APPENDIX A. 
69 
APPENDIX A. 
NOTE ON CONCENTRATES FROM CHAKSAM ON THE TSANGPO. 
Two samples of concentrates from the Tsangpo, near Chaksam, were examined 
by Mr. J. M. Maclaren and described as follows : — No. i weighed 500 grains 
and was thie result of washing 112 lbs. of gravel from the left bank of the river, 
one mile above Chaksam. 399 grains, or 80 per cent., of the concentrate, proved 
to be magnetite, while the greater part of the remainder was composed of zircons. 
Of gold, there were only four extremely fine specks, far too fine to be weighable. 
No. 2 sample, of 790 grains, was the result of washing 160 lbs. of gravel from 
the right bank of the Tsangpo above the Chaksam ferry. This contained 612 
grains of magnetite sand or 77 per cent., nearly the same as the preceding. The 
residue of 178 grains was carefully washed and yielded a number of extremely 
small grains of gold, weighing "02 grain. The total gold content per ton of these 
gravels is "28 grain, or a little more than \ grain, of a value of one half-penny. 
The minerals associated with the gold are magnetite and zircon, making up, 
as already stated, nearly the whole of the concentrates. There are also occasional 
grains of rutile, of tourmaline and of hercynite. With the gold, and impossible 
to separate from it by ordinary washing, there remained a little dust, which was 
resolved, under the high powers of the microscope, into black, cubical crystals 
with cubical cleavage. These, from their extremely high specific gravity, their 
crystalline form and their colour, are probably uraniniteor pitchblende. 
The washings were made at a wide portion of the river, and gold was obtained 
in the dish only when washing was carried on in the coarser gravels, the stones of 
which ranged up to 6 inches in diameter. There is no record of gold-washing 
along the Tsangpo, and the poverty of its gravels, as indicated by the above results, 
confirms previous assumptions that the gold of the Assam valley has not been 
derived from the Tibetan highlands. The extreme fineness of the gold, combined 
with its flaky character, — the largest grain is no more than "3 mm. long and 'oi 
mm. thick — indicates a distant source, possibly as far distant as the gold-regions 
of the Manasarowar lakes. 
Sample No. 2 was sent to the Imperial Institute on the suggestion of Profes- 
sor Wyndham R. Dunstan, F.R.S., in order that a special examination might 
be made tor minerals of the so-called " rare earths," and Professor Dunstan 
reports as follows : — 
The ss;mple was described in the Records of the Geoltgical Survey of India 
as consisting of 77 per cent, of magnetite, the residue containing zircon, rutile, 
tourmaline, hercynite, gold and minute cubical crystals, which were supposed to 
be uraninite but which I suggested might prove to be thorianite. Most of the 
abovementioned minerals appeared to be present in the sample sent to the Imperial 
Institute, and monazite in addition, but the residue left after removing the magne- 
tite was only 2*3 per cent, of the total. 
A sample of the material was tested in the Wilson electroscope and exhibited 
slight radio-activity. 
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