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[en] The US Department of Energy is constructing and operating the Waste Isolation Pilot Plant (WIPP), a research and development facility near Carlsbad, New Mexico, to determine whether or not defense-generated high-level radioactive waste can be stored safely in bedded salt. The goal of the WIPP modeling program is to develop the capability to predict room responses from one site to another without a priori knowledge of the actual room responses. Data from one of the early WIPP excavations, called the South Drift, have already been used to form an initial evaluation of computational models for predicting room closures as a result of salt creep. In that study, a significant unresolved discrepancy existed between predicted and measured room closures. It was suggested that future studies address alternate forms of the constitutive law. In this paper, an alternate form of the creep model for salt is used that is founded upon the deformation-mechanism map for the micromechanical deformation processes. This model embodies both steady-state and transient creep. Also, quasi-static plasticity is incorporated into the complete constitutive model for salt. The conclusion is drawn that the combination of the mechanistic creep model, plasticity, and flow potential can approximate the late time South Drift deformation. Further improvement of the model fit of plasticity in the future is expected to further improve the simulation
[en] The phase equilibriums of Na, K, Mg, Ca//SO4, Cl-H2O at 50 deg C in the range of kainite crystallization (KCl·MgSO4·3H2O) are studied by means of translation method. On the basis of obtained data the fragment of diagram of phase equilibriums of Na, K, Mg, Ca//SO4, Cl-H2O at 50 deg C in the range of kainite crystallization (KCl·MgSO4·3H2O) is constructed.
[en] We have attempted radiometric dating of halide-sulfate salts and clay minerals from the Delaware Basin, New Mexico, USA, as part of geochemical study of the stability of the evaporite sequence at the WIPP (Waste Isolation Pilot Plant - a US DOE facilty) site. We undertook this dating to determine: (1) primary age of evaporite genesis or time(s) of recrystallization; (2) if previously undated evaporite minerals (leonite, polyhalite, kieserite) give useful data; and (3) if the detrital clay minerals have been radiometrically reset at any time following their incorporation into the evaporite medium. We have shown earlier that polyhalites can indeed be successfully dated by the K-Ar method, and once corrections are applied for admixed halide minerals, dates of 210-230 Ma for the Delaware Basin are obtained. Rb-Sr isochrons from early stage sylvites-polyhalites- anhydrites yield 220 +- 10 Ma, even when some sylvites yield lower K-Ar dates due to loss of *40-Ar. K-Ar dates on leonites and kieserities are also low due to *40-Ar loss, but their Rb-Sr dates are higher. Detrital clay minerals from the Delaware Basin collectively yield a highly scattered isochron (390 +- 77 Ma), but samples from a local area, such as the WIPP Site, give a much better age of 428 +- 7 Ma. These dates show that the interaction between the clay minerals and the evaporitic brines was insufficient to reset the clay minerals Rb-Sr systematics. In a related study, we note that a dike emplaced into the evaporite at 34 Ma had only very limited effect on the intruded rocks; contact phenomena were all within 2 m of the dike. All of our geochemical (radio-metric and trace element) studies of the WIPP site argue for preservation of the isotopic and chemical integrity of the major minerals for the past 200 Ma
[en] 16 δ34S- and 12 δ18O-data of sulphate minerals (kieserite, langbeinite, glaserite, polyhalite, anhydrite) from the potash seam 'Stassfurt' of the South Hartz region are presented. Due to microstratigraphical sampling the data are comparable. Though exposures at the margin of he basin are onshore influenced (enlarged clay strata) a nonmarine contribution of sulphate during the sedimentation and transformation of the potash seam cannot be proved. From sulphate balance calculations and S-isotopes it is referred that the SO4 of K-sulphate minerals is derived from kieserite. Recrystallization took place under closed conditions - with the exception of polyhalitic hard salt. Oxygen of the primary sedimentary MgSO4 is not in isotopic exchange equilibrium with ocean water. Due to epigenetic long-term influence of marine low-content solutions on the potash seam the isotopic exchange equilibrium is later favoured resulting in an 18O-enrichment in sulphate. The following reversal to lower δ18O-data is likely the result of meteoric influences. (author)
[en] The first potassium salts ores found in Colombia are presented and described; they are located in the Santander province, in La Mesa de los Santos area, between Los Santos village and the rio Chicamocha Canyon. From a geological point of view, the mineralization is associated to the sediments of the Paja Formation, Early Cretaceous in age, and is located near the base of the formation. In the study area the main structure is the Villanueva syncline which involves, from bottom to top, Los Santos, Rosablanca, Paja, Tablazo and Simiti formations.The mineralization consists of small veins where the main mineral is singenite (K2Ca[SO4]2- H2O) with small amounts of carbonates and accidental minerals. In the host rock, minerals like langbeinite (K2Mg2[SO4]3) andrinneite (K3Na[Fe,Cl]6) are present; they show that the rock was formed in an evaporitic environment and that detailed studies of that sequence may lead to the discovery of other mineralizations of economic interest.
[en] Polyhalite (K2Ca2Mg(SO4).2H2O) is an important mineral present in the bedded evaporites of the WIPP site, southeastern New Mexico. Polyhalite contains two structurally bonded water molecules, and it is thus important to know if this mineral formed at or close to the time of sedimentation or, as proposed by others more or less continuously throughout the Mesozoic and Cenozoic. If formed much later than original evaporite formation, then this implies a new source of water in order for polyhalite to form in turn raising questions about water abundance and mobility in the bedded evaporites. Polyhalite is not well suited for Rb-Sr geochronologic study because of the large amounts of common Sr, but it has been shown to be suitable for study by the K-Ar geochronologic methods. Pure polyhalites and those mixed with very small amounts of impurities yield K-Ar dates in the range of 200 to 220 MYBP and indicate little if any, loss of 40Ar. Polyhalites mixed with sylvite, halite, and (Na,K)Cl yield lower ages due to loss of 40Ar from the halides. Apparent age lowering is proportional to halide content and an extrapolated age of formation of near 225 MYBP results. Collectively, the K-Ar data convincingly show that the polyhalites formed at the time of sedimentation (except for isolated occurrences near dike intrusions) in Late Permian time. Finally, thermodynamic calculations, supported by petrographic study, show that polyhalite is often stable with respect to carnallite, sylvite and other minerals formerly thought to be older than polyhalite. 1 figure, 1 table
[en] In southeastern New Mexico, Marker Bed 139 (referred to in this report as MB139) is one of 45 numbered siliceous or sulfatic units within the Salado Formation of the northern Delaware Basin. MB139 is divided into five zones. Zones I and V are the upper and lower contact zones, respectively. Zone II is a syndepositionally deformed subunit of polyhalitic anhydrite. Zone III is mixed anhydrite and polyhalitic anhydrite, a distinctive pale-green and pink, with subhorizontal fractures. Zone IV consists of interlayered halite and anhydrite without the overprint of polyhalite. This sequence was transitional between submarine and subaerial. The anhydritic units of MB139 formed in salt-pan or mudflat environments or both. Undulations observed along the upper contact of MB139 are interpreted to result from traction deposits or from reworking of the upper portion of the marker bed during the transition from anhydrite to halite deposition. Zones II and III exhibit soft-sediment deformation and later traces of dewatering; e.g., formation of stylolites. Such deformation is not observed in the halite above MB139 or in Zone V and the halite units below MB139. A distinctive set of subhorizontal fractures occurs in MB139 in mid-Zone III and, to some extent, in Zone IV. These fractures are partially infilled with halite and polyhalite. Brine occurrences at the mined facility horizon at the Waste Isolation Pilot Plant may be related to these fractures. The fractures formed either in response to stress cycles that were functions of sedimentation and erosion, or in response to deformation in the underlying Castile Formation. The subhorizontal orientation, dominant in the sampling to date, is more consistent with the interplay between stress and sedimentation cycles
[en] Chemical data indicate the occurrence of three types of brines in the Asse salt Mine: (a) Mg-Cl type, of carnallitite origin with Li < 30 mg/kg; (b) Na-Cl type brines, of rock salt origin, with Li > 100 mg/kg; and (c) almost pure MgCl2-type brines with Li > 100 mg/kg. The first group may be subdivided into brines with Li < 4.0 mg/kg and brines with Li between 18 and 30 mg/kg. Lithium is shown to be an efficient complementary tool in tracing the origin of the brines. Isotopic data of brines that were sampled directly from seepages indicate that these brines are not a mixture with relatively fresh ground water from the overburden sediments. The stable isotope composition (18O and D) of hydration water in carnallite, kieserite and polyhalite were also studied. It is shown that water extracted from the so-called primary carnallite is isotopically different from water extracted from secondary carnallite. The isotopic fractionation factors for 18O and D between carnallite hydration water and mother solution were studied in the laboratory. Assuming that crystallization water of the so-called primary carnallite samples is not altered, the isotopic composition of the mother solution is evaluated. (author)
[en] Calorimetric measurements have been performed to determine the heat of dissolution of polyhalite K2SO4. MgSO4.2CaSO4.2H2O and its analogues K2SO4.MSO4.2CaSO4.2H2O (M = Mn, Co, Ni, Cu, and Zn) at T = 298.15 K. The dissolution experiments were carried out in NaClO4 solution with varying concentrations (0.5 to 2.0) mol kg-1. All polyhalites dissolve exothermically. Exothermicity increases with concentration of NaClO4. An extrapolation to infinite dilution was done using the SIT model. Within the limits of experimental uncertainty, the enthalpies of dissolution for the triple salts K2MgCa2(SO4)4.2H2O with M = Mg, Mn, Ni, and Zn coincide. The value for the cobalt salt is noticeably less exothermic. Dissolution enthalpy of leightonite K2CuCa2(SO4)4.2H2O, which does not crystallize in the polyhalite structure, deviates considerably within the series
[en] A pretest reference calculation for the Geomechanical Evaluation or Room G experiment is presented. The Geomechanical Evaluation is one of several large-scale in situ tests currently under construction near Carlsbad, New Mexico, at the site of the Waste Isolation Pilot Plant (WIPP). The Room G experiment consists of isolated, two-dimensional drifts with different room spans, an isolated drift intersection, and a wedge pillar. The primary purpose of the experiment is to provide data for validating computational modeling capabilities used in analyzing nuclear waste repositories in salt. The calculation presented here addresses only one portion of the test, namely isolated drift configurations which are initially 6.1 m (20 ft) wide by 3.05 m (10 ft) high. The Geomechanical Evaluation is heavily instrumented for monitoring deformations due to creep of the salt. Data from the experiment are not available at the present time, but the measurements for Room G will eventually be compared to the results presented in this report to assess and improve structural modeling capabilities for the WIPP. The model used for this calculation represents the state of the art at the present time. A large number of plots are included since an appropriate result is presented for every gage location associated with the 6.1 m wide drifts. 53 refs., 53 figs., 3 tabs