ATS Gold Mine Example

For product-optimised transactions, ATS does not schedule a destination until the end of the period. Once it knows all the ore that has been mined in the period, it decides what to do with it based on the costs and revenues applied to the movement and processing of the material. 

The rules in the Product Specifications step define the positive and negative cash flows derived from each activity. 

• Positive Cash Flows: the dollar per tonne in revenue for dumping a material at a location, ie. Oz to crusher.
• Negative Cash Flows: the dollar per tonne in cost for dumping a material at a location, ie. rehandle cost per tonne onto stockpile; process cost per tonne into crusher.
• Grade Penalties: the dollar per tonne per point deviation from grade targets. 
• Grade Limits: minimum and maximum weighted average product grade at the end of the period. 
• Blend Limits: minimum and maximum average material ratios at the end of the period. 

Generally a Tactical Scheduler project should have at least one of the following: 

• Positive Cash Flow for ore to crusher. 
• Negative Cash Flow for material to a rehandle stockpile.
• Neutral Cash Flow for material to a long term stockpile. 
• Grade limits for feed.

If the crusher isn't being fed, it is almost always due to missing positive cash flows or due to conflicting grade limits. 

Gold Mine Example

Take the following gold mine setup:

Destination Logic

Destination Logic describes the final resting place at the end of the period. The Crusher is not a final destination (it feeds the Cone), instead it is listed in the Steps Logic as a waypoint.

• Ex-Pit:
  • Waste to dump
  • HG* to ROM, Cone, Mill
  • LG to LTS, ROM, Cone, Mill
• Rehandle:
  • ROM to Cone, Mill
  • LTS to Cone, Mill

Where HG* represents materials HG1, HG2, HG3. 

Steps Logic

Steps Logic describes the in-period waypoints between original source and final destination, and what fleet (or conveyor) is used on each leg. 

• Ex-Pit
  • Ore => ROM => Crusher => Cone => Mill 
  • Ore => ROM => Crusher => Cone 
  • Ore => ROM
  • LG => LTS
• Rehandle
  • LTS => ROM => Crusher => Cone => Mill 
  • LTS => ROM => Crusher => Cone 
  • ROM => Crusher => Cone => Mill 
  • ROM => Crusher => Cone 
  • Cone => Mill 

Constraints

When material is routed through the Crusher via the Steps Logic, it does not count as crusher throughput. Therefore we must add constraints to limit the Crusher feed.

• Standard Constraint "Crusher Limit" applies to:
  
  • (Pit, LTS, ROM) => (Cone, Mill)

Product Specifications

Suppose we want to apply the following rules to the optimisation:

• Higher grade material should be fed preferentially.
• Higher grade material should be stockpiled preferentially.
• Mill feed should not exceed 10% Oxide (>90% Fresh) 

We can achieve this with the right cash flows and blend targets.

Worked Example

During the period, the Agent mines blocks. If the Destination Logic rule is marked as "Crusher Feed", then the material is held in a virtual stockpile until the end of the period. At the end of the period, the Agent assesses the product specifications and assigns the material to its final destination.

Destination optimisation (not considering oxide ratios):

The oxide ratio rules act as an additional cap on feeding the Mill or the Cone. Assuming capacity remains in the Mill, the optimiser will continue to maximise revenue (progressively feeding HG1, HG2, HG3, LG oxides), until it hits the 10% cap. At this point the next least costly option is the Cone, which is filled in the same order until the 10% cap is reached. If both Mill and Cone hit the 10% oxide limit, then the material defaults to the ROM.