MAKUM COAL FIELD

Presented by-Mridusmita BorahShalini Barua.Tarangini Sonowal

INTRODUCTION:

The Makum Coal field is the best developed coal field in Assam.

The coal measures extend over as length of 29 km and nearly 4.8 kms in width,over an area of nearly 30 sq kms.

The field lies between the latitudes 27 ͦ 15΄and 27 ͦ 25΄N and longitudes 95 ͦͦ 40΄to 95 ͦ 55΄E towards the northeastern fringe of Dibrugarh District adjacent to Margherita town.

Though the coal measures run from the Dirak river in the West upto the hair-pin bend of the Tirap river in the east and biyond,the productive parts lie between the Namdang and the Tipongpani rivers containing the Namdang,Baragolai ,Ledo,Tirap and Tipong collieries owned by Assam Railway and Trading Company.

Geology of the Area: The area is mainly composed of Tertiary to Quarternary

rocks,alluviums and thick highly carbonaceous sediments.

Barail sediments in Upper Assam show maximum development with thick coal seams which is within the Tikak Parbat Formation and overlies conformably the Disang Group of Eocene age.

The massive Tipam Sandstone is well exposed in the area and the Dihing boulder and pebble bed is found in the Dihing river bed at Margherita.

The Dihing Group rests unconformably over the Tipam Sandstone and Alluvium and high level terraces also found in this area .

Surmas are almost absent in the area.

The stratigraphic subdivision of the coalfield area are given below:

AGE GROUP FORMATION

Recent and Pleistocene

Alluvium and high level terrace UNCONFORMITY

Dihing Group

UNCONFORMITY

Tipam Sandstone

UNCONFORMITY

Barail Group

Disang Group(over 3000m thick)

Pliocene

Middle Miocene

Oligocene to U.Eocene

Eocene

Tikak Parbat(475m)Boragolai(300m)Nagaon(2400m)

The members of this group are seen in the sections of the Khasi Hills and Tirap rivers and in the southern part of the coalfield.

The beds are highly folded and the sedimentary structures are seldom seen here.

The contact between this Group and the overlying Barail Group is Gradational.

NAOGAON SANDSTONE FORMATION:

Mallet (1876) included this in the Disang Group,but now its believed to be the oldest formation of the Barail Group which rests conformably over the Disang Shales.

The formation is consisting of hard,grey and well bedded sandstone and the thickness is about 2400 metres.

The quartzitic sandstone are well exposed towards the south east of the Namdang Colliery and the outcrops are confined to the south of the Haflong-Disang thrust,against which override the rocks of the Baragolai and Tikak Parbat Formations.

BARAGOLAI FORMATION:

This,along with the Upper Tikak Parbat Formation,was grouped originally into ‘the Coal Measure Sub-series’by Mallet which later designated by Evans as ‘Coal Measures’.

A number of coal seams,varying in thickness from 0.5 m to 0.8 m has been traced in the Baragolai Formation,but nowhere in the area under investigation the seams attain workable thickness.

The Baragolai Formation consists of alternating sandstone and shales which sometimes may be of carbonaceous nature.

TIKAK PARBAT FORMATION:Thinest formation of the Barail Group and rests over the

Baragolai Formation which is the main coal bearing formation.

It comprises medium to fine grained tough quartzose sandstone,well bedded sandy shales,clays,mudstone and carbonaceous shales.

The basal part of the formation contains all the five workable coal seams.

The sandstones are pink in colour and shales are highly carbonaceous which exhibit very good leaf impressions and also rich in pyrite.

This formation shows maximum development of coal seams in Upper Assam.

TIPAM GROUP:In this area only the lowermost part of Tipam Group is

exposed and the beds cover a wide area in the central and south-eastern part of the coalfield.

Pebbly sandstones and thin conglomerate beds ,coarse grained feldspathic sandstones constitute the sequence found here.

The sandstones and conglomerate beds consist of numerous rounded pebbles of quartz and jasper.

Bluish-green and greenish coloured sandy shales,shaly sandstones and clays occur at places which attributed to the presence of chlorite.

The sandstones are current bedded and sometimes form high cliffs and water falls.

Silicified and semi-carbonised wood and lignitic material are also seen at places in the sandstones.

DIHING GROUP:Outcrops of the Dihing Group are small and isolated along

the base of the foot-hills in between the eastern extremity of the abandoned Tirap quarry and Lekhapani to the west and Tirap river in the north.

In most of the places the rocks are concealed under alluvium and high level terraces.

The group consists of alternate pebble beds and loose,coarse,greyish to greenish feldspathic sandstones,which are at places ferruginous.

The sandstones,on weathering turn brownish and the pebbles are mostly of quartzitic sandstones.

Material And Method of Makum Coal Field:-

• Twenty seven representative samples were prepared after crushing all the 112 samples collected from freshly exposed mine and quarry faces in Namdang, Baragolai, Ledo-Tirap and Tipong collieries.

• Individual samples thus prepared represent a seam section.

• Additional samples were used wherever a thick clean coal section was encountered .

• Twenty-seven particulate pellets were prepared and studied on Leitz MPV-1 and MPV-3 units under normal reflected light and reflected blue light excitation.

Chemical Characteristics:-

• The coal seams of Makum Coalfield show a lower rank by their high volatile matter & fixed carbon contents whereas on the basis of their low moisture content and high calorific value a higher rank can be assigned.

• The Makum coals are low in ash content but sulphur content is higher .

• This type of coal is taken as good coking coal and high swelling index.

• So, for manufacturing metallurgical coke 10-15% .• Makum coal is mixed with coking coals of Tharria.

• On the basis of overall proximate chemical data of coal seam 1 and 3 appear to be identical- seam no.1 differs from seam no.3 in having lower ash and sulphur contents, higher fixed carbon and calorific value.

• Seam no.3 has highest total sulphur content amongst five main coal seams in the coalfield.

• Total sulphur content in all the five coal seams vary widely without any trend both laterally and vertically.

• The abnormality in rank in relation to chemical properties of these coals has been attributed to their high sulphur content.

• On analysis they show 81.6 to 83.0 per cent carbon, relatively high hydrogen (5.3-5.9%) and low oxygen (8.5%)

Megascopic Character:

• The Tertiary coal seams of Assam, in general those of the Makum coalfield are jet black in color with vitreous lustre, devoid of any perceptible lithotype banding and are entirely made up of vitrain ( Mishra,1981) .

• The coal is blocky in nature, because of two sets of fracture planes and crumbles easily on separation from the seam.

• It breaks with subconchoidal to conchoidal fracture.• Tiny pyrites specks are frequent in the coal.

Microscopic Character:under normal incident light:

The Makum coal seam is rich in collinite. The coal seam nos.1 & 3 are rich in desmocollinite (30.0-

47.1%) & telocollinite plus minor amount of telinite (20.0-32.4 %).

Desmocollinite and telocollinite are highly gelified. They show spongy or granular texture. The liptinite macerals are in subordinate amount (5.0-9.5%)

mainly consisting of resinite (2.5-6.3%) & sporinite (0.9- 2.4%).

Low to moderate proportion of inertinite macerals (9.1-20.5%) are chiefly formed by sclerotinite (2.6-9.8%), inertodetrinite (1.5-9.6%) & semifusinite plus fusinite (0.9-6.0%).

The associated inorganics (4.4-12.4%), concretionary calcite (0.4-9.0%) and clastic minerals-clay and quartz (1.1-7.8%)

Under blue light excitation:

• Coal seams nos. 1 & 3 of Makum coalfield have high productions of fluorescing macerals (78.4-88.6%) of which 41.8-63.5 per cent is formed by per hydrous vitrinite.

• The Makum coal field of tertiary coals of northeast India have fluorescence properties of various macerals.

• Non-fluorescing vitrinite and inertinite macerals together (10.9-22.0%) are low to moderate in amount in both the seams.

STRUCTURE• The Makum coalfield area represents a well defined

asymmetrical syncline,plunging towards north-east.

• The closure of the syncline being at Namdang,is referred to as the “Namdang Syncline”.

• The Namdang Syncline is bounded on the north and south by two large thrusts-the northern one being the “Margherita Thrust” and Southern being the “Halflong-Disang Thrust”

• In Northern part of the coalfield,the rocks of Barail and Tipam have overridden the younger Dihing Group.

• In the Southern part of the area the beds of Nagaon sandstone override the rocks of the Barail Group along Halflong-Disang thrust.

• The northern limit of the syncline extends in a North-easterly direction from Namdang to Ledo. At Ledo the limb is again folded into an anticline, known as “Ledo Anticline”

COAL SEAMSFrom Namdang colliery in the west to the Tipong colliery in the

east,there are 5 regionally persistent coal seams.

These are confined to basal 200m section of the Tikak Parbat Formation.

All these seams contain bands of clays or shales.

1. 60 ft seam : • This is the thickeast and most important seam of the Makum

coalfield and serves as datum for correlation of other coal seams.

• This seam is exposed in the bed of the Namdang river near the Namdang mines and is folded into a syncline with a plunge towards ENE.

• The thickness of the seam is 10.8m,while further west in the Boragolai mines area it is 11.8m. In its adjoining tikak colliery area the seams have a maximum thickness of20.58

2. New seam:• Thickness-2.16-2.53m• It has been worked only in the Boragolai colliery and an

equivalent has been met in the Ledo colliery area.

3. 20ft seam:• This seam has been worked in all collieries.• Exposures are not continuous.• Crops out in Ledo and Tirap collieries.• Has variable thickness-thickening and thinning within

short distances in Tipong area.

4. 5ft seam:• Worked in the Boragolai,Tikak,Ledo and old Tirap mines.• Thickness varies from-1.3 to 1.5m• Outcrops rare.

5. 8ft seam:• Worked in Boragolai, Tikak and old Tirap

collieries.• Outcrops not found• Recognised in abandoned seams.

QUALITY:Makum coal is of good quality with low ash

content and high C.ICoal being subjected to tectonic disturbances is

pulverised at places.8ft seam being impersistent is not considered for

calculation of reserves.

GENESIS• Geological informations on the coal bearing sediments of

Tikak Parbat and Boragolai Formations of Barail Group indicates that rising of Himalayas, coinciding with regression of sea during Oligocene epoch,initiated deltaic sedimentation in Nagaland, Eastern parts of Assam and South-Eastern Arunachal Pradesh.

DEPOSITIONAL ENVIRONMENT:

• The wide spectrum of lithofacies and their frequent lateral and vertical variations reflect a sequence of depositional environments varying from shallow marine,swampy,lagoonal and fluviatile.

• Isolated backwater bodies or lagoons paralleling the shoreline on the prograding delta complex served as sites for peat accumulation.

• Presence of arenaceous foraminifera and formation water salinity indicate that the sediments of Barail Group were deposited under brackish water mileau.

References:Basant K.MisraCoal fields of North eastern India;GSI