560 MINING INDUSTET. 



The percentage of the value contained in the rock which this yield 

 represents cannot be very definitely stated, because the actual value of the 

 ore before treatment can only be approximately estimated. But few assays 

 of stamp-rock are made, and even if their number were multiplied many 

 fold, the difficulty of getting fair representative samples of ore, in which the 

 percentage of gold is not only very small but also very irregularly distributed, 

 would stand in the way of obtaining absolutely certain results. The tailings 

 afford more reliable samples, because by the crushing of the ore, and the 

 consequent intimate mixture of its particles, the whole mass becomes more 

 uniform in character ; but in the course of the milling process there is, doubt- 

 less, a little, and possibly much, of the gold washed away in the stream and 

 carried beyond recovery in the tailings. How much this may be is variously 

 estimated and probably over-estimated by maiiy. Judging, however, of the 

 efficiency of the work by the contents of the tailings or residue alone, it 

 would appear that the proportion of the original value of the ore that is 

 extracted by the usual milling process, not including the subsequent pro- 

 duct of the tailings, does not much, if at all, exceed 50 or 55 per cent, of the 

 gold contained, and a small percentage of the silver, the value of which is, 

 practically, unimportant. 



In this connection the following results of some experiments made by 

 the First National Mining Company are interesting. This company, while 

 working their claim, on the Burroughs lode, adjoining that of the Ophir, 

 caused a series of assays to be made of the ore before sending it to the crush- 

 ing mill. The quantity treated during the last four months of 1869 amounted 

 to over 1,100 tons. A sample, consisting of a shovelful of rock, was taken 

 from the front and rear end of each wagon load of ore, as it was sent from the 

 mine. The accumulated samples of each week were mixed together and 

 crushed, and one sample for assay obtained from the lot ; thus affording one 

 assay for about 80 tons of ore. The table shows the number of tons crushed; 

 the assay value, in coin, per ton, as determined by the method just described, 

 showing the proportionate value of the gold and silver, the yield per ton in 

 coin, and the percentage of value obtained. The last column shows the rela- 

 tion of the yield obtained to the assay value of the gold alone, disregarding 

 the silver, since the percentage of that metal which is saved is not only very 



