Granites alteration

Alderton, D.H.M., Pearce, J.A. and Potts, J. (1980) Rare earth element mobility during granite alteration evidence from southwest England. Earth Planet. Sci. Lett., 49, 149-165. 

Correlation of total surface inventories, obtained by selective extraction of the mixing-cell, to thg degree granite alteration and to temperature, indicates that Co and DSe show a positive correlation with both alteration and temperature. Cobalt-60 and Se inventories for the experiments conducted with fresh granite at 20°C and at 60°C (Reference No. 37 and 34, Table III) indicate about a factor of two increase at 60 C, as would be expected from the production of oxyhydroxides baggd on th alter-ation rate data. Other residual inventories for Co and Se (Table III) follow a pattern consistent with increased oxyhydr-oxide inventories due to both alteration and elevated temperature. 

Cesium inventories in Table III show no effect of granite alteration or temperature. This is consistent with the observation that cesium prefers micaceous and clay minerals which are not expected to form under the conditions of these experiments. 

It has been shown that cesium diffuses into the lattice of micaceous minerals, resulting in its entrapment (12) The 35 to 40% "fixed" cesium (Figure 4) is, therefore, likely bound internally at lattice sites, which would have to be destroyed in order to release the cesium. The extraction of cesium by KTOX in these experiments is likely due to dissolution of iroir-bearing minerals, such as biotite and horneblende rather than oxyhydroxides. If sorption by oxyhydroxides had been involved, a trend of increasing sorption with granite alteration, similar to that exhibited by cobalt and selenium, should have been observed. 

Blancaneaux, P. and Pouyllau, M. (1977). Formes d alteration pseudokarstiques en relation avec la geomorphologie des granites precambriens du type Rapakivi dans le territoire Federal de I Amazone, Venezuela. Cah. ORSTOM Ser. Pedol. 15,131-142. 

It is thought that submarine hydrothermal alteration of basalt took place in the Besshi-subtype mineralization area in Sanbagawa. However, no study on the hydrothermal alteration of basalt (basic schist) has been carried out and it is clearly necessary. The contact metamorphosed rocks and sulfide ores caused by Tertiary granitic intrusion are found in deeper part of the Besshi mine and Makimine mine (Tatsumi, 1952 Kase, 1972). 

Host rocks in the Hitachi area suffered regional metamorphism, contact metamorphism by Cretaceous granitic rocks and hydrothermal alteration associated with sulfide mineralization. 

We will take an example of closed-system meteoric-hydrothermal alteration of a granitic rock (modified from Taylor, 1978). A granitic rock with 8lsO= +8 and 8D=—65 is invaded by meteoric water (8180= —16, 8D= —120). Assume that... 

Figure 11.23 shows the isochron obtained by Marshall and De Paolo (1982) for the granite batholith of Pikes Peak (Colorado). The effectiveness of the double-spike technique is evident, especially when we see that aliquot-spiked samples do not fall on the best-fit interpolant (York s algorithm York, 1969). The obtained age (1041 32 Ma) is consistent with that previously obtained with Rb-Sr whole rock analyses (1008 13 Ma see Marshall and De Paolo, 1982, for references). The initial ratio ( Ca/ Ca)o of 151.0 is identical, within the range of uncertainty, to upper mantle values, indicating negligible contamination by old crust components the relative K/Ca abundance in the earth s mantle is about 0.01, a value too low to alter the primordial (" Ca/" Ca)o composition. 

Geological Setting The area is underlain by Birimian meta-volcanic and meta-sedimentary rocks that have been intruded by granites. The meta-volcanic rocks are of basaltic and gabbroic compositions and most have been altered to various schists. The metasedimentary rocks consist of sandstones, siltstones, tuffs, carbonaceous phyllites, tuffaceous phyllites, cherts and maganeferous rocks (Leube et al. 1990). 

Criss et al. (1987) and Gregory et al. (1989) developed a theoretical framework that describes the kinetics of oxygen isotope exchange between minerals and coexisting fluids. Figure 2.17 shows characteristic patterns in 8-5 plots for some hy-drothermally altered granitic and gabbroic rocks. The arrays displayed on... 

Thermodynamic model calculations, which take into account the current temperature gradient in the Rhine graben and the composition of the altered granite, have shown that the hydrothermal fluids present in the granite cause a new stage of alteration (Komninou Yardley 1997). Model calculations have been performed in order to predict the formation of new... 

Ledesert, B., Berger, G., Meunier, A., Genter, A. Bouchet, A. 1999. Diagenetic-type reactions related to hydrothermal alteration in the Soultz-sous-Forets granite, France. European Journal of... 

Sausse, J. 2001. Hydromechanical properties and alteration of natural fracture surfaces in the Soultz granite (Bas-Rhin, France). Tectonophysics, 348, 169-185. 

Fig. 11. (a) Thermodynamic reaction pathway for the initial oxidative alteration of the spent fuel matrix at pH 8, calculated by using the PHREEQC code (adapted from Bruno etaL 1995). (b) Thermodynamic reaction pathway for the alteration of schoepite in granitic/bentonite groundwater at pH 8, calculated by using the PHREEQC code (adapted from Bruno et al. 1995 with permission). 

The Hostrock and Backfill Material. Most crystalline igneous rocks, including granite and gneiss, are composed of a comparatively small number of rock forming silicate minerals like quartz, feldspars (albite, microcline, anorthite etc.) micas (biotite, muscovite) and sometimes pyroxenes, amphiboles, olivine and others. Besides, there is a rather limited number of common accessory minerals like magnetite, hematite, pyrite, fluorite, apatite, cal cite and others. Moreover, the weathering and alteration products (clay minerals etc.) from these major constituents of the rock would be present, especially on water exposed surfaces in cracks and fissures. 

---