74 DRESSING OF ORES 



(B.) Took two parcels of argentiferous lead ore, associated with carbonate of iron, 

 a little quartz, and blonde. Weight 34^ tons, which assayed 42 per cent, for lead, 

 and 29 ozs. of silver per ton of metal. Crushed and care'fully elaborated the same 

 through jigging and buddle apparatus, obtained 14^p tons of ore, giving 54^ per cent, for 

 lead, and 22 ozs. of silver per ton of metal. The produce for lead was therefore 

 raised 12 units at a loss of 49 per cent, of the initial quantity of metal and 95 ozs. of 

 silver. The commercial loss attending this operation, after making the several charges 

 and allowances incident to the mctallurgic reduction, was Sll. 14s., or equal to 2/. 145. 

 per ton on the original weight. 



Numerous instances of heavy losses incurred in the concentrating processes could 

 bo adduced if space permitted. But it may be observed that excessive loss of oro will 

 always occur from an excessive reduction of the stuff; that in the stamping or 

 crushing of complex ores the softer ores will suffer a greater loss than the harder ore ; 

 that the proportion of loss in water dressing is generally in proportion to the fineness 

 of the grains ; that a maximum loss will occur when the stuff is so treated as to <l<-t;irh, 

 instead of shattering the ore ; and that the loss of silver associated with lead ore, fre- 

 quently increases with every separate reduction and washing of the grains. 



In order to determine the loss of metal which may arise in enriching ores, accurate 

 assays and notations should be made of the quantity of vein-stuff lodged on the floors, 

 which should be compared with the metallic contents rendered merchantable, and the 

 differences estimated. 



It is not possible to ascertain the value of an improvement which would secure an 

 additional one per cent, from the quantity of orey stuff annually sent to surface from 

 the several mines in the United Kingdom ; but if it be reckoned only upon the sale 

 value it would be scarcely less than 40,000. per annum. 



In determining the site for a dressing floor, and in making the mechanical arrange- 

 ments, various points suggest themselves ; since, if they are overlooked, much loss 

 will ensue to the undertaking, or otherwise it is evident that they can only be 

 corrected by involving the proprietary in an increased outlay as well as a greater 

 current expenditure. The first consideration should be to secure an ample supply of 

 water, with a good fall, and an extensive area of ground. With advantages of this 

 nature the machinery will be worked cheaply, the stuff gravitate through the various 

 processes without returning to create double carriage expenses, whilst the castaways 

 may be sent to the waste heaps at a minimum cost. The second point to be settled, 

 is the class of machinery to be employed. This must obviously be based upon the 

 character which the ores may present. If massive, and associated with light waste, 

 simple apparatus will suffice ; but if the ore be sparsely diffused through heavy 

 vein-stone, it is probable that the various apparatus will have to be constructed 

 with great nicety, varied in their principles of action, and that much precaution will 

 have to be observed in order to create as little slime as possible, as well as to 

 secure the initial quantity of ore against undue loss. In the disposition of the 

 machinery there is also considerable scope for practical intelligence : it is not enough 

 to wash, crush, jig, and buddle the ores, mixing the resulting smalls incongruously 

 together ; but a judicious sorting should be commenced at the wash kilns, and upon 

 this basis the various sizes kept distinct whilst passing through tho washing floors. 

 The dresser should also take care to keep the several ranges of mineral produces and 

 degrees of fineness together. 



With the view of assisting the judgment in deciding upon the machinery to be 

 employed, the following Table of Specific Gravities is given : 



TABLE OF SPECIFIC GRAVITIES. 



Metals* Specific gravity 



Gold 19-26 



Mercury , , 13'20 



Lead . , 11-35 



Silver 10-47 



Copper 8-89 



Iron 7'78 



Tin 7'30 



Zinc 7-00 



Hnrd nesa Specific gravity 

 Lead: Sulphide (galena) . . . . 2-5 to 2'75 7 1 -") to ?<; 



Sulphate 2'3 27 6'25 ,, 6-29 



Carbonate (white) . . .3'0 ,, 3'5 G'4G ,, G'48 



