USEFUL METALS 



151 



faulted strata, ranging from pre-Cambrian to Cretaceous. Often 

 the fault plane forms a boundary for the ore body. The intru- 

 sions of a granitic magma have metamorphosed Carboniferous 

 limestones and produced characteristic contact minerals. The 

 ore-bearing solutions have risen from unknown depths and tin- 

 ores occur as replacement deposits in the limestones. The sur- 



ro;~i,v Limestone 

 V-/TvJj partly 

 /r'/T'jv altered 







aoofeet 



FIG. 90. Vertical cross section of the Joy Vein, Clifton Morenci district, 

 Arizona. (After W. Lindgren, U. S. Geological Survey.) 



face ores were originally sulphides of copper, lead and zinc. 

 These remain unaltered at the lower depths but in the upper 

 portions of the ore bodies the oxygenated ores of copper, cuprite, 

 malachite and azurite appear. (See Fig. 89.) 



(2) The Clifton-Morenci District: This district from a geo- 

 logical standpoint embraces many conditions closely related to 



