The vein quartz is drusy and carries cassiterite, wolfram, arsenical pyrites, pyrite, chalcopyrite and black tourmaline. Cassiterite and wolfram occur in intimate intergrowths and also separately. The wolfram-bearing area of the Yamethin district is situated close to the summit of Byingyi, a peak which rises 6,254 feet above the level of the sea, on the borders of the Yamethin

Wolfram in the Yamethin District.

district and

Loi Long State in the Southern Shan States. Here, several thin veins occur in granite and carry wolfram, molybdenite and beryl.

etc.

A few wolfram concessions have been taken up from time to time. in Yengan, one of the most northerly of the States of the Myelat division of the Southern Shan States. In one of these, which lies 15 miles due east of Thedaw railway station, at mile 322 from Rangoon, in the direction of Mandalay there are two main granite exposures separated by a series of hardened sedimentary rocks, chiefly clay slates and white quartzites. Both groups of Wolfram in the Southern Shan States, rocks are traversed by quartz veins, varying in thickness from a few inches to three feet. Close to the granite contact they contain wolfram but become barren further away. Molybdenite occurs in one part of the concession, and the oxidised compounds of copper and iron, which are found in the upper parts of the veins, appear to indicate the presence of sulphides of these metals below the zone of decomposition. Insignificant quantities of wolfram have been found in the Mawnang State and in the Sabedaung Forest reserve of the Kyaukse district. These occurrences mark the northern limit of the tin and tungsten bearing zone of Burma.1

and Cassiterite Veins.

The foregoing notes demonstrate that all the wolfram and cassiterite veins of Burma are closely associated Origin of the Wolfram with an intrusive granite, found throughout the Province from the vicinity of the Southern Shan States to the extreme limit of the Mergui district, forming the cores of the Indo-Malayan mountain ranges. It is believed that the ores were formed partially under conditions closely allied to strictly magmatic ones, were also produced by processes in which gaseous agencies, including compounds of fluorine, and sulphur, to some extent played a part, and, in rarer cases, by hydrothermal reactions which followed as a consequence

1J Coggin Brown and A. M. Heron: (15), pp. 235 237.

of the former ones. The whole process of mineral vein formation associated with the great granite chain which extends through the Tenasserim ore province, appears to be a direct sequence of processes of differentiation or fractional crystallization, through a series of varying phases, induced in the original magma by decreasing temperature. 1

Ores of Antimony

and Lead in the Tenasserim Province.

It has already been shown how galena and more rarely stibnite occur sometimes as a late phase of the mineralisation which brought about the cassiterite and wolfram association of Lower Burma. Evidence is not wanting to show that in some cases at least these and other sulphides, such as pyrrhotite and chalcopyrite, accompanied a re-opening of the other vein fissures in which the tin oxideand the tungstates had already been formed, though it is not certain that this was always the case.

There still remain to be considered certain examples in which galena and antimonite occur in veins alone, and as these have not been studied in great detail or are situated in isolated districts of which the geological structure is still unravelled, their origin is still obscure, though in some cases there is reason to believe that they occur in rocks similar to the Moulmein limestones or to parts of the Plateau Limestone. They include the galena and cerrusite deposits of the Pagah range in the Amherst district and the lead and copper ores of the Yunzalin valley in the Salween district.

There are several references in the older literature to antimonite deposits scattered about the Amherst district, including one at Lekka Taung, about 23 miles south of Moulmein. Here, stibnite and cervantite occur in pockets in quartz veins (described as “a whitish quartzose sandstone, filling dykes or fissures") traversing sandstone.

A narrow quartz vein containing stibnite has been traced for 600 or 700 feet in slates which presumably belong to the Mergui Series, and crop out along the crest of a low ridge, on the western. slopes of the eastern of the two parallel ranges of the ThatonMartaban hills, seven miles to the west of Katun railway station in the Thaton district.

A. M. Heron has described the antimonite deposit of Thabyu in the Amherst district.2 It is situated in the extreme south-east.

1 J. Coggin Brown and A. M. Heron: (16), p. 338.

A. M. Heron: (32), pp. 34-43.

COGGIN BROWN: Mineral Deposits of Burma.

101

PART 1.] about 9 miles to the south of a police outpost of the same name on the Siam frontier. The veins themselves are very large, the biggest measured, which was followed for 600 feet, had an observed. thickness of at least 20 feet. The stibnite occurs in bunches of radiating or parallel crystals up to 4 and 5 miles long, and in massive aggregates. Oxidation is pronounced and the massive sulphide. has been converted to a depth of several inches to white, yellow and reddish, soft and earthy, antimony ochres, cervantite or stibiconite. The vein stuff is a yellow and white calcareous chert, showing distinct. brecciation and often a cellular structure. Small angular fragments of slate occur in the veins which are believed to fill tension cracks and to have been deposited from water at a comparatively low temperature, and at a moderate depth from the surface. The veins are thus quite different in their character and origin from the wolfram and cassiterite-bearing veins of Lower Burma. The slates in which the veins are found are very uniform, black, fissile rocks similar to the argillites of the Mergui Series.1

6. BROMLY, A. H. (189697).

7. BROWN, C. BARRINGTON AND JUDD, J. W. (1897).

8. BROWN, J. COGGIN (1912).

9. BROWN, J. COGGIN (1913).

10. BROWN, J. COGGIN (1914).

11. BROWN, J. COGGIN (1916).

Notes upon Gold mining in Burma ". Trans. Inst. Min. Eng., Vol. XII, pp. 506-514.

The Rubies of Burma and associated
Minerals". Phil. Trans. Roy. Soc.,
London, Vol. 187A. For an abstract

of this paper see Proc. Roy. Soc.,

London, Vol. LVII, p. 387.

Report on Certain Gold-bearing Deposits of Mong-Long, Hsipaw State, Northern Shan States ". Rec. G. S. I., Vol. XLII, pp. 37-51. "Contributions to the Geology of Yunnan, 1. The Bhamo-Têngyüeh area". Rec. G. S. I., Vol. XLIII, pp. 173-205.

17. BURTON, R. C. (1918). "Petrology of the Volcanic Rocks of