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Contributions to Mineralogy and Petrology

, Volume 161, Issue 5, pp 765–776 | Cite as

Highly evolved hypabyssal kimberlite sills from Wemindji, Quebec, Canada: insights into the process of flow differentiation in kimberlite magmas

  • Shannon E. Zurevinski
  • Roger H. Mitchell
Original Paper

Abstract

Kimberlite sills emplaced in granite located near the town of Wemindji (Quebec, Canada) range from 2 cm to 1.2 m in thickness. The sills exhibit a wide variation in macroscopic appearance from fine-grained aphanitic dolomitic hypabyssal kimberlite to ilmenite/garnet macrocrystal hypabyssal kimberlite. Diatreme or crater facies rocks are not present. Multiple intrusions are present within the sills, and graded bedding and erosional features such as cross-bedding are common. The sills exhibit a wide range in their modal mineralogy with respect to the abundances of spinel, apatite, phlogopite and dolomite. Olivine is the dominant macrocryst, with an average composition of Fo90. Garnet macrocrysts are low chrome (2–3 wt. %) pyrope (G1/G9 garnet). Ilmenite occurs as rounded macrocrysts (7–13 wt. % MgO). Phlogopite microphenocrysts are Ti-poor and represent a solid solution between phlogopite and kinoshitalite end members. Spinel compositions mainly represent the Cr-poor members of the qandilite–ulvöspinel–magnetite series. The principle carbonate comprising the groundmass is dolomite, with lesser later-forming calcite. Accessory minerals include apatite, Sr-rich calcite, Nb-rich rutile, baddeleyite, monazite-(Ce) and barite. While some of these accessory minerals are atypical of kimberlites in general, it is expected that differentiation products of an evolved carbonate-rich kimberlite magma will crystallize these phases. The Wemindji kimberlites offer insight into the process of crystal fractionation and differentiation in evolved kimberlite magmas. The macroscopic textural features observed in the Wemindji sills are interpreted to represent flow differentiation of a mantle-derived, very fluid, low viscosity carbonate-rich kimberlite. The diverse modes and textural features result entirely from flow differentiation and multiple intrusions of different batches of genetically related kimberlite magma. The mineralogy of the Wemindji kimberlites has some similarities to that of the Wesselton and Benfontein calcite kimberlite sills but differs in detail with respect to dominant carbonate (i.e. dolomite versus calcite), and the character of the rare earth-bearing accessory minerals (i.e. monazite-(Ce) versus rare earth fluorocarbonates).

Keywords

Kimberlite Wemindji Spinel Dolomite Flow differentiation Sills Monazite-(Ce) 

Notes

Acknowledgments

This project has been supported by the National Science and Engineering Research Council of Canada (NSERC) and Lakehead University. Majescor Resources and Jaques Letendre are thanked for the samples used in this study. The authors would like to thank the following for technical support of this project: Anne Hammond, Sam Spivak, Al MacKenzie and the Lakehead University Centre for Analytical Services (LUCAS).

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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  1. 1.Department of GeologyLakehead UniversityThunder BayUSA

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