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June 18, 2023 nflg 0 Comments


In India, iron ore deposits mostly occur in dense forest areas and on hill tops, which are water shed of important river valley and these deposits of iron ore are located in the states of Jharkhand, Orissa, Chattisgarh, Goa and Karnataka. The iron ore deposits of the Eastern, Central and Southern zone do not contain much overburden material except laterite and some low grade ferruginous shales and BHQ patches, whereas, in Western zone (Goa region) more than 30 MT of iron ore is produced during 2006-07 and another 2.5 to 3.5 times of the waste is excavated as overburden. Normally, iron ore mining in India is done by opencast method and on the basis of mining methods, the mining can be broadly divided into two categories, i.e. manual and mechanized. Majority of the large mechanised mines are in the public sectors whereas manual mines are mainly in the private sector. The present production capacity of iron ore in India is around 160 MT per year.

Manual Mines

This method of mining is generally confined to float ores. Mining of reef ore is also being done manually on a small scale. The float ore area is dug – up manually with picks, crowbars and spades, and the material is manually screened to separate plus 10 mm float ore, which is then stacked up. The waste is thrown back into the pits. Generally, the recovery of float ore ranges from 30 to 50% or at times even more. As regards to reef ore workings, holes of 0.6 m deep and

35 – 40 mm diameters are drilled with hand-held Jackhammers with a spacing of about 0.6m and each hole is charged with 150 – 200 g gunpowder or special gelatine cartridges. Usually Jackhammer drills are operated with the help of portable air – compressors. The tonnage broken per kg of gunpowder is around 2.5 – 3 tones. The blasted ore is manually loaded into trucks for transport either to the railway station or to the buyers’ destination directly. Cost of mining and OMS (output per man per shift) varies from mine to mine. Presently, OMS in manual iron ore mines for producing 10 – 30 mm lump is about 1.5 – 2.0 tones and the –10 mm fraction is rejected at site. This method of mining is still prevalent in the two important zones of the Indian iron ore sector namely, Barajamda (Bihar & Orissa) and Bellary – Hospet (Karnataka). To increase the production from manual mines, setting up of centralised crushing & screening plants will be required, which also helps in optimal utilisation of resources.

Mechanised Mines

The history of mechanised mining operation starts with the establishment of iron ore mines in Gua in Singhbhum district, Jharkhand followed by TISCO’s Gorumohisani mine in Mayurbhanj district, Orissa and Noamundi iron ore mine in Singhbhum district, Jharkhand. Mechanisation in Goan iron ore mines came into effect from the late 50s. With the establishments of integrated steel plants in India, setting up of captive mechanized iron ore mines was developed at Kiriburu, Rajhara, Bailadila, Barsua, Joda, Bolani, Daitari, Donimalai, Kudermukh, Meghahatuburu and Goa.

Apart from a few mines developed for iron ore export, most of the fully mechanised mines are captive to various steel plants and have been developed up to their requirements. In these mines, the methodology being adopted for mining of ore / overburden by shovel-dumper combination, mining is invariably done systematic formation of benches by drilling and blasting. The loading operations are also fully mechanised and transportation is facilitated by maintaining mine haul roads. Further, ore handling, washing and screening operations are mechanised. The degree of mechanisation and the size of the machinery vary with the material required to be handled by the mines.

In iron ore mines in India, generally, benching is started from the top of the hill and carried downwards as the ore at the top gets exhausted. Except in uniform deposits, if the direction of the bench is along the strike of the beds, it encounters different beds of ores as the working face advances, resulting in considerable fluctuations of the grade of ore produced, unless many benches are worked simultaneously at different depths. This, in turn, requires a large number of smaller machines which create their own problems of supervision, maintenance, etc. It is therefore, commonly preferred to open – up benches as far as possible across strike of the beds, so that more uniform grade of the ore is produced.

The height of the benches is dependent on several factors, such as output requirement, shape, size and depth of occurrence of ore body, geological disturbances suffered by the ore body, hardness and compactness of ore body, type and size of the machinery proposed to be deployed, availability of finances, etc. All are interdependent factors. The bench height generally adopted in fully mechanised mines varies between 8 and 14 m. However, in Goa region, where the ore is softer, hydraulic excavators (backhoe) and wheel loaders is the principal loading equipment used; height of benches is restricted between 4 and 7 m. The length of the face is also dependent on various factors, such as contours of deposit, output required, variation in grade and blending requirements, capacity of loading machinery, etc. and varies between wide limits from as small as 60 m to as large as 400 m. The width of the bench is governed to a large extent by the size of the largest machinery deployed and varies, i.e. three times of the width of the dumper.

As an universal practice, iron ore is dislodged by drilling blast holes according to a particular pattern which depends on the bench height, the hole diameter, the drilling machinery deployed, nature of rock and the types of explosives used. These blast holes are vertical but can be inclined also for obtaining better blasting results.

The 310 mm dia rotary drill is the largest so far being deployed in India. Rotary drill is used normally in the size from 150 to 250 mm. Thus, the depth and diameter of the holes allow expanded drilling patterns in general and help in reducing generation of fines in softer ores. On the other hand, in hard ores or in strata where the hard bands are present, they can give poor fragmentation and toe formation. The poor fragmentation leads to lower rate of loading and increased wear and tear on the loading machinery. Investigations carried out by the Swedish State Power Board, by comparing the performance with 100 mm and 50 mm diameter blast holes, have shown that the digging rate of the shovels was 50 percent higher with small diameter blast holes. Drilling with 150 mm diameter blast holes has been the common practice in Indian iron ore mines. Probably, this is due to ready availability of indigenous drill machines of the size. But higher rate of production makes the incumbent to adopt greater bench heights and larger diameter holes. The greater bench heights permit the use of large shovels, which in turn can handle larger boulders and permit larger spacing and burdens. All the above drills are equipped with dry dust extraction system or wet drilling arrangements, sound proof cabin, dust hood at the collar of the hole to prevent air pollution due to drilling in the major iron ore mechanised mines in India. However, in Bellary – Hospet of Karnataka, where the rainfall is less than 750 mm per annum and there is a scarcity of water, the wet drilling practice is absent. To cope up with the need of higher production of iron ore, blasting materials are also being developed / manufactured at the same pace. From the conventional explosives, development has taken place in stages from NG based explosives, ANFO, Slurry, Emulsions are in use in the country today. Development of most advanced ICI’s computer aided blast model SABREX, VIBREX etc. are already in use in the iron ore mines in India with significant improvement in productivity and blast induced environmental hazards. In the field of blasting accessories significant improvement has been made due to introduction and adoption of “non-electric delay initiation system” for reducing blast induced ground vibration and air blast noise. Introduction of “Bulk Explosive Systems” in India like global experience, use of slurry, emulsions, ANFO and HANFO in bulk explosive systems have been well established with considerable benefit to Indian Iron ore Mining Industries. Introduction of “Opti Blast” and “Air decking” techniques are already in use at Kudremukh Iron Ore Mines for reducing consumption of explosives, ground vibration and Air Blast Noise etc. Controlled blasting techniques are also in use in the major iron ore mechanised mines in India. Secondary drilling and boulder blasting in mines is usually done by jackhammer drills powered by compressed air and with slurry / gelatin cartridges. However, in order to avoid secondary blasting and to reduce noise due to blasting, the major iron ore mines are using hydraulic rock breaker instead of boulder blasting. Due to availability of high capacity ripper dozers (700 hp), in some cases, drilling/blasting, especially in case of overburden removal, is eliminated. High capacity dozer can rip and doze more effectively where contact plane of overburden/ore and that of different grade ores is uneven.

This ripping/dozing operation is eco-friendly; noise/vibration is practically nil and generation of dust is very less.

For loading of blasted ore, generally electric rope shovels of capacity 3.5 m3 to 6m3 bucket capacity are in use in the mechanised haematite iron ore mines but large capacity shovels of 10 m3 are in use in magnetite iron ore mine at Kudremukh in Karnataka. For haulage of the blasted ore larger dumpers have been deployed indigenously of 35 to 120tonnes capacity. However, imported dumpers of 120 t and 170 t capacity are also being used in India. Because of the large sized equipment deployed in the mining front, the processing plant has also made significant developments matching with mining machineries. The size of crushers , conveyors etc., have gone up and processing plant equipments of capacity 2000 – 3000 tonnes per hour have been installed for iron ore mines to match the size of mining equipments. Further innovations have been made in loading plant equipments such as bucket wheel reclaimers, wagon loaders etc., of matching capacity. However, the reclaimers and wagon loaders needed larger layout of railway tracks and while the loading track itself required a length of 1 Km, the length of railway yard is about 2 to 3 times of the loading tracks. Of late, flood loading system has come into prominence which is out dating the reclaimer-wagon loader combination of loading equipments. In India, the system of bunker loading exists at many mines and for shunting purpose, some locos have been maintained by the mining companies where the operation level is high.

As mechanised open cast iron ore mines becoming larger, deeper and more capital intensive, continuing efforts are being made to improve upon the open cast mining activities through advances in the equipment size / design and practices and also through introduction of innovative techniques. Significant results have been achieved through increasing size of stripping and hauling units, which apparently has reached a plateau, efforts on further improvements are being spear headed through new concepts in equipment utilization by restoring to automation and control. The application of high capacity continuous surface mining techniques to harder formations, new concept of high angle belt conveying system, in-pit crushing systems (mobile and semi-mobiles), high capacity dumpers, automatic truck dispatch system, non-electric blast initiation systems etc. and developments in the area of bulk explosive systems hold out almost unlimited opportunities for upgrading the performance of opencast iron ore mining in India.

The reserves of high grade iron ore are limited. Therefore, it would be necessary at this stage to ensure conservation of high grade ore by blending with low grade ores. As a matter of policy, only low and medium grade iron ore, fines and temporary surplus high grade iron ore (+67 % Fe), particularly from Bailadila (Chattisgarh) need to be exported in the coming years. R&D efforts are needed for developing necessary technologies for utilising more and more fines in the production of steel as a measure of conservation of iron ores. With the present high capacity of iron ore mines, total utilisation of iron ore has become the need of the hour so as to obtain maximum returns. In most of the mechanised mines more than 50 to 60 % fines (except for Bailadila and some mines in the eastern zone where the ore is very hard) are generated. Blue dusts in these mines are to be fully utilised to make various value added products. Blue dust can also be used as additive in concentration of iron ore fines to the extent of 20-40 % for use in steel plants. Further, in the iron ore mines where wet processing of the ore is done, around 10-20 % of ROM is lost as slime, depending on the nature of ore feeds and in this context, coarse fines can be recovered up to 5 % by introducing hydro-cycloning and slow speed classifiers in wet circuit system, even though, the Fe content of such fines will be slightly low which can be blended.

Efforts are also necessary to utilise the tailings/waste as well. It has been found feasible to make bricks using 8 % of binding material such as cement and lime in slimes and 12 % in shale. As reported by IBM, a mixture of slimes and shale in the ratio of 4:1 by weight with 8% binder cement has shown good results in brick making. In the Bellary-Hospet area of Karnataka, the production of iron ore fines from the private mines is substantial, but the fines are unwashed and contain high percentage (40% of -100mesh fraction). In various R&D studies carried out so far, it has been found feasible to consume –100 mesh fraction up to 30% blue dust in concentrate feed. The fines from Bellary-Hospet region generally have 63-64 % Fe content and if 100 mesh fractions can be limited to 3%, these fines can be used as sintering feed. In case of magnetite deposits of Kudremukh, it is estimated that the weathered ore in the leasehold of KIOCL is underlain by 400 million tonnes of primary BMQ in the area. Whereas with the prevailing production rate, the weathered ore reserves would last for another five to six years, the hard / compact, fine grained and silicious nature of the primary ore does not make it amendable for mining. Hence, the techno-economic aspects of mining and beneficiation of primary magnetic ore in Karnataka for production of concentrates need to be examined at this stage.

In general, iron ore mining in India being done by developing benches from the top of the hill and carried downwards as the ore at the top gets exhausted. The methodology being adopted for winning of iron ore is by shovel – dumper combination in case of major mechanised iron ore mines. The bench height generally adopted in iron ore mines in India is ranging from 6 Mts. To 14 Mts. and the slope of the benches ranging from 450 to 600 depending on the consistency / tensile strength of the rock. However in Goa region where the ore is softer, hydraulic excavator and wheel loaders are the principal loading equipment used, height of benches is restricted between 4 Mts. and 7 Mts.

The Iron ore industry in Goa operates under certain difficult conditions specific to Goan iron ore mines. Some of these are listed below:

• Mining activity in several places is being carried out below the water table, which required dewatering of pits for operation to continue.

• Restricted drilling and blasting due to limited lateritic overburden, presence of villages and inhabited areas in the vicinity of the mines.

• Restricted lateral mine development due to smaller areal extension since the lease area of individual mines is less than 100 ha.

• Transport is a problem within the mine, due to greater working depth.

• High overburden to ore ratio (of an average of about 2.5 to 3.0:1) implies that a large amount of overburden is generated when ore is extracted. Since the mining leases are less than 100 ha, there is very limited space (or non at all) available within the lease area to dump the waste material. This leads to requiring land outside the lease area for dumping rejects.

• Land being in short supply, dumps are typically steep with slopes greater than 30o and height of 30-50 Mts. Many waste dumps are situated in the upper part of the valley regions and during monsoon, run off from dumps is common, which blankets agricultural fields and settles in water courses.

• Because of small holdings, large amount of ore is blocked in barriers of adjoining mines; Operations could be carried out close to common boundaries of two lease holders with mutual understanding. Structurally, majority of ore deposits are in synclinal form. Consequently, almost 60% (by volume) of ore production comes from terrain below ground water table.

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