471 



NOTES ON SOME OXIDIZED COPPER ORES FROM THE TORREON 



MINES, IN THE PROVINCE OF CHIHUAHUA, MEXICO. 



By J, H. COLLINS, F.G.S. 



General remarks on go%%ans. Tlie connexion of gozzan with 

 copper-ores has long been well understood in Cornwall. This 

 substance consists essentially of hydrous oxide of iron mingled 

 with more or less of quartz or other siliceous substance, and 

 sometimes with the oxides of copper, tin and other metals. 

 Silver, too, is not unfrequently present, some of the Cornish 

 gozzans having been especially rich in this metal. '^" 



A good gozzan, however, does not necessarily indicate a 

 valuable lode of copper, since it may be merely the result of the 

 oxidation of iron pyrites ; on the other hand no Cornishman 

 would be disposed to place much trust in a copper-lode unless it 

 had a good gozzan — and if at the same time the gozzan were 

 stained with salts of copper it would be at once recognized as 

 indicating " a keenly bal." Copper mining in the West of 

 England is now, unfortunately, almost a thing of the past, but 

 there are still men who remember the fine gozzans of Fowey 

 Consols and Devon Great Consols, extending '60, 60, or even 90 

 fathoms down from the '' bryle of the lode." 



Limits of the gozzans in depth. — In all such cases it is found 

 that there is very little oxidized ore below the " water level of 

 the country." As soon as this " permanent level " is reached 

 the ores are found to be almost exclusively sulphides, and even 

 above this level it is usual to find masses of sulphide ore, chalco- 

 pyrite, erubescite, or chalcocite, which are only oxidized at the 

 surface, so that no-one who has reallj^ studied the subject doubts 

 that originally the whole of the metallic oxides of the gozzan 

 existed as sulphide, and that they have been oxidized either by 

 the action of the free oxygen in the air or of that dissolved in 



* An intei-esting paper on Cornish gozzans by Mr. Wm. Argall will be found 

 in the Report of the Miners' Association of Cornwall and Devon for 1871, at 

 p. 37. 



