268 



KEMPS ORE DEPOSITS. 



to the ore-bearing solutions. The ores are deposited in both meta- 

 morphic and unaltered sedimentary rocks. 



2.15.03. Example 50a. Sulphur Bank. This is in the same 

 general region as the last, but from its peculiar character has been 

 one of the best known of ore deposits. A great flow of basalt has 

 come down to the shores of Clear Lake from the west. Waters 

 charged with alkaline (including ammonia) carbonates, chlorides, 

 borates, and sulphides, and with CO 2 , H 2 S, SO 2 , and marsh gas, 

 have circulated through it. Sulphur and sulphuric acid have 

 formed at the surface, and the latter has dissolved the bases of 

 the rock, leaving pure white silica behind. Lower down, cinnabar 



FIG. 66. Section of the Great Western cinnabar mine. After G. F. 

 Becker, Monograph XIII. , U. S. Geol. Survey, p. 360. 



is found, both in the basalt and in the underlying sedimentary 

 rocks, with other sulphides and chalcedony. Leconte attributed 

 its precipitation to cold surface waters, charged with sulphuric 

 acid, which trickled down and met the hot alkaline solutions. 

 Becker refers the same -to the ammonia set free toward the sur- 

 face by diminished heat and pressure. The California cinnabar 

 deposits have been often, but wrongly, referred to vapors of the 

 sulphide volatilized by internal heat and condensed above. 



2.15.04. Example 50&. Steamboat Springs, Nevada. These 

 springs are in Nevada, only six miles from the Comstock Lode. 

 Granite is the principal rock, while on it lie metamorphic rocks 

 of the Jura-Trias, and much andesite and basalt. The hot springs, 

 coming up through small fissures, deposit chalcedony in some 



