COLLECTIONS IN ECONOMIC GEOLOGY AND METALLURGY. 27 



After the amalgamation is complete the material is run out from the 

 pans into settlers, which are similar to the pans, except that they do 

 not grind. In these the i)ulp is made much thinner by the addition of 

 water, and the agitation of the material is so graduated as to keep the 

 fine light ore in suspension, and to allow the heavy amalgam and mer- 

 cury to sink to the bottom. 



From time to time the water holding the waste material in suspension 

 isdrawnoffat the top, and the amalgam and excess of mercury from the 

 bottom. After leaving the mill the water carrying the tailings, or waste 

 material, is allowed to deposit the tailings, which soon accutnulate in 

 large amounts. 



The object of the whole operation is to remove as much as possible 

 of the silver, so that these tails will be worthless. They are never entirely 

 free from silver, and in some cases, owing to the bad working of the 

 mill from various causes, or to a special rebelliousness of the ore, they 

 have to be run through the mill again. In some cases, while yet con- 

 taining a considerable amount of silver, they are allowed to accumulate 

 until they can be treated more cheaply'. 



The amalgam from the settlers is thrown into stout canvas bags, which 

 retain the amalgam, but allow the excess of mercury to strain through; 

 this mercury is then ready to be used over again. The hard dry amal- 

 gam remaining in the strainers is collected, put into cast-iron retorts, 

 and heated to drive off the mercury, which is collected and is ready for 

 use again. The silver sponge or bullion remaining in the retort is 

 melted in crucibles, and cast into ingots of suitable size. 



The fineness or amount of silver in 1,000 parts of this bullion varies 

 greatly, and depends upon the character of the ore, since the other 

 metals found associated with the silver are affected more or less in the 

 same way as the silver, and follow along through the whole operation 

 with it, and are found in the bullion. This impure bullion has to be 

 subjected to a refining operation in order to separate the silver, this, 

 however, is generally carried on at a separate works, and especially at 

 the mints. 



A cross-section of a mill suited to this operation is shown in pl. hi 

 and the interior of a pan mill for extracting the silver by amalgamation 

 in PL. IV. 



To illustrate this operation two collections are shown. The first is 

 from the Ontario Mill, Park City, Summit County, Utah, and the sec- 

 ond from the Moulton Mill, Butte, Silver Bow County, Montana. 



THE OXTARIO MILL. 



This mill treats only the ores extracted from the Ontario tnine. The 

 ores from the Ontario mine, in the upper levels, consist of entirely de- 

 composed material, being quartz stained by decomposition products, 

 but in the lower levels unaltered sulphides make their appearance, 

 especially galena, blende an<l tetrahedrite. Imbedded in the compact 



