10 COLORADO FERBERITE AND THE WOLFRAMITE SERIES. 



men from Ward, still farther north and beyond the territory which up 

 to this time has been productive, shows a wolframite which is prob- 

 ably not f erberite and which occurs in long, slender crystals of a habit 

 totally different from that of the f erberite of the main tungsten area. 

 Embedded with this mineral in white quartz are pyrite and chalcopy- 

 rite, apparently of the same general age, though the chalcopyrite is of 

 later deposition, as it is pierced by the wolframite. The ore is said to 

 carry both gold and silver. Although the data at hand are not very 

 extensive, it seems probable that the connection between the three 

 classes of veins may be fairly close and that there may not be a great 

 difference in the ages of the several types. The manganese content of 

 the tungsten mineral seems to increase somewhat progressively across 

 the field from the Gilpin County line to Ward that is, from south to 

 north. A few miles south of the tungsten field in Gilpin County pitch- 

 blende has been found in considerable quantity in close connection with 

 gold and silver bearing veins, which lie in the same mineral belt. 

 Forbes Rickard has recently noted 1 a close relationship between the 

 ferberite veins of Boulder County and the pitchblende veins of Gilpin 

 County. 



The ferbftri^ yfflpa much resemble those carrying gold telluride. 

 They occur in sheeted or crushed zones and are reticulated, the indi- 

 vidual veins ranging from a small fraction of an inch to several inches 

 in thickness, while the ore-bearing body may reach a width of 14 feet, 

 as in the Philadelphia mine of the Wolf Tongue Mining Co. The veins 

 cut granite, gneiss, and pegmatite, and though the ore may extend 

 from the granite into the gneiss it may be cut off at the contact, its 

 continuity depending on local conditions, but there are only a few 

 productive veins in the gneiss. 



A d 



CHARACTERISTICS OF THE ORE. 



The amount and character of gangue in the veins differ greatly in 

 differ ent parts of the field. Quartz, the universal vein mineral, occurs 

 in much less quantity in the ferberite veins than in most veins. Only 

 a very little visibly crystallized quartz in the ferberite veins has come 

 to my attention. There is, however, in most if not in all of the veins of 

 the northeastern part of the field, and in many of the wider veins of 

 the southwestern part of the field, a very fine grained gray or brown 

 quartz, known as "bone," which has a fracture much like that of 

 chalcedony and which is largely a replacement of the country rock. 

 The ferberite in the northeastern half of the field appears to be less 

 well crystallized than in the southwestern half. It occurs in some of 

 the veins in minute particles mixed with quartz (see PL VI, p. 15), so 

 that in many places the ore is difficult to concentrate, although the 



i Pitchblende from Quartz Hfll, Gilpin County, Colo.: Min. and Soi. Press, June 7, 1913, p. 852. 



