Fluid inclusions observation

Parry, W. T. (1998). Fault-Fluid Compositions from Fluid Inclusion Observations and Solubilities of Fracture-Sealing Minerals. Tectonophysics 290(1-2), 1-26. 

These predictions are generally in agreement with the observations homogenization temperatures of fluid inclusions in quartz from siliceous ore zone and in barite from black ore zone in the Kuroko deposits is relatively high, ranging from 350 to 250°C, and low, ranging from 250 to 150°C, respectively. 

Abstract world class unconformity-related U deposits occur in the Proterozoic McArthur Basin (Northern Territory, Australia) and Athabasca Basin (Saskatchewan, Canada). Widespread pre-to post-ore silicifications in the vicinity of the deposits, allow proper observation of paragenetically well-characterized fluid inclusions. We used a combination of microthermometry, Raman microspectroscopy and Laser Induced Breakdown Spectroscopy (LIBS), to establish the physical-chemical characteristics of the main fluids having circulated at the time of U mineralization. The deduced salinities, cation ratios (Na/Ca, Na/Mg) and P-T conditions, led to the detailed characterization of a NaCI-rich brine, a CaCl2-rich brine and a low-salinity fluid, and to the identification of mixing processes that appear to be key factors for U mineralization. 

The precise determination of the composition of individual fluid inclusions in the H20-NaCI-(Ca,Mg)Cl2 system from low temperature microthermometry is often limited by the difficulties in observing the melting of salt hydrates and by their common metastable behaviour. To add, the liquid phase can fail to nucleate any ice or hydrate during cooling down to -190°C. 

We observe that the solid volume fraction Qs is closely related to the determinant of the microstretch Us and that the sum of volume fractions is equal or less to one depending on whether the pores are completely filled by the fluid inclusion or not 8f I 8S - I — f r < 1, where (3V is the volume fraction of the bare sites of matter in pores. Here, we suppose that the solid matrix is unsaturated, so fiv > 0. 

Based on the work of Philippot et al. (1998), one might expect to observe a certain proportion of chlorine-rich fluid inclusions in mantle-derived xenoliths, but inclusions in these xenoliths are overwhelmingly C02-rich, and chlorine-rich inclusions have not been reported (cf. reviews by Roedder, 1984 Pasteris, 1987 Andersen and Neumann, 2001), with the intriguing exception of the brines reported as inclusions in some diamonds (Johnson et al., 2000 Izraeli et al., 2001). The lack of direct observation of chlorine-rich fluid inclusions in mantle-derived xenoliths may be a result of the lack of examination of appropriate samples that record a previous history as subducted oceanic crust, an absence of these fluids in deeper samples because of participation of these fluids in other petrological processes, such as melt production, or because such fluids do not survive subduction below the slab dehydration limit. Conversely, the presence of chlorine in fluid inclusions in diamonds argues for the existence of chlorine-rich fluids at least in some circumstances in the mantle in the pressure range of diamond stability. 

Figure 4. PT pathways followed by a fluid inclusion heated from ambient conditions (path 1 to 4) then further cooled. Photomicrographs show the successive occluded fluid states observed. The bold curve is the saturation curve and the stars qualitatively represent the seven temperature steps chosen for the kinetic study.

Firstly the negative pressure appearance in fluid inclusions was found by Roedder (1967), who observed melting in pure water inclusion in quartz at + 6.5°C and from slope of L-S equilibrium estimate pressure in the inclusion as - 80 MPa. 

Minimal values Th-Tn for different samples are between 12 and 20°C. It is mean, that nucleation of vapour phase never observed before overcooling inclusion on 10°C (or smaller) below L-V equilibrium. At average slops of water isochors as 1.5-1.6 MPa per 1°C, it corresponds to nucleation pressures from -20 to -30 MPa. Last values are very similar to cavitation pressures, estimated by other methods (see review Herbert et. al., 2006). By other words, in some fluid inclusions formation of vapour phase begin at the same pressure (rate of tension) as in capillaries, optic or other cells, but in other inclusions with same water density the cavitation take place at much higher tension (larger values of Th-Tn). 

The formation temperatures of ankerite and calcite in the Oseberg reservoir derived from fluid inclusions are in good agreement with petrographic observations indicating a late diagenetic precipitation. Combined with the thermal history of the reservoir, these temperatures imply that ankerite... 

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