Minerals and Metals in Ancient India v1.c18.s2: Ancient Copper Mines and Metallurgy in Rajasthan
Minerals and Metals in Ancient India v1.c18.s2
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Ancient Copper Mines and Metallurgy in Rajasthan
v1.c18.s2.1
Hegde *et al.* (1985) carried out a survey of six ancient copper ore mining and smelting sites in the Aravalli Hills extending over a thousand kilometres: Khetri and Kho Dariba in the north-eastern part, Kankaria and Piplawas in the central part, and Deri and Ambaji in the south-western part. Ambaji was studied in detail.
v1.c18.s2.2
In the south-western and central zones, there were many evidences of superficial gouging of the oxide-rich gossan cap; these were the earliest attempts at mining copper ore in Rajasthan. A large majority of these pits measure 7-8 metres in diameter and three to four metres in depth. There is evidence of fire-treating of the host rocks on the mine walls to widen the rock joints.
v1.c18.s2.3
In all the six sites visited, the investigators noticed (Hegde *et al.* 1985) mine shafts which were very deep, opening into galleries and narrow tunnels following the natural configuration of ore veins at different levels. There were ventilation holes at regular intervals. These deep shafts probably represented mining activity of later periods; however, there are evidences to believe that some of the mines were worked during the Chalcolithic period. Timber supports recovered from a gallery at a depth 120 metres at Rajpura-Dariba mines in Udaipur District were dated by radiocarbon to 3120 ± 160 years before the present (1987). This date corresponds to the zinc-containing copper artefacts of Atrañjikhera. There are some Mauryan C-14 dates such as 2310 ± 105 B.P. from the Dariba Mines area also.
v1.c18.s2.4
The small size of furnace and high yield of metal indicate that the ore used to be roasted to oxide stage and the smelting technology was efficient. Many groups of ore-crushing pits were found near the foot of the hills. Larger pits among them measure 60 cm in diameter and 70 cm in depth. Smaller ones measure 30 cm in diameter and 40 cm in depth. The finely crushed ore was concentrated by gravity separation at the smelting sites which were invariably located near the banks of the hill streams. Ore separation devices found are smooth gently inclined rock surfaces, nearly marked with rows of round shallow pits, 3 to 4 cm in diameter and 3 to 4 cm depth. Presumably, the finely crushed ore was allowed to slowly flow down the inclined plane and by repeating this process, much of the gangue was effectively separated from the ore. Flowing film segregation, settling of the heavier ore particles in the pits and elutriation of the lighter gangue particles were the principles involved.
v1.c18.s2.5
The smelting charge probably constituted of crushed quartz, about equal weight of the ore, and crushed charcoal, nearly twice the weight of the ore. Residues of small, hand-made, fistfulls of spherical lumps were found sticking to the furnace walls. Coarse size of the feed lumps enabled easy flow of air coming from the bellows.
v1.c18.s2.6
Large slag heaps were found spread out in the terraces, littered with broken remains of furnaces and broken tuyere. Some of the slag pieces clearly revealed the cylindrical flow structure and the fact that the tapped slag was molten.
v1.c18.s2.7
The examination of the unbroken upper part of the furnace showed that this was assembled by putting three curved segments (made of clay) together, one of them containing the luted tuyere, another with the slag tapping hole, and a plain third one. The bottom part of the furnace was not found, and this was conceptualized using the size and shape of the copper ingots or buns recovered in the excavations of the Chalcolithic sites of Lothal, Harappa and Mohenjo-Daro. The Lothal bun is smoothly curved at the bottom (corresponding to the bottom part of the furnace), 10 cm in diameter, 4 cm in height and weights 1.438 kg. (Rao 1979 and 1985) On the basis of the above data, Hegde et al. (1985) visualised the approximate dimensions of the ancient furnace : 35 cm in height, and diameter 18 cm at the rim, 14 cm at a mid-level and 10 cm near the base. (fig. 10.1)
v1.c18.s2.8
Thus, it appears that the ancient Indian copper smelting furnace was a small, crucible-shaped, clay-walled, slag-tapping furnace worked on forced draught blown into it from bellows. It was a composite structure made of three moulded segments, set up on a brick platform and was surrounded with bricks and earth to keep the three segments of the furnace tightly in position and also to conserve the heat within the furnace.
v1.c18.s2.9
The main component of the slag is fayalite which melts at 1170°C. The melting point of copper is 1083°C. Molten copper of high specific gravity 8.89 collected below the molten slag of the 4.0 sp. gr. The molten slag was evidently tapped on the edge of the terrace. When the furnace was cooled, the copper ingot was taken out by breaking its bottom. Hegde et al. (1985) may be right when they comment that “this simple furnace appears to have been continuously used in India over the millennia without little innovation”.
v1.c18.s2.10
In the previous chapters we have mentioned the discoveries of small furnaces and crucibles in the Harappan and Chalcolithic sites. The facilities near the settlements, far away from mining regions, were mostly purification and fabrication facilities and not primary smelting outfits. Bun-shaped copper ingots used to be transported from the Ganeshwar area along the Sarasvati-Hakra riverine route and remelted, purified and fabricated near the Harappan metropolis. There must have been itinerant metal-smiths in the copper-hoard culture carrying ingots over considerable distances and fabricating them anew to suit the specifications of the customers. The *Rg Veda* (9.112.2) refers to such itinerant metal-smiths.