SHAFT SINKING
Shaft sinking at scale
The Oyu Tolgoi Underground project is one of the biggest underground mine developments taking place across the globe .
At a forecast cost of $ 7.06 billion , it is a significant financial investment for majority owner Rio Tinto . The rewards for making this investment are massive , too , with the combined open-pit and underground operations expected to produce around 500,000 t / y of copper on average from 2028 to 2036 .
Developing one of the world ’ s biggest block cave mines involves a significant amount of shaft infrastructure , with the planned development being serviced by five shafts in total .
Shaft sinking activities have been steered by The Redpath Group along with Hasu Megawatt , through joint venture company , Dayan Contract Mining .
Damian Rogers , Underground Project Director , Oyu Tolgoi , recently provided an update on shaft sinking progress at the operation to mine visitors from the financial community .
With Shaft 1 , 2 and 5 complete , the current focus is on Shaft 3 and 4 , which are critical activities to the support the ramp-up from Panel 1 and Panel 2 at the block cave operation .
“ These ventilation shafts enable us to make , firstly , the step change in the lateral development required for Panel 1 and Panel 2 , and of course they ’ ll ventilate the mine all the way through the full production ,” Rogers said .
Shafts 3 and 4 are , according to Rio Tinto , the largest ventilation shafts currently being constructed in the world – 1,148 m and 1,149 m deep , and 11 m and 10 m in diameter , respectively . Once commissioned , Shaft 4 will exhaust 1,800 cu . m / sec of air from the mine .
Rogers said : “ I ’ ve been around a lot of shaft construction ; it ’ s often hard to comprehend the scale of an 11-m diameter shaft , like Shaft 4 . When we completed the 8.5-m diameter Shaft 10 at Resolution ( in Arizona , owned in a joint venture with BHP ), it was one of the largest and deepest completed in North America at the time , then we quickly followed that up with the 6.7-m diameter Shaft 9 there , and connected them in Arizona .
“ So , in shaft volume terms , or in cross-sectional area terms , both of those shafts would fit inside Shaft 4 at Oyu Tolgoi . Same thing for both the Woodsmith mine shafts getting constructed in the UK ( owned by Anglo American ) now , or any of the four shafts getting constructed in Australia . So , the scale here is phenomenal .”
Rio Tinto , via the Dayan Contract Mining joint venture , is using a firstof-a-kind sinking system at these shafts , leveraging four vertical shaft muckers in one shaft .
Rogers said the main reason the company has progressed with this system is the ability to advance sinking without having people on the shaft bench during mucking operations . “ Really , as an industry , we ’ ve been working towards that for some time , because this is the part of the sinking cycle that really presents , historically , a very high risk to people in the shaft around that mucking equipment ,” he said . “ So , with our system , there ’ s nobody on the shaft bench while we ’ re mucking ; it eliminates that risk .”
While finetuning this innovative system did lead to slow progress on sinking in the initial phases , the company is now seeing both the safety and schedule performance it expected would come from using this technology , with monthly average daily sink rates coming in at around 1.6 m in June for Shaft 3 and 1.5 m for Shaft 4 .
Rogers commented : “ These are really large cross-section shafts , and our last quarter advance is something that you might hope to see on much smaller shafts , so they ’ re really moving along in quite a stable and predictable way now .”
He said the company was able to achieve this productivity after enlisting some Rio Tinto and external productivity specialists to deeply analyse every aspect of the sinking cycle . This focused on high-value areas such as the shaft lining and the mucking part of the cycles .
“ We delivered multiple targeted improvements in those areas ; they ’ re repeatable tasks , so any benefit there really adds to or improves the shaft sinking rate ,” he said . “ And the final focus area that really saw us embed the improvement was the introduction of an upgraded maintenance and equipment reliability program , and that saw us reduce our top 10 equipment delay events significantly , which also made quite a positive impact on these rates .”
Rio Tinto said at the end of June , Shafts 3 and 4 reached 627 m and 740 m below ground level , respectively , with both shafts expected to be commissioned in the second half of 2024 . while making sure safety is never compromised ,” he said . “ We ’ re now achieving monthly sinking advances again that are starting to be on par with sinking advances of the 1980s , recently achieving 105 metres in a month at one of our sites and looking to increase this .”
At the company ’ s operations in Brazil , for instance , it is using “ cactus grabs ” for mucking ; a practice previously outlawed at UMS by Macnab , but now being employed safely where no personnel are exposed at the shaft bottom .
This project – involving the construction of a new external shaft to service the lower levels of the Pilar Mine at Ero Copper ’ s wider Caraíba Operations – involves raiseboring a vertical hole in the centre of the shaft from certain points underground to the surface to expedite the sinking process through the “ slipe-and-line ” method .
Macnab said in mid-July that the headgear for the project was being erected and installed , with sinking operations – starting at around 1,500-m depth in the underground complex – set to begin towards the end of the year .
UMS , showcasing its contracting flexibility , is also acting as a service supplier for JDS Mining at Lucara Diamond Corp ’ s Karowe underground project in Botswana . This project involves the sinking of two shafts – a ventilation shaft and production shaft – to access the underground orebody . UMS oversaw the engineering and design of these 750-m-deep shafts but is not carrying out the actual shaft sinking .
UMS is also working with another company in the US on a blind sink project outside of the mining sector .
Macnab concluded : “ I have been a consultant , a client and a contractor , so I know what all parties are after . We at UMS understand that , for a client , the most important thing is project schedule and safety so wherever we – regardless of scope – can offer up advice on these fronts , we do .
“ A lot of decisions made during projects are often made for short-term gains . We , through the wider UMS Group , can highlight what the unintended consequences of these changes might be , even if that does not impact on our scope as a contractor .
“ Our aim is ultimately for the project to win .”
An experimental SBS sink
Master Drilling ’ s exploits in the blind sinking space are all geared towards transitioning from being considered a “ general mining contractor ” to a “ specialised constructor of blind sink shafts ”, Koos Jordaan , Executive Director and Technical Director , Master Drilling , told investors earlier this year .
The company has been providing innovations in raiseboring technology for decades , in the process achieving world record feats . It has also been looking to speed up and improve safety in the mine development space with its Mobile Tunnel Borer .
32 International Mining | SEPTEMBER 2023