THE MINERALS OF IDAHO 199 



epidote; in the Eureka district it is present in some of the veins; in 

 the Mineral Hill district it appears with the ores, especially in the 

 Pine Creek deposits; and in the Spring Mountain district, it is 

 developed in large quantities in the low-grade copper deposits of the 

 Bruce estate, where it occurs as a contact mineral in limestone 

 adjacent to an intrusion of quartz-diorite. 8 The magnetite is mixed 

 with bornite and ludwigite. 



SHOSHONE COUNTY 



Magnetite is common in the Success mine on Ninemile Creek in 

 fine granular masses mixed with sphalerite and pyrite. It is extracted 

 in chunks from the ore with large magnets before milling. It may 

 also be present in considerable amounts in the ores of the Helena- 

 Frisco and Rex (Sixteen-to-one) mines, which resemble those of the 

 Success mine. In the Greenhill- Cleveland and Standard-Mammoth 

 ore bodies magnetite was abundant in the lower levels where it was 

 intergrown with pyrite and siderite. The magnetite seemed in some 

 cases to have resulted from alteration of siderite and sometimes 

 occurred in masses preserving the granular structure and imperfect 

 rhombohedral cleavage of the siderite. The ore minerals galena 

 and sphalerite are not contemporaneous with this magnetite-bearing 

 aggregate but are present in later seams. It appears that here a 

 normal siderite-galena ore was deposited and later increases in tem- 

 perature, and changes in conditions caused the removal of the ore 

 minerals to a higher level with coincident reduction of siderite to 

 magnetite and deposition of large quantities of pyrrhotite. At a 

 later period this base aggregate -was shattered and the fractures 

 filled with ore minerals, including galena, tetrahedrite, jamesonite, 

 boulangerite, chalcopyrite, and even pyrargyrite (q.v.). Magnetite 

 has been noted in considerable masses in quartz from the outcrops 

 of the Palisade mine, Pine Creek district. 



WASHINGTON AND ADAMS COUNTIES 



Magnetite is found in the Blue Mountain gold belt, Mineral dis- 

 trict. 



MINIUM (244) 



RED LEAD 

 Lead oxide, 2PbO.Pb0 2 Pulverulent. 



BLAINE COUNTY 



The rare mineral minium has been found in ores of the Wood River 

 district, especially at the Jay Gould mine, where it coated native 

 lead or occurred as an impregnation in quartz containing native lead. 8a 



8 J. B. Umpleby. U. S. Geol. Survey, Bull. 528, p. 77, 1913. 



»" William P. Blake. Araer. Journ. Sci., vol. 25, p. 101, 18S3. W. F. Hillebrand, U. S. Geol. Survey, 

 Bull. 20, p. 99, 1885. E. S. Dana, System of Mineralogy, p. 231, 1895. Waldemar Limlgrcn, 20th Ann. 

 Rept. U. S. Geol. Survey, pt. 3, p. 189. 



