Fluid inclusions composition

Ayora, C., J. Garcia-Veigas J.-J. Pueyo, 1994b. The chemical and hydrological evolution of an ancient potash-forming evaporite basin in Spain as constrained by mineral sequence, fluid inclusion composition, and numerical simulation. Geoch. Cosmoch. Acta. 58 3379-3394. 

The quantitative imaging capability of the NMP is one of the major strengtiis of the teclmique. The advanced state of the databases available for PIXE [21, 22 and 23] allows also for the analysis of layered samples as, for example, in studying non-destmctively the elemental composition of fluid inclusions in geological samples. 

A large number of geochemical studies on Kuroko deposits (fluid inclusions, gas fugacities, chemical and isotopic compositions of ore fluids etc.) have been carried out. These are summarized below. 

Some mechanisms of anhydrite deposition in Kuroko deposits. Shikazono et al. (1983) considered the depositional mechanism of anhydrite based on the mode of occurrence, texture, Sr content, nature of the contained fluid inclusions and isotopic composition of Sr, S and O in anhydrite together with the mineralogy of the sekko ore, combined with their experimental study on the patitioning of Sr between coexisting anhydrite and aqueous solution. The following is their discussion on the depositional mechanism of anhydrite. 

Origin of ore fluids is constrained by (1) chemical compositions of ore fluids estimated by thermochemical calculations (section 1.3.2) and by fluid inclusion analyses, (2) isotopic compositions of ore fluids estimated by the analyses of minerals and fluid inclusions (section 1.3.3), (3) seawater-rock interaction experiments, (4) computer calculations on the seawater-rock interaction, and (5) comparison of chemical features of Kuroko ore fluids with those of present-day hydrothermal solutions venting from seafloor (section 2.3). 

Isotopic compositions of minerals and fluid inclusions can be used to estimate those of Kuroko ore fluids. Estimated isotopic compositions of Kuroko ore fluids are given in Table 1.10. All these data indicate that the isotopic compositions lie between seawater value and igneous value. For instance, Sr/ Sr of ore fluids responsible for barite and anhydrite precipitations is 0.7069-0.7087, and 0.7082-0.7087, respectively which are between present-day. seawater value (0.7091) and igneous value (0.704-0.705). From these data, Shikazono et al. (1983), Farrell and Holland (1983) and Kusakabe and Chiba (1983) thought that barite and anhydrite precipitated by the mixing of hydrothermal solution with low Sr/ Sr and seawater with high Sr/ Sr. 

Numerous geochemical data (fluid inclusions, stable isotopes, minor elements) on the epithermal vein-type deposits in Japan are available and these data can be used to constrain geochemical environment of ore deposition (gas fugacity, temperature, chemical compositions of ore fluids, etc.) and origin of ore deposits. 

The ranges of /sj and temperature for epithermal Au-Ag vein-type deposits in Japan have been clearly defined based on the chemical composition of sphalerite and electrum, and homogenization temperatures of fluid inclusions (Shikazono, 1985d). Values of /s for the Tsugu deposit are lower than the typical ranges of values for the epithermal Au-Ag vein-type deposits in Japan (Fig. 1.176). Such a low f 2 is in accord with the high Hg content of electrum in the Tsugu deposit. 

The Ag content of electrum is very low (Fig. 1.186) and FeS content of sphalerite is high (6-17 FeS mol%) (Fig. 1.187) (Shikazono and Shimizu, 1987). Combining these compositional data with homogenization temperatures of fluid inclusions, /sj of ore fluids was estimated (Fig. 1.188). Estimated /sj range is lower than that of epithermal Au-Ag vein ore fluids. 

Etoh, J., Taguchi, S. and Izawa, E. (2001) Gas compositions in fluid inclusions from the Hishikari epithermal gold deposit, southern Kyushu, Japan. Proceedings of International Symposium on Gold and Hydrothermal Systems, pp. 99-104. 

Ohmoto, H. and Rye, R.O. (1974) Hydrogen and oxygen isotopic compositions of fluid inclusions in the Kuroko deposits, Japan. Econ. Geol, 69, 947-953. 

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. 

Geological, mineralogical and geochemical features of these deposit types (distribution, age, associated volcanism, host and country rocks, fluid inclusions, opaque, gangue and hydrothermal alteration minerals, chemical features of ore fluids (temperature, salinity, pH, chemical composition, gaseous fugacity, isotopic compositions (O, D, S, Sr/ Sr, Pb), rare earth elements)) were summarized. 

Harmon RS, Schwarcz HP, O Neil JR (1979) D/H ratios in speleothem fluid inclusions A grride to variatiorrs in the isotopic compositions of meteoric precipitation Earth Planet Sci Lett 42 254-266 Harmon RS, Thompson P, Schwarcz HP, Ford DC (1975a) Late Pleistocene paleoclimates of North America as irrferred from stable isotope studies of speleothems. Quat Res 9 54-70 Harmon RS, Thompson P, Schwarcz HP, Ford DC (1975b) Uranium-series dating of speleothems. Nat Speleolo cal Soc Bull 37 21-33... 

Table 22.1. Composition of ore-forming fluids at the Albigeois district, as determined by analysis of fluid inclusions (Deloule, 1982)...

Improvements in analytical techniques have made possible reconstruction of ancient seawater composition from fluid inclusion trapped in marine halites. This has forced marine chemists to accept that the major ion composition has changed significantly— at least over the past 500 million years. Since marine halites older than 500 million years are rare, little is known about the major ion composition of seawater prior to the Phanerozoic eon. Thus, current modeling effiarts are directed at simulating changes in seawater composition over the Phanerozoic. 

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. 

Derome D., Cathelineau M., Fabre C., Boiron M.-C., Banks D.A., Lhomme T., Cuney M. 2007. Paleo-fluid composition determined from individual fluid inclusions by Raman and LIBS Application to mid-proterozoic evaporitic Na-Ca brines (Alligator Rivers Uranium Field, northern territories Australia). Chemical Geology 237(3-4), 240-254. 

Chlorine is the major anion in surface- and mantle-derived fluids. It is the most abundant anion in hydrothermal solutions and is the dominant metal complexing agent in ore forming environments (Banks et al. 2000). Despite its variable occurrence, chlorine isotope variations in natural waters conunonly are small and close to the chlorine isotope composition of the ocean. This is also true for chlorine from fluid inclusions in hydrothermal minerals which indicate no significant differences between different types of ore deposits such as Mississippi-Valley and Porphyry Copper type deposits (Eastoe et al. 1989 Eastoe and Guilbert 1992). 

E. Roedder, Composition of Fluid Inclusions , Geol Surv. Prof. Pap. (VS), 1972, 440-JJ. 

Other geochemical characteristics of Italian volcanism are also not easily explained by the plume hypotheses. For example, deep mantle plumes are commonly associated with high 3He/4He ratios (e.g. Farley and Neroda 1998). However, measurements carried out on fluid inclusions in olivine phenocrysts from mafic Italian rocks have yielded low He isotopic ratios with R/Ra < 7.5 (e.g. Sano et al. 1989 Graham et al. 1993 Marti et al. 1994 Di Liberto 2003 Martelli et al. 2004), which are much lower than compositions found for plume-related magmas. 

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