SECONDARY DEPOSITS OF COPPER MINERALS 199 



minerals rich in copper; in fact that they do often find copper glance, 

 bornite, and chalcopyrite, together with galena, zinc blende, tetrahedrite, 

 etcetera, usually accompanied by some quartz, in the cracks and fissures 

 in the pyrite, and these minerals are, without doubt, of younger, second- 

 ary formation. These secondary ores sometimes fill the cracks so large 

 that they can be separately mined, and the mining done by the Romans 

 was chiefly confined to these rich streaks within the poorer mass of 

 pyrite. More commonly, however, the rich ores occur in quite small 

 fissures which form a branching network in the main body of pyrite. 

 That the copper contents of these secondary minerals has been derived 

 from the weathered ore near the surface is shown quite clearly by the 

 fact that these little veins are most common in the zone immediately 

 under the gossan. They usually extend to some 100 meters or more in 

 depth, while below this the pyrite is firm, little cracked, and compara- 

 tively poor in copper. In discussing these observations Professor Vogt 

 says : 



"The enrichment described by Klockmann of the copper contents of the upper 

 part of the ore bodies undoubtedly plays a very important role. From my own 

 examination of the different mines I have obtained, however, the impression that 

 this process alone was not sufficient to account for the phenomena described, and 

 that the decreasing copper contents in depth is in part of a primary nature." 



For the sake of analogy he also mentions the fact that the copper 

 contents of the ore body of the Vigsnas mine in Norway, which is now 

 known to have a depth of 735 meters, becomes less in depth, and that 

 this is also the case at Fahlun, where the pyrite body has been worked 

 to a depth of 350 meters. 



At Gold Hill, North Carolina, the workings of the Union Copper com- 

 pany show very fine examples of secondary sulphide enrichment, but 

 there is no well defined zone or continuous mass, as the veins are frac- 

 tured by vertical fissures. The unaltered ore is chalcopyrite, which 

 occurs in quartz veins traversing schists, following the foliation in part. 

 The ore occurs only in the quartz, which forms lenticular masses, as is 

 commonly the case in schistose rocks. The veins have been worked 

 during the 40 or 50 years past, the deepest openings being 800 feet. 

 They were worked as gold properties, but showed an increase of copper 

 in descending which prevented amalgamation and led to the closing 

 down of the property. The Union Copper company is now working 

 several of these veins, one of them, the Big Cut copper vein, yielding 

 considerable ore, which has been shipped. Superficial alteration has 

 rotted and decomposed the upper part of the vein so that it closely re- 

 sembles the saprolites of the adjacent schists, though redder in color. 



