NATURAL VARIATIONS IN THE ISOTOPIC CONTENT OF SULPHUR AND THEIR SIGNIFICANCE

Abstract

Mass spectrometer abundance measure menu made on the isotopes of sulphur for samples obtained from a wide variety of sources show considerable variations. The isotopic ratios S32/S33 and S32/S34 were found to vary by as much as 2.5 and 5% respectively. This would mean a corresponding variation of 10% in the S32/S36 ratio. Variations in the S32/S34 ratio were determined with a precision of ± 0.05%. In general, sulphates whether present as gypsum deposits or in solution were found to be enriched in the heavier isotopes of sulphur. On the other hand, the hydrogen sulphide of sulphuretted well waters was usually low in these isotopes even though present in the same solutions with the sulphates. These variations are in the direction expected from theoretical considerations. A correlation between crystallization temperature of pyrites and isotopic content has been found for crystals removed from the same specimen. However, no correlation was found between crystallization temperature or geological age and isotopic content for pyrite samples collected from different geographical locations. The results indicate that the changes in the isotopic content of sulphur that occur are related to the differences in chemical properties of isotopic sulphur compounds.