THE MINERALS OF IDAHO 55 



evidently having separated during the oxidation. Placer gold is 

 commonly purer than that in the veins of the same area. Further- 

 more the gold of gravel deposits is usually higher in grade the greater 

 the amount of wear and the further it has been transported from its 

 source, which are indicative of the length of time the particles have 

 been exposed to the purifying influences of the ground water. An 

 example of this cited by Lindgren 12 illustrates the progressive 

 refining of the gold in the Warren district. Here vein bullion is 300 

 to 500 fine (30 to 50 per cent Au), the placer gold in small streams 

 is 650 fine (65 per cent Au), that in the larger streams and main 

 creeks is 725 fine (72.5 per cent Au), while the gold along Salmon 

 River derived from this district is 800 to 825 fine (80 to 82.5 per cent 

 Au). For obvious reasons fine particles of gold are more rapidly 

 purified by this process than are larger nuggets. The purest gold 

 known in the State is the very finely divided " flour" gold of Snake 

 River, all of which is better than 900 fine (90 per cent Au). While 

 the view that placer gold becomes purer by the chemical action of 

 ground water in the gravels is well founded, there is no evidence in 

 support of the common fallacy that nuggets of gold grow by accre- 

 tion from solutions in the alluvial deposits. In addition to the 

 chemical purification by the above process, long wear by water tends 

 to eliminate impurities mechanically, the pounding tending to crush 

 and expel the brittle gangue minerals such as quartz. 



Idaho is not known to have produced any exceptionally large 

 masses of placer gold, the maximum recorded weight being in the 

 neighborhood of 40 ounces (Coeur d'Alenes and Idaho Basin). Few 

 samples of placer or lode gold from the State have been available for 

 examination, but such as are in the possession of the National 

 Museum are described below. 



In the following outline the most noteworthy gold localities of the 

 State are mentioned, although a detailed discussion of the occur- 

 rences of this metal in the State would occupy too much space. The 

 figures of production as given are not extremely modern, many of 

 the records being as old as 1896, and do not take into consideration 

 the production of recent years, which in some cases exceeds that of 

 the earlier period. They serve, however, to indicate the relative 

 commercial importance of the various mines or districts. The ar- 

 rangement follows the outline given in the list of Idaho mining dis- 

 tricts above. 13 



" 2 Waldemar Lindgren. 20th Ann. Rept. U. S. Qeol. Survey, pt. 3, p. 242, 1900. 



1 3 The data given in this outline are not in any sense original, but are compiled, without further specific 

 acknowledgment, from the several works cited in the bibliographic references given, for each of the nu- 

 merous mining districts, in the preceding pages. 



