Abstract
Exploration for diamond-bearing kimberlites in the Chidliak project area by Peregrine Diamonds has generated a grid-like till sampling pattern across four discrete areas of interest totalling 402 km2 that is densely populated with research-grade compositional data for 10,743 mantle-derived Cr-pyrope garnets. The available dataset is well suited to statistical analysis, in part due to the relatively unbiased spatial coverage. Previous workers showed empirically that the TiO2 and Mn thermometry (Ti-TMn) attributes of Cr-pyrope populations at the Chidliak project may serve as source-specific “fingerprints”. In this work, we employ a simplified version of the multivariate Mahalanobis distance technique to formally examine the variability of, and differences between, Ti-TMn attributes of Cr-pyrope subpopulations recovered from a Laurentide-age glaciated terrain that also contains 30 known kimberlites within the four areas of interest. We show the simplified Mahalanobis distance approach enables accurate discrimination of Cr-pyrope subpopulations with subtly to distinctly different Ti-TMn attributes, and permits proper demarcation of their respective kimberlite source(s), specifically in areas with straightforward glacial histories. Redistribution and blending of Cr-pyrope subpopulations from known kimberlite sources is also observed, and typifies areas at Chidliak with complex late-glacial histories. Our results support <1 km horizontal scale subtle to obvious variability in the proportions of TiO2-rich and high-temperature (> 1100 °C) Cr-pyropes between closely spaced kimberlite source(s) and also between physically adjacent magma batches within single kimberlite pipes. The local scale variability is attributed to protokimberlite fluid or melt interacting with, and metasomatizing discrete conduits within, the ambient diamond-facies peridotitic mantle at times closely preceding eruption of kimberlite magma batches at Chidliak.
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Acknowledgements
The authors acknowledge support and encouragement provided by Peregrine Diamonds Limited, and the permission granted to publish these results. Overburden Drilling Management Limited and C.F. Mineral Research Limited are thanked for providing the year-on-year consistent, research-grade indicator mineral data that underpin our work. We are grateful to the Editor-in-Chief of the journal for meticulous editing, rapid turn-around and constructive comments to improve overall presentation. Two anonymous peers also provided brief comments.
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Grütter, H.S., Pell, J.A. & Fitzgerald, C.E. Use of a simplified Mahalanobis distance approach to constrain the dispersion and provenance of Cr-pyrope populations at the Chidliak kimberlite province, Nunavut, Canada. Miner Petrol 112 (Suppl 2), 707–718 (2018). https://doi.org/10.1007/s00710-018-0578-7
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DOI: https://doi.org/10.1007/s00710-018-0578-7