Integrity – Do all mine plans have it?

By Tracey Rock.

As an Engineer, I am drawn to tools that make my work easier and result in a better outcome. In my 27 years in the industry, mine planning software has developed as a tool that makes it easier to evaluate multiple, often 10’s and 100’s of mine planning options, but this does not mean that there isn’t a human element involved and this often results in scheduling errors and mistakes.

In 1978 Dan Bricklin an Electrical Engineer/Computer Science graduate who was doing an MBA at Harvard Business School was daydreaming during a lecture whilst looking at a spreadsheet on a blackboard.

He was thinking how great it would be if there was a computer program that could do the blackboard calculations automatically. His computer spreadsheet (VisiCalc) was released in 1979 and eventually revolutionized the accounting industry. Spreadsheets went from being paper sheets stuck together where accounting firms would spend days calculating client’s finances to computers taking seconds to do the same thing. This did not spell the end to the accounting industry though, because as accounting became cheaper, clients started asking the now common question – “What if?”, and companies started to have a better understanding of their business. What resulted though, was a tool that gives the illusion of accuracy.



Example of VisiCalc (left) and Dan Bricklin, VisiCalc developer  (Right)


In a 1984 article a technology journalist wrote ‘’the spreadsheet is a tool, and it is also a world view – reality by the numbers”. Spreadsheets are fundamentally constructed by humans, who make mistakes. The biggest example being the London Whale, where $6.2 billion dollars was lost due to on an error in a single cell. Packages like ExcelAnalyser was designed to detect errors in excel spreadsheets because there is a human element involved.

The history of mine planning software is not as well defined, but were released as a product in 1985 and these and other developers have provided mining engineers with ever improving tools to answer the question ‘What if’ for their employers. But have we got a tool that checks mine plans for human errors? Or do we assume that the software doesn’t allow errors?

A mine plan is the key instrument used for the commercialisation of an asset. A mine plan contains a schedule that is made up of sequencing thousands upon thousands of individual tasks, each with varying rates and time. It is an ever-changing complex challenge that is undertaken across every mine site in the world, using numerous software packages and varying engineering skill.

Just like spreadsheets and the accounting industry, mine planning software helps mining companies make short work of multiple iterations of a mine plan. Pioneering scheduling packages can be completed across multiple planning horizons. The goal of each mine plan may vary from maximizing profit, providing consistent product or ensuring no unplanned downtime for critical equipment. To achieve this goal, a life of asset plan may only include a schedule of major equipment and tasks, whereas a three-month plan may include a schedule of all equipment and tasks.

Where all tasks are not scheduled, allowances or assumptions for the unscheduled tasks need to be included in the schedule. This is usually done by making sure there is a sufficient time gap between two scheduled tasks (e.g., eight weeks between Bench A and B in the same strip to allow for de-coaling and drill and blast). These rules are not generally included in the documentation and presentations with the critical equipment rates and production time, and they aren’t visual in the animation or Gantt charts because they are not assigned a resource. This can lead to human error.

In addition to the issues of tasks not being scheduled all mine sites have unique sequencing rules that need to be applied to make sure the mining sequence does not allow undercutting or enable equipment to be in the same place at the same time (albeit doing two different tasks).

Mine planning software can apply rules, sequences and constraints, but with multiple scheduling blocks, complex dig sequences and the 65th iteration of a schedule that is not achieving all required outcomes, these are often disabled to allow for manipulation and smoothing of ore/coal flow or to speed up the bench sink rate. As thousands of tasks are being sequenced, there is a risk that relaxations and over-rides are sometimes lost in the process.

Checking the sequence in the animation of mine design software is a common way of carrying out an initial check on the rules and assumptions. It provides a sanity check on the sequence and identifies areas at the start and end of the sequence that have been missed. In the same way, checking the scheduled and resourced animation in the mine scheduling software is used to confirm in more detail that the mining is as per intended assumptions, rules, sequence, and resources on a high-level basis. Generally, there is no artifact created from these checks and the published mine plan contains no reference to where the rules are being broken.

The output from a mine plan that breaks the rules and ignores some assumptions will still be presented in the same way as a mine plan that has been meticulously planned. In this way, it is like the humble spreadsheet, where the output can look polished and well put together but can contain erroneous assumptions within. As an industry do we know the integrity of the mine plans we put forward or make decisions on?  Or do we need to understand the impact of the human component on our mine plans?

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