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

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.