Tag Archives: dry-stacked tailings

Samarco iron ore pellet operations restart five years after Fundão tailings dam spill

BHP and Vale have confirmed their joint venture Samarco iron ore business has restarted operations in Brazil, more than five years after the failure of the Fundão dam led to its suspension.

Samarco’s gradual restart of operations incorporates concentrator 3 at the Germano complex in Minas Gerais and pelletising plant 4 at Ubu in Espírito Santo, as well as a new system of tailings disposal combining a confined pit and tailings filtering system for dry stacking, BHP said.

With the new filtration process, Samarco expects to be able to substantially dewater sand tailings, which represent 80% of total tailings by volume, and safely stack these filtered sand tailings in piles, Vale said. The remaining 20% of tailings are planned to be deposited in the Alegria Sul pit, a bedrock self-contained structure. Additionally, Samarco is progressing in the decommissioning of the Germano tailings dam to improve safety standards.

“Independent tests have been carried out on Samarco’s preparations for a safe restart of operations,” BHP added.

Samarco expects initially to produce around 7-8 Mt/y of iron ore pellets from the use of one of three concentrators to beneficiate iron ore from the Germano complex and one of four pellet plants in the Ubu complex, representing 26% of Samarco’s productive capacity.

Vale explained: “The integrated restart of operations occurs after an extensive commissioning test, ensuring a safe resumption after five years.”

Following the Corrective Operation Licence received in October 2019, Samarco expects to be able to restart a second concentrator in around five years to reach a range of production of some 14-16 Mt/y. The restart of the third concentrator could happen in around nine years, Vale said, when Samarco expects to reach a production volume of around 22-24 Mt/y.

The extensive work undertaken by the Renova Foundation, a collaboration between Vale, BHP Billiton Brasil Ltda and Samarco, to remediate and compensate for the damages of the failure of the Fundão dam in November 2015 continues, BHP said. The foundation is responsible for carrying out programs to repair the social and environmental impacts.

By November 2020, Renova had spent approximately $2.1 billion on its remediation and compensation programs. By November 2020, around $620 million had been paid in indemnities and emergency financial aid to approximately 325,000 people.

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.

TAKRAF dry-stacked tailings test work boost for Los Andes Copper’s Vizcachitas project

Los Andes Copper says it has received additional positive results from the ongoing prefeasibility study (PFS) metallurgical test work at its Vizcachitas project in Chile.

These results show improved filtration rates for both the fine and coarse fraction tailings compared with previous testing, it said, reinforcing the decision to adopt dry-stacked tailings at the project.

An October press release regarding PFS metallurgical test work carried out by SGS demonstrated that the Vizcachitas tailings were amenable to being filtered and dry-stacked.

These same coarse and fine representative tailings samples were sent to the TAKRAF laboratories for further settling and filtration assessments. Los Andes said the TAKRAF work tested various settling and filtration parameters, including those previously tested.

The studies demonstrated that for the coarse fraction vacuum filtration, the rates improved from 1.9 t/h/sq.m to 3.4 t/h/sq.m when compared with the previous results. For the finer fraction, the settling velocities improved from 8.4 m/h to 16 m/h and the pressure filtration rates improved from 0.6 t/h/sq.m to 0.7 t/h/sq.m. The expected cake moistures for both filtration technologies were 15%.

These positive results mean that the Vizcachitas project, processing 110,000 t/d of ore, would only need to use eleven standard 162 sq.m belt filters and four 2.5 m x 2.5 m pressure filters for the tailings dewatering operation, Los Andes said, noting that other operations in the world were successfully operating with similar filter arrangements.

“Tailings filtration reduces water consumption by 50% when compared to thickened tailings disposal alternatives,” Los Andes said. “Furthermore, filtered tailings can be handled by trucks, conveyors and shovels, eliminating the need for the construction and operation of a tailings dam.

“The adoption of this technology puts the Vizcachitas project at the forefront of the environmentally responsible practices being adopted for the future of sustainable mining globally.”

OZ Minerals eyes up block cave opportunities at Carrapateena underground mine

A prefeasibility study on an expansion of OZ Minerals’ Carrapateena copper-gold underground mine, in South Australia, has indicated a block cave conversion in the lower portion of the Carrapateena resource has the potential to almost double average production from 2026.

It is these results, plus the potential Block Cave 1 and Block Cave 2 expansion net present value of circa-A$770 million ($534 million) at final investment decision in 2023, that has seen the company confirm it will progress the plan to feasibility study stage, with the Carrapateena Block Cave Expansion Feasibility Study Stage 1 report expected before the end of 2021.

The PFS plan includes the potential to transition to dry-stacked tailings to reduce reliance on groundwater resources and a trial of electric light vehicles and establishment of a renewable energy hub – both of which are aligned with OZ Minerals’ strategy and aspirations, OZ Minerals Chief Executive Officer, Andrew Cole, said.

Carrapateena produced first concentrate in December 2019 following a three-year construction period and is targeting a 12-month ramp-up period to achieve a production rate of 4.25 Mt/y by the end of this year.

Currently an underground sub-level cave operation with an estimated mine life of 20 years, the latest study, which comes with a A$1.2-1.3 billion capital expenditure bill shows the potential for a future expansion of the bottom half of the operation into a series of block caves.

Cole said: “The prefeasibility study analysed the whole Carrapateena Province and determined that replacing the lower half of the current sub-level cave with a block cave and expanding the expected annual throughput rate from 4.7-5 Mt/y (currently planned from 2023) to 12 Mt/y, has the potential to create significantly more value than the sub-level cave alone.”

He said the block cave would leverage existing underground infrastructure, supported by expanded surface processing capability.

OZ Minerals added: “The proposed block cave is different from previous Carrapateena block cave studies as it targets a smaller, higher-grade footprint in BC1 (block cave one) with 600 m height of draw, followed by a lower-grade BC2 (block cave 2) with 400 m height of draw. The Carrapateena block cave builds on modern block caving experience, and aims to deliver an automated, electrified, data-driven mine with technology embedded in the design.”

The conversion to block cave operations enables a series of future add-on block caves, all of which were considered in the Life of Province scoping study, Cole added.

The plan could see annual production double to around 110,000–120,000 t of copper and 110,000–120,000 oz of gold from 2026, with life of mine all-in sustaining costs of some $0.75-0.85 c/lb ($1,654-1,874/t), he said.

Key upgrades to underground infrastructure include faster conveying systems with improved utilisation and a larger crusher station three for the block cave with increased capacity over that required for the sub-level cave.

An additional primary ventilation fan and circuit will be required for the transition period from sub-level cave to block cave before a reduction in the mine’s ventilation requirements for the life of mine, the company added.

The prefeasibility study currently recommends the process plant upgrade to 12 Mt/y via a parallel processing circuit to minimise brownfield interfaces and introduce energy load scheduling via the vertical roller mill as the primary surface crushing option, OZ Minerals said.

“The parallel process plant approach also allows both plants to be run independently, and for mine production to continue during plant shutdown periods,” the company said.

However, pivoting back to a traditional SAG/ball grinding circuit in the parallel process plant or tertiary crushing, to increase sub-level cave process plant throughput, will remain as options until final detailed design, OZ Minerals explained. This will not have a material impact on project value and allow time for optimisation of the current sub-level cave process plant before a final decision, it added.

Los Andes Copper addressing Vizcachitas project energy and water needs in PFS

Los Andes Copper has ideas on adding to the number of large open-pit mines in Chile’s copper industry with the development of its Vizcachitas project, but it is eyeing up a different route to many of them that includes the use of energy-efficient HPGR technology and dry-stacked tailings.

In an update on its pending prefeasibility study (PFS), the company said it was re-evaluating the conceptual plan it laid out in its June 2019 preliminary economic assessment, which envisaged a base case 110,000 t/d operation using a SAG mill grinding circuit and thickened tailings dam.

The PFS is currently underway and areas of work being advanced include processing, the tailings facility, infrastructure, geology, the mine plan, environmental and social and community engagement, it said.

While delaying some of the metallurgical test work and field work, the current COVID-19 situation had not impacted the progress of the main engineering study, according to Los Andes. “All employees and subcontractors are working from home where possible and only a small group of individuals are working to prepare samples in the company’s Santiago core storage area,” it said.

The full PFS is not expected until the March quarter of 2021, but the company did outline some engineering leaps it has made since the PEA publication.

It said test work had shown that a HPGR circuit is feasible for the project and could provide “enhanced project economics with lower energy consumption and increased operating flexibility”.

The PEA outlined a SAG and ball mill crushing circuit with a target grind size of P80 (240 microns), but the more recent test work had shown room for an alternative with a three-stage crushing circuit using secondary crushers in open circuit and HPGR as a tertiary crusher in closed circuit. This circuit would target a grind size of P80 between 240-300 microns, the company said.

Such a change would avoid the use of a coarse ore stockpile, reduce energy consumption, reduce maintenance, and reduce the project footprint, it said.

HPGRs have previously been used at Chile mining operations, including the Compañía Minera del Pacífico-owned Mina Los Colorados iron ore mine and KGHM’s majority-owned Sierra Gorda operation.

Los Andes clarified: “HPGR technology has been identified as the most attractive grinding alternative given the data obtained from the preliminary test work conducted to date.”

The next big advance was made on the tailings side, with the company saying test work had shown that the project is amenable to filtering and dry-stacked tailings.

“This change would significantly reduce the project’s water consumption, footprint and environmental impact,” it said. It would also, one would expect, provide a much smoother environmental permitting route for Vizcachitas considering the negative sentiment surrounding thickened tailings dams in the industry.

There are knock-on benefits to this move too, with the reduced footprint required for dry-stacked tailings meaning all project infrastructure could fit into one operating complex in the Rocin Valley of Chile, around 150 km northeast of Santiago. The PEA previously outlined the use of infrastructure in both the Rocin Valley and the Chalaco Valley.

The preliminary filtration circuit Los Andes is working with shows the coarse fraction (87% of total tailings) could be filtered in belt filters, with the fine fraction (13%) filtered in pressure filters.

Recent studies on other dry-stack tailings project have tended to use either belt filters or pressure filters, but Los Andes said the combination of the two added flexibility to the tailings filtration operation at Vizcachitas and reduced operational risks due to variability of the finer fraction in tailings.

This would see the company require 12 belt filters and three filter presses for the 110,000 t/d copper-molybdenum operation.

According to the company, dry-stacked tailings would:

  • Reduce water consumption by around 50%;
  • Reduce the project’s footprint;
  • Be better suited for areas of high seismic activity;
  • Be transported by trucks or conveyors;
  • Eliminate the need for a traditional dam wall; and
  • Reduce the environmental risk by avoiding contact with ground water.