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 Bureau of Mines Information Circular/1983 
 
 A Guide to Geologic Features 
 in Coal Mines in the Northern 
 Appalachian Coal Basin 
 
 By Paul W. Jeran and Jacqueline H. Jansky 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
: r." "t 
 
Information Circular 8918 
 •1 
 
 A Guide to Geologic Features 
 in Coal Mines in the Northern 
 Appalachian Coal Basin 
 
 By Paul W. Jeran and Jacqueline H. Jansky 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 James G. Watt, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 
This publication has been cataloged as follows: 
 
 V 
 
 !^ 
 
 <j 
 
 
 Jeran, P. Vi 
 
 A guide to geologic features ia coal mines in the northern Appa- 
 lachian Coal Basin, 
 
 (Information circular ; 8918) 
 
 Bibliography: p. 16. 
 
 Supt.ofDocs.no.: 128.27: 8918. 
 
 1. Coal mines and mining— Appalachian Region— Safety measures. 
 2. Coal— Geology— Appalachian Region. 3. Ground control (Mining). 
 I. Jansky, Jacqueline H. II. Title. III. Series: Infomiation circu- 
 lar (United States. Bureau of Mines) ; 8918. 
 
 -^f^m&^^\H 622s [622.8] 82-600359 
 
'1 CONTENTS 
 
 -0 
 
 V 
 
 Page 
 
 Abs t ract 1 
 
 Introduction. 2 
 
 Orientation 2 
 
 Llthology 4 
 
 Sands tones 4 
 
 Shales 4 
 
 Limes tones 6 
 
 Bedding 6 
 
 Sedimentary features 7 
 
 Structural features 10 
 
 Clay veins and mud-filled fractures 15 
 
 Summary 16 
 
 Bibliography 16 
 
 ILLUSTRATIONS 
 
 1. Diagram illustrating strike and dip 3 
 
 2. Orientation aid 3 
 
 3. Illustration of orientation aid use 3 
 
 4 . Wet bedding plane 5 
 
 5 . Normal bedding 6 
 
 6 . Crossbedding 6 
 
 7 . Sandstone channel cutting out coalbed 8 
 
 8. Sandstone channel with coal layers terminating against sandstone 8 
 
 9. Sandstone channel with coal layers deformed next to sandstone 8 
 
 10. Supported kettlebottom 8 
 
 11. Kettlebottom with surrounding roof rock sloughed 9 
 
 12. Void left by fallen kettlebottom 9 
 
 13. Anticline and syncline 11 
 
 14. Mud-filled fractures in roof 11 
 
 15. Joints in roof rock 12 
 
 16. Slickenside showing polishing and grooving 12 
 
 17. Slickenside showing curved surface. 13 
 
 13. Slickenside showing planar surface 13 
 
 19. Faults 14 
 
 20. Faults recorded on a section map 14 
 
 21. Clay vein 15 
 
 22. Mud-filled fracture transecting coalbed 15 
 
LIST OF UNIT 
 
 OF MEASURE ABBREVIATIONS USED IN THIS REPORT 
 
 cm 
 
 centimeter m meter 
 
 in 
 
 inch pet percent 
 
 ft 
 
 foot 
 
A GUIDE TO GEOLOGIC FEATURES IN COAL MINES IN THE NORTHERN 
 
 APPALACHIAN COAL BASIN 
 
 By Paul W, Jeran and Jacqueline H, Jansky 
 
 ABSTRACT 
 
 This Bureau of Mines report has been prepared to provide a means 
 whereby mineworkers without specific geologic training can recognize and 
 record the existence of potentially hazardous geologic features en- 
 countered in coal mines. Each geologic feature described in this report 
 has been implicated in roof failure. Through the recording of the ob- 
 servations of mineworkers, based on this report, a geologic map of mine 
 workings and the associated ground control problems can be compiled. 
 From such maps, the trends of changes and features can be determined and 
 projected ahead of mining. The face crew can be alerted to a potential 
 problem and what to look for as the face is advanced. 
 
 
 
 'Geologist/ Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
 
INTRODUCTION 
 
 Roof falls are a major cause of death 
 and injury to underground coal miners. 
 Aside from the human tragedy, many days 
 of nonproductive work are used to clean 
 up and resupport fallen roof. The Bureau 
 of Mines, through its ground control re- 
 search program, is analyzing the roof 
 fall problem and developing techniques 
 that will reduce the number and severity 
 of accidents due to ground failure. 
 
 Areas of bad roof are local occurrences 
 in the majority of coal mines. The dif- 
 ference between good and bad roof can 
 usually be attributed to a change in the 
 roof strata, provided that the mining 
 method or technique has not been changed. 
 Geologic evidence for this change is usu- 
 ally present but goes unnoticed until the 
 situation becomes critical and sometimes 
 is not noticed even then. 
 
 This report has been prepared to 
 acquaint the readers with potentially 
 hazardous geologic features that they can 
 readily observe and record. Each of the 
 features described in this report has 
 been implicated in roof failures; how- 
 ever, no feature or change in roof strata 
 guarantees that roof control problems 
 
 will or will not occur. With time and 
 experience, a geologic map of a mine's 
 workings and the associated ground con- 
 trol problems can be compiled. From such 
 maps, the trends of changes and features 
 can be determined and projected ahead of 
 mining. The face crew can be alerted to 
 a potential problem and what to look for 
 as the face is advanced. 
 
 This report describes a method of de- 
 termining the orientation of planar fea- 
 tures. It has sections on general rock 
 description (lithology), features devel- 
 oped during deposition of strata (sedi- 
 mentary features), and features that 
 result from the rocks being deformed by 
 geologic forces (structural features). 
 
 Illustrations are used to provide vis- 
 ual examples of each feature. The black 
 and white stick used in the photo- 
 graphs (all from mines in the northern 
 Appalachian Coal Basin) is a reference 
 scale to give the viewer an idea of the 
 size of each feature. The alternating 
 bands on the stick are 6 in (15.2 cm) 
 long, and the entire stick is 30 in 
 (0.76 m) long. 
 
 ORIENTATION 
 
 Most geologic features occur in groups, 
 i.e., where one is observed others may be 
 expected. For this reason, it is impor- 
 tant to record each occurrence of each 
 feature on a suitable scale mine map. 
 With planar features, such as bedding, 
 clay veins, slips, and joints, the ori- 
 entation of each is important, 
 
 A geologist records the attitude or 
 orientation of any plane by two values — 
 strike and dip (fig. 1). Strike is the 
 direction with respect to some reference 
 (usually north) of a horizontal line in 
 the plane. In a flat-lying coal mine 
 (grades less than 10 pet), the intersec- 
 tion of the plane and the roof is usually 
 a reasonable approximation of a horizon- 
 tal line. In figure 1 the strike is a° 
 to the right of the reference direction 
 
 (inby entries). The dip is the angle 
 measured in the vertical plane perpen- 
 dicular to the strike downward from the 
 horizontal plane to the feature plane. 
 In figure 1 the dip is b° downward to the 
 right of the strike. 
 
 The symbol used to denote strike and 
 dip on a map is shown in figure 1. The 
 long line is drawn parallel to the strike 
 direction with respect to the reference 
 direction. The short line indicates the 
 dip direction and has the dip angle 
 written next to it. Figure 1 shows the 
 map symbol for the illustrated strike and 
 dip. 
 
 Geologists usually use magnetic com- 
 passes with clinometers to measure ori- 
 entation. These are readily available 
 
FIGURE 1. = Diagram illustrating strike and dip. 
 
 for under $100 each, and with a little 
 training almost anyone can use one. How- 
 ever, as an alternative, a simple orien- 
 tation aid card (fig. 2) method is sug- 
 gested for use underground. 
 
 The reference direction chosen is inby 
 parallel with the entries. To determine 
 the strike of a planar feature, the card 
 user stands facing inby with the trace of 
 the planar feature overhead. The orien- 
 tation aid card is held flat in the hand 
 and the arrow is oriented so that it 
 points inby parallel to the entries at 
 the location of the measurement. By 
 using the upper half of the aid (labeled 
 strike), the direction of the trace 
 of the feature in the roof is estimated 
 relative to the reference direction 
 (fig. 3). The number of degrees left or 
 right (strike direction) is recorded. 
 
 To estimate the dip, the card user 
 faces, in the same direction as the 
 strike, the trace of the feature plane in 
 the rib (fig. 3). The orientation aid 
 
 ° 80 90 80 
 
 FIGURE 2, - Orientation aid. 
 
 Read dip 
 {card vertical) 
 
 y 
 
 / -Trace of plane 
 / in floor 
 
 FIGURE 3. - Illustration of orientation aid use. 
 
card is held vertically, and the left or 
 right edge is aligned with the trace 
 of the plane in the rib. A weighted 
 string is held at the center of the dia- 
 gram and is allowed to fall within the 
 lower arc on the card (labeled dip). The 
 number of degrees and their relationship 
 (right or left) to the strike are 
 recorded. 
 
 These data should be transcribed to the 
 mine section map later. Maps with these 
 data should be kept, not discarded, 
 when the section is mined out. Con- 
 sultation of these maps when mining in 
 the vicinity of old workings will alert 
 the crew to the features and orientations 
 they may encounter as they advance the 
 face. 
 
 LITHOLOGY 
 
 Within the coal mining industry there 
 are many terms used to describe the rocks 
 encountered in mining. While these terms 
 have meaning within a given mine or min- 
 ing area, this meaning can vary from one 
 mine or area to another. This can lead 
 to confusion and misunderstanding when 
 the experience gained from one area is 
 related to a mine in another area. Ge- 
 ologists use a rock classification system 
 that describes rocks precisely. This 
 system is too complex for general use. 
 This section has been included to provide 
 the readers with a basic rock classifica- 
 tion that is compatible with the geologic 
 classification, 
 
 Lithology is the description of rocks 
 based on color, mineralogic composition, 
 and grain size. In U.S. coalfields, the 
 rocks associated with bituminous coalbeds 
 generally fall into one of the three 
 types of sedimentary rocks — sandstone, 
 shale, or limestone. Sedimentary rocks 
 are (1) the result of weathering and ero- 
 sion of the preexisting rock, (2) the 
 product of deposited organic material, or 
 (3) the chemicals left when seawater 
 evaporates. Thus sedimentary rocks can 
 be classified as fragmental, biological, 
 or chemical. The following is a brief 
 coimnentary on distinguishing each of the 
 three sedimentary rock types. 
 
 SANDSTONES 
 
 Sandstones are fragmental sedimentary 
 rocks made of visible sand-sized grains 
 cemented together by a filler materi- 
 al. Sandstones are sandy to the touch 
 (like sandpaper). The color of sand- 
 stone ranges from a gray to red to tan. 
 
 Sandstones can be identified by the visi- 
 ble sand grains. 
 
 Occasionally sandstones contain the 
 mineral mica. This mineral looks like 
 small flakes of shiny cellophane. Where 
 mica is lying on a bedding plane, the 
 bedding plane will appear shiny and the 
 sandstone will tend to separate along 
 this layer. Where observed, this should 
 be noted as micaceous sandstone. From a 
 distance, e.g., when looking at the top 
 of a high roof fall from its base, a 
 mica-covered bedding plane may appear as 
 shiny as a slickenside but will not have 
 the grooves or scratches. A close in- 
 spection of the rock should determine if 
 the shiny surface is a micaceous bedding 
 plane or a slickenside. 
 
 SHALES 
 
 Shales are also fragmental sedimentary 
 rocks, but the grains are so small that 
 no individual grains can be seen by the 
 naked eye. These rocks are formed by the 
 compaction of mud. Shales tend to break 
 into layers and feel smooth to the touch. 
 Usual colors are gray or black but can be 
 tan, red, or green. Shales may be iden- 
 tified by their very fine grains, smooth- 
 ness, ease with which they can be 
 scratched by a piece of steel, and a 
 tendency to break into flat pieces. When 
 a piece of shale is scratched, the re- 
 sulting powder is the same color as the 
 rock itself. Shales associated with 
 coalbeds may contain the imprint of fos- 
 sil leaves. Bedding planes in shale can 
 be highly reflective when wet (fig. 4). 
 Wet bedding planes should not be mistaken 
 for slickensides. 
 
FIGURE 4. - Wet bedding plane. 
 
LIMESTONES 
 
 Limestones are sedimentary rocks that 
 can be fragmental, biological, and/or 
 chemical. Limestones are made of the 
 mineral calcite, which generally exists 
 as small grains. They are generally mas- 
 sive rocks, may contain seashell fossils, 
 and rarely break into flat slabs as does 
 shale. Limestones are generally gray 
 to tan in color, but when scratched, 
 the resulting powder is light gray to 
 white. Note that this is different from 
 shale, which produces powder essentially 
 the same color as the rock itself. 
 
 BEDDING 
 
 Any description of a roof problem 
 should give at least the rock type(s) 
 involved and their thickness. The 
 
 individual layers making up the rock 
 stratum are called bedding, and where 
 this can be observed, the bedding thick- 
 ness should be noted as well as the 
 thickness of the rock type. There are 
 two types of bedding that may be observed 
 and noted. First is normal bedding 
 (fig. 5) , where the bedding parallels 
 the coalbed. Second is crossbedding 
 (fig. 6), where the bedding is other than 
 parallel with the coalbed. 
 
 Categorization of a rock layer as 
 crossbedding should be done carefully. 
 To be considered crossbedding, all the 
 bedding must be inclined to the coalbed. 
 If only one or two surfaces are inclined 
 and the balance of the bedding is paral- 
 lel to the coalbed, a group of slicken- 
 sided surfaces has been encountered, not 
 bedding. 
 
 
 FIGURE 5. - Normal bedding. 
 
 Complex 
 crossbedding 
 
 Normal bedding-^j^^^ 
 
 Simple 
 crossbedding - 
 
 Normal bedding 
 
 FIGURE 6. - Crossbedding. 
 
Geologists use the term "fades change" might be expected. Where observed, this 
 
 to describe the lateral change of rock 
 types. When the immediate and/or main 
 roof rock changes types within a distance 
 of 200 ft (61 ra) or less, then problems 
 
 should be noted on the mine map. Roof 
 
 bolting machine operators can be very 
 
 helpful by noting, during drilling, where 
 and when such changes occur. 
 
 SEDIMENTARY FEATURES 
 
 the usual 
 
 miners are 
 
 out," or 
 
 thinned by 
 
 One particular rock feature is the 
 sandstone channel. This feature may 
 affect only the roof, or may partially or 
 wholly cut out the coalbed. Where the 
 coalbed has been cut out, 
 descriptive terms used by 
 "want," "wash out," "pinch 
 "fault," Where the coal is 
 rock protruding from the roof, the fea- 
 ture is commonly called a "roll" or 
 "pinch out." Where these can be traced 
 to a sandstone bed or channel, they 
 should be called a sandstone channel. 
 Since "fault" Is a specific structural 
 feature, this term should never be 
 applied to a sandstone channel. Details 
 to be noted on a mine map are (1) the 
 trend of the sandstone channel, (2) the 
 width of the feature measured at the top 
 
 of the coalbed, and (3) the 
 coal remaining in place. 
 
 thickness of 
 
 Sandstone channels can be observed in 
 two distinct occurrences. First is the 
 true cutout where the individual layers 
 of coal are cut by the sandstone 
 (figs. 7-8). Note that the layers of 
 coal terminate at the sandstone and there 
 is little change in coal thickness as 
 mining approaches the channel. The 
 second occurrence is where the sandstone 
 has been pushed into the coalbed, causing 
 the coal to be squeezed out to either 
 
 side of the sandstone channel (fig. 9). 
 The layers of coal are bent downward, 
 which may show some wrinkling, and the 
 coalbed may double in thickness on either 
 or both sides of the sandstone. Slicken- 
 sided surfaces are common. 
 
 Another lithologic feature is the ket- 
 tlebottom. This feature is also called 
 "caldron bottom," "pot bottom," or "coal 
 pipe," It is the mud cast of a fossil 
 trunk or root of a tree or fern, which 
 extends upward into the roof rock above a 
 coalbed. It is commonly surrounded by a 
 thin layer of coal and/or slickensides. 
 This feature may fall at any time without 
 warning. Where kettlebottoms are com- 
 monly found, roof control plans contain 
 specific methods of supporting or taking 
 them down. Figure 10 shows a supported 
 kettlebottom in place. Figure 11 shows a 
 kettlebottom with the rock around it hav- 
 ing sloughed off; the shape of the bark 
 of the original tree can be seen. Fig- 
 ure 12 shows the void left by a kettle- 
 bottom that has fallen. 
 
 Kettlebottoms are usually found 
 groups. The location and diameter 
 
 m 
 of 
 
 each kettlebottom should be noted on the 
 mine map. If a kettlebottom has fallen 
 out, the thickness of the fallen piece 
 should also be recorded. 
 
^■;^!;-: Sandstone" 
 ■^r'.rv- channel ". 
 
 I Width of channel] 
 I measured at top 
 of coalbed I 
 
 TTTT- 
 
 No coal below channel 
 \ 
 
 FIGURE 7. - Sandstone channel cutting out 
 coalbed. 
 
 FIGURE 8. - Sandstone channel with coal lay- 
 ers terminating against sandstone. 
 
 .Sandstone channel-.'. 
 
 / / / / / y y / x2^ '•'•■: '•''-''■' '■■'■ '■■'''/\, - 
 fCoalbed_ ' ^^ ' ■■"■■■■' '-■■ ■''- ' ^^ 
 
 Normal 
 coalbed 
 
 iBedding.Width of channel I Thicken- 
 
 bent measured at top jng of 
 
 I down I °^ coolbed coalbed 
 
 _Coalbed disturbed by_ 
 sandstone channel 
 
 Normal 
 coalbed 
 
 30 in of coal below channel 
 
 Coalbed 9 ft thick 
 this side of channel 
 
 r'>-;"i:o/ 6/ Slip, 9 in-offset, dips 
 -i'lv;^;/ r 30° toward U 
 
 FIGURE 9. - Sandstone channel with coal lay- 
 ers deformed next to sandstone. 
 
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 FIGURE 10. - Supported kettlebottom. 
 
FIGURE n. - Kettlebottom with surrounding roof rock sloughed. 
 
 
 FIGURE 12. " Void left by fallen kettlebottom. 
 
10 
 
 STRUCTURAL FEATURES 
 
 When sufficient stresses are applied to 
 rock strata, the strata will either bend 
 or break. Where rock strata are bent, 
 geologists use the term fold. Folds are 
 usually described as either anticlines, 
 where the beds form an arch, or syn- 
 clines , where the beds form a trough 
 (fig. 13). Occasionally, minor folds may 
 be observed in the working place. These 
 usually result from the local movement of 
 the coal or associated rocks past each 
 other. The major folds found in coal 
 basins are generally so broad that an 
 entire mine would lie within only a small 
 portion of one. 
 
 Breaks in the rock strata are easily 
 observed. The geologist uses the general 
 term "fracture" to describe all breaks or 
 cracks. All fractures should be noted, 
 particularly their orientation, length, 
 and the distance between fractures having 
 the same or similar orientations. Some- 
 times the fractures have deposits in 
 them, and this should be noted (fig. 14). 
 
 There are several types of fractures 
 that have been given specific names be- 
 cause of their shape. The most common of 
 these is the joint. Joints are reason- 
 ably straight and smooth cracks in rock 
 along which there has been no movement. 
 Soft-coal miners are generally familiar 
 with cleat in coal. Cleat in coal is the 
 same as joint in rock. Where a crack or 
 group of cracks that look like coal cleat 
 is found in the roof or floor rock, the 
 term "joint" is used to describe them. 
 Figure 15 shows joints in roof rocks; 
 some material is in place, and some is 
 partially fallen. 
 
 Generally speaking, the cleats and 
 joints within a mine are consistent in 
 orientation or spacing. To verify this, 
 they should be measured at intervals 
 [about every 500 ft (152 m) ] . Should any 
 change be found in either orientation or 
 spacing, it should be noted and recorded 
 on the mine map. Experience has shown 
 that such changes are indicators of local 
 geologic disturbance and potential mining 
 problems . 
 
 Where there has been movement of the 
 rock or coal along a fracture, the result 
 may be a slickensided surface. Movement 
 of less than 1 in (2.54 cm) can create a 
 slickensided surface. These surfaces are 
 generally polished with either scratches 
 or grooves all in one direction 
 (fig. 16). Small slickensided surfaces 
 are usually curved (fig. 17), while 
 larger ones tend to be fairly planar 
 (fig. 18). The orientation of these sur- 
 faces should be measured and also the 
 direction of last movement. The direc- 
 tion of last movement can be determined 
 by rubbing the surface in the same direc- 
 tion as the grooves or scratches. One 
 direction will feel smoother than the 
 other. This smoother direction is the 
 direction in which the missing block of 
 rock last moved relative to the rock sur- 
 face being rubbed. 
 
 For practical purposes, three terms may 
 be used to describe a fracture where 
 the rocks and/or coal have moved — slick- 
 enside, slip, and fault. Slickenside 
 should be used where a slickensided sur- 
 face is observed but the amount of move- 
 ment cannot be determined. Slip should 
 be used where the feature is confined to 
 three or fewer entries. Fault should be 
 used where the feature can be traced 
 across a section or several entries. In 
 general, slips will exhibit smaller move- 
 ment than faults. 
 
 The description of a slip should in- 
 clude its orientation, the direction of 
 last movement, the amount of offset, and 
 the length it can be traced across the 
 mine workings. If only a small portion 
 [about 1 ft2 (0.29 m^)] of slip is ob- 
 served, then it would be better to call 
 this a slickenside. 
 
 The description of faults is more com- 
 plex. The orientation of the fault and 
 the direction and amount of movement must 
 be measured and recorded. Faults may 
 occur with one or more planes of movement 
 and with relative movements in opposite 
 directions. Where more than one plane of 
 movement is present, the proper term is 
 
11 
 
 Anticline Syncline 
 
 FIGURE 13. - Anticline and syncline. 
 
 FIGURE 14. - Mud-filled fractures in roof, sometimes called hill slips. 
 
12 
 
 FIGURE 15, - Joints in roof rock. 
 
 FIGURE 16. - Slickenside showing polishing and grooving. 
 
13 
 
 FIGURE 17. - Slickenside showing curved surface. 
 
 FIGURE 18. = Slickenside showing planar surface^ 
 
14 
 
 fault zone (fig. 19). The width of the 
 fault zone should be measured and its 
 orientation estimated. The offset of the 
 strata on either side of the zone should 
 be measured or estimated. 
 
 Faults may dip at any angle from per- 
 pendicular to parallel to bedding. At 
 the two extremes it is necessary to re- 
 cord direction of last movement or the 
 direction of the scratches or grooves in 
 the slickensided surfaces of the fault 
 planes. 
 
 Larger faults may not exhibit slicken- 
 sides but may have a zone of ground mate- 
 rial in them. This material comes from 
 the rocks and coals adjacent to the fault 
 that were crushed when the movement took 
 
 place along the fault. If present, this 
 material should be noted and its thick- 
 ness measured and recorded. 
 
 When recording faults on the mine map, 
 solid lines should be used only where the 
 fault crosses entries and has been ob- 
 served. Dotted or dashed lines can be 
 used where it crosses pillars or barri- 
 ers. Except for faults that parallel the 
 bedding, all faults have one side that is 
 higher than the other. This should be 
 noted on the mine map by placing a U (for 
 up side) on the side of the fault that is 
 higher or a D (for down side) on the side 
 of the fault that is lower. The dip of 
 the fault plane can then be recorded as 
 toward the high or low side. 
 
 ^^ ^ A- Fault zone 
 
 \A 
 
 ^\ 
 
 ^^. xSlip plane 
 
 
 " ^^(^'^'■f^''^:'^'-^^'^-'''''"^^^^^^^''^'^'^'^-'^^ 
 
 /'Cloy vein 
 
 yV^. ' ^jr'.■■V.^kV■- ' jy■^^ j ^i^>^!yj:'^^^ 
 
 mifim 
 
 ^Him^MM 
 
 
 Offset — 
 
 ^ Fault zone 
 crushed material 
 
 FIGURE 19. - Faults. 
 
 nn/pnnnnnnnc 
 
 nmnnnnnnnc 
 
 njnnnnnnnnc 
 
 DcJannnnnnnnE 
 
 ■\ 
 
 fZone is 20 to 40 ft wide 
 Fault Offset is 4 ft 
 
 < Dips 65° toward u 
 
 Slip offset is Iff, dips 45° toward 5 
 
 nDDnnnnc 
 nnnnnnE 
 nnnnnDL 
 
 DDDDDE 
 
 Vf Off set ranges from 
 ^ ,j I ft in entry I to 
 FaultiRft in entry 5 
 
 Clay vein~N 
 in roof • 
 
 /Clay vein 
 V in floor 
 
 w ■ • III ciiii J ^ 
 Dips 40° toward D 
 
 nnnnnnnc 
 
 nnnnnnnc 
 
 nnnnnnc 
 
 DDDDDE 
 
 Horizontal fault is 2 ft above 
 bottom, crushed zone is 4 in 
 thick. Clay vein shows offset 
 
 FIGURE 20. - Faults recorded on section mop. 
 Note faults rarely are perfectly straight. 
 
15 
 
 The fault sketches in figure 19 are ex- 
 posures in the outside rib of entry No. 1 
 of figure 20, which illustrates each of 
 
 these faults as they might be recorded on 
 a map of the section. 
 
 CLAY VEINS AND MUD-FILLED FRACTURES 
 
 Clay veins and mud-filled fractures 
 are found in several of the northern 
 Appalachian coalbeds. Increased methane 
 emissions and water 
 reported when these 
 penetrated by mining. 
 tures penetrate the coalbed from above, 
 unstable roof commonly occurs. Miners 
 
 inflows have been 
 
 features are first 
 
 Where these fea- 
 
 usually call any rock-filled fracture a 
 "clay vein" or "spar." These two fea- 
 tures differ markedly in shape and should 
 be recorded separately. The clay vein 
 (fig. 21) is typically "Christmas tree" 
 shaped with the coal-rock contact being 
 interf ingered. The mud-filled fracture 
 (fig. 22) is usually planar with the 
 coal-rock contact relatively smooth. 
 Where the two features occur together, 
 they should be measured and recorded 
 separately. 
 
 To describe either feature, its orien- 
 tation and thickness should be measured. 
 The length of penetration into the coal- 
 bed should be noted [for example, clay 
 vein from roof 36 in (0.9 m) into 48-in 
 (1.2-m) thick coalbed, strike 30° right, 
 dip 80° left, tapers from 12 in (0.3 m) 
 wide at roof line to zero] . 
 
 FIGURE 21. = Clay vein. 
 
 FIGURE 22, = Mud-filled fracture transecting 
 coalbed. 
 
16 
 
 SUMMARY 
 
 This report has been prepared to give a 
 nongeologist a means of recognizing, 
 describing, and recording potentially 
 hazardous geologic features commonly en- 
 countered in underground coal mining. 
 The major geologic features present in 
 coal mines in the northern Appalachian 
 Coal Basin that may pose ground control 
 hazards during mining are illustrated. 
 The report cannot possibly cover all geo- 
 logic features. If the user finds a fea- 
 ture that is not covered in this report, 
 he or she should describe and record what 
 is seen in as simple words as possible. 
 Very often a simple sketch with the 
 written description can be very helpful 
 in conveying to others what was observed. 
 
 Most mines have encountered one or more 
 of the illustrated features and have, 
 with varying degrees of success, mined 
 through them. No records are usually 
 
 kept when changes have been made in min- 
 ing method and/or roof support to cope 
 with such hazards. Then when similar 
 problems are encountered several years 
 later, the whole process of finding a 
 solution must be repeated. 
 
 If remedial methods are recorded along 
 with the geologic features on mine maps, 
 then, over the course of a mine's life, 
 these maps may be consulted as similar 
 features are encountered, and what did 
 not work in the past can be avoided. As 
 sufficient data are gathered, the mining 
 method and roof support can be tailored 
 to meet specific local conditions, there- 
 by saving both time and money while 
 safely and efficiently mining the coal. 
 In addition, the use of standard ter- 
 minology will allow the transfer of min- 
 ing experience from one area to another 
 with respect to specific features. 
 
 BIBLIOGRAPHY 
 
 1. Bates, R. L. , and J. A. Jackson. 
 Glossary of Geology, 2d ed. 1980, 
 749 pp. 
 
 2. Cox, R. M. Why Some Bolted Mine 
 Roofs Fail. Trans. AIME, v. 256, 1974, 
 pp. 167-171. 
 
 3. Headlee, A. J. W. Fracture Zones 
 in Mine Strata. Min. Cong. J., v. 30, 
 No. 4, April 1944, pp. 57-60. 
 
 Geological Survey, 4th Ser, Inf. Circ. 
 75, 1974, 17 pp. 
 
 6. Lahee, F. H. Field Geology. 
 McGraw-Hill Book Co., Inc., New York, 
 5th ed., 1952, 883 pp. 
 
 7. McCabe, K. W. , and W. Pascoe. 
 Sandstone Channels: Their Influence on 
 Roof Control in Coal Mines. MSHA IR 
 1096, 1978, 24 pp. 
 
 4. Kearns, E. G. , Jr. Clay Dikes in 
 the Pittsburgh Coal of Southwestern 
 Greene County, Pennsylvania. M.S. The- 
 sis, WV Univ., Morgantown, WV, 1970, 
 50 pp. 
 
 5. Kent, B. H. Geologic Causes and 
 Possible Prevention of Roof Fall in Room- 
 and-Pillar Coal Mines. Pennsylvania 
 
 8. Stahl, R. L. Guide to Geologic 
 Features Affecting Coal Mine Roof. MSHA 
 IR 1101, 1979, 18 pp. 
 
 9. Thrush, Paul W. (comp. and ed. by). 
 A Dictionary of Mining, Mineral, and Re- 
 lated Terms. BuMines SP 2-68, 1968, 
 1269 pp. 
 
 li-U.S. GOVERNMENT PRINTING OFFICE: 1983-605-015/09 
 
 INT.-BU.OF MIN ES,PGH.,P A. 20625 
 

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