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Lota mechanises.

As part of its drive to become economic, Chile's major underground coal mine has adopted hard rock development technology

This decade has been difficult for Chile's Empresa Nacional del Carbon (Enacar), which has struggled for survival against both economic and political pressures. The company has developed a plan of modernisation, Project 2001, which aims to see it reach a breakeven situation by the end of 1997, past debts having been forgiven. Critical to achieving this plan at Lota is a major improvement in the speed of development. The plan will also see the mine's total employment decline by some 20% from 1,812 today to 1,432.

Chile's consumption of coal totals 6 Mt/y, 4.5 Mt of steam coal and 1.5 Mt metallurgical. Enacar produced 300,000 t (washed) last year and 120,000 t of that came from the country's largest underground coal mine, Lota. This year Enacar's total output should be 400,000 t with 220,000 t from Lota. The plans call for continuing growth with Lota producing 500,000 t in 1998 out of a total Enacar output of 650,000 t. Lota's washed coal represents 52% of total output, so the run-of-mine production is about twice that saleable.

There are three main seams suitable for extraction at Lota, seams 2, 3 and 5, with a 12 m vertical interval between 2 and 3 and seam 5 lying a further 55 m below seam 3. Seam 5, the best coal, is classed as metallurgical quality, with a heating value of 7,500 kcal/kg, sulphur content of 0.3% and 2.5% ash. Seam 3 (7,000 kcal/kg) contains 0.8% sulphur and 12% ash and seam 2 3% sulphur and 18% ash. Thus, seam 2 coal has to be blended with the other coals to obtain a saleable product; 3 t of seam 2 with each tonne of seam 3 and 5 t per tonne of seam 5. The maximum saleable sulphur content is 2% and some contracts call for less than 1% sulphur. Seam 2 is the thinnest, averaging 1.2 m thick but contains no partings. Seam 3 is 2.3 m thick and contains 25% partings while the 2 m thick seam 5 contains 40% partings.

Currently the mine is divided into three main areas; two in production, Esperanza and Victoria, and Laraquete under exploration and development, with its first production planned for 1997. There are two faces in seam 3 in the Esperanza block, one face in seam 2 in Victoria and a fourth face in Victoria's seam 3 is being developed. Lota's shaft system is set on the coast and the seams dip at 22 [degrees] to the west, making the average depth of the mine 500 m below sea level. All the underground activity is below the sea, the maximum depth of the Pacific ocean in this area being 50 m, so there is 450 m of hard rock between the underground operations and the sea floor.

Lota is served by four shafts, the upcast Grande and Alberto and the downcast Carlos 1 and 2 shafts. The Laraquete area, which is to replace the Esperanza mining area, is up to 9 km from the shaft system. There is still plenty of coal in the Esperanza block but its extraction would require mining to move even farther away from the main haulage system whereas Laraquete offers coal closer to the haulage system. Development of Laraquete Norte (north) has started and Laraquete Sur (south) is being explored, using the mine's new Atlas Copco Craelius Diamec rig.

The vast undersea distances of the mine mean that personnel transport and coal haulage are problems. At present it takes miners at least one hour to reach their working place, but the mine does plan to invest in a new high-speed rail system. Lota is also preparing to improve its compressed air reticulation by installing underground compressors. Currently compressed air is provided by two 1,600 kW compressors on surface, but the equivalent of almost the whole output of one of the units is lost because of the great distance to the working areas.

Further into the future, if the mine can prove its viability in today's market, plans to sink new decline accesses to the coal from further down the coast are to be considered. Such development would provide much more efficient access to the reserves. There is a fault some 2 km from the Laraquete area which throws the seams down by 300 m. The plan at this stage, though the need to progress through the fault is some considerable time away, is to develop through the fault and work back to the coast, utilising a new decline and ramp system.

The mine's future beyond this major fault is considered in Project 2010. However, Project 2001 has to be completed successfully, proving that costs can be reduced and productivity and efficiency raised, to give credibility to plans for 2010 and beyond. Currently Lota has 11 Mt in reserves, of which 3 Mt has been prospected and developed for mining. Further investment will be required to develop the remainder of the 11 Mt. Beyond the fault there is a further 200 Mt. However, much more exploration of this resource is required. For instance, at this stage it is not known whether it is a single fault or a series of faults that have caused the 300 m displacement of the seams.

Another possibility for the future is Seam 7, which is only 700 mm thick in present areas, and therefore uneconomic, but is believed to get thicker with depth. A general rule at Lota is that the coal quality gets higher with increasing depth.

Hard rock development

Until recently all longwall development (retreat faces) has been undertaken with handheld drills and slusher winches. Slow development has been a major problem recently and Project 2001 calls for full mechanisation. The mine has therefore purchased this year three Atlas Copco Boomer H281 single-boom jumbos and three Atlas Copco Wagner ST3.5S LHDs for development. Three Dux DT-15 trucks will soon join this development fleet. These three trucks have been purchased with two dump bodies and two fiat beds allowing them to be used for both rock haulage and to move equipment underground as required. There are also some secondhand machines, a Wagner ST2D and a small Bohler crawler-mounted jumbo, as well as three 0.7 [m.sup.3] capacity Bobcat loaders for small scale development work. The latter machines are primarily for development in Esperanza which is not considered in Project 2001.

The new Atlas Copco jumbos and LHDs are all flameproofed units; the Wagners were delivered as flameproofed machines from Portland while the Boomers were flameproofed locally by Atlas Copco Chilena. Methane is well controlled at the mine, and kept below the 1.5% level. For each tonne of coal extracted, about 30 [m.sup.3] of methane is generated.

As part of the purchase contract, Atlas Copco Chilena provided one drill jumbo technician and one Wagner Scooptram technician in the first months that the machines were at the mine, providing maintenance support and operator training. A repair and maintenance contract between the mine and Atlas Copco Chilena is under discussion.

Rock mechanics problems, including severe floor heave, prohibit development in coal and Lota selected the jumbo/LHD development option as the quickest and most economical method of development in hard rock. To produce 80 t of coal requires 1 m of development work. Total development in 1995 was just 4,000 m and this year's plan calls for 9,000 m, though management realistically expects to achieve 7,000 m of the target. All development drifts are 3.5 m high and vary in width from 3 to 5 m.

Lota employs three Anderson shearers and one Eickhoff machine. Faces are normally 150 m long and the panels are 600 m long. Four-leg shield supports for the thinnest, Seam 2, faces are all made at the mine, using Westfalia (Deutsche Bergbau-Technik - DBT) hydraulics. Workings in Seam 3 are supported by 2.5 m shield chocks supplied by DBT.

Lota has an extensive, well-equipped workshop to maintain the coal mining and other equipment and manufacture the thin-seam shields, at a rate of ten per month. Currently there are 80 Enacar personnel in the workshop, plus a further 75 contractor personnel. Conventional underground workshops are being construct ed for the new trackless equipment.

Past and future

Coal mining at Lota started back in 1844, but only became a properly planned commercial venture in 1852 with the formation of Compania Cousino & Garland, under the direction of Matias Cousino. The mine has been under the control of different companies over the years from Cousino & Garland (1852-1856) to Compania Carbonifera e Industrial de Lota (1933-1964). In 1964 it was merged with Compania Carbonifera y de Fundicion Schwager. ENACAR was established in 1973 and later took over control of other coal mining companies including Compania Carbonera Victoria de Lebu (Carvile), Compania Carbonera Colico Sur and Compania Carbonera de Pilpilco.

The main problem facing Enacar at present is one that has been experienced widely in Europe, whether or not to continue with coal mining that is barely economic or turn to imported coal and bear the socio-economic problems that come with the decision to close mines. Lota has good quality coal, and very significant reserves. But it has to prove that this coal can be mined reasonably economically.

Lota is not the only mine, or coal prospect in the area. To the southwest (see map) is Carvile another Enacar mine and preparation plant managed from Lota. Between Lota and Lebu is the old Trongol mine and La Chulita mine project, which is currently under study.
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Title Annotation:developments at one of Chile's Empresa Nacional del Carbon's coal mines
Author:Chadwick, John
Publication:Mining Magazine
Date:Sep 1, 1996
Words:1628
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