Hydrothermal Alteration Zoning and Kinetic Process of Mineral-Water Interactions

Vol. 76 No.3ACTA GEOLOGICA SINICASept. 2002351Hydrothermal Alteration Zoning and Kinetic Process of Mineral-Water InteractionsZHANG Ronghua, HU Shumin and SU Y anfengOpen Research Laboratory of Geochemical Kinetics, Institute of Mineral Resources,Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing 100037, ChinaAbstract This study reports the kinetic experimental results of albite in water and in KCl solution at 22 MPa in thetemperature range of 25 to 400°C. Kinetic experiments have been carried out in an open flow-through reaction system(packed bed reactor). Albite dissolution is always incongruent in water at most temperatures, but becomes congruent at300°C (close to the critical point 374°C). At temperatures from 25 to 300°C, the incongruent dissolution of albite isreflcted by the fact that sodium and aluminum are easily dissolved into water; from 300 to 400°C it is reflected bysilicon being more easily dissolved in water than Al and Na M aximum albite dissolution rates in the flow hydrothermalsystems have been repeatedly observed at 300°C, independent of flow rates.The kinetic experiments of albite dissolution in a KCl aqueous solution (0.1 mol KCI) indicate that the dissolutionrate of albite increases with increasing temperature. Maximum silicon release rates of albite have been observed at400°C, while mximum aluminum release rates of albite at 3749C. The reaction rates of albite also depend on thepotassium concentration in the aqueous solution.These results can be used to interpret the mechanism for forming hydrothermal alteration. The kinetic experiments ofmineral- aqueous solutions interactions in the hydrothermal system from 25 to 400°C and at 22 MPa indicate that theformation of the feldspar-mica-kaolinite zoning occurring in some ore deposits may depend not only on the mineralstability but also on the kinetics of feldspar hydration, which is affected by the water property variation when crossingthe critical point.Key words: albite dissolution, reaction rate, incongruent dissolution, critical pointIntroductionIn many alteration zones， however, there exhibitchemical kinetic controls (e.g.， an alteration zoningIn the lithosphere, water rock interactions mostly takeprofile formed under a temperature gradient) Hemleyplace at temperatures and pressures above the criticalet al, 1969; Montoya and Hemley, 1975). Recently,point of water. It is necessary to carry out hydrothermalsome scientists considered that the nature of thereaction experiments at temperatures from a sub-criticalhydrothermal fluids in mineral deposition might notto a super-critical state of water to understand theonly be dependent on mineral stability but also affectedmineral-water interactions in nature.by the kinetic process of mineral-water interactions.The famous hydrothermal alteration experiment“There has been lttle to no information available onmade long ago was the feldspar hydration studyreaction rates of ore-forming minerals at elevatedconducted by Meyer and Hemley (1967). It was antemperatures, and this has been a serious impediment toequilibrium thermodynamic investigation proving thatunderstanding processes of formation of hydrothermalthe ax+/qy+ (or qva+/q+) ratio might determine thedeposits" (D. Crerar’s letter to Li Tingdong, 1984).conversion process from feldspar to mica and then theDuring the past 20-odd years, the kinetics ofhydration alteration of mica to montmorillonite. Thisreactions of many minerals with water has been studiedprocess may also be called hydrogen metasomatism, i.e.,repeatedly. But kinetic experiments on mineral-waterhe replacement of K and Na in the feldspar byinteractions at temperatures higher than 300°C havehydrogen ions. Those experiment results reflect thebeen few (Hellmann et al., 1989; Zhang Ronghua et al.,conditions under which the alteration zoning of1989，1992，中国煤化工1993，1997;porphyry copper deposits is formed.Hellmann,YHCNMH G.352Hydrothermal Alteration Zoning and Kinetic Process of Mineral-W ater InteractionsZhang et al. .Generally, the ratio of molar concentrations amongdissolution and Si easily enters into the solution. At thethe Na, Al and Si ions dissolving in a solution is not temperature of 300°C, congruent dissolution occurs. Inconsistent with the atomic number ratio among Na, Althe case of albite dissolution in water, the AI/Si andand Si in solid when albite dissolves in water. It is anNa/Si release ratios decrease from a positive value toincongruent dissolution. Research results show thatzero as the temperature increases from 25 to 300°C, i.e.,when the albite- water interaction occurs, some ionsAl (or Na) positive incongruent dissolution changeseasily enter into the solution through ion exchanges and gradually to congruent dissolution.hydrolysis reactions on the solid surface. In most cases,Up to now, there have been no reports on kineticNa and Al enter into the solution prior to Si, thusexperiment results of feldspar dissolution aforming a leaching layer on the solid surface.temperatures > 300°C. That makes it difficult for us toAlternatively, at high temperatures Si more rapidlyunderstand the water-rock interactions occurring in thedissolves in water. Therefore, someone reported that aslithosphere. Therefore, we carried out albite dissolutionthe albite dissolution rate represents a steady stateexperiments in the temperature range from 25 to 400°C,balance between surfaceleaching and silicateand at a pressure of 22 MPa, aiming to reveal theframework hydrolysis, the release rates of all ionskinetic behaviors of feldspar dissolution underentering into the solution are the same (Brantley andconditions from sub-critical state to supercritical stateStillings, 1996). Other scientists suggested a model of of water. Moreover, it will be useful for understandingcoupling between a leaching layer and surface reaction, .the nature of water-rock interactions in the lithosphere.which considered that albite dissolution processesdepend on the reactions within the surface leaching2 Experimental Approachlayer, particularly the open structure and the transitionproperty of the leaching layer (Hellmann et al, 1989;A packed bed-flow reactor was used to perform theHellmann, 1995).kinetic study of albite dissolution at 22 MPa and in theIn the fluid flowing reaction system, the Al/Si and temperature range of 25 to 400°C.Na/Si release ratios are used to ilustrate thThe equipment used in the present experiments wasincongruent and congruent dissolution of feldspar. The the same as described in previous studies (Zhangdefinition of the release ratio, log(rrr )x is as followsRonghua et al, 1990, 1992, 1998, 1999， 2000a, bZhang and Hu, 1996), and included a pressure vessel,log(rr.)x=(1liquid pump， back pressure regulator, temperature(X /Si)soid .controller, heat source (furnace)， pressure gauge,where X refers to the molar concentration of Na or Al inelectric conductivity detector and computer.a solution, subscript “aq”refers to the aqueous solution,Natural albite crystals were obtainedfrom theand“solid” refers to the original mineral material. A Geological Museum, Beijing. The mineral grains wererelease ratio > 0 indicates positive incongruentcrushed in a shatter box and sieved to 20 to 40 meshes.dissolution, a logarithm value of 0 indicates congruentThe pure albite crystals were then handpicked with thedissolution，and a logarithm < 0 indicates negativeaid of an optical microscope at a 50 times magnification.incongruent dissolution.Then the mineral grains were crushed again in a shatterWe have reported the reactions of feldspar in waterbox and sieved to 20 to 120 meshes， cleanedover the temperature range of 25- 300°C (Hellmann et ultrasonically using acetone to remove fine grains,al., 1989; Zhang Ronghua et al, 1992). In an acidicrinsed with distilled water, and dried at 70 - 80°C.solution (pH= 2-5), at temperatures≤1009C, the Al/Si Surface areas of representative samples were measuredrelease ratio is > 0 and Al shows a positive incongruentwith a single point BET method, using Ar-He as thedissolution. In the temperature range 100- -300°C, Al isabsorbate gas. For grains of 20-40 meshes, the surfaceof negative incongruent dissolution, indicating that Si isarea is 1.1 m/g. The mineral composition of an albitebeing released faster than Al. In the aqueous solutionsample is An3 Abg7, and Na/Si = 0.272, AI/Si = 0.347.with pH of 10 to 12, at temperatures < 100°C, Al is ofThe total mass of grains placed into the pressure cellpositive incongruent dissolution. In the temperatureweighed 13中国煤化工f the grainrange 100- -200。C， Al is of negative incongruentpacking) and thapproximatelyTYHCNMHG.Vol.76No.3ACTA GEOLOGICA SINICASept. 20023533ml..The pressure vessel was mounted vertically， an1.5albite grains were put in the pressure vessel. DeionizedAl/Siand degassed water was introduced into the vessel from1.the bottom at different flow rates (0.5- -3 ml/min).Output solutions were sampled and the composition ofthese solutions was analyzed using the ICP/MS method0.0-(with ICAT9000， Earth Science College， PekingUniversity). The fluids after reaction flowed out of the-0.5-reactor through a titanium filter, and then passedthrough a back pressure regulator. In fixed conditions0.1-(with constant T, P, and flow rate), three aqueous0 50100150200250300350400450samples (5- -10 ml) were collected as a steady state ofT(C)Na/Sihe dissolution process reached. The steady statecompositions of the output solution were generally1.0attained after an elapsed time ranging from 1-2 h,depending on the flow rate if changed， or thetemperature.e0.0:3 Experimental Results of Albite-Water-0.5Reaction-10-3.1 Incongruent dissolution of albite501001502002503003504004500.0AI/Si release ratioAINa).2 tThe albite dissolution experiments in this study showg-0.4-that the A/Si and Na/Si release ratios decreased from apositive value to zero as temperature increased from 25to 300°C (Fig. 1a and b). Na, Al and Si ions entered-0.8.into the aqueous solution through ion exchange and-1.0-hydrolysis reactions. However, as shown in Fig. 1a, the.2 -Al/Si release was congruent at 300°C. In the case of T.4-≤250°C, as temperature increased from 25 to 250*C,the release ratios became negative, indicating that Al50100150200_250300350400450was being released faster than Si. As temperatureincreased from 300 to 4009C, the release ratios becameig. 1. The relative release ratios for AI/Si, Na/Si and Al/Na as anegative, indicating that Si was being released fasterfunction of temperature.than AI.The release ratios were measured at 25, 50, 100, 150, 200, 250,300, 350, 374, and 400°C, respectively, at a constant pressure of~23 MPa. The data have been taken at each temperature to showNa/Si release ratiothe variation of release ratios with the change of flow velocities.As shown in Fig. lb, the Na/Si release ratio is zero atThe compositions of reaction products at each temperature weremeasured at several flow velocites, and at each flow velocity300°C, which means that Na and Si are of congruentsetting three samples were collected.dissolution. In the temperature range from 25 to 300°C,the Na/Si release ratio varies from positive to zero withAlNa release ratioincreasing temperature. As temperature increasesfromFigure 1c shows the relation between the Al/Na release300 to 400°C, the Na/Si release ratio decreases fromratio and the temperature. The Al/Na release is .zero to negative, which indicates that Si enters into thecongruent at 3中国煤化工io is negtivesolution more easily than Na.over the temP0°C except atMHCNMHG.354Hydrothermal Alteration Zoning and Kinetic Process of Mineral-W ater InteractionsZhang et al. .300°C. Al is more difficult to enter into the solutionthan Na.4F Albute waer 22MPAWe consider that the surface ion exchange reactionS 48F or(S) +r(A) orNa)between Na+ (solid surface) and H (solution) is rapid inthe first stage of albite dissolution, which can occur in a! 36-low temperature condition. Al and Si are composed to3(silicate framework, which are more difficult to dissolvethan Na. The silicate framework can be dissolved at邑18high temperatures. The dissolution rate of Si increases12with temperature, which causes the Na/Si and AI/Si号6release ratios to change from positive to negative in theheating process. Boemite precipitation on albite surface06+0082030400T (C)will also cause the Al/Si release ratio to increase(Zhang Ronghua et al, 1992, 1999; Zhang and Hu,1998; Zhang Xuetong et al, 2000).Fig. 2. Plot of albite dissolution rates (release rates of Si, Aland Na) as a function of temperature.3.2 Dissolution rates of albiteIn a flow-through experimental reactor, the dissolutionvelocity (Fig. 2). The maximum release rates of Na, Alrate of the mineral (mol: min-. m-2) is derived from thend Si in the flowing hydrothermal systems under allfollowing mass balance expression for thflow velocities were always observed at 300°C. Theconcentration of the ith solute in a reactor cell:release rates increased as the temperature increaseddCldt = Rate v(A/V)-(C-G)/t(2from 25 to 300°C，but decreased as the temperaturewhere v is the stoichiometric coefficient of the ithincreased from 300°C to 400°C (Fig. 2 and Table 1).solute in the mineral, C; is the total output concentrationThe solubility of some inorganic salts decreasing in(mol/L) of species i, G, is the initial concentration ofsupercritical water was reported before (Shaw et al.,species i, A is the total reactive surface area of the1991).mineral (m2), t is the average fluid residence time, andV is the volume of the pressure vessel (ml). For3.3 Mechanism of albite-water reactionderivation of this equation, please refer to ZhangThe dissolution reaction of albite in water can beRonghua et al, 1992. As dC/dt = 0, in steady stateexpressed asconditions, equation (2) may be rewritten as .NaAlSiO3+8H2O=Na*+Al(OH)4 +3H,SiO4(4)Assuming that the above reaction is the key step ofRate =(3)the whole albite dissolution process, then the reactiont(AIV)mechanism in the experimental system can be evaluatedBecause various types of reaction vessels are used bytheoretically based on the dissolution rate data (seethe investigators it is necessary to derive differentTable 1).expressions for mass balance (Dove and Crerar, 1990;Given fixed conditions for the chemical kineticZhang Ronghua et al, 1990; Hellmann, 1995; Cama et :experiment (25 to 400°C, 23 MPa), the chemicalal., 1999). Equation (3) holds for the albite dissolutionequilibrium of albite with water was calculated usingrate in the case of a flow-through experiment and isShvarov' s software HCh, which is used for predictionsimilar to that reported for the mineral dissolution inof chemical equilibria in multi-component systemsflow-through experiments (Hellmann et al， 1989(Shvarov, 1989; personal communication). ThisHellmann, 1995; Mogollon et al, 1996). The maximumsoftw are contains a database of thermodynamicrelease rates (Na, Al and Si release rates) in aqueousparameters of various chemical substances related tosolutions were measured as functions of temperaturethe albite dissolution process. This database is similarand flow rate. Albite dissolution is described by theto that of the new version SUPCRT. It allows us torelease rates of Si, Al and Na, r'si, rAI and rNcalculate the molar concentrations and activityrespectively, against temperature for a specific flowcoefficients o中国煤化工that co-existYHCNMH G.Vol.76No.3ACTA GEOLOGICA SINICASept. 2002355Table 1 Gibbs free energy of the reaction between albite and waterS.R (SijPS.R (AI) S.R (Na)C (Si)C (AI)C (Na)s(No. T(°C) U (ml/min)(ppm)log (Q/K)keal/mo1D(mol+ min'.m2 (mol. min'.m2 (mol. min'. m210)x10)21.3830.6480.04940.76-4.56826-6.2333500.197160.015620.28211.3750.7500.08011.05-4.27132-5.8281780.227010.025210.3878430.8980.5890.09040.93-4.57724-6.245599 .0.120590.019260.232610.6120.6470.12620.42- 5.08582- 6.9395550.092400.018740.073210.620.5660.136409-4.71785-6.4374640.081770.020510.158831.9140.6090.10831.04- 3.08108-4.2041080.24670.045610.514101 .500.6070.11340.58- 5.60477-8.28892 10.2058:0.040010.240165(0.6180.5030.06441.02_ 5.58604-8.2612110.0725:0.009650.1794540.940. 4580.1310.79- -5. 56055- 8.2235130.097990.029260. 206160 402n 1316 .060_5 82040. 123830.042090 2590018590.69-8.00/ 806016181 .0055151.8590.4100.750.1618150.84- 6.07829-8.9892010.119410.092030.8270.83- 6.67603-11.400850.120480.022690.147601.3390.960.183010.018820.160291.6091.23-5.623730.314010.033530.293251.445 .0.18811.25- -5.70045-9.7348290.433770.058770.458401.5071.5610.19141.11. -5.63374-9.6209060.512260.065370.444991001.881 .1.6890.08970.86-6.07523-10.374850.67324 .0.037210.41878500.3082.0880.0798132-7.06539-13.682510.153620.006110.11864593.6130.28981.72- -5.68343-11.006280.489800.040890.284851.1432.8930.27671.21-6.16215-11933350.739950.073660.378061.0512.610.29311.65-6.11754-11.846950.618120.072250.4773771501.4212.3760.25371.24-6.41585-12.424650.739900.082230.4717382.0380.2012-6.82187-13.210920.739630.076000.425622000.9094.1930.42431.83-6.41976-13.901240.868260.091450.4629391.2053.5970.35211.8-6.70681-14.522800.965350.098360.5901415.652.4553.98- 3.73635-8.0906245.442390.888671.69083 .1.43620.363. 34.85-3.24299-7.0223116.400101.085671.862491032001.20921.733. 9455.06- 3.12524-6.767335.849411.105381.663971062000.95524.494 97;5.45- 2.90951-6.3002005.309061.123301.443340 96911. .783042 74- 5.24433-12 556022. 588370.29824073548112 7501 20054. 391410. 75-2 0333. - 4 86822014. 56393. 38371351651..1.4171075-207059.17. 08434.074004 0793211.9111.71-2.0426117.30104.197374.843411.93610.319.0418.09094.385554.5129738.699.32218.32694.596375.20807 .0.957103.522.12-1.14105- 2.99303322.48075.001155.479411.181125.22.1424.95-0.66827-1.75290732.99128.815658.031711323001.119.11.4124.6-0.75628-1.98374736.597810.04679.234681353001.531115.70.3824.2-0. 80393-2.10874538.504810.52409.838751403001.883115.824.4-0.79742-2.09165946.201212. 803611.8926 .143002.238110.7.0324.25-0.56391-1.47915451.189014.454313.69881453500.95108.624.2720.75-0.92446-2.63644923.42865.450055.468621481.13326.920.90332.850.125580.3581366.830100.238560.883361523501.29653.847.5349.25-2.37702-6.77892615.43462.248183239481533501.35136.882.1274.25-4.07936-11.6337810.97600.658921 .545211573500.93763.2319.0415.6-1.70083-4.85052813.46764.221324.059141593501.44865.597.6858.2-2.18594-6.23399320.77182.33353.172441633740.94417.10.362-6.30382-18.670023.667420.080810.196501663741.12418.840.45- -6.48508-19.20686.745330.075970.1 38461703741.34320.770.352 10.88-5.99777-17.763596.148540.10849031824173 3740.87382.24- -5.02870-14.893507. 830930.29371088367175 3741. 86742 3172228.3_ -2 86418-8.48284816.75642.977214.015681773742.19.46.237. 767.8- -2.72917-8.08298620.98933.669224.326250001165E0.348674634349009 .0076120 00090180 40016.65-17.70266000070. 2022917.320.33570.52-5.921234.563960.092070.1673922.60.540.1097324.69.35540.668.269140.123890.2700324.680.44731.78-4.84112 .-14.913969.896390.186700.87195196 4002.22925.982.313.2-3.80375-11.7181711.97261.110011.80154Notes: D sG, represents Gibbs free energy in kcal/mol;②S.R. refers to the surface dissolution rate in中国煤化工"YHCNMH G.356Hydrothermal Alteration Zoning and Kinetic Process of Mineral-W ater InteractionsZhang et al. .with albite in an equilibrium state.activity of species i in the rate determining reactionTheoretical calculation mayforecast the raised to power mconcentrations of various aqueous species in thAs proved by experiments, in a far from equilibriumsaturated solution when albite dissolves. Such a condition (the reaction product is a sufficiently dilutecalculation shows that Nat, HSiO4, Al(OH)4 and OHsolution) the dissolution rate does not depend on theare dominant in aqueous species in aqueous solutions△G value (Helgeson et al, 1984; Nielson, 1984; Zhangwith pH ranging from 10 (25°C) to 7.9 (300°C), and toRonghua et al., 1990, 1992; Nagy and Lasaga, 1992;8.5 (400°C) at ~23 MPa. Theoretical calculation provesSteefel and Lasaga, 1994; Nagy et al, 1999). However,that equation (2) expresses the chemical reaction of in a far from equilibrium condition, where the△G valuealbite dissolution.(or chemical affinity term) in the rate equation isIn order to express the dependence of the measured negligible, equation (7) could be reduced torates on the deviation from equilibrium, the equilibriumRme=-k,Ia"8)solubility has to be defined first; we have chosen toThe calculation proves that in most cases, albitewrite the overall reaction as equation (4).dissolution is far from an equilibrium state except atSuppose that this reaction is near equilibrium, or that 300°C.it has two reaction rates in both positive and negativeDissolution rates in the incongruent dissolutiondirections，then thproximity of the reaction tprocess have rarely been discussed. When the activityequilibrium or saturation state of the solution isproduct of the output solution is calculated, thedescribed by Gibbs free energy (or chemical affinity A)relations between the dissolution rate and the activityof the reaction (Lasaga, 1986).product will be revealed, whether a linear relationship0G,=RTIn(Q/K)exists, as shown in Fig. 3. The activity product can bewhere R is the gas constant, T is temperature (K), Qexpressed as aaarepresents the activity product calculated by usingaaa = aNa*GAN(OH)4 a HSiO,(9)experimental data, and K is the equilibrium constant.We suggest that the relations between dissolution ratesThe values of Q were calculated from the expressionsand activities of each aqueous species in outputfor the reaction as written in equation (4) with actualsolutions also need to be discussed.activities of aqueous species. The law of mass actionRegression of experimental data was performed withfor the reaction of equation (4) can be expressed bychemical affinityA =- RT ln (Q/K) .6)the relation logr; = n,log(a)+logk, yielding the rateconstant k; and the order ny (Murphy and Helgeson,where K = GIxa*GAs(OH)4 a HSsIO41987, 1989; Zhang Ronghua et al., 1992, 1998; Devidalwhere the activity of water is assumed to equal 1, and K et al., 1997). And, the log(aaa) Vs. logr relation wasdesignates the equilibrium constant for the reaction ofalso revealed and shown in Fig. 3.Eq. (4).In relatively far from equilibrium and near congruentThe 0G, function can be obtained readily if thedissolution conditions:reaction is an elementary reaction. In this case, theRecent experimental studies have shown thatdependence of the rate on sG,, as derived from the dissolution rates of the alumino-silicate minerals (e.g.Transition State Theory (TST), has been demonstratedfeldspar, analcime and kaolinite) are inversely related to(Lasaga, 1981; Aagaard and Helgeson 1982). Therefore,the aqueous aluminum ion (or species) concentration ina general rate law for mineral dissolution andconditions that are relatively far from equilibriumprecipitation can be written as(Chou and Wollast, 1985; Davidal et al, 1992; OelkersRre=-k,Ia" (1-exp( 0G,/RT)7)and Schott, 1994, 1999; Murphy et al, 1996).where Rnet (mol- min 1 m-) is the net rate of the reactionThe forward reaction rate (release rate of Si) r+ in the(forward rate minus reverse rate), k, (mol- min-'m2) isconditions of congruent dissolution and relatively farthe rate constant of the forward reaction, a; is the from equilibrium at 250- -200°C could be expressed as:Fig. 3. Plot of dissolution rates vs. activity products of dissolvingspecies: At temper” 中国煤化工rates iceasewith increasing activity product aaa until it reaches a relatively large value. As aaa in:ient value, thedissolution rates decrease.YHCNMHG.Vol. 76 No.3ACTA GEOLOGICA SINICASept. 20023574.2- Albite- water25C 22 MPa8e-s.0f留-s.4鲁-s.6-s.or(Si) +r(A) ◆r(Na)s.8 soc 22 MPa口r(Si) +r(I)or(Na),o0L24-244.8-2525.3 24.9-24.-24.1 -23150C 22 MPa，100C22MPa。。0:3自4.2旨s.-5.3曾-s.9口r(S) +r(AI) or(Na)Dr(Si) +r(AI) or (Na)+ 2322 + -28 226-2246.3-22 -21.9 -21.52.1; 200公22 MPa(e2.7 250C 22 MPa百-34F3.6F百3F:q :3o4.0I 4.r(S) +r(AI) or(Na).0- -21-20一 18十 t4.54-18.6-17.8-16.2 -15.4(g)，t 350C 22 MPa)300个22 MPa日-2.5t-3.22.7曾4.2E3.15or (Si) +r (ADor (Na)|(Si) +r(AI)@rNa)3.3- 13.93.713.34.6- 市15“t 374 22 MPa可[400C 22 MPa。)百-35昌314.3曾4.5or (Si) tr (Al)or (Na)口(S) +r (A)or (Na)-.3- -1953.575 -165 -1555s3-.3 -185中国煤化工苏一log antaucmniah.so,THCNMHG.358Hydrothermal Alteration Zoning and Kinetic Process of Mineral-W ater InteractionsZhang et al. .-r+ = k+ (AIoH)"(10)the difference mq+-m + at temperatures < 374°Cwhere n=-0.72 (250°0) and n= -2.05 (200°O. The n(Fig. 5). The variations of albite dissolution rates in thevalues can be calculated based on the relation of logr vs.KCl solution with respect to aqueous Al are depicted inloga. Theresults indicate that in the above caseFig. 5.dissolution rates decreased with an increase ofBased on analyses of Fig. 4 and Fig. 5， theconcentration of the Al-aqueous species.concentration of aqueous Al in the output solution ismuch lower than that of Si. The consumption of K't, i.e.Kinetics of the Albite-KCl Solutionmg+-m. +, is also much higher than the concentrationReactionof aqueous Na in the output solution (Fig. 5).Taking account of these observations, possibleA 0.1 mol KCl aqueous solution was introduced to the reactions of rates controlling the albite dissolution inreaction vessel, flowed through an albite particle bed atthe KCl solution can be expressed as:several selected flow rates, and the dissolution reactionNaAlSiO&+8H2O = Na*+3HSiO4+HAlO4(11)rates at a constant pressure of 23 MPa but differentNaAISiO&+K+ = Na*+KAISi;Og(12)temperatures (25°，100°, 200, 300, 374° and 400°C,Because the concentrations of output aqueous Al arerespectively) were measured.much lower than those of aqueous Si and theAfter the reaction between the KCl aqueousconsumption of K is much greater than the dissolutionsolution and albite, the K concentration of the outputof Na, the following reactions would occursolution was lower than that of the input solution. PartKAISjOg + 2HAIO4of the K+ ions remained on the surface of the albite. The=KAl(SisAI)O1o(OH)2+2H2O+2OH(13)output concentration of Na+ in the output solution wasThese reactions can cause the reaction solution to behigher than that entering the solution during therich in Na+ and HSiO4, and Al to precipitate on thedissolution reaction of albite in pure water. The molaralbite surface. The release rate of Si is also related toconcentration of Na+ in the output solution was farthe activity of the dissolving species of Al, as shown inlower than the consumption of Kt during its reaction. Inthe output solution, the molar concentrations of Na andSi were much higher than that of Al. Obviously, the4.2 Effects of temperature on kinetic behaviors ofdissolution of albite in the 0.1 mol KCl solution doesthe reactionnot follow the law of mass conservation during thThe effects of temperature on the reaction betweencongruent dissolution of albite in water.albite and KCl solution are shown in Fig. 6. Thedissolution rate of Si increases with temperature; that of4.1Relationship of dissolution rate with thAl reaches its peak at 374°C, but drops slightly in theconcentrations of soluble hydrates in the outputtemperature range from 374 to 400°C; and that of Nasolutionvaries irregularly. In addition, the dissolution rate of NaThe albite dissolution rate is calculated based on themay also reach its peak at 3749C.aqueous Si concentration in the output solution. Thedissolution release rate of Na is higher than its reaction 4.3 Influence factor of the reaction ratesrelease rate in water, while that of Al is lower than itsThe experiments of the dissolution of albite in KCldissolution rate in water.solution indicate that the Na concentration in the outputm。+-m_+ is the difference between the input andsolution is usually higher than that in water in the sameoutput K* concentrations. Although m。+ -m,+ and thephysical conditions. K and Na ion exchanges take placedissolution rate of Si both increase with temperature,on the albite surface, and K-feldspar is formed on thetheir variation trends are different when the temperaturesurface. K ions in the input solution are more consumedis above 300°C and below 300°C (Fig. 4). Thethan needed to form K-spar on the albite surface. Thisdissolution rate of Si increases rapidly with increasingis caused by the formation of K-mica on the albitedifference mg+- m+ as temperature increases untilsurface. Therefore, the concentration of Si in the output300°C.solution is highrater. And also,The dissolution rate of Al rises with the increase inthe concentrati中国煤化工_that of albiteYHCNMHG.Vol.76No.3ACTA GEOLOGICA SINICASept. 2002359Ab+0.1 mol KCl-4.△200Ab+0.1 mol KCL心25C(间)4.2 + 300口100C* 374C-4.58400.4.4。400C.4.6。400t+#+*0.5.05.21-5.5-5.4<>。、-5.8-3.5-3.0-2.5-2.-1.-0.5 -1.25-1.20 -1.15 -1.10 -1.05-1.00 -0.95log m (k-k)Fig. 4. (a) Logarithms of albite dissolution rates (release rate of Si) from 25 to 400°C depicted as a function of the logarithm ofthe dffrence in molality between the input aqueous K* and output aqueous K*; (b) at 200, 300, 374 and 400°C, the linear curveshave a slope of 0.16 at 200°C (R2 of the linear curve at 200°C is 0.66), -0.0435 at 374°C (R2 = -0.54) and -0.049 at 400°C (R2=-0.64), the linear curve at 300°C has a low value of R. As we have theoretically calculated the activity coefficient of thedissolving species, we can figure out the activity difference (a-4.0Ab+0.1 mol KCI80。rQNa)百7。r(S)4.560sr(AD)” 50|。冒40[-5.5-0 25C昌30o 100C▲200C邑20-x 3006.sL-5.5 -3 -5.10200300log m (AI)T(C)(Left) Fig. 5. Logarithms of albite dissolution rates (release rate of Si) from 25 to 400°C depicted as a function of the logarithm ofmolality of output aqueous Al. The linear curves have a slope of 0.203 at 200°C (R2=0.38), 0.324 at 374°C (R'=0.44) and -1.62 at400°C (R*=-0.67). After theoretical calculation of the dissolving species, for the aqueous Al species dominated in the solution, theactivity cofficients are close to 1.(Right) Fig. 6. Variation of the dissolution rate of albite in aqueous KCI solution with temperature.dissolving in water.-r=k(ai+-ay+ )"(aq+)" (ay3+)P(14)The variations of water properties in the critical statewhere m, n and p are the order of the rate lawalso affect the dissolution of albite in the KCl solution.coefficient; a+ and ax+ refer to the activities of KThe maximum release rate of Al occurs at 3749C. Theions in the input solution and the output solutionrelease rates of Si vary with the difference mi+ -mx+respectively; ap+ is the activity of the H ion in thethe influence of which in the temperature range from 2output solution and aA3+ is the activity of the aqueousto 374°C is different with that when T > 374°C. Whenspecies Al+ in the output solution. The experimentalT>374°C, the reduction of K in the solution will results allow us to figure out the m, n and p valuesprohibit increasing of the release rates of Si.based on the Correlation between the logarithm of theIn dealing with our data on albite dissolution in thedissolution rate'中国煤化1ogan"(SceKCl solution, the rates could be assumed asFigs. 5 and 6).TYHCNMH G.360Hydrothermal Alteration Zoning and Kinetic Process of Mineral-W ater InteractionsZhang et al. .4.4 Spectroscopic study of the reaction betweenThese FT-IR observations allow us to predict that thealbite and KCl solutionabove reactions of Eqs. (15) to (18) would haveIn a columnar reaction vessel, albite may behappened in the reaction system.accumulated as high as 20 cm. When the 0.1 mol KClsolution flows upward, the albite after reaction forms anDiscussion and Application: Kineticalteration replacement column or a reaction column.Constraints inHydrothermalAlterationAfter the dissolution rates were tested, samples of theZoningalbite after reaction were taken out of the vessel frombottom to top. Then, the mineral surface was analyzedThe kinetic experiments provide new data of theby an FT-IR spectrometer (in-situ DRFTIRS) (Fig. 7).reaction rate for albite dissolution and its surface-It was found that there was a great change on theleaching layer. This paper will not discuss the reactionsurface of the reacted albite at the bottom. In therate expression and its control factor in detail. But thesespectrum background of the albite, another mineral data can be used to interpret the kinetic process ofspectrum appeared with the characteristic spectrum offorming hydrothermal alteration zoning.3095- -3309 cm-, which is boehmite. In the middle ofthereaction columnmontmorillonitization an5.1 Hydrothermal alteration zoningmuscovitization occurred with characteristic peaks ofI arge mineral deposits often show large-scale alteration3629 and 3435- -3447 cm1 respectively, of which thezones centered at hydrothermal ore accumulation zones.former is the position of the OH bond. In the upper partThe examples include iron deposits in volcanic terrains,of the reaction column, surface modification of themarine volcanic (Cyprus-type) deposits， porphyryreacted albite was weak， thus forming a weakcopper deposits in the middle-lower Yangtze valley,muscovitization on themineralsurface.The changes of the mineral surfacein the reaction column are divided, indescending order, into the following10. Abthree parts: the weak reaction surface(or weak muscovitization) in the upper9. Abpartfhecolumn; .8. Abmuscovitization in the middle; and theboehmite and montmorillonitization7. Ser+Ab(albite) in the lower part. Th6. Ser+Abfollowing occur in descending order:-25. Ser+Ab_Mont+K+Mica+Ab; (3) Mont; (2)4. Mont+ Ser+ Ab .Mont+Boem+Ab; (1) Boem+Ab. Thisshows that the surface ion exchange3. Mont+Abvaried from a weak to a stronghydrogen ion replacement of cations.2. Mont+ Boem+AbAn important conclusion is drawn. Boem+Mont+Abfrom the IR spectrum study of the-sH本post-reaction mineral surface. In theopen flow-through reaction system, no出600 5500“ 4500 3500“ 2500 15001 500Wavenumber (cml)equilibrium has been reached in thereaction between the albite and the 0.1mol KCl solution and a spatial zoningFig. 7. Infrared spectra of thesurface of albite after reaction in aqueous KClsolution using in-situ DRFTIRS.of products is formed on the mineralThe numbers show the samples fron中国煤化工of the verticalsurface in the vertical pressure vessel.vessel. Ab - albite; Ser - sericite; M=boehmite.YHCNMHG.Vol.76No.3ACTA GEOLOGICA SINICASept. 2002361and the W- Sn-polymetallic deposits in Nanling. Theirdominated by metasomatism of pyroxene, actinolite,alteration zoning is unique and quite regular. The most and alkaline feldspars (chiefly albite).typical is the pattern composed of two alteration zones:If the contours of homogenization temperatures andthe outer and the inner ones. The outer zonesalinities of the mineral fluid inclusions are also plottedleucocratic and dominated by silcified, argillized ancin the profile of these alteration zones, it can be seensericitized rocks, while the inner one is melanocraticthat in the temperature range of 300- -374°C thereand dominated by altered rocks of feldspar and darkoccurs a change in the nature of the zones (see Fig. 8).minerals (mainly pyroxene， garnet amphibole andThe formation temperatures of the inner zone exceedbiotite) (Chang， 1974; Zhang Ronghua, 1979, 1980,374°C, mainly in the range of 400- 600°C, while those1981, 1986; Zhang and Lu, 1981).of the outer zone are largely lower than 300°C (Chang,The leucocratic alteration zones are symmetrical1974; Zhang Ronghua, 1980; 1981; 1986). Recently, anaround a contact zone or fissure and generally includeinvestigation for hydrothermal vents in the mid-oceanthe following: (1) the quartz + kaoliniteridge also revealed that in the geological profile of the(montmorillonite) zone; (2) the mica (sericite) zone;ocean basalts there is an alteration zone boundary alongand (3) the albite (or K-feldspar) zone. In acidic rocks,the 300- -350°C contours, which also devided the alteredthis pattern prevails, whereas in basic rocks there arebasalts into two parts: the upper part is leucocraticlso dark minerals (such as chlorite and carbonatealteration; the lower part is melanocratic alterationminerals) coexisting with feldspars (prophylic(Seyfried et al， 1991; Seyfried and Ding， 1994;alteration) (Fig. 8). Melanocratic alteration iSeyfried and Mottl, 1995).Scale300 mSurface.........Ab- SerSer.Ser. KaolMont.-Kaol.δSp=0Salinity13%Q-Py-Anh昔.14%g|Kaol-Mont虽Pyx-AbAb-Pyx-(Ch)450CPyx~OIAlkali basalt550^C上| Pyx-01l Pyx-Ab 2 Anh-Pyx3 Py-Anh |4Q |sKaol 6 |Ser|]7 8-.----- 13Fig.8. Cross section of magnetite deposits in the lower Y angtze valley volcanic area.1. Pyroxene oligoclase zone; 2. pyroxene albite zones; 3. anhydrite pyroxene zone; 4. pyrite anhydrite zone; 5. silicationio (quartz) zone; 6. kaolinite zone 7.kaolinite-sercite zone; 8. anhydrite deposit:9. magnetic mineralization (ore); 10. hemtite mineralization中国煤化工”lrain 213. contour of 84Spy values; 14. flling temperature of fluid inclusions in anhydrite; 15. contour of saThose zones areseparated by dashed lines.MHCNMH G.362Hydrothermal Alteration Zoning and Kinetic Process of Mineral-W ater InteractionsZhang et al. .As reported by Rose and Burt (1979), the mineralogyWe have studied the mechanism of alteration zoning,and character of hydrothermal alteration of porphyryand carried out calculations of chemical compositionscopper deposits are zoned laterally over hundreds toof altered rocks based on the metasomatism theory. Thethousandsof feet, commonly exhibiting a crudelyresults show that Si in the inner zone was leached out,concentric pattern of alteration types (Rose, 1970). In while that in the outer zone was precipitated (in thesome districts, the vertical zoning of alteration is alsoupper part of the zoning). In the case of the zoning-documented. All of the alteration profiles of porphyryforming process, Al and Na easily entered the solution,copper deposits exhibit a temperature gradient.and Al was precipitated in the upper part of the outerAccording to the data of fluid inclusions in minerals,zone at lower temperature (Chang, 1979; 1980; Zhangthe temperature interface between the inner and outerRonghua, 1986). In the alteration zones, the change ofzones is near 350°C.hydrogen metasomatism from strong to weak is quitePrevious studies have proved that alteration zoningsimilar to the regular pattern of incongruent dissolutionis basically caused by hydrolysis of feldspar， and and surface leaching of albite over the temperaturesrelated to the temperature gradient. Meyer and Hemleyfrom high to low.(1967) conducted a well-known experiment on theThe maximum dissolving reaction rate of albiteformation of alteration rocks of porphyry copper in theoccurred at 3009C, which is a significant phenomenon.1960s. Their experiment proved that the feldspar- mica-In the deeper part of the inner zone of alteration, thekaolinite (montmorillonite) alteration zoning is relateddissolution reaction of albite (or common feldspar) wasto the a/aq* ratio the hydrothermal fluids, and alsoslow at temperatures from 300°- -400°C and > 400°C.corresponding to the mineral-solution equilibrium state.Due to the AI/Si negative incongruent dissolution ofA most definitive concept proposed at that time waalbite (rAr< rsi), the Si content in the altered productshydrogen metasomatism. It was considered a scientific(such as epidote and zeolite) decreased. Aconcept of the mineral hydration process. The stabilitytemperatures below 300°C, due to the AI/Si positiveof feldspar, mica and clay is commonly controlled byincongruent dissolution, Al entered more easily into thehydrolysis, in which K, Na, Ca, Mg and other cationswater solution than Si, and large quantities of silicifiedare transferred from mineral to solution, and H entersrocks might occur. In the temperature range ofinto the solid phase (Hemley and Jones, 1964; Meyer200- 100°C, the dissolution reaction of feldspar wasand Hemley, 1967). At temperatures below ca. 300°C,very slow, Al migrated into the upper part of the outerthe stability of potassium-feldspar, mica and koalinite iszone to form argillaceous alteration rock, and claylimited by the following reactions:minerals occurred in large quantity .3/2KAISi,O3+H=l/2KAIsSiqOn(OH)2+3SiO2+K+ (15)The albite-KCl solution reaction experimentsKAISi,O1o(OH)2+H*+3/2H2Oindicate that the Si release rate continued decreasing=3/2Al2Si2O,(OH)4+K+(16with lowering temperature from 400 to 25°C, and theExperimental data on these reactions are summarizedmaximum Al release rate occurred at 374°C， whichby Montoya and Hemley (1975).proves that the alteration zoning was controlled by theWe consider that the kinetic experiments on thekinetic factor.hydrolysis of feldspar provide the new information thatThe experiments show that the zoning exhibited bythe alteration zoning is controlled not only by thethe altered products on the surface of albite within themineral stability but also by the kinetics of mineral reaction column is of great significance. It is veryhydrolysis.similar to the zoning formed in nature. This reflects theeffects of chemical kinetic factors on the formation of5.2Kinetics of feldspar-water reaction in thezoning and also indicates that the zoning is producedcritical areathrough the action of a flowing hydrothermal solution.Our kinetic experiments suggest that Si is readilydissolved from feldspar at 300- -400°C and easily.3Hydrogen metasomatism related to waterprecipitated below 300°C. The incongruent dissolutionproperties in the critical areaof albite is the reason for forming regular alterationThe alteration中国煤化Iydration, orzoning.hydrogen metavariation of"TYHCNMHG.Vol.76No.3ACTA GEOLOGICA SINICASept. 2002363water properties in the critical area (300- -400°C). This6 Conclusionsis a very important new problem. Kinetic experimentsindicate that dissolution reaction rates of minerals are(1) The kinetic experiments on the reaction ratescommonly very low in the critical and supercritical between albite and water or aqueous KCl solution havestates of water. When the temperature drops to a valuerevealed that the hydrolysis depends on both thelower than the critical point, the reaction rate increases,temperature and water properties. The incongruentwhereas at a temperature just below the critical point,dissolution of albite in water varies with temperature.the hydration of minerals may vary drastically. ThisAs temperature continues to rise from 25 to 400°C, theimplies that a drastic fluctuation in reaction rates occursAl/Si release ratio changes from positive incongruent atT<300°C to negative at T>300°C. The Na/Siwhen crossing the critical point of water.Water at a temperature below the critical point canincongruent dissolution also changes with temperature.Thisvariation of incongruent dissolution withdissolve ionic bond substances, while that above it canreadily dissolve polar-bond substances (Shaw et al.,temperature is caused by changes of water properties1991; Levert Stengers, 1993).from the super-critical to sub-critical state, and then toThe nature of the mineral hydration is closely relatedlower temperature. Previous kinetic experiments onto the property of water in the critical state. After themineral hydrolysis have not pay much attention to thedecomposition of minerals, the property of hydratednature of water at the critical state because very fewkinetic experiments have been carried out ations and that of their dissociation reactions are botaffected by fluctuations in the critical property of watertemperatures above 300°C.(2) The experiments have revealed that the albite(Levelt Stengers, 1993).It is generally considered that the Al-O bridge bondincongruentdissolutioncoincidesthecharacteristics of feldspar-mica-kaolinite zoningis comparatively long and weak， and more easilyoccurring in nature.broken than the Si-O bridge bond. At roomThis kinetic behavior of albite dissolving in atemperature, the Al-O and Si-O bridge bonds exhibittemperature range of 25 to 300°C is different from thatthe ionic bond property and the polar bond property,at 300-400C. Within the alteration zoning， arespectively. As temperature rises, due to the decreasestemperature gradient(data from mineral fluidin water density and dielectric constant, the waterinclusions) has been found, which represents agradually becomes capable of dissolving polar-bondtemperature-lowering profile form high temperatures insubstances (e.g.. breaking up the Si-O bond). Therefore,the deeper parts to low temperatures in the upper parts.during the temperature rise, there is a chance for theThe water-rock interaction in nature often occurs inbreakup of both the A-O and Si-O bridge bonds bythe profile having a temperature gradient and in thewater molecules. This event probably occurs at 300°Cprocess of crossing the critical point. The evolution ofunder 22 MPa, when a congruent dissolution of ablitewater properties from the near-critical, critical totakes place.supercritical state will affect the regular pattern ofAt the critical point, the rapid decreases in thealteration zoning of mineral deposits because waterdielectric constant and density of water result in theproperties will have influences on the kinetic behavior.destruction of the hydrogen bond framework of water,This is probably one of the causes for the formation ofwhich may affect the rates of ionic reaction and silicatetwo alteration types.skeleton hydration. Therefore， in the process o(3) The experiments on albite-KCl solution reactioncrossing the critical point of water (at 300- -400°C),found that the surface modification sequence is similarboth the ionic and hydration reactions are weakening.to the natural alteration zone. The results alsoHowever, owing to differences in polarizabilitydemonstrated that the zoning of hydrates on the mineralbetween the Al-Obr and Si-Or bonds, the latter is moresurface within the reaction column is coincident witheasily hydrated at 300- -400°C, and supercritical waterthe alteration zoning found in nature.can more readily hydrate substances with a polar bond.It proves the fact that the activities of aqueous K, AlThus the release of Si is faster.nd hydrogen"ill affect the中国煤化工dissolution ratemodifications.TYHCNMH G.364Hydrothermal Alteration Zoning and Kinetic Process of Mineral-W ater InteractionsZhang et al. .The effects of activities of aqueous Al, K and pH on theCampbell, A.C., Bowers, T.S., and Edmond, J.M, 1988. A timedissolution rates at T<374°C are different from those atseries of vein fluid compositions from 21°N, EPR (1979, 1981,and 1985) and the Guaymass Basin, Gulf of Calfornia (1982,T>374°C.1985). Journal Geophysical Research, 93: 4537-4549.(4) The kinetic experimentsof feldspar hydrationChang Jung Hua, 1974. On the zoning of country rock alterationhave revealed the mechanism of alteration zoning,and its genesis of an iron mineral deposit. Acta Geologicaunder a temperature gradient in nature, and of theSinica, 48(1): 53- 90 (in Chinese with English abstract).water- rock interaction in the lithosphere. These natural Chou, L, and Wollast, R., 1985. Steady-state kinetics andprocesses would always occur in flowing fluids of opendissolution mechanisms of albite. Amer. J. Sci, 285: 963- 993.systems. The kinetic behavior will play an importantDavidal, J.L., Dandurand, J.L., and Schott J., 1992. Dissolutionnd precipitation kinetics of kaolinite as a function ofrole in these processes.chemical afinity (T = 150PC, pH = 2 and 7.8). In: Kharaka, Y.and Maest, A. (eds.), Proceedings of the Seventh InternationalAcknowledgmentsConference on Water Rock Interaction, Park City Utah.Rotterdam: Balkema, 93- 96.We would like to thank the Ministry of Science andDavidal, J.L., Schott, J., and Dandurand, JL., 1997. Anexperimental study of kaolinite dissolution and precipitationTechnology and the Ministry of Land and Resourceskinetics as a function of chemical affinity and solutionfor supporting our project. The experimental resultscomposition at 150°C, 40 bars, and pH 2, 6.8, and 7.8.presented in this paper were obtained with the financialGeochim. Cosmochim. Acta, 61: 5165-5186.support of GTB basic research fund 9502215,Dove， P.M， and Crerar, D.A.， 1990， Kinetics of quartz20010302,DK2001022,andthe support odissolution in electrolyte solutions using a hydrothermal2001DEA20023, 2001DEA30041, G1999043212, andmixed flow reactor， Geochim. Cosmochim. 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Experimental study ofChina (series D) 39(6): 561- -575.kyanite dissolution rates as a function of Al and Si Zhang Ronghua and Hu Xhumin, 1998. B asic problems ofconcentration. Miner. Mag. 58A: 659 - 660.chemical kinetics of ore-forming origin. Mineral Deposits,Oelkers, E.H., and Schott, J, 1999. Experimental study of kyanitesup 17: 1035- 1038.dissolution rates as function of chemical affinity and solution Zhang Ronghua, Hu Shumin and Crerar, D.. 1992. Chemicalcomposition. Geochim. Cosmochim. Acta, 63: 785-797.Kinetics of Minerals in Hydrothermal Systems and MassRose, A.W., 1970. Zonal relations of wall rock alteration andTransfer. Beijing: Science Press, 158 p (in Chinese withsulfide distribution at porphyry copper deposits. Econ. Geol,detailed English abstract).65: 920- 936.Zhang Ronghua, Hu Xhumin, Tong Jianchang and Jiang LuRose, A.W., and Burt, D.M, 1979. Hydrothermal alteration. In:1998. Mineral-Fluid Reaction Kinetics in Open Systems.Barnes, HL. (Ed)， Geochemistry of Hydrothermal OrBeijing: Science Press (in Chinese with detailed EnglishDeposits. A Wiley -Interscience Publication, John, Wiley &Sons. 173-235. .Zhang Ronghua, Hu Shumin and Zhang Xuetong, 2000a.Seyfried, W.E. Jr., and Ding. K，, 1994. Phase Euilibria inKinetics of hydrothermal reactions of minerals in near-criticalSubseafloor Hydrothermal Systems: A Review of Role ofnd supercritical water. Acta Geologica Sinica， 74(2):Redox, Temperature, pH and Dissolved CI on the Chemistry ofHot Spring Fluids at Mid-Ocean Ridges, Seafloor Zhang Ronghua, Hu Shumin and Zhang Xuetong, 2000b.Hydrothermal Systems: Plhysical, Chemical, Biological, andKinetics of mineral dissolution in near-critical andGeological Interactions. Geophysical Monograph, 91supercritical water, (abstract). Sixth International Symposiumon Hydrothermal Reaction & Fourth International ConferenceSeyfried, W.E. Jr, Ding, K., and Berndt, M.E, 1991. Phaseon Solvo-Thermal Reactions, July 2000, Japan.equilibria constraints on the chemistry of hot spring fluids atZhang Ronghua and Lu C.， 1981. On the mineralization,mid- ocean ridges.Geochim. Cosmochim. Acta, 55:alteration of iron deposits located at a volcanic basin in theMiddle-Lower Yangtze Valley. Chinese Acad. Geol. Sci, ser 3,Seyfried, Jr. W.E., and Mottl, M.J., 1995. Geologic setting and1: 83-103 (in中国煤化工Borcsik, M.chemistry of deep-sea hydrothermal vents. In: Karl, (ed.), TheZhang Ronghua,fYHCNMHG.366Hydrothermal Alteration Zoning and Kinetic Process of Mineral-W ater InteractionsZhang et al. .Crerar, D., and Hu Shumin, 1990. Kinetics of mineral-waterin 1966. As a visiting professor, he did research work inreactions in hydrothermal flow systems at elevatedthe Dept. of Geol. and Geophys. Science, University oftemperatures and pressures, Science in China (series BCaliformnia, Berkeley, during 1981- 1984; and worked atEnglish edition), 33(9): 1136- 1152.Zhang Ronghua, Zhang Xuetong and Hu Shumin, 1999. Kineticsthe Dept. of Geol. and Geophys. of Princetonof ore-forming fluids in epithermal systems. Chinese ScienceUniversity during the periods of 1983- 1984,Bulletin, 44(supp.):5- 6.1986-1987 and 1989- 1990. As director of the OpenZhang Xuetong, Zhang Ronghua, Hu Shumin and Yu WenbingResearch Laboratory of Geochmical Kinetics and a2000. Mineral surface after reacted with aqueous solution athigh temperatures and pressures. Acta Geologica Sinica, 74(2): .coordinator of key research projects at the Ministry of406- -411.Land and Resources and also a coordinator of importantprojects of basic research from the Ministry of Scienceand Technology, he engages in the research on chemicalAbout the first authorkinetics of minerals in hydrothermal systems and on theZhang RonghuaBorn in 1938; graduated fromstudy of extreme conditions.Peking University in 1963 and took graduate courses atthe Chinese Academy of Geological Sciences (CAGS)中国煤化工MHCNMH G.