TY - JOUR

T1 - Influence of fluorine on the solubility of manganotantalite (MnTa2O6) and manganocolumbite (MnNb2O6) in granitic melts - An experimental study

AU - Fiege, Adrian

AU - Kirchner, Clemens

AU - Holtz, François

AU - Linnen, Robert L.

AU - Dziony, Wanja

N1 - Funding Information: This research was supported by the German Science Foundation (DFG project 1337/20 ). M. René provided the natural rock sample (NG) used for the experiments. We would like to thank Otto Diedrich for preparing the samples and thin sections, Eric Wolff for help with the EMP analyses as well as Renat Almeev, Sarah Cichy and Alexander Bartels for help with the experimental high pressure facilities. Copyright: Copyright 2011 Elsevier B.V., All rights reserved.

PY - 2011/3

Y1 - 2011/3

N2 - Solubility experiments of manganotantalite (MnTa2O6) and manganocolumbite (MnNb2O6) were conducted under nearly fluid-saturated conditions in synthetic haplogranitic (HPG) and natural granitic (NG) melts containing different amounts of fluorine at 800 to 1000°C and 200MPa. The experiments were carried out in cold seal pressure vessels (at 800°C) with water or Ar as a pressure medium and in internally heated pressure vessels (1000°C) with Ar as a pressure medium. The F contents vary from 0 to 11.43wt.% in experiments using HPG melts and from 0.61 to 3.78wt.% in experiments using NG melts. Additionally, the NG melt contains minor amounts of P2O5 (0.44 to 0.64wt.%).In HPG melts (alumina saturation index including Mn (ASIMn): 0.88 to 0.99) the solubility product values at 800°C yield log (KspTa) and log (KspNb) ranging from -3.36±0.10 to -2.92±0.10mol2/kg2 and from -3.01±0.11 to -2.87±0.06mol2/kg2, respectively. In NG melts the log (KspTa) and log (KspNb) vary from -3.00±0.04 to -2.35±0.13mol2/kg2 and from -2.83±0.06 to -2.67±0.18mol2/kg2 at 800°C, respectively. The solubility products of both MnTa2O6 (KspTa) and MnNb2O6 (KspNb) are not significantly affected by the F content for a given melt composition (data are virtually identical within error). The variation of the solubility products observed in this study is rather attributed to the changes in melt structure (e.g. polymerization) and, in particular, to the alumina saturation index. By contrast, there is no evidence for the formation of complexes associating F and Nb and/or Ta. Our results also indicate that the structural changes caused by the incorporation of F in natural water-rich silicate melts are not expected to significantly influence the maximum concentrations of Nb and Ta in granitic or pegmatitic melts coexisting with manganotantalite and manganocolumbite.

AB - Solubility experiments of manganotantalite (MnTa2O6) and manganocolumbite (MnNb2O6) were conducted under nearly fluid-saturated conditions in synthetic haplogranitic (HPG) and natural granitic (NG) melts containing different amounts of fluorine at 800 to 1000°C and 200MPa. The experiments were carried out in cold seal pressure vessels (at 800°C) with water or Ar as a pressure medium and in internally heated pressure vessels (1000°C) with Ar as a pressure medium. The F contents vary from 0 to 11.43wt.% in experiments using HPG melts and from 0.61 to 3.78wt.% in experiments using NG melts. Additionally, the NG melt contains minor amounts of P2O5 (0.44 to 0.64wt.%).In HPG melts (alumina saturation index including Mn (ASIMn): 0.88 to 0.99) the solubility product values at 800°C yield log (KspTa) and log (KspNb) ranging from -3.36±0.10 to -2.92±0.10mol2/kg2 and from -3.01±0.11 to -2.87±0.06mol2/kg2, respectively. In NG melts the log (KspTa) and log (KspNb) vary from -3.00±0.04 to -2.35±0.13mol2/kg2 and from -2.83±0.06 to -2.67±0.18mol2/kg2 at 800°C, respectively. The solubility products of both MnTa2O6 (KspTa) and MnNb2O6 (KspNb) are not significantly affected by the F content for a given melt composition (data are virtually identical within error). The variation of the solubility products observed in this study is rather attributed to the changes in melt structure (e.g. polymerization) and, in particular, to the alumina saturation index. By contrast, there is no evidence for the formation of complexes associating F and Nb and/or Ta. Our results also indicate that the structural changes caused by the incorporation of F in natural water-rich silicate melts are not expected to significantly influence the maximum concentrations of Nb and Ta in granitic or pegmatitic melts coexisting with manganotantalite and manganocolumbite.

KW - Columbite solubility

KW - Fluorine

KW - Granitic melt

KW - Tantalite solubility

UR - http://www.scopus.com/inward/record.url?scp=79551682420&partnerID=8YFLogxK

U2 - 10.1016/j.lithos.2010.12.012

DO - 10.1016/j.lithos.2010.12.012

M3 - Article

AN - SCOPUS:79551682420

VL - 122

SP - 165

EP - 174

JO - Lithos

JF - Lithos

SN - 0024-4937

IS - 3-4

ER -