A new silicate dissolution procedure for isotope studies on garnet and other rock forming minerals

Abstract

A new silicate digestion technique, based on sequential acid treatment (HBr → HF-HNO3 → HNO3), is presented. The main features are: (i) only "off the shelf" equipment is needed, (ii) it avoids HClO4 and H2SO4, (in) precipitates which may coat residual grains and inhibit total dissolution are removed by ultrasonic agitation, (iv) cations which are likely to form fluorides in the course of dissolution are largely extracted from the silicates before HF is applied, thus minimising the danger of laboratory fractionation (of e.g. Sm/Nd or U/Pb) and incomplete spike-sample equilibration, (v) the procedure can be optimised for specific silicates (or mineral chemistries), (vi) thanks to the use of transparent beakers the state of dissolution can be traced without interrupting the process and residual fluorides are easily detected and (vii) blank contribution is easily traced. This technique is an alternative to steel jacketed Teflon® bomb digestion and an improvement over traditional closed vial approaches.