16 COLOKADO FERBERITE AND THE WOLFKAMITE SERIES. 



Analyses of tungsten concentrates treated at the Clarasdorf mill, near Boulder, Colo. 



The first analysis indicates a wolframite of the composition MnWO 47 

 26 per cent; FeWO 4 , 74 per cent a composition close to that of the 

 Gordon Gulch wolframite (analysis No. 58, p. 31). After satisfying 

 the MnO present only 8.8 of the 39.31 per cent FeO given is required 

 to combine with the WO 3 . The second analysis indicates a wolfram- 

 ite of the composition MnWO 4 , 22.7 per cent; FeWO 4 , 77.3 per cent. 

 This composition requires for combination with WO 3 only 8.7 of the 

 34.01 per cent FeO. The form in which the iron is present is unknown, 

 but the possibility that it maybe specular hematite is at once suggested 

 by knowledge of the occurrences mentioned. The sulphur shown in 

 the analyses indicates, of course, that a small quantity of iron is pres- 

 ent as pyrite. 



Occurrences of specular hematite with wolframites are not un- 

 known. At South Crofty mine, Cornwall, "the presence of specular 

 iron has caused trouble in obtaining a high-class wolfram concen- 

 trate." 1 



It seems probable that deeper workings on the Rogers tract may 

 show specular hematite, to the decomposition of which may be due 

 the brown color of much of the ferberite from that tract. 



Limonite. Limonite, under which term are here included all hy- 

 droifs ^xades of iron, occurs in many veins, and nearly all the ore 

 on the Rogers tract, about 2 miles nortfieast of Nederland, is stained 

 brown with it. The crystals of ferberite are not only brown on the 

 outside, but when broken show brown sections. (See p. 38 and PL 

 IV, Aj p. 13.) The origin of the limonite and its relationship to the 

 ferberite are unknown, but in part at least it is possibly altered from 

 specular hematite, as already stated. Iron-bearing carbonates occur 

 in some tungsten deposits, notably the scheelite deposits of Atolia, 

 Cal. Carbonates decompose much more easily than specular hema- 

 tite, and one may have been originally inclosed in the ferberite of 

 the Rogers tract and some other places. 



ite^ Magnetite is recorded by George 2 as occurring with 

 the lerberite. Magnetite seems to be a probable associate of ferberite, 



i Anon., Cornwall (editorial): Min. Mag., London, vol. 8, p. 165, 1913. 



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

 p. 75, 1909. 



