90 W. P. Headden — Columbite and Tantalite. 



the same county, and also in the Nigger Hill district in Law- 

 rence Co. It is found with all of the stream tin, very sparing- 

 ly, however, in that from Two Bit and Mace gulches in the 

 Nigger Hill or northern district. Its presence with the stream 

 tin suggests its possible association with the cassiterite in the 

 veins whence the stream tin has been derived. This inference 

 is only partially correct. The columbite is not always associ- 

 ated with the cassiterite, but I have found no columbite where 

 cassiterite did not occur in the same vein — sometimes, but not 

 always, intimately associated with it. 



The chief occurrence of columbite in the Black Hills is at 

 the Etta mine. It is abundant in the upper part of the open 

 work on the southwestern and southern sides of the hill, where 

 it occurs in a zone of beryl. In other parts of the mine it is 

 associated with spodumene, feldspar,. and sometimes quartz. 



The line between the beryl and the tin ore, which in this 

 case is a mixture of albite and muscovite, carrying an almost 

 black cassiterite. is sharply defined. Sometimes there is an 

 intervening band of pink feldspar, the mass of which is formed 

 of radiating plates, and has a well defined but undulating and 

 jagged upper boundary. This feldspar is probably an altera- 

 tion product, as is suggested by its mode of occurrence and by 

 the fact that the small spodumene crystals which occasionally 

 occur in this association, have undergone complete change. 

 The columbite occurring here is, in a general way, confined to 

 the beryl, the crystals standing with one end upon or even pene- 

 trating the tin ore, while the crystals themselves are imbedded 

 in the massive beryl. The individual crystals are comparatively 

 small, crowded together, and often penetrate one another. This 

 is not true, however, of other parts of the mine, where the 

 crystals occur of larger size, but as isolated individuals or form- 

 ing groups of a few crystals. The largest individual -crystal 

 in my possession weighs 14 pounds, and the largest group, con- 

 sisting of two and a part of a third crystal, weighs 30J pounds. 



The Peerless mine, about half a mile north of the Etta, has 

 furnished but one or two larger aggregates of crystals and a 

 few thin plates which occur in the interstices of the quartz 

 masses. One of these larger masses was found on the surface, 

 where the weathering away of the granite had probably left it. 



The largest mass of which I have personal knowledge occurs 

 in the Sarah mine, about one-quarter mile northwest of the 

 Etta. The section of this mass as it is exposed is 8 in. X 14 in. 

 I could obtain no information as to how much has already been 

 removed, and there is no exposure showing how far the rem- 

 nant extends into the enclosing rock mass. This is the only 

 specimen which I could find in the mine ; there is, however, 

 not much work done at this point. 



