Brine reflux as a possible first order control on the alkali geochemistry of baseline sedimentary rocks in the Proterozoic North Australian Zinc Belt

Abstract

The Proterozoic McArthur Basin is economically significant because it contains the world-class McArthur River camp of stratiform Zn-Pb deposits hosted in shales in the c. 1640 Ma Barney Creek Formation. Despite periods of strong interest from minerals explorers and research groups over the past forty years, significant additional resources have not yet been discovered in the terrane. High potassium (K) concentrations in rocks in the McArthur Basin are noted since the earliest literature. One hypothesis for high K concentrations in the Barney Creek Formation is the development of authigenic K-feldspar (K-feldspathisation) by exposure to a low temperature brine reflux flow system during early diagenesis. This is significant to minerals exploration because the genetic link between low temperature brine reflux and sediment-hosted ore formation is an emerging topic in economic geology. K-feldspathisation of sedimentary sequences may be a key identifier of regional potential for development of McArthur River type mineralisation.Gianfriddo et al. (2022) characterise K-feldspathised and non-feldspathised Barney Creek Formation using SEM imagery and whole rock inorganic geochemistry. Here we demonstrate that public domain geochemistry data for basinal sedimentary rocks in wider Proterozoic northern Australia broadly conform to the same K-feldspathised and non-feldspathised fields defined by Gianfriddo et al. (2022). Based on the assumption that the alkali signature in the regional data reflects the presence/absence of authigenic K-feldspar analogous to that described in the Barney Creek Formation case study, and the interpretation that this is controlled by K-feldspathisation during brine reflux, these data indicate a preliminary framework for extensive fluid flow that is geographically coherent and consistent with current understanding of the tectono-sedimentary evolution of Proterozoic northern Australia.We caution that our model is speculative at this stage and requires detailed studies of the mineralogy and facies of the samples for validation. While readers are encouraged to consider this approach in their mineral exploration or academic work, other components such as lithology, facies, mineralogy, diagenesis, and provenance need necessarily also be considered especially at the local scale.