Yugawaralite (CaAl2Si6O16.4H2O) occurs most commonly in active geothermal areas and is associated with other zeolites including laumontite and wairakite. The stability field of yugawaralite was experimentally investigated using conventional hydrothermal apparatus over a p-T range of 200-350℃ and 0.25―2 kbar and run duration of 14 to 61 days. The reversal experiments indicate that the p-T curve of the reaction yugawaralite = wairakite + 2SiO2 + 2H2O passes through 225±5℃ at 0.25 kbar, 233±5℃ at 0.5 kbar, 238±5℃ at 1 kbar and 245±5℃ at 2 kbar pfluid. The thermodynamic parameters of yugawaralite were calculated: 0 ΔSf = -2175.46±12.01 J/mol-K, 0 f ΔG = -8387.69±4.01 kJ/mol, 0 f ΔH =-9036.19±4.01 kJ/mol. The equilibrium curve, yugawaralite = laumontite + 2SiO2, was estimated by employing the thermodynamic data and the calculated slope of 31.3 bars/℃. Present and previous experiments define an invariant point where yugawaralite, wairakite and laumontite are stable. The invariant point was located at 234℃ and 550 bars in experimental conditions where H2O p =ptotal. In geothermal systems where H2O p is about 1/3 H2O p, the occurrence of yugawaralite is restricted to depths not much greater than 0.5 km. This result is consistent with its limited occurrence in active geothermal areas.

Na-F solutions with different pH were allowed to react under flow conditions with limestone, dolomite and siderite at 300 and 400℃ at 500 bars, in order to understand the geochemical characteristics of the interaction between rock and F-bearing hydrothermal solutions. The mineralogical and chemical composition of these carbonate rocks was studied by chemical analysis, XRD and SEM/EDAX before and after reaction with Na-F solutions. Based on an approximate thermodynamic calculation the formation of alteration phases is discussed. The pH value at room conditions and the contents of K, Na, Ca, Mg, Fe, F, SiO2 and total dissolved CO2 in solution after interaction with carbonate rocks were determined. From solution chemistry data, it is found that the amount of Na and F in the reacted solutions seemed to have roughly similar fluctuations with time, and hence, carbonate might be an effective precipitating agent for Fe in hydrothermal solutions. The present experimental study demonstrates that hydrothermal metasomatism played a very important role in the formation of the Baiyun Ebo iron deposit.

The interactions between andesine grains (0.25―0.45 mm) and NaCl and KCl+NaCl solutions were experimentally studied under flow-through conditions (flow rates of solution: 7 ml/h and 1 ml/h) at 300oC and 50 MPa. For comparison, corresponding static runs were performed at the same pressure and temperature. All of these experiments were carried out in a flexible gold cell hydrothermal apparatus. The emphasis of the present study was laid on the changes in the composition of solid surface and solution chemistry at the early stage of the interaction. After the reaction an appreciable amount of etch pits and crystallites of alkali-rich feldspar appeared on the surface of the andesine. The statistical treatment of the SEM/EDAX data for the surface of the mineral reacted showed an increase in the atomic ratio of Si/Al, (K+Na)/Ca and (K+Na)/Al and a decrease in the ratio of Ca/Al, compared with the starting andesine. During the interactions, pH of solutions increased and considerable amounts of Si and Ca were transferred into the aqueous phase. In the NaCl solution experiment at a flow rate of 7 ml/h, the variations of the Si, Al, Ca and K concentration with time were very distinct. The static or "low" flow rate (1 ml/h) reaction conditions and the presence of KCl in solution seemed to hinder the release of Si in andesine to aqueous solution. It is concluded that alkali-metasomatism of andesine at flow-through condition involves the dissolution of the mineral, and the formation of alkali-rich feldspar.

The Xihuashan, Dangping and Piaotang deposits in the Jiangxi Province, south China can be considered as typical high-temperature hydrothermal quartz vein-type W-Sn mineralization, that is temporally and spatially related to Mesozoic S-type granite. Microthermometric studies of fluid inclusions in various minerals from these deposits were conducted to obtain homogenization temperature and salinity data. Major organic and inorganic aqueous components of the fluid inclusions were extracted by a crush-leaching, and concentrations of short-chain carboxylate (formate, acetate, propionate, oxalate), fluoride, chloride and sulfate anions in the leachates were determined using ion chromatography. The results indicate the presence of formate and acetate as well as minor amounts of oxalate and propionate in leachates, and the dominance of formate over other carboxylates. The molar ratio of acetate to formate appears to be a potential indicator of the redox state for the ore fluid system. Oxygen and hydrogen isotopic data show that inclusion water in quartz is mainly magmatic in origin. It is postulated that the dissolved carboxylate anions in the ore fluids for the deposits probably were generated by the breakdown of kerogen in "primitive sedimentary rocks" during the formation of S-type granites. The possibility of inorganic synthesis of the carboxylate species in a C-H-O system can not be excluded.

The carboxylate (formate, acetate, propionate and oxalate) and common inorganic anions (F-, Cl- and SO2-4) compositions for aqueous fluid inclusion leachates from 17 mineral samples collected from various deposits have been determined using ion chromatography in conjunction with microthermometric measurements on the fluid inclusions of their host minerals. The minerals, quartz, fluorite, barite, beryl and a fewore' minerals (wolframite, pyrite and galena), came from hydrothermal vein-type deposits in felsic igneous rocks or Archean metamorphic rocks. The results indicate that short-chain carboxylates are common components in hydrothermal fluids and can be present in considerable amounts. Formic acid (as formate) is the dominant species over other carboxylic acids. The present study raises new questions about the origin and geochemical significance of carboxylates in hydrothermal ore-forming processes.