Geology:

 

(1) Geological antiquities :

 

With regard to the Geological history of the earth, only the early and late periods are recorded in Assam; the palaeozoic and the greater part of the Mesozoic are missing. Only the Archaean, the late Cretaceous (Maestrichtian to Danian),Tertiary and Quaternary are represented in Assam.

 

The Geological succession of undivided Assam is given in the table at page 33 from top downwards.

 

In Assam, the most ancient rocks are the Archaean rocks, which consist of Gneisses and Schists. Though the geological data relating to the older rocks of Assam are very fragmentary yet the rocks are correlated with the Archaean and Pre-Cambrian rocks of other parts of India.

 

It deems necessary to mention here that in different regions in India there are representatives both marine and fresh-water formations, of the Palaeozoic Starta; but in the Assam region the only Palaeozoic Starta are the Permian coal-bearing Gondwans which are met with along the southern side of the Eastern Himalayas (Arunachal Himalayas)from the Abor country through that of the Daflas, the Akas and Bhutan into the Darjeeling region about Bagrakot. In this part of the country, crushed seams of coal, equivalent to those of Raniganj coalfield

 

 

 

have been found. It is expected that these strata might be found to the south also under the alluvium.

 

Mesozoic Rocks : The geological history of the Assam region is also fragmentary throughout the Mesojoic era,but there is evidence that a sea extended into ,what is now known as the Khasi Hills towards the close of Cretaceous time after a period of volcanic eruptions; which are correlated with the out pouring of the Rajmahal basaltic lavas. The Cretaceous rocks of Assam have been dealt with by many geologists and so has the Sylhet Trap (equivalent of Rajmahal Traps);and many dykes of this basaltic doleritic material have been found in Assam including the Abor Volcanic Group in the Eastern Himalayas, and various instrusions seen among the Archaean gneisses and schists of the Tura Range as well as in the Lower Gondwana Sandstones near Singimari. the Mesozoic sea has merely left a mark in the Assam region and indicates marine conditions over Sylhet near the close of the Cretaceous time.

 

Pre-Cambrian rocks occur over the whole of the Shillong Plateau including the Garo Hills and in some portions Karbi Anglong Hills of Assam. Patches of such rocks are found near Tezpur,Nagaon,Guwahati,Goalpara and Dhubri.Near Tezpur,Guwahati and Goalpara,the Brahmaputra is confined to these pre-cambrian rocks.

 

Territary Rocks : From the beginning of the Teritary era to the present day the geology of Assam is fairly clear stratigraphically .After a pause,the Mesozoic sea appears to have been followed by a belt of lagoons over the area of the Assam Range of-to-day,but these marshes were depended into open sea along the southern half of the main Assam Range early in Eocene times. The so-called cherra sandstone of the Shillong plateau and the coal-bearing Tura Sandstone of the Garo Hills was deposited during this period,in the lagoons, in early Eocene times,and followed by the deposit of the Sylhet or Nummulitic Limestone in the warm,shallow and open sea of the Eocene in southern Assam. This sea appears to have been muddy in the direction of Tura, but to have continued westwards into what is now south western Bengal. To the east and north-east the Nummulitic Eocene sea spread upto Karbi Anglong and might have been connected with an estuary, which entered the Assam region from the north-east and was splited partly south-westwards and partly south-ward into northern Burma, where Eocene rocks with Nummulites are found.

 

Although the physical geography of the Eocene period in Assam and Burma areas has not been fully elucidated across the watersheds between the Brahmaputra and the Barak rivers and the Chindwin river, there are grounds for believing that the Nummulitic beds were represented in the Naga Hills and the Barail Range by a Group of Sandstones and related rocks with the well-known coal measure of Upper Assam (once believed to be Miocene but now recognised as younger Oligocene between Eocene and Miocene).Although the Barail Group is coal bearing and evidently esturine deposits, they are not as old as the coal-bearing rocks south of Shillong in the so-colled Jaintia group which includes the Nummulitic Limestone. The coal-bearing rocks of the Garo Hills (Tura Standstone) and Karbi Anglong are older and were once believe to be Creataceous in age. There is hiatus above the Barail Group of rocks, but above this come the Upper Tertiary beds, the next beds upwards being the Surma Group of Miocene age, the Tipam Group of Upper Miocene age and Dihing group of Pliocene to Pleistocene age. The estimated thickness of the Assam Tertiary strata has been completed as follows.

 

              Dihing Group approximately       5,000 ft.

                    Tipam Group        ,,                 12,000 ft.

                    Surma Group        ,,                13,000 ft.

                    Barail Group         ,,                 15,000 ft.

                    Jaintia Group        ,,                  4,000 ft

 

Moreover,in respect of the Geological history there is little doubt that until the close of the Palaeozoic Era the Assam region appears to have been an integral part of the continental mass known as Gondwanaland.

 

Further,with the volcanic eruptions at the close of the Mesozoic Era,the outpouring of the Abor, Sylhet and Rajmahal Traps, followed shortly by the vast eruptions of basaltic lavas at the deccan Plateau,there appears to have began a general uplift of the northern ocean. In early Eocene times the northern area had become land an estuary had appeared in north-eastern Assam,allowing the drainage to entire Assam and Burma. In middle Tertiary times,the estuary had extended southward and only shallow muddy seas washed the lands along the south and west of what is now the Assam plateau.

 

(ii)Geological structure :With regard to the geological structure a closer studies of the Assam Himalaya,the Brahmaputra Valley,the Assam range,the Sylhet and Surma Valley and the bordering hills of Chittagong, the Lushai Hills, and the Naga hills show the sediments which were once laid down horizontally as sands, silts, clays etc., may be found transformed by pressure and shearing, into sandstones and quartzites, shales and slates, etc.,which may be inclined at any angle and even overturned as well as buckled and dislocated. Along the southern side of the Assam Himalaya the strata, from the newest to the oldest including the Gondwana beds,are seen to be pushed over from the northwards, and indeed, a zone of over-thrusting appears to continue along the foot hills of the Himalaya. In the Brahmaputra Valley where the rocks are exposed from near Dhubri eastwards to Karbi Anglong and onto the extreme north-east at daphabhum, only the most ancient Gneisses and Schists of Archaean age show up from under the alluvium or the youngest Tertiary. The same is largely true for the northern part of the main Assam Range,but along its southern side the Lower Tertiary beds are seen to bend over and dip into the alluvium of the Sylhet and Myanmensingh plains. The axis of Assam range is roughly parallel with the Eastern Himalaya.

South of the Brahmaputra valley in Upper Assam the Tertiary rocks have been bucked by tetonic forces acting from the southwards(Burma),and shearing (overthrusting)has been from an opposite direction to that of the eastern Himalaya,so that valley in Sibsagar and part of Lakhimpur are typical structural valley of the Ramp type. However, traced south-west the Naga Hills and the Manipur Ranges (which continue southwards into Burma as the Arkan Yoma) show the push to have been from the east, and this push from Burma, combined with the push from the Himalaya has caused complicated shearing in the 'gap', west of the Barail Range and is directly responsible for the important dislocation known as the Haflong Fault. Some kind of release of shearing has occurred in southwest Assam since the hills of southern Sylhet and Tripura have their axis parallel to the Manipur and Lushai Hills and therefore at right angles to the axis of the Assam Range, as seen in the Garo, Khasi and Jaintia Hills.

 

The great forces acting from the north and east have produced the up lifts of the Assam range and the Baril range and caused the structural features of the Brahmaputra and Barak Valleys as clearly visible highlands and plains,but these slow acting forces have also been responsible for the faulting and dislocation which are only noticed during geological map making. However,a gradual increase of strain along an old fault and a new line of stress will,if the strain is released suddenly by shearing,cause the earthquakes which are so common in Assam. The whole region is subjected to the northward thrust from the Himalaya and to the westward thrust of push from Burma,and if frequent small earthquake shocks are felt,the general evidence is the release of strain is being effected and the danger from a great earthquake is largely removed. If, however, a considerable diminution in small earthquake shocks becomes noticeable, say, in the Garo Hills to Jaintia Hills region, then there are increasing potentialities of stronger shocks.

 

Economic mineral plays a very significant role in the development of a region. But the mineral Allophane which has been detected at present in the coal bearing strata near Margherita showing roughly 19 per cent Silica,38 per cent Alumina with about 40 per cent water, is of scientific interest. However,this important mineral wealth does not occur a commercial quantities to be used as a substitute for Kaolinite.

 

Of the major minerals,namely,coal and gas,limestone,sillimanite and corundum,refactory clay,kaolin,glass sand , silica rock, gold, copper, salt felspar, vermiculite, fluorspar, beryl, iron and pyrite are reported to occur in the State. Coal, oil and gas, limestone, refractory clays, fire-clay, glass-sand, salt, gypsum and pyrite occur in the late Cretaceous and Tertiary. The rest occur in sedimentary and igneous rocks of pre-Cambrian age.

 

The pre-cambrian rocks as occur in the individual districts of Assam are as follows :

In Kamrup district, members belonging to the pre-Cambrian Gnessic-group, exposed sporadically. In the north of the district, exposures of Siwalik or Teritiary rocks are noticed. As a general rule the distinctive rock types occur in close association with each other and occasionally enter into the composition of landed, streaky or composite gneiss.

The geological history of Sibsagar district and for that matter,of the Upper Assam Valley as a whole, is related to two long narrow subsidiary through (Geosynclines) lying on either side of an old rigid continental shield (foreland).The foreland is geologically the north-eastern constitution of the Shillong and Karbi Anglong Hills plateau which is concealed in the valley by a great thickness of alluvium and Tertiary rocks. Oil and Natural Gas Commission aided by drilling for oil have shown that under the alluvium there are many thousands of feet of thickness of Tertiary sediments which lie over an Archaean basement complex. The tertiary rocks represent the foreland facies and are distinguishable from the geosynclinal facies of Tertiary rocks which from the hills on the south and south-east of the district.

 

In Darrang , Archaean gneisses which from the base of the district and low hills near the Brahmaputra are an extension of the pre-Cambrian shield of the Karbi Anglong Hills. Barring the isolated hillocks exposing the Archaean gneisses in the southern part and occasional outcrops of the Upper Tertiary sandstones at places over the northern boundary at the foot-hills of the Himalaya, the entire district of Darrang is covered by alluvial deposits of Recent and Sub-Recent origin. The Archaean gneisses represent a complex group of the biotite and hornblende gneisses with occasional small granitic and pagmetetic bodies intrusive into them. The Upper Teritary sandstones mainly covering the foothills of the Himalaya across the northern boundary consist of fine to medium grained,bluish to greenish grey ferruginious ''pepper and salt'' type sandstones with partings of dark grey splintery shales and occasional lumps,streaks and fragments of lignite and carbonised wood resemble the Tipam sandstones of Upper Assam. Along the base of the foothills,these sandstones are covered by a thick accumulation of unstratifield and unconsolidated terrace deposit of the Sub-Recent age.

 

The older alluvium is of fluviatile origin being carried down by the Himalayan rivers and deposited along their original area of inudation which has later been raised to its present position. the recent alluvium covering the major part of the district consists of loosely consolidated sands,clays,and single beds with occasional accumulation of vegetation.

 

In Goalpara district,the Pre-Cambrian rocks are exposed in a number of hillocks. Rock belonging to the Tipam group (Miocene) of the Tertiary Supper group are exposed along the Bhutan border between the Rekhajoli and the

schistose rocks are also seen this area,At Gauripur of Dhubri district granite gneiss is exposed in a small hill pebble bed or older alluvium are seen on the north of the Brahmaputra.

The undivided district of Lakhimpur (present Lakhimpur, Tinsukia, Dibrugarh and Dhemaji districts)consists of wide alluvial plain composed of mixture of sand and clay in varying proportion and surrounded on the sides by hills belonging to the Tertiary Time. The hills of the south consists of sandstones and shales interpersed with valuable col mines and iron stones. The Geological deposits of economic value are gold, coal, petroleum, lime. kaolin and salt. To the north of the undivided district,the ground is by alluvium. Drilling for oil has shown the existence of the whole Tertiary succession from the Eocene to the Pleistocene Time. Seismic survey has revealed the presence of Archaean rocks below the Tertiaries.

 

In the undivided Cachar, the upper tertiary rocks extend in an unbroken range of the Barail. These rocks are horizontal, consisting of fine-grained sandstones and shales. In the district, high level alluvial deposits (older alluvium)occur in the two plateau,one lying at about 61-107 m. above the alluvial near Kumbhir, north-east of Silchar; and the other near Dewan, east of Silchar, at about 30m.above the alluvial. The Barak Valley appears to mark the junction of two movements of rocks in different directions,one from the north and the other from the east, and to have suffered in consequence. The Barail range strike east-west and the Disang and the Barails have been folded into anticline with an east-west axis. South of the Barak the strata have been folded into north-south wave like corrugation which rise to the alterations of the lines of hills and valleys. In the corrugation the tops are usually narrower than the buttoms of the throughs and the inclined flanks separating the crest from the trough are very steep, the strata dipping at high angels. In many instances, one of the flanks of the fold is much steeper than the other and in these asymmetric anticlines it is common to find strike-faulting accompanied by vertical and inverted strata.

 

So far as the undivided district of Nagaon is concerned,only three periods of the geological history are represented in the outcropping surface, namely, the Quaternary, the Tertiary and the pre-Cambrian. Quaternary is represented by the recent alluvium of the Brahmaputra and in some of its tributaries. Similarly rocks belonging to the Tertiaries are exposed near Lumding .These belong to the Jaintia, the Barail and the Surma Group. The pre-Cambrian rocks are exposed in the low hillocks. They from the eastern edge of the Shillong plateau before it sinks below the alluvium. They are com posed of gneisses and granite. These older gneisses are uniform in character having white to light grey colours.

 

Comprehensive accounts in respects of geological antiquities,geological formation etc.,of the different district of Assam are available in the gazetteers of the districts and such these are not reproduced here.

(iii)Mineral Wealth: It has been mentioned earlier that the state of Assam occupies a very significant place in the map of mineral wealth of the country. But Assam is lagging far behind the other states in the matter of proper exploitation of such wealth.

Out of the different types of mineral wealth,only four types of mineral wealth,only four types,namely coal,oil and gas,limestone, quartz and clay are being exploited at present.

Coal:Coal in Assam at present occurs in the district of Dibrugarh, Sibsagar, Tinsukia and Karbi Anglong (Erstwhile Mikir Hills).Due to the bifurcation of Assam most of the coalfields of Garo Hills have gone to the newly state of Meghalaya. In undivided Assam,the most attractive coalfields belong to the Eocene and Oligocene age (i)The Lower Eocene of the Garo and Karbi Anglong Hills, (ii)the Middle Eocene of the Karbi Anglong, and (iii)the Upper Eocene to Oligocene of the Naga Hills,etc.

 

The discovery of Coal in Assam took place when the administration of the province was taken over by the British Government. The coal of the Naga Hills near Borhat in Sibsagar district and Jaipur in the present Dibrugarh district was reported by Mr. Jenkins in the year 1838.Coal also reported to have occurred in the Karbi Anglong Lunglai areas. The occurrence exposes a 3.64m seam dipping 12 to 20 degrees to the north-west. The Coal has overage 4 to 5 per cent moisture,50 to 57 per cent volatile matter,about 25 per cent volatile matter,about 25 per cent fixed carbon and between 13 to 20 per cent ash,which is very resinous (high volatile matter)type of coal or lignite. There are also records of coals of better quality within 12 miles (19.30 km.)of Lumding. It is stated that coal is also found in the Namber area within Sibsagar district. In the Nazira area with in the same district the coal mines of Borjan and Kanjan (now in Nagaland) have been worked by Messrs. Shaw Wallance and Company. The Nazira coal-field is partly drained by the Saffrai river, which exposes coal measures with in 5 miles (8kms) of Saffrai station. Some of the coal from the Nazira coal-field is among the best in India .Analysis showed that the coal contain 4 to 10 per cent moisture,36 to 44 per cent volatile matter,under 1 to 4 per cent ash. Much of the low moisture material is of caking quality and some of the samples from wakching,etc.,are strongly caking character.

 

Northward from the Disang river at Namrup the coal measures extend north-eastwards into Lakhimpur (undivided).The Jaipur coalfield is now in the present Dibrugarh district and marks the southwestern end of the richest coal-bearing strata (Tikak Parbat Formation)of Upper Assam,which extends onwards beyond Lakhimpur (undivided)into the frontier tract beyond the Tirap river and on to the Namphuk river. Coal fields are lso there at Mergherita and Makum areas .All the coal mining operations in the Makum and the Margherita north-eastwards area is conducted by the North Eastern Coal Fields,Coal India Ltd. In succession from the west, the collieries of Margherita area are as follows :

Namdang, Bargolai, Tikak, Ledo, Lakhapani and Tipong quarry. Mr. G.E. Hines,Geological expert states that the coal measures (Tikak Parbat formation)are of Oligocene age. The thickness of the seams and the excellence of the coal must be unique in India. But the Coal which occurs in the Tikak Parbat Formation of the Barail Group is conducted under many difficulties where the worst natural conditions in India have to be faced. The bottom of 120 metres of this formation is very carbonaceous and includes one seam in the Makum Coal-field varying in thickness from 18 metres to nearly 30 metres and another six metres thick besides a number of thinner ones. The coal-bearing horizon to the south-east of the Makum Coal field is of great areal extent as revealed in the oil wells drilled at Naharkatia and Rudrasagar.

In the Makum coal field alone the reserves have been estimated at 1,000million tons. The reserves estimated in the Namphuk area is 600 million tons.

The hard coke formed in the Makum coal, being high in Sulphur is not used as a metallurgical coke for iron smelting Sulphide ores such as the lead, Copper and Zinc ores of Upper Burma, and the Sulphur could be recovered as Sulphuric Acid. In both the low and the high temperature carbonisation the Gas must be excellent calorific value and therefore useful as fuel in itself.

The Chemical composition of the coals from the different coal fields so far they relate to Assam is given to the table below: 15

 

Coal fields                                              Composition in percentage by weight C

 

                                              M        ASH       VM         FC      S          CV

1.Dilli Collieries

   (a) Seam 1                          6.30     1.40       42.80     49.50   1.31  12,999 BTU

   (b) Seam 2                          5.30     4.10       43.90     46.70   2.58    2,740 ,,

   (c) Seam 3                          5.90     5.50       41.60     47.00   4.68    2,150 ,,

   (d) Seam 4                          5.60     6.30       40.50     47.60   4.53   11,730 ,,

 

2.Namdang                             2.10    19.30      35.50    43.00  5.57     14,308 ,,

3.Borgolai                               2.40      4.80      42.20    50.60  2.35     13,670 ,,

4.Ledo                                    1.80     2.46       40.15    55.59   …...     …...... ,,

5.Tipong                                  2.50     5.90       43.70   50.80  2.52      13.870 ,,

6.Disangmukh borehole.         16.30     1.70        37.00    37.40 …...       …...... ,,

 

Abbreviation :-M-Moisture,Vm-Volatile matter, FC-Fixed Carbon.

Among all the districts of Assam,the present district of Tinsukia has huge deposits of coal in comparatively young Tertiary rocks. But the presence of the injurious constituent sulphur and the inaccessibility of the coal fields have impeded large scale exploitation upto Miobum in Arunachal Pradesh. In Dibrugarh and Tinsukia districts, coal exposures are found in the Jaipur, Namdang and Ledo areas upto Tipang river. In all cases, the workable coal seams are exposed along the northern flank of the Naga-Patkai Ranges facing Sibsagar and Lakhimpur (undivided) districts. It has been stated earlier that individual coal seams vary in thickness at places from 3.04m to 18.28m. Recently, a 3.04m thick coal seam has been encountered in the Assam Oil Company's first bore hold at Naharkatiya at a depth of little less than 3048m. The coal is of good quality. The district of Sibsagar is also rich in respect of coal mines. It is mainly mined in Nazira coal field. Coal is also found in the Jhanji and Disoi rivers. The seams in both these cases are few, thin, and highly inclined. The coal have 3.4 per cent to 6.8 per cent moisture, 4.8 to 6.5 per cent ash, 33.8 per cent to 36.9 per cent volatile matter and 52.9 to 54.9 p.c fixed carbon.16

The Nazira coal field is nearly twenty-five kilometres long and situated about six kilometres south of Naginimara railway station upto the Dihang river. But except for a small outcrop of coal measures within eight kilometres of Saffrai railway station, the coal field lies in Nagaland.

In Jaipur outcrops of the seams are seen along a strip of forty kilometres long, about half of which lie in Dibrugarh district. A thickness of more than 13.71m of coal in six seams is exposed in the Dilli river. The coal-bearing rocks dip to the east with a high degree of inclination (30o to 80o) on the Sibsagar side the coal is worked out by the Dilli Collieries (Assam) Limited. The Colliery has an area of four square miles (10.36 Sq. Kms.),which was closed in June, 1970.

The following brief statistical table shows the production.17

 

         Year         Production.(000 metric tonnes)

 

        1974             507

 

          1975             582

 

          1980             575

 

          1981             646

 

          1985             835

 

          1986            864

 

          1987            922

    

          1988          1000

 

          1989            840

 

          1990            612

 

          1991            982

 

          1992           1069

 

The Statement below shows the colliery-wise production of coal in Assam.18 (In '000 metric tonnes )

 

    Colliery                 District              1990                  1991                1992 p*

  1. Ledo                    Dibrugarh            196                     564                    627

  2. Bargolai                    ,,                     95                     127                    105

  3. Tipong                      ,,                    145                     146                    154

  4. Jaypur                      ,,                      27                      26                      24

  5. B.G/OCA                  ,,                     149                    119                      81

  6. Garampani            N.C. Hills             ....                      ....                        7

  7. Assam                                            612                    982                  1069

                         *P - Provisional 

 

Mineral Oil : Like coal, mineral oil also occurs mainly in the Upper Assam region of the Brahmaputra Valley. In Assam at the present time,the quest for oil has been directed in the northeast of the Brahmaputra Valley and the broad belt of Tertiary rocks extending from the Moiban range in Arunachal Pradesh to Tripura through Cachar district and Mizoram. Oil is found in three stratigraphical horizons in the geological column. Prior to the discovery of oil fields in recent years at Naharkatia, Hugrijan, Rudrasagar, Moran, Lakwa, etc., Digboi was the only oil field in independent India. The discovery oil in the Digboi area took place in 1886,when on the recommendation of the Late H.B. Medlicott, of the Geological Survey of India,drilling for oil was also started near Margherita and Jaipur. These borings met with partial success and due to poor production rates and lack of good communication, no interest was paid on them. The availability of coal in that area led to construction of a railway line from Ledo to Dibrugarh for the purpose of carrying the same,the presence of an oil show near Digboi was discovered by chance. The drilling of the first well was completed in 1890,which gave 200 gallons (908 liters) of oil per day. Within nine years (in 1899), fourteen wells had been drilled. In 1899, the Assam Oil Company was formed to take over the management of the oil interest in this area. In 1921,the Burma Oil Company took over the commercial and technical management, giving it much needed financial assistance,up-to-date equipment and modern transport and refining facilities. In about ten years time,the production had stepped up to 180,000 gallons (8,18,273 liters)per day compared to about 12,000 14,000 gallons (55,550-63,640 liters)per day before 1921.During 1931,the Digboi oil field met about 11.5% of the crude requirements of the then undivided Indian Empire,which included Burma.19

After failures to find oil at Namphuk, Namchik, Makum-Namdang ,Barjan, Dhekiajuli, Barsilla, Bandersulia, Nichuguard,etc.,efforts were made to find additional oil fields in the alluvial areas of the Assam Valley. Drilling in the Upper Assam Valley,on the basis of the results of geophysical and regional geological survey,has shown that the Barail rocks, from which the oil has migrated into upper Tipam sands in Digboi, is also oil-bearing in the Naharkatia-Hugrijan area at the depth of about 10,000 (3048 metres )feet. The first well in this area was competed in 1953 and the area so far explored by drilling stretches between 10 to 20 miles (16 to 32 kilometres) west of Digboi. At Moran ,about 20 miles(32 kilometres), further west from Naharkatiya the first test-well was successfully completed in 1956 and production was proved in the same rock Groups as at Naharkatiya. Further drilling in the Naharkatia-Hugrijan area,where 30 wells were completed upto the end of 1957,had already proved a potential of nearly 2.5 million tons of oil per year together with about 45 to 50 million cu.ft.(21.66 to 35.12 million. cu.m.) gas per day.20

 

The discovery of oil at Naharkatia in 1953, has radically changed the prospects for oil in Assam. In earlier period,oil was found in higher horizons,namely in Tipams and the Surmas, although a little was also found in the top of the Barails and in sharply folded anticlines,whereas at Naharkatiya oil was found in the Barails in very gently folded beds with definite dips on the flanks but rather indefinite pitches, and oil was found not only in structural traps but also in fault traps and especially in areas with a thick cover of alluvium and at greater depth than tested before. In fact, the whole of the alluvial tract in Upper Assam has become oil prospective. In the Naharkatiya oilfield (including Moran),the reserves of crude oil are estimated at 47 million metric tonnes and of associated and dry gas 7,90,000 million cubic feet.21

 

Mineral oil was also found in Cachar district within the former Surma Valley. Petroleum is reported to occur in the Patharia Reserve Forest. In the Badarpur-Masimpar field, petroleum was obtained from the Bhuban stage of the Surma Group. The first well was actively proposed by the Burma Oil Company Ltd. for 18 years from 1915 to 1933,but oil-bearings sands were of restricted extent and their exhaustion led to the final abandonment of the field. The Company drilled 63 wells obtained 1,864,000 barrels of crude oil which was refined at the Digboi refinery. Statement below shows the production of crude oil and natural gas from the oil fields of Assam.

 

Year         Crude oil (1,000 metric tonnes)          Natural gas (utilised million                                                                                                             cubic metre)

 

1970                       3,358                                                    360

 

1975                       4,190                                                     621

 

1981                       5,112                                                     875

 

1985                       4,790                                                    751

 

1990                       4,927                                                    987

 

1991                       4,838                                                    967

 

1992*                      4,703                                                   1030

 

                         P* -Provisional

 

Sillimanite: It is also an important mineral wealth of Assam. The Assam Sillimanite is in the form of massive rock from which cubes can been sawn for direct use in furnaces. The largest boulder of massive Sillimanite in Assam and Meghalaya was estimated to weigh 300 tons.

Refactory clay: At present in Assam,it is found only in Karbi Anglong. It has a refractoriness of orton cone and is stated to be quite suitable for the manufacture of refractories.

Gold :During the Pre-British time this important material was collected in many rivers in Assam. A section of people,known as Sonowal Kachari was engaged for this purpose. Even now alluvial gold occurs in many rivers of Upper Assam such as Dikrong ,Subansiri, Sisi, Dihing, Dibong, Noa-Dihing, Dhansiri, Disoi, Buridihing, Bhoroli, Burigong, Bargang,etc..Although gold-bearing sand used to be panned in ancient items,it is now no longer an economic proposition.

Alum Shale : It is mentioned in the district Census Handbook, Lakhimpur,1961, that dark-coloured Pyritiferous shales are found in several places from the coal bearing areas in the district. it is suggested that these shales could be used for the preparations of alluminium sulphate and alum. For the proper utilisation of this economic material,an Alum plant is going to be established at Namrup.

Fire-clay: It is known that fire-clays occur with coal measures of the Makum coalfield and that the Assam Railways and Trading Company prepared fire-bricks and refractories from these clays for their own requirements. Similar clay my be found in the Karbi Anglong Hills where the lower Eocene (Cherra State)coal,seam,etc.,occur. It is also known that at the falls of the Nambor river in Golaghat district, such clays are available in Golaghat. There are thus extensive Occurrences of these white clays in Assam wherever the lower Eocene beds are met with.

Lithomarge : Lithomarge occurs abundantly in association with the coal-beds. It is stated that some of the clays or shales found along the coal fields of upper Assam have been profitably utilised for the preparation of ''oil-well drilling mud'.

Potter's clay: In the alluvial tracts of the State the Potter's clay is found in abundance. The Pottery industry,which mainly depends upon the availability of local clay,provides employment opportunities to a large number of persons. In the plains and valleys of the State,the pottery clay is the alluvial material found in the rivers

and beds of bils.

Kaolin or China clay :Kaolin is found in good quantities in the Dora river of the old Lakhimpur district.

Copper: It is mentioned in the Census Report of Assam,1961(General Report),that the occurrence of copper has been located in two places within Assam, one near Barduar in Kamrup district and another near Mahamaya Hills in Goalpara district. In both the places,the copper has been found in rocks of the Archaean age. On account of small and scattered show of the metal in both the places, proper investigation is required for exploitation of the same.

Salt :In certain places within Cachar district brine springs occur and in the past salt was in the district. Salt was also made near Sadiya and Borhat in the undivided Lakhimpur district. But now-a days due to the availability of salt at cheaper rates in market these difficult and remote places have lost their importance.

Felsper: Felsper occurs in small quantity in the Karbi Anglong Hills in Assam.

Beryl :This mineral has been reported from some of the pregmatite veins in the gneissic area in the Karbi Anglong Hills.

Gypsum :Crystals of selenite have been found near Longloi in the Karbi Anglong Hills. It is known that gypsiferous shale occurs in the Dimasa Reserve Forest in the said district.

Iron-ore : Quartz-magnetic rocks are stated to be available in the Hahim area within Kamrup district. These rocks belong to the Dharwar system.23

The following brief statement shows the volume of production and value of major minerals of the State (including Meghalaya) for the year 1960. 24

 

Name of mineral               Year 1960  production           Value  (in Rs)

                                         

 

        Coal                                      663,000                             Rs. 187,57,000

    (in tonnes)

 

   Limestones                                 49,000                               Rs. 3,81,000

   (in tonnes)

 

     Crude oil                                  118,304,000                        Rs. 479,73,000

   (in gallons)

 

   Mineral gas                                530,482,492                        Rs. 21,74,160

   (cubic feet)

 

   Sillimimanite                                7,000                                Rs. 1,38,000

     (in tonns)

 

production of all these minerals increased many times in recent years.

 

Earthquake: Assam, including the North-eastern region of India lies in the seismic region and liable to suffer from sever earthquake. The frequency of earthquakes in Assam is closely related to the geology of the province. A list of dates of occurrence of some big earthquakes in Assam during the last 500 years has been furnished below.

 

                    1.In the year 1548                          8.In the year 1759

                    2.In the year 1598                          9.In the year 1780

                    3.In the year 1601                          6.In the year 1838

                    4.In the year 1642                          7.In the year 1842

                    5.In the year 1660                         12.In the year1875 (September)

                    6.In the year 1696                         13.In the year 1897 (June)

                    7.In the year1732                          14. In the year1950 (August)

 

Amongst the recorded earthquakes, the most severe, according to B.C. Allen, was one which took place on June 12 th, 1897. It was perceived over an area of 45,32,000 square kilometres from Rangoon in the South-East to Jaintiapur in the North-West from the Himalayas Masulipatam. Extensive damage was done to masonry buildings over an area of 78,000 square kilometres. The area of maximum disturbance was a tract of country in the shape of a cocked hat, whose base line ran from Rangpur to Jaintiapur, while the top of the crown was near Barpeta in Kamrup district. The second major earthquake that took place in Assam was on August 15 th,1950. This earthquake with the epicentre at about 200 miles (322 kms) north of Sadiya was one of the most disastrous events that the State had ever experienced. Upper Assam districts namely Lakhimpur, Dibrugarh and Sibsagar suffered extensive damage of life and property. The long- range effect of this earthquake was keenly felt in Assam during the decade 1951-61.The epicentre of this earthquake was near Rima just above the Indo-Tibetan border, and in most parts in the eastern Himalayas. Heavy Landslides occurred locking mountain streams and rivers and causing lakes to be built up in the Himalayas. During the decade and afterwards, many of these lakes burst open carrying an immense amount of soil, sands and debris into the plains of Assam. Large areas of the present Dibrugarh and Lakhimpur districts between the Brahmaputra and the foot-hills have been converted into sandy stretches. As a result of the after-effects of the earthquake, the bed of the Brahmaputra has risen above its normal depths all along the Brahmaputra valley. The river Brahmaputra became the main agent of destruction in Assam. Many parts of the state like Dibrugarh town, Sadia, Saikhowaghat, Tarabari, Palasbari, etc.,suffered heavy damages due to after-effects of the earthquake.