1116 A TREATISE ON METAMOEPHISM. 



rhodonite, and that in the Golden Fleece vein rhodochrosite "forms with 

 quartz the gangue of the rich free gold ore." a At Rico also, according to 

 Ransonie, rhodochrosite "is important in these mines as a rough indication 

 of good ore." 6 



Since manganese is not a very abundant metal, and since as a sulphide 

 it has j)recedence over all other sulphides in its reactions upon oxidized 

 salts of the other metals, being at the same time transformed to an oxidized 

 product, it is natural to expect that manganese as rhodochrosite and rhodonite 

 would be the dominating forms of manganese minerals in ore veins, and 

 that manganese sulphide would be very rare, and such are the facts. 



While manganese sulphide in many veins has doubtless been an 

 important agent in the precipitation of ores of the first concentration by 

 ascending water, it is probable that the much more abundant iron sulphide 

 is of even greater importance in this connection. Just as oxidized salts of 

 manganese are produced by the precipitation of the valuable metals by 

 manganese sulphide, so the precipitation of such metals by iron sulphide 

 produces oxidized salts of iron. Siderite is an even more important gang-ue 

 in ores of the first concentration than rhodochrosite or rhodonite, thus 

 indicating that the reaction suggested has taken place. Since, however, 

 iron is so much more common than manganese, ordinarily not all of the 

 iron sulphide has thus been oxidized, and hence in the veins pyrite is a 

 very common gangue. 



The reactions which caused the precipitation of the sulphides of the 

 various metals from their oxidized solutions by the sulphides of other metals 

 were not written out by Anthon and Schurmann, but recently Stokes has 

 investigated the reaction in the case of iron sulphide with some of the solu- 

 tions. Thus he has shown that pyrite and marcasite precipitate copper 

 sulphide from cupric sulphate according- to the following reaction: 



5FeS 2 -hl4CuS0 4 +12H 2 0=7Cu 2 S+5FeS0 4 +12H 2 S0 4 . 



This reaction took place at 100° C. and above. Stokes has shown also that 

 where sodium carbonate or potassium bicarbonate is present with the 

 sulphide of iron and carbonates of various metals at 180° C, sulphides are 



« Ransonie, F. L., A report on the economic geology of the Silverton quadrangle, Colorado: Bull. 

 U. S. Geol. Survey, No. 182, 1901, p. 73. 



& Ransome, F. L., The ore deposit of the Rico Mountains, Colorado: Twenty-second Ann. Rept. 

 U. S. Geol. Survey, part 2, 1901, p. 252. 



