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Minerals and Metals in Ancient India v1.c25.s4: Ancient Lead-Silver-Zinc Mines in Rajasthan

Minerals and Metals in Ancient India v1.c25.s4

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Ancient Lead-Silver-Zinc Mines in Rajasthan

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During 1982-89, a spectacular series of discovery was made in the field of mining archaeology in India by K.T.M. Hegde of Baroda University in collaboration with Hindustan Zinc Limited, Udaipur and his British colleagues such as P.T. Craddock of the British Museum and Lynn Willies of the Peak District Mining Museum. (Willies et al., 1984, 1987, 1989) Their findings about the ancient Zinc mine in Zawar would be presented in the next chapter. We may summarise their observations on the following ancient mines: (a) Rajpura-Dariba, (b) Rampura-Agucha, and (c) Zawar, related to the lead-silver ore, in this chapter.

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Rajpura-Dariba is about 80 km north-east of Udaipur (vide fig. 17.3a). Metamorphic calc-silicate rocks derived from mineralised sandy-dolomite rocks of Pre-Cambrian age from conspicuous ridges in this area, with the plain formed form thicker and weathered graphite schist. Ancient workings have been found in the South Lode (100 m depth; C-14 dated 1260-1050 BC, vide Table 17.1), North Lode, and East Lode (263 m depth, 375 BC onwards), now a depression filled with water and flanked by extensive waste heaps.

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The objective in the North Lode (fig. 17.3b) was mainly silver-rich anglesite and cerussite ore, though some copper ore might have been also mined. Both opencast and underground methods are apparent. The earliest working appears to be marked by narrow shafts sunk in pairs, often at intervals of only a few metres. There are evidences of the applications of stone maul, crushing stone and selective mining.

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In the South Lode (fig. 17.3b) firesetting used to be done using a timber platform at a depth of 100 m. The earliest C-14 dates of the timber (Table 17.1) conclusively prove that underground mining started in India in the thirteenth century BC, if not earlier. The dam and ladder provide clear evidences of the system of water removal. Remains of woven baskets (to carry up the broken ore) and of ropes about 2.5 cm diameter have been found in the workings.

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The East Lode (fig. 17.3b) has been almost quarried at the outcrop, the opencast now being a lake of several hectares. The water level was never more than a few metres below surface; this was lifted as a rare gift for agriculture in the neighbouring drought-stricken lands. The East Lode is characterised by extensive timberwork of 16 m height and for a length of at least 150 m, C-14 dated 375 BC to AD 110 (vide Table 17.1 showing one 120 BC date for the South Lode also), indicating five centuries of mining in this area reaching a depth of 263 m. At the north end of the pit, there are nine large mortar holes in the quartzitic rock, each about 30 cm across and up to twice as deep, with rounded bottoms. These were undoubtedly worked as stamps for the ore. The pea- to sand-sized product was found scattered in the adjoining area.

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Rajpura-Dariba showed enormous quantities of 20-30 m high mine debris and two vast heaps of glassy slag with average depths of 4-5 m and covering areas 500 m x 200 m and 650 m x 350 m (the slag volume measures up to more than one million cubic metre!). A piece of lead metal recovered from the slag dump was analysed and found to contain 97.5 per cent lead and 150 ppm silver. The evidences show ‘the gregarious nature of working’ of the Lead-Silver ore in the area during the successive Pre-Maurya, Maurya, Śuṅga and Kuṣāṇa periods of the Indian history. Copper-zinc ore was also noted in Rajpura-Dariba, suggesting the possibility of local production of brass in this area. (Paliwal *et al.*)

Rampura-Agucha Mines

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Agucha village 25°50 'N 74°44 '15" E) is located 15 km south-east of the industrial town of Gulabpura. This is about 240 km from Udaipur, and near Bhilwara and Ajmer (fig. 17.3 a). A major zinc-lead deposit (assaying 12 per cent and 2 per cent in the said metals respectively) has been discovered in this area recently, but the ancient mining was done on the Rampura-Agucha deposit located 1.5 km north-east of the Agucha village.

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Excavation by Willies *et al.* (1984, 1987, 1989) showed the clear base of a gossan at about 15 m depth from which marmatite, pyrite and sphalerite (ZnS) were selectively oxidised and leached, leaving galena-cerussite-anglesite ore body enriched in terms of silver. The very soft weathered gneiss could be easily cut by wedged-end chisels rather than gads. (Willies, 1987: 94) The timbers from Fig. 17.3: (a) Lead-Zinc ore mining areas in Rajasthan; (b) Ancient mine workings at Rajpura-Dariba.

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3(a) STATE OF RAJASTHAN Jodhpur Ajmer Jaipur RAMPURA AGUCHA RAJPURA DARIBA Udaipur ZAWAR AMBAJI Devnimori Kota Ratlam 0 km 80 LW 1987

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3(b) 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 NORTH LODE Area Surveyed 300m Opencast beneficiation Opencast ancient beneficiation Main Shaft Modern Beneficiation Plant SOUTH LODE Modern Inclines slag waste from surface working waste from underground 521m 518m Cu + Pb slag Temple water in opencast revetment waste from opencast EAST LODE shaft Ancient Mine Workings at Rajpura-Dariba

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the 30 m depth level have been C-14 dated as 370 and 250 BC (Table 17.1). Several carbonized woven baskets were found at the bottom of the pit. A substantial portion of the ancient working, so far revealed, is open-cast mine. Some of the water-logged bore-holes have been converted to well for irrigation.

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Tiwari *et al.* (1984: 85) drew attention to the depths of 80-125 m in some places of the mine and to the striking evidences for selective mining. The deposit was worked towards its narrow northern extremity, and also at preferential locations in the south, following lead mineralisation and pure galena veins in preference to the zinc ore veins.

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Tiwari *et al.* also pointed out the existence of huge slag dumps of 0.3-0.4 m. height occupying an area of 70,000 sq m. The analyses of four composite slag samples are provided in Table 17.4.

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The petrographic thin sections of slag sample (such as No. 1) indicate the presence of quartz and feldspar grains which have not undergone much change, and thus suggest incomplete and low temperature smelting. Lead smelts at 327°C, and the simple smelting operation, as noticed and recorded by Dixon (1831) at Ajmer, might have been operational in the earlier centuries. The analysis of the slag sample No. 1 also reveals unrecovered lead as well as zinc. Probably silver was the main target of the smelting operation.

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Table 17.4

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Elemental Percentages in Rampura-Agucha Slag

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| No. | Description | Lead | Zinc | Iron | Copper | Silver (ppm) |
| 1. | Composite sample from main ‘slag-spread’ | 4.20 | 2.80 | 8.30 | 0.10 | 28 |
| 2. | Same as above, but with ‘tarnished shades’ | 1.60 | 0.16 | 6.80 | 0.01 | 22 |
| 3. | Composite sample from the mounds | 1.90 | 0.87 | 4.70 | 0.01 | 25 |
| 4. | Slag attached to the earthen appliance used for smelting | 9.30 | 0.01 | 4.60 | 0.002 | 10 |

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Discussing Pliny’s remark about ‘the Indian silver among the Setae’, Ball (1880: 231) commented that the galena deposits in Taragarh hill, Ajmer, Jodawas in Alwar and the Zawar Mines at Udaipur might contain some silver, “but, so far as I (he) could ascertain, there is no record of the mines having produced silver”.

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The present data strongly suggest that silver was recovered from the extracted lead by the cupellation process. The slag dump area showed several retort-like pieces, which are cylindrical, approximately 20 cm long with walls about 4-5 cm thick and an innermost pipe like feature with a coating of dirty white material, mainly zinc sulphate. The used retorts had closed pointed ends. (Paliwal *et al.*) The analysis of slag sample No. 4 (Table 17.4), attached to the baked earthen appliance or cylindrical retort, assayed 0.01 per cent zinc and as high as 9.30 per cent lead. Considering the fact that the ore-body assays 12 per cent zinc and 2-3 per cent lead, Paliwal *et al.* rightly commented that an appreciable amount of zinc might have been obtained by smelting using the retorts and following the process better developed at the Zawar Mines.

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There is no historical account of the ancient mining in this area, but there are three archaeological mounds: Rampura, Gardar-ka-Bagh and Agucha, the last one being the biggest and studied in detail by Nagarch and Trivedi (1981). The Agucha mound shows three distinct periods of occupation: I. Early Historical or Pre-Maurya Period with PGW/NBPW potteries, punch-marked coins, terracotta Mother Goddess, iron slag etc. II. Śuṅga and Kuṣāṇa period brick structure and III. Gupta Period artefacts. The slag pieces obtained from the mound (No. 3 in Table 17.4) assay quite similar to the slag spread near the mining area (Nos. 1 and 2). These data together with the C-14 date of 370 BC for the timber in the neighbouring mine clearly connect the antiquity of lead-zinc-silver mining in the area to the fourth century BC.

Pre-Mauryan era Lead Slag at Zawar Mines

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The third mine-system investigated by Willies *et al.* is the Zawar Mines, 30 km south-west of Udaipur (*fig.* 17.3 a). The host rock at Zawar is a metamorphosed sheared dolomite, hard and compact, which, except within the weathered zone, had mainly been worked by firesetting. There was evidence of retreat working of the pillars. Dumping of waste was done systematically. The C-14 dates of the timber samples show that the Zawar Mala and Zawar & Mochia mines were active during 430-380 BC period and again during 200 BC-AD 60 period. There are also evidences for the mine being active in the seventh century AD and later for medieval period thirteenth-eighteenth century AD.

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Zawar Mine area exhibits wide-ranging evidences for ancient mining and smelting of zinc ore, which we would present and discuss in the next chapter. Zawar has also yielded considerable evidence for the smelting of lead, in the form of at least sixteen deposits of slag, distributed along 13 km of the valley of the River Tiri, the main water course in the area. These slag deposits, containing several pieces of lead metal as smelting residues, are of two types: (a) glassy and (b) crystalline. Analyses are provided in Table 17.5.

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Analysis of Crystalline and Glassy Lead Slags at Zawar Mine, Rajasthan

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| Sample No. | Pb (%) | Zn (%) | Fe (%) | Ag (ppm) | Site | Morphology |
| 1 | 5.25 | 0.72 | 32.0 | 31 | 5 | Crystalline |
| 2 | 2.21 | 1.80 | 18.5 | 10 | 5 | Crystalline |
| 3 | 2.57 | 2.41 | 21.0 | 12 | 5 | Crystalline |
| 4 | 2.30 | 2.72 | 25.1 | 10 | 5 | Crystalline |
| 5 | 3.50 | 10.30 | 8.1 | 9 | 1 | Glassy |
| 6 | 4.73 | 10.56 | 9.4 | 8 | 1 | Glassy |
| 7 | 7.20 | 8.71 | 9.0 | 11 | 4 | Fine crystalline (stoney) |
| 8 | 7.02 | 8.26 | 8.1 | 8 | 4 | Glassy |
| 9 | 6.30 | 7.09 | 8.7 | 16 | 4 | Glassy |

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The reserve of glassy slag is estimated to be 30,000-35,000 tons. (Straczek et al. 1967) The glass slag, not associated with zinc smelting debris, assays high in zinc (7-10 per cent) and contains sparsely crystalline phases such as zincian melilite Ca₂ZnSi₂O₇, Zincian olivine, magnesium-rich clino-pyroxene CaMgSi₂O₆ etc. The crystalline slags assay lower zinc per cent but much higher iron content. Scanning electron microscopy revealed the existence of fayalite, Fe₂SiO₄ and iron rich clinopyroxene CaFe Si₂O₆ (Freestone et al., 1985, 1987). The author of this monograph and his colleagues (Gangopadhyay et al., 1984) detected hemimorphite Zn₄(OH)₂ Si₂O₇, H₂O, willemite, Zn₂SiO₄, hydrozincite, Zn₅(CO₃)₂(OH)₆, esperite Ca₃Pb(ZnSiO₄)₄, larsenite, PbZnSiO₄ etc. as some of the major phases in the slag.

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It may be inferred that the glassy slags were obtained in the early stages to recover lead (and silver) but not zinc. At a later stage, the value of zinc was realised, sphalerite removed carefully from the lead ores, and the resulting reduction of the flux content was compensated by adding more iron as pyrite which precipitated in the crystalline slag as fayalite (Freestone et al., 1987).

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Chatterjee et al. (1981: B.78) recorded that in the modern Zawar mine, the run-of-mine ore assays 0.7-1.4 per cent lead, 3.5-4.4 per cent zinc and about 40 ppm silver yielding on beneficiation, zinc concentrate (assay 52 per cent zinc, 1.3 per cent lead, 140 ppm silver) and lead concentrate (assay 63.7 per cent lead and nearly 0.1 per cent or 980 ppm silver). Thus most of the silver is associated with the galena or lead sulphide fraction. The ancient zinc distillation retort residue assays 120-260 ppm of immobile silver (Freestone et al., 1985: 9) whereas the Table 17.5 shows that the lead slags assay 10 ppm or even less in silver. These data coupled with the fact that pieces of metallic lead were found in the slag, strongly suggest that lead-smelting was followed by recovery of silver from molten lead by a process such as cupellation.

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The above trend was also exhibited in Rajpura-Dariba as well as Rampura-Agucha. The extensive mining traditions in the fourth-third century BC. India are recorded in Kauṭilya’s Arthaśāstra which would be discussed in our Vol. II chapter 5. The Arthaśāstra described the ores of lead (2.12.13), argentiferous galena (2.12.6) and silver (2.13.10-14), and also the uses of lead in purifying gold (2.13.47) and silver by the cupellation process (2.13.49). It is quite likely therefore, that the silver in the punch-marked coins, bent-bars and jewelleries found at Taxila, was obtained through the contemporary smelting practices at Ajmer and Zawar as described in the Arthaśāstra of the Maurya Period.

Cites (3)