COPPER 



171 



QUANTITY OF COPPER ORE, IN MILLIONS OF SHORT TONS 



Figure 22. — Size and grade characteristics of selected copper ore bodies. Diagonal lines show tons of copper metal per de- 

 posit; world and U.S. mine production of copper metal are shown for comparison by diagonal dashed lines. Data from 

 unpublished compilation by A. R. Kinkel, Jr., and others and from Peters (1970). 



VEINS, PIPES, AND REPLACEMENT DEPOSITS 



Copper-rich veins, pipes, and replacement depos- 

 its may be localized in felsic plutonic rocks with 

 local porphyry intrusions as at Butte, Mont. (Meyer 

 and others, 1968) ; in favorable host rocks near a 

 porphyry copper deposit as at Bingham, Utah, and 

 Bisbee, Ariz. ; or near barren felsic intrusive rocks 

 as at Magma, Ariz. (Hammer and Peterson, 1968) 

 or Mission, Ariz. (Kinnison, 1966). Veins are 

 formed when metal-rich solutions, emanating from 

 a crystallizing intrusion, deposit minerals in faults 

 or fractures. They are tabular in form and may 

 show mineral textures indicating growth of crystals 

 in open cavities as well as replacement of wallrocks 



by copper minerals. Many veins show several gen- 

 erations of mineral deposition related to opening 

 and reopening of fault zones by tectonic movements. 

 Hydrothermal alteration envelopes may accom- 

 pany the veins, indicating chemical reaction be- 

 tween wallrocks and mineral-rich solutions. Sales 

 and Meyer (1949), in their monumental study of 

 quartz-sulfide veins at Butte, Mont., described a 

 sequence of alteration zones outward from the veins 

 into the quartz monzonite wallrocks. The sequence 

 is consistently sericite to kaolin to montmorillonite 

 to fresh wallrock. Comparison of the chemical com- 

 position of these zones suggests diffusion of some 

 ions from the rock into the vein and simultaneous 

 migration of hydrogen ions into the wallrocks. There 



