Geology, petrology and utilisation potential of some Tertiary coals of the northeastern region of India

International Journal of

ELSEVIER

International Journal of Coal Geology 30 (1996) 65-100

Geology, petrology and utilisation potential of some Tertiary coals of the northeastern region of India H.K. Mishra *, R.K. Ghosh Central Mine Planning and Design Institute Ltd., Exploration Division, Ranchi, Bihar 834 00, b~dia

Received 13 September 1994; accepted 13 October 1995

Abstract The coal-bearing Tertiary sediments of the northeastern region of India range in age from Palaeocene to Oligocene. The coal deposits of Meghalaya and the Mikir and North Cachar hills of Assam contain generally thin seams of Eocene age and were formed under stable shelf condition in peripheral platform areas. The coal deposits of Oligocene age occur in a narrow, linear belt of overthrusts referred to as the 'belt of Schuppen', that extends from Nagaland through Assam to Arunachal Pradesh; they were deposited in near-shore, deltaic, wet forest swamps to marshy environments, close to a geosynclinal trough. The coal seams attain considerable thickness in the Makum and Namchik-Namphuk coalfields. Comparisons of coal type and rank variations in the Eocene and Oligocene coals indicate that the coals are broadly similar. The coals are vitrinite-rich ( > 70 vol%, mineral-matter-free hereafter referred as mmf), with moderate amounts of liptinite ( > 8 vol%, mmf) and inertinite ( > 5 vol%, mmf). The coals are high in volatile matter (38-57 %, dry, mineral-matter-free basis, hereafter referred as dmf), sulphur (1-10 %) and hydrogen contents ( 4 - 9 % dmf). The carbon content of the coals ranges from 68% to 85% (dmf). The coals have caking properties in restricted zones. The vitrinite reflectance of the Oligocene coals (%R r = 0.53-0.74) is slightly higher than that of the Eocene coals (%R r = 0.37-0.67). As per ASTM Standard, the Eocene coals are classified as sub-bituminous C to high volatile bituminous C, and the Oligocene coals as sub-bituminous A to high volatile bituminous B. Microscopic examination of the coals shows a number of features which indicate that the northeastern coals may have generated hydrocarbons. Most of the Eocene and Oligocene coals are suitable for combustion and conversion (e.g., liquefaction) processes. The coals with caking properties are being used at rates up to 5 - 1 0 ~ in blends for metallurgical coke provided their sulphur content is below 3% and their ash content below 10%.

* Corresponding author. 0166-5162/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSDI 0166-5162(95 )00038-0

66

H.I(2 Mishru, R.IK Ghosh / International Journal of Coal Geology 30 (1996) 65-1 O0

1. Introduction

The northeastern region of India (lat. 25030 ' to 28°0'N and long. 9000 ' to 96°5'E) comprises the states of Arunachal Pradesh, Assam, Nagaland, Manipur, Tripura, Mizoram and Meghalaya. Tertiary coal deposits occur in the states of Arunachal Pradesh, Assam, Nagaland, and Meghalaya; there are some 67 individual minor to moderately large coal deposits in these states (Fig. 1). These coal deposits with a total resources of 0.86 × 109 t ~ constitute 0.4% of India's total coal resources of 197 x 10 9 t (GSI, 1994). The resources are divided into three categories, viz. proved, indicated and inferred, based on the degree of reliability (Table 1). Although quantitatively the resources are meagre, they play an important role in the development of the region by virtue of their location far away from the major coal deposits of the country, and due to their unusual coal properties (Ramachandran and Ghosh, 1993). The total production from these deposits currently is 3.5 × 106 t per year; nearly 1 × 10 6 t are produced by Coal India Ltd. from the largest coalfield (Makum); the balance is produced by small private owners from scattered, isolated deposits. Although chemical properties of these coals have been studied, petrographic studies are limited (Navale and Mishra, 1980; Ahmed and Bharali, 1985; Goswami, 1985; Chaudhuri and Ghosh, 1990; B.K. Mishra, 1992a).The main objectives of this paper are to: 1. establish the variation of the coal type and rank of the Eocene and Oligocene coals, on the basis of chemical and petrographic studies; 2. interpret depositional environments of the peat-forming swamps; 3. compare the coals with other Tertiary coals of the world; and 4. evaluate their potential technological applications.

2. Geology

The Tertiary coal deposits of northeastern India occur in two distinct geotectonic settings (Fig. 2): 1. Eocene coal deposits are found as isolated patches in the southern part of the Shillong Plateau (Meghalaya) and the Mikir and North Cachar hills (Assam); they were formed on platform areas peripheral to the Indian shield, under stable shelf conditions. 2. Oligocene coal deposits are found in pericratonic downwarps in the 'belt of Schuppen' on the northern flank of the Naga-Patkai range; they extend over the states of Nagaland, Assam and Arunachal Pradesh. 2.1. Eocene coal deposits

The Eocene coal deposits of the Garo, Khasi and Jaintia hills of Meghalaya were formed over the peripheral platform areas of the Shillong Plateau which is an extension 1 t - l metric tonne=

10 3

kg.

ILK. Mishra, R.K. Ghosh / International Journal of Coal Geology 30 11996) 65-100 .~

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Fig. 1. Map showing distribution of coalfields in the northeastern region of India and locations of sampling points (for the names of the coalfields refer to Table 4, where the sampling points correspond to the serial numbers).

Table 1 Inventory of coal resources in the northeastern region of India for seams 0.9 m and above in thickness up to a depth of 600 m (GSI, 1994) State

Coalfields

Assam

1. Makum 2. Dilli-Jeypore 3. North Cachar and Mikir Hills

Arunachal Pradesh Meghalaya

Nagaland

Total 1 Mt = l09 kg.

Depth

Reserves (Mt)

(m)

proved

indicated

inferred

0-600 0-300 0-300

123.66 9.03 0.69

50.19 14.19

61.81 30.80 2.02

235.66 54.02 2.71

4. Namchik-Namphuk

0-300

31.23

11.04

47.96

90.23

5. West Daranggiri 6. Balphakram-Pendengru 7. Siju 8. Langfin 9. Mawlong-Shella 10. Minor Coalfields of Khasi Hills 11. Bapung 12. Minor Coalfield of Jaintia Hills

0-300 0-300 0-300 0-300 0-300 0-300 0-300 0-300

64.47 11.34 2.17 11.01

62.53

107.03 125.00 3 1.46 3.83 7.09 22.65 3.65

127.1/0 107.03 125.110 50.00 6.1/0 7.//9 33.66 3.65

13. Borjan 14. Jhanzi-Disai Valley 15. Tuen Sang 16. Tiru Valley

0-300 0-300 0-300 0-300

3.43

1.35

-

5.22 2.08 1.26 6.60

10.00 2.08 1.26 6.60

0-600

257.03

146.50

458.46

861.99

7.20

total

°

F'~

I

90

92.t

I

50

K m.

X X X X

L E G E N D

~"~}

.-'x x x x x x x

JAINTIA SERIES OISANG SERIES - EOCENE

~

96.

GRANITE- UPPER PROTEROZOIE

26 °

28"

F9-9~ SHILLONG GROUP-MIDDLE PROTEROZOI

/

~;~.

~

THRUST

ALIGNMENT

SYLHET TRAP-LOWER CRETACEOUS ['E'~E]GNEISS - AREHEAN

KHASI GROUP-UPPER CRETACEOUS

'!~

>,::pr~'il ...... "~...'?

SURMA SERIES ~ BAGFIMARA FORMATION-MIOCENE

S C A L E

I

0

Y

Fig. 2. Geological and tectonic map of the northeastern region of India (GSI, 1974).

TIPAM SERIES CHENOAPARA FORMATION-PLIOEENE

DNNG SERIES DUPITILA SERIES-PLE ISTOCENE

ALLUVIUM

'% SHILLONG PLA ¢--~-'EA ~:=x x x x x x x x /

~',~.

MAP OF NORTH EASTERN

JITITFJ BARAIL SERIES ~ SIMSANG FORMATION-OLiGOCENE

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25

50

GEOLOGICAL PART OF INDIA

~.

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H.K. Mishra, R.K. Ghosh/ lnternational Journal of Coal Geology 30 (1996) 65-100

69

of the ancient Precambrian Indian Peninsular shield. During the Cretaceous, the shield was uplifted to a 'horst' structure; subsequent peneplanation levelled the topography to the present plateau surface. The shield's tectonic evolution is closely linked to the outpouring of basaltic lava flows (Sylhet Trap) during the Jurassic period. The coal measures were deposited during the Palaeocene to Eocene and overlie Cretaceous sediments along the southern periphery of the plateau. The Palaeogene rocks were primarily deposited on a shallow marine shelf as indicated by the interbedding of coal seams with Foraminiferal limestones, the high organic sulphur content of the coals, and the coal facies. The shelf area apparently extended as an embayment into the Mikir and North Cachar hills of Assam. Oscillations in the marine strand line account for the interfingering of neritic shelf and littoral facies. The lateral variation of lithofacies of Palaeogene rocks contributed to the diverse lithostratigraphic nomenclature of rocks (GSI, 1981, GSI, 1989). Usually, the beds are subhorizontal in attitude and form monoclinal flexure, closely associated with the Dawki fault which passes along the southern boundary of the plateau. The sequence of the Tertiary sediments in Meghalaya is given in Table 2 (GSI, 1974). In the Garo hills, there are five coalfields; the most important ones are Siju, West Daranggiri and Balphakram-Pendengru. The coal seams occur in the Tufa Sandstone Formation (Eocene) of the Jaintia Group. Thirteen coalfields occur in the Khasi hills, of which the Langrin field is the most important. The coal seams occur in the Lakadong Sandstone Formation (Eocene); however, in the Lumdidom field, the coal seams occur in Lower Sylhet Sandstone of Palaeocene age. Among the eight coalfields of the Jaintia hills, the Bapung coalfield is the most prominent one. The coal seams occur in the Lakadong Sandstone Formation of Eocene age and also in the Therria Sandstone Formation (Lower Sylhet Sandstone) of Palaeocene age. The coal seams in the West Daranggiri coalfield of the Garo hills attain thicknesses of up to 2 m. The coal seams in the coalfields of Meghalaya are generally below 1 m thick and are characterised by pinching and swelling. In the Mikir and North Cachar hills of Assam, there are twenty-one reported occurrences of coal. The coal seams are generally around 0.50 m thick and occur in the Sylhet Sandstone Member of the Shella Formation of the Jaintia Group; they are of Eocene age. 2.2. Oligocene coal deposits

The Oligocene coal deposits on the northern flank of the Naga-Patkai range occur in a belt that is > 300 km long, broadly trending ENE-WSW. They extend over the states of Nagaland, Assam and Arunachal Pradesh. The belt, referred to as the 'belt of Schuppen', is defined by a series of at least eight complex thrust faults that are arranged imbricately along which the Naga hills and moved northwest relative to the foreland ridges. The genetic history of the 'belt of Schuppen' commenced during Late Eocene times with the emplacement of ophiolites in the eastern part of Naga-Patkai range along

Sylhet Trap (600)

Jurassic

Archaean

Khasi

Upper Cretaceous

Upper Shella

Middle Shella Jaintia Lower Shella (600)

siltstone-sandstone alternations, sand shale, sandstone, marl fossiliferous, argillaceous limestone sandstone with calcareous bands foraminiferal limestone

Simsang (1150) Kopili (500) Prang/Siju limestone (150) Narpuh sandstone (30) Umlatdoh limestone (110)

Garo

Oligo-Miocene

Palaeo-Eocene

feldspathic sandstone, pebble conglomerate, clay, silty clay

Baghmara (530)

Dupi Tila (1050)

coal-bearing quartzitic sandstone Tura/Lakadong sandstone (250) fossiliferous limestone Lakadong limestone (60) ferruginous, quartzitic sandstone, thin coal seams, carbonaceous shale Therria sandstone (80) calcareous shale, sandstone, limestone Langpar (100) arkose (glauconite) Mahadek (150) sandstone, arkose Bottom Conglomerate (25) sandstone, conglomerate alternations Jadukata (140) ............ Unconformity . . . . . . . . . . . . basalt, alkali basalt, rhyolite, acid tuff ............ Unconformity . . . . . . . . . . . . gneissic complex

sand, clay, pebble, gravel and boulder deposits Unconformity . . . . . . . . . . . . mottled clays, feldspathic sandstone and conglomerate Unconformity . . . . . . . . . . . . sand, siltstone, clay, marl

Mio-Pliocene

unclassified ............ unclassified ............ Chengapara (700)

older alluvium

Litho-units

Pleistocene

Formation (thickness, m)

Group (thickness, m)

Geological age

Table 2 Generalised stratigraphic sequence of Shillong Plateau (Meghalaya) and Mikir Hills (Assam)

I

,,o

g~

e:

-M

Eocene

Oligocene

Miocene

Mio-Pliocene

Pliocene

Litho-units

Dihing (1800) -

mostly pebbly sandstone with thin greyish clay beds ............ Unconformity . . . . . . . . . . . . Namsang (800) fine- to coarse-grained sandstone with bands of clay ............ Unconformity . . . . . . . . . . . . Girujan clay (1800) mottled clay with greyish, soft sandstone Tipam Tipam sandstone (2300) ferruginous fine- to coarse-grained micaceous to feldspathic sandstone ............ Unconformity . . . . . . . . . . . . Tikak Parbat (600) greyish to yellowish white sandstone, sandy shales, coal seams Barail Baragolai (3500) greyish to bluish-grey or yellowish-red mudstone, shale, sandstone, carbonaceous shales and thin coal seams Naogaon (2200) compact, fine-grained, dark-grey sandstone with bands of splintery shales splintery dark-grey shale and thin sandstone interbands Disang (3000)

Geological age Group Formation (thickness, m) (thickness, m)

Table 3 Generalised stratigraphic sequence in Nagaland, Assam and Arunachal Pradesh

I

tm

c~"

=

3"

72

ILK. Mishra, R.K. Ghosh/ lnternational Journal of Coal Geology 30 (1996) 65-100

the margin of the Indian plate. The uplifting of the Indo-Burmese range resulted from the suturing of Indian and Eurasian plates. During Oligo-Miocene times large molasse basins developed which extended from Nagaland through Assam to Arunachal Pradesh, containing thick coal measures. The platform areas underwent block adjustment mainly due to vertical movements. Late Miocene folding of the continental margin sequence and of the molasse sediments led to the development of large-scale, open, upright folds which created the pronounced linearity of this structural belt. Syntectonic adjustment of the basement and associated push against the rigid block to the west resulted in crustal shortening, leading to the development of major thrust faults. The outer and inner limits of the 'belt of Schuppen' are defined by the Naga and Halflong-Disang thrust faults (GSI, 1989). The structure of the 'belt of Schuppen' is further complicated by folds, faults, and thrust surfaces; dips are fairly steep to near vertical. A thick sequence of 2 - 6 km of Tertiary sediments accumulated in the trough flanking the Indo-Burmese range. The stratigraphic sequence of Tertiary sediments established in this zone is given in Table 3 (GSI, 1981). The sediments along the marine strand line were deposited under the deltaic facies. The regional palaeoslope during the deposition of the upper part of the Barail Group was possibly from northeast to southwest with more coal accumulation in the Upper Assam (Makum coalfield) (GSI, 1989). In the northern part of the belt, the coal seams attain considerable thickness in the Makum and Namchik-Namphuk coalfields. There are five to seven coal seams in these two fields and the maximum thickness of one particular seam is 18 m in the Makum coalfield, split into two to three sections. In the southern part, the larger coalfields are Dilli-Jeypore, Borjan and Jhanzi-Disai and minor coalfields are Tiru and Tichak, apart from a few other small occurrences. The coal seams in these fields rarely attain a thickness of 1.5 m; they are characterised by splitting with considerable variation in the thickness of individual splits and total seam thickness.

3. Samples and method of study Forty-six coal samples from outcrops and mine sites were collected as either grab or channel samples, and also as run of mine samples, from the Tertiary coalfields covering the entire northeastern region (Fig. 1). The method of sampling and sample preparation for the chemical analysis was carried out according to Indian Standard (IS) 436 (IS, 1964). The chemical analyses were carried out according to IS 1350 (Parts I and III) (IS, 1969a, IS, 1969b), for proximate analyses and determinations of sulphur, respectively. The ultimate analysis method was followed as per IS 1351 (IS, 1959a) and the Caking Index, Swelling properties and Gray-king assay coke type were done according to IS 1353 (IS, 1959b). For petrographic studies, the coal samples were prepared as per IS 9127 (Part II) (IS, 1979). Maceral analyses and vitrinite reflectance measurements were carried out following the procedures outlined in the International Handbook o f Coal Petrography (ICCP, 1971) and IS 9127 (Part III) (IS, 1992). Vitrinite reflectance measurements were undertaken using a Leitz Orthoplan polarising microscope fitted with a MPV3 microscope photometer that was calibrated against the Leuco sapphire standard of 0.58% and

H.K. Mishra, R.K. Ghosh/ International Journal of Coal Geology 30 (1996) 65 100

73

a glass prism standard of 1.23%. Samples were analysed in DIN 5884 immersion oil with a refractive index of 1.518 at 2 3 ° + I°C. A minimum of 50 measurements were made on each sample. Fluorescence mode observations were used in conjunction with reflected white light. A Leitz Orthoplan microscope was equipped with a 100 W quartz iodine lamp for reflected light and a 100 W mercury lamp for fluorescence m o d e For ultraviolet/violet light excitation, a filter system comprising a 3 mm BG3 excitation filter, a TK400 dichroic beam splitting mirror and a TK490 suppression filter were used. For maceral analysis about 500 points were counted on each block. Skip lengths and traverse spacings were altered relative to grain sizes of the sample in order to obtain representative counts. Approximately 90% of the area of each block was covered during the point counting. Each point was examined in reflected white light and in fluorescence mode. The number of points counted for mineral matter and macerals were expressed as percentages by volume.

4. Results

The analytical results of the samples collected are presented in Tables 4-7. The serial number under column 1 refers to the sampling points in Fig. 1. 4.1. Chemical characteristics

The chemical parameters of Eocene and Oligocene coals are given in Table 4 and the total sulphur and sulphur distribution in Table 5. Wherever data of certain parameters of individual samples could not be analysed, a range for the coalfield has been shown from CMPDI (1991) to broadly indicate the character of the coal. The range of chemical characteristics of the Eocene and Oligocene coals are summarised below: Parameters

Eocene

Oligocene

1- 12 3-34 2-7

1--6 2--29 1-- 10

38-57 68-83 4-9 6500-8500

41-52 74-85 5--7 6255-8650

Air-dried basis:

Moisture (%) Ash (%) Total sulphur (%) DO', mineral-matter-free basis:

Volatile matter (%) Carbon (%) Hydrogen (%) Calorific value (kcal/kg)

Chemically Eocene and Oligocene coals are not significantly different, except that the Eocene coals are slightly less mature, having on the average lower carbon contents than the Oligocene coals. Generally, the coals are of high volatile bituminous rank (generally > 40%, dry, mineral-matter-free basis, hereafter referred as dmf); they have a high

2

1

Karaibari Rongrenggiri Siju West Daranggiri Balphakram-Pendengm Balphakram-Pendengru

Langrin Mawlong Shella Mawlong Shella Laitryngew Laitryngew

b. 7a. b. 8a. b.

9a. b.

Jarain-Tkentalang Jarain-Tkentalang

iii. Jaintia Hills:

Langrin

6a.

ii. Khasi Hills:

1. 2. 3. 4. 5a. b.

i. Garo Hills:

A. Meghalaya:

EOCENE COALS:

Coalfield/area

S1. No

971 970

1080 1081 974 973 972 976

3.1 1.7

6.5 6.9 1.9 1.9 1.5 1.0

14.2 7.2

3.3 3.8 9.2 20.9 7.7 31.3

6.6 17.4 5.4 2.7 18.3 3.8

5

4

11.5 10.1 6.8 8.4 4.5 3.5

(%)

(%)

1567 1565 1566 1564 1561 1563

ash

(44.5) (50.2) (43.6) (45.4) (48.4) (42.1)

(57.0) (59.2) (43.2) (46.5) (53.2) (51.4)

40.5 (48.1) 46.9 (51.5)

40.1 44.8 38.8 36.2 43.7 30.3

46.7 43.6 37.9 41.3 41.9 47.6

6

(%)

volatile matter

Proximate analysis (air-dried) moisture

Sample

No.

Table 4 Chemical characteristics of coal of the northeastern region

(55.5) (49.8) (56.4) (54.6) (51.6) (57.9)

(43.0) (40.8) (56.8) (53.5) (46.8) (48.6)

42.2 (51.9) 44.2 (48.5)

50.1 44.5 50.1 41.0 47.1 37.4

35.2 28.9 49.9 47.6 35.3 45.1

7

(%)

fixed carbon

6.7 5.5

2.3 2.3 4.7 3.9 4.2 4.0

3.0 4.7 3.5 2.3 4.4 4.2

8

(%)

Total sulphur

26 31

18

32 t8

9

Caking index

G G3

5 6~2

3 2 3 3

1~

C/D G4 G G4 G

1½

C/D

1 2~2

5.2-6.3

6.0-6.6

4.0-4.9 6.7 6.2 8.8 5.6-7.3 6.7 6.3

13

(%)

80.0

5.7

78.7-7-83.2 5.8-6.5

76.0-81.7

78.0-81.2

77.7-79.6 72.6-79.5 80.6 79.4

67.5-70.2 75.4

12

(%)

Ultimate analysis (dmf) C H

B -

11

Swelling Index

B

C C/D E F/G

1(1

Coke type

I

g~

.~

Garampani Khota Arda

Bapung Bapung Bapung Bapung Bapung Bapung Khliehriat Sutnga Sutnga Sutnga Malwar-Musiang Lamare Malwar-Musiang Lamare Lumshnong Lumshnong

18

b.

17a.

Borjan

Jhanzi-Disai Changki-sector Jhanzi-Disai Changki-sector

A. Nagaland:

OL1GOCENE COALS:

15. 16.

B. Assam:

14a. b.

b.

10a. b. c. d. e. f. 11. 12a. b. c. 13a.

6.5

24.7 28.1

6.7

12.9 23.4 15.6 12.t 6.0 8.7 7.5 34.1 13.5 15.6

4.3 1.3 3.2-6.4

1432

1433

Range

6.6 28.5

6.2

7.8

5.6-6.2 4.8-6.7 3.0-5.7 22.1-27.1

1.1 1.5

1034 968

Range Range

1.0

3.0 2.9 4.5 3.0 5.4 0.9 1.2 1.1 1.7 1.5

1033

2.9

967

1028 977 1029 1030 1031 1032 969 1035 1036 975 4.6 3.9 4.2

55.0 (59.6) 44.3 (61.8) 42.2 (62.4)

37.3 (40.4) 29.9 (38.2) 28.2 (37.6)

48.7 (54.1)

43.8 (45.9) 38.1-39.7

50.9 (58.4)

37.0 (41.6)

45.0-42.6 35.4-36.8

35.6 (41.8)

36 32

49

33 31 21 32 24 47 31 26 38 40

33

2.4-6.0 NonCaking

2.2-4.9 NonCaking

1.9 3.3 1.3-1.9 -

5.8 3.7 6.0 5.2 5.0 6.9 5.9 4.9 4.8 4.7

(53.2) (52.6) (53.6) (53.8) (57.4) (50.7) (57.1) (57.2) (56.4) (58.2)

44.1 37.5 42.0 45.0 50.9 45.8 52.1 35.1 47.1 47.3

44.5-44.6 33.1 36.8

4.6

47.5 (52.4)

40.0 36.2 37.9 39.9 37.7 44.6 39.2 29.7 37.7

(46.8) (47.4) (46.4) (46.2) (42.6) (49.3) (42.9) (42.8) (43.6)

43.1 (47.6)

G3 G3

G3

G2 G1 E G3 F G3 G3 D G3 G3

G2

9 6

9

5½ 4 2½ 7 2½ 9 8 3'2 8½ 6½

4~

4.8 77.3

77.1-78.9

76.3-78.6

5.1-5.6

5.2-5.9

5.1-5.8

5.2-6.0

75.9-82.3

80.8-84.2

5.6-6.4

79.9-83.l

I

2

1

Makum: Baragolai 60' seam Tikak 60' seam Tikak 60' seam Tikak 60' seam Lachitkhani 60' seam Tirap 60' seam Tirap 60' seam Tirap 60' seam Tipong 60' seam Tirap 20' seam Tirap 20' seam Tipong 20' seam

20. a. b. c. d. e. f. g. h. i. j. k. 1.

Namchik-Namphuk Namchik Namphuk Namchik-Namphuk

1379 1620 1621

1321 1320 1079 1076 1074 1319 1075 1077 1316 1318 1078 1317

1619

3

Sample No.

5

4

2.7 4.1 2.2

1.5 1.9 1.3 1.2 1.2 1.5 1.0 1.3 2.3 1.3 1.1 2.0

1.6 5.8 8.8

7.1 8.4 12.4 3.0 1.7 7.5 8.0 9.1 27.2 5.6 2.7 15.1

1.9

(%)

(%)

4.8

ash

moisture

(44.3) (42.9) (51.7) (44.4) (41.3) (41.2) (42.7) (44.6) (43.8) (42.7) (45.2) (47.7)

40.3 (42.0) 44.1 (49.0) 42.2 (47.4)

40.9 39.1 41.2 42.7 40.2 37.9 39.3 40.6 32.4 40.1 43.7 36.3

44.7 (47.9)

6

(~)

volatile matter

Proximate analysis (air-dried)

10

11

Index

C

(55.7) (57.1) (48.3) (55.6) (58.7) (58.8) (57.3) (55.2) (56.2) (57.3) (54.8) (52.3)

55.4 (58.0) 46.0 (51.0) 46.8 (52.6)

50.5 50.6 45.1 53.1 56.9 53.1 51.7 49.0 38.1 53.0 52.6 46.6

48.6 (52.1)

12-27

20 35

2.0-6.5

1.8-4.9

15-37

NonCaking

1.9-4.0

1.3-9.8

D-G

G G4

F-G3

1 ~2

-

-

79.5-82.8

79.1-81.6

80.3-85.3

73.7-79.9

5.8-6.6

5.3-6.6

5.3-6.6

5.4-6.7

13

(%)

H

Ultimate analysis (dmf)

12

9

type

Swelling

(%) 8

index

Coke

7

carbon

Caking

(%)

sulphur (%)

fixed

Total

Analytical data expressed in range are taken t'rom CMPDI (1991). SI Nos. in column 1 refer to sampling points in Fig. 1. Figures in parentheses are on dry, mineral-matter-free basis (dmf). The moisture (air-dried) represents inherent moisture.

21 a. b. c.

C. Arunachal Pradesh:

Dilli-Jeypore

19.

B. Assam:

OLIGOCENE COALS

Coalfield/area

S1. No

Table 4 (Continued)

I

k,l

c~


a,

ga

~,

H.K. Mishra, R.K. Ghosh/ International Journal of Coal Geology 30 (1996) 65-100

77

sulphur content (generally > 2%), are low in carbon content (generally < 80%, dmf) and high in hydrogen content (generally > 5%, dmf). The Eocene coals of the Lumshnong in the Jaintia hills, and the Oligocene coals of the Makuta coalfield, however, have slightly higher carbon contents (Fig. 3). The in-situ ash content is generally low ( < 10%). Some of the samples have rather high ash contents, largely due to admixture of dirt bands. The interesting feature in these coals is the development of caking property in some of the samples. The Eocene coals of the Garo hills (Karaibari, West Daranggiri and Siju coalfields) are high in moisture (4-11%) and are noncaking, with a low carbon content (68-80%, dmf). The coals of the Khasi hills (Langrin and other minor coalfields) and the Jaintia hills (Bapung coalfield) are caking and have a lower moisture (1-5%) and higher carbon content (76-84%, dmf) than the Garo hills coals. The Eocene coals of the Mikir and North Cachar hills are noncaking. The Oligocene coals, like the Eocene coals, also exhibit both caking and noncaking character. While, the Oligocene coals of the Dilli-Jeypore, Borjan, etc., coalfields in Assam and Nagaland are noncaking, with relatively high moisture (3-6%) and low carbon contents (74-80%, dmf), those of the Makuta coalfield in Assam and the Namchik-Namphuk coalfield in Arunachal Pradesh are caking with lower moisture (1-3%) and higher carbon contents (79-85%, dmf) than the coals from the Dilli-Jeypore, Borjan, etc., coalfields. 4.2. Coal petrographic characteristics 4.2.1. Coal type uariation

Coal type variations between the Eocene and Oligocene coals were evaluated by microscopic methods in terms of macerals and mineral matter contents.

Fig. 3. Lateralvariationsof carbon content(dmf) of Eoceneand Oligocenecoals.

2

1

Sample No.

Total sulphur

Langrin Langriu Mawlong Shella Laitryngew

11. 12.

e.

d.

C.

10a. b.

9.

Jarain-Tkentalang Bapung Bapung Bapung Bapung Bapung Khliehriat Sumga

iii. Jaintia Hills:

6a. b. 7. 8.

ii. Khasi Hills:

1035 1036

1028 1029 1030 1031 1032

-

1080 1081

4.9 4.8

5.9 5.8 6.0 5.2 5.0 6.9

2.3 2.3 1.3-4.0 2.31-4.27

Siju

3. 4. 5. 1563

3.19-5.57 0.80-7.58 1.21-3.68 4.24

-

Rongrenggiri

2.

West Daranggiri Balphakram-Pendengru

1.36-6.01

-

4

Karaibari

3

1.

i. Garo hills:

A. Meghalaya:

EOCENE COALS:

Coalfield

S1. No.

Table 5 Total sulphur and sulphur forms of coals of the northeastern region

0.07-1.90 (2.6-45.0)

(37.2) (41.8) (54.6) (40.8) (58.1) (72.8) 3.76 (77.1) 2.63 (54.8)

2.21 2.42 3.27 2.11 2.90 5.05

0.08 (3.4) 0.08 (3.3) Nil-0.88 (Nil-23.1) 0.64-3.60 (27.7-45.6)

0.30 2.06(9.4 44.8) 0.21-5.53 (1.1-57.4) Nil-0.96 (Nil-33.1) 1.73 (40.8)

5

Pyritic sulphur

Sulphate sulphur

(1.2) (4.3) (2.2) (3.9) (2.4) (1.4) 0.11 (2.2) 0.05 (1.0)

0.07 0.25 0.13 0.20 0.12 0.10

0.06 (2.6) 0.08 (3.6) 0.05-0.18 (2.5-4.8) 0.08-0.25 (1.9-6.4)

0.13-1.03(2.8-18.5) 0.02-0.96 (0.7-30.4) 0.01-0.51 (0.4-19.5) 0.21 (4.9)

0.15-1.68 (6.0-34.7)

6

Organic sulphur

(61.6) (53.8) (43.2) (55.3) (39.5) (25.8) 1.01 (20.7) 2.12 (44.2)

3.66 3.11 2.59 2.86 1.97 1.79

2.19 (94.0) 2.10 (93.1) 1.28-3.40 (72.1-96.2) 1.57-2.63 (39.8-68.0)

2.39 3.61 (52.4-81.2) 0.66-7.16 (25.5-94.4) 1.07-2.33 (56.7-97.8) 2.30 (54.3)

0.61-2.43 (28.7-91.3)

7

I

L,a

Garampani Khota Arda

B. Assam:

Malwar-Musiang Lamare Lumshnong

Dilli-Jeypore Makum 60' seam 20 ~ seam Namchik-Namphuk

B. Assam:

Jhanzi-Disai Borjan

-

-

1033 1034

1.3-9.8 1.9-4.0 5.26-5.90 1.8 4.9

2.2-4.9 2.4-6.0

4.6 3.9

0.05-4.30 0.16-1.42 (7.4-45.2) 0.35-1.30 (6.0-22.7) 0.17 3.24 (9.4-66.1)

0.01-0.78 0.34-1.89

1.01 (22.2) 1.63 (41.7)

0.02-1.47 0.05-0.43 (1.3 12.8) 0.06 0.32 (1.1-6.0) 0.07-1.35 (0.4-27.6)

0.01-0.55 0.36-1.37

O. 15 (3.3) O. 14 (3.6)

0.51-3.78 1.25 3.15 (51.9-87.6) 4.19-4.73 (75.2 89.3) 1.0-2.7 (29.0-87.9)

0.08-3.60 1.33-3.93

3.39 (74.5) 2.14 (54.7)

Figures within parentheses are expressed as percentage of total sulphur. Figures expressed in range are taken from CMPDI (1991). The total sulphur is on air-dried basis.

2 t.

19. 20.

17. 18.

A. Nagaland:

OLIGOCENE COALS:

t 5. 16.

13. 14.

I

H.K. Mishra, R.K. Ghosh / International Journal of Coal Geology 30 (1996) 65-100

80

Table 6 Mean maceral group composition (mmf) and mean random vitrinite reflectance (%R r) of the coals of the northeastern region S1. No. 1

Coalfield 2

Sample No.

%R,.

(vol%) vitrinite

liptinite

inertinite

3

4

5

6

7

1567 1565 1566 1564 1561 1563

84.2 82.2 77.9 75.1 83.8 84.5

4.2 13. l 4.1 6.9 I 1.6 5.6

11.6 4.7 18.0 18.0 4.6 9.9

0.37 0.37 0.48 0.45 0.48 0.54

1080 1081 974 973 972 976

79.0 78.3 80.3 80.5 74.3 65.2

10.9 10.7 8.5 12.7 12.4 12.2

10.1 11.0 11.2 6.8 13.3 22.6

0.56 0.54 0.63 0.59 0.56 0.55

971 970 967 1028 977 1029 1030 1031 1032 969 1035 1036 975 1033 1034 968

73.2 75.8 68.8 83.9 90.4 66.6 84.1 65.8 88.3 67.8 97.1 65.1 95.0 95.0 95.1 96.6

11.4 13.4 10.9 3.1 7.4 6.9 6.7 6.8 8.5 11.0 2.2 8.2 3.0 3.9 3.1 1.3

15.4 10.9 20.3 13.0 2.2 26.5 9.2 27.4 3.2 21.2 0.7 26.7 2.0 1.1 1.8 2.1

0.54 0.53 0.58 0.59 0.63 0.59 0.63 0.54 0.63 0.67 0.64 0.61 0.83 0.78 0.84 I).85

EOCENE COALS:

A. Meghalaya: i. Garo hills: I. 2. 3. 4. 5a. b.

Karaibari Rongrenggiri Siju West Daranggiri Balphakram-Pendengru Balphakram-Pendengru

ii. Khasi hills: 6a. b. 7a. b. 8a. b.

Langrin Langrin Mawlong-Shella Mawlong Shella Laitryngew Laitryngew

iii. Jaintia Hills: 9a. b. l 0a. b. c. d. e. f. 11. 12a. b. c. 13a. b. 14a. b.

Jarain-Tkentalong Jarain-Tkentalong Bapung Bapung Bapung Bapung Bapung Bapung Khliehriat Sutunga Sutunga Sutunga Malwar-Musiang Lamare Malwar Musiang Lamare Lumshnong Lumshnong

The maceral

group compositions

of the Eocene

and Oligocene

c o a l s a r e l i s t e d in

T a b l e 6. T h e m a c e r a l a n d t h e m i n e r a l m a t t e r c o n t e n t s o f c o a l s a r e s h o w n in T a b l e 7. B o t h a r e r i c h i n v i t r i n i t e ( F i g . 4). D e s m o c o l l i n i t e ( v i t r i n i t e B ) a n d t e l o c o l l i n i t e ( v i t r i n i t e

H.K. Mishra, R.K, Ghosh / lnternational Journal of Coal Geology 30 (19961 65-100

81

Table 6 (continued) SI. No. I

Coalfield

Sample No.

2

3

(vol%) vitrinite

liptinite

inertinite

%R,

4

5

6

7

EOCENE COALS:

B. Assam: North Cachar Hills: 15. 16.

Khota Arda a Garampani

-

88.8 90.7

3.8 2.6

7.4 6.7

0.43 0.52

1432 1433 NZ- 1

97.7 95.8 82.9

1.6 3.6 9.6

0.7 0.6 7.5

0.74 0.72 0.61

1619

76.6

14.7

8.7

0.60

1321 1320 1079 1076 1074 1319 1075 1077 1316 1318 1078 1317

94.6 84.6 90.0 82.0 88.0 92.8 74.0 86.0 87.2 91.7 77.0 90.1

4.0 9.1 5.0 14.0 8.0 4.8 13.0 l 1.0 10.8 6.1 11.0 8.1

1.4 6.3 5.0 4.0 4.0 2.4 13.0 3.0 2.0 2.2 12.0 1,8

0.66 0.62 (I.69 0.77 0.70 0.6? 0.65 0.62 0.62 0.66 0.63 0.62

1379 1620 1621

89.8 90. l 77.8

6.2 6.1 t 7.6

4.0 3.8 4.6

0.68 0.55 0.53

OLIGOCENE COALS:

A. Nagaland: 17a. b. 18.

Jhanzi-Disai, Changki Sector Jhanzi-Disai, Changki Sector Borjan b

B. Assam: 19. 20. 20a. b. c. d. e. f. g. h. i. j. k. 1.

Dilli-Jeypore Makuta: Baragolai 60' seam Tikak 60' seam Tikak 60' seam Tikak 60 ~ seam Lachitldaani 60' seam Tirap 60' seam Tirap 60' seam Tirap 60' seam Yipong 60' seam Tirap 20' seam Tirap 20' seam Tipong 20' seam

C. Arunachal Pradesh: 2 t a. b. c.

Namchik-Namphuk Namchik-Namphuk Namchik-Namphuk

Sources: ~ CSL (1982, CSL (1983); b B.K. Mishra (1992b).

2

1

Langrin Langrin Mawlong-Shella Mawlong-Shella Laitryngew Laitryngew

9a. b.

Jarain-Tkentalong 970 Jarain-Tkentalong 971

iii. Jaintia Hills:

6a. b. 7a. b. 8a. b.

ii. Khasi Hills:

1080 1081 974 973 972 976

1563

b.

BalphakramPendengru

1567 1565 1566 1564 1561

3

Sample No.

i. Garo hills: 1. Karaibari 2. Rongrenggiri 3. Siju 4. West Daranggiri 5a. BalphakramPendengru

A. Meghalaya:

EOCENE COALS:

Sample details (coalfields/area)

S1. No.

5

4

67.8 65.4

74.2 74.4 74.9 67.9 69.4 52.1

79.2

7.4 7.1

8.0 8.0 4.6 5.3 6.7 6.7

2.0

0.3 1.0 0.9 2.9 3.5

sporinite

vitrine

64.1 60.0 62.1 69.6 63.5

liptinite

total

(vol%)

0.6 0.3

0.7 0.5

0.4 0.5 1.4 2.4 1.1 1.5

2.0

0.7

0.2 0.6 0.1 0.4 0.1 0.5

0.9 5.2 0.8 1.9 2.7

7

resinite

1.5 2.1 1.0 0.4 0.5

6

cutinite

3+3 2.3

1.2 1.1 1.8 2.6 3.7 1.1

0.5

0.4 1.3 0.5 1.2 2.1

8

liptodetrinite

Table 7 Maceral and mineral matter content of coals of the northeastern region

12.0 10.2

10.3 10.2 7.9 10.7 11.6 9.7

5.2

3.1 9.6 3.2 6.4 8.8

9

total liptinite

4.5 5.9

7.0 6.5 4.7 1.6 5.0 11.8

5.8

5.5 2.1 3.0 7.6 0.5

10

semi fusinite

inertinite

0.1 0.3

0.3 0.1 0.2 0.5

0.1

0.1 0.5 0.2 0.3 0.1

11

sclerotinite

2.6 3.1

2.2 2.6 2.4 2.6 3.7 3.5

2.4

1.2 0.8 7.0 8.1 1.9

12

inertodetrinite

2.4 4.5

0.4 1.0 3.3 1.4 3.7 2.3

l+l

2.1 4.2 0.7 1.0

13

micrinite

9.6 13.8

9.6 10.4 10.5 5+8 12.4 18.1

9+4

8.9 3.4 14.8 16.7 3.5

14

total inertinite

3.6 4.5

5.0 4.6 6+0 12.8 4.6 12+9

5.2

20.6 14.7 15.5 7.1 21.2

15

quartz+ clay

7.0 6.1

0.9 0.4 0.7 2.8 2.0 2.3

0.3

3.3 12.3 4.8 0.2 3.0

16

pyrite

10.6 10.6

5.9 5.0 6.7 15.6 6.6 20.1

5.5

23.9 27.0 20.3 7.3 24.2

total mineral matter 17

identifiable mineral matter

I

g~

~z

Bapung Bapung Bapung Bapung Bapung Bapung Khliehriat Sutnga Sutnga Sutnga Malwar-Musiang Lamare Malwar Musiang Lamare Lumshnong Lumshnong

Garampani Khota Arda

17a. b. 18.

Jhanzi Disai Jhanzi-Disai Borjan

A. Nagaland:

OLIGOCENE COALS:

15. 16.

B. Assam:

10a. b. c. d. e. f. 11. 12a. b. c. 13a. b. 14a. b.

1432 1433 NZ-I

967 1028 977 1029 1030 1031 1032 969 1035 1036 975 1033 968 1034

86.8 87.9

65.7 77.0 70.8 53.2 80.6 60.8 80.3 60.2 77.6 58.6 87.0 87.8 77.5 78.0

0.5 1.0

5.0 1.0 3.1 4.1 3.8 3.4 5.2 6.1 2.6 6.0 2.0 2.3 0.8 2.5

0.2 0.2 .

0.4 0.3 0.5 0.1 0.4 0.4 0.4 0.2 0.1 0.3 0.3 -

.

0.2 1.2

3.2 0.5 1.0 1.0 0.4 0.6 0.6 1.5 0.5 0.8 0.5 0.4 1.0 -

.

0.5 0.9

1.8 1.0 1.2 1.3 1.8 2.3 1.5 1.8 0.8 1.0 0.2 0.6 1.0 -

.

1.4 3.3 .

10.4 2.8 5.8 6.5 6.4 6.3 7.7 9.8 3.9 8.0 2.8 3.6 3.1 2.5

0.1 0.2 .

7.0 5.2 0.1 10.0 2.9 11.4 0.9 10.9 0.6 12.0 0.7 0.9 0.1 0.4

0.5 0.2 .

0.2 0.2 0.4 0.4 0.4 0.1 0.1 0.3 -

0.2

m

8.8 5.1 0.4 8.4 2.4 5.5 1.1 6.7 8.3 0.5 0.8 0.3

-

0.5 0.8

3.4 1.5 1.2 1.4 3.1 8.0 0.9 1.2 3.1 0.5

1).6 0.6

19.4 12.0 1.7 20.2 8.8 25.3 2.9 18.8 0.6 23.4 1.8 1.0 1.7 1.5

4

8.8 7.6

3.9 5.9 21.0 11.8 1.3 5.3 1.3 4.4 7.4 4.8 6.1 7.0 15.0 3.7

2.4 0.6

0.6 2.3 0.7 8.3 2.9 2.3 7.8 6.8 10.5 5.2 2.3 0.6 2.7 14.3

11.2 8.2

4.5 8.2 21.7 20.1 4.2 7.6 9.1 11.2 17.9 10.0 8.4 7.6 17.7 18.0

I

E"

2

1

3

Sample No.

Dilli-Jeypore 1619 Makuta: Baraqolai 60' seam 132t Tikak 60' seam 1320 Tikak 60' seam 1079 Tikak 60' seam 1076 Lachitkhani 60' seam1074 Tirap60' seam 1319 Tirap 60' seam 1075 Tirap 60' seam 1077 Tipong60' seam 1316 Tipong 20' seam 1317 Tirap 20' seam 1318 Tirap 20' seam 1078

83.0 83.7 68.0

2.2 1.3 3.0

1.9 3.3 1.3 4.0 2.8 1.7 5.1 5.6 2.3 2.1 1.2 3.3

88.2 77.1 85.0 80.0 83.0 83.7 72.0 82.0 71.1 79.8 85.1 72.1/

5

4

1.7

sporinite

73.4

liptinite

total

vitrine

(vol%)

Cutinite % in column 6 includes suberinite.

21a. Namchik-Namphuk 1379 b. Namchik-Namphuk 1620 c. Namchik-Namphuk 162t

C. Arunachal Pradesh:

19. 20. a. b. c. d. e. f. g. h. i. j. k. 1.

B. Assam:

OLIGOCENE COALS:

Sample details (coalfields/area)

SI. No.

Table 7 (continued)

0.2 0.3 2.4

0.3 0.8 0.1 0.2 0.8 6.2 0.3 0.5 0.5 0.5 0.6

0.5

6

cutinite

0.3 3.0 6.8

1.0 2.6 0.6 6.9 0.5 1.0 1.3 1.0 1.1 1.6 1.5 2.7

7.8

7

resinite

1.0 1.1 3.2

0.5 1.4 2.0 2.9 3.7 0.8 0.4 3.1 4.9 3.1) 2.5 3.4

4.1

8

liptodetrinite

3.1 2.0 1.1

0.3 1.5 0.6 1.0 1.2 0.4 3.8 0.2 0.4 3.5

3.7 8.1 4.0 14.0 7.0 4.3 3.0 10.0 8.8 7.2 5.7 10.0

3.7 5.7 15.4

2.1

10

semi fusinite

inertinite

14.1

9

total liptinite

0.9 0.9 0.9

0.5 0.8 0.4 0.2 0.8 0.5 0.4 0.4 0.8 0.4 0.3

0.5

11

sclerotinite

0.9 0.1 1.3

0.3 2.6 1.9 1.5 2.3 0.4 4.8 2.2 0.5 1.0 5.7

1.7

12

inertodetrinite

0.8 0.5 0.7

0.2 0.8 2.3 1.3 0.5 0.6 3.9 0.2 0.3 0.3 0.2 1.5

4.11

13

micrinite

5.7 3.5 4.0

1.3 5.7 5.0 4.0 4.0 2.2 13.0 3.0 1.6 1.6 2.0 ll.0

8.3

14

total inertinite

6.8 6.2 8.9

5.9 6.2 4.4 1.7 5.0 8.5 0.7 2.6 16.4 11.4 6.6 5.6

3.8

15

0.8 0.9 3.7

0.9 2.7 1.6 0.3 1.0 1.3 1.3 2.4 2.1 0.6 t.4

0.4

16

pyrite

7.6 7.1 t2.6

6.8 8.9 6.0 2.0 6.0 9.8 2.0 5.0 18.5 11.4 7.2 7.0

4.2

total mineral matter 17

identifiable mineral matter quartz+ clay

I

tJi

tao

H.K. Mishra, R.K. Ghosh / International Journal of Coal Geology 30 (1996) 65-1 O0

85

VITRINITE fO0

~

INDEX o OLIGOCENE

~

I00 LIPTINITE

v

7'5

V

50

e ECOCENE

V

2-5

I00 INERTINITE

Fig. 4. Comparisonof maceralgroup compositionbetween Eocene and Oligocenecoals. A) (Plate 1, 1 and Plate 2, 4) are the dominant macerals, with subordinate amounts of telinite, corpocollinite, porigelinite and corpovitrinite. Vitrodetrinite is also abundant in some samples. Attrinite and densinite have also been observed in a few samples with low reflectance. In fluorescence examination of samples, telocollimte and desmocollinite show yellowish orange to dull orange colours. However, some of the telocollinite is nonfluorescing. In the Eocene coals the vitrinite content generally ranges from 73% to !)7% (mineral-matter-free hereafter referred as m m f ) . Regionally, it varies from 82% to 84% in the western part in the Garo hills; 73% to 81% in the central part in part of the Garo and Khasi hills; and 87% to 91% in the eastern part in the Jaintia and Mikir hills. However, in the southern part of the Jaintia hills, the vitrinite content is above average, varying from 95% to 97% (Table 6; Fig. 5). Six samples from the Jaintia hills have low vitrinite contents (65-69%); these samples are rich in inertinite compared to other Eocene coals. The vitrinite content of the Oligocene coals ranges from 74% to 98%. The coals of the Jhanzi-Disai coalfield in Nagaland exhibit a very high vitrinite content of 96-98%.

86

H.K. Mishra, R.K. Ghosh / International Journal of Coal Geology 30 (1996) 65-100

Plate 1. 1. Sclerotiniteassociated with vitrinite,Tirap Colliery,60' seam, Makum Coalfield, R r = 0.65%, field width = 0.18 mm, reflected white light. 2. Suberinite associated with vitrinite A, cutinite, inertodetriniteand sclerotinite,Tirap Colliery, 60' seam, Makum Coalfield, Rr = 0.65%, field width = 0.18 mm, reflected light.

An increase in the content of vitrinite has been observed from the southwest in the Borjan (Nagaland) and Dilli-Jeypore (Assam) coalfields to the northeast in the Namc h i k - N a m p h u k coalfield (Arunachal Pradesh) (Table 6; Fig. 5). The liptinite content ranges from 1% to 13% in the Eocene coals and 2% to 18% in the Oligocene coals. Resinite (Plate 2, 3 and 4), sporinite, liptodetrinite, suberinite (Plate l, 2), cutinite and fluorinite are dominant over alginite and phytoplankton. Exsudatinite is abundant in the cracks in vitrinite and exhibits green to greenish-yellow fluorescence.

H.K. Mishra, R.K. Ghosh / International Journal of Coal Geology 30 (1996) 65-100

87

:iii~iiiii~ ~ y ! ....

Plate 2. 3. Resinite (bright yellow), sporinite (dull yellow), Tirap Colliery, 60' seam, Makum Coalfield, R,. - 0.65%, field width = 0.28 mm, fluorescence mode.

4. As 3, but in reflected white light. Resin bodies (dark) associated with vitrinite groundmass.

Sporinite, cutinite and liptodetrinite generally show yellow to yellow-orange, to dull orange fluorescence colours. The resinite fluoresces bright yellow (Plate 2, 3). Fluorinite fluoresces green to greenish yellow, whereas B o t o , ococcus-type telalginite fluoresces bright yellow. The inertinite content of Eocene and Oligocene coals varies between 1% and 18% and 1% and 13%, respectively. Six samples of Eocene coals, however, show a particularly high inertinite content (20-27%). The most abundant inertinite macerals in these samples are semifusinite and inertodetrinite. Semifusinite, inertodetrinite and

88

H.K. Mishra, R.K. Ghosh / International Journal of Coal Geology 30 (1996) 65-100 l

..l.,..J

\

I/.-~~0~

~

Fig. 5. Lateral variation of vitrinite content (mmf) of Eocene and Oligocene coals.

micrinite are dominant over sclerotinite and fusinite. Fungal materials preserved as sclerotinite (Plate 1, 1) are more common in the Oligocene than the Eocene coals. The mineral matter in the Eocene and Oligocene coals ranges from 4% to 27% and 2% to 19%, respectively. The main minerals are clay minerals, quartz, pyrite and calcite.

J"f I['W/V

--

-~--'"

~ -

"°'

w

o";;'~-o..o

Fig. 6. Lateral variation of mean random vitrinite reflectance (%R~) of Eocene and Oligocene coals.

H.K. Mishra, R.K. Ghosh / International Journal of Coal Geology 30 (1996) 65-100

89

Table 8 Comparison of petrographic compositionof Eocene and Oligocenecoals Maceral group

Eocene

Oligocene

72 60-80 1.5 desmocollinite,telocollinite,attrinite, densinite,corpovitrinite,porigelinite, eugelinite

80 71-88 1.49 telocollinite,desmocollinite,corpovitrinite, porigelinite

7 3-12 0.64 sporinite,resinite,fluorinite, suberinite, [iptodetrinite,cutinite

8

Vitrinite (%):

Mean Range Standard error Common macerals

Liptinite (%):

Mean Range Standard error Common macerals

1 - 15

0.99 sporinite, liptodeterinite,fluorinite, resinite, cutinite, snberinite

lnertinite (%):

Mean 9 Range 1-25 Standard error 1.34 Common macerals semifusinite,inertodetrinite,micrinite, sclerotinite

4 1 [3 0.82 Semifusinite,inertodetrinite,micrinite, sclerotinite

Mineral matter (%):

Mean Range Standard error Common minerals

12 4-26 1.4 clay minerals,quartz, pyrite, calcite

8 2-18 0.93 clay minerals,quartz, pyrite, calcite

%Rr

0.37-0.67

0.53-0.74

Pyrite occurs as framboidals, granules and crystals; generally, it is associated with vitrinite macerals. Calcite occurs in cracks of vitrinite. Quartz is found finely disseminated in vitrinite-rich grains. Clay fills cell lumens of semifusinite and vitrinite. A general comparison of the maceral groups, the mineral matter content and the vitrinite reflectance of the Eocene and Oligocene coals is shown in Table 8. The coals are similar, except that in the Oligocene coals the inertinite content tends to be lower and the reflectance is slightly higher than in the Eocene coals. The high inertinite content in some of the Eocene coals suggests that locally the peat swamp was exposed to the atmosphere. 4.2.2. C o a l r a n k uariation

Mean random vitrinite reflectance (R r) was measured on 46 samples (Table 6). The reflectance of Eocene coals ranges from 0.37% to 0.54% in the western part (Garo hills),

Vitrinite:

38

No. of samples

20

2 1-3 C1, Pyt

7 4-11 Sf, Mic, Scl, Indt

6 4-9 Res, Lipt, Sub, Sp

85 77-89 0.62-0.70

72

2 tr.-3 CI, Pyt

3 1-7 Sf, Fus, Scl, lndt

6 2-15 Res. Lipt, Sp

89 81-95 0.38-0.83

35

2 1-5 C1, Pyt

5 tr.-9 Sf, Scl

2 tr. 9 Lipt, Res, Sp

91 79-97 0.60-1.41

(Newman and Newman, 1982)

New Zealand

Australia

34

tr. tr. 1 CI, Pyt

2 tr.-5 Scl. Indt

11 5 17 Lipt, Sub, Sp

86 76-95 0.24-0.36

Victoria (Daulay, 1985)

mmf

2 0-5 Scl, Sf, Fus

8 2-25 Sp, Res

86 60 95 0.3-0.6

upper eastern view

mmf

1 0-4 Scl, Fus, Sf

8 2-45 Sp, Sub, Res

92 50-98 0.20-0.40

Latrobe Valley

Gippsland Basin (Smith and Cook, 1984)

Key: Sp = sporinite; Fus = fusinite; Res = resinite: Qtz = quartz; Lipt = liptodetrinite" Sid = siderite; Algi = alginite; Pyr = pyrite; Sf = semifusinite; Kaol = kaolinite; lndt = inertodetrinite; tr. = < 0.5%; Cut = cutinite; Sub = suberinite: Mic = micrinite; S c l = sclerotinite.

11 2-29 CI, Pyt

8 2-20 Scl, sf, lndt

8 3-11 Res, Lipt, Sub, Sp

74 53-88 0.54-0.85

(Daulay, 1985) (H.K. Mishra, 1986)

Indonesia

northeastern region India (this study)

Assam

India

Mean Range Common minerals

Mineral matter:

Mean Range Common macerals

lnertinite:

Mean Range Common maceral

Liptinite:

Mean Range R v max % range

k

Table 9 Comparison of maceral group and mineral matter contents of Tertiary coals of India, Indonesia, New Zealand and Australia

I

t~

~-

ga

"~

H.K. Mishra, R.K. Ghosh / International Journal of Coal Geology 30 (1996) 6 5 - IO0

9l

0.56% to 0.63% in the central part (Khasi hills) and 0.53% to 0.67% in the eastern part of the study area (Jaintia hills) (Table 6; Fig. 6). The Eocene coals in the North Cachar hills of Assam have low reflectance values (0.43-0.52%). However, higher-rank coals (0.78-0.85%) occur in the Malwar-Musiang-Lamare and Lumshnong area and as isolated patches in the southern part of the Jaintia hills. In Oligocene coals, R r values range from 0.61% to 0.74% in the southwestern part (Nagaland), 0.60% to 0.73% in the central part (Assam), and 0.53% to 0.68% in the northeastern part (Arunachal Pradesh). Based on ASTM (1991) classification of coals by rank, the Eocene coals may be classified as sub-bituminous C to high volatile bituminous C and the Oligocene coals as sub-bituminous A to high volatile bituminous B. 4.3. Depositional environments of the coal seams In order to establish a correlation between coal facies indicators and the environment of deposition, two parameters were calculated. These are the Gelification Index (GI) and

Table 10 Comparison of maceral group and mineral matter contents of the Tertiary coals of some countries Taiwan (A.M. Depers, pers. commun., 1986)

Turkey (Yagmurulu, 1986)

Germany (yon der Brellie and Wolf, 1981)

Canada (Goodarzi et at., 1985)

96 94-97 0.87-1.39

76 68-83 -

93 80-95

81 64-98 0.20-0.63

tr.

2 1-4 Res, Sp, Lipt

5 1-12 Sp, Res, Cut

6 2-10 Sp

7 1-12 Sf, Fus, Indt

2 tr. 3 Scl, lndt

13 1-32 Sf, Fus

3

Vitrinite: Mean Range R~ max % range Liptinite: Mean Range Common macerals

Sp

lnertinite: Mean Range Common macerals

l tr.Sf

1

Mineral matter: Mean Range Common minerals

15

tr.

tr.

-

7-18

-

-

CI

CI, Pyt, Mar

CI

No. of samples

6

5

20

Mar = marcasite; for further explanations, see Table 9.

20

H.K. Mishra, R.K. Ghosh / International Journal of Coal Geology 30 (1996) 65-100

92

TREE DENSITY ~Decreases Increases - - -

LIMNO TELMATIC

TELMATIC

200 +

+ +

-P 4-

100 RSH

+ +

50

+

.x,

!

.-I+ +

+

+ u..

+

WEST FOREST +SWAMP •

5.0

tNO~X

+ Oligocene

1.0

• Eocene

0.5

DRY FOREST SWAMP

t 1.0

I

21.0

t

TERRESTRIAL t t I

t

t.

J

61.0

t

3.0 ~.0 S0 TISSUE PRESERVATION INDEX tTPI)

Fig. 7. Gelification Index versus Tissue Preservation Index plots for the Eocene and Oligocene coals (Diessel, 1986).

the Tissue Preservation Index (TPI) (Diessel, 1986). These relationships can be summarized as follows: vitrinite + macrinite GI=

Semifusinite + Fusinite + Inertodetrinite vitrinite A + semifusinite + fusinite

TPI =

vitrinite B + macrinite + inertodetrinite

The Oligocene coals have very high GI (up to 157). In contrast, the Eocene coals have moderate GI (up to 15). The TPI ranges mostly from 1 to 6 in both Oligocene and Eocene coals; but it is < 1 in one sample of Eocene coal (Fig. 7). The predominantly wet conditions of the peat formation in the Eocene and Oligocene coals are demonstrated by moderate to high GI values. However, the abundance of inertinite in the Eocene coals as compared to the Oligocene coals indicates drier

H.K. Mishra, R.K. Ghosh / International Journal of Coal Geology 30 (1996) 65-100

93

VITRINITE I00

A

V I00 LIPTINITE

75

- -

TAIWAN TERTIARY COALS

V

V

50

25

ioo INERTINITE

Fig. 8. Maceral group composition of Tertiary coals of India, Indonesia, Taiwan and Turkey.

conditions, or frequent alterations between high and low groundwater tables due to periodic drainage of the peat surface. The moderate to high GI and moderate TPI values indicate that the Eocene coals were deposited in wet forest swamps; the Oligocene coals were deposited in wet forest swamps and in marshy environments. The presence of organic sulphur and framboidal pyrite indicates marine influence.

4.4. A general comparison of the Tertiary coals of lndia with some other coals of similar age An attempt has been made in the present study to utilise published and unpublished data to make a general comparison between the Tertiary coals of India with some other Tertiary coals of the world. However, only few detailed petrographic descriptions of coals from other countries are available in the literature thus restricting the scope of such a study. Mean values of maceral group and mineral matter contents of coals from India, Indonesia, New Zealand and Australia are shown in Table 9, and from Taiwan, Turkey, Germany and Canada in Table 10. The vitrinite content is high in all the Tertiary coals. The inertinite content in the Indian Tertiary coals is higher than that of the Taiwanese, Turkish and Indonesian coals

94

H.K. Mishra, R.K. Ghosh / International Journal of Coal Geology 30 (1996) 65-100 VITRINITE I00

6ERMANY TERTIARY COALS NEWZEALAND TERTIARY CUALS

CANADIAN TERTIARY COALS

LATROBE UPPER EASTERN VIEW CUALS IAustralla|

75

"

I

25

50

I00 LIPTINITE

V 75

V 50

V 25

IOO INERTINITE

Fig. 9. Maceralgroupcompositionof Tertiarycoals of New Zealand,Australia, Germanyand Canada. (Fig. 8). Fungal sclerotinite is commonly present in the Tertiary coals; it rarely exceeds 2 vol%. The liptinite content of the Latrobe upper coal of Australia is higher (Fig. 9) than in other coals and is dominated by liptodetrinite, suberinite and sporinite; resinite is more common in Indian and Indonesian coals. The Tertiary coals of New Zealand, Canada, Taiwan, Turkey and Germany are also broadly similar to Indonesian and Indian coals (Tables 9 and 10; Figs. 8 and 9) (H.K. Mishra, 1986). According to Cook (1981), White (1983) and Bustin et al. (1983), the Late Cretaceous and Tertiary flora comprised an increased number of angiosperms as compared to earlier times. Smith (1982) indicated that in the Gibbsland basin of Australia, the Palaeocene to Eocene was characterised by high temperatures and high amounts of rainfall whereas the Oligocene to Miocene was more consistently wet and cool. Palynological studies by B.K. Mishra (1992b) indicated that angiospermous evergreen forest vegetation grew under humid tropical conditions during the Palaeocene and Oligocene in India.

5. Discussion

Megascopically, the Tertiary coals of this region are friable, soft, dark black and highly vitrainous, and exhibit conchoidal fractures. The chemical parameters indicate that both the Eocene and Oligocene coals are sub-bituminous to high volatile bitumi-

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95

nous. The carbon and volatile matter contents indicate that northeastern coals are noncaking to, at the best, weakly caking. However, the coals from the Khasi and Jaintia hills of Meghalaya and the Makum and Namchik-Namphuk coalfields exhibit strong caking properties with swelling index values ranging from 3 to 9. Such types of coal have also been recorded from Yugoslavia, New Zealand, Yorkshire, Borneo, New South Wales and Pakistan (Brooks, 1956; GSI, 1981). The role of high organic sulphur present in the northeastern coals in imparting the caking properties is not clearly understood. The organic sulphur in the coal can not be removed by mechanical methods. Research indicates that changes in molecular structure of coal may have been caused by replacement of oxygen in coal by sulphur (Lahiri, 1965). Therefore, these coals have a relatively low oxygen content. Recent studies (CFRI, 1993) indicate that sulphur is present in these coals in the form of disulphides, thiol, thioether, thiophene, pyrite, sulphate and thioketone. The study also revealed that thioketonic sulphur is more common than disulphide in caking coals. In the case of noncaking coals the thioketonic sulphur is usually less than disulphide. The carbon content (dmf) of the Eocene coals generally increases from 67% in the west in the Garo hills to 78% in the east in the Khasi hills. However, in the southern part of the Jaintia hills in Lumshnong, the coal attains a carbon content of > 80% (Fig. 3). In the Oligocene coals, the carbon content (dmf) varies from 76% in the southwestern part in Nagaland to 83% in the northeastern part in Arunachal Pradesh. The Eocene coals attain caking properties in the east in the Khasi and Jaintia hills; the Oligocene coals develop caking properties in the east in the coalfields of Assam and Arunachal Pradesh. This high rank is reflected in the lower moisture content and higher reflectance (Fig. 6). During carbonisation, the coals produce spongy coke that lacks the strength for use as direct feed for metallurgical purposes due to high vitrinite ( > 75% mmf) and high volatile matter contents. However, the coals can be used in a blend up to 10% to produce coke suitable for metallurgical use. The reflectance of Eocene coals ranges from 0.37% to 0.67% and that of Oligocene coals ranges from 0.53% to 0.74%. The somewhat higher rank of Oligocene coals is due to deeper burial compared to Eocene coals. However, the occurrence of high-rank Eocene coals (carbon 80-85%, dmf; R r = 0.78-0.85%) in Lumshnong and MalwarMusiang Lamare in the Jaintia hills can be attributed to the effect of igneous intrusives below the seam (possibly at a depth of 600-700 m; Evans and Mathur, 1964). Microscopic examination of the Tertiary coals of the northeastern region shows a number of features which may indicate that these coals generated liquid hydrocarbons. The most striking feature is the presence of green fluorescing material, similar to crude oils, and other features including the occurrence of fluorinite and exsudatinite. Fluorinite was observed in many samples having reflectance values in the range of 0.37-0.67%. Fluorinite is typically associated with cutinite and resinite. Teichmiiller (I 974) regarded fluorinite to be primarily derived from essential plant oils because of its shape and size and close association with cutinite in leaf-derived tissue. Cook and Struckmeyer (1986) pointed to the possibility that fluorinite may represent "secondary high-pour oil" that was generated in the coal from certain cell fillings. The exsudatinite that fluoresces strongly green to yellow typically occurs as filling of cracks, cavities and cell lumens. It has been regarded as a newly formed solid bitumen

96

H.K. Mishra, R.K. Ghosh / International Journal of Coal Geology 30 (1996) 65-100

derived from resinite (Teichmiiller, 1974). It is thought to be directly related to the formation of liquid hydrocarbon. In the fluorescence mode of examination, oil droplets were observed in a variety of microlithotypes; they are most common in vitrite, clarite and trimacerite, over the vitrinite reflectance range of 0.40-0.75%. The release of this green to greenish-yellow fluorescing substance that is similar to crude oil has also been observed in some oil reservoirs. Sakia and Dutta (1980) and Desikachar (1984) indicated that the Oligocene (Barail Group) brackish-water mudstone and shales are rich in organic matter and are believed to be the oil source rocks in the northeastern region of India. The close geographical and geological proximity of coal and oil, the transition between coal- and oil-beating facies, and the distribution of n-alkanes in crude oils from various oil fields suggests a plant-derived organic matter source (Sakia and Dutta, 1980; Desikachar, 1984) for the hydrocarbon occurrences of the northeastern region. Tissot and Welte (1978), Snowdon and Powell (1982) and Thomas (1982) concluded that oil generation from land-plant-dominated organic matter occurs between vitrinite reflectance 0.7% and 0.8% and reaches its peak around 0.9%. Initial oil generation from some source rocks may occur at maturation levels as low as 0.4% vitrinite reflectance (Snowdon and Powell, 1982; Smith and Cook, 1984). The Oligocene coals have vitrinite reflectance values ranging from 0.43% to 0.80% and some are rich in liptinites. Coal sourced oil occurs in the coal-shale sequence of the Barail Group in Assam (Biswas, 1987). The maturity and abundance of liptinite, oil droplets and vitrinite in the Oligocene coals indicate that the source potential for hydrocarbon generation of this sequence is very good. 6. Utilisation

The coals of the northeastern region are used as domestic fuel and in brick burning, and they have potential in the cement industry, industrial coke making, manufacture of carbon black and coke for carbide, in gasification and conversion to oil. These coals are well suited for conversion to oil due to a high hydrogen index (mg C H / g Corg~,i~) and their low ash content. The average hydrogen index of Oligocene coals is 405. Rock-Eval tests in the laboratory have indicated an oil (syncrude) yield of 300 l / t from the coals of the Makuta field (Prasad et al., 1990). Studies by the Central Fuel Research Institute, India, have also indicated that these coals can be converted to syncrude by hydrogenation where the sulphur in coal acts as a catalyst and 80-98% of the coal can be liquefied (Lahiri, 1965). The coking coals of the northeastern region can be used in blends for the manufacture of metallurgical coke. Experimental studies in the steel plants have shown that 5-10% of these coals can be blended with Gondwana coking coals to produce metallurgical coke with a sulphur content within tolerable limits, provided their ash and sulphur contents are limited to 10% and 3%, respectively. The Indian Gondwana coking coals tend to have a relatively high ash content and the low ash of these coals would help to reduce the ash in the overall blend. Their relatively high sulphur content could be diluted to within the tolerable limit in the blended coal on account of the low sulphur content of Indian Gondwana coking coals.

H.K. Mishra, R.K. Ghosh / lnternational Journal of Coal Geology 30 (1996) 65-100

97

7. Conclusions The following conclusions have been drawn from the studies: 1. The Eocene coal deposits of the Garo, Khasi and Jaintia hills of Meghalaya and the Mikir and North Cachar hills of Assam have been formed over the peripheral platform areas of the Shillong Plateau under stable shelf conditions. The Oligocene coals of Nagaland, Assam and Arunachal Pradesh were deposited in near-shore, deltaic, wet forest swamps and marshy environment. 2. Vitrinite is the dominant maceral in both Eocene and Oligocene coals. The vitrinite content of the Eocene coals ranges between 60% and 80% (mean 72%): in the Oligocene coals it ranges between 71% and 88% (mean 80cA). 3. Liptinite is abundant in both sets of coals; it consists of sporinite, resinite, fluorinite, exsudatinite, suberinite and liptodetrinite. 4. The inertinite content in Eocene coals (mean 9%) is higher than that in Oligocene coals (mean 4%). The dominant macerals are semifusinite, inertodetrinite, micrinite and sclerotinite. 5. The mineral matter content of Eocene coals (mean 12%) is higher than that of Oligocene coals (mean 8%). Clay minerals, mainly kaolinite, and quartz are the most common minerals present in both coals. Calcite is a minor component and generally infills fractures. Framboidal pyrite and pyrite crystals are commonly present in both coals. The relatively high inertinite and mineral matter content of the Eocene coals suggest exposure to oxidation in the peat stage. 6. Coal facies analyses based on petrographic analysis suggest that the Tertiary coals were deposited in wet forest swamps and also in marshy environments. 7. Eocene coals have vitrinite reflectances ranging from 0.37% to 0.67%; Oligocene coals have slightly higher reflectance values, ranging from 0.53% to 0.74%. The coals have high volatile matter contents (37-57%), high total sulphur ( I - 1 0 % ) and high hydrogen content (4-9%); the carbon content ranges from 67% to 85% (all on a dmf basis). These data suggest that as per ASTM Standard the Eocene coals are classified as sub-bituminous C to high volatile bituminous C and the Oligocene coals as sub-bituminous A to high volatile bituminous B. 8. Petrographic analyses suggest that the coals may be a source rock for hydrocarbons. 9. Most of the Eocene and Oligocene coals are suitable for combustion and liquefaction processes. The caking coals can be used in coking coal blends up to about 10% provided their sulphur content is less than 3% and their ash content less than 10%. 10. Comparison of the petrology of the Tertiary coals of the northeastern region of India with the Tertiary coals in Indonesia, New Zealand, Australia, Taiwan, Turkey, Germany and Canada indicates broad similarities.

Acknowledgements The authors are grateful to Mr. B.C. Misra, Chairman-cum-Managing Director, Central Mine Planning and Design Institute Ltd., for according permission to freely use the data in this publication. The authors also express gratitude to Mr. B.B.P. Shrivastava

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H.K. Mishra, R.K. Ghosh / lnternational Journal of Coal Geology 30 (1996) 65-100

and Dr. N.D. Mitra for critical review of the manuscript and fruitful discussions. Suggestions and discussions with Mr. T.N. Basu are also thankfully acknowledged. Contribution of Mr. V. Ramachandran, Dr. (Miss) J. Moitra, Mr. P.K. Sharan and Dr. P.K. Roy in the study of the samples and the preparation of illustrations are thankfully acknowledged. The paper was reviewed by Drs. A.C. Cook and H.H. Damberger and their suggestions for improvement of the manuscript are highly appreciated. The views expressed in the paper are not necessarily those of the Institution to which the authors belong.

References Ahmed, M. and Bharali, D., 1985. Petrographic characteristics of Tertiary coals, Nangwalbibra, West Daranggiri Coalfield, Meghalaya. Proc. Vth Geophytology Conf., Lucknow, pp. 242-245. ASTM (American Society for Testing and Materials), 1991. Classification by coal by rank. In: 1991 Annual Book of ASTM Standards, Section 5, Petroleum Products, Lubricants and Fossil Fuels, Vol. 05.05, Gaseous Fuels: Coal and Coke. Am. Soc. Test. Mater., Philadelphia, PA, ASTM D388, pp. 202-205. Biswas, S.K., 1987. Coal and hydrocarbon source rock. In: R.M. Singh (Editor), Proceedings of National Seminar on Coal Resources of India, 27-29 Dec+ 1986. Banaras Hindu University, Banaras, pp. 42 55. Brooks, J.D., 1956. Organic sulphur in coal. J. Inst. Fuel, 29: 82-85. Bustin, R.M., Cameron, A.R., Grieve, D.A. and Kalkreuth, W.D., 1983. Coal petrology, its principle, methods and applications. Geol. Assoc. Can., Victoria, B.C., Short Course Notes 3, 273 pp. CFRI (Central Fuel Research Institute), 1993. A report on chemical desulphurization of high sulphur Assam coals. Cent. Fuel Res. Inst., Rep. No. TR/CFRI/3.1.93, 140 pp. (unpublished). Chaudhuri, S.G. and Ghosh, S., 1990. Fluorescence technique-- its application for better prediction of properties of certain Indian coals. Int. J. Coal Geol., 14: 237-253. CMPDI (Central Mine Planning Design Institute), 1991. Compendium on the Coal Occurrences of the Northeastern Region, Vols. l-III. Compiled for Northeastern Council, Shillong, 408 pp. (unpublished). Cook, A.C., 1981. Temporal variation of type and rank of Australian coals. Bull. Cent. Rech. Explor. Prod. Elf-Aquitaine, 5: 443-459. Cook, A.C. and Struckmeyer, H., 1986. The role of coal as a source rock of oil+ In: R.C. Glenie, (Editor), Second Southeastern Australian Oil Exploration Symposium, 14-15 Nov. 1985, Melbourne+ Vic., pp. 419-432. CSL (Coal Survey Laboratory), 1982. Annual Report. Coal Surv. Lab., Jorhat, 56 pp. CSL (Coal Survey Laboratory), 1983. Annual Report. Coal Surv. Lab., Jorhat, 50 pp. Daulay, B., 1985. Petrology of some Indonesian and Australian coals. M.Sc. Thesis, The University of Wollongong, Wollongong, N.S.W., 265 pp. (unpublished). Desikachar, S.V., 1984. Exploration plays in northeast Indian hydrocarbon bearing province. In: L.L. Bhandari, B.S. Venkatachala, P. Mitra, R. Kumar, D.C. Shrivastava and S.N. Swamy (Editors), Petroliferous Basins of India. Pet. Asia, J., 7(I): 51-59. Diessel, C.F.K., 1986. On the correlation between coal facies and depositional environments. In: Advance Study on Sydney Basin. 20 Newcastle Symp. Proc, pp. 19-22. Evans, P. and Mathur, L.P., 1964. Oil in India. Int. Geol. Congr., 22rid Sess., New Delhi, pp. 80-96. Goodarzi, F., Foscalos, A.E. and Cameron, A.R., 1985. Mineral matter and elemental concentrations in selected Western Canadian Coals. Fuel, 64: 1599-1605. Goswami, D.N.D., 1985. Macerals and low temperature tar of the Tertiary coals of Assam, Meghalaya and Nagaland. Geosci. J., 6(1): 95-102. GSI (Geological Survey of India). 1974. Geology and mineral resources of the states of India. Geol. Soc. India, Misc. Publ. No. 30, Part IV, pp. 1-78. GSI (Geological Survey of India), 1981. Coalfields of India, Bulletin Series A, No. 45.I, Coalfields of northeastern India, Geol. Soc. India, pp. 1-75.

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