The Logrosan granite was affected by an intense hydrothermal alteration accompanied with tourmalinization,
greisenization and formation of an intragranitic stockwork of Sn (W) veins (Vindel et al., 2014).
Argillization usually post-dated the greisenization of topaz-bearing granites during decreasing temperature and pressure of later hydrothermal fluids (Merceron et al., 1992).
The older quartz generation (quartz I) is formed by fine- to medium grained aggregates, and the younger quartz (quartz II), originated during greisenization, frequently forms distinctly larger anhedral grains.
In the
greisenization process, often taking place in the fractured rock above a magma chamber, feldspar and muscovite are converted to an aggregate of quartz, topaz, tourmaline and lepidolite by the action of water vapor containing fluorine (Jackson, 1997).
Clearly, hydrothermal breccias, related pervasive alteration and mineralization (silicification, chloritization, and
greisenization) in GRI and GRII (Kooiman et al.
Silicification and
greisenization of wall rock are the wallrock alteration patterns in Degana.
It provided the heat and chemical components for alkali and boron metasomatism, for greisenization (as at Krantzberg), and for mineralization in the roof of the granite intrusion and in the surrounding country rocks.
The tungsten mineralization originated from greisenization events associated with the Erongo Granite emplacement (Schlogl, 1984).
The U mineralization is associated with intense hydrothermal alteration, whereas massive quartz-topaz-cassiterite greisenization accompanies the tin mineralization.
The role of greisenization in cassiterite precipitation at the East Kemptville tin deposits, Nova Scotia.
Once
greisenization ended, rhodochrosite precipitation began.