Geochemical study of pyrite persistence in the sedimentary records

This doctoral thesis aims to evaluate the oxidative weathering of pyrite in geological records. Since this project belongs to the chemical sciences curriculum, we focus on the development of methodologies for the characterization of the samples, the identification of weathering products on the surface and the assessment of their spatial distribution. In addition, pyrite oxidation has been simulated at laboratory scale, to provide some insights on the factor that influences the process. Consequently, all these methodologies were guided by data analysis methods, which are a powerful tool for many fields of science today, demonstrating how they can help in tackling complex geological problems. The main research activities carried out could be divided into four topics: -Acquisition of a Raman library of several mineralogical samples and the development of software in MATLAB for library management and data pre-processing facilities. The spectra acquired in this first part of the PhD project and the software have been fundamental for the rest of the activities carried out. -Development of a methodology based on Hyperspectral Imaging for the evaluation of pyrite oxidation products, validated by the analysis of a severely weathered pyrite sample. This approach can be used to provide a quantitative assessment of weathering products on the surface of sulfide minerals. -Data-driven experiments were carried out in the laboratory for the simulation of pyrite oxidation, providing results on the significant variables that positively or negatively affect this mechanism. In total, three factors resulted to be statistically significant for the oxidation of pyrite in acidic environments. -Application of the analytical methods previously employed in the PhD project to a case study from Taiwan, where unweathered pyrite was found in river sands. The objective of this study was to find a chemical explanation on pyrite’s persistence in this geological context.