Instrumental neutron activation analysis and the classification of granites from the Bushveld igneous complex

Instrumental neutron activation analysis has characteristics that make it a favourable technique for the multi-element analysis of geological materials. In this work the elements that can be determined by this method in a particular rock suite have been examined with a view to establishing whether they can contribute to the solution of a petrological problem. Within the granites of the Bushveld Igneous Complex of South Africa there exists such a problem in the question of the extent of a younger phase within the body of the granite. The methods of 14 MeV, 3 MeV and reactor thermal and epithermal, instrumental neutron activation analysis and a mathematical model of the activation analysis process was developed and applied to find the optimum values of the experimental parameters, the irradiation and decay times. This method was used to compare thermal and epithermal neutron activation as multi-element techniques for the analysis of the granites. It was established that a total of thirty-four elements can be determined in the granites by instrumental neutron activation analysis. Twenty-two elements were determined in all of the samples by a simple thermal neutron procedure. A novel procedure, that of stepwise discriminant analysis, was applied to the selection of the variables. It is concluded that a combination of instrumental activation analysis and discriminant analysis could provide the diagnostic criterion necessary to establish the extent of a younger, possibly mineralised phase, within the Bushveld granite. The confirmation of this must however await further work in this and other areas