Tectonic setting and mineralisation potential of the Cowley Ophiolite Complex, north Queensland

Abstract

Northeast Queensland contains multiple slices of mafic–ultramafic units, strung out along regional faults that mark major tectonic boundaries. One such complex is the Cowley Ophiolite Complex, which is situated along the Russell-Mulgrave Fault. The Cowley Ophiolite Complex is a differentiated mafic–ultramafic complex composed of gabbro, chlorite schist, anthophyllite schist and serpentinite. We interpret that the alteration assemblages observed throughout the Cowley Ophiolite Complex reflect an amphibolite facies metasomatic overprint within a supra-subduction zone setting. This interpretation is consistent with geochemical discrimination of the gabbro, and chromite grains from the anthophyllite schist. The Cowley Ophiolite Complex records a higher metamorphic grade than the surrounding Hodgkinson Formation, and we interpret this to reflect the allochthonous structural setting of the complex, positioned along an ancient subduction margin. This subduction margin is represented today by the Russell-Mulgrave Fault. Metasomatism and emplacement of the complex probably pre-dated deposition of the Mossman Orogen’s active margin successions. Our interpretation of an active subduction complex, which pre-dated the formation of the Mossman Orogen, suggests that the Russell-Mulgrave Fault is a Paleozoic, continental suture zone. The Cowley Ophiolite Complex presents little indication of economic mineralisation; however, much of the complex remains unexplored.

KEY POINTS

1. The Cowley Ophiolite Complex is a differentiated, mafic–ultramafic complex formed within a supra-subduction zone setting.

2. Emplacement of the Cowley Ophiolite Complex, along the Russell-Mulgrave Fault, pre-dated the formation of the Hodgkinson Province.

3. The Russell-Mulgrave Fault represents an ancient subduction margin, and is interpreted as a Paleozoic, continental suture zone.

Keywords:

• geology
• tectonics
• geochemistry
• Tasmanides
• ophiolite
• mineral potential
• critical metals

Acknowledgements

The authors would like to thank Kevin Blake from the Advanced Analytical Centre at James Cook University (JCU) for his technical support during EPMA data collection and processing and Laurie Hutton and Solomon Buckman for their reviews and constructive criticism of the original manuscript. Author contributions: AE and IS are responsible for conceptualisation, methodology, investigation, visualisation, supervision; AE wrote the original draft, and the writing, review and editing was carried out by all authors.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article or its supplementary materials.

Additional information

Funding

The authors would like to thank the Geological Survey of Queensland for their funding of the project. The first author would like to acknowledge and thank JCU for the Australian Government Research Training Program Domestic Stipend Scholarship, and the Economic Geology Research Centre (EGRU) at JCU for housing this research.