4 PEOCEEDINGS OF THE NATIONAL MUSEUM vol. 6:. 



the benjaminite. It forms grains isolated in the quartz and small 

 areas grown on the ])enjaminite or apparently, in some cases, re- 

 placing the benjaminite. This mineral is mainly clearly later than 

 the benjaminite although a very little may be contemporaneous 

 with it. The relations of the chalcopyrite are shown in figures 1, 2, 

 and 3. 



Covellite occurs in minute amount as a later replacement, along 

 cracks, of both chalcopyrite and benjaminite, preferring the latter. 

 The field showing the greatest amount of this mineral is that shown 

 in Figure 1. The amount of covellite present in the analyzed ma- 

 terial was so exceedingly small that it could not have any effect on 

 the analytic results. 



Chalcocite was seen as a few rare and very minute areas replacing 



covellite. 



PARAGENESIS. 



The minerals may be arranged in the following paragenetic order 

 although there is some doubt as to the mutual age relations of some 

 of the earlier ones. 



1. Quartz. 



2. Muscovite. 



3. Molybdenite. 



4. Pyrite. 



5. Fluorite. 



6. Benjaminite. 



7. Quartz. 



8. Chalcopyrite. 



9. Covellite. 

 10. Chalcocite. 



While a considerable time gap may have intervened between the 

 first five and the second five of these minerals it is most probable 

 that the whole series belongs to a single genetic sequence although 

 the covellite and chalcocite may be products of downward secondary 

 enrichment. The benjaminite, a silver-bismuth ore mineral, is thus 

 a constituent of a vein characterized by mica, molybdenite, and 

 fluorite, minerals typical of high temperature veins of pegmatitic 

 affiliations. Such a silver deposit is more or less unique. 



GENERAL DESCRIPTION OF BENJAMINITE. 



The benjaminite is the only abundant metallic mineral in the ore 

 and carries the silver for which the mine was explored. It forms 

 irregular masses up to 5 cm. in maximum diameter which have 

 clearly developed ahmg fractures in the quartz, apparently by replace- 

 ment. The benjaminite contains some pyrite although many masses 

 are free from it and it all contains fine grains of chalcopyrite developed 

 along later minute quartz filled cracks. The color on fresh fracture 



