Dear Arun Kumar Singh, we talk about hydrothermal synthesis when reactions are carried out above the boiling point of water (100 °C) under pressure. The maximum temperatures depend on your equipment, i.e. if you use thick-walled glass tubes or autoclaves made of steel. Specially designed thick-walled glass tubes can be operated up to ca. 300 °C at pressures up to 10 bar. The maximum temperatures and pressures when using autoclaves vary in a wide range depending on the material and the construction.
Dear Mr. Singh,
One of the last mineralogists and economic geologists Schneiderhöhn (1962) has conducted a classification of the hydrothermal interval in mineralization < 100° C (anothermal), 100-200°C (epithermal), 200-300 °C (mesothermal), and 300-350/450 ° C (katathermal). This classification scheme has been applied by German and some European mineralogists and geochemists but was not well entrenched into the international literature because epithermal and mesothermal are more than technical terms to constrain the temperature of formation. Unfortunately they are used to classify shallow ore deposits enriched in Au and Cu and held to be the smoking guns of porphyry copper deposits with which they share the same geodynamic setting. The same holds true for mesothermal which isfrequently used for a special vein-type gold deposit. Epithermal and mesothermal as such lost their connotation in terms of temperature of formation excluding so-called metamorphic bitumens such as epi-, meso- and kata-impsonites which still can roughly be correlated with the above mentioned Schneiderhöhn classification scheme of hydrothermal oe deposits. I myself used the boundary between the supercritical and critical state of H2O as the boundary between hydrothermal sensu stricto and mineralizations formed under pegmatitic or low-grade metamorphic conditions.
The lower boundary between hydrothermal –epigenetic and late diagenetic is difficult to be drawn. The best correlation may be achieved using clay minerals and the maturity of bitumens which are determined by means of reflectance measurements (vitrinite reflectance).
I myself used to refer to the classification scheme which I apply and the marker minerals or organic compounds held to be diagnostic . Browsing the literature you will see that this level of around 370° plays an important part in many classification schemes in the magmatic-hydrothermal system and in the metamorphic-hydrothermal system when it comes to set an upper limit to the hydrothermal systems. The lower limit I would like to define with the aid of organic matter.
Maybe the two classification schemes and two comprehensive papers may shed some light on this issue addressed in your question.
DILL, H.G. (2010) The “chessboard” classification scheme of mineral deposits: Mineralogy and geology from aluminum to zirconium.- Earth Science Reviews, 100: 1-420. (Attachment 2)
DILL, H.G. (2020) A geological and mineralogical review of clay mineral deposits and phyllosilicate ore guides in Central Europe - A function of geodynamics and climate change.- Ore Geology Reviews 119 (in print) (Attachment 1)
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