Core lithology, Valles caldera No. 1, New Mexico

Gardner, Jamie N.; Goff, Fraser; Goff, S.; Maassen, L.W.; Mathews, K.; Wachs, Daniel; Wilson, D.

doi:10.2172/6524236

Cited by 1 publication

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“…In general, we found clays only in VC-1 core samples from the VClO and VClT. The clays were principally illite, and may represent a weathering surface (also identified in the core log, Gardner et al 1987) rather than a zone of hydrothermal alteration.…”

Section: 113mentioning

confidence: 70%

“…In a detailed study Pense (1977) Initially we obtained samples from the VC-1 corehole (figure 2.1). The VC-1 core log (Gardner et al, 1987;Self et al, 1988) describes two sets of contacts between obsidian and tuff. At a depth of 486 ft, contact 1 occurs between the BBO and a thin tuffaceous unit (originally considered to be the BRT).…”

Section: Geologic Backgroundmentioning

confidence: 99%

“…High-temperature devitrification of rhyolite domes and flows is thought to release F-and C1-rich g&, and these gases have apparently metasomatized the underlying pyroclastics in several topaz-rhyolite localities (Burt et al, 1982). At some locations, there are extensive zones of devitrification and red staining at or within a few meters of the BBO-BRT contact (figure 3.6); the VC-1 core logs (Gardner et al, 1987) indicate at least 50 m of the flow are devitrified to some extent, so there probably was an ample supply of C1-and Frich gas given off as the Valles flow cooled. The thin plates of feldspar found at site 12 (figures 4.21-4.24) are reminiscent of lithopysae textures, suggesting the tuffs adjacent to the contact were subject to alteration by high-temperature gases.…”

Section: Vapor Phase Transport Of Metalsmentioning

confidence: 99%

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The Valles natural analogue project

Stockman¹,

Krumhansl²,

et al. 1994

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The folloivlng documents in the NUREG serles are avallable for purchase from the Government Printing Offlce:formal NRC staff and contractor reports, NRC-sponsored conference proceedings, International agreement reports, grantee reports, and NRC booklets and brochures. Also avallable are regulatory guldes, NRC regulatlons In the Code of Federal Regulatlons. and Nuclear Regulatory Commission Issuances. ABSTRACTThe contact between an obsidian flow and a steep-walled tuff canyon was examined as an analogue for a high-level waste repository. The analogue site is located on the southwest rim of the Valles Caldera in New Mexico, where the massive Banco Bonito obsidian flow filled a paleocanyon in the Battleship Rock tuff. The obsidian flow provided a heat source, analogous to waste panels or an igneous intrusion in a repository, and caused evaporation and migration of water. The tuff and obsidian samples were analyzed for major and trace elements and mineralogy by INAA, X R F , X-ray diffraction, and scanning electron microscopy and electron microprobe. Samples were also analyzed for D/H and 39Ar/40Ar isotopic composition.Overall, the effects of the heating event seem to have been slight and limited to the tuff nearest the contact. There is some evidence of devitrification and migration of volatiles in the tuff within 10 meters of the contact, but variations in major and trace element chemistry are small and difficult to distinguish from the natural @re-heating) variability of the rocks. Apart from devitrification, the p~ncipal mineralogic change in tuff near the contact is the development of feldspar-sifica linings on voids in the pumiceous tuff matrix; we found no significant development of zeolites in the samples examined for this study. Age determinations by 394r/40Ar are ambiguous, and do not provide resolution necessary to map paleoisotherms from the heating event.A simple model is developed to predict the temperatures in the obsidian and tuff as a function of time. The model predicts the movement of a boiling front several tens of meters into the tuff over several hundred years, and is relatively insensitive to the assumed saturation. Flowing-steam experiments show that F and C1 are readily lost by the glassy tuff at temperatures as low as 200 "C. Loss of F is consistent with diffusionantrolled release, and could produce condensates with tens to hundreds of ppm F in the region behind the boiling zone. ISeveral mechanisms for producing compositional variations in the tuff are examined. A simple evaporation-capillarity model can explain the concentration of F above background levels. It is shown that the remobilization of silica, predicted by several workers, would probably not be detected in bulk analyses, and may be masked in microscopic analyses by the effects of alkali metasomatism. Significant gas phase transport of metals at the analogue site is shown to be improbable.iii

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Section: 113mentioning

confidence: 70%

Section: Geologic Backgroundmentioning

confidence: 99%