1. Use to top up the processing stream if the mine is “mine limited”
2. Use to manage grade if mine is “mill limited”
3. Use to extend the life of mine (plant)
What Stockpile?
Do You Need a Stockpile(s)
Definitely yes if:
1. The mined orebody has high grade variability
2. You want to optimize grade cut-offs
To improve cash flow, ROR
3. You are selling / providing a variety of products
Benefits
1. Allow blending so:
a. The mill is supplied with uniform grade ore
b. No preparation/processing is required
2. Provide buffer capacity to smooth out production variations
3. Facilitate higher overall value recovery
a. Easier cut-off grade management
b. Maximize ore recovery
All Roses Have Prickles …
1. Rehandling is involved; it costs money
2. Space needs to be available to accommodate stockpiles
More stockpiles = more needed space
3. Stockpiled material may deteriorate
Recovery drops?
4. Additional expense related to logistics and stockpile management
Material Flow With Stockpiles
How Many Stockpiles?
1. The more, the better
a. Grade control
b. Uniformity of mill feed
c. Product quality
2. Stockpile grades not to overlap!
3. The more, the worse
a. Space is needed; may be at premium!
b. Logistics and material handling costs
Minimum Stockpile Grade
For one element:
Rehandling Cost + Processing Cost
-------------------------------------
SR x PR x Price
SR – Stockpile recovery
PR – Processing recovery
Price – Unit price of product
Using A Stockpile After Lane, 1988
….calculate mine cut-off assigning no value to waste and feed the stockpile material to mill when, and as long as, the result is an increase in the cash flow ….
… it might be better to draw lower grade material from stockpile when the price is low in order to preserve the higher grade material for the expected improvement in price…..
Optimizing Grade With Stockpiles Whittle’s Opti-Cut
1. When the project is “mine limited”, uses stockpile material to top up processing stream to improve cash flow
2. Process stockpile material after ore is mined out to provide additional cash flow
More of Opti-Cut
Stockpile vs. Leach Pile
1. Leach pile
a. No rehandling cost
b. No stockpile management cost
c. Usually earlier return on money spent
2. Stockpile
a. Grade management
b. Better mill / mine capacity utilization
c. Possible savings on processing cost