ROOF STRATA OF THE HERRIN [NO. 61 COAL MEMBER IN MINES OF ILLINOIS: THEIR GEOLOGY AND STABILITY. Summary report. {JLA Sou^j *-3.

Transcription

1 5 {JLA Su^j *-3 ROOF STRATA ILLINOIS MINERALS NOTE 72 May 1979 OF THE HERRIN [NO. 61 COAL MEMBER IN MINES OF ILLINOIS: THEIR GEOLOGY AND STABILITY Summary reprt H.-F. Krausse, H. H. Damberger, W. J. Nelsn, S. R. Hunt, C. T. Ledvina, C. G. Trewrgy, and W. A. White ILLINOIS STATE GEOLOGICAL SURVEY Jack A. Simn, Chief Urbana, IL 61801

2 COVER: A cmpsite crss sectin f defrmatinal structures cmmn in Herrin (N. 6) Cal and rf strata. (Cmpare figures 18 and 19 and figures 33 and 34.) Krausse, Hans-Friedrich Rf strata f the Herrin (N. 6) Cal Member in mines f Illinis: their gelgy and stability: summary reprt/by H.-F. Krausse et al.-urbana: Illinis State Gelgical Survey, May p. illus. (Illinis-Gelgical Survey. Illinis Minerals Nte 72) Appendix. References: p Mine rfs- Illinis. 2. Cal mines and mining- Illinis. I. Title. II. Series. S 14.GS: Imn 72 ILLINOIS STATE GEOLOGICAL SURVEY

3 ROOF STRATA OF THE HERRIN (NO. 61 COAL MEMBER IN MINES OF ILLINOIS: THEIR GEOLOGY AND STABILITY Summary reprt H.-F. Krausse, H. H. Damberger, W. J. Nelsn, S. R. Hunt, C. T. Ledvina, C. G. Trewrgy, and W. A. White CONTENTS ABSTRACT 1 INTRODUCTION 1 The gelgic setting f the Illinis Basin Cal Field 1 Techniques emplyed 6 ROOF TYPES OF THE HERRIN (NO. 6) COAL MEMBER IN ILLINOIS 8 Gray shale rf types 9 Black shale-limestne rf types 21 MAPS AND EXPLANATION OF THE GEOLOGY IN SELECTED STUDY AREAS 31 OBSERVATIONS AND DISCUSSION OF ROOF FAILURE TRENDS 40 MATERIAL PROPERTIES AND DESIGN CRITERIA 40 CONCLUSIONS 41 Gelgic interpretatins 41 Recmmendatins 44 ACKNOWLEDGMENTS 45 APPENDIX 47 REFERENCES 54 Figures 1. Stratigraphic sectin f the Carbndale Frmatin 2 2. Gelgic structures f Illinis 3

4 7 3. Distributin f the Herrin (N. 6) Cal in Illinis 4 4. Schematic sectin f the interval between the Herrin (N. 6) Cal and the Piasa Limestne Member 5 5. Map shwing area cvered by cmputer mapping 7 6. Phtgraph f rf fall in planar-bedded sandstne f the Energy Shale Member H 7. Sketch f typical rll Phtgraph f a rll f medium-gray shale Phtgraph f a large siltstne-f illed rll Phtgraph f a rll in planar-bedded sandstne and siltstne Detail f figure Detail f figure Gelgic map f study area 4 ^ 14. Map f rlls and rf lithlgies in study area Map f shear bdy, rf lithlgies, and rf falls in study area Gelgic map f study area Phtgraph f lwer bundary f shear bdy in study area Detail f figure Phtgraph f rll truncated by shear planes in study area Phtgraph f micrfaulted shale and siltstne in shear bdy, study area Detail f figure Diagram f black shale-limestne rf sequence at mine A Map f rf lithlgies in study area Map f rf lithlgies in study area Map f rf lithlgies in study area Phtgraph f Breretn Limestne rf 27. Phtgraph f wedging relatinship f rck layers in black shale-limestne rf 28. Phtgraph f hrizns in Lawsn Shale Phtgraph f syneresis cracks in the Lawsn Shale Phtgraph f clay dike and clay-dike fault Detail f figure Phtgraph f cmplex clay dike in the Herrin (N. 6) Cal Diagram f clay-dike faults 34. Diagram f clay-dike faults frming a graben 35. Map f structural features in study area Map f structural features in study area Map f structural features in study area Cmputer-generated map f the tp f the Herrin (N. 6) Cal 35 in study areas 6 and Map f the thickness f the Anna Shale Member in Bnd and 36 Mntgmery Cunties 40. Map f the thickness f the Breretn Limestne Member 36 in Bnd and Mntgmery Cunties 41. Phtgraph f a majr clay-dike fault shwing false drag Map f rf lithlgies and rf falls in study area Diagram f rck strength f rf-pillar-flr materials 44. Diagram f the relatinship f rf lithlgy t cal tpgraphy 45. Interpretative sequence f rll frmatin A. Map f lithlgy and structural features in study area 1 48 B. Map f lithlgy and structural features in study area 2 50 C. Map f lithlgy and structural features in study area 3 52 J

5 ROOF STRATA OF THE HERRIN (NO. 6) THEIR GEOLOGY AND STABILITY COAL MEMBER IN MINES OF ILLINOIS: Summary reprt H.-F. Krausse, H. H. Damberger, W. J. Nelsn, S. R. Hunt, C. T. Ledvina, C. G. Trewrgy, and W. A. White ABSTRACT Rf failures in undergrund cal mines are related t the lithlgy and gelgic structure f the rf. There are tw distinct suites f rf rck abve the Herrin (N. 6) Cal in Illinis, and each has distinctive patterns f structure and rf failure. In black shale-limestne rf areas, rf instability is crrelated with thinning f limestne beds and presence f faults and clay dikes. In gray shale rf regins, the prime rf hazards are psed by rlls, shear bdies, and presence f cal r carbnaceus partings in the rf. Mst structural features examined are believed t have frmed during early stages f sediment diagenesis and cmpactin. Structural trends and lithlgic patterns are strngly interdependent fr this reasn. In many cases gelgic patterns are s cmplex and lcally variable that predictin f rf stability far in advance f mining is difficult. The need fr greater flexibility in rf cntrl planning is apparent. INTRODUCTION Every year rughly half the injuries in American cal mines are caused by falls f rf and rib. The gelgic cmpsitin f rf rck strata has an imprtant bearing n the stability f rf and rib, but the relatinship is prly understd. Therefre, the U.S. Bureau f Mines has supprted a number f studies n the influence f gelgic factrs n rf stability. The Illinis State Gelgical Survey has cllected data that applies t such research, but this study is mre systematic and intensive than any previusly attempted. The financial supprt f the U.S. Bureau f Mines (cntract n. H02A2017) between 1974 and 1976 allwed the research that is reprted here. Rf studies cntinue t receive high pririty in the Survey's cal-related prgrams. The Herrin (N. 6) Cal was the mst apprpriate fr this study because it prvides rughly 80 percent f the state's current cal prductin and almst half f the cal resurces f Illinis. Mst f this cal (85 t 90 percent) lies at depths greater than 150 feet (50 m) and can be recvered nly by undergrund mining. Objectives f this study were t find and describe the gelgic factrs that influence rf cnditins in undergrund mines. The primary methd f study was detailed mapping in mines, supplemented by reginal cmputer mapping using drill-hle data, clse-range phtgrammetry, physical testing f cre samples, and clay mineralgical investigatins f rf material. Over a perid f three years, a large vlume f data has been generated. The results have been reprted in tw vlumes that include a detailed accunt f the methd f study, the data gathered, and the cnclusins reached (Krausse et al., 1979). The summary presented here is intended fr general use f the majr findings and cnclusins. The gelgic setting f the Illinis Basin Cal Field The Illinis Basin Cal Field cvers mre than 65 percent f the state f Illinis, alng with adjacent prtins f suthwestern Indiana and western Kentucky. All cmmercial cal in the Illinis Basin Cal Field

6 . -2- ccurs in strata f the Pennsylvania!! System. In Illinis, 92 percent f the identified resurces lie in the Carbndale Frmatin (fig. 1). The Herrin (N. 6) Cal Member f the Carbndale Frmatin accunts fr 42 percent f the cal resurces and 80 percent f the current prductin in Illinis (Smith and Stall, 1975). The Herrin (N. 6) Cal subcrps arund the margin f the Illinis Basin Cal Field and attains a maximum depth f abut 1300 feet (abut 400 m) in the Fairfield Basin (fig. 2) in Wayne Cunty (Allgaier and Hpkins, 1975). The cal, dips gently tward the center f the basin and is essentially flat-lying thrugh mst f its range. Inclinatin rarely exceeds 1 t 2 percent except alng the La Salle Anticlinal Belt in eastern Illinis, the Du Quin Mncline, and the Cttage Grve Fault System in suthern Illin6is, where dips exceeding 15 degrees have been recrded. Figure 1 Energy Shle MEMBERS Danville (N 71 C Gaium Ls AMenby C Bnksln frk LS Anvil Rck Ss LOwSOn Sn Cnant Ls James'wn C Bfere'n Ls Ann Sh (N 6! C lnville Ss B'iar Hill (N 5A) C Cnln Sh Si David Ls Dykersburg Sh Harnsburg (N.5) C Cvei Hnver Ls E«ce" Sh Summum (N4) C Breezy HJI LS Rdhuse C Pieasantview Ss. Puringtn Sh Shwneetwn c Oak Grve Ls Mecca Quarry Sh Jke Creek Ss. Francis Creek Sh Cardiff C Clchester (N 2) C ISGS 1979 Stratigraphic sectirn f the Carbndale Frmatin, Kewanee Grup, shwing the psitins f the mst imprtant cals within the Pennsylvanian System in Illinis. (After W. H. Smith, 1975.) The Herrin (N. 6) Cal is the mst widespread cal in Illinis and exceeds a thickness f 60 inches (1.52 m) ver brad areas (fig. 3). The cal rank has been determined t be high-vlatile A, B, and C bituminus and has a sulfur cntent nrmally varying frm 3 t 5 percent. In the "Quality Circle" area f Franklin and Williamsn Cunties in suthern Illinis (fig. 3), a maximum cal thickness f abut 14 feet (4.3 m) has been reprted, and the sulfur cntent ranges frm less than 1 t 2 percent. Sme f this lw-sulfur cal is f the quality used fr manufacturing metallurgical cke in blends with higher-ranked cal. The general sequence f rcks verlying the Herrin (N. 6) Cal is shwn in figure 4. Althugh a wide variety f lithlgies and depsits f varius gelgic envirnments are represented, tw majr rf rck assemblages have been studied in detail. One is the gray shale rf type cmprising the Energy Shale

7 -3- m Fault, dwnthrwn side indicated Anticline Syncline y Mncline 40 mi 50 km Mississippi Embayment ISGS 1979 Figure 2. Gelgic structures f Illinis.

8 -4- Subcrp f ^ Walshville channel, cal missing * Anvil Rck Channel, cal missing Cal thickness in inches Cal erded Mapped area f gray shale rf Cal thin, split, r absent V Vm Undergrund mine Surface mine 40 mi 50 km Figure 3. Distributin f the Herrin (N. 6) Cal in Illinis.

9 -5- Farmingtn SK Piasa ],' Ls 1/ i /Danville (N. 7) Cal -rrr-^- Mdest Fm. f the McLeansbr Gr. Carbndale Fm. f the Kewanee Gr. Figure 4. Schematic sectin f the interval between the Herrin (N. 6) Cal Member and the Piasa Limestne Member. (After G. J. Allgaier, June 1974.) Member and the sandstnes, siltstnes, and shales in the Walshville channel (left side, fig. 4). The ther rf type is the black shale-limestne rf type, an assemblage including the Anna Shale Member and verlying units (right side, fig. 4). Distinctive lithlgic and structural assemblages and a variety f mining and rf cnditins are assciated with the tw majr rf rck types. The sediments f the Energy Shale assciated with the Walshville channel frm the gray shale rf type. They are believed t be depsits f a majr river system that existed cntempraneusly with peat accumulatin. In the Walshville channel itself, the Herrin (N. 6) Cal is absent. Alng the channel margins the cal is generally split. Flanking the channel, the cal is verlain by gray shale, siltstnes, and sandstnes f the Energy Shale Member. The Energy Shale attains a maximum thickness f abut 100 feet (30 m) and laterally decreases in thickness away frm the Walshville channel. Overlying the Energy Shale are marine strata f the black shale-limestne rf type, which tend t be lenticular r pinch ut as the Energy Shale thickens. Where the Energy Shale is absent, the black shale-limestne sequence frms the immediate cal rf. A clse interdependence exists between the sulfur cntent f the cal and the characteristics f verlying strata. Where the nnmarine Energy Shale is mre than abut 20 feet (6 m) thick, the cal has a relatively lw cntent f sulfur. This relatinship has been bserved in several areas and is particularly ntable in the "Quality Circle" area f suthern Illinis. It is suppsed that the Energy Shale represents crevasse-splay and verbank depsits frm the river that frmed the Walshville channel and that the

10 -6- depsits cvered the cal-frming plant material befre marine ingressin and prtected it against implacement f sulfur (Gluskter and Hpkins, 1970). The black shale-limestne rf type includes seven named stratigraphic rck members relevant t mine rf stability (fig. A). All are highly persistent reginally, but shw cnsiderable lcal variability. The lwest member is the Anna Shale Member, typically a black, carbnaceus, phsphatic, fissile shale, rarely exceeding 5 feet (1.5 m) in thickness. The Anna Shale is thught t represent depsitin in shallw lagnal envirnments. Overlying is the Breretn Limestne Member, a generally fine-grained, argillaceus, f ssilif erus rck representing mre pen marine cnditins. In suthwestern Illinis, its thickness may exceed 18 feet (5.5 m), but 4 t 5 feet (1.2 t 1.5 m) is mre cmmn. The Jamestwn Cal Member is thin but widespread in mst f Illinis, increasing t minable thickness in extreme eastern Illinis and western Indiana. Where the Jamestwn Cal is thin, the interval between the underlying and verlying members includes nt nly cal, but als a distinctive dark-gray carbnaceus shale cntaining ndules f chert and small lenses f medium-gray limestne, prbably f freshwater rigin. This interval is referred t as the "Jamestwn Cal interval" in this study. The verlying Cnant Limestne Member appears t be lithlgically similar t the Breretn Limestne; hwever, it is thinner, abut 6 feet (1.8 m) at maximum, but typically less than 1.5 feet (0.32 m). Next in sequence are the Lawsn Shale and the Anvil Rck Sandstne Members, highly hetergeneus facies equivalents. They include generally mttled, greenish shales and claystnes; lcally calcareus shale with marine fssils; firm, gray, silty shales; siltstnes; sandstnes; and, in places, cnglmerates. A well-develped channel system f the Anvil Rck Sandstne has been mapped in which underlying strata lcally including the Herrin (N. 6) Cal were erded. Channels filled by Anvil Rck Sandstne are shwn in figure 3. The highest stratigraphic member expsed in many rf falls f undergrund mines is the Bankstn Frk Limestne. Mst ften it cnsists f several benches f light-gray t buff, fine-grained, ndular limestne, interstratif ied with ne r mre bands r layers f mttled greenish shale r claystne. Its fauna f mainly brachipds and fusulinids demnstrates pen-marine envirnment f depsitin. Techniques emplyed A variety f techniques have been emplyed t analyze and describe the relatinship between gelgic cnditins and mine-rf stability, including: 1. Detailed gelgic mapping within selected study areas in undergrund mines 2. Reginal cmputer mapping using drill-hle data 3. Clse-range phtgrammetry

11 -7-4. Cre drilling in undergrund mines 5. Labratry testing f drill cres 6. Clay mineralgy studies The in-mine mapping was the mst significant and als mst timecnsuming wrk perfrmed in this study. Seven selected study areas in three undergrund cal mines were mapped in detail. The base maps, generally at a scale f 1:1200, were prvided by the mining cmpanies. Within each mapping area all accessible mine headings were walked, and all features were pltted directly n the base maps. The features mapped included all gelgic structures such as faults, jints, rlls, and clay dikes; the lithlgy f the immediate rf; the bserved sequence f rf strata; and the rf falls. Varius cmbinatin and cmpilatin maps were prepared frm the field maps. Reginal cmputer mapping was applied t 23 cunties where reserves f the Herrin (N. 6) Cal are significantly large (fig. 5). Data n thickness and elevatin were evaluated fr all rck units frm the Herrin (N. 6) Cal Herrin (N. 6) Cal subcrp line Cunty cmpilatin cmpleted 50 km Z3 40 mi Figure 5. Area in the suthern half f Illinis fr which data n thickness and facies f rf strata abve the Herrin (N. 6) Cal extending up t the Piasa Limestne were cllected and cmpiled in cmputer-prcessible frm.

12 thrugh the Piasa Limestne Member (fig. 4), using thusands f cre descriptins, drillers' lgs, and gephysical lgs frm the drill-hle recrd library at the Illinis State Gelgical Survey (ISGS). An average f abut ne hle fr each tw square miles was used. The maps were cmputer-generated using GEOMAPS, a prgram package develped by the Illinis State Gelgical Survey frm ILLIMAP (Swann, et al., 1970), and STAMPEDE (IBM Crp., 1968). Maps generated include structural cntur maps f the tp r base f the cal, maps shwing thicknesses f the significant rf rck units, and maps shwing thicknesses f particular rck intervals f specific interest fr the study, such as the interval frm the tp f the cal t the base f the first cmpetent limestne bed. In additin, the cmputer was emplyed t prduce structural cntur maps f cal seams at the mines selected fr detailed mapping. A clse-range phtgrammetric technique was develped t cllect infrmatin n rientatin f cleats, jints, and shear planes in areas that were t steep r dangerus fr direct apprach and measurements. It was als used t map an advancing strip-mine highwall t btain a three-dimensinal picture f the shape f rf rck bdies. (Details n phtgrammetry are presented in vlume 2 f Krausse et al., 1979, and in Brandw et al., 1975). A limited amunt f cre in undergrund mines was drilled t btain fresh samples fr testing uncnfined cmpressive strength and Yung's mdulus. A ttal f six cres were taken: three f rf rck, ne hrizntal cre f cal, and tw hrizntal cres f a large sandstne rll. A variety f mechanical, ptical, chemical, radigraphical, and x-ray diffractin analyses were perfrmed fr clay-mineralgy studies f rf and flr shales. Rck prperties tested included grain and particle size, clay mineralgy, Atterberg limits, slake durability, rientatin f clay minerals, texture, and internal structure. Details are presented in vlume 2 f Krausse et al., ROOF TYPES OF THE HERRIN (NO. 6) COAL MEMBER IN ILLINOIS Tw majr rf types verlie the Herrin (N. 6) Cal in Illinis. The gray shale rf type cmprises primarily gray, nnmarine sandstnes, siltstnes, and shales f the Energy Shale Member. The black shale-limestne rf type includes bth marine and nnmarine depsits f the Anna Shale and verlying stratigraphic units. A third type is transitinal, having cmpnents f bth gray shale and black shale-limestne rf types. Fr this investigatin, we designated study areas 1 thrugh 3 (in mine A) under black shale-limestne rf and study areas 4 and 5 (in mine B) and 6 and 7 (in mine C) under gray shale rf fr detailed examinatin and mapping. N transitinal rf areas were mapped r studied clsely. The gray shale rf type and the black shale-limestne rf type are distinct lithlgically and each cntains unique and distinctive structural defrmatin features. These assciatins between structure and lithlgy lead t specific patterns f mine rf stability fr each rf type.

13 : Gray shale rf types and Three distinct dminant facies f the Energy Shale were recgnized mapped 1. Dark-gray shale facies (at base) 2. Medium-gray shale facies 3. Planar-bedded siltstne and sandstne The dark-gray shale facies is the lwest stratigraphically, frming the immediate rf in large areas f mine B. Its thickness ranges frm zer t five feet (0 t 1.5 m) and is mst cmmnly less than tw feet (0.6 m) thick. It is cnfrmably verlain by medium-gray shale. The dark-gray shale ranges frm medium-dark gray t almst black; its dark clr results frm abundant, finely dispersed, carbnaceus debris. It is hard, smth, and generally narrwly laminated. The presence f fssils, including small pectinid pelecypds and Anthracsiidae, indicates a depsit in fresh t brackish water, Jinting in the dark-gray shale generally is much mre regular and clsely spaced than in the ther Energy Shale facies. The dark-gray shale is variable with regard t rf stability. Over wide areas it is stable, but in sme places, where it acts as a "draw slate," rf falls can ccur, particularly where the shale is thick. Medium-gray shale is the dminant facies f the Energy Shale. It verlies the dark-gray shale in mine B and frms the immediate rf in much f mine C. Medium-gray shale may attain thicknesses f 50 feet (15 m) r mre. It cntains much less carbnaceus material than the dark gray shale, and laminatins and jints are distinctive r absent. In sme places mica and plant debris cating the bedding planes permit the mine rf t separate in layers and t break in large slabs, but elsewhere the rck is a massive mudstne that frms a stable rf, except where structural anmalies r defrmatinal features are present. The medium-gray shale is susceptible t misture slaking, and ver lng perids f time large falls may develp, althugh the shale generally is stable. The medium-gray shale may grade bth laterally and vertically int silty shale, siltstne, and sandstne; hwever, the planar-bedded siltstne and sandstne mapped in mine C is a distinct facies that was depsited adjacent t the Walshville channel. It verlies the medium-gray shale with a sharp, apparently uncnfrmable cntact, and in part f the study area the shale is absent and sandstne rests directly n the cal. The planar-bedded siltstne and sandstne is marked by clsely spaced regular partings f carse mica and carbnaceus plant debris n bedding surfaces. The rck easily splits and separates alng thse partings, and spectacular rf falls are cmmn (fig. 6). In additin, the sandstne may cntain water, which weakens the underlying medium-gray shale and prmtes mre falls; the seepage r flw f water int mining areas causes serius prblems. Any f the Energy Shale facies described may be underlain by a basal carbnaceus layer cntaining abundant calified plant debris, including sme that may be hazardus t miners, such as fssilized tree stumps, whse cres may fall ut f the rf. The entire basal layer is generally unstable, but is thin enugh (less than a ft) t be relatively unimprtant t verall rf stability.

14 -10- Rlls, prtrusins f rf material int cal, are the mst typical and widespread structural features f cal and rf in areas where the gray shale verlies the cal. Mst rlls are elngate, linear features shaped rughly like ftballs in crss sectin (fig. 7). The length f rlls may reach several hundred feet, the width ranges frm a few inches t abut a hundred feet, and thickness ranges frm a few inches t the height f the cal seam. Mst rlls bserved in ur studies are asymmetrical and have a blunt "te" alng which a splayed-ut cal "rider" curves upward int the rf. At the "tail" end f the rll, cal riders are prly develped, but large slickensided cmpactinal faults are cmmn. The cmbinatin f cal riders and faults seriusly weakens the rf abve the main bdy f the rll, which may break dwn as sn as it is undermined. Rlls are abvndant in areas f medium-gray shale and planar-bedded siltstne and sandstne rf, but they are small and rare where dark-gray shale frms the immediate rf. The lithlgic material f the rll is usually the same as the material frming the rf abve the rll. The interir bedding f the rll cmmnly is distrted, especially at and near the "te" f the rll. The rlls in figures 8 thrugh 12 are typical. Rlls at mine B tend t strike parallel with bundaries between mediumgray shale and dark-gray shale (figs ). A pattern f sandstne rlls in mine C is less apparent, but there is a general trend fr rlls t strike parallel t the edge f the sandstne rf area (fig. 16). The internal structure and mapped distributin and rientatin f rlls suggest that they are lad structures that frmed as slump features in which sft sediments squeezed int the upper layers f the cal-frming material. N indicatins f cal ersin have been fund that indicate the rlls riginated as in-filled stream channels. Slips and small faults nt assciated with rlls are cmmn thrughut the mapped areas in the gray shale rf type. The maximum displacement alng these small faults is tw t three feet (0.6 t 0.9 m), but cmmnly it is much less. Generally, small faults die ut within the cal seam, and rarely d they extend far int the rf strata. Their rientatin may be rughly parallel t bundaries f facies-changes, but in cntrast t thse in the black shale rf type, many f the slips and small faults in the gray shale rf type shw n preferred rientatin. All indicatins are that these slips resulted frm differential cmpactin f the sediments. Slips and small faults lcally may be a rf hazard, especially where tw r mre intersect abve the cal seam. A large bdy f pervasively sheared rf rck was encuntered in study area 5, mine B (fig. 15). This rck bdy, herein termed a "shear bdy," is mre than 2500 feet (760 m) lng, 200 t 300 feet (60 t 90 m) wide, and at least 30 feet (9 m) thick. It is irregular in utline, trending rughly east and west thrugh the study area. The lwer bundary is a series f shear planes (figs. 17, 18) that are almst parallel t bedding and lie n r clse t the tp f the cal in the heart f the shear bdy. They curve upward int the rf alng its margins. The cal and rck belw the shear bdy are almst undefrmed. The frmatin f the shear bdy pstdates frmatin f rlls, as indicated by truncatin f the tps f rlls by the shear bdy (fig. 19).

15 -11- Figure 6. Rf fall in planar-bedded sandstne f the Energy Shale Member. Bedding surfaces are cated with mica and calified plant fragments. N prminent jints are visible. Sandstne failed and brke almst straight up alng the pillar rib. Lcatin: "Quality Circle," near Walshville channel, mine C. Splayed cal stringers Bdy (shwing almst cncentric bedding) Frnt cal "rider" ver te Pstsedimentary "flw" f clastic material (mass mvement) Te with recumbent sft sediment flds " Nrmal fault (extensinal and cmpactinal) Tail with small tail cal "rider" and extensin fault Figure 7. Sketch f typical rll (sft-sediment prtrusin f clastic materials int surrunding sediments cal, shales, siltstnes, and sandstnes).

16 -12- Figure 8. Rll f medium-gray shale f the Energy Shale Member intruded int tp layers f the Herrin (N. 6) Cal. Te (at the left) splits flded cal strata int several stringers. Tail has been truncated by cmpactinal nrmal fault (at the right). The rd is abut 4 feet (1.2 m) lng. Lcatin: "Quality Circle." Figure 9. Large rll (10 feet [3 m] wide) f siltstne material. The te f the rll displays slight sft-sediment defrmatin. Cal "rider" extends ver tw-thirds f the rll. Lcatin: "Quality Circle," suthern Illinis, mine C.

17 -13- Figure 10. Rll in planar-bedded siltstne and sandstne f the Energy Shale Member. Near the te f the rll (arrw), recumbent sftsediment flds and lwangle shear planes are visible. These features suggest that the silt and sand filling the rll intruded frm right t left between the layers f peat. (Nte the cal "rider" riginating at the te and extending almst entirely ver the rll.) The large lw-angle slips at the tail f the rlls may have frmed later by j differential cmpactin. Detail f figure 10. Figure 12.

18 . 14- D E.... F, G, _ > Medium-gray shale Rll 1 M «if. v.. ' ' ^a^^^" Minr fault, less than ne ft displacement f tp f cal.a Jints ' > <s? Cncretins 4HH Majr rf fall S> Minr rf fall 1 x I j.r Kink zne in rf strata i I Rib rashing :.* Timber prps i I H. 1 ^Q"a - /A :. ' ;;; "#*% e-. Figure 13. Lithlgy, structural features, and rf falls f the Hernn (N. 6) Cal and its immediate rf rcks in study area 4, mine B. The immediate rf strata are Energy Shale, lwer prtin (nt stippled) dark-gray shale and upper prtin (stippled) medium-gray shale. The majrity f rlls and faults ccur in medium-gray shale, whereas all but ne f the rf falls and ther features f instability (e.g., kink znes and rib rashing) are distributed in areas f dark-gray shale. Jinting is als much mre prminent in the well-bedded dark-gray shale. Grid interval is 200 feet (61 m).

19 Majr rf fall Minr rf fall Kink zne in rf Rib rashing Crib Timber prps Well-bedded dark-gray shale, lwer prtin f Energy Shale Prly bedded medium-gray shale, upper prtin f Energy Shale Bundary between rck units ^-^^-^^ Shear plane high angle (minr fault) LLLLLLi- Shear plane lw angle (minr fault) -*--~-~-- Clay dike -rrntt a" Symmetrical rll - 1 > I \ IS Asymmetrical rll (tail at pen end f semicircle) Figure 14. Distributin f sft-sediment rlls with assciated minr faults in relatin t the lithlgy f the immediate rf and rf falls f Herrin (N. 6) Cal in study area 5, mine B. The map displays the clse interdependence f sft-sediment structural features, mainly rlls and slips, with the distributin and lateral bundaries f the Energy Shale rf strata. Althugh the immediate rf in areas f medium-gray shale with rlls and slips cmmnly is very rugh and irregular, the rf falls are mre abundant in areas f dark-gray shale. Rf falls in areas f medium-gray shale ccur mainly within the shear bdy. Grid interval is 200 feet (61 m).

20 x * $- / -16- i> ^- *^.' / / X / \ ** \ Jfr ^ \ Majr rf fall Minr rf fall Kink zne in rf Rib rashing Crib Timber prps mi±u-l±±m±> Well-bedded dark-gray shale, lwer prtin f Energy Shale Prly bedded medium-gray shale, upper prtin f Energy Shale Bundary between rck units Bundary f shear bdy Fault and shear plane high angle ii\jj_lll y \iy \M A^I- Fault and shear plane lw angle Multiple m aj '' shear planes within shearbdy Intensely sheared area with dense spacing f numerus small shear planes Directin f striatins Figure 15. Outline and majr shear structures f the shear bdy in study area 5, mine B. Rf falls have ccurred mst ften in the area f the shear bdy and t a lesser degree under dark-gray shale, in the immediate vicinity f the shear bdy. Defrmatinal features lder than the shear bdy have nt been drawn n this map, but can be cmpared in their interrelatinship t lithlgic differences in figure 14. The shear bdy is nt restricted t a particular lithlgy but affects dark-gray shale and medium-gray shale and, lcally, the tp f the Herrin (N. 6) Cal as well. Grid interval is 200 feet (61 m).

21 l J A B D l 8 T T 8 i ^T V N I ' / f ~\ ( ( J ^ T Vs.V -^ «P 8 )k> ^ DRY, /i \ /-, T ( \ r "\ # >*.? \ A^tH --^' 4 ~~\V^± 8reht>i«n 3 TV-*' / ' '-<mt#i j L Rib rashing n/w/wv Flr heaving X\\>.V»,^>w>X Kink zne in rf Timber prps T Tp cal '*m m # # # Cribs ""^ Small fault *. s. 4 Sh Sandstne rf f the Energy Shale Gray shale rf f the Energy Shale (thickness in feet) B -*- Bedding, strike, and dip directin indicated ' ^TTngl symmetrical rll j \ ( \ l\~ Asymmetrical rll (tail at pen end f semicircle) ^, " "" Bundary between wet and dry rf T T T D ISGS 1879 Figure 16. Lithlgy, rlls, and fault structures f the Herrin (N. 6) Cal and its immediate rf strata and the distributin f rf falls, ther induced instabilities, and additinal rf supprt (timber and cribs) in the area belw siltstne and sandstne with water seepage (wet). Study area 7, mine C. Grid interval is 200 feet (61 m).

22 -18- Figure 17. Almst undisturbed Herrin (N. 6) Cal and sme beds f finely laminated silty shale truncated by a nrthward-dipping (t the left) set f majr shear surfaces and verlain by the shear bdy. Lcatin: suthern Illinis, "Quality Circle," study area 5, mine B. Figure 18. Detail f figure 1 7 majr shear surfaces, a set f very lw-angle nrmal faults brdering the shear bdy (light rck, upper part f pht) and truncating finely laminated shale belw. Nte the assciated drag flds (sft-sediment flds abve cmpass) within the shear zne.

23 -19- Within the shear bdy, a peculiar def rmatlnal facies f rck has develped. The dminant lithlgy is sft, greenish claystne r altered shale having highly cntrted bedding, intensely sheared. Als fund are blcks and layers f finely laminated, micrfaulted siltstne r sandstne (figs. 20, 21), brecciated dark-gray shale with siderite, and blcks f bny cal. Nthing similar has been fund in any ther study area. This defrmatinal facies is penetrated by a great number f hrizntal t gently dipping slickensided shear surfaces. Rf failures in the shear bdy are abundant. As shwn in figure 15, many rf falls have develped in the shear bdy and alng its margins. The average height f falls is 15 t 20 feet (4^ t 6m). Entries essential fr haulage, air, and travel culd be kept pen nly by additinal supprt such as massive cribbing and steel beams. Rf blts did nt sufficiently anchr in the intensively sheared rck, and failed. Althugh this is the first shear bdy ever t be described in strata abve the Herrin (N. 6) Cal, there is n reasn t assume it is unique. Its rigin is believed t be the result f gravitatinal sliding. Similar features have been described fr ther regins (Ptter, 1957, and Vigt, 1969). Significant jinting is encuntered nly in the dark-gray shale facies at mine B. The jints strike N 60 t 80 E and generally penetrate less than ne ft vertically int the rf. Their spacing is generally abut five t ten jints per ft. These jints may cntribute t slabbing f the immediate rf, but generally d nt cause majr rf falls. Figure 19. Nearly hrizntal shear zne f a set f shear surfaces enclsing dragged, flded, and sheared dark-gray shale; main shear mvement f each upper shear bed is tward the left and has truncated the tp f a majr rll f silty mediumgray shale. This indicates that frmatin f shear bdy cntinues after r even pstdates frmatin f rlls; hwever, small lw-angle antithetic faults truncate shear zne f dark-gray shale and remnant f rlls, s these pstdate bth rl and shear zne. Sectin frm bttm f pht t tp: (A) cal slightly defrmed by fault in rll (left side f pht), (B) laminated silty shale within the rll, (C) flded, sheared, and intensively cntrted dark-gray shale in shear zne, and (D) greenish claystne f main shear bdy. Scale: hles in aluminum frame are ne ft (30.5 cm) apart. Lcatin: suthern Illinis, "Quality Circle," study area 5, mine B.

24 -20- Figure 20. Micrfaulted laminated silty shale and siltstne. Lw-angle and high-angle shear planes are adjacent and are f a single defrmatinal actin.the micrfault pattern resembles the lwer prtin f seismites described by Seilacher (1969). dwnward, and each lwer prtin has mved laterally tward the suth (left in pht). Mass mvement in general is Majr shear plane is subparallel t bedding just abve cal. Cal itself is affected nly at extreme tp. Lcatin: suthern Illinis, "Quality Circle," study area 5, mine B. Figure 21. Detail f figure 20.

25 -21- In study area 4, mine B (fig. 13) rf falls and kink znes have a strng tendency t extend in a nrth-suth directin. (Kink znes are narrw znes f cmpressinal cracking and sagging which develp in the immediate rf after mining.) The cause f this nrth-suth weakness is nt knwn, but it shuld be nted that it trends parallel with the Rend Lake Fault System that passes abut 1000 feet (300 m) west f the study area. Black shale-limestne rf types Three areas having the black shale-limestne rf type were mapped in mine A. This rf type was als examined in less detail at several ther surface and undergrund mines. The gelgic and rf cntrl prblems in the black shale-limestne rf type differ cnsiderably frm thse fund in gray shale rf. The generalized rf rck sequence at mine A is shwn in figure 22. The lwest stratigraphic member is the Anna Shale, which reaches a maximum thickness f five feet (1.5 m) and is usually tw t three feet (0.6 t 0.9 m) thick; hwever, the Anna Shale may be absent lcally. Thickness ft m X Underclay X A Bankstn Frk Limestne; upper r mam bench B Shale parting in the Bankstn Frk Limestne C Bankstn Frk Limestne; lwer benches D Calcareus cncretins in the Lawsn Shale E Lawsn Shale; upper greenish, light-gray, and lwer medium-gray t medium-dark-gray shale F Cnant Limestne; calcareus t dlmitic cncretins G Jamestwn Cal; generally dark carbnaceus shales and irregular ndular and lenticular limastne between tw thin layers f cal "Jamestwn Cal interval" (dark carbnaceus shales and ndular and lenticular limestne) Breretn Limestne; cmmnly has limy "cld" at the base Anna Shale; upper part prly bedded, nnfissile prtin layered with phsphatic ndules Calcareus and pyritic cncretins in the Anna Shale Anna Shale; lwer part well-bedded, fissile, abundantly well jinted, "slaty" prtin i-'-s Herrin (N. 6) Cal ISGS 1979 Figure 22. Black shale limestne rf; sequence f rck stratigraphic members at mine A.

26 Tw distinct subunits f the Anna Shale have been recgnized at mine A. The lwer subunit is black, hard, fissile, "slaty" shale, significantly well jinted and cntaining large spheridal cncretins. The upper subunit cnsists f a prly bedded, mttled, weak shale cntaining tw persistent thin bands f phsphatic ndules. Where the Anna Shale is less than ne ft (0.3 m) thick, the entire member is fissile. Where the Anna Shale is mre than ne ft thick, it shws bth subunits in mst cases. The Anna Shale generally is a firm rf material, althugh the lwer layers tend t slab alng jint planes. Cncretins pse a lcal hazard that can be cuntered by pulling them dwn r blting thrugh them. Lcal rf falls t the base f the verlying limestne ccur where the upper mttled subunit is nt strng enugh t be self-supprting; hwever, large rf falls in the Anna Shale d nt result frm its lithlgic cmpsitin alne, but are related t slips, minr faults, and densely spaced jints that penetrate the entire Anna Shale and add t ther structural weaknesses. Overlying the Anna Shale, r frming the immediate rf where the Anna Shale is absent, is the Breretn Limestne. This member is the key t rf stability at mine A. Where it frms the immediate rf, it is five t mre than ten feet (1.5 t >3 m) thick, and rf falls are practically unknwn (figs ). The basal "cld" layer, cnsisting f a few inches f calcareus shale, tends t crumble away between header bards, but is nly a minr hazard in the mines studied (fig. 26). As the Anna Shale thickens beneath the Breretn Limestne, the limestne thins and at many places pinches ut (fig. 27). The limestne was nt bserved t fail where mre than tw feet (>0.6 m) thick, but rf falls are cmmn where the limestne is less than tw feet thick, and slips r ther defrmatinal structures weakened the chesiveness. The "Jamestwn Cal interval" at mine A ranges in thickness frm a few inches t a little mre than a ft (>0.3 m) and includes carbnaceus shale, lenticular limestne, and thin layers f cal. It is an interval f the rf prne t fail withut the supprt f the underlying Breretn Limestne, but where it is underlain by tw r mre feet (>0.6 m) f limestne, rf stability is satisfactry. In small areas (figs. 24 and 25), all lwer units are absent and the "Jamestwn Cal interval" directly verlies the Herrin (N. 6) Cal. Majr rf falls are abundant in these areas because f the absence f cmpetent strata clse t the cal (fig. 28) The Cnant Limestne abve the Jamestwn Cal interval is the mst persistent rf rck member at mine A and maintains a thickness f abut ne ft thrughut the study areas. It is neither thick enugh nr strng enugh t prevent rf failure where the Breretn Limestne is absent, hwever. The Cnant Limestne is nt knwn t frm the immediate rf within the mapped areas. Overlying the Cnant Limestne is the Lawsn Shale, a very weak member f the rf sequence at mine A. This member, tw t fifteen feet (0.6 t 4.6 m) thick, cnsists mainly f weak, prly bedded, mttled, greenish shale with abundant slickensided surfaces. Where the Lawsn Shale is thick, tw subunits can be distinguished: a lwer, mderately firm, dark-gray shale, lcally calcareus, and an upper mttled shale. Where the Lawsn Shale is expsed by failure f underlying strata, massive falls extending thrugh the Lawsn Shale t the base f the Bankstn Frk Limestne may

27 J B X \ \ v.x \ -23- U -r; -v- \ / I \ I I \ \ \ < - --> n ^ * \ \ \ ^ ^k>< \ ^ \ I V. \v -*epfe-.v.v :::.-..: ''\, \ y \ f ^c^ x mwm v\ XX ' XX r vv,iii f/ll J \\v.v tx i m % / 4 A r\ \ I / \ 1\ v I \ V;V;'.. ; \\\. ::Vi::-.::V.v:i Breretn Limestne i,x\ :M\ ^ wjk\ M ;^r Ispachs f Anna Shale; numbers indicate thickness in feet 4HNfr Majr rf falls ^ 25 Minr rf falls V \ +***\ < w m \ >> Kink zne in rf > v^ii ^ Rib rashing # * * Crib Timber prps rv/ " vx X/ Flr heave Figure 23. A B F Distributin f rf falls and their relatin t the immediate rt strata. N rf falls ccur where Breretn Limestne directly verlies the Herrin (N. 6) Cal, althugh sme shallw flaking f "cld" may ccur lcally. Study area 1, mine A, west-central Illinis. Grid interval is 200 feet (61 m). T F G

28 ' ' I -24- _l_ B ^ i ^ Majr rf falls Breretn Limestne 12 Minr rf falls Kink zne in rf "Jamestwn Cal interval" fri ill 12 Rib rashmg Crib Timber prps Flr heave 10 - Ispachs f Anna Shale; numbers indicate thickness m feet ;, $f -5 (M \\ 10 // '.KA 3. n <-* Mill? : / 1 '<N < \ Pill. K» I / Wm / Np ) mmi \\*,\ ^^S!^:l:?j^^^jvjji L4&SV /fc: '-'. /,' '""1 * " ' \ \\ '' - -' ^ 1 '>;, rv ' ' ' ' Ifcil -(4 #4-> 4:.: - \^/ / '-'::: ' Figure 24. Distributin f rf falls and their relatin t the immediate rf strata. N rf falls ccur where Breretn Limestne directly verlies the Herrin (N. 6) Cal, althugh sme shallw flaking f "cld" may ccur lcally. Study area 2, mine A, west -central Illinis. Grid interval is 200 feet (61 m).

29 :. ml -25-1, i-_!,'""-m V^N\: ; L ir\ n ' ' t t > i / r\ N ib>-\vl \ w "?.-.,... -v--- ' * A ^i \ a; J* ra i c jr c < T3C r tr <) c -C S a> a s 0) 3 c O d T3 CO : - XM f * JfwE?' a; E \nssi :> 2 «a «P.,i c -I S P! ^> ISN '\S ** :::::: : :-..y.:: ;-. :. ;' //^ ' I.:-.-::y.----i< ^ y' I r "" c y (0 < \ \;. V -. 1 V ;V iv.-.v; :,. 03 0) ^ E 00 a hi d> CD ra a > a: n t 3 E CO Q O U. y <* fr '>*<:.':; k y y /r:-:-:-f ::.'.::: :: X \ C >^ c 5 \ \ ' ' : \4Z~~~*. ' : u t

30 -26- Figure 26. Limestne f the Breretn frms stable rf. Abut the lwest 3 inches (7 t 10 cm) f sft flaky "cld" have fallen, except abve the header bards. Lcatin: mine A, west-central Illinis. Figure 27. Wedging relatinship f rf rck layers; bth the Anna Shale and the Breretn Limestne pinch ut (tward left side f pht). The "Jamestwn Cal interval" has thin cal streaks and cntributes t bedding separatin. The verlying Cnant Limestne is t thin t bridge stresses frm ne pillar t the next. The Lawsn Shale is sft and mttled and cntains numerus lw-angle shear planes and syneresis cracks. Lcatin: mine A, west-central Illinis.

31 -27- ccur (figs. 28, 29). In very few falls the Bankstn Frk Limestne als has failed, expsing even higher strata. The distributin f rf rck bdies at mine A is irregular and variable (figs ). The Anna Shale is laid ut in a patchy pattern f irregular lenses, mst f which are several hundred feet in diameter. N preferred rientatin f these lenses is apparent. The Breretn Limestne frms the immediate rf in rather narrw belts r trughs between the lenses. Rf rck units belw the Bankstn Frk Limestne shw a reciprcal relatinship in thickness; where ne unit increases in thickness the ther units f the sequence thin (fig. 22). Lwest rf stability ccurs where the Anna Shale and the Lawsn Shale are thick and the Breretn Limestne is thin. Defrmatinal structures bserved in the black shale-limestne rf type differ cnsiderably frm thse fund in mines with the gray shale rf type. The characteristic structural feature f mine A is the clay dike. Damberger (1970 and 1973) has given a general descriptin f clay dikes in Illinis. This study has yielded many mre details that may be fund in vlume 2 f Krausse et al., Clay dikes are irregular intrusins f clay frm the rf int the cal seam (figs ). Their inclinatin varies frm rughly vertical t lw angle, and they range frm a mere film f clay alng a minr fault t majr "hrsebacks" several feet wide. The larger dikes cnnect with the rf, althugh they seldm extend mre than a ft r s int it. Only the larger dikes penetrate the entire cal seam t the underclay. The filling f clay dikes cnsists f sft, usually light-gray clay r silty clay with fragments f cal and rf rcks included in the matrix. The filling was bviusly intruded frm abve, but the filling bears little resemblance t the rf shales because f its alteratin; hwever, the clay minpralcgical cntent f clay-dike filling is much clser t that f the rf shale than tc that f the underclay (Stepusin, persnal cmmunicatin, 1978). Directly related t clay dikes are minr faults we have termed claydike faults (figs. 33, 34). These are usually lw-angle nrmal faults that lack clay filling but shw assciated secndary defrmatinal features in the cal and rf strata which are typical fr clay dikes, specifically: 1. The fault plane is generally shallw in the rf and the tp prtin f the cal. It steepens dwnward thrugh the cal and cmmnly dissipates within the cal in a series f near-vertical extensin fractures that are generally mineralized and frm an en echeln pattern ("gat beards"). 2. "False drag," in which the cal layers curve upward in the ftwall and dwnward in the hanging wall, that is, ppsite t the directin f nrmal drag, is abundant (fig. 34). As a result, bedding adjacent t the fault plane tends t be perpendicular t the fault plane. 3. Cnvergence f cal bedding at the ends f lateral fracture fillings (fig. 33).

32 -28- Bankstn Frk Limestne Greenish mttled upper part nt f i Shale Lawsn Very dark gray, Shale l t Lawsn Herr -n (N. 6) 6~ar ~ - Figure 28. Lawsn Shale. Tw distinct hrizns can be mapped: a lwer part that cnsists f very dark gray t almst black sh, that is very calcareus in places and cntains cncretins (left side f pht) and an upper part that cnsists f abun dantly mttled sft greenish medium-gray shale having numerus syneresis cracks. Lcatin: mine A, west-centra Illinis. Figure 29. Mttled shale with syneresis cracks in greenish medium-gray shale, abve very dark gray shale, prbably Lawsn Sh, (with syneresis cracks) abve Anna Shale. Nte rf blts hang ut bare; the sft shales have fallen because f mis slaking; in the center f rf fall, even blt anchrs have fallen ut. Lcatin: a mine in east-central Illinis.

33 -29- Figure 30. Clay dike and clay-dike fault in Herrin (N. 6) Cal. Angular fragments f unaltered and altered black shale frm the rf and f cal in the clay matrix demnstrate the brittle behavir f the material during defrmatin. Synthetic and antithetic minr faults are displayed. Nte als the plastic behavir f cal, particularly at the end f the small clay intrusin upward, in the upper ftwall blck. Displayed there is a cnvergence structure f the cal laminae. Lcatin: mine A, west-central Illinis. Figure 31. Detail f figure 30.

34 -30- -fuj?«s Figure 32. Cmplex clay dike in the Herrin (N. 6) Cal. Rf is Breretn Limestne, which is displaced dwnward t the east. Fusain layer in the center f the cal seam is bent dwnward east f clay dike, fractured within the clay dike, and ffset immediately west f the dike. Nte the assciated small lw-angle clay-dike faults and the numerus extensin fractures ("gat beards") and the cal fragments in the clay matrix. ^ Lawsn Shale Cnani Umeslne - r : " ' '"" Cal interval" l8»-r8l' Figure 33. Clay-dike faults dissecting the Herrin (N. 6) Cal and assciated rck strata. The faults result nt frm vertical mvements, but mainly frm hrizntal extensin f the strata, as indicated by cllapsed grabenlike structures in the upper cal benches and rebund hrstlike structures in the underclay and lwest cal benches. Nte the cnvergence f the cal bedding in places, the en echeln extensin fractures ("gat beards") and the splitting and dwnward steepening f the faults in the cal seam. Lcatin: mine A, westcentral Illinis. Figure 34. Clay-dike faults frming graben at the tp (nte the intensely sheared gray shale) and a hrst at the bttm f the Herrin (N. 6) Cal. Lw-angle nrmal faults in shales abve the cal steepen dwnward int the cal and dissipate in the frm f en echeln extensin fractures ("gat beards"). Farther dwn in the cal seam, faults als frm an en echeln pattern and prduce a step-faulted hrst. Nte cnvergence features f cal beds (upper left area) and false drag. Ttal defrmatin is due mainly t hrizntal extensin with little r n vertical thrw f strata. Lcatin: a mine in west-central Illinis.

35 Clay-dike faults usually strike parallel t lithlgic bundaries in the immediate rf and dip tward the rck bdies in which they ccur. 5. The underclay is mstly buckled upward where clay dikes r the assciated faults penetrate the entire cal seam. The abve features indicate that clay dikes and clay-dike faults were frmed by lateral extensin f the cal seam during diagenesis. In many cases, clay squeezed in alng the pening fissures, frming clay dikes. In ther places where the amunt f extensin was insufficient, n clay entered, but slickensided clay-dike faults develped. Clay dikes themselves rarely cause majr rf falls because they seldm extend mre than a ft r tw int the rf. Larger clay-dike faults, hwever, can seriusly affect rf stability, particularly where tw r mre intersect abve the cal seam. The largest clay-dike faults fund ffset the cal as much as 18 feet (5.5 m) and displace strata thrugh the Bankstn Frk Limestne. Majr rf falls result frm these faults and alteratin in the mining plan is necessary. Mre details are presented n this tpic in the next sectin. As in mines B and C, jints at mine A cntribute nly t a few large rf falls, but slabbing between jint planes is a cmmn hazard. Jints are cmmn in cnjugate vertical sets in an rientatin N 55 t 80 E and N 145 t 160 E with a spacing f abut three t ten per ft. Jints nrmally penetrate nly the lwer, fissile prtin f the Anna Shale and result in nly minr slabbing f that unit. All majr rf falls at mine A are caused by absence f cmpetent strata (Breretn Limestne) in the rf sequence, especially where clay-dike faults are present. MAPS AND EXPLANATION OF THE GEOLOGY IN SELECTED STUDY AREAS Seven study areas in three mines were mapped in detail, and a wide variety f gelgic maps were prepared. Only the cmpilatin maps are presented here (figs , 23-25, and 35-37). Fr a mre cmplete suite f maps, the reader is directed t vlume 2 f Krausse et al., Similarly, nly three examples f reginal cmputer-generated maps (figs ) have been included here. Additinal nes are included in vlume 2 f the cmplete reprt. Figures 39 and 40 present a generalized picture f the thicknesses and structures. Because f the wide spacing f the datum pints (an average data density f less than 1 datum pint per square mile), the features f the maps are interpretive and d nt shw true thickness. They are, hwever, useful as guides fr thickness trends and statistical variability f the rck units in different areas f the state. The maps f study areas 1 t 3 at mine A (figs , 35-37) display similar lithlgic, structural, and rf-stability patterns. The relatinship between rf lithlgy and rf stability is apparent. N significant rf falls ccur in areas f immediate limestne rf, but numerus falls have been sptted in regins f Anna Shale r "Jamestwn Cal interval" rf. Fewer falls ccur adjacent t immediate limestne rf areas than farther away frm them, because adjacent t limestne rf areas the Breretn Limestne is present abve the Anna Shale. Limestne tends t thin and pinch ut as the Anna Shale thickens.

36 Figure 35. Distributin f clay-dike faults and clay dikes in the Herrin (N. 6) Cal and its immediate rf strata and f rf falls and ther induced instabilities in study area 1, mine A. The ccurrence f rf falls is a functin f tw gelgic variables: (1 ) lithlgic distributin and pattern f rf rcks and (2) structural setting and fault pattern. Rf falls are abundant alng faults and slips; hwever, there appears t be a greater affinity f rf falls t the lithlgy than t faults. Grid interval is 200 feet (61 m). (See als appendix figure A.)

37 .Li. '. 4 i u S c D E -rp -T- Q I ^ Figure 36. Distributin f clay-dike faults and clay dikes in the Herrin (N. 6) Cal and its immediate rf strata and f rf falls and ther induced instabilities in study area 2, mine A. The ccurrence f rf falls is a functin f tw gelgic variables: (1 ) lithlgic distributin and pattern f rf rcks and (2) structural setting and fault pattern. Rf falls are abundant alng faults and slips; hwever, there appears t be a greater affinity f rf falls t the lithlgy than t faults. Grid interval is 200 feet (61 m).

38 v ' -34- U) r u *z* t vviri v-v, i XV c r sz _ t O M 01 O ra»- O TO TO _w as,s 5^ ±! 5 3 O TO *- r vv;v r IS!i X v 1 I VAVVvV O -**. C _ TO si TO TO ^ ra» O _ O TO * *- «- O " f TO r fc 6 a. S I S» C ~ ih >»? ^ «a ^ O TO 4- r»_ a - 2 c c r r ^ r TO 1' c.2 >.9 5: '»- TO 5 2 CD tt \\ \ if 2 ~ ^3.. r C c Q) r _aj. r "S r CL' ~ 5 J J d > -7 O a> l±j v X \ S4- I ' lu Q.s si t 9) > -*- I S u a. *:.5 ^ "5 c "O «r <" c «" - > 5 r r.2.2 i u c O :til > >> CJ r». - CM ^ C. TO 00 & / \ TO 5 ^ " 8 5 _ C O Q, -c < E -P u qj D C I I cvi

39 -35- Datum pint Study area 800 ft 200 rr ISGS 1979 Figure 38. Cmputer-generated map f the elevatin f the tp f the Herrin (N. 6) Cal at mine C, study areas 6 and 7. Structural anmalies f the tp f the cal reflect anmalies in the rf strata f mainly laminated siltstne and sandstne, which lcally impse severe prblems fr rf cntrl. Cntur interval: tw feet; grid size: 100 feet.

40 ' Cntur -36- * T.11N Til T. ION T.ION T.9N 7.6N T.8N T.7N T.7N interval: 1 ft; ] AvC vhighest cntur selected: 6ft ICn tu r i n terval : 2 ft highest cntur selected: 14 ft R.OW B.iHi R 3W R.3H R. IW -I.5H P.4W R 1W P.2W -MM ISGS 1979 ISGS 1979 Figure 39. Thickness trends f the Anna Shale Member in Bnd and Mntgmery Cunties. The ispach map shws the patchy and very lenticular ccurrence f the Anna Shale just as it was bserved fr the "Quality Circle" area and fr the rest f. suthern and suthwestern Illinis. The Anna Shale is generally less than fur feet (1.2 m) thick but may lcally exceed six feet (1.8 m) in thickness. Neither a regular distributin pattern nr a trend in Anna Shale thickness is visible. The lenticular pattern, hwever, has been bserved in study areas 1, 2, and 3. Figure 40. Thickness trends f the Breretn Limestne Member in Bnd and Mntgmery Cunties. The Breretn Limestne ccurs in lenticular patches. The ispach map at first appears similar t the previus ne f the Anna Shale, but in many places a reciprcal relatinship between the thickness f the Breretn Limestne and the Anna Shale is shwn, just as it has been fund in study areas 1, 2, and 3. Figures 39 and 40. Size f area 1,620 miles (3,226 km 2 ); Average distance between pints 1.6 miles (2.58 km); Grid size 5,000 feet (1,525.0 m); Maximum search distance -50,000 feet (15,240.0 m); Number f data pints-817 (abut 250 f these were utside the map area). Areas with >2 miles between data pints: 7N-1W, 6N-1W, 5N-1 W, 4N-1W, 1 1 N-4W, 1 1 N-3W, 10N-5W. The heavy utline f the areas f thin, split r missing cal was hand drawn independently frm these maps using a greater data pint density.

41 Clay-dike The relatinship f faults t lithlgy is cmplex, but is well shwn n the maps. Three general classes f faults can be defined: 1. Majr clay-dike faults that have a displacement f a seam's thickness r mre (directinal dip indicated n map by slid triangle). A set f these faults is shwn in the nrthern part f the area in figure 35. These large faults tend t frm an en echeln pattern alng the strike and cut acrss rf lithlgic bundaries. A tectnic rigin fr these faults cannt be cmpletely ruled ut, but certain features, ntably the false drag and the shallw dip angle (fig. 41) strngly suggest that they frmed while sediments were nt yet cmpletely cnslidated. Their distributin and rientatin might be cntrlled by larger-scale depsitinal r cmpactinal gelgic settings nt reflected in the immediate rf rck, and thus in the maps. 2. Clay dikes and clay-dike faults displacing the tp f the cal seam mre than ne ft and extending int the underclay. These are shwn by pen-square dip symbls. Like the majr faults, many f them tend t fllw rather straight curses withut regard fr lithlgic bundaries and are frmed during diagenesis in respnse t large-scale patterns nt directly reflected in the immediate rf (fig. 36, diagnally thrugh center f map) 3. Minr clay dikes and clay-dike faults displacing the rf generally by less than ne ft, but nt displacing the flr f the cal seam, are shwn n the maps by hachured lines. These faults shw a strng parallelism t rf lithlgic bundaries. Mst faults f this type dip tward the center f the lithlgic bdy within which they ccur. Clay Figure 41. fault. Lw-angle nrmal fault (dip angle 35 t 50 ) with mre than twelve feet (3.6 m) f thrw (n figure 35, area A/9 t D/ 7). Shales, calcareus strata, and lwer prtin f Herrin (N. 6) Cal shw nrmal drag, whereas upper prtin f the cal diplays false drag. Strata frm the underclay f Springfield (N. 5) Cal up t the Bankstn Frk Limestne are truncated. Pht shws: A-underclay; B-Herrin (N. 6) Cal; C-Breretn Limestne; D-"Jamestwn Cal interval"; E-Cnant Limestne; and F-Lawsn Shale. Lcatin: study area 1, mine A, west-central Illinis.

42 -38- dikes are mst ften fund under limestne rfs, but clay-dike faults are just as abundant under shale rfs as under limestne rfs. The pattern bserved strngly suggests that the minr clay dikes and faults frmed during sediment cmpactin and were influenced r generated by differential cmpactin. As the vlume f cal and f the assciated rck bdies changed during cmpactin, extensin fractures and slip surfaces develped t adjust fr differences in cmpactin rates. The maps f study area 4, mine B, shw the dminantly dark-gray Energy Shale rf (fig. 13). Medium-gray shale rf (stippled pattern n map) frms a cmplex, digitate pattern. Rlls are clearly cnfined t medium-gray shale and shw rugh parallelism t lithlgic bundaries; hwever, rf failure ccurs mainly alng nrth-suth headings and apparently is independent f structure and lithlgy. As stated previusly, this nrth-suth rientatin f rf falls and kink znes is nt fully explained. It may be related t the nrth-suth-trending Rend Lake Fault System, which passes west f the study area. In study area 5, mine B, rlls are again cnfined t medium-gray shale rf areas. The map (fig. 14) shws a strng tendency f the rlls t parallel lithlgic bundaries, but the dminant feature cntrlling rf stability is the shear bdy, utlined by the bld dashed line in figure 15. The spacing f rf falls in the shear bdy area is much denser than in any ther area mapped fr this study. Were it nt fr extensive cribbing and use f rail bars fr rf supprt, many large falls undubtedly wuld have ccurred. As the map f study area 6, mine C (fig. 42) indicates, the mst severe rf falls and rib rashing ccur where the planar-bedded sandstne lies clse t r directly n tp f the cal seam. The line f demarcatin between wet and dry rf als relates t the height f sandstne abve the cal. In the nrtheastern crner f the map, where 20 feet r mre f medium-gray shale intervenes between cal and sandstne, rf and ribs are dry and stable. A similar pattern is seen in study area 7, mine C (fig. 16). Additinal mining prblems resulted frm steep inclinatin f the cal and frm large sandstne rlls, which generally strike sutheastward, parallel with the sandstne-shale rf bundary. The largest rll, marked n the map as the "mega-rll," necessitated alteratin f the mining plan and grading entries thrugh rck, as face equipment culd nt fllw the steep inclinatin f the cal. The verall relatinship between study areas 6 and 7 is shwn n the cmputer-generated map f the tp f the cal (fig. 38). In mst f the map area, the cal is rughly flat-lying and has small circular dmes and depressins, but in the vicinity f areas 6 and 7, cntur lines trend nrthwest t sutheast, parallel with the rf lithlgic and structural trend. This parallelism is evidence that present structural features may still reflect ancient tpgraphic features and thus that depsitin f rf sediments may have been influenced by cal tpgraphy. Tw small-scale reginal maps (figs. 39 and 40) are presented as examples f cmputer-generated mapping. Figure 39 is a map f the thickness f the Anna Shale in Bnd and Mntgmery Cunties. The patchy, lenticular distributin f Anna Shale is reflected n the reginal scale and has been mapped similarly in mine A n a larger scale. Figure 40 shws the

43 ' Kr I I -39- rr> c\j : x > H ; i j i r «-' K.>-/ j "\ p IT /I " :K.-* ; i.25 / i CO H D c UJ D /, a>? w c c OJ O I s ( *..\ Tfc- 0) v> i? 'I «) "O O u C J t O u. c^^ if/ -7./ LL LU if ^f ^ / J i 4f'r t "-if' i?! I. r '*-..& (ft v \, :m? ' Wt St - I *v»r -3* t>^2 i «w 'is; i > E> c UJ a > < U «B ~ - I a T3 C 0) O) O if a> - ca ' UJ Q O O JJ II $ jj si J-. u e u (0 3 *-> O trt C3 "I CM c LU ra IS CD 00 c XI r E n ~ c D t XT O) U c X. c _i E r%i -* ID CO

44 1 i i -40- thickness f the Breretn Limestne fr the same area. Althugh n clear pattern f preferred lithlgic distributin trends emerges, a general reciprcal relatinship between the thicknesses f the Anna Shale and the Breretn Limestne can be bserved by clse cmparisn f the tw maps. OBSERVATIONS AND DISCUSSION OF ROOF FAILURE TRENDS An attempt was made t quantify the bservatins made during in-mine mapping. A series f tables crrelating rf failure with rf lithlgy and structures in the varius study areas was prepared. As expected, the tables cnfirm the inferences derived frm a study f the maps. Fr presentatin f tables and detailed discussin, the reader is directed t vlume 2 f Krausse et al., The best rf cnditins under the black shale-limestne type f rf are fu where thick limestne frms the immediate rf. Black shale cntaining clay dikes and clay-dike faults is less stable than black shale withut these structural interruptins. Rf stability increases in direct prprtin t thickness f the limestne verlying the black shale. In study areas with the gray shale rf type, undisturbed medium-gray shale is the mst stable rf rck, fllwed by dark-gray shale, with planar-bedded siltstne and sandstne the least stable. Again, presence f slips and rlls decreases rf stability, but the highest percentage f fallen intersectins was recrded within the shear bdy. Wet rf is cnsiderably mre prne t failure than dry rf in study areas 6 and 7. MATERIAL PROPERTIES AND DESIGN CRITERIA Cal, flr, and rf materials vary widely in relative stiffness (Yung's mdulus) and strength (uncnfined cmpressive strength), as shwn in figure A3. Similarly, test values fr rf-blt pullut vary greatly; a range f 6,000 t 12,000 punds pullut frce was 10 7 recrded at ne mine. In general, massive rcks such as limestne r a 10 6 CO D _l D Q O 5 CO b O >- / underclay cal 4>* siltstnes unlaminated siltstne will hld blts better than well-bedded rcks where bedding-plane separatin can be expected, such as in the planar-bedded sandstne f mine C. The laminated carse clastic rcks als are lwer in cmpressive strength than nnlaminated, massive shale r siltstne. Anther imprtant factr is misture cntent; e.g., shales high in misture generally are less stable in mine penings than shales lw in misture. i in" 10^ Figure J 10" COMPRESSIVE STRENGTH, psi ISGS 1979 Generalized rck strength f rf-pillar-flr 10 materials in Illinis, based n intact cre samples. Petrgraphic factrs and the rck fabric have a bearing n rf stability, but their effect is generally verwhelmed by structural discntinuities and disturbances such as bedding separatin, fractures, faults, and rlls:

45 Rcks that cntain relatively little clay and are cemented with calcite, dlmite, siderite, r silica generally make stable rf (e.g., siltstne and massive sandstne). 2. Black shale, despite its fissility, is als a relatively stable rf material because the rganic matter in the shale is chiefly in a cllidal stage and acts as binder fr the particles, and the clay minerals are riented parallel t bedding. 3. Argillaceus siltstnes, mudstnes, prly bedded shales, and very argillaceus limestnes cause rf instability because f the abundance f slickensides and syneresis cracks, and because f their permeability alng fractures and affinity fr water. 4. Claystnes result in the mst unstable rf because f their high cntent f randmly riented clay minerals, great affinity fr water, and numerus slickensides and syneresis cracks. CONCLUSIONS Gelgic interpretatins The lithlgic distributin patterns in bth gray shale and black shale-limestne rf types are much mre intricate, irregular, and patchy than previusly suspected. Explratry drilling can prvide cal cmpanies with nly a general idea f rf cnditins in the area, but cannt be used t map lcal, yet relevant, lithlgic patterns tens t a few hundred feet in size. It is precisely these lcal irregularities which have the greatest influence n rf stability. Present-day distributin f rf rck reflects cnditins that existed in the cal-frming swamp during and immediately after peat accumulatin. In the vast, almst level, swamps, minr lcal variatins in tpgraphy and cmpactin f the plant material prbably had a prfund effect n lcal sediment depsitin, regardless f whether cnditins were marine (black shale-limestne), nnmarine (gray shale), r transitinal (fig. 44) In any depsitinal envirnment, small depressins in the swamp surface wuld have been the first sites f depsitin. The sediment might have been dark-gray mud in the nnmarine envirnment r black mud in the marine situatin. These sediments, which became the dark-gray facies f the lder Energy Shale and the yunger Anna Shale, respectively, bth have much in cmmn. Bth are fine grained, finely laminated, and cntain a high cntent f carbnaceus matter; these cnditins indicate depsitin in quiet anxic water. As the dark sediments accumulated, their weight caused the underlying spngy peat t cmpress, deepening and widening the depressin and allwing cntinued sedimentatin up t a certain cmpactinal stage f the peat, until a mre reginal change in depsitinal envirnment, such as transgressin r regressin f the sea, ccurred t change the nature f the sediment being depsited. Medium-gray mud began t accumulate abve the dark-gray shale in nnmarine areas, and the Breretn Limestne was depsited

46 -42- medium-gray shale facies planar-bedded and crss-bedded siltstne and sandstne facies Breretn Limestne medium-gray shale facies Anna Shale Anna Shale Breretn Limestne / high Figure 44. Diagram f the cmmn relatinship between the first tw units f rf rck immediately abve the Herrin (N. 6) Cal and their effect n tpgraphy f the surface f the cal. (Vertical scale is greatly exaggerated.) abve the Anna Shale in marine areas. Even yunger sediments were depsited ver the lder sediments r n tp f the still uncvered peat. During all this time, the cal-frming material cntinued t cmpact differentially depending n the amunt f previus cmpactin and the additinal weight f the accumulating verburden. Eventually, early cmpactin decreased as the peat apprached cmpressibility limits in the areas f lngest and thickest sedimentatin. Sedimentatin slwed in these areas, whereas adjacent areas, where tne peat was still cmpactable, cntinued t receive sediment. Thus, an inverse thickness relatinship culd develp, e.g., the areas with thickest Anna Shale wuld receive the thinnest limestne, and vice versa. The primary depsitinal shape f the rck bdies was defrmed lcally by varius prcesses, such as lading, cmpactin, r gravity sliding. The mst spectacular example is the shear bdy at mine B. Smaller-scale sft-sediment flw and slump is indicated by flded laminatins near rlls in gray shale and sandstne. In the black shale-limestne rf type, less direct evidence f lateral flw and flding has been fund, but lateral adjustment als ccurred in shale units during cmpactin, as shwn by secndary thinning f beds. Practically all the defrmatinal features mapped during this study can be attributed t sft-sediment defrmatin in a brad sense, that is, they were frmed befre the sediments were fully cmpacted and lithified. Sediments vary widely in their riginal mechanical and chemical prperties and in their rates f lithif icatin. Sme rck units, ntably cal, may have reacted t verburden stress by brittle defrmatin, while ther lithlgies reacted by ductile flw r plastic defrmatin. In sme cases, plastic and brittle defrmatin have ccurred side-by-side in the same cal r rck unit. The different defrmatinal elements in the gray shale rf type in cntrast t thse in the black shale-limestne rf type prbably relate t different physical prperties f the riginal sediments. Depsitinal envirnment, rate f accumulatin, and rate f cmpactin certainly als have a majr influence n defrmatin. As yet, hwever,

47 -43- we cannt shw what prperty f medium-gray shale is cnducive t rll frmatin, r what prperties f the black shale-limestne rf lead t frmatin f clay dikes. Fr the area f mine B, Edwards (1976) has suggested a hypthesis n rll frmatin, which, hwever, is nt easily applicable t rll frmatin in ther areas, as, fr instance, that f mine C: the first stage is depsitin f dark-gray shale in depressins in the peat swamp (fig. 45a). Next, medium-gray shale is laid dwn as a blanket depsit ver the peat and darkgray shale (b). In the third stage, cmpactin f the peat creates an inversin f tpgraphy, leaving dark-gray shale lenses as highs (c) dwn which medium-gray shale culd slump. Masses f gray shale culd then intrude int irregularities in the peat, lifting up the tp layers t frm the "rider." The final result is that lenses f shale remain within the cal, with cal "riders" abve. As previusly nted, the shear bdy in study area 5 is interpreted as a gravitatinal sliding. It is yunger than rlls, as shwn by truncatin f the tps f rlls by the shear bdy (fig. 19). The triggering event might have been an earth tremr, r simply pure verburden stress initiating the slide alng a very gently slping surface. Clay dikes and clay-dike faults are the dminant defrmatinal features f the black shale-limestne rf type. Like rlls, they are diagenetic defrmatinal features, frmed under sediment cver. They apparently develped after the first calif icatin stage f the plant material, but prir t rdinary cleat frmatin, as cal cleats are nt defrmed in the vicinity f clay dikes. The clay definitely was intruded frm abve. The structure f faults, dikes, and assciated features indicates that lateral extensin, rather than vertical mvement, predminated. The stretching and fracturing f the cal seam might have been a gradual prcess during diagenesis. A sudden reactin and relief f verburden lading may have caused the fracturing f the cal and frmatin f clay dikes, r, as Damberger (,1970, 1973) has suggested, earthquakes may have been respnsible fr rupturing the cal and intrusin f the clay. Medium-gray shale Dark-gray shale Peat (cal) Figure 45. Interpretive sequence f rll frmatin. (Frm Edwards, 1976.)

48 -44- Recmmendatins This investigatin has shwn that rf stability is clsely related t the gelgic setting and patterns that are highly variable, intricate, and difficult t predict in advance f mining. Rf cnditins may change abruptly within a distance f less than 100 feet (30 m). In ne entry the rf may remain stable fr the life f the mine with a minimum f artifical supprt, while the adjacent entry may cllapse immediately unless additinal supprt has been installed. Therefre, much greater flexibility in rf cntrl planning is needed. In gray shale rf areas, rlls can be a majr rf hazard. Rf blts always shuld be anchred well abve the cal "rider" s that separatin cannt ccur alng this plane f weakness. Fr small rlls it might be advantageus t bring dwn the shale lens belw the "rider" befre blting. Very large rlls may require timbers r cribs in additin t rf blts. Planar-bedded siltstne and sandstne als make the mine rf difficult t cntrl. Where rf blts f equal length are used, the siltstne strata tend t separate at the next bedding plane in r abve the blt anchrs. In this case rf cntrl might be imprved by using blts f several different lengths t reduce the splitting effect anchrs may impse and t distribute the lad ver several bedding surfaces. Resin blts culd help further by binding rck layers tgether alng the entire length f the blt. In many cases, hwever, blts wuld have t be supplemented by cribs r timbers. A shear bdy like that encuntered in study area 5 presents a real challenge in rf cntrl. Mechanical blts are f little value, as their anchrs will nt take sufficient hld in densely sheared rck. Use f resin blts f different lengths wuld prbably be an imprvement, but a cmprehensive rf cntrl prgram wuld demand additinal supprt by cribs, 3-piece sets, and rail bars set int the ribs. This additinal supprt shuld be placed as sn as the sheared rf cnditin is recgnized. In black shale-limestne rf areas, the Breretn Limestne as immediate rf requires the minimum artificial supprt. In mined-ut areas, entries with limestne rf have remained stable fr mre than 20 years withut any artificial supprt. In areas f black shale, rf blts shuld be anchred at least ne ft (0.3 m) int the first limestne bed mre than tw feet (>0.6 m) thick. The psitin f the limestne can be determined by drilling test hles with the blting machine. Where n limestne mre than tw feet thick exists within an interval f 10 t 15 feet (3 t 4.5 m) abve the tp f the cal, timbers may be needed fr lng-term supprt. Clay-dike faults are generally t variable in strike and cntinuity t allw majr alteratins f the mining plan t avid them; hwever, lcal changes in pillar layut can be made t avid having large faults run parallel t mine penings ver a lng distance. Majr tectnic faults and fracture znes, and kink znes such as the nrth-suth set encuntered in study area 4, are mre predictable. Frequently rf cntrl may be imprved by turning entries at an angle t fracture r kink znes.

49 -45- In lng-term mine planning and prjectins, cre drilling is the mst imprtant methd f btaining data. Drilling data, hwever, cannt prvide a detailed map f rf cnditins in advance f mining, but it can and shuld be used t determine the rf rck type and sequence and its range f variability. Attentin t cring the rf and flr shuld be given. A minimum f 30 feet (9 m) f rf and 10 feet f the flr shuld be cred in every test hle. Sme drill hles shuld prvide cres f the entire bedrck successin t mre than 10 feet belw the cal t establish crrelatin f stratigraphic units. The cres shuld be carefully lgged and the data used t cmpile lithlgic thickness and facies maps. In additin, the cres shuld be sampled t gain getechnical data, particularly fr the purpse f rck-mechanical and mineralgic-petrgraphic analysis, t supplement the gelgic interpretatins. Cal mine planners shuld attempt t learn as much as pssible abut earlier mining experience in the area in which they cntemplate mining. Knwledge f many previusly experienced factrs, fr instance, rf rck type, faults, and kink zne rientatin, can help greatly in laying ut a mine t minimize rf prblems. Many rf failure patterns ccur cnsistently thrughut a mining district. The Illinis State Gelgical Survey maintains a large quantity f infrmatin n gelgic cnditins in cal mines in Illinis. Additinal recmmendatins include training undergrund persnnel in basic recgnitin f gelgic features that pse a hazard t rf stability and maintaining a mapping prgram t recrd (1) rf lithlgy, (2) structural gelgic features, (3) lcatin and time f rf falls in relatin t time f cal remval, (4) blting type, spacing, and pattern, and (5) lcatin and time f additinal rf supprt. Intensificatin f undergrund surveying and systematic sampling f cal and flr and rf rcks fr gelgic and rck-mechanical testing and analysis is als recmmended. Data frm explratin drilling and mapping, mine surveys, structural analysis, cal analysis, technical analysis f rf and flr rck, rck-mechanical testing, and rf failures in particular areas may be cnveniently stred and retrieved with the aid f a cmputer as a supplement t existing data files that are pen t the public, such as thse at the Illinis State Gelgical Survey. ACKNOWLEDGMENTS This reprt is based n detailed gelgic investigatins in mines f Illinis and includes the results btained frm 1974 thrugh Between March 1974 and February 1976, the investigatin was financially supprted by the U.S. Department f the Interir, Bureau f Mines (cntract n. H ). The cntract was administered under the grund cntrl prgram f the U.S.B.M. Denver ffice; Mr. Duglas Blstad acted as technical prject fficer and Mr. David Askin as cntract administratr. We are grateful t the numerus fficials and emplyees f the cal mining cmpanies in Illinis wh assisted ur wrk by prviding valuable infrmatin and acting as discussin partners and guides. Our special thanks g t Cnslidatin Cal Cmpany, Freeman United Cal Mining Cmpany, Inland Steel Cal Cmpany, Mnterey Cal Cmpany, Old Ben Cal Cmpany, Peabdy Cal Cmpany, and Zeigler Cal Cmpany, wh pened their mines t us, permitted us t use drillhle data, and stimulated and prmted ur wrk in many ways. The detailed mapping in undergrund mines was perfrmed mainly by Heinz H. Damberger, Hans- Friedrich Krausse, Christpher T. Ledvina, and W. Jhn Nelsn; the reginal cmputer mapping was carried ut by Clin G. Trewrgy; the studies in surface mines and the develpment and applicatin f clse-range phtgrammetry methds were cmpleted by Vincent D. Brandw, H.-F. Krausse, W. Jhn Nelsn, and Clin G. Trewrgy; Christpher T. Ledvina was in charge f cre drilling in

50 -46- undergrund mines; the labratry testing f the drill cres was carried ut by Caner Zanback and Lester S. Fruth under the supervisin f Albert S. Niet, Department f Gelgy, University f Illinis, Urbana; data and infrmatin n rck mechanics and rf failure trends were evaluated by Stephen R. Hunt; W. Arthur White was in charge f the clay mineralgy studies. The entire prgram was guided and directed by H. H. Damberger and H.-F. Krausse, and the final reprt was written and crdinated by H.-F. Krausse, H. H. Damberger, and W. J. Nelsn. We acknwledge valuable assistance by many Survey staff members, nt listed as authrs, in particular, M. E. Hpkins, wh initiated the rf study, Harld J. Gluskter, William H. Smith, Lawrence E. Bengal, Rger B. Nance, and Gerge J. Allgaier.

51 -47- APPENDIX

52 -48-

53 -49- r CO a a w» u a *"* a «*_ 2 a x 2 0) 3 -C ^ re < CO frri O 111 CO C X J2 c O 3 IT) < c,- re O re re % re c.c C re 2 n a> <u CO c CD E Zi c O m CO x: CO 0) c < E i 3 (1).c re «/> T3 a) E E c LL 2 3 re a 6 E.c re re 2 c O O re 3 <0 LL 're 5 c re m re" 5 a; i re a 3 3 re O re vt re T3 c O.Q U re - O) O c i 3 > re O 3 3 re 3 re 5 re c c O) ai c -C c re.a ir n 6 CD "O ~ CM 3 <"> 2 w >.5> _re m- O. (1) < < *j a> :r c ' - c *-.2 re ~ CD S3

54 -50-

55 -51-9 d >. j < U CO s; O < Ii \ i I, CD Q Hi ^ t- E 3 00 (/) O If) r c\j HJ.1N08 ST^TB GEOLOGICM. SOW* LIBRAE

56 -52- Figure C. Distributin f lithlgy, f clay-dike faults and clay dikes in the Herrin (N. 6) Cal and its immediate rf strata, and f rf falls and ther induced instabilities in study area 3, mine A. (See als fig. 37, p. 34.)

57 -53- Majr rf falls Minr rf falls Kink zne in rd I H I H II Rib rashing Crib Majr faults with mre than 1 ft thrw f tp f cal als displacing the flr f cal Faults with mre than 1 ft thrw f tp f cal nt displacing the flr f cal Minr faults with less than 1 ft thrw f tp f cal Clay dikes assciated with faults Lithlgic bundaries "Jamestwn Cal interval" v Flr heave Breretn Limestne Anna Shale

58 : -54- REFERENCES Allgaier, G. J., 1974, Reserves f the Herrin (N. 6) Cal in the Fairfield Basin in sutheastern Illinis: unpublished draft, Illinis State Gelgical Survey. Allgaier, G. J., and M. E. Hpkins, 1975, Reserves f the Herrin (N. 6) Cal in sutheastern Illinis: Illinis State Gelgical Survey Circular A89, 31 p. Brandw, V. D., H. M. Karara, H. H. Damberger, and H.-F. Krausse, 1976, A nnmetric clse-range phtgrammetric system fr mapping gelgic structures in mines: Phtgrammetric Enginnering and Remte Sensing, v. 42, n. 5, p Damberger, H. H., 1970, Clastic dikes and related impurities in Herrin (N. 6) and Springfield (N. 5) Cals f the Illinis Basin, in Depsitinal envirnments in parts f the Carbndale Frmatin western and nrthern Illinis: Illinis State Gelgical Survey Guidebk 8, p Damberger, H. H., 1973, Physical prperties f the Illinis Herrin (N. 6) Cal befre burial, as inferred frm earthquake-induced disturbances: Cmpte Rendu, Seventh Internatinal Cngress f Carbniferus Stratigraphy and Gelgy, v. 2, p Edwards, M. J., 1976, Analysis f lithlgic and structural patterns in the Energy Shale at the Orient #6 Mine, Jeffersn Cunty, Illinis: unpublished bachelr's thesis, University f Illinis, Urbana, 32 p. Gluskter, H. G., and M. E. Hpkins, 1970, Distributin f sulfur in Illinis cals, in Depsitinal envirnments in parts f the Carbndale Frmatin western and nrthern Illinis: Illinis State Gelgical Survey Guidebk 8, p IBM Crpratin, 1968, Surface techniques, anntatin, and mapping prgrams fr explratin, develpment, and engineering (STAMPEDE), DOS system , prgram number 360D Krausse, H.-F., H. H. Damberger, W. J. Nelsn, S. R. Hunt, C. T. Ledvina, C. G. Trewrgy, and W. A. White, 1979, Engineering Study f Structural Gelgic Features f the Herrin (N. 6) Cal and Assciated Rck in Illinis: Vlume 1 Summary reprt. Vlume 2 Detailed reprt. U.S. Department f the Interir, Bureau f Mines, cntract H Ptter, Paul E., 1957, Breccia and small-scale lwer Pennsylvanian verthrusting in suthern Illinis: Bulletin f the American Assciatin f Petrleum Gelgists, v. 41, n. 12, p Seilacher, A., 1969, Fault-graded beds interpreted as seismites: Sedimentlgy, v. 13, p Smith, W. H., and J. B. Stall, 1975, Cal and water resurces fr cal cnversin in Illinis: Illinis State Gelgical Survey Cperative Resurces Reprt 4, 79 p. Swann, D. H., P. B. DuMntelle, R. F. Mast, and L. H. Van Dyke, 1970, ILLIMAP A cmputer-based mapping system fr Illinis: Illinis State Gelgical Survey Circular 451, 24 p. Vigt, E., 1962, Friihdiagenetische Defrmatin der turnen Planerkalke bei Halle/Westphalen als Flge einer Grssgleitung unter besnderer Beriicksichtigung des Phacid-Prblems Mitteilungen Gelgisches Staatsinstitut Hamburg, v. 31, p

59 . MINERAL ECONOMICS BRIEFS SERIES (in print) Summary f Illinis Mineral Prductin in Shipments f Illinis Crushed Stne, Mineral Resurces and Mineral Industries f the East St. Luis Regin, Illinis Mineral Resurces and Mineral Industries f the Extreme Suthern Illinis Regin Mineral Resurces and Mineral Industries f the Springfield Regin, Illinis Mineral Resurces and Mineral Industries f the Western Illinis Regin Mineral Resurces and Mineral Industries f the Nrthwestern Illinis Regin Mineral Resurces and Mineral Industries f the Nrtheastern Illinis Regin Directry f Illinis Mineral Prducers INDUSTRIAL MINERALS NOTES SERIES (in print) 13. Summary f Illinis Mineral Industry, Pelletizing Illinis Flurspar Binding Materials Used in Making Pellets and Briquets Chemical Cmpsitin f Sme Deep Limestnes and Dlmites in Livingstn Cunty, Illinis Illinis Natural Resurces An Industrial Develpment Asset Limestne Resurces f Jeffersn and Marin Cunties, Illinis Thermal Expansin f Certain Illinis Limestnes High-Purity Limestnes in Illinis Clay and Shale Resurces f Clark, Crawfrd, Cumberland, Edgar, Effingham, Jasper, and Vermilin Cunties Lightweight Bricks Made with Clay and Expanded Plastic Clays as Binding Materials Silica Sand Briquets and Pellets As a Replacement fr Quartzite Cmputer-Calculated Lambert Cnfrmal Cnic Prjectin Tables fr Illinis (7.5-Minute Intersectins) Kankakee Dune Sands As a Cmmercial Surce f Feldspar Alumina Cntent f Carbnate Rcks As an Index t Sdium Sulfate Sundness Cllidal-Size Silica Prduced frm Suthern Illinis Tripli Tw-Dimensinal Shape f Sand Made by Crushing Illinis Limestnes f Different Textures An Investigatin f Sands n the Uplands Adjacent t the Sangamn River Fldplain: Pssibilities As a "Blend Sand" Resurce Lwer Mississippi River Terrace Sands As a Cmmercial Surce f Feldspar Clay and Shale Resurces f Madisn, Mnre, and St. Clair Cunties, Illinis ILLINOIS MINERALS NOTES SERIES (in print) (The Illinis Minerals Ntes Series cntinues the Industrial Minerals Ntes Series and incrprates the Mineral Ecnmics Briefs Series) 49. Clay and Shale Resurces f Peria and Tazewell Cunties, Illinis By-Prduct GypMim in Illinis- A New Resurce? Cal Resurces f Illinis Prperties f Carbnate Rcks Affecting Sundness f Aggregate- A Prgress Reprt The Energy Crisis and Its Ptential Impact n the Illinis Clay Prducts Industry Cmmercial Feldspar Resurces in Sutheastern Kankakee Cunty, Illinis Electric Utility Plant Flue-Gas Desulfurizatin: A Ptential New Market fr Lime, Limestne, and Other Carbnate Materials The Distributin and Physical Prperties f Chert Gravel in Pike Cunty, Illinis Factrs Respnsible fr Variatin in Prductivity f Illinis Cal Mines Behavir f Cal Ash in Gasificatin Beds f Ignifluid Bilers Place f Cal in the Ttal Energy Needs f the United States Directry f Illinis Mineral Prducers, Illinis Cal: Develpment Ptential Illinis Mineral Industry in Mnrket Ptential fr Cals f the Illinis Basin Illinis Mineral Industry in 1975 and Review f Preliminary Mineral Prductin Data fr Industrial Minerals Publicatins f the Illinis State Gelgical Survey, thrugh December Illinis Mineral Industry in 1976 and Review f Preliminary Mineral Prductin Data fr Abundance and Recvery f Sphalerite and Fine Cal frm Mine Waste in Illinis

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