By THAN HTUN (GEOSCIENCE MYANMAR)
Sir Edwin Hall Pascoe (17 February 1878 – 7 July 1949) was born in London to Edwin Pascoe and Mary A Hall, he went to St John’s College, Cambridge, and joined the Geological Survey of India (GSI) in 1905. He became the Director of the GSI in 1921 and retired from it in 1932. He had long ago made a name for himself through his excellent work in connection with the petroleum resources of India and Burma, and, during the War, in Iraq on behalf of the Government. He followed a policy of caution and restraint in advising the Government on mineral matters as also in matters of recruitment for new appointments in the expanded Survey.
As the advisory work on the Tin and Wolfram areas of Tavoy was over, Coggin Brown was sent to London in 1919 to act as Mineral Adviser in the newly started Imperial Mineral Resources Bureau, where he remained till 1921, when he was relieved of that work by Fox, who continued in that capacity in London till 1923, when the post was abolished on the plea of the economy. Later it was found necessary to re-establish this post as a part of the personnel of the High Commissioner for India in London and G H Tipper, after he retired from the Survey, became the Mineral Adviser in London from 1929 to 1946.
Regarding the coal survey, with the increased strength of officers, in 1921, Pascoe increased the number of field parties from three to six and allotted an increased number of men to Burma. In Burma, Vinayak Rao, F W Walker, E L G Clegg, and B B Gupta carried out systematic mapping in Mergui, Tavoy, Amherst, Minbu, and Pukokku districts with G de P Cotter in charge at first and under J C Brown afterwards, when the strength of Burma party was reinforced by the addition of C T Barber, A K Banerji, P Leicester, H L Chhibber, V P Sondhi and M R Sahni, and Sethu Rama Rau for a short period. Sondhi carried out an interesting investigation of Late Tertiary vulcanicity, including a study of the explosion craters in Upper Burma. M R Sahni continued the work of La Touche in the Shan States and discovered a unique assemblage of Permian and Mesozoic ammonites, gastropods, and lamellibranchs in the Plateau Limestone. Clegg continued the mapping of the early workers in the Minbu district, and Vinayak Rao and Leicester in the Mergui district. Cotter and F W Walker surveyed the Loi-an coalfield near Kalaw in the southern Shan State.
H L Chhibber commenced the survey of the jade mines area of Myitkyina district in Upper Burma and described a variety of igneous rocks which had been intruded in the Tertiaries. The most interesting feature of this region lies in the preservation of the record of several periods of igneous activity dating from end-Permo-Carboniferous up to sub-Recent times. In 1929 Brown and Banerji began a large-scale geological mapping of the Mogok Stone Tract and divided the Archaean rocks into a number of stages, which were mapped separately. This work was continued by Clegg and L A N Iyer. Coggin Brown studied the Pyu earthquakes of 3 and 4 December 1930, and subsequent Burma earthquakes up to January 1932, and delineated a well-defined seismic zone, aligned (N-S), in the Tertiary belt of Burma. It was Pascoe, who introduced the system of placing an officer of the department as a Resident Geologist in the oil fields of Burma for day-to-day contact with the progress of the investigations and development work in the oilfields. C T Barber was the first Resident Geologist at Yenangyaung appointed by Government.
Before he left India Pascoe had the official Geological Map of India, compiled in 1911 by Hayden, brought up-to-date. The revised map was published in 1932 on a scale of 1”=32 miles and incorporated the surveys during the intervening period. During the period (1921-30) a large number of publications were issued, of which concerning Burma were: Sethu Rama Rau’s Geology of the Mergui district; Murray Stuart’s Geological account of a traverse from Assam to Myitkyina through the Hukong valley and to the Chinese Frontier. After his retirement in 1932, he was engaged in the preparation of a revised edition of the Manual of Geology of India and Burma in four volumes. The first volume of this work, which was published just after his death on 7 July, 1949, is a monument to his love for work, thoroughness in mastering details, and encyclopaedic knowledge of the subject. The remaining volumes will be of enduring value to all students of Indian and Burma Geology. Pascoe wrote his famous book “The Oil-fields of Burma” and published it in 1912.
Serpentine Intrusions of Burma
The Volume III of the Manual of Geology of India and Burma described the Serpentine Intrusions of Burma. The summary of the report is as follows:-
In Burma, the Deccan Trap in its normal facies has not been identified, but sundry occurrences of basic and ultrabasic intrusions appear to belong to some phase of this period.
The Andaman Islands: Basic igneous rocks cover a considerable area in the Andaman Islands. Altered basic and ultrabasic intrusions of plutonic type occupy many of the hills and ridges of the central and eastern parts of Middle Andaman (including Saddle Peak and Saddle Hill) and occur in Rutland Island, and the Twins, the Cinque Islands, and many other places. These rocks vary from augite, enstatite, and bronzite peridotite with picotiter, to more felspathic types of the gabbro group; with occasional crystals of chromite to be seen, and the olivine is often largely altered to a dark green serpentine with veins of chrysotile. Dolerite dykes are seen here and there.
The jaspers, quartzites, calc-gneisses, and porcellanic limestones of Middle Andaman Island, are believed to be of Neocomian age. Fragments and pebbles of serpentine, in fact, often form part of the Eocene conglomerates of Northern Andaman Island. Serpentines, gabbros and diorites are also found in the Nicobar group, a bronzite peridotite playing a prominent part among the basic intrusions on Batti Malv.
Basic intrusions are recorded in the granite and the Mergui argillites of Tavoy. They are restricted to certain localities, for instance, Danithagya, near Kandaung, between Kyaungdaung-maw-gyi and Mawshyi, and near Tavoy Point, and are extraneous in origin to the granite. They run irregularly and vary greatly in size, the largest observed, an exceptionally wide one, being 20 feet across. Generally, they are fine-grained and their minerals are much altered and difficult to determine. Some appear to be basalt but they are of heterogeneous composition.
Thaton: Talc-schists have been found in various parts of Thaton and are thought by Leicester to have been derived from basic or ultrabasic igneous rocks. In the same neighbourhood occur green epi-diorites in which segregations of magnetite are found and a highly altered basic rock which was probably a gabbro originally. Nothing is known regarding the age of any of these rocks.
The Arakan Yoma: Intrusions of serpentine, sometimes decomposed to a steatitic rock, are not common along the eastern foothills of the Arakan Yoma of the Henzada, Prom and Thayetmyo districts, especially among the Negrais beds. Generally, they have irregularly shaped bosses of varying dimensions, but dykes also occur, especially to the northwest of Prome. The rock is a characteristic, dark-coloured serpentine which, in the Prome district, frequently passes into gabbro with phenocrysts of magnesite.
In the western part of the Henzada and the northern end of the Bassein districts, there are some twenty-three distinct and isolated occurrences of serpentine scattered over a length of twenty-six miles from north to south. According to Chhibber, the serpentine is sometimes traversed by narrow veins of light green chrysotile or whitish steatite. The intrusions are thought by Murray Stuart to have altered the surrounding Tertiary sandstones and shales as well as Negrais rocks. Chhibber supports this view and concludes that igneous activity extended over some period from the late Cretaceous to the early Eocene.
The steatite deposits of eastern Kyaukpy, of Minbu, and probably also of Pakokku, occur in serpentine. In the steatite mines of western Minbu, the mineral is of good quality and forms veins in the serpentine. Hayden records here dykes and intrusions of grey dolerite in great masses in the Chin Shales; this is the nearest approach to the Deccan Traps in Burma.
The native copper and copper ores were found associated with chromite of the Pakokku Hill Tracts and the Naga Hills, which seem to have been introduced into cracks in the serpentine and, according to Coggin Brown, have perhaps been deposited from the aqueous solution which brought about serpentinization.
The Jade Mines: The serpentine of the Tawmaw area is seen on both sides of the Uru Chaung in four surface outcrops, the total area of which cannot be less than 8,000 square miles. In one of these outcrops occurs the intrusive dyke of jadeite which has made the locality famous. With a general N E – S W trend, the dyke is 200 yards wide and over 300 yards long but varies very much in thickness, it is worked by Chinese traders who use a primitive process of cracking the rock by fire. The serpentine hills of this area are much alike, with steep sides crowned by a long narrow plateau; west of Nanyaseik there are several serpentine intrusions forming range upon range. Tawmaw is made up of a large mass of peridotite, partially or wholly altered to serpentine; among the types represented are dunite, mica-hornblende peridotite, diallage-peridotite, dillage-perknite, pyroxenite and amphibolite, saussurite-gabbro and saussurite-hornblende gabbro. The serpentine is of a normal type with remnants of olivine altering to chrysolite, with crystals of magnetite, and with chromite in crystals, grains, irregular concretions, and veinlets. A rock moderately plentiful in small pieces at the jadeite mines is a dark green chromite-bearing member of the epidote group, also Maw-Sit-Sit, but Bleeck named Tawmawite.
Jadeite is regarded as a member of the pyroxene group. The dull green colour often affected by the mineral is due to the presence of iron compounds, but the brilliant emerald green so characteristic and so much prized is the result of the presence of chromium. The jadeite is accompanied by albite, the combination forming a dyke rock that has intruded the serpentine, producing signs of contact metamorphism, the most conspicuous of which is the development of new minerals such as chlorite, clinozoisite, tawmawite, chloritoid, and soda-amphibole; along the zone of contact, the jadeite-albite rock often assumes a banded and schistose character caused by numerous parallel inclusions of amphibolite. The original intrusive is believed by Bleeck to have been a nepheline-albite rock, the jadeite having been developed under very high pressure by the combination of one part of albite with one part of nepheline; the mineral nepheline has been repeatedly recorded in jadeite. Jadeite has been found at Mamon, six or seven miles south of Tawmaw as boulders in the alluvial deposits of Uru Chaung, along the upper reaches of which it has been observed as far as Sanka; seven or eight miles still further south the mineral occurs as boulders in a Tertiary conglomerate at Hweka.
Bhamo and Myitkyina: In Myitkyina and Bhamo, parallel to the general strike of older rocks, are long strips of igneous rocks intruded, according to Griesbach, into fissures of dislocation. These intrusions are accompanied by numerous dykes which also penetrate the neighbouring formations, the more basic varieties in certain localities carrying the mineral jadeite.
In western Bhamo, at both ends and also in the middle of the Second Defile of the Irrawaddy, as noted by Clegg 1941, are outcrops of serpentine that show an intrusive relationship towards adjacent Cretaceous sediments. At the lower end of the defile, these intrusions terminate the Cretaceous abruptly on both banks of the river, and at the upper end on the right bank; in the middle portion, they separate an outcrop of old sediments of possibly Chaung Magyi age from the Cretaceous. The intrusions consist mostly of dark green serpentine, but less altered specimens point in some cases to a doleritic ancestor. This serpentine outcrop may be continuous with that noted between Bhamo and Sinbo further north. Another line of intrusion is reported to occur in an N-S direction along longitude 97º 30’as far as the “Confluence” between the Mali Kha and the Ninai Kha.
Kachin: In the Hukawng valley, altered peridotites and serpentines have been found by Chhibber surrounded by crystalline schists similar to those of the Jade Mines area. The graphitic and chloritic schists, which are highly crumpled and extensively injected with quartz veins, are accompanied by limestone.
References: E. H. Pascoe. 1949: A manual of the geology of India and Burma, Vol. III, 3rd Edition.