Only a few years ago, Phu Bia Mining, a subsidiary of copper and gold producer PanAust, faced a potentially devastating problem with the throughput at its Phu Kham open pit copper-gold mine in Laos. “We knew anecdotally that there were pockets of extremely hard material in there but we just didn’t know when we were going to come across it,” said Duncan Bennett, principal metallurgist at PanAust. “It was quite scary for throughput to suddenly drop dramatically and you’re just not ready for it.” The Phu Kham deposit is heterogeneous to the extreme, with complex and variable mineralogical, geological and geotechnical properties. Among the many factors causing this high variability is that weathering and water table contact have created a soft leached zone on top of areas with supergene chalcocite-dominant secondary copper mineralization, resulting in periodic throughput-slowing batches of hard rock. At its deeper levels, the deposit has extremely hard rock.

“We didn’t know when, or even if, we’d need to put in additional crushing because we didn’t have a basic model,” said Bennett. A new crusher is no trivial expense – Bennett estimates the cost at $24 million – so Phu Kham staff needed help deciding if the extra equipment was really worth it.

In 2012 Phu Kham engaged Metso Process Technology and Innovation to conduct a full integration and optimization survey that included blasting, crushing and grinding. Metso provided an innovative solution that not only helped Phu Kham make an informed decision for its long-term needs but also empowered the mine operators with ongoing throughput forecasting, allowing them to more effectively process the mine’s extremely heterogeneous deposit – starting with just the right blast force.

Prior to working with Metso, Phu Kham had relied on a traditional throughput forecasting model. Performed by geometallurgists, traditional modelling relies on dividing a deposit into cubic blocks with 10-metre sides, taking samples and testing them for such parameters as structure, hardness and ore grade, which govern how the ore will be processed in the concentrator and what the projected throughput will be. Since a mine can be divided into millions of blocks, testing each one is impossible. That is why mines only test some of the blocks and then use geostatistical methods to infer the most likely parameters for the rest. This method can be quite reliable, as long as there are no hidden surprises. In the case of Phu Kham, however, the mine simply did not have enough data for an accurate and detailed model of its heterogeneous deposit, which is full of surprises.

The SmartTag advantage

For years, Metso has helped mines optimize and solve problems in their processing operations by measuring the effect that blasted ores have on the crushing, grinding and flotation processes. But it is not always easy to keep track of the ore after each blast since it often ends up in stockpiles and mixes with other ores. So in 2007, David La Rosa, manager of mining technology at Metso, helped develop the SmartTag ore tracking system. SmartTags come in three different sizes, with the largest looking like a 60 mm by 30 mm hockey puck, and each one having a chip with a unique identification code. They are dropped in the stemming columns of blast holes and, just before detonation, the ore characteristics of the specific area, as well as the tags’ GPS location, are recorded using a handheld device. Designed to withstand crushing, the tags then travel with the rest of the blasted rock and their signal is picked up by antennas that can be placed permanently or temporarily at critical points across the processing stream. How the specific tagged ore responds to each phase in the process is then recorded and analyzed. Phu Kham has used around 5,000 SmartTags in the past year, says La Rosa: one per blast hole and about 100 per blast.

More recently, Metso has built on the SmartTag technology to develop a geometallurgical application called GeoMetso, which uses the data collected with the SmartTags to automatically update the mine’s block model in real time. “We’re measuring what the plant is actually doing at an instant in time and then we’re taking that measurement and putting it back into the block model so we can compare what we thought we were going to get in throughput to what we actually got,” said La Rosa. “And if there’s some shortfall, we can then look at the reasons why. For example, do we need to blast harder?”

Blasting

“One of the things geometallurgy doesn’t take into account is how the material is actually blasted,” remarked La Rosa. “You can blast something with a low powder factor and not produce much fines, but if you blast with more energy, you get much finer material and very different results in the concentrator.”

It took about a year of collecting data at Phu Kham for Metso to identify nine different ore domains based on the data it gathered with the SmartTags, and to conduct simulations for each one to determine the optimal blasting design needed for the desired throughput. The result was nine different “cookbooks” that provide the “recipe” for the optimized blast design for each ore domain at Phu Kham. With GeoMetso, the data obtained through the SmartTags is linked to the plant control system so real-time data can be folded back into the mine’s block model. Having the right blasting recipe has been key for Phu Kham.

“Two months ago, we hit some really hard ore and we used some extremely energy-intensive blasting and had some really good results,” said Bennett. “We got way more throughput than if we’d just used the standard blasting patterns. We were able to get 1,900 tonnes an hour. If we’d done nothing, we’d have been lucky to get 1,500 tonnes an hour.”

Long-term planning

With actual data, Metso was able to predict throughput over the life of the mine. The good news is that the mine will only be hitting the very hard rock threatening its throughput for about a year. Now, instead of a major investment, Phu Kham operators can focus on more strategic blasting to manage their throughput, while the company is able to tell shareholders when, and for how long, it will be dealing with the extremely hard rock. “The cost of each tag is $10 so it’s not super cheap, but the alternative is to not know, and if we’d had to put additional crushing that would have been $24 million,” said Bennett. “The more data the system collects, the better the predictions. There’s a very strong economic benefit in developing and understanding how the material in the ground is going to get through the plant.”

There was, however, one positive surprise to the project. “It helps break silos as it goes across disciplines,” said Bennett. “Geologists don’t always think about how this material is going to go through the plant. Now they have an understanding of some of the criticalities of some of these measures for future throughput, so they’re thinking about what’s going to happen in the future. It gets everyone thinking from beginning to end, how it’s all interconnected. That’s a really positive thing.”