TREATMENT OF THE COMSTOCK ORES. 245 



Relation of Yield to Assay Value. — A glance at the columns of 

 tlie foregoing tables, stating the percentage of the assay value obtained by 

 milling, will show that the yield frequently exceeds sixty-five per cent, of 

 the contained value. This is indeed more notable in the first of the two 

 years referred to, because in the last year the ore of this mine has not only 

 been of lower grade but has carried with it more base mineral, rendering 

 the extraction of the precious metals more difficult, and consequently dimin- 

 ishing the yield obtained. 



The impression generally existing that only sixty-five per cent, of the 

 value is obtained by pan process and that thirty-five per cent, is lost is erron- 

 eous ; for the return of sixty-five per cent, is based on the result of treating 

 the ore in the pan and collecting the amalgam in the settler ; in some mills 

 the additional product of the agitator is returned with that of the pan and 

 settler, while in other mills this is not done, especially if the required stand- 

 ard of sixty-five per cent, has been already reached by pan and settler with- 

 out further addition. Moreover, the return of sixty-five per cent, includes 

 nothing of what is, or may be, obtained from the subsequent treatment of 

 slimes and tailings ; and, furthermore, it is to be considered that the ore, as 

 charged to the account of the mill, contains an average of six or seven per 

 cent, of moisture, for which, in the return, no allowance is made ; the sample 

 for assay, by which the return is made, being previously dried, sixty-five per 

 cent, of the dry sample is really equivalent to sixty-nine or seventy per cent. 

 of the wet rock. 



This may be illustrated by the following data, concerning the operations 

 of the Savage mill, during six months ending December 31, 1867. 



During that time 5,830 tons were worked. The assay value of this ore 

 was $318,639 80 per mill samples, and $324,206 72 per wagon samples ; or 

 $54 65 per ton, by mill samples, and $55 61 per ton, by wagon samples. 

 The total yield obtained was $220,785 17 ; equal to 69^ per cent., by mill 

 samples, and 6Syo per cent, by wagon samples. This yield was obtained by 

 the ordinary operation of crushing, amalgamating in the pan, and collecting 

 the amalgam in the settler ; this much constituting the process to which all 

 ore is submitted in all mills. It will be observed that the required standard 

 of sixty-five per cent, was already exceeded by this alone, without including 



