The advent of neodymium (Nd) isotope maps of selected terranes in Australia, more recently complemented by zircon hafnium (Hf) and whole rock / ore lead (Pb) isotope maps (e.g., Geoscience Australia’s ‘Isotopic Atlas of Australia’), allows a powerful image of the (covered) crystalline basement to be resolved. These individual radiogenic isotope systems provide distinct (often complementary) constraints on geological processes, geological reservoirs, and rock types (Champion and Huston, 2016). Furthermore, identifying isotopic signatures from different material scales (e.g., single mineral, mineral populations, to whole rock) can further elucidate geologic processes from mineralisation to global secular changes in crustal evolution. Taking a multi-layered approach extended to isotopic systems at different analytical scales, may allow different fractionation processes to be tracked and inform on the extent of secondary alteration. For example, hydrothermal alteration may greatly affect the Rubidium (Rb) - Strontium (Sr) system when investigating the whole rock yet initial compositions may be retained within (i) specific minerals (e.g., apatite) un-affected by alteration or recrystallization (e.g., Creaser and Gray, 1993); or (ii) where a different isotopic system may remain undisturbed (e.g., Sm-Nd). Furthermore, different isotopic systems within different minerals will also have dissimilar detection limits permitting a more complete spatial coverage. Here we compile literature and newly acquired isotopic data from a variety of radiogenic isotope systems determined at the crystal to whole rock scale to identify inconsistencies or differences in isotopic behaviour at the terrane scale. Specifically, we present the results of a case study from a suite of granitic samples across the Ida Fault in the Yilgarn craton, Western Australia. Utilizing the power intrinsic to differing sensitivities of isotopic systems to geologic processes, we aim to derive cumulative maps that provide new insights into crustal evolution and thus inform on the mechanisms that control mineralisation. Comparison of isotopic tracer maps with geochronology layers (e.g., uranium-lead) provides the framework for the 4D understanding of a wide range of natural processes.

Reference(s)

Champion, D. C. and Huston, D. L. 2016. Radiogenic isotopes, ore deposits and metallogenic terranes: Novel approaches based on regional isotopic maps and the mineral systems concept. Ore Geology Reviews v.76, p.229–256, https://doi.org/10.1016/j.oregeorev.2015.09.025

Creaser, R.A. and Gray, C.M. 1993. Preserved initial 87Sr/86Sr in apatite from altered felsic igneous rocks: A case study from the Middle Proterozoic of South Australia. Geochimica et Cosmochimica Acta v.56, p.2789-2195, https://doi.org/10.1016/0016-7037(92)90359-Q