Olivo, G.R., Chang, F., and Kyser, T.K., 2006. Formation of the ...

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$Fayek & Kyser 2000 uraninite fractionations.pdf - Queen's University$

616 OLIVO ET AL. FIG. 7. Paragenetic sequence for (A) Sigma (North Dipper) and North zone North Dipper veins and (B) North Dipperrelated veins. Dipper vein in order to characterize the different fluids associated with the mineralized and barren North Dipper systems. Microthermometric measurements were conducted on more than 400 fluid inclusions hosted in quartz (from barren and mineralized veins) and on a few inclusions hosted by scheelite (from the barren vein only), using the Linkam THMS-G-600 heating-freezing stage at Queen’s University. The stage was calibrated using the Synflinc synthetic fluid inclusion standards. The error associated with temperature measured below 30º and above 100ºC was ±0.2º and ±2ºC, respectively, following the equipment specifications and standard measurements. Distribution, nature, and morphology of fluid inclusions Fluid inclusions are abundant in quartz and scheelite and occur mainly along healed fractures of various orientations that transect quartz grain boundaries and reworked grains or in clusters close to these fractures (Fig. 9A). Three compositional types of fluid inclusions were identified: (1) H 2 O-CO 2 , (2) CO 2 -rich, (3) monophase, two-phase, and three-phase H 2 O-rich. Fluid inclusions in scheelite are commonly very small (
FORMATION OF THE AURIFEROUS AND BARREN VEINS IN THE SIGMA MINE, VAL D’OR 617 FIG. 8. Features of the barren North zone North Dipper vein. A. Outcrop of the barren North zone North Dipper vein, showing its geometry and contact with the host rocks. B. Detail showing the tourmaline fibers in the vein margin, indicative of late extension. C. and D. Photomicrographs showing the complex internal geometry of the vein with various generations of tourmaline and quartz. Early generations are strongly deformed, however, the late generations show open-space filling textures. and high birefringence were observed in two- (AQ SL ) and three-phase (AQ SLV ) fluid inclusions and are interpreted to be carbonate crystals. Because these crystals have an uneven distribution, vary in proportion, and do not change their morphology during cooling and heating experiments, they are interpreted as trapped crystals. Monophase aqueous fluid inclusions (AQ M ) are most common in the barren North zone North Dipper vein and minor or rare in the auriferous North Dipper and North Dipper-related veins. They occur mainly along intersections of healed fractures or close to grain boundaries. Microthermometry: Data and interpretation The results of the microthermometric analyses are summarized in Appendix 1, represented graphically in Figure 10A- B, and interpreted below. Temperatures related to phase changes vary slightly along single healed fractures or in clusters of inclusions and more significantly between samples of a given vein type or from different vein types. H 2 O-CO 2 fluid inclusions (AC): Most of the aqueous-carbonic (AC LL and AC LLV ) fluid inclusions decrepitated before homogenization (90% in North Dipper and about 60% in North Dipper-related veins). Where observed, homogenization was to the liquid phase at a wide range of temperatures varying from 228° to 440°C, but most inclusions homogenized between 228° and 270°C. The highest temperatures were documented in the North Dipper-related veins (App. 1, Fig. 10B). Melting of the carbonic phase (T m(CO2 )) in inclusions from the North Dipper-related veins occurred at lower temperatures than for the inclusions from the North Dipper veins (–58.3°C), which indicates the presence of small concentrations of other gases, most likely methane (Kerkhof, 1990, Olivo and Williams-Jones, 2002). Homogenization of the CO 2 (T h(CO2 )) to the liquid phase occurred from –10° to 0361-0128/98/000/000-00 $6.00 617
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Olivo, G.R., Chang, F., and Kyser, T.K., 2006. Formation of the ...

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