Fluid inclusions (FI) are micron-sized geological systems represented by tiny cavities, filled with fluid as a consequence of any fluid-assisted Earth processes, i.e., formation of igneous, sedimentary and metamorphic rocks, besides hydrothermal ore deposits. These tiny bubbles are representative of ancient hydrothermal systems, which formed ore deposits in geologic past, contrary to the modern or live hydrothermal systems that are currently forming sulfide ore deposits. The inclusion size varies from sub-microscopic (nanometers) to several micrometers and rarely reaching millimeter sizes, as in coarse-grained rocks like pegmatites. However, the size of the FI in hydrothermal deposits is generally less than 100 μm in maximum dimension and mostly falls in the range between 5 and 20 μm. Literature on various aspects of FI is voluminous and is much more than any other conventional tools in Earth Science. Exhaustive reviews on FI in ore-forming hydrothermal systems are available in Roedder (1984), Shepherd et al. (1985), Roedder and Bodnar (1997), Wilkinson (2001), Bodnar et al. (2014), Hurai et al. (2015) and Chi et al. (2021). Fluid inclusions are viewed and studied in transmitted light polarizing microscopes. For this purpose, gangue minerals such as quartz, calcite, dolomite, baryte, tourmaline that are paragenetically coprecipitated with the ore minerals are generally used. Because of its ubiquitous nature, quartz provides the major bulk of the FI data that are available on hydrothermal deposits. Some of the non-metallic ore minerals such as fluorite and baryte are transparent and are excellent for FI studies. However, majority of ore minerals including sulfides and oxides are opaque to visible light and cannot be studied by the conventional methods of transmitted light microscopy. A glaring exception being some sphalerites that are honey yellow in color. Nevertheless, inclusions in any opaque ore mineral can be studied using a microscope with infra-red light source (Shepherd et al., 1985). Fluid inclusions have provided many valuable physico-chemical data of the ore-forming fluid such as temperature, pressure, salinity, density, chemical, and isotopic compositions. Most importantly, the last two decades witnessed stupendous advancement in the instrumental front toward in situ chemical/isotopic analysis of the inclusion fluids. In this chapter, we review the current status of fluid inclusion study that includes fundamental aspects such as petrography, microthermometry, thermobarometry, along with chemical analysis of the trapped fluids.

Fluid Inclusions

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发表日期：

2026年

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Biswajit Mishra,
Dewashish Upadhyay

摘要

Fluid inclusions (FI) are micron-sized geological systems represented by tiny cavities, filled with fluid as a consequence of any fluid-assisted Earth processes, i.e., formation of igneous, sedimentary and metamorphic rocks, besides hydrothermal ore deposits. These tiny bubbles are representative of ancient hydrothermal systems, which formed ore deposits in geologic past, contrary to the modern or live hydrothermal systems that are currently forming sulfide ore deposits. The inclusion size varies from sub-microscopic (nanometers) to several micrometers and rarely reaching millimeter sizes, as in coarse-grained rocks like pegmatites. However, the size of the FI in hydrothermal deposits is generally less than 100 μm in maximum dimension and mostly falls in the range between 5 and 20 μm. Literature on various aspects of FI is voluminous and is much more than any other conventional tools in Earth Science. Exhaustive reviews on FI in ore-forming hydrothermal systems are available in Roedder (1984), Shepherd et al. (1985), Roedder and Bodnar (1997), Wilkinson (2001), Bodnar et al. (2014), Hurai et al. (2015) and Chi et al. (2021). Fluid inclusions are viewed and studied in transmitted light polarizing microscopes. For this purpose, gangue minerals such as quartz, calcite, dolomite, baryte, tourmaline that are paragenetically coprecipitated with the ore minerals are generally used. Because of its ubiquitous nature, quartz provides the major bulk of the FI data that are available on hydrothermal deposits. Some of the non-metallic ore minerals such as fluorite and baryte are transparent and are excellent for FI studies. However, majority of ore minerals including sulfides and oxides are opaque to visible light and cannot be studied by the conventional methods of transmitted light microscopy. A glaring exception being some sphalerites that are honey yellow in color. Nevertheless, inclusions in any opaque ore mineral can be studied using a microscope with infra-red light source (Shepherd et al., 1985). Fluid inclusions have provided many valuable physico-chemical data of the ore-forming fluid such as temperature, pressure, salinity, density, chemical, and isotopic compositions. Most importantly, the last two decades witnessed stupendous advancement in the instrumental front toward in situ chemical/isotopic analysis of the inclusion fluids. In this chapter, we review the current status of fluid inclusion study that includes fundamental aspects such as petrography, microthermometry, thermobarometry, along with chemical analysis of the trapped fluids.