1. The Quasi - Open Pit Methods Mnge 315
©Dr. B. C. Paul spring 2003

2. Open Pit Mines In some senses all forms of surface mines are open pits
Strip Mines tend to refer to coal operations with some very significant differences from open pits in the metal/ industrial mineral sense
Quarries also tend to be unique subset
Placer and dredge operations also unique subset

3. Classic Open Pit
Characterized by a series of stair-step like benches that each act as a working area
Pit shapes tend to be more configured to geology of the deposit more than equipment needs/convenience
Many pits are ovals
Fits the geometry of disseminated metal deposits
Pits tend to be wider relative to length
Pits tend not to move like strip mine – pit develops in place

4. Differences not Necessarily Simple
Working Benches were encountered in “Strip Mines”
Advance benches using trucks and shovels developing ahead of dragline
Multiple coal seams may need a bench for each
Contour haulback operations often had benches lined up with layers of concern
Mountain Top Removal can be developed as truck shovel benches
Local and Industry Specific Word Usage
Coal people like to “strip” mine
Metals/Industrial Minerals people like to “Open Pit”
Aggregate people like to Quarry

5. Terrace Pit Mining Add Picture
Note that all characterized by benches – often set up on truck shovel equipment
Working heights. Can also be used with multi-seam coal mining

6. Factors Controlling Terrace Pit
Bench Heights are often controlled by the digging height of the shovel
In past drill accuracy limits have been important
Benches often give more gradual over-all slope
Dragline highwall is mostly angle of repose
May need a specific bench width to provide working room – smaller over-all slope to highwall

7. More Terrace Pit Control
Trucks and Shovels often control OB movement rather than draglines
Dragline has limited boom length – favors narrow pits
Trucks and Shovels need room for equipment to drive across without getting tangled up or caught on steep slope
Tends to favor wider pits
Need for ramps tends to favor shorter pits rather than having long moving range like dragline

8. Dipping Thick Coal Seams
Common in Western part of U.S. for coal

9. Mining on the Strike or the Dip
Area Strip mines
Dragline moves down the strike with pickup and dump sequence moving down dip
Conspicuously advances down dip

10. Mining Down the Strike Contour Haulback schemes
Overburden movement is along the strike
Add picture

11. Coal Terrace Pits
With relatively flat seam overburden moves across the dip
With steeper dip overburden movement tends to be down strike
Even possible to have full pit width developed at once with contour mine like advance

12. Evolving to True Open Pit
Benches advance down the dip
Pit length is limited for manageable network of truck haul roads
Overburden is not deposited in the same pit
Hauled to a distinct and separate pit along the strike
Phosphate Operations mine dipping phosphorous rich limestones that way

13. Note the Distinct Feature
Pit is developed out to its stripping ratio limit leaving the pit open the entire time
Only at end of the pit life is the pit backfilled
Geometry and Equipment limitations in hardrock and industrial minerals defies a workable concurrent reclamation in the SMCRA sense
One reasons the law was only applied to coal