100 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



Pittsburg. In some of these ores the sphalerite occurs in separate 

 streaks and bunches but the majority of the ores the two minerals 

 are intergrown in dense masses in microscopic grains, the aggregate 

 looking like neither mineral. A small group of prospects differs from 

 the majority of Pine Creek mines in that the ore consists of relatively 

 clean granular galena with ankerite in white quartz. These are all 

 adjacent to the quartzitic member of the middle Prichard formation. 

 The principal mines of this group are the Lookout Mountain, Hypo- 

 theek, Northern light, and Carbonate. 



In the drainage basin of the North Fork of the Coeur d'Alene dis- 

 trict a number of galena-bearing veins have been opened in the 

 Prichard formation, some of which have fairly clean galena, while in 

 others the galena is intimately mixed with sphalerite. Prominent 

 among these are the Paragon, Jack Waite, Terrible Edith, Monarch, 

 and Bear Top mines. 



Galena occurs also in grains and masses in the gold veins near 

 Murray with auriferous pyrite, chalcopyrite, and scheelite. 



The galena from all of the principal mines of the Coeur d' Alene 

 region is granular, usually of medium grain but varying from the very 

 fine grained material called steel galena to rare occurrences where 

 cleavages several centimeters broad are obtained. The very finest 

 grained material is homogeneous and sectile and shows no visible 

 cleavages whatever. In most cases this very fine material seems to 

 have been reground, as it occurs along fissures, contains polished 

 galena-faced slickensides, and grades into varieties having gneissic 

 structure. Gneissic structures, obviously due to pressure, are very 

 common in galena of various grain sizes. A small ore body in the 

 Alhambra mine has galena which has been ground along a fissure and 

 rehardened so that it resembles black graphitic slate. The coarser 

 cleavages are usually bent, crumpled, or folded as in the mineral from 

 the Minnie Moore mine in Blaine County. 



The galena is all argentiferous, the average in the Bunker Hill mine 

 being from 40 to 60 ounces of silver to the ton, although in other 

 mines, notably the Hercules, the silver content is higher. The 

 higher silver values accompany tetrahedrite and the silver may all 

 be contained in this mineral. Specimens of galena from the Bunker 

 Hill mine showing 0.08 per cent and 0.09 per cent of silver, respective- 

 ly, proved to contain microscopic grains of tetrahedrite when ex- 

 amined on polished surfaces with the metallographic microscope as 

 did specimens containing 0.108 per cent of silver from the Hercules 

 mine. 68 



The galena is practically always massive, crystals with euhedral 

 faces being exceedingly rare and of small size. 



68 F. N. Quild. A microscopic study of the silver ores and their associated minerals. Economic Ge- 

 ology, vol. 12, pp. 305-306, 1917. 



