SUPERFICIAL ALTERATION OF ORE DEPOSITS. 315 



bromides and iodides in association with the salt. Such ores, in 

 some of the mines that have gone to sufficient depths, have 

 passed into various other silver compounds, such as the sulphide 

 (argentite), argentiferous galena, etc., which represent the 

 original condition of the ores. This transition proves the 

 chlorides and other haloid compounds to be of only superficial 

 extent. 



This transition to haloid compounds is not confined to silver 

 ores, for the basic chloride of copper (atacamite) occurs at 

 Jerome in Arizona, and both chlorides and bromides of copper 

 occur in the Bloody Tanks district west of Globe in Arizona, 

 though here, as elsewhere in Arizona, the other copper minerals 

 already mentioned, such as carbonates, sulphides, etc., form the 

 bulk of the copper deposits. 



In parts of Mexico, Chile, and Peru, where saline materials 

 have collected in a manner somewhat similar to that in the arid 

 regions of the United States, the chloride of silver is one of 

 the important ores mined, and it sometimes occurs intimately 

 mixed with chloride of sodium, or common salt, forming the 

 mineral huantajayite or the lechedor of the miners. The brom- 

 ides of silver are also abundant in Chile, and, in fact, at the 

 mines of Chanarcillo, a common ore is the double chloride 

 and bromide known as embolite. Again, the atacamite, or 

 basic chloride of copper, from the Desert of Atacama is well 

 known. 



It seems probable that this transformation of the silver and 

 copper minerals did not necessarily occur exclusively while the 

 deposits were covered by saline lakes, but may have occurred 

 even more actively afterwards, when the surface waters were 

 highly impregnated with chlorides from the residue left by the 

 lakes, and when oxidation in the ore deposits was much more 

 active than when they were covered by water. This seems all 

 the more likely when we consider that the original silver and 

 copper minerals probably had to be oxidized before they were 

 converted to chlorides, etc. Of course the oxidation may have 

 partly occurred before, or during, the existence of the lakes, but 



