Microanalysis in galena by secondary ion mass spectrometry for determination of sulfur isotopes

The possibilities and limitations of isotopic analysis as one main field of application of SIMS (secondary ion mass spectrometry) for analytical geochemistry were investigated systematically. For the problem of accurate determination of sulfur isotopic ratios, optimum operational conditions were developed to eliminate the influence of interferences; also several other effects, like nonlinearity of the counting system and instrumental mass discrimination which limit precision and accuracy of results, were studied. By use of a series of lead sulfide specimens with known isotopic ratios, it could be demonstrated that even at high mass resolution (M/Δm greater than or equal to 5000) a precision and accuracy of 2-3% for the 34S/32S ratio can be obtained in an analyzed area of 8 μm diameter. In practical application a variation of the sulfur isotopic ratio in zonal growth structures of single galena octahedrons could be observed. 26 references, 5 figures, 1 table