Micro-Raman Spectroscopy: InVia QONTOR

Since 2016, BGR has a confocal Raman microscope. The Invia QONTOR by Renishaw is integrated with a Leica microscope DM 2700 with six objectives, a highly precise motorized stage, and an automatic focusing unit with four lasers (532 nm, 633 nm, 785 nm, and 1064 nm). The optical path is semi-automatically adjusted for each wavelength. Three detectors are available for signal acquisition: a CCD, an EMCCD, and an InGaAs camera.

It supports point measurements, profiles, as well as 2D and 3D mappings. A unique feature is the QONTOR technique, enabling simultaneous sample focusing and Raman signal acquisition at a high data acquisition rate. Consequently, even rough and uneven samples can be measured under optimal conditions. There are numerous data analysis possibilities. Spectra can be interpreted mineralogically by comparing them to proprietary or international databases, and if necessary, visualized as mineral distribution patterns. Furthermore, additional information, such as the crystallinity of individual phases, can be obtained through peak intensities, -ratios, and -shifts, which can be represented in 2D or 3D.

Figure 1: Raman microscope Invia QONTOR from Renishaw Source: BGR

Figure 2: Example Merensky Reef: The Raman mapping (785nm Laser, 1200 grid, 1 sec, 50%, 1500 x 800 pixel, 50x objective) shows the assignment of the measured spectra to the identified mineral phases bronzite, Cr-diopside und Cr-actinolite as alteration phases Source: BGR

Micro-Raman spectroscopy has been utilized in the field of geosciences for decades to gather information on inorganic and organic phases, molecules, fluid inclusions, or crystallinities in solid materials. In our subdivision, the focus lies on identifying mineral phases in the context of ore genesis and the utilization of residual materials, particularly fine-grained alteration products, which may not be definitively determined using conventional methods such as microscopy, scanning electron microscopy, microprobe, µ-XRF or LIBS.

Detailed 3D mappings can define grain volumes and potentially clarify mineral relationships, offering insights into complex questions related to ore and rock genesis and their alteration history. The instrument can be extended for ex-situ applications, such as in the µRFA Sigray Attomap through additional components like fiber optic cables.

Literature

• Berkh, K., Majzlan, J., Meima, J.A., Plášil, J., Rammlmair, D., 2023. The effect of chemical variability and weathering on Raman spectra of enargite and fahlore. European Journal of Mineralogy 35, 737-754. https://doi.org/10.5194/ejm-35-737-2023
• Merk, V., Berkh, K., Rammlmair, D., Pfeifer, L., 2023. Chemical and Mineralogical Analysis of Samples Using Combined LIBS, Raman Spectroscopy and µ-EDXRF. Minerals 13, 729. https://doi.org/10.3390/min13060729
• Berkh, K., Rammlmair, D., 2022. The effect of Co substitution on the Raman spectra of pyrite: potential as an assaying tool. European Journal of Mineralogy 34, 259-274. https://doi.org/10.5194/ejm-34-259-2022