In this paper we show that the pegmatite-forming processes responsible for the formation of the Malkhan pegmatites started at magmatic temperatures around 720 °C. The primary melts or supercritical fluids were very water- and boron-rich (maximum values of about 10% (g/g) B 2O 3) and over the temperature interval from 720 to 600 °C formed a pseudobinary solvus, indicated by the coexistence of two types of primary melt inclusions (type-A and type-B) representing a pair of conjugate melts. Due to the high water and boron concentration the pegmatite-forming melts are metastable and can be characterized either as genuine melts or silicate-rich fluids. This statement is underscored by Raman spectroscopic studies. This study suggested that the gel state proposed by some authors cannot represent the main stage of the pegmatite-forming processes in the Malkhan pegmatites, and probably in all others. However there are points in the evolution of the pegmatites where the gel- or gel-like state has left traces in form of real gel inclusions in some mineral in the Malkhan pegmatite, however only in a late, fluid dominated stage.
References
[1]
Peretyazhko, I.S.; Prokof’ev, V.Y.; Zagorskii, V.E.; Smirnov, S.Z. Role of boric acids in the formation of pegmatite and hydrothermal minerals: Petrologic consequences of sassolite (H3BO3) discovery in fluid inclusions. Petrology 2000, 8, 214–237.
[2]
Smirnov, S.Z.; Peretyazhko, I.S.; Prokof’ev, V.Y.; Zagorskii, V.E.; Shebanin, A.P. The first finding of sassolite (H3BO3) in fluid inclusions in minerals. Russ. Geol. Geophys. 2000, 41, 193–205.
Zagorsky, V.Y.; Peretyazhko, I.S. The Malkhan gem tourmaline deposit in Transbaikalia, Russia. Miner. Obs. 2008, 13, 4–39.
[5]
Badanina, E.V.; Thomas, R.; Syritso, L.F.; Veksler, I.V.; Trumbull, R.B. High boron concentration in a Li-F granitic melt. Dokl. Earth Sci. 2003, 390, 529–532.
[6]
Badanina, E.V.; Thomas, R.; Syritso, L.F. Evolution of silicate melts during formation of the granite-pegmatite system of the Malkhany pegmatite field, Russia. Geochim. Cosmochim. Acta Suppl. 2005, 69, 240.
[7]
Thomas, R.; Badanina, E.; Veksler, I. Extreme boron enrichment in granitic melt revealed by melt inclusions from Malkhan pegmatite, Russia. In Proceedings of the 8th Pan-American Current Research on Fluid Inclusions Meeting (PACROFI VIII), Halifax, Nova Scotia, Canada, 21-26 July 2002.
[8]
Thomas, R.; Davidson, P. Water in granite and pegmatite-forming melts. Ore Geol. Rev. 2012, 46, 32–46, doi:10.1016/j.oregeorev.2012.02.006.
[9]
Thomas, R.; Davidson, P. Evidence of a water-rich silica gel state during the formation of a simple pegmatite. Mineral. Mag. 2012, 76. in press.
[10]
Roedder, E. Fluid Inclusions. In Reviews in Mineralogy; Ribbe, P.H., Ed.; Mineralogical Society of America: Washington, DC, USA, 1984; Volume 12, p. 644.
[11]
Zagorsky, V.E.; Peretyazhko, I.S. First 40Ar/39Ar age determination on the Malkhan granite-pegmatite system: Geodynamic implications. Dokl. Earth Sci. 2010, 430, 172–175, doi:10.1134/S1028334X10020054.
Thomas, R.; F？rster, H.-J.; Heinrich, W. The behaviour of boron in a peraluminous granite-pegmatite system and associated hydrothermal solutions: A melt and fluid inclusion study. Contrib. Mineral. Petrol. 2003, 144, 457–472, doi:10.1007/s00410-002-0410-5.
[14]
Thomas, R. Estimation of the viscosity and the water content of silicate melts from meltinclusion data. Eur. J. Mineral. 1994, 6, 511–535.
[15]
Massare, D.; Métrich, N.; Clocchiatti, R. High-temperature experiments on silicate melt inclusions in olivine at 1 atm: Inference on temperature of homogenization and H2O concentration. Chem. Geol. 2002, 183, 87–98, doi:10.1016/S0009-2541(01)00373-4.
[16]
Portnyagin, M.; Almeev, R.; Matveev, S.; Holtz, F. Experimental evidence for rapid water exchange between melt inclusions in olivine and host magma. Earth Planet. Sci. Lett. 2008, 272, 541–552, doi:10.1016/j.epsl.2008.05.020.
[17]
Severs, M.J.; Azbej, T.; Thomas, J.B.; Mandeville, C.W.; Bodnar, R.J. Experimental determination of H2O loss from melt inclusions during laboratory heating: Evidence from Raman spectroscopy. Chem. Geol. 2007, 237, 358–371, doi:10.1016/j.chemgeo.2006.07.008.
[18]
McGee, J.J.; Slack, J.F.; Herrington, J.R. Boron analysis by electron microprobe using MoB4C layered synthetic crystals. Am. Mineral. 1991, 76, 681–684.
[19]
Thomas, R. Determination of water contents of granite melt inclusions by confocal laser Raman microprobe spectroscopy. Am. Mineral. 2000, 85, 868–872.
[20]
Thomas, R.; Kamenetsky, V.S.; Davidson, P. Laser Raman spectroscopic measurements of water in unexposed glass inclusions. Am. Mineral. 2006, 91, 467–470, doi:10.2138/am.2006.2107.
[21]
Thomas, R.; Webster, J.D.; Heinrich, W. Melt inclusions in pegmatite quartz: Complete miscibility between silicate melts and hydrous fluids at low pressure. Contrib. Mineral. Petrol. 2000, 139, 394–401, doi:10.1007/s004100000120.
[22]
Sun, Q.; Qin, C. Raman OH stretching band of water as an internal standard to determine carbonate concentrations. Chem. Geol. 2011, 283, 274–278, doi:10.1016/j.chemgeo.2011.01.025.
[23]
Oliver, B.G.; Davis, A.R. Vibrational spectroscopic studies of aqueous alkali metal bicarbonate and carbonate solutions. Can. J. Chem. 1973, 51, 698–702, doi:10.1139/v73-106.
[24]
Thomas, R.; Davidson, P. The application of Raman spectroscopy in the study of fluid and melt inclusions. Z. Dt. Ges. Geowiss. 2012, 163, 113–126.
[25]
Thomas, R.; Webster, J.D.; Rhede, D.; Seifert, W.; Rickers, K.; F？rster, H.-J.; Heinrich, W.; Davidson, P. The transition from peraluminous to peralkaline granitic melts: Evidence from melt inclusions and accessory minerals. Lithos 2006, 91, 137–149, doi:10.1016/j.lithos.2006.03.013.
[26]
Thomas, R. Determination of the H3BO3 concentration in fluid and melt inclusions in granite pegmatites by laser Raman microprobe spectroscopy. Am. Mineral. 2002, 87, 56–68.
[27]
Peretyazhko, I.S.; Smirnov, S.Z.; Thomas, V.G.; Zagorsky, V.Y. Gels and melt-like gels in high-temperature endogeneous mineral formation. In Metallogeny of the Pacific Northwest: Tectonics, Magmatism and Metallogeny of Active Continental Margin; Khanchuk, A.I., Ed.; Dalnauka: Vladivostok, Russia, 2004; pp. 306–309.
[28]
Thomas, R.; Davidson, P.; Hahn, A. Ramanite-(Cs) and ramanite-(Rb): New cesium and rubidium pentaborate tetrahydrate minerals identified with Raman spectroscopy. Am. Mineral. 2008, 93, 1034–1042, doi:10.2138/am.2008.2727.
[29]
Gmelin, L. Gmelins Handbuch der Anorganischen Chemie System-No.25 Caesium; Springer: Berlin, Germany, 1938; p. 268.
[30]
Thomas, R.; Webster, J.D.; Davidson, P. Be-daughter minerals in fluid and melt inclusions: Implications for the enrichment of Be in granite-pegmatite systems. Contrib. Mineral. Petrol. 2011, 161, 483–495, doi:10.1007/s00410-010-0544-9.
[31]
Thomas, R.; Davidson, P. Water and melt/melt immiscibility, the essential components in the formation of pegmatites; evidence from melt inclusions. Z. geol. Wiss. Berl. 2008, 36, 347–364.
[32]
G？tze, J.; Nasdala, L.; Kleeberg, R.; Wenzel, M. Occurence and distribution of “moganite” in agate/chalcedony: A combined micro-Raman, Rietveld, and cathodoluminescence study. Contrib. Mineral. Petrol. 1998, 133, 96–105, doi:10.1007/s004100050440.
[33]
Peretyazhko, I.S.; Zagorskii, V.E.; Smirnov, S.Z.; Mikhailov, M.Y. Conditions of pocket formation in the Oktyabrskaya tourmaline-rich gem pegmatite (the Malkhan field, Central Transbaikalia, Russia). Chem. Geol. 2004, 210, 91–111, doi:10.1016/j.chemgeo.2004.06.005.
[34]
Zagorskii, V.Y. Malkhan gem tourmaline deposit: Types and nature of miaroles. Dokl. Earth Sci. 2010, 431, 314–317, doi:10.1134/S1028334X10030116.
Ihinger, P.D.; Hervig, R.L.; McMillan, P.F. Analytical methods for volatiles in glasses. Rev. Mineral. 1994, 30, 67–121.
[37]
Xue, X.; Kanzaki, M. Dissolution mechanisms of water in depolymerized silicate melts: Constraints from 1H and 29Si NMR spectroscopy and ab initio calculations. Geochim. Cosmochim. Acta 2004, 68, 5027–5057, doi:10.1016/j.gca.2004.08.016.
Thomas, R.; Davidson, P.; Schmidt, C. Extreme alkali bicarbonate- and carbonate-rich fluid inclusions in granite pegmatite from the Precambrian R？nne granite, Bornholm Island, Denmark. Contrib. Mineral. Petrol. 2011, 161, 315–329, doi:10.1007/s00410-010-0533-z.
[40]
Smirnov, S.Z.; Thomas, V.G.; Kamenetsky, V.S.; Kozmenko, O.A.; Large, R.R. Hydrosilicate liquids in the system Na2O-SiO2-H2O with NaF, NaCl and Ta: Evaluation of their role in ore and mineral formation at high T and P. Petrologiya 2012, 20, 300–314.
[41]
London, D.; Morgan, G.B., VI. The pegmatite puzzle. Elements 2012, 8, 263–268, doi:10.2113/gselements.8.4.263.
[42]
London, D. Pegmatites; Mineralogical Association of Canada: Ottawa, Canada, 2008.
[43]
Thomas, R.; Davidson, P.; Beurlen, H. The competing models for the origin and internal evolution of granitic pegmatites in the light of melt and fluid inclusion research. Mineral. Petrol. 2012, 106, 55–73.
[44]
McKenzie, D. The extraction of magma from the crust and mantle. Earth Planet. Sic. Lett. 1985, 74, 81–91, doi:10.1016/0012-821X(85)90168-2.
[45]
Audétat, A.; Keppler, H. Viscosity of fluids in subduction zones. Science 2004, 303, 513–516.
