3917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 401 



C. N. Catlin, associated with the Arizona Agricultural Experi- 

 ment Station from time to time; and to the helpful advice of 

 Dr. Howard S. Eeed. of the University of California Graduate 

 School of Tropical Agriculture, in connection with the physio- 

 logical part of the work herein described. The publication, also, 

 has been criticized to its advantage by Dr. C. B. Lipman of the 

 Universitv of California. 



DISTRIBUTION OF COPPER COMPOUNDS THROUGH- 

 OUT THE CLIFTON-MORENCI AND GILA RIVER 

 MINING AND IRRIGATION DISTRICTS 



Sources of Copper 



The original source of the copper found in this district, 

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

 trusion of acidic porphyries to which, in the Clifton-IMorenci 

 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 ma.ss into adjoining strata and there deposited, espe- 

 ciall}' 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 

 chalcoeite 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 



- U. S. Geological Survey, Professional Paper No. 43, 1905. 



