metasomatisering

Metasomatism is a geological process involving the chemical alteration of a rock by hydrothermal or other chemical-bearing fluids. This process results in the introduction or removal of chemical constituents and the formation of new minerals. Unlike metamorphism, which is driven primarily by changes in temperature and pressure, metasomatism is characterized by the movement of fluids through the rock. These fluids can be derived from magmatic intrusions, metamorphic reactions, or groundwater.

The chemical changes associated with metasomatism can be extensive, leading to significant alterations in the rock's composition and texture. Common examples include skarns, which are rocks formed by the metasomatism of carbonate rocks (like limestone or dolomite) by silica-rich, high-temperature fluids, often associated with igneous intrusions. Another example is greisenization, a process where granitic rocks are altered by fluorine- and boron-rich hydrothermal fluids, often resulting in the formation of quartz, mica, and topaz. Serpentinization, the hydration and metamorphism of ultramafic rocks, is also considered a form of metasomatism.

Metasomatism plays a crucial role in the formation of many ore deposits. Hydrothermal fluids carrying dissolved metals can deposit these metals in favorable locations as they cool or react with the surrounding rock. This process is fundamental to the genesis of various metallic ores, including gold, copper, lead, zinc, and tungsten deposits. The study of metasomatism is therefore important for understanding mineral exploration and the behavior of fluids within the Earth's crust.