Abstract

We report new and reinterpreted geological and geophysical results for the basement to the Stuart Shelf, in the north-eastern Gawler Craton. Regridding of gravity and magnetic datasets at optimal cell sizes allows resolution of basement structures with subtle geophysical expression. New processing techniques applied to these data, such as multi-scale edge detection (worming), and reassessment of available drill cores permit a reinterpretation of the stratigraphy and structure of units underlying the Pandurra Formation and Neoproterozoic cover sequences. In particular, we describe a three-fold Palaeoproterozoic basement sequence, analogous to that exposed in the southern Gawler Craton on the Eyre and Yorke Peninsulas. From west to east, we identify deformed BIF, schists, and gneisses equivalent to the Hutchison Group; orthogneisses equivalent to the Donington Granitoid Suite; and deformed and preserved metasedimentary rock equivalent to the Wallaroo Group. Intruded into the basement are structurally-controlled, high-level plutons of the ~1590 Ma Hiltaba Suite. These magmas fed extensive, flat-lying felsic sheets of the Gawler Range Volcanics (GRV), as well as more localised mafic centres equivalent to the Roopena Volcanics. Forward modelling of potential-field data and worming reveal that basement appears to have formed in a thick-skinned, transpressive regime. Structures suggestive of duplexes, megaboudinage, positive flower structures, and thrust stacks with non-ramp, flat geometry are consistent with modelled solutions. A similar structure to (or extension of) the Kalinjala Shear Zone is inferred to lie beneath the Stuart Shelf and GRV. In contrast, the ~1590 Ma volcanic-plutonic province appears to have formed in an overall extensional regime, with plutons elongated NE/SW in inferred dilational jogs within a conjugate dextral transtensional fault system. Thicker depocentres of GRV also appear to have formed in graben and half-graben nested above reactivated basement faults. To the south-west, four major sheets of GRV are inferred to rest on a basement of Archaean paragneisses. There is no geophysical requirement for a massive, sub-horizontal, mafic underplate. All geophysical anomalies can be explained with reference to realistic petrophysical properties of basement rocks found elsewhere in the Gawler Craton. Mass-balance calculations for a deposit such as Olympic Dam show that the source-rock volume for Cu is in the order of 102-103 km3. Under the hypothesis that the mineral system is controlled by faulting related to ~1590 Ma extension, faults of about 50-100 km by 10 km are required to create a large enough strain-envelope to ensure that fluids have access to the required volume of source-rock; and that those fluids may be mobilised and transported (Cox et al., 2001). Further, faults of this size are capable of tapping fluids from a variety of rock-types. Assuming that the regional NNW-to NW-trending transtensional structures penetrate to 10 km, their interpreted lengths are sufficient for them to have imposed a first-order control on the mineral system. The loci of mineralisation may be controlled by the second-order, NE- to ENE-trending, normal faults that connect the first-order regional structures and define the margins of the dilational jogs. The limiting factor to the size and spacing of deposits may be the quantity of metal available to the system, particularly Cu.
Google map showing geographic bounding box with values North bound -29.0 East bound 138.0 West bound 133.0 South bound -34.0
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Product Type/Sub Type

nonGeographicDataset - PowerPoint

Constraints

license
Creative Commons Attribution 3.0 Australia Licence

IP Owner

Commonwealth of Australia (Geoscience Australia)

Author(s)

Date (publication)

2002

Product Type

nonGeographicDataset

Topic Category

geoscientificInformation

Keywords

PowerPoint
geochemistry
Earth Sciences

Resource Language

English

Resource Character Set

utf8

Resource Security Classification

unclassified

Geographic Extent

North bound
-29.0
East bound
138.0
West bound
133.0
South bound
-34.0

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Unknown

Digital Transfer Options

onLine

DISTRIBUTION Format

pdf

Distributor

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distributor
Organisation Name
Geoscience Australia
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address

Metadata File Identifier

a05f7892-eb49-7506-e044-00144fdd4fa6

Metadata Standard Name

ANZLIC Metadata Profile: An Australian/New Zealand Profile of AS/NZS ISO 19115:2005, Geographic information - Metadata

Metadata Standard Version

1.1

Metadata Date Stamp

2008-11-21

METADATA SECURITY CLASSIFICATION

unclassified

Metadata Contact

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pointOfContact
Organisation Name
Geoscience Australia
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address
Downloads
For information on acquiring this product,
please contact the Geoscience Australia Sales Centre via:

fax:
+61 2 6249 9960; or
phone:
1800 800 173 (within Australia);
 
+61 2 6249 9966 (outside Australia).

Please note that support hours are 9 am to 5 pm weekdays