Traceability and Grade Control

Mining companies use grade control – and grade control drilling – to understand the distribution of mineral deposits within a pit area and identify where the highest quality deposits are concentrated.

Sounds pretty simple, right? But a lot is riding on the grade numbers being as accurate as possible, since it is this grade information that will determine how plans are made, resources are deployed and, ultimately, how much the mine will return on investment. What if those numbers are off?

Identifying variances from pit to plant to product

Being able to do a daily comparison of grade at the mine source against grade at the start of the plant processing circuit (where more reliable daily head grades can be found) is essential for an accurate and complete understanding of mineral distribution, yet there is currently no easy way for most mines to make that comparison – which means they are missing out on the opportunity to make quick and timely adjustments that will not only improve grade confidence but also increase the overall productivity of the mine.

Right now, doing a daily comparison of grade at the mine source with grade at the start of processing usually entails the Geology Department manually contacting the Plant Department to check the received grade for variance, which can be appreciable. Some mines have reported a large discrepancy between grade expected by Geology and the grade reported by the plant. However, by then it is too late for Geology to correct any issue.

A better approach is for mines to store their grade information through advanced mine operations management – such as that offered by Dassault Systèmes’ Mine Operations Management (MOM) solution – that can help mines visualize, highlight and quickly rectify any variances between mine grades and plant grades before there is any loss of confidence in grade data and control.

This can be done in four ways:

1. Recording grade data from pit to plant

Recording planned, estimated and actual grade information from pit to plant allows mines to create detailed stochastic models (stochastic modelling estimates the probability of various potential outcomes where randomness or uncertainty is present).

Grade confidence for the same movement

2. Mapping daily grades to movements

Mapping daily grades to any movement at different confidence values makes it possible for mines to create rich graphics that compare grade variances between all sources of relevant mining data.

With feedback on grade variance between planned and actual, geologists can improve their grade estimates and better meet plant feed requirements, which will then improve mine final product output.

3. Capturing dilution

Dilution ­– the waste material not separated from the ore in mining, usually caused by “overbreak” from blasting – will lower the grade expected at the plant. The less dilution the better because it means increased metal recovery at the plant.

Advanced Mine Operations Management can help mines:

• capture dilution on headings and blocks shift-by-shift to provide feedback to the drill and blast crew
• record the history of grades for a mine source to improve future estimates for the same material/grade
• determine whether dilution caused a lower grade and thereby assign the correct diluted tonnage and grade to loaded movements.

4. Increasing traceability

To make the most accurate grade estimates possible, mines need to able to trace ore grade not just from pit to plant, but from pit to finished product and customer sale.

However, source materials may be mixed in stockpiles – leading mines to use mathematical techniques to compensate for the mixture, such as proportionally allocating material to the source locations based on their proportion of contribution to the stockpile.

On the other hand, by providing the ability to record and store all movements and ore source locations, makes it possible to match finished product grades to their exact source. And from there, it’s easy to analyse the flow of the mine, and identify where and how to improve exploration, grade analysis, and planned vs. actual grade.

Conclusion

In addition to enabling mines to track, record, analyze and improve ore grade, a mine operations management solution provides the ability to integrate grade information with other data – such as equipment/operator performance, which we discussed in Article 1 of this series – gathered from pit to plant to port.

From there, it is an easy step for mines to:

• demonstrate to shareholders that they are delivering on their sustainability promises, and

• increase mineral resource transparency now required by governments.