Fluid-silicate melt Cl partition and its implications on magmatic fluid exsolution and hydrothermal ore genesis

Abstract

Partition coefficients for Cl between felsic melts and a supercritical aqueous fluid ( ∼ 4-16 wt.% NaCl eq ) were experimentally determined to better constrain Cl behavior during magmatic fluid exsolution in upper-crustal magma chambers. Experiments were conducted at 850 ° C, 200 MPa, and oxygen fugacity near NNO + 0.5, using a range of melt and fluid compositions. At constant total chlorinity of 1 mol/kg H₂O, Dfluidmelt_Cl values range from 11.3 to 21.1, negatively correlated with both the melt’s aluminum saturation index (ASI) and the HCl/total Cl ratio in the fluid. For a fixed melt composition (ASI = 1.02), Dfluidmelt_Cl values increase linearly from 18.7 to 60.1 as total chlorinity rises from 1 to 4 mol/kg H₂O. Rayleigh fractionation modeling of fluid exsolution from upper-crustal magmas using these data indicates that during progressive crystallization, chlorinity of exsolved fluids rapidly decline before stabilizing at ∼ 1 mol/kg H₂O ( ∼ 4 wt.% NaCl eq ), regardless of initial fluid chlorinity or H₂O content in melt. This implies that the majority of exsolution fluids released from felsic magmas in the upper crust are of low salinity ( ∼ 1 mol/kg H₂O). Copper transfer modeling further suggests that efficient metal extraction occurs in Cl- and H₂O-rich magmas, particularly where early H₂O saturation is achieved, thus favoring the formation of high-grade porphyry copper deposits.

Keywords

Chlorine / Fluid-melt partitioning experiments / Magmatic fluid exsolution / Upper crustal magma chamber / Magmatic-hydrothermal deposits

CRediT authorship contribution statement

Jianping Li: Writing - review & editing, Writing - original draft, Visualization, Validation, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Xing Ding: Writing - review & editing, Visualization, Validation, Methodology, Investigation, Funding acquisition, Formal analysis. Huayong Chen: Writing - review & editing, Visualization, Validation, Supervision, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the Chinese National Natural Science Foundation (42003031), the Strategic Priority Research Program of Chinese Academy of Sciences, China (XDA0430301), the Chinese National Natural Science Foundation (42230807, 42330305) and Guangdong Research Center for Strategic Metals and Green Utilization (2024B0303390002). We are grateful to Zhuoyu Liu and Huili Zhang for their assistance with sample treatment and the analyses. Finally, we gratefully acknowledge the Associate editor of Federico Lucci and the constructive comments from two anonymous reviewers that helped us to improve the manuscript significantly. This is contribution No.IS-3724 from GIGCAS.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.gsf.2025.102187.

References

[1] Alletti, M., Baker, D.R., Scaillet, B., Aiuppa, A., Moretti, R., Ottolini, L., 2009. Chlorine partitioning between a basaltic melt and H₂O-CO₂ fluids at Mount Etna. Chem. Geol. 263, 37-50.

[2] Audétat, A., Simon, A.C., 2012. Magmatic controls on porphyry copper genesis. Econ. Geol. 16, 553-572.

[3] Audétat, A., 2019. The metal content of magmatic-hydrothermal fluids and its relationship to mineralization potential. Econ. Geol. 114, 1033-1056.

[4] Audétat, A., Edmonds, M., 2020. Magmatic-hydrothermal fluids. Elements 16, 401-406.

[5] Bakker, R.J., 2013. Erratum to: Package FLUIDS. Part 4: Thermodynamic modelling and purely empirical equations for H₂O-NaCl-KCl solutions. Miner. Petrol. 107, 629.

[6] Beermann, O., Botcharnikov, R.E., Nowak, M., 2015. Partitioning of sulfur and chlorine between aqueous fluid and basaltic melt at 1050 °C, 100 and 200 MPa. Chem. Geol. 418, 132-157.

[7] Bodnar, R.J., Burnham, C.W., Sterner, S.M., 1985. Synthetic fluid inclusions in natural quartz. III. Determination of phase equilibrium properties in the system H₂O-NaCl to 1000 °C and 1500 bars. Geochim. Cosmochim. Acta 49, 1861-1873.

[8] Botcharnikov, R.E., Behrens, H., Holtz, F., Koepke, J., Sato, H., 2004. Sulfur and chlorine solubility in Mt. Unzen rhyodacitic melt at 850 °C and 200 MPa. Chem. Geol. 213, 207-225.

[9] Brugger, J., Liu, W., Etschmann, B., Mei, Y., Sherman, D.M., Testemale, D., 2016. A review of the coordination chemistry of hydrothermal systems, or do coordination changes make ore deposits? Chem. Geol. 447, 219-253.

[10] Burnham, C.W., 1997. Magmas and hydrothermal fluids. In: Barnes H.L. (Ed.), Geochemistry of Hydrothermal Ore Deposits. John Wiley & Sons, New York.

[11] Candela, P.A., Holland, H.D., 1984. The partitioning of copper and molybdenum between silicate melts and aqueous fluids. Geochim. Cosmochim. Acta 48, 373-380.

[12] Candela, P.A., Piccoli, P.M., 2005. Magmatic processes in the development of porphyry-type ore systems. Society of Economic Geologists, Inc. Econ. Geol. 100th Anniversary Volume, pp. 25-37.

[13] Chappell, B.W., 1999. Aluminium saturation in I- and S-type granites and the characterization of fractionated haplogranites. Lithos 46, 535-551.

[14] Crerar, D.A., Barnes, H.L., 1976. Ore solution chemistry; V, Solubilities of chalcopyrite and chalcocite assemblages in hydrothermal solution at 200° to 350°C. Econ. Geol. 71, 772-794.

[15] Cooke, D.R., Hollings, P., Walshe, J.L., 2005. Giant porphyry deposits: Characteristics, distribution, and tectonic controls. Econ. Geol. 100, 801-818.

[16] Driesner, T., Heinrich, C.A., 2007. The system H₂O-NaCl. Part I: Correlation formulae for phase relations in temperature-pressure-composition space from 0 to 1000 °C, 0 to 5000 bar, and 0 to 1 X_NaCl. Geochim. Cosmochim. Acta 71, 4880-4901.

[17] Frank, M.R., Candela, P.A., Piccoli, P.M., Glascock, M.D., 2002. Gold solubility, speciation, and partitioning as a function of HCl in the brine-silicate melt-metallic gold system at 800 °C and 100 MPa. Geochim. Cosmochim. Acta 66, 3719-3732.

[18] Frank, M.R., Simon, A.C., Pettke, T., Candela, P.A., Piccoli, P.M., 2011. Gold and copper partitioning in magmatic-hydrothermal systems at 800 °C and 100 MPa. Geochim. Cosmochim. Acta 75, 2470-2482.

[19] Guo, H., Xia, Y., Bai, R., Zhang, X., Huang, F., 2020. Experiments on Cu-isotope fractionation between chlorine-bearing fluid and silicate magma: Implications for fluid exsolution and porphyry Cu deposits. Natl. Sci. Rev. 7, 1319-1330.

[20] Grondahl, C., Zajacz, Z., 2017. Magmatic controls on the genesis of porphyry Cu-Mo-Au deposits: The Bingham Canyon example. Earth Planet. Sci. Lett. 480, 53-65.

[21] Grondahl, C., Zajacz, Z., 2022. Sulfur and chlorine budgets control the ore fertility of arc magmas. Nat. Commun. 13, 4218.

[22] Hedenquist, J.W., Lowenstern, J.B., 1994. The role of magmas in the formation of hydrothermal ore deposits. Nature 370, 519-527.

[23] Helgeson, H.C., 1969. Thermodynamics of hydrothermal systems at elevated temperatures and pressures. Am. J. Sci. 267, 729-804.

[24] Holtz, F., Johannes, W., Tamic, N., Behrens, H., 2001. Maximum and minimum water contents of granitic melts generated in the crust: A reevaluation and implications. Lithos 56, 1-14.

[25] Hsu, Y.J., Zajacz, Z., Ulmer, P., Heinrich, C.A., 2019. Chlorine partitioning between granitic melt and H₂O-CO₂-NaCl fluids in the Earth’s upper crust and implications for magmatic-hydrothermal ore genesis. Geochim. Cosmochim. Acta 261, 171-190.

[26] Kesler, S.E., Simon, A.C., Simon, A.F., 2015. Mineral resources, economics and the environment. Cambridge University Press.

[27] Keppler, H., Wyllie, P.J., 1991. Partitioning of Cu, Sn, Mo, W, U, and Th between melt and aqueous fluid in the systems haplogranite-H₂O-HCl and haplogranite-H₂O-HF. Contrib. Mineral. Petrol. 109, 139-150.

[28] Kouzmanov, K., Pokrovski, G.S., 2012. Hydrothermal controls on metal distribution in porphyry Cu (-Mo-Au) systems. Soc. Econ. Geol. Special Publication 16, 573-618.

[29] Kravchuk, I.F., Keppler, H., 1994. Distribution of chloride between aqueous fluids and felsic melts at 2 kbar and 800 °C. Eur. J. Mineral. 6, 913-923.

[30] Landtwing, M.R., Pettke, T., Halter, W.E., Heinrich, C.A., Redmond, P.B., Einaudi, M.T., Kunze, K., 2005. Copper deposition during quartz dissolution by cooling magmatic-hydrothermal fluids: the Bingham porphyry. Earth Planet. Sci. Lett. 235, 229-243.

[31] Lee, C.T.A., Luffi, P., Chin, E.J., Bouchet, R., Dasgupta, R., Morton, D.M., Jin, D., 2012. Copper systematics in arc magmas and implications for crust-mantle differentiation. Science 336, 64-68.

[32] Liu, X., Xiong, X., Audétat, A., Li, Y., Song, M., Li, L., Ding, X., 2014. Partitioning of copper between olivine, orthopyroxene, clinopyroxene, spinel, garnet and silicate melts at upper mantle conditions. Geochim. Cosmochim. Acta 125, 1-22.

[33] Masotta, M., Keppler, H., 2015. Anhydrite solubility in differentiated arc magmas. Geochim. Cosmochim. Acta 158, 79-102.

[34] Morgan, G.B., London, D., 1996. Optimizing the electron microprobe analysis of hydrous alkali aluminosilicate glasses. Am. Mineral. 81, 1176-1185.

[35] Ni, H., Shi, H., Zhang, L., Li, W.C., Guo, X., Liang, T., 2018. Cu diffusivity in granitic melts with application to the formation of porphyry Cu deposits. Contrib. Mineral. Petrol. 173, 1-10.

[36] Rusk, B.G., Reed, M.H., Dilles, J.H., Klemm, L.M., Heinrich, C.A., 2004. Compositions of magmatic hydrothermal fluids determined by LA-ICP-MS of fluid inclusions from the porphyry copper-molybdenum deposit at Butte, MT. Chem. Geol. 210, 173-199.

[37] Seedorff, E., Dilles, J.H., Proffett, J.M., Einaudi, M.T., Zurcher, L., Stavast, W.J., Barton, M.D., 2005. Porphyry deposits: Characteristics and origin of hypogene features. Econ. Geol. 100th Anniversary Volume, pp. 251-298.

[38] Seward, T.M., Williams-Jones, A.E., Migdisov, A.A., 2014. 13.2-The chemistry of metal transport and deposition by ore-forming hydrothermal fluids. Treatise Geochem. 13, 29-57.

[39] Shinohara, H., Iiyama, J.T., Matsuo, S., 1989. Partition of chlorine compounds between silicate melt and hydrothermal solutions: I Partition of NaCl-KCl. Geochim. Cosmochim. Acta 53, 2617-2630.

[40] Shinohara, H., 1994. Exsolution of immiscible vapor and liquid phases from a crystallizing silicate melt: Implications for chlorine and metal transport. Geochim. Cosmochim. Acta 58, 5215-5221.

[41] Shishkina, T.A., Botcharnikov, R.E., Holtz, F., Almeev, R.R., Portnyagin, M.V., 2010. Solubility of H₂O- and CO₂-bearing fluids in tholeiitic basalts at pressures up to 500 MPa. Chem. Geol. 277, 115-125.

[42] Sillitoe, R.H., 2010. Porphyry copper systems. Econ. Geol. 105, 3-41.

[43] Signorelli, S., Carroll, M.R., 2000. Solubility and fluid-melt partitioning of Cl in hydrous phonolitic melts. Geochim. Cosmochim. Acta 64, 2851-2862.

[44] Simon, A.C., Pettke, T., Candela, P.A., Piccoli, P.M., Heinrich, C.A., 2006. Copper partitioning in a melt-vapor-brine-magnetite-pyrrhotite assemblage. Geochim. Cosmochim. Acta 70, 5583-5600.

[45] Steinberger, I., Hinks, D., Driesner, T., Heinrich, C.A., 2013. Source plutons driving porphyry copper ore formation: Combining geomagnetic data, thermal constraints, and chemical mass balance to quantify the magma chamber beneath the Bingham Canyon deposit. Econ. Geol. 108, 605-624.

[46] Sullivan, N.A., Zajacz, Z., Brenan, J.M., Hinde, J.C., Tsay, A., Yin, Y., 2022. The solubility of gold and palladium in magmatic brines: Implications for PGE enrichment in mafic-ultramafic and porphyry environments. Geochim. Cosmochim. Acta 316, 230-252.

[47] Tattitch, B.C., Blundy, J.D., 2017. Cu-Mo partitioning between felsic melts and saline-aqueous fluids as a function of X_NaCleq, fO₂, and fS₂. Am. Mineral. 102, 1987-2006.

[48] Tattitch, B., Chelle-Michou, C., Blundy, J., Loucks, R.R., 2021. Chemical feedbacks during magma degassing control chlorine partitioning and metal extraction in volcanic arcs. Nat. Commun. 12, 1774.

[49] Webster, J.D., Holloway, J.R., 1988. Experimental constraints on the partitioning of Cl between topaz rhyolite melt and H₂O and H₂O+CO₂ fluids: New implications for granitic differentiation and ore deposition. Geochim. Cosmochim. Acta 52, 2091-2105.

[50] Webster, J.D., 1992. Fluid-melt interactions involving Cl-rich granites: Experimental study from 2 to 8 kbar. Geochim. Cosmochim. Acta 56, 659-678.

[51] Webster, J.D., 1997. Chloride solubility in felsic melts and the role of chloride in magmatic degassing. J. Petrol. 38, 1793-1807.

[52] Webster, J.D., Vetere, F., Botcharnikov, R.E., Goldoff, B., McBirney, A., Doherty, A.L., 2015. Experimental and modeled chlorine solubilities in aluminosilicate melts at 1 to 7000 bars and 700 to 1250 ℃: Applications to magmas of Augustine Volcano, Alaska. Am. Mineral. 100, 522-535.

[53] Wen, C., Zhao, P., Grondahl, C., Tsay, A., Zajacz, Z., Yuan, S., 2025. Cesium partitioning between granitic melts and aqueous fluids: Is Cs in hydrothermal fluids an accurate proxy of the degree of fractionation of parental magmas? Geochim. Cosmochim. Acta 396, 159-169.

[54] Williams, T.J., Candela, P.A., Piccoli, P.M., 1997. Hydrogen-alkali exchange between silicate melts and two-phase aqueous mixtures: An experimental investigation. Contrib. Mineral. Petrol. 128, 114-126.

[55] Williams-Jones, A.E., Heinrich, C.A., 2005. 100th Anniversary special paper: Vapor transport of metals and the formation of magmatic-hydrothermal ore deposits. Econ. Geol. 100, 1287-1312.

[56] Williams-Jones, A.E., Migdisov, A.A., 2014. Experimental constraints on the transport and deposition of metals in ore-forming hydrothermal systems. Soc. Econ. Geol. Special Publication 18, 77-95.

[57] Yan, H.B., Ding, X., Liu, J.F., Tu, X.L., Sun, W.D., Chou, I.M., 2024. Osmium transport and enrichment from the lithosphere to the hydrosphere: New perspectives from hydrothermal experiments and geochemical modeling. J. Geophys. Res.-Solid Earth 129, e2023JB028261.

[58] Yan, S., Zhou, R., Niu, H.C., Feng, Y.X., Nguyen, A.D., Zhao, Z.H., Zhao, J.X., 2020. LA-MC-ICP-MS U-Pb dating of low-U garnets reveals multiple episodes of skarn formation in the volcanic-hosted iron mineralization system, Awulale belt, Central Asia. Geol. Soc. Am. Bull. 132, 1031-1045.

[59] Yuan, S., Williams-Jones, A.E., Bodnar, R.J., Zhao, P., Zajacz, Z., Chou, I.M., Mao, J., 2025. The role of magma differentiation in optimizing the fluid-assisted extraction of copper to generate large porphyry-type deposits. Sci. Adv. 11, eadr8464.

[60] Zajacz, Z., Halter, W.E., Pettke, T., Guillong, M., 2008. Determination of fluid/melt partition coefficients by LA-ICPMS analysis of co-existing fluid and silicate melt inclusions: Controls on element partitioning. Geochim. Cosmochim. Acta 72, 2169-2197.

[61] Zajacz, Z., Seo, J.H., Candela, P.A., Piccoli, P.M., Tossell, J.A., 2011. The solubility of copper in high-temperature magmatic vapors: A quest for the significance of various chloride and sulfide complexes. Geochim. Cosmochim. Acta 75, 2811-2827.

[62] Zajacz, Z., Candela, P.A., Piccoli, P.M., Sanchez-Valle, C., 2012. The partitioning of sulfur and chlorine between andesite melts and magmatic volatiles and the exchange coefficients of major cations. Geochim. Cosmochim. Acta 89, 81-101.

[63] Zajacz, Z., Seo, J.H., Candela, P.A., Piccoli, P.M., Heinrich, C.A., Guillong, M., 2010. Alkali metals control the release of gold from volatile-rich magmas. Earth Planet. Sci. Lett. 297, 50-56.

[64] Zen, E.A., 1986. Aluminum enrichment in silicate melts by fractional crystallization: Some mineralogic and petrographic constraints. J. Petrol. 27, 1095-1117.

[65] Zhang, P., Zhang, L., Wang, Z., Li, W.C., Guo, X., Ni, H., 2018. Diffusion of molybdenum and tungsten in anhydrous and hydrous granitic melts. Am. Mineral. 103, 1966-1974.

[66] Zhao, P., Zajacz, Z., Tsay, A., Chu, X., Cheng, Q., Yuan, S., 2022a. The partitioning behavior of Mo during magmatic fluid exsolution and its implications for Mo mineralization. Geochim. Cosmochim. Acta 339, 115-126.

[67] Zhao, P., Zajacz, Z., Tsay, A., Yuan, S., 2022b. Magmatic-hydrothermal tin deposits form in response to efficient tin extraction upon magma degassing. Geochim. Cosmochim. Acta 316, 331-346.

[68] Zhao, P., Zajacz, Z., Grondahl, C., Tsay, A., Mao, J., Cheng, Q., Yuan, S., 2024. Indium partitioning between silicate melts and magmatic fluids: Implications for indium ore genesis and the tracing of magma degassing. Geochim. Cosmochim. Acta 374, 146-155.