Microthermometry

Peter, J.M. and Scott, S.D. (1988) Mineralogy, composition, and fluid inclusion microthermometry of seafloor hydrothermal deposits in the Southern Trough of Guaymas Basin, Gulf of California. Can. Mineral, 26, 567-587. 

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. 

Oligocene to Miocene origin, as determined by microthermometry (Kretzschmar, 1982). The chert mineralization and the supply of iron was controlled by low-temperature hydrothermal fluids. In the immediate vicinity of the fungal stromatolites, haematitic veins are present and support the assumption of hydrothermal influence. 

Gehdr S. and Lindblom S. (2002) Textural, microthermometry and laser ablation ICP-MS investigations of fluid inclusions... 

Walderhaug, O. 1997. Precipitation rates for quartz cement in sandstones determined by fluid-inclusion microthermometry and temperature-history modeling. J. Sedim. Res., in press. 

Keywords microthermometry, experimental kinetics, microvolumes, pure water, natural systems... 

Microthermometry. The key characteristics of the studied no 31-7 fluid inclusion are the homogenization and the nucleation temperatures (Th and Tn,... 

Microthermometry was successfully applied to one pervasively cemented sample from the Murgental area. The inclusions were all one-phase, primary aqueous inclusions, yielding a range of final ice melting temperatures between -2.0°C and -0.5 °C. This range of values can be converted to... 

Figure 12 demonstrates the results of pore water oxygen isotopic composition determination, calculated using Friedman O Neils (1977) fractionation equation for the Upper Marine Molasse (Fig. 12A) and for the Lower Freshwater Molasse (Fig. 12B). The temperature constraints used in the calculations were those obtained from textural data and microthermometry.

Fluid inclusion microthermometry indicates the presence of moderately saline waters in the calcite cements of both units. 

Fluid inclusion microthermometry data from the Sonnenberg samples indicate very low, practically freshwater, salinities (Table 2). 

Textural evidence and fluid inclusion microthermometry suggest that most calcites formed at low temperatures, probably at around 50 °C. The oxygen isotopic composition of formation waters ranged from -9 to +2%o SMOW in the Lower Freshwater Molasse and from -5 to +l%o smow in the Upper Marine Molasse. Final ice melting temperatures suggest the presence of moderately saline waters in both formations. 

Last but not least, Stienstra (1992) cites fluid inclusion microthermometry data by Bone (1989) showing that poikilotopic calcite cements precipitated at temperatures between 85 and 120°C in the Jurassic Adori Sandstone (Fig. 2) of the Tantanna, Marana and Strzelecki Fields (Fig. lA) (Bone, 1989). In these fields, the calcite cement has the same petrographic and isotope characteristics (Fig. 8b) as the calcite in the Namur Sandstone of the Gidgealpa Field. 

Bone, Y. (1989) Paleotemperature analysis, Eromanga Basin, South Australia—fluid inclusion microthermometry auto-fluorescence microscopy and cathodolumines-... 

Pressure (MPa) used in study for calculating phase equlibria and for correcting fluid-inclusion microthermometry data.. 

Fluid inclusions in quartz cement are situated both in close proximity to the boundary between detrital quartz grains and cement as well as within the overgrowths themselves. The inclusions chosen for microthermometry are interpreted as primary inclusions that were trapped during growth of quartz cement. Inclusions located in healed fractures were not selected for analysis. 

Formation of water filled inclusions is well known and documented but some elements of the formation of HC inclusions are in part less well understood. Whilst inclusion formation is readily rationalized for minerals with oil wetting characteristics, e.g. carbonates or evaporates, the formation is somewhat more difficult to rationalize in water wetting minerals like quartz. Quartz and plagioclase are well suited for determining the time of entrapment by the use of microthermometry (cf. Karlsen et al. 1993 Roedder 1984) of oil in reservoirs as these minerals are generally less likely to dissolve or experience recrystallization in the temperature range experienced by a progressively buried HC trap. 

Microthermometry Fluid inclusion analysis that involves the heating and cooling of samples to determine the temperature of phase changes. 

Detailed fluid inclusion petrography techniques have already been outlined (Section 30.2.1) and are not repeated here. However, there is a range of additional spectroscopic methods that can be combined with traditional petrography and microthermometry that yield additional information on fluid inclusions. A thermody-... 

During the past ten years a number of papers have shown the interest of fluid inclusion studies in many different domains Metambrphism of the Westem Alps (Poty, 1969 Poty et al., 197 ), hydrothermal metamorphism of the oceanic crust (Jehl, 1975 Jehl et al., 1976), pegmatite evolution in low pressure type Hercynian metamorphism (Weisbrod and Poty, 1975) granulite facies and related rocks (Touret, 197 Hollister and Burruss, 1976). The results of these works are summarized elsewhere (Weisbrod et al., 1976). This paper will review some basic principles of the study of fluid inclusions in rocks. For reasons of space, only some aspects and techniques (notably microthermometry) will be discussed in detail and for a more general presentation the interested reader must consult the classical papers of Roedder, notably Roedder,... 

Without any sophisticated instrumentation, some most important types of fluid inclusion are easily recognized under the petrographic microscope (for a complete and detailed description of the criteria see Roedder, 1972). Most common fluids may be classified as aqueous H2O (Fig. 1.2), H2O + NaCl (Fig. 1.3), H2O + NaCl + many other daughter minerals (l + in Volhynia pegmatite, each a different species, lyakhov, I967), H2O + immiscible hydrocarbons and oil, carbonic (CO2 dissolved hydrocarbons. Fig. l.k and 5) and composite (H2O + CO2, Fig. l.l). Similar in appearance to some of these fluid inclusions are glassy (Clochiatti, 1975) and empty low density gas inclusions, which must be checked by microthermometry (see below). ... 

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