“There is not the slightest doubt that before very long many of the deep alluvial flats that are some distance from the shallow and more easily worked tin ground will be worked. The values may turn out to be poorer than the shallow ground, but the natural facilities are better owing to the water supply being sufficient for continuous working without the expense of erection of dams. On the other hand, when you get out of the granite country, the further you are away from the source of the tin the greater are the impurities mixed with it. The numerous creeks, after passing through the schists and other rocks emptying into the main river, all tend to this, and titanic iron, tourmaline, rutile, and gem sand form a large percentage of the concentrates. However, if on boring, the deep ground turns out payable, there should be no difficulty in getting rid of the impurities and dressing the tin up to 70 per cent.”
Mr. L. H. L. Huddart, writing on this subject in his report on the South Juga property, says:
“Sources of the Tin.—The black tin is probably derived from the granite of which it is a rock constituent, and from stockworks in the granite quartz porphyry occurs very similar to the ‘elvans’ in Cornwall.
“Nature of the Wash.—In the upper end the wash is a fine whitish granite, containing no large pebbles or boulders, and is near the original source of some of the Juga tin. The surface is slightly cemented with iron oxides in which cassiterite often grows. The whole wash very easily breaks down with water. The ground further down the property is similar except that the alluvial has travelled further, and consequently has been sorted to a greater extent.
“Taken generally, the tin bearing is the product of denudation from the granite of which the bed-rock, and sides of the valley are composed. The tin occurs in the wash right up against the granite on both sides of the valley. The topaz is abundant in the wash, and with some zircon and rootile is almost the only mineral besides cassiterite occurring in the concentrates.”
In his report on the Kurdum River Tin Concession, Mr. Huddart says:
“Geology.—The base rock is a foliated gneiss and schist; the great granite massif forming the Jarawa Hills lies to the west of the property. There is a good deal of granite on the property, with some dolerite. The rocks are compact, and show considerable signs of regional metamorphism.
“Source of the Tin.—The tin has been carried down from the rich placers at the head water of the Kurdum River, and form feeders that come in above the property from the Jarawa and Fuersum country. In one or two places the natives work the river-bed, an indication in itself of high value, as it does not pay them to work any but rich gravel. The alluvial ground is a quartz gravel with sand near the top. There is very little clay, and long boulders are unlikely, and the wash is friable and easy to work. The river-bed gravel where coarse is very rich.
“Concentrates.—These contain usually minerals such as ilmenite, rootile, zircon, and some topaz and garnet. The tin is of good quality, and varies in colour from black to ruby and pale yellow. A little monazite is found, and an occasional colour of gold. There should be no difficulty in shipping concentrates that will assay 71 or 72 per cent. metallic tin. The tinstone is of a good average size for saving in the sluice boxes which can be given a good grade.”