Microscopy and Fluid Inclusion Laboratory – Research Applications

Optical Cathodoluminescence Microscopy

Optical cathodoluminescence (CL) microscopy is a powerful analytical tool that is used in a wide range of geoscience applications to visualize the defect structure of minerals. The CL signal produced by minerals can be related to either lattice defects such as vacancies and broken bonds or to the structural incorporation of trace elements. The optical CL system used in the laboratory allows the inspection of thin sections during electron bombardment using a modified optical microscope. The CL is observed in true color and changes in color during electron excitation can be inspected in real time. Much of the work currently conducted focuses on the CL of quartz as this gangue mineral is common in a wide range of deposit types such as porphyry deposits, epithermal deposits, and orogenic gold deposits. The CL investigations allow distinction of different generations of quartz and the mapping of zoning or alteration patterns. Imaging is also conducted to better understand the textural setting of fluid inclusion assemblages. In addition to ore deposit research, optical CL microscopy is performed on energy systems to study the nature of diagenetic materials and as part of forensic studies to fingerprint the provenance of minerals and other solids.

Fluid Inclusion Research

Fluid inclusions are fluid-filled vacuoles contained in minerals. They can be thought of as time capsules storing information about the conditions (temperatures, pressures, and fluid compositions) at which the host mineral was formed or overprinted. Fluid inclusion research encompasses simple petrographic investigations, microthermometric analyses, or sophisticated geochemical analyses of the inclusion contents. Research in the laboratory focuses on the fluid inclusion inventory of ore minerals and common gangue phases such as quartz and fluorite. Based on fluid inclusion research, the evolution of magmatic-hydrothermal and hydrothermal systems is reconstructed. At present, particular emphasis is placed on the study of porphyry deposits, epithermal deposits (low-, intermediate, and high-sulfidation), and orogenic gold deposits. In addition to ore deposit research, fluid inclusion studies are performed on energy systems. Fluid inclusion hosted in diagenetic minerals provide critical information on basin evolution and provide insights into the nature of fluids that were present during diagenesis.

Textural Studies and Mineral Paragenesis

Microscopic observations constraining the textural relationships between different minerals can be made by transmitted and reflected light microscopy. Careful studies of the intergrowth relationships unravel whether certain ore minerals, with or without gangue, have formed as an assemblage, which means they have formed at the same time from the same fluids at the same conditions or not. Textural constraints also allow the identification of the chronological order of mineral deposition, which is known as the paragenetic sequence. Understanding the paragenetic sequence of ore deposits is key to the reconstruction of the evolution of the magmatic-hydrothermal or hydrothermal systems forming these deposits and understanding of the processes of metal deposition. Research currently focusses on deposit types in which ore is contained in veins. In many of these deposits, paragenetic relationships are complicated to unravel as the veins have been reopen multiple times resulting in the formation of complicated textural relationships. 

Alteration Studies and Mineral Replacements

Rock-forming minerals are commonly not stable during fluid-mineral interaction and are partially or entirely transformed to alteration products. Alteration processes involve complex textural, chemical, and structural changes. Understanding the nature of reactions between fluids and minerals is critical to the reconstruction of fluid evolution of magmatic-hydrothermal and hydrothermal processes. The study of alteration processes involves the study of mineral replacement textures and pseudomorphs using a wide range of analytical methods, including optical and electron microscopy. At present, research focuses on unraveling the alteration of volcanic rocks in the high-sulfidation epithermal environment, resulting in the formation of vuggy textures and the alteration of volcanic glass to sheet silicates at different temperatures in volcanic-hosted massive sulfide deposits.