.l/AT.l/.N 



minerals of the alkaline earth group. Not infrequently there 

 appears within the quart/ varying amounts of pyritc. and even 

 limit fd quantities of copper and lead. These are free milling 







F G. 43. Vertical section showing the forking of the Pike's Peak vein, 

 Cripple Creek district, Colorado. (After Penrose.) 



ores. By a free milling ore is meant one that does not require 

 roasting before amalgamation will take place. Dry ore is the 

 term often used (Fig. 44). 



FIG. 44. Horizontal section in the Elkton mine, Cripple Creek 

 district, Colorado, showing the relation of the vein a to the dike 6 and to 

 the country rock c. (After Penrose.) 



The third class of gold ores is auriferous copper ores. These 

 are widely distributed throughout the United States and much of 

 the chalcopyrite is gold bearing. Yet in many cases the yellow 



