Venetia K08 Pipe Development

Author(s): 
Wayne Barnett, S. Kurszlaukis, M. Tait, P. Dirks
Date: 
Saturday, October 1, 2011
First presented: 
Bulletin of Volcanology
Type: 
Published paper
Category: 
Geology

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 hangingwall into a subterranean 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 2.7x109 kJ (656 tons 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.

Feature Author

Dr. Wayne Barnett

Wayne Barnett has 18 years of experience in the mining and exploration industry. He specializes in providing operational support by defining the structural geology of mining projects and properly characterizing their rock masses in order to manage risks and solve problems in active mining operations. He also characterizes the structural geology for scoping- to feasibility-level studies.

Wayne has a PhD in structural geology and industry certification in rock mechanics, and worked as a geotechnical engineer for two mining operations over a period of 8 years.

Principal Structural Geologist
PhD, PrSciNat
SRK Vancouver
SRK Turkey