THE MINERALS OF IDAHO 227 



The ratio of Mn + Fe to Mg is 1.00 to 0.69, and that of the other 

 bases to lime is 1.00 to 0.98. 



While it is not practical to differentiate in the field between mag- 

 nesian ankerite and ferriferous dolomite, it is practical and possible 

 to separate the members of the ankerite-dolomite series from siderite 

 and for field use the name ankerite may be used for the magnesian 

 series. They differ from the siderites in their white to grayish color 

 when fresh, whereas the true siderite is always a clean light buff on 

 fresh fracture. Upon weathering the siderites become dark brown 

 to black, depending upon the manganese content, while the ankerites 

 become pearly golden brown. Finally, when completely oxidized the 

 siderites give a dark brown to black manganiferous limonite, while 

 the ankerites yield a light brown ocher. 



The ankerites of the Mullan area occur in veins in the Wallace and 

 St. Regis formations. Ankerite has been noted in quartz stringers 

 in the Wallace formation in the Florence (Dallaire) prospect on Elk 

 Creek east of Kellogg and in the Hill and other prospects in the 

 Wallace formation in Slaughterhouse Gulch at Wardner. It also 

 occurs abundantly in numerous economically unproductive veins in 

 the Prichard formation along the South Fork of the Coeur d'Alene 

 River, between Osburn and Kellogg, where the carbonate is associ- 

 ated, in bluish quartz, with pyrite, pyrrhotite, and some chalcopyrite. 

 Among the prospects of this group in which ankerite has been espe- 

 cially noted are the Enterprise claim of Fred Donaldson, between 

 Big Creek and Gold Run, the Wisconsin and Teddy claims north of 

 the river west of Moon Gulch, and the Evolution near Osburn. 



In the Evolution ankerite occurred in a vein developed in the 

 shaft, although the carbonate of the main vein exposed in the tunnel 

 is calcite and not ankerite. In the Teddy this carbonate is prominent 

 in some of the veins cut by the lower tunnel. In the Wisconsin 

 (later called Gold Leaf Consolidated) prospect the ankerite occurs as 

 granular masses which become brown on the dump and occasionally 

 as small acute and curved rhombohedral crystals associated with 

 quartz crystals lining small vugs in the vein. The carbonates of the 

 ankerite series have also been seen in the Paymaster or Tillicum 

 vein north of the mouth of Elk Creek, the Lucky Boy, south of 



