Corporate Employees Dig into Mine Planning
26 October 2018
Describing mine planners as detail-oriented would be an understatement.
After all, it’s up to them to come up with a master plan for making a profit over the entire life of a mine based on thousands of educated assumptions and estimates that pixel down into the tiniest of details.
Assumptions are mine planner’s stock in trade, because answering literally thousands of questions about a prospective ore body and generating assumptions determines if, what, where, when and how the company will profitably mine.
So, given that mine planners spend their days dealing with thousands of questions, it was only natural for a primer on mine planning to morph into an impromptu, extended question-and-answer session haft-way through the fourth FCX Connects: Dig into series presentation. The series provides employees the opportunity to learn about different corporate functions.
Going around in circles
Mine planning is an alternative process, a never-ending cycle of adapting to changes in everything from rock type and recovery rate to fuel prices and global economic trends.
Essentially everything that can affect the efficiency and costs involved in mining an ore body – including how efficiently every company employee works – factors into a mine plan.
The iterative wheel mine planners traverse starts with developing a set of estimated and assumptions based on the exploratory holes geologists drill and study. The geologists build a 3D model of the ore body to identify the best concentration of copper and from that model, mine planners break up the mineral deposit into individual blocks, assigning information specific to each block.
Though block sizes can vary on the mine site, most North American sites are 50-foot cubes. Providing some perspective on just how many blocks can comprise a model is the company’s Cerro Verde operation, which contains more than 21.5 million blocks measuring 20x20x15 meters each.
Making that number even more impressive is what each block contains.
“Each block can contain more than 100 variables, and there are hundreds of millions of blocks, and all the information from each block goes into our large model of the deposit,” said Karen Wallace, Chief Mine Engineer-Oro Valley. “We put all this information into a computer, which looks at every single block and decides where to route each of those hundreds of millions of blocks – to the mill, to a leach pile or to waste.”
The economic model evolves into the mine-design stage, where the planners generate the ultimate pit limit and situate the best location for roads, mills, maintenance shops, offices, stockpiles, etc.
Lerchs Who?
That all-important ultimate pit limit is designed with a heavy dose of mathematical mojo known as the Lerchs Grossman Algorithm, which converts the block model into the most profitable mineable shape.
Using Lerchs Grossman, planners generate long-, medium-, and short-range plans for how the ore will be mined, stockpiled and processed. That leads to the stage where the value of the pit is derived based on revenue, costs, profit and other factors.
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