Drilling accuracy proves golden for aussie mine

In January, 2022, Hexagon acquired Minnovare, a leading provider of drilling technology that improves the speed, cost and accuracy of underground drilling. Like Hexagon, Minnovare built its business by enabling connectivity: connecting people, processes and workflows with integrated technology. The following is a customer case study illustrating the benefits of Minnovare’s Production Optimiser.

In early 2018, the Cracow Gold Mine, located 500 kilometres northwest of Brisbane, Australia, faced challenges of dilution and stope performance due to inaccurate drilling. The drilling operations team decided to implement Minnovare’s Production Optimiser technology to address the challenge. The initial implementation led to increased drilling accuracy and thus to an immediate reduction in blast-hole deviation and a 62% reduction in average dilution.

Following the Production Optimiser’s successful implementation, Cracow engineers began experimenting with a new Zipper drill pattern since the mine was facing very narrow stopes which would’ve been uneconomical to mine using the current DICE-5 pattern method.

The aim was to replace the traditional DICE-5 pattern on the narrowest vein stopes. Due to the nature of the design, the Zipper pattern relies on a high degree of drilling accuracy — reducing the total number of holes drilled per stope and the average stope width to just 1.5 metres.

Two trial Zipper stopes were drilled and subsequently blasted. One of these stopes recorded 495 tonnes less dilution compared to what would have been mined using a traditional DICE-5 pattern. This represented an approximate 25% reduction in waste tonnes for the Zipper stope — which is a considerable sustainability benefit, not to mention a significant cost saving.

Phil Jones, at the time senior drill and blast engineer at Cracow, stated: “We estimate that 10% of our stope tonnes going forward can now be mined using the Zipper pattern instead of Dice-5.

At 390,000 stope tonnes per year, a similar 25% reduction equates to approximately 10,000 tonnes less waste/low grade ore that would otherwise have been hauled and processed, which at current cost works out to approximately AUD$1 million (USD$0.7 million) a year.”

Minnovare recently caught up with Thao Nguyen, senior mining engineer at Cracow, now under new owners, Aeris Resources.

“Our stope sizes have dropped significantly over the years. Originally the majority of stope designs were much larger, 2.5 metres to 3.5 metres. Now, on average the majority of our stopes are 1.5 metres to 2.5 metres wide. If a stope is 2.5 metres wide, we would still use the Dice 5 pattern. However, if we expect our stopes to be less than 1.5m wide, we use our Zipper pattern, with a hole spacing of 0.9 metres. To which, we add 0.3 metres planned over-break either side of the stope, making the designed width 1.5 metres wide.

That’s pretty narrow — typically equating just 2,000 stope tonnes. The margin for error is very fine, hence requiring a high degree of drilling accuracy.

Before the introduction of the Production Optimiser technology on our long-hole rigs, very narrow stopes such as these would have been difficult to recover economically.”

Following analysis of Cracow’s reconciliation data for FY20 and FY21 stopes with <2,000 tonnes equated to 119 stopes or around 53% of total production. Based on this, Cracow have been able to recover AUD$59 million worth of gold ounces that were at risk due to the narrow vein nature of the stopes. The all-in cost of mining these stopes was approximately AUD$27 million, generating an additional AUD$32 million profit.

“That’s a big positive – ensuring we extract the maximum value possible over the remaining life of mine,” says Nguyen.

“Optimiser has allowed us the flexibility to continue drilling optimally with both narrow vein and wider stopes, whilst also maintaining the accuracy from setup that we established back in 2018. Being agile to move between Dice-5 and Zipper pattern as needed has allowed us to maximise gold recovery and reduce dilution.”