1.10 Bulletin 80 



DISTRIBUTION OF COPPER COMPOUNDS THROUGH- 

 OUT THE CLIFTON-MORENCI AND GILA RIVER 

 MINING AND IRRIGATION DISTRICTS 



Sources op Copper 



The original source of the copper fomicl in this district, 

 according to Lindgren.- is a Cretaceous or early Tertiary in- 

 trusion of acidic porphyries to which, in the Clifton-]\Iorenei 

 district, all ore deposits may be finally referred. The original 

 porphyries contain as little as 0.02 per cent of copper ore in 

 the form of chalcopyrite. Under the influence of superheated 

 waters emanating from the porphyry, this chalcopyrite. together 

 with other metallic compounds, was carried out from the molten 

 intrusive mass into adjoining strata and there deposited, espe- 

 cially along fissures, in the form of concentrated masses or veins 

 of chalcopyrite and other minerals. Through erosion these de- 

 posits were afterward subjected to atmospheric oxidation, fol- 

 lowed by downward percolation and a period of secondary enrich- 

 ment due to numerous reactions mainly between the oxidized 

 compounds of copper and other minerals present. 



In limestones and shales, these processes resulted in the 

 formation of oxidized ores containing azurite, malachite, chryso- 

 colla, and cuprite. In porphyry, the main final result was 

 chalcocite or copperglance, the principal constituent of the sul- 

 phide ores of the Clifton-Morenci district. 



In general, therefore, the metasomatic changes associated, 

 first, with superheated waters arising from the original intrusion 

 of molten porphyry and, second, with meteoric waters percolating 

 downward with oxidizing effects through copper-bearing rocks. 



2 U. S. Geological Survey, Professional Paper No. 43, 190.5. 



