Page:The Journal of geology (IA journalofgeology21894univers).pdf/331
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 bromides of silver are also abundant in Chile, and, in fact, at the mines of Chañarcillo, 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