The Heritage Minerals team, led by Drilling Manager, Shane Charlton, has been achieving depths of 46 m with high-quality 86 mm samples using Dando Drilling’s Terrier percussive drill rig, the drilling manufacturer says.
The depth is a record for the Terrier rig, according to Dando.
Heritage Minerals is currently working on the historied Mount Morgan mine in Queensland, Australia. One of Australia’s oldest mines, Mount Morgan was active from 1882 through to the 1980s. In the process, tens of millions of tonnes of tailings were generated.
Today, these tailings present both a problem and an opportunity; a problem because they were subject to old, polluting technologies for processing gold, but an opportunity because they still contain reserves of gold, copper and other minerals.
Heritage Minerals is employing innovative processing technologies such as ReCYN, developed by partner GreenGold Engineering, to clean pollutants from the tailings and returning them to safe land.
Heritage chose a Dando Terrier rig to sample the tailings at Mount Morgan for several reasons, Dando said.
“Foremost, the unconsolidated geology of tailing fines is very hard to sample with conventional rotary equipment,” it said. “The Terrier’s Duplex Sampling System, which is driven into the ground by a 64 kg anvil and simultaneously cases-off and samples, provides excellent recovery in this type of unconsolidated geology for metallurgical and in-situ density measurements.”
Charlton proved and refined the drilling method he used in the mineral sands of Kalimantan, Indonesia, where he sampled alluvials to over 20 m for lab analysis, Dando says. This is an impressive feat for a rig that has a large user base for geotechnical sampling, standard penetration testing and dynamic probe testing, most often at depths of less than 15 m.
More than doubling this to 45 m was no easy task, Charlton explained: “At depth, it took almost 10 minutes to trip the drive rods and retrieve the sample, but the quality of the sample and the economies in terms of cost per metre offset the sometimes slow drilling.”
Heritage has recently purchased a second Terrier rig from a Dando customer in Australia and Charlton has made some modifications to the design to facilitate drilling beyond the original specifications of the rig.
“We’ve fitted a permanent casing extractor to help pull sample tubes and casing if they get stuck, as well as modifications to assist with tripping rods more quickly,” he said.
To achieve these depths, the team are using a reaming method whereby they sample using an 86 mm windowless sampler tube, and then ream out using a larger 116 mm tube before returning to the 86 mm sampler to continue. This reduces frictional forces along the side of the borehole and abrasive tailing materials, according to Dando.
The percussive hammer system allows sampling without flush, minimising the need for cumbersome mud tanks or air compressors while preventing contamination of the sample or the environment, it added.