604 



riiOVEEDlNGS OF THE NATIONAL MUSEUM. 



Analyses of argentiferous janicsonite from Nevada. 



Lead(Pb) 



Silver (Ag).... 

 Copper (Cu)... 



Iron (Fe) 



Antimony (Sb). 

 Sulphur (S).... 



Total. 



43.86 



6. 14 



1.55 



.05 



29.26 



19.06 



99.92 



The formula derived by Burton from this analysis is : 



2(Pb,Ag,Cu)S.Sb,S3. 



NAUMANNITE FROM IDAHO. 



In the course of a general mineralogical investigation of the 

 Economic Geology Collections of the United States National Mu- 

 seum, the writer recently examined a specimen, supposed to be 

 argentite, from the De Lamar mine. Silver City district, Owyhee 

 County, Idaho. This specimen has been proven by analysis to 

 consist of naumannite, the rare selenide of silver, which has not 

 heretofore been reported from any locality in the United States. 



OCCURRENCE. 



The specimen in question, which is labeled "Argentite nugget 

 coated with clay, De Lamar Mine," was collected by Eldridge in 

 1893, and is catalogued as number 201 of the set of ores illustrating 

 his report on a Geologic reconnaissance across Idaho.^ 



The De Lamar mine has been in the past an exceedingly rich and 

 profitable gold-silver mine, having produced precious metals to the 

 value of $6,000,000 within as many years after the discovery of the 

 main ore body. Several veins of the same system have been worked. 

 The inclosing rock is rhyolite, and the veins are filled fissures, the 

 gangue being mainly a peculiarly platy quartz, which is pseudo- 

 morphous, probably after calcite or barite. All of the veins terminate 

 abruptly at a great transverse fissure filled with soft kaolinitic clay, 

 derived by crushing and alteration of the material of the walls. This 

 great clay gouge, which is locally designated the " iron dike," has had 

 the effect of damming the mineralizing solutions and greatly localiz- 

 ing the deposition of the ores. Near the under side of the clay vein 

 were the " silver stopes," where the veins upon approaching the " iron 

 dike " were unusually rich, and bunches of rich ore also occurred in 

 the separating country rock. In the crevices immediately adjacent to 



Eldridge, George H., U. S. Geol. Survey, Ann. 16, pt 2, 1805. 



