Basalt migration

Figure 12. Profiles of Th to Nb ratios for four Hawaiian soils developed on lava flows with ages ranging from 20 ka to 4100 ka (Kurtz et al. 2000). In these soils, Nb is assumed to be an irmnobile element. Variations of Th/Nb ratios, with lower values than those of basalt (greyed area) in the upper part of the profile and higher values in the lower part indieate an internal downward migration of Th in these fom weathering profiles. Cireles = 20 ka Laupahoehoe site, triangles = 150 ka Kohala site, squares = 1400 ka Molokai site, diamonds = 4100 ka Kauai site.

Steinmann, M., Stille, P., Mengel, K. Kiefel, B. 2001. Trace element and isotopic evidence for REE migration and fractionation in salts next to a basalt dyke. Applied Geochemistry, 16, 351-361. 

A key problem in the present natural analogue study is the distinction between chemical variations related to trace element migration during basalt alteration and variations due to magmatic fractionation and other syn-intrusive processes. The detailed evaluation of the available data has shown that the chemical and isotopic composition of the HC1 residues is largely controlled by fractional crystallization and syn-intrusive assimilation of salt. In contrast, the chemical composition of the leachates is strongly modified by post-intrusive alteration (Steinmann et al. 1999). 

In order to trace the migration of basalt-derived REE in the salt, REE distribution patterns (Fig. 7) and Nd isotopic compositions (Fig. 8) have been determined in a salt horizon adjacent to a basalt dyke (Fig. 2). The flat REE distribution patterns and the almost basaltic Nd isotopic composition of the salt samples collected at the basalt-salt contact point to a basaltic origin of the REE for this sample. With increasing distance from the contact, the patterns are more and more depleted in Ce, Pr, Nd, Sm, and Eu and the Nd isotopic compositions are slightly shifted towards lower eNd values, which, however, still remain above values typical for continental crust or Permian seawater (Stille et al. 1996, and citations therein). This evolution of the REE distribution patterns and the Nd isotopic compositions could basically be due to mixing between a basalt and a salt end member or, alternatively, it could have been fractionation of the REE during migration in the salt that modified the REE patterns. 

Material similar to anthraxolite, but of lower rank, was found in amygda-loidal cavities in the Triassic basalts of New Jersey and Connecticut by Russell (32). Both Chapman and Hunt (7, 21) listed Canadian localities where anthraxolite migrated into igneous host rocks, and Arschinow described examples from the Crimea, Siberia, Scandinavia, India, and Argentina (1) where quartz and calcite are also associated with the carbon. 

Sahagian DL (1985) Bubble migration and coalescence during the solidification of basaltic lava flows. J Geology 93 205-211... 

The groundwater transport of radionuclides through waterbearing interbed layers in the Columbia River basalt formation will be controlled by reactions of the radionuclides with groundwater and interbed solids. These interactions must be understood to predict possible migration of radionuclides from a proposed radioactive waste repository in basalt. Precipitation and sorption on interbed solids are the principle reactions that retard radionuclide movement in the interbeds. The objective of the work described herein was to determine the sorption and desorption behavior of radionuclides important to safety assessment of a high-level radioactive waste repository in Columbia River basalt. The effects of groundwater composition, redox potential, radionuclide concentration, and temperature on these reactions were determined. 

Interaction of Groundwater and Basalt Fissure Surfaces and Its Effect on the Migration of Actinides... 

Unaltered basalt appears to effectively limit the migration of actinides dissolved or suspended in the ground-water. 

There was no perceptible difference in groundwater/ basalt interactions or actinide migration due to laboratory analog apparatus construction materials (Hastelloy vs. Monel). 

Vandergrift GF, Bowers DL, Gerding TJ, et al. 1984. Interaction of groundwater and basalt fissure surfaces and its effect on the migration of actinides. Washington DC American Chemical Society. 

The basaltic rocks of Mururoa and Fangataufa offer two advantages with respect to the containment of the explosion products. First, their low permeability opposes the vertical migration of radioactive products. Second, under the effect of the heat generated by the explosion, the basalts melt to form glasses, which trap the majority of these products (approximately 98% of the elements with half-lives longer than 30 years are trapped in this way). 

Studies of the migration of Pu in limestones and basalts indicate that the absorption coefficients are dependent on the types and amounts of other ions present in the solution. Migration coefficients were measured for flow along the surface of fissures and through the porous stone. At least two chemical forms of Pu were present in neutral solutions and one of these, presumably a polymerized Pu oxide, migrated 10 times faster than the other form. 

The experiments were of two types. In the first set, studies were made of the migration of solutions of Pu through cores of Niagara limestone and basalts. A high pressure chromatographic absorption appa-... 

The results of these experiments yielded a migration coefficient, m = 30 10 fim/m of water flow for the limestone and 61 8 /xm/m for the basalts, where m is the average distance traveled by the Pu atoms for every meter traveled by the H2O molecules. 

To test this model of the relationship of the surface absorption coefficient to the migration rate through the fissure, we constructed a model fissure. This was done by sealing a smooth slab cut from a basalt core to the face of a Teflon block that had a 0.0127-cm depression milled dovm its face. This then formed a Assure that was 0.0127 X 1 X 4 cm in size, tracer was dissolved in 10 ml of water and allowed to... 

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