52 HATCH : THE KOLAR GOLD-FIELD. 



slimes are settled and the excess water is drawn off. Cyanide solu- 

 tion is then added and the slimes agitated by a centrifugal pump 

 or other mechanical means for a short time ; they are then allowed to 

 settle and the clear solution carrying about 80 per cent, of the gold is 

 drawn off. 



It is stated on the Kolar field that the direct process would not 

 be a success, as exposure to the atmosphere for a considerable time 

 is essential to successful leaching. This of course is a matter for 

 experiment, which I hope will be made, as the successful initiation 

 of the direct method would lower working costs. 



The following details of the plant in use and of the materials con- 

 sumed at some of the mines were collected : — 



At the Mysore Mine there are separate plants for the treatment 



of the mill-tailings and of the old accumulations of tailings and slimes 



that have been through the Wheeler pans. The plant for mill-tailings 



from the 120-stamp mill (see PI. 19) has a nominal capacity of 10,000 



tons per month. It consists of nine steel percolating vats of 30 feet 



diameter by 6 feet deep ; four masonry sumps of 28 feet diameter and 



8 feet deep ; and one steel reservoir of 30 feet diameter by 8 feet 



deep. The average charge assay is 3 dwts. 17 grains per ton; and 



the average discharge assay 1 dwt. 8 grains per ton, the extraction 



being 64 per cent. The strength of the strong liquor is o'28 per cent. 



Consumption of cyanide, i^lbs. and of zinc, '15 lbs. per ton treated. 



The other plant has a nominal capacity of 4,000 tons per month. It 



consists of 12 circular wooden percolating vats of 21 feet 6 inches 



diameter by 4 feet deep: three sumps and two reservoirs of 22 feet 6 



inches diameter by 6 feet deep. The average charge assay is 2 dwts. 



8 grains, and the average discharge assay 1 dwt. and 20 grains per 



ton ; the extraction being also 64 per cent. The strength of the 



strong liquor is 0*12 per cent. Cyanide consumption, i'2lbs., zinc 



consumption, o*i4lb. per ton treated. On the average o*681b. of 



mercury are recovered from each ton of slimes treated. During the 



year 1899, 57,815 tons of tailings were treated, yielding 7,290 ounces 



of bullion and 23,743 tons of slimes (old accumulations from Wheeler 



pans) yielding 2,032 ounces of bullion. 



