An Australian provenance for the eastern Otago Schist protolith, South Island, New Zealand: evidence from detrital zircon age patterns and implications for the origin of its gold

ABSTRACT

Uranium–lead age patterns of detrital zircons in Otago Schist meta-sandstones from eastern Otago, including areas of orogenic gold mineralisation, are mostly consistent with a Rakaia Terrane (Torlesse Composite Terrane) accretionary wedge protolith. Southwest of the Hyde-Macraes and Rise & Shine shear zones the depositional age is regarded as Middle–Late Triassic. At the south and west margins, there are two areas in the Late Triassic Waipapa Terrane protolith. Northeast of the Hyde-Macraes Shear Zone, the schist protolith has Middle to Late Triassic and middle to late Permian depositional ages of Rakaia Terrane affinity. At the northeastern margin of the Hyde-Macraes Shear Zone, there is a narrow strip with a mid-Carboniferous protolith, which may be a counterpart of the Carboniferous accretionary wedge in the New England Orogen, eastern Australia. Ordovician–Silurian zircons are a minor but distinctive feature in many of the protolith age patterns and form significant age components at hard-rock gold locations. These constrain the provenance of Rakaia Terrane protolith sediments to Late Triassic time and within the Permian–Triassic magmatic arcs at the northeastern Australian continental margin and partly within the Ordovician–Silurian granitoids of the Charters Towers Province hinterland and environs. The latter have extensive gold mineralisation and thus upon exhumation might be the origin of Otago gold.

KEYWORDS:

• U–Pb dating
• detrital zircon
• provenance
• terranes
• gold mineralisation
• Otago Schist
• New Zealand

Acknowledgements

The authors thank colleagues Nick Mortimer (GNS Science), Ben Baxter (Oceana Gold) and Dave Craw (Otago University) for sharing their extensive knowledge of Otago Schist regional geology and history of gold mineralisation. Mark Rattenbury and Tony Christie provided substantial reviews of an initial version of the manuscript. Norman Pearson and Will Powell at the Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS) and GEMOC at Macquarie University, Sydney provided valuable technical assistance throughout the program. The analytical data were obtained using instrumentation funded by DEST Systemic Infrastructure Grants, ARC LIEF, NCRIS/AuScope, industry partners and Macquarie University. This is contribution 998 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au) and 1172 in the GEMOC Key Centre (http://www.gemoc.mq.edu.au). Philip Carthew at GNS Science is thanked for careful preparation of the diagrams.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary papers

Table A1. Otago Schist detrital zircon U–Th–Pb isotopic ratios and U–Pb age data.

Table A2. U–Pb zircon age data, Ordovician, Silurian/Devonian Granites, Charters Towers Province, north Queensland.

Additional information

Funding

This is contribution 998 from the ARC Centre of Excellence for Core to Crust Fluid Systems ("http://www.ccfs.mq.edu.au/"http://www.ccfs.mq.edu.au) and 1172 in the GEMOC Key Centre ("http://www.gemoc.mq.edu.au/"http://www.gemoc.mq.edu.au).