Correlation between sub-micron surface roughness of iron oxide encrustations and trace element concentrations

Area of Science:

• Geochemistry
• Environmental Science
• Mineralogy

Background:

• Iron oxide encrustations form on black slates during oxidative weathering.
• Trace elements are released and can be trapped within these encrustations.
• Previous studies suggested a link between surface topography and uranium concentration.

Purpose of the Study:

• To investigate the relationship between surface topography and trace element concentrations in iron oxide encrustations.
• To determine if this relationship extends to submicron scales.
• To analyze geochemical and topographical data from multiple sites.

Main Methods:

• Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for geochemical analysis.
• Laser scanning microscopy for detailed surface topography measurements.
• Analysis of encrustations from various locations with similar weathering histories.

Main Results:

• Trace elements such as V, Cu, As, Mo, Pb, Th, and U are concentrated in iron oxide encrustations.
• The relationship between surface topography and uranium concentration extends to submicron-sized half-pores (100-500 nm).
• Uranium, phosphorus, copper, and zinc concentrations inversely correlate with surface roughness (parameter F, a proxy for Rq).

Conclusions:

• Micrometer- to submicrometer surface topography variations at fluid-rock interfaces significantly control trace element sequestration.
• The findings highlight the environmental importance of surface micro- and nanostructure in element trapping.
• This study expands the understanding of trace element behavior during slate weathering.