COPPER. 



147 



directly on the limestone, while others are surrounded by the de- 

 composed porphyry. As included masses of limestone, with as- 

 sociated ore, are found in the decomposed porphyry, it is probable 

 that these ore bodies may have originally replaced such. The 

 ores are jnalachite, azurite, cuprite with some metallic copper 

 and malachite, in a gangue principally of limonite. Wad is 

 also frequent. Much clay of a residual character occurs with the 

 ores. 



2. Deposits in limestone. These are closely associated with 



PIG. 37. Geological section of the Metcalf mine, Clifton district, Arizona. 



After Wendt. 



the first class, and have apparently formed as outlying bodies in 

 the limestone, as they are connected by ore channels with the 

 principal lines of circulation along the contact. They appear 

 to contain more wad and lime than the typical contact de- 

 posits. 



3. Deposits in porphyry. These form sheets and pockets in 

 porphyry, or impregnate the solid rock itself. They are oxidized 

 at the surface, but pass in depth into chalcocite. The principal 

 gangue is kaolinized porphyry. 



According to Wendt, the Coronado vein fills a longitudinal 

 fissure in a quartz porphyry dike. It afforded chalcocite above, 



