Tag Archives: sub-level caving

AngloGold Ashanti confirms caving plans in Colombia

The Massmin 2020 crowd got a glimpse of just what will be required to build Colombia’s first underground caving mine during a presentation from AngloGold Ashanti’s Lammie Nienaber this week.

Nienaber, Manager of Geotechnical Engineering for the miner and the presenter of the ‘Building Colombia’s first caving mine’ paper authored by himself, AngloGold Ashanti Australia’s A McCaule and Caveman Consulting’s G Dunstan, went into some detail about how the company would extract the circa-8.7 Moz of gold equivalent from the deposit.

The Nuevo Chaquiro deposit is part of the Minera de Cobre Quebradona (MCQ) project, which is in the southwest of Antioquia, Colombia, around 104 km southwest of Medellin.

A feasibility study on MCQ is expected soon, but the 2019 prefeasibility study outlined a circa-$1 billion sublevel caving (SLC) project able to generate an internal rate of return of 15%. Using the SLC mining method, a production rate of 6.2 Mt/y was estimated, with a forecast life of mine of 23 years.

The MCQ deposit is a large, blind copper-gold-silver porphyry-style deposit with a ground surface elevation of 2,200 metres above sea level (masl, on mountain) and around 400 m of caprock above the economic mineralisation.

Due to the caving constraints of the deposit, the first production level to initiate caving (undercut) is expected to be located around 100 m below the top of the mineralisation at 1,675 masl (circa-525 m below the top of the mountain), with the mining block extended around 550 m in depth (20 production levels at 27.5 m interlevel spacings).

The main ore transfer horizon is located 75 m higher in elevation than the mine access portals at 1,080 masl and the proposed valley infrastructure. The initial mining block will be accessed by twin tunnels developed in parallel for 2 km at which point a single access ramp will branch up towards the undercut; the twin tunnels will continue another 3.7 km to the base of the SLC where the crushing and conveying facilities will be located.

The company is currently weighing up whether to use tunnel boring machines or drill and blast to establish these tunnels.

Nienaber confirmed the 20 level SLC panel cave layout would involve 161 km of lateral development and 14 km of vertical development. There would be six ore pass connections on each level, four of these being ‘primary’ and two acting as backups. The crusher would be located on the 1155 bottom production level.

Due to the ventilation requirements in Colombia the mining fleet selected for Quebradona is predominantly electric, Nienaber said, adding that the units will initially be electric cable loaders powered by 1,000 v infrastructure.

Fourteen tonne LHDs were selected for the production levels based on their speed, bucket size (enables side-to-side loading in the crosscut and identification of oversize material) and cable length, the authors said. On the transfer level, 25 t loaders were specified to accommodate the shorter tramming lengths and limited operating areas (there are a maximum of two loaders per side of the crusher due to the layout).

As battery technology improves in the coming years, the selection of loader sizes may change as additional options become available, according to the authors.

The selection of the present Sandvik fleet was predominantly based on the electric loaders and the OEM’s ability to provide other front-line development and production machines required to undertake SLC mining, the authors said.

This decision also accounted for the use of automation for the majority of production activities, with the use of a common platform seen as the most pragmatic option at this stage.

It has also been proposed that the maintenance of the machines be carried out by Sandvik under a maintenance and repair style contract since there is a heavy reliance on the OEM’s equipment and systems.

An integrated materials handling system for the SLC was designed from the ore pass grizzlies, located on the production levels, to the process plant.

Due to the length of the ore passes (up to 500 m), and the predicted comminution expected by the time the rock appears on the transfer level, larger than industry standard grizzly apertures of 1,500 mm have been selected.

The design criteria for the underground crusher was that it needed to reduce the ore to a size suitable for placement on the conveyor belt and delivery to the surface coarse ore stockpile, after which secondary crushing prior to delivery at the process plant will be undertaken.

Assuming the maximum size reduction ratio for the crusher of circa-6:1 at a throughput rate of 6.2 Mt/y, a 51 in (1,295 mm) gyratory crusher was selected. This crusher is also suitable to support block cave mining should the conversion of mining method occur, according to the authors.

The process plant will include high pressure grinding rolls as the main crushing unit on the surface, supported by a secondary crusher to deal with oversize material. The ore then feeds to a ball mill before being discharged to the flotation circuit.

The gold-enriched copper concentrate will be piped to the filter plant for drying and the removal of water down to a moisture content of 10%, according to the company, while the tailings will be segregated to pyrite and non-pyrite streams before being distributed to one of two filter presses.

Dry stacking of the tailings will be used, with the pyrite-bearing tailings being encapsulated within the larger inert tailings footprint.

With the feasibility study due before the end of the year – and, pending a successful outcome – the proposed site execution works could start in the September quarter of 2021, Nienaber said.

Polymathian finds funding for automation work at OZ Minerals’ Carrapateena

Polymathian will be spearheading a A$2 million ($1.5 million) industrial mathematics project funded by industry partners and METS Ignited, and focused on OZ Minerals’ Carrapateena mine in South Australia.

This project will form part of the Industry Growth Centre’s latest Tranche 4 Collaborative Project funds totalling a combined investment of A$6 million, METS Ignited said.

The grant was awarded to Polymathian’s project at OZ Minerals’ Carrapateena copper-gold mine where, in collaboration with OZ Minerals, Downer, Deswik and others, the company is applying industrial mathematics to deploy the world’s first highly automated short interval control (SIC) system for the near real-time optimisation of sub-level cave development and production mining.

Project Lead and Partner at Polymathian, Steven Donaldson, said: “This funding allows us to marry industrial mathematics, automation and mine planning to optimise asset value at Carrapateena and explore how SIC can be done going forward.”

By applying industrial mathematics to the SIC process, the project collaboration automates the optimisation of the mine plan and autonomously dispatches tasks to the underground fleet by responding to live data.

Plans can be updated to respond to dynamic changes in the mine, as live data is received and assumptions change, according to the company. For example, at a weekly level, plans are updated as required for a rolling seven-day window, rather than on a set schedule for a fixed seven-day period. This avoids having fixed weekly plans that are at risk of becoming out-dated.

Matthew Fargher, OZ Minerals’ Senior Engineer for Long Term Planning at Carrapateena, said: “This project pursues a world first in mine planning where the mine plan is autonomously optimised and tasks dispatched in semi real-time to the underground fleet. By doing so, we can potentially remove value destroying constraints such as self-imposed time horizons and subjectivity in decision making to deliver the next best decision.

“We are excited to be a part of the team that’s delivering the blueprint for mine planning and executional change globally.”

Donaldson added: “The potential market for this tool is really quite large as the way we are solving the problem is very generic. We see this solution having potential to optimise operations across all hard-rock underground mines in Australia and globally.”

The project also has the potential to create new jobs at Polymathian including accelerating the growth of its newly opened Perth office.

METS Ignited Chief Executive, Adrian Beer, says the quality and capability of the funding applicants is becoming increasingly more sophisticated, with a number of the solutions having broader applicability across a number of sectors.

“This round of project fund recipients demonstrates just how capable our leading global METS sector is, and what is possible within our local technology sector,” Beer said.

“We are extremely proud of what has been achieved by the project fund recipients to date, and this new addition to the project funding shows that we have a huge potential to build upon.”

Appian, Atlantic Nickel reinvigorate Santa Rita as nickel sulphide fortunes rise

At the height of the most recent nickel boom – when prices were over $20,000/t on the LME – the Santa Rita mine looked like a great option to gain exposure to the stainless steel raw material.

Mirabela Nickel, the mine owner, represented a pure-play nickel stock; Brazil, as a jurisdiction, was looked at favourably by investors; and the operation, itself, was one of the largest open-pit nickel sulphide mines in the world slated to produce 16,500 t/y of nickel sulphide in concentrate.

Gaining exposure to such a large, low grade asset is great when the underlying commodity price is tracking well, but, as has been shown time and again, it proves problematic when the price moves south.

Such a price deterioration came to pass in the years following the mine’s start up in 2009.

The asset, in north-eastern Brazil, was eventually placed on care and maintenance in the March quarter of 2016 as Mirabela Nickel declared bankruptcy. This was the same year the nickel price dipped below $10,000/t.

Fortunately for the local community and personnel that had invested much hope in the development of the $1 billion-plus mine, Appian Capital Advisory more recently took the view that there was a way forward for Santa Rita.

Picking up on an emerging trend for clean and green nickel sulphide concentrate from the electric vehicle and stationary storage market, plus the ability to re-engineer the operation and make it a much more robust asset, the company carried out a six-month due diligence process on Santa Rita.

This process led Appian to refine its understanding of the presence of nickel sulphides within the deposit, as opposed to the asset’s total contained nickel. With this understanding in hand, a more defensive and low-cost mine plan was developed to see the asset through nickel price peaks and troughs.

Appian ended up acquiring Santa Rita and setting up the Atlantic Nickel operating entity to enact these changes.

Having restarted open-pit mining just over a year ago, the asset is starting to pay back the faith Appian has placed in this plan.

“Our resource now focuses on the estimation of nickel sulphide within the deposit and benefits from additional drilling we’ve undertaken post-acquisition,” Adam Fisher, Principal, Appian Capital Advisory LLP, explained to IM. “The mine design we’ve developed extracts the deposit more selectively and also moves less waste, resulting in the low cost performance we’ve been able to achieve to date.”

In the first half of 2020, the company declared first quartile C1 cost performance of $3.17/lb ($6,989/t) nickel, net of by-products. This compares favourably with Mirabela Nickel’s $6.19/lb operating cost recorded in the September quarter of 2013.

“Among the operating changes we’ve implemented are the use of a smaller, locally procured, equipment fleet of 40 t trucks (Santa Rita previously used Caterpillar 777 90 t and 785 137 t payload trucks), the use of shorter benches – we’ve gone from 10 m down to, on average, 6 m – and tighter blasting patterns,” Fisher said.

All this work is being carried out by a Brazil-based consortium of contract miners.

“With smaller benches, tighter blasting patterns and smaller equipment fleets, we have more consistent control on the grade and fragmentation of the material that is fed to the crusher,” Fisher said.

The focus has gone beyond the near term, with more than 100,000 m of drilling executed in the underground resource area. The drilling was optimised for resource growth and classification confidence. The program was extremely successful and supported the declaration of the underground resource of 168 Mt at 0.59% NiS and 0.19% Cu. The 2020 drill programs continue to intersect similar widths and grades while stepping out from the declared resource, the company added.

The NI 43-101 technical report, released earlier this month, outlined a 34-year mine life for Santa Rita, with eight years of open-pit production, underpinned by proven and probable reserves of 50.6 Mt at 0.31% NiS, followed by 26 years of underground mining.

While still preliminary, this represented a very different approach to the previous Santa Rita owner.

“The last owners designed an open-pit mine with a 6:1 strip ratio and were planning to mine a lot deeper into the resource via open-pit methods,” Fisher said. “This was back in a very different nickel market when prices were greater than $10/Ib.

“All we did was find the optimal transition to bulk methods at depth to understand that it only makes sense to mine this as an open pit over eight years at a strip ratio that comes down to, on average, 2.7:1.”

Backing up this open-pit mine plan has been a 6.5 Mt/y plant, which, having started production in 2009, was completely refurbished and recommissioned in the second half of 2019 to align with the nickel sulphide recovery focus.

The plant consists of crushing, grinding, flotation, thickening and filtration unit operations to produce a saleable nickel sulphide concentrate. Flotation tailings are pumped to a tailings storage facility, while grinding is performed by a SAG mill, two ball mills and two pebble crushers. This is followed by a conditioning circuit and a flotation circuit, with the final concentrate thickened and pumped to storage tanks ready for filtration. Concentrate is filtered in a Larox (Metso Outotec) pressure filter. Following filtration, the final concentrate is trucked to the port of Ilhéus where it is loaded onto ships for transport to market.

Since the restart, more than five shipments have been made to the mine’s offtake partners.

“While the mine and plant are still ramping up, the open-pit operation is not far off from achieving the PEA estimates of being able to produce 20,000-25,000 t/y of contained nickel sulphide equivalent at a C1 cost of $2.97/Ib nickel,” Fisher said.

Beyond this, the company is looking to leverage innovation to create one of the largest and most efficient sub-level cave (SLC) operations in the world able to produce more of the highly sought after nickel sulphide product Santa Rita is becoming known for.

Caving in

“When carrying out the due diligence on Santa Rita, we knew all along that there was some good, thick intersections underground, with the orebody getting thicker at depth and the nickel sulphide grade improving,” Marcus Scholz, Head of Underground Mining at Appian Capital Advisory, told IM.

This was evident in the PEA, with underground mining inventory of 134.1 Mt grading 0.54% NiS and 0.17% Cu, comparing favourably – in terms of grade – with the proven and probable reserves of 50.6 Mt at 0.31% NiS and 0.11% Cu calculated for the eight-year open-pit operation.

“You’re looking at a massive orebody with moderate grades,” Scholz said. “Factoring that in, the lowest cost methods will generate the better margins in this case. With SLC having come a long way in the last 20 years in terms of practices, philosophies and the ability to control dilution through effective planning and modelling, plus the suitable geometry of the Santa Rita orebody, it was a good fit.”

This low-cost caving method allows the company to exploit more of the resource than other methods such as long-hole open stoping with backfill, plus fill the existing plant, Scholz explained.

Scholz was keen to point out that the company did not come to this conclusion on its own. It sought assistance from Power Geotechnical out of Australia, which has worked on other sub-level cave operations such as Carrapateena and Ernest Henry, when assessing its options.

Ernest Henry, operated by Glencore in Queensland, Australia, is a good analogue here. The Ernest Henry orebody is located at a similar depth below a pit and has a similar width and dip, but Santa Rita is about twice the size due to it being longer along strike, according to Scholz. It also comes with a similar 6 Mt/y profile.

Photography of Glencore’s Ernest Henry Mine near Cloncurry in Western Queensland

The SLC mining layout in the PEA comprises 37 mining levels spaced at vertical intervals of 25 m. Each level is made up of parallel and evenly spaced drill drives from which production drilling and blasting occur. Once blasted, the mineralisation is loaded from the drill drives using LHDs and loaded into trucks for haulage to the surface during the initial ramp-up phase, and later to ore passes feeding an underground crushing station and conveying to surface via an inclined tunnel.

The PEA plans will have the company mine directly beneath the open pit to start with, hence the reason it expects to start up production in 2028 after open-pit mining has concluded.

The underground operation will start with two years of waste development ahead of ore production, followed by ore truck haulage over a three-year period, Scholz outlined. After this, the operation will transition to underground conveyor haulage, ramping up to 6 Mt/y capacity over the next four years.

Asked why the company was starting with truck haulage before moving to conveyors, Scholz said it was an economic decision.

“If we truck first, we can delay some of the underground spend in terms of getting the underground crusher in,” he said.

Over the life of the underground mine, the company plans to install two underground crushers, being fed with roughly equal amounts of ore. The first will serve the upper half of the deposit and the second crusher the lower half (circa-6 Mt/y each, staged as mining progresses deeper in the deposit).

The first crusher will be positioned about 650 m below surface, or 450 m below the ultimate depth of the open pit.

“This will take a bit of time to get down there and access it (in terms of mine development), so it makes sense to start haulage with trucks,” Scholz said.

Appian is looking to lease the 60 t trucks required for this stage of the operation, explaining that Atlantic Nickel will operate the 12 machines needed at the height of truck haulage, which is when mining rates hit the annualised 2.5 Mt/y mark.

The truck haulage route will be a short one, travelling some 200-300 m below surface to access material before going back above ground.

After the conveyor transition, the trucks are expected to be used in later years for waste haulage, which could amount to some 500,000 t/y of material, according to Scholz.

Automation and electrification transition

It is when the conveyor starts up that the automation element of Santa Rita Underground really kicks into gear.

The company assumed the use of automated LHDs, longhole drilling and jumbo development drilling in the PEA. This saw Epiroc, Caterpillar and Sandvik provide price inputs, with design layouts anticipating such equipment.

Scholz expanded on this for IM: “We foresee that loaders going from the SLC drawpoints to the ore passes would be automated, meanwhile, at the collection level at the bottom of ore passes, we would probably have up to three large automated loaders that transfer material to the crusher.”

Longhole drills would also be automated for the SLC, while the company plans to automate face drilling activities on the development jumbos it will use.

“I think in another eight years’ time when we start up production, a lot of this technology is going to be the norm in the industry,” Scholz said.

The current study assumes the use of a diesel-powered load and haul (initially) fleet, though electric vehicles could provide upside in future studies and further reduce energy costs, equipment maintenance costs and ventilation power costs, an Appian spokesperson recently told IM.

“Both tethered- and battery-powered machines will be looked at for specific applications within the mine, such as loading from drawpoints and feeding the underground crusher from the bottom of ore passes,” the spokesperson explained.

While much of the industry’s larger load and haul equipment has not yet made the commercial leap to battery power, the company is keen to pursue developments in the future as the technology became available, Scholz said.

The circularity of such a move will not be lost on Appian or Atlantic Nickel, knowing the nickel sulphide concentrate it will be offloading could end up in these battery-powered machines. In eight years, these end users will most likely be factoring such emissions-reducing technology into their raw material procurement choices.

For the time being, the company is focused on completing the underground drilling program at Santa Rita, which has, to date, shown much promise.

Fisher said every hole has intersected nickel sulphides to this point meaning the chances of a further underground resource upgrade in the early part of next year were high.

These figures will be factored into a prefeasibility study later in 2021, which will include more detailed geotechnical information on the SLC, as well as subsidence modelling, Scholz said.

Orica keen to collaborate on path to blasting automation

Orica’s Angus Melbourne told a packed Austmine 2019 crowd in Brisbane this week that the blasting specialist is committed to developing automated solutions for both the underground and surface mining sectors and is working with both customers and industry partners to make this aim a reality.

During his speech on Wednesday, Melbourne, Orica’s Chief Commercial and Technical Officer, walked delegates through a number of achievements the company had achieved over its 140-year history, but also looked ahead to how Orica is focused on revolutionising the drill and blast operations of the future.

“Blasting is one of the few processes in the mining value chain that remains largely untouched by automation,” Melbourne said. “As mines go deeper and orebodies become more remote, the case for blasting automation becomes clearer.”

Among a number of benefits of blasting automation were the ability to remove people from harm’s ways, grant access to difficult ore reserves and reduce operational delays, he explained.

“Due to the complexities associated with a typical blast operation, this is no trivial endeavour,” he said.

Melbourne said progress was already being made with Orica’s automation efforts, singling out its Orica’s WebGen™ wireless initiation technology, in particular. Launched in 2018, WebGen improves safety by removing people from hazardous situations and enhances productivity through the removal of constraints previously placed on operations by wired connections.

“Since its release, more than 130 WebGen wireless blasts have been executed globally across four industry segments,” Melbourne told delegates.

Newmont Goldcorp’s Musselwhite mine has been an advocate of the wireless initiation technology, recently saying the blasting tests it has carried out at the Ontario mine were “a decisive step on the path towards full automation of drill and blast operations in the future”.

The wireless initiation technology is leading to the development of new blasting options, according to Melbourne, who said, in the last 12 months, Orica has co-developed more than seven new techniques that are “revolutionising the way our customers are planning and executing their mining operations”.

On stage, Melbourne then played a short video from CMOC Northparkes in New South Wales, Australia, a miner that recently converted its entire sub-level cave copper mine to WebGen wireless initiation blasting; an Australia and world first, according to Melbourne.

He said Northparkes has seen significant improvements in safety, productivity and ore recovery since the transition. Melbourne’s words were echoed later that day when Orica received the Austmine METS Innovation Award for the use of WebGen at Northparkes.

Melbourne pointed to a second collaborative development that was helping shape the company’s blast automation efforts during his time on stage; this time with an original equipment manufacturer.

The company has been working with MacLean Engineering out of Canada to test the first fully-mechanised drawpoint hang-up blasting solution, he said.

Capable of drilling and charging up to eight blast holes remotely, the solution is underpinned by WebGen wireless technology and, once again, removes people from harm’s way.

“Hang-up blasting is a major issue for block and sub-level cave mines around the world,” Melbourne said. “In fact, at any one time, up to 30% of all drawpoints can be unavailable due to oversize material. All current solutions are either high risk mining activities or are highly inefficient to implement.”

He then played a video highlighting this industry-first solution, before remarking: “This is a significant step towards fully-autonomous production in underground mines. It’s an exciting time for everyone involved and is just one example of an industry collaboration to deliver blast automation.”

Melbourne concluded his presentation by saying, in the future, integrated, automated and intelligent systems will deliver the critical data necessary for executing real-time change and quantifiable impact on all parts of the value chain “through an ‘ecosystem of insight’ never seen before in mining.

“To capture the full potential of rapidly-evolving technology will require new ways of thinking, new ways of working, and a new spirit of collaboration across the industry.”