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June 16, 2010

A Discussion of Radon and the Mitigation Strategy at Henderson Mine. Dave Loring Senior Mine Engineer. June 16, 2010. Outline. Introduction to Henderson Radon sampling Radon mitigation strategy Off-normal events Corrective actions developed. Harrison Mountain.

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June 16, 2010

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  1. A Discussion of Radon and the Mitigation Strategy at Henderson Mine Dave Loring Senior Mine Engineer June 16, 2010

  2. Outline • Introduction to Henderson • Radon sampling • Radon mitigation strategy • Off-normal events • Corrective actions developed

  3. Harrison Mountain Red Mountain ~12,300 ft Elevation Glory Hole Original Topo Urad Cave Red Mt Porphyry Silver Plume Granite Urad Haulage Henderson Ore Body Geologic Cross-Section of Red Mt. 8100L 7700L 7500L 7210L Urad Porphyry HP SP VP DP Geology • Classic Climax type porphyry molybdenum deposit • About 600,000 feet of core drilling • Limited accessory mineralization

  4. Production & Development Cycle

  5. Geology and Radon • Trace amounts of uranium minerals and Rare Earths in orebody • Euxenite • Aeschynite • Ilmenorutile • Uraninite and Thorite have been noted in tails assays

  6. Henderson Ventilation System

  7. Henderson Levels and Their Uses • 8100 / 8035 – Former production / ventilation levels • Now pumps & exhaust ventilation • 7700 – Former production level (mostly sealed) • Assay lab, warehouse, ventilation • 7635 / 7655 – Ventilation levels • Includes radon exhaust • 7500 – Former train haulage level • Now mud settlers & exhaust ventilation • 7270 – Undercut level • 7210 – Production level • 7150 – Ventilation level • 7065 – Truck haulage level • 7025 – Drain level (also truck level exhaust ventilation)

  8. Radon Sampling • Performed per 30 CFR 5037 • Minimum of once per month at each measurement point • Most points are exhausts of working areas and exhaust drifts • Some intake locations • A TM372 Portable Counter (EIC) is used with an SKC dust pump • Radon sampling is another tool for monitoring the effectiveness of the ventilation system

  9. 7210 Production LevelRadon Measurement Points

  10. Typical Measurement Points and 4-year Averages

  11. Radon Reduction in Cabbed Equipment

  12. Radon Mitigation Program • Cave Isolation • Bulkhead drifts that the cave will compromise • Seal any intake sources • Negative pressure on the cave • Pull high-radon air from the cave into main exhaust paths • Exhaust regulators, fans when needed • Positive pressure on the active undercut level

  13. 7635/55 Ventilation Level Cave Isolation Bulkheads

  14. Idealized Undercut Pressurization (Immature Cave)

  15. 7210 Cave Profile 88C Cave Fan N 858 Regulator & Crusher Ex. Fans` 92LD Cave Fan

  16. 7210 Cave Profile and Positive/Negative Pressure Scheme 88C Cave Fan N 7500 LD isolation bulkheads Pressure directions 858 Regulator & Crusher Ex. Fans` 92LD Cave Fan

  17. Cave Advance on 7700 (2001-2007)

  18. 2002-2007 7700 LevelExhaust Monitoring

  19. 2006 – 96LD Event Description7210 Production Level N

  20. 2005-2007 Production Exhaust Monitoring

  21. 65A/B Orepasses 65A & B o/p’s 66 o/p

  22. 65A/B Orepasses 65A o/p 66 o/p

  23. Corrective Actions • Bulkhead inspection program initiated • Isolation bulkheads planned a year or more in advance of 60° crack line • Prerequisite work such as chute removal planned accordingly

  24. 7210 Production Level Sampling Points July 2008

  25. Discovery of 7500 bulkhead breach Results of 92LD fan and bulkhead sealing project 2008 Production Exhaust Monitoring

  26. 7500 Cave Breach & 92LD Cave Fan Sealed regulator damaged, ~15 kcfm leakage to cave Replaced with 50hp fan exhausting 35-40 kcfm N Bulkhead damaged, ~20 kcfm leakage to cave

  27. 7500 9EC Bulkhead Damage

  28. Corrective Actions • Installed 92LD exhaust fan • Locked, restricted area • Replace Styrofoam bulkheads w/ shotcrete • Seal 75W raises • Additional source of potential leakage (difficult to access)

  29. 7270 7270 7210 7210 7150 7150 Undercut Level – 7150-7210Intake Fans • Early 2009 – 40hp intake booster fans added along 7150 hanging wall intake raises to 7210 Production Level • Increased air volume across entire production panel • Changes were also made to 7270 Undercut ventilation to increase flow through drill drifts due to heat • Modified pressure profile forced air onto the undercut, increasing radon

  30. Undercut Level – 7150-7210 Intake Fans • An exhaust booster fan on the Undercut Level exhaust raise was shut off • Auxiliary systems from the hanging wall were improved • This returned the pressure profile to normal and allowed the 92LD cave exhaust fan and undercut forcing fans to work as planned

  31. Conclusions • The geologic characteristics and mining method at Henderson make the control of radon daughters an important ventilation challenge • Regular monitoring and a control / mitigation strategy have helped maintain low concentrations at Henderson • Unforeseen events can occur due to the dynamic nature of caving • Recent steps taken by the ventilation group have reduced the frequency and magnitude of these events

  32. Thank You

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