The Burma Circle of the Geological Survey of India and their Contributions to the Geology of Myanmar

EPISODE:59

 

By THAN HTUN (GEOSCIENCE MYANMAR)

 

JADEITE FROM BURMA

 

I previously discussed ‘Jadeite in the Kachin Hills, Upper Bur­ma’ by Bleeck in Episode 25 on 9 December 2023 and ‘Jadeite and other rocks from Tammaw in Upper Burma’ by Bauer Max’s work in 1895 in Episode 31 on 21 March 2024. HL Chhibber provided a comprehensive report on ‘Jadeite from Burma’ in his renowned book Mineral Resources of Burma in 1934. Key details from his report are outlined below.

 

Regarding the acceptability of Professor Chhibber’s works, he is considered one of the outstanding authorities on Burma’s phys­ical geography, geology, and mineral resources. His classic books, particularly Geology of Burma and Mineral Resources of Burma (1934), are highly rated books on the subject. The publication of these books helped establish his international reputation as the most celebrated scholar of the geology of Burma.

 

In the Mineral Resources of Burma, HL Chhibber has sys­tematically described all the mineral resources of the country, their modes of occurrence, how they are worked, and their uses and trade. It is worth noting that Burma at that time was the most important province of the British Empire in India from the point of view of mineral resources. His description of occurrences and formation of jadeite and amphibolites are most interesting and complete. He considers jade rocks as a unique petrographical type. The jadeite-albite rocks occur as dykes and sills, intrusive into serpentinized peridotites. Chhibber considers these rocks as products of interaction between a soda-granite-aplite magma and the wall rock under high pressure, so high that the molecules that would normally have crystallized as nepheline were unstable and reacted with albite to form jadeite molecule. The excess of silica combined with the olivine of the peridotites to form amphibolites, which is commonly associated with jadeite. He also gave a detailed historical account of the working of jade mines. It is the most de­tailed account of the geology of the jadeite deposits ever produced. Dr Chhibber spent two years (1928-30) doing fieldwork in this area. HL Chhibber’s ‘The Mineral Resources of Burma’ is a classic work on the subject. Chhibber’s study was extensive and remains to this day the most detailed look at the mines in print. (S Alam, 2016)

 

HL Chhibber pointed out in his ‘The Mineral Resources of Burma’, 1934, that the chapter on jadeite may appear too lengthy, but that is perhaps justifiable. Despite my efforts to reduce the ac­count to a reasonable size, I could not shut out the mental picture of the area I had before me. I spent about two years in the field alone in the Jade Mines area, and the same amount of time has been spent in the laboratory study of the rocks. It may be added that the chapter contains only the gleanings of my observations on the jadeite deposits. Then he mentioned that ‘the chapter on jadeite may appear too lengthy, but this is perhaps justifiable. Despite my efforts to reduce the account to a reasonable size, I could not shut out the mental picture of the area I had before me.

 

The history of the jadeite trade

 

The history of the jadeite trade from very early times up to 1893 has been summarized by Mr Marry of the Chinese Consular Service and was reprinted in the Myitkyina District Gazeteer compiled by WA Hertz in 1912.

 

The first geologist to visit the jadeite mines was F Noetling, whose preliminary report on the economic resources of the Amber and Jade Mines area in Upper Burma was published in 1892. The same author published an article on the occurrences of jadeite in Upper Burma and illustrated the account with a small-scale map. Professor Max Bauer described the rocks and minerals collected by Noetling. But he was at a serious disadvantage because he had not studied the field relationships of these rocks. AWG Bleeck visited the area in 1907, and reference to his work will be made in the sequel. Recently, the Professor commenced the systematic survey of the jadeite-bearing region in 1928, and a brief resume of his conclusions has been published in the General Reports of the Geological Survey of India for the years 1928, 1929, and 1931.

 

Area and Extent.: The area so far known at present in which the mineral jadeite is found in Burma is situated between 25° 28’and 25° 52’N latitude and 96° 7’and 96° 24’E longitude. The coordinates given above include the main, well-known area which supplies almost the entire output of jadeite obtained in Burma. However, there are other places where jadeite is known to exist: one locality lies about ten miles east of Mohnyin (24° 46’50”, 96° 22’30”), and another one occurs on the bank of the Chindwin River (might be Khamti region). Jadeite also exists about 200 miles north of Myitkyina, but the place is inaccessible, and the quality of the jadeite is reported to be poor.

 

The region is a highly dissected upland, consisting of ranges of hills from the Chindwin-Irrawaddy watershed. It is higher in the north than in the south, and Tawmaw (25°41’13”, 96°15’18”), which is situated on the plateau, is 2,755 feet above the sea. The highest point in the area is Mount Loimye, 5,124 feet above sea level.

 

The Uru Chaung, the area’s mainstream, runs along the foot of the plateau from northeast to southwest. Not infrequently, this river has cut deep gorges, often flanked by cliffs or sheer precipices several hundred feet high. The current is rather strong and during periods of flood, carries away whatever comes in its way, so much so that more than half the important and flourishing village of Hpakan (25° 36’38”, 96° 18’ 40”), the centre of the jadeite trade, was washed away in 1927. The Uru is an important degrading stream, and its banks and small feeders are the scene of much mining activity for jadeite.

 

Tawmaw, where the true outcrop jadeite mines are situated, is about 68 miles by road from Mogaung railway station, which lies on the Sagaing-Myitkyina branch of the Burma Railways. From Mogaung to Nanyaseik (25° 37’6”, 96° 35’) there is an unmetalled motor road, but the portion between Kamaing (25° 31’38”, 96° 43’5”), the headquarters of the jadeite mines region, and Nanyaseik be­come very difficult after a few showers of rain. The tracks are flat for about another four miles from Nanyaseik, but beyond that, there is only a well-graded, though locally very steep, mule track passing over a range of hills.

 

Geology of the Area

 

There are serious difficulties in the way of detailed geological mapping: survey work is impeded by the almost impenetrable jungle, which in places is so thick that it is possible to see only a few feet ahead. Further, it is a particularly unhealthy region and the jungle is infested with insect pests.

 

Within the area, much of the surface is occupied by Tertiary rocks. To the west lies a great intrusive complex consisting es­sentially of serpentinised peridotites, the outcrop being elongated northeast to southwest and roughly oval. This complex is surround­ed by crystalline schists, which include types derived from both sedimentary and igneous rocks. The former appears to represent the country rock into which the plutonic complex was injected. The Uru Boulder Conglomerate of Pleistocene to Sub-Recent data oc­cupies a considerable area north-eastwards from Nammaw and is important because of its jadeite workings. A brief account of each of the formations occurring in the Jade Mines is mentioned. The succession is summarised in tabular form below:

 

XIII.      Alluvium - Recent.

XII.       Uru Boulder Conglomerate - Pleistocene - Sun-Recent.

XI.        Volcanic Rocks - Late Tertiary- Recent.

X.         Granodiorite - Late Tertiary.

IX.        Gabbro - Late Tertiary.

VIII.      Namting Series - Mio-Pliocene.

VII.       Hkuma Series - Oligo-Miocene.

VI.        Highly altered picrites and Volcanic

Breccias - Early Tertiary age.

V.         Jadeite-albite rocks - Early Tertiary age.

IV.        Granites - Late Cretaceous-early Eocene.

III.        Serpentinised peridotites - Late Cretaceous -early Eocene.

II.         Crystalline schists - Partly of unknown age and partly of early Tertiary

I           Limestone - Palaeozoic, possibly Per­mo-Carboniferous.

 

The Plateau Limestone.

 

Small outcrops of limestone are common, and their characters have been described in the author’s Geology of Burma in 1934. The limestone is generally crystalline, approaching marble, where it has been invaded by igneous intrusions. It is well jointed, and oc­casionally it is highly brecciated.

 

The ordinary limestone, under the microscope, consists of calcite, forming irregular mosaics in places, set in a dusky, opaque material, which under high power resolves itself into extremely fine-grained calcareous matter. A network of veins of calcite traverses the rock in all directions. The limestones yielded the remains of Fenestella and foraminifera, including Fusulina elongata, Textularia and various forms of Globigerinidae. Minute circular and rod-like sections of rhabdoliths and Coccoliths respectively are frequently observed under the microscope.

 

About one furlong west-south-west of the confluence of the Hwehka and Nammon Chaungs, the limestone near its contact with serpentinized peridotites has undergone metasomatic replacement.

 

Crystalline Schists.

 

The name “Crystalline Schists” included the duel complex of basic igneous rocks, ranging from diorites and gabbros to pyrox­enites, peridotites, and true schists. The latter are older than the serpentinized peridotites and other igneous rocks of the area and form a basement upon which the subsequent formations were de­posited. The ortho- and para-schists in places are so intermingled that it is impossible to separate them on the present one-inch maps. The ortho-schists encircle the peridotites and serpentines and are most probably the result of differentiation of the same magma, etc.

A rock obtained from the bed of the Sanhka chaung, about 2 ¾ miles northeast of Tawmaw (25° 41’13”, 96° 15’28”), contains, in addition to amphiboles and felspar (saussurite), colourless augite, garnet, zircon, and zoisite. The augite is colourless and clear with an extinction angle of 48°and shows simple twinning. The garnet is colourless and occurs either in dodecahedral or circular sections. Some secondary quartz is also present. Irregular aggregates of chromite are scattered all through the rock.

 

Graphite-schists: Graphite-schists are fairly common in the area. It is not improbable that the epidiorites described above in places have been altered into these schists. They are greyish-black in colour, sometimes with conspicuous reddish-brown pseudomorphs, which appear like garnets at first sight. With a pocket-lens graphite, quartz, and some ferruginous material can be seen.

 

Quartz-schist: Macroscopically, the quartz-schists are whit­ish, finely foliated schists that consist of quartz and felspar with reddish-brown streaks due to iron staining. Under the microscope, a mosaic of the same two minerals is seen with a yellowish or yellowish-brown amorphous mineral, which, in places, assumes a reddish-brown colour on account of iron staining.

 

Glaucophane-schist: Glaucophane-schists are quite common in the area and are greyish-blue rocks that, under the microscope, are seen to consist of glaucophane with some muscovite set in a granular mosaic of quartz. Given the presence of jadeite-bearing rocks in the neighbourhood, these glaucophane schists are signif­icant, as glaucophane contains the jadeite molecule.

 

Due to limited space, some notes on kyanite schists, chlorite schists, and vesuvianite schists could not be described. (To be continued).

 

References:

1. Chhibber, HL, 1934: The Mineral Resources of Burma, Mac­millan and Co Limited, St Marti’s Street, London.

2. Alam, Sarfaraz. 2016: Harbaans Lal Chhibber, Banaras Hindu University.