Constraining models of the tectonic environment of the giant Olympic Dam iron oxide-copper-gold deposit, in South Australia, using seismic reflection imaging  

Authors / CoAuthors

Drummond, B.J. | Jones, L.E.A. | Goleby, B.R. | Lyons, P.

Abstract

The tectonic setting of the giant Olympic Dam iron oxide-copper-gold ore deposit in South Australia has been uncertain to date. Given the economic significance of the Olympic Dam deposit and its influence in defining the mineral deposit class, resolving its tectonic setting is important. To help address this, two orthogonal deep seismic reflection profiles, centred on the ore deposit, were recorded to 18 s TWT. An approximately north-south line, 193 km long, was oriented as near to a regional dip direction ?defined by potential-field data? as land access would allow. It imaged units of the Archaean?Proterozoic Gawler Craton and a possible allochthonous Proterozoic terrane to the north. A shorter east-west cross-line (57 km long) provided information on any out-of-plane structures imaged on the longer profile in the region of the ore deposit. The seismic data show that the Olympic Dam deposit lies between two distinctly different pieces of crust. To the north of the deposit and the craton, the upper crust beneath the cover sequences shows south-dipping reflectors, interpreted as shear zones that cut through an upper crust of moderate sub-horizontal reflections and a lower crust of higher-amplitude reflections. To the south, the upper crust and lower crust have signatures indicating thrusting towards the craton, in a pattern indicative of a fold and thrust belt of crustal scale. However, in the south, the upper crustal deformation is decoupled from lower crustal deformation at a 3-4km thick band of sub-horizontal reflectors centred at about 12km depth (4s TWT). This zone is mostly un-deformed, except where, in places, it is thrust and duplicated. The middle to lower crust in the region between the two distinctly different crustal types in the north and south contains few reflections, and appears anomalous but homogenised compared with the crust to the north and south, and is interpreted as a likely source region for the Burgoyne batholith which hosts and is approximately coeval with the Olympic Dam ore deposit. Four hypotheses are tested for the lower crustal heat source that generated the granite melt. The intrusion of mafic sills into the lower crust is not favoured because no evidence of widespread seismically reflective underplate can be seen in the data. Heating by a plume is not favoured because the region contains no plume-related geological evidence, and the signature in the seismic data would probably be similar to that of underplating. Extension is not favoured, because the data show no evidence of crustal extension accompanied by surface subsidence and sediment deposition; rather they can be interpreted to show crustal shortening at the time. Heating by radioactive decay is worthy of further consideration because of the high concentrations of heat producing elements in the granite.

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nonGeographicDataset

eCat Id

61890

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Keywords

• External PublicationScientific Journal Paper

( Theme )

• seismic sections

( Theme )

• seismics

• AU-SA

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

Publication Date

2005-01-01T00:00:00

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Australian Government Security ClassificationSystem    

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Creative Commons Attribution 4.0 International Licence    

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unknown

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geoscientificInformation

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[-32.0, -29.0, 136.0, 138.0]

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