Identification of fluid inclusions in relation to their host microstructural domains in quartz by cathodoluminescence

MC Boiron, S Essarraj, E Sellier, M Cathelineau… - … et Cosmochimica Acta, 1992 - Elsevier
MC Boiron, S Essarraj, E Sellier, M Cathelineau, M Lespinasse, B Poty
Geochimica et Cosmochimica Acta, 1992Elsevier
The geometry of fluid trapping in relation to microfracture healing or filling was investigated
using massive quartz vein samples characterized by multistage deformation and fluid
trapping. The multidisciplinary approach used in this study includes• 1) mapping of oriented
thin sections of quartz using the cathodoluminescence (CL) mode of a scanning electron
microscope (SEM). SEM CL images display areas of different intensities from dark to white,
which correspond to the intensity of the CL and are caused by trace elements present in the …
Abstract
The geometry of fluid trapping in relation to microfracture healing or filling was investigated using massive quartz vein samples characterized by multistage deformation and fluid trapping. The multidisciplinary approach used in this study includes
  • 1) mapping of oriented thin sections of quartz using the cathodoluminescence (CL) mode of a scanning electron microscope (SEM). SEM CL images display areas of different intensities from dark to white, which correspond to the intensity of the CL and are caused by trace elements present in the quartz. Microfracture healing by newly formed quartz crystallization may occur under physical-chemical conditions different from those which characterized the early quartz matrix formation. Thus, evidences of linear cathodoluminescent markers have been searched and identified by paralleling SEM CL images and transmitted light microphotographs. Data show that cathodoluminescence makes clearly visible the healed crack networks which are only detected in part by transmitted light microscopy. The technique is essential to establish the microcrack chronology and to estimate the width affected by healing along a fluid inclusion trail. Such data are useful for the estimation of the microfracture permeability changes throughout the history of fluid migration;
  • 2) systematic and statistical analysis of the microstructural markers in horizontal and oriented planes using an interactive videographic analyzer which gives the geometry of the paleofluid pathways (orientation, dip and width of the veinlets, fluid inclusion trails, and cathodoluminescent microdomains);
  • 3) microthermometric and Raman analyses of fluid inclusions in selected fluid inclusions, for the determination of the P-V-T-X conditions of fluid migration in a specific microcrack network.
Studied quartz samples come from Au-mineralized quartz veins from the French Massif Central, and some quartz samples from the Cassiar Mountains in British Columbia, have been observed for comparison. In all samples, the quartz matrix exhibits intense microfracturing, suggesting strong brittle deformation which postdates the main stage of quartz lens formation. The quartz veins are characterized by multistage quartz crystallization. Healed microfractures, clear quartz bands, as well as quartz comb veinlets, were studied as functions of the physicochemical conditions in relation to stages of deformation and ore deposition. This study shows that systematic measurements of microstructural marker orientations together with detailed fluid inclusion and mineral petrography and microthermometry may lead to a precise determination of ore fluid pathways and chronology.
Elsevier
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