Microscopy and Fluid Inclusion Laboratory – Research Applications

Optical Cathodoluminescence Microscopy

CL image of a quartz vein sample from the Grass Valley orogenic gold district that consists of two distinct quartz types. The large Q1 grain
exhibits oscillatory growth zoning as well as sector zoning. The recrystallized Q2 has CL colors that are similar to those of Q1, but is fine-grained and associated with sulfide minerals. Some of the larger Q2 crystals in the right side of the image exhibit growth zoning.

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.

Selected Publications
  • Sun, M., Monecke, T., Reynolds, T.J., and Yang, Z., 2020, Understanding the evolution of magmatic-hydrothermal systems based on microtextural relationships, fluid inclusion petrography, and quartz solubility constraints: insights into the formation of the Yulong Cu-Mo porphyry deposit, eastern Tibetan Plateau, China: Mineralium Deposita. Published online. doi:10.1007/s00126-020-01003-6
  • Taylor, R.D., Monecke, T., Reynolds, T.J., and Monecke, J., 2020, Paragenesis of an Orogenic Gold Deposit: New Insights on Mineralizing Processes at the Grass Valley District, California. Economic Geology. Published online. doi:10.5382/econgeo.4794
  • Pommer, M., and Sarg, J.F., 2019, Biochemical and stratigraphic controls on pore-system evolution, Phosphoria Rock Complex (Permian), Rocky Mountain Region, USA: SEPM Special Publication No. 112, p. 25–60. doi: 10.2110/sepmsp.112.13
  • Monecke, T., Monecke, J., Reynolds, T.J., Tsuruoka, S., Bennett, M.M., Skewes, W.B., and Palin, R.M., 2018, Quartz solubility in the H2O-NaCl system: A framework for understanding vein formation in porphyry copper deposits: Economic Geology, v. 113, p. 1007-1046.
  • Holley, E.A., Monecke, T., Bissig, T., and Reynolds, T.J., 2017, Evolution of high-level magmatic-hydrothermal systems: New insights from ore paragenesis of the Veladero high-sulfidation epithermal Au-Ag deposit, El Indio-Pascua belt, Argentina: Economic Geology, v. 112, p. 1747-1771.
  • Kempe, U., Götze, J., Enchbat, D., Monecke, T., and Poutivtsev, M., 2012, Quartz regeneration and its use as a repository of genetic information. In: J. Götze and R. Möckel (eds.) Quartz: Deposits, Mineralogy and Analytics. Springer, p. 331-355.
  • Monecke, T., Stolze, S., and Kelly, N., 2012, Application of combined cathodoluminescence and automated scanning electron microscopy in forensic soil investigations [abs.]: International Geological Congress, 34th, Brisbane, Australia, 2012, Proceedings, p. 347.
  • Monecke, T., Giorgetti, G., Scholtysek, O., Kleeberg, R., Götze, J., Hannington, M.D., Petersen, S., and Herzig, P.M., 2007, Textural and mineralogical changes associated with the incipient hydrothermal alteration of glassy dacite at the submarine PACMANUS hydrothermal system, Eastern Manus Basin: Journal of Volcanology and Geothermal Research, v. 160, p. 23-41.
  • Monecke, T., Kempe, U., and Götze, J., 2002, Genetic significance of the trace element content in metamorphic and hydrothermal quartz: A reconnaissance study: Earth and Planetary Science Letters, v. 202, p. 709-724.

Fluid Inclusion Research

Secondary planes of fluid inclusions in a quartz crystal from the Far Southeast Cu-Au porphyry, Philippines. Both hypersaline liquid and vapor-rich inclusions are present together on the same healed plane, which is definitive evidence for entrapment during phase separation.

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.

Selected Publications
  • Sun, M., Monecke, T., Reynolds, T.J., and Yang, Z., 2020, Understanding the evolution of magmatic-hydrothermal systems based on microtextural relationships, fluid inclusion petrography, and quartz solubility constraints: insights into the formation of the Yulong Cu-Mo porphyry deposit, eastern Tibetan Plateau, China: Mineralium Deposita. Published online. doi:10.1007/s00126-020-01003-6
  • Taylor, R.D., Monecke, T., Reynolds, T.J., and Monecke, J., 2021, Paragenesis of an Orogenic Gold Deposit: New Insights on Mineralizing Processes at the Grass Valley District, California. Economic Geology. Published online. doi:10.5382/econgeo.4794
  • Becker, S.P., Bodnar, R.J., and Reynolds, T.J., 2019), Temporal and spatial variations in characteristics of fluid inclusions in epizonal magmatic-hydrothermal systems: Applications in exploration for porphyry copper deposits: Journal of Geochemical Exploration, v. 204, p. 240-255.
  • Monecke, T., Monecke, J., Reynolds, T.J., Tsuruoka, S., Bennett, M.M., Skewes, W.B., and Palin, R.M., 2018, Quartz solubility in the H2O-NaCl system: A framework for understanding vein formation in porphyry copper deposits: Economic Geology, v. 113, p. 1007-1046.
  • Holley, E.A., Monecke, T., Bissig, T., and Reynolds, T.J., 2017, Evolution of high-level magmatic-hydrothermal systems: New insights from ore paragenesis of the Veladero high-sulfidation epithermal Au-Ag deposit, El Indio-Pascua belt, Argentina: Economic Geology, v. 112, p. 1747-1771.
  • Moncada, D., Mutchler, S., Nieto, A., Reynolds, T.J., Rimstidt, J.D., and Bodnar, R.J., 2012, Mineral textures and fluid inclusion petrography of the epithermal Ag–Au deposits at Guanajuato, Mexico: Application to exploration: Journal of Geochemical Exploration, v. 114, p. 20-35.
  • Simmons, S.F., Simpson, M.P., and Reynolds, T.J., 2007, The significance of clathrates in fluid inclusions and the evidence for overpressuring in the Broadlands-Ohaaki geothermal system, New Zealand: Economic Geology, v. 102, p.127-135.
  • Hedenquist, J.W., Arribas, A., Jr., and Reynolds, T.J., 1998, Evolution of an intrusion-centered hydrothermal system: Far Southeast-Lepanto porphyry and epithermal Cu-Au deposits, Philippines: Economic Geology, v. 93, p. 373-404.
  • Reynolds, T.J., 1998, Ancient fluids at the Sweet Home mine: Mineralogical Record, v. 29, p. 127.
  • Bodnar, R.J., Reynolds, T.J., and Kuehn, C.A., 1985, Fluid-inclusion systematics in epithermal systems: Reviews in Economic Geology, v. 2, p. 73-97.
  • Goldstein, R.H., and Reynolds, T.J., 1994, Systematics of fluid inclusions in diagenetic minerals: SEPM Short Course, v. 31, 198 p.
  • Reynolds, T.J., and Beane, R.E., 1985, Evolution of hydrothermal fluid characteristics at the Santa Rita, New Mexico, porphyry copper deposit: Economic Geology, v. 80, p. 1328-1347.
  • Anthony, E.Y., Reynolds, T.J., and Beane, R.E., 1984, Identification of daughter minerals in fluid inclusions using scanning electron microscopy and energy dispersive analysis: American Mineralogist, v. 69, p. 1053-1058.

Textural Studies and Mineral Paragenesis

Reflected light image of chalcopyrite and pyrite occurring along the margin of a reopened AB vein from the Yulong Cu-Mo porphyry, China. The sulfide vein crosscuts the quartz. The arrows point to examples where the quartz was corroded during sulfide formation. The chalcopyrite is intergrown with sericite.

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. 

Selected Publications
  • Zeeck, L.R., Monecke, T., Reynolds, T.J., Pfaff, K., and Hennigh, Q.T., 2020, Textural Characteristics of Barren and Mineralized Colloform Quartz Bands at the Low-Sulfidation Epithermal Deposits of the Omu Camp in Hokkaido, Japan: Implications for Processes Resulting in Bonanza-Grade Precious Metal Enrichment. Economic Geology. Published online. doi:10.5382/econgeo.4795
  • Sun, M., Monecke, T., Reynolds, T.J., and Yang, Z., 2020, Understanding the evolution of magmatic-hydrothermal systems based on microtextural relationships, fluid inclusion petrography, and quartz solubility constraints: insights into the formation of the Yulong Cu-Mo porphyry deposit, eastern Tibetan Plateau, China: Mineralium Deposita. Published online. doi:10.1007/s00126-020-01003-6
  • Taylor, R.D., Monecke, T., Reynolds, T.J., and Monecke, J., 2021, Paragenesis of an Orogenic Gold Deposit: New Insights on Mineralizing Processes at the Grass Valley District, California. Economic Geology. Published online. doi:10.5382/econgeo.4794
  • Monecke, T., Monecke, J., Reynolds, T.J., Tsuruoka, S., Bennett, M.M., Skewes, W.B., and Palin, R.M., 2018, Quartz solubility in the H2O-NaCl system: A framework for understanding vein formation in porphyry copper deposits: Economic Geology, v. 113, p. 1007-1046.
  • Holley, E.A., Monecke, T., Bissig, T., and Reynolds, T.J., 2017, Evolution of high-level magmatic-hydrothermal systems: New insights from ore paragenesis of the Veladero high-sulfidation epithermal Au-Ag deposit, El Indio-Pascua belt, Argentina: Economic Geology, v. 112, p. 1747-1771.

Alteration Studies and Mineral Replacements