Granites hydrothermal alteration

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... 

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... 

The autoradiographs also show some sorption on the granite obtained from the Eye-Dashwa Lakes pluton (Figure 6). Even though the iron concentration is low, hydrothermal alteration of the granite has resulted in the infilling of the minute fractures in the microcline feldspar with iron oxides, which show technetium sorption, while there is no sorption on the biotite crystals. 

Ferry JM (1979) Reaction mechanisms, physical conditions, and mass transfer during hydrothermal alteration of mica and feldspar in granitic rocks from South-Central Maine, USA. Contrib Mineral Petrol 68 125-139... 

Hecht, L., Thuro, K., Plinninger, R.J., Cuney, M., 1999. Mineralogical and geochemical characteristics of hydrothermal alteration and epi-syenitization in the Konigshain granites, northern Bohemian Massif, Germany. Int. Joum. Earth Sciences 88, pp 236-252. 

It is primarily formed by weathering or low-temperature hydrothermal alteration of feldspars, muscovite and other Al-rich silicates of acidie igneous rooks (granite, rhyolite, quartz diorite ete.). Hydrolysis is the chemical weathering reaction that brings about this transformation. 

Hydrothermal and residual deposits are classified as primary occurrences, although some authorities call them secondary as they are found in the rocks from which they have been formed. Sedimentary deposits are always secondary. The kaolins are formed by the hydrothermal alteration and weathering of feldspathic igneous and metamorphic rocks (especially granite) under relatively low temperatures and pressures. The most common parent minerals are feldspars and muscovite micas. The primary deposits will usually be mixed with unaltered granite, mica, feldspar and quartz. Secondary deposits are usually found in layered qualities with very variable purity. 

In confirmation of these findings it should be noted that Li, Sn and B are all closely associated with the subsequent hydro-thermal ore-forming events in the Cornubian batholith. Li in stream sediments shown on the Wolfson atlas s is in the range 200-400 ppm in the vicinity of hydrothermally altered and kaolinized granite. Sn has a widespread occurrence in vrin-type mineralization and boron is the matrix of diatremes such as the Wheal Remfry breccia in the St Austell granite. ... 

Table 5. Estimated redox-front velocities in unaltered and hydrothermally altered granites, and in fractures. Ranges correspond to variations in mineral abundances (see Table 3)...

Hydrothermal alteration of granite by meteoric fluid an example from the Carnmenellis Granite, United Kingdom. Contributions to Mineralogy and Petrology, 96, 391-405. 

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... 

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