NRE NO. 1 COLLIERY
The NRE No. 1 Colliery (formerly South Bulli Colliery) was acquired by Gujarat NRE Coke Ltd, through its subsidiary Gujarat NRE Australia Pty Ltd. in December 2004. The mine located in the Southern Coalfields of New South Wales, approximately 10 kilometers north of Wollongong and around 60 kilometers south of Sydney in Australia will ensure a steady supply of high quality raw material for its coke ovens operations in India in a highly volatile environment and provide insurance against price volatility. The Colliery will also create employment in the Illawarra area and in India with benefits to both the nations.
Regional Geology
NRE No. 1 Colliery lies in the Southern Coalfields, which is part of the Sydney Basin of New South Wales and is situated towards the southernmost extremity of the Sydney - Bowen Basin of eastern Australia. The Sydney basin is largely of Permo-Triassic age, and extends from Batemans Bay in the south to Newcastle in the north, and from Lithgow in the west to Murrurundi in the north west. The colliery holding is adjacent to the south eastern margin of the basin. Depositionally, the basin had been active during Permian and Triassic times with phases of tectonism and/or igneous activity extending from Permian to recent times. In the Southern Coalfield, the general sequence, from top to bottom, consists of the Hawkesbury Sandstone, the Narrabeen Group, and the Illawarra Coal Measures.
At least seven phases of cyclic sedimentation have been recognised in Sydney sub-group. The most important of these depositional cycles are the three sequences at the top of the Sydney sub-group, which contain, from bottom to top, the Wongawilli coal seam, the Balgownie coal seam, and the Bulli coal seam. The Bulli seam lies immediately below the Coal Cliff sandstone of the Narrabeen Group. The Illawarra Coal Measures are underlain in the Wollongong area by marine sediments of the Upper Shoalhaven Group.
Mine Geology
The mine spread over 6421 hectares and having reserves of around 300 million tonnes of coking coal comprises three coal seams, the Bulli seam, which occurs at the top of the Illawarra Coal Measures, the Balgownie seam, some 8 to 10 metres below it, and the Wongawilli seam, which lies between 22 and 25 metres below the Balgownie seam. Two minor seams, the Cape Horn seam and the Hargraves seam, lie between the Balgownie and Wongawilli seams, but are too thin to have any economic significance.
The average seam thickness of the Bulli, Balgownie and Wongawilli seams are 2.01 metres, 1.25 metres, and 9.75 metres respectively, though only the basal 2.5 metres of the Wongawilli seam is regarded as the working section. The Bulli seam has been worked extensively in the mine area for almost 120 years, the Balgownie seam was worked between 1967 and 1982 and again in 2002. There has been no systematic production from the Wongawilli seam in this colliery. Both the Balgownie and the Wongawilli seams are largely untapped resources.
Bulli Coal
This seam forms the uppermost unit of the Illawarra Coal Measures of Late Permian age. It has a thickness varying between less than 1.4 and more than 2.8m in current wordings and un-mined areas.
The thinning of the seam in a westerly direction represents the general trend, but highly variable spot thicknesses occur, reflecting roof and floor irregularities, wash-outs, roof and floor rolls, and false-bottoms.
The immediate roof may be carbonaceous shale, a mudstone-shale or a laminite. Sandstones and conglomerates, statistically almost as important as the other roof types, form an intricate network of erosive channels, representing a formation much younger than the original roof they replaced. All roof lithologies may occur within a distance of 100 m, and the sandstone, when not the immediate roof, is almost never higher than 3.5 m above the immediate roof horizon.
The Immediate floor is usually a coaly shale grading down to shale, to siltstone, to laminite, to sandstone. This last sandstone layer is many metres thick and forms the roof of the underlying Balgownie Seam.
The thickness of the Balgownie-Bulli interburden varies between less than 8m (outcrop area and boreholes SR3 and SR6 in the extreme northwest) and more than 12m (Survey work around borehole SB13 area).
Balgownie Seam
The interburden strata between the top of the Wongawilli Seam and the base of the Balgownie Seam (Eckersley Formation), comprises 2 coal members {Hargrave and Cape Horn seams), sandwiched between 2 sandstone units, Novice Sandstone Member at the base, and the Lawrence Sandstone Member at the top. Both "sandstone" units are actually rich in shale, mudstone and siltstone layers and beds, especially within 1-2 metres of the adjoining coal units. Both Hargrave and Cape Horn coal members are too thin to be of any economic interest.
The total thickness of the interburden, including the top (uneconomic) portion of the Wongawilli Coal, varies between less than 19m (Borehole S515 in Corrimal Colliery) to more than 30m in parts of the northern marginal zone of the Cataract Reservoir (Boreholes SB15, SB22, WB25, WB26).
Most seam intersections are subdivided into an upper 'best seam section', containing predominantly coal and a lower transitional section composed of mudstone and shale with variable proportions of coal. The lower section is more variable in western areas.
The roof is invariably cross-bedded sandstone, and the floor is formed by a carbonaceous mudstone grading down to mudstone and to siltstone.
Seam thickness varies between 1.0 m and 1.5 m in most areas with an average of 1.17 m for the whole Colliery Holding, excluding areas where thickness is smaller than 1.0 m. Within a 2 km wide strip along the northern boundary, a thinning of the seam to less than 0.5 m was observed.
Wongawilli Coal
The full seam thickness varies between 7m and 11m, however, only the lower 1.8m to 2.6m of the seam is of economic interest. Most tuffaceous bands in this lower portion are named and correlatable. One such band (Clay Bend) has been selected in the Colliery Holding as the working roof.
The floor is composed of mudstone or siltstone grading down into a laminate.
HIGHLIGHTS OF THE MINE
The Market Demand for "Balgo"
The coal products from the NRE No. 1 Colliery are world class due to their very low phosphorous levels (<0.005ppm), high calorific value, low ash coal and low sulphur content and their suitability for direct feed into coke oven to produce blast furnace coke, ranked among the best in the world.
The low phosphorous level in Balgownie Seam coal (Balgo) represent some of the lowest known levels of phosphorous in the world. The merits of the Balgownie low volatile metallurgical coals are:
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Strong coke
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Low phosphorous
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Low sulphur
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Good Fluidity
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Nil oven wall pressure
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Adequate reflectance
There is also a strong, diversified demand for the Bulli coals, due to its quality characteristics. By mining to produce a blend of Balgownie and Bulli coal, the quality of both the hard coking coal and the thermal coal products are enhanced. The low phosphorous coking coal will be a premium product in the world coal market and be in high demand by European steel mills.
Historically iron ore mines concentrated on mining low phosphorous iron ore deposits. Such deposits have been heavily exploited over the last 30 years and as a consequence mines are now forced to mine deposits with higher concentrations of phosphorous. The availability of low phosphorous coking coal offsets the issue of high phosphorous iron ore facing the iron ore miners and steel mills. There is also potential to prepare a third saleable product, PCI coal, which is intermediate in value between coking and thermal coal.
Methane Gas Reserves
There is scope to develop extensive high quality methane gas resources (estimated in excess of 50 years), existing within the Wongawilli seam which contains the largest field of gas in the region. The presence of gas up to 10m3/t with acceptable CO2 ratios in the Bulli and Balgownie seams may also be exploited for gas sales or power generation. Government incentives and grants are available in projects, which reduce greenhouse gas (methane) emissions for which the Balgownie project may qualify.
MINING METHODS
Gujarat NRE has adopted new approaches to mining in the NRE No 1 Colliery as compared to what was being practiced by the earlier owners. Where mining has for a number of decades been conducted using Longwall mining, it intends to use Pillar extraction method to increase the recovery level in the remaining levels. While mining in the colliery has always been concentrated on the Bulli seam, the Balgownie and the Wongawilli seams have hardly seen much activity.
Pillar extraction mining in the Bulli seam uses the Continuous Miner method supported by BLS breaker line support. Continuous miner is a speedy and efficient process having high productivity and is designed for a variety of seams and mining conditions. The continuous miner cuts a network of “rooms” into the seam. As the rooms are cut, the continuous miner simultaneously loads the coal onto a shuttle or ram car where it will eventually be placed on a conveyor belt that moves it to the surface. The roof is supported by installation of steel “roof bolts” into the stone above the coal seam, and pillars of coal are left behind to support the roadways. These pillars are later removed with the continuous miners and the roof is allowed to collapse in a controlled manner. The breaker line support helps to provide a safe working environment near the continuous miner by pushing upwards against the roof.
The company further intends to mine the Wongawilli seam also using Longwall Mining Machines.
It proposes to mine the Balgownie seam using Thin Seam Mining methods which as the name suggests is used for mining coal seams with thickness less than 1.5 metres. Hence, this method is most suitable for mining Balgownie seam, the thickness of which ranges from 0.46 to 1.5 metres. Thin seam differs in that it involves forming smaller pillars of coal that would be found in the Bulli or Wongawilli seam. Each mining “panel” forms up to seven roadways. The miner cuts these road ways in a sequence that allows a mobile bolting machine to come in after the coal has been removed for up to 15 metres, and to support the roof the miner is driven on the tracks (fitted) to another roadway where it cuts another 15 metres. This is known as the “cut and flit” method. In this system, the pillars of coal are not removed by pillar extraction methods. This mining system achieves a higher-than-normal recovery of the resources on the advance.
EXPANSION PLANS
The management team is currently developing major expansion plans for the mine that will be implemented in 2007. It is planned to re-establish the mine as a longwall operation, with longwall faces operating in both the Wongawilli and Bulli seams. A full feasibility study will be conducted this year, with an aim to produce up to 4MTpa from the various coal seams.
A new set of main entries is to be formed from the Russell Vale side of the operation in the Wongawilli seam. These roadways will allow for the installation of a high capacity conveyor belt and a parallel track road. These will totally replace the existing roads in the Bulli and Balgownie workings. These headings, to be known as “Wonga Mains”, will offer the mine greater security against the problems that the older workings currently present.
The three new entries will be commencing in December 2007. Significant amount of preparation has been undertaken to date. The photos below show the current status of the Conveyor Portal and the Rubber Tyred Vehicle Portal. |
