576 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



trict in the adjoining countiy rocks he was led to make extended investiga- 

 tions of the comatiy rocks of ore deposits in general, not contenting himself 

 with a simple lump analysis of the rock, but sepai-ating out its individual 

 constituents and analyzing them separately. He now claims that he has 

 thus been able to discover all the metals occurring in veins, and that they 

 are mainly contained in the basic silicates of crystalline rocks, such as mica, 

 hornblende, and augite. He has also analyzed the waters of man}^ thermal 

 springs, and concludes that the metals contained in these are not deposited 

 in their channels, but only at the mouths, where they are practically in con- 

 tact with the atmospliere, and, while he considers further similar investiga- 

 tions desirable, he holds that what he has already determined proves the 

 general inapjjlicabilit}" of the thermal-spring origin for fissure veins, which 

 have mostly been formed at depths where the influence of the atmosphere 

 would not be felt. Whether Dr. Sandberger's conclusions be accepted in 

 their entirety or not, the results of his investigations are certainly very sug- 

 gestive. Both he and Bischof consider the silicates more probable sources 

 of the metals than the disseminated pyrites so abundantly found in erup- 

 tive rocks, which they hold not to be original constituents thereof 



In the present investigation it was not feasible to follow Sandberger's 

 method of analyzing the separate constituents of all the diflferent rocks, 

 which involves a great expenditure of time and the use of elaborate chem- 

 ical apparatus. Moreover, the porphyries in the vicinity of LeadviJle con- 

 tain no basic silicates in a sufficiently undecomposed state to be separated 

 out. Lump analyses alone were then practicable, but by the employment 

 of dry methods it was possible to make a greater number of tests and detect 

 extremely minute traces of silver and gold, which by Sandberger's method 

 could hardly have been found. Lead and barium were also sought for in 

 the wet way. The other principal constituents of the ores, silica, iron, and 

 manganese, are so universally disseminated that a special search was con- 

 sidered unnecessar}'. The methods pursued and the details of the results 

 obtained are set forth in Appendix B. More than twice the number of 

 assays there given for gold and silver were originally made, but after they 

 had all been completed a possible source of error was discovered, which led 

 to a repetition of the test in the case of all for which material remained. 



