NOTES ON AN ANDORITE-BEAKING SILVER ORE FROM 



NEVADA. 



By Earl V. Shannon, 



Assistant Curator, Department of Geology, United States National Museum. 



INTRODUCTION. 



A sj)ecimen of rich silver ore recently examined in the laboratory 

 of the United States National Museum proved to consist largely of 

 the rare lead-silver sulphantimonite andorite (2PbS.Ag2S.3Sb2S3). 

 This mineral has previously been found at Felsobanya in Hungary, 

 and at Oruro, in Bolivia, but has not heretofore been identified from 

 any locality in North America. The ore is described in some detail 

 below. The specimen came to the Museum from the Centennial Ex- 

 position (1876) and was catalogued by former Curator F. P. Dewey 

 (Cat. No. 15,908) as from Mr. M. F. Randolph, Keyser Mine, Morey 

 District, Nye Countj^, Nevada. 



DESCRIPTION OF THE ORE. 



The andorite ore specimen will average perhaps 1,000 ounces of 

 silver a ton, most of which is in the form of andorite oi^ an altera- 

 tion product of andorite. As judged from a study of this single 

 specimen the earliest mineralization of the vein was a pale pinkish 

 manganiferous carbonate containing a very small amount of finely 

 divided contemporaneous pyrite. The carbonate filled most of the 

 available Qpen space, except some narrow vugs, which were lined 

 with acute rhombohedral crystals of the rhodochrosite. Later move- 

 ment resulted in extensive brecciation of the carbonate mineraliza- 

 tion followed by the introduction of much granular quartz accom- 

 panied by silver minerals, which partly replaced the brecciated car- 

 bonate and were deposited in the quartz, and later zinc sulphide, 

 wliicli replaced the quartz. Small open cavities in the quartz are 

 lined by drusj^ quartz crystals upon which rest very rare grains of 

 pyrargyrite and stephanite. One vug contained a crj^stal of selenite 

 gypsum as the last mineral deposited. 



DESCRIPTION OF THE ANDORITE. 



The andorite forms prismatic grains which are apparently con- 

 temporaneous with the quartz and range from pure andorite to 



No. 241 1— Proceedings U. S. National Museum, Vol. 60. Art. 16. 



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