Technique for the extraction and partial chemical analysis of fluid-filled inclusions from minerals

A method has been developed for the extraction and limited chemical analysis of the materials in solution in the fluid from the very minute fluid-filled inclusions such as commonly occur in whitish or milky quartz. The method may also be applied, with some reservations, to a variety of other minerals. As the amounts of substances in the fluid are small compared with possible contaminants, great care is needed in sample purification and cleaning; an electrolytic method has been found to be the only satisfactory final cleaning step. Following this, the inclusions are opened by ball milling of the cleaned sample, with deionized water, in an alumina ball mill using alumina grinding media. The ions present in the resultant slurry are separated from the ground quartz by electrodialysis and analyzed. Other methods, such as the decrepitation of a sample in an absorption train, are used to estimate the amount of H2O and CO2 in the inclusions. The most significant part of the analytical work has been to determine the ratios between the alkali metals.

The materials in solution in the fluid-filled inclusions from 11 samples of quartz have been analyzed by the ball milling-electrodialysis method. Although there are large differences between samples, the average weights of the alkali metal ions found, for all samples, in milligrams per kilogram of quartz, are: Li+-0.92, Na+-99, K+-133, Rb+-0.45, Cs+-0.38 (atomic ratios, in the same sequence: 0.03/1.00/0.79/0.001/0.0007). In addition, 27 to 193 milligrams of CI", and 5 to 140 milligrams of SOr were found, per kilogram of quartz. H2O and COa were determined on only one sample. Six of the samples were from gold-quartz veins in the Grass Valley district, California. In these six the Na+/K+ ratios were all very similar, but the amounts of Li+, Rb+ and Cs+ found varied greatly. Although there are serious limitations to this and to all other techniques developed, it is felt that the results presented are sufficiently encouraging to warrant further study and possible application to specific geologic problems, such as the identification of epochs of quartz deposition