Palabora underground ramping up to 30,000 t/day

The Palabora Underground Mine, which is expected to be running at its planned 30,000 tonnes of ore a day target by the end of the year, will extend the life of the mine by at least 20 years.

At the end of 2002, Palabora Mining Company had spent about US$400 million on the Palabora Underground Mining project and it is expected that this will be completed under budget. However Palabora has announced that it has been in discussions with several leading domestic and international bankers to refinance the company. The requirement to do this is a direct result of the strengthening of the rand against the US dollar, and the delayed ramp up of the underground mine's production to design capacity. 

Palabora began work to convert its open pit operation to an underground block caving mine during 1996, with output from the underground mine intended to coincide with the depletion of open pit resources. The closure of the open pit to large-scale mining took place at the end of April last year and smaller scale contract mining of the open pit ramps, which began in May last year to supplement ore from underground, has been very successful. This will continue to June this year. But the original target for Palabora to reach its 30,000 t/day production target was the end of 2002, and this has been delayed, mainly due to oversize rock hang-ups in the drawbells and consequent damage to secondary breaking equipment. Consequently, production levels of between 10,000 and 12,000 tonnes per day are being achieved against an expected 30,000 tonnes per day. 

Past practices in the mining industry have allowed oversize rock hang-ups to be freed by manually placing small explosive charges in the blocked draw bells. However, this can be a fatally dangerous practice and Palabora's management will not expose its miners to this risk – hence the decision to use alternative, safe methods of secondary breaking. While the ramp up of production has been slower than planned, these are early stages of the mine life and experience at other similar mines around the world suggests that fragmentation will improve as the cave develops and that the need for secondary breaking will decline considerably. 

The cumulative effect of these issues is that Palabora will require additional finance facilities during 2003. The company currently has borrowing facilities of US$185 million and aims to increase these by some US$90 million. Palabora has therefore approached a number of leading domestic and international banks in order to commence the process of obtaining these facilities. In light of the current US$/Rand exchange rate, the low copper price and the delayed ramp up to full production, Palabora's major shareholder, Rio Tinto has agreed to provide a short-term loan facility of up to US$50 million at commercial rates until the refinancing programme is in place. The discussions with the bankers are progressing and indications are that the necessary refinancing of the business will be in place during the second half of the year. 

Once the full production rate is achieved the mine will hoist almost 11 million tonnes of ore a year at a grade of 0.7 grams or copper per tonne. While this will not fill the Palabora smelter's capacity it will be sufficient for satisfactory throughput. The mine does have the option of using imported concentrates to maintain or increase anode production. With the reduced output from mining operations at Palabora the concentrator, smelter and refinery will carry on with the same functions, though on a reduced scale. Parts of the concentrator have been mothballed and Palabora's heavy minerals plant was closed down and dismantled. In addition to remaining long term copper ore stockpiles, which are being used up to maintain smelter feedstock, the mine also has extensive stockpiles of low grade magnetite on site, amounting to in excess of 100 million tonnes. Palabora is exploring avenues to market this magnetite, some of which is sold to coal mines for coal washing purposes.

In 2002 Palabora produced 64,367 tonnes of copper in concentrate in total, of which 52,197 tonnes was new copper from the underground mine. Smelter secondaries and low-grade concentrate stockpiles made up the balance. Imported concentrate, stock pile concentrates and scrap copper resulted in a total refined copper production of 81,392 tonnes. By-products of the copper stream include gold, silver, nickel, platinum and palladium, which are contained in the refinery tankhouse slimes. The nickel is extracted via a small nickel sulphate plant, whilst the remainder of the slimes are put into drums for export.

The Underground Project 
Palabora has a history and a reputation for technical innovation. One of these was the decision to implement block-caving heights of 500 metres, a world first and typically double the caving distances widely used for this mining method by the global mining industry. With the orebody at Palabora being one large deposit, the company is able to take advantage of block caving which is a safe and cost effective method of underground mining as it utilises natural stresses to break the rock. The cave is initiated by the removal of an undercut, a thin horizontal slice of rock below the future cave, which cause the rockmass overhead to fracture without costly drilling and blasting. The caved ore gravitates to drawpoints, of which the mine will have 166, from where load and haul dumpers (LHDs) remove the material and transport it to a tipping point in large tunnels. The ore is then fed into underground crushers and then conveyed to the production shaft from where it is hoisted to surface for further processing.

The mine has managed to achieve the envisaged block caving heights, though it has had to overcome challenges of fragmentation and wall stability. Because the Palabora orebody is unique and the underground mine is the largest block caving project in the world, the challenges that have arisen have necessitated innovation on a large scale. Rigs manufactured for smaller operations have had to be redesigned. The nature of the rock in the cave has proved to be a formidable challenge to mining engineers, who have responded by using state of the art techniques and creativity. Engineers from other disciplines have been called in for brainstorming sessions and the processes have been subjected to integrated process management system (IPMS) teams that carry out systems modelling exercises to help target achievement through productivity. As a result there have been a number of breakthrough ideas.

These have included the development of a prototype concussion rig, with encouraging results and a production unit is in the design stage. In addition, after the explosive charge is placed and used in the hang-up, an adapted LHD pokes the hang-up to test for stability before a medium range rig (MRR) is used. Another innovation is the use of small cone charges to break oversized rock collected in blasting bays, and this relieves the load on the mine's robust rigs.

Another record Palabora sets with its underground project is the production shaft headgear height of 105.6 metres, which makes that the tallest headgear in the world. The service shaft headgear has a height of 69.6 metres. Some 15,200 m3 of concrete and 1,400 tonnes of reinforcement were used in the construction of the headgears. In total the Palabora Underground Mining Project has used about 190,000 m3 of concrete, for civil, roadway and shotcreting applications, with the material for this supplied by LA Crushers. The concrete work on the project has included the use of high performance concrete, supplemented by high performance materials, such as Super-Pozz, a new generation ultra-fine pozzolan.

Overall the underground mine has four shafts. Three of these are concrete lined, these being the 1,290 metre, 7.4 metre wide production shaft, the 1,270 metre long 9.9 metre diameter service shaft, and the 960 metre 4.8 metre diameter exploration shaft. The fourth shaft is the 930 metre deep, 5.8 metre wide ventilation shaft. Two friction winders with integrated motors and a skip payload of 30 tonnes each operate in the production shaft. In the service shaft the main winder is also a friction winder with a cage large enough to accommodate the largest item of equipment working underground. A Mary-Ann winder provides ad hoc access. Four double toggle jaw crushers, able to crush ore at an average rate of 900 t/hour will feed onto a 1.32 km long, 1,200 mm wide conveyor belt taking the ore to the Production Shaft. Three of these crushers are in place and the fourth will be commissioned in April this year.

Currently the mine has five medium reach rigs, which are used for clearing hang-ups in drawbells up to 11 metres. The mine has four robust rigs, which are used for dealing with oversized rock on the ground, and there are currently 12 LHDs each with a payload of 14 tonnes. To date 33 km of lateral underground development has taken place in addition to 3.5 km of ventilation shaft development. An 18 MW ammonia refrigeration plant artificially cools the intake air into the underground workings. This plant is designed to ensure that the underground reject temperature will not exceed a wet bulb temperature of 27.5oC. Thirty PLCs, linked to 10 operator stations, provide all the control functions throughout the mine. An integrated information network enables operators, at the surface control room, to monitor and direct the activities of the entire underground operation. Visualisation software based on Windows NT allows transfer of data to office systems to prepare statistics or management information.

The underground mine will operate with about 400 employees. At the moment there are about 700 additional contractors working on the underground project, all of whom will be off site by the end of the year. The underground mine's proven and probable copper reserves are some 242 million tonnes at a grade of 0.7 g/t of copper and unit production costs of copper and other minerals are expected to be in line with historical unit costs at Palabora.

In addition to the development of its underground project Palabora Mining Company has achieved a number of other milestones over the past few years. The company has implemented a number of business initiatives to improve its equipment efficiencies and operating costs and it completed the implementation of the system application process (SAP) on time within the budget.

Palabora's ZBS plant
In December last year Palabora completed an upgrade to its zirconium basic sulphate (ZBS) plant, and this plant is now producing zirconium sulphate within customer specifications. The upgrade of the ZBS plant involved the replacement of fusion equipment with a rotary kiln. Last year Palabora sold 1,100 tonnes of ZBS and is working on ramping up sales. The ZBS plant's life will extend as long as there is a profitable market and a viable source of zircon sand raw material, which is currently being sourced from Richards Bay via rail. Previously Palabora supplied the market with Baddeleyite, but as the open pit moved towards closure the company replaced its baddeleyite products with ZBS.

PMC's role in the world Vermiculite market
Over the last two years Palabora has improved its vermiculite recoveries from about 48% to about 60% and expects to produce vermiculite over the next 20 years at the current production rates of about 190,000 tonnes a year. However new developments in vermiculite end markets could see significant growth in sales, commencing this year.

Palabora supplies about 40% of the world vermiculite market and with this company being such a large supplier it is the price leader in that commodity, though other suppliers do have an influence. China is becoming a key player in that regard. Trading is order based but there is a high degree of customer relationship management involved. In many cases customers' processes are designed for the particular vermiculite used and switches between suppliers is not the norm. 

Palabora mines vermiculite at a grade of around 25% contained vermiculite and its vermiculite ore has been derived from three on site sources. One of these is the original vermiculite mine, which is an open cast truck and loader operation. The pit is roughly 1,600 m long on the north-south axis and 1,400 m wide on the east-west axis. Overall depth is 50 m below average surface elevation. The original plant tailings dump, the second source, has become economically more significant due to an ever increasing demand for the finer grades of vermiculite. The dump is reclaimed using trucks and front-end loaders. The third source is the Palabora phosphate and vermiculite (PP&V) mine, a deposit mined as an open cast truck and loader operation similar to the original pit. 

After blasting, broken rock is loaded onto haul trucks. Ore is transported to the processing plant whilst waste is transported to the waste dump. After screening and crushing, ore is fed to a stockpile from where it is distributed to three rotating driers. In the driers the moisture content of the crushed ore is reduced to less that 2%. At an average feed rate of 230 tonnes per hour the driers can evaporate 130 tonnes of water a day. After drying, the ore passes into the ore treatment plant, where it falls into an air stream which causes the lighter vermiculite particles to be deflected whilst falling, a process known as winnowing. Here it is progressively winnowed, crushed and screened. 

Vermiculite is used as loose fill insulation, as a lightweight aggregate and is gaining acceptance as a growing medium in the horticultural industry. It also used to manufacture fireproof acoustic and decorative plasters. Because it is safe and inert, it has displaced asbestos in a number of applications, particularly in the manufacture of dimensionally stable boards and panels.