More than 80 percent of the potassium salts produced in the United States comes from three mines in Eddy County in southeastern New Mexico, where these salts occur in gently dipping beds of the upper Permian Salado formation. Sylvite (KCl) is produced from the same stratigraphic level at each of the three mines, and langbeinite (K 2 SO 4 .2MgSO 4 ) from a level 100 feet higher at one of the mines. Detailed geologic studies of the langbeinite zone have shown that the potash salts. are discontinuous within the zone and occur as irregular-shaped lenses. These studies further show that the potassium salts are concentrated where certain stratigraphic marker beds are farthest apart and are absent or occur only in trace quantities where the marker beds are close together. Variation of the distance between marker beds results from the relative change in position of the lower bed; this change is interpreted as resulting from irregularities on the floor of the evaporating pan that existed at this stage of salt deposition. Areas in which the most prominent marker bed is locally structurally low, and which contain the concentrations of potassium minerals, are thought to represent basins, whereas areas in which this bed is locally structurally high represents ridges.Langbeinite and sylvite occur in the same stratigraphic interval; the lateral transition from a concentration of one mineral to the other and from a concentration of one of the potassium minerals to halite is often abrupt and the interface is not marked by any recognizable stratigraphic or structural feature. Langbeinite generally predominates where the distance between marker beds is maximum, and sylvite is more abundant where the distance is somewhat less than maximum. The interpretation made is that the potash salts were precipitated directly from brines in small open basins at the top of the accumulating salt body and were subsequently covered by succeeding layers of salt, or that they were precipitated after burial from potash-rich brines that were trapped in porous but impermeable halite in the basins. The first possibility is favored because of the writer's belief that variations of temperature were very important and were greater in the open basins. The lateral change from langbeinite to sylvite or to halite at the same stratigraphic level may have been influenced by irregularities on the floor of the evaporating pan that resulted in segregation of brines of different richness, and caused variation in temperature of the brines; factors that would result in the precipitation of one salt rather than another.The writer believes that continuation of the type of study described in this report offers the only hope of finding a geologic guide to the distribution of the potash ore bodies.

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