Ultrafast Phase Mapping of Thin-Sections from An Apollo 16 Drive Tube − A New Visualisation of Lunar Regolith

Polished thin-sections of samples extracted from Apollo drive tubes provide unique insights into the structure of the Moon's regolith at various landing sites. In particular, they allow the mineralogy and texture of the regolith to be studied as a function of depth. Much has been written about such thin-sections based on optical, SEM and EPMA studies, in terms of their essential petrographic features, but there has been little attempt to quantify these aspects from a spatial perspective.

In this study, we report the findings of experimental analysis of two thin-sections (64002,6019, depth range 5.0 – 8.0 cm & 64001,6031, depth range 50.0 – 53.1 cm), from a single Apollo 16 drive tube using QEMSCAN®. A key feature of the method is phase identification by ultrafast energy dispersive x-ray mapping on a pixel-by-pixel basis. By selecting pixel resolutions ranging from 1 – 5 microns, typically 8,500,000 individual measurement points can be collected on a thin-section.

The results we present include false colour digital images of both thin-sections. From these images, information such as phase proportions (major, minor and trace phases), particle textures, packing densities, and particle geometries, has been quantified. Parameters such as porosity and average phase density, which are of geomechanical interest, can also be calculated automatically.

This study is part of an on-going investigation into spatial variation of lunar regolith and NASA's ISRU Lunar Simulant Development Project.