THE TELLUKIDE ORES. 1125 



produced in nature not by the reaction of metallic tellurium but by tellu- 

 rous salts which, according to Lenher, precipitate silver by the following- 

 reactions : 



(a) 2TeCl,+H,0=Te+TeCl 4 +H 2 



(b) 4AgNb 3 +3Te=2Ag 2 Te+Te(NO s ) 4 



While the reactions given may possibly explain the formation of a 

 part of the silver telluride in the rare mineral hessite, it is to be remem- 

 bered that pure silver telluride is very exceptional. 



Commonly, so far as silver occurs Avith tellurium, it is in minerals in 

 which there is also telluride of gold, and frequently telluride of lead, mer- 

 cury, and antimony. It therefore follows that the conditions under which 

 the telluride of silver is precipitated must be the same in most cases as those 

 which cause the formation of the 'telluride of gold. Hence the solution of 

 the problem of the precipitation of tellurides of gold will probably also be 

 the solution of the problem of the precipitation of the telluride of silver. 



The oxide ores that are deposited by ascending water below the belt in 

 which the effect of descending* waters is evident are dominantly hematite 

 (Fe 3 3 ) and magnetite (FeO . Fe 2 3 ), and possibly zincite (ZnO), franklinite 

 ((FeZnMn)O . (FeMn) ? 3 ), and cassiterite (Sn0 2 ). 



The association of hematite and magnetite with the sulphides of the 

 first concentration far below the belt where oxidizing waters can act is so 

 well known that it is not necessary to amplify by giving illustrations. 



So far as I know the chief occurrences of zincite and franklinite in 

 deep-seated deposits with no evidence of superficial oxidation are in New 

 Jersey, especially at the famous localities of Franklin Furnace and Sterling a 

 It is notable that here magnetite also occurs associated with the zincite and 

 franklinite. Magnetite associated with pyrite and marcasite occurs very 

 extensively in the Lake Superior region, especially in Canada, although 

 these minerals are found together on the south shore of Lake Superior, as 

 at the Republic trough. The question at once arises whether the metals 

 were transported to their present positions in solution and deposited by 

 ascending waters, or, on the contrary, were produced by alterations of solid 



<*Kemp, J. F., The ore deposits of Franklin Furnace and Ogdensburg, New Jersey: Trans. New 

 York Acad. Sci., vol. 13, 1893-94, pp. 76-96. 



