ALTERATION OF COPPER MINERALS 191 



2CuS0 4 + 2CaC0 3 = 2CuO f 2CaS0 4 + 2C0 2 . The CuO is reduced to Cu 2 by 

 organic matter in the limestone. 



Cu 2 + H 2 SC\ = Cu + CuSO, + H 2 or else 3Cu 2 + 3FeS0 4 = 6Cu -f Fe 2 3 + 

 Fe 2 (SO,) s . 



Specimens collected from the Union Copper company's mine at Gold 

 Hill, North Carolina, are especially interesting. The primary ore is a 

 rather fine grained gray quartz carrying small bunches, strings, and 

 shreds of chalcopyrite. 



The ore body is fractured by vertical planes down which the surface 

 waters percolate and alter the vein, forming the well denned zone of 

 oxidized ores and penetrating to a greater or less depth along the vertical 

 cracks. As already noted in the preceding pages, the yellow stained 

 oxidized ore passes into an ore in which the quartz is no longer trans- 

 lucent and solid but is opaque, white, and more or less saccharoid, and 

 often porous, while the fragments of included schist have been changed 

 by the acid waters to a white, clayey material. Specimens of this ore 

 collected by me show the lower tip of a vertical " pipe " of oxidized 

 ore surrounded by the altered but not yet oxidized ore. In the latter 

 mineral black, sooty masses are seen whose form and distribution accord 

 exactly with those of the chalcopyrite in the unaltered primary ore. The 

 yellow stained oxidized ore differs in showing about its borders a band 

 of massive crystalline glance often mixed with cuprite, the oxide pre- 

 dominating toward the very sharp line marking the limit of the yellow 

 iron stained ore. The specimen shows that there has been a transposi- 

 tion of material and a redeposition of the copper as glance. This border 

 or halo of enrichment is very common in the ore from this mine. In 

 the more perfectly oxidized and iron stained ore the cuprite is changed 

 to malachite, and the latter sometimes to chrysocolla. In other specimens 

 from Gold Hill the altered whijte quartz carries copper glance, beautiful 

 crystalline cuprite, and native copper. The glance occurs not only scat- 

 tered through the ore but in little clusters of crystals through the clay 

 and rotten quartz. Other specimens show massive crystalline glance a 

 quarter of an inch thick coating the specimen, the surface of the glance 

 coated with a very thin or felty covering of native copper. 



In the main body of the vein there are also bunches several feet in 

 diameter of massive, coarsely crystalline quartz. In this material the 

 chalcopyrite is in masses an inch or more across. Where this ore has 

 been altered the chalcopyrite has been changed directly to massive glance 

 showing a crystalline texture, and the quartz about it is more or less iron 

 stained and the glance surrounded by a film of red oxide of copper 

 changing to fibrous malachite along cracks in the quartz. 



In ores from Copperopolis, Meagher county, Montana, glance also 



