Geology and geochronology of the Two-Thirty prospect, Northparkes district, NSW

Abstract

The Northparkes district, central New South Wales, hosts several economic Cu–Au deposits associated with discrete, thin, porphyry intrusive complexes emplaced in the Late Ordovician during formation of the Macquarie Arc. The recently discovered Two-Thirty Cu–Au–(Mo) prospect is a mineralised magmatic–hydrothermal breccia complex that is hosted by the moderately east-dipping Goonumbla Volcanic Complex on the western limb of the Milpose Syncline ∼15 km south of the Northparkes porphyry district. Generation of the magmatic–hydrothermal breccia complex is interpreted to be related to the 448.0 ± 4.4 Ma emplacement of the Two-Thirty porphyry. However, Re–Os dating of molybdenite from the breccia complex indicates a potential for a ca 440 Ma mineralising event that has similar timing to economic porphyry mineralisation in the Northparkes district. The discovery of the Two-Thirty prospect has important implications for exploration in the Northparkes district and the broader Macquarie Arc. Two-Thirty is only the second known occurrence of magmatic-hydrothermal breccia-hosted mineralisation discovered within the Macquarie Arc, with the other being Cadia Quarry. Mineralisation at Two-Thirty is potentially older than the Northparkes and Cadia deposits, and younger than the epithermal and calc-alkaline deposits at Cowal, Marsden and Ridgeway.

KEY POINTS:

1. The Two-Thirty is a polyphase magmatic–hydrothermal breccia complex that hosts Cu–Au (Mo).

2. The Two-Thirty is the first significant breccia-hosted mineralisation found in the Northparkes district.

3. U–Pb zircon crystallisation ages of the causative intrusion at Two-Thirty pre-date mineralisation at Northparkes.

4. Re–Os dates of molybdenite from the Two-Thirty breccia complex are coeval with syn-mineralisation at Northparkes, supporting the model of periodic release of melts and fluids from underlying magma chambers during the formation of porphyry mineralisation in the Northparkes district.

Keywords:

• Macquarie Arc
• Northparkes
• porphyry
• magmatic–hydrothermal breccia
• Cu–Au (Mo)

Acknowledgements

The authors would like to acknowledge the help and support of the analytical and professional staff at the University of Tasmania; Karin Orth, Sean Johnson, Anita Parhabakar-Fox, Aleksandr Stepanov, Matt Cracknell, Ayesha Ahmed, Jay Thompson, Brian McNulty, Margaret Hawke, Thomas Schaap and Thomas Osterson; Northparkes Mines Exploration geologists and field staff: Jeneta Owens, Corey Jago, Katrina Thiel, Alison Row, Emily Cooke, Phillipa Cook; Richard Lesh from Terrasearch and finally Danielle Pretty, Georgia Wells, Daemon and Christopher Black.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The data that support the findings of this study are openly available in the University of Tasmania data repository at: https://doi.org/10.25959/5fc9b098bf588

Additional information

Funding

This research is funded by Australian Research Council sponsors of the Lachlan ARC Linkage Project ‘LP160100483’ CMOC-Northparkes, Rio Tinto, Evolution Mining, IMEx Consulting, Heron Resources, Sandfire Resources NL, New South Resources, AngloGold Ashanti, Alkane Resources, Geoscience Australia, The University of Tasmania, Australian National University, University of Melbourne, CCFS, Curtin University, the New South Wales, Tasmanian and Victorian state governments.