514 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



Only the latter was accessible at time of visit, and here the vein is double, the 

 two branches being separated by ten or twelve feet of decomposed porphyry. 

 The gangue is nothing more than thoroughly decomposed porphyry, being 

 a white, clayey material in which only the quartz grains of the original por- 

 phyry remain unaltered ; scarcely any metallic contents are visible. In the 

 old workings, where the ore was rich, free gold could be seen, and in the 

 deeper workings considerable iron and copper pyrites and some galeua and 

 tennantite were found. Gold occurred in both pyrite and galena, and a piece 

 of ore containing galena crystals, connected by a filament of wire gold, was 

 one of the show specimens of the mine. Selected specimens are said to have 

 contained 122 ounces of gold to the ton, and the average assay is given at three 

 to four ounces. The vein has varied in thickness from one inch to four feet, 

 with an assumed average of seven inches. On the Avest wall, from the sur- 

 face down to a depth of 200 feet, were branches or stringers extending out 

 into the porphyry, sometimes as much as three feet thick and containing 

 ore of similar quality to the vein, though of different color and hardness. 

 South drifts from the shaft of the Upper Printer Boy were said to be cut off, 

 successively, at a distance of a few hundred feet, by a cement deposit, which, 

 from the description given by those working the mine at that time, would 

 seem to be a portion of Lake beds deposited in the bay that, as already 

 shown, existed where now is the spur separating California from Iowa gulch. 

 In the Upper Printer Boy the normal Printer Boy Porphyry, which is 

 a coarse-grained, greenish-gray rock with large feldspar crystals, was over- 

 laid by a white, fine-grained porphyry, resembling decomposed Pyritiferous 

 Porphyry from which the pyrite has been dissolved out. It is said that the 

 former was only found at one hundred to two hundred feet below the sur- 

 face, but this does not agree with observations which show the Printer Boy 

 Porphyry in all the prospect holes around the Upper Printer Boy shaft. 

 Both rocks occur in the Gray Eagle tunnel (M-53), west of Eureka gulch, 

 and it is probable that part of the main body of Pyritiferous Porphyry orig- 

 inally covered this portion of the hill and that from the pyrite in it the 

 waters derived the metallic contents which now are deposited in the veins. 

 A number of other small gold-bearing veins are also found in the Printer Boy 

 porphyry, the most important of which is the Five-Twenty, from which a 



