140 ECONOMIC GEOLOGY 



ducing 10,000,000 Ib. of copper per annum, but in the later years 

 much of the ore has not exceeded 3 per cent, copper. 



According to Thomas and MacAlister, sulphidic copper ores 

 occur in South Australia in veins sometimes 30 ft. in width and 

 of hydatogenetic origin. They occur in the mica schists of Cam- 

 brian age and the associated minerals are pyrite, hematite and 

 molybdenite. They also describe in New South Wales the exist- 

 ence of interbedded veins of a cupriferous pyrrhotite with 

 chalcopyrite, chalcocite and magnetite present. 



Metasomatic replacements of copper ores occur at Bisbee, 

 Arizona, and in the Lake Superior region. The high grade cop- 

 per ores of northern Italy are considered by some to be of the same 

 origin (Fig. 81). 



The form then that the various copper deposits assume are 

 veins, contact zones, impregnations and replacements in sedimen- 

 tary rocks. 



Geographical Distribution. The copper ores of the United 

 States form five distinct belts: (1) The Appalachian belt; (2) 

 the Lake Superior region; (3) the Cordilleran section; (4) the 

 Pacific Coast belt, and (5) the Alaskan belt. 



(1) The Appalachian Belt. This belt extends from Alabama 

 on the south in a northeasterly direction to Newfoundland on 

 the north. The richest deposits occur in Tennessee, Vermont 

 and Newfoundland. The largest producing mine in the belt is 

 at Ducktown, Tennessee. The ore occurs as true fissure veins 

 in the crystalline schists. It consists chiefly of chalcopyrite in 

 pyrrhotite and pyrite with a little quartz and is the richest where 

 the pyrrhotite is the most abundant. According to H. Ries this 

 district was one of the earliest producers of copper in the United 

 States. The operations were commenced as early as 1850. The 

 ores resulting from secondary enrichment were soon worked out 

 and it was not until 1890 that the underlying low-grade sulphides 

 were successfully worked. Since that time the mine has been a 

 steady producer. 



At Gold Hill, North Carolina, chalcopyrite occurs in true 

 fissure veins found along sheeted planes in the metamorphics. 

 Pyrite is associated with the copper ore. 



At Virgilina, Virginia, the ore is bornite with a little chalcopy- 

 rite and pyrite. It occurs in true fissure veins filled with quartz 

 and sulphides. The veins conform to the banding of the mica 

 schists. Replacements of the wall rock are rare. In Green 



