Mining Technology: Indian Perspective

Mining industry in India is posed for spectacular growth in light of the immense demand for raw materials. The concern now is whether the supplies can really catch up with demand. A look at the mining technology is need of the hour from the perspectives of production capacity, productivity and economics of mining investment.

Surface Mining Technology

Surface mining has become prominent method for both coal and metaliferrous mining sectors. Almost entire iron ore and bauxite production is achieved by surface mining methods. About 87% of coal produced in the country is mined by open cast methods, primarily due to shallow deposits and favorable economics of mining. However, with the depletion of shallow deposits, underground mining may be preferred.

In the surface mines, the major heavy earth moving equipments currently used are rope and hydraulic shovels, draglines, dumpers and drills. The surface miners are also used where the ore is relatively soft, for example, for coal and limestone. The lignite mines have been using bucket wheel excavators for mining in conjunction with flexible conveyor transportation systems. With large sized surface mines planned and the level of mechanization already improving, the equipment sizes are going to be larger. Currently, rope shovels of sizes 4.5 to 20 cubic meters are common in Indian coal mines, but larger production capacities in deeper and higher stripping ratio mines will necessitate use of 55 and 70 cubic meter shovels. Matching the size of shovels, the dumper capacities are also expected to be 240 and 360 tonnes. Surface miners are useful for selective mining and have improved control on quality and eliminate the processes of drilling and blasting. They have used in Thalcher area of Mahandi Coalfields Limited for coal winning and for limestone mining in Gujarat Ambuja Mines.

Surface mines have higher productivity in comparison to underground methods. For coal, the output per man-shift (OMS) in the opencast mines is about 7.5 tonnes. The other measures of productivity are availability and utilization of equipment. As may be inferred from the data below from Coal India Limited, utilization of equipment has been a concern. With large production requirements, there may not be any alternative to large sized equipment but lower utilization can impact the economics of investment.

Equipment Availability Utilization
Draglines 83% 86%
Shovels 71% 47%
Dumper 66% 30%
Dozer 64% 29%
Drill 74% 16%

The large equipment may increasingly be leased or contracted out with minimum performance guarantees in place. There may be investment required in stocking spares for these equipments. In a recently published PwC Mineral Industry Survey of Australia, it has been observed that lead times for procurement of equipment and spares have gone up significantly. The lead time, for example, for dumper tyres have increased from 3-4 months to about 25 months. Similar trend is observed for other equipment as well, and the scenario is no different in India.

These developments have significant cost impact and may make investment decision tough.

Underground Mining Technology

In the coal sector, the underground mines produced about 13% of the total production in 2006-07. Level of coal production from underground mines has declined from 69 million tonnes in 1997-98 to 57.7 million tonnes in 2006-07.

For the underground coal mining, there is a definite case for mechanization if the productivity levels have to justify investments. The output per man-shift (OMS), the key measure of productivity in the underground mines has been significantly lower than the surface mines. According to the recently published data of Coal India Limited, OMS for underground mines have been near 0.75 tonnes. If the deep seated deposits have to be exploited through underground mines, there is no alternative to higher degree of mechanization and improvement of productivity. This is equally important from the occupational environment and safety perspectives.

There are around 300 underground mines of Coal India Limited, about 64% of which are manual or semi-mechanized bord and pillar (B&P) workings. Of the rest 33% are mechanized B&P and just about 6 mines with powered supported longwall mines and 2 mines with continuous miners. There exists scope of mechanization and performance improvement in all these underground mines.

The selection of technology and hence, the equipment for underground mining is key to the successful implementation. Longwall technology for coal promises high productivity and coal recovery (more than 75%) but the technology does not have a good record in India. Apart from lower than expected production and productivity, there have been failures at Charcha and Kotadih mines. Several factors have contributed to these, including geo-mining conditions, hard roof strata, compatibility with other equipment, lack of adequate maintenance systems and lack of trained staff. The technology has been quite successful in several countries, particularly so in China, where about 90% of the annual production of around 2 billion tonnes per annum comes from underground mines.

There are other underground mining methods for coal that are being planned for implementation. Shortwall mining, which is continuous mining system with movable support system used for pillar extraction, can used to increase coal recovery. Continuous miners and sometimes, road headers, may used for shortwall mining method, however, these methods have lower production capacities and productivity in comparison to longwall method. Highwall mining may also be used to enhance coal recovery with extraction from the face of a coal seam under a highwall in a surface mine, which has reached the final highwall position due to uneconomic stripping ratios or due to local constraints which limit further surface mining. Singareni Collieiries Company Limited has planned for highwall mining in Andhra Pradesh.

There is a concern over supplies of underground mining equipment. Such is the urgency of matter that underground mining equipment company, namely, Mining and Allied Machinery Corporation (MAMC) which had gone out of business is being revived by CIL.

In the metaliferrous mining, copper, lead, zinc, gold, and uranium have been mined through underground methods. Narwapahar mine of Uranium Corporation of India Limited is well developed with declines to transport run-of-mine. With increased base metal prices and performance improvements, the underground mines of Hindustan Copper Limited and Hindustan Zinc Limited have produced profits. Methods of mining generally used in metaliferrous mines are cut-and-fill stoping, sub-level stoping, sub-level caving, room-and-pillar mining, and block caving. These mines use Drill Jumbos for drilling and Load-Haul-Dump (LHD) equipment for haulage.

Innovative technologies in underground mining methods focus on lower turn-around times, higher ventilation efficiency, and safer working conditions through strata control and roof support systems. Improvements in technology are being made to enhance the shaft sinking speed and shorten development period.

From the economic perspective, underground mines may have higher capital and operational costs but they compensate in terms of lower environmental and social costs. These methods also permit extraction of reserves that are under forest cover. Underground mining may be the only method to extract deposits with prohibitive stripping ratios for surface mining. Real option evaluation methods can be useful to determine the application of underground mining methods.

(This article was published in Power Line in August 2007 issue)