THE OXIDE ORES. 1127 



from this ferric iron hematite can he produced by the action of certain 

 carbonates and alkaline carbonates without oxidation. By reactions of 

 zinc, lead,. and silver carbonates with an excess of alkaline bicarbonate, he 

 has produced hematite according to the following reactions: 



8FeS 2 +14ZnC03+Na 2 C0 3 =4Fe i 3 -t-14ZnS+Na 2 SjOj+15C0 2 

 8FeS 2 +14Pb0O 3 +Na 2 CO 3 =4Fe 2 O 3 +14PbS+Nai ! S 2 O 3 +15OO 2 



8FeS 2 +15Ag 2 C0 3 +Na.,C0 3 =4Fe 2 3 +15Ag 2 S+Na 2 SOi+16c6, 



He has also produced hematite from the sulphide through the reaction of 

 the alkaline carbonate alone at temperatures of 100° C. and 190° C, thus: 



8FeS 2 +15Na 2 C0 3 ^4Fe 2 3 4-14Na 2 S+Na 2 8 2 3 +15C0 2 



This last reaction is reversible, but Stokes remarks it will proceed to an 

 end if the sulphide and thiosulphate be carried away, as by a circulating 

 solution, or if there be present a metallic salt capable of precipitating 

 the alkaline sulphide as fast as it is formed, as in the first three reactions 

 above given. 



cassiterite. — In reference to cassiterite (Sn0 2 ) Lindgren calls attention to 

 the work of Winkler, Sandberger, and Verbeek, which shows that tin 

 "may be held in solution and deposited at ordinary pressure by thermal 

 waters'" 1 However, in this connection it is to be remembered that both 

 Vogt and Beck strongly insist that cassiterite is formed, to use the words 

 of Vogt, "by eruptive after-action." Vogt says of the cassiterite veins that 

 their "material contents were extracted from the not }^et fully congealed 

 granite." 6 Further, Vogt and Beck, if I understand them correctly, follow- 

 ing Elie de Beaumont and Daubrde, regard the extraction from the "not 

 yet fully congealed granite" as accomplished by pneumatolytic processes. 

 Upon the point that tin ore may be thus formed I express no opinion. 



I do not doubt that tin, like other metals, has been transported by 

 underground waters, and from such solutions precipitated as cassiterite. 

 As is well known, tin may be readily carried by water as the sulphate, 

 nitrate, or chloride, and doubtless is also transported in other forrns. From 

 stannic solutions at ordinary temperatures hydrated stannic oxide is tin-own 

 down by the alkaline carbonates. It may be that at the relatively high 



a Lindgren, Waldernar, Metasomatic processes in fissure veins: Trans. Am. Inst. Min. En». vol. 

 30, 1901, p. 625. 



6 Vogt, J. H. L., Problems in the geology of ore deposits: Trans. Am. Inst. Min. Kng., vol. 31, 

 1902, p. 135. 



