Hydrothermal alteration is defined as any alteration of rocks or minerals by the reaction of hydrothermal fluid with preexisting solid phases.
How does hydrothermal alteration occur?
Hydrothermal fluids cause hydrothermal alteration of rocks by passing hot water fluids through the rocks and changing their composition by adding or removing or redistributing components. Temperatures can range from weakly elevated to boiling. Fluid composition is extremely variable.
What causes sericite alteration?
Sericitic alteration or sericitization is a process of mineral alteration caused by hydrothermal fluids invading permeable country rock. Sericitic alteration occurs within the phyllic alteration zone. …
What is wall rock alteration?
wall-rock alteration A reaction of hydrothermal fluids with enclosing rocks, causing changes in mineralogy that are most marked adjacent to the vein and become less distinct further away.
Which is a common type of alteration geology?
ØPropylitic alteration is probably the most widespread form of alteration. ØIntermediate argillic alteration affects mainly plagioclase feldspars and is characterized by the formation of clay minerals kaolinite and the smectite group (mainly montmorillonite).
How is serpentinite rock formed?
The serpentinite is formed by the hydrous alteration and low-temperature metamorphic alteration of igneous ultramafic rocks. These rocks are composed of olivine and pyroxene in different ratios to form peridotite and pyroxenite.
How is sericite formed?
Sericite is produced by the alteration of orthoclase or plagioclase feldspars in areas that have been subjected to hydrothermal alteration typically associated with copper, tin, or other hydrothermal ore deposits. Sericite also occurs as the fine mica that gives the sheen to phyllite and schistose metamorphic rocks.
What are the types of alteration?
Types of alterations
- Potassic alteration.
- Phyllic (sericitic) alteration.
- Propylitic alteration.
- Argillic alteration.
- Silicification.
- Carbonatization.
- Greisenization.
- Hematitization.
What are alteration zones?
Alteration zones can be created around a number of the structural features (faults, shear zones, plugs, dykes and unconformities), and are defined as either alteration haloes, where the pre-existing rock property values are enhanced or depleted, or as replacement zones, where the original rock property values ar …
What type of rock is serpentinite?
Serpentine is considered by geoscientists to be the metamorphosed remains of magnesium-rich igneous rocks, most commonly the rock peridotite, from the earth’s mantle. The mantle is a thick layer of rock just below the earth’s crust.
Why is serpentinite an important rock where plates move?
Serpentine rock, so called because the pattern of the rock surface resembles a serpent’s skin, is actually a rock type originally formed from ultramafic rock. Ultramafic rock migrates across the ocean floor along with the crust. A process called plate tectonics drives crustal movement.
What is the origin of chloritoid?
Chloritoid, Named in 1837 by Gustav Rose for the visual similarity to chlorite-group minerals, is a silicate mineral of metamorphic origin. It was first described from localities in the Ural Mountains region of Russia. Manganese-rich chloritoid is known as ottrelite; the magnesium-rich variety is called sismondine.
What type of crystal structure does chloritoid have?
Chloritoid crystallizes in the monoclinic or triclinic system; both modifications are equally common and often form dense concretions. The mineral usually occurs in the form of poorly developed tabular crystals and concretions (chloritoid porphyroblasts in metamorphosed schists) and in the form of plumose aggregates.
What is the hardness and density of a chloritoid?
Chloritoid has a hardness of 6.5 on Mohs’ scale and a density of about 3,600 kg/m3. It is brittle and exhibits perfect cleavage parallel to the flattening of the crystals.
