Summary of results. Joint NTGS-GA geochronology project: Aileron Province, Jinka and Dneiper 1:100 000 mapsheets, 2020

Abstract

This Record presents data collected in July 2020 as part of the ongoing Northern Territory Geological Survey–Geoscience Australia SHRIMP geochronology project under the National Collaborative Framework agreement and Geoscience Australia’s Exploring for the Future Program. New U–Pb SHRIMP zircon geochronological results derived from four samples of meta-igneous rocks from the Aileron Province in Jinka and Dneiper (HUCKITTA) in the Northern Territory are described herein. Samples of Bacardi Granite (HU16EEB1346) and Captain Morgan Metadolerite (HU18BLR2038) were collected from exposures located ~6.4 km east-southeast and 3.8 km south-southeast of No. 4 Bore in eastern Dneiper respectively. The Bacardi Granite is a foliated biotite-hornblende granite and the Captain Morgan Metadolerite is a glomerophyric metadolerite - both outcrop widely but sparsely across Dneiper and both are previously undated. Magma mingling between these units has been recognised in outcrop. The two units are mapped and interpreted as constituents of the ca 1.81 Ga Black Label Suite, a bimodal suite that also includes the ca 1805 Ma Dneiper Granite. The Black Label Suite is interpreted to intrude the ca 1.82-1.79 Ga Deep Bore Metamorphics. Felsic intrusives of the ca 1.79 Ga Molyhil Suite and the ca 1.72 Ga Marshall Granite locally intrude rocks of the Black Label Suite. Zircons in sample HU16EEB1346 yield an interpreted magmatic crystallisation age of 1808 ± 5 Ma, minor Archaean to Proterozoic inheritance, and evidence for disturbance during an early Palaeozoic event. Zircons in sample HU18BLR2038 are composite, with oscillatory zoned cores yielding an interpreted magmatic crystallisation age of 1805 ± 6 Ma. Ubiquitous rims and embayments cross-cut and overprint primary zoning in the cores and yield an age of 1723 ± 7 Ma, interpreted to record new zircon growth during the regional Palaeoproterozoic metamorphic cycle. Magmatic crystallisation ages for the Bacardi Granite and Captain Morgan Metadolerite confirm a ca 1.81 Ga emplacement age for the Black Label Suite. A sample of Yam Gneiss (HU15BLR872) was collected from an exposure ~2.1 km east-northeast of the Molyhil tungstenmolybdenum deposit. The Yam Gneiss is a strongly weathered, biotite-bearing quartzofeldspathic gneiss that outcrops sparsely in central Jinka; an isolated outcrop of the gneiss is also noted in the Mopunga Range in western Jinka. The gneiss is of indeterminate protolith but is interpreted to have been most likely igneous in nature. The Yam Gneiss is intruded by dykes of ca 1.72 Ga Marshall Granite and has not previously been dated. Zircons in sample HU15BLR872 yield an interpreted magmatic crystallisation age of 1797 ± 7 Ma. Zircon rims are interpreted to record metamorphism at 1736 ± 6 Ma during the regional Palaeoproterozoic metamorphic cycle, and evidence of isotopic resetting during an early Palaeozoic event. A sample of Narbarloo Granite (HU15EEB1015A) was collected from an exposure ~3.7 km northeast of Ross Bore in western Jinka. The Narbarloo Granite is a foliated to locally gneissic hornblende±biotite granite that outcrops widely in the eastern Mopunga Range. The granite is interpreted as a constituent unit of the ca 1.79 Ga Molyhil Suite and is intruded by dykes of ca 1.72 Ga Marshall Granite. Previous dating of the Narbarloo Granite includes a magmatic crystallisation age of 1791 ± 3 Ma for a sample of hornblende-biotite granite in eastern Dneiper (Kositcin et al 2011); this was formerly considered to be Marshall Granite but has been reinterpreted as Narbarloo Granite based on new mapping. Zircons in sample HU15EEB1015A yield an interpreted magmatic crystallisation age of 1792 ± 3 Ma, confirming the Narbarloo Granite belongs to the ca 1.79 Ga Molyhil Suite. Zircon rims record metamorphism at 1728 ± 8 Ma during the regional Palaeoproterozoic metamorphic cycle, and show evidence of isotopic resetting.