REPLACEMENT ORE DEPOSITS IN THE SIERRAS 



399 



of three powdered feldspars separately in 50 cm a distilled water, 

 at 70 F., with the following results: 



Percentage of alkali 

 dissolved 



0.16 K,0 

 0.07 N 2 

 0.09 N 2 



Orthoclase 



Albite (Amelia Co., Va.) 

 Oligoclase (Bakersville, N. C.) - 

 This would show a greater solubility for orthoclase than for 

 albite, but it is more to the point to observe the relative solubil- 

 ity of the feldspars with water charged with carbon dioxide. 

 R. Midler 1 obtained the following results : 



SOLUBILITY OF METAL OXIDES OF FELDSPARS IN CARBONATED 



WATER 



It is clear here that the soda of the oligoclase is more solu- 

 ble than the potash of the orthoclase, and that the lime of oli- 

 goclase is more soluble than the alkali. No quantitative state- 

 ment of the solubility of pure albite in carbonated waters has 

 been noted. The apparent readiness with which the albite of the 

 dike rocks described in the paper goes into solution and is again 

 deposited as albite in cracks, seems certainly to indicate that 

 under certain unknown conditions this mineral is readily soluble. 

 Dr Becker 2 describes the Treadwell mine on Douglas Island 

 in Alaska as being an impregnation of a dike of sodium syenite, 

 which has been mineralized in apparently exactly the same way 

 as the sodium syenite dikes of the Mother lode above described. 

 Becker states that the Treadwell syenite is composed chiefly of 

 albite with subordinate amounts of soda-lime-feldspar, augite, 

 amphibole, and biotite. 



The ore associated with the syenite is separable into two distinct varieties. 

 Of these one consists of stringers of quartz carrying some calc.te and occupy- 

 ing interstitial spaces between more or less decomposed syenite fragments. 

 'Braun's Chemische Mineralogie, 1896, p. 39^- 

 'Eighteenth Ann. Rep. U. S. Geol. Surv., Part III. p. 38 and p. 64. 



