Applications of Atom Probe Tomography in Earth Sciences

Atom Probe Tomography (APT) enables high-resolution elemental analysis at the nanoscale, making it an essential tool in Earth sciences. Recent advancements have focused on trace element distribution, mineral element migration, and water content analysis at the nanoscale. In this study, we present APT-based techniques for analyzing trace element enrichment in arsenian pyrite, water content and occurrence in glass, and isotope analysis with nanometer resolution.

Arsenian Pyrite in Carlin-type Gold Deposits:
We investigated arsenian pyrite with banded structures from a Carlin-type gold deposit using APT combined with SEM-EBSD, EPMA, LA-ICP-MS, and STEM. This multi-method approach revealed the structural and compositional characteristics of pyrite at micro- to nanoscale resolutions. Our findings show that Au, As, and Cu are hosted in pyrite in a substitutional form, while Sb, Pb, Hg, and Tl are concentrated as non-structural impurities in lattice defects. The accumulation of trace elements is coupled with the formation of lattice defects during pyrite’s growth, which transitions from a layered to an island-like growth pattern and back to a layered structure. The study also highlights the crucial role of As in promoting metal enrichment, and surface adsorption of Au as a key mechanism for gold mineralization.

Water Content and occurrence in Glass:
We applied APT in combination with NanoSIMS to study the nanoscale water content, occurrence, and distribution in water-bearing glass samples. The detection limit was achieved down to 0.02 at% for hydroxyl water. We identified nano-sized hydroxyl-water inclusions in glass, with higher hydroxyl water content in these inclusions correlating with increased water content in the surrounding glass. This demonstrates APT’s ability to analyze nanoscale water content and to distinguish hydroxyl water and nano-sized inclusions in mineral samples.

Silicon Isotope Analysis:
APT was also used to analyze silicon samples, including both standard pure silicon and silicon with different isotope ratios. After background correction and mass ranging, we achieved precise nanoscale isotopic ratio analysis. Studies on AVO28 and UHP silicon samples revealed homogeneous distribution of isotopes at the nanoscale without impurities. Our results matched those obtained by MC-ICP-MS and SIMS, demonstrating APT's potential to provide high spatial resolution isotopic analysis for geological sample analysis.

In conclusion, APT offers a powerful tool for exploring nanoscale trace elements, water content, and isotope ratios in geological samples, advancing our understanding of Earth and planetary materials.