P–T conditions of metamorphic and hydrothermal events at Tick Hill gold deposit, Mount Isa, Queensland, Australia

Abstract

Tick Hill gold deposit is a unique gold mineralisation style in the Mary Kathleen Fold Belt in the Mount Isa Inlier. The gold at Tick Hill is generally pure without silver and was formed during two discrete metamorphic-deformation events (D₁ and D₃). Early gold was observed as inclusions or coarse grains hosted within D₁ peak-metamorphic diopside, scapolite and hornblende from the garnet–biotite–hornblende (tschemakite)–plagioclase (andesine)–quartz assemblage. Late gold is closely associated with bismuth selenide, chlorite, albite, sericite and K-feldspar, and formed during D₃. The syn-D₁ garnet–plagioclase–hornblende–quartz–biotite assemblage was used to constrain the pressure and temperature (P–T) conditions of metamorphism and mineralisation using the garnet–plagioclase–hornblende–quartz barometer and the hornblende–plagioclase, garnet–biotite and garnet–hornblende thermometers. The results show that peak metamorphism at Tick Hill reached P–T conditions of 6.0–7.6 kbar and 720–760 °C. These P–T conditions together with gneissic and migmatisation textures recorded in different rock types at the Tick Hill area indicate that the peak metamorphism preserved in the area occurred at the amphibolite–granulite facies, compared with the amphibolite facies at the southern Mary Kathleen and Eastern Fold Belt. The D₃ chlorite, which formed during stage 2 to stage 4 mineralisation events, displays a wide range of compositions reflecting a gradual retrograde temperature change from ∼380 °C to ∼130 °C. The pressures during D₃ could not be reliably determined, but the presence of various Bi-selenides suggests that towards the waning stages of D₃, the rocks may have been exhumed to a pressure less than 1 kbar.

KEY POINTS

1. The 1790–1770 Ma D₁ peak metamorphism at Tick Hill reached 6–7.6 kbar and 720–760 °C.

2. The 1525–1520 Ma D₃ hydrothermal mineralisation at Tick Hill Deposit occurred at temperatures between ∼380 °C and ∼130 °C.

3. The main D₃ gold accumulation episodes at Tick Hill occurred at temperatures ranging from ∼380 to 160 °C.

Keywords:

• Tick Hill
• gold deposit
• Mary Kathleen
• Mount Isa
• geobarometry
• geothermometry

Acknowledgements

We would like to thank the Geological Survey of Queensland (GSQ), the Economic Geology Research Centre (EGRU, JCU) and Rick Valenta, who provided support to conduct this study. We would like to thank Peter Rea and Alex Brown from Glencore, Mount Isa Mines, and Paul Tan, Brett Davis and Rob Watkins from Carnaby Resources for providing logistical support during fieldwork, providing access to the drill core and mine site, and providing data sets. We would like to thank Nick Oliver for donating the Tick Hill samples for this study. We would like to thank the Ho Chi Minh University of Science for supporting the study project (code T2023-53) in comparing the SEM-based mineral thermometry with the EPMA-based one.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The geological map of the Tick Hill Area is mainly updated from the exploration maps (Rutherford, N. F., 2000) that, which can be found inat .data.qld.gov.au/report/cr031587 https://geoscience.data.qld.gov.au/report/cr031587.

Additional information

Funding

Funding for this study was provided by the Department of Natural Resources, GSQ and the VNU-HCM University of Science, Ho Chi Minh, Vietnam under the study project code T2023-53.