Association of coal macerals, sulfur, sulfur species and the iron disulphide minerals in three columns of the Pittsburgh coal

International Journal of Coal Geology, 17 ( 1991 ) 21-50

21

Elsevier Science Publishers B.V., Amsterdam

Association of coal macerals, sulfur, sulfur species and the iron disulphide minerals in three columns of the Pittsburgh coal J o h n J. R e n t o n a a n d D. Scott B i r d b

aDepartment of Geology and Geography, West Virginia University, Morgantown, WV 26506, USA bChevron USA, Inc., New Orleans, LA 70112, USA (Received February 10, 1989; accepted in revised form May 30, 1990)

ABSTRACT Renton, J.J. and Bird, D.S., 1991. Association of coal macerals, sulfur, sulfur species and the iron disulphide minerals in three columns of the Pittsburgh coal. Int. J. Coal Geol., 17:21-50. This study of the Pittsburgh coal supports the premise that the amount of sulfur contained in coal, especially that represented by the iron disulphide minerals, is largely the product of the same swamp chemistry that determines the relative abundances of the various coal macerals. Through its control of the microbial degradation of plant debris and peat, the swamp water pH determines the relative abundances of the vitrinite and exinite macerals. At swamp water pH values above 4.5, increased microbial degradation of the plant and peat materials would decrease the abundance of pre-vitriniticmaterials, increase the pre-exinitic materials, produce disulphide ion via the microbial reduction of sulfate ion which would subsequently precipitate as iron disulphide minerals and result in an increase in mineral matter in the pre-coal peat. The subsequently produced coal would be more exinite rich, high in mineral matter and sulfur, especially pyritic sulfur. Within the Pittsburgh coal, the layers at the top and bottom of the coal bed and above and below the middle parting reflect non-ideal conditions of organic preservation. Because of the common chemical control for the production of exinites and iron disulphide minerals, the abundance of exinite and sulfur exhibit a strong statistical association within the Pittsburgh coal. Below pH 4.5, reduced microbial activity results in the preferential accumulation of the pre-vitrinitic woody tissues and the subsequent suppression of the relative abundance of pre-exinitic spores, pollen and cuticles. The same low-pH conditions solubalize the metals, especially iron, suppress the bacterial reduction of the sulfate ion to the disulphide ion and as a result inhibit the formation of the iron disulphide minerals. A coal produced under conditions of low pH would be bright, the sulfur content would be low and dominantly organic and because of the high degree of preservation of the plant debris, the mineral matter in the coal would be relatively low. Within the Pittsburgh coal, the general decrease in mineral matter and sulfur and increase in vitrinite content downward from the tops of both benches reflects the more ideal conditions for organic preservation prevalent within the original swamp. The degradation of plant debris and peat via dissolved oxygen in percolating groundwater or rainwater will result in an enrichment in the pre-exinitic materials but will inhibit the formation of the iron disulphide minerals. Some exinite-rich coal layers are therefore low in sulfur and dominated by organic sulfur. The amount of sulfur contained within partings will depend upon their mode of origin. If the partings formed by the extreme microbial degradation of the peat, they will usually be enriched in sulfur

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© 1991 - - Elsevier Science Publishers B.V.

22

,i.,t Rt N r ( ) N A N I ) I).S BIRI)

as illustrated by the high sulfur content o f the middle parting. O n the other hand, if the x formed b3 the slow oxidation of the peat or are of detrital origin, the sulfur content m a y b~" t o ~

INTRODUCTION

The importance of coal quality upon optimum coal utilization depends upon the intended use. The acceptable upper limits for concentrations of ash and sulfur for metallurgical coal are less than 6.0 and 0.5 weight percent respectively. All coking coal can therefore be said to be of high quality. For coals used for combustion on the other hand, the amount and kind of mineral matter and the sulfur content are critical (Reiter, 1955; Sage and Mclllroy, 1959; Cain and Nelson, 1961; Borio et al., 1968; Paulson et al., 1972 ). Liquefaction of coal is significantly influenced by the abundance of mineral matter (Davis et al., 1974; Given et al., 1975). Pyrite has been shown to have a positive catalytic effect on coal liquefaction (Tarrer and Guin, 1976 ). Some feel that the pyrite is converted to pyrrhotite in the liquefaction process which subsequently serves as a catalyst (Wright and Severson, 1972; Montano and Granoff, 1980). The maceral content of coal is determined both by the kind of plants contributing to the peat and the kind and degree of degradation to which the plant debris and peat are subjected. There are three basic degradation processes: ( 1 ) microbial; (2) slow oxidation via the percolation of oxygenated swamp waters (groundwater or rainwater) or exposure to the atmosphere; and (3) rapid oxidation via swamp fires. Of the three, the first two are the most important. Microbial degradation is largely bacterial; the activity of which is pH controlled (Baas Becking et al., 1960). Because the bacteria preferentially degrade the woody tissue and have little effect upon plant parts such as spores, pollen and the cuticles of leaves and roots, the degree of microbial degradation largely affects the relative abundance of the vitrinite and exinite macerals in the subsequently formed coal. Degradation by oxygen dissolved in swamp water (groundwater or percolating rainwater) preferentially carbonizes the woody tissue and produces the inertinites. Rapid oxidation of the plant debris and peat by swamp fires produces fusinite. Probably the majority of mineable coal forms from peats that accumulate within the interiors of coal forming swamps as opposed to peats that accumulate along the margins of the swamp. The amount of detritus transported into the interior of coal-forming swamps is restricted by the acidity of the water (Frazier and Osanik, 1969; Staub and Cohen, 1979). The overall amount of mineral matter contributed from the wind must be considered negligible. The source of most of the mineral matter emplaced in mineable coal is the inorganic component of the swamp plants and the ions dissolved in the swamp water (Cecil et al., 1979; Renton et al., 1979 ).

SULFUR CONTENTS OF PITTSBURGH COAL

23

All plants contain mineral matter (Conner and Shacklette, 1975 ). Upon degradation, these materials will be release into the accumulating peat formed from the swamp plants either in solid form or by dissolution. X-ray diffraction and X-ray fluorescence analyses of the low-temperature ashes of swamp plants conducted by one of the authors (JJR) showed that most of the solid materials consisted of amorphous alumino-silicates and quartz. It is reasonable to presume that these materials give rise, through diagenesis, to the silicate mineral component of coal ash, the clay minerals and quartz. The remaining mineral components form from the reaction between the ions contained within the swamp water and ions provided by the plants through dissolution and from the organic mass by exsolution during coalification. The chemistry which controls the degree of microbial degradation of the organic materials controls both the amount of mineral matter accumulating within the peat and the availability of metal and disulphide ions in the swamp waters. At low levels of pH, where organic preservation is favored, the amount of mineral matter contributed to the peat from the degrading plant debris would be minimal and metal ions such as iron would be readily solubalized and removed from the peat. At the same time, the concentration of sulfate ion would be expected to be low and bacterial reduction of sulfate ion to the disulphide ion would be minimal. Such conditions would not be conducive for the formation of the iron disulphide minerals. With increasing swamp water pH, the abundance of mineral matter introduced into the peat increases relative to the organic material as the plant tissues degrade. At the same time, the ionic concentrations of metals, in particular iron, and of the bacterially produced disulphide ion would increase in the swamp water, resulting in the formation of the iron disulphide minerals. If the swamp water is enriched in oxygen, ferrous ion would oxidize with subsequent precipitation of iron oxyhydroxides while the sulfur would be maintained in solution as sulphate ion. As a result, the ions necessary for the formation of the iron disulphide minerals would not be available. The overall makeup of a coal bed is therefore the result of the complex spatial and temporal intensity of these degradation scenarios within the swamp. Because the kinds and abundances of minerals in coal, in particular the iron disulphide minerals, and the kinds and abundances of coal macerals are determined by the same chemical controls, it would appear that a basic association should exist between the various kinds of coal macerals and the associated sulfur within a coal bed. It was the purpose of this study to investigate and to establish the degree of that association. STRATIGRAPHY

The Pittsburgh coal has the largest continuous areal extent of the coal beds of the Monongahela Group. Cross ( 1952 ) reports that most of the Pittsburgh

~4

,I.,i, R E N T O N -XNL) D.S. B I R D

coal bed appears to have been deposited simultaneously throughout much of the Pittsburgh coal swamp. In the Appalachian Basin, the Pittsburgh coal occurs in mineable thickness (0.7 to 6.6 m) in a large portion of southwestern Pennsylvania, southeastern Ohio, the northern half of West Virginia and parts of western Maryland (see Fig. 1 ). The coal has been removed to the northwest and west by erosion and thins southward and southwestward. It is recognizable as a bone coal or black shale throughout the margins of the Dunkard Basin (Cross, 1952 ). The continuity of the Pittsburgh coal suggests accumulation on a broad level surface with little detrital influx or erosion. Cross (1952) stated that the Pittsburgh coal in north-central West Virginia was deposited on a near-planar surface with few breaks in continuity or accumulation. The bottom of the Pittsburgh coal is defined as the base of the Monongahela Group of the Upper Pennsylvania Series (Proposed Pennsylvanian System Stratotype, Virginia and West Virginia, 1979 ). It is immediately underlain by the shales of the Casselman Formation and in some areas by the Little Pittsburgh Sandstone/Limestone facies of the Conemaugh Formation. The Pittsburgh coal is often overlain by a 0.1-0.3-m-thick shale unit called the "draw slate". Associated with and usually overlying the draw slate is the roof coal or coaly zone which varies from 0.7 to 2.7 m in thickness (Thiessen and Sprunk, 1935 ). The main coal bed commonly contains a number of partings including a laterally continuous middle parting. In the study area, the coal bed is 3 m thick and the middle parting occurs approximately 1 m beneath the top of the bed. A bone coal or shale parting occurs 8 to 20 cm beneath the 7

I

Pennsylvania

1

/ \, /J"

Ohio

Maryland

½

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~,

Kentucky

~

j

~/ ~ - ~ "

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o 5o ml, ~T n n ~ o 50 kin.

Fig. 1. Regional extent of the Pittsburgh coal.

SULFURCONTENTSOF PITTSBURGHCOAL

!=

c,

jj

Llthology

I

Member

I II I LIJ ' I I

I

i

.

J

I

I

Arnoidaburg Sandstone I

I

~ i ~ 1 ! i -'.'." _---Z~

I

[

B. . . . . d Limestone Sawickley Sandstone .

i

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and C o a l B e d

Uniontown L|meatone

- :-:-:-:--2~.....

~~

25

-

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~

~-~-

--

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,

Fiahpot Sandstone Fiahpot Coal Redstone Sandstone Redatone Coal Redstone Limestone Pittsburgh Sandstone Pittsburgh Rider Coal

Pittsburgh Coal

Little Pittsburgh Sandstone/Limestone Little Pittsburgh Coal C . . . . llsvllle Sandstone Little Clarkaburg Coal Lower Connellsvllle Sandstone Clarkaburg Limestone Morgantown Sandstone

Elk Lick Coal .

[

.

=- ( n n " .

.

i i~ ~ - ~ - - ~ i II II II I [ II

, ~

,

Shale

k

West Milford Coal Grafton Sandstone

mlm~

Ames Limestone

Limestone Sandatone Coal

Fig. 2. Stratigraphy of the Pittsburgh coal interval.

middle parting. Together, they are called the "bearing-in-bands" because they define a small layer of the coal within the bed which is informally termed the "bearing-in-bench". Figure 2 shows the stratigraphy enclosing the Pittsburgh coal in northern West Virginia. SULFUR IN COAL

Sulfur occurs in coal primarily in two forms: organic and pyritic. Pyritic sulfur includes sulfur contained in either of the two common iron disulphides, pyrite and to a lesser extent, marcasite. The sulfur in coal can be of both syngenetic and epigenetic origin. Most of the sulfur in coal is syngenetic with early syngenetic sulfur being implaced during the peatification phase and late syngenetic sulfur being accumulated during the gelification-humification stage of coalification. Epigenetic sulfur is present in cleat and fracture fillings. In West Virginia coals, the epigenetic sulfur is less abundant than syngenetic sulfur.

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SAMPLING

Sample location and collection: Three complete columns of the Pittsburgh coal were collected as oriented blocks from adjacent surface mines in Harrison County, West Virginia (see Fig. 3 ). The experimental design was to recover two columns relatively close together (column PK1 and PK4 were 40 m apart) and another some distance away (column PK5 was approximately 0.7 km to the southwest) to test the continuity of petrographic zones within the surface mines. Figure 4 shows the stratigraphy at the sample locations. Each coal block was marked as to position and orientation in the bed. The stratigraphic thickness of each individual block was variable depending on natural breaks in the coal such as bedding planes, cleats and fractures. An average of 20 blocks were recovered at each location. Thin partings were included within the coal blocks. When possible, the roof and floor lithologies were sampled. The lower 37 cm of column PK5 was not recoverable as an

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rface M ~ ~ I /_x ~ J Permit76-79 ~ SO0~...... #) (/ ~ P K t I Wolf Summit PK4 7.5' Quadrangle

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/I

I

PENNSYLVANIA

Harrison Co . . ~ . ~

I ~j~j~z~

OHiOJWolfSumm~tt

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Fig. 3. Sample location map.

~,!

27

SULFURCONTENTS OF PITTSBURGH COAL Horizontal Distance in Motors NE

0

SW

20

40

60

80 100 110 12

10-

450 460 470 O~--L~ 1

DESCRIPTION Gray Shale

9-

Redstone Coal, poor quality Gray Clay Seatrook

lU >

6-

Redstone Limestone, massive

•

5-

Gray Shale with Limestone Interbeds

--=

4-

Gray Shale

"3Blank Shale ,,

2-

>

t-

Coaly Zone,

O-

:~

-1

PK4

PK5

poorly developed Bone Coal, persistent Upper Bench, dull parting, discontinuous Middle Porting, continuous Rearing In Bench Lower Bench, bright, blocky Dark Gray Claystone Seatrock

LITHOLOGY E__~-'--~"~Carb. . . . . . . . Shale

Shale

2"I SCALE

~ = = ~ Limestone

1~

I

oJo

I COs,

Meters

~'o 4'o

Fig. 4. Stratigraphy of collection sites.

oriented block because the coal was highly fractured, possibly as a result of the mining operation. ANALYTICAL P R O C E D U R E S

Lithotype description: Each block was embedded in plastic, cut perpendicular to bedding and parallel to face cleat. The oriented cut surface was then polished and described as to lithotype after the method of Stopes ( 1919). A minimum thickness of 5 mm was arbitrarily assigned for a lithic unit. Following lithotype description, each lithic unit was cut from the polished block, crushed to - 20 mesh and prepared for petrographic analysis.

Sulfur analysis. Sulfur analyses were performed using a LECO IR33 sulfur analyzer. Pyritic sulfur was determined on a HCL-leached low-temperature ash. Sulfate sulfur was determined by LECO analysis of the coal before and after HCL leach. Organic sulfur was calculated as the difference between total

2t~

I

R[iNI()N \ N I ) i ) S . BIRD

sulfur and the sum of the pyritic and sulfate sulfur. All analyses were performed in triplicate.

Petrographic analysis. Each lithotype sample was prepared in two pellets. Maceral analyses were performed by counting 500 points on each of the two pellets. The distribution and maceral associations of the iron disulphide morphologies were recorded according to the classification scheme of King (1978). The iron disulphide morphological types were determined as percentages of the total iron disulphide in each lithotype interval. The petrographic analyses of the three columns are graphically illustrated in Figures 5 and 6 for the upper and lower benches respectively. The point-count data produ.ced from the individual lithotype bands were converted to equal t 0-cm increments using a technique termed Stratified Randon Sampling (Mendenhall et al., 1971, section 5.6 ). For this investigation, Stratified Random Sampling was used to redefine the composition of each 10 cm interval by taking into account the compositions of the number of small layers or bands which composed each interval. Each small band was weighted according to its thickness as compared to that PK1 PK4

PK5

8

0 ~

50 100 % of Volume

0

50 100 % of Volume

Vltrinite

~

Inertln,te

Exinlte

mid

Mineral Matter

0 50 100 % of Volume ~150 cm 0

Fig. 5. Petrographiccomposition,upper bench.

29

SULFUR CONTENTS OF PITTSBURGH COAL 85.t

70.1 80

gO 90 100 100 110 110 120 12(~ 130 130 140 14C 150 15C

16(] 160 170 17(]

10(] 150 100 190 200 205.1

200

; . . . . 510 ' ' '1;0 % of Volume 21(]

~

Vitrlnita

~l.,ta Inartlnlte

simms

Mineral Matter

220

;

221,1

.... do'"

% of

'~;o

Volume

I .... i .... J 0 50 100 % of Volume

Fig. 6. Petrographic composition, lower bench.

of the thickness of the re-calculated (10-cm) interval. The data were converted for the following reasons: ( l ) The surface mine samples were recovered as oriented blocks of various sizes which were then subdivided into a number of smaller intervals with a wide range of thicknesses. (2) Because of the lateral variability of individual lithotypes, correlation was not possible on a band to band basis. Conversion of the petrographic data to larger more persistent intervals was necessary to facilitate correlation. ( 3 ) Division of the data into equal intervals provided an even distribution of information in vertical profile. This facilitated both statistical analyses and the presentation of compositional information on illustrations.

3(I

i I R.t-NI()N

PK1 PK4

PK5

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~ '°1

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.... 0

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50 % of V o l u m e

100

•

Vitrinite

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Inertinite

F ~

Exinite

I

Mineral Matter

0

50 % of V o l u m e

100

Fig. 7. Incremental petrographic composition, upper bench. PK1 85.1

PK4

PK5

78,1

90"

:1 1

90-

100-

100 ~ -

110-

-

-

-

110

. . . . . .

120

.

120 .

.

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.

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130 . . . . . 140 . . . . . . . .

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160

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170

170

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......

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.... 50 % of Volume

[ ~ J

100

Vitrinite

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Inertinite

Exinite

~

Mineral M a t t e r

50 % of V o l u m e

Fig. 8. Incremental petrographic composition, lower bench.

100

~\NI)t)%.BIRI~

SULFUR CONTENTS OF PITTSBURGH COAL

31

(4) The presentation of all data on the same basis allowed comparisons to be made among samples. Figures 7 and 8 show the petrographic composition of the sample columns in terms of the calculated 10-cm increments. D I S T R I B U T I O N O F T O T A L S U L F U R A N D S U L F U R SPECIES

Total sulfur The average total sulfur for all three columns is 3.78%. The sulfur content of the upper bench was 4.74% whereas that of the lower bench was 3.42%. The range of total sulfur values within the two benches was quite similar. The sulfur content of the upper bench ranges from 2.16% to 8.15% whereas that of the lower bench ranges from 1.77% to 7.22%. Plots of the vertical sulfur distribution in the benches showed that total sulfur reached maxima at three zones within the coal bed: ( 1) at the top of the coal bed; (2) at the base of the coal bed; and (3) associated with the middle parting. This same relationship has been demonstrated for other coals in the Dunkard Basin (Fumich, 1982 ). According to the chemical model proposed by Cecil et al. (1979) and Renton et al. (1979), these zones represent peats that had been subjected to accelerated microbial degradation as the result of increased swamp water pH. The accelerated rate of organic degradation resulted in the increased accumulation of plant derived inorganics, in particular the amorphic aluminosilicates which were the precursors to the silicate minerals, the clay minerals and quartz. The conditions promoting increased microbial degradation of the organic materials also resulted in the bacterial reduction of sulfate ion to the disulphide ion which then reacted with the iron ion to form the iron disulphide minerals. The zones at the base of the coal bed (and often above major partings) reflect chemical conditions within the swamp that were becoming increasingly more favorable for the preservation of organic material. The comparable zones at the top of coal beds and commonly below partings represent progressively deteriorating conditions for organic preservation. The partings themselves are often authigenic, representing layers of peat that have been subjected to high-pH conditions ( > pH 6) resulting in organic degradation of such intensity so as to preclude the preservation of sufficient organic material to produce a coal (Renton and Hamilton, 1988 ). These conditions would also be ideal for the precipitation of the iron disulphide minerals. As a result, such partings would be expected to contain higher sulphur contents than the enclosing coal. Other partings may form by the slow oxidation of the peat resulting from a depressed watertable or may be the result of the introduction of detrital overbank materials such as a crevasse splay deposit. In either case, the sulfur content of the parting would be expected to be lower than the enclosing coal. In the three sections of the Pittsburgh coal studied,

the total sulfur concentration in the middle parting, although higher than that of the enclosing coal, was less than at either the base or top of the bed,

Pyritic sulfur In the upper bench, pyritic sulfur was the most abundant of the sulfur species (2.17%). The pyritic sulfur content of the lower bench was much lower (0.63%). The range of pyritic sulfur values in the upper bench (0.25% to 8.15%) was greater than that of the lower bench (0.20% to 1,74%). Pyritic sulfur showed a maximum concentration at the top of the upper bench. There are two distinct pyritic sulfur maxima in the lower bench; one at the base and one beneath but not including the middle parting. The distribution of pyritic sulfur values is much more variable in the lower bench than the upper bench.

Organic sulfur Organic sulfur shows little variability between benches although the concentration of organic sulfur in the lower bench was slightly higher than that of the upper bench (2.50% versus 2.05%). The range of organic sulfur values in the lower bench ( 1.02% to 5.86%) was larger than the range of organic sulfur in the upper bench (0.59% to 3.37%). Organic sulfur was the most abundant of the sulfur species in the lower bench. The vertical distribution of organic sulfur in the two benches remained reasonably constant in each bench except for a few large anomolous occurrences. The bright coal layers of the lower portion of the lower bench contained the highest organic sulfur contents. The lowest organic sulfur values in the lower bench occurred in association with the dull coal layers beneath the middle parting. In the upper bench, very low organic sulfur values occur in association with the upper carbonaceous shale layers. The highest values occur in the clarain layers of the upper central portion of the bench. Based upon the higher average vitrinite content (Table 1 ), it appears that the peat that formed the lower bench accumulated under more ideal (lower pH) conditions of preservation. One would expect less pyritic sulfur and more organic sulfur emplacement under such conditions. As will be shown later, framboidal pyrite was also more prevalent in the lower bench. Framboidal pyrite appears to be the dominant morphological form under the more ideal conditions of preservation while the massive forms are favored by higher pH conditions.

Sulfate sulfur Sulfate sulfur was the least abundant of the sulfur species in both benches. Some layers contained no measurable sulfate sulfur, most notably in the lower bench. The vertical distribution of sulfate sulfur was similar to that of the total sulfur; probably because the sulfates are produced by the weathering of the disulphides (Neavel, 1966) and therefore can be expected to increase where the amount of available disulphide increases.

SULFURCONTENTS OF PITTSBURGH COAL

33

TABLEI

Comparison of the petrographic composition of the column samples divided by bench with the maceral associations of the iron disulphides in the benches Column/ Bench

Vitrinite 1

In )Vitrintte 2

Exinite 1

In 2 Exinite

Inertinite 1

In Inertinite 2

PKI Upper

71.66

52.89

6.82

16.23

11.57

3.74

PK4 Upper

57,46

58.36

I t.67

20.23

16.13

3.84

PK5 Upper

66.96

61.44

5.51

19.26

11.99

3.95

Average Uaper

65.36

57,56

8.10

18.57

13.23

3.84

PK1 Lower

74,39

69°09

9.23

16.41

11.32

4,48

PK4 Lower

78.04

51.92

8,06

29.76

10.07

6.72

PK5 Lower

79.06

65.70

6.37

18.32

11.35

5.85

Average Lower

77.16

62,24

7.59

21.50

10.91

5,68

Average All Columns

71.26

59.56

7.99

19.40

12,07

4.63

1 petrographic comtoosition is I~ercentage of volume 2 maceral association is percentage of total iron disulfide

DISTRIBUTION OF IRON DISULPHIDES

Figures 9 and 10 display the vertical distribution of the total amount of iron disulphides (in volume percent) in the three columns for the upper and lower benches respectively. All three vertical profiles are similar in that their sulfur maxima occur at approximately the same stratigraphic level. The largest concentration of the iron disulphides was in the upper 10 cm of each column in what are mostly carbonaceous shales. It is not uncommon in coal beds to observe the coal grade into a carbonaceous shale toward the top and the bottom of the bed. These shales are commonly high in pyritic sulfur. These layers are interpreted as having formed from peat that was being subjected to increasingly non-ideal conditions for organic preservation. The plant debris and peat were being solubalized and removed, plant-derived mineral matter was concentrating and the conditions were becoming increasingly conducive for the formation of iron disulphides. The percentages of iron disulphides decrease rapidly downward in each upper bench. Column PK5 has a higher percentage of iron disulphide in its upper layers than do the equivalent layers of columns PKI and PK4. The upper parting in column PK1 contains more iron disulphide than the adjacent coal

34

.I.J RENF(.)N AND I ) S g i r l )

PK1 PK4 o

10

0

20

.............

'°5 5o,,

_ , ....... .......

10

~49 PK5 i

0

24.3

::

6o~J-- ............~

2

!

-1

6070-

....

,oil

6o,, ,

8O 85.1

.......... -1 i 10

% of V o l u m e

% of V o l u m e

% of V o l u m e

Fig. 9. Iron disulphide concentration of 10-cm increments, upper bench. PK1

PK4

85.1

PK5 61.9

~;:

9O 70

............

IO0 80 110 90 120 100

. . . . . . . . .

110

.

130 .

.

.

.

140 120 150 130

~--

160 140 !

......

170 150 180 160

. . . . . . . . .

190 2OO

196.5 J f - ~ - 0 0

50 % o! V o l u m e

100

F~[ r - ~ - - ~ 50 1 O0 % of V o l u m e

Fig. 10. Incremental iron disulphide concentration of 10-cm increments, lower bench.

layers. The same is true for the middle partings in all three columns. These high sulfur contents would argue for a degradational origin for the partings. The lower bench (see Fig. 10) shows two iron disulphide maxima in vertical profile in addition to the minor maximum which occurs just below the middle parting. The first maximum, which is most distinctive in PK4, is in

SULFUR CONTENTS OF PITTSBURGH COAL

35

the lower central portion of the bench. The second maximum is at the base of the coal bed. DESCRIPTION AND DISTRIBUTION OF THE INDIVIDUAL IRON DISULPHIDE MORPHOLOGIES

Framboids Framboids are spherical aggregates ofeuhedral iron disulphide crystals. The diameters of the framboids ranged from 5 to 20 microns with most spheres being at the lower end of the range. The size of the individual crystals in each framboid was similar and was usually less than 1 micron. Framboids were virtually always observed in association with other small pyrite euhedra. Framboids are generally rare throughout the coal bed and were relatively most abundant where the total iron disulphide was low. Approximately 3% of the total iron disulphide in an average upper bench coal was composed of framboids whereas framboids comprised approximately 7% of the iron disulphides in an average lower bench coal. Figures 11 and 12 show the relative abundance distribution of framboids and the three morphological subclasses of framboids in the column samples. The morphological subclasses are based on the amount of coalescence between the individual euhedra composing each sphere. Discrete framboids are free of infilling iron disulphide and show complete definition of the crystal faces of the individual crystals making up each framboid. The discrete framboids are the most common subclass. The completely coalescent subclass includes framboids in which the intercrystallite voids are infilled by iron disulphide. This form appears as smooth spheres. The partial coalescent category includes all framboids in which the spaces between individual euhedra are partially filled. Coal layers where framboids were most abundant were in the lower-central portion of the lower bench (see Fig. 12). These layers (180-190 cm of PK1 and 190-200 cm of PK4) were zones in which the total iron disulphide was less than 2%. The other layers of relatively high abundance were located in layers containing low total iron disulphide. There was much lateral variability in the relative abundances of framboids in the columns. In the lower bench, the highest concentrations were generally at similar stratigraphic levels, but in the upper bench there was very little horizontal similarity among the profiles (see Fig. 11 ). Isolated euhedra Isolated euhedra are small crystalline iron disulphide grains which occur individually or in groups in which no crystal is in contact with another. Most isolated euhedra observed were octahedrons or cubes and were less than 10 microns in largest dimension. Euhedra less than 5 microns were more abun-

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PK1 PK4

~

0 i t 10~-- . . . . . . . . . . . .

20 - ~ 30 . . . . . . . . .

20 -~. . . . . . ,' 30-.~ .

©

40~ ............

' /

PK5

.

.

.

.

.

.

o --~ .

50

............

60

i3°~

!

' 4050

T~--~ ~ = 78. I ~ - ~ - ~ - F • • ~-I 61.9-~ 5O 100 0 50 100 0 % of Total % of Total Iron Disulfide Iron Disulfide

i ..............

80 ~-b-, , 85.1

•

Discrete

I

i

i 20-~ . . . . . . . . . . . . . . . . . . . . q [

4 9 ~

~, 8o

. . . . .

tO

.

, ~

~

50 % of Total Iron Disulfide

t tO0

Complete Coalescence

~t""""'~ Pa r t i a I Coalescence

Fig. l 1. Percent framboids of total iron disulphides, upper bench. PK1

PK4

PK5

85.1

78.1 r

10090 - i

90~- ............. ~ '° I 100~-- ............ ~ 8°t

110120130-

1 61.9

1,0¢- ........

! 00

1204- .....

-i 100

140150160170180-

190200205.1-

0

•

Discrete

IlI

10 % of Total tron Disulfide

20

Iron Disulfide

Complete Coalescence

Partial Coaleacence

Fig. 12. Percent framboids of total iron disulphides, lower bench.

~, B I R ! t

37

S U L F U R CONTENTS O F P I T T S B U R G H COAL

dant than those greater than 5 microns. Isolated euhedra smaller than 5 microns comprised approximately 16% of the total iron disulphides in a typical upper bench sample and 22% of the iron disulphides in a typical lower bench sample. Isolated euhedra greater than 5 microns maximum dimension averaged less than 4% of the total iron disulphide in any sample. Usually, the abundance of euhedra larger than 5 microns increased as the total amount of isolated euhedra increased. Figures 13 and 14 present the distribution of isolated euhedra in the column samples. The zones of maximum relative abundance were generally at the same stratigraphic levels in all three columns. The lower bench contained more isolated euhedra, higher relative percentages of isolated euhedra and more euhedra larger than 5 microns than did the upper bench (see Fig. 14). Similar to framboids, isolated euhedra were most abundant in coal layers that contained little iron disulphide. In the upper bench, the three zones of high relative abundance were all within layers in which the total iron disulphide was less than 2%. Except for the base of column PK4, this relationship was also true for the lower bench (see Fig. 14 ). The occurrence of euhedra larger than 5 microns was almost totally limited to the lower bench and in intervals with high vitrinite contents, although the intervals with the highest vitrinite content do not always contain the maximum occurrences of the large euhedra. Coal layers which contained the most mineral matter (top, partings, base) also contained low percentages of isolated euhedra. PK1 '0 =

10

PK4

lili i i i i i i!il PK5

8 ,o

lji J

ao

~-

lOil

4.0

20

50

: ........................

I

3O 4G 5C

~

8085.1

.... 0

~ .... 25 % of Total Iron Disulfide

71 50

25 % of Total Iron Disulfide

•

Larger than 5 microns

~

S m a l l e r than 5 microns

50

O

25 % of Total Iron Disulfide

50

Fig. 13. Percent isolated euhedra of total iron disulphides, upper bench.

38

J.J. RENTON AND I).S. BIRD

PK 1

PK4

PK5

85.1 90-

I00110120© 130~.

140-

2 ~

150"

u.

160-

~-

170180-

190200205.1-

0

25

50 =vv

i

% of Volume 0

0

25

50

%

25

50

of Volume

% of Volume

m

Larger than 5 microns

~

Smaller than 5 microns

Fig. 14. Percent isolated euhedra of total iron disulphides, lower bench.

Aggregates of euhedral crystals Euhedral aggregates are similar in appearance to groups of isolated euhedra except that there is some degree of contact among individual crystals. The degree of contact exhibited by the individual euhedra in each aggregate was used to divide the occurrences into the coalescence subclasses shown in Figures 15 and 16. Discrete aggregates show contact between individual crystals at only a few points such that all crystal faces or edges are clearly visible. Complete coalescent groups are aggregates in which all crystals are in contact forming a continuous mass. This subclass is similar to the "patches" of euhedra described by Grady (1977). Euhedra overgrown by iron disulphide were also recorded as completely coalescent. Also classified as euhedral aggregates are groups of small euhedra and subhedral grains that occur within exinite macerals. When viewed with a scanning electron microscope, these occurrences appeared as irregular, nodular or crystalline grains less than 1 micron in diameter. This type of euhedral aggregate was usually recorded in the partially coalescent subclass and was most common in dull coal layers, partings and at the base and top of the coal bed. Aggregates of larger and more regularly shaped euhedra were more common in bright coal layers and were rarely

39

SULFUR CONTENTS OF PITTSBURGH COAL

PK1 0 lC

PK4

m

0 o

~

8c

8

. . . . . . . . . .

0

25 % of Total Iron Disulfide

Discrete

7~

50

25 % of Total Iron Disulfide

o

~

50

0

25 % of Total Iron Disulfide

50

Complete Coalescence

Partial C o a l e s c e n c e

Fig. 15. Percent aggregates ofeuhedral crystals of total iron disulphides, upper bench. PK 1

PK4

PK5

85.1 g01001100

120130-

p-

140150180170180190200205.1 °

0

Discrete ~

~

25 % of Volume

50

Complete Coalescence

Partial C o a l e s c e n c e

Fig. 16. Percent aggregates ofeuhedral crystals of total iron disulphides, lower bench.

4[!

~ I I-tI, N I ~ t N \ N F ) [ : ~ ' ~ , B I R I )

observed in close proximity to the small subhedral varieties associated with exinite macerals. Figures 15 and 16 show the distribution of aggregates of euhedral crystals in the sample columns. Significant variability exists among the columns although certain zones of maximum occurrence are present in stratigraphically similar zones in all three. The upper bench profiles show higher concentrations at the top and bottom of the bench most notably in the intervals overlying the middle parting (see Fig. 15). The majority of the euhedral aggregates in these intervals were partially and completely coalescent aggregates of microcrystals within exine material. Maximum occurrences of this subclass occurred in the lower bench in association with dull coal (below the parting) and at the base. The other zones of high concentration in both benches, especially in the lower bench, were the result of aggregates of regular euhedra in association with vitrinite.

Cleat and jkacture fillings The occurrence of iron disulphide within cleat and fractures in the Pittsburgh coal was minor and showed very little systematic stratigraphic or lateral persistence between samples (see Figs. 17 and 18 ). The amount of cleat and fracture fillings was often high where the total amount of iron disulphide was also large, such as the top of column PK4 (see Fig. 17). This positive relationship was supported by the Spearman correlation coefficient between cleat and fracture filling disulphide and total disulphide which was 0.485 at a 0.0001 level of significance. On a megascopic scale, vitrain and clarovitrain layers were often sites of visible cleat and fracture fillings, perhaps because of their brittle nature. Microscopic examinations, however, did not confirm this relationship. There were several relatively high cleat and fracture filling ocPK1

PK4

o

PK5

20

........

10

o 30 .

.

.

.

.

10- ~ 20

50-

40 I

60 . . . . . . . . . . . .

50@ 6° j÷

30 ............. 40

70 i 80 ~ 85.1, ~ - T ~ - ~ - - ~ 5 % of Total Iron Disulfide

70 i

.

.

.

.

.

.

.

.

.

.

.

50

............

78.1-t~--~T '- - ~ - ' ~ 61.9 ~ - - ~ T - ~ - 10 0 5 10 0 5 % of Total % of Total Iron Disulfide Iron Disulfide

10

Fig. 17. Percent cleat and fracture filling of total iron disulphides, upper bench.

41

S U L F U R CONTENTS O F P I T T S B U R G H COAL PK4

PK1 85.1

78,1

lOO

90

J 9o . . . . . . . . . . .

PK5 61.9 70 80

lOO-

110

I

90 110-

120-

lOO 120-

130-

11o. 130

140140 150-

130 150-

160

140 160-

170

150 170 !

180

59.~ 1804

190

Concealed

190 2OO 205.1

0

....

5 ....

% of Volume

10200 210

96.E

221.1

.... o

i .... 5 % of V o l u m e

5 % of V o l u m e

10

10

Fig. 18. Percentcleat and fracturefilling of total iron disulphides,lower bench. currences in bright coal layers such as the 130 to 150 cm levels of PK4 (see Fig. 18) but the correlation coefficient between cleat and fracture iron disulphide and the amount of vitrinite (a major constituent of bright layers) in the coal was - 0 . 2 9 3 at a 0.0256-level of significance. Apparently, factors other than the availability of abundant fractures control the occurrence of iron disulphide cleat and fracture fillings.

Irregularforms Large ( > 10 microns) and massive irregularly shaped grains of iron disulphide were the most common morphologies in the Pittsburgh coal. In general, the occurrence of irregular massive morphologies were located in layers with high total iron disulphide contents. Approximately 60% of the total iron disulphide in the sample intervals having the highest iron disulphide contents (upper 10 cm of each column) was composed of the irregular massive morphologies. The remainder of the total iron disulphide in these intervals consisted mostly of euhedral aggregates and to a lesser extent, isolated euhedra. The irregular massive iron disulphide particles displayed a wide variety of shapes and sizes. Macroscopically, the irregular grains a~ppeared most often as spherical blebs, lenticular nodules or massive intergrown layers. Large nodules (5 to 20 cm diameter) were occassionally observed in certain coal layers. Irregular massive morphologies comprised 56% of the total iron disulphide

42

JJ. RENFON A N I ) D.S. BIRD

PK1 PK4

PK5 0 3

104

20-

2

304050a

85 0

I ~

50 % of Total Iron Disulfide

7 100

0

61.9 50 10o % of Total Iron Disulfide

:II S,,oo,ureO"'"°d

50 % of Total Iron Disulfide

100

,.,,,,.out Oe,, S,ruo,uro

Contorted Cell Structure

Fig. 19. Percent irregular forms of total iron disulphides, upper bench.

in the upper bench and 35% of the total iron disulphide in the lower bench. The irregular forms which lacked any evidence of individual component crystals were divided into three subclasses based upon the presence and degree of compaction of preserved cell structure. Irregular varieties without cell structure were the most abundant subclass. Irregular massive iron disulphide without cell structure was most abundant near the top of the coal bed (see Fig. 19 ), the upper-central portion of the lower bench and the base of the lower bench (see Fig. 20 ). Irregular massive iron disulphide containing contorted vitrinite cell wall structures were rare in the column samples and generally displayed maximum occurrences where the total amount of irregular massive iron disulphides was highest. Irregular morphologies which contain distinct fusinite cell wall structures were the least abundant subclass. It showed maximum occurrences where the total amount of irregular massive morphologies was highest, such as in the 30- to 50-cm intervals of column PK4 (see Fig. 19). MACERAL ASSOCIATIONS OF THE IRON DISULPHIDES

Most of the iron disulphide occurrences in the coal were observed to be confined to particular coal macerals. Many of the iron disulphide grains in sample intervals with high mineral matter contents have no maceral association but instead are surrounded by other mineral matter, usually clay minerals and quartz. Such maceral associations were recorded as "unknown maceral association" according the the iron disulphide classification scheme.

43

S U L F U R C O N T E N T S O F P I T T S B U R G H COAL

PK4

PK1

PK5

86.1 90100110-

,~

12o-

8

130t40-

:E

150160-

t~

~

180 ~

190 2 0

50

10

% of Volume 0 0

50

100

% of Volume

m

Well Defined Cell Structure

~

Without Cell Structure

Contorted Cell Structure

Fig. 20. Percent irregular forms of total iron disulphides, lower bench.

The largest percentages of the total iron disulphide in the coal are associated with the vitrinite maceral group. The least quantities are associated with the inertinite macerals. The maceral association of the iron disulphides is highly variable and often is quite different from the relative abundances of each of the maceral groups in a sample interval. Perhaps the most significant observation was the selective occurrence of iron disulphides within the exinite macerals. In a number of sample intervals, as much as 73% of the total iron disulphide is associated with exinite.

Iron disulphide in vitrinite All classes of iron disulphide morphologies were observed to occur within vitrinite macerals (see Figs. 21 and 22) The amount of iron disulphide within vitrinite varied with the total amount of vitrinite in the coal. The proportion of the total iron disulphide in vitrinite decreased as the content of vitrinite decreased. However, a small decrease in vitrinite content was usually associated with a large decrease in the percentage of iron disulphide within vitrinite. This relationship was particularly evidence above, below and within the middle parting. The high percentages of iron disulphide in vitrinite in the

44

!

I

R[!Nif)N.\N[',I).~,

BIRI)

PK1 o

fo

~

PK4

. . . .

,I

~_

2oL

~o

!

8o~. 7o~r:

i

° l ........

i

L,-i'ol .....

ii! ~°

..... i.....1

,

~

, 5or

.......

-

PK5

~..... i

8°r

j

t

.

.

.

.

.

.

/ .

I

30

I14o 50-

~l

8o~.

8S.l:L . . . . . . . • . . . . . 0

781~ ~ - , T .

50 100 % of T o t a l Iron Disulfide

0

,-Astg~

50 % of T o t a l Iron Disulfide

100

50 % of Total Iron Disulfide

100

Fig. 21. Percent iron disulphide in vitrinite of total iron disulphides, upper bench. PK1

PK5

PK4 78.1

85.1 90

90-

100-

100110110120120-

130140-

150160 170-

180" 190 200205,1 0

50 100 % of Volume

9: ...... 0

50

100

2 0

50 % of V o l u m e

100

Fig. 22. Percent iron disulphide in vitrinite of total iron disulphides, lower bench.

upper intervals of columns PKI and PK5 occurred in intervals where the irregular iron disulphide forms replace exinite macerals. The abundance of iron disulphide in exinites was so great in these layers that it often obscured the exinite material to the extent that the iron disulphide appeared to be associated only with the surrounding vitrinite. This relationship occurred where the

45

SULFUR CONTENTS OF PITTSBURGH COAL

total amount of iron disulphide in the coal was the highest. Where mineral matter other than iron disulphide was highest, such as at the top of the bed and above, below and within partings, only small percentages of the total iron disulphide were associated with vitrinite. Apparently, the conditions which degrade the organic material and concentrate inorganic substances have a significant effect on the abundance of iron disulphide minerals contained within vitrinite.

Iron disulphide in exinite Table l is a comparison of the maceral group composition of the coal benches in the sample columns with the maceral associations of the iron disulphides in each bench. The comparison shows that the percentage of iron disulphides in exinite macerals is consistently higher than the total amount of exinite in the coal. Figures 23 and 24 show that the selective occurrence of iron disulphide within exinite macerals was the highest above, below and within the middle parting. The amount of iron disulphide within resinite increased to levels which were much greater than the total amount of resinite in the same intervals. Throughout the rest of the coal bed, most of the iron disulphide occurred within sporonite. In bright coal layers, these occurrences were usually small euhedra or euhedral aggregates of euhedral and subhedral crystals within microspores, megaspores, cutinite and resinite. The occurrence of iron disulphide within cutinite was irregular, in some cases increasing at the top and bottom of columns (PK4) and also adjacent to the middle parting (PK5). Commonly, cutinite with well developed rims of iron disulPK1 PK4

0

~

10!

0 0

^^

PK5

u. w

V. o 8~

0

25

50

7 0

% of Total kon Disulfide

25 % of Total Iron Disulfide

6 1 . 9 ~ " 50

0

25 % of Total Iron Disulfide

' 50

Sporlnite (Includes Megespores)

Cutinite

~

Reelnite

Fig. 23. Percent iron disulphide in exinite of total iron disulphides, upper bench.

46

3J. REN FON AN[) D S, BIRD PK 1

85.1 90-

I00-

110-

110-

~0 1200

120

130-

~

130

140-

140-

150-

~ pZ

PK5

90-

fO0co

PK4

78.1

160170180-

170180 !

--

,159'5 ]

19019 O

200205.10

25 % of Total Iron Disulfide

C o n c s a I•

50200 210 221.1

d

eje.o ~ . 5 ~ [ ~:. : ~ ~

0

....

0

25

% of Total Iron Disulfide

50

25 % of Total Iron Disulfide

50

Sporinlte (Includes Megaeporos) Cutinite

~

Resinite

Fig. 24. Percent iron disulphide in exinite of total iron disulphides, lower bench.

phide particles occurred next to another cutinite fragment with no associated iron disulphide. According to the chemical model, the chemical conditions conducive to the degradational concentration of pre-exinitic materials also result in the precipitation of iron disulphide minerals. This would explain why the iron disulphide minerals associate with exinite more so than the other macerals. It would also explain the high concentration of exinite related iron disulphides within the middle parting. Iron disulphide in inertinite The occurrence of iron disulphide within inertinite macerals was minor as compared to the amount of iron disulphide associated with vitrinite and exinite. The amount of iron disulphide associated with inertinite was always less than the percentage ofinertinite in the coal (see Table 1 ). Figures 25 and 26 show the stratigraphic distribution of iron disulphide within inertinite. The associations were approximately divided equally between semifusinite and fusinite. Fusinite contained more iron disulphide than did semifusinite perhaps because of its higher porosity. Most of the iron disulphide occur-

47

SULFUR CONTENTS OF PITTSBURGH COAL

PK1 PK4 o

1

PK5 2 20

31

I!~':~~"~i~ ~

4 ,o

5

Fiii

3C ,

4O I

80-t 70"

6O t

8085.1-

61.9 J . . . .

O

m

10 % of Total Iron Disulfide

20

0

10 % of Total Iron Disulfide

20

0

I .... 10 % of Total iron Disulfide

20

Fusinite 8emifuelnite

Fig. 25. Percent iron disulphide in incrtinite of total iron disulphides, upper bench.

PK1

PK4

0

10 % of Total iron Disulfide

PK5

20

Iron Disulfide

Fueinito Semlfuslnlte

Fig. 26. Percent iron disulphide in inertinite of total iron disulphides, lower bench.

rences within semifusinite and fusinite were irregular morphologies although occasionally, euhedra and framboids were observed within cell cavities. No iron disulphides were observed within macrinite, micrinite, sclerotinite or inertodetrinite. Figures 25 and 26 show that there was much variability in terms of relative abundance of the iron disulphides among columns. However, the m a x i m u m occurrences of the iron disulphides were usually at the same stratigraphic levels in all three columns. The largest concentrations of iron disulphide in inertinite were in the lower bench below the middle parting and at the base of the bed. The highest iron disulphide concentrations in the central lower bench coincided with the high inertinite zone of the lower bench. However, this was also a zone containing low amounts of iron disulphide. Two unusual relationships are evident on Figures 25 and 26: ( 1 ) the lower bench contained more iron disulphide in inertinite than does the upper bench: and (2) the partings contained virtually no iron disulphide in inertinite even though the concentration of inertinite was very high. It is possible that mineral matter may have filled the voids in the fusinite and semifusinite and prevented subsequent iron disulphide precipitation. SUMMARY AND CONCLUSIONS

The increased sulfur content at the top and bottom of the coal bed reflects the less than o p t i m u m chemical conditions for organic preservation that existed within the swamp during the initiation and demise of peat accumulation. At the bottom of the bed, the conditions of low pH necessary for the preservation of sufficient peat to be a precursor to the coal were just developing. The coal at the top of the bed formed from peat that was accumulating in a deteriorating swamp where the conditions for preservation of coal forming peat were coming to a close. These same conditions are also observed both above and below major partings. The statistical association between exinite and sulfur is a direct reflection of the geochemical conditions within the swamp. Conditions of elevated pH enhance the degradation of pre-vitrinitic plant materials which in turn result in the accumulation of the pre-exinitic materials. These same elevated conditions of pH increase the availability of dissolved metals, in particular iron, enhance the bacterial reduction of the sulfate ion to the disulphide ion and result in the precipitation of the iron disulphide minerals. Where sulfur contents were in excess of 1 weight percent, the massive varieties of iron disulphide were more abundant. The more massive forms of pyrite appear to associate with those zones of the coal bed where the conditions of preservation were less than ideal, i.e. where the increasing swamp water pH favored the presence of dissolved iron and the bacterial reduction of sulfate ion.

SULFUR CONTENTS OF PITTSBURGH COAL

49

Although the data are limited to only three sections of a single coal bed and broad generalizations based upon such a restricted database would be questionable, the data do appear to support the original premise of the work that the chemistry which determined the basic maceral makeup of a coal bed also determined the abundance and distribution of sulfur within the coal. Geochemical conditions of low swamp water pH which promote the preservation of pre-vitrinitic materials or oxygen-rich conditions such as found in raised bogs that generate pre-inertinitic materials are less conducive for the formation of iron disulphide minerals. High-sulfur implacement is promoted by elevated swamp water pH. The high statistical association between sulfur and vitrinite is explained simply by the compositional dominance of vitrinite in most coals. However, the exceptional correlation between sulfur concentration and exinite abundance directly reflects the association of sulfur implacement and geochemical conditions of elevated pH. Petrographic zones can be delineated within columns of coal that can be correlated laterally within the dimensions of a mine to a distance of approximately 0.7 km. However, the variability in the abundance and distribution of sulfur, sulfur species and iron disulphide morphologies observed in these data appear to be too great to allow stratigraphic correlation.

REFERENCES Annual Book of ASTM Standards, Gaseous Fuels; Coal and Coke, D2797. Baas-Becking, L.G.M., Kaplan, I.R. and Moore, D., 1960. Limits of the natural environment in terms of pH and oxidation-reduction potentials. J. Geol., 68 (3): 243-284. Borio, R.W., Hensel, R.P. and Ulmer, R.C., 1968. Study of means for eliminating corrosiveness of coal to high temperature surface of stream generating units. Combustion, 39 (8): 12-20. Cain, C. Jr. and Nelson, W., 1961. Corrosion of superheater and reheaters of pulverized coal fires boilers. J. Eng. Power, 83 (4): 468-474. Cecil, C.B., Stanton, R. and Dulong, F.T., 1979. Geologic factors that control mineral matter in coal. In: A.C. Donaldson, M.W. Presley and J.J. Renton (Editors), Carboniferous Coal Guidebook, vol. 3. W.V. Geol. Econ. Surv., Morgantown, WV, pp. 43-56. Conner, J.J. and Schacklette, H.T., 1975. Background geochemistry of some rocks, soil, plants and vegetables in the conterminous United States. U.S. Geol. Surv. Prof. Pap. 574-5, 168 pp. Cross, A.T., 1952. The geology of the Pittsburgh coal: Stratigraphy, petrology, origin, composition and geological interpretation of mining problems. Proc. 2nd Conf. on the Origin and Constitution of Coal, N.S. Dept. Mines & N.S. Res. Found., pp. 142-155. Davis, A., Spackman, W. and Given, P.H., 1974. The influence of the properties of coals on their conversion into clean fuels. Symposium on the Role of Technology in the Energy Crisis, Am. Chem. Soc., Washington, D.C., pp. 461-483. Donaldson, A.C., Renton, J.J. and Presley, M.W., 1985. Pennsylvanian deposystems and paleoclimates of the Appalachians. Int. J. Coal Geol., 5:167-180. Frazier, D.E. and Osanik, A., 1969. Recent peat deposits-Louisiana Coastal Plain. In: E.C. Dapples and M.E. Hopkins (Editors), Environments of Coal Deposition. U.S. Geol. Surv. Spec. Pap., 114: 63-85.

50

J.J RENT()NANDD.S, BIRD

Fumich, J.M., 1982. Vertical Distribution of Pyrite and Marcasite in Some Monongahela Group Coals. Masters thesis, West Virginia University, Morgantown, WV, 168 pp. (unpubl.)~ Given, P.H., Gronauger, D.C., Spackman, W., Lovell, H i . , Davis, A. and Biswas, B., 1975. Dependence of coal liquefaction behavior on coal characteristics. Fuel, 54: 34-49. Grady, W.C., 1977. Microscopic varieties of pyrite in West Virginia coals. A I.M.E. Trans., 262: 268-274. King, H.M., 1978. The morphology, maceral association and distribution of iron disulphide minerals in the Waynesburg coal at a surface mine. Masters thesis, West Virginia University, Morganton, WV, 181 pp. (unpubl.). Mendenhall, W., Ott, L. and Sheaffer, R.L., 1971. Elementary Survey Sampling. Wadsworth Publishing, Belmont, CA, 247 pp. Montano, P.A. and Granoff, B., 1980. Stoichiometry of iron sulphides in liquefaction residues and correlation with conversion. Fuel, 59:214-216. Neavel, R.C., 1966. Sulfur in coal: Its distribution in the seam and in mine products. PhD dissertation, Pennsylvania State University, State College, PA, 351 pp. (unpubl.). Paulson, L.E., Becerking, W. and Fowkes, W.W., 1972. Separation and identification of minerals from northern Great Plaines Province lignite. Fuel, 51 (3): 224-227. Proposed Pennsylvania System Stratotype, Virginia and West Virginia, 1979, Editors: K.J. England, H.H. Arndt and T.W. Henry, U.S.G.S., Am. Geol. Inst. (Publ.), A.G.I. Selected Guidebook Series, No. 1, 138 pp. Reiter, F.M., 1955. How sulfur content of coal relates to ash fusing characteristics. Power Eng., 59(5): 98-100. Renton, J.J. and Hamilton, W.M., 1988. Petrographic zonation within the Waynesburg Coal. Int. J. Coal Geol., 10: 261-274. Renton, J.J., Cecil, C.B., Stanton, R. and Dulong, F., 1979. Compositional relationships of plants and peats from modern peat swamps in support of a chemical coal model. In: A.C. Donaldson, M.W. Presley and J.J. Renton (Editors), Carboniferous Coal Guidebook, vol. 3. W.V. Geol. Econ. Sure., Morgantown, WV, pp. 57-100. Sage, W.L. and McIllroy, J.B., 1959. Relationship of coal ash viscosity to chemical composition. Combustion, 31 ( 5 ): 41-48. Staub, J.R. and Cohen, A., 1979. The Snuggedy Swamp of South Carolina: A bask-barrier esturine coal-forming environment. J. Sediment. Petrol., 49:133-143. Stopes, M.C., 1919. On the four visible ingredients in bituminous coal. Studies in the Composition of Coal, no. 1. R. Soc. London Proc. B., 90: 470-487. Tarrer, A.R. and Guin, J.A., 1976. Effect of coal minerals on reaction rates during coal liquefaction. Prepr. Pap, Am. Chem. Soc., Div. Fuel Chem., 21 (5): 59-77. Thiessen, R. and Sprunk, G.C., 1935. Microscopic and petrographic studies of certain American coals. U.S. Bureau Mines, Tech. Pap. 564, 71 pp. Wright, C.H. and Severson, D.E., 1972. Experimental evidence for catalyst activity of coal minerals. Prepr. Paper, Am. Chem. Soc., Div. Fuel Chem., 16(2): 68-92.