DRESSING OP ORES 



155 



Top skimmings 

 Second . 

 Clean ore, middles 

 bottom 



Fine Slime 



Total 



. 4 cwts., assayed 



1 

 . 1 



. 17 



20 per cent. 



45 



65 



It may be remarked, that none of the various processes of dressing is more satis- 

 factory than that of dollying, since, if carefully conducted, little or no loss of the 

 total quantity of ore can occur. 



Vanning is a method commonly practised by the tin-dressers of Cornwall and Devon- 

 shire, by which they ascertain approximately the richness and properties of the ore 

 to be treated. If the object be to determine the value of a pile of stuff, it is care- 

 fully divided, then sampled, and a portion, say a couple of ounces, given to the 

 vanner. If the stuff thus given should be rough, it is reduced to the tenure of fine 

 sand, and in this state put upon the vanning shovel. The operator now resorts to a 

 cistern or stream of water, and by frequently dipping the shovel into it, and impart-, 

 ing to the shovel when withdrawn a kind of irregular circular motion, he succeeds 

 in getting rid of a greater or less portion of the waste : that which remains on the 

 shovel is then considered equal to dressed work and assayed. So accurately- is this 

 operation performed by many of the tinners, that parcels containing only fifteen 

 pounds of tin ore per ton of stuff, are sold by it to the mutual satisfaction of both 

 buyer and seller. 



The vanning process is also well adapted for determining the properties of an 

 ore. If, by this method, vein-stuff should withstand concentration, no machinery is 

 likely to dress it. If also the loss of ore is found great, then the apparatus to be 

 employed for effecting the enrichment will have to be carefully considered and con- 

 structed. 



760 



Pig. 760. The vanning shovel A, is 14 inches long, and 13 inches wide at the 

 top, the edge of which is slightly turned up. The shovel is also formed with a 

 hollow or depression. The handle is about 4 feet long. The vanning cistern is 

 shown at B. 



Hushing. It often occurs, that the water employed on the dressing floors makes 

 its escape below the refuse or waste heaps. This may be used for the purpose of 

 hushing, which operation is performed in the following manner. The husher diverts 

 the escape water into a rivulet and introduces a given quantity of waste. He then 

 builds a dam or reservoir, with a door or trap valve at the high end, in order to collect 

 the necessary water for hushing, and puts aside all the large stones lying in the 

 middle of the hush gutter in order to form them into a wall. After this, he starts his 

 hush by lifting the door of the dam, which slides in a wooden frame adapted for that 

 purpose. 



This allows the water to rush out, and displaces the waste to a certain depth, at the 

 same time driving it forward. 



If the hush has bared or uncovered a further quantity of large stones in the 

 middle of the gutter, they are again removed to one side, since they would retard the 



