SANU LIMESTONE MINES
Owner: Rajasthan State Mines and Minerals Limited
Sanu Limestone Mines,
Rajasthan State Mines & Minerals Limited
Jaisalmer Ramgarh Road, Jaisalmer, Rajasthan, India
Steel Melting Shop (SMS) Grade Limestone of Jaisalmer is considered to be the best for steel plants among other mineable limestone reserves by-virtue of its engineering and chemical properties. The saleable mineral is in the form of sized gitti in size range of +30 mm to -80 mm. Mining of this mineral by mechanized opencast single (composite) bench mining method is adopted, ROM comprising limestone in various sized fraction mixed with clayey matrix, is crushed & screened at the sizing plants to produce the saleable Gitti and segregate different mineral rejects thereof. Finished product, Gitti, is dispatched to the customers wherein the
mineral rejects are backfilled into the worked out pits in the manner to match the topography of the original ground, thereafter plantation of pre-mining flora and other endemic species is carried out over the low grade reject backfill dumps. This methodology is adopted to address mineral conservation and reclamation simultaneously.
Mine is situated in the Jaisalmer district of Rajasthan at 55 Km NW from District HQ on Jaisalmer-Ramgarh road. Border Road Organization (BRO) maintains this road. Jaisalmer is a part of Thar Desert situated at the Western tip of the country where the climatic condition is very harsh. The temperature goes as high as 50 deg. C in summer and 0 deg. C in winter. Average rainfall is below 200 mm.
High quality Limestone is a technological necessity for Steel Plants with the basic oxygen furnance technology where it is used as a flux. After the closure of limestone quarries at Dehradun by the historic judgment of the Hon’ble Supreme Court the limestone from Jaisalmer found enormous importance in the Steel Industry. It was the recommendation of the technical team constituted by Govt. of India in the year 1986 after assessing the various limestone deposits available in the country that the low silica limestone available from Jaisalmer is the best suited for use in the Steel Industry. Based on the recommendation mining of Limestone was commenced by the company since 1988 for supply to different Steel Plants from their mines at Sanu. Jaisalmer limestone is best suitable for use in Steel Industry because of low silica and high decrepitation index. Hence the total production is dispatched to various Steel Plants of SAIL and TISCO. The company is the largest producer & supplier of steel grade limestone in the country.
This high grade, low silica, hard compact limestone is available in Khuiyala formation of Eocene age of Tertiary period. The company have around 20.00 square KM area near village Sanu at a distance of 56 Km from Jaisalmer on Jaisalmer – Ramgarh road & is well connected with all weather tar road maintained by Border Road Organization. The total mineral reserves under the areas held with the company are 167 Million Tonnes of S.M.S grade limestone & 2153 Million Tonnes of Cement grade limestone. Company has enhanced its mineral reserve status by applying few more areas in the same belt.
Open cast mining method with single bench, deploying HEMM and conducting deep hole blasting is in practice. The sizing of ROM limestone is carried out by four nos. fully mechanized Sizing & screening plants of the total capacity 20.00 lac MT per annum. The different size products are dispatched from mines as well as by rail from Jaisalmer Railway sidings of the company. Jaisalmer is the terminus Railway station of the North-Western Railway connected with Broad gauge link.
The Lime stone belongs to the Khuiyala formation forming the part of lower to middle Eocene age. The Limestone is fine grained, hard compact fragmental to nodular on the surface but massive and bedded below surface. The area is practically devoid of overburden/ soil. Limestone outcrops are prominently exposed through out the area. The average depth of mineral is 4.0 m. The proved saleable reserves of SMS grade limestone (+30-80mm sized gitti) as on 01.04.2006 are 12.94 MT at mine no.1 and 17.74 MT at mine no.2.
Lithology of the area
S.No Nature of formation Commercial Grade Thickness in m 1 Top soil – 0-0.30 m. 2 Hard Compact & Bouldery Limestone SMS 3 to 5.00 m. 3 Chalky Limestone Cement 10 to 15 m.
The lease area is characterized by almost flat topography with gentle undulation. The area is party covered with thin discontinuous aeolian sands with maximum area marked by bouldery limestone outcrops. Sparsely vegetated area contains bushes & trees, which are the only flora available.
From quality control point of view mining of composite bench is planned, instead of mining of overburden and/or top layer of loose bouldery limestone separately, therefore mining of mineral is carried out through Mechanized opencast mining methodology with single bench mining, with shovel dumper combination and deep hole blasting has been adopted to mine out SMS grade limestone. As the depth of deposit is 4m single bench mining with ramp at the gradient of 5% to 6.25% is adopted. The pit bottom confirms to the contact zone between SMS lime stone and chalky limestone. However, it is not intended to mine chalky limestone at present. 102 mm dia blast holes are drilled at spacing of 3/3.5 m and burden of 2/2.5 m in staggered pattern. Wet drilling is in practice for dust suppression and collaring of top 2 m of holes, as the top 2 m layer limestone boulders, which are embedded in clay and the collar formation technique maintain the holes intact till blasting. Blasting is carried out using cap sensitive slurry/emulsion explosive as primer charge and ANFO as column charge to loosen the hard compact bottom layer of limestone. 25 ms delay is given between the rows, electric detonator is used for detonation. Powder factor varies between 6-8 te of rock per Kg of explosive. Blasted material is than excavated by backhoe type Hydraulic Excavator (0.90 to 1.2 cum. Bucket capacity), preferably with backhoe attachment and loaded into the dumpers (9 te to 30 te pay load capacity). ROM is hauled up to the crushing & screening plant and dumped it into the hopper or at the stockyard near hopper. The dumpers also carry the mineral rejects from crushing & screening plant to the pit for backfilling. Regular water sprinkling is done on the haul roads, ramp etc. where dumpers are plying, for effective dust suppression.
CRUSHING & SCREENING PLANT
By virtue of mining of composite bench comprising various size fractions of limestone and clayey matrix etc. it become imperative to screen the undersized fines in ROM, crush the oversize material and finally screen out and segregate the finished product (saleable product) and the mineral rejects in different size fractions, which has been taken care by the Crushing & Screening Plants, located within the lease area. The saleable product is sized ‘Gitti’ in the size range of +30mm to -80mm.