Determining Stripping Ratio

Stripping Ratio (SR) & Breakeven Stripping Ratio (BESR)

What is Stripping Ratio?
Stripping ratio simply refers to the amount of waste handled in order to recover certain amount of ore. 
It is mathematically expressed  as the ratio of waste to ore. 

However a wide variety of units are used as well as indicated below:

Hence the maximum allowable stripping ratio at pit limit is given as:

SR (Overall) = Volume of Waste/Volume of Ore

For Example: 

Determine the Stripping Ratio of the ore section (green zone) shown below:

We know; SR = Waste/Ore, therefore;

SR = 2500/5000 = 1:2 (i.e. 0.5) (i.e. one unit of waste is removed to recover 2 units of ore)

Note: We proceed by determining the area of waste materials by calculating the respective areas of the representing triangles on the section and divide it by the area of rectangle representing ore.

Break-even Stripping Ration

The maximum allowable Stripping Ratio (SRmax) defines break even stripping ratio (BESR). This represents the highest possible units of waste that can be handled. If the SR exceeds the BESR then the operation will be uneconomical as the income generated by the ore is insufficient to offset the costs incurred in mining.  It appears there is a calculation that helps determine the breakeven point beyond which the cost to remove overburden becomes prohibitive.
The BESR 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. Generally, the BESR can be determined as follows:

BESR = I - CT / CW

I = Revenue/tonne of ore
CT = production cost per tonne of ore (incl. all costs to the point of sale, excluding stripping)
CW = stripping cost per tonne of waste

(NB: These Initial may vary from person to person depending on their own preference)

For example:
Determine the BESR in mining and processing a 0.60% copper ore deposit if the selling price of copper in concentrate is $1.63/kg and the overall unit costs are $6.80/ton and the cost of handling unit weigh of waste is $7.50/ton. The overall recovery is 92%.

a.       Calculate the BESR

BESR = [(0.006*0.92*1.63*1000) – (6.8)]/7.5

         = 0.29 = 0.3 is the maximum allowable stripping ratio for break even

This mean the income generated by one unit of 0.6% graded copper is able to offset the cost of 3 units waste at no profit (Income = Cost).

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Determining Stripping Ratio Determining Stripping Ratio Reviewed by CEDRICK KAU on April 04, 2016 Rating: 5

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