DRESSING OF ORES 



Hr.rcl::c"8 Specific Gravity 



Phosphate (green and brown) . 3-5 4'0 6-08 , 7'04 



Chromate (bright red) . ... 2-5 3'0 6'0 6'04 



Molybdate 27 3'0 67 6'8 



Tin: Oxide of tin 6'0 7'0 6-5 7"! 



Tin pyrites 3'0 4'0 479 5'1 



Copper: Sulphide . . . . .2-5,, 3-0 5-5 5'8 



Oxide ' . 3-5 4-0 5'9 6-0 



Carbonate 3'5 4'0 4'0 4'1 



Pyrites . . . .... -3'S 4*0 4-15 4'16 



Sulphate 2-2 2-21 



Silico-carbonatc . . . . 2-0 3'0 - 2-0 2-2 



Zinc: Ked oxide . . . . . 4-0 4'5 5'43 5'52 



Sulphide 3-6 4'0 4'02 4'07 



Carbonate 5'0 4-33 4'44 



Silicate . . . . . 3'43 



Antimony: Sulphide ..... 2'0 4'51 4'62 



Jamesonite 2-0 2-5 5'5 6'8 



Minerals associated with Ores. 



Hardness Specific gravity 

 Wolfram . . . . . . . 6-0 to 5-5 7'1 to 7 '4 



Iron pyrites (white) 6'0 6-5 4'67 4'84 



Mundic . 6-0 6'5 4'83 5-01 



Sulphate of baryta 2'5 3'5 4'3 , 4-8 



Carbonate of baryta 3'0 375 4'29 , 4'3 



Carbonate of iron 3'0 4'5 3'73 , 3'82 



Fluor-spar 4'0 3'0 , 3'33 



Quartz or silica 7'0 2-6 , 27 



Carbonate of lime 2'5 3'5 2'5 , 3'8 



Ore-bearing Bocks. 



Specific gravity 



Hornblende rock . . . . . . 2'8 to 3'2 



Syenite 27 3'0 



Trap or basalt , . . . . . 2'8 3'2 



Grauwacke . 2-5 2-9 



Porphyry, trachyte, and felspar . , . ' 2-3 27 



Granite and gneiss 2'4 27 



Mica slate 2'6 2-9 



Clay slate . . . . . . . 2-6 



Limestone and dolomite .... 2'5 2*9 



Sandstone , 2'4 27 



The following general deductions will also be found serviceable: 



First. Absolute perfection in separation according to specific gravity cannot be 

 arrived at, chiefly on account of the irregularity of form of the various grains to be 

 operated upon. 



Second. The more finely divided the stuff to be treated, the greater is the amount 

 of labour and care required, and the more imperfect will be the separation. 



Third. That reducing machine may be considered the most perfect which produces 

 the least quantity of stuff finer than that which it is intended to produce. 



Fourth. It is necessary in determining the degree of fineness to which a mineral 

 should be reduced, to consider the metallurgic value of the ore contained in it, and to 

 set against this the value of the loss which will probably be incurred, together with 

 the labour and expense attendant upon the manipulation. 



Fifth. The vein-stuff should be reduced to such a degree of fineness that the 

 largest proportion of deads and clean ore should be obtained by the first operation, 

 thus saving the labour and preventing the loss incident to a finer subdivision of the 

 ore and more extended treatment. 



Sixth. That apparatus or plan of dressing may be considered the most efficient 

 which, with stuff of a given size, allows at an equal cost of the most perfect separation, 

 and of the proper separation of stuff of nearly equal specific gravity. 



The average percentage to which the crop is to be brought, and the highest 

 percentage to be allowed in the castaways being determined, it is evident that the 

 more perfect the degree of separation the greater will be the amount of crop and 



