of chlorite. Lastly, the HR-ICP-MS data showed that between the bedrock and laterite, nickel and cadmium amounts generally decreased on average and other metals increased significantly through the laterization process.
Link to Accessible Tables: Accessible Tables: XRF and HR-ICP-MS
(Left) Pictures of the outcrop with scale and person for reference showing the geologic complexity of the outcrop with laterite following deep fractures or topography. (Right) Initial handheld XRF data show in in parts per million. Samples (#1-3) are laterite, and the 3 Mn-ox are from this location with 2.7 samples being nearby for general comparison.
Powder X-ray diffraction data with major peaks labeled showing serpentine in the bedrock samples and goethite –diaspore in laterite. Peaks at 2.93 Å and 2.50 Å are interpreted as ferroan enstatite persisting in the laterites. Not all peaks are labeled to avoid over crowding. Specific forms of serpentine are not yet determined and other phases may exist.
An EDS spectra that shows that the mineralogy is dominated by Fe and Al. Traces of Ni and Cr are evident, Cu and Au grid scatter.
Example EDS map showing the mixing of elements within a mineral aggregate. Composite EDS spectra is above. This particle displays a maximum length of 2.5 microns and the uniform contrast suggests uniform mineral composition.
This particle has a length of around 2 microns and a width of around 3 microns. The pronounced acicular morphology of crystals is consistent with goethite – diaspore mineralogy.
This particle is the largest with a length of 6.5 microns and a width of around 3 microns. The acicular morphology of crystals is consistent with goethite – diaspore mineralogy.