Using laboratory hyperspectral imaging for mineralogical mapping of Lefika la Noka tufa cores in the Cradle of Humankind, South Africa

Lefika la Noka (LLN) tufa is located within the Cradle of Humankind (Cradle) UNESCO World Heritage Site, South Africa. LLN tufa has the potential to bridge gaps in palaeoclimate and palaeoenvironmental knowledge of the Cradle by complementing existing data of the continental interior predominantly derived from speleothems, rare wood remains and faunal and palynological studies. Five boreholes were drilled to study the LLN tufa's stratigraphy and sedimentology as the groundwork for further geological studies. To rapidly assess the mineralogical and textural composition of LLN tufa without destructive sample preparations, we used laboratory-based hyperspectral imaging to supplement field mapping and core logging. Through hyperspectral imaging, the mineralogy was mapped for approx. 40 m of tufa core from five drill holes. The hyperspectral imaging of the cores in the visible-near and shortwave infrared wavelength region was used to identify the presence of calcite, montmorillonite, muscovite, illite, and mineral mixtures of smectite-calcite and white mica-calcite. Furthermore, the imaging of the cores in the longwave infrared wavelength region confirmed the presence of calcite and quartz, with most of the quartz occurring as mineral mixtures of quartz-smectite-calcite in two out of the five boreholes. Petrographic analyses were used to supplement the hyperspectral imaging results and identify Fe-Mn-oxyhydroxides in the tufa. Grain size variations across boreholes influenced spectral profiles, revealing nuances in carbonate textures. The results demonstrate the utility of hyperspectral imaging in understanding the drill cores, providing mineralogical and grain size variations that assisted in the decision-making for further sampling of LLN tufa cores.