Secondary Ion Mass Spectrometry (SHRIMP)

SHRIMP II A was commissioned at Curtin in 1993 following a 5 year effort to raise the required funds by the three partners in SHRIMP:

• Curtin University of Technology
• Geological Survey of Western Australia
• University of Western Australia

The Sensitive High Resolution Ion Microprobe (SHRIMP) allows in situ isotopic analysis of chemically complex materials with a spatial resolution of 5 to 20 micrometers and can be used for routine measurement of the isotopic composition of Mg, Si ,S, Ca, Ti, Cr, Fe, Sr, Hf, Pb and U, and the abundances of most elements in the Periodic Table in geological, cosmochemical and experimental samples. The main application of the SHRIMP at Curtin is in U-Th-Pb geochronology of geological samples. Zircon and other U bearing minerals, such as perovskite, monozite, uraninite, badelleyite, rutile, apatite, xenotime, cassiterite, tantalite and sphene, often have multiple growth zones and this complexity is best addressed by ion microprobe analysis.

Stable isotope geochemistry examines the change of the isotopic composition of an element (H, Li, B, C, N, O, S) produced by chemical or physical processes, SHRIMP measurement of S isotopes has been used to understand mineral growth mechanisms, follow changes in fluid compositions and to constrain the conditions under which rocks and ore deposits form.

The SHRIMP has also been used for isotopic tracing of S, Hf and Pb to constrain petrogenic models of igneous systems. For example, SHRIMP analysis of small sulphide inclusions (<50 microns) within eclogitic and periodotitic diamonds from kimberlites have established a relationship between the diamond content of kimberlites and the nature of the source material. Groundmass perovskite has been used to date kimberlite intrusions, when megacyrstic phases give a range of ages. Included minerals in diamonds, such as titanite, have also been dated.

SHRIMP analysis has been applied to numerous problems in trace element geochemistry, such as:

• Measurements of the concentration and distribution of trace elements within individual grains, fluid inclusions, and teeth.
• Measurement of chemical and and isotopic diffusion rates.
• Partitioning of elements between phases, and dissolution rates of minerals.

The SHRIMP ion microprobe can also provide images or maps of isotopic composition and concentrations across the surface of the sample. In this way boundaries and enrichments on the micron scale are identifiable.

A second SHRIMP was commissioned in 2002. The new SHRIMP B is a state-of-the-art secondary ion mass spectrometer capable of rapid in situ isotope and chemical analysis of natural and synthetic materials. It is used predominantly as a means of dating mineral samples using radiogenic isotopes, but can be applied to stable isotope studies also. The new SHRIMP has more automated features than SHRIMP A, and is unrivaled in terms of mass resolution and sensitivity.