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Sphalerites {n the ores of the upper Mississippi Valley zinc-lead district exhibit colorbanding. This banding is uniform across the district and a sphalerite stratigraphy can be described. The stratigraphy can be divided into three stages: A (early), B (middle), and C (]ate). It is possible to correlate individual bands over a few hundred meters {nan orebody, and certain bands may be correlated many kilometers across the ore district. The color of the sphalerite bands {s related to the FeS content. Light colors correspond to a low FeS content and dark colors to a high FeS content. The variability of the FeS content within any single band {s small, suggesting the existence of uniform chemical conditions during deposition of any band across the district.Ore textures and the uniformity of the sphalerite stratigraphy across the district during any ore deposit{on interval are more compatible with ore formation from a fluid carrying both metals and sulfur than from mixing of metal-rich and sulfur-rich fluids of different or{gin.

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