GOLD AND SILVER MINING 211 



the owner, with the aid of his aged mother. Tlie modern 

 stamp mining process is described as follows: 



''Gold stamp milling is that particular process in which 

 a heavy cylindrical body is made to fall upon the ore in such 

 a manner as to crush it, and thereby facilitate a separation 

 between the gold and the vjduelcss minerals by which the 

 gold is incased. The latter weigh less than the former and 

 are removed by the aid of water. The gold is then collected 

 through the agency of mercury, with which it readih^ forms 

 an alloy or amalgam. From this combination it is finally 

 extracted by the distillation or retorting of the mercur}^ 

 The mechanism of the stamp acts on principles similar to 

 those underlying the crudest devices used by man. It may 

 be likened to a hammer, of which the shoe is the hammerhead, 

 the stamp stem is the handle, and the die is the anvil. The 

 ore itself has been compared to a nut struck by a hammer, 

 whose blow has separated the valueless shell (the quartz) 

 from the valuable kernel (the gold). Water covers the 

 die and the ore lying upon it. The blow of the falling stamp 

 not only crushes the ore but also causes a violent pulsation 

 of the water. That pulsation becomes converted into an 

 irregular splash against the sides of the mortar. The latter 

 has an opening in front through which the water is dis- 

 charged, carrying with it the crushed ore. This, called the 

 pulp, spreads itself over tables placed on an inchne, which 

 are lined with a metal, usually copper, having an amalgamated 

 surface, such as will arrest the particles of gold and at the 

 same time permit the grains of quartz and other valueless 

 material to pass over it and out of the mill." 



With the further progress of gold mining a point was 

 reached where the stamp mill was found inadequate. After 

 the gold bearing veins had been worked to a certain depth 

 usually a few hundred feet, below the surface, the gold would 

 cease to be free milling and, because of the lack of those 

 changes which are due to the penetration of water from the 

 surface, would become refractory, that is, locked up in union 

 with iron pyrite and other materials, so that it would not 

 amalgamate with quicksilver. Many mines were abandoned 

 when the free milling ores gave out. In Gilpin county, Colo., 



