stripping ratio and break even stripping ratio, Lecture notes of Mining Engineering

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STRIPING RATIO AND BESR

IN OPEN PIT MINING

Cont.

2.2.2 Open pit mining

Mainly refers to the situation in which the

surface mines are rarely above a few

hundred meters radius in area extend

(width and length) but proceed

downwards leaving a large empty

excavation (hole) which is open to the

surface for the duration of the mine's

life. ( most open pit mines are metal

mines)

Example of an Open Pit Mine

Strip Ratio (S)

The strip ratio (S) the ratio of the number of

units of waste that must be moved for one unit

of ore to be mined. The units can be tones of

waste/tonne of coal or cm of waste /tonne of coal

or cm waste /cm of coal.

From a pit design we can determine the tones of

waste and coal that the pit contains.

The ratio of waste and ore for the entire pit

design will give the average strip ratio for that pit.

Strip ratio (s)

Break even stripping Ratio (B.E.S.R) or

Cut-off stripping ratio

 The Break Even stripping ratio is that S.R at which the

costs of mining the ore (coal) and waste (w1+w2)

are same as the revenue for that block of ore/coal.

 B.E.S.R refers only to the last increment mined along the

pit wall. It is calculated for the point at which break even

occurs and the necessary stripping is paid for by the net

value of the ore removed.

coal

w

w

Economic ‘’Cut - off ‘’Limit for surface mining

method.

When the minerals/coal extend deep in the groun d, the

removal of the waste rock becomes too cumbersome and

expensive and the mine operation must be changed to

underground operations where economics allow; or

abandoned.

As open pit mining continue downwards a point is

reached where surface mining operations become

UNECONOMIC and a change to underground

methods is necessary This point is called an economic

‘’CUT –OFF’ LIMIT.

Basic production cost equation for surface

mining and the economic stripping ratio.