Il8 THE RAND GOLD MINING INDUSTRY. 



greater value to the State, and supports a much larger proportion 

 of the community than does a small rich mine. A mine crush- 

 ing ore under 5 dwt. per ton in value contributes nearly half as 

 much again of the indirect taxes included in working costs per 

 ounce of gold recovered as does a 7}^ dwt. mine. The value 

 of the gold-mining industry to South Africa is peculiarly evi- 

 dent at the present time, when, but for our gold export, the 

 whole country would have but little to send in return for its 

 many million pounds' worth of imports in the shape of food- 

 stuffs and manufactures. 



The paper b}- the author previously referred to was written 

 shortly after the ending of the South African War, when the 

 mining industry had hardly recovered from a prolonged sus- 

 pension of its activities. Large though the scale of operations 

 was at' that time, the scope of these has now greatly increased, 

 and various possibilities foreshadowed in the paper are now 

 routine actualities. Among these is the economic increase of 

 the percentage recovery of the gold contents of the ore, then 

 estimated at 90 per cent. The possibility of increasing this per- 

 centage to any desired figure by finer crushing of the ore, 

 causing more perfect exposure of the gold particles, and more 

 efficient cyanide treatment, was indicated ; the use of tube-mills 

 for finer crushing has now enabled the amount of gold lost per 

 ton of residue to be reduced to one-quarter of the pennyweight 

 per ton of ore, then stated to be the usual total residue value. 

 At the present time, in a well-equipped and adequate modern 

 reduction plant, and at a cost well under the value of i dwt. of 

 gold, a total residue worth only about is. per ton can be pro- 

 fitably obtained,* which, on ore assaying 8 dwts. per ton in value, 

 would be equivalent to an extraction of 97 per cent. This per- 

 centage would be capable of still further increase but for the 

 consideration that " metallurgy "' is the art of making money 

 out of ores," and that the treatment operations involved must 

 hence stop short of the point where any additional gold re- 

 covered would cost more to obtain than its value. Such limit 

 is not, however, a fixed standard since a variation in the cost 

 of any factor involved in ore treatment, such as labour, power, 

 stores, or changes in local conditions, immediately raises or 

 lowers working costs, and consequently the " economic limit "of 

 extraction. 



With reference to the improvements in metallurgical 

 methods, detailed progress is constantly being made, which in 

 the aggregate is of great importance, although a device or 

 method merely " dift'erent " is liable at times to be mistaken for 

 something " better." Radical improvements, however, occur 

 seldom, and in the history of the Rand few can be reckoned as 

 such beyond the application of the cyanide process, first for 

 the leaching of sand, and subsequently for the decantation treat- 



* Annual Report of the Consolidated Gold Fields of South Africa for 

 the year ended 30th June, iqt-I. P- -^o- 



