Water- and Boron-Rich Melt Inclusions in Quartz from the Malkhan Pegmatite, Transbaikalia, Russia

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) B2O3) 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.

[1]  E. Fluck,et al.  Gmelins Handbuch der anorganischen Chemie , 1936, Nature.

[2]  J. Slack,et al.  Boron analysis by electron microprobe using MoB4C layered synthetic crystals , 1991 .

[3]  M. Portnyagin,et al.  Experimental evidence for rapid water exchange between melt inclusions in olivine and host magma , 2008 .

[4]  J. Götze,et al.  Occurrence and distribution of “moganite” in agate/chalcedony: a combined micro-Raman, Rietveld, and cathodoluminescence study , 1998 .

[5]  P. Davidson,et al.  Extreme alkali bicarbonate- and carbonate-rich fluid inclusions in granite pegmatite from the Precambrian Rønne granite, Bornholm Island, Denmark , 2011 .

[6]  M. Mikhailov,et al.  Conditions of pocket formation in the Oktyabrskaya tourmaline-rich gem pegmatite (the Malkhan field, Central Transbaikalia, Russia) , 2004 .

[7]  P. Davidson,et al.  The application of Raman spectroscopy in the study of fluid and melt inclusions , 2012 .

[8]  P. Davidson,et al.  Evidence of a water-rich silica gel state during the formation of a simple pegmatite , 2012, Mineralogical Magazine.

[9]  P. Davidson,et al.  Laser Raman spectroscopic measurements of water in unexposed glass inclusions , 2006 .

[10]  P. Davidson,et al.  Water in granite and pegmatite-forming melts , 2012 .

[11]  D. McKenzie.  The extraction of magma from the crust and mantle , 1985 .

[12]  P. McMillan,et al.  Analytical methods for volatiles in glasses , 1994 .

[13]  C. Mandeville,et al.  Experimental determination of H2O loss from melt inclusions during laboratory heating: Evidence from Raman spectroscopy , 2007 .

[14]  R. Thomas.  Determination of water contents of granite melt inclusions by confocal laser Raman microprobe spectroscopy , 2000 .

[15]  Ekkehard Fluck,et al.  Gmelins Handbuch der anorganischen Chemie , 1931, Nature.

[16]  Qiang Sun,et al.  Raman OH stretching band of water as an internal standard to determine carbonate concentrations , 2011 .

[17]  P. McMillan,et al.  Vibrational spectroscopy of silicate liquids , 1995 .

[18]  W. Heinrich,et al.  The behaviour of boron in a peraluminous granite-pegmatite system and associated hydrothermal solutions: a melt and fluid-inclusion study , 2002 .

[19]  V. Prokof’ev,et al.  Role of boric acids in the formation of pegmatite and hydrothermal minerals: Petrologic consequences of sassolite (H3BO3) discovery in fluid inclusions , 2000 .

[20]  P. Davidson,et al.  Be-daughter minerals in fluid and melt inclusions: implications for the enrichment of Be in granite–pegmatite systems , 2011 .

[21]  R. Thomas.  Determination of the H3BO3 concentration in fluid and melt inclusions in granite pegmatites by laser Raman microprobe spectroscopy , 2002 .

[22]  W. Heinrich,et al.  The transition from peraluminous to peralkaline granitic melts: Evidence from melt inclusions and accessory minerals , 2006 .

[23]  R. Thomas.  Estimation of the viscosity and the water content of silicate melts from melt inclusion data , 1994 .

[24]  H. Keppler,et al.  Viscosity of Fluids in Subduction Zones , 2004, Science.

[25]  David R. Reichman,et al.  Soft colloids make strong glasses , 2009, Nature.

[26]  P. Davidson,et al.  Ramanite-(Cs) and ramanite-(Rb): New cesium and rubidium pentaborate tetrahydrate minerals identified with Raman spectroscopy , 2008 .

[27]  X. Xue,et al.  Dissolution mechanisms of water in depolymerized silicate melts: Constraints from 1H and 29Si NMR spectroscopy and ab initio calculations , 2004 .

[28]  N. Métrich,et al.  High-temperature experiments on silicate melt inclusions in olivine at 1 atm: inference on temperatures of homogenization and H2O concentrations , 2002 .

[29]  B. B. Zvyagin,et al.  Borocookeite, a new member of the chlorite group from the Malkhan gem tourmaline deposit, Central Transbaikalia, Russia , 2003 .

[30]  W. Heinrich,et al.  Melt inclusions in pegmatite quartz: complete miscibility between silicate melts and hydrous fluids at low pressure , 2000 .

[31]  B. G. Oliver,et al.  Vibrational Spectroscopic Studies of Aqueous Alkali Metal Bicarbonate and Carbonate Solutions , 1973 .

[32]  R. Large,et al.  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 , 2012, Petrology.

[33]  David London,et al.  The Pegmatite Puzzle , 2012 .

[34]  I. S. Peretyazhko,et al.  First 40Ar/39Ar age determinations on the Malkhan granite-pegmatite system: Geodynamic implications , 2010 .

[35]  P. Davidson,et al.  The competing models for the origin and internal evolution of granitic pegmatites in the light of melt and fluid inclusion research , 2012, Mineralogy and Petrology.