248 BROWN & HERON. GEOLOGY AND ORE DEPOSITS OE TAVOY 



1,800 feet. Most of the wolfram from this mine comes from the 

 Middle Lode, which is worked to the 240 fathom level. At the 

 South Crofty mine the distribution of wolfram is irregulftl ; it is 

 most abundant in the middle levels and cannot be depended on 

 below 245 fathoms (1,470 feet). The best lode is not payable below 

 205 fathoms (1,230 feet), at which the average yield of tin ore and 

 wolfram is 23 lbs. per ton. In the eastern section of the same 

 mine development is being carried on down to the 310 fathom level 

 (1,860 feet). At this bottom level the North Lode is 2 feet wide 

 and carries 40 lbs. per ton. 1 



According to Hess, Grey and Winters conclude that the wolfram 

 deposits In the aplites of Yenberrie, Northern Territory, Australia, 

 give promise of a considerable persistence in depth. 



At White Oaks, N. Mexico, hiibnerite has been found at a 

 depth of 1,350 feet. In the Boulder field of Colorado, no ferbeiite 

 ores have been found at a depth greater than 900 feet, but the 

 question of depth cannot be considered as settled for the field. 

 According to George, the ferberite in these deposits is distributed 

 along the veins in bunches and pockets or rarely shoots, and up 

 to the present nothing has occurred to suggest that the downward 

 distribution is less regular than the lateral. In fact a considerable 

 number of the best ore bodies have had greater vertical than lateral 

 dimensions. 



Hess points out that the minerals associated with wolfram are 

 those usually considered characteristic of deposits formed at consi- 

 derable depths below the surface, and that it is thought that pegma- 

 tites were extruded from great depths. He concludes that most 

 tungsten deposits doubtless extend to depths as great as those 

 reached by deposits containing other metals. " Many tungsten 

 veins, like veins carrying deposits of gold, silver, tin, copper, and 

 other metals, will give out at shallow depths, and only the excep- 

 tional mine may be expected to yield ore of good quality in commer- 

 cially valuable quantities to great depths. Probably not one in five 

 hundred gold-bearing veins carries commercially valuable ore below 

 a depth of 100 feet. Possibly tungsten veins may carry ore at 

 depths greater than those reached by workable gold veins, but this 

 possibility has not yet been demonstrated by actual developments 



1 Dewey and Broraehead, "Tungsten and Mangan ©so Ores," Geological Surrey of 

 Great Britain, 1917, pp. 20-21. 



