Recent Publications

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  African expansion lifts SRK Consulting (2013)
The present uncertainty surrounding the mining industry has so far had little effect on SRK Consulting (SA), which according to its Chairman, Roger Dixon has a very healthy order book and is currently expanding its staff complement rather than cutting it back. Dixon says the health of the consultancy owes much to a renewed focus on the African market, making SRK less dependent on the troubled South African mining sector which, in recent months, has been impacted by widespread labour unrest.
  The rock mechanics of kimberlite volcanic pipe excavation (Journal of Volcanology and Geothermal Research 2008)
  Wayne Peter Barnett, Mineral Resource Management, De Beers Group Services (Pty) Ltd, P.O. Box 82232, Southdale 2135, South Africa
  The rock mechanics theory for deformation of open pit and underground mining excavations can be used to better understand aspects of the growth and geometry of kimberlite volcanic pipes. Large scale rock mass behaviour around an excavation, such as a volcanic pipe, is dependent on the rock mass strength, the in-situ rock stress conditions and the excavation geometry. Rock mass strength is empirically derived from the intact rock strength and quantification of the shear strength, frequency and orientation of rock discontinuities. Tensile slope or sidewall failure typically occurs in shallow level (~ 0–1000 m) conditions in which pre-existing structures shear due to gravity-driven forces. The orientation of the pre-existing structures provides an important control on the size, shape and position of the rock mass failure. Slope failures are shown to influence the development of many kimberlite volcanic craters and the distribution of layered volcaniclastic facies in the crater. Explosions or removal of key-blocks in a pipe sidewall can cause undercutting and collapse of the sidewall, with the rock unravelling along pre-existing structures towards surface. Many lithic-rich breccias commonly found on the margins of kimberlite pipes are interpreted to form in this way. At intermediate (N 1000 m) to deep (N 2500 m) depths, the increasing compressive stress can cause fractures to develop around an excavation. Stress-induced fractures should cause scaling of a volcanic pipe's sidewalls and expansion perpendicular to the maximum component of compressive stress. A larger horizontal tectonic stress ratio and a lower internal pipe pressure will promote pipe sidewall fracturing. Volcanic pipe expansion will also be increased in rate by (i) mechanical sidewall erosion by flowing magma and/or pyroclasts, (ii) by failure on large intersecting fault or dyke structures, and (iii) by reduction in the country rock mass strength by volcanic explosions. The final pipe shape and distribution of some internal facies is therefore a consequence of the dominant rock mechanical failure processes in the pipe sidewalls. The type of failure is dependant on the rock mass strength, geological structures, stress and depth below surface.
  Upward Ancillary Kimberlite Pipe Growth in the Venetia Cluster (9th International Kimberlite Conference Extended Abstract No. 9IKC-A-00026, 2008)
  Wayne Barnett (1,3), Stephan Kurszlaukis (2), Mark Tait (1), Paul Dirks (4)
1 Mineral Resources Managment, De Beers Group Services, Johannesburg, South Africa
2 Kimberlite Petrology Unit, De Beers Canada Inc., Toronto, Ontario, Canada
3 SRK Consulting, Vancouver, Canada
4 Geological Department, Witwatersrand University, South Africa
  Current kimberlite pipe development models strongly advocate a downward growth process as the pipe cuts down onto its feeder dyke by means of volcanic explosions (e.g. Lorenz, 1975; Sparks et al., 2006). Evidence is presented from a detailed study of the K08 pipe within the Cambrian Venetia kimberlite cluster, Southern Africa, that some pipes or sub-components of pipes develop upwards. This paper investigates the growth history of the K08 pipe and the mechanics of pipe development based on observations in the pit, drill core and thin sections, from geochemical analyses, particle size distribution analyses, and 3D modeling.


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