(Q) 3. Mining Method
Surface mining was practiced in Quinsam Coal for a few years until 1991. Since then, coal has been extracted by underground method from the #1 and #3 Seams. The #2 Seam is too thin to be mined. At present, 2 North Mine in the #1 Seam is operated under a cover of about 120m (400 feet) for one shift per day. The part of the #1 Seam overlying 4 South Mine is fragmented and hence mining in this part of the #1 Seam is infeasible. 4 South Mine in #3 Seam has a cover of 90m (300 feet), it is currently idle.
Room and pillar mining is currently adopted in Quinsam Coal. The #1 Seam has an average thickness about 2.6 ~ 3m in the current mining area. Panels are developed from the rise to the dip direction. Depillaring is done during retreat from the dip to the rise by the split and fender method using Christmas tree cut sequence (Figure Q4). Floor coal recovery is simultaneously carried out during retreat resulting in 75% coal recovery in situ. Freshly exposed roof is supported by systematic bolting within 24 hours. There are three panels currently in operation in the 2 North Mine:
- #7 panel and #8 panel are being depillared and
- #9 panel is being developed.
There is a medium grained massive sandstone in the roof strata overlying the #3 Seam. This layer is responsible for the gob overriding squeezing the pillars. In addition, there is a subsidence problem below the swampy area at the surface over 4 South Mine. Partial extraction leaving yield pillars in a checkerboard pattern is therefore employed in the 4 South Mine (Figure Q5).
Continuous miner is used for coal extraction and loading. Shuttle cars are used for transportation from the continuous miner to the conveyor. The coal is transported to the surface by conveyor belts (Figure Q6).
(Q) 3.3 Development Method & Equipment
Mains are driven with a 3-roadway system along the strike towards North (Figure Q6). The panels are developed towards dip. In case of fault in the roof, the entry-width is reduced to 5.2m locally depending on the roof condition.
In 2 North Mine, #1 to #8 panels are accessed by 9 entries, #9 panel is accessed by 5 entries. Each panel in 4 South Mine is accessed by 5 entries.
Roadheader is used for development work.