Depletion Models

The three depletion models defined for Pitram are:

• Weighted Average. An average that takes into account the proportion of each parcel of material (its weight and grade) in the whole, rather than treating each component equally. The grade of this depletion model is independent of the sequence that the material is dumped or extracted - any parcel of material has the weighted average grade of the whole.

Where the weighted average is:

(X1 @ x1 grade) + (X2 @ x2 grade)...(Xn @ xn grade)/X1 + X2...+Xn

• FIFO. First in first out. The first parcel dumped is the first to be extracted. The material extracted may consist of all the first parcel (X1 quantity) that was dumped and a portion (X2 quantity) of the one that was dumped prior to the first. The total tonnage and grade of the material extracted is computed using weighted average.



An ore pass is an example of a FIFO location. The material first dumped is the material first extracted.

• LIFO. Last in first out. The last parcel dumped is the first extracted. The material extracted may consist of all the last parcel (X1 quantity) that was dumped and a portion (X2 quantity) of the one that was dumped prior to the last. The total tonnage and grade of the material is computed using weighted average.

A stockpile is an example of a LIFO location: the material is dumped on the top of the pile and extracted from the top of the pile.

Depletion Models