Fernandez et al_Kromdraai Geochem and Dating

Sediment geochemistry
Aim/rationale:
The purpose of this study is to analyse the geochemistry of the objects, especially in terms of trace elements. The ultimate goal is to give a geochemical characterization of the Kromdraai sedimentary units where the samples come from.

Methodology:
Objects are sampled (a few 100 grams each). The bulk will be remain in South Africa, exported samples will be destroyed. Samples are dissolved in 4.5 mol/L HNO3. One aliquot is taken from each sample and used for measuring trace elements abundance on a quadrupole ICP-MS, with In as an internal standard.
The exported samples will be dissolved, and thus destroyed.

Geological sample dating
Aim/rationale:
The purpose of this study is to perform a U-Pb dating on the objects. The ultimate goal is dating the Kromdraai sedimentary units where the samples come from.

Methodology:
Objects are sampled (a few 100 grams each) and the rest will be returned to South Africa. Samples are leached, for cleaning, with cold 0.1 mol/L acetic acid. Saples are dissolved in 4.5 mol/L HNO3. One aliquot is taken from each sample and used for measuring REE abundance and the 238U/206Pb ratio on a quadrupole ICP-MS, with In as an internal standard. Another aliquot is taken and used to extract U on anion exchange resin. Matrix is eluted with 9 mol/L HCl, U is eluted with 0.1 mol/L HCl. This aliquot is then used to measure the 234U/238U ratio on a multi-collector ICP-MS, with standard (NIST) bracketing to correct instrumental drift. The rest of each sample is used to extract Pb on anion exchange resin. Matrix is eluted with 1 mol/L HBr, Pb is eluted with 6 mol/L HCl. This fraction is then used to measure Pb isotope composition on a multi-collector ICP-MS, with Tl doping to correct mass-dependent instrumental isotope fractionation and standard (NIST) bracketing to correct instrumental drift.

The speleothem part of each object will be sampled (5 to 10 samples per object, a few 100 grams in total)

Statement why this study cannot be done in South Africa:
The laboratory with the material to treat the samples (clean room, mass spectrometers, standards) is in France. The researchers doing the analysis are based in France.

Time frame:
Export to France in October 2024
Beginning of sampling and analysis in January 2025
End of the analysis by August 2025