Thesis Format

Integrated Article

Decoding kimberlite petrogenesis and advancing diamond exploration: Structural-chemical correlations and deformation analysis of Kimberlite Indicator Minerals

Author

Song Gao, The University of Western OntarioFollow

Degree

Doctor of Philosophy

Program

Geology

Supervisor

Flemming, Roberta L.

Abstract

Kimberlites have attracted decades of study due to their scientific importance and economic value. However, the complex and hybrid nature of kimberlites has led to ongoing debates and their origin and evolution remain contentious. The rarity of economically viable kimberlites has intensified the need of continued diamond exploration and the development of robust reconnaissance methods to vector future exploration. This work investigates the structural-chemical correlations and deformation characteristics of key kimberlite indicator minerals (KIMs) as a new exploration tool and petrogenetic indicator. An important contribution is the creation of Unitcube, an interactive program for non-linear least-squares refinement using advanced optimization algorithms, addressing the scarcity of non-commercial software while improving refinement proficiency for crystallographic and mineralogical research. Detailed strain and geochemical studies on zinc-rich chromite and uvarovite garnet from the Pikoo Property indicate that these minerals form through fluid-induced metasomatism unrelated to kimberlite magmatism. Thus, caution is advised in the use of zinc-rich chromite as a kimberlite indicator mineral. The present research also proposes a new petrogenetic model for mica from the Drybones Bay and Mud Lake kimberlites to explain the correlations between mineral chemistry and strain-related mosaicity measurements Σ(FWHMχ). This model reveals that deformation textures in mica cannot be used as a reliable indicator of xenocrystic origin in the mantle. Further, this research establishes robust structural-chemical trends for garnet classification. Unit cell parameters of mantle-derived peridotitic Cr-pyrope and eclogitic almandine garnets (< 11.770 Å) are dramatically compressed compared to kimzeyite (12.365-12.477 Å) and Ti-rich garnets (12.061-12.198 Å) while crustal garnets (uvarovite, andradite and grossular) feature intermediate unit cell parameters (11.837 Å-12.122 Å). Strain analysis in garnet from coarse and sheared peridotites elucidates the factors affecting its creep strength, revealing that variations in strain-related mosaicity are directly linked to chemical composition, pressure and presumably, metasomatic processes. Overall, the compilation of unit cell parameters, strain measurements, petrographic observations and mineral chemistry of KIMs offers new methodologies and insights that could refine future diamond exploration strategies and enhance our understanding of mineral deformation behaviors and their implications for kimberlite petrogenesis and mantle geology.

Summary for Lay Audience

No active kimberlite eruptions have been observed, nor are they expected to occur in the near future. Kimberlites are rare, ancient volcanic rocks that have captured the interest of scientists and industry experts because they are the “windows” into the deep Earth and they can transport diamonds to the surface. However, understanding how these rocks form and evolve is still a matter of debate. Given that less than 1% of kimberlites are economically viable for mining, there is a consistent need to improve exploration methods for locating diamondiferous kimberlites. In addition to diamonds, kimberlites also carry a significant amount of so-called Kimberlite Indicator Minerals (KIMs) during their ascent to the Earth’s surface. This research focuses on improving our current understanding of the origin and evolutionary history of kimberlites by measuring the deformation intensity of representative KIMs and exploring new exploration methods through the correlation of crystal structural parameters and chemical composition of these minerals. To derive the crystal structural parameters, an interactive computer program called Unitcube was developed, which will be valuable for future diamond research. This study also examines zinc-rich chromite and uvarovite garnet crystals from a crustal occurrence on the same property that elsewhere contained kimberlites. New findings show that zinc-rich chromite may not actually be linked to kimberlite as previously thought, so caution is needed when using it as a kimberlite indicator mineral in diamond exploration. Additionally, the present research provides fresh insights on where mica deforms in kimberlites, which could change how scientists interpret mineral deformation within the Earth. By analyzing the structural-chemical data for a variety of garnet grains, this study further offers a crystallographic way to classify them to infer whether they are derived from the mantle or crust and to understand what factors influence the strength of garnets in the mantle. This work not only develops new methods for diamond exploration but also deepens our knowledge of how KIMs behave under different conditions and the complex geological processes that shape kimberlite rocks.

Recommended Citation

Gao, Song, "Decoding kimberlite petrogenesis and advancing diamond exploration: Structural-chemical correlations and deformation analysis of Kimberlite Indicator Minerals" (2025). Electronic Thesis and Dissertation Repository. 10788.
https://ir.lib.uwo.ca/etd/10788

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