136 EECENT COPPEE-EXTEACTIXG PEOCESSES. 



that a digest of tlie yarioiis plans adopted, a comparison of tlieir 

 merits, and an attempt to point out in wMcli particular cases 

 tlieir individual excellence consists, may do mucli good in further- 

 ing the development of the Colony's resources. 



It is sought to impress upon mineral explorers that methods 

 are available for giving a value to mining propertj', without 

 preliminary large outlay ; but it is not intended to imply that, 

 after inexpensive proof of value has been obtained, economy and 

 profit may not be better attained by the introduction of labour- 

 saving appliances, even at great outlay, though it is urged that the 

 large outlay can be deferred until its justification is definitely and 

 conclusively demonstrated. 



Beginning with one of the most simple processes, and one witli 

 which most people are tolerably familiar, that known as the 



StTLPHUEIC A.CID PeOCESS, 



we find that in South Australia, at a mine of some reputation in 

 times past, known as the Kapunda, the sulphuric acid process is 

 in use for the extraction of copper from an ore containing only 

 f of 1 per cent, of metal. But the conditions here are peculi- 

 arly favourable, inasmuch as the mineral operated upon consists of 

 a vast heap of many thousands of tons of debris, or tailings, which 

 have already passed through the dressing machine : consisting 

 principally of oxides and carbonates, it requires no preliminary 

 desulphuration ; while the sulphitric acid is made on the spot 

 from iron pyrites, which exists in great abundance on the pro- 

 perty. The ore is digested in the acid until all the copper is 

 dissolved out, several successive portions being treated in the 

 same liquor up to the point of saturation ; it is then allowed to 

 settle, run off clear into a large vessel containing scrap iron, 

 when the copper is precipitated at the expense of the iron in. the 

 form of cement copper, of about 70 per cent. The quantity of 

 iron dissolved is equal to a little less than the weight of the 

 copper precipitated, in neuti^al solutions ; the cement copper is 

 sold to the smelters, and has only to be passed through the 

 refinery, and run into ingots. The acid is no doubt heated when 

 used, and probably kept nearly up to boiling point, by the intro- 

 duction of a jet of steam, and the material kept agitated to 

 facilitate the action of the acid. Taking 16s. as the value of one 

 unit of metallic copper, and seeing that tliis material contains 

 only I of 1 per cent., or 14 lbs. of copper, in one ton of 

 material, the gross value is only 10s., so that to yield a profit the 

 cost of treatment, including the cost of sulphuric acid, labour, 

 refiniQg of the ceme.nt copper, and wear and tear of apparatus, 

 must be less than 10s. per ton of ore treated. 



Of course it is not supposed that we can readily find places in 

 this Colony where the conditions will be precisely the same — 



