Further examination of the ragged edge of the Herrin Coal Bed, Webster County, Western Kentucky Coal Field

International Journal of Coal Geology 46 Ž2001. 145–155 www.elsevier.comrlocaterijcoalgeo

Further examination of the ragged edge of the Herrin Coal Bed, Webster County, Western Kentucky Coal Field James C. Hower a,) , David A. Williams b a

UniÕersity of Kentucky Center for Applied Energy Research, 2540 Research Park DriÕe, Lexington, KY 40511, USA b Kentucky Geological SurÕey, Henderson, KY 42420, USA

Abstract The Herrin ŽWestern Kentucky No. 11. coal bed in the Dixon 7 1r2 min quadrangle, Webster County, Kentucky, displays another manifestation of the thinning margin of the coal bed. Previous studies in adjacent Hopkins County have demonstrated that the coal is brecciated as the margin is approached. The brecciated coal is not always thin; 1.5 m of brecciated, inertinite-rich coal was previously described to the southeast of the present study area. In general, the brecciated coals are considerably thinner than the 1.5–2-m-thick, AnormalB Herrin coal. Both cores studied are thin Ž22.6 and 33 cm. and display petrographic characteristics different from thicker Herrin coals. The cores described in the present study show some signs of brecciation; in certain cases, the fragmented macerals are cemented by exsudatinite. Multiple generations of pyrite mineralization were noted in one core, with total sulfur exceeding 13% in the upper 8.48 cm lithotype. Overall, the cores investigated in this study, along with examples from previous studies, illustrate the progression of the Herrin coal from its absence, either through nondeposition or erosion, through thin, brecciated coals, to mineable coals. No other economic coal in western Kentucky shows as many examples of the depositional edge as does the Herrin. All of the examples studied are from cores, emphasizing the need to study more than just the thick, mineable coals if the total extent of the coal body is to be understood. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Kentucky; Coal; Petrology; Geochemistry; Herrin coal; Illinois basin

1. Introduction Few coals have revealed such a wide array of boundaries as the Herrin ŽWestern Kentucky No. 11. coal bed. Hower et al. Ž1987. and de Wet et al. Ž1997. documented several areas where the coal passed from a mineable thickness to no coal within a transition zone about one kilometer in width. In the previous papers, such a transition was referred to as the Aragged edgeB of the Herrin due to the breccia) Corresponding author. Tel.: q1-859-257-0261; fax: q1-859257-0360. E-mail address: [email protected] ŽJ.C. Hower..

tion of the coal. The Herrin transition is similar to the depositional boundary of the Paradise ŽWestern Kentucky No. 12. coal bed, a few meters above the Herrin, as described by Austin Ž1979.. In this study, we add another location to the list of Herrin ragged edges with a study of the petrology and geochemistry of the coal in the Dixon 7 1r2 min quadrangle, Webster County, Kentucky. The study area is small, two sites 3.45 km apart; however, along with the sites discussed in the previous studies, the opportunity to study the nature of the margin of a coal is worthwhile. Western Kentucky, and the Illinois Basin, in general, does not have an abundance of road cut or natural exposures as do the Ap-

0166-5162r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 6 - 5 1 6 2 Ž 0 1 . 0 0 0 1 7 - 9

146

J.C. Hower, D.A. Williamsr International Journal of Coal Geology 46 (2001) 145–155

palachian coal fields. Economic coals, such as the Herrin, are well exposed in mines; however, mining is halted before the coal diminishes to the thicknesses seen here. Only in cores have we found evidence of the nature of the margins of the Herrin coal body.

2. Previous studies Hower et al. Ž1987. described two sites where the Herrin coal bed was too thin or too brecciated and mineralized to be mineable ŽFig. 1.. The coal in the Gil-21 core, as described by Hower et al. Ž1987. in Ohio County is thin, with a brecciated durain or cannel lithology in the upper 9.8 cm of coal Žsplit by 7.5-cm-thick claystone parting, the Blue band.. The so-called Hopkins County core ŽHower et al., 1987. consists of more than 1.5 m of coal with a claystone parting, the characteristic ABlue bandB of the Herrin coal bed, in the lower third of the coal bed and a 3.1 cm fossiliferous limestone parting in the upper third of the coal bed. The coal is brecciated throughout the core, with massive fusinite and semifusinite dominating the maceral assemblages. Cementing the coal fragments is a carbonate-rich matrix Žbased on petrographic observation; supported by CaO content, see Table 1.. The lower portion of

the coal is characterized by a Mg–Fe–Mn carbonate. Mg–Fe–Mn contents diminish to the top of the coal bed. The Herrin coal bed thins from about 2 m to zero thickness in a distance of about 1 km in the Nebo 7 1r2 min quadrangle in western Hopkins County. The organic petrology and ash geochemistry was described at six sites by de Wet et al. Ž1997. Žsee Table 2.. Cores from potentially mineable areas, up to 2 m thick, were not made available for study. The sites, in order of increasing complexity, pass from a 1.03 m section that is limited to 31 cm coal above the Blue band Žcore 199.; to several thin coals with no Blue band Žcores 179 and 180.; to progressively brecciated coals Žcores 193 and 197.; to a brecciated, fusinized coal Žcore 181.. The contrast between cores 197 and 181 illustrates the transitional nature of the boundary. The lower 4 cm of core 197 represents AnormalB Herrin coal, with 87% vitrinite and 2.45% pyritic sulfur. The middle 7 cm has nearly equal amounts of fusinite and semifusinite. Pyritic sulfur drops to 0.66%, indicative of the oxidizing environment of deposition. The upper 8.31 cm is dominated by fusinite. The entire thickness of core 181 is dominated by fusinite. The inertinite-dominated lithotypes also have a carbonate matrix with a relatively high concentration of Mn. Overall, de Wet et al. Ž1997. described a complex story of the development of both the coal and the overlying carbonates in this particular marginal setting.

3. Procedure

Fig. 1. Location of Herrin coal bed Aragged edgeB study sites in the Western Kentucky coal field. The AHopkins County coreB is from Hower et al. Ž1987., the Nebo quadrangle sites are from de Wet et al. Ž1997., and the Dixon quadrangle sites are from this study.

Cores of the Herrin coal were obtained from two boreholes in the Dixon 7 1r2 min quadrangle, Webster County, KY. The coal cores were described megascopically and split into multiple benches. Each subsequent bench was crushed for petrographic and chemical analyses, all conducted at the Center for Applied Energy Research. Petrographic analysis was conducted on polished pellets of epoxy-bound minus 20 mesh particles using reflected-light, oil-immersion microscopy at a final magnification of 500 = . Proximate and ultimate analyses were conducted following ASTM procedures. Major oxides and a suite of minor elements were analyzed by X-ray fluorescence following techniques described by Hower and

J.C. Hower, D.A. Williamsr International Journal of Coal Geology 46 (2001) 145–155

147

Table 1 Ash chemistry of Hopkins County core coal samples discussed by Hower et al. Ž1987. Sample Bench

7866 7867 7868 7869 7870 7871 7872 7873 7874 7875

1r10 Žtop. 2r10 3r10 4r10 5r10 6r10 7r10 8r10 9r10 10r10

Sample Bench

7866 7867 7868 7869 7870 7871 7872 7873 7874 7875

1r10 Žtop. 2r10 3r10 4r10 5r10 6r10 7r10 8r10 9r10 10r10

Thickness Ash Žcm. Ždry.

S Žtotal. XRF Ž%, ash. Ždry. MgO Na 2 O Fe 2 O 3 TiO 2 SiO 2

17.60

27.25 2.66

12.75 9.58 11.00 17.93 18.69 22.10 17.70 15.06 9.88

40.46 32.87 15.33 18.18 31.90 38.40 51.22 39.63 38.32

Thickness Ash Žcm. Ždry.

2.14 2.94 4.24 4.05 3.01 3.06 2.20 1.76 2.37

1.10 0.51 0.73 1.30 0.55 1.60 7.14 7.73 15.42 10.69 10.45

0.63 0.63 0.45 0.32 0.47 0.55 0.50 0.53 0.48

27.25 2.66

12.75 9.58 11.00 17.93 18.69 22.10 17.70 15.06 9.88

40.46 32.87 15.33 18.18 31.90 38.40 51.22 39.63 38.32

2.14 2.94 4.24 4.05 3.01 3.06 2.20 1.76 2.37

K 2 O P2 O5 Al 2 O 3 SO 3

5.27

0.21

30.57 37.19 0.60

0.64

7.08

14.80

4.17 7.61 20.38 16.70 14.31 11.93 10.79 12.88 12.66

0.59 0.35 0.21 0.21 0.17 0.21 0.11 0.13 0.13

48.23 44.09 28.09 14.77 21.59 27.98 11.19 23.14 21.86

21.75 18.32 22.08 27.57 29.73 27.07 47.92 34.14 33.42

0.53 1.00 0.53 0.45 0.47 0.68 0.29 0.47 0.46

0.14 0.78 1.96 0.05 0.58 0.07 0.05 0.26 0.26

13.11 8.07 5.62 4.61 4.06 6.65 3.60 5.37 5.28

8.00 15.60 19.10 31.60 19.70 16.50 9.17 8.60 13.70

Ni

Co

Cr

Ba

V

Mn

Rb

Sr

S Žtotal. XRF Žppm, ash. Ždry. Mo Zn Cu

17.60

CaO

Zr

42

227

6

97

23

63

238

167

1499

46

385 109

48 121 72 43 87 76 25 98 47

14 240 26 33 8 19 5 154 246

31 13 52 16 25 1 42 0 13

56 91 67 8 15 35 41 22 54

17 22 36 28 29 28 32 29 34

61 126 85 24 21 14 83 0 24

260 271 228 142 307 281 219 154 220

107 155 140 58 50 58 130 58 38

1930 1680 1380 2186 5141 4851 4890 5400 5464

35 59 27 30 35 45 49 18 28

232 278 415 149 247 322 395 565 457

162 118 333 177 73 86 122 90 88

Major oxides Ž%. and minor elements Žparts per million. both on ash basis. Chemistry not previously published.

Bland Ž1989.. Additional trace elements were analyzed by inductively coupled plasma-mass spectroscopy ŽICP-MS. following procedures outlined by Meier et al. Ž1996..

4. Discussion The Herrin coal is at the top of the Carbondale Formation ŽWestphalian D. ŽFig. 2.. ANormalB sections of the Herrin and Paradise coal beds, as mined through central Hopkins, Muhlenberg and Ohio counties, total to about 4 m of coal. The two coals have nearly equal thicknesses within 6 m coal– limestone–coal sequences. To the north, the Paradise coal thins, progressively losing benches from the top of the coal. Austin Ž1979. described marine shale partings bearing marine fossils within the coal. Such

partings eventually merge with the identical roof rock as the coal vanishes. The limestone parting in the Herrin coal, as described by Hower et al. Ž1987., is similar to the limestone roof of the Herrin. The Herrin coal, through the progressive north- to northwestward loss of the top lithotypes, thins via much the same mechanism as the Paradise coal. Complicating the demise of the Herrin coal is the brecciation observed in the previous studies ŽHower et al., 1987; de Wet et al., 1997., a feature observed at one Paradise coal site ŽAustin, 1979.. Rogers Ž1985. mapped the northward thinning of the Herrin coal bed to a zero edge in much of the Nebo 7 1r2 min quadrangle to the south of the present study area. The thin coals in cores 623 and 668, with coal plus partings thicknesses of 22.6 and 33.0 cm, respectively, demonstrate that the Dixon 7 1r2 min quadrangle sites are north of the Azero-

148

Core

Sample

Bench

Thickness Žcm.

Ash

S Žtotal.

S Žpyritic.

Vitrinite

Fusinite

Semifusinite

Micrinite

Macrinite

Liptinite

181

71544 71543 71542 71627 71628 71629 71630 71631 71632 71660 71661 71662 71633 71634 71635 71636 71643 71644 71645 71646

1r3 Žtop. 2r3 3r3 1r3 Žtop. 2r3 3r3 1r3 Žtop. 2r3 3r3 1r3 Žtop. 2r3 3r3 1r4 Žtop. 2r4 3r4 4r4 1r4 Žtop. 2r4 3r4 4r4

9.40 8.38 12.70 8.31 7.01 3.99 9.80 13.00 14.10 10.01 12.29 13.49 13.11 8.00 9.50 6.71 30.99 19.05 30.48 26.16

66.39 45.13 53.24 37.24 36.76 22.42 13.12 21.69 9.30 14.01 8.48 8.98 33.75 14.65 16.26 24.59 12.45 10.44 20.81 11.83

1.06 1.22 1.29 1.38 1.73 4.56 3.48 9.67 2.45 2.91 2.08 2.82 2.57 2.57 2.71 11.03 4.39 6.22 12.44 2.38

0.48 0.22 0.31 0.70 0.66 2.45 1.51 4.01 0.63 1.09 0.54 0.95 1.19 0.86 0.93 6.32 2.46 4.64 11.16 0.74

0.5 0.0 0.0 0.1 5.9 87.3 83.2 82.7 91.5 87.6 94.7 89.5 68.5 94.1 85.3 84.6 85.7 90.6 83.6 92.4

96.1 97.1 91.3 50.0 4.8 5.6 7.8 10.0 2.9 4.6 1.5 3.3 23.4 2.7 4.9 6.0 5.4 3.7 6.2 2.6

0.9 1.6 3.0 48.5 86.5 2.6 6.0 4.4 2.4 4.0 1.2 2.3 6.5 1.0 4.8 6.6 5.2 3.4 8.0 3.0

0.0 0.0 0.1 0.0 0.8 0.2 0.5 0.3 0.3 0.3 1.1 0.4 0.0 0.5 0.9 0.5 0.6 0.3 0.1 0.1

2.4 1.3 5.1 1.3 0.0 0.0 0.0 0.1 0.1 0.2 0.0 0.0 0.1 0.0 0.2 0.0 0.0 0.0 0.0 0.0

0.1 0.0 0.5 0.1 2.0 4.3 2.5 2.5 2.8 3.3 1.5 4.5 1.5 1.7 3.9 2.3 3.1 2.0 2.1 2.1

197

179

180

193

199

Core

Sample

Bench

SO 3

MgO

Na 2 O

Fe 2 O 3

TiO 2

SiO 2

CaO

K 2O

P2 O5

Al 2 O 3

181

71544 71543 71542 71627 71628 71629 71630 71631 71632

1r3 Žtop. 2r3 3r3 1r3 Žtop. 2r3 3r3 1r3 Žtop. 2r3 3r3

4.01 7.51 6.48 8.27 8.84 11.74 1.95 0.80 2.39

0.97 1.18 1.02 0.56 0.42 0.60 0.41 0.52 0.89

0.83 0.46 0.58 0.51 0.27 0.12 0.41 0.34 0.47

3.28 2.46 2.29 3.52 3.92 19.50 20.89 44.96 14.22

0.56 0.15 0.32 0.18 0.16 0.48 1.00 0.63 0.91

53.92 32.87 38.92 39.48 64.89 49.73 52.46 38.90 57.78

19.77 47.85 37.36 36.84 16.12 8.08 2.40 0.79 2.78

2.14 0.43 1.04 0.21 0.45 0.99 1.65 1.40 2.49

0.41 0.19 0.85 0.42 0.06 0.10 0.05 0.03 0.05

13.26 5.34 9.34 6.57 3.68 6.46 17.64 10.78 18.08

197

179

J.C. Hower, D.A. Williamsr International Journal of Coal Geology 46 (2001) 145–155

Table 2 Ash chemistry and organic petrology of coal samples from Nebo quadrangle sites discussed by de Wet et al. Ž1997.

180

193

199

181

197

179

180

193

199

1r3 Žtop. 2r3 3r3 1r4 Žtop. 2r4 3r4 4r4 1r4 Žtop. 2r4 3r4 4r4

Sample

Bench

71544 71543 71542 71627 71628 71629 71630 71631 71632 71660 71661 71662 71633 71634 71635 71636 71643 71644 71645 71646

1r3 Žtop. 2r3 3r3 1r3 Žtop. 2r3 3r3 1r3 Žtop. 2r3 3r3 1r3 Žtop. 2r3 3r3 1r4 Žtop. 2r4 3r4 4r4 1r4 Žtop. 2r4 3r4 4r4

1.99 3.90 0.59 5.89 2.91 2.41 2.36 0.76 1.81 0.74 8.18

0.86 0.69 0.63 0.40 0.51 0.61 0.41 0.77 0.25 0.18 0.65

0.36 0.54 0.36 0.35 1.06 0.46 0.34 0.39 0.28 0.29 0.41

12.98 10.65 17.50 7.95 12.59 12.97 45.38 30.06 59.24 71.04 10.78

0.84 0.83 0.77 0.30 0.57 0.62 0.54 0.88 0.54 0.32 0.73

57.97 61.70 56.73 71.00 65.92 64.50 36.12 46.97 25.72 18.33 51.83

Mo

Zn

Cu

Ni

Co

Cr

0 1 9 468 550 184 88 0 13 10 26 14 221 7 4 0 358 0 0 7

270 097 1920 43 129 1320 141 8750 316 425 358 0 213 1030 163 184 690 152 164 151

73 72 70 69 72 270 294 382 276 186 219 305 110 192 216 439 288 443 380 96

82 70 159 184 198 930 465 342 540 468 167 0 242 540 305 282 930 250 45 173

19 19 27 19 16 39 40 18 40 39 40 44 20 30 29 19 39 0 0 38

324 307 466 262 257 690 413 243 354 408 412 440 214 239 268 266 670 414 199 312

Major oxides Ž%. and minor elements Žparts per million. both on ash basis.

2.50 5.15 1.25 4.84 3.11 2.64 2.64 0.97 2.07 1.07 7.93

2.22 2.07 2.15 0.65 1.42 1.88 1.45 1.71 0.65 0.62 1.95

0.04 0.04 0.04 0.04 0.04 0.04 0.48 0.12 0.04 0.04 0.49

18.54 16.41 17.22 77.00 11.09 13.01 9.65 15.93 8.11 6.13 15.41

Ba

V

Mn

Rb

Sr

Zr

323 72 210 284 940 279 630 421 740 870 810 820 690 1990 920 276 1620 1570 220 488

312 254 392 179 325 1760 870 208 367 452 443 339 264 215 197 339 1230 630 168 452

920 2030 1340 2630 1220 770 300 52 380 199 408 339 373 303 316 248 410 201 58 493

170 22 71 13 50 87 154 80 233 165 135 139 78 142 187 74 122 28 26 127

640 1230 1330 2910 352 155 292 56 428 190 330 278 268 288 246 134 164 121 9 359

307 194 235 281 225 1480 860 93 496 398 236 403 540 227 248 217 510 144 78 301

J.C. Hower, D.A. Williamsr International Journal of Coal Geology 46 (2001) 145–155

Core

71660 71661 71662 71633 71634 71635 71636 71643 71644 71645 71646

149

150

J.C. Hower, D.A. Williamsr International Journal of Coal Geology 46 (2001) 145–155

thickness coalB embayment he described. Spacing of the cores, and the lack of additional coverage, does not permit further definition of the edge of the coal. Lithologic descriptions of the coal cores are shown on Table 3. The coal in core 623 is thinner, more brecciated, and lower in sulfur than the coal in core 668, 3.45 km to the north ŽFig. 1.. The Herrin coal in core 623 has a duller appearance than the northern occurrence. The Herrin coal in core 668 is dominated by bright clarain with thin fusain and pyrite bands included in the sampled coal Žthe 2.0 cm pyrite band

Table 3 Lithologic descriptions of coal from two cores in the Dixon 7 1r2 min quadrangle, Webster County, Kentucky Sample no.

Thickness Žcm.

Lithology

1.3 0.3 0.7 5.4 2.6 1.2 8.1 4.8 0.5

shale roof dull clarain clarain siltstone clarain blue band dull clarain clarain clarain dull clarain

1.2 0.4 0.3 0.4 4.0 0.1 2.4 2.0 3.4 0.1 1.0 0.2 1.0 0.2 0.2 0.2 0.2 6.8 3.2 4.1 1.9

green shale roof bright clarain fusain bright clarain fusain bright clarain pyrite bright clarain pyrite bright clarain pyrite bright clarain pyrite bright clarain pyrite bright clarain fusain bright clarain clarain silty shale bright clarain clarain

Core 623 71799

Žnot sampled. 71800 71801

Core 668 71833

Žnot sampled. 71834

Fig. 2. Geologic column of a portion of the coal-bearing section of the Dixon quadrangle Žfrom Hansen, 1976.. Coal thicknesses are in inches Ž1 in.s 2.54 cm. and unit thickness are in feet Ž1 ft s 0.304 m..

71835 Žnot sampled. 71836

J.C. Hower, D.A. Williamsr International Journal of Coal Geology 46 (2001) 145–155

was excluded from the sample.. The latter attributes are typical of many Western Kentucky coals. The petrography and chemistry of the Dixon quadrangle Herrin samples are shown on Tables 4 and 5. The coals are high volatile A bituminous, with 0.73% vitrinite maximum reflectance in sample 71836. 4.1. Core 623 The coal in core 623 shows an upward increase in ash yield and decrease in total sulfur. The lowermost sample, 71801, is characterized by a high vitrinite content. Pyrite occurs in the most massive form of any of the core 623 samples. Perhaps the most striking attribute of sample 71801 is the high Sr content, 22,500 ppm on the ash basis. Sr is high throughout the core and the upward decrease may be a function of the diluent effects of the abundant clays in the upper portions of the coal. Sr may be associated with phosphate minerals; note the P2 O5 concentration of 1.1%. The relatively high concentration of rare-earth elements in the basal lithotype compared to the upper two lithotypes may also be a function of concentration in phosphates. The suggestion of a Sr and REE association with phosphate minerals is an inference based on the coincidence of high concentrations of the elements. Phosphate minerals were not found in SEM observations. The top two samples both show some signs of disrupted banding, although not to the extreme degree seen in previous studies discussed above. Broken macerals, primarily semifusinite, are recemented in part by exsudatinite ŽFig. 3.. Examples of other brecciated macerals are shown on Fig. 4. Overall, semifusinite and fusinite increase upwards to a total exceeding 36% ŽTable 4., an

151

indication of oxidation of the peat. Pyrite occurs as fine framboidal and euhedral forms in the upper sample Ž71799.. 4.2. Core 668 Core 668 shows a progressive upward increase in total sulfur. Details of the variation in pyrite forms will be discussed in detail. The maceral content is not as varied as in core 623. Inertinite macerals are important constituents in the coal, although not to the degree found in sample 71799 from core 623. Sample 71836, the lowermost sample of core 668, contains small framboidal pyrite clusters, some of them internally overgrown with a second generation of pyrite. Massive overgrowths of framboidal clusters were observed. Sample 71835 contains overgrowths of framboidal clusters, some as very massive multigenerational overgrowths. Smaller euhedral pyrite crystals are not overgrown. An unusual pyrite form consists of rounded globules truncated by fusinite. Brecciation of the coal was observed as a rare phenomenon. The maceral assemblages contain high-relief textured inertinites and abundant liptinites, including cutinites with included resinite. Sample 71834 has a brighter megascopic appearance than the underlying clarain of sample 71835. This observation is not necessarily borne out by the maceral analysis, sample 71834 has the highest fusinite plus semifusinite content of any of the core 668 samples. As in the underlying sample, there is some evidence of brecciation. High-relief textured inertinite macerals were observed. Carbonate occurs in fusinite lumens. Pyrite consists of very massive over-

Table 4 Maceral content Ž%, mineral free basis. of coal samples from Dixon quadrangle cores Core

Location

Sample

Bench

Thickness Žcm.

Vit

Fus

Sfus

Mic

Mac

Ex

Res

668

Dixon 14-M-22

623

Dixon 16-M-22

71833 71834 71835 71836 71799 71800 71801

1r4 Žtop. 2r4 3r4 4r4 1r3 Žtop. 2r3 3r3

8.48 6.50 6.78 5.99 5.41 9.40 5.33

74.4 65.6 79.2 77.9 51.9 74.2 92.7

12.0 17.6 8.5 10.5 6.0 5.9 2.5

9.5 9.5 3.6 7.9 30.4 11.5 1.9

0.6 0.1 0.1 0.0 3.5 0.5 0.2

0.2 0.0 0.1 0.1 0.2 0.1 0.0

2.2 6.3 6.2 3.0 4.0 2.9 1.5

1.1 0.9 2.3 0.3 4.0 4.9 1.2

152

Table 5 Ash chemistry of coal samples from Dixon quadrangle cores Core

Location Dixon 14-M-22

623

Dixon 16-M-22

Core

Bench

Thickness Žcm.

Ash Ždry.

S Žtotal. Ždry..

XRF Ž%, ash basis. MgO Na 2 O Fe 2 O 3

TiO 2

SiO 2

CaO

K 2O

P2 O5

Al 2 O 3

SO 3

31.21 27.68 27.26 26.18 59.96 40.54 17.54

13.33 10.07 9.74 4.24 2.38 3.18 3.58

1.18 0.78 0.76 0.57 0.62 0.28 0.66

0.16 0.32 0.23 0.34 0.40 0.22 0.28

43.24 30.58 27.51 10.45 5.41 6.79 15.94

0.48 0.83 1.07 1.10 1.67 1.16 0.70

16.96 25.60 37.28 44.47 64.49 57.29 41.22

9.33 7.82 2.92 1.19 0.20 0.31 1.50

0.36 0.77 1.51 1.62 2.16 0.98 2.07

0.30 0.14 0.37 0.11 0.18 0.50 1.10

12.65 16.83 18.81 21.29 22.20 27.87 27.00

8.67 7.70 1.84 0.82 0.10 0.19 1.60

71833 71834 71835 71836 71799 71800 71801

1r4 Žtop. 2r4 3r4 4r4 1r3 Žtop. 2r3 3r3

8.48 6.50 6.78 5.99 5.41 9.40 5.33

Location

Sample

Bench

XRF Žppm, ash basis. Mo

Zn

Cu

Ni

Co

Cr

Ba

V

Mn

Rb

Sr

Zr

668

Dixon 14-M-22

623

Dixon 16-M-22

71833 71834 71835 71836 71799 71800 71801

1r4 Žtop. 2r4 3r4 4r4 1r3 Žtop. 2r3 3r3

124 53 45 31 42 68 117

1652 19 83 143 72 38 398

0 29 119 226 84 30 41

150 38 94 102 83 124 610

102 62 62 23 20 24 62

108 131 307 496 211 129 106

2297 4160 461 348 363 560 1520

182 186 351 540 236 199 352

456 440 164 73 36 1 44

49 60 96 125 274 112 154

425 278 143 279 2220 13700 22500

145 163 188 312 570 870 1110

Core

Location

Sample

Bench

ICP-MS Žppm, ash basis.

71833 71834 71835 71836 71799 71800 71801

1r4 Žtop. 2r4 3r4 4r4 1r3 Žtop. 2r3 3r3

668

Dixon 14-M-22

623

Dixon 16-M-22

Y

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Th

28 74 87 47 24 28 28

170 77 85 152 79 97 177

17.6 10.2 11.5 16.2 7.1 9.8 20.8

55.3 43.4 51.6 55.8 20.4 32.9 82.5

7.1 12.6 15.1 9.3 2.6 5.0 16.6

1.4 3.4 3.6 1.9 0.5 0.8 2.6

8.2 15.7 14.9 8.3 3.2 3.9 10.2

0.7 2.5 2.5 1.0 0.3 0.5 0.9

3.9 13.6 14.2 6.9 2.0 2.7 5.4

0.7 2.5 2.5 1.3 0.4 0.5 0.9

2.0 7.5 7.5 4.0 1.3 1.5 3.0

0.3 1.0 1.0 0.6 0.2 0.2 0.5

1.9 6.5 6.3 3.7 1.3 1.5 3.2

4.9 11.7 18.8 32.8 7.0 3.9 6.3

Major oxides Ž%. and minor elements Žparts per million. both on ash basis.

J.C. Hower, D.A. Williamsr International Journal of Coal Geology 46 (2001) 145–155

668

Sample

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Overall, the Herrin coal in core 668 shows an increasing epigenetic overprint from the base of the coal to the upper lithotype. Pyrite mineralization is supplemented by a minor amount of sphalerite and by carbonate mineralization.

5. Summary

Fig. 3. Ža. Semifusinite cemented by exsudatinite Žsample 71799. Ž330 mm across long axis; oil immersion, reflected white-light image.. Žb. Semifusinite fragment in mixed maceral–mineral matter matrix. Žsample 71799. Ž330 mm across long axis; oil immersion, reflected white-light image..

growth forms and globular overgrowths ŽFig. 5., the latter containing 5 mm cores overgrown by 50-mmdiameter pyrite globules. Sample 71833, separated from the lithologically similar sample 71834 by a 2.0 cm pyrite band, contains several types of epigenetic pyrite. Massive pyrite occurs in both fusinite and vitrinite. Fusinite lumens can also be filled with carbonate and sphalerite ŽFig. 6.. Overgrowths of framboidal clusters, outer rims of pyrite around the overgrowths, are present, as in the underlying samples. Euhedral crystals, approximately 10 mm in diameter, occur in the coal and smaller isolated and clustered euhedra are found along the banding. The only evidence of brecciation appeared to be in the inertinites.

Together, the two cores illustrate the progression of the Herrin coal from its absence, as known from the work of Rogers Ž1985. and de Wet et al. Ž1997.; through its appearance as thin, brecciated, and oxidized during deposition; to a thicker Žalbeit still not mineable. coal with extensive emplacement of syngenetic and epigenetic sulfides and epigenetic carbonates. Mineable thicknesses of the Herrin coal are not found in the Dixon quadrangle and, indeed, mining of the Herrin has not been conducted in northern Webster County. No other economic coal in western Kentucky is known to show as many examples of the depositional edge as the Herrin. If nothing else, the trilogy of Herrin ragged edge studies ŽHower et al., 1987; de Wet et al., 1997; this study. illustrates the importance of retaining thin or otherwise uneconomic core samples for future study. None of the examples published came from an underground or a surface mine. Unless abrupt changes Žundocumented by exploratory drilling. in the coal quality or thickness occur, we should not expect to see the full extent of a coal body in mining situations. Core 623 contains the brecciated maceral assemblage characteristic of the previously investigated sites. Also, characteristic of the coal at other sites is the fusinized breccia. The coarse fusinite and semifusinite suggest that oxidation occurred at the time of the deposition and subsequent reworking of the peat. The breccia is mixed with clay, further indication of the reworking experienced by the peat at the location of core 623. In contrast, core 668 does not show the intense reworking as in the southern core, although subtle signs of brecciation were observed, particularly, among the inertinites. The Herrin coal in core 668 is characterized by an upward increase in epigenetic

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J.C. Hower, D.A. Williamsr International Journal of Coal Geology 46 (2001) 145–155

Fig. 4. Ža–d. Liptinite-rich fragments in maceral and maceral–mineral matter breccia Žsample 71799. Ž330 mm across long axis; oil immersion, reflected white-light image..

Fig. 5. Pyrite and marcasite overgrowths of framboidal aggregates. Multiple generations of sulfide growth can be seen from the original framboids to the successive overgrowth stages, to the emplacement of a AspongyB sulfide between the overgrown sulfide globules. Žsample 71834. Ž330 mm across long axis; oil immersion, reflected white-light image..

Fig. 6. Fusinite fragment with pyrite Žp., sphalerite Žs., and carbonate Žall other unlabeled fusinite lumens. filling of lumens Žsample 71833. Ž330 mm across long axis; oil immersion, reflected white-light image..

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pyrite, carbonate, and minor sphalerite. Complexity of pyrite overgrowths of syngenetic and early epigenetic forms increase in the upper lithotypes of the core. No one series of sites can be considered representative of all marginal depositional settings, and the Herrin models will certainly not hold for all coal bodies. The similarity of all of the known Herrin margins supports the notion that the lateral termination of the coal body involved the progressive loss of the upper lithologies through a combination of nondeposition and marginal erosion and reworking. In this manner, the lowermost bench of the coal is also the most widespread. Upper benches and partings, notably the Blue band, were added with progressively less aerial extent as deposition progressed upwards, a structure not unlike a tiered layer cake. Similar models were advanced for the overlying Paradise coal bed ŽAustin, 1979.. Indeed, the Herrin and Paradise coals, at least along the southern margin of the coal field, should be considered as component coals in the same depositional system, with the Paradise adding benches to the south of the margin of the full development of the Herrin.

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References Austin, S.A., 1979. Depositional environment of the Kentucky No. 12 coal Bed ŽMiddle Pennsylvanian. of Western Kentucky, with special reference to the origin of coal lithotypes. PhD thesis, The Pennsylvania State University, University Park, PA, 390 pp. de Wet, C.B., Moshier, S.O., Hower, J.C., de Wet, A.P., Brennan, S.T., Helfrich, C.T., Raymond, A.L., 1997. Disrupted coal and carbonate facies within two Pennsylvanian cyclothems, southern Illinois basin, United States. Geological Society of America Bulletin 109, 1231–1248. Hansen, D.E., 1976. Geologic map of the Dixon quadrangle, Webster County, Kentucky. U.S. Geological Survey Map GQ1293, 1:24,000. Hower, J.C., Bland, A.E., 1989. Geochemistry of the Pond Creek coal bed, Eastern Kentucky coalfield. International Journal of Coal Geology 11, 205–226. Hower, J.C., Trinkle, E.J., Graese, A.M., Neuder, G.L., 1987. Ragged edge of the Herrin ŽNo. 11. coal, Western Kentucky. International Journal of Coal Geology 7, 1–20. Meier, A.L., Lichte, F.E., Briggs, P.H., Bullock, J.J., 1996. In: Arbogast, B.F. ŽEd.., Analysis of Coal Ash by Inductively Coupled Plasma-Mass Spectrometry: Analytical Methods for the Mineral Resources Surveys Program, U.S. Geological Survey Open File 96-525, pp. 109–125. Rogers, T.J., 1985. Sedimentation and contemporaneous structures in part of the Western Kentucky Coal Field. MS thesis, The University of Kentucky, Lexington, 52 pp.