Clastic dike

Figure 10 Deep clastic dike in a coal of the Weller Coal Measures of the Allan Hills, Antarctica, interpreted as infill of periglacial polygonal patterned ground (E. S. Krull and hammer for scale).

A clastic dike is typically a vertical or near-vertical seam of sedimentary material that fiUs a crack in and cuts across sedimentary strata—the dikes are found in sedimentary basin deposits worldwide. Clastic dikes form rapidly by fluidized injection (mobilization of pressurized pore fluids) or passively by water, wind, and gravity (sediment swept into open cracks). Dike thickness varies from millimeters to meters and the length is usually many times the width. 

The irregular, veriical-to-inclined masses of certain materials (clay, silt, or sand) that interrupt a coal seam are called clastic dikes (Figure 1.5). They have also been called horsebacks, a name also applied (in some areas) to rolls. These dikes may vary from mere inches to several feet wide and usually extend laterally for distances up to hundreds of feet. They may also extend for some distance into the strata overlying the coal and may contribute to a weakened roof condition when the coal is mined. 

FIGURE 1.5 A clastic dike interrupting a coal seam and the overlying strata. 

Clastic dikes and clay veins found in coal mines have caused numerous injuries and fatalities. These structures plague all phases of mining, including entry development, pillar recovery, and panel extraction. Clastic dikes and clay veins also increase production costs and may disrupt or halt mining. 

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