93 



pounds of the metal in the veins that were deposited at 

 approximately the same time as the cobalt-nickel minerals. 

 The present writer believes that at least by far the greater 

 part of the native silver is of primary origin. The recent 

 interesting experiments of Messrs. Chase Palmer and 

 Edson S. Bastin,* on the precipitation of silver from solu- 

 tions by cobalt-nickel minerals, appear to confirm the 

 opinion that the native silver is a primary deposit, and did 

 not come from the decomposition of silver compounds in 

 the veins. The work of these gentlemen shows that where 

 silver solutions come in contact with cobalt-nickel minerals 

 the silver is deposited rapidly and essentially as native silver. 

 Since there is much calcite in the veins with the native 

 silver, it would appear that the metal was carried in solution 

 as a carbonate,- or double carbonate. Under ordinary con- 

 ditions of temperature and pressure, silver carbonate is 

 slightly soluble in water. For example, sufficient of the 

 carbonate can be dissolved in an ordinary beaker of water 

 to make a distinct precipitate of metallic silver when cobalt- 

 nickel minerals are placed in the beaker. 



It has been proved, by the experience gained in mining 

 at Cobalt, that the presence of rich silver ore is dependent 

 on proximity to the diabase sill. Over much of the pro- 

 ductive area, not only the upoer wall of the sill but the sill 

 itself and more or less of its foot- wall have been removed 

 by erosive agencies. Owing to little of the upper or hang- 

 ing wall remaining in the productive area, most of the ore 

 has come from the foot-wall of the sill, or from what was 

 the foot-wall before erosion took place. In these veins, in 

 the foot-wall of the sill, it is the exception to find rich silver 

 ore extending more than two or three hundred feet below 

 the surface. Most veins are productive to a lesser depth. 

 After rich silver ore disappears, with increase in depth, 

 cobalt-nickel ore frequently continues downward in the veins. 

 This seems to be due chiefly to the strong precipitating 

 effects that the cobalt-nickel minerals had on the silver in 

 the waters that worked downward beneath or along the sill. 

 The silver was deposited before it reached a great depth. 

 In certain cases, where veins with cobalt-nickel minerals 

 contain no rich silver ore. or in which the silver extends to 



•Ec. Geology, March, 1913. 



