Minerals and Metals in Ancient India v1.c18.s1: Artefact-Ore Correlation
Minerals and Metals in Ancient India v1.c18.s1
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Artefact-Ore Correlation
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In pursuing the laudable objective of establishing that the metals were produced indigenously in the ancient India, our archaeologists have sought correlation between the artefacts and ores in the sub-continent.
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Most of the enthusiastic investigators ignored the cautionary remarks of Thomson (1958) pointing out the hazards in ore-correlations, and reported ‘positive correlation’s which may not be considered to be conclusive. Recently Biswas (1990) has pointed out that the ore-metal correlation depends upon:
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(a) the type of ore, oxide of sulphide or silicate, the nature of impurities, (b) the precise conditions of smelting, such as temperature, nature of fuel, flux etc., and several other factors. The ore-type itself is a variable even within a single mine.
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A ‘correlation’ can only be probabilistic. A positive correlation of the trace element profile between ore and metal cannot be accepted as sufficient or conclusive evidence for indigenous manufacture. On the other hand, lack of correlation does not construe necessarily a negative evidence. As we have said, ore types vary even within a region of hundred square kilometres.* Besides, certain impurities such as arsenic might have been eliminated through certain simple pre-smelting operations such as roasting.
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So far as the use of metals in the ancient sites are concerned, the existence or absence of mines in the neighbourhood areas in the modern age hardly establishes any truth. On the one hand, the currently known mines might have been unknown to the ancient people, and on the other, some small near-surface reserves might have been thoroughly exploited by the ancient miners, so that we do not know them at present.
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Having stated the hazards of ore-metal correlation, let us report some of the ‘positive correlations’ obtained by our archaeo-metallurgists. Friedman *et al.* (1966) claimed that with regard to copper artefacts, the elements of silver, arsenic, bismuth, iron, antimony and lead were the most important metallic impurities in relating the metal back to the original type of ore. Following this argument, Agrawal (1971, 1984) suggested that Chanhu-Daro celt and Mohenjo-Daro spearhead were made from Khetri chalcopyrite ore, since all the three materials contained trace impurities of Sb, Pb but not Fe and As.
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In chapter 7, we have mentioned that Hegde (1969) compared the artefacts from Ahar with the chalcopyrite ore from Khetri, and the similarities led him to conclude that “copper metal of the Ahar artefacts was probably smelted from the ore of the Aravalli region”. While the conclusion can certainly be supported from other evidences such as slag dumps and ancient mines, Hegde’s argument is hazardous. ‘The Aravalli region’ alluded to by Hegde corresponds to a vast area and ores of more than one type; the Ahar region is hundreds of kilometres away from Khetri.
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Hegde (1989) has himself modified his view and suggested that the Ahar artefacts were possibly made from the nearby region of the Aravalli which constitutes of not-too-hard tremolite-chlorite schists rather than the far-off Khetri ore embedded in quartzite rocks, hard and less easily extractable. While impurity patterns of the ores in different parts of the Aravalli may be similar, the lead isotope ratios markedly differ in the north-eastern, central, and south-western parts of Aravalli. (Hegde, 1985) Efforts are in progress to correlate metal artefacts and specific ore deposits through lead isotope ratio analysis.
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∗ Hegde failed to detect the impurity elements of Cr, Co, Ni, Bi and Mo (present in the Devnimori silver coin) in the Zawar galena ore, but Shekar found them in the Ambamata deposit only a hundred km away (vide our Table 17.7). Silver did not have to be ‘imported’!
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S.R. Rao (1979, 1985) considered the facts that whereas Mohenjo-Daro copper and Rajasthan ore contain arsenic, the copper artefacts from Lothal were remarkably arsenic-free. From these facts divergent inferences could be drawn: Mohenjo-Daro people obtained copper from Rajasthan or from some other source and resorted to deliberate arsenic-alloying (which they did in some instances). Lothal copper might have been imported from Oman (as suggested by S.R. Rao), or the Lothal technicians practised, like the Aharians, roasting of copper ore to make it arsenic-free. Evidently, these conclusions are not compatible with each other. Rao himself reported the analysis of a copper ore from Rajasthan which contained negligible quantity of arsenic. Thus it is hazardous to draw any positive correlation between the artefacts and any ore-deposit.
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H.C. Bhardwaj (1979: 97) found that Rajghat copper artefacts (600 BC) and Bihar ore show the presence of Fe, S, Ag, Ni, Co, Mo, Bi, Ca, Mg, Al and Si. Frequency of Pb, As, Sb is less in both Rajghat samples as well as Bihar ores compared to Khetri ore. From the point of view of proximity, it is quite possible that Rajghat copper was made from Bihar ore, but the question still remains: from which part of Bihar?
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For conclusive evidences on indigenous technology in the areas of minerals and metals, we should better look for: (a) mines of antiquity, (b) outfits for smelting, furnaces and crucibles, (c) heaps of slags and slag-ore correlation regarding the non-metallic phases, and (d) a reasonably large number of artefacts at different stages of manufacture and of composition and properties varying within narrow limits. Fortunately, several such evidences for indigenous metallurgy in India have been obtained from Mehrgarh, Ganeshwar-Jodhpura, Chanhu-Daro, Lothal, Ahar, Khetri (for copper), Atrañjikhera, Ujjain (iron), Zawar (zinc) etc.