Slope Stability Assessment of the Letlhakane DK1 Mine

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Slope Stability Assessment of the Letlhakane
(DK1) Mine

• Keabetswe Keith Makuku

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Project AIMS

• Assess and Evaluate the Stability of the Ultimate
  slopes
• Propose Remediation measures where applicable

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Letlhakane Mine Information

• Location Southern Africa, Central Botswana, 200
  km west of Francistown and 50 km east of Orapa
• Establishment - 1977
• Current Life of Mine 12 years as an open pit at
  current production levels
• Ownership - Debswana
• Mining Method Open Pit
• Employees Orapa and Letlhakane 3200
• Production during 2002 Ore treated 3.6 million
  tons
  Diamonds recovered 1.03 million
  carats Recovered Grade
  25.7 carats per 100 tons Total
  Waste stripped 15.25 million tons

www.debswana.bw
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Geology and Topography

• Kalahari Sands and Calcrete - 10 meters
• Stomberg Basalts (135 meters massive 10-15 m
  thick flows with
• near horizontal top and base. Localised worm
  like calcite amygdales)
• Ntane Sandstones - 120 meters thick, hard-medium
  grained, crossbedded
• and Interbedded by fine, weak red mudstone
  lenses)
• Kimberlite (Diamond Ore body) - Intruded into
  the Karoo sequence
• during the Cretaceous period (90 million years
  ago)
• Flat topography- area lies at an altitude of
  1000 m.a.m.s.l and
• undulates gently with no significant
  physiographic features

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LETLHAKANE MINE GEOLOGY SECTION THROUGH D/K1
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Work Done

• Geological Mapping
• Point Loads
• Scan-line survey
• Geotechnical Core logging
• Weathering Exercise
• Groundwater seepage Mapping
• Density Measurements
• Triaxial Test

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Data Analysis

• MRMR, RMR,Q-system
• Rock DATA (rock strength parameters)
• DIPS (preliminary assessment-stereonet)
• Swedge (deterministic and probabilistic)

WEDGE POTENTIAL
TOPPLING POTENTIAL
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Remediation

• Dentition

Sub-horizontal Drainage
(Concrete of higher strength parameters)
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• Dewatering Boreholes
• Sub-horizontal dewatering holes

(Weathering effect only effective towards the
day-lighting zone of the rock unit)
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References

• www.debswana.bw
• Rock Slope Engineering E Hoek J Bray
• Detecting Problems with Mine Slope Stability.
• Jami M Girad and Ed Mo turgh
• An Investigation of the Main Failure Planes at
  Letlhakane mine (2001)
• P.H.G.M. Dirks
• Engineering rock mass classifications,
• Wiley-Interscience, New York (1989) Z.T
  Bieniawski