Lecture 2 2011 Ore Body Geometry

8/4/2019 Lecture 2 2011 Ore Body Geometry

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Surface Mining

Ore Body Geometry2011 Dr. B. C. Paul

Note- Concepts given here are considered to be common knowledge to thoseinvolved in early stage ore estimation. Geometric concepts used are found in

most books on geometry. Acknowledgement is given to SME for model P.E.exams that guided the choice of some materials chosen for review.


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Need to Define a Size of anOrebody

In more advanced stages of miningorebodies are often modeled as millions of

tiny blocks that are analyzed by computer In early stages approximate magnitude of

orebody size is often determined by

comparison to basic geometric objects.


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Example The Coal Seam

Coalstrip Coalmining Company has obtained therights to 6 sections of coal bearing land

measuring 10,560 ft X 15,840 ft. The coal seamis approximately horizontal and is about 7 feetthick on average. It is bituminous coal with atypical density of 80 lbs/cubic foot. If the

company wants a 20 year reserve and willrecover 90% of the coal, what mining ratewould they use?


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Step #1 Get the Coal volume

This is a big box (but not a very tall one)Volume for a 3D box is

Length*Width*HeightApply 15,840 * 10,560 * 7 =

1,170,892,800 cubic feet


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Step #2 Convert the Volume to aWeight

We know that a cubic foot of coal weighs80 lbs therefore the weight is

1,170,892,800 * 80 = 93,671,424,000 lbs

We also know there are 2000 lbs in ashort ton (the kind used in US coal

mining) therefore the weight in tons is 93,671,424,000 / 2000 = 46,835,712 tons


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Step #3 Adjust for Recovery

Only 90% of the coal in place will actuallybe recovered by mining

46,835,712 tons * 0.9 = 42,152,141 tons


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Step #4 Get the Average MiningRate

The reserve will be mined over 20 yearstime

42,152,141 / 20 = 2,107,607 tons/yearAs a practical matter one would say

mining rate is about 2.1 million tons per

year


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Why is this information Important?

Early in the definition of a deposit you will needto know how you might mine it Knowing how big something is will help you to see

what is practicalA 2.1 million ton per year surface mine makes senseA 50,000 ton per year surface coal mine does not make a lot

of sense

Total amount of recoverable coal may give you anidea of how much profit you could make. Theamount you can invest in the deposit must be lessthan this amount.


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Lets take this coal deposit one stepfurther

Suppose we assume that the coal will pickup about 7% material that is not really

coal (out of seam dilution) Suppose we figure the preparation plantwill have a yield of 70%

How many tons of clean coal will wemarket and how big had the coalpreparation plant better be.


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Feed to the Preparation Plant

The 42,152,141 tons of coal will be dilutedby 7% more out of seam material

42,152,141 * 1.07 = 45,102,791 tons Over 20 years average feed per year is

45,102,791 / 20 = 2,255,140

About 2.25 million tons per year

Incidentally our coal loading equipment at themine better be able to move that tonnage too.


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Size Up the Prep - Plant

About 2,250,000 tons per year A typical coal prep plant will run 250 days per

year, 2 shifts per day, with about 7 hours of realrun time on a shift

250 * 14 = 3500 operating hour per year

Size the Plant 2,250,000 tons/year / 3500 hours/year = 643 tons

per hour

About 650 tons/hour


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More Observations

With the scale of operations approximatedwe can make good guesses on our capital

investment and operating costs We are set up to do early economic

evaluation to determine if we should invest inmore exploration and planning.


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Lets Try a Dipping Vein Next Thismight be a phosphate deposit

We have popped three holes in the deposit on aline every 30 metersA top 30 m bottom 56

B top 68 m bottom 98 C top 106 m bottom 140

What is the thickness of the vein of layer? (Note we cannot really get the dip of the deposit

because we would need to know the holes ranperpendicular to the strike of the depositwhich we do not know).


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Depth to deposit midpoint

A is at 43 meters B is at 83 meters

It went down 40 meters for 30 meters over

C is at 123 meters It went down 40 meters for 30 meters over

We are going down 40 meters for 30 over

40

30

Arctan(40/30) = 53.1 degrees ofApparent dip


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Look at Our Drill Hole InterceptDistance

Hole A 26 meters Hole B 30 meters

Hole C 34 metersAverage Intercept is 30 meters But we Hit it like this

Our intercept isClearly not the seamthickness


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Correcting to Get Seam Thickness

53

30*cos(53) = thickness =18.05 metersAbout 18 meters


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A Dipping Seam Tonnage

The strike of a phosphate bed runs for1000 meters

It dips at 53 degrees for a distance of 500meters

It is 18 meters thick

The density is 2.45 tonnes/cubic meter


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Step #1 Get the Volume

This time the box is dipping 1000 * 500 * 18 = 9,000,000 cubic Meters

Step #2 convert to weight 9,000,000 cubic meters * 2.45 tonnes/cubic

meter

22,050,000 metric tonnes

Lecture 2 2011 Ore Body Geometry

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