DIAMONDS: Geophysical signature of the Argyle lamproite pipe, Western Australia

Abstract

The Argyle lamproite diatreme is located close to the eastern margin of the Halls Creek Mobile Zone, in the East Kimberley, 120 km south of Kununurra. The pipe was discovered by the Ashton Joint Venture during reconnaissance gravel sampling of the East Kimberley in late 1979. The Argyle diatreme is intruded into Revolver Creek Formation and Carr Boyd Group Proterozoic sedimentary rocks. The diatreme is an elongate body 2 km long and oriented approximately north-south, with widths varying from 150 to 500 m. It is composed dominantly of pyroclastic rocks. A range of geophysical techniques have been used over the Argyle pipe, partly to assist in prospect evaluation but mainly to test their suitability for locating lamproite diatremes in adjacent areas. Airborne and ground magnetic and electromagnetic methods were used with varying degrees of success and a limited borehole logging programme carried out. None of the methods produced a definitive response over the Argyle pipe. Results indicate that the Argyle pipe is, at best, weakly magnetic, mainly in the northern bowl area, and weakly conductive, making it a very difficult target to locate using geophysical exploration techniques. Severe topographic problems which affected both airborne and ground survey results compounded the inherent problem of locating a subtle geophysical response.