Detecting element migration from ore systems: an LA-ICP-MS method for the in situ measurement of element contents and 207 Pb/ 206 Pb values on rough fracture coatings

Abstract

In situ elemental content and 207 Pb/ 206 Pb values in three rough fracture coatings within drill cores from the McArthur River unconformity-related uranium deposit, Athabasca Basin, Canada, were measured using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) image mapping. Fracture-coating samples were located proximal and distal to the ore deposit. Samples required minimal preparation in this method, with areas ( c . 500 × 500  μ m) targeted in a cell-spaced grid pattern using a 50  μ m spot, spaced 200  μ m on the x -axis with an offset of 100  μ m on the y -axis, to overcome sample surface topography. A 5 s acquisition time was applied to elemental content measurements and a 2 s acquisition time was applied to 207 Pb/ 206 Pb measurements. These parameters increased the spatial resolution and analytical sensitivity and minimized the contribution of the host rock underlying the fracture surface to the geochemical signal in comparison to extended acquisition times. In addition, laser ablation temporal profiles allow for the interpretation of the timing of element/isotope migration and fixation on the rough fracture coating. Rasterized maps generated in Iolite™ v.4 demonstrate the chemical distribution of elements and 207 Pb/ 206 Pb values on the rough fracture coatings, allowing for the identification of mineral phases hosting pathfinder elements, pathfinder element associations and the generation of bulk in situ or specific mineralogy geochemical values. Bulk in situ values calculated using an integration of the 2D image data and targeting the c . 500 × 500  μ m surface of the fracture coating compared to previous bulk geochemical methods obtained by sampling the fracture coating with a microdrill (i.e. modified aqua regia (HCl: HNO 3 : H 2 O) and weak acid leach (2% HNO 3 )) highlights that in situ analysis greatly improved detection of pathfinder elements on the fracture surface. This study is the first application of in situ LA-ICP-MS for measuring element contents and 207 Pb/ 206 Pb values on rough fracture coatings and demonstrates its importance as a new geochemical tool to the mining industry for future mineral exploration.