In experiments, metallic copper was dissolved, in the absence of air and the presence of silica, by solutions of sodium chloride, carbonate and sulphate; calcium chloride; and carbon dioxide, at temperatures of 200 degrees C. and 300 degrees C. On cooling, native copper was deposited. In the presence of air, cuprite and native copper precipitated from sodium chloride solutions. Experiments with similar solutions, with datolite, prehnite and apophyllite, at room temperature yielded copper oxides and carbonates, but no native copper. Metallic silver was dissolved by sodium carbonate and calcium chloride solutions at 300 degrees C. and 200 degrees C. respectively and deposited as native silver.Consideration of the experimental data, as well as mine water analyses and mineral paragenesis, suggest that the native copper of the Michigan and similar deposits formed at temperatures above 100 degrees C., and probably above 200 degrees C., by cooling of copper-bearing solutions rich in sodium, calcium and chloride, but relatively poor in iron and sulphide.

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