Text 3. Khetri copper complex

Khetri Copper Complex is a major constituent part of Hindustan Copper Ltd. (HCL), a Government of India enterprise established in November 1967. Other principal HCL units include the Malanjkhand Copper Project - a large new open-pit copper mine in a Madhya Pradesh - and the Indian Copper Complex (ICC), a group of underground copper mines, concentrators, smelter and refinery in Bihar State. Malajkhand and ICC were both described (Mining Magazine, November 1983, pp. 334-41 and pp. 343-53).

Khetri is located in the Jhunjhunu District of Rajasthan some 190 km southwest of Delhi, and 180 km north of Jaipur, the State capital.

The copper deposits were mined in ancient times, some workings dating from the Mauryan Period, over 2000 years ago. The mines were active again in the times of the Moghul Emperors, a report of 1590 referring to them ("Aanai-aAkban", written by Abu Pazal, a courtier of Emperor Akba). More recently they were worked by local people who paid a royalty on production to the Princely State of Khetri. Two mines were functioning in the towns of Siaghana and Khetri until closed by the British in 1869. Regular mining ceased in 1872, although sporadic activity continued until 1910. From 1944 to 1955 the lease was held by the Jaipur Mining Corporation LTD but not worked.

The Geological Survey of India began prospecting the area in 1954 and exploratory mining by the Indian Bureau оf Mines began in 1957. The project was handed over to the National Mineral Development Corporation in 1961 for further investigation.

Initial feasibility studies were completed in 1963; a new source of copper was needed in India, as for almost two decades the national output had remained static at about 10,000 t/y, principally from the Indian Copper Corporation mines Bihar (now HCL's Indian Copper Complex division). There was a pressing need to increase indigenous production to narrow the gap between India's own output and the steadily rising demand.

The decision to proceed with the development of Khetri Copper Complex was taken in 1962. Shaft sinking and mine development began in 1964 anf the first production of ore took place in 1970. The project was transferred to the newly created Hindustan Copper Limited in November 1967.

The finance for the surface installations was not available immediately, and construction of the concentrator and smelter did not begin until 1970. The concentrator came on stream in 1973, followed by the smelter start-up the following year. A fertilizer plant, based on the sulphur acid by-product from the smelter, plus phosphate rock from southern Rajasthan, began production in 1975.

There are four mines in the Khetri Complex - the two major Khetri and Kolihan underground mines, the Chahdmaril open pit, and the 100 t/d Dariba underground mine, with a matching concentrator, in the Alwar District of Rajasthan State, some 220 km away from Khetri. The ultimate capacities of the first three are designed to be 5000 , 3000 and 1000 t/d respectively but very severe power shortages over the last four years have limited output and constrained development, so that the average production in 1983/4 was 3675 t/d (fig.44).

Fig. 44. The map shows the location of the Khetri Copper Complex and gives some indication of regional geology

GEOLOGY

The rocks in the Khetri district belong to the Delhi super-group of Precambrian age, which is sub-divided into the Alwar and Ajabgarh groups. The older Alwar rocks are derived from predominantly arenacous sediments, while the younger Ajabgarh rooks were originally of a more argillaceous nature, the transition between the two being gradational. All these formations are metemorphozed to quartzites, shcists and phyllites. Some intrusive dolerite dykes are present, and veins of quartz and carbonates are common.

The general strike of the formations is NNE-SSW with steep to gentle dips towards the WNW. The economic mineralization which gives rise to the orebodies is mainly localized in the upper parts of the amphibole-chlorite quartzite and garnet-amphibole-chlorite quartz/schist. The mineralization occurs in the form of veins, veinlets, stringers and disseminations (rarely massive), oriented in general parallel to the foliation plane (fig.45).

Fig. 45 Geological section through the Khetri mine showing are lenses (based on a cut-off grade of 0,5% Cu): l - quartzites; 2 - chiorite rock; 3 - metadolerite; 4 - ore-grade mineralization; 5 - quartzveln; 6 – antdalusite shist/phyilites; 7 - aluvium/ scree

In Khetri mine there are two distinct ore lodes, namely in Madhaa (or footwall) lode and the Kudhan (or hanging-wall) lode. The Madhan lode is fairly persistent, containing а number of оre lenses. The Kudhan lode, on the other hand, is narrower, poorer in copper. It is well formed in the central part of the mine. At the kolihan mine, three distinct lode systems have been identified, Lode 1 (South Lode), Lode II (North Lode) and Lode III (East or Footwall Lode). Of these, Lodes, 1 and III are persistent, but Lode II is not persistent in depth.

The feldspar quartzite rocks which form the footwall highly jointed but are, nevertheless, quite competent, the hanging wall consists of phyilites. At the Kolihan mine there is a shear zone in the phillites which poses some atability problems during stoping. There are a number of transverse faults and shear planes, plus a number of longitudinal shears within the area of both underground mines.

Chalcopyrite is the principal copper mineral in the ore. The mineralogical composition of the Khetri and Kolihan ore types, for which the concentrator was designed, are as follows:

Mineral

Indexes, %

Kherti

Kolihan

Chalcopyrite

Pyrite

Pyrrhotite

Magnetite

Silica

11,7

0,1

15,7

1,0

71,5

The Kharkhara river flows in a valley immediately in the hanging wall of the mineralized rocks in the Khetri mine area. There is some make of water into the mine through transverse faults having access to the river bed. To ensure stability, the ore lenses near the hanging wall have not been worked in the upper levels of the mine.

At the Kolihan mine, although the water table is only a little way below ground surface, no serious water problems have been encountered.

Ore reserves at the two major underground mines and the open pit mine are in Table.

The initial exploration of the deposits was carried out from surface by diamond core drilling, and there is a continuous on-going program of core drilling from underground to prove reserves: 1,800 holes total 140000 m have yielded 6280 intersections with ore.

Ore reserves at Khetri, Kolihan and Chandmari mines