The Na/K ratio of fluid inclusions in pegmatitic quartz and its genetic implications. A study by neutron activation analysis

Samples of quartz and its fluid inclusions (f.i.) from Black Hills pegmatites and from graphic granites were analyzed for Na, K, Rb and Cs by neutron activation analysis. The Na/K ratios of the whole quartz and its f.i. seem unrelated. The spatial locations for six samples from the Helen Beryl pegmatite were known. The Na/K ratios of their f.i. are mainly a function of their vertical positions in the pegmatite. The ratios of the central-core quartz f.i. seemingly indicate a much higher temperature than those closer to the upper wall. This is consistent with the theory of pegmatite genesis by Jahns & Burnham. The f.i. of quartz from two graphic granites give very different Na/K ratios, seemingly related to differences in their formation history.