Alkali partitioning between beryl and hydrothermal fluids: an experimental study at 600 °C and 1.5 kbar
Manier-Glavinaz, Valerie; D'arco, Philippe; Lagache, Martine
European Journal of Mineralogy Volume 1 Number 5 (1989), p. 645 - 656
published: Nov 16, 1989
manuscript accepted: Jun 15, 1989
manuscript received: Jan 16, 1989
ArtNo. ESP147050105005, Price: 29.00 €
Abstract A natural lithian-caesian beryl was re-equilibrated with hydrothermal chloride solutions of Li, Na or Cs, at 600 °C and 1.5 kbar. The alkali elements substitute one another in the mineral, suggesting that they occupy the same structural position. Beryl composition depends on the absolute amount of alkalis present in the solution and not on the alkali concentration. Partition coefficients, Pi, are defined as follows: Pi = Xi(Bl)/Xi(fl) where Xi(Bl) and Xi(fl) are i/(Li+Na+Cs) ratios of the beryl and of the solution, respectively, i = Li, Na or Cs is expressed in μmol per 100 mg of beryl or 100 μl of solution. Average values are: PLi = 1.12, PNa = 0.51 and PCs = 2.10. These coefficients are independent of chlorinity but in fact slightly depend on the solution (and solid) alkali composition. Using these coefficients, and assuming equivalent crystallization conditions, the Li-, Na- and Cs-ratios of mineralizing fluids have been estimated on the basis of the compositions of several natural beryls ; their relative constancy may reflect the buffering of the pegmatite system by alkali-aluminosilicates.