RE: Price Reaction to RNS8 Feb 2022 13:25
Mathematically, the minimum acceptable grade to mine, i.e. the cutoff grade, occurs when the cost to mine and process the material, (M&P cost), is equal to the value of the product, i.e. its selling price, SP.
M & P cost = SP
We will account for the dilution and recovery losses in the right side of the equation, as these losses are reducing the value of the in-place ore.
M&P cost=SP*(1-D)*(R)*G
where:
M&P cost = mining & processing cost, $/T
SP = selling price of the copper, $/lb
D = dilution
R = plant recovery
G = grade
Assume the following: we have a dilution of 5%, a plant recovery of 92%, a mining and processing cost of $6.80/ton and a selling price of $0.74/lb. Be careful with the units!
Solving the equation for grade, we have:
G=(M&P cost)/{SP*(1-D)*R}
(Equation 3.2.11)
And substituting our values,
G=($6.80/T){$0.74/lb*(1-0.05)*(0.92)*(2000lb/T)}
G=0.499?0.5=.5%
*Imagine a situation in which your resource contains significant tonnage at slightly less than 0.5%. Likely you will reexamine your dilution and plant recovery assumptions, and explore options for improving both so that you can economically mine the lower grade ore*