Art. XIII. — Notes on the Dressing of Tin Ore. 

 By J. Cosmo Newbery, B.Sc. 



[Read 9th August, 1883.] 



During the past five years numerous tin-bearing lodes have 

 been discovered in this and other Australasian colonies. 

 The mines have been opened and expensive machinery 

 erected, but the results in many instances have been dis- 

 appointing to the investors. A great many samples of these 

 ores have passed through my hands for assay and report, 

 and I have come to the conclusion that, in part at any rate, 

 the disappointment has been due to the want of a proper 

 consideration of the question of how best to extract the 

 ore from the gangue or associated mineral matter. This is 

 especially the case where the gangue is a hard quartzose or 

 granitic rock. According to the general custom, these ores are 

 reduced to fine sand in the ordinary stamping battery, such 

 as is used to reduce our auriferous ores. The latter, of course, 

 require to be crushed very fine, so that the small particles 

 of gold may be beaten out and separated from the quartz ; 

 but in the case of these tin ores this fine, crushing reduces 

 the brittle tin stone to a slime, while the hard tough rock 

 with which it is associated is being converted into sand. 

 With this result the separation of the tin ore becomes a 

 matter of very great difficulty, for we have forgotten the 

 cardinal principle of ore-dressing, which is, that the ore 

 shall not be broken finer than is absolutely necessary to 

 separate the rich mineral from the gangue or accompanying 

 rock, and it would be well, I think, to remind those who are 

 engaged in this work of the following general principles of 

 ore-dressing : — 



" 1. Absolute perfection in separation according to specific 

 gravity cannot be arrived at, chiefly on account of the 

 irregularity of the various grains to be operated on. 



" 2. The more finely divided the stuff to be treated, the 

 greater is the amount of labour and care required, and the 

 more imperfect the separation. 



" 3. The reducing machinery may be considered the most 

 perfect which produces the least quantity of stuff finer than,, 

 that which it is intended to produce. 



