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This paper is a review of the application of Raman spectroscopy to fluid inclusions and geological fluids. Most fluid inclusion workers should be aware that microthermometry alone couldn’t provide enough information to fully characterize inclusion fluids in terms of their composition and density. In order to determine pressure/temperature conditions from microthermometric data, it is necessary to have independent analysis of the composition of the fluid, which must be provided by another technique, such as Raman spectroscopy.;Raman spectroscopy uses the effect of molecular vibrations on the frequency of light from a laser. The laser can be focused directly into an inclusion through a microscope, and confocal optics allow the signal from above and below the inclusion to be rejected, concentrating just on the material of interest. The technique is non destructive, and rapid.;The most common use of Raman spectroscopy in fluid inclusions is to analyse the vapour bubble or carbonic phase, which allows identification and quantification of the proportions of gases such as CO 2, N 2 and CH 4. But Raman spectroscopy can do far more than analyse the inclusion gases. Raman analysis at low temperatures, using a traditional heating/freezing stage, allows the study of gas hydrates (clathrates) ( e.g. Murphy and Roberts, 1995, 1997). This is important because the formation of clathrate changes both the density and the composition of the residual fluid. Species in solution can also be analysed. Direct analysis and identification is possible for molecular ions such as SO 4 2- and CO 3 2- . Individual ions such as Na + or Cl - cannot be identified directly, as they contain no bonds, but low temperature Raman analyses of the salt hydrate can allow identification of the ions in solution. This type of analysis has shown that phase changes previously though to be metastable eutectic melting are in fact the formation of salt hydrates at low temperature (Samson and Walker, 2000). Analysis of daughter or trapped minerals is possible, although the most common daughter mineral, halite, is not Raman active. The identification of unusual daughter minerals such as Burbankite ((Na,Ca) 3(Sr,REE,Ba) 3(CO 3) 5) or Ferropyrosmalite (Fe 8Si 6(OH,Cl)) give important information about the chemistry of the fluid and the solubility of elements such as rare earths or iron in the solution. In melt inclusions crystallized phases can also be easily identified. For all solid phases, the availability of searchable mineral databases makes identification simple. Geological fluids are also studied through experimental work, involving fluids or synthetic fluid inclusions. Raman analyses can be carried out at a range of temperatures and pressure with suitable furnaces or pressure cells. Such analyses allow identification of metal species in solution, and the determination of how these species change with change conditions of P , T or pH. The speciation of a metal in solution is important ads it affects the solubility and precipitation mechanisms. Direct observations of speciation using Raman is straightforward and may highlight differences which cannot be detected using solubility experiments: for example, for gold chloride complexes the transformation from Au(III) to Au(I) at high temperature has been shown to occur only in the presence of metallic gold (Murphy et al ., 2000). Solubility experiments, by definition, involve metallic gold and could not show this constraint. This type of Raman analysis can equally be well applied to metals in solution at low temperatures (such as environmental problems in acid mine drainage) or to other materials such as silica.
This paper is a review of the application of Raman spectroscopy to fluid inclusions and geological fluids. Most fluid inclusion workers should be aware that microthermometry alone could not provide enough information to fully characterize inclusion fluids in terms of their composition and density. determine pressure / temperature conditions from microthermometric data, it is necessary to have independent analysis of the composition of the fluid, which must be provided by another technique, such as Raman spectroscopy. ; Raman spectroscopy uses the effect of molecular vibrations on the frequency The light can be focused directly into an inclusion through a microscope, and confocal optics allow the signal from above and below the inclusion to be rejected, concentrating just on the material of interest. The technique is non destructive, and rapid. ; The most common use of Raman spectroscopy in fluid inclusions is to analyze the bubble bubble or carbonic pha se, which allows identification and quantification of proportions of gases such as CO 2, N 2 and CH 4. But Raman spectroscopy can do far more than analyze the inclusion gases. Raman analysis at low temperatures, using a traditional heating / freezing stage, allows the study of gas hydrates (clathrates) (eg Murphy and Roberts, 1995, 1997). This is important because the formation of clathrate changes both the density and the composition of the residual fluid. and identification is possible for molecular ions such as SO 4 2- and CO 3 2-. Individual ions such as Na + or Cl - can not be identified directly, as they contain no bonds, but low temperature Raman analyzes of the salt hydrate can allow identification of the ions in solution. This type of analysis has shown that phase changes previously though to be metastable eutectic melting are in fact the formation of salt hydrates at low temperature (Samson andWalker, 2000). Analysis of daughter or trapped minerals is possible, although the most common daughter mineral, halite, is not Raman active. The identification of unusual daughter minerals such as Burbankite ((Na, Ca) 3 ) 3 (CO 3) 5) or Ferropyrosmalite (Fe 8Si 6 (OH, Cl)) give important information about the chemistry of the fluid and the solubility of elements such as rare earths or iron in the solution. In melt inclusions crystallized phases can also all easily identified. For all solid phases, the availability of searchable mineral databases makes identification simple. Geological fluids are also studied through experimental work, involving fluids or synthetic fluid inclusions. Raman analyzes can be carried out at a range of temperatures and pressure with Suitable furnaces or pressure cells. Such analyzes allow identification of metal species in solution, and the determination of how these species change with change conditions of P, T or pH. The speciation of a metal in solution is important ads it affects the solubility and precipitation mechanisms. Direct observations of speciation using Raman is straightforward and may highlight differences which can not be detected using solubility experiments: for example, for gold chloride complexes the transformation from Au (III) to Au (I) at high temperature has been shown to occur in the presence of metallic gold (Murphy et al., 2000). Solubility experiments, by definition, involve metallic gold and could not show this constraint. This type of Raman analysis can equally be well applied to metals in solution at low temperatures (such as environmental problems in acid mine drainage) or to other materials such as silica.