Mineralogy of the Rustler Formation in the WIPP-19 core

The mineralogy of the Rustler Formation is a critical element in many of the radionuclide release models for the Waste isolation Pilot Plant (WIPP), and it is necessary to know the abundances of the various minerals present, their compositions, their textures and locations with respect to water-bearing features, and their interrelationships. Clay mineralogy in particular is of vital importance because of the ability of clay minerals to sorb contaminant cations. Furthermore, the minerals present in the different units of the Rustler Formation are possible sources for solutes present in waters taken from various boreholes in the vicinity of the WIPP site. This report characterizes the mineralogy of the Rustler Formation as represented in core from borehole WIPP-19. The major components, as determined by x-ray diffraction (XRD), are halite, anhydrite, gypsum, dolomite, magnesite, quartz, and clay. Minor components include calcite, pyrite, feldspar and phyllosilicates of metamorphic origin (muscovite, biotite, and chlorite). Clay minerals, identified by XRD, include illite, serpentine, chlorite, and mixed-layer chlorite/smectite (including corrensite). In general, this study should be considered a detailed analysis of the Rustler section mineralogy. It is unlikely that any other minerals are present elsewhere in the Rustler Formation in any great quantity. Abundances of individual minerals may vary considerably in other areas of the formation. 20 refs., 39 figs., 5 tabs