Gold in the Chaung Magyi Series.

LaTouche has drawn attention to the small quantities of gold that are obtainable from many of the streams draining areas of rocks belonging to the Chaung Magyi Series. These have not proved to be of any great economic importance but sometimes support casual indigenous gold-washing efforts. Amongst others especial mention may be made of the gravels in the streams around Loi Sar in the MongLong State1 and also of those in the streams which drain the northern slopes of Loi Twang, a mountain situated at the junction of the Mong Tung, Kehsi Mansam and Mong Kung States.2

THE MINGIN GROUP.

The Mingin, or Maingthong, Hills stretch from north-north-east to south-south-west, between the valleys of Orography. the Mu and Meza rivers, both tributaries of the Irrawaddy, in the Katha district of Upper Burma, and attain their maximum breadth of 30 to 35 miles about latitude 24° 10′. It is difficult to decide with which region they should be classified or whether they should be grouped alone. As they form an isolated unit in the midst of unsurveyed areas, as the age of the rocks of which they are formed is quite unknown, and in some respects the characters of the rocks themselves are unique, it is most satisfactory to separate them entirely from the other regions as a single group. This action is perhaps justified by their metallogenetic sequence which is a gold-telluride one, entirely distinct from any other mineral association as yet discovered in Burma. The highest point in the southern portion of the range which is the only one that has been examined geologically is Maingthon Hill, 5,510 feet above sea level, but the peak of Taung-thon-lon, 5,621 feet, is perhaps in its northern continuation. The hills are buried in impenetrable jungle growing out of a thick carpet of vegetable mould which together place almost insuperable difficulties in the way of geological research.

According to Noetling, eruptive rocks alone take part in the formation of the hills proper while the lower ground to the east, south and west of the

Geology.

eruptive mass consists of Miocene beds.

1 J. Coggin Brown: (8), pp. 37-51.

2 T. H. D. LaTouche: (38), pp. 102-113.

3 F. Noetling: (51), p. 116.

Quartz diorite forms the centre of the massif with numerous dykes of a different composition radiating from it while barren veins of white quartz also occur in it. The outskirts of the hilly tract are made of a hardened volcanic ash which in some places is studded with minute grains of magnetite, pyrites and pyrrhotitethe latter containing a trace of gold. Compact and altered agglomerates and fragments of amygdaloidal andesite are also found. Intruded into the volcanic ashes, which Noetling believed to be generically connected, are two types of dykes, the first closely related to the diorite in composition, the second consisting chiefly of felspathic quartz which contains a more or less considerable quantity of auriferous pyrites. Five localities are known on the eastern side of the hill tract where veins containing auriferous pyrites occur, and three others where the same mineral has been mined from volcanic ash by the Burmese. In the valley of the Nam Maw on the western side of the hills, an aphanite vein, intrusive into volcanic ash and about 4 feet thick, is composed principally of lath-shaped plagioclase crystals, hornblende and relics of augite with considerable quantities of granular magnetite. The cracks in this are filled with argentiferous cerrusite, which also forms thin layers encrusting the rock.1

One of the veins mentioned above was mined near Kyaukpazat between the years 1898 and 1903, when the Kyaukpazat Gold Mine. pay shoot was lost and mining abandoned. According to J. M. Maclaren the country rocks are composed of consolidated and fairly well stratified tuffs and breccias of andesitic facies, intruded in places by quartz diorites. The vein itself averaged 3 feet in width and was highly pyritic though of low grade. Its length was about 240 feet and below the 310 foot level of the mine the quartz was associated with calcite. It was occasionally clean but more often well mineralised, carrying five per cent. of chalcopyrite, pyrite, galena, franklinite and altaite, the rare telluride of lead.2 Similar veins occur Legyin, 11 miles further north and in the vicinity of Banmauk.

at

1 F. Noetling: (51), p. 118.

2 J. M. Maclaren (44), p. 113; A. H. Bromley: (6), pp. 506-514

(61), pp. 59-63.

G. A. Stonier:

Orography.

THE SHAN-YUNNAN REGION.

The Shan States of Burma form a broad triangle with its base on the Irrawaddy plains and its apex on the Mekong, but this is a political rather than a geological boundary, for the typical Palæozoic rocks of the Burmese Shan States extend far into the neighbouring province of Yunnan in Western China. Over the greater portion of the Northern States in Burma, the country possesses a Plateau-like character which begins in the north about latitude 23° and extends westwards and southwards where it narrows in on the borders of Mongnai and Mawkmai States about latitude 20° 20′. South of latitude 21° 45′ however the country has not been systematically geologically surveyed. On the west of the plateau the hills rise boldly from the Irrawaddy plains and soon reach heights of about 4,000 feet above the sea. Portions of the main plateau about the western edge have been let down by a series of step faults, of comparatively recent date, which trend north and south. Practically the whole of its surface is occupied by dolomites of Paleozoic age from which Devonian and Permo-Carboniferous fossils have been obtained in a few localities. On the north, it is bounded by an exceedingly broken, hilly region occupied by Silurian, Ordovician and PreCambrian rocks which in their turn give place to the Archæan gneisses and crystalline limestones of Mogok and the adjacent areas. To the south and east of Hsipaw the country is very hilly, but beyond this again, the plateau extends from the Nam Tu river to the lofty peaks of Mong Tung in the south-east and the ranges bordering the Salween to Loi Ling (8,771 feet) in the east, and, with some breaks, to the north-east beyond Lashio. Nearly the whole area is drained by the Nam Tu, a tributary of the Irrawaddy, and its feeders, which often flow in narrow, profound gorges through the limestones. In the eastern limits of the States the Salween pursues its way southward to the sea in a deep, constricted valley, without receiving any tributaries of major importance. The plateau of the Northern Shan States to which all these remarks apply, has been aptly described as a country of gentle declivities and rounded interlacing. hillocks, covered after the rainy season with a dense matting of elephant grass, interspersed in places with low scrub jungle and in others with park-like savannahs of scattered oak trees. The hills. are often separated by narrow V-shaped valleys buried in dense. jungle or sometimes clothed with pine forests. Viewed as a whole,

the majority of the ridges commence with a north-west to southeast trend which bends more to the north and south, further to the south. The majority of these have heights of between 4,000 and 5,000 feet rising to peaks of 6,000 or 7,000 feet. The highest peak is that of Loi Ling in South Hsenwi which rises to 8,842 feet. The older Palæozoic rocks are best exposed along the fringes of the plateau, in the deep gorges where the Geology. covering of dolomite has been eroded through, or in the hill folds where it has been planed away. Mention must be made of the red clay which hides the surface of the plateau everywhere under a thick blanket and which sometimes contains important deposits of residual iron ores.1 In numerous places there are flat basins of lacustrine and fluvio-lacustrine origin which are of Plio-Pleistocene age and often bear thick seams of lignite.2 La Touche, from whose memoir most of these details are taken, is of the opinion that the area occupied by the gneisses and crystalline limestones was continuous with Gondwana land, that a great system of clastic rocks was accumulated as a result of its denudation in pre-Ordovician times, and, that towards the close of the end of this period of deposition, or during the interval of upheaval and disturbance that followed it, some exhibition of volcanic energy took place resulting in the emission of lavas and tuffs of an acid type, which are typically developed around Bawdwin. The oldest fossilferous strata show great variations in thickness, contain no really coarse materials, and would appear to have been laid down in a shallow and tranquil sea which flowed over the remains of the folds. of the older rocks, and derived its accumulations from a land surface near by and but little raised above sea level. The crystalline and metamorphic rocks with their extensions to the far north are believed to have constituted a prolongation of the Gondwana continent from the earliest ages. This separated the basin of the Tethys from the ancient Chinese ocean of which the Shan and Yunnan seas formed a part. Only in some such way is it possible to account for the marked differences between the pre-Carboniferous faunas of Yunnan and the Shan States on one hand and those of the Himalayas on the other. It is not necessary to suppose even

1 J. Coggin Brown: (11), pp. 137-141; E. L. G. Clegg: (19), pp. 431-435.

2 T. H. D. LaTouche and R. R. Simpson: (41), pp. 117-124; 'R. R. Simpson: (58), pp. 125 126; E. Moldenke: (48), pp. 30-31.

that the barrier was submerged in. Permo-Carboniferous times, indeed, like the great mass of the Indian Peninsula it may never have been under the sea since the pre-Cambrian era. Omitting for the sake of brevity any allusion to the interesting but local palæogeographical details of the Shan States in the Silurian period, we find some evidence for the existence of an unconformity between the Silurian and Devonian rocks and a great deal more which leads us to conclude that the Plateau Limestone was deposited in a gradually deepening and widening sea which extended far into China, Siam and Indo-China. The Devonian fauna of Padaukpin in the Shan States possesses a purely European character but above this horizon there are Permo-Carboniferous limestones, both in the Shan States and in Yunnan, which carry a fauna exceedingly closely related to that of the Middle Productus limestones of the Punjab Salt Range and the Himalayas. After the formation of these limestones an elevation of the Shan-Yunnan province took place, the old sea bottom was not merely exposed but was worn into hills and hollows during the remainder of the Permian, and throughout the greater part of Triassic times. At the end of this period of emergence the surface of the limestone was again covered by the sea and the Rhætic shales and limestones accumulated. They are followed by the sediments of Jurassic age known as the Nam Yaw beds. No traces of any marine strata of later age have been found either in the Shan States or in Yunnan, where the sequence of main events was much the same, though there continental deposits date back to the Upper Permian and there are abundant remains of both marine and estuarine Triassic deposits.1

The final uplift of the plateau of the whole region in general, together with the more recent folding that it exhibits, are believed to correspond in great part with the movements that produced the Himalayas. Contemporaneous with these upheavals, indeed forming a connected part of the same events, was the uplift of the IndoMalayan mountain chains further south.

The great silver-lead, zinc ore deposits of Bawdwin in the Northern Shan States are by far the most Argentiferous galena and zinc blende deposits important in this particular ore province. They are connected with the Mandalay-Lashio section of the Burma Railways, by a narrow-gauge line, 50 miles

of Bawdwin.