Age constraints on the timing of iron ore mineralisation in the southeastern Gawler Craton

Abstract

SHRIMP U–Pb zircon data obtained from a magnetite gneiss deposit in the southeast Gawler Craton indicate that the protoliths were deposited between 1750 and 1735 Ma. Previously, these iron-rich gneisses were thought to have been a metamorphosed banded iron formation and part of the Neoarchean to early Paleoproterozoic Sleaford Complex. Detrital zircon data provide maximum depositional ages between 1765 Ma and 1740 Ma, with ϵNd(1750) values between –4.6 and –3.3. Metamorphic zircon ages are 1735–1725 Ma, indicating that the magnetite gneiss was formed during the 1730–1690 Ma Kimban Orogeny. The pelitic mineralogy of the magnetite gneiss and presence of detrital zircon demonstrate that the protoliths were not a pure chemical sediment. Correlation with the greenschist facies Price Metasediments in the southern Gawler Craton suggests a series of iron-bearing basins were developed prior to the onset of the Kimban Orogeny and suggest that metamorphism played a role in ore formation.