Zondereinde mine is located on the northern end of the western limb of the South African Bushveld Complex.
Operational since 1993, the mine is established and continues to operate at steady state levels and remains cash generative and profitable producing some 280 000oz of platinum group metals (PGMs) annually. Zondereinde mines both the UG2 and Merensky reefs. Given the geological complexities associated with mining the Merensky reef, the mining ratio is steadily shifting to a UG2: Merensky ratio of 60:40 to balance the depletion of the resource. As such the combined head grade has more recently dropped, but is anticipated to stabilise at approximately 4.9g/t.
Nevertheless, the revised ore mix has contributed to better cost performances from Zondereinde.
The deepening project was started in order to open up additional conformable Merensky reef. This project is progressing well and is being equipped with a conveyor and a chairlift. On 16 level the lateral development has started with the crosscuts to the reef.
In October 2016, Northam announced that an agreement was concluded to acquire the Tumela resource from Anglo American Platinum Limited on the north-western boundary of Zondereinde. The acquisition will provide access to additional higher-grade Merensky and UG2 reef and extend the life of mine (LoM) to beyond 30 years.
Key facts and statistics
- Wholly-owned by Northam Platinum Limited
- At the northern extremity of the western limb of the Bushveld Complex in Limpopo province; adjacent to Amplats' Tumela mine near Thabazimbi
- Access and infrastructure
- Well-established infrastructure, tarred roads, railway, water, Eskom power
- 7 625 hectares; strike length 8km
- Life of mine
- Greater than 30 years
- Production profile
- Steady state, mature operation; annual output of ˜280 000oz
- Underground mining activites focused on Merensky and UG2 reefs, shifting to a higher ratio of UG2. Average depth of 1 750m. Hydropowered equipment used for stoping and development. Surface infrastructure includes concentrators for Merensky and UG2; base metals removal plant and smelter. In-house marketing and sales to customers in North America, Japan, Europe
Zondereinde mines both the Merensky and the UG2 reefs, both of these reefs being well-recognised ore bodies, with lateral continuity well established across the Zondereinde mine lease area. The lease area is characterised by major structural features some of which are water-bearing. This creates challenges in the mining environment, and is something that Zondereinde staff has dealt with very well up to now.
The Merensky reef comprises the normal reef sub-facies and the regional pothole sub-facies. The regional pothole sub-facies is further divided into three different reef types. Reef type changes are difficult to predict. To mitigate this risk, an extensive prospect drilling programme is in place.
|MERENSKY REEF||Current mining ratio|
NP2 reef type
P2 reef type
Footwall P2 reef type
The UG2 reef occurs between 20 and 40 metres below the Merensky reef and displays more consistent characteristics than those of the Merensky reef, with insignificant reef disturbances. As a result the UG2 reef is not subdivided into different facies. The UG2 reef is largely mined below where the Merensky reef has previously been mined.
The UG2 comprises three chromitite layers separated by pyroxenite which is some 15cm thick. The main member is approximately 80cm thick and the leaders about 20cm. The layers are separated by a 15cm-thick pyroxenite layer. The grade is generally higher in the main members; lesser in the leaders and minor in the intermediate pyroxenite.
Subsequent to Northam acquiring contiguous additional resources at Zondereinde, the life of mine is estimated in excess of 30 years.
Typical extraction rates
|Merensky reef||UG2 reef|
|13% geological losses (faults, dykes)||13% geological losses|
|78% extraction of balance (potholing)||74% extraction of the balance|
|67% total extraction||65% total extraction|
Mining and engineering
Mining at Zondereinde dates back to 1987. Zondereinde is the deepest platinum mine in the world. Underground workings are characterised by particularly high virgin rock temperatures (VRT) that demand considerable refrigeration capacity. At average mining depth of 1 750m below collar the VRT is 72 degrees C.
The mining method employed is traditional drill and blast narrow tabular reef mining on a standard breast layout. The vertical interval (distance) between levels is 63 metres. The orebody dips at 20°.
Ore is transported to the main shaft ore passes by battery powered locos pulling spans of eight hoppers. Broken ore is transported to a conventional shaft ore-pass system, with separate rock handling facilities for Merensky reef, UG2 reef and waste. Mining equipment such as rock drills, roof bolters and other equipment is hydropowered, used in conjunction with electric scraper winches.
The underground workings are accessed from a twin vertical shaft system. No 1 shaft extends to 12 level and No 2 shaft serves workings down to 8 level. The shafts are 90 metres apart and are interconnected at an intermediate pump chamber at 1 019 metres below surface, and also on another six levels.
Ore reserve development is a critical feature of mining. At Zondereinde, given the complex geology, there is a constant focus on establishing adequate reserves to mine. Amongst other constraints, the loss of mineable resources on the east side of the mine prompted a deepening project at Zondereinde. This project, which extends below 12 level down to 18 level at 2 200 metres below collar, contributes to improved Merensky reserves. Below 12 level a decline access way can accommodate both people and materials, and is equipped with a conveyor belt system that transports broken rock.
Given the temperatures encountered at depth in the Bushveld Complex, refrigeration is critical. Without it, nobody could work in these conditions. A refrigeration plant with the capacity of 56MW, comprising six York and two Sulzer 7MW refrigeration systems provides cool air to the underground workings. The downcast air is chilled to 10°C, at 875m3 per second. At the working face the average air velocity measures 0.8m per second.
Five of these units run continuously. In peak summer conditions this is increased to six or seven machines, with the balance available as standby capacity. The plant runs each day at 98% availability. All the units run on the environmentally friendly refrigerant R134A.
The chilled water circuit cools water to 5ºC at the refrigeration plant, which then transfers partially to the surface bulk air coolers at the shaft, reducing air temperatures from nominal 25º to nominal 10º before transfer into the shaft and down into the workings. The remaining chilled water is fed underground in lagged pipes that feed to the stope and development hydropower reticulation systems. In certain areas spot coolers are used.
Support in underground mining areas
Engineering and technology solutions have been designed around Zondereinde's specific geological and mining features. Support systems underground are therefore extensive and varied. Zondereinde makes use of a combination of backfill, pre-stressed elongates (mine poles) and tendon support (end anchored resin bolts) and sets for support underground.
Support standards are rigorously monitored, and no work is allowed to take place more than 1.5m away from any support. In development ends the remotely operated roofbolter is applied to support the hanging wall.
Backfill for support
The principal support regime in the Merensky and UG2 reef mining areas is the placing of backfilled bags at intervals of 1.5m. Backfill is placed in 60% of the mined out areas.
Between 60% and 70% of all panels are being backfilled concurrently with the advancing faces, thereby enhancing both local and regional stability. Backfill provides a valuable means of regional support by restricting full closure and also serves to control ventilation in working areas and reduces the transmission of heat from the surrounding rock.
The backfill (waste) is supplied from the surface metallurgical plant backfill silo in a slurry form. It is pumped to the shaft and gravity fed to the stope horizon. The classified tailings are pumped into porous ‘backfill bags’ that retain the +45 micron sediments, yet release the water, to leave a restricted compression structure to resist and contain roof lowering.
A sound backfill bulkhead and paddock design, which exceeds industry standards is in place and practices exceed industry standards. Backfill quality and installation is strictly controlled.
Supporting stopes and development
In order to provide support in underground working areas, Camlok jacks are used as temporary support and pre-stressed elongates (mine poles), pre-stressed packs, backfill and tendons provide permanent support. Immediate face support consists of wooden elongates/sticks or packs spaced every 1.5m in the Merensky and UG2 workings. These are pre-stressed to 20 tonnes using pack setter pressure plates.
In poorer ground conditions, support densities are increased and additional headboards are used in friable areas.
Temporary support (Camlok jacks with headboards) is installed at a maximum distance of 1.5m from the face on strike and 1.5m on dip. Pre-stressed elongates are installed at a maximum of 3.0m from the face after blasting, and 1.5m on dip.
In off-reef development 1.8m long full column grouted end anchors (tendons) on a 2m diamond pattern are used, and 3.0m long tendons in breakaway areas. Over the past two years, 1.8m long full column grouted end anchors on a 1m diamond pattern have also been introduced in all on-reef development. This latter development has resulted in considerably improved conditions particularly in raise lines, minimising raise collapses.
Secondary development support in the form of arched sets with void fill, 4.0m long x 25 tonne long anchors, polyfibre reinforced wetcrete, tunnel guard, and RSJ clamp sets are being used successfully in problem areas. Specialised contractors are employed for these installations.
Merensky and UG2 concentrator plants
Crushing/screening circuit: In the crushing/screening circuit the ore is crushed to reduce its size before it reports into the mill.
Milling: Merensky ore feeds into a fully autogenous mill (FAG mill). In the UG2 plant the crusher product feeds into a high pressure grinding roll crusher (HPGR) and this then goes into a primary ball mill.
Flotation: The circuit includes rougher cells, scavenger cells and cleaner columns. In the UG2 plant the secondary roughers consist of a bank of tank cells.
In the UG2 circuit, sparger columns act as a cleaner and help to produce a final UG2 concentrate at half the original chrome content while maintaining PGM recoveries.