Caleb Cook, Kappes, Cassiday & Associates Dan Kappes, Kappes, Cassiday & Associates Conveying and Stacking Systems Design for Heap Leach Applications Kappes, Cassiday & Associates 7950 Security Circle Reno, Nevada Telephone: (775)

Heap Leaching: Permeability is Key to Success Permeability of top Working Surface Uniform Permeability of the Heap Permeability of Intermediate Layers Between Lifts Permeability of Drainage Layer Below Heap

Truck StackingConveyor Stacking Crushed ores and ores high in clay Lower operating cost compared to truck stacking Flexibility to add moisture or chemicals before stacking Less compaction (generally) of top of heap Operation flexibility When conveying options become too large ROM applications Stacking Methods Vs.

Four Main Configurations: Discharge from a tripper on a bridge conveyor which straddles the heap (small tonnage, on-off heaps) Discharge from a tripper on a long traveling belt supported on bulldozer tracks running on the heap Retreat stacking Top advance stacking Conveyor Stacking of Heaps

Bridge Conveyor & “Racetrack” Design Stacking: Thin Layer Heap Leaching Pros: On-off style leaching Good for low permeability heaps Fast recoveries Useful for acid leaches Cons: Generally low lift heights (1-4 m) Not suited for multi-lift heaps For “racetrack” design – very capital intensive

Bridge Conveyor & “Racetrack” Design Stacking: Thin Layer Heap Leaching - Continued “Racetrack” design on-off heap leach at Round Mountain Permanent Heap New Heap Being Stacked Old Heap Being Removed

Pros: Similar to bridge conveyor arrangement Can climb slopes and construct multi-lift heaps Results in a very permeable heap Rahco-type Stacker for Permanent Heaps Cons: Capital intensive Very large machines which require regular geometries or large area for turning

Rahco-type Stacker for Permanent Heaps Rahco stacker at Chuquicamata, Chile – copper heap leachRahco stacker building “racetrack” style heap. Tracks are on the “permeable” heap base. Alternatively, the stacker can stack on top of the lift and advance forward, avoiding traveling on saturated ore.

Most common type of conveyor stacking system Easy to operate for single lifts up to 8 m Can be used for multiple lifts, but may result is a reduction of ore permeability at the working surface Retreat Stacking Retreat stacking system at Yatela operation in Mali

Ideal for multiple lift heaps Well suited for valley fill heap leaching If designed properly should be lighter in weight compared to retreat stacker No limit to lift height Top Advance Stacking Top advance stacking at Ocampo in Mexico

Often not considered with the ore type or overall process in mind Generally left to the stacker supplier with minimal design criteria Ideally project metallurgist or design engineer should work with stacker supplier to properly select a stacker Stacker design should include considerations for: Ore type, heap configuration, size, etc. Design for minimal need for support equipment (cranes, loaders, dozers) As light weight as possible (while maintaining structural integrity) Low ground pressures Stacking Equipment Design

Insufficient or over designed equipment structural strength Excessive equipment weight / ground pressure of tires or tracks Poor design of systems used for equipment movement on heap Deficiencies of Conveyor Stacking Systems Index Conveyor at Ocampo – tipped while moving

Manufacturer generally biased towards making equipment too heavy Good for equipment durability, not necessarily for heap leaches Equipment overdesigned due to the fear of equipment failure on leach pad Too heavy equipment = increased chance of failure of the heap. Can result in excessive use of mobile equipment to aid in positioning Ideal design requires No mobile equipment on the heap. Insufficient or over designed structural strength and equipment weight

Heap surfaces are irregular with water saturated material System should travel on the heap without leaving visible wheel or track ruts Ground pressure of 10,000 kg/m 2 or less is generally acceptable Large flotation tires or caterpillar-type tracks are ideal Excessive Ground Pressure of Tires and Tracks Stacker tires with tracks at Ruby Hill mine

Stacking system must continually move on heap up to several meters per day Movement should be done by equipment itself to avoid having any more additional equipment (bulldozers, loaders, cranes) on the heap than necessary Excessive equipment movement on heap will inevitably result in some lost recovery Equipment drives should be powerful enough so that the equipment can extract itself when it runs into depressions in the surface Poor Design of Systems for Moving Equipment

Stackers should be equipped with stingers to minimize movement on the heap Correctly designed equipment can build a flat heap Poor Design of Systems for Moving Equipment - Continued Comco Silver Heap Leach – Potosi, Bolivia

There are several different ways to place ore onto heaps Not all of these are optimal in all circumstances Poor choices may result in loss of recovery Conclusion