lecture 4 calculating stripping ratios for area strip mines
TRANSCRIPT
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7/29/2019 Lecture 4 Calculating Stripping Ratios for Area Strip Mines
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Calculating Stripping Ratios forArea Strip Mines
Mnge 315
Dr. B. C. Paul spring 2003 revised 2010
Note These notes contain information considered commonknowledge to those familiar with Strip Mining. Books such as
Elements of Practical Coal Mining and SMEs SurfaceMining were specifically referenced
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Stripping Ratio as a Fundamental
Ability to surface mine depends on the value ofthe ore being high enough to offset the cost ofOverburden Removal
Stripping Ratio determines relative amounts of eachto be moved
If coal generates a $5/ton earning andoverburden costs 45 cents per cubic yard tomove what is the maximum economicstripping ratio
$5.00/ 0.45 = just over 11 cubic yards per ton Called a Break Even Stripping Ratio
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Complexities Warning
Units of Stripping Ratio depend on convenienceof the industry
Coal overburden is normally light and machines arelimited by volume in cubic yards
Coal is sold by the ton
Cubic Yards/ton makes sense
Hard Rock Metal Both ore and overburden are trucked
Both are heavy and trucks are usually weight limited
Tons/ton makes sense (unit-less)
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More Warnings
Geometry problems usually measurevolumes which convert to tons only if
density is the same for all materials Material may be rehandled
Get operating and geologic stripping ratios
Dont use 40 cents per cubic yard to figurestripping ratio off of geometry if you have 10%rehandle
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Fixed and Variable Costs
Example of the Car If you have a car
Insurance
Licensing Fees Storage or Parking Space These Costs constant per unit of time regardless of
use of car
Variable Costs Gas Tires Oil Changes Largely Dependent on mileage you drive
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Fixed and Variable Costs in Mining
Some mining costs are fixed (manyadministrative features for example)
Others are variable direct materialshandling cost
What goes into Break Even Stripping Ratio
Direct materials costs go into Break Even Fixed Costs are charged to the average
stripping ratio you mine over the time
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Simple Stripping RatiosBottom of a
Strip MineTop of a Strip Mine
For a pit 1 mile long and
160 ft across, how significantly
Different is the length at the top
And bottom of the pit?
Volumes are Length * Width * Height
Ratio is A/B
What happens if the length term in
Both A and B is the same number
It cancels Long strip pits can be
Analyzed as 2D problems!!!
Life is Good
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The 2D Cross Section
Overburden
Area = Base * Height
Interest Item Slope Angle
Has no effect
Base for both coal and the overburden is the same
That means the base will cancel!
The problem is 1D
Only depends on
Thickness and density
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The Coal Area Strip Mine Formula
Strip Ratio = OB Thickness (in ft) * 11.11/Coal thickness in inches
Assumes coal is 80 lbs/ft^3 (good forbituminous)
Area Strip Mine Geometry
Geologic Stripping Ratio no accounting forrehandle or less than 100% coal recovery
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Your Turn
Use What You Have Learned AboutCalculating Stripping Ratios for Strip Mines
and Break Even Limits to Determine theSize of a Coal Reserve
Do Assignment #3
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A Little Explanation
Very seldom is a coal seam the sameDistance from the surface always
Less overburden meansMore profit. Project worth is increased if you take the
Biggest profits first thus strip mines startShallow and work into deeper stuff.
Is it possible that eventually the coalWill get deep enough to exceed the break-evenStripping ratio of course!
In your homework you will look at a coal reserve start shallow and work until it isDeep enough you cant afford it anymore. Then youll tell me how far you could mine.