CHARACTERISTICS OF THE ORE. 17 



but in several specimens of powdered ferberito examined I have not 

 been able to separate it with a horseshoe magnet nor to find it by 

 microscopic examination with reflected light in polished and etched 

 specimens from the Western Star and Nugget claims. In the ore 

 from the Eagle Rock mine, however, a small auantity^of mft f[ 

 material which is probably magnetite was louna. 



MolvMenite. George * and Lindgren 2 report, though Lindgren 

 doubtfully, that molybdenite occurs with the ferberite in Boulder 

 County. I have not seen this association. Molybdenite is a rom- 

 mon associate of wolframite in Queensland 3 and is also found with it 

 in Saxony 4 and England, 5 but the association is rare in this country, 

 though molybdenite occurs with wolframite and tourmaline on the 

 Black Horse claims, 10 miles southeast of Daisy, Stevens County, 

 Wash., and in small quantity with ferberite at Cave Creek, Ariz. 



OpaL Opal mixed with chalcedony and a little limonite forms a 

 thin opaque yellowish-gray coating on ferberite crystals in the Black 

 Hawk No. 1 vein, 1J miles south of Nederland, and is probably a 

 constituent of the siliceous coating on the ferberite from other mines. 



Pyn/r. Pyrite is rare, except where the ferberite veins approach 

 the gold and silver veins, though here and there a little may be found. 

 At one place in the Conger mine a vein of pyrite 2 inches thick cut 

 across the ferberite veins. Iron sulphide in quantities reaching 3.25 

 per cent 8 is indicated by analyses of concentrates from a number of 

 places, as noted under hematite. 



Quartz. -Quartz occurs in all veins in comparatively small quantity. 

 In most places it is so finely granular that it has a fracture like chal- 

 cedony. Very little of it shows crvstalJorm. 



Scheelite. For discussion of the occurrence of scheolite see pages 

 11-12. 



Sphalerite. Sphalerite is noted by George (see Galena, p. 12), and 

 Moses 7 states that he found small yellow crystals upon ferberite 

 specimens from the Boulder field. 



Slvanite. As has been noted, sylvanite occurs with ferberite at 

 George 8 also notes this association in the vein exposed 

 by tne Wheelmen Tunnel in the lower part of the canyon of Boulder 

 Creek and in a mine near Sunshine. 



1 George, R. D., The main tungsten area of Boulder County, Colo.: Colorado Geol. Survey First Kept., 

 p. 75, 1909. 



Econ. Geology, vol. 2, p. 461, 1907. 



'Cameron, W. E., Wolfram and molybdenite mining in Queensland: Queensland Geol. Survey Kept. 

 188, 13 pp., 1904. 



Beck, R.,Uber ein kiirzlich aufgeschlossenes Wolframerzgangfeld und einige andere neue Aufschlusse 

 In sachsischen Wolframerzgruben: Zeitschr. prakt. Geologie, vol. 15, pp. 38,40, 1907. 



Finlayson, A. M., The ore-bearing pegmatites of Carrock Fell and the genetic significance of tungsten 

 ores: Geol. Mag., vol. 7, pp. 19-28, 1910. 



Hills, V. G., Tungsten mining and milling: Colorado Sci. Soc. Proc., vol. 9, p. 149, 1909. 



Moses, A. J., The crystallization of luzonite and other crystallographic studies: Am. Jour. Sci., 4th ser., 

 vol. 20, p. 282, 1905. 



Op. cit., p. 76. 



35659 Bull. 58314 2 



