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Bulletin of Volcanology

, Volume 73, Issue 8, pp 941–958 | Cite as

Kimberlite wall-rock fragmentation processes: Venetia K08 pipe development

  • W. P. BarnettEmail author
  • S. Kurszlaukis
  • M. Tait
  • P. Dirks
Research Article

Abstract

Current kimberlite pipe development models strongly advocate a downward growth process with the pipe cutting down onto its feeder dyke by means of volcanic explosions. Evidence is presented from the K08 kimberlite pipe in Venetia Mine, South Africa, which suggests that some pipes or sub-components of pipes develop upwards. The K08 pipe in pit exposure comprises >90 vol.% chaotic mega-breccia of country rock clasts (gneiss and schist) and <10 vol.% coherent kimberlite. Sub-horizontal breccia layers, tens of metres thick, are defined by lithic clast size variations and contain zones of shearing and secondary fragmentation. Textural studies of the breccias and fractal statistics on clast size distributions are used to characterize sheared and non-sheared breccia zones and to deduce a fragmentation mechanism. Breccia statistics are compared directly with the statistics of fragmented rock produced from mining processes in order to support interpretations. Results are consistent with an initial stage of brecciation formed by upward-moving collapse of an explosively pre-conditioned hanging wall into a sub-terranean volcanic excavation. Our analysis suggests that the pre-conditioning is most likely to have been caused by explosions, either phreatic or phreatomagmatic in nature, with a total energy output of 2.7 × 109 kJ (656 t of TNT). A second stage of fragmentation is interpreted as shearing of the breccia caused by multiple late kimberlite intrusions and possible bulk movement of material in the pipe conduit related to adjacent volcanism in the K02 pipe.

Keywords

Breccia Fractal Mechanics Growth Particle size distribution 

Notes

Acknowledgements

De Beers Consolidated Mines is thanked for the support we received and permission to publish the data. Tom Gernon and Claude Jaupart are thanked for their constructive and thoughtful reviews. Comments by Dirk van Schalkwyk are appreciated and helped simplify thoughts gone awry. Special thanks to Matthew Pierce, Toni Kojovic and Steve Sparks for discussions, analysis and well aimed questions. Venetia Mine geologists are acknowledged for their aid in sampling drill core. Brad Meiring and students Marie, Martin and JP are thanked for their contributions to data collection.

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • W. P. Barnett
    • 1
    • 2
    Email author
  • S. Kurszlaukis
    • 3
  • M. Tait
    • 1
  • P. Dirks
    • 4
  1. 1.Mineral Resources ManagementDe Beers Group ServicesSouthdaleSouth Africa
  2. 2.SRK ConsultingVancouverCanada
  3. 3.Kimberlite Petrology UnitDe Beers Canada Inc.TorontoCanada
  4. 4.School of Earth and Environmental SciencesJames Cook UniversityTownsvilleAustralia

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