USEFUL METALS LOT 



The<e three minerals have been repeatedly intlentified as of mag- 

 matic differentiation. They are doubtless the primary <-t.m- 

 pounds from which the other ores in most cases were derived. 

 B. Lotti has reported chalcopyrite, bornite and chalcocite in 

 Tuscany as original segregations in serpentinized rocks. J. F. 

 Kemp has reported primary bornite in a pegmatite vein near 

 Princeton, British Columbia. The various sulphides of copper 

 are often of hydatogenetic origin. Sulphides of more electro- 

 positive metals may have served as precipitating reagents. Cu- 

 pric solutions formed in the upper part of copper- bearing ore 

 bodies reacting upon pyrite precipitate chalcocite. Covellite may 

 be precipitated from copper sulphate solutions by the reaction of 

 chalcocite. Chalcocite may alter into chalcopyrite and bornite. 



According to Thomas and MacAlister chalcopyrite may be of 

 metasomatic origin. The mode of deposition of chalcopyrite 

 in a certain number of deposits like those formed in limestone or 

 at its contact with other rocks leads to this conclusion. The same 

 authors state that the solutions may have come from above or 

 below. The solutions were transported in the form of sulphates, 

 either due to the oxidation of pyrite in the neighboring rocks, or 

 in the form of aqueous emanations from an igneous magma dur- 

 ing the later stages of its cooling. They also state that the 

 metasomatic chalcopyrite deposits are due to ascending or de- 

 scending solutions of sulphides carrying hydrogen sulphide and 

 alkaline sulphides. 



The sulphates of copper are formed by the oxidation of the 

 surface ores of copper and iron and the concentration of the mine 

 waters. At Wicklow, Ireland, and Rio Tinto, Spain, chalcan- 

 thite thus formed has been a workable deposit. According to 

 H. Ochmichen, chalcanthite occurs in Chili as an impregnation 

 deposit in partially decomposed granite rocks with the hydrous 

 carbonates and silicates as associated minerals. Brochantite is 

 far more common than is usually supposed and can be easily 

 formed by natural reaction. 



The two basic carbonates of copper, malachite and azurite. 

 are common copper ores of secondary origin. They are formed 

 in the upper portion of ore bodies by the action of carbonated 

 waters upon copper compounds or by the reactions between 

 cuprous solutions and limestone. At Corinth, Vermont, the 

 author has found fine specimens of both malachite and azurite 

 formed from chalcopyrite by the action of carbonated waters. 



