Fluid inclusions in quartz associated with copper-and molybdenum-bearing breccia pipes in northern Sonora, Mexico, contain from 4,000 to 16,000 ppm copper and similar amounts of iron. These values suggest that the base-metal transporting capability of some postmagmatic fluids is considerable.

Metal-bearing hydrous fluids of magmatic origin may undergo sufficient dilution by nonmagmatic waters to lose their magmatic identity and still represent major metal-transporting agents. Thus, stable-isotope data that indicate the predominance of nonmagmatic water during the formation of an ore deposit may be misleading in terms of the true origin of the metals involved.

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