SECONDARY DEPOSITS OF COPPER MINERALS 197 



I examined the old black copper workings at Ducktown and found 

 that the layer of this ore conformed in a general way to the surface 

 contour of the ground or more nearly to the surface of the under- 

 ground waters. The accumulation of the ore in a well defined band or 

 layer is believed to be due to the massive nature of the original ore, 

 which is unusually free from vertical Assuring such as would afford 

 access for waters to seep downward, while it does show flat or gently in- 

 clined fracture planes. The occurrence of the black ore, its impregnation 

 with copper sulphate, the fact that it is generally moist with strongly 

 acid water, all show that the process is still going on, and indeed, in 

 small clefts in the upper surface of the pyrrhotite ore, what appeared to 

 be recently deposited amorphous black copper ore was found. No crys- 

 talline ore was found in place, nor has any been seen in specimens of 

 the ore in various collections. The deposit appears to be wholly a loose 

 textured sintery mass of amorphous copper sulphide, often containing 

 a residual skeleton of pyrrhotite. It is not, however, tenorite (CuO). 

 nor has any tenorite been found in numerous samples from the Duck- 

 town region tested by or for me. 



The Stone Hill (Alabama), Ore Knob (North Carolina), and Hills ville 

 (Carroll county, Virginia) copper mines, all of which closely resemble 

 the Ducktown deposits in occurrence and character of ore,* also showed 

 the same enrichment — a layer of "iron black friable, drusy, crystalline 

 sulphuret ore inclosing grains of quartz, garnet, magnetite, and a black 

 non-magnetic mineral. This ore carried 36 per cent of copper and had 

 the mineralogical character of purple and vitreous ores."t 



In Arizona oxidized ores of copper are described as passing in depth 

 to chalcocite, and this into chalcopyrite below, at the Coronado vein, X 

 and in minor deposits near Bisbee.§ 



The first statement that secondary enrichments of copper veins were 

 of general occurrence, and that the ores consist of crystalline glance and 

 bornite, appears in a paper by De Launay.|| He says chalcopyrite and 

 cupriferous p} r rite alter to bornite, chalcocite, cuprite, and gray copper, 

 which form deposits that do not extend far in depth. The deposits of 

 Monte Catini, in Tuscany, those of Rio Tinto and San Domingo, in Spain, 

 and Butte, Montana, are cited as examples. The secondary nature of 

 the last mentioned deposits is also maintained by Emmons in a report 



*Sterry Hunt: Trans. Am. Inst. Mining Engineers, vol. ii, 1874, p. 123; E. E. Olcott, in Trans. 

 Am. Inst. Mining Engineers, vol. iii, p. 391 ; R. P. Rothwell, in Engineering and Mining Journal. 



f Hunt : Trans. Am. Inst. Mining Engineers, 1874. p. 123. 



X A. F. Wendt : Trans. Am. Inst. Mining Engineers, vol/xv, p. 52. 



g James Douglas : Copper resources of the United States. Trans. Am. Inst. Mining Engineers, 

 September, 1891. 



|| Annales des Mines, vol. xii., 1897, pp. 191-195, 



