

12 COLORADO FERBEEITE AND THE WOLFRAMITE SERIES. 



Co.'s claim at Crisman are lined with clear brownish and colorless 

 scheelite crystals, the largest three thirty-seconds of an inch (2 milli- 

 meters) thick. Vugs in ore from the Bogers tract, near the center of 

 the area, are lined with reddish-brown scheelite, which also occurs 

 through the quartz in small quantity. Some of the vugs are of almost 

 microscopic size. (See PL V.) As seems to be usual in tungsten 

 deposits, the scheelite formed later than the mineral of the wolframite 

 series, but it is not a secondary mineral. In cleaning certain ferberife 

 crystals with hydrofluoric acid deep pits with rather regular outlines 

 I are made, accompanied by the formation of yellow tungsten trioxide, 



I and it seems possible that the pitting may be due to the removal of 

 scheelite. 



MINERALS ASSOCIATED WITH THE FERBERITE. 



Associated minerals, other than quartz, are few and scarce in the 

 ferberite veins of the main part of the field. Near the gold-silver 

 bearing areas there is of course a mixture of the minerals of the several 

 vein groups. 



The following minerals accompany ferberite in the veins: 



Adularm. Adularia forms a coating one-sixteenth of an inch (2 

 millimeters) thick on the walls of the Black Hawk No. 2 vein, 1J 

 miles south of Nederland. It is beneath most of the ferberite, but 

 was probably deposited with the first of the ferberite. Adularia in 

 microscopic grains is found in many of the veins. 



Calcite. The gangue in the Conger mine carries microscopic parti- 

 cles of a carbonate, which is probably calcite. 



Chalcedony. Chalcedony mixed with more or less opal and hydrous 

 iron oxide coats crystals from many of the veins. 



Chalcopyrite. Chalcopyrite occurs at Ward in veins carrying some 

 wolframite, which seems to approach ferberite in composition, though 

 no analysis of the mineral is at hand. 



Galena. George 1 reports the occurrence of galena and sphalerite 

 in veins with ferberite near Magnolia. The galena is said to occur 

 generally in minute cubes but in considerable quantity. 



Gold and silver. Gold and silver are reported to occur in some of 



^^^^VBMiBB^ * 



the ferberite veins other than those in which sylvanite is present. 

 In the ore seen which is said to be gold-bearing small quantities of 

 sulphides are present and the gold is probably associated with the 

 pyrite. Hills 2 states that eight assays of concentrates gave an 

 average of 0.01 ounce of gold to the ton. 



Greenawalt 3 gives three analyses of concentrates which carried 

 silver hi quantities of 1.2, 2.4, and 3.1 ounces to the ton. The speci- 



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

 p. 75, 1909. 



* Hills, V. G., Tungsten mining and milling: Colorado Sci. Soc. Proc., vol 9, p. 150, 1909. 



'Greenawalt, W. E., The tungsten deposits of Boulder County, Colo.: Eng. and Min. Jour., vol. 83, p. 

 951, 1907. 



