Characterization of gold samples using LA ICP-MS and X-ray fluorescence techniques

The main objective of this research is the characterization of gold samples using archaeometry and geochronology techniques to determine their geographic origin by the ratios between lead isotopes present as traces. The samples used for analysis were collected in several geographically distinct Brazilian mines and in the Colombia mine. In developing the project, laser ablation techniques and inductively coupled plasma mass spectrometry analysis were used to determine the ratio of lead (Pb) isotopes present in the samples.

Initially, the samples were mounted in epoxy resin and polished to ensure better functioning of the laser ablation system. Then, the amounts of Pb isotopes in the samples were measured. Such measurements were carried out at parts per billion (ppb) levels, giving rise to graphs relating pairs of isotopes. From them, a characteristic signature can be established for the region where the samples were collected. The results show that the isotopic ratios are quite different for the Brazilian and Colombian samples, although these differences are also very consistent between the Brazilian samples, even though they were extracted from very close geological regions.

In addition, a simple and non-destructive method, X-ray fluorescence, was used to perform analyzes to identify and evaluate the proportions of other elements such as silver and copper. Interestingly, Brazilian gold samples contain significant amounts of silver, while Colombian samples have a higher degree of purity, with copper being the element with the greatest presence.