The geology of the Mount Edgar and Corunna Downs igneous complexes; East Pilbara Craton, Western Australia

The Mount Edgar and Corunna Downs Igneous Complexes are located near the eastern margin of the Pilbara Craton in northwest Western Australia. The Mount Edgar Igneous Complex occurs on parts of the 1:250,000 geological sheets: Yarrie, Port Hedland, Marble Bar and Nullagine.  The Corunna Downs Igneous Complex occurs on parts of the 1:250,000 geological sheets: Marble Bar and Nullagine. The regional geological setting of the Pilbara Craton is described by Hickman (1983).
The first geological observations were by explorer F.T. Gregory in 1861.  In the 1890s there were several geological investigations of the Pilbara Craton by the Government Geologist H. P. Woodward to assess mineral discoveries and to describe the geology (Hickman, 1983).  The first geological survey of the Pilbara Craton was by Maitland (1904, 1905, 1906, 1908).  The surveys by Maitland formed part of the 1:250,000 geological sheets Marble Bar and Nullagine published by Noldart &amp; Wyatt (1962).  Further regional mapping of 1:250,000 geological sheets included Balfour Downs (de la Hunty, 1964), Port Hedland (Low, 1965), Roebourne (Ryan, 1966), and Pyramid (Kriewaldt &amp; Ryan, 1967).  During the period 1972 to 1975 another regional mapping program covered Yarrie (Hickman &amp; Chin, 1976), Marble Bar (Hickman &amp; Lipple, 1978), Nullagine (Hickman, 1979), and Port Hedland (Hickman, 1977). 
More detailed studies in the igneous geology commenced in the late 1970's. The Geological Survey of Western Australia undertook a regional reconnaissance rock sampling program in the Mount Edgar and Corunna Downs Igneous Complexes to assess the potential for tin deposits (Blockley, 1980).  Davy &amp; Lewis (1981) undertook a geochemical study of Mount Edgar Batholith producing geochemical maps showing widely divergent patterns between different components with no evidence for systematic fractionation or differentiation. Detailed mapping, structural analysis, geochemistry and Rb-Sr isotopic systematics were undertaken by Collins (1983) to determine the nature, origin and evolution of the Mount Edgar Igneous Complex.  A regional geochemical and petrography study within the Corunna Downs Igneous Complex was undertaken by Davy (1989). 
To enhance the geological understanding of the north Pilbara region, airborne surveys measuring total magnetic intensity, gamma-ray spectrometry, and surface altitude with a flight line spacing of 400m were undertaken during 1995-1996.  The interpretation of these data is discussed by Wellman (1999). 
This report is based on a reconnaissance level field survey, detailed air-photo interpretation, in conjunction with analysis and interpretation of airborne gamma ray spectrometric and magnetic surveys (Wellman, 1998, 1999). Detailed interpretation of aerial photography and geophysical imagery over the Mount Edgar and Corunna Downs Igneous Complexes suggests the presence of a numerous discrete units. Where these units fall geographically within defined suites and have similar rock properties to these suites they are included as a sub-unit though they have not been formally named.  Where the units fall geographically outside obvious suites they have been organised on the basis of geographic distribution and/or common rock properties and are labelled as Ungrouped. Although these units have been labelled separately, many do not have detailed descriptions.

Tags: AU-WA, Earth Sciences, GA Publication, Published_External, Record, geology
Organization: Geoscience Australia Data