Development of a Numerical Model for the PVTX Properties of Na-K-Ca-Fe-C1 Solutions in Magmatic/Hydrothermal Ore Deposits

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BodnarEAR-0125918A three-year experimental study will be conducted to determine the temperature-pressure-composition (PTX) limits of fluid immiscibility over the temperature and pressure range appropriate for magmatic-hydrothermal ore deposits associated with shallow granitic magmas. The study will focus on fluid compositions in aqueous solutions containing Na, K, Ca, and Fe chlorides, starting with the less-complex sub-systems containing Na-K, Na-Ca, and Na-Fe chlorides. Samples of immiscible fluids will be trapped in situ using the synthetic fluid inclusion technique, and compositions of the fluids will be determined using standard microthermometric analytical techniques. The compositional data will be used to develop an empirical numerical model to predict P-T conditions attending magmatic-hydrothermal processes. The model will require only information that is easily obtainable during conventional microthermometric and/or microchemical analysis of fluid inclusions. The feasibility of the project has been documented by preliminary studies on the water-NaCl-KCl system. The data confirm that the synthetic fluid inclusions trap a representative sample of the fluid(s) present at experimental run conditions, and maintain these compositions during quenching to ambient laboratory conditions. Moreover, conventional microthermometric analysis of the coexisting liquid-rich and vapor-rich inclusions can be employed to determine the fluid compositions. Preliminary data for the water-NaCl-KCl system show that partitioning of sodium and potassium between coexisting liquid and vapor varies systematically with both temperature and pressure. Specifically, sodium partitioning into the liquid phase becomes less pronounced with increasing temperature and with decreasing pressure.