EPISODE:61
By THAN HTUN (GEOSCIENCE MYANMAR)
JADEITE FROM BURMA
This article serves as a continuation of Episode 60, “Jadeite from Burma”, originally reported by HL Chhibber in 1934. It provides further insights into the specific geology and methods of mining in the jadeite mining area. Due to space constraints, a summary of the report is included.
Jadeite-Albite Rocks.
The alignment of the known jadeite outcrops suggests that there are at least four jadeite-albite dykes or sills intrusive into the peridotites and serpentines described above, and they may be designated (1) the Tawmaw dyke, (2) the Mienmaw dyke, (3) the Pangmaw dyke, and (4) the Namshamaw dyke. The petrological account of these rocks is dealt with in the account of mines.
The jadeite mines of the region can be classified as follows: -
1. Outcrop mines.
2. Detrital boulder workings.
3. Jadeite workings in the Tertiary conglomerates.
4. The Uru Boulder Conglomerate workings.
5. Jadeite workings in the Uru chaung.
1. Outcrop Mines.
(a) The Tawmaw Jadeite-Albite intrusion.
Discovery of the Jadeite at Tawmaw: The most enormous outcrop of jadeite is at Tawmaw (25º 41’13”, 96º 15’28”), discovered about 54 years ago. The discovery was purely accidental. The story narrated to the author is that about sixty years ago a hunter named Ninjar of Sanhka reached the site of Tawmaw while hunting and started cooking rice on a range of stones. One of the stones cracked and proved to be valuable jadeite. Subsequently, the Kachins started mining on the spot. The story recorded by Batemen, Assistant Superintendent, Kamaing, in his diary dated 28th February 1907, is slightly different. “Some 26 years ago, a Kachin who was on a hunting expedition shot at and wounded an elephant. He tracked the elephant to the spot now being quarried and found the animal dead there. He removed its tusks and was trying to knock some of the flesh off them on a hard rock close by when the weight of the tusk broke off a fragment of the rock, which proved to be a valuable bit of jade. After a fashion, this area’s development has continued since.” The proved outcrop’s length and width at Tawmaw are a little over 300 and 200 yards, respectively. The intrusion has been regarded as a dyke, but it is quite probable, as especially seen in the Kadondwin and elsewhere, that the injection took place in the form of a sill. The thickness is irregular, probably depending on the fissure into which the jadeite-albite mass was intruded. The general trend is N-E - S-W, which swings between N-N-E - S-S-W and E-N-E - W-S-W
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Old Kachin Workings.: Many old Kachin workings are to be seen to the southwest of the Dwingyi (big mine). When the jadeite was first discovered here at Tawmaw there were only three of four feet of overburden in places, and the covering of serpentine was practically absent. The depth of the numerous deserted pits seldom exceeds six feet. The abandoned water races used to sluice away the overburden are still to be seen. The general section of the intrusion exposed at Tawmaw is as follows: at the top, a very thick overburden of red earth represents the soil and subsoil formed by weathering of serpentinised peridotites, which form the country rock into which the jadeite-albite mass is intrusive. Below serpentinised peridotites lies a thin, earthy, very light green chlorite-schist, which is locally called “byindone”. The latter is underlain by a siliceous cherty mass which, in the mine, has the appearance of schistose serpentine. Below the chart comes an amphibole-schist or amphibolite (locally called “shin”). Next to the amphibolite is a banded amphibole-albite rock, which is underlain by albitite and, in turn, by jadeite. Below the layer of jadeite, the relationships of the rocks are seldom visible; in rare sections, however, the sequence may be repeated in the footwall, but albite is not present as a rule below the jadeite, i.e. the latter may be directly underlain by amphibolite. In places, albite is absent altogether, but in others, it is absent from the footwall only. It may occur at only one in ten localities and commonly occurs at the top of the sill. In the Kadondwin, in the hanging wall, albitite occurs in the middle, and jadeite is found above and beneath it, while in the footwall, jadeite occurs in lenses in the albitite.
Outcrop Mines of Tawmaw.
The outcrop mines are situated at Tawmaw. There are two of these: (1) the Dwingyi (meaning “big mine”), and (2) Kadon dwin (“dwin” in Burmese means a mine).
The Dwingyi: The Dwingyi is certainly the more important of the two and the mine consists of shafts and tunnels driven along the jadeite “dyke”. There are six shafts in all, and in 1927 the mine subsided in one place making the total number of surface openings seven. The shafts were originally put down by different people and are named after them.
In addition, there are a few small deserted pits that represent attempts at winning in the past. About 200 yards southwest of the Dwingyi, numerous old Kachin workings are to be seen. At this site, jadeite was found almost at the surface; only three or four feet of overburden had to be removed to reach it. Serpentine was particularly absent. The depth of these pits did not exceed six feet.
Method of mining.: The mines are worked for only about three months in a year, i.e. from March to May, and all mining activity ceases with the advent of rains. During the rainy season, the mines get filled up with water, and as a result, the first operation when work is recommenced is to pump out this water. It may be noted in passing that since A W G Bleeck’s visit in 1907, mining methods have changed considerably. Kachins then emptied the mines by removing water with kerosene tins, but nowadays draining is performed by a steam pump. When the mine is properly cleaned, operations can be started. The owners of the Dwingyi installed a compressed air drilling machine with which they work thin star-bit jack-hammer drills. Generally, the drills are four-rayed, but sometimes they are six-rayed with a maximum diameter of one and three-quarter inches. A hole about six to nine inches in depth is drilled in the jadeite, and then pieces of jadeite are broken off by driving a wedge into the hole with big hammers. But when the compressed air-drilling machine is not operating the miners then work only with blunt chisels, wedges, and hammers. The wedges are five inches in length and two inches in breadth. It is noteworthy that jadeite is a very tough and hard mineral and it is extremely difficult to break it. In a few minutes, a chisel or wedge loses its sharp edge.
The primitive method of cracking jadeite with burning charcoal continues. This practice is very injurious both to the mineral and to the miner. The former gets calcined as a result of this treatment while the value of the stone is considerably reduced on account of the development of cracks in it. The fumes of carbon monoxide emitted from the charcoal fires have their poisonous effects on the miners working underground.
Kadon Dwin.
The Kadon Dwin is run on more scientific and up-to-date methods by Mr C W Chater of the Burchin Syndicate. The main vertical shaft, which is about fifteen feet square and fifty feet deep, leads to drive No 1, which is one hundred feet long, 30º north of east, and represents the hanging wall of the jadeite dyke. It opens out into a winze about 23 feet in depth, and this leads to the stope No 2, which represents the footwall of the dyke and is about 50 feet in length 10º east of north. The main shaft is entirely serpentine, and drive No 1 represents the workout portion of jadeite with contact rocks, viz. “chloritic schist” and amphibolite in the hanging wall of the dyke. The average thickness of the jadeite here was about 4 feet. The winze or shaft No 2 is entirely in albite, and stope No 2 has been driven in the footwall of the dyke. The albite is traversed by vertical joints, which, in some cases, are filled with white veins. It is underlain by amphibolite, and beneath this is the jadeite, the thickness of which varies from 5 to 7 feet. Remarkably, the jadeite in the footwall occurs in the form of lenses. Amphibolite and albite with some albitite-breccia intervene between the successive lenses of jadeite. The jadeite was seen dipping 30º east at the working face.
Industry declining at Tawmaw: The mining industry at Tawmaw is gradually declining, chiefly due to the increasing depth of the mines; further, the old primitive methods of the Kachins cannot successfully cope with the present-day condition of mines. Unsettled conditions in China, which is the main consumer of jadeite, must also be partly responsible. To be productive, the mines must be run on scientific and commercial lines, which requires capital much beyond the means of poor Kachins. It is true that about 20 years ago, the output of jadeite was much more significant than at present, and three Mawoks (headmen), a Kachin, a Shan, and Chinaman had to be maintained. Even about five years ago, 400-500 miners were working at Tawmaw, but in 1927 and 1928, however, only some 50 to 60 miners had been engaged.
On the Tawmaw alignment are situated the three other outcrops of (1) Sarmamaw, (2) Malinkamaw, and (3) Sanhkamaw and summarized as follows:
Sarmamaw.: It is interesting to record the discovery of the following outcrops of jadeite, hitherto unknown to science. About one mile south-west of Tawmaw (25º 41’13”, 96º 15’28”) is an outcrop of Samamaw which occurs on the right bank of a small stream called Sarma hka, named after the Kachin Sawbwa of the neighbourhood of Mogaung. At the top is an overburden 10 feet 2 inches thick, and an inner pit about 13 feet deep with a diameter of about 10 to 15 feet. In places, the joints are only about one to two inches apart.
Malinkamaw.: Malinkamaw is about two miles northeast of Tawmaw (25º 41’13”, 96º 15’28”). The rock here has greenish-black inclusions of amphibole. The overburden measured only about 8 feet. Jointing in the northeasterly direction is well-marked and simulates bedding.
Sanhkamaw.: The third locality is situated in the Sanhka hka, about 2 ¾ miles northeast of Tawmaw. This locality does not leave a shadow of doubt as to the intrusive nature of the jadeite into serpentine. The thickness of the serpentine at the top is about 12 feet, which is underlain by a soft chloritic schist about 1 foot thick. The serpentine is highly jointed. Another probable outcrop of jadeite lies N-W of Mienmaw on the path that connects this village with the old Kansi-Tawmaw path. Several bounders of albitite (“palun”) were seen lying near the pit, and apparently, the Kachins did not reach the jadeite underneath the albitite. (To be continued).
References: Chhibber, HL, 1934: The Mineral Resources of Burma, Macmillan, and Co Limited, St Martin’s Street, London.
