An integrated development plan (IDP) on the Platreef palladium, platinum, rhodium, nickel, copper and gold project in South Africa has shown the potential to fast-track the development into production.
Consisting of an updated feasibility study and a preliminary economic assessment, the IDP marks an “important step in our vision of building and operating the world’s next great precious metals mine, together with our local community and Japanese partners”, Ivanhoe Mines Co-Chair, Robert Friedland, said.
Ivanhoe indirectly owns 64% of the Platreef project through its subsidiary, Ivanplats. The South Africa beneficiaries of the approved broad-based, black economic empowerment structure have a 26% stake in the project, with the remaining 10% owned by a Japanese consortium of ITOCHU Corporation, Japan Oil, Gas and Metals National Corporation, and Japan Gas Corporation.
The Platreef 2020 feasibility study builds on the results of the 2017 feasibility study and is based on an unchanged mineral reserve of 125 Mt at 4.4 g/t 3PGE+Au, project designs for mining, and plant and infrastructure as in the 2017 study; except with an increased production rate from 4 Mt/y to 4.4 Mt/y, in two modules of 2.2 Mt/y, for annual production of more than 500,000 oz of palladium, platinum, rhodium and gold; plus more than 35 MIb of nickel and copper.
The 2020 feasibility study includes an updated production schedule based on the current project status, costs and economic assumptions, with the schedule for the latest study driven by the sinking of the project’s second, larger shaft (Shaft 2), where early works have commenced. The 2020 study envisions Shaft 2 equipped for hoisting in 2025, allowing for first concentrate production in the latter half of the year. The initial capital cost for the Platreef 2020 feasibility study is estimated at $1.4 billion.
The Platreef IDP also includes the Platreef 2020 preliminary economic assessment, which is an alternate, phased development plan that fast-tracks Platreef into production. The plan uses the project’s first shaft (Shaft 1) for initial hoisting and mine development, with 825,000 t of annual total rock hoisting capacity, of which 125,000 t is allocated for development rock. The alternate plan envisions building an initial concentrator with a capacity of 770,000 t/y, and could produce first concentrate in mid-2024.
“The recently-completed sinking of Shaft 1 has created the opportunity to access early, high-grade tonnes in this scenario,” the company said. “While the 700,000 t/y initial mine is being operated using Shaft 1, there would be opportunities to refine the timing of subsequent phases of expanded production, which is driven by the sinking of Shaft 2.”
Once completed, two 2.2 Mt/y concentrator modules would be commissioned, and the initial concentrator would be ramped up to its full capacity of 770,000 t/y; increasing the steady-state production to 5.2 Mt/y for annual production of more than 600,000 oz of palladium, platinum, rhodium and gold, plus over 40 million pounds of nickel and copper. The initial capital cost for 700,000 t/y under the Platreef 2020 assessment is estimated at $390 million – substantially lower than the Platreef 2020 feasibility study that requires Shaft 2 for first production.
Detailed engineering has commenced on the mine design, 770,000 t/y concentrator and associated infrastructure for the phased development plan, which will be incorporated into an updated feasibility study in 2021, Ivanhoe said. The Shaft 1 changeover will take place simultaneously in preparation for permanent hoisting by early 2022. The budget for 2021 is $59 million, which includes $10 million for commencement of the construction of the headframe to the collar of Shaft 2.
“The Platreef IDP reflects the first phase of development for the Platreef Mine,” the company said. “It is designed to establish an operating platform to support potential future expansions to 12 Mt/y and beyond, as demonstrated in previous studies, which would position Platreef among the largest platinum-group metals producing mines in the world, producing in excess of 1.1 Moz of palladium, platinum, rhodium and gold per year.”
Friedland said: “The thick and flat-lying nature of the high-grade mineralisation of Platreef’s Flatreef deposit will accommodate the use of mechanised and state-of-the-art, automated mining techniques; allowing us to efficiently and safely bring material to surface to produce precious metals vital to a proliferation of modern technologies.”
Marna Cloete, Ivanhoe’s President and CFO, said approximately 60% of the mine’s tailings will be sent back underground to fill mined-out voids, and the remainder will be treated using sustainable, dry-stacking technology.
Mining zones in the current Platreef mine plan occur at depths ranging from around 700-1,200 m below surface. Once expanded mine production is achieved, primary access to the mine will be by way of a 1,104-m-deep, 10-m-diameter production shaft (Shaft 2). Secondary access to the mine will be via the 996-m-deep, 7.25-m-diameter ventilation shaft (Shaft 1) that recently has been sunk to its final depth. During mine production, both shafts also will serve as ventilation intakes. Three additional ventilation exhaust raises (Ventilation Raise 1, 2, and 3) are planned to achieve steady-state production.
Mining methods included in the studies are longhole stoping and drift-and-fill. Each method will use cemented backfill for maximum ore extraction. The production plans in both the PEA’s initial five-year drift-and-fill mining operation off of Shaft 1 and the larger feasibility study expansion are focused on maximising higher-grade areas, which was achieved through optimisation based on stope locations, stope grades, mining method, and zone productivities. The orebody was targeted to recover around 125 Mt at the highest net smelter return.
The ore will be hauled from the stopes to a series of internal ore passes and fed to the bottom of Shaft 2, where it will be crushed and hoisted to surface.
Comminution and flotation test work has indicated that the optimum grind for beneficiation is 80% passing 75 micrometres. Platreef ore is classified as being ‘hard’ to ‘very hard’ and thus not suitable for semi-autogenous grinding; a multi-stage crushing and ball-milling circuit has been selected as the preferred size reduction route, Ivanhoe said.
Improved flotation performance has been achieved in test work using high-chrome grinding media as opposed to carbon steel media. The inclusion of a split-cleaner flotation circuit configuration, in which the fast-floating fraction is treated in a cleaner circuit separate from the medium- and slow-floating fractions, resulted in improved PGE, copper and nickel recoveries and concentrate grades.
A two-phased development approach was used for the flowsheet design comprising a common three-stage crushing circuit, feeding crushed material to milling-flotation modules. Flotation is followed by a common concentrate thickening, concentrate filtration, tailings disposal and tailings-handling facility. The phased approach allows for increased processing flexibility and introduces process redundancy while allowing for phasing of capital and mine ramp-up, the company said.
To further evaluate optimisation opportunities and confirm additional detail design parameters, a mini pilot plant test work program is proposed and will be undertaken as part of the project implementation phase.
The proposed tailings storage facility (TSF) will be developed as a dry stack TSF with an estimated operating life of 32 years. During this time, some 55.4 Mt of tailings will be stored within the dry stack TSF, with the remainder of the tailings to be used as backfill in the underground mine. The dry stack TSF design also caters for an 8 Mt/y ramp-up in production to be explored in future studies.
The dry stack TSF is compliant in terms of required tonnage profile production split between the backfill requirement and dry stack TSF of 35% on average, but is conservatively designed for 40% of non-ore material reporting to the TSF.
Since the Platreef 2017 FS, a hybrid paddock deposition methodology was proposed; however, Ivanplats has decided to change the TSF deposition methodology from upstream design to dry stacking in the Platreef 2020 studies.
Following a study undertaken by Golder Associates Africa in December 2016, it was concluded that stacked tailings storage facilities are deemed to be safer in that there is no hydraulic deposition, hence the risk will be minimal to flood the surrounding areas with tailings in the unlikely event of a catastrophic failure.
“Stacked tailing storage facilities are more water efficient in that the majority of water in the tailings is captured in the dewatering plant, pumped directly back to the concentrator and re-used within the process,” the company said.
The stacked facility will comprise a starter dam constructed primarily of rock fill, engineered tailings, nominally compacted tailings, and random fill. Tailings will be delivered to the dewatering plant situated at the stacking facility using the same pumping systems from the processing plant. Dried tailings will be delivered to the stacking facility using load and haul transportation with trucks from the dewatering plant.
Aside from the rock fill in the starter dam and drainage elements, which include a return water dam, the facility will be developed using dewatered tailings. The infrastructure will have to be in place upon start-up.
For the Platreef 2020 PEA development scenario, it is envisaged to use the approved rock dump footprint within the immediate Platreef mine and concentrator areas, as a dry stacking tailings facility for the initial 700,000 t/y mine. Golder Associates currently is performing the design work to apply for the relevant licences and/or amendments to the existing authorisations.
