One of the most important pieces of information to consider when trying to investigate the genesis of an ore deposit, or mineralisation in general, is the temperature of ore deposition. This can have significant implications associated with the categorising of an ore deposit (for example SEDEX vs Skarn) and understanding the mineralogy and/or zonation within an ore deposit. In this blog we explore three geothermometers that are easy to apply in ore deposit studies.
GGIMFis Geothermometer
This geothermometer is one of the easiest to apply and is particularly handy for any sort of Zn-bearing deposit. This geothermometer was first established by Frenzel et al (2016) who found a good correlation between the temperature of ore deposition and a PCA factor. The PCA factor can be explained by variances in the elements Ga, Ge, In, Mn & Fe, which can be put into a simple equation (for more detail, see Frenzel et al (2016)) to determine an estimate of the precipitation temperature. On average, the accepted variation for the GGIMFis geothermometer is ± 50°C. Although it can produce reliable temperature estimates >400°C, it is suggested that it has a thermal resetting temperature of ~350°C (Frenzel et al., 2016). The GGIMFis geothermometer has been further modified and refined by Zhang et al (2022), who produced two variations of the geothermometer, TFAS & TFA6. The TFAS geothermometer uses variations in the concentration of the elements Mn, Fe, Co, Cu, Ga, Ge, Ag, Cd, In, Sn, and Sb in order to determine an estimated sphalerite precipitation temperature (Zhang et al., 2022). Alternatively, the TFA6 uses the variation in the elements Mn, Fe, Ga, Ge, In, and Sb to determine an estimated sphalerite precipitation temperature (Zhang et al., 2022). Although the equations used to calculate the sphalerite formation temperature can be overwhelming, the publication includes an easy-to-use spreadsheet with the built-in calculations, making the use of the geothermometer simple.
Mg in Magnetite
This geothermometer is exactly what it sounds like. Based on a range of experiments conducted at different temperatures with varying pressures and levels of oxygen fugacity, it was found that the amount of Mg within magnetite is strongly dependent upon the temperature from which the magnetite precipitated (Canil & Lacourse, 2020). This geothermometer was found to replicate 72% of experiments within 50°C (Canil & Lacourse, 2020). Although this geothermometer was calibrated at very high temperatures 700-1050°C, a range of analyses compiled from a range of ore deposits successfully reproduced temperatures consistent with estimates established from a variety of different geothermometers (Canil & Lacourse, 2020). However, as this geothermometer was calibrated to be used within an igneous system and magnetite formed from a coexisting silicate liquid, not a hydrothermal fluid, caution is still advised when using the magnetite geothermometer to estimate the precipitation of ore deposition.
Clumped Isotope Thermometry
This geothermometer is less readily applied than the GGIMFis and Mn-in Magnetite geothermometers, but if the laboratory has the right setup, it can be a relative breeze. This thermometer can be applied on carbonated, mainly dolomite and calcite (Anderson et al., 2021). Although this thermometer has been used regularly to reconstruct paleotemperatures for >10 years (Eiler, 2011), its application to hydrothermal fluids is relatively new (Mering et al., 2018). The basis of this geothermometer is that there is a temperature dependent basis upon the degree to which the heavy isotopes of C (13C) & O (18O) are bonded with, or near each other (e.g., clumped), rather than the lighter isotopes in the carbonate phase. The temperature dependent relationship has been calculated up to 1100°C (Anderson et al., 2021). It is important to mention that this geothermometer has its limits, and calcite can be readily reset by regional scale metamorphism which results in solid-state reordering upon cooling and/or exhumation (Quesnel et al., 2022). In this case, the geothermometer produces unrealistically low temperature of ~150°C (Quesnel et al., 2022). However, it has been shown that dolomite may be more reliable at higher temperatures, producing a reliable temperature estimate of 300-400°C at the Mount Isa Cu deposit (Mering et al., 2018).
Conclusion
In summary, this blog demonstrates three simple methods to calculate the temperature of ore deposition. The GGIMFis geothermometer (Frenzel et al., 2016) correlates ore deposition temperature with a PCA factor based on the elements Ga, Ge, In, Mn, and Fe, and has been revised in more recent studies (Zhang et al., 2022). The Mn in Magnetite geothermometer uses the concentration of Mn within magnetite to calculate the temperature of ore formation (Canil & Lacourse, 2020). Clumped Isotope Thermometry utilizes the clumping of heavy isotopes in carbonates to estimate the temperature of ore deposition but has multiple caveats that must be considered when applied (Mering et al., 2018; Quesnel et al., 2022). Overall, the use of these geothermometers can provide a valuable insight into ore genesis, aiding in the understanding and categorisation of ore deposits.
References
Anderson, N. T., Kelson, J. R., Kele, S., Daëron, M., Bonifacie, M., Horita, J., … Petschnig, P. (2021). A unified clumped isotope thermometer calibration (0.5–1,100 C) using carbonate‐based standardization. Geophysical Research Letters, 48(7), e2020GL092069.
Canil, D., & Lacourse, T. (2020). Geothermometry using minor and trace elements in igneous and hydrothermal magnetite. Chemical Geology, 541, 119576.
Eiler, J. M. (2011). Paleoclimate reconstruction using carbonate clumped isotope thermometry. Quaternary Science Reviews, 30(25–26), 3575–3588.
Frenzel, M., Hirsch, T., & Gutzmer, J. (2016). Gallium, germanium, indium, and other trace and minor elements in sphalerite as a function of deposit type—A meta-analysis. Ore Geology Reviews, 76, 52–78.
Mering, J. A., Barker, S. L. L., Huntington, K. W., Simmons, S., Dipple, G., Andrew, B., & Schauer, A. (2018). Taking the temperature of hydrothermal ore deposits using clumped isotope thermometry. Economic Geology, 113(8), 1671–1678.
Quesnel, B., Jautzy, J., Scheffer, C., Raymond, G., Beaudoin, G., Jørgensen, T. R. C., & Pinet, N. (2022). Clumped isotope geothermometry in Archean mesothermal hydrothermal systems (Augmitto-Bouzan orogenic gold deposit, Abitibi, Québec, Canada): A note of caution and a look forward. Chemical Geology, 610, 121099.
Zhang, J., Shao, Y., Liu, Z., & Chen, K. (2022). Sphalerite as a record of metallogenic information using multivariate statistical analysis: Constraints from trace element geochemistry. Journal of Geochemical Exploration, 232, 106883.