[1] Elemental fractionation effects during analysis are the most significant impediment to obtaining precise and accurate U-Pb ages by laser ablation ICPMS. Several methods have been proposed to minimize the degree of downhole fractionation, typically by rastering or limiting acquisition to relatively short intervals of time, but these compromise minimum target size or the temporal resolution of data. Alternatively, other methods have been developed which attempt to correct for the effects of downhole elemental fractionation. A common feature of all these techniques, however, is that they impose an expected model of elemental fractionation behavior; thus, any variance in actual fractionation response between laboratories, mineral types, or matrix types cannot be easily accommodated. Here we investigate an alternate approach that aims to reverse the problem by first observing the elemental fractionation response and then applying an appropriate (and often unique) model to the data. This approach has the versatility to treat data from any laboratory, regardless of the expression of downhole fractionation under any given set of analytical conditions. We demonstrate that the use of more complex models of elemental fractionation such as exponential curves and smoothed cubic splines can efficiently correct complex fractionation trends, allowing detection of spatial heterogeneities, while simultaneously maintaining data quality. We present a data reduction module for use with the Iolite software package that implements this methodology and which may provide the means for simpler interlaboratory comparisons and, perhaps most importantly, enable the rapid reduction of large quantities of data with maximum feedback to the user at each stage.

We present data for the rare earth elements and yttrium (REY) in the National Research Council of Canada natural river water reference material SLRS-4 and 19 natural river waters from small catchments in South-East Queensland, Australia, by a direct ICP-MS method. The 0.22 lm filtered river water samples show a large degree of variability in both the REY concentration, e.g., La varies from 13 to 1157 ppt, and shape of the alluvial-sediment-normalised REY patterns with different samples displaying light, middle or heavy rare earth enrichment. In addition, a spatial study was undertaken along the freshwater section of Beerburrum Creek, which demonstrates that $75% of the total REYs in this waterway are removed prior to estuarine mixing without evidence of fractionation.

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Laser ablation ICP‐MS represents a promising new development for the acquisition of elemental and isotopic images from a variety of different materials. Compared to existing methods for imaging, it offers relatively rapid throughput, very wide dynamic range, a relatively clean mass spectrum, utility at a variety of scales (from μm to cm) and multi‐element/isotopic capability. Although developing rapidly in the biological sciences, the method has not yet seen widespread application to geological materials. This contribution documents some preliminary experiments aimed at understanding the fundamental aspects of elemental and isotopic image acquisition using laser ablation ICP‐MS. In particular, we note that ablation cell designs must be optimised to promote rapid system response, in contrast to the signal‐smoothing that is often preferred for simple spot analyses. Furthermore, experimental parameters must be carefully evaluated on a system‐by‐system basis to avoid the blurring effects of re‐sampling phenomena. With careful attention to these details, and development of appropriate data processing software, laser ablation ICP‐MS imaging has much to offer workers in the Earth and environmental sciences.

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