Master of Science
Planetary Science and Exploration
McCausland, Phil J. A.
Flemming, Roberta L.
In this work, I make a quantitative and mineralogical comparison of Howardite-EuctriteDiogenite (HED) meteorites with terrestrial samples from the Bushveld Igneous Complex (BIC) to assess how geophysical surveys of 4 Vesta or of V-type asteroids could detect BIClike ore deposits. Petrophysical methods in this work include bulk and grain density, derived porosity (using helium pycnometry, the Archimedean method, and X-ray micro-computed tomography), magnetic susceptibility, induced polarization and resistivity, and P-wave velocity. Mineralogical methods in this work include optical microscopy, micro X-ray diffraction, micro X-ray fluorescence element mapping, and electron beam methods. Howardite NWA 15199 was classified as part of this work. Comparing HED and BIC sample properties, the magnetic susceptibility, acoustic P-wave, and electrical properties were all effective at distinguishing HED material from BIC ores, indicating that geophysical surveys of asteroids could employ magnetic and electrical methods from an orbiter to evaluate the presence and scale of chromite-bearing ore deposits.
Summary for Lay Audience
As human space exploration continues to grow and human presence in space becomes more permanent, it will eventually make sense to shift from Earth-based resources to using accessible resources in space. Asteroids are numerous in the solar system, and Near-Earth Asteroids (NEAs) are some of the most accessible to the Earth-Moon system. NEAs periodically cross Earth’s orbit and have been favourable targets for exploration and sample return missions. There are ~764 identified NEAs of diameters above 1 km.
On Earth, knowledge of ore-forming processes and regional geology is used to inform exploration for important minerals. It makes sense to take what we have learned on Earth and apply it to prospecting asteroids in search of the same minerals. Earth is a differentiated terrestrial body, with a metallic core, a hot rocky mantle, and a cool rocky crust, and igneous processes are responsible for the creation of some valuable mineral ores. When the Dawn spacecraft visited the asteroid 4 Vesta, the asteroid was found a differentiated rocky body, with a core-mantle-crust structure. Dawn also found evidence confirming that igneous processes have occurred on 4 Vesta.
4 Vesta orbits over twice as far from the sun as Earth, well beyond the orbit of Mars in the inner asteroid belt, making it difficult to access. However, 4 Vesta is thought to be related to the V-type asteroid family, a subset of which are NEAs. These asteroids appear to be the source of the Howardite-Eucrite-Diogenite clan of meteorites, which are typically interpreted as representing rocks from various formation depths on 4 Vesta or on a similar asteroid. These meteorites contain minerals and rock types that are similar to those found in large plutonic igneous provinces like the Bushveld Igneous Complex (BIC) in South Africa, so a comparison between the BIC and the HEDs can be drawn.
This thesis makes use of petrophysical and mineralogical methods to investigate and compare the petrophysical properties of HED and BIC samples. This comparison is used to show that chromite and platinum-group element ore should be detectable using spaceborne geophysical surveys of V-type asteroids.
Louwerse, Lukas, "Petrophysical Properties of the HED Meteorites and the Bushveld Igneous Complex: Implications for Future Asteroid Prospecting Missions" (2023). Electronic Thesis and Dissertation Repository. 9612.
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