THE MINERALS OF IDAHO 209 



hematite. In the oxidized portions of ore bodies limonite occurs as 

 cellular masses of light yellow to dark brown color, sometimes soft 

 and earthy and at other times hard and compact. Only a few local- 

 ities for such a widespread mineral can be mentioned. 



ADAMS COUNTY 



In the Seven Devils and other districts of Adams County limonite 

 occurs commonly as typical gossans or "iron-cappings," forming 

 the outcrops of the contact-metamorphic copper deposits and of large 

 low-grade masses of pyritic material. 



ADA, BOISE, CLEARWATER, ELMORE, AND IDAHO COUNTIES 



In the gold-producing districts of central and southern Idaho 

 limonite occurs commonly in the upper portions of gold veins, filling 

 cavities in quartz originally occupied by auriferous sulphides, chiefly 

 pyrite and arsenopyrite. The original gold content of the sulphide 

 remains in the secondary limonite in the form of native gold. Such 

 gold which has been liberated from its inclosing sulphide by weather- 

 ing is readily extracted by amalgamation and such oxidized and 

 limonitic ores are the "free milling" ores formerly so important in 

 Idaho. Sometimes the limonite formed by the oxidation of pyrite 

 crystals is a hard and lustrous dark-brown material which has the 

 form of the original crystal of pyrite, thus being a pseudomorph of 

 limonite after pyrite. A specimen from the Lolo Claim, Wieppe 

 district, Clearwater County, contains limonite pseudomorphs after 

 pyrite showing faces of the cube and pentagonal dodecahedron, up to 

 2 cm. in diameter. 



BLAINE COUNTY 



In the Wood River district the limonite which was abundant in 

 the surface ores was probably in considerable part derived from 

 siderite. In the Muldoon district large masses of limonite have been 

 mined for use as a flux. 



CUSTER COUNTY 



In the Alder Creek district limonite occurs in the usual forms, 

 although here earthy hematite is more abundant. In the lead-silver 

 deposits of the county limonite, probably in large part derived from 

 siderite, is abundantly mixed with cerusite. It occurs in the oxidized 

 portions of all veins, its amount dependent only upon the amount of 

 iron supplied by the primary mineralization. In a tributary to 

 Wildhorse Canyon limonite is deposited in large amount as a slimy 

 yellow mud by the water of a mineral spring. 



FREMONT COUNTY 



In the Skull Canyon district limonite occurs in the Weimer Copper 

 mine as a dense jaspery material containing malachite. In the 

 Kaufman and Weaver mine it forms a soft earthy ocher mixed with 

 lead carbonate. 



