PRECIOUS MET A I N r,'. 



Telluride District: In the vicinity of Telluridc there is a very 

 interesting development of veins. The Smuggler vein is very 

 persistent. It is definitely known that it extends four miles 

 across the high divide that separates the Marshall basin from 

 the valleys of Canon Creek. Many of the veins consist of closely 

 spaced fissures filled with ore. The pay portion rarely comprises 

 the entire vein but rather forms a narrow strip following either 

 the hanging wall or the footwall. The gold is often encased in 

 pyrite and chalcopyrite with quartz gangue. The silver is in the 

 galenite and freibergite, but the double sulphides of silver with 

 antimony and arsenic, as polybasite, stephanite and proustite 

 are known. According to" F. L. Ransome the downward percola- 

 tion of meteoric waters dissolved the alkalis from the andesites and 

 rhyolites as sulphides. These solutions rose in temperature as 

 they approached the magma and became charged with sulphuric 

 and carbonic acids derived from volcanic sources. These acids 

 gathered the metals and their gangue minerals from the more 

 basic material and while penetrating the open spaces of the fis- 

 sured zone, deposited the metals and gangue minerals at higher 

 altitudes. The carbonates were deposited upon the walls of the 

 fissures while the gold, to some extent, penetrated the walls. 



Silverton: The Silverton district lies to the east of the Tellu- 

 ride. The Tertiary volcanics are separated from the Carbon- 

 iferous terranes by a conglomerate. According to H. Ries, the 

 ore depoits fall into three classes. (1) Lodes, which include 

 most of the known productive deposits, (2) stocks, which in- 

 clude most of the ore bodies formally worked on Red Mountain, 

 and (3) metasomatic replacements, which comprise a few de- 

 posits in the limestones or rhyolites. 



The lodes occur in all terranes from the pre-Cambrian to the 

 Tertiary irruptives. 



The Tertiary fissuring is most pronounced in a northeast and 

 southwest direction. The lodes are simple fissure veins. Some- 

 times these veins bear both native gold and silver. The gold is 

 often encased in chalcopyrite and the silver in galenite, tetrahe- 

 drite and enargite. The common gangue minerals are quartz and 

 calcite. The ores were deposited from hot ascending solutions 

 with depth of origin unknown. 



Ouray District : The Ouray district surrounds the picturesque 

 city of Ouray. The terranes comprise limestones, conglomerates 

 quartzites, sandstones and shales overlain by Tertiary volcanics. 



