Article 3: Recording and Reconciling Mine Production

Many mines use a number of ad-hoc and often disconnected methods – usually a mixture of paper, spreadsheets and specialized programs – to record mine production. These methods might include simple Excel spreadsheets as well as a:

• geological mine planning system
• mine scheduling system for long-term planning of a year or more
• laboratory information management system or sample database to track sample grade and location
• fleet management or dispatch system
• plant historian to record plant processing, and
• enterprise resource management system.

Some of these methods – used by geologists, mine planners, engineers, lab technicians, financial planners, etc. in many different parts of the mining process – require users to take data from one system (paper log sheets, for example) and manually enter it into another system, or to extract Excel data and email it to a co-worker who asked for it so that another employee can then paste the data into yet another spreadsheet system, before it then (maybe) gets stored in a shared network folder or emailed on.

This is slow. It eats up employee time. And it practically encourages mistakes. It also makes it difficult for mine management to know about, react to and correct production issues in a timely way.

An advanced mine operations management solution – such as Dassault Systèmes’ Mine Operations Management (MOM) – not only eliminates time-consuming entry/re-entry issues and reduces the possibility of error, it also integrates materials data from pit to port and ensures that data is securely stored and flows automatically, without human intervention, to wherever it is needed.

More accurate material reconciliations

Most importantly for mine production, you can consolidate all material data in a single database, allowing for far more detailed and accurate material reconciliations.

For example, right now, some mines simply subtract the pit survey at the end of each month to determine the amount of material moved. But that leaves out essential information from the other end of the process: the plant. How much of the original material actually arrived for processing?

An advanced mine operations management system, on the other hand, connects material movements end-to-end – recording the tonnes of all movements from pit to plant – and performs what is called a “Material Balance” that adjusts all movements to compare the balance of original claimed values against actual values.

Using a reporting tool, you can analyse the material balances to expose any anomalies, such as a larger than usual material adjustment or a consistent over-estimation of weights. With that information in hand, it’s easy for mines to identify areas needing improvement and make informed decisions about the best corrections to make to increase production.

Here's how it works:

Material Balance process

Material Balance uses all recorded information about movements within a mine to balance flows from pit to plant, in order to identify where previously accepted values need to be corrected.

This balance is usually based on a “high-confidence” flow – a flow known to be highly accurate. For example, the last movements in the production chain, such as crusher weightometers or finished products, are good starting points for a balance because the output measurements from these envelopes are definite, meaning they have a high-confidence value that needs no correction. From there, material movements between envelopes must balance, so you can change other flows to bring them into line with the high-confidence flow.

The process is iterative, moving back to balance the previous envelope in the chain, and so on, until reaching the mine source.

Typical Material Balance Diagram

Adjustments

Because, in a complex mine production process with many flows, the same data can be measured several times with different accuracy, you can also account for inaccuracy. Material movements from more accurate envelopes will adjust measurements from less accurate envelopes so that they balance. In addition, because the movement and adjustment of numbers will grow increasingly more complex as more material flows throughout the movement chain, a typical balance calculation also involves adjusting movement quantities based on opening and closing survey differences.

For a stockpile, for example, the following formula, derived from the law of conservation of mass, would be used:

Opening Balance + Inputs – Outputs – Closing Survey = 0

Any amount of difference from zero is a discrepancy and is referred to as an “imbalance.” In order to balance this equation, one of the values should be adjusted – typically, the lowest confidence value. If the stockpile’s confidence values looked like this:

then it is the truck factor that should be adjusted to balance the stockpile.

Because all hauling input movements need to be proportionally adjusted by multiplication with (900/1000), if the input in this case consisted of 10 Hauls of 100t, the input would be adjusted proportionally – decreased by 100 to 900 – like so: 100 * 900/1,000 = 90. And the new hauling movements would be 90t each.

The change to the truck weights tells the mine that the trucks are being loaded below their capacity and intervention needs to occur to address the issue.

In addition

But not all material balancing is an adjustment of input. In the pit, for example, waste is often reconciled by balancing output.

All pit movements can be adjusted by a proportional factor so that the sum of all bank cubic metre movements (BCM) equals survey-calculated BCMs mined from the pit during the month. Again, areas with the greatest variances will immediately be visible, and mines can intervene appropriately.

In addition, Mine Operations Management can assist with Sarbanes Oxley (SOX) reporting of production figures by giving mines the opportunity to lock periods that have been balanced, establishing proof of compliance.

Next week, in the last article of this series, we discuss how to use advanced Mine Operations Management to report mine production.