324 BROWN & HERON : GEOLOGY AND ORE DEPOSITS OF TAVOY. 



with use this amount decreases and it is safer to take 12 per cent, 

 as the figure. Now the ratio between the effective pressure head 

 and the height to be lifted is 5-4, which means that with 100 per cent, 

 efficiency, 1 cusec of pressure water would lift 5-4 cusecs of tailings. 

 But with only 12 per cent, efficiency the amount lifted is 12 per cent, 

 of 5-4, or 0-G5 cusecs of tailings. The 20 cusecs available must 

 now be divided in the proportion of 1 to 0-G5, or 12 cusecs will be 

 absorbed by the elevator leaving only 8 for the monitor. Such an 

 elevator will require a 4 inch nozzle and the monitor nozzle 

 will have to be reduced to ?>\ inches. The daily yardage will conse- 

 quently be reduced from 2,000 to 800. The velocity in the upraise 

 pipe should be about 12 feet per second and the diameter of the pipe 

 should be 18 inches. The friction in the upraise pipe may be taken 

 at from 2 to 2£ times the clean water friction. For pipes 12 to 18 

 inches in diameter an addition of 7 feet for each 100 feet in length 

 will roughly cover the friction head. 



Gravel pumps— The next step is the substitution of the gravel 

 pump for the elevator. A gravel pump will give an efficiency of 

 from 35 to 45 per cent. If the pump is driven by a Pelton wheel 

 the overall efficiency may be taken at 30 per cent., if the tail water 

 can be disposed of without elevating. Treating this in the same 

 manner as the elevator calculation, the ratio of the pressure water 

 to monitor water is now as 1 to 1-6, so that the pump will consume 

 only 7| cusecs, leaving 12£ for the monitor. A 4-inch nozzle can 

 be used and the daily yardage increased to 1,225. 



The pump is generally mounted on a barge for convenience in 

 moving up to the face, and thus the conditions of dredging are ap- 

 proached. If water can be obtained from a source very much 

 higher than is necessary for hydraulicing, it may be used to drive 

 a nozzle pump ; in this way a small supply of water under a great 

 head may pump a much greater volume of nozzle water and tailings. 

 Such a method is adopted at Kanbauk, but owing to the difficulty 

 of making pipe connections each time the barge is moved, electrical 

 distribution from a permanent generating station is adopted. 



Dry dredges. — The system of operating such installations is 

 practically the same as hydraulicing except that the same water 

 is used repeatedly. The barge is erected in a paddock and, as this 

 becomes enlarged and the face recedes, it is flooded and the barge- 

 floated to a new site. The tailings are pumped behind a brush- 



