268 BROWN & HERON: GEOLOGY AND ORE DEPOSITS OF TAVOI 



and further to the east the brown clay passes Into a mottled reddish- 

 brown and yellowish material and white fine clay with groups of 

 boulders at irregular intervals. It includes a few curved .stringers 

 of granulated quartz which are displaced and broken by later settle- 

 ment. There are also blue and black patches and layers of pure 

 white kaolin in this material, which in its turn is surmounted by a 

 thin layer of ordinary surface detritus. On weathering the mottled 

 silt assumes a uniform brownish -white appearance. Bands of it 

 have in places undergone lateritisation and in extreme cases form 

 masses of hard black ironstone. Further east still and close to 

 the bed of the present stream, the upper layers of the deposit are 

 not so stony but the stones themselves are rounded and quartz 

 is commoner. 



The complexities of the structural geology of the Kanbauk 

 valley deposits are too many to consider here, especially as much 

 of the available evidence is derived from bore holes made by the 

 percussive drill, but it may be pointed out that they are very much 

 disturbed, that patches of Mergui rocks appear to occur with alluvium 

 underlying them, that there are vertical subterranean cliffs of 

 argillites with alluvium banked up against them, and that the 

 bedded alluvium has been folded into vertical and inverted positions. 

 Apart from the rapidly changing conditions during the time of 

 deposition, which include soil creep, and river and lake action, 

 possibly with the occurrence of land slides by which blocks of 

 Mergui rock bodily overrode the older alluvium in places, profound 

 disturbances have been brought about later both by recent or sub- 

 recent faulting and by the solution of the calcareous portions of 

 the underlying floor, resulting in collapse of patches of the deposits. 



The whole of these valley deposits carry wolfram and cassi- 

 terite and they have been tested systematically by means of pits 

 and bore holes. According' to H. D. Griffiths, at the end of 1917, 

 " the area proved exceeds 173 acres, and a conservative computa- 

 tion gives 8 million cubic yards capable of being worked at a profit." 1 



The wolfram content of the concentrate obtained by the treat- 

 ment of these deposits decreases as the distance from the western 

 hill slopes increases, but the cassiterite contents increase at the 

 same time, until in the middle of the valley a rich cassiterite con- 

 centrate is found. In the article quoted Mr. Griffiths states that 



1 H. D. Griffiths, (13), p. 215. 



