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BROWN & HERON: GEOLOGY AND ORE DEPOSITS OF TAVOY. 



tailings discharged from a race will spread out with an average 

 inclination of 1 in 15 and at the sluice boxes at least 5 feet and as 

 much as 12 feet extra fall should be allowed to enable grizzlies, 

 distributing boxes, etc.. to be installed. 



Grade Une.—Ii the tail race and sluice box line as plotted on the 

 section rises above the bed rock line it is obvious that the ground 

 between cannot be treated by gravitation and some form of elevator 

 becomes necessary. 



Pipe line and monitors.— Mr. Lyons made use of a theoretical 

 case in which it was assumed that a reliable flow of 20 cusecs was 

 available, which could be brought to the head of the pipe line 

 by a flume or ditch at an elevation of -100 feet above the working 

 face. In this case the water may be taken there in 20 inch pipes, 

 I inch thick and double rivetted with slip joints. With ordinary 

 care these should have a life of 5 years. 



If the pipe line necessary to convey the water to the working face 

 is \ mile long, the frictional loss of head will be about 50 feet, so that 

 the nozzle pressure will be equivalent to a head of 350 feet. The 

 breaking efficiency of a nozzle increases rapidly with increase of 

 diameter, so that in hard ground it is better to use one large nozzle 

 than two smaller ones delivering the same quantity of water. The 

 larger flow from the bigger nozzle will also move stones of greater 

 weight to the race. Speaking roughly, a 4 inch jet in hard or stony 

 ground will break and convey from the face as much ground as 

 six 2 inch jets, though it consumes only two-thirds the amount of 

 water. 



Sluice boxes. — Australian practise favours a width of 2 J feet 

 or more for each cusec. At Kanbauk 2 feet is found sufficient. 

 The grade should be 1 in 20 at least, The theoretical case under 

 consideration, of 20 cusecs, would require a width of 40 feet. This 

 box should be divided into 3 compartments, each 13 feet 4 inches 

 in width. A fourth compartment may be added to divert the 

 flow when cleaning up. The length of the box should be from 100 

 to 150 feet and to ensure proper working all stones above 1 inch 

 should be eliminated by a grizzly. Of the extra 12 feet allowed in the 

 grade line at the boxes, 4 feet will be absorbed by the grizzlies, 

 the distributing boxes will take another 4 feet, and there will be a 

 clear drop into the box itself to allow for filling up with rough con- 

 centrates. The stones from the grizzly should drop into a steel 

 chute laid at a grade of 1 in 10, along which a small volume of water 



