6 BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



the lighter material will float away leaving the gold and heavier min- 

 erals behind. Mercury is often used to catch and hold the gold. Nug- 

 gets of gold of considerable size are picked by hand from the ore, and 

 occasionally very large masses are found. 



The simplest of all washing tools is the pan or batea, in which the 

 ore is broken np iu successive portions of water, the large pebbles 

 picked out by hand and the lighter material removed by giving the 

 water a peculiar circular motion. This operation is continued until 

 nothing but the gold anil heavier minerals remain. A final delicate 

 manipulation spreads the material in the pan into a form like a fan 

 with the gold at the point, and it can then be scraped out of the pan 

 free, or nearly so, from the heavy minerals. This process is applicable 

 only to the richer portions of the deposits. 



Poorer ores are treated in various hand-rocking arrangements, such 

 as cradles and long toms, through which water runs while the ore is 

 thrown in and broken up, both by the water and the shovel. Still 

 poorer ores are treated in ditches and channels, where the heavy ma- 

 terials are caught by riffles, and sometimes reworked in rockers. 



For carrying on the extraction of placer gold a good supply of water 

 is required, and the absence of sufficient water limits the working of 

 some deposits to the richest portions, while the working of other de- 

 posits is prohibited altogether by this cause. The extraction of gold 

 from this material is very irregular and uncertain, especially in newly 

 discovered regions, since there is no way of predicting the richness or 

 extent of the sand. 



Gold separated from placer deposits is fully illustrated in the free 

 gold series of mineral specimens. 



To illustrate the special variety of placer gold, known as hydraulic 

 gravel, five specimens are shown : 



(1) Sbovv'iug several Hakes of free gold, rich material ; taken 18 feet above bed 

 rock, 46 feet above bottom of cbauiber. (The specimen has been varnished to pre- 

 vent disintegration.) French Corral Mine, Nevada County, California. (14864.) 



(2) Showing the ordinary run of the material. (The specimen has been varnished 

 to prevent disintegration.) French Corral, Mine, Nevada County. California. 

 (148fM.) 



(;{) Showing free gold. Indian Hill Gravel Mining Company, Gold Run, Placer 

 County, California. (14878.) 



(4) Showing the ordinary run of the material. (The specimen has ,)een varnished 

 to prevent disintegration.) Cherokee Butte Mine, Cherokee Flat, Butte County, 

 California. (1488:i.) 



(5) Showing the ordinary run of the material. Brewer Mine, Chesterfield County, 

 South Carolina. (.S55.J9.) 



QUABTZOSE GOLD ORES. 



These ores are generally known as gold quartz or gold-bearing or 

 auriferous quartz, but frequently contain large amounts of other mate- 

 rial besides quartz. 



