510 



GEOLOGY AND MINING INDUSTRY OF LEADVJLLE. 



PRINTER BOY HILL. 



The existence of the three transverse dikes crossing the slopes of 

 Printer Boy Hill and of the cross-cutting bodies of Pyritiferous Porphyry 

 on its north side, in the upper part of California gulch, is an indication of 

 probable mineral concentration in this region, and developments, so far as 

 they have gone, tend to confirm this idea. 



On the south slope the curving outcrop of the contact of Blue Lime- 

 stone and White Porphyry has been very extensively prospected near the 

 surface, and evidence of replacement action has been found at almost every 

 point. Figure 4 shows an ideal section of the middle portion of the south 

 slope and the relative amount of vein material, as far as can be determined 

 by present workings. 



ly Porphyry. 



The principal development of ore has been thus far found in the Flor- 

 ence mine, which is at the crest of the fold. The vein material, Avhich is 

 the usual clayey matter, carrying oxides of iron and manganese, has here 

 a maximum thickness of thirty to thirty-five feet, and seems to thin out to 

 the east and west, respectively, but to the north or into the hill it has as 

 yet been explored but a short distance. The ore occurs at the surface and 

 rather irregularly through this vein material ; besides the usual carbonate 

 of lead and chloride of silver, it contains several minerals not common in 

 the district, among which may be mentioned native gold, visible to the 

 naked eye, and a sulfo-carbonate of bismuth. (See Appendix C'.) In a 

 tunnel directl)- below the main workings of the Jlorence a gash vein of 

 galena in limestone several feet in thickness was found. Above, it connects 



