Petrography and rank of the Bhangtar coals, southeastern Bhutan

International Journal of Coal Geology, 15 (1990) 219-243

219

Elsevier Science Publishers B.V., A m s t e r d a m - - Printed in The Netherlands

Petrography and rank of the Bhangtar coals, southeastern Bhutan

H.S. Pareek BH 23, Pallav Puram, Meerut 250 110, India (Received July 21, 1988; revised and accepted July 3, 1989 )

ABSTRACT Pareek, H.S., 1990. Petrography and rank of the Bhangtar coals, southeastern Bhutan. Int. J. Coal. Geol., 15: 219-243. In Bhutan, a potential coal deposit is exposed at Bhangtar in the "landslide zone", Nineteen coal seams are encountered in this area, and occur in the Lower Gondwana Supergroup preserved in between the Main Boundary Fault and the Thrust. The coal is low in moisture, < 1.76%, but the coal cores show moisture values of 3.16%. The ash content is up to 48.87% and increases substantially in the younger seams. The volatile content (on a pure coal basis ) ranges from 23.38% to 41.02%. The sulphur content is less than 0.61%. The coals are non-coking. The amount of trace elements in the coal is quite low. The average petrographic composition of the Bhangtar coal is vitrinite - 31%, exinite - 2%, inertinitc 31%, and mineral and shaly matter - 36%, the vitrinite proportion decreases from the older to the younger seams, which are shaly. Vitrinite (telinite) is derived mainly from cordaitalean wood, and is fractured or unfractured showing an oil reflectance (Rm) range of 0.71-0.72% and 0.54-0.60%, respectively. The oil reflectance variation is governed by a similar variation in the volatiles of the coal. Exinite is mainly sporinite and cutinite and is constituted of organic matter from Upper Permian mioflora, so that a Late Permian age can be assigned to the Bhangtar coal. Based on oil reflectance, the rank of the coal is metalignitous to hypobituminous. The average microlithotype composition of the coal is vitrite - 30%, clarite - 1%, vitrinertitc V 14%, vitrinertite I - 11%, durite - 3%, fusitc - 14%, and carbominerite - 27%. Vitrite decreases in proportion towards the younger seams, "intermediates" show a concomitant increase, while durite and fusite remain constant. Carbonaceous shale contains fragmentary inertinite and vitrinite macerals and is interlayered with micro-bands of shaly coal which is characterised by abundant fragments of fusinite and vitrinite. The coal is very fragile and thus amenable to economic beneficiation. The removal of carbonaceous shale in this process increases the vitrinite content, thereby reducing the inertinite. The coal is used as fuel in electric power plants. The petrographic composition of the Bhangtar coal has been compared with those of the Upper and Lower Permian coals of the Gondwana coalfields of Peninsular India. The Bhangtar coal is characteristically distinct from the Gondwana coals of India in petrography and rank, but correlates petrographically with the Kameng coals ofArunachal Pradesh, India. -

0166-5162/90/$03.50

© 1990 Elsevier Science Publishers B.V.

H.S.PAREEK

220 INTRODUCTION

Bhutan is located along the northeastern border of India, encompassing an area of 46,000 km 2, between the coordinates N 2 6 ° 4 2 ' - 2 8 ° 2 0 ' 5 0 '' and E 8 8 ° 4 5 ' - 9 2 ° 7 ' 4 0 '' (Fig. 1 ). On the north, it is b o u n d e d by the Tibetan plateau of China, on the east by Arunachal Pradesh, on the west by Sikkim and Darjeeling in West Bengal, and on the south by Assam, India. Bhutan forms part of the Himalayan range and the mountain ranges rise from the foot-hills in the south from about 150 m to snow-clad peaks in the north of heights 7550 m, forming the Greater Himalayas. Geological mapping and assessment of the mineral resources of the kingd o m of Bhutan have been the subject of detailed studies by several geologists I

68*

64*

I

72" I

76i

80"

84" I

i

88"

92"

-.,

-.~ 52°

r"

SCALE

",-

,.,.:~

e"5 •

"t,_ '~.,...

,,,.r

"?"

IN

,

32*

CHINA .._.~ BHUT~N ,.z" 'L 28" ~-~.~.4C"-,...,-,...0/...z~-. •.')..a-/ ,.,.J . ...,. _ _ ~.~:.~ ( "~"'~'~-1 "~,~ " - ' - ' r t~' 24"

D IA

20°

~ ARABIAN

1 f

iNpUt.,,

,.,_,.~" -'-X

200 400 600 8 0 0 Krns.

~

'F"

/ 2,"

0

"LJ'~') /

I

As"

96*

I

\

~(

~

./

20*

Ut-SH

" ,o.

OF

ENGAL

12"

12"

RI LANKA

eel

7~'1

'¢1

8o-

8,"I

~"

9~"I

Fig. 1. Map of India showing the geographical location of Bhutan, and the locations of the Gondwana coalfields of Peninsular India, referred to in the text, for comparative petrographic studies, l=Hura, 2=Brahmani, 3=Saharjuri, 4=Raniganj, 5=Jharia, 6=East Bokaro, 7= Singrauli, 8= Sohagpur.

PETROGRAPHY AND RANK OF THE BHANGTAR COALS, SOUTHEASTERN BHUTAN

221

and considerable data have by now been acquired (see Gansser, 1964; Gokul, 1981 ). The potential deposit of coal is exposed along the Bor Nadi, near Bhangtar (26 ° 49' 10"; 91 ° 42' 15" ), where nineteen coal seams (numbered I - X I X ) have been encountered in the precipitous scarp face, referred to as the "landslide zone". The author undertook geological traverses in the coalbearing areas of the Bhutan Himalaya and made a systematic and representative collection of pillar samples of the coal and also from a bore hole in operation. The petrography and rank characteristic of the Bhangtar coal is described here. COALGEOLOGY

The geological setting of the rock formations of Bhutan Himalaya is complex and marked by several orogenies and intense tectonism. The beds are highly disturbed, dislocated, acutely folded, repetitively faulted and vertically uplifted. The rock formations range in age from Precambrian to Paleozoic, Mesozoic, Miocene to Pleistocene and Recent. The general dip of the beds is towards the north. The tectonic succession of the rock formations, after Gokul ( 1981, p. 159), is given below. Permo-Triassic Shumar Group ............................ Thrust ............................ Upper Carboniferous Duiri Series ........................ Thrust ....................... Permo-Triassic Gondwana Supergroup ............... Main Boundary Fault .............. Middle Miocene to Pleistocene Siwalik System The Gondwana Supergroup of rocks occur as an elongated strip extending for about 75 km, bulging near Bhangtar and tapering away easterly as well as westerly. The strike of the beds is E-W and the beds dip 50 ° northerly. The rocks underlying those of the Gondwana Supergroup are boulder slates, pebbly phyllites with thin bands of phyllites, slates and quartzites without any pebbles; these constitute the Duiri Boulder bed. The overlying rock sequence belongs to the Siwalik System which includes current bedded sandstones, carbonaceous slates, claystones, siltstones, lignite lenses, quartzitic sandstone, nodules of limestone and boulder conglomerate. The Gondwana Supergroup is marked by a thrust on the northern boundary and by the Main Boundary Fault on the southern boundary. Tectonism has had impacts on the rock sequence by intense faulting, mylonisation of the rocks and shearing. Gokul ( 1981, p. 167) states that mylonisation has produced slaty carbon-phyllite and semianthracitic coal. The original extent of the Gondwana outcrops is considered by Gansser

222

H.S. PAREEK

(1964) to have probably been larger than that which can be deduced from the scattered outcrops. Gokul ( 1981 ) considers these outcrops to be the westerly extension of those ofArunachal Pradesh, India. Existence of a belt of the Gondwana outcrops could thus be inferred in the Eastern Himalaya. Misra et al. ( 1987 ) have studied the petrography and rank of coals from Elephant Flat area, Arunachal Pradesh and described them to be associated with Permian sediments and the coals attained semianthracite stage.

Coal seams The coal seams are associated with greyish coarse- to medium-grained felspathic sandstone, carbonaceous sandstone, carbonaceous shale and grey shale. The coal seams are frequently shaly and bands of carbonaceous shale persist laterally. The coal shale ratio is 1 : 1 in thick seams (more than 1.5 m thick), while thinner seams (less than 1.5 m thick) are very frequently shaly. The thick seams are IV, V, VI, VII and X. Some of these coal seams at Bhangtar are mined. Coal occurs at several localities in the extreme southeastern part of Bhutan, extending for over 75 km from Kherkheria in the east to Piu Ri in the west in the southern part of the Samdrup Jongkhar district. Prominent coal occurrences in this east-west-trending belt are located near southwest Deothang (Dewathang), Jaibar Nadi, Diglai Nadi, Chemrang Nadi, Kalapani Nadi, Nunai Nadi, Bhorila Rash Ri, Nagor Khola, Khaurang-Lashing Ri and Bor Nadi. A reserve of over 10 million tonnes within a depth of 30 m is presently estimated to be available from these occurrences. The exposed thickness of the coal seams at Bhangtar is about 40 m in the scarp face of about 200 m vertical height. The coal is fragile and brownish to brownish-black with shining lustre on the surfaces across the bedding. Such a lustrous coal is characteristic of the locality where slickensiding is very common in the coal seams and the associated strata. The coal is highly cleaved, fractured and each of the fragments display banding. The coal appears oxidised and is of low rank. Until recently, this coal was being regarded as seminathracitic by Gokul ( 198 I, p. 167 ). The coal seams are surface mineable. SAMPLES C O L L E C T E D A N D P R O C E S S I N G

The nature of coal, as seen by visual examination of the lithotypes of coal, is fairly similar throughout the entire seam sections. There are no visible rapid variations in the physical composition of the coal. While vitrain is quite conspicious as thin tapering sheets in the coal seams, fusain is not so c o m m o n but the broken surfaces do exhibit charred fragments. Pillar sections were prepared across all the seams and the nature of coal was examined for each of the seams. Bands of carbonaceous shale and shale were

PETROGRAPHYAND RANKOF THE BHANGTARCOALS,SOUTHEASTERNBHUTAN

223

found frequently alternating with thick bands of coal. It is quite easy to separate the two types of bands in view of the hard and blocky nature of the former and fragile nature of the latter. Coal samples were collected from seams IV, V, VI, VII and IX, and also from bore hole cores as cuttings. COAL G E O C H E M I S T R Y

The proximate analysis of the samples of coal from Bhangtar area (Table 1 ) indicates that moisture is 0.60-1.76% in outcrop samples (serial nos. 1TABLEI Proximate analysis of samples of coal from coal seams of Bhangtar area, district Samdrup Jongkhar, Bhutan Serial No.

SampleNo.

1 2 3 4 5 6 7 8 9 10

6 BH 5 BH BTR/VIIA/3 BTR/VIIB/4 BTR/VI/2 3 BH BTR/IV/1 2 BH 1 BH 7 BH

11

8 BH

Seam No.

IX VII VII VII VI V IV IV Top IV Bottom Depth: 39m Depth: 39.5m

Moisture (%)

Ash (%)

Volatile matter

Fixed carbon

Volatiles (pure coal basis)

0.60 1.24 1.28 1.76 0.79 1.14 0.70 0.72 1.07

66,71 35,95 32.82 48.87 12.36 36.28 32.02 10.82 20.63 46.91

27.19 25.78 15.40 31.20 26.17 26.62 36.93 32.95 18.49

36.26 40.16 34.45 54.68 36.76 40.22 51.55 45.70 32.53

39.42 35.91 23.38 35.40 38.01 36.81 41.02 40.33 31.27

3.16

28.64

11.28

56.92

12.89

(%)

(%)

(%)

BH samples collected by H.S. Pareek and analyzed by S.R. Paul; BTR samples collected by B. Chaudhuri and analyzed by S.R. Paul and H. Naskar.

TABLE 2 Ultimate analysis on mineral matter-free basis of samples of coal from coal seams of Bhangtar area, district Samdrup Jongkhar, Bhutan Serial NO.

Sample No.

1 2 3 4

BTR/VIIB/4 BTR/VIIA/3 BTR/VI/2 BTR/IV/1

Seam No.

C

H

N

S

O

(%)

(%)

(%)

(%)

(%)

VII VII VI IV

85.04 84.55 81.29 83.99

5.21 4.81 4.58 4.64

1.28 1.73 0.92 1.22

0.59 0.57 0.58 0.61

7,88 8,33 12.63 9.54

30

-

38

30

l0

30

40

5

40

20

Cu

120

10

70

300

10

100

35

Ni

Sr an d Zr not d e t e r m i n e d . Analysts: D.K. Indra, S.B. D as a n d S. D ut t a.

5

50

10

Average c o m p o s i t i o n (Aver. of 6 )

-

-

-

70

10

-

20

10

6BH IX 5BH VII 3BH V 2BH IV I BH 1V

7BH Bore hole core

Pb

Sn

S am p le No. and Seam

30

l0

30

70

-

15

10

Co

9

-

5

30

-

-

-

Mo

200

50

200

210

30

20

700

10

10 300

120

130

Mn

300

250

V

Trace e l e m e n t s ( in p p m ) in coal s a m p l e s f rom B h a n g t a r area, B h u t a n

TABLE 3

1

l

1

1

1

1

1

Ag

10 10

30 150

52

10

2

-

-

10

30

30

In

Ga

50

20

50

50

20

70

70

Nb

212

70

50

600

50

150

200

La

108

30

40

250

10

130

120

Y

45

20

15

120

20

30

30

Yb

10

-

-

10

20

10

10

Ba

117

50

50

250

10

160

140

Cr

50

40

40

80

-

70

80

B

32

-

10

120

-

-

-

Ge

-

46.91

20.63

10.82

35.28

35.95

66.71

Ash (%)

b~ 4x

225

PETROGRAPHY AND RANKOF THE BHANGTARCOALS,SOUTHEASTERNBHUTAN TABLE 4

Average trace-elemental composition of Lower Permian coals of coalfields of some Gondwana basins of India, compared with that of the Bhangtar coal, Bhutan Basin:

Rajmahal

Coalfield:

Hura

Brahmani

Trace e l e m e n t s ( p p m ) Ag I 1 Pb 40 30 Cu 500 200 Ni 300 150 Co 120 80 V 400 250 Mn 200 140 Nb 30 40 La 150 250 Y 120 400 Ba 350 1000 Sr 180 300 Cr 350 120 B 40 60 Zr 50 60 Ge ND ND Sn 20 20 Mo 20 20 Ga 40 30 In 30 Yb 20 60 Ash (%)

6.64

16.84

Deogarh

Damodar Valley'

Son Valley

Bhutan

Saharjuri

Jharia

East Bokaro

Sohagpur

Bhangtar

1 35 150 150 30 70 300 40 200 100 1000 300 50 20 60 ND l0 10 10 10 20

22 50 132 46 18 120 500 6 91 20 710 605 126 80 246 ND 17 4 20 6 10

1 43 81 77 26 92 200 71 100 39 > 1000 > 1000 95 85 80 ND 7 8 19 3 10

1 500 > 1000 175 165 450 310 105 120 20 600 425 310 115 300 ND 15 5 27 5 12

1 38 30 120 30 200 210 50 212 108 10 117 50 32 5 9 52 2 45

7.09

38.76

19.65

7.61

36.21

ND = not determined.

9), while in the core samples (serial nos. 10,11 ) moisture is 3.16% with 28.64% ash and 12.89% volatile matter on pure coal basis. The outcrop samples are thus characterised by low moisture content ( < 1.76%) with volatile matter up to 41.02%. The inference that can, therefore, be drawn is that samples of coal outcrops have low moisture and high volatile contents, while those at depth contain more moisture and less volatiles. The ultimate analysis of samples from seams IV, VI and VII (Table 2) characterises these coals to have high C and very low sulphur contents. The trace-elemental composition of six samples appears in Table 3. The content of the different trace elements is quite low. This could possibly be due to the very low proportion of sulphide minerals in the coal. The association of Pb could be related to galena, Cu with chalcopyrite, Co, Ni, Y and V for clays, Mo for molybdenite, B for illite, and Mn for siderite in these coals. The

226

H.S. PAREEK

trace elements derived from organic source are low (Cu, Mo, In, Nb, B), while those from inorganic source (Mn, Ni, V, Ba, Cr) (Pareek and Bardhan, 1985 ) are comparatively higher. The data are semiquantitative and were obtained using a Jarrel-Ash Grating Spectrograph at 12 A anode excitation. The average trace-element composition of the Bhangtar coals has been compared with that of some of the other Gondwana coal of Peninsular India (Table 4). Table 4 shows that the Bhangtar coal is high in ash, but that the trace elements are quite low in proportion, when compared to the other coals. The low content of Cu, Co and Ba is characteristic for this coal. COAl_ PETROGRAPHY

Previous work The Bhangtar coal was regarded as a semianthracite till recently, when a systematic and integrated study was planned and initiated by the author. This study classified the coal to be of lignitobituminous rank and of Late Permian age (Pareek, 1986a, b). Studies on Deothang coals were made by Banerjee et al. (1986). Their age was considered comparable to the Middle Barakar and the coal described to be rich in exinite (1.3-17.6%) and R m a x = 0 . 6 5 % . The Deothang, Bhangtar (Seam No. 4) and Samrang coals were studied in channel and bulk samples by Mukherjee et al. (1988); they reported chemical, maceral (not microlithotype) and average oil reflectance values showing closer affinity with Eastern Raniganj coals (Upper Permian) of the Damodar Valley. This work, therefore, presents data on the maceral value, microlithotype and rank, and also on the trace elements of all the thick seams of the Bhangtar area, for the first time. Present studies The maceral and microlithotype compositions (Table 5 ), nature of the macerals (Plates 1-3) and coal rank by vitrinite oil reflectance (Table 6) are presented here. Maceral composition The maceral composition determined for these coals (Table 5 ) indicates that vitrinite ranges from 9 to 47% (average 31%), exinite from 1 to 5% (average 2%), and inertinite from 15 to 55% (average 31%), while mineral and shaly matter varies from 8 to 58% (average 36%). The minerals are 10%, and the shaly matter is 26%, on average. The proportion of vitrinite in the coal core samples (7 BH and 8 BH) is fairly similar to that of the coals of the seams V (3 BH), VI ( B T R / V I / 2 ) and VII (5 BH, BTR/VIIA/3, BTR/VIIB/4). The inertinite content in the bore hole cores is similar to that of the younger seams. It is, therefore, brought out

PETROGRAPHY AND RANK OF THE BHANGTAR COALS, SOUTHEASTERN BHUTAN

227

TABL E 5

Maceral and microlithotype compositions of the samples of coal from coal seams of Bhangtar area, district Samdrup Jongkhar, Bhutan Serial No.

I

Sample No.

2 3

5 BH BTR/VIIA/3 BTR/VIIB/4

4

BTR/VI/2

5 6 7 8 9 10

3 BH BTR/IV/I 2 BH 1 BH 7 BH 8 BH

Serial

Maceralcomposition

Seam No.

VII VII VII VI V IV IV IV -

Vitrinite Exinite Fusinite Semi~sinite

Micrinite

(%)

(%)

(%)

47 21 20 32 32 9 28 37 32 47

1

5

7

9

1 1 1 1 4 5 5 1 1

3 i0 5 5 15 15 12 3 8

8 10 3 8 11 15 14 9 7

10 11 7 11 23 25 18 7 8

(%)

(%)

Mi ne ra l a nd Shaly matter (%) 41 57 58 52 43 8 12 14 48 29

Microlithotype composition

No.

Vitrite

Clarite

(%)

(%)

Duroclarite

Clarodurite

Vitrin-

Vitrin-

Durite

Fusite

ertite V

ertite I

(% )

(%)

(%)

(%)

I%)

(%)

Carbominerite

I°/°)

1

43

1

1

-

12

7

3

9

2 3 4 5 6 7 8 9 10

18 13 29 38 33 44 40 18 19

1 1 2 1 1

1 1 1 1 1 1

2 -

12 7 12 14 16 17 15 13 16

12 9 7 10 19 9 10 15 18

1 ~ 1 2 5 4 3 3 5

7 25 7 8 17 19 18 11 22

24 50 44 44 26 7 5 11 38 18

Petrographic analysis by H.S. Pareek.

that the inertinite exhibits the tendency to decrease in proportion from seam IV to VII, and also that the inertinite proportion of the bore hole cores ( 7 BH and 8 BH) resembles that of seam VII (serial nos. 1-3 ). The inorganic matter increases in the younger seams and has made the seam IX extremely shaly. The bore hole cuttings display a composition similar to that of the younger seams. Shaly matter predominates over mineral matter in all the seams. In conclusion, it can be stated that the Bhangtar coals are extremely low in exinite, and vitrinite increases from seam IV to the younger seams. Inertinite is quite high in seam IV and low to very low in the younger seams. Inertinite

22g

H.S. PAREEK

TABLE 6

Vitrinite oil reflectance and rank of the samples of coal from coal seams of Bhangtar area, district Samdrup Jongkhar, Bhutan Seam

Sample No.

Vitrinite oil reflectance Range (%)

Average (%)

Coal rank

Metalignitous to hypobituminous

1X

6 BH

0.55-0.65

0.61

VII

BTR/VIIB/4 BTR/VIIA/3 5 BH

0.67-0.79 0.55-0.60 0.54-0.63

0.71 0.58 0.56

Metalignitoas Metalignitous

VI

BTR/VI/2

0.67-0.75

0.71

Hypobituminous

V

3 BH

0.70-0.79

0.71

Hypobituminous

1V

BTR/IV/1 2 BH 1 BH

0.52-0.60 0.51-0.57 0.54-0.63

0.57 0.54 0.60

Metalignitous Metalignitous Metalignitous

Bore hole cores

Depth 39 m Depth 39.5 m

0.63-0.79 0.51-0.57

0.72 0.54

Hypobituminous Metalignitous

Hypobituminous

macerals occur in a similar proportion in all the coals. There is a gradual and progressive change in the composition of the seams and this could be related to the governing conditions during coalification controlled by geological factors, like the subsidence of the Bhangtar basin of deposition.

Nature of the macerals Vitrinite: Vitrinite occurs as disintegrated, degraded and fragmentary shreds, bits and tissues, as well as microbands and megabands of lenticular pattern. Collinite is more common and telinite is quite frequent. Collinite has a homogeneous surface and occurs as fragments, in spindle shapes and as sheets (Plate 1-1; Plate 2-1; Plate 3-2). Fragmentary collinite (Plate 3-3 ) lacks the banding pattern. Transverse and oblique fractures (Plate 2-1 ), cleat planes (Plate 3-3) and micro-faults (Plate 1-1 ) are prevalent. Telinite occurs as distinct bands showing varying stages of preservation of the original microstructure of the secondary wood and bark from which it has been derived. The structural details are preserved either indistinctly or very

E X P L A N A T I O N O F PLATES 1-3 ( Plate 1-1 is from polished section, under oil immersion, and the rest are all from thin sections. All figures are of magnification--85, excepting Plate 1-3 which is of magnification × 600).

PETROGRAPHY AND RANK OF THE BHANGTAR COALS, SOUTHEASTERN BHUTAN

229

PLATE 1. 1. Vitrinertite I, vitrite and vltrinertite V composing the coal. Cutinite (c) forms part of vitrinertite V. Two microfaults affect the organic layers, across the bedding, and are infilled by post-consolidation clayey matter (cl). 2. Telinite derived from cordaitales wood. Medullary rays up to eight cells height (m) are distinguishable. Yellowish resinite infills the cell cavities, profusely. 3. Telinite derived from cordaitales wood, showing resinite infilled cells. Resinous substances show gas inclusions and minute opaque grains (g).

230

H.S. PAREEK

well preserved (Plate 1-2,3, Plate 3-1 ) permitting identification of the coalforming plants. The wood is derived from principally cordaitales pointing towards the gymnospermous origin of the coal-forming vegetation . The tracheid fibres solely compose the telinite, while the cell lumen and the cell cavities are infilled by a yellowish resinous substance containing fine opaque inclusions or gas cavities. Medullary ray cells are up to eight cells height (Plate 1-2,3). Bark tissues are also recorded as contributing towards the vitrinite formation of these coals (Plate 3-2 ). They are quite thick-walled with cell lumen infilled by a dark coaly substance as well as a pale yellow resinous substance, characterised by gas blebs and minute opaque inclusions in some cells. Vitrinite is of two types - - fractured and unfractured. Telinite is cracked and fractured, intensely or entirely free from any of such post-coalification features (Plate 1-2,3, Plate 2-2 ). Exinite: Exinite includes sporinite, resinite and cutinite. Sporinite appears as streaky spore exines (Plate 2-2), flattened along the bedding, megaspore (Plate 2-3) and sporogenous body (Plate 3-1 ). Resinite appears mainly as cell fillings of telinite (Plate 1-3 ). Cutinite is recorded as thin serrate leafy cuticles (Plate 1-1 ). The examination of the spore assemblage in macerated residues had indicated the existence of a Late Permian mioflora. Inertinite: Inertinite includes fusinite, semifusinite, micrinite, sclerotinite and inertodetrinite. The fusinitised wood is of secondary origin and is distributed as fragmentary bits, lenticles, and also occasionally as lenticular sheets and sheets. The cell walls are thin-walled, moderately thick-walled and also thick-walled. Cell lumen form the bulk of the cell component in thin walled cells and is invariably infilled by sclerotic bodies or inorganic mineral matter which has been identified as either clayey matter, carbonaceous matter, silica, siderite or pyrite. Semifusinite occurs as lenticles. Sclerotinite is oval to ellipsoidal with or without filamentous cavities, hard and highly reflecting and also shows preservation as fungal mycelium. The composition of the inertinite is shown in Table 5. As can be seen from the table, fusinite, micrinite and semifusinite occur in more or less similar proportions. Plates 2 and 3 depict the nature of these macerals.

PLATE 2. I. Clarodurite in between vitrite bands (v). Clarodurite shows abundant tiny quartz grains in intimate association with the macerals. Vitrite shows ample cracks and cleats. 2. Duroclarite in between bands of telinite (t) and collinite (c), showing large-sized quartz grains, along the banding, and flattened spore exines. Telinite is clarite and collinite is vitrite and show absence of any fractures. 3. Vitrinertite V showing fusinite (f), micrinite (m), inertodetrinite (1), semifusinite (sf), sclerotinite (sc), and dispersed submicroscopic subangular mineral matter, with abundant vitrinite (v).

b~

Z

Z ,-e

I.n

m

©

Z

W

© "rl

Z

Z

©

m --t

b,~

PETROGRAPHY AND RANK OF THE BHANGTAR COALS, SOLITHEASTERN BHUTAN

233

Microlithotype composition The microlithotype composition of the Bhangtar coals is given in Table 5, and their average composition in Table 7. The principal microlithotypes of the coal are vitrite, vitrinertite I, vitrinertite V, fusite and durite. Carbominerite is quite high. Clarite, clarodurite and duroclarite are less than 1%. Based on the classification of Alpern (1981, Fig. 13, p. 287), these coals are fusic (V < 65%) and v itric (V > 65%) which occur in a 60:40 ratio. The proportion of vitrite and clarite tends to decrease from seam IV to VII, concomitant with an increase of"intermediates"-vitrinertites. Durite and fusite tend to show a stable character. The bore hole core samples have a composition similar to that of the seam VII samples. Thus, the petrographic composition of the seam encountered in bore hole BE 6 at 39 m depth resembles that of the outcropping seam VII.

Nature of the microlithotypes Vitrite is very c o m m o n in these coals and occurs as persistent sheets (Plate 1-1; Plate 2-1 ). Clarite is vitrinite with resinite (Plate 1-2,3; Plate 2-2). Duroclarite (Plate 2-2) and clarodurite (Plate 2-1 ) are rare and occur as gradations in between vitrite bands. Vitrinertite V (Plate 2-3; Plate 3-3) and vitrinertite I (Plate 3-1 ) are prevalent throughout the seam sections. Durite is predominantly micrinite. Fusite is sclerotic. Carbominerite is frequently and ubiquitously interstratified with almost all the microlithotypes, but more commonly with the "intermediates".

Nature of mineral and shaly matter Mineral matter: This forms a very significant constituent of these coals. The preponderant mineral is silica (mainly quartz and some chalcedony) followed by carbonates, siderite, ankerite, pyrite and galena. Silica grains are angular to subhedral and marked by undulose extinction. They pervade the matrix in variable proportions and concentrations (Plate 2-3 ). Their distribution in the organic layers is spread in such delicate way that their separation by specific gravity methods for beneficiation is fraught with difficulties. Silica is also seen infilling the cell lumen of fusinite and is more confined PLATE 3. 1. Vitrinertite I showing abundant balls and lenticles of fusinite (J), massive micrinite (m), i nertodetrinite (I), sporogenus body (s) and shreds of vitrinite (v) in intimate association with inorganic mineral grains, and balls of carbonaceous shaly matter (cs). 2. Thick-walled secondary bark (t), vitrinite (v) with sclerotinite (s), micrinite (m) and semifusinite (sJ), constituting clarite, vitrinertite I, and vitrite. 3. Intensely degraded and disintegrated vitrinite, with carved out margins, semifusinite (sf), granular and massive micrinite (m) with abundant tiny to large sized subangular quartz grains (ram), constituting vitrinertite V in the Bhangtar coal. Vitrinite shows cleat plane, but fractures and microfaulting are absent.

'v

VT"

0

work , -

Seam ~

Previous

, after Mukhefjee

~-- Borehole Cores

Seam

Seam

[]

•

Seam

Seam

GEND

•

/~

L.,E

I

e~ 0i~j([9881

Oil

04

Reflectance

'

Metalignitous

(Rm)

I

06

(%)

I

•o

[]

Hypobituminous

I

©

I

10

Fig. 2. Volatiles (pure coal basis) - Oil reflectance (Rm) and Carbon-Oil reflectance (R m variation diagram showing the plots of Bhangtar coal.

90-

80-

.

70-

60-

I

ol

+

+

[]

"v

t~9

PETROGRAPHY AND RANK OF THE BHANGTARCOALS,SOUTHEASTERNBHUTAN

235

to the distintegrated macerals forming the "intermediates" than the vitrite layers. Plagioclase felspar is sporadic. Carbonates comprise mainly calcite, although dolomite could also be traced. Kaolinite is very c o m m o n and forms an integral part of vitrinertite I, durite and fusinite. Siderite and ankerite appear as small nodules. Pyrite and galena appear occasionally as specks. Shaly matter: Shaly matter is invariably carbonaceous in these coals and is ubiquitously observed to be dispersed and associated with inertinite macerals fine granular micrinite and fragmentary fusinite. Shaly matter occurs as layers, sheets, lenticles, globular bodies, fragments and massive bodies. Persistent bands of shale very commonly alternative with organic layers. Their beneflciation is a feasiblity in view of their size and association with inertinites. It reduces the calorific value of these coals and hence beneficiation holds possibilities for cleaner coal being available for utilisation, on a comparative scale. -

-

COALRANK

Vitrinite oil reflectance studies were undertaken on the coals from the different seams to determine coal rank and the data are tabulated in Table 6. The bore hole cores gave data where the range and averages are different for each of the samples. Thus two types of vitrinites are present in these coals, which are present throughout the seam sequence. The first vitrinite type has an oil reflectance between 0.54% and 0.65%, while the second type has 0.710.72%. The reflectance data were plotted against volatiles and carbon (Fig. 2 ). The volatile content is directly related to reflectance and a decrease in the volatile matter content is directly related to increase in the reflectance. Two types of vitrinites can be distinguished from the variation diagram and can be assigned metalignitous and hypobituminous rank. The reflectance data of Mukherjee and others for seam IV corroborate this contention, since the plot of their data falls in the higher reflectance field. The core samples from the same seam also display presence of two vitrinite types, but the lower plot in low volatile matter field (12.89%) appears to be due to the fact that the coal has very high fixed carbon (56.92%). The Bhangtar coals can, therefore, be inferred to have two vitrinite types, based on oil reflectance, volatile matter and carbon data (Fig. 2 ), and can be assigned to a metalignitous-hypobituminous rank after Alpern ( 1981 ). EFFECTS OF THRUSTS ON COAL

As stated earlier, the coal-bearing sediments are separated from the underlying strata by a thrust and from the overlying rock formations by the Main Boundary Fault. Besides that, there are also thrusts affecting the younger se-

236

H.S. PAREEK

quence of rock formations. The effects of these thrusts have been recorded by the entire sequence of rock formations of the Bhutan Himalaya. The Gondwana Supergroup of rocks have displayed in field the effects of tectonism and orogenies. As is well known, coal is the most sensitive indicator of geological processes and has preserved the evidences witnessed as after-effect of these thrusts. Chemically, the coals exhibit loss of moisture (see Table 1 ). Based on the volatile matter contents, etc., these coals can be assigned to High Volatile Bituminous B2 rank of the ISI classification ( 1978 ), where the moisture range of such coals should be between 7% and 11%. Considering that there has been some loss of moisture at the outcrop resulting in the present figures of 0.60%1.76%, the moisture for the coal core samples collected at 39 m depth could be taken as representative; the analysed moisture is 3.16% (Table 1 ). Thus the loss of moisture has been of the order of 6%, if average moisture of the deposit was 9%. This loss of moisture could be attributed to resulting in fragile nature of the coals. The area displays slickensiding very commonly. This feature is also traversing the coal seams, and could be responsible for also imparting shine or lustre across the bedding to the coals. This effect has made the coals lustrous as a result of which it is always possible to misjudge and consider the coals as having reached semianthracite stage. There are no field evidence that there has been any increase of rank in the Bhangtar coals, due to the effect of the thrusts. The microscopic effects recorded include dislocation of the organic layers, fracturing of the macerals/microlithotypes and compression of the beds. The thrust effect is recorded differently by different macerals, depending upon their degree of resistance to the effect. Vitrinite shows fractures along the thickness of the bands, or in oblique direction, rarely only along the banding. Fusite bands are showing differing resistance depending upon as to whether the cell cavities are mineral-filled or empty. The "intermediates" - - vitrinerrite V and vitrinertite I - - preserve microfaulting affecting the continuity of the layers. Plate 1-1 displays microfaulting affecting the organic layers, and infilling of the faulted zone by post-consolidation clayey matter. Such repititive microfaulting is a very c o m m o n observation in these coals, and is a very significant p h e n o m e n o n left as a remnant of the effect of thrust on coal. As stated earlier, there are two types of vitrinites in these coals, i.e. fractured and unfractured. It is possible to find in the same layer both types of vitrinites. The fact that one type could be easily fractured, while the other one remained unaffected, points out to the botanical difference in the vitrinite types. These studies have indicated that telinite with resin-filled cells forms the unfractured vitrinite, while the homogeneous vitrinite displays the maxim u m fracturing capacity.

PETROGRAPHY AND RANK OF THE BHANGTAR COALS, SOUTHEASTERN BHUTAN

237

COMPARATIVE PETROGRAPHIC STUDY WITH THE COALS OF GONDWANA BASINS OF PENINSULAR INDIA

The Gondwana basins of Peninsular India are developed along the principal river valley systems, known as Godavari-Pranhita, Mahanadi, Son, Narmada, Koel and Damodar Valley and Deograh and Rajmahal Groups of coalfields (Pareek, 1967, Fig. 1; Pareek, 1988, Fig. 1 ). Petrographic data on the major coalfields of these basins are now available (Pareek, 1988) and have been used to compare these coals with the Bhangtar coal. The petrographic data of the Upper Permian coals of Raniganj coalfield (Damodar Valley basin), and of Singrauli coalfield (Son Valley basin); the Lower Permian coals of Hura and Brahmani coalfields of Rajmahal, Saharjuri of Deogarh, Jhari and East Bokaro of Damodar Valley, and Sohagpur and Singrauli of Son Valley basins (for locations see Fig. 1 ) are given in Table 7. Petrographic composition is also plotted in Vitrinite-Exinite-Inertinite (Fig. 3 ) and vitrite plus clarite-"Intermediates"-durite plus fusite (Fig. 4) triangular diagrams. Petrographic comparisons are brought out as follows.

Vitrinite-exinite-inertinite triangular diagram (Fig. 3) The Upper Permian coals have high vitrinite (65-72%) and exinite ( 1219%), and very low inertinite ( 12-17%) contents. These coals are also very low in mineral and shaly matter. Vitrinite is mostly macrofragmental ( > 50 /tm width), being distributed as vitrite and clarite, and the microfragmental vitrinite forms the "intermediates". Thus, there is a wide variation in the size of vitrinites in these coals. In inertinite, micrinite is the major maceral and fusinite is absent to very low ( < 2%). The Lower Permian coals are very low in exinite (5-9%) and show wide variations in the contents of vitrinite and inertinite from one coalfield to another. Vitrinite is quite low (32%) in Hura, and very high (69%) in Brahmani coalfields; these coalfields are at the northerly and southerly ends of the basin and exhibit entirely different compositions. To differentiate from the Upper Permian coals, their exinite content is very low, and distribution of vitrinite is as vitrite. A lower vitrinite content characterises the petrographic composition of the Singrauli (10%), Saharjuri (25%), Hura (32%), and Sohagpur (37%) coalfields. A high vitrinite content ( > 50% ) characterises the East Bokaro (60%) and Jharia ( 71% ) coalfields, as is characteristic for Upper Permian coals, but low exinite content and lack of microfragmental vitrinite as clarite distinguish them from Upper Permian coals. The Godavari Valley coals (Navale et al., 1983; Pareek, 1986c) are dominantly inertinite and with a high exinite content.

238

H.S. PAREEK

TABLE 7 Average petrographic composition of certain Upper Permian (Raniganj) coals of Damodar and Son Valley basins, and Lower Permian (Barakar) coals of Rajmahal and Deogarh Group of Coalfields, and of Damodar and Son Valley basins of Peninsular India, compared with that of Bhangtar coals, Bhutan Age

Upper Permian

Lower Permian

Basin:

Damodar

Son

Coalfield:

Raniganj

Singrauli

Rajmahal

Deogarh Saharj uri

Hura

Brahmani

Main

Main

Tulsidabar, Chitra Saharjuri

Coal seam:

Dishergarh

Jhingurdah

Source:

Pareek (1969)

Pareek (1969, 1970)

Pareek (1986c)

Pareek (1986c)

Pareek et al. (1988)

Bottom

Top

Maceral composition (%) Vitrinite

62 (65)

58 (71)

60 (72)

24 (32)

55 (69)

21 (25)

Exinite

18 (19)

10 (12)

12 (15)

4 (5)

5 (6)

8 (9)

Inertinite

15 (16)

13 (17)

11 (12)

47 (63)

20 (25)

55 (66)

19

17

25

20

16

40 (44)

20 (25)

28 (31)

10 (11)

34 (38)

(7)

Clarite

15 (16)

15 (19)

20 (23)

-

4 (5)

"Intermediates"

20 (22)

22 (28)

22 (25)

41 (48)

41 (46)

5 (5)

18 (22)

15 (17)

3 (3)

12 (13)

5 (6)

3 (4)

31 (37)

7 (8)

Carbominerite

8

20

12

15

11

Rm (%)

0.81-0.84

Mineral and Shaly matter

5

Microlithotype composition (%) Vitrite

Durite Fusite

0.50

0.50

0.38-0.45

3 (3)

0.45-0.54

(50) (18) (24)

0.59-0.69

( ) Data on mineral and shaly matter-free basis.

The Bhangtar coal is low in exinite (3%) and has equal vitrinite (48%) and inertinite (49%) contents, on mineral matter-free basis (Fig. 3). The

PETROGRAPHYAND RANKOF THE BHANGTARCOALS,SOUTHEASTERNBHUTAN

Lower Permian

239

Lower Gondwana

Damodar

Son

Bhangtar

Jharia

East Bokaro

Sohagpur

Singrauli

Bhangtar

X, XI, XIII, XVI, XVIII

Jarangdih, Uchitdih, Kargali

Rungta, Burhar, Kotma

Purewa. Turra

IV, V, VI, VII

Pareek ( 1969, 1988)

Pareek (1987)

Pareek ( 1969, 1970)

Present work

67 (71)

58 (60)

30 (37)

8 (10)

31 (48)

2 (2)

9 (9)

6 (7)

7 (8)

2 (3)

25 (26)

29 (30)

47 (56)

65 (81)

31 (49)

6

4

17

20

36

(58)

(30)

13 (14)

(5)

30 (41)

(2)

(7)

3 (3)

(5)

1 (1)

(6)

(49)

30 (33)

(37)

25 (34)

(26)

(7)

6 (6)

(35)

3 (4)

~8)

(7)

38 (44)

(18)

14 (20)

10 1.30-1.45

0.79-1.09

0.41-0.58

27 0.60-0.62

0.54-0.72

c o m p o s i t i o n is u n l i k e a n y o f t h e c o a l s a n d t h i s m a k e s i t s f i e l d d i s t i n c t a n d separate. A comparison with the Kameng coals ofArunachal Pradesh (Misra

240

H.S. PAREEK

LEeEND Composition

@- Mocerol X- Microlithotype Coolfields1 Ronioonj 2 Singrouli 3 Hura 4 Brahmoni 5 Soharjuri 6 Jharia 7 EOSIBoKaro

Upper Permian

Lower Permian

98 SlngrouhS°hogpur

/

/

F

ARE. . . . .

, 2 , ~ / d~/

E R/-~ /-"

(o 7 \4 t \ /

7 \~/~

AREA OF LOWER PERMIAN COALS

,o I

v EXINITE

V

50

INERTINITE

Fig. 3. Vitrinite-Exinite-lnertinite triangular diagram showing the plots of maceral composition, on mineral and shaly matter-free basis, of Upper and Lower Permian coals of Peninsular India and Bhangtar coal, Bhutan.

TABLE 8 Comparison of average maceral composition of the Bhangtar coal, Bhutan, and Kameng coal, Arunachal Pradesh, India Coalfield:

Bhangtar/Bhutan

Source:

Present work

Petrographic composition (%): Vitrinite 31 (48) Exinite 2 (3) Inertinite 31 (49) Mineral and Shaly matter 36 R m (%)

0.54-0.72%

Mukherjee et al., 1988

Elephant Flat area, Kameng district, A.P. Misra et al., 1987

34.9 4.3 21.6+2.9 34.9

44.94 ( 52.69 ) 40.75 (47.31) 14.71

0.73-0.74%

( ) Data within parenthesis is on mineral and shaly matter-free basis.

2.02-2.31%

P E T R O G R A P H Y A N D R A N K O F T H E B H A N G T A R COALS, S O U T H E A S T E R N B H U T A N

241

et al., 1987 ) brings points of similarity in maceral composition of these coals (see Table 8 ).

Vitrite, clarite-"Intermediates"-durite, fusite triangular diagram (Fig. 4) High vitrite and clarite contents characterise the field of Upper Permian coals; "intermediates" and durite + fusite are of equal composition. Low vitrite and clarite contents distinguish Hura (11%), Saharjuri (7%), Sohagpur (17%) and Singrauli (5%) coals, with "intermediates" and durite plus fusite in similar high (50%) proportions. The Lower Permian coals of East Bokaro, Brahmani and Jharia coalfields have vitrite+clarite content of 37%, 43% and 60%, respectively. They are very low in durite+ fusite (less than 15%) or substantially low (5%) in "intermediates". Vitrinite is either macrofragmental, distributed as vitrite, as in Jharia, or microfragmental occurring in "intermediates". The pattern of a

Vifrife

__/

Clorife

REA O F UPPER PERMIAN COALS

/

/AREA

+

OF LOWER 4

2,:,,

\

T

\

--~--/

/ o~_ Inferrnediofes"

V

50

__

Ourife 4- Fusife

Fig. 4. Vitrite plus clarite - "Intermediates" - Durite plus Fusite triangular diagram showing the plots of average microlithotype composition, on carbominerite-free basis, of Upper and Lower Permian coals of Peninsular India, and of Bhangtar coal, Bhutan.

242

H.S. PAREEK

similar distribution of "intermediates", on one hand, and of durite + fusite, on the other, as in Upper Permian coals, is absent in the Lower Permian coals. The microlithotype composition of the Bhangtar coal resembles that of Jhingurdah Bottom seam (Fig. 4).

Vitrinite oil reflectance Table 7 depicts the range of vitrinite oil reflectance in the different coalfields. All coals are within the range 0.38-1.45%; this variation is related to the variable geological coal-forming factors. The Bhangtar coal shows similarity in rank to the Gondwana coals of India. It is, however, distinguishable in rank from Kameng coal (Table 8) which has oil reflectance range of 2.02-2.31%, which is attributable to the effects of Himalayan orogeny and tectonism, resulting in a semianthracite coal stage. The Bhangtar coal, though occurring in the same Himalayan Gondwana belt, escaped development of high rank because of certain geological and tectonic factors, the discussion of the which is besides the scope of this work. CONCLUSIONS

The Bhangtar coal is characterised by very low moisture ( < 3.16%) and is of high-volatile bituminous B2 rank. It is very high in ash (up to 48.87%) and very low in trace-elemental proportion - - Cu ( 30 ppm ), Ba ( 10 ppm ), Sn ( 5 ppm), In (2 ppm), Ga (52 ppm), Yb (45 ppm) and B (50 ppm). Petrographically, the coal is very low in exinite (3%) and has almost similar vitrinite (48%) and inertinite (49%) proportions. Vitrinite is of two types - fractured and unfractured - - the former as a result of the effects of thrusts, during the Himalayan orogeny, which caused loss of moisture of the coals and development of micro-faulting and intense shearing and slicken siding. Vitrinite is derived from cordaitales wood and the mioflora is of Late Permian age. The coal seams show two sets of vitrinite oil reflectance, being either 0.540.60% or 0.72-0.73%. Thus, two types of vitrinites are prevalent throughout the seam sequence. The coals are of metalignitous to hypobituminous rank. Vitrinite content tends to decrease towards the younger seams, while carbominerite increases from the older to the younger seams. Carbominerite is intimately admixed with inertinite macerals and this is suggestine of utilisation through beneficiation processes. The Bhangtar coal is distinct and different in maceral and microlithotype compositions from the coals of Gondwana coalfields of Peninsular India (Table 7, Figs. 3, 4), but it shows affinity in maceral composition to the coals of Elephant Flat area, district Kameng, Arunachal Pradesh. The coals are of the same age, and continuity of the Bhutan-Arunachal Pradesh Gondwana basin is strengthened by this petrographic similarity. The semianthracite stage of Kameng coals is related to local tectonism of the area.

PETROGRAPHY AND RANK OF THE BHANGTAR COALS, SOUTHEASTERN BHUTAN

243

REFERENCES Alpern, B., 198 I. Pour une classification synthetique universelle des comustibles solides. Bull. Centres Rech. Explor.-Prod. Elf-Aquitaine, 5 ( 2 ): 271-290. Banerjee, M., Das Gupta, R., Chandra, D., Ghosh, R. and Choudhuri, S.G., 1986. Palyno-petrography and depositional environment of Lower Gondwana coal from Bhutam Eastern Himalaya. Ind. J. Earth Sci., 13( 1 ): 76-90. Gansser, A., 1964. Geology of the Himalayas. Interscience Publishers. John Wiley & Sons, London, 189 pp. Gokul, A.R., 198 I. Geology and Mineral Resources of Bhutan. Him. Geol. Seminar, New Delhi, Section l-B, Geology, Stratigraphy and Palaeontology. Geol. Surv. Ind., Misc. Pub., 41 (ll): 156-171. Indian Standards Institution, 1978. Classification and codification of Indian coals and lignites. I S 270 - 1977, October 1978. Mukherjee, A.K., Alam, M.M. and Ghose, S., 1988. Gondwana coals of Bhutan Himalaya Occurrence, properties and petrographic characteristics. Int. J. Coal Geol., 9 (3): 287-304. Misra, B.K., Ahmed, M, and Navale, G.K.B., 1987. Petrological, chemical and depositional aspects of Eastern Himalayan coals from Elephant Flat area, Kameng district, Arunachal Pradesh, India. Int. J. Coal Geol., 8: 279-297. Navale, G.K.B., Misra, B.K. and Anand Prakash, 1983. The microconstituents of Godavari coals, South India. Int. J. Coal Geol., 3: 131-161. Pareek, H.S., 1967. Some observations on the lithology of coal-bearing beds and the nature of coal of the major Gondwana basins of India. Gond. Stratig., lUGS Syrup., Buenos Aires, pp. 883-903. Pareek, H.S., 1969. The application of coal petrography to coking property of Indian coals. Econ. Geol., 64: 809-821. Pareek, H.S., 1970. Petrology of coal, burnt coal and para lava from Singrauli coalfield, M.P., U.P.J. Geol. Soc. Ind., 11 (4): 333-347. Pareek, H.S., 1986a. On the nature of Bhangtar coal, district Samdrup Jongkhar, Bhutan. Workshop on Geology, and Mineral & Power Resources of Bhutan and Their Potential for Industrial Development, Phuntsholing, Bhutan, Geol. Surv., Ind.. 12-14 March, Abstracts, p. II7. Pareek, H.S., 1986b. Chemical, trace elemental and petrological compositions of coal from Bhangtar area, district Samdrup Jongkhar, Bhutan. Presented before the Workshop on Geology, and Mineral & Power Resources of Bhutan and Their Potential for Industrial Development, Phuntsholing, Bhutan, 13 March, 1986. Pareek, H.S., 1986c. The role of coal petrographic characteristics in evaluating the non-coking nature of the coals of Ramagundam and Kothagudem coalfields, Godavari Valley basin. Abdhra Pradesh, India. Int. J. Coal Geol., 6: 181-198. Parcck. H.S, 1987. Petrographic, chemical and trace-elemental composition of the coal of Sohagpur coalfield, Madhya Pradesh, India. Int. J. Coal. Geol., 9:187-207. Pareek, H.S., 1988. Petrographic characteristics of the solid fuels of India with the particular reference to the coking coals. Int. J. Coal Geol., 10: 285-307. Pareek, H.S. and Bardhan, B., 1985. Trace elements and their variation along seam profiles of certain coal seams of Middle and Upper Barakar Formations ( Lower Permian ) in East Bokaro coalfield, district Hazaribagh, Bihar, India. Int. J. Coal Geol., 5:281-314. Pareek, H.S., Bardhan, B. and Chakrabarti, N.C., 1988. Seam sedimentaD' cycles, sedimentary petrography of bore hole core samples of Lower Damuda (Lower Permian) Group, and petrography of the coal seams, Saharjuri coalfield, district Santhal Pargana, Bihar. Rec. Geol. Surv. Ind., 118(2): 9-32.