John Curtin Distinguished Professor Steven Reddy is a geoscientist with research interests spanning large-scale tectonics, rock deformation, and advanced mineral characterisation. He is Science Director of the Geoscience Atom Probe Facility at Curtin University and has spent the last decade focusing his research on the development and application of atom probe tomography to geologic materials. His contributions to this field have resulted in him being made a Fellow of the International Field Emission Society and an awardee of the John Sanders Medal from the Australian Microscopy and Microanalysis Society. He is currently the Dean of Research for Curtin University’s Faculty of Science and Engineering.

Abstract

Rocks are natural polycrystalline aggregates composed of mineral grains separated by a network of interfaces. Although these interfaces are only a few nanometres wide, they play a crucial role in determining the physical properties and mechanical behaviour of the bulk rock. Despite their geological significance, mineral interfaces remain poorly understood.

Atom probe tomography (APT) data collected from various mineral interface types, including phase-, grain-, and twin-boundaries, reveals the widespread presence of nanometre-scale segregations with distinct compositions compared to the adjacent host grains. These interfacial segregations play a crucial role in mineral aggregates and serve as significant reservoirs for geologically and economically important trace elements. Moreover, they affect grain boundary diffusion, fluid advection, metamorphic reactions, bulk-rock rheological properties and electrical conductivity. Understanding the distribution of critical elements in interfaces has the potential to lead to improved efficiencies in the extraction of trace elements needed for the energy transition and net zero mining. Interfaces may also serve as valuable repositories for carbon and environmentally hazardous elements like uranium.

This presentation provides an overview of mineral interface geochemistry based on APT analysis. I outline a workflow for studying mineral interfaces, discuss the factors that affect their chemical evolution, and explore how trace element segregation at interfaces can impact mining and geophysical exploration. The geological examples reveal similarities with grain boundary interfaces observed in manufactured materials, potentially providing materials scientists and engineers with valuable insights into complex systems, with varying temperature and fluid histories, and aging over extremely long timescales.

Keywords: Interface; Geoscience; Trace element segregation