Tag Archives: Epifluorescence

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Optical Microscopy

We make extensive use of optical microscopy for both collection of petrography data (textural and modal analysis) and also for more descriptive work.

We are well equipped with research grade, Zeiss optical microscopes capable of :

  • Transmitted plane and cross polarised light
  • Reflected illumination (for investigation of reflective minerals)
  • Epifluorescence microscopy

All the microscopes are equiped with digital cameras (with live view imaging on attached PC’s), and we have stepping stages (but driven using our own, in-house, software) that we use for modal analysis and acquisition of images for preparation of digital thin-sections and deep zoom images.

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Epifluorescence

We use epifluorescence predominantly to investigate the character and distribution of hydrocarbons trapped within fluid inclusions. Our system is equipped with a Zeiss HBO UV illuminator and “Epiplan Neofluar” objectives covering a wide range of magnifications (x1.25 up to x100).  Using the digital camera attached to this microscope we are able to capture images of specific inclusions under the very low light levels that are commonly encountered during epifluorescence imaging.

Epifluorescence image of hydrocarbon in fluid inclusions
Image captured using mixed transmitted (plane polarised) light and incident UV (epifluorescence) illumination, showing a cluster of fluid inclusions trapped within vein calcite. Within this cluster, the inclusions trap different proportions of an aqueous fluid (non-fluorescent, so appears colourless in this image) and a brightly blue fluorescent hydrocarbon liquid. Where the inclusions only trapped the aqueous liquid, they have remained monophase at room temperature (i.e. have failed to nucleate a vapour bubble). In contrast, in the inclusions that trap a mixture of water and hydrocarbon, vapour bubbles are prominent within the hydrocarbon phase. (Field of view ~180um.)

The colour of the fluorescence is a reflection of the composition of the hydrocarbon, and can be used in a qualitative sense to approximate oil API gravity.  Where samples have seen multiple generations of hydrocarbon of differing compositons / maturities, epifluorescence can be used to differentiate between different generations of fluids.  This, combined with microthermometric analysis of the fluid inclusions, can be used to reconstruct filling / fluid histories.

Paired Epifluorescence and plane polarised light images of minute inclusions trapped along growth zones in quartz.
Paired epifluorescence and plane polarised light images showing planes of very fine, blue-fluorescent hydrocarbon inclusions trapped along growth planes in authigenic quartz (field of view of each image ~430um).