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Volcanic Deposits
Magma chambers provide the heat mechanism which causes associated groundwater to expand and surge upward. Additionally, this magmatic water contains chemical components of the magmatic body because the heated water is more capable of dissolving mineral constituents from adjacent rocks and sediment. In other words, the surging water contains dissolved igneous constituents, most notably rich in elements such as sulfur, iron and magnesium. When igneous magma extrudes to the surface, it is volcanic; similarly, when dissolved igneous components are expelled into seawater from a hydrothermal vent, they will eventually precipitate out of solution and the sediments they create are volcanic in nature. Thus, sediments surrounding and connected to hydrothermal vents are unique to the area of the sea floor around the vent, as they are volcanic sediments that contain minerals formed from dissolved igneous components. The magma chamber that provides the energy and hydrothermal circulation mechanism involved in hydrothermal vents also contributes chemical components which help to classify sediments around hydrothermal vents.
Metamorphic-Sedimentary (Meta-Sedimentary) Deposits
Many rocks overlaying hydrothermal vents are fractured and permeable sedimentary rocks. As groundwater that is both heated and chemically altered by magma expands and rises, it can also interact with the surrounding sedimentary rocks and create a variety of chemical, mineralogical and textural changes to the surrounding rocks. The temperature, permeability, chemical composition and nature of the both the uprising fluid and the surrounding rocks are dependent variables that can control the degree and nature of metamorphism. Additionally, the fluid to rock ratio and the duration of the hydrothermal system contribute to the degree and nature of metamorphism. Because a great variation of hydrothermal systems and associated rocks exists, there is also a great variation in the products of metamorphism as well, including quartz, feldspar, clay minerals, chlorite, calcite, epidote, sulfides, zeolites, biotite, actinolite, diopside and garnet, for example. Ultimately, a myriad of metamorphosed sedimentary rocks can be formed by and deposited around hydrothermal vents.
Metamorphic-Volcanic (Meta-Volcanic) Deposits
Similar to sedimentary rocks, many rocks overlaying hydrothermal vents are metamorphic-volcanic rocks. Groundwater interacts with the surrounding volcanic rocks and creates a variety of physical and chemical changes. The same dependent variables that can control the degree and nature of metamorphism described for sedimentary rocks, exist for volcanic rocks. Additionally, volcanic glass and other mafic minerals, such as gabbro or basalt, have been described as even more susceptible to metamorphic alteration. Again, similar to the sedimentary rocks described above, a myriad of metamorphosed volcanic rocks can be formed by and deposited around hydrothermal vents.