Experimental study on the ordering of opal-CT.

Kano, Kazuhiko; Taguchi, Kazuo

doi:10.2343/geochemj.16.33

Cited by 21 publications

(18 citation statements)

References 15 publications

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“…It is noteworthy that the disappearance ofclinoptilolite and mordenite as major phases coincides closely with the disappearance ofcristobalite as a major phase, supporting the conclusions of Kerrisk (1983). The deepest occurrence of cristobalite in USW G-2 core corresponds to an I/S temperature of about 100~ If temperature is the controlling variable in the transformation of cristobalite to quartz (Ernst and Calvert, 1969;Kano and Taguchi, 1982), then this reaction may have provided an indirect temperature control on the elinoptilolite-to-analeime reaction. The disappearance of cristobalite as a major phase would have resulted in a lower aqueous silica activity, thus destabilizing clinoptilolite.…”

Section: Bulk-rock Mineral Stabilitysupporting

confidence: 56%

Paleogeothermal and Paleohydrologic Conditions in Silicic Tuff from Yucca Mountain, Nevada

Bish

Aronson

1993

Clays and clay miner.

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Abstract--The clay mineralogy of tufts from Yucca Mountain, Nevada, the potential site of the nation's first high-level radioactive waste repository, has been studied in order to understand the alteration history of the rocks and to predict potential future alterations. Bulk-rock samples and clay-mineral separates from three drill holes at Yucca Mountain (USW G-l, USW G-2, and USW GU-3/G-3) were studied using X-ray powder diffraction, and supporting temperature information was obtained using fluid inclusion data from calcite. Twelve K/Ar dates were obtained on illite/smectite (US) separated from the tufts from the two northernmost drill holes, USW G-I and G-2. The predominant clay minerals in the Yucca Mountain tufts are interstratified I/S, with minor amounts of chlorite and interstratitied chlorite/smectite. The I/S reactions observed as a function of depth are similar to those observed for pelitic rocks; I/S transforms from R = 0 interstratifications through R = 1 and R -> 3 interstratifications to illite in USW G-2 and to R > 3 I/S in USW G-I. The R = 0 I/S clays in USW GU-3/G-3 have not significantly transformed. K/Ar dates for the I/S samples average 10.4 my. These data suggest that the rocks at depth in the northern portion of Yucca Mountain were altered 10.0-11 my ago, soon after creation of the Timber Mountain caldera to the north. Both I/S geothermometry and fluid inclusion data suggest that the rocks at depth in USW G-2 were subjected to postdepositional temperatures of at least 275~ those in USW G-1 reached 200~ and rocks from USW GU-3/G-3 probably did not exceed 100~ These data suggest that no significant hydrotbermal alteration has occurred since Timber Mountain time, ~ 10.7 my ago.Estimates of the temperature of formation of illite/smectites yield probable stability limits for several minerals at Yucca Mountain. Clinoptilolite apparently became unstable at about 100~ mordenite was not a major phase above 130~ and analcime transformed to albite above 175"-2000C. It appears that cristobalite transformed to quartz at 90*--100~ in USW G-2 but must have reacted at considerably lower temperatures (and for longer times) in USW GU-3/G-3. The reactions with increasing depth appear coupled, and clinoptilolite and cristobalite disappear approximately simultaneously, supporting aqueous silica activity as a controlling variable in the clinoptilolite-to-analcime reaction. The reaction of clinoptilolite to analcime also coincides with the appearance of calcite, chlorite, and interstratified chlorite/ smectite. Although the hydrothermal fluids may have been a source for some cations, breakdown of clinoptilolite (and mordenite) probably provided the source of some of the Ca for calcite, Mg for chlorite, K for the I/S found deeper in the section, and Na for analcime and albite.Using the rocks in USW G-l, G-2, and GU/G-3 as natural analogs to repository-induced thermal alteration suggests that the bulk of the clinoptilolite-and mordenite-bearing rocks in Yucca Mountain will not react to less sorptive phases such as ...

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Section: Bulk-rock Mineral Stabilitysupporting

confidence: 56%

Paleogeothermal and Paleohydrologic Conditions in Silicic Tuff from Yucca Mountain, Nevada

Bish

Aronson

1993

Clays and clay miner.

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“…Clear evidence, however, is presented for the appearance of cristobalite before quartz crystallization commences. Kano and Taguchi (1982) studied the crystallization of amorphous silica in pH = 12.6 solutions at 200, 270, and …”

Section: Silica-phase Transitionsmentioning

confidence: 99%

Kinetics of silica-phase transitions

Duffy¹

1993

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“…The d(101) spacing of Neogene siliceous sediments is correlated closely with the maximum temperature to which the sediments have been subjected (IInMA and TADA) 1981). On the other hand, the decreasing rate of d(101) spacing is experimentally found to be remarkably dependent on the reaction temperature (MIzuTANI, 1977;KANO, 1979;KANO and TAGUCHI, 1982).…”

Section: Introductionmentioning

confidence: 99%

“…Based on the experiments under dry and hydrothermal conditions (JONES and SEGNIT, 1971;MIZUTANI, 1977;KANO, 1979;KANO and TAGUCHI, 1982), the decreasing rate of d (101) spacing was formulated by KANO (1979) and KANO and TAGUCHI (1982) as an empirical equation:…”

Section: Introductionmentioning

confidence: 99%

“…In that process, opal-CT becomes progressively ordered as is distinctly indicated by the decrease in d(101) spacing.Based on a kinetic equation experimentally found by KANO (1979) and KANO and TAGUCHI (1982) , the decreasing rate of d(101) spacing has been calculated from previously reported d (101) spacings (MITSUI, 1975) and thermal history of sediments in a borehole, MITI Hamayuchi. The calculated rate makes a subtle difference between the reported and calculated d(101) spacings , suggesting the availability of the equation applied.…”

mentioning

confidence: 99%

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Ordering of opal-CT in diagenesis.

Kano

1983

Geochem. J.

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Opal-CT in sediments is formed from opal-A and is converted to quartz during diagenesis. In that process, opal-CT becomes progressively ordered as is distinctly indicated by the decrease in d(101) spacing.Based on a kinetic equation experimentally found by KANO (1979) and KANO and TAGUCHI (1982) , the decreasing rate of d(101) spacing has been calculated from previously reported d (101) spacings (MITSUI, 1975) and thermal history of sediments in a borehole, MITI Hamayuchi. The calculated rate makes a subtle difference between the reported and calculated d(101) spacings , suggesting the availability of the equation applied. However, even if compared at the same temperature, the rate is much slower than that in hydrothermal alkaline conditions. Thus, the ordering process of opal-CT is more or less chem ically controlled.Taking the thermal history of sediments into account, a model based on the kinetic equation well fits the previously reported relationship between the d(101) spacing of Neogene siliceous sediments and the maximum temperature to which the sediments have been subjected (IIMIMA and TADA, 1981), suggesting that the ordering process of opal-CT in diagenetic conditions is controlled mainly by temperature . The features of distribution of d(l01) spacing in sediment piles have been discussed by using the model .

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Experimental study on the ordering of opal-CT.

Cited by 21 publications

References 15 publications

Paleogeothermal and Paleohydrologic Conditions in Silicic Tuff from Yucca Mountain, Nevada

Paleogeothermal and Paleohydrologic Conditions in Silicic Tuff from Yucca Mountain, Nevada

Kinetics of silica-phase transitions

Ordering of opal-CT in diagenesis.

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