A modified crush-leach method for the analysis of fluid inclusion electrolytes

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Abstract
A procedure is described which has yielded chemical analyses for 15 elements from inclusion fluids trapped in quartz, and requires about 10 g of cleaned sample. Problems of contamination and adsorption that have bedeviled crush-leach analysis in the past have been overcome and good charge balances obtained. New data are presented on the adsorption of ions released during crush-leach analysis onto the new quartz surfaces generated. These show very significant losses of divalent cations from solution when using pure water as a leachate, thus leading to systematic analytical errors. Further experiments were conducted using H+ and La3+ in the leach solution as adsorption inhibitors and from the results a new crush-leach analysis procedure is proposed in which errors due to adsorption effects are minimal. The new technique utilises a variety of leaches tailored to minimise adsorption of specific ions, while being compatible with standard analytical procedures. Methods of analysis used are Atomic Absorption Spectrometry, Flame Emission Spectrometry, ICP-AES, Mass Spectrometry, Fluorimetry and Specific Ion Electrode. At present analyses can be performed for Na, K, Li, Rb, Ca, Mg, Sr. Ba, Fe, Mn, Zn, Al, Cl, B and F. Preliminary results on inclusions in quartz veins from both low and high grade metamorphic rocks show good agreement with theoretically predicted compositions from fluid-mineral equilibria for Na, K, Fe, Mn and Zn. However Ca and sometimes Mg are present at levels far higher than predicted. This is thought to be due to the presence of Ca-rich inclusions (which have been identified microthermometrically in some of the samples). A second set of data from post-metamorphic gold bearing quartz veins from the Monte Rosa district of Italy, where only one generation of inclusion fluids is present, show better agreement with calculated compositions with no excess Ca or Mg.

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