Coal Layer Shape

Coal Layer Shapes

The shape of the basin, the sedimentation process, the geological process during and after the Coalification process will determine the coal layer, knowing the shape of the coal layer is very decisive in calculating the reserves and planning how to mine them. There are several forms of coal seam including:

1. Horse Back Shape

This shape is characterized by a layer of coal and the rock covering it curves upwards due to compression force. the thickness towards the literal coal layer is likely to be the same or become smaller or thinning.

Figure 2. 1. 5.1. Horse Back Shape Coal Coating

2. Pinch Shape

This shape is characterized by a thinning layer in the middle. In general, the base of the coal seam is plastic rocks such as the horizontal rock above the coal layer is locally covered by sandstone which is laterally a filling of a groove.

Figure 2. 1. 5.2. Pinch Shape Coal Coating

3. Clay Vein Shape

This form occurs when between two parts of the coal deposit is targeted, occurring if one of the coal deposits has a fault, which is then in the field of fault that is an open fracture, filled by clay or sand material.

Figure 2. 1. 5.3. Clay Vein Shape Coal Coating

4. Burried Hill Shape

The main contribution of frozen rock intrusion onthe structure of the coal layer is the heating and devolatilization effect (evaporation of vollatile matter)that occurs when hot magma forms a sill or lacolith near the coal layer, or when the corok (dike) penetrates the coal formation. Lacolith andsill have a greater area of warming influence on surrounding rock formations than the corok. The quality of coal or carbon content will increase with the closer the distance of the coal layer to the heat source. The onion of gradations in this rank is due to differences in devolatilization rates affected by heat.

Figure 2. 1. 5.4. Frozen Rock Intrusion on Coal Seam

5. Fault Shape

This form occurs when in areas where coal deposits experience several series of faults. this situation is messed up in the backup calculation due to the removal of the layer due to the vertical shift.

Figure 2. 1. 5.5. Coal Seam Fault Shape

6. Folding Shapes

This form occurs when in areas where coal deposits are multiplying. The more intensive the force that works the formation of the fold will the more complex the fold occurs.

Figure 2. 1. 5.6. Folding Shape Coal Coating

7. Split Coal

Split Coal is a separate layer of coal by parting clay, shale, or sandstonewith the thickness of te rtentu resulting in a separate layerthat cannot be mined simultaneously(Thrush, P.W., and staff of Bereau of Mines, 1968).

Figure 2. 1. 5.7. Split Caused By The Clay That Goes Into The Coal Levy.

8. Wash Out

Wash Out is a cut out of coal seam. Cut out itself is defined as a clay stone, stone flake or clay stone that fills the eroded part in the layer coal (Dictionary of Geological Term, 3^Rd edition).  According to Robert Stefanko, 1983, washed out is the loss of part or all of the coal layer which is then replaced by other sediment deposits due to erosion and deposition.

The loss of the coal seam could be caused by the depletion of ancient rivers andrecent rivers,or glaciers.

Figure 2. 1. 5.8. Wash Out Due to River Erosion