Tin mining and smelting in the Transvaal during the Iron Age by H. M. FRIEDE*. Ph.D. and R. H. STEEL* (Visitors)
SYNOPSIS This paper reviews the historical, archaeological, and metallurgical evidence on Iron Age tin mining and tin smelt- ing in Southern Africa. The results of the analysis of twenty samples of tin ore, tin slag, and tin ingots found associated with Iron Age materials in the Transvaal (mostly in the Rooiberg area) are reported and discussed. The types of ingots preserved in local collections are described. A small experimental tin-smelting furnace was constructed and worked according to traditional African Iron Age technology. Qualitative and quantitative results of this experiment are reported.
SAMEVATTING Hierdie verhandeling gee 'n oorsig oor die historiese, argeologiese en metallurgiese bewyse van die ontginning en smelting van tin in Suidelike Afrika gedurende die Ystertydperk. Die resultate van die ontleding van twintig monsters van tinerts, tinslak en tingietblokke wat saam met materiale uit die Ystertydperk in Transvaal (hoofsaaklik in die Rooiberggebied) gevind is, word aangegee en bespreek. Die tipe gietblokke wat in pJaaslike versamelings bewaar is, word beskryf. Daar is 'n klein eksperimentele tinsmeltoond volgens die tradisionele tegnologie van die Afrikaanse Ystertydperk gebou en bedryf. Die kwalitatiewe en kwantitatiewe resultate van hierdie eksperiment word aangegee.
HISTORY OF TIN MINING Ellenbergerl4, who records that Chief More detailed information on tin AND WORKING Mokgosi of the Malete tribe (Bot- comes from a report that Jan van de swana) once stated that his ancestors Capelle, an official of the Dutch East Almost all our knowledge of tin dug for white iron in the quarries India Company at the Delagoa Bay mining and tin working in Iron Age of Ditshiping, which is in the trading station, sent to the Governor Southern Africa is derived from the Transvaal. (White iron 'tshipi e of the Cape of Good Hope in 172321. reports on the Rooiberg tin mines - tshweu' is considered to be the Van de Capelle wrote: published in the early part of this - name for tin, whereas 'tshipi e [In the later part of the year 1722,1 century by Baumannl, Trevor2,3, there were black people at La Goa who ntsho' refers to black iron15.) Wagner4, and Stanley5, 6. More came from the lands of Paraotte and It has been stated that ancient Machicosje, who brought with them, recently a few notes have been workings have been found near the not only copper, but also tin, to barter published (e.g., by Thompson7,8, at that place. . . . This tin is beautiful Brandberg in South West Africa16, in colour but a bit soft and light as White and Oxley Oxland9,1°, and at Rusapi17 and Umniati Railway can be seen from two pieces of bars Kiiselll). [which I had the honour to submit to Bridge Mine18 in Rhodesia, and near the Honourable Governor]. One [of It is interesting to note that a Longwe in Malawi19, but no definite these pieces] is much harder in sub. large number of tin mines have evidence of Iron Age tin production stance than the other, as can be found out by smelting. . . . [The black people] been opened up in Southern Mrica has been found at these places. say that they had found the tin in since the beginning of this century, A short note in the Bronkhorst- the land Machicosje along the riverbeds but Rooiberg (in the Waterberg and that they had collected it in baskets verslag, a report on the 1836 Voor- and had the sand washed out and District of the Transvaal, approxi- trekker Commissie Trek, says that then. . . had it made into bars for mately 60 km from Warmbaths) is '[at Rhenosterpoort on the Rand- barter. All the inland people use this still the only place where indisput- tin, also what they buy from us, to berg] we also found good tin which smelt it with their copper for necklaces able remains of Iron Age ('ancient') [the people there] extract from the and bracelets. . . . [They also] cast tin workings have been found. ingots from the tin for barter. (Free Randberg and make rings of, calling translation from Van de Capelle's There are many vague references it "white iron" '2°. It has been report.) to tin mining and tin smelting in suggested that this Randberg may This description appears to be the reports of the missionaries, be the area - or an area nearby- factual in many respects, but the traders, hunters, and prospectors where the rich mines of the Pot- report on the provenance of the who travelled in Southern Africa gietersrus tin fields are now situated. tin ore is probably hearsay evidence. in the early nineteenth century. No remains of ancient workings It has been suggested that the Moffat12 mentioned that tin was have been found in this area, but country Machicosje mentioned by found in the Bakone country, and it could have happened that all Van de Capelle is the land of a Livingstone13 that this metal was the old tin workings there have tribe living on both sides of the mined by the Bagalaka people13. been carefully filled in according Lebombo Mountains22. However, be- Both these localities could refer to to the strange habit of the Iron fore accepting this suggestion, one the Rooiberg area. An interesting Age tin miners, or that the tin should remember a warning that reference is found in an article by mentioned was a trade product was included in the Journal of the brought from Rooiberg, which is Dutch East India Company on the ...Archaeological Research Unit, University situated a few days' walking to 21st August, 1726, when a ship from of the Witwatersrand, Johannesburg. the southwest. Rio de la Goa arrived at the Cape:
JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY JULY 1976 461 'The reports of the blacks are so DESCRIPTION AND ANALYSIS the time being it is not possible to confused and doubtful that it is OF TIN FINDS decide from the analysis of a tin evident that they do not wish us ingot or a tin ornament found at an Ores to know much about their country'23. archaeological site whether it was So, Van de Capelle's report could All the tin ores analysed came derived from Rooiberg ore. from the Rooiberg area and were just as well refer to a tin field Slags somewhere in the central Transvaal, taken at or near the ancient workings or even to the rich alluvial deposits of there. Small slag heaps associated with pieces of tuyeres and pottery sherds Swaziland, which are much nearer 'Tin feeds' were found at the Delagoa Bay. excavation of several old smelting are found at many places in the furnaces at the sites of Rooiberg Rooiberg area. The best known of the It appears that the tin trade from and Blaauwbank. Samples of these old smelting sites is Smelters Kop, the interior to Delagoa Bay was ores are preserved in the collection a steep, fairly flat-topped hill about only on a small scale. The records of of the former Archaeological Survey, 2 km from Rooiberg Mines. On a the Dutch East India Company now the Archaeological Research nearby hill was another smelting contain only a single detailed entry Unit, University of the Witwaters- place where several furnace bottoms, for the tin trade at Delagoa Bay: rand. weighing about 12 Ib each, were Van de Capelle reported21 on the discovered3. 14th December, 1731, that The analysis of these ores (AI, Five samples of slag from Rooi- Heeden quamen de machicossers A2, A4 of Table I) shows the tin weeder aan board met haar Eliphands content to vary from 15,3 to 31 berg sites have been analysed. The tanden, en een partij tin, w' kogten per cent. These values are typical results of these analyses, together van haar: . . . with two others previously pub- 56 staven thin, aIs for the selected high-grade cassiterite 20 ps groote plat ronde en ore worked by the Iron Age miners, lished, are given in Table I (B1-B4, 36 ps kIeene lange ronde who understood how to find such B6, I, 11). The tin content of the 56 ps staven thin kosten te samen samples varies widely from 0,14 Coral: Ib 103. ores either in rich deposits near the - surface or in pipes of almost pure to 38 per cent. It is possible that It is interesting to note that two cassiterite. Some of the ore mined the low-value slags are the products different types of tin ingot are may have been of poorer quality of the smelting, not of tin ore, but mentioned in these reports: large and could have been enriched by of iron or copper ores. On the other flattened rounds and small long washing in baskets or by panning. hand, some slag specimens are very rounds (sometimes called 'staafjes'). 'The spruit running through the rich in tin; for example, specimen 11 The cast ingots found in the Tram- Rooiberg property was probably the (Table I), on which P. Wagner vaal also belong to two main types: principal scene of these washing reported '[In this specimen tin was heavy rounded bars and long light operations, but in one case [the present] almost entirely as graim rods. miners] appear to have used an old of unreduced cassiterite, from which Unfortunately, the dimensions and working as a slime pit'l. it is concluded that this particular masses of the ingots traded at slag resulted from the frothing over The composition of the ores Delagoa Bay are not stated, but an of the furnace into which the tin analysed is not uniform since the entry in the books of the Company ore was fed'4. Other tin-rich slags cassiterite, embedded in the quartz- at the Cape (16th February, 1732) enclosed small particles of metallic ites and sandstones of the Lower mentions that the ship De Snuffelaar tin in the shape of granules, pellets, Waterberg Series, is generally coming from Rio de la Goa brought and small buttom. It appears that associated with tourmaline and iron 2131b of tin to the Cape23. This the average tin content of typical pyrites. Arsenical and copper pyrites consignment apparently refers to tin slags ranged from 2 to 15 per and other minerals in smaller the ingots mentioned by Van de cent. amounts may also be present in Capelle in his record of 14th addition to various gangue minerals1. The fluctuation of the tin content December, 1731. The analysis of the 'tin feed' ores in smelting slags indicates the The available archaeological and from Rooiberg therefore shows a vagaries of the primitive tin-smelting historical evidence gives no indica- number of minor and trace elements, process, which could not be con- tion of the presence of larger tin as well as comiderable variation in trolled properly - much in contrast mines and tin workings in Southern their distribution. No single 'indi- to the traditional iron-smelting pro- Africa, with the exception of the cator' element or combination of cess, where slags of a fairly uniform Rooiberg tin-mining centre. In a such elements that could be con- iron content were produced larger frame, the verdict of Cline, sidered typical for all the ores of regularly. However, the metallurgy who made a critical survey in 1937, the Rooibcrg complex has been of tin extraction is in several appears to be still valid: 'Only two found. Boron and tungsten are respects more complicated and diffi- tin mining centres have been found associated with most of the Rooiberg cult than that of iron. in Negro Africa: the Transvaal and ores analysed, but these elements The values for elements other Bauchi Province in Northern are possibly also present in tin than tin also vary considerably in Nigeria'24. ores from India and Europe. For the analysed samples. This is to be
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464 JULY 1976 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY expected since, as has been men- considering the number of associated from 800 to 2100 g, and their tin tioned, the composition of tin ores minerals in the ores: arsenical, iron, content from 95 to 99,4 per cent. varies from one deposit to another. and copper pyrites, wolframite, The hemispherical or pIano-convex Silicon dioxide contents are in the scheelite, galena, annabergite, cal- shape of the bun ingots indicates range 26 to 57 per cent, aluminium cite, and siderite1. Therefore, it is that they represent furnace bottoms oxides from 2 to 32 per cent, and to be expected that arsenic, copper, or that liquid tin was run into iron oxides from 9 to 39 per cent- nickel, lead, antimony, tungsten, clay pots direct from the furnace. values corresponding to those in etc. will find their way from the The lower, convex surface of these ores based on quartzites and sand- ores into the slags in larger or ingots is fairly smooth, whereas the stones. The alkali metals contained smaller amounts. upper flat surface shows fissures in tin ores are also found in the Ingots and cracks formed on cooling (Fig. slags derived from them. There Not many 'ancient' tin ingots have 1). Stanley5 reports the analysis of appears to be no need to interpret survived in South Africa. Table n two ingots from Rooiberg that the presence of lime or magnesium (No. 1-7) gives descriptions, contained 99,5 and 94,9 per cent as resulting from the use of fluxes measurements, and analyses of seven tin respectively - values similar to in the smelting process. ingots preserved in collections in those found for the bun ingots A rather unusual slag analysis is Johannesburg, Rooiberg, and Pot- mentioned in Table n. It is possible reported by Baumannl, who states gietersrus. A previously published that the lower tin values and the that a slag discovered at Haarte- analysis of an ingot in the lost higher iron contents of some ingots beestfontein (near Rooiberg) con- Lepehne collection (Potgietersrus) is indicate 'crude' tin and the higher tained, in addition to 2,5 per cent also included (No. 8). tin values refined tin, but such tin, not less than 30 per cent oxide The tin ingots described in Table differences could, of course, also of tungsten. Small amounts of n belong to three different types, be the result of variations in the tungsten are present in nearly all which can be called 'bun' ingots, composition of the ores or in smelt- the slags found in the Rooiberg area. 'rod' ingots, and 'bar' ingots. ing conditions. The analyses of three A great variety of minor and Bun ingots bun ingots are given in Table n trace elements are found in the All the known bun ingots have (No. 1-3). slags of the Rooiberg smelting sites been found in the Rooiberg area. In the collection of the Rooiberg - a fact that is not surprising The mass of these ingots ranges Minerals Development Company, there is an odd-shaped tin object SIBASA INGOT 5'fS1 (tin content 91 per cent) that was found in the Rooiberg Northern Workings. The shape of this speci- ~~ BAKEDa.AY MOUlD men- an irregularly formed cylin- ) FOUtD NEAR 8EJERSKDP (ROO8IIG, TYL der - suggests that it was probably designed as an ornament or that C2~ it was a cast from which tin bangles A were made. '.0 The analysis of the group of Rooiberg ingots preserved in the collection of the University of the Witwatersrand revealed an un- expected fact. One of the ingots (specimen 21-39-2) resembled the DU bun tin ingots described in dimen- sions, mass, and superficial appear- ance, but in the test for hardness MALABOG 'BAR' INGOT AA7;3 it had a much higher value, a [ -le) V.P.N. (Vickers Pyramidal Hard- -- ness Number) of 114 against a A~ V.P.N. of 12,5 for tin ingot 21-39-3. MALABOG'ROD'INGOT ~~ 811011 This unusual ingot (21-39-2) con- C-- tained little tin (1,18 per cent), but, : in addition to some iron (1,51 per cent) and lead (0,07 per cent), it contained high amounts of copper (66 per cent) and arsenic (5,5 per \~~~D cent) (analysis given by the National Institute for Metallurgy). This ingot must therefore be described as an mm - arsenical bronze. Such arsenical Fig. I-Tin ingots from South African collections bronzes are known from Early
JOURNAL Of THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY JULY 1976 465 Bronze Age sites (e.g., from Israel25 been marks to indicate the value of dence of imports of tin to the East and Central Europe26) and were a metal ingot, or they were perhaps Coast is found in trade reports. possibly the first alloys known to an ornamental pattern of a forgotten The factor of S(I)fala, De Brito, man. A number of priUs and pellets tradition. noted in 1519: 'A ship from Cam- from Blaauwbank-Rooiberg4 and the The analyses of three bar ingots baya discharged at Kilwane tin well-known Blaauwbank bronze are given in Table II (No. 6 to 8). from Cambaya'30, and Jan van de slug27 also belong to this type. A variant of the bar ingot is the Capelle, an official of the Dutch It is not likely that these South so-called 'Sibasa' ingot, which has East India Company at Delagoa Mrican arsenical bronzes were a rather peculiar history. This ingot Bay, records in 1723: cOok het [de alloyed intentionally. They were was found buried 2 ft below the negers] thin van ons inkoopen'21. probably the results of the uninten- surface by an Mrican who uprooted There is little doubt about the tional addition of copper- and a tree in the Levubu settlement considerable antiquity and the large arsenic-containing ores to the furn- (Sibasa district, northern Trans- extent of the Rooiberg tin-mining ace charge. The problem of these vaal). The original mass of the ingot activities. Tin mining in this area arsenical bronzes needs more detailed was almost 2,5 kg, but for some goes back at least to the mid- metallurgical investigation. unknown reason the ingot was cut fifteenth century. This dating is Rod ingots up into several pieces. Thompson, based on a (corrected) radiocarbon The rod ingots found in South who wrote a report on this ingotS, determination on a piece of mining Mrica are slender tin sticks, 400 mentions that 'the ingot has the timber (Burkea africana, or wilde to 500 mm in length, roughly tri- appearance of having been cast in sering) found in an ancient shaft31. angular in section, each side measur- sand at two castings. A circular The quantity of ores removed ing 8 to 9 mm (Fig. I). Such ingots, bar. . . was cast; on top of this a from the ancient Rooiberg tin mines which can easily be cut into pieces, second casting was added. . . . When may have been very high. Some would have been quite suitable for found, at the bottom of each end estimates give figures up to 18 000 the making of rings and bangles. of the ingot was a circular stud tons1, from which at least 500 tons The analyses of two rod ingots are decoration'. (See reproduction of of tin metal should have been given in Table II (Nos. 4 and 5). drawing in Fig. 1.) The mutilated extracted. One of the puzzles of ingot was seen in 1951 by C. van South African prehistory is what Bar ingots Riet Lowe, who retained a narrow could have happened to such large These ingots are much more section of it (analysis of this section quantities of tin. It is p03sible that massive than the rod ingots. Of the is given in Table II as No. 7). What much tin was exported to Rhodesia two extant specimens, one, which happened to this ingot afterwards is and the East coast along an old was obtained in the Malabog location unknown. trade route, which, according to near Pietersburg, is now in the Punt29, led from Rooiberg to the collection of the University of the bigot moulds Nylvlei and the Sandriver and then Witwatersrand; the other, found Ingot moulds, either made from to the Zoutspanberg and the Lim- 6 ft below the surface of a cave clay or carved into stone, have popo. near Thabazimbi, is in the National been found at various places, e.g. Cultural History Museum, Pretoria. at Maric02S (Transvaal), at Smelters MODEL OF A TIN-SMELTING Both these bar ingots shttw the Kop, Rooiberg (Fig. I), and at FURNACE horns at both ends of the bar, a Potgietersrus29. peculiar feature of this type of Provenance of ingots The evidence for Iron Age tin ingot (Fig. I). One can be reasonably certain smelting in Southern Mrica is There were two more such ingots that the tin smelted at Rooiberg meagre. As far as is known, no in the Lepehne collection, which and the tin ingots found there were well-preserved tin-smelting furnace before 1949 was kept in the old produced from locally mined ore. has ever been found in Southern Potgietersrus Library. Unfortun- The pieces of high-grade tin ore and Mrica. However, foundations of ately, this collection, which also the heaps of tin-containing slags saucer-shaped hearth fttTIlaces were contained nine rod ingots, has since lying next to smelting furnaces, discovered on the Blaauwbank smelt- disappeared. However, Thompson7 as well as priUs of tin sticking to ing sites (near Rooiberg) by Wagner has given a good description of the furnace bottoms, are ample evidence and Gordon4, who report: 'Only the lost ingots. One bar ingot closely for this belief. bottoms of these [furnaces] remain, resembled the University of the It is less easy to state whether so that it is not possible accurately Witwatersrand specimen, whereas the rod and bar ingots found at to reconstruct them. . . . There is the second showed a most interesting other places in the Transvaal- definite evidence that tin was feature: on the top of the bar a near the present Potgietersrus, on smelted in these furnaces, as one number of small but distinctive the Blaauwberg, and in Vendaland had slag containing prills of tin studs could be seen sticking out- - or the crude tin used for the stuck in the bottom'. fairly similar to the stud or nipple casting of these ingots also came Since no reliable knowledge of tin pattern typical of the Mu-Tsuku from Rooiberg. It cannot be ex- smelting in Iron Age Southern copper ingots of the Messina area cluded that tin imported from India Mrica is available, it was thought (Fig. I). The purpose of such or Europe was also used at South that some relevant information could 'studs' is unknown. They may have Mrican smelting sites. Some evi- be obtained from the construction
466 JULY 1976 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY SECTION AB
0 A , C B " ~ ~--- ~~. /
FLOOR PLAN ~
A B
C
D
0 10 20 30 L----..... I cm
Fig. 2-Floor plan and section of the experimental tin-smelting furnace. A-B dia- meter offurnace floor, C discharge opening, D discharge trough, E hole for thermo- meter
JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY JULY 1976 467 and working of an experimental furnace. The model was designed on the general pattern of the metal- smelting furnaces found in Southern Mrica, some features being based on descriptions of old Nigerian tin-smelting furnaces32,33.Even if it is unlikely that the tin-smelting technology of Southern Mrica is directly related to that of far away Nigeria, it is possible that there was a common source for all the smelt- ing technology in Mrica.
Construction of the Furnace The structure and the dimensions of the experimental furnace are shown in Figs. 2 and 3. The furnace, 640 mm high, had the shape of a truncated cone, with the large diameter at the bottom. The furnace chamber was built from fire bricks, a ceramic pipe being used as a chimney shaft. An opening in front of the furnace chamber allowed the discharge of the smelted metal and the slag. An aperture at the back of the furnace served for the insert- ion of a tuyere, which was directed towards the slightly forward-sloping furnace bottom. The outside of the furnace was covered with insulating layers of puddled clay and daga. The temperature in the furnace could be measured by a thermo- couple probe inserted through a hole in the furnace wall. Details of the air supply (from a compressor blower delivering a vol- Fig. 3- The experimental tin-smelting furnace ume of air equivalent to that sup- plied by two traditional skin bellows) mining area, where old workings washing process that was probably were given in a previous article34. still exist. The ore had a tin content used by the Iron Age miners1. For the mild blowing action re- of 6,3 per cent. When this ore was The ore was washed under a running quired at the end of the firing used in the original state in the tap and was then screened through period, a small electric blower (drier smelting experiments, very little a 3 mm sieve. In this process, much type) was used. metallic tin was recovered. Nearly of the original ore material including Use was made of the same type all the reduced tin was in the shape the tin-containing sand was lost, of Natal braaivleis charcoal (made of minute granules and globules but the black and black-and-white from wattle wood, Acacia nigra) as embedded in the slag, from which speckled particles rich in cassiterite had proved satisfactory in the the metal could not be separated (tin stone) could be easily hand- copper-smelting experiments34. How- mechanically. It appeared that the picked from the residue of stony ever, it is possible that the charcoal clayey and sandy material, which material. The final concentrate, used by the Iron Age metal workers, was present in large amounts in the which had a tin content of 26,3 per burnt from the wood of selected ore, caked and fused in the fire cent, was found to be suitable for indigenous trees, was superior to and coated the tin minerals, in- the experiments (Batches 7, 8, and the modern product. hibiting complete reaction with the 9). charcoal. Any reduced tin was also A second type of Rooiberg ore Ore coated with a clayey layer, which used in the experiments was 'tin Through the generosity of the tended to prevent the formation feed' ore collected at various smelting Rooiberg Minerals Development of larger tin particles. sites and kept as demonstration Company, a large quantity of tin For this reason, the ore was samples in the Archaeological Re- ore was obtained from Rooiberg A3 washed in imitation of the stream- search Unit at the University of the
468 JULY 1976 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY Witwatersrand. A small amount were added to the ore charges, but, (from the quartzite and sand- (445 g) of each of three samples in spite of the high tin content of stone present in the ore) can was used, the combined amounts the slag (20 to 30 per cent), the tin combine with tin oxide and being just sufficient for a single yield did not increase. form tin silicates that remain in smelting experiment (Batch 10). The separated crude tin (which the slag35. The analyses of the enriched ore had a tin content of about 98 per 3. Much of the reduced tin is and of the tin feed samples are cent) was collected in a clay crucible finely divided on and in the given in Table I. and reheated in a crucible furnace. slag and can be recovered only This type of furnace, based on the by a re-smelting process. (Such OPERATION OF THE EXPERI- pattern of a smelting furnace found a process was a regular feature MENTAL FURNACE at Blaauwbank-Rooiberg4 had been of Nigerian tin smelting32.) previously used for the smelting of 4. If, in the presence of air, tin A small fire was started in the copper34. The temperature of the is kept at higher temperatures furnace with a few dry sticks, charcoal fire round the crucible was for extended periods, a consider- followed by charges of charcoal brought to between 900 and 1000 DC. able amount of already reduced (15 to 25 mm). After the front When the tin in the crucible became tin may be re-oxidized. opening of the furnace had been liquid, the crucible was quickly In these experiments, losses also closed with large stones and clay, removed from the fire and placed resulted from the small size of the air was blown through the tuyere on a bed of glowing charcoal. The experimental furnace and the short and some more charcoal was added scum formed by the impurities was operation time. In furnaces as large until the furnace was about half skimmed off repeatedly until the as the Nigerian furnaces, if the full. When the furnace charge was surface of the tin stayed clean and smelting process is prolonged by well aglow, a few handfuls of ore shiny. Then the liquid metal was continuous charging of ore and (10 to 20 mm) were thrown in from poured into the moulds that had charcoal over periods lasting 12 to 18 the top and covered with a layer of been prepared in sand. The refined hours as was traditional in African charcoal. This procedure was re- tin contained 98,8 to 99,15 per cent smelting, the temperature in the peated at intervals of about ten tin, 0,5 to 1 per cent copper, and smelting chamber would be much minutes until the furnace was three- small amounts of other elements higher and more equally distributed. quarters full. (The total charge of (Table II). As a result, the reduction rate, as ore in the experiments varied from well as the separation and lique- 1 to 1,8 kg.) When the fire in the The recovery of tin from the ore faction of tin, would be better and chimney showed an orange-yellow was low in all the experiments. The the yields would be higher. It is glow, the compressor air was stopped yields in three smelting experiments also to be expected that the use and replaced with a mild blast from in which washed and sorted ore of higher-quality ore combined with an electric blower. At that stage, a from the Rooiberg A3 area was the use of a more suitable charcoal strong upward draught had de- used varied from 12,8 to 19,1 per would give better results. veloped and, when the temperature cent, calculated on the tin content The proper regulation of ore in the furnace had reached between of the ore. The corresponding yield additions, temperatures, and blow- 1200 and 1250 DC (measured by in one experiment in which a com- ing rates as used in a primitive thermocouple potentiometer), the bined 'tin feed' sample from Rooi- process can be learnt only by long blower was worked only inter- berg smelting sites was used was experience. Such empirical know- mittently. Charcoal was added when 19 per cent. ledge gained over many generations necessary, and 2t to 3 hours after The yields recorded are much was incorporated in the traditions the fire had started, the tuyere hole lower than would be expected from of the metal workers of the Mrican was blocked and the fire was allowed the calculated value, but high losses Iron Age. to burn down. When the furnace are probably an inherent feature of It is much to the credit of these had cooled down, the stones block- the traditional process of Iron Age people that they could handle the ing the front opening were removed tin smelting. Some of the following difficult process of tin smelting and the furnace contents raked could be reasons for the low yields. efficiently, achieving a reasonable out onto the discharge trough. 1. The use of too much charcoal, output of tin of good quality. No liquified tin was observed in producing an excess of carbon any of the experiments. The metallic monoxide, may result in the CONCLUSIONS tin generally adhered to the slag in reduction of the metal oxides the form of semi-solid beads and that are present in the ore in (1) A survey of the literature on pellets (2 to 9 mm in diameter), addition to tin oxide35. Reduced the history of tin mining and and sometimes larger chunks of iron in larger amounts is especi- tin metallurgy in Southern tin were found. Mter the slag had ally undesirable since, at the Africa shows that nearly all cooled down completely, it was higher temperatures, it may the relevant reports refer to broken up by being hammered, and form with tin intermetallic com- the Rooiberg-Waterberg area the loosened tin particles were pounds that do not separate in the Transvaal. picked out. properly from the liquid tin on (2) The available records on the In two experiments, small portions cooling. tin trade indicate a small volume of slag obtained in previous firings 2. At high temperatures, silica of trading at Delagoa Bay.
JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY JULY 1976 469 (3) The analyses of slags and ingots ment Co. and his staff; Mr A. Dieper- 14. ELLENBERGER, V. History of the Ba-Ga-Ma1ete of Ramoutsa. Trans. found at Rooiberg give evidence ink (The A. Dieperink Museum, Roy. Soc. S. Afr., vol. 25. 1937. p. 46. of a relatively efficient local Potgietersrus) and Mr Van der 15. SCHAPERA,I. Ditirafalo tsa merafe ya mining and smelting industry. Waal (National Cultural History BaTswana. 1940. p. 213. Tin ingots found at other places Museum, Pretoria); and Miss Z. 16. Natal Daily News, 11th Nov., 1939. 17. Bulawayo Chronicle, 9th Dec., 1933. in the Transvaal have a high Martin, who did the drawings for pp. 31-33. purity, but it is not clear this paper. 18. SUMMERS, R. Ancient mining in whether all the tin used was Rhodesia. Nat. Mus. Rhod. 1969. p.59. produced by African Iron Age REFERENCES 19. LIVINGSTONE, D. Narrative of an smelters or whether it was expedition to the Zambesi. 1866. p. 315. 1. BAuMANN, M. Ancient tin mines of 20. VAN DER MERWE, P. J. Nog verder imported. the Transvaal. J. Chem. Metall. Min. (4) The problem arising from the noord. 1962. pp. 167, 170. Soc. S. Afr., vol. 19. 1919. pp. 120-131. 21. THEAL, G. M. Records of south- presence of high amounts of 2. TREVOR, T. G. Some observations on eastern Africa. vol. 1. 1898. pp. 104, ancient mine workings in the Trans- 413-417, 497. arsenic in some 'bronze' speci- vaal. J. Chem. Metall. Min. Soc. S. Afr., vol. 12. 1912. pp. 271-2. 22. PAVER, F. R. Trade and mining in mens from the Blaauwbank- the pre-European Transvaal. S. Afr. Rooiberg area needs closer in- 3. TREvoR, T. G. Some observations on J. Sci., vol. 30. 1933. p. 605. the relics of pre-European culture in vestigation. Rhodesia and South Africa. J. Roy. 23. LEIBBRANDT, H. C. V. Precis of the (5) The operation of an experi- Anthrop. Inst., vol. 60. 1930. pp. Archives of the Cape of Good Hope, 394, 397. Journal 1699-1732. 1896. pp. 304, mental tin-smelting furnace 4. W AGNER, P. A., and GORDON, H. S. 331. showed that the smelting of Further notes on ancient bronze 24. CLINE, W. Mining and metallurgy in Negro Africa. 1937. p. 76. tin under conditions available smelters in the Waterberg District, Transvaal. S. Afr. J. Sci., vol. 26. 2.";. KNAUER, P. et al. The metal smiths. to Iron Age people is a compli- 1929. pp. 563-575. Time-Life Books, 1974. pp. 55-56. cated and difficult process. The 5. STANLEY, G. H. Composition of 26. SINGER, C. et al. A history of tech- yield of tin in these operations prehistoric bronzes. S. Afr. J. Sci., nology. vol. 1. 1954. p. 589. vol. 26. 1929. pp. 48-49. 27. FRIEDE, H. Notes on the composition was low, but the tin produced 6. STANLEY, G. H. Primitive metallurgy of pre-European copper and copper- was of high purity. in South Africa. S. Afr. J. Sci., vol. alloy artefacts. J. S. Afr. Inst. Min. 26. 1929. pp. 740-741. Metall., vol. 75. 1975. p. 189. 7. THoMPsoN, L. C. Ingots of native 28. MASON, R. J. Prehistory of the Trans- ACKNOWLEDGEMENTS manufacture. N ADA, No. 26. 1949. vaal. 1952. p. 421. pp. 14-16. Sincere thanks are due to the 29. PUNT, W. The relationship between 8. THoMPsoN, L. C. A native-made tin the pioneer routes in the Transvaal following, who assisted in various ingot. NADA, no. 31. 1954. pp. 40-41. and ancient trade routes. S. Afr. ways: Professor R. J. Mason, Direc- 9. OXLEY OXLAND, G. St. J., and Archaeol. Soc. Wits. Centre occas. WHITE, H. Ancient mining practices tor of the Archaeological Research paper. 1975. p. 18. in the Rooiberg area. J. S. Afr. Inst. 30. CAToN-THoMPsoN, G. The Zimbabwe Unit at the University of the Min. Metall., vol. 74. 1974. p. 245. culture. 1931. pp. 64, 243. Witwatersrand; Dr R. E. Robinson, 10. WHITE, H., and OXLEY OXLAND, 31. VOGEL, J. C. Radiocarbon, vol. 12. G. St. J. Ancient metallurgical 1970. pp. 441-471. Director General of the National practices in the Rooiberg area. J. S. 32. MEEK, C. K. The northern tribes of Institute of Metallurgy and his Afr. Inst. Min. Metall., vol. 74. 1974. pp. 269-270. Nigeria. vol. I. 1952. pp. 149-157. staff, especially Mr H. Stoch and 11. KiisEL, U. S. Extractive metallurgy 33. STAUDINGER, P. Zinnschmelzen Afri- Mr J. Stanko; Mr E. L. Psaros and in Iron Age South Africa. J. S. Afr. kanischer Eingeborener. Zeitschr. Ethnol., vol. 43. 1911. pp. 147-153. Mr 1. Ogilvie of Messrs McKechnie Inst. Min. Metall., vol. 74. 1974. pp. 246-249. 34. FRIEDE, H., and STEEL, R. Notes on Brothers S.A. (Pty) Ltd; Mr M. 12. MoFFAT, R. Missionary labours and Iron Age copper-smelting technology. Evers, Mr F. Shaw, and Mr P. scenes in Southern Africa. 1842. p. 584. J. S. Afr. Inst. Min. Metall., vol. 75. Luck; Mr G. C. Clatworthy, Manager 13. LIVINGSTONE, D. Missionary corres- 1975. pp. 221-231. pondence, 1841-56. (Edited by 1. 35. LOUIS, H. Metallurgy of tin. 1911. of the Rooiberg Minerals Develop- Schapera.) 1961. p. 97. pp. 21, 84.
Refractory Colloquium
The Nineteenth International Re- themes in refractories. The following Professor Majdic (Federal Republic fractory Colloquium, which is to be have agreed to speak: Professor of Germany). The colloquium langu- held in memory of Professor Aleixandre (Spain), Professor Hassel- ages are German, English, and K. Konopicky, will be held in man (U.S.A.), Professor Forssberg French. Aachen on 14th and 15th October, (Sweden), Professor Letort (France), For further information, contact 1976. Dr Nameishi (Japan), Professor Nek- Forschungsinstitut der Feuerfest- The colloquium will have no rasov (U.S.S.R.), Dr Piatkowski Industrie An der Elisabethkirche 27 general theme, but invited speakers (Poland), Professor Savioli (Italy), D - 5300 Bonn, and Institut fUr from many countries that have often Dr Staron (C.S.S.R.), Professor Tro- Gesteinshiittenkunde der RWTH been represented at Aachen Collo- jer (Austria), Professor White (G.B.), Aachen Mauerstr. 5 D - 5100 quia will present papers on topical and Professor Kienow, Dr Kronert, Aachen.
470 JULY 1976 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY