Provenance of the Copi North heavy mineral sands deposit, Murray Basin, Australia, based on the geochronology and geochemistry of detrital zircon, rutile and monazite

Abstract

The Murray Basin hosts one of the world’s largest strandplain systems and has enormous potential for heavy mineral sand resources of titanium, zircon and rare earth elements. Further discovery of heavy mineral sand deposits can be aided via improved understanding of the source and transport of detrital heavy minerals of the basin. In this study, the provenance of two heavy mineral sand units of the Copi North deposit (western NSW) was determined using U–Pb geochronology and geochemistry of detrital zircon, rutile and monazite. Results from the two units are similar, indicating they derive from the same sources. Approximately 42% of the zircon population is aged <470 Ma and is interpreted to have been derived from the Tasmanides. Older zircon populations, up to ca 2.5 Ga, were largely derived from the Adelaide Superbasin and Delamerian Orogen, or from metasedimentary rocks of the Lachlan Orogen. Over 90% of rutile U–Pb ages are between 570 and 450 Ma, correlating either to Delamerian metamorphism or to detrital rutile from the Darling Basin; both sources are supported by rutile geochemistry that is indicative of a metasedimentary source. Most monazites have U–Pb ages of ca 600 Ma, which is consistent with an ultimate source from the Mt Arrowsmith Volcanics and/or Antarctica. A minor proportion of the monazite was sourced from igneous rocks of the New England Orogen. Temporal changes in sediment source regions can be inferred when considering the detrital mineral record for Copi North with other mineral sand deposits of the basin. Older (>ca 6.7 Ma) deposits such as Copi North feature a significant proportion of post-350 Ma detritus, reflecting the important role of the ancestral Darling River in supplying sediment from the north at the earliest stages of Murray Basin development. Post-6.7 Ma deposits lack a major component of detritus for far northern sources, and instead consist of sediment derived dominantly from western (Adelaide Superbasin) and eastern (Lachlan Orogen) sources, the latter delivered via the Murray River.