Platinum Mining at Rustenburg GROWTH: OF THE WORLD’S LARGEST PRODUCER

The scale of operations at Rustenburg Platinum Mines has been extended many times over the last thirty years to meet increusing demand, the most recent expansion programme providing for an output of one million ounces of platinum a year. This article describes the mineral resources available and the mining methods and extraction processes in we to provide the world’s largest source of the platinum metals.

Demand for platinum has increased sub- South African mines are worked primarily stantially over the past ten years or so, and for the platinum metals and yield copper and indications for the next few years are that no nickel as by-products, whereas elsewhere the slackening in the pace is to be expected. Of converse is the case. Rustenburg is in fact the the three principal sources, Rustenburg Plati- world’s largest single source of platinum and num Mines in South Africa, International the only major mine whose main business is Nickel in Canada, and the Russians, only one, the production of the platinum metals. Rustenburg, has been able to respond sig- The pattern of expansion at Rustenburg is nificantly to increased demand because the familiar to readers of this journal. Output has

The upper levels of the mine are still being worked from incline haulage sys- tems, but these are followed in depth by vertical shafts. The headgear for the most recent addition, known as the Frank shaft, is now in course of construction. This will exploit the ore body to a depth of 3,000 feet

Platinum MetalsTev., 1969, 13, (l), 15-22 15 A machine crew drilling holes for 6lasting in the development end of a haul- age tunnel

been increased from some 200,000 ounces of Today Rustenburg constitutes the largest platinum in 1963 to 850,000 ounces a year at underground mining operation in the Republic present, with a further expansion programme of South Africa, its two mines together in hand to yield I,OOO,OOO ounces a year extending more than eighteen miles from one by 1971. Corresponding increases have, of end to the other, and providing about 60 per course, taken place in the output of the other cent of the Western world’s needs of platinum. members of the platinum group of metals - palladium, rhodium, ruthenium, iridium Relating Supply to Demand and osmium. One of the problems faced by Rustenburg - This has been achieved by very substantial and by Johnson Matthey as its refiner and capital expenditures on the sinking of new distributor - is the forecasting of demand in shafts, the installation of additional grinding, the face of the hard fact that a decision to milling and flotation equipment, and the expand output does not result in an increase building of an additional modern smelting in the supply of refined metal for a full three plant, together, of course, with a consequent years. Decisions to expand, involving many expansion in all the facilities and services, millions of pounds and taken on the best including the housing of some 20,000 em- available data, can therefore be vulnerable to ployees. The expenditure involved in the changing conditions, and this lengthy period expansion programme over the seven years between conception and realisation has 1967 to 1973 will probably exceed L37 million. inevitably led to criticism by some users whose

Platinum MetalsTev., 1969, 13, (1) 16 predictions of future needs were too cautious industry, about 25 per cent in petroleum or too tentative. Forecasting demand neces- reforming, 20 per cent in electrical and allied sarily depends upon reliable projections from uses, and 10 per cent in the glass industry, users and potential users, who in turn have with some 15 per cent covering dental, their own uncertainties to consider. For- medical, jewellery and miscellaneous applica- tunately, when predictions of demand turn tions. Thus the use of platinum is not out to need revision, Rustenburg is capable - associated with one or two industries, and given the necessary time - of expanding its many of its applications are in areas of operations very considerably. At any pres- industrial growth. ently conceivable rate of production the ore reserves known to be available will ensure Mineral Resources continuity of operations well into the next The deposit worked by Rustenburg Plati- century. num Mines forms part of the Merensky Reef Because platinum is capable of being of the Bushveld Igneous Complex. This reef, recovered from many of its important fields named after the geologist Hans Merensky of application and used again, a continuing who was responsible for the prospecting demand for increased supplies of new metal programme that led to its discovery in the depends upon a steady growth in technologic- 1920s~is shown in red on the map on page 20. ally advanced industries. During the last It has been traced on outcrop a distance of five years the consumption of newly-mined some 75 to 80 miles along both the eastern platinum has been accounted for as to and western limbs of the Complex. The approximately 30 per cent in the chemical eighteen miles of outcrop which are mined at

From the working face the platinum ore is loaded into small panel cars, tipped into a central gulley and then scraped into a stope box. Here it is being transferred from the stope box into haulage cars for conveyance to the surface

Platinum MetalsTev., 1969, 13, (1) 17 A general view of one of the reduction plants taken from the waste rock dump. The operations curried out here include crushing the ore, milling and flotation the two operations, the Rustenburg section a some twenty inches in thickness, but its few miles to the East of the town, and the regularity makes for relatively straight- Union section about sixty miles to the North, forward mining. The dip and strike of the are considered to contain the highest grades ore bodies on each property are consistent, of the entire igneous complex - most of the and although an occasional dyke is met with remainder containing lower grades which will there is generally an absence of faulting. no doubt be profitably turned to account Although the Merensky reef persists to depths some time in the future. beyond the limits of practical mining, the The reef at Rustenburg dips at approxi- reserves down to a depth of 3,000 feet are mately IOO to the north-north-east, but the immense. dip steepens to about 22' at the Union section. Platinum values at these two sections show a Mining Methods very even tenor, the platinum being partly The length of strike and the comparative in the form of native metal, invariably alloyed shallowness of the deposit have made pos- with iron as ferro-platinum, and partly as the sible the rapid development of large areas of sulphide, arsenide and sulph-arsenides, these ground whenever a greater demand for always occurring in intimate association with platinum has arisen - one reason why the sulphides of iron, copper and nickel. Rustenburg has been able to follow world Associated with platinum, the predominant demand so closely. In both sections mining metal, are smaller proportions of palladium, technique is virtually the same. In the ruthenium, rhodium, iridium and osmium, in shallower portions of the deposit inclined descending order. haulages are sited about 2,500 feet apart and The platinum bearing reef averages only are connected by drives on reef. The deeper

Platinum MetalsTev., 1969, 13, (1) 18 areas have been opened up by means of four tion, is carried out in two reduction plants, vertical shafts ranging in depth from 500 to an older unit and a more modern mill erected 2,000 feet, while two further shafts are in the last few years, while a third mill is currently being sunk to exploit the ore body now in course of construction to handle the to a depth of 3,000 feet. increased output. From the shaft systems a network of The ore is first crushed in a series of jaw cross-cuts and haulages extends to intersect crushers and fed to the primary and then the the ore body, and shallow gullies divide the secondary ball mills which are in closed cir- working face into panels. Ore broken on the cuit with hydrocyclone classifiers. This is face is washed down, loaded into small panel followed by gravity concentration on corduroy cars and tipped into a central gully, from tables to separate the course particles of plati- which it is removed by a scraper winch into num-bearing minerals and the free metallic a stope box and loaded into trains of 4-ton particles. The corduroy concentrate is hopper trucks hauled by electric locomotives dressed on an elaborate system of shaking conveying the ore to the shaft for hoisting to tables up to a final high grade concentrate the surface. which is sent directly to the Johnson Matthey A great deal of thought and investigation refineries in England. has gone into the laying down of standard The tailings from the tables are returned working methods to ensure the delivery to the to the mill circuit, the final pulp from here mill of a product of the highest value at the being treated in a series of thickeners before lowest cost. going to the flotation plant. Here banks of cells are arranged in a normal rougher-cleaner Reduction Practice circuit which recovers most of the remaining Treatment of the ore, comprising crushing, platinum-bearing minerals. The flotation ball milling, gravity concentration and flota- concentrates, consisting mainly of nickel,

After preliminary crushing the ore is fed to the primary and secondary ball milling sections

Platinum MetalsTev., 1969, 13, (1) 19 Mines Plutinurn Rustenburg by operated mines two the with together red, in shown reejis Merensky platinum-bearing the of location The

Platinum MetalsTev., 1969, 13, (1) 20 One of the flotation plants at Rustenburg. The concentrates are thickened,$ftered, dried, and pelletised before smelting to a matte copper and iron sulphides with the balance of anodes. Both the copper and the nickel anodes the platinum metals, are thickened, filtered, are electrolytically refined to pure metals, the dried and pelletised, ready for the smelter platinum group metals being recovered in the while the tailings are dumped. form of adherent anode residues. At the two matte treatment plants in Smelting and Refining South Africa and in England new and im- The initial stage in the recovery of the proved processes have been introduced in platinum metals is to smelt to a copper- which the nickel and copper are separated nickel-iron matte in a series of blast furnaces. more efficiently and the platinum metals are This matte is then tapped periodically into further enriched. ladles, transferred to a group of converters, Final concentration and separation of the and blown to a high-grade matte which is platinum metals is carried out in the Johnson cast into moulds and then broken up in a Matthey refinery in England, but an additional jaw crusher. Part of this converter matte is refinery is now under construction in South shipped to the Johnson Matthey smelter in Africa to supplement supplies by treating England, the balance being treated by Matte some part of the output of Matte Smelters. Smelters, a joint subsidiary of Johnson After roasting and leaching to remove the Matthey and Rustenburg, in a plant adjacent last of the copper, nickel and iron, the en- to the mine. In both plants the matte is riched anode residues join the platinum-bear- treated by smelting to separate the copper ing gravity concentrates shipped from South and nickel sulphides. The copper sulphide Africa and together enter the wet process is blown in converters to give blister copper refinery, where the platinum metals are which is cast into anodes, while the nickel brought into solution for their separation and sulphide is roasted, reduced to metal in individual refining. The complete cycle of reverberatory furnaces and also cast into treatment is very complicated but basically

Platinum MetalsTev., 1969, 13, (1) 21 Pouring blown matte from one of the converters. After casting and breaking up, the matte is shipped to Johnson Matthey for the extraction of copper, nickel and the six platinum metals

From this refinery, which has of course been enlarged in line with the Rustenburg ex- pansions, the six platinum metals are supplied in pure form to independent fabri- cators and catalyst manu- facturers and to the Johnson Matthey group of companies throughout the world. it involves their precipitation as complex salts Throughout all the stages of extraction and followed by successive stages of recrystal- refining new and improved methods are under lisation and then by calcination under care- constant development, and the numerous fully controlled conditions in electrically extensions to plant both at Rustenburg and heated muffle furnaces, to produce the metals in the Johnson Matthey refineries have been in the form of sponges or powders suitable designed to take full advantage of more for melting. sophisticated metallurgical techniques.

Osmium Complexes Containing Four Metal Atoms The preparation of interesting new com- This new compound is red in colour, mono- plexes containing four metal atoms has been meric and a non-conductor in solution, and reported by C. W. Bradford, of the Johnson has an infra-red spectrum in the C-0 stretch- Matthey Research Laboratories, working ing region which is consistent with a linear under the guidance of Professor Sir Ronald arrangement of the Au-0s-0s-0s moiety. Nyholm (Chem. Comm., 1968, 867). These The corresponding bromo-compound : are obtained by reacting osmium carbonyl, Br - 0s- 0s- 0s- AuPPh, Os,(CO),,, with triphenylphosphine gold Ill halides. It appears that only one of the (CO),(CO), (W, three 0s-0s bonds in the original triangular has also been isolated and has properties cluster is broken and this gives rise to what is similar to those of the chloride. possibly the first case of a linear arrangement If X-ray crystallographic studies at present of four covalent bonded metal atoms: being made show that a linear arrangement is PhJ'AuX + Os,(CO),,+ indeed present, then it is interesting to speculate on the possibility of synthesising C1- 0s- 0s- 0s- AuPPh, Ill from these compounds other compounds (cola (COh (CO)* containing even longer chains of metal atoms.

Platinum MetalsTev., 1969, 13, (1) 22