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Partial Backfill Alternative - January 21, 2010

 

Partial Backfill Alternative
January 21, 2010
Cooperator’s Meeting Presentation
February 3, 2010
ID Team Meeting
 
Partial Backfill Alternative
Considerations
• Be responsive to an Issue
• Minimize water that collects in the pit
• Return waste rock to the pit
• Minimize resources that are used in backfilling
• Minimize air impacts
 
Partial Backfill Alternative Environmental Considerations
• Compliance with all applicable regulations including ADEQ BADCT and air regulations
• Maintain a Hydraulic Sink
• Geochemical considerations with the addition of a mix of finer grained materials
• Stormwater controls during backfill
• Effect on concurrent reclamation and on reclamation planning
 
Pit Lake Development
 
Hydrogeologic Study Results
Period Pit Lake
Elevation
(ft amsl)		 Pit Lake Depth
(feet)
Mine Closure (None) 0
Closure + 20 years 3,591 541
Closure + 50 years 3,751 701
Closure + 100 years 3,869 819
 
• Backfill elevation – 3825 ft amsl (est.)
• Elevation was estimated to maintain sink (modeling to confirm elevation estimation with operational adjustments as necessary)
 
Other Considerations
• Heap Leach remains undisturbed
• Haulage fleet used will be consistent in size to current fleet
• Loading equipment (shovel used will be consistent with current loading equipment)
• Waste rock density is 11.95 ft3/ton
• Swell factor for the rock is 1.3
• Amount of material necessary for backfill is 90 million tons (46 million cubic yards)
• Allowance of 5% added for construction of ramps for downhill haulage
• Total material rehandled 94 million tons
• 36-months required to complete backfill
• Hauls will incorporate 3 switchbacks at -10% grade at a maximum 13 mph
Backfill and Excavation Area
• Excavation on 50 foot benches
• Start elevation approx 5470 ft amsl
• Final elevation 5200 ft amsl
• Dumped into pit from 3825 ft elevation
 
Productivity by Bench
Bench
Elevation
(ft amsl)		 Tonnage
(x 1,000)		 Cumulative
Tonnage
(x 1,000)		 Haulage
Production
(tons/hour)
5420 8,938 8,938 379
5400 18,435 27,373 387
5350 18,689 46,062 395
5300 16,277 62,338 403
5250 12,977 75,315 411
5200 8,720 84,036 419
This information was used to determine the appropriate haulage fleet for this activity matched to one shovel.
 
Required Haulage Hours and Units
Post‐Mining
Year		 Rehandle
Tons
(x 1,000)		 CAT 793C Truck Fleet
Operating
Hours		 Units
1 28,774 74,740 16
2 28,853 72,439 16
3 26,409 64,021 15
Total 84,036 211,201 16
Modeling indicates that 16 trucks will be required in the first 19 months of the project and 15 for the remainder.
 
Support Equipment in Addition to Haulage Equipment
• One Electric Shovel
• One Front End Loader
• One 600 HP Track Dozer (D10)
• One 850 HP Track Dozer (D11)
• One 500 HP Wheel Dozer
• Two Graders
• Two Water Trucks
   
Discussion Points/Conclusion
• Hydraulic – can maintain sink with partial backfill
• Economic – negative cost implications (~$90 million)
• Energy/Resource Conservation – 3 additional operational years for electric and diesel use plus water for dust control
• Air Quality – 3 additional years of mining fugitives
• Employment – approximately 100 people for 3 years
• Reclamation– concurrent reclamation of area cannot be effectively started
• Visual Result – no appreciable change to overall landform (~6% of total material)
• Water Quality– potential for short term flow through condition
• Traffic – 3 additional years of 100 employees commuting
• Biology – continued operations presence for mining
• Future Mineral – sulfides at the bottom of the pit no longer accessible
• Pit Reservoir for Regional Water Storage – eliminates some storage that may otherwise available