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Geochemical Journal
Geochemical Journal An open access journal for geochemistry
Published for geochemistry community from Geochemical Society of Japan.

Mixing diagrams for hydrothermal solutions: Applications to interpretation of fluid inclusion data of hydrothermal ore deposits in Japan

Yasuhiro Shibue
Geochemical Journal, Vol. 25, No. 2, P. 75-93, 1991


Temperature-chloride mixing diagrams at 500 and 1000 bars, and at vapor-saturated pressures, are calculated in order to demonstrate the mixing behavior of saline (up to 40 NaCl wt%) high-temperature solutions with 1 wt% low-temperature solutions, with the results applied to interpreting fluid inclusion data. The temperature of the initial saline solutions is 450°C at 500 bars, 600°C at 1000 bars, or 300°C at vapor-saturated pressures. The temperature of the diluent is 100° or 300°C at 500 and 1000 bars, and 100°C at the vapor-saturated pressure. Mixing diagrams at 500 and 1000 bars are recast onto the relation between homogenization temperature and chloride concentration of fluid inclusion using densities of NaCl solutions. Temperature-chloride mixing diagrams indicate that mixing of 40 wt% fluids with dilute solutions at 1000 bars is not linear, but shows a greater decrease in temperature with up to 3 wt% NaCl deviation. The deviations are larger (up to 9 wt%) with respect to homogenization temperature versus concentration relations. In contrast, mixing lines for 30 to 10 wt% initial fluids at 1000 bars and those for 40 to 10 wt% fluids at 500 bars are nearly linear with respect to temperature (or homogenization temperature) and NaCl concentration, within ±3 wt% deviations. At vapor-saturated pressures, 300°C and 25 to 5 wt% initial solutions show nearly linear mixing relationships under the condition that vapor/liquid volume ratios are less than 1. Potassium chloride solutions show almost identical temperature-chloride relations with sodium chloride solutions, up to 325°C, 500 bars, and 6 mole/kg, when the molalities of saline and dilute solutions are same for both solutes. The relations between homogenization temperature and concentration for KCl solutions show slightly smaller slopes than those for NaCl solutions. Application of these results to fluid inclusion data of the Ohe, Toyoha, and Fujigatani-Kiwada deposits in Japan indicates that high temperature and high salinity fluids (335°C and 6.3 wt% for the Ohe deposit; 325°C and 4.6 wt% for the Toyoha deposit; 360°C and 7.4 wt% for the Fujigatani-Kiwada deposits) mixed with low temperature and low salinity solutions (221°C and 1.6 wt% for the Ohe deposit; 209°C and 0.0 wt% for the Toyoha deposit; 250°C and 1.9 wt% for the Fujigatani-Kiwada deposits).

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