The deep penetration of focussed hard X-ray and MeV proton beams allows sub-surface features to be excited and imaged via fluoresced characteristic X-rays. The practical depths achievable are set primarily by the escape of these X-rays. This can be a serious complication in thick, fine-grained samples. But it can also be an asset, which allows the detection of rare buried phases that may be missed using more surface-sensitive techniques. This approach extends microanalysis “2020 vision” to depths of some tens of microns or more, which greatly enhances the chance of detecting rare particles. Further enhancement comes from large area mapping in order to extend the search and construct element images to tens and hundreds of millions of pixels enabled using a very large solid-angle detector array with a high count-rate capability.
In this work, we report using the Maia detector array of 384 detectors combined with focussed synchrotron X-rays and MeV energy protons to produce major and trace element images to beyond 100 M pixels, at 2 µm resolution, that include meaningful distributions of rare phases at rates of only one particle per ~0.1 to >1 M pixels. Recently, this approach has been extended to larger spatial scales using the Maia Mapper, a laboratory X-ray source based system, which enables XRF mapping over sample sizes to 500 mm at a spatial resolution of 30 µm that can capture subtle trace zonation at the <1 to >100 mm scales and detect rare phases as a complement to conventional microanalysis. The system is applied to sectioned diamond drill core obtained in mineral exploration and mine development as part of the Advanced Resource Characterization Facility (ARCF), which provides an integrated suite of characterization tools that span spatial scales from single atoms to the hundreds of metres sampled in drilling.