Paul Gertzbein HBSc thesis abstract

Thesis Title: 
Cesium Concentration in Volcanic Rocks from the Freemans Cove Volcanic Suite by Neutron Activation Analysis

Forty eight rock powder samples from Freemans Cove volcanic suite were analysed for cesium using neutron activation analysis.  The samples analysed vary in composition and may fit into the following three series:

    i)  A sodic nephelinite-basanite (phonolite) series

    ii) A mildly potassic nepheline-basanite (phonolite) series

   iii) A mildy alkakine (sodic transitional) basalt suite.

The cesium was radio-chemically separated using an inorganic cation exchanger, Ammonium 12 moybdophosphate.  The gamma ray spectrometry was carried out using a Norland 5400 Ino Tech Multichannel Analyser.

The cesium concentration ranged from a low of 0.03 ppm, in a basalt to a high of 5.87 ppm, in a basanite or nephelinite.  The K/Cs ratio ranged from 3900 for a basalt to 702500 for a Ne bearing trachytoid of phonolitoid.  The majority of the samples have K/Cs ratios between 14,500 and 40,000.  The Rb/Cs ratio ranges between 8.6 for a basalt to 3747 for a Ne bearing trachytoid or phonolitoid.  The majority of points lye between Rb/Cs ratios of 25 to 100.

Graphs of Rb vs Cs and K vs Cs show trends that are very similar.  These trends show a loss of cesium without the loss of either rubidium or potassium.  These trends may indicate a degassing of cesium due to it's volatile nature, but these trends are found only in two rock groups, basalts and Ne bearing trachytoids and phonolitoids.

The graph of K vs Rb shows a linear trend indicating not only comagmatism, but also a coherence of potassium and rubidium through magma evolution.