Other
Scientific paper
Apr 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012gecoa..83..195f&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 83, p. 195-204.
Other
Scientific paper
A magmatic volatile phase (MVP) may be a supercritical fluid, low salinity vapor, or high salinity brine. The MVP causes hydrothermal alteration and can also transport metals in ore forming environments. Unfortunately, there is a lack of experimental data regarding mineral alteration by high salinity liquids (brines) in porphyry systems. This study was designed to expand the experimental data set on mineral alteration by chloride-rich subcritical, vapor-undersaturated high-salinity brines. The phase stability and equilibrium brine compositions in the K-feldspar-andalusite/sillimanite-quartz-brine system (the brine was 70 wt% KCl equivalent; KCl-HCl-H2O) were determined from 600 to 750 °C and 50 to 80 MPa for the equilibrium:KAlSiO+HCl=1/2AlSiO+KCl+5/2SiO+1/2HO. The stable mineral phase was ascertained by an examination of crystal morphology, optical microscopy, and by the compositions of the run products. The mineral stability fields were plotted as a function of temperature, pressure, and molar (KCl/HCl) concentration ratios, CKClbrine/CHClbrine, of the brine. K-feldspar was observed to be stable over the entire temperature range of the experiments whereas andalusite was only stable at temperatures <750 °C, sillimanite was found to be the stable Al2SiO5 polymorph at 750 °C. The K-feldspar-andalusite/sillimanite-quartz-brine equilibrium boundaries at 80 MPa and 600, 650, 700, and 750 °C are at CKClbrine/CHClbrine of 38 ± 6, 29.5 ± 0.5, 22 ± 8, and 6 ± 2, respectively (uncertainties are half-widths of the reversal brackets). Pressure effects were examined by fixing temperature at 600 °C while varying pressure to 50, 65 and 80 MPa. The K-feldspar-andalusite-quartz-brine phase boundaries at 600 °C and 50, 65 and 80 MPa were determined to be at CKClbrine/CHClbrine of 11 ± 3, 30 ± 10 and 38 ± 6, respectively. These data show that with increasing pressure and/or decreasing temperature, the equilibrium boundaries shift to higher CKClbrine/CHClbrine values in the brine. These phase boundaries are not consistent with the metastable extensions of the reaction boundaries involving low salinity fluids and illustrate that the chloride content of the MVP has an impact on the equilibrium KCl/HCl during potassic alteration. A thermodynamic model was developed from the determined equilibrium boundaries that allows for the comparison of low- and high-salinity systems. The model shows that there is a more substantial deviation from ideality in high-salinity systems when compared to low-salinity systems and that these deviations can be quantified by the calculated activity, aKClbrine/aHClbrine, and activity coefficient, γKClbrine/γHClbrine, ratios determined in this study.
Frank Mark R.
Vaccaro David M.
No associations
LandOfFree
An experimental study of high temperature potassic alteration does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with An experimental study of high temperature potassic alteration, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and An experimental study of high temperature potassic alteration will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1116512