Solubility of manganotantalite, zircon and hafnon in highly fluxed peralkaline to peraluminous pegmatitic melts
Tóm tắt
The behavior of tantalum and zirconium in pegmatitic systems has been investigated through the determination of Ta and Zr solubilities at manganotantalite and zircon saturation from dissolution and crystallization experiments in hydrous, Li-, F-, P- and B-bearing pegmatitic melts. The pegmatitic melts are synthetic and enriched in flux elements: 0.7–1.3 wt% Li2O, 2–5.5 wt% F, 2.8–4 wt% P2O5 and 0–2.8 wt% B2O3, and their aluminum saturation index ranges from peralkaline to peraluminous (ASILi = Al/[Na + K + Li] = 0.8 to 1.3) with various K/Na ratios. Dissolution and crystallization experiments were conducted at temperatures varying between 700 and 1,150°C, at 200 MPa and nearly water-saturated conditions. For dissolution experiments, pure synthetic, end member manganotantalite and zircon were used in order to avoid problems with slow solid-state kinetics, but additional experiments using natural manganotantalite and zircon of relatively pure composition (i.e., close to end member composition) displayed similar solubility results. Zircon and manganotantalite solubilities considerably increase from peraluminous to peralkaline compositions, and are more sensitive to changes in temperature or ASI of the melt than to flux content. A model relating the enthalpy of dissolution of manganotantalite to the ASILi of the melt is proposed: ∆H
diss (kJ/mol) = 304 × ASILi − 176 in the peralkaline field, and ∆H
diss (kJ/mol) = −111 × ASILi + 245 in the peraluminous field. The solubility data reveal a small but detectable competitivity between Zr and Ta in the melt, i.e., lower amounts of Zr are incorporated in a Ta-bearing melt compared to a Ta-free melt under the same conditions. A similar behavior is observed for Hf and Ta. The competitivity between Zr (or Hf) and Ta increases from peraluminous to peralkaline compositions, and suggests that Ta is preferentially bonded to non-bridging oxygens (NBOs) with Al as first-neighbors, whereas Zr is preferentially bonded to NBOs formed by excess alkalies. As a consequence Zr/Ta ratios, when buffered by zircon and manganotantalite simultaneously, are higher in peralkaline melts than in peraluminous melts.
Tài liệu tham khảo
Baker DR, Conte AM, Freda C, Ottolini L (2002) The effect of halogens on Zr diffusion and zircon dissolution in hydrous metaluminous granitic melts. Contrib Mineral Petrol 142:666–678
Bartels A, Holtz F, Linnen RL (2009) Solubility of manganotantalite and manganocolumbite in pegmatitic melts. Am Mineral (in review)
Behrens H, Meyer M, Holtz F, Benne D, Nowak M (2001) The effect of alkali ionic radius, temperature, and pressure on the solubility of water in MAlSi3O8 melts (M = Li, Na, K, Rb). Chem Geol 174:275–289
Berndt J, Liebske C, Holtz F, Freise M, Nowak M, Ziegenbein D, Hurkuck W, Koepke J (2002) A combined rapid-quench and H2-membrane setup for internally heated pressure vessels: description and application for water solubility in basaltic melts. Am Mineral 87:1717–1726
Černý P (2005) The Tanco rare-element pegmatite deposit, Manitoba: regional context, internal anatomy, and global comparisons. In: Linnen RL, Samson IM (eds) Rare-element geochemistry and mineral deposits, Geol Assoc Canada Short Course Notes 17:127–158
Černý P, Ercit TS (2005) The classification of granitic pegmatites revisited. Can Mineral 43:1005–2026
Černý P, Meintzer RE, Anderson AJ (1985) Extreme fractionation in rare-element granitic pegmatites: selected examples of data and mechanisms. Can Mineral 23:381–421
Dolejs D, Baker DR (2007) Liquidus equilibria in the system K2O–Na2O–Al2O3–SiO2–F2O–1–H2O to 100 MPa: II. Differentiation paths of fluorosilicic magmas in hydrous systems. J Petrol 48:807–828
Ellison AJ, Hess PC (1986) Solution behavior of +4 cations in high silica melts—petrologic and geochemical implications. Contrib Mineral Petrol 94:343–351
Hanchar JM, Watson EB (2003) Zircon saturation thermometry. Rev Mineral Geochem 53:89–112
Hanchar JM, Finch RJ, Hoskin PWO, Watson EB, Cherniak DJ, Mariano AN (2001) Rare earth elements in synthetic zircon: part 1. Synthesis, and rare earth element and phosphorus doping. Am Mineral 86:667–680
Holtz F, Dingwell DB, Behrens H (1993) Effects of F, B2O3 and P2O5 on the solubility of water in haplogranitic melts compared to natural silicate melts. Contrib Mineral Petrol 113:492–501
Horng WS, Hess PC, Gan H (1999) The interactions between M+5 cations (Nb+5, Ta+5, or P+5) and anhydrous haplogranite melts. Geochim Cosmochim Acta 63:2419–2428
Keppler H (1993) Influence of fluorine on the enrichment of high field strength trace elements in granitic rocks. Contrib Mineral Petrol 114:479–488
Kohn SC, Charnock JM, Henderson CMB, Greaves GN (1990) The structural environments of trace elements in dry and hydrous silicate glasses; a manganese and strontium K-edge Xray adsorption spectroscopic study. Contrib Mineral Petrol 105:359–368
Linnen RL (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic melts with Li and Li + F: constraints for mineralization in rare metal granites and pegmatites. Econ Geol 93:1013–1025
Linnen RL (2005) The effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts. Lithos 80:267–280
Linnen RL, Cuney M (2005) Granite-related rare-element deposits and experimental constraints on Ta–Nb–W–Sn–Zr–Hf mineralization. In: Linnen RL, Samson IM (eds) Rare-element geochemistry and mineral deposits, Geol Assoc Canada Short Course Notes 17:45–68
Linnen RL, Keppler H (1997) Columbite solubility in granite melts: consequences for the enrichment and fractionation of Nb and Ta in the Earth’s crust. Contrib Mineral Petrol 128:213–227
Linnen RL, Keppler H (2002) Melt composition control of Zr/Hf fractionation in magmatic processes. Geochim Cosmochim Acta 66:3293–3301
London D (1986) Magmatic-hydrothermal transition in the Tanco rare-element pegmatite: evidence from fluid inclusions and phase equilibrium experiments. Am Mineral 71:376–395
London D (2008) Pegmatites. The Canadian mineralogist, special publication 10
London D, Hervig RL, Morgan GB (1988) Melt-vapor solubilities and elemental partitioning in peraluminous granite–pegmatite systems: experimental results with Macusani at 200 MPa. Contrib Mineral Petrol 99:360–373
Mysen BO, Richet P (2005) Silicate glasses and melts, properties and structure. Elsevier, Amsterdam, p 544
Mysen BO, Holtz F, Pichavant M, Beny JM, Montel JM (1999) The effect of temperature and bulk composition on the solution mechanism of phosphorus in peraluminous haplogranitic magma. Am Mineral 84:1336–1345
Salvi S, Williams-Jones AE (2005) Alkaline granite-syenite-hosted rare metal deposits. In: Linnen RL, Samson IM (eds) Rare-element geochemistry and mineral deposits, Geol Assoc Canada Short Course Notes 17:269–297
Saunders AD, Tarney J, Marsh N, Wood D (1980) Ophiolites as ocean crust or marginal basin crust: a geochemical approach. In: Panayiotou F (ed) Ophiolites: proceedings of the international ophiolite symposium Cyprus 1979, Ministry of Agriculture and Natural Resources, Geological Survey Department Cyprus, pp 193–204
Stilling A, Černý P, Vanstone PJ (2006) The Tanco pegmatite at Bernic Lake, Manitoba. XVI. Zonal and bulk compositions and their petrogenetic significance. Can Mineral 44:599–623
Toplis MJ, Dingwell DB (1996) The variable influence of P2O5 on the viscosity of melts of differing alkali/aluminium ratio: implications for the structural role of phosphorus in silicate melts. Geochim Cosmochim Acta 60:4107–4121
Van Lichtervelde M, Linnen RL, Salvi S, Beziat D (2006) The role of metagabbro rafts on tantalum mineralization in the Tanco granitic pegmatite, Manitoba. Can Mineral 44:625–644
Van Lichtervelde M, Salvi S, Beziat D (2007) Textural features and chemical evolution in tantalum oxides: magmatic versus hydrothermal origins for Ta mineralization in the Tanco lower pegmatite, Manitoba, Canada. Econ Geol 102:257–276
Van Lichtervelde M, Gregoire M, Linnen RL, Beziat D, Salvi S (2008) Trace element geochemistry by laser ablation ICP-MS of micas associated with Ta mineralization in the Tanco pegmatite, Manitoba, Canada. Contrib Mineral Petrol 155:791–806
Van Lichtervelde M, Melcher F, Wirth R (2009) Magmatic vs. hydrothermal origins for zircon associated with tantalum mineralization in the Tanco pegmatite, Manitoba, Canada. Am Mineral 94:439–450
Watson EB (1979) Zircon saturation in felsic liquids—experimental results and applications to trace-element geochemistry. Contrib Mineral Petrol 70:407–419
Watson EB, Harrison TM (1983) Zircon saturation revisited: temperature and composition effects in a variety of crustal magma types. Earth Planet Sci Lett 64:295–304
Zhang AC, Wang RC, Hu H, Zhang H, Zhu JC, Chen XM (2004) Chemical evolution of Nb-Ta oxides and zircon from the Koktokay No. 3 granitic pegmatite, Altai, northwestern China. Mineral Mag 68:739–756