Strip mining involves removing surface layers of soil and rock to access shallow mineral deposits. It is efficient for relatively flat, horizontal deposits close to the surface. Large machines like draglines, shovels, and bucket wheel excavators remove material in long, parallel strips, placing the overburden in the mined out areas. While low-cost and safe, strip mining significantly impacts the environment by destroying natural communities and can cause erosion and acid drainage into waterways. The economics depend on the stripping ratio of overburden to ore.

1. Surface Mining
OPEN CAST/STRIP MINING

2. Method Description
Strip mining is ideally applied where the surface of the ground and the ore body itself
are relatively horizontal and not too deep under the surface, and a wide area is
available to be mined in a series of strips.
Typical examples of this type of mining are the larger tonnage coal mining operations
Favourable conditions are:
Relatively thin overburden (0-50m maximum otherwise stripping ration and cost of
stripping becomes too high)
Regular and constant surface topography and coal layers (not more than 20º variation
from horizontal on the coal seam –topography can vary more since pre- stripping can
be used to level it – but this is expensive to apply)
Extensive area of reserves (to give adequate life of mine (LOM) and to cover all capital
loan repayments – typically more than 20 years life at 4-14mt per annum production)

3. Application Conditions
Factor Condition
Ore Strength Any
Rock Strength Any
Deposit Shape Tabular, bedded
Deposit Dip Any, prefer horizontal or low dip
Deposit Size Prefer continuous deposit, large in lateral extent
Ore Grade Can be low if other conditions are favorable
Ore Uniformity Uniform,
Depth Shallow to intermediate to control striping ratio

4. Sequence of development
► Land clearing
► Surface plant is located and constructed
► Coal dumping, storage, processing and trans[ort facilities are located
logically with respect to the mining
► Equipment selected
► Initial pit development takes plce
► First cut
► Simultaneous development and exploitation can then proceed in a
normal way

5. Main Operations
► Cleaning
► Drilling
► Blasting
► Pre-stripping
► Dragline stripping
► Coal mining

6. Auxiliary Operations
► Slope stability of dumped material
► Reclamation
► Haul road construction and maintenance
► Drainage pumping
► Communications
► Power distribution
► Dust control
► Safety

7. Types of Strip mining
► Contour Mining
► Haul back
► Box cut
► Block cut
► Area Mining
► It is accomplished using
► Draglines, Stripping Shovels and BWE

8. Contour Mining
► Employed usually in highly terrain where a
steep slope limits the width of the area that
can be economically mined from the mineral
outcrop. The operation is often followed by
augering the exposed mineral bed
(particularly coal). The diagram below
illustrate this type of mining.
► The specific methods used in contour mining
are:
1. Haulback.
2. Box-cut.
3. Block-cut mining

9. Haul back Mining
► In this method mining proceeds in a series of square rectangular pits following
the outcrop for as much as several kilometers.
► The pit width is dictated by the economic stripping ratio and steepness of
topography.
► Since mining follows a contour, the path of mining is generally sinuous with
both outside and inside curves.
► Mining progresses by first removing a box-cut and hauling the overburden to a
suitable disposal site.
► Thereafter, overburden is broken, excavated, and hauled by truck, scraper or
conveyor to fill previously mined-out pits.

10. Box-Cut Contour Mining
► It is practiced in moderately sloping terrain.
► It is essentially the same as area mining where the total number of strips is limited to two or
three.
► The strips are oriented parallel to the outcrop line and progresses uphill into the highwall.
► The first strip is a consecutive series of box-cuts, which provides an open pit for spoil cast from
the second strip.
► A dozer is normally used to clear vegetation over the box-cuts and down-slope from outcrop
line.
► Overburden is then pushed from the box cuts to the outslope area. Once the coal is uncovered, it
is removed, and a shovel is used to remove the overburden from the second cut.
► Upon reaching the economic limit of mining, dozers push the spoil uphill to cover the highwall
before revegetation commences.

11. Block-Cut Mining
► This can either be applied to area or contour mining.
► It differs from conventional area or contour mining in that blocks of
overburden in excess of 20m wide are removed as a unit and deposited in
mined out areas either perpendicular to the direction of advance ( area
mining) or along the outcrop direction (contour mining).
► If the mineral commodity is relatively a shallow with more or less uniform
cover, the overburden can be removed by front end loaders or pushed by
dozer to the disposal site in one operation.

12. Area Mining
► Equipment used:
► In area mining removal of overburden is accomplished
with:
1. Large draglines.
2. Stripping shovels.
3. Bucket Wheel Excavators. (BWEs)

13. Area Mining
► These machines excavate and deposit material in one continuous operation.
► The same action can be accomplished in part, through the use of explosives
(cast blasting).
► Conventional excavation and haulage techniques (truck and shovel, scrapers or
dozers) are also used by themselves, or in conjunction with casting machines.
Conventional excavation and haulage may be dedicated to top soil removal
only, or it may be employed in removing both topsoil and overburden.
► Area mining usually progresses in a series of parallel, deep trenches referred to
as furrows or strips that may exceed 1 km in length.

14. Area Mining
► Material is removed from the undisturbed area on the highwall side forming a
deep trench.
► It is then placed in the open pit at the angle of repose forming a spoil ridge.
► The width of the open pit is typically 23 to 46m, the height of the highwall may
be up to 60m, and the height of the spoil ridge may be up to 76m.
► Typically highwall angles range from 50° to vertical.
► Typical spoil angles range from 30 to 45° measured from the horizontal.

15. Dragline

16. Stripping Shovel

17. Bucket Wheel Excavator

18. Strip Mining
Very efficient for high level flat lying ore bodies.
Overburden and top soil can be replaced minimizing environmental
damage

19. 2. Strip Mining
► The cheapest and safest method, but can have a
significant impact environmentally on the surface.
Why?
► The ore is close to the surface of the land (30m) but
has one or more layers of rock and dirt on top of it.
To mine the ore, these layers have to be taken off.
► This mining is done in long, narrow strips. When the
ore is done in one strip, the miners begin to create
another strip next to it. The waste, dirt, and rock that
they take off of the top of the next strip is put on top
of the last one.

21. Economics of strip mining depend on stripping ratio
stripping ratio = h1
/h2

22. Strip Mining of Coal
Kansas Geological Survey

24. Strip mining destroys the environment
Strip mining removes soil Discolored water is a sign of acid drainage

25. Strip mining removes surface soil and rock
► Strip mining = layers of soil and rock are removed to expose the resource
► Overburden = overlying soil and rock that is removed by heavy machinery
► After extraction, each strip is refilled with the overburden
► Used for coal, oil sands, sand, gravel
► Destroys natural communities over large areas and triggers erosion
► Acid drainage = sulfide minerals form sulfuric acid and flow into waterways

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

29. 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

30. 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

31. 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

32. END