THE MINERALS OP IDAHO 



231 



from the Blackbird and Blue Wing districts; 48 a specimens bowing 

 minute drusy crystals from the Blue Wing district is illustrated by 

 Umpleby. 47 



SHOSHONE COUNTY 



Siderite is the most abundant and characteristic gangue mineral 

 of the Coeur d'Alene lead-silver deposits and its presence as a re- 

 placement of quartzite constitutes a noteworthy feature of the ores. 

 In the typical deposits the mineral is massive, the ordinary gangue 

 of the Bunker Hill and Sullivan mine, for example, being a pale 

 brown fine-grained aggregate of siderite not always distinguishable, 

 at a casual glance, from the quartzite of which it is, in considerable 

 part, a replacement. In the vicinity of the ore 

 bodies all gradations may be observed from 

 nearly pure massive siderite to a somewhat 

 sericitic quartzite. Coarsely crystalline varie- 

 ties or phases of the siderite are rarer and occur 

 where the mineral is associated with vein quartz 

 as a filling of open spaces. 



Siderite is by no means equally abundant, 

 even in all of the lead-silver mines. It is a 

 particularly prominent constituent of the ores 

 of the Wardner and Mullan groups. In the 

 Canyon Creek group the mineral is fairly abun- 

 dant in the Tiger-Poorman and Standard-Mam- 

 moth lodes, but in the Helena-Frisco and Her- 

 cules it is rather inconspicuous and in the Hecla 

 mine occurs only sparingly as a microscopic 

 constituent. The ores of the Ninemile Creek 

 group apparently contain no siderite and it 

 appears to be absent from the gold-quartz veins 

 near Murray. 48 The siderite is practically all massive-granular but 

 a few crystals of curved rhombohedral habit up to 3 or 4 mm. in 

 size have been seen lining cavities in quartzite on the dump of the 

 No. 2 tunnel of the Last Chance mine at Wardner and small translu- 

 cent brown rhombohedrons line cavities in quartz in ore from the 

 Gold Hunter mine. The latter are often filled with minute needles 

 of boulangerite and perfect siderite rhombohedrons are sometimes 

 found impaled in a boulangerite needle or embedded in fine wooly 

 boulangerite. These are simple unit rhombohedrons as illustrated 

 in Figure 48. The carbonate gangue of the lead-silver ores in 

 quartzite is all siderite, but the galena-sphalerite ores in the 



"J. B. Umpleby. U. S. Geol. Survey, Bull. 528, p. 79, 1913. 



« J. B. Umpleby. Idem, pi. 8 B, p. 72. 



" F. L. Ransome. U. S. Qeol. Survey, Prof. Paper 62, p. 97, 1908. 



Fig. 48.— Siderite. Unit 

 rhombohedron. gold 

 Hunter mine, Sho- 

 shone County 



